Citation Nr: 21064083 Decision Date: 10/19/21 Archive Date: 10/19/21 DOCKET NO. 16-31 448 DATE: October 19, 2021 ORDER Entitlement to service connection for a low back disorder, to include as secondary to service-connected lower extremity peripheral neuropathy, is denied. Entitlement to service connection for a left hip disorder, to include as secondary to service-connected lower extremity peripheral neuropathy, is denied. Entitlement to service connection for a right hip disorder, to include as secondary to service-connected lower extremity peripheral neuropathy, is denied. Entitlement to service connection for a left knee disorder, to include as secondary to service-connected lower extremity peripheral neuropathy, is denied. Entitlement to service connection for a right knee disorder, to include as secondary to service-connected lower extremity peripheral neuropathy is denied. Entitlement to service connection for a left foot condition, hallux valgus (bunions) and hammertoes, also claimed as secondary to service-connected lower extremity peripheral neuropathy, is denied. Entitlement to service connection for a right foot condition, to include hallux valgus and hammertoes, also claimed as secondary to service-connected lower extremity peripheral neuropathy, is denied. FINDINGS OF FACT 1. A lumbar spine disorder, to include degenerative joint disease and lumbago, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a lumbar spine disorder caused or aggravated by peripheral neuropathy. 2. A left hip disorder, to include degenerative joint disease, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a left hip disorder caused or aggravated by peripheral neuropathy. 3. A right hip disorder, to include degenerative joint disease, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a right hip disorder caused or aggravated by peripheral neuropathy. 4. A left knee disorder, to include degenerative joint disease, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a left knee disorder caused or aggravated by peripheral neuropathy. 5. A right knee disorder, to include degenerative joint disease, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a right knee disorder caused or aggravated by peripheral neuropathy. 6. The evidence of record demonstrates that the Veteran's bilateral hallux valgus was noted on entrance examination, and was clearly and unmistakably not aggravated by such service. 7. A left foot disorder, to include hammertoes, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a left foot disorder caused or aggravated by peripheral neuropathy. 8. A right foot disorder, to include hammertoes, was not manifest in service, within one year of separation from service, and is not otherwise related to the Veteran's active service; nor does the Veteran have a right foot disorder caused or aggravated by peripheral neuropathy. CONCLUSIONS OF LAW 1. The criteria for service connection for a lumbar spine disorder, to include degenerative joint/disc disease and a lumbago, have not been met. 38 U.S.C. §§ 1101, 1110, 1112, 1116 (2012); 38 C.F.R. §§ 3.303, 3.307, 3.309, 3.310 (2020). 2. The criteria for service connection for a right hip disorder, to include degenerative joint disease, have not been met. 38 U.S.C. §§ 1101, 1110, 1112, 1116 (2012); 38 C.F.R. §§ 3.303, 3.307, 3.309, 3.310 (2020). 3. The criteria for service connection for a left hip disorder, to include degenerative joint disease, have not been met. 38 U.S.C. §§ 1101, 1110, 1112, 1116 (2012); 38 C.F.R. §§ 3.303, 3.307, 3.309, 3.310 (2020). 4. The criteria for service connection for a left knee disorder, to include degenerative joint disease, have not been met. 38 U.S.C. §§ 1101, 1110, 1112, 1116 (2012); 38 C.F.R. §§ 3.303, 3.307, 3.309, 3.310 (2020). 5. The criteria for service connection for a right knee disorder, to include degenerative joint disease, have not been met. 38 U.S.C. §§ 1101, 1110, 1112, 1116 (2012); 38 C.F.R. §§ 3.303, 3.307, 3.309, 3.310 (2020). 6. The criteria to establish entitlement to service connection for a right foot disorder, to include hallux valgus and hammertoes, have not been met. 38 U.S.C. §§ 1101, 1110, 1111, 5107; 38 C.F.R. §§ 3.102, 3.303, 3.306, 3.310 (2020). 7. The criteria to establish entitlement to service connection for a left foot disorder, to include hallux valgus and hammertoes, have not been met. 38 U.S.C. § 1101, 1110, 1111, 5107; 38 C.F.R. §§ 3.102, 3.303, 3.306, 3.310 (2020). REASONS AND BASES FOR FINDINGS AND CONCLUSIONS The Veteran, who is the appellant, had active service from February 1970 to September 1971. The Veteran appeared at a videoconference hearing before the undersigned Veterans Law Judge in June 2019. A transcript of the hearing is of record. In October 2019, the Board remanded this matter for further development. The requested development has been completed and the matter is now ready for appellate review. Service Connection Service connection is warranted where the evidence of record establishes that a particular injury or disease resulting in disability was incurred in the line of duty in the active military service or, if pre-existing such service, was aggravated thereby. 38 U.S.C. § 1110; 38 C.F.R. § 3.303. Arthritis is a "chronic disease" listed under 38 C.F.R. § 3.309(a); therefore, the presumptive service connection provision of 38 C.F.R. § 3.303 (b) apply to that claim. Walker v. Shinseki, 708 F.3d 1331 (Fed. Cir. 2013). If a condition noted during service is not shown to be chronic, then generally a showing of continuity of symptomatology after service is required for service connection. 38 C.F.R. § 3.303(b). Service connection may be granted for any disease initially diagnosed after service when all the evidence, including that pertinent to service, establishes that the disease was incurred in service. 38 C.F.R. § 3.303(d). Arthritis will be presumed to have been incurred in service if manifested to a compensable degree within the first year following separation from active duty. 38 U.S.C. §§ 1101, 1112, 1113; 38 C.F.R. §§ 3.307, 3.309. In this regard, in order to establish service connection for the claimed disorder, there must be (1) medical evidence of a current disability; (2) medical, or in certain circumstances, lay evidence of in-service incurrence or aggravation of a disease or injury; and (3) medical evidence of a nexus between the claimed in-service disease or injury and the current disability. See Hickson v. West, 12 Vet. App. 247, 253 (1999). If a veteran was exposed to an herbicide agent during active military, naval, or air service, certain diseases shall be service-connected if the requirements of section 3.307(a)(6) are met even though there is no record of such disease during service, provided further that the rebuttable presumption provisions of section 3.307(d) are also satisfied. 38 C.F.R. § 3.309 (e). The diseases listed at 38 C.F.R. § 3.309(e) shall have become manifest to a degree of 10 percent or more any time after service, except that chloracne, porphyria cutanea tarda, and acute and subacute peripheral neuropathy shall have become manifest to a degree of 10 percent or more within a year after the last date on which the veteran was exposed to an herbicide agent during active military, naval, or air service. 