Glenohumeral pressure with surface replacement arthroplasty versus hemiarthroplasty.

It is not known whether significant differences in the glenohumeral center of pressure and contact pressure exist between surface replacement arthroplasty and hemiarthroplasty compared with the native joint. Twelve fresh-frozen cadaveric shoulders were dissected free of soft tissue, and the joint capsule was removed. The scapula was potted with the glenoid parallel to the ground. A pressure-sensitive sensor was placed in the glenohumeral joint, and each specimen was tested in sequence: intact, surface replacement, and hemiarthroplasty. Loading was done with a 440-N compression load at 0.5 Hz with the shoulder in 4 different positions. The center of pressure and contact pressure were measured at each position. The glenohumeral contact pressure with surface replacement was not different from intact pressure in 2 arm positions. Pressure with hemiarthroplasty was significantly different compared with the intact shoulder at all 4 arm positions and compared with the surface replacement group at 2 arm positions (P≤.05). Change in the anterior-posterior center of pressure from intact was significantly smaller with surface replacement compared with hemiarthroplasty with the humerus at 0° flexion/0° abduction and at 0° flexion/90° abduction (1.11±0.89 mm vs 2.38±1.62 mm, P=.02, and 0.68±0.50 mm vs 2.37±2.0 mm, P=.01, respectively). Change in the superior-inferior center of pressure was significantly smaller with surface replacement vs hemiarthroplasty at 0° flexion/0° abduction and at 90° flexion/90° abduction (0.98±1.16 mm vs 2.33±1.38 mm, P=.02, and 1.50±1.28 mm vs 2.90±1.92 mm, P=.04, respectively). Compared with hemiarthroplasty, surface replacement arthroplasty more closely replicated the contact pressure and center of pressure in the intact glenohumeral joint.