COMPUTER-SIMULATION OF GLENOHUMERAL AND PATELLOFEMORAL SUBLUXATION - ESTIMATING PATHOLOGICAL ARTICULAR CONTACT

Analytic stereophotogrammetry and an interactive computer graphics pro gram were used to obtain first order assessments of joint contact patt erns in patellofemoral and glenohumeral joints, simulating normal and abnormal articulations. Precise (90 micron accuracy) computer graphic representations of the humeral head, glenoid, patella, and femoral art icular surfaces were obtained from cadaver knees and shoulders. These surface representations were then manipulated into an articulated posi tion, and joint contact areas computed by a proximity criterion. Patho logic states were then simulated, and contact recomputed. Simulated gl enohumeral subluxations dramatically reduced contact area, and focused it eccentrically on the glenoid rim. Simulated size mismatch of humer al heads to glenoids reduced contact area, producing a pattern of peri pheral contact on the glenoid if the humeral head had a larger radius of curvature, and central contact on the glenoid if the humeral head h ad a smaller radius of curvature. At 30 degrees knee flexion, the pate llofemoral joint demonstrated a broad distribution of contact along th e distal aspect of the patella and proximal aspect of the trochlea. Si mulated lateral tilt (5 degrees) and translation (5 mm) of the patella resulted in shift of the predominant contact area laterally, along wi th a drastic decrease in the contact area. These results have implicat ions for prosthetic sizing and biomechanical modeling of the glenohume ral and patellofemoral joints, and in selecting models for more rigoro us empiric studies of joint contact. Furthermore, this technique allow s a first order assessment of the effects specific surgical reconstruc tions on articular mechanics.