38 C.F.R. § 3.307(a)(6)(ii). Pursuant to Section 3 of the Agent Orange Act of 1991, Public Law No. 102-4, 105 Stat. 11, the Secretary of Veterans Affairs (Secretary) entered into an agreement with the National Academy of Sciences (NAS) to review and summarize the scientific evidence concerning the association between exposure to herbicides used in Vietnam and various diseases suspected to be associated with such exposure. The NAS was to determine, to the extent possible, whether there was a statistical association between the suspect disease and herbicide exposure, taking into account the strength of the scientific evidence and the appropriateness of the methods used to detect the association; the increased risk of disease among individuals exposed to herbicides during the service in the Republic of Vietnam during the Vietnam era; and whether there is a plausible biological mechanism or other evidence of a causal relationship between herbicide exposure and the suspect disease. The NAS was required to submit reports of its activities every two years. The Secretary, under the authority of the Agent Orange Act of 1991 and based on the studies by the NAS, has determined that there is no positive association between exposure to herbicides and any condition for which the Secretary has not specifically determined that a presumption of service connection is warranted. See Notice, 59 Fed. Reg. 341-346 (1994); see also Notice, 61 Fed. Reg. 41,442-449, and 61 Fed. Reg. 57,586-589 (1996); Notice, 64 Fed. Reg. 59,232-243 (Nov. 2, 1999); Notice, 67 Fed. Reg. 42,600-08 (June 24, 2002); Notice, 72 Fed. Reg. 32,395-407 (June 12, 2007); Final Rule, 74 Fed. Reg. 21,258-260 (May 7, 2009); Final Rule, 75 Fed. Reg. 53,202-16 (Aug. 31, 2010). Notwithstanding the foregoing, the Veteran may still establish service connection with proof of actual direct causation. See Combee v. Brown, 34 F.3d 1039, 1043-44 (Fed. Cir. 1994); see also McCartt v. West, 12 Vet. App. 164, 167 (1999). "Of particular relevance to an analysis of medical evidence supporting such a nexus are factors such as whether a medical professional finds studies persuasive, whether there are other risk factors that might be the cause of the condition for which benefits are sought, and whether the condition has manifested itself in an unusual manner." Polovick v. Shinseki, 23 Vet. App. 48, 53 (2009). A statistical correlation between AO and a disease not on the presumptive list may not be the only basis for a positive nexus opinion; it may be part of the analysis, but the entirety of the analysis provided by the medical professional must be weighed and considered. Polovick, 23 Vet. App. at 53-54. Service connection may also be granted for disability which is proximately due to or the result of a service-connected disease or injury. 38 C.F.R. § 3.310; Allen v. Brown, 7 Vet. App. 439, at 448 (1995) (holding that service connection on a secondary basis requires evidence sufficient to show that the current disability was caused or aggravated by a service-connected disability). To establish secondary service connection, the law states that there must be (1) evidence of a current disability; (2) evidence of a service-connected disability; and (3) nexus evidence establishing a connection between a service-connected disability and the current disability. See Wallin v. West, 11 Vet. App. 509, 512 (1998). It is the defined and consistently applied policy of VA to administer the law under a broad interpretation, consistent, however, with the facts shown in every case. When, after careful consideration of all procurable and assembled data, a reasonable doubt arises regarding service origin, the degree of disability, or any other point, such doubt will be resolved in favor of the claimant. 38 C.F.R. § 3.102. In evaluating the evidence in any given appeal, the Board has been charged with the duty to assess the credibility and weight given to evidence. Davidson v. Shinseki, 581 F. 3d 1313 (Fed. Cir. 2009); Jandreau v. Nicholson, 492 F. 3d 1372 (Fed. Cir. 2007); Buchanan v. Nicholson, 451 F. 3d 1331 (Fed. Cir. 2006); Klekar v. West, 12 Vet. App. 503, 507 (1999); Wood v. Derwinski, 1 Vet. App. 190, 193 (1991). Indeed, the Court has declared that in adjudicating a claim, the Board has the responsibility to do so. Bryan v. West, 13 Vet. App. 482, 488-89 (2000); Wilson v. Derwinski, 2 Vet. App. 614, 618 1992). The Veteran maintains that his current back, hip, knee, and foot disorders had their onset in service or are otherwise related to service, to include by way of exposure to AO. In the alternative, the Veteran has claimed that his current disorders are caused and/or aggravated by the service-connected lower extremity peripheral neuropathy. Service treatment records reveal that at the time of the Veteran's February 1970 induction examination, he was noted to have hallux valgus. There were no complaints or findings of low back, hip, knee, or foot trouble in service. At the time of the Veteran's September 1971 service separation examination, normal findings were reported for the spine, lower extremities, and feet. The Veteran indicated that he was in good condition. There were no complaints or findings of lower back, hip, knee, or foot problems in the years immediately following service of for many decades thereafter. In support of his claim, the Veteran submitted a May 2016 letter from his treating chiropractor, K. B., D.C., indicating that the Veteran first reported noticing muscle spasm upon returning from serving in Vietnam in the 70s. Dr. B. stated that since that time, the Veteran continued to be burdened by recurrent muscle spasm of multiple muscle groups located in various regions of his body, including his neck, back, and upper and lower extremities. She noted that there was currently no proof that exposure to Agent Orange directly caused spasm of the muscles, although there was direct correlation with the Veteran's return home when his symptoms first began. She did indicate that the Veteran had other medical conditions which were linked to Agent Orange, including neuropathy and diabetes. The Veteran also submitted a July 2018 letter from his treating VA physician. He noted that he had been caring for the Veteran since July 2015. He indicated that the Veteran had service-connected conditions of diabetes mellitus, type 2; paralysis of the sciatic nerve, and paralysis of the anterior crural nerve. He also had known Agent Orange exposure. The physician stated that due to these conditions, which were service-connected, he had peripheral neuropathy, particularly in the legs. The Veteran also had, over time, since the onset of his neuropathy, developed significant spasm of the muscles in the back. He indicated that after reviewing the Veteran's pertinent records, it was his professional opinion that it was more likely than not that the Veteran's muscle spasms and back pain were the result of his peripheral neuropathy due to the service-connected conditions mentioned above. He stated that it was well known that people with peripheral neuropathy had abnormal gait and feeling in their lower extremities, thereby leading to problems with proprioception. As a result, he had had compensatory mechanisms from the musculature of the spine, causing chronic muscle spasm and tightness. He noted that the Veteran had been receiving regular massage for treatment of his muscle spasms related to the lower extremity peripheral neuropathy. He also stated that he had recommended that the Veteran consider trigger point injections and/or acupuncture in the future. In October 2019, the Board remanded this matter for further development, to include performing VA examinations and obtaining opinions. Following a December 2019 VA examination, the examiner opined that it was less likely than not that that the Veteran's neuropathy aggravated his lumbago and osteoarthritis to the hips and knees. She noted that osteoarthritis was due to aging and lumbago was nonspecific and could also be due to osteoarthritis, which the Veteran had. She stated that neuropathy did not cause muscle spasms either and that spasms of skeletal muscles were most common and were often due to overuse and muscle fatigue, dehydration, and electrolyte abnormalities. In an October 2020 VA examination report, a different VA examiner opined that recent foot examination in July 2019 revealed normal sensory examination with normal/intact monofilament testing. Gait was noted as normal. Peripheral neuropathy of the feet causing no limping or abnormal gait was unlikely to create low transmission of any significant magnitude to cause additional stress on the spine or other leg. Evidence suggested that an injury in one extremity rarely caused a major problem in the opposite or uninjured extremity, except when damage to the leg resulted in a major displacement of the center of gravity of the body while walking, significant shortening of the injured limb, and when the abnormal gait pattern had been present for an extended period of time. The examiner stated that the Veteran's medical record and his medical documentation did not provide any evidence of a gait disturbance. His diabetes mellitus had been well-controlled and present for a short