Intrinsic stability of unused and retrieved polyethylene glenoid components.

The surface geometry of polyethylene components can be altered by in vivo use. The purpose of this investigation is to document the effects of these changes on the intrinsic stability provided by the glenoid component. We validated a method of measuring the intrinsic stability of glenoid components as indicated by the balance stability angle (the maximal angle between the glenoid centerline and the resultant humeral force before dislocation of the humeral head occurs). We compared observed values with those predicted for unused glenoid components for which the geometry was known. We then applied this method to retrieved glenoid components in which the surface geometry had been altered by in vivo use. The balance stability angles measured in retrieved glenoids were often substantially reduced: 11 of 24 glenoids had diminished balance stability angles of at least 30% in at least one direction. We concluded that the surface geometry of polyethylene glenoid components can be altered by in vivo use in a manner that may compromise their contribution to glenohumeral stability.

Upper extremity overuse injuries in swimming. A discussion of swimmer's shoulder.

Treatment of shoulder pain includes the following: 1. Avoid all painful activities. 2. A 2-week course of nonsteroidal anti-inflammatory medication and ice. 3. Decreased anterior capsule stretching and increased posterior capsule stretching. 4. Increased rotator cuff exercise with emphasis on external rotators. 5. Scapular-positioning muscle exercises and increasing body roll. Shoulder pain can be prevented by the following: 1. Avoid all painful activities, and notify coach of shoulder pain immediately. 2. Do not use nonsteroidal anti-inflammatory medications or ice on a chronic basis. 3. Spend equal time stretching the posterior and anterior capsules. 4. Perform general rotator cuff exercises. 5. Perform scapular-positioning muscle exercises, with emphasis on body roll. [figure: see text] Shoulder pain in swimmers is common and can be debilitating. Most of the pain is caused by instability, which stems from swimming-specific demands that increase performance but decrease shoulder stability. These sport-specific demands are (1) increased shoulder range of motion, (2) increased internal rotation and adduction strength, and (3) prolonged, fatiguing, shoulder-intensive training. Instability leads to [figure: see text] inflammation and pain and can become a self-perpetuating process. Treatment consists of patient education, cessation of all activities that cause pain, activity modifications to increase shoulder stability, and pharmacologic treatment of the inflammation. In patients who do not improve using this regimen, surgery can be of benefit, either to reduce capsular laxity or to remove chronic inflammation and scar tissue. The patient must be aware of the risk of decreased performance.

Filtering closed curves.

A closed curve in the plane can be described in several ways. We show that a simple representation in terms of radius of curvature versus normal direction has certain advantages. In particular, convolutional filtering of the extended circular image leads to a closed curve. Similar filtering operations applied to some other representations of the curve do not guarantee that the result corresponds to a closed curve. In one case, where a closed curve is produced, it is smaller than the original. A description of a curve can be based on a sequence of smoothed versions of the curve. This is one reason why smoothing of closed curves is of interest.