Hochreiter, Am J Sports Med 2025 - Posterior Shoulder Stability Can Be Restored by Posterior Acromial Bone Grafting (Scapinelli) in a Cadaveric Biomechanical Model with Normal Glenoid Anatomy - Article Summary

Posterior Shoulder Stability Can Be Restored by Posterior Acromial Bone Grafting (Scapinelli) in a Cadaveric Biomechanical Model with Normal Glenoid Anatomy

Hochreiter, Gerber, et al.·Am J Sports Med·2025·8 citations·Biomechanical study

Background

A high and flat acromion seems to be a risk factor for posterior shoulder instability. Biomechanically, the surgical correction of acromial malalignment can restore glenohumeral joint stability.

Purpose

The purpose was to assess (1) the stabilizing effect of a posterior acromial bone graft (PABG) in moderate and severe acromial malalignment (high and flat) and (2) contact patterns under posterior humeral head displacement. It was hypothesized that a PABG would significantly (1) increase resistance to posterior humeral head displacement, (2) restore stability, and (3) increase acromiohumeral contact pressure.

Methods

Study Design: Controlled laboratory study.

A total of 8 fresh-frozen human cadaveric shoulders, with normal glenoid anatomy, were examined in a shoulder simulator in the load and shift and jerk test positions.
Each specimen underwent 5 testing conditions using 3-dimensional printed cutting and reduction guides, with the joint left intact for each condition: (1) severe acromial malalignment, (2) severe acromial malalignment + PABG, (3) moderate acromial malalignment, (4) moderate acromial malalignment + PABG, and (5) corrected acromial alignment.
The humeral head was translated posteriorly until reaching either a peak force of 150 N or a maximum posterior displacement of 50% of the glenoid width.
Force, displacement, and acromiohumeral contact pressure were recorded.

Results

At 30° of flexion, the force needed to displace the humeral head 50% increased by 659% when a PABG was added to a moderately malaligned acromion and by 1249% when a PABG was added to a severely malaligned acromion.
At 60° of flexion, it increased by 293% and 348%, respectively.
This stabilizing effect increased progressively with increasing displacement ( P < .05 for all comparisons after ≥5% of displacement).
Compared with acromial correction, a PABG allowed comparable posterior displacement but required different amounts of force, depending on the scenario.
At 30° of flexion after 30% of displacement, a PABG provided significantly greater stability ( P < .05 for all comparisons).
Mean contact pressure was significantly reduced on the rotator cuff and significantly increased on the acromial undersurface in moderate and severe acromial malalignment, whereas a PABG restored acromiohumeral contact pressure comparable with corrective osteotomy, particularly at 30° of flexion.

Conclusions

The study provides quantitative evidence showing that a PABG significantly enhanced resistance to displacement and compensated for deficient posterolateral acromial coverage by extending the natural mechanical buttress.

Clinical Relevance: Experimentally, a PABG provided comparable or superior stability to that after surgical acromial reorientation while representing a technically simpler and potentially less invasive approach.

Supplemental

Posterior Shoulder Stability Can Be Restored by Posterior Acromial Bone Grafting (Scapinelli) in a Cadaveric Biomechanical Model with Normal Glenoid Anatomy

Hochreiter, Gerber, et al.Am J Sports Med20258 citationsBiomechanical study