ABSTRACT
Objective By studying biomechanical responses of the femur-prosthesis-tibia complex under normal standing condition after tumor-type hinged knee arthroplasty, to investigate the cause of femoral perforation in patients after knee arthroplasty, so as to provide a theoretical basis for optimal design and manufacturing of tumor-type hinged artificial knee prosthesis. Methods By coupling CT and 3D optical scanning, the finite element model of the subject-specific femur-prosthesis-tibia complex was established and was validated regarding its availability, so as to analyze stress distribution and stress shielding phenomenon of the complex in standing position. Results (1) Under the loading state of standing, the stress on the femur was significantly larger than that on the tibia, and presented an evident concentration phenomenon. The proximal 1/3 of femoral shaft presented a larger stress, with a stress shielding effect. (2) As the model was based on geometry and bone characteristics of the patient in clinic, the location of femur stress concentration was close to that of femur perforation in the patient, which indicated that femur injury behavior might occur when its own gravity was applied such as the patient condition. Conclusions After implantation of the tumor-type hinged artificial knee prosthesis, the prosthesis marrow needle goes deep into marrow cavities, which brings certain pressure to the marrow cavities even under normal standing condition. The produced stress shielding effect and the match of the prosthesis marrow needle to the marrow cavity are all likely to cause stress concentration on the femur, even make femur crack or perforation, and eventually affect the surgery quality. Thus, the prosthesis design should be carefully optimized before surgery in order to reduce or avoid such phenomenon that is related to the postoperative complication rate.
ABSTRACT
<p><b>OBJECTIVE</b>To explore methods and therapeutic effects of transpedicular bone graft in treating thoracolumbar fractures through Wiltse approach.</p><p><b>METHODS</b>From March 2009 to February 2012,56 patients with thoracolumbar fractures were treated by transpedicular bone graft through Wiltse approach. Among them, there were 36 males and 20 females, ranging in age from 14 to 55 years old (mean, 41 years old). The time from injury to operation from 2 to 15 d (mean,3 d). Twenty-five cases were caused by falling down, 7 cases were caused by slipping, 20 cases were caused by car accident and 4 cases were caused by crush trauma. MRI was performed before operation to exclude pathological fracture. The distance between multifidus muscle and longissimus to midcourt line was measured. Self-made trocar was applied in operation. According to AO classification,there were 33 cases with type A1 compression fracture,5 cases with type A2 cleavage fracture and 18 cases with type A3 burst fracture. Sixteen cases of the 56 cases combined with spinal cord injury. Based on Frankel neurologic grading system, preoperative neurological function was grade B in 5 cases, grade C in 2 cases, gade D in 9 cases. Preoperative Denis gading were P5. Frankel and lumbago Denis clssification were used to evaluate neurological function and lumbago. The imaging data before, after operation and the latest follow-up were used to evaluate correction vision.</p><p><b>RESULTS</b>All patients were followed up over 24 months. At the time of the latest follow-up, Frankel B were 3 cases, Frankel C were 2 cases, Frankel D were 4 cases and Frankel E were 7 cases. According to lumbago Denis clssification, P1 (painlessness) were 32 cases, P2 ( slight pain without treatment) were 18 cases, P3 ( moderate pain and taking medicine occasionally) were 6 cases. The anterior vertebral height improved from preoperative (13.38 +/- 4.72)mm to postoperative (22.18 +/- 1.44)mm. The Cobb's angle decreased from preoperative (28.39 +/- 2.64) degrees to (10.07 +/- 3.05) degrees. There were no nails broken, rod broken, internal fixation lossen and vertebral body recompression.</p><p><b>CONCLUSION</b>Transpedicular bone graft for thoracolumbar fractures through Wiltse approach can reduce intraoperative blood loss and postoperative complications, and aviod "eggshell" vertebral body. Mastering revealed way, drafting detailed preoperative plan and eariler exercise is the key to the success of treatment.</p>