Biomechanical benefits of anterior offsetting of humeral head component in posteriorly unstable total shoulder arthroplasty: A cadaveric study

Restoration of joint stability during total shoulder arthroplasty can be challenging in the face of severe glenoid retroversion. A novel technique of humeral head component anterior‐offsetting has been proposed to address posterior instability. We evaluated the biomechanical benefits of this technique in cadaveric specimens. Total shoulder arthroplasty was performed in 14 cadaveric shoulders from 7 donors. Complementary shoulders were assigned to either 10° or 20° glenoid retroversion, with retroversion created by eccentric reaming. Two humeral head component offset positions were tested in each specimen: The anatomic (posterior) and anterior (reverse). With loads applied to the rotator cuff and deltoid, joint contact pressures and the force and energy required for posterior humeral head translation were measured. The force and energy required to displace the humeral head posteriorly increased significantly with the anterior offset position compared to the anatomic offset position. The joint contact pressures were significantly shifted anteriorly, and the joint contact area significantly increased with the anterior offset position. Anterior offsetting of the humeral head component increased the resistance to posterior humeral head translation, shifted joint contact pressures anteriorly, and increased joint contact area, thus, potentially increasing the joint stability in total shoulder arthroplasty with simulated glenoid retroversion. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:666–674, 2016.     

Accuracy of patient-specific instrumentation in anatomic and reverse total shoulder arthroplasty

Purpose:Glenoid component malposition is associated with poor function and early failure of both anatomic and reverse total shoulder arthroplasty. Glenoid positioning is challenging particularly in the setting of bone loss or deformity. Recently, the use of computer assistance has been shown to reduce implantation error. The aim of this study is to evaluate the accuracy of patient-specific instrumentation in cases of anatomic and reverse shoulder replacement in vivo.Methods:Twenty patients underwent total shoulder arthroplasty using a computed tomography (CT)-based patient-specific instrumentation (PSI) system, ten anatomic and ten reverse. Preoperative three-dimensional digital templating of glenoid component position was undertaken and surgery then performed using a custom-made guide. Postoperative CT scans were used to compare final implanted component position to the preoperatively planned position in the same patient.Results:Final component position and orientation closely reflected the preoperatively templated position. Mean deviation in the glenoid version from planned was 1.8° ±1.9° (range, 0.1°–7.3°). Mean deviation in inclination was 1.3° ±1.0° (range, 0.2°–4.5°). Mean deviation in position on the glenoid face was 0.5 ± 0.3 mm (range, 0.0–1.3 mm) in the anteroposterior plane and 0.8 ± 0.5 mm (range, 0.0–1.9 mm) in the superoinferior plane. Actual achieved version was within 7° of neutral in all cases except for one where it was deliberately planned to be outside of this range.Conclusion:PSI in both anatomic and reverse shoulder arthroplasty is highly accurate in guiding glenoid component implantation in vivo. The system can reliably correct bony deformity.     

Posterior Chondrolabral Cleft: Clinical Significance and Associations with Shoulder Instability

Background

A high signal intensity cleft between the labrum and articular cartilage of the posterior glenoid is commonly visible on MRI and has been suggested to be anatomic variation [3, 10, 23]. The association of a posterior cleft with variations in glenoid morphology or with shoulder instability is unknown.

Questions/Purposes

The purposes of this study were to determine if posterior chondrolabral clefts are associated with variations in glenoid morphology, and to determine if they are associated with shoulder instability.

Patients and Methods

Shoulder MRI was performed in 1,264 shoulders, 1,135 male (89.8%), and 129 female (10.2%). A musculoskeletal radiologist blinded to history and outcomes evaluated the MR images for linear high signal intensity at the posterior chondrolabral junction and a rounded or truncated contour of the posterior glenoid. Glenoid version and depth were measured. Patients were followed prospectively for shoulder instability for 4 years. Univariate and multivariate statistical analysis were performed.

Results

Posterior chondrolabral cleft was present in 114/1,264. Posterior chondrolabral cleft was associated with a rounded or truncated posterior glenoid. There were 9.5° retroversion in shoulders with a posterior cleft, and 7.7° retroversion in shoulders without a cleft. Shoulders with a posterior chondrolabral cleft were more likely to develop shoulder instability.

Conclusions

Posterior chondrolabral clefts are not uncommon on MRI. They are associated with a rounded or truncated posterior glenoid and a small but significant increase in glenoid retroversion. They are associated with shoulder instability.