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.

Observations on retrieved polyethylene glenoid components.

It is recognized that retrieved polyethylene hip and knee components may undergo substantial changes from their preimplantation form. Little information is available, however, regarding retrieved polyethylene glenoid components. We report on 39 glenoid components removed at an average of 2.5 years after implantation. Of components for which clinical data were available, the commonest reason for the revision arthroplasty was loosening of the glenoid component; many components also showed glenohumeral instability. The articular surface contours of most of the components were altered. Of components, 28 had obvious erosion of the rim, 27 had surface irregularities, 11 were fractured, and 9 had central wear. These observations in retrieved glenoid components point to the potential of polyethylene for deformation in vivo, especially when the mechanics of the arthroplasty are compromised.

Management of the stiff shoulder.

Shoulder stiffness occurs as a result of (1) contractures of the intraarticular capsule or muscle-tendon units or (2) adhesions within the extraarticular humeroscapular or scapulothoracic motion interface. These contractures or adhesions may occur independently or in combination. A thorough history and physical examination usually reveal the diagnosis (idiopathic frozen shoulder or posttraumatic stiff shoulder) and the anatomical locations of fibrosis that is causing stiffness, and identifies other treatable conditions associated with shoulder stiffness (such as diabetes). A gentle home program of passive stretching is effective in most patients. When the home program is not effective, a manipulation or surgical release may be indicated. If manipulation is not effective, capsular contractures are best released arthroscopically as this allows circumferential release without damaging the rotator cuff and thus allows rehabilitation without the need to protect the rotator cuff. The humeroscapular motion interface adhesions can be released either open or arthroscopically, but we believe that an open release combined with an arthroscopic capsular release is quicker and does not interfere with rehabilitation. When necessary, operative management coupled with an aggressive rehabilitation program can provide significant relief of pain and restoration of shoulder motion. Approximately 90% of patients can expect a good result with this treatment algorithm.

The lateral impaction of the shoulder.

17 patients had radiographic demonstration of injury to the clavicle, scapula and ribs from an impact delivered to the lateral shoulder. The study included 13 males and 4 females whose ages ranged from 18 to 83 years (average 45 years). Most injuries were sustained in falls or motor vehicle accidents. Analysis of these cases suggests a biomechanical hypothesis concerning the transmission of the impact forces within the shoulder girdle. According to this hypothesis, the impaction force applied to the lateral shoulder is transmitted from outside inward following two paths. The anterior and superior path passes through the acromio-clavicular joint, the clavicle, the costo-clavicular joint and the sterno-clavicular joint. The posterior and inferior path is transmitted within the gleno-humeral joint, the scapula and the scapulo-thoracic joint. Major impacting force is required to disrupt the anterior and posterior arches of the shoulder girdle. When both of these supporting structures are damaged, the patient is at risk for more serious injuries, including disruption of the thorax, shoulder joint, brachial plexus and neck.