In vivo assessment of AP laxity in healthy shoulders using an instrumented arthrometer

Arthrometric assessment for glenohumeral (GH) laxity is currently unprecedented in orthopedic practice. Clinical evaluation of GH laxity is based on manual tests that lack objectivity and reliability. We have developed an arthrometer that quantifies AP laxity relative to applied load. Forty healthy shoulders were assessed for AP laxity at 67-, 89-, 111-, and 134-N load levels. A factorial ANOVA revealed significant mean (+/- SD) differences between directions (p < .0001) and between loads (p < .001). Our results demonstrate the quantified relationship between applied directional loads and GH translation in vivo. We determined bilateral symmetry within subjects and demonstrated excellent reproducibility of the device. Frequency distributions for AP laxity revealed a bell-shaped curve, indicating a normal distribution. Anterior laxity was significantly greater then posterior laxity, and it demonstrated better compliance between the selected load levels.