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Despite the well-recognized association between poorly reduced intraarticular fractures and late degenerative changes, current guidelines regarding the reduction precision necessary to avoid excessive cartilage pressures are based largely on anecdotal clinical observations. To gain a quantitative appreciation of the relation between local pressure elevations and fracture reduction imprecision, a simplified laboratory cadaver model of minimally displaced tibial plateau fractures was developed. Cartilage contact stress distributions were measured as a function of depressed fragment malreduction in seven knees, using high-resolution (100 pixels/mm2) digital image scans of Fuji-film stain patterns. The contact stress data showed a general trend of increases of peak local pressure with increasing fracture site incongruity, and in a few isolated instances the effect was very pronounced. Across the whole series, however, statistically significant departures from anatomic pressure levels did not occur until the fragment stepoff was greater than 1.5 mm. Even at the 3-mm stepoff level, for which the depressed fragment usually no longer made contact with the femoral condyle, the peak local pressure values on the intact side of the fracture line averaged only approximately 75% greater than those prevailing anatomically. Given the successful clinical outcomes normally achieved for conservatively managed simple tibial plateau fractures having stepoff magnitudes (5-10 mm) clearly sufficient to insure fragment articular noncontact, the present laboratory results suggest that nominally factor-of-two peak local pressure elevations, provided that they occur over only small portions of the cartilage surface, are probably within the long-term overall tolerance range of an articular joint.

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The purpose of this study was to evaluate the relative contributions of ankle and knee position to tension in the Achilles tendon and to determine whether there exists a position of plantarflexion at which the passive tensioning effect of knee extension is eliminated. Seven matched pairs of fresh-frozen cadaver lower extremities were tested. A buckle transducer was used to measure forces in the tendon throughout the full range of knee motion, with the hindfoot fixed. Positioning the hindfoot in 20 degrees to 25 degrees of plantarflexion effectively eliminates tension in the Achilles tendon, regardless of knee position. This information is directly applicable both to the nonoperative treatment of ruptures of the Achilles tendon employing a short leg cast and to surgical repairs, in which tension must be controlled precisely.