Biomechanical Comparison of Cadaveric and Commercially Available Synthetic Osteoporotic Bone Analogues in a Locked Plate Fracture Model Under Torsional Loading.

OBJECTIVES: Biomechanical studies of osteoporotic bone have used synthetic models rather than cadaveric samples because of decreased variability, increased availability, and overall ease of the use of synthetic models. We compared the torsional mechanical properties of cadaveric osteoporotic bone with those of currently available synthetic osteoporotic bone analogues. METHODS: We tested 12 osteoporotic cadaveric humeri and 6 specimens each of 6 types of synthetic analogues. A 5-mm fracture gap model and posterior plating technique with 4.5-mm narrow 10-hole locking compression plate were used. Torque was applied to a peak of ±10 N·m for 1000 cycles at 0.3 Hz. Data were continuously collected during cyclical and ramped loading with a servohydraulic materials testing system. RESULTS: Cadaveric bone had a 17% failure rate before completing 1000 cycles. Three osteoporotic bone models had 100% failure (P < 0.05), 2 had 17% failure, and 1 had 0% failure before 1000 cycles. Significant differences in the stiffness of the 3 types of synthetic bone models that survived cyclic loading were noted compared with the cadaveric bone model (P < 0.05). Osteoporotic bone analogues had torsional mechanical properties different from those of osteoporotic cadaveric specimens. CONCLUSIONS: The differences between osteoporotic cadaveric humeri and synthetic osteoporotic bone analogues ranged from profound with complete catastrophic failure after a few cycles to subtler differences in stiffness and strain hardening. These findings suggest that different bone analogue models vary substantially in their torsional mechanical properties and might not be appropriate substitutes for cadaveric bone in biomechanical studies of osteoporotic bone.

How much vertical displacement of the symphysis indicates instability after pelvic injury?

BACKGROUND: Measures of pubic symphyseal widening are used by at least two classification systems as determinants of injury grade. Recent work has challenged the commonly used parameter of 2.5 cm of pubic symphysis as an accurate marker of pelvic injury grade and has suggested a role of rotation in the flexion-extension plane as a determinant of pelvic stability. We investigated pelvic stability in the flexion-extension plane to determine a threshold of rotational displacement of the hemipelvis above which the potential for instability exists. METHODS: Cadaveric specimens were mounted onto a servohydraulic biaxial testing machine and subjected to a vertically directed flexion moment. Position of hemipelvis was recorded using a three-dimensional motion capture system and video recording. Displacement of the pubic symphysis and changes in length and position of the sacrospinous and sacrotuberous ligaments were recorded. Amount of force applied was measured and recorded. A yield point was determined as the first point at which the force plot exhibited a decrease in force and was correlated to the corresponding displacement. RESULTS: The mean vertical displacement of the pubic symphysis at the yield point was 16 mm (95% confidence interval, 11-22 mm). Mean sacrospinous ligament strain at yield point was 4% (range, 1.0-9.5%). CONCLUSION: Pelves with vertical rotational symphyseal displacement of less than 11 mm can reasonably be expected to have rotational stability in the flexion-extension plane. Those with displacement of greater than 22 mm can be expected to have lost some integrity regarding resistance to pelvic flexion. These values may allow clinicians to infer pelvic stability from amount of vertical symphyseal displacement.

Investigation of multiligamentous knee injury patterns with associated injuries presenting at a level I trauma center.

OBJECTIVES: To characterize multiligamentous knee injury patterns and describe associated morbidities. DESIGN: Retrospective. SETTING: Level I trauma center. PATIENTS: One hundred two patients (106 knees) with multiligamentous knee injuries and/or dislocations from 2000 through 2008. Subgroup of 82 knees with appropriate magnetic resonance images available assessed for ligamentous injury patterns. INTERVENTION: Data obtained from medical records for 106 knees. MAIN OUTCOME MEASUREMENTS: Presence of arterial injuries, nerve injuries, associated fracture patterns, and whole-body morbidities. RESULTS: The most common (43%) injury pattern was a combined disruption of the anterior cruciate ligament, posterior cruciate ligament, and posterolateral corner. Twenty-five percent of knees had associated ipsilateral tibial plateau fractures, and 19% had associated ipsilateral femoral fractures. Peroneal nerve injury occurred in 25% of knees, arterial injury in 21%, and compartment syndrome in 16%. An intra-abdominal injury was present in 13% of patients, a severe closed head injury in 10%, and a symptomatic pulmonary embolism in 5%. CONCLUSIONS: Nearly half the multiligamentous knee injuries involved the anterior cruciate ligament, posterior cruciate ligament, and posterolateral corner; one-fourth had associated ipsilateral tibial plateau fractures. The incidence of peroneal nerve injury (25%) was higher than previously reported (20%), whereas the incidence of arterial injury (21%) was comparable to previous reports (19%). Posterolateral corner injuries were more prevalent than previously reported and were highly associated with peroneal nerve injury. We found a substantial incidence of associated morbidities of the whole body. Multiligamentous knee injuries are a marker of concomitant trauma and should be closely evaluated at presentation and during the hospital course to allow for early intervention for life- or limb-threatening comorbidities.