Relief of patellofemoral contact stress by anterior displacement of the tibial tubercle.

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Abstract
Elevation of the patellar tendon by means of displacement of the tibial tubercle has been advocated by Maquet, Ficat and Hungerford, and Murray as an alternative to patellectomy for the treatment of patellofemoral arthralgias. Although tubercle elevation certainly reduces the over-all patellofemoral contact force, its effects on the complex local patterns of contact stress are of more direct significance. In a laboratory series using fresh amputation material, arrays of six miniature contact stress sensors were embedded in the retropatellar cartilage of knees subjected to isometric quadriceps-extension forces. The experimental data revealed that elevation of the patellar tendon generally afforded relief of local contact stress regardless of the joint configuration (zero degrees, 45 degrees, or 90 degrees of flexion), but that its effects were most pronounced at 90 degrees of flexion. Progressive increase in the tendon elevation caused progressive reduction in the contact stress. Most of the contact stress relief was achieved, however, with the first one-half inch of tendon elevation; further elevations to one and one and one-half inches were only marginally useful. In view of the increased superior patellar pole contact associated with distal pole flotation, the results indicate that under most circumstances the optimum amount of elevation of the tibial tubercle is about one-half inch.

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