duration. As such, the Veteran's bilateral knee degenerative arthritis, bilateral hip degenerative arthritis, foot condition with hammer toes/hallux valgus, were not aggravated by his peripheral neuropathy. He noted that diabetes had been well controlled (A1c less than 7.0), that it had been of short duration, that there was no documentation of condition worsening beyond natural course after diabetes diagnosis/peripheral neuropathy, and no evidence of a gait abnormality secondary to peripheral neuropathy. The examiner stated that degenerative joint disease was most often the result of normal age-related degenerative change and was commonly seen on x-rays of individuals over age 50. He noted that age related, non-traumatic, degenerative joint disease was usually bilaterally symmetrical. The Veteran was 70 years of age and had bilateral knee, hip, and foot osteoarthritis. He also had degenerative joint disease of the spine. He reported that symmetrical joint arthritis of the same magnitude was less likely due to trauma and more likely due to age-related degenerative changes. He indicated that calling degenerative joint disease a disease was somewhat misleading because these changes occurred with normal aging and frequently caused no symptoms. In fact, many people of age 50 years and over had degenerative joint changes in most joints seen on x-rays or other imaging studies but have no pain or symptoms. In an additional October 2020 VA examination report, the examiner indicated that it was less likely than not that the multilevel degenerative disc disease of the spine was caused by or aggravated beyond its natural progression due to agent orange exposure. The examiner stated that there were no objective clinical randomized trials to support a causal association between degenerative disc disease of the spine and exposure to agent orange. He noted that the weight of the medical literature was against a causal relationship between exposure to agent orange and the development of degenerative disc disease (DDD) of the spine. The examiner stated that the clinical history of Veteran's back pain, including multiple joint pain with mild degenerative joint disease, was pathophysiologically consistent with age-related degenerative joint disease. He had multilevel DDD and bilateral joint arthritis of all joints. Symmetrical joint arthritis of the same magnitude was less likely due to exposure to agent orange and more likely due to age-related degenerative changes. There was no significant medical evidence or rationale supporting a causal relationship between exposure to agent orange and having degenerative joint arthritis after the age of 50. A current musculoskeletal problem with no evidence of continuous symptoms and no evidence of continuous medical treatment since military discharge, was most likely due to a significant intervening interceding event, and less likely related to a musculoskeletal condition of the same body part documented during military service. He observed that most patients who presented with back pain to primary care settings will have nonspecific back pain. Such patients will typically improve over a few to several weeks with conservative or self-care (Deyo & Weinstein, 2001 and Chouet al., 2007). The examiner noted that the Veteran established care at the VA in 2010 and did not complain of any joint pain except that the physician mentioned some mild degenerative joint disease with multiple joint pain. This was an intervening injury related to his age and had nothing to do with exposure to agent orange. The examiner noted that the Veteran was 70 years old and it was normal to have degenerative joint disease after the age of 50. As to the Veteran's bilateral foot conditions, including hammer toes/hallux valgus, the examiner noted that these were not caused nor aggravated by exposure to agent orange. The examiner indicated that there was no known causal association between exposure to agent orange and the subsequent development of hammer toes or hallux valgus. This was a condition that is very prevalent amongst males 50 years and older. It was noted that many theories had been proposed, but the precise etiology of hallux valgus (HV) deformity was unknown. Most likely, HV deformity was multifactorial in origin and included such factors as: abnormal foot mechanics affecting the first ray, abnormal first metatarsophalangeal anatomy, joint hypermobility, and genetic influences. HV was also associated with conditions such as inflammatory joint disease [(Hallux valgus deformity (bunion), 2017]. As to the Veteran's bilateral hip degenerative arthritis/OA, the examiner indicated that it was less likely caused by or aggravated beyond its natural progression by agent orange exposure. The examiner indicated that there were no objective clinical randomized trials to support a causal association between degenerative joint disease of the hip and exposure to agent orange. He noted that the weight of the medical literature was against a causal relationship between exposure to agent orange and the development of degenerative joint disease of the hip. The examiner stated that the clinical history of the Veteran's back pain, including multiple joint pain with mild degenerative joint disease, was pathophysiologically consistent with age-related degenerative joint disease. He had bilateral joint arthritis of all joints. Symmetrical joint arthritis of the same magnitude was less likely due to exposure to agent orange and more likely due to age-related degenerative changes. There was no significant medical evidence or rationale supporting a causal relationship between exposure to agent orange and having degenerative joint arthritis after the age of 50. Osteoarthritis (OA) was a complex interplay between mechanical, cellular, and biomechanical factors leading to end-stage pathology. Multiple risk factors had been linked to OA. OA was the most common form of arthritis in the US, and a leading cause of disability. It was typically defined in epidemiologic studies on the basis of radiographic findings and consideration of symptoms. Its incidence and prevalence were rising, likely related to the aging of the population and increasing obesity. Risk factors for OA included a number of person-level factors, such as age, sex, obesity, and genetics, as well as joint-specific factors that were likely reflective of abnormal loading of the joints. (Neogi & Zhang, 2013). Moreover, a current musculoskeletal problem with no evidence of continuous symptoms and no evidence of continuous medical treatment since military discharge, was most likely due to a significant intervening interceding event, and less likely related to a musculoskeletal condition of the same body part documented during military service. As to bilateral knee degenerative arthritis/OA, the examiner stated that this was less likely caused by or aggravated beyond its natural progression due to agent orange exposure. The examiner indicated that there were no objective clinical randomized trials to support a causal association between degenerative joint disease of the knee and exposure to agent orange. The weight of the medical literature was against a causal relationship between exposure to agent orange and the development of degenerative joint disease of the knee. The clinical history of the Veteran's back pain including multiple joint pain with mild degenerative joint disease was pathophysiologically consistent with age-related degenerative joint disease. The Veteran had multilevel DDD and bilateral joint arthritis of all joints. Symmetrical joint arthritis of the same magnitude was less likely due to exposure to agent orange and more likely due to age-related degenerative changes. There was no significant medical evidence or rationale supporting a causal relationship between exposure to agent orange and having degenerative joint arthritis after the age of 50. OA was a complex interplay between mechanical, cellular, and biomechanical factors leading to end-stage pathology. Multiple risk factors had been linked to OA. OA was the most common form of arthritis in the U.S., and a leading cause of disability. It was typically defined in epidemiologic studies on the basis of radiographic findings