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.
"), and the results have been summarized in a systematic review favoring TSA (Radnay et al. 2007). A cadaver study found that RHA more closely restores the mechanics of the shoulder than SHA (Hammond et al. 2012); however, there have been no previous clinical studies comparing RHA with other arthroplasty designs. "
[Show abstract][Hide abstract] ABSTRACT: Purpose
We used patient-reported outcome and risk of revision to compare hemiarthroplasty (HA) with total shoulder arthroplasty (TSA) and stemmed hemiarthroplasty (SHA) with resurfacing hemiarthroplasty (RHA) in patients with glenohumeral osteoarthritis.
Patients and methods
We included all patients reported to the Danish Shoulder Arthroplasty Registry (DSR) between January 2006 and December 2010. 1,209 arthroplasties in 1,109 patients were eligible. Western Ontario Osteoarthritis of the Shoulder index (WOOS) was used to evaluate patient-reported outcome 1 year postoperatively. For simplicity of presentation, the raw scores were converted to a percentage of the maximum score. Revision rates were calculated by checking reported revisions to the DSR until December 2011. WOOS and risk of revision were adjusted for age, sex, previous surgery, and type of osteoarthritis.
There were 113 TSAs and 1096 HAs (837 RHAs and 259 SHAs). Patients treated with TSA generally had a better WOOS, exceeding the predefined minimal clinically important difference, at 1 year (mean difference 10, p < 0.001). RHA had a better WOOS than SHA (mean difference 5, p = 0.02), but the difference did not exceed the minimal clinically important difference. There were no statistically significant differences in revision rate or in adjusted risk of revision between any of the groups.
Our results are in accordance with the results from other national shoulder registries and the results published in systematic reviews favoring TSA in the treatment of glenohumeral osteoarthritis. Nonetheless, this registry study had certain limitations and the results should be interpreted carefully.
"Total shoulder resurfacing (TSR) provides a reliable and robust solution for the treatment of glenohumeral arthritis. Resurfacing is more bone preserving, allows for accurate reconstruction of glenohumeral version, restores the geometric center of the humeral head and provides a more anatomical construct than with stemmed humeral components. It has been shown to provide pain relief whilst maintaining a satisfactory range of functional movement. "
[Show abstract][Hide abstract] 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. DOI:10.4103/0973-6042.118910 · 0.65 Impact Factor
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