In vitro analysis of anterior and posterior fixation in an experimental unstable burst fracture model

STUDY DESIGN: A biomechanical comparison of fixation constructs in an experimental fracture model. OBJECTIVE: To determine the relative postoperative stability of anterior graft and plating with that of posterior or combined fixation constructs in an unstable thoracolumbar burst fracture model. SUMMARY OF BACKGROUND DATA: Several treatment modalities have been proposed for unstable thoracolumbar burst fractures, but the optimal technique is unclear. Previous cadaveric biomechanical studies in unstable burst fracture models have not considered the commonly used posterior (interpedicular) and anterior (plate) constructs. METHODS: Nine human spine segments (T11-L3) were potted in epoxy and scanned using dual energy x-ray absorptiometry and computed tomography. Intact specimens had baseline flexibility testing. Unstable L1 burst fractures as verified by computed tomography were created using an impulse load and posterior surgical osteoligamentous destabilization (ie, transection of the lamina, interspinous ligaments, facet capsules, and ligamentum flavum). Specimens were instrumented posteriorly with pedicle screws and rods and tested to 6 Nm in flexion-extension, lateral bending, and torsion. Corpectomy and strut grafting were then performed, and testing was repeated in varying order with posterior fixation, anterior plating and circumferential fixation. Range of motion (ROM) and neutral zone was calculated for each test and fixation groups were compared using analysis of variance. RESULTS: All specimens had AO B1.2 (unstable burst) fractures. Mean ROM for posterior-only constructs was significantly less than that of the intact in lateral bending, flexion, and extension (P<0.001). Anterior-only constructs after corpectomy and strut grafting generally resulted in a smaller ROM versus intact in flexion (NS: P=0.1) and lateral bending (P<0.001). In contrast, all anterior-only and posterior constructs had greater ROM than intact in torsion (all at P<0.05). Circumferential fixation resulted in statistically smaller ROM compared with all other constructs (P< or =0.04), and reached that of the intact specimen in torsion. Increased ROM was correlated with greater fracture comminution for posterior-only fixation (P<0.05), and was weakly correlated with lower dual energy x-ray absorptiometry score (R=0.3) for anterior-only fixation. CONCLUSIONS: Circumferential instrumentation provided the most rigid fixation, followed by posterior fixation with anterior strut grafting, posterior fixation alone, and by anterior fixation with strut grafting. These results were dependent on bone quality and the comminution severity of the fracture. These results should aid surgical decision making in addition to other factors in the overall clinical situation.     

Case report: The nest technique for management of a periprosthetic patellar fracture with severe bone loss

Periprosthetic patellar fracture with marked loss of bone stock presents a significant problem in total knee arthroplasty. Treatment outcomes are often unsatisfying and may lead to disruption of the extensor mechanism of the knee. We present a patient with a Type IIIb periprosthetic patellar fracture treated by a novel approach. Three Steinmann pins were used to reduce the patella and form scaffold for bone graft and a patellar button was cemented into the construct. At 7 years followup, the patient has maintained excellent range of motion, reports no knee pain, has healed the patella fracture, and has restored patellar bone stock.     

CT appearance of mycotic abdominal aortic aneurysms

The CT appearance of three cases of infected aortic aneurysms is reported with clinical and pathological correlation. Two of our cases had unique features: the disappearance of aortic calcifications, and an irregular, thickened aortic wall with peripheral enhancement. The nonspecific clinical presentation and high mortality make mycotic aneurysm an important consideration in the differential diagnosis of abnormal soft tissue contiguous with the aorta.     

Validation, reliability, and complications of a tethering scoliosis model in the rabbit

This study was conducted to refine a small animal model of scoliosis, and to quantify the deformities throughout its growth period. Subcutaneous scapula-to-contralateral pelvis tethering surgery was selected due to its minimally invasive nature and potential applicability for a large animal model. The procedure was performed in 7-week-old New Zealand white rabbits. Group A animals (n=9) underwent the tethering procedure with a suture that spontaneously released. Group B animals (n=17) had the identical procedure with a robust tether and pelvic fixation, which was maintained for 2 months during growth. All animals developed immediate post-operative scoliosis with a Cobb angle of 23° (range, 6–39°) in group A and 59° (range, 24–90°) in group B animals. During the 2 month post-tethering, group A animals lost their tether and scoliosis resolved, whereas all animals in group B maintained their tether until scheduled release at which time the mean scoliosis was 62°. Immediately after tether release, group B scoliosis decreased to a mean 53°. Over the following 4 months of adolescent growth, the scoliosis decreased to a mean of 43° at skeletal maturity; the decrease usually occurred in animals with less than 45° curves at tether release. Radiographs revealed apical vertebral wedging (mean 19°) in all group B animals. Sagittal spinal alignment was also assessed, and for group B animals, the scoliotic segment developed mild to moderate kyphosis (mean 28°) and torsional deformity, but the kyphosis resolved by 4 months after tether-release. Complications specific to this technique included a high rate of transient scapulothoracic dissociation and cases of cor pulmonale. In conclusion, this tethering technique in immature rabbits consistently produced scoliosis with vertebral wedging when the tether was intact through the first 2 months of the protocol. The transient exaggeration of kyphosis suggests that the production of scoliosis is not necessarily dependent on lordosis in this model. Because this technique does not violate thoracic or spinal tissues, it may be useful in the investigation of secondary physiologic effects of mechanically-induced scoliosis, and may be scalable to larger animal species.