Biomechanical comparison of anatomic humeral head resurfacing and hemiarthroplasty in functional glenohumeral positions.
ABSTRACT Resurfacing of the humeral head has gained interest as an alternative to traditional hemiarthroplasty because it preserves bone stock and respects the native geometry of the glenohumeral articulation. The purpose of this study was to compare the biomechanics of the intact glenohumeral joint with those following humeral head resurfacing and following hemiarthroplasty.
Seven fresh-frozen cadaveric shoulders were tested with the rotator cuff, pectoralis major, and latissimus dorsi musculature loaded with 20 N and the deltoid muscle loaded with 40 N in a custom shoulder testing system. Each specimen was tested in 20°, 40°, 60°, and 80° of vertical abduction. The articular surfaces of the humeral head and the glenoid were digitized to calculate the positions of the geometric center and apex of the humeral head relative to the geometric center of the glenoid at each testing position. The contact area and contact pressures were also measured with use of a Tekscan pressure sensor.
The geometric center of the humeral head shifted by a mean (and standard error) of 2.2 ± 0.3 mm following humeral resurfacing and 4.7 ± 0.3 mm following hemiarthroplasty (p < 0.0002). The apex of the humeral head was shifted superiorly at all abduction angles following hemiarthroplasty (p < 0.03). Both humeral resurfacing and hemiarthroplasty decreased the glenohumeral contact area and increased the peak pressure.
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.
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ABSTRACT: Total shoulder resurfacing (TSR) provides a reliable solution for the treatment of glenohumeral arthritis. It confers a number of advantages over traditional joint replacement with stemmed humeral components, in terms of bone preservation and improved joint kinematics. This study aimed to determine if humeral reaming instruments produce a thermal insult to subchondral bone during TSR. This was tested in vivo on 13 patients (8 with rheumatoid arthritis and 5 with osteoarthritis) with a single reaming system and in vitro with three different humeral reaming systems on saw bone models. Real-time infrared thermal video imaging was used to assess the temperatures generated. Synthes (Epoca) instruments generated average temperatures of 40.7°C (SD 0.9°C) in the rheumatoid group and 56.5°C (SD 0.87°C) in the osteoarthritis group (P = 0.001). Irrigation with room temperature saline cooled the humeral head to 30°C (SD 1.2°C). Saw bone analysis generated temperatures of 58.2°C (SD 0.79°C) in the Synthes (Epoca) 59.9°C (SD 0.81°C) in Biomet (Copeland) and 58.4°C (SD 0.88°C) in the Depuy Conservative Anatomic Prosthesis (CAP) reamers (P = 0.12). Humeral reaming with power driven instruments generates considerable temperatures both in vivo and in vitro. This paper demonstrates that a significant thermal effect beyond the 47°C threshold needed to induce osteonecrosis is observed with humeral reamers, with little variation seen between manufacturers. Irrigation with room temperature saline cools the reamed bone to physiological levels and should be performed regularly during this step in TSR.International Journal of Shoulder Surgery 07/2013; 7(3):100-4.
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ABSTRACT: Since Neer's early work in the 1950s shoulder arthroplasty has evolved as a treatment option for various glenohumeral joint disorders. Both hemiarthroplasty and total shoulder prostheses have associated problems. This has led to further work with regards to potential resurfacing, with the aim of accurately restoring native proximal humeral anatomy while preserving bone stock for later procedures if required. Hemiarthroplasty remains a valuable treatment option in the low demand patient or in the trauma setting. Additional work is required to further define the role of humeral resurfacing, with the potential for it to become the gold standard for younger patients with isolated humeral head arthritis.The Open Orthopaedics Journal 01/2013; 7:334-337.