Optimal side plate fixation for unstable intertrochanteric hip fractures.

OBJECTIVES: To quantitatively determine the minimal screw number needed for stable side plate fixation to the femoral shaft in treating unstable intertrochanteric hip fractures. DESIGN: Laboratory/biomedics study. SETTING: Orthopaedic biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: The convenience sample was made up of one saw bone, one steel pipe, and ten human cadaveric femur specimens. Human specimens were selected by ruling out pathology and excess osteopenia. Ten specimens were tested to completion. INTERVENTION: Telescoping hip screw and hip screw side plate secured with various numbered combinations of side plate screws. MAIN OUTCOME MEASURES: Decreases in tension experienced by all previously inserted screws when an additional screw was applied were recorded and labeled as "protection." RESULTS: Protection offered by a third screw on all previous screws was 787.3 newtons in the steel pipemodel, 71.2 newtons in the sawbone model, and 158.3 newtons in the human model (p < 0.005). A fourth bone screw did not decrease tension in previous screws by more than 11 newtons. The protective effect of the fourth screw on screw #3 increased with decreasing screw application torque by a maximum of 21.8 newtons (p < 0.005). CONCLUSION: This study suggests that three bone screws provide an optimal distribution of tensile forces. The insertional torque used to place screws, once screw-plate contact has been established, does not play a significant role in screw protection. Additional studies are needed to assess the role of cortical bone density, and cyclical loading and bending forces experienced by the side plate screws, before definite clinical recommendations can be made.

Development and use of an animal model for investigations on rotator cuff disease.

Although both intrinsic and extrinsic factors have been implicated in the cause of rotator cuff disease, previous studies have not been designed to test hypotheses of this disease, partly because of the lack of an appropriate animal model. Thirty-three animals were evaluated according to a 34 item checklist of criteria to determine their appropriateness as an animal model for investigations on the rotator cuff. Only the rat shoulder satisfactorily fulfilled all criteria, with a prominent supraspinatus tendon passing under an enclosed arch. Once the rat was identified, 36 rats were randomized to three experimental groups. One group (n = 12) was treated with an intratendinous injection of bacterial collagenase simulating an acute intrinsic injury, another group (n = 12) was treated with an acromial alteration to reduce the subacromial space simulating an external compression, and the third group (n = 12) was treated with a combination of both modifications. Significant increases in cellularity, number of fibroblasts, and collagen disorganization were seen in all experimental tendons compared with a contralateral control group. Semiquantitative grading of histologic sections revealed marked changes in all groups at 4 and 8 weeks. Injuries appeared to be healing at 12 weeks except in the combination group, which seemed to demonstrate persistent alterations. This study supports the rat as an appropriate model for investigating rotator cuff disease. In addition, this study demonstrates that both intrinsic and extrinsic alterations can induce changes in the supraspinatus tendon, which may have similarities to human tendon disease.