and consideration of symptoms. Its incidence and prevalence were rising, likely related to the aging of the population and increasing obesity. Risk factors for OA included a number of person-level factors, such as age, sex, obesity, and genetics, as well as joint-specific factors that were likely reflective of abnormal loading of the joints. (Neogi & Zhang, 2013). Moreover, a current musculoskeletal problem with no evidence of continuous symptoms and no evidence of continuous medical treatment since military discharge, was most likely due to a significant intervening interceding event, and less likely related to a musculoskeletal condition of the same body part documented during military service. As to the DeLuca requirements, there were no additional functional limitations of these joints, including no additional loss of range of motion, during flare-ups, or secondary to repetitive use of the joint, painful motion, weakness, and excessive fatigability, lack of endurance or incoordination. As to the issue of degenerative joint disease secondary to peripheral neuropathy, the examiner opined that the Veteran's degenerative disc disease of the spine was less likely caused by or aggravated by his peripheral neuropathy beyond its natural progression. The examiner indicated that lower extremity peripheral neuropathy did not cause problems with the spine, except when it led to abnormal gait over a very long period. The Veteran had a normal gait and there was no clinical documentation of a limp disorder in his records. He noted that evidence suggested that an injury in one extremity such as peripheral neuropathy affecting the limbs rarely caused a major problem in the spine except when it damaged the legs and resulted in a major displacement of the center of gravity of the body while walking, significantly shortening of the limb, and the abnormal gait pattern had been present for an extended period of time. The Veteran's service treatment records and his medical documentation did not provide any evidence of a gait disturbance secondary to peripheral neuropathy. He established care at the VA in 2010 and did not complain of any joint pain except that the physician mentioned some mild degenerative joint disease with multiple joint pain. This was an intervening injury related to his age and had nothing to do with peripheral neuropathy. He was 70 years of age and it was normal to have degenerative joint disease after the age of 50. In a November 2020 addendum report, the October 2020 VA examiner indicated that the lumbago condition claimed was less likely caused by a claimed in-service injury, event or illness. He noted that the Veteran established care at the VA in 2010 and did not complain of any joint pain except that the physician mentioned some mild degenerative joint disease with multiple joint pain. This was an intervening injury related to his age and had nothing to do with exposure to agent orange. He was 70 years of age and it was normal to have degenerative joint disease after the age of 50. The only time peripheral neuropathy may affect the back is if it caused abnormal gait pattern for such a long time affecting the biomechanics of the spine. The Veteran did not have any evidence of limping secondary to peripheral neuropathy of the feet. Moreover, the peripheral neuropathy was in both feet and would not lead to leg length discrepancy that might affect the biomechanics of the spine. The examiner further indicated that the lumbago was less likely caused by incident in service, including agent orange exposure. He noted that there were no objective clinical randomized trials to support a causal association between degenerative disc disease of the spine and exposure to agent orange. The weight of the medical literature was against a causal relationship between exposure to agent orange and the development of DDD of the spine. The September 1971 separation examination was silent for any back condition and the entire service treatment record was negative for any back injury while in the service. This was an intervening injury related to his age and had nothing to do with exposure to agent orange. He was 70 years of age and it was normal to have degenerative joint disease after the age of 50. The examiner also opined that it was less likely that the Veteran's bilateral hallux valgus was caused by his service-connected peripheral neuropathy of the lower extremities. He noted that HV deformity (ie, bunion) was a common, potentially debilitating deformity consisting of lateral deviation of the hallux on the first metatarsal. Although conclusions regarding causality could not be made, it was well documented in the Veteran's February 1970 enlistment physical examination that his bilateral hallux valgus deformity was a pre-existing condition. Many theories had been proposed, but the precise etiology of HV deformity was unknown. Most likely, HV deformity was multifactorial in origin and included such factors as: abnormal foot mechanics affecting the first ray, abnormal first metatarsophalangeal anatomy, joint hypermobility], and genetic influences. The examiner further opined that it was less likely that the Veteran's bilateral hallux valgus was related to any incident in service. It was clearly and unambiguously documented in his enlistment examination that the condition was pre-existing. The examiner also opined that it was less likely that the Veteran's bilateral hammertoes were caused by his service-connected peripheral neuropathy of the lower extremities. He stated that there was no known causal association between peripheral neuropathy and hammertoes. The mechanism underlying hammertoe deformities was complex. Collapse of the transverse arch was associated with breakdown of the trans-metatarsal ligaments and the plantar plate beneath the metatarsals. If the metatarsal heads "drop" and become entrapped in a defect in the plantar plate, the toe becomes trapped in flexion. This causes some hyperextension of the first phalanx on the MTP joint and may cause flexion at the proximal interphalangeal (PIP) joint, depending on the pattern of tissue injury. The distal interphalangeal (DIP) joint usually remains neutral. Pain may be felt at the plantar surface over the MTP joint. Often when the flexion contracture is significant the dorsum of the PIP joint is pushed against the shoe and calluses form over the joint. These are commonly referred to as traumatic "knuckle pads" and may become painful or cause skin ulceration. The examiner further indicated that it was less likely that the Veteran's bilateral hammertoes were related to any incident in service. He stated that it was an interceding intervening injury that developed decades after leaving active duty service. The separation examination was silent for foot pain or hammer toes. Medical records for many decades after leaving service were silent for hammer toes or foot injuries. A current musculoskeletal problem with no evidence of continuous symptoms and no evidence of continuous medical treatment since military discharge, was most likely due to a significant intervening interceding event, and less likely related to a musculoskeletal condition of the same body part documented during military service. The examiner further opined that it was less likely that the Veteran's bilateral osteoarthritis of the hips had been caused by the service-connected peripheral neuropathy of the lower extremities. He indicated that symmetrical joint arthritis of the same magnitude was less likely due to peripheral neuropathy and more likely due to age-related degenerative changes. There was no significant medical evidence or rationale supporting a causal relationship between peripheral neuropathy of bilateral lower extremity and having degenerative joint arthritis of both hips after the age of 50. A current musculoskeletal problem with no evidence of continuous symptoms and no evidence of continuous medical treatment since military discharge, was most likely due to a significant intervening interceding event, and less likely related to a musculoskeletal condition of the same body part documented during military service. The examiner further opined that it was less likely that the Veteran's bilateral