Increased peak contact stress after incongruent reduction of transverse acetabular fractures: a cadaveric model.

BACKGROUND: The objective of this study was to determine the peak contact pressure with varying degrees of articular cartilage step-off in a transtectal acetabular fracture model. METHODS: Five fresh frozen cadaveric hip joints were potted in a custom loading fixture. The five specimens were then tested at loads of 445 N (newton) (100 lb) and 1,335 N (300 lb) intact and after a transverse osteotomy at step-off levels from 0 to 5 mm in 1-mm increments. RESULTS: Articular cartilage step-off of greater than 1 mm led to significantly increased contact stress at the loaded acetabular articular surface. Mean peak pressure measured at 1,335 N of loading in all intact specimens before the osteotomy was approximately 10 MPa. Peak pressure after a transverse acetabular fracture did not change when the fracture was perfectly reduced. At 1 mm of step-off, the peak pressure increased by approximately 20% but was not statistically significant. With step-off of > 2 mm or greater, the peak pressure increase was approximately 50% and was statistically significant. CONCLUSION: On the basis of our study, transverse acetabular fractures with greater than 1 mm of displacement can lead to significant increase in peak pressure at the articular surface.

Correlation of anthropometric measurements, strength, anterior cruciate ligament size, and intercondylar notch characteristics to sex differences in anterior cruciate ligament tear rates.

We performed a prospective study based on the hypothesis that physiologic differences exist between men and women in strength after adjustments for body weight; that the size of the anterior cruciate ligament is proportionate to the strength of its antagonists, the quadriceps muscles; and that women have a relatively small anterior cruciate ligament, thus predisposing them to a disproportionate number of anterior cruciate ligament injuries. One hundred matched high school basketball players, 50 male and 50 female, were evaluated with anthropometric measurements, body fat analysis, muscle strength evaluation, and magnetic resonance imaging measurements of the intercondylar notch and cross-sectional area of the anterior cruciate ligament at the outlet. The male players were taller and heavier than their female counterparts, although they had 11% less body fat. Male players had statistically greater quadriceps and hamstring muscle strength than female players, even when adjustments were made for body weight. With adjustments for body weight, the size of the anterior cruciate ligament in girls was found to be statistically smaller than in boys. There was no statistically significant difference in the notch width index between the sexes. The study data support our hypothesis that sex differences in anterior cruciate ligament tear rates are caused primarily by several interrelated intrinsic factors. Most importantly, stiffness and muscular strength increase stress on the anterior cruciate ligament in female athletes. The anterior cruciate ligament, when adjustments have been made for body weight, is smaller in female athletes, and therefore, probably does not compensate for the lack of stiffness and strength.

Clinical analysis of the pivot shift tests: description of the pivot drawer test.

A clinical analysis of the pivot shift was performed by evaluating 100 patients with unilateral anterior cruciate ligament (ACL) insufficiency in an office setting. Each patient was examined in a random order using the Macintosh, Losee, Hughston, Slocum, pivot drawer, and flexion rotation drawer versions of the pivot shift test. Pathologic anterior tibial displacement was estimated with the Lachman test and quantitatively measured using the KT-1000 knee ligament arthrometer. Pivot shift was graded as 0 (absent), grade I (slight), grade II (definite subluxation), and grade III (subluxation and momentary locking). The presence or absence of any degree of pivot shift was correlated with the arthroscopic finding of a torn ACL. Results indicated the "drawer type" tests were significantly more sensitive than other versions of the pivot shift because they can be performed without causing significant pain and muscle spasm, and the limb position maximizes pathologic coupled motion. A correlation between increasing displacement estimated with the Lachman test and measured displacement with the KT-1000 arthrometer revealed that as pathologic displacement increases so does the grade of the Slocum, pivot drawer, and flexion rotation drawer tests. We recommend using the pivot drawer or flexion rotation drawer as a standard method for assessing the pivot shift phenomenon.

Secondary intramedullary nailing of complicated fractures of lower extremities.

Between 1984 and 1991, 16 patients with 23 fractures of the lower extremities were treated with external skeletal fixation and subsequent intramedullary nailing. There were 7 closed fractures, 1 closed fracture with vascular injury, 2 Grade I, 3 Grade II and 10 Grade III injuries, sansistiny of 5 Grade IIIA, 2 Grade IIIB and 3 Grade IIIC fractures. The fractures were maintained in external fixation for an average of 14 days (range 4 to 32 days) after which the fixateur was removed and an intramedullary nail placed during the same procedure in all cases. Two of the twenty-three fractures, 9%, subsequently developed deep infections involving the intramedullary canal, both of which resolved with antibiotics while retaining the nail. Thus we were able to place intramedullary fixation in these difficult and often contaminated injuries in less than one month with a relatively low incidence of complications.