Stability of tuberosity reattachment in proximal humeral hemiarthroplasty.

Hemiarthroplasty can be an effective treatment for 4-part fractures of the proximal humerus; however, results are often unpredictable. Proper surgical technique is critical for success. Reconstruction of the displaced tuberosities should attempt to impart maximal interfragmentary stability. To our knowledge, a comparison of different tuberosity reconstruction methods has not been reported. We evaluated 5 techniques of tuberosity reattachment on 8 humeri. Four-part fractures were simulated by an oscillating saw in fresh-frozen cadaveric shoulders. In the control construct, the greater and lesser tuberosities were attached to the humeral shaft with nylon strap ties (2.4 x l mm) applied at 9.1 N with closure of the rotator interval. Five anatomic reconstructions were then performed:(1) the control tuberosities were attached to each other with strap ties, and (2) the control tuberosities were attached to each other with strap ties, incorporating the anterior fin of the prosthesis. To each of these 3 constructs, a circumferential cerclage (4.8 x 1.25-mm strap tie) applied at 39.2 N was placed around the tuberosities and incorporated into the medial hole of the prosthesis (techniques 3, 4, and 5). Through use of a robot articulator at a rate of 10 degrees /s, passive external rotation from 0 degrees to 60 degrees was performed on the control and the 5 test constructs of each specimen. Interfragmentary displacement of the bony fragments was measured with mercury strain gauges and strain calculated. This strain was minimal and statistically less (P <.05) in those constructs in which a cerclage was used. Incorporation of the nylon strap into the fin of the prosthesis did not enhance stability. In those constructs in which a cerclage was used, maximal displacement was 0.14 +/- 0.7 mm (38% +/- 19% strain), as compared with 0.72 +/- 0.5 mm (204% +/- 133% strain) without it. Reconstruction of 4-part proximal humerus fractures with hemiarthroplasty should incorporate a circumferential medial cerclage. This will decrease interfragmentary motion and strain, maximize fracture stability, and facilitate postoperative rehabilitation.