Possible role of carpal hyperextension in superficial digital flexor tendinopathy.

The research article investigates the potential role of carpal hyperextension (over-extension of the wrist joint) in causing strain on the superficial digital flexor tendon (SDFT) in horses. It suggests that such strain may contribute to the development of superficial digital flexor tendinopathy, a common and serious injury in horses.

Objective and Methods

• The study aims to understand the biomechanical circumstances that lead to excessive strain on the horse’s SDFT, specifically considering the impact of carpal joint hyperextension during the part of a horse’s walk where the limb is carrying the maximum weight (the middle of stance).
• The researchers used in vitro loading on seven cadaver horse limbs to measure strains on the SDFT and the suspensory ligament (SL). The loading simulated the middle of stance at a walk, and was carried out in two conditions: once maintaining carpal extension (normal movement), and once allowing carpal hyperextension (over-extension).
• The effect of this hyperextension on strains and joint angles was then statistically analysed through repeated measures ANOVA.

Results

• Generally, SL strains were found to be higher than SDFT strains under both conditions. However, carpal hyperextension lead to increased strains on both ligaments, with a notably greater increase seen in the SDFT.
• Carpal hyperextension also resulted in slight increases in joint angles across the limb, indicating increased flexion (bending).

Conclusions

• The study concludes that carpal joint hyperextension is likely to induce a disproportionately higher strain on SDFT than on SL, which may increase the risk of developing superficial digital flexor tendinopathy.
• It suggests that factors influencing carpal stability, such as ligament strength or physical therapy practices, might also play a role in managing or preventing this risk.