In vivo quantification of capsular end-point in the nonimpaired glenohumeral joint using an instrumented measurement system

Study Design: Single-group factorial. Objectives: Quantify glenohumeral joi nt translations as a function of force using an instrumented measurement sy stem. Our first specific aim was to compare the magnitude of force (N) requ ired to reach capsular end-point between the anterior, posterior, and infer ior directions. Our second specific aim was to compare the magnitude of tra nslation (mm) at capsular end-point between the anterior, posterior, and in ferior directions. Background: Manual force-displacement techniques are subjective in nature, and the clinician must rely on "feel" to determine capsular end-point. Seve ral investigators have attempted to utilize more objective measures at the glenohumeral joint, however none have quantified the force or displacements necessary to achieve a true capsular end-point. Methods and Measures: An arthrometric technique was used to measure anterio r, posterior, and inferior glenohumeral translations in 20 nonimpaired shou lders (11 women and 9 men with a mean age of 20.9 +/- 3.6 years). Results: The magnitude of applied force required to reach capsular end-poin t was significantly different between directions of translations. Anterior- directed translations required a significantly greater magnitude of applied force to reach capsular end-point than inferior-directed translations. The magnitude of translation was not significantly different between direction s at capsular end-point. Conclusions: Applied forces in the range of 181 to 203 N are necessary to r each capsular end-point in subjects with nonimpaired shoulders. Anterior tr anslation required significantly higher forces (203.1 =/- 13.1 N) to reach capsular end-point than inferior translation (181.4 +/- 31.9 N).