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

Abstract

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. ß

Total shoulder arthroplasty with an anterior-offset humeral head in patients with a B2 glenoid

“…Recent biomechanical data have demonstrated increased resistance to posterior humeral head translation and improved joint contact pressures in shoulders with significant glenoid retroversion treated with an anterior-offset technique. 11 Finite element analysis has confirmed an anterior shift in the center of pressure with an anterior-offset humeral head in the setting of increased glenoid retroversion. 12 Hsu et al 9 have reported good outcomes for a series of 33 patients undergoing either total shoulder arthroplasty or hemiarthroplasty who required an anterior-offset humeral head technique to correct intraoperative posterior humeral head subluxation.…”

“… 14 Over time, the soft tissues about the shoulder adapt to the posterior position of the proximal humerus, and these forces can be difficult to overcome with corrective reaming or augmented components that realign the humerus anteriorly. In fact, Kim et al 11 postulated that correcting the humeral position may escalate the posterior pull of the soft tissues. Anteriorly offsetting the humeral head allows the head center to have congruent alignment to the glenoid center while allowing the proximal humerus to remain in a relatively posterior position, thus mitigating the adaptive posterior pull of the soft tissues.…”

“…A cadaveric model evaluating this technique has shown increased resistance to posterior humeral head translation and anteriorly directed joint contact pressures in shoulders with significant glenoid retroversion. 11 Finite element analysis has demonstrated that anterior offset of the humeral head leads to significant increases in anterior-directed centering pressures of the humeral head on the glenoid component. 12 Anterior humeral head offset has been described clinically to address intraoperative posterior humeral head subluxation in patients undergoing either hemiarthroplasty with a ream-and-run technique or total shoulder arthroplasty with good results in a small patient sample.…”

Effect of glenoid perforation during total shoulder arthroplasty on glenoid component cement fixation and suprascapular nerve

“…Specimens were randomly assigned to two groups; the control group (n ¼ 3) was comprised of specimens with no perforation of the glenoid, while the perforation group (n ¼ 7) was comprised of specimens with glenoid perforation. In the perforation group, we simulated an arthritic glenoid by eccentrically reaming the posterior glenoid more than the anterior glenoid to create approximately 15 of retroversion as described previously by Kim et al 9 In both groups, each specimen was prepared for routine TSA by the attending surgeon according to the standard surgical technique utilizing a deltopectoral approach. The humeral head was resected at the level of the anatomic neck, but no humeral component was implanted.…”

Autografting for B2 Glenoids

“…Biomechanical studies show that dialing the humeral head eccentricity anteriorly may reduce posterior eccentric loading and increase the force required to posteriorly dislocate the shoulder. 34 Theoretically, anterior overhang of the humeral head may potentially increase pressure on the subscapularis repair, although this has not been reported as a cause for subscapularis failure postoperatively. 35 Bone grafting of the posterior glenoid allows for glenoid version correction and decreased edge loading at the implant-bone interface, while enhancing bone stock.…”