osteoarthritis of the knees had been caused by his service-connected peripheral neuropathy of the lower extremities. He noted that symmetrical joint arthritis of the same magnitude was less likely due to peripheral neuropathy and more likely due to age-related degenerative changes. There was no significant medical evidence or rationale supporting a causal relationship between peripheral neuropathy of bilateral lower extremity and having degenerative joint arthritis of both knees after the age of 50. A current musculoskeletal problem with no evidence of continuous symptoms and no evidence of continuous medical treatment since military discharge, was most likely due to a significant intervening interceding event, and less likely related to a musculoskeletal condition of the same body part documented during military service. Evidence suggested that an injury in one extremity rarely caused a major problem in the opposite or uninjured extremity except when damage to the leg resulted in a major displacement of the center of gravity of the body while walking, significantly shortening of the injured limb, and the abnormal gait pattern had been present for an extended period of time. The Veteran's service treatment records and his medical documentation did not provide any evidence of a gait disturbance secondary to his service-connected injury. Lumbar Spine, to include Degenerative Joint/Disc Disease, and Lumbago After a review of all the lay and medical evidence of record, the Board first finds that service connection for a lumbar spine disorder, to include degenerative joint/disc disease and lumbago, on a presumptive basis as due to exposure to herbicides is not warranted. The Veteran's DD Form 214 shows that he served in the Republic of Vietnam. As such, exposure to herbicides, including AO, during active service is presumed. See 38 C.F.R. § 3.307 (a)(6)(iii). However, the Veteran's current lumbar spine disorders are not diseases that have been deemed associated with herbicide exposure under VA regulation; therefore, a medical nexus may not be presumed as a matter of law. 38 C.F.R. § 3.309(e), Note (2). Moreover, the VA examiners, in several reports, have specifically stated that it was less likely than not that the Veteran's current lumbar spine disorders are related to his AO exposure, indicating that the Veteran's current lumbar spine disorders were the result of other circumstances. Given the foregoing, service connection for a lumbar spine disorder, to include degenerative joint/disc disease and lumbago, on the basis of exposure to AO, is not warranted. The Board is still obliged to fully consider the Veteran's claim on a direct basis. See Combee, 34 F.3d at 1043-44. The Board next finds that the weight of the evidence shows that no lumbar spine injury or disease occurred during service, and no chronic symptoms of a lumbar spine disorder were manifested during service. The service treatment records show no complaint of, diagnosis of, or treatment for a lumbar spine problem. At the Veteran's September 1971 service separation medical examination, normal findings were reported for the spine. The service treatment records, which are complete, show no lumbar spine disorder or disease or symptoms of a lumbar spine disorder/disease during service. Such conditions would have ordinarily been recorded during service because the lumbar spine was evaluated during service. The Board finds that the weight of the evidence demonstrates that there were no "chronic" symptoms of a lumbar spine disorder/disease in service. Therefore, the criteria for presumptive service connection under 38 C.F.R. § 3.303(b) based on "chronic" symptoms in service are not met. The Board next finds that the weight of the evidence is against a finding that symptoms of a lumbar spine disorder, to include degenerative joint disease, were continuously manifested since service, including to a degree of ten percent disabling within one year of service separation. The Board notes the May 2016 letter from K. B., D.C., wherein it was noted that the Veteran first reported noticing muscle spasm upon returning from serving in Vietnam in the 70s. However, the earliest evidence of a lumbar spine disorder diagnosis reflected in the evidence of record is shown decades after service. The absence of post-service findings of, diagnosis of, or treatment for a lumbar spine disorder for decades after service separation is one factor that tends to weigh against a finding of a lumbar spine disorder in service or continuous symptoms after service separation, including to a compensable degree within the first post-service year. See Buchanan v. Nicholson, 451 F.3d 1336 (Fed. Cir. 2006) (the lack of contemporaneous medical records is one fact the Board can consider and weigh against the other evidence, although the lack of such medical records does not, in and of itself, render the lay evidence not credible); see also Maxson v. Gober, 230 F.3d 1330, 1333 (Fed. Cir. 2000) (the passage of many years between discharge from active service and the medical documentation of a claimed disability is one factor to consider as evidence against a claim of service connection). The above contemporaneous evidence is more probative than his recent assertions that his current back disorder had its onset in service, voiced many years after service and in connection with a claim for disability benefits. See Curry, 7. Vet. App. at 68 (1994) (noting that contemporaneous evidence has greater probative value than history as reported by a veteran). Insomuch as the Veteran has attempted to establish a continuity of symptomatology or nexus through his own lay assertions, the Board finds that the etiology of a lumbar spine disorder, to include degenerative joint/disc disease/lumbago falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. See Jandreau, 492 F.3d 1372, 1377 n.4. Opinions as to causation involve making findings based on medical knowledge and clinical testing results, and the musculoskeletal system is complex and involves unseen systems processes and disease processes that are not observable by the five senses of a lay person. Although the Veteran is competent to report having had low back problems in service, he has not been shown competent to identify symptoms or relate symptoms, to a diagnosis of a low back disorder. The evidence does not show clinical documentation of a low back disorder until many years after service. Consequently, the Veteran's opinion that purports to establish continuity of symptomatology or relate a lumbar spine disorder to active service is of no probative value. Moreover, as noted above, the VA examiners, following comprehensive reviews of the record and a thorough examination of the Veteran, opined that a low back disorder, to include degenerative joint/disc disease, and lumbago were less likely than not (less than 50% probability) incurred in or caused by the claimed in-service injury, event or illness, providing detailed rationale to support the opinion. Because the record does not show a lumbar disorder/disease or chronic symptoms of a lumbar spine disorder/disease in service, continuous symptoms of a lumbar spine disorder/disease since service, a lumbar spine disorder/disease manifested to a compensable degree within one year of service separation, or a lumbar spine disorder otherwise related to service, direct and presumptive service connection, including as due to herbicide exposure, for a lumbar spine disorder may not be established. 