Biomechanical Analysis of Posterior Open-Wedge Osteotomy and Glenoid Concavity Reconstruction Using an Implant-Free, J-Shaped Iliac Crest Bone Graft

Abstract

Background: Posterior open-wedge osteotomy and glenoid reconstruction using a J-shaped iliac crest bone graft showed promising clinical results for the treatment of posterior instability with excessive glenoid retroversion and posteroinferior glenoid deficiency.

Purpose: To evaluate the biomechanical performance of the posterior J-shaped graft to restore glenoid retroversion and posteroinferior deficiency in a cadaveric shoulder instability model.

Study design: Controlled laboratory study.

Methods: A posterior glenoid open-wedge osteotomy was performed in 6 fresh-frozen shoulders, allowing the glenoid retroversion to be set at 0°, 10°, and 20°. At each of these 3 preset angles of glenoid retroversion, the following conditions were simulated: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-shaped graft (at 0° of retroversion). With the humerus in the Jerk position (60° of glenohumeral anteflexion, 60° of internal rotation), stability was evaluated by measuring posterior humeral head (HH) translation (in mm) and peak translational force (in N) to translate the HH over 25% of the glenoid width. Glenohumeral contact patterns were measured using pressure-sensitive sensors. Fixation of the posterior J-graft was analyzed by recording graft micromovements during 3000 cycles of 5-mm anteroposterior HH translations.

Results: Reconstructing the glenoid with a posterior J-graft to 0° of retroversion significantly increased stability compared with a posterior Bankart lesion and posteroinferior glenoid deficiency in all 3 preset degrees of retroversion (P < .05). There was no significant difference in joint stability comparing the posterior J-graft with an intact joint at 0° of retroversion. The posterior J-graft restored mean contact area and contact pressure comparable with that of the intact condition with 0° of retroversion (222 vs 223 mm², P = .980; and 0.450 vs 0.550 MPa, P = .203). The mean total graft displacement after 3000 cycles of loading was 43 ± 84 µm, and the mean maximal mediolateral graft bending was 508 ± 488 µm.

Conclusion: Biomechanical analysis of the posterior J-graft demonstrated reliable restoration of initial glenohumeral joint stability, normalization of contact patterns comparable with that of an intact shoulder joint with neutral retroversion, and secure initial graft fixation in the cadaveric model.

Clinical relevance: This study confirms that the posterior J-graft can restore stability and glenohumeral loading conditions comparable with those of an intact shoulder.

Keywords: biomechanics; glenoid dysplasia; glenoid retroversion; open-wedge osteotomy; posterior J-graft; shoulder instability.

Figure 1.

Photograph from superior showing the mounted external fixator for controlling the different angles of glenoid retroversion of a left shoulder. (A) The posterior osteotomy is opened so that glenoid retroversion is set at 0° according to the individual native version. (B) The posterior osteotomy is closed so that glenoid retroversion is set at 20°. A, acromion; C, clavicle; G, glenoid; HH, humeral head; OT, osteotomy; SS, scapular spine.

Figure 2.

The J-shaped iliac crest bone graft typically measures 25 mm wide (superoinferior dimension of the glenoid in the en face view), 30 mm long (long leg; anteroposterior [AP] dimension), and 10 mm high (graft surface; AP dimension). The graft surface is molded to a ramplike structure to reconstruct the concavity of the posteroinferior glenoid. The dimension of the short leg of the J-graft usually measures 20 to 25 mm (mediolateral dimension). The long leg and short leg are composed of cortical bone on the outside and cancellous bone on the inside to facilitate bony ingrowth.

Figure 3.

Illustration of the posterior J-graft for correction of glenoid retroversion and reconstruction of posteroinferior glenoid deficiency. (A) The osteotomy was performed 15 mm medial to the glenoid surface from posterior to anterior, aiming into the base of the coracoid with the anterior cortex kept intact. (B) The osteotomy was then opened to fit the graft. (C) The J-graft was impacted into the osteotomy site with a press fit. The ramp-shaped graft surface reconstructed the glenoid concavity and compensated the posteroinferior glenoid deficiency.

Figure 4.

Illustration of the custom shoulder-testing system with 6 degrees of freedom of glenohumeral joint positioning. Solid arrow in black indicates joint compression force (22 N and 50 N, respectively) generated by a static weight via a lever arm. Rotation (ry), abduction (rx), and horizontal abduction (rz) could be set according to the testing protocol. Anteroposterior translation was generated by a universal materials testing machine (not displayed), which was connected by a steel cable running from the translation plate to the actuator of the machine. A counterweight, which was positioned opposite to said translation plate, allowed cyclic loading (respectively, automatic repositioning) when load from the machine was removed.

Figure 5.

(A) The amount of posterior humeral head (HH) translation (in mm) with a posteriorly directed force of 20 N against a compressive load of 22 N with the arm in the Jerk test position is shown for the 3 glenoid retroversion (retro) angles (0°, 10°, and 20°) and the following glenoid conditions: (1) intact, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-graft at 0° of glenoid retroversion. (B) The peak translational force (in N) needed to translate the HH posteriorly over 25% of the glenoid width against a compressive load of 22 N with the arm in the Jerk test position is shown for the 3 glenoid retroversion angles (0°, 10°, and 20°) and the following glenoid conditions: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-graft at 0° of glenoid retroversion. Values are presented as mean and SE bars. *Level of significance: P < .005. n.s., nonsignificant.

Figure 6.

Glenohumeral (A) contact area and (B) contact pressure with the arm in the Jerk test position is shown for the 3 glenoid retroversion (retro) angles (0°, 10°, and 20°) and the following glenoid conditions: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-graft at 0° of glenoid retroversion. Values are presented as means and SE bars. *Level of significance: P < .005. n.s., nonsignificant. HH, humeral head.