Desmotomy of the accessory ligament of the superficial digital flexor muscle in equine cadaver limbs.

This study investigates the role of an equine’s accessory ligament in the superficial digital flexor muscle by examining the effects of its removal on cadaver horse forelimbs under various degrees of pressure.

Research Methodology

• The researchers used eight equine cadaver forelimbs to perform this experiment.
• Initially, they applied longitudinal compression on these limbs and noted the changes. The pressure was gradually increased from 890 Newtons to 3115 Newtons.
• They carefully examined the impact compression had on the metacarpophalangeal (MCP) and carpal joints, and on superficial digital flexor (SDF) and deep digital flexor tendons.
• Following this initial analysis, they then performed a transection on the accessory ligament of each limb (this procedure is called a desmotomy), and noted the immediate and subsequent changes.

Initial Impact of Compression

• Upon increasing the compression from 890 N to 3115 N, they observed that the MCP and carpal joints hyper-extended by 20 degrees and 4 degrees, respectively.
• Strain in the SDF and deep digital flexor tendons also increased. The SDF strain increased by 3.5%, while the deep digital flexor tendons saw a strain increase of 1.4%.
• The accessory ligament remained unaffected, with no noticeable elongation under the increased pressure.

Desmotomy and Its Effects

• Following the transection of the accessory ligament under the load of 3115 N, a 2.8 mm gap formed between the ends of the ligament.
• The muscle belly of the SDF muscle lengthened and moved distally (towards the hoof).
• Additionally, the MCP joint hyper-extended 15.8% further and strain on the SDF tendon increased a further 11.2%.
• This suggested that the accessory ligament was previously taking on significant load and transferring it away from the muscle belly of the SDF.
• After desmotomy, the transferred load likely ended up being redistributed and applied back to the SDF musculotendinous unit.

Conclusions

• The findings of this study illustrate that the accessory ligament plays a critical role in load management within the equine limb, especially in diverting pressure away from the superficial digital flexor muscle.
• The decrease in the MCP joint angle after desmotomy indicates that the accessory ligament also contributes to the support of the MCP joint when under load.
• The increase in strain on the SDF following desmotomy suggests that this change could likely be due to the increased length of the SDF musculotendinous unit, and the shift in the moment about the MCP joint.