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Abstract

A Novel Method for Fetlock Arthrodesis: A Comparison of the Wire/Plate Method and an Intramedullary Interlocking Nail Method

Amy Cockerham, Jeffrey P. Watkins, D.V.M., M.S, Diplomate, A.C.V.S

Abstract

Objective - To overcome the biomechanical problems of fetlock arthrodesis using an intramedullary interlocking nail technique.

Animals- Twelve pairs of horse legs collected from the Texas A&M University Necropsy Lab.

Procedure- All horse legs were obtained from the Texas A&M Necropsy Lab.  All horses used were adult, full size horses that were not euthanized for orthopedic problems.

The case number and right/left were indicated, and the legs were wrapped in a saline soaked towel and frozen until needed.  The plate/wire technique was performed on one leg of each pair.  To begin the procedure, the superficial and deep digital flexor tendons and the suspensory ligament were cut to mimic the suspensory breakdown that actually occurs in the racehorses.  An incision was made longitudinally on the dorsal surface of the cannon bone, and a 14 hole broad plate was placed on the dorsal surface.  Each hole in the plate was drilled, tapped, and then fitted with a 5.5mm cortical screw.  A 1.5mm tension band wire was placed in a figure eight pattern on the palmar surface of the joint. (doubled).  The intramedullary interlocking nail was implanted into the second leg of the pair.  First, the fetlock joint was disarticulated, and the medullary cavity of the cannon bone was reamed using increasing sizes of drill bits.  The metacarpal component of the nail was inserted into the cavity, and a targeting jig was used to place the cortical screws in this half of the implant.  Then, the proximal phalanx was reamed in a similar manner being careful to maintain the alignment.  Again the targeting jig was used to place the cortical screws in this section of the implant.  The pair of legs was then taken to the materials testing lab to undergo hydraulic compression.  Each leg was placed in the machine and compressed at the rate of 1" per minute until notable failure of either the construct was noted.