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Mechanics of Glenohumeral Arthritis.

Last updated Thursday, January 27, 2005

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Introduction

The humeral head and the glenoid normally articulate through smooth, congruent and well lubricated joint surfaces.

About arthritis of the shoulder

Glenohumeral arthritis results when these joint surfaces are damaged by congenital, metabolic, traumatic, degenerative, vascular, septic, or nonseptic inflammatory factors. These conditions are common, especially in older populations where the prevalence approaches 20% (Chard and Hazleman, 1987; Jenkinson et al., 1989; van Schaardenburg et al., 1994) In degenerative joint disease, the glenoid cartilage and subchondral bone are typically worn posteriorly, sometimes leaving intact articular cartilage anteriorly. The cartilage of the humeral head is eroded in a pattern of central baldness, often surrounded by a rim of remaining cartilage and osteophytes. In inflammatory arthritis, the cartilage is usually destroyed evenly across the humeral and glenoid joint surfaces. Cuff tear arthropathy occurs when a chronic large rotator cuff defect subjects the uncovered humeral articular cartilage to abrasion by the undersurface of the coracoacromial arch. The erosion of the humeral articular cartilage begins superiorly rather than centrally. Neurotrophic arthropathy arises in association with syringomyelia, diabetes, or other causes of joint denervation. The joint and subchondral bone are destroyed because of the loss of the trophic and protective effects of its nerve supply. In capsulorrhaphy arthropathy prior surgery for glenohumeral instability leads to joint surface destruction. In this situation excessive anterior or posterior capsular tightening forces the head of the humerus out of its normal concentric relationship with the glenoid fossa. The eccentric glenohumeral contact increases contact pressures and joint surface wear. Most commonly, overtightening of the anterior capsule produces obligate posterior translation, posterior glenoid wear, and central wear of the humeral articular cartilage.

Mechanics of arthritis and arthroplasty

Four basic mechanical characteristics are essential to the function of the normal shoulder: motion, stability, strength and smoothness. Each of these is commonly compromised in the arthritic shoulder and can potentially be restored by shoulder arthroplasty. The approach to glenohumeral arthritis is guided by an understanding of the necessary elements for optimal shoulder mechanics.

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