38 C.F.R. §§ 3.303, 3.307, 3.309. As to the Veteran's belief that his low back disorders are secondarily related to his service-connected peripheral neuropathy, as noted above, the Board finds that the etiology of the Veteran's current lumbar spine disorder falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. See Jandreau, 492 F.3d 1372, 1377 n.4. Consequently, the Veteran's opinion that purports to establish a relationship between his service-connected peripheral neuropathy and his current lumbar spine disorders is of no probative value. Next, service connection may be granted when the evidence establishes a medical nexus between a claimed disability and a service-connected disability. When evaluating the weight of medical evidence, the Board is guided by the principle that the probative value of a medical opinion largely rests upon the extent to which such opinion is based upon a thorough evaluation of the Veteran's medical history, including but not limited to the medical evidence contained in the claims file. See, e.g. Miller v. West, 11 Vet. App. 345, 348. The Board may examine the factual foundation of a medical opinion, including whether the physician had access to relevant information of record. Nieves-Rodriguez v. Peake, 22 Vet. App. 295, 303-304 (2008). As noted above, the Veteran submitted a July 2018 letter from his treating VA physician indicating that it was his professional opinion that it was more likely than not that the Veteran's muscle spasms and back pain were the result of his peripheral neuropathy. The Board finds the opinions rendered by the VA examiners that the Veteran's current lumbar spine disorders were not caused or aggravated by his peripheral neuropathy to be the most probative of record. The VA examiners reviewed the Veteran's entire claims file, which at the time included his service treatment records, VA treatment records, private treatment records, statements from the appellant, and the letters submitted by the Veteran's physicians. Based on all of the evidence, the examiners rendered opinions that were supported by a detailed and complete rationale. There was no indication that the VA examiner was not fully aware of the Veteran's past medical history or that he misstated any relevant fact. He also cited to specific evidence and addressed the evidence noted in the prior Board remand. Thus, the Board finds these opinions to be the most probative evidence of record. Given the foregoing, the claim for service connection for a lumbar spine disorder on a direct, presumptive, and secondary basis must be denied. As the weight of the evidence is against the claim, the benefit-of-the-doubt doctrine does not apply. 38 U.S.C. § 5107(b) (2012); 38 C.F.R. § 3.102; Gilbert v. Derwinski, 1 Vet. App. 49 (1990). Left and Right Hip After a review of all the lay and medical evidence of record, the Board first finds that service connection for a left or right hip disorder, to include degenerative joint disease on a presumptive basis as due to exposure to herbicides is not warranted. The Veteran's DD Form 214 shows that he served in the Republic of Vietnam. As such, exposure to herbicides, including AO, during active service is presumed. See 38 C.F.R. § 3.307 (a)(6)(iii). However, the Veteran's current left and right hip disorders are not diseases that have been deemed associated with herbicide exposure under VA regulation; therefore, a medical nexus may not be presumed as a matter of law. 38 C.F.R. § 3.309(e), Note (2). Moreover, the VA examiners, in several reports, have specifically stated that it was less likely than not that the Veteran's current left and right hip disorders are related to his AO exposure, indicating that the Veteran's current left and right hip disorders were the result of other circumstances. Given the foregoing, service connection for a left or right hip disorder, to include degenerative joint disease, on the basis of exposure to AO is not warranted. The Board is still obliged to fully consider the Veteran's claim on a direct basis. The Board next finds that the weight of the evidence shows that no left or right hip injury or disease occurred during service, and no chronic symptoms of a left or right hip disorder were manifested during service. The service treatment records show no complaint of, diagnosis of, or treatment for a left or right hip problem. At the Veteran's September 1971 service separation medical examination, normal findings were reported for the lower extremities. The service treatment records, which are complete, show no right or left hip disorder or disease or symptoms of a right or left hip disorder/disease during service. Such conditions would have ordinarily been recorded during service because the lower extremities were evaluated during service. The Board finds that the weight of the evidence demonstrates that there were no "chronic" symptoms of a left or right hip disorder/disease in service. Therefore, the criteria for presumptive service connection under 38 C.F.R. § 3.303(b) based on "chronic" symptoms in service are not met. The Board next finds that the weight of the evidence is against a finding that symptoms of a left or right hip disorder, to include degenerative joint disease, were continuously manifested since service, including to a degree of ten percent disabling within one year of service separation. The earliest evidence of a left or right hip diagnosis reflected in the evidence of record is shown decades after service. The absence of post-service findings of, diagnosis of, or treatment for a left or right hip disorder for decades after service separation is one factor that tends to weigh against a finding of a left or right hip disorder in service or continuous symptoms after service separation, including to a compensable degree within the first post-service year. Insomuch as the Veteran has attempted to establish a continuity of symptomatology or nexus through his own lay assertions, the Board finds that the etiology of a right or left hip disorder, to include degenerative joint disease, falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. Opinions as to causation involve making findings based on medical knowledge and clinical testing results, and the musculoskeletal system is complex and involves unseen systems processes and disease processes that are not observable by the five senses of a lay person. Although the Veteran is competent to report having had right or left hip problems in service, he has not been shown competent to identify symptoms or relate symptoms, to a diagnosis of a left or right hip disorder. The evidence does not show clinical documentation of a left or right hip disorder until many years after service. Consequently, the Veteran's opinion that purports to establish continuity of symptomatology or relate a left or right hip disorder to active service is of no probative value. Moreover, as noted above, the VA examiners, following comprehensive reviews of the record and a thorough examination of the Veteran, opined that left or right hip disorder, to include degenerative joint disease, were less likely than not (less than 50% probability) incurred in or caused by the claimed in-service injury, event or illness, providing detailed rationale to support the opinion. Because the record does not show a left or right hip disorder/disease or chronic symptoms of a left or right hip disorder/disease in service, continuous symptoms of a left or right hip disorder/disease since service, a right or left hip disorder/disease manifested to a compensable degree within one year of service separation, or a right or left hip disorder otherwise related to service, direct and presumptive service connection, including as due to herbicide exposure, for a right or left hip disorder, to include arthritis, may not be established. 38 C.F.R. §§ 3.303, 3.307, 3.309. As to the Veteran's belief that his left and right hip disorders are secondarily related to his service-connected peripheral neuropathy, as noted above, the Board finds that the etiology of the Veteran's current left and right hip disorder falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. Consequently, the Veteran's opinion that purports to establish a relationship between his service-connected peripheral neuropathy and his current left or right hip disorders is of no probative value. Next, service connection may be granted when the evidence establishes a medical nexus between a claimed disability and a service-connected disability. The Board finds the opinions rendered by the VA examiners that the Veteran's current left or right hip disorders were not caused or aggravated by his peripheral neuropathy to be the most probative of record. The VA examiners reviewed the Veteran's entire claims file, which at the time included his service treatment records, VA treatment records, private treatment records, statements from the appellant, and the letters submitted by the Veteran's physicians. Based on all of the evidence, the examiners rendered opinions that were supported by a detailed and complete rationale. There was no indication that the VA examiners were not fully aware of the Veteran's past medical history or that they misstated any relevant fact. The examiners also cited to specific evidence and addressed the evidence noted in the prior Board remand. Thus, the Board finds these opinions to be the most probative evidence of record. Given the foregoing, the claim for service connection for a left or right hip disorder on a direct, presumptive, and secondary basis must be denied. As the weight of the evidence is against the claim, the benefit-of-the-doubt doctrine does not apply. 