The authors disclose that this study was funded by a grant from Arthrosurface (which was the resurfacing prosthesis used in this study) and that one of the authors has a consultancy arrangement with Arthrex (which markets this prosthesis).
The model was of a normal shoulder, not of a shoulder with any of the types of conditions for which shoulder arthroplasty is performed. In contrast to the clinical situation where shoulder joint replacement is indicated, the glenoid anatomy was normal.
The resurfacing technique involved reaming away the surface of the normal humeral head around a guidewire and then placing a resurfacing cap over the guidewire. In this procedure the humeral head is not removed. When approaching a patient with shoulder arthritis, both sides of the joint (the humeral head and the glenoid) are almost always involved. Retaining the humeral head severely compromises access to the glenoid making the glenoid arthroplasty (which fails most often) even more difficult. When using a humeral hemiarthroplasty the humeral articular surface can be sized with respect to thickness and radius of curvature and positioned at the height, version, medial/lateral and anteroposterior configuration that best suits the kinematics of the shoulder after the arthritic glenoid has been managed by either a ream and run or a total shoulder arthroplasty.
The hemiarthroplasty technique involved removing the humeral head which, in a real patient, would be important for accessing the glenoid so that the glenoid arthroplasty could be optimized.
With in vitro testing in 20 different positions, the glenohumeral contact area (Table I), the mean contact pressure (Table II), and the peak contact pressure (Table III) were not significantly different among the three preparations (intact, resurfacing and hemiarthroplasty). The peak pressure was significantly elevated, compared with that in the intact condition, in five of the twenty positions following resurfacing and in two of the twenty positions following hemiarthroplasty.
With in vitro testing in 20 different positions, the glenohumeral contact area (Table I), the mean contact pressure (Table II), and the peak contact pressure (Table III) were not significantly different among the three preparations (intact, resurfacing and hemiarthroplasty). The peak pressure was significantly elevated, compared with that in the intact condition, in five of the twenty positions following resurfacing and in two of the twenty positions following hemiarthroplasty.
The authors' conclusions: "Resurfacing more closely restored the geometric center of the humeral head than hemiarthroplasty did, with less eccentric loading of the glenoid. Compared with hemiarthroplasty, humeral resurfacing may limit eccentric glenoid wear and permit better function because the glenohumeral joint biomechanics and the moment arms of the rotator cuff and the deltoid muscle are restored more closely to those of the intact condition" seem valid in a cadaver model of a normal shoulder. However the realities of the clinical management of the arthritic shoulder do not suggest that a resurfacing provides the necessary access to the glenoid, where the real challenges lie, nor the flexibility in humeral head reconstruction that are offered by a stemmed humeral component.
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