DETERMINATION OF SAFE DEPTH OF PIN PENETRATION FOR REPAIR OF DISTAL FEMORAL PHYSEAL FRACTURES IN IMMATURE DOGS - A COMPARISON OF NORMOGRADEAND RETROGRADE PIN PLACEMENT

Objective-The purpose of this study was to determine the depth that im plants may be safely placed into the distal femoral epiphysis (DFE) fo r the repair of distal femoral physeal fractures. Study Design-The dep th of the DFE was related to the radiographic thickness of the patella in this experimental study. Animals or Sample Population-Twenty immat ure canine cadavers. Methods-Patella thicknesses were measured from la teral radiographs. Actual DFE depths were determined for pins driven i n normograde fashion and for pins driven retrograde from the central d epression between the metaphyseal pegs and from the cranial pegs. The association of DFE depth and patella thickness was evaluated using lin ear regression analysis. Using 95% confidence intervals, rules for est imating the safe depth of implant placement into the DFE were determin ed. Results-DFE depth had significant correlation with patella thickne ss for pins placed in retrograde fashion from the central depression b etween the metaphyseal pegs (r(2) = .83) and from the cranial pegs (r( 2) = .82) and for pins placed in normograde fashion (r(2) = .65). Conc lusions-Based on 95% confidence intervals, pins placed in retrograde f ashion from the central depression between the metaphyseal pegs may be safely driven into the DFE a distance equal to 140% of patella thickn ess. Pins placed from the cranial metaphyseal pegs may be driven to a depth equal to 80% of patella thickness, and pins placed in normograde fashion may be driven to a depth equal to 30% of patella thickness. C linical Relevance-Measurement of patella thickness assists the surgeon in determining the approximate depth that pins may be driven into the DFE without penetrating the articular surface of the stifle joint. (C ) Copyright 1997 by The American College of Veterinary Surgeons.