Possible role of carpal hyperextension in superficial digital flexor tendinopathy.

REASONS FOR PERFORMING STUDY

The specific biomechanical circumstances that induce excessive superficial digital flexor tendon (SDFT) strain in horses are unknown.

HYPOTHESIS

Carpal joint hyperextension during axial limb loading during the middle of stance disproportionately enhances SDFT strains compared to suspensory ligament (SL) strains.

METHODS

Superficial digital flexor tendon and SL strains were measured in 7 cadaver limbs during in vitro loading that maintained carpal extension or allowed carpal hyperextension by constraining, or allowing rotation of, the radius during loading conditions that simulated the middle of stance at the walk. The effect of carpal hyperextension on SDFT and SL strains and joint angles was assessed using repeated measures ANOVA.

RESULTS

Limb loading generally resulted in higher SL strains than SDFT strains for both carpal extension and hyperextension loading conditions. Compared to carpal extension, carpal hyperextension resulted in increased strains in both the SDFT and the SL; however, a greater increase in strain was seen in the SDFT. On average, carpal hyperextension caused approximately 3° greater carpal extension, 1° greater metacarpophalangeal joint hyperextension, 1° greater proximal interphalangeal joint flexion and <1° greater distal interphalangeal joint flexion than did carpal extension.

CONCLUSIONS AND CLINICAL RELEVANCE

Carpal joint hyperextension is likely to induce disproportionately higher strain in the SDFT than in the SL. Factors that affect carpal stability are likely to affect the risk for superficial digital flexor tendinopathy.