38 U.S.C. § 5107(b) (2012); 38 C.F.R. § 3.102; Gilbert v. Derwinski, 1 Vet. App. 49 (1990). Left and Right Knee After a review of all the lay and medical evidence of record, the Board first finds that service connection for a left or right knee disorder on a presumptive basis as due to exposure to herbicides is not warranted. The Veteran's current left and right knee disorders are not diseases that have been deemed associated with herbicide exposure under VA regulation; therefore, a medical nexus may not be presumed as a matter of law. 38 C.F.R. § 3.309(e), Note (2). Moreover, the VA examiners, in several reports, have specifically stated that it was less likely than not that the Veteran's current left and right knee disorders are related to his AO exposure, indicating that the Veteran's current left and right knee disorders were the result of other circumstances. Given the foregoing, service connection for a left or right knee disorder, to include degenerative joint disease on the basis of exposure to AO is not warranted. The Board is still obliged to fully consider the Veteran's claim on a direct basis. The Board next finds that the weight of the evidence shows that no left or right knee injury or disease occurred during service and no chronic symptoms of a left or right knee disorder were manifested during service. The service treatment records show no complaint of, diagnosis of, or treatment for a left or right knee problem. At the Veteran's service separation medical examination, normal findings were reported for the lower extremities. The service treatment records, which are complete, show no right or left knee disorder or disease or symptoms of a right or left knee disorder/disease during service. Such conditions would have ordinarily been recorded during service because the lower extremities were evaluated during service. The Board finds that the weight of the evidence demonstrates that there were no "chronic" symptoms of a left or right knee disorder/disease in service. Therefore, the criteria for presumptive service connection under 38 C.F.R. § 3.303(b) based on "chronic" symptoms in service are not met. The Board next finds that the weight of the evidence is against a finding that symptoms of a left or right knee disorder, to include degenerative joint disease, were continuously manifested since service, including to a degree of ten percent disabling within one year of service separation. The earliest evidence of a left or right knee diagnosis reflected in the evidence of record is shown decades after service. The absence of post-service findings of, diagnosis of, or treatment for a left or right knee disorder for decades after service separation is one factor that tends to weigh against a finding of a left or right knee disorder in service or continuous symptoms after service separation, including to a compensable degree within the first post-service year. Insomuch as the Veteran has attempted to establish a continuity of symptomatology or nexus through his own lay assertions, the Board finds that the etiology of a right or left knee disorder, to include degenerative joint disease, falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. Although the Veteran is competent to report having had right or left knee problems in service, he has not been shown competent to identify symptoms or relate symptoms, to a diagnosis of a left or right knee disorder. The evidence does not show clinical documentation of a left or right knee disorder until many years after service. Consequently, the Veteran's opinion that purports to establish continuity of symptomatology or relate a left or right knee disorder to active service is of no probative value. Moreover, as noted above, the VA examiners, following comprehensive reviews of the record and a thorough examination of the Veteran, opined that a left or right knee disorder, to include degenerative joint disease, was less likely than not (less than 50% probability) incurred in or caused by the claimed in-service injury, event or illness, providing detailed rationale to support the opinions. Because the record does not show a left or right knee disorder/disease or chronic symptoms of a left or right knee disorder/disease in service, continuous symptoms of a left or right knee disorder/disease since service, a right or left knee disorder/disease manifested to a compensable degree within one year of service separation, or a right or left knee disorder otherwise related to service, direct and presumptive service connection, including as due to herbicide exposure, for a right or left knee disorder, to include arthritis, may not be established. 38 C.F.R. §§ 3.303, 3.307, 3.309. As to the Veteran's belief that his left and right knee disorders are secondarily related to his service-connected peripheral neuropathy, as noted above, the Board finds that the etiology of the Veteran's current left and right knee disorder falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. Consequently, the Veteran's opinion that purports to establish a relationship between his service-connected peripheral neuropathy his current left or right knee disorders is of no probative value. Next, service connection may be granted when the evidence establishes a medical nexus between a claimed disability and a service-connected disability. The Board finds the opinions rendered by the VA examiners that the Veteran's current left or right knee disorders were not caused or aggravated by his peripheral neuropathy to be the most probative of record. The VA examiners reviewed the Veteran's entire claims file, which at the time included his service treatment records, VA treatment records, private treatment records, statements from the appellant, and the letters submitted by the Veteran's physicians. Based on all the evidence, the examiners rendered opinions that were supported by detailed and complete rationale. There was no indication that the VA examiners were not fully aware of the Veteran's past medical history or that they misstated any relevant fact. They also cited to specific evidence and addressed the evidence noted in the prior Board remand. Thus, the Board finds these opinions to be the most probative evidence of record. Given the foregoing, the claim for service connection for a left or right knee disorder on a direct, presumptive, and secondary basis must be denied. As the weight of the evidence is against the claim, the benefit-of-the-doubt doctrine does not apply. 38 U.S.C. § 5107(b) (2012); 38 C.F.R. § 3.102; Gilbert v. Derwinski, 1 Vet. App. 49 (1990). Right and Left Foot After a review of all the lay and medical evidence of record, the Board first finds that service connection for left or right foot disorders, to include hallux valgus and hammertoes, on a presumptive basis as due to exposure to herbicides is not warranted. The Veteran's current left and right foot disorders are not diseases that have been deemed associated with herbicide exposure under VA regulation; therefore, a medical nexus may not be presumed as a matter of law. Moreover, the VA examiners, in several reports, have specifically stated that it was less likely than not that the Veteran's current foot disorders are related to his AO exposure, indicating that the Veteran's current left and right foot disorders were the result of other circumstances. Given the foregoing, service connection for a left or right foot disorder, to include hallux valgus and hammertoes, on the basis of exposure to AO is not warranted. The Board is still obliged to fully consider the Veteran's claim on a direct basis. As to the Veteran's bilateral hallux valgus, a veteran is presumed to have been sound upon entry into active service, except as to conditions noted at the time of the acceptance, examination, or enrollment, or where clear and unmistakable evidence demonstrates that the condition existed before acceptance and enrollment and was not aggravated by such service. 