Which anatomical region determines a positive flexion test of the distal aspect of a forelimb in a nonlame horse?
Authors: Kearney C M, van Weeren P R, Cornelissen B P M, den Boon P, Brama P A J
Journal: Equine veterinary journal
Summary
# Editorial Summary When a flexion test produces lameness in a clinically sound horse during prepurchase or lameness evaluation, practitioners have traditionally assumed the positive response indicates pathology throughout the distal forelimb; however, this 2010 study systematically challenged that assumption by using selective nerve blocks to isolate which anatomical structures actually contribute to the flexion-induced lameness response. Eight Dutch Warmblood horses underwent standardised flexion testing (250 N force, 60 seconds duration) followed by sequential nerve blocks—targeting the low palmar digital nerves, palmar nerves at the base of the proximal sesamoids, high palmar, ulnar, and low 4-point regions—with lameness scoring before and after each block in separate sessions. Notably, blocking structures distal to the metacarpophalangeal joint (low palmar digital and abaxial sesamoid nerve blocks) produced no significant reduction in flexion-induced lameness, whereas blocks of the ulnar and high palmar nerves significantly reduced the response, with the low 4-point block producing the most dramatic effect. These findings indicate that positive flexion tests in nonlame horses predominantly reflect soft tissue or joint involvement at the level of the metacarpophalangeal joint itself, rather than the digital structures, suggesting that practitioners should focus further investigation on the fetlock region when a distal forelimb flexion test proves positive, and may need to reconsider the test's relevance for identifying isolated problems in the foot or pastern.
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Practical Takeaways
- •Use the distal forelimb flexion test to specifically assess the metacarpophalangeal joint and surrounding structures; results may be less informative for investigating distal structures such as the digital tendon or collateral sesamoidean ligaments
- •A positive flexion test response does not necessarily indicate pathology distal to the fetlock—focus diagnostic follow-up accordingly
- •The flexion test is relatively insensitive for lesions in the distal interphalangeal joint, navicular region, or deep digital flexor tendon in sound horses
Key Findings
- •Low palmar digital nerve blocks and abaxial sesamoid nerve blocks did not significantly reduce flexion test-induced lameness
- •Ulnar, high palmar, and low 4-point nerve blocks significantly reduced flexion test lameness scores (P<0.05)
- •Anatomical structures distal to the metacarpophalangeal joint contribute minimally to positive flexion test responses
- •The metacarpophalangeal joint region is the primary anatomical area responsible for flexion test outcomes in nonlame horses