Lateral acromion osteotomy: biomechanical comparison of three osteosyntheses methods

PURPOSE The superior approach to the shoulder joint according to Codman using "sabre cut" and lateral acromion osteotomy, is most convenient for the exposure of the glenoid for arthroplasty. The drawback of this procedure are frequent non-unions of the acromion due to the poor stability of the osteosynthesis. MATERIAL AND METHODS Three osteosynthese methods were tested at random in 18 cadaver scapulae using a Zwick-Universal material testing device (1). Osteosynthesis with 4 screws and a plate according to Grammont (2). Osteosynthesis using special designed Y-plate according to Rozing (3). Osteosynthesis with a tension-wire-band construct using 2 mm threaded wires. The load was applied above the M. deltoideus, parallel to the osteotomy in the sagittal plane and in 90 degress to the acromion in the frontal plane. All constructs were tested until failure occurred. The maximum postoperative stability values (N) and the average apparent stiffness values (N/mm) were calculated. RESULTS The average maximum stability value for Grammont osteosynthesis was 270.1 +/- 17.3 (243.3-294.0) N, for Rozing osteosynthesis 404.7 +/- 49.1 (312.9-445.4) N and for tension-wire-band osteosynthesis 491.9 +/- 60.1 (419.6-558.8) N. The differences were statistically significant (p < 0.01). The highest stiffness values were achieved for tension-wire-band osteosynthesis (13.27 +/- 0.80 N/mm; 12.03-14.35) in comparison with Rozing osteosynthesis (12.86 +/-0.68 N/mm; 11.88-13.67) and Grammont osteosynthesis (10.64 +/- 0.25 N/mm; 9.72-10.44). CONCLUSION Experimentally, the tension-wire-band technique and the Y-plate according to Rozing provided a higher stability and stiffness for lateral acromion osteosynthesis than the Grammont method.

shoulder, acromion, Delta prosthesis, osteosynthesis, biomechanical.