38 U.S.C. § 1111; 38 C.F.R. § 3.304(b); Wagner v. Principi, 370 F.3d 1089 (Fed. Cir. 2004). The Veteran was noted to have hallux valgus at his February 1970 enlistment examination. The VA examiner found that the Veteran's bilateral hallux valgus was clearly and unambiguously documented in his enlistment examination and that the condition was pre-existing. Thus, he is not presumed sound on induction. Service treatment records make no reference to any findings or complaints of right or left foot disorders. Moreover, at the time of the Veteran's September 1971 service separation examination, normal findings were reported for the feet. There were also no reports or findings of right or left foot problems in the years following service. The VA examiner also opined that the Veteran's hallux valgus was not related to any incident in service. Based on the foregoing, the Board finds there was no increase in the severity of the Veteran's preexisting hallux valgus, the presumption of aggravation does not apply. The Board does not doubt the sincerity of the Veteran regarding his perceptions of his foot condition since service and pertaining to service. However, the examination at service entry and discharge provide objective evidence of his foot condition, which demonstrated preexisting hallux valgus at service entrance but normal feet at exit. As indicated previously, the Veteran is not competent to relate foot pain to a diagnosis or to address the etiology or severity of such disorder. Based on the foregoing, the Board finds that the Veteran's hallux valgus, which was noted upon entry into active service, did not increase in severity during service. In reaching this decision, the Board has considered the applicability of the benefit of the doubt doctrine. However, the preponderance of the evidence is against the Veteran's claim of entitlement to service connection for hallux valgus. As to the other foot disorders, including hammertoes and arthritis, the Board next finds that the weight of the evidence shows that no right or left foot injury or disease occurred during service, and no chronic symptoms of a left or right foot disorder were manifested during service or within a year of service. The service treatment records show no complaint of, diagnosis of, or treatment for a left or right foot problem. At the Veteran's service separation medical examination, normal findings were reported for the feet. The service treatment records, which are complete, show no right or left foot disorder or disease or symptoms of a right or left foot disorder/disease during service. Such conditions would have ordinarily been recorded during service because the feet were evaluated during service. The Board finds that the weight of the evidence demonstrates that there were no "chronic" symptoms of a left or right foot disorder/disease in service. Therefore, the criteria for presumptive service connection under 38 C.F.R. § 3.303(b) based on "chronic" symptoms in service are not met. The Board next finds that the weight of the evidence is against a finding that symptoms of a left or right foot disorder, identified as hammertoes and degenerative joint disease, were continuously manifested since service. The earliest evidence of a left or right foot diagnosis, including hammertoes, reflected in the evidence of record is shown decades after service. The absence of post-service findings of, diagnosis of, or treatment for a left or right foot disorder, to include hammertoes and arthritis, for decades after service separation is one factor that tends to weigh against a finding of a left or right foot hammertoes or arthritis in service or continuous symptoms after service separation. Insomuch as the Veteran has attempted to establish a continuity of symptomatology or nexus through his own lay assertions, the Board finds that the etiology of a right or left foot disorder, to include hallux valgus, hammertoes, and degenerative joint disease, falls outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. Although the Veteran is competent to report having had right or left foot problems in service, he has not been shown competent to identify symptoms or relate symptoms, to a diagnosis of a left or right foot disorder. The evidence does not show clinical documentation of hammertoes or arthritis until many years after service, and, as noted above, hallux valgus was shown to have preexisted service and was not aggravated by service. Consequently, the Veteran's opinion that purports to establish continuity of symptomatology or relate a left or right foot disorder to active service is of no probative value. Moreover, as noted above, the VA examiners, following comprehensive reviews of the record and a thorough examination of the Veteran, opined that left or right foot disorders, to include hallux valgus, arthritis, and hammertoes, were less likely than not (less than 50% probability) incurred in or caused by the claimed in-service injury, event or illness, providing detailed rationale to support the opinion. Because the record does not show a left or right foot disorder (other than preexisting hallux valgus) or chronic symptoms of a left or right foot disorder in service, continuous symptoms of a left or right foot disorder since service, foot problems within one year of service, or a right or left foot disorder otherwise related to service, direct and presumptive service connection, including as due to herbicide exposure, for a right or left foot disorder, may not be established. 38 C.F.R. §§ 3.303, 3.307, 3.309. As to the Veteran's belief that his left and right foot disorders are secondarily related to his service-connected peripheral neuropathy, as noted above, the Board finds that the etiology of the Veteran's current left and right foot disorders fall outside the realm of common knowledge of a layperson and the Veteran is, thus, not competent to provide evidence on the issue of causation. Consequently, the Veteran's opinion that purports to establish a relationship between his service-connected peripheral neuropathy and his current left or right foot disorders is of no probative value. Next, service connection may be granted when the evidence establishes a medical nexus between a claimed disability and a service-connected disability. The Board finds the opinions rendered by the VA examiners that the Veteran's current left or right foot disorders were not caused or aggravated by his peripheral neuropathy to be the most probative of record. The VA examiners reviewed the Veteran's entire claims file, which at the time included his service treatment records, VA treatment records, private treatment records, statements from the appellant, and the letters submitted by the Veteran's physicians. Based on all of the evidence, the examiners rendered opinions that were supported by a detailed and complete rationale. There was no indication that the VA examiners were not fully aware of the Veteran's past medical history or that they misstated any relevant fact. They also cited to specific evidence and addressed the evidence noted in the prior Board remands. Thus, the Board finds these opinions to be the most probative evidence of record. Given the foregoing, the claim for service connection for a left or right foot disorders on a direct, presumptive, and secondary basis must be denied. As the weight of the evidence is against the claim, the benefit-of-the-doubt doctrine does not apply. 38 U.S.C. § 5107(b) (2012); 38 C.F.R. § 3.102; Gilbert v. Derwinski, 1 Vet. App. 49 (1990). K. Parakkal Veterans Law Judge Board of Veterans' Appeals Attorney for the Board T. S. Kelly, Counsel The Board's decision in this case is binding only with respect to the instant matter decided. This decision is not precedential and does not establish VA policies or interpretations of general applicability. 38 C.F.R. § 20.1303.