We studied the biomechanical behaviour of three sliding fixation devices for trochanteric femoral fractures. These were a titanium alloy sideplate and lag screw, a titanium alloy sideplate and dome plunger with cement augmentation, and a stainless-steel sideplate and lag screw. We used 18 mildly osteoporotic cadaver femora, randomly assigned to one of the three fixation groups. Four displacement and two strain gauges were fixed to each specimen, and each femur was first tested intact (control), then as a two-part fracture and then as a four-part intertrochanteric fracture. A range of physiological loads was applied to determine load-bearing, load-sharing and head displacement. The four-part-fracture specimens were subsequently tested to failure to determine maximum fixation strengths and modes of failure. The dome-plunger group failed at a load 50% higher than that of the stainless-steel lag-screw group (p < 0.05) and at a load 20% higher than that of the titanium-alloy lag-screw group (NS). All 12 lag-screw specimens failed by cut-out through the femoral head or neck, but none of the dome-plunger group showed movement within the femoral head when tested to failure. Strain-gauge analysis showed that the dome plunger produced considerably less strain in the inferior neck and calcar region than either of the lag screws. Inferior displacement of the femoral head was greatest for the dome-plunger group, and was due to sliding of the plunger. The dome plunger with cement augmentation was able to support higher loads and did not fail by cut-out through the femoral head.(ABSTRACT TRUNCATED AT 250 WORDS)

A cadaver study was performed to determine the effect of arm position and capsular release on rotator cuff repair. Artificial defects were made in the rotator cuff to include only the supraspinatus (small) or both supraspinatus and infraspinatus (large). The defects were repaired in a standard manner with the shoulder abducted 30 degrees at the glenohumeral joint. Strain gauges were placed on the lateral cortex of the greater tuberosity and measurements were recorded in 36 different combinations of abduction, flexion/extension, and medial/lateral rotation. Readings were obtained before and after capsular release. With small tears, tension in the repair increased significantly with movement from 30 degrees to 15 degrees of abduction (p < 0.01) but was minimally affected by changes in flexion or rotation. Capsular release significantly reduced the force (p < 0.01) at 0 degree and 15 degrees abduction. For large tears, abduction of 30 degrees or more with lateral rotation and extension consistently produced the lowest values. Capsular release resulted in 30% less force at 0 degree abduction (p < 0.05).