Acromioclavicular joint arthrosis in persons with spinal cord injury and able-bodied persons.

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Abstract

[Indexed for MEDLINE] 8. Am J Sports Med. 2025 Sep;53(11):2684-2694. doi: 10.1177/03635465251362854. Epub 2025 Aug 18. Posterior Shoulder Stability Can Be Restored by Posterior Acromial Bone Grafting (Scapinelli) in a Cadaveric Biomechanical Model With Normal Glenoid Anatomy. Hochreiter B(1)(2), Nguyen N(3), Calek AK(1)(2), Sigrist B(4), Ackland DC(3), Ernstbrunner L(3)(5), Ek ET(1)(6), Gerber C(7). Author information: (1)Melbourne Orthopaedic Group, Melbourne, Victoria, Australia. (2)Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland. (3)Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia. (4)Research in Orthopedic Computer Science Group, Balgrist University Hospital, University of Zurich, Zurich, Switzerland. (5)Department of Orthopaedic Surgery, Box Hill Hospital, Box Hill, Victoria, Australia. (6)Department of Surgery, Monash Medical Centre, Monash University, Melbourne, Victoria, Australia. (7)Orthopaedic Research Center, Balgrist Campus, Zurich, Switzerland. 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/HYPOTHESIS: 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. STUDY DESIGN: Controlled laboratory study. METHODS: 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. CONCLUSION: 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. DOI: 10.1177/03635465251362854 PMCID: PMC12381383