Mid-term to long-term results of open posterior bone block grafting in recurrent posterior shoulder instability: a clinical and CT-based analysis

Posterior shoulder stability depends on acromial anatomy: a cadaveric, biomechanical study

BACKGROUND

Failure rates in the management of recurrent posterior shoulder instability remain a concern. Cadaveric studies have established that posterior capsulolabral tears, glenoid retroversion, and posterior glenoid bone loss result in increased posterior humeral head translation in the setting of a posteriorly directed force. A high and flat acromion has recently been associated with posterior instability. Therefore, the purpose of this study was to evaluate a potential stabilizing effect of the acromion against posterior humeral head displacement.

METHODS

Eight fresh-frozen human cadaveric shoulders were biomechanically tested in a shoulder simulator in the load-and-shift and Jerk test positions. Prior to testing, computed tomography scans were performed to measure native glenoid width, glenoid retroversion, posterior acromial coverage (PAC), sagittal acromial tilt (SAT), and posterior acromial height (PAH). Each specimen underwent 4 testing conditions using preplanned and 3D printed cutting and reduction guides: (1) Intact joint, native acromion; (2) Intact joint, severe acromial malalignment (SAT 69°, PAC 47°, PAH 26 mm); (3) Intact joint, moderate acromial malalignment (SAT 59°, PAC 57°, PAH 20 mm); (4) Intact joint, corrected acromial alignment (SAT 48°, PAC 70°, PAH 11 mm). The degree of acromial malalignment and acromial reorientation was chosen based on a previous study that defined acromial anatomy in patients with posterior instability. The humeral head was translated posteriorly until reaching either (1) a peak force of 150N or (2) a maximum posterior displacement of 50% of the glenoid width. Forces (N), displacement (mm), and acromiohumeral contact pressures (kPA) were simultaneously recorded.

RESULTS

The force needed to displace the humeral head by 50% of the glenoid width decreased between 23% and 60% in moderate to severe acromial malalignment (high and flat acromion) and increased up to 122% following surgical correction of acromial alignment (low and steep acromion) when compared to the native condition. Correction of acromial alignment significantly increased stability compared to all other scenarios after ≥5% of displacement (P < .05 for all comparisons). Furthermore, it increased acromiohumeral contact pressures compared with severe malalignment in 30° flexion and with moderate and severe acromial malalignment in 60° flexion (P < .05 for all comparisons).

CONCLUSION

The acromion acts as a mechanical buttress to posterior humeral head displacement. Surgical correction of acromial malalignment cannot only effectively restore but increase glenohumeral joint stability. Future studies are needed to define the quantitative relevance of the different factors contributing to posterior shoulder instability and assist in defining the optimal amount of correction needed in an individual situation.

Recurrent posterior shoulder instability-Long-term results after arthroscopic posterior bone block with capsular reconstruction

Purpose

This study reports the long-term post-operative clinical outcomes after arthroscopic posterior bone block augmentation with posterior capsular repair.

Methods

Eighteen shoulders (13 patients) with unidirectional posterior shoulder instability were treated with an arthroscopic posterior bone block augmentation and posterior capsular repair in 2011 and 2013 in a single specialized orthopaedic clinic. These patients were invited to participate in a clinical and radiological follow-up examination to receive long-term results regarding clinical outcomes, instability, and development of osteoarthritis (OA).

Results

From the initial study group, 13 patients (18 shoulders) could be obtained for a follow-up examination. The mean follow-up period was 111 months. At the final follow-up, two patients (two shoulders) reported recurrent subluxations with a positive apprehension sign. No redislocation was reported. Screw fixation was still in place in seven patients (38.9%). Overall, good clinical outcomes were achieved among Constant-Murley score (77.6 ± 16; p = 0.55), Rowe score (67.5 ± 22.1; p = 0.34), Walch-Duplay score (58.3 ± 28.2) and Western Ontario Shoulder Index (40.4 ± 23.3%; p = 0.96), showing insignificant changes compared with the 2-year results. Three shoulders developed severe OA (Samilson and Prieto III). No patient required arthroplasty.

Conclusion

Arthroscopic posterior bone block augmentation with posterior capsular repair represents a salvage procedure that can achieve long-term shoulder stability with overall moderate clinical results. Patients have to be informed about the probable need for implant removal and the high risk of OA development, especially in the presence of pre-existing cartilage damage, beforehand.

Level of Evidence

Level IV.

The Kouvalchouk procedure vs. distal tibial allograft for treatment of posterior shoulder instability: the deltoid "hammock" effect exists

BACKGROUND

In 1993, Kouvalchouk described an acromial bone block with a pedicled deltoid flap for the treatment of posterior shoulder instability. This procedure provides a "double blocking" effect in that the acromial autograft restores posterior glenoid bone loss and the deltoid flap functions as a muscular "hammock" resembling the sling effect of the conjoint in the Latarjet procedure. The primary aim of this study was to compare the Kouvalchouk procedure to distal tibial allograft (DTA) reconstruction for the management of posterior shoulder instability with associated bone loss, while the secondary aim was to evaluate the deltoid hammock effect.

METHODS

Ten upper extremity cadavers were evaluated using a validated shoulder testing apparatus in 0° and 60° of glenohumeral abduction in the scapular plane. Testing was first performed on the normal shoulder state and was followed by the creation of a 20% posterior glenoid defect. Subsequently, the Kouvalchouk and DTA procedures were conducted. Forces of 0N, 5N, 10N, and 15N were applied to the posterior deltoid tendinous insertion on the Kouvalchouk graft along the physiological muscle line-of-action to evaluate the 'hammock" effect of this procedure. Testing was additionally performed on the Kouvalchouk bone graft with the deltoid muscle sectioned from its bony attachment. For all test states, a posteriorly directed force was applied to the humeral head perpendicular to the direction of the glenoid bone defect, with the associated translation quantified using an optical tracking system. The outcome variable was posterior translation of the humeral head at an applied force magnitude of 30N.

RESULTS

The Kouvalchouk procedure with the loaded deltoid flap (10N: P = .039 and 15N: P < .001) was significantly better at reducing posterior humeral head translation than the DTA. Overall, increased glenohumeral stability was observed with increased force applied to the posterior deltoid flap in the Kouvalchouk procedure. The 15 N Kouvalchouk was most effective at preventing posterior humeral translation, and the difference was statistically significant compared with the 20% glenoid defect (P = .003), detached Kouvalchouk (P < .001), and 0N Kouvalchouk (P < .001). The 15 N Kouvalchouk procedure restored posterior shoulder joint stability to near normal levels, such that it was not significantly different from the intact state (P = .203).

CONCLUSIONS

The Kouvalchouk procedure with load applied to the deltoid was found to be biomechanically superior to the DTA for the management of posterior shoulder instability with associated bone loss. Additionally, the results confirmed the presence and effectiveness of the deltoid "hammock" effect.

Arthroscopic Posterior Glenoid Reconstruction With Distal Clavicle Bone-Block

Posterior glenoid bone loss is a potential cause for failure in arthroscopic capsulolabral repair. Although multiple techniques have been described to reconstruct posterior bone defects, they do not reliably yield improved patient outcomes and have high complication rates. We present a technique to reconstruct posterior glenoid bone loss using a distal clavicle autologous bone graft harvested by a mini-open approach and secured arthroscopically with suture buttons. The graft is positioned extra-articularly by repairing the posterior labral complex with a knotless fixation using labral tape.