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.