Microangiographic comparison of the effects of the three-loop pulley and six strand Savage tenorrhaphy techniques on the equine superficial digital flexor tendon

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Virginia Tech

Injuries to the equine distal limb are common and often involve synovial, tendinous and/or ligamentous structures. Historically, lacerations involving the equine digital flexor tendons carried a poor prognosis for return to athletic function due to contamination of the site at presentation, involvement of multiple anatomic structures and the need for immediate weight bearing after surgery. The need for weight bearing after surgery places strain on the tenorrhaphy site that exceeds the strength of the repair itself. Extrapolation of complex, stronger tenorrhaphy patterns from human literature and applying them to equine patients has been challenging.

Human tenorrhaphy techniques initially focused on strong repairs, which are able to match or exceed the strength of tendon itself. Adhesion formation is problematic in human flexor tenorrhaphies, as most injuries occur to tendons surrounded by synovial structures. Human literature now focuses on using repairs that provide initial strength, minimal damage to intrinsic tendon architecture, and allow for early mobilization. This treatment protocol has greatly improved the functional outcome of human tenorrhaphies.

Recent studies have evaluated the strength of complex tenorrhaphy patterns in equine superficial digital flexor tendons, using modifications of the Savage technique. The newly evaluated patterns are stronger than previously tested and commonly used techniques, such as the three-loop pulley (3LP). A review of tendon vasculature across species and healing characteristics of tendons highlights the importance of intrinsic tendon vasculature in the healing process. Using tenorrhaphy techniques that preserve this vasculature may improve the clinical outcome in these cases. Only one study has previously evaluated the effect of tenorrhaphy patterns on intrinsic tendon vasculature in equine superficial digital flexor tendon.

This study compared perfusion of intrinsic tendon vasculature of equine superficial digital flexor tendon (SDFT) after 3LP and six-strand Savage (SSS) tenorrhaphies. We hypothesized that the SSS technique would significantly decrease vascular perfusion compared to the 3LP technique.

Under general anesthesia, eight pairs of forelimb SDFTs were transected and either SSS or 3LP tenorrhaphy was performed on each forelimb. The horses were heparinized, euthanatized, and forelimbs perfused with barium sulfate solution then fixed with formalin under tension. The tendons were transected every 5mm and microangiographic images were obtained using a Faxitron X-ray cabinet with computed radiography imaging. Microvascular analysis of sections proximal to the tenorrhaphy, throughout the tenorrhaphy and distal to the tenorrhaphy was completed using Image J software and a custom macro.

A significant reduction in the number of perfused vessels was seen in the SSS compared to the 3LP at two locations within the tenorrhaphy (p=0.004 and 0.039). The SSS technique took on average 4.7 ± 0.9 times longer to place.

The SSS technique causes a reduction in tendon perfusion compared to the 3LP, which may limit its clinical use. Further research is required to elucidate the clinical significance of this difference.

tendon, perfusion, equine, laceration