The strain at bone-implant interface determines the effect of spinopelvic reconstruction following total sacrectomy: a strain gauge analysis in various spinopelvic constructs.

PURPOSE: There is still some controversy regarding the optimal biomechanical concept for spinopelvic stabilization following total sacrectomy for malignancy. Strains at specific anatomical sites at pelvis/sacrum and implants interfaces have been poorly investigated. Herein, we compared and analyzed the strains applied at key points at the bone-implant interface in four different spinopelvic constructs following total sacrectomy; consequently, we defined a balanced architecture for spinopelvic fusion in that situation. METHODS: Six human cadaveric specimens, from second lumbar vertebra to proximal femur, were used to compare the partial strains at specific sites in a total sacrectomy model. Test constructs included: (1) intact pelvis (control), (2) sacral-rod reconstruction (SRR), (3) bilateral fibular flap reconstruction (BFFR), (4) four-rods reconstruction (FRR), and (5) improved compound reconstruction (ICR). Strains were measured by bonded strain gauges onto the surface of three specific sites (pubic rami, arcuate lines, and posterior spinal rods) under a 500 N axial load. RESULTS: ICR caused lower strains at specific sites and, moreover, on stress distribution and symmetry, compared to the other three constructs. Strains at pubic rami and arcuate lines following BFFR were lower than those following SRR, but higher at the posterior spinal rod construct. The different modes of strain distribution reflected different patient's parameter-related conditions. FRR model showed the highest strains at all sites because of the lack of an anterior bracing frame. CONCLUSIONS: The findings of this investigation suggest that both anterior bracing frame and the four-rods load dispersion provide significant load sharing. Additionally, these two constructs decrease the peak strains at bone-implant interface, thus determining the theoretical surgical technique to achieve optimal stress dispersion and balance for spinopelvic reconstruction in early postoperative period following total sacrectomy.

Pedicle screw fixation for traumatic fractures of the thoracic and lumbar spine.

BACKGROUND: Spine fractures are common. The treatment of traumatic fractures of the thoracic and lumbar spine remains controversial but surgery involving pedicle screw fixation has become a popular option. OBJECTIVES: To assess the effects (benefits and harms) of pedicle screw fixation for traumatic fractures of the thoracic and lumbar spine. SEARCH METHODS: We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (March 2011), the Cochrane Central Register of Controlled Trials (CENTRAL; The Cochrane Library, 2011 Issue 1), MEDLINE (1948 to March 2011), EMBASE (1980 to 2011 Week 11), the Chinese Biomedical Database (CBM Database) (1978 to March 2011), the WHO International Clinical Trials Registry Platform (March 2011), reference lists of articles and conference proceedings. SELECTION CRITERIA: Randomised controlled trials (RCTs) and quasi-randomised controlled trials comparing pedicle screw fixation and other methods of surgical treatment, or different methods of pedicle screw fixation, for treating traumatic fractures of the thoracic and lumbar spine. DATA COLLECTION AND ANALYSIS: Three review authors independently performed study selection, risk of bias assessment and data extraction. Limited meta-analysis was performed. MAIN RESULTS: Pedicle screw fixation versus other methods of surgery that do not involve pedicle screw fixation was not looked at in any of the identified trials. Studies that were identified investigated different methods of pedicle fixation.Five randomised and three quasi-randomised controlled trials were included. All were at high or unclear risk of various biases, including selection, performance and detection bias. A total of 448 patients with thoracic and lumbar spine fractures were included in the review. Participants were restricted to individuals without neurological impairment in five trials. The mean ages of study populations of the eight trials ranged from 33 to 41 years, and participants had generally experienced traumatic injury. Mean follow-up for trial participants in the eight trials ranged from 28 to 72 months.Five comparisons were tested.Two trials compared short-segment instrumentation versus long-segment instrumentation. These studies found no significant differences between the two groups in self-reported function and quality of life at final follow-up. Aside from one participant, who sustained partial neurological deterioration that was resolved by further surgery (group not known), no neurological deterioration was noted in these trials.One trial comparing short-segment instrumentation with transpedicular bone grafting versus short-segment fixation alone found no significant difference between the two groups related to patient-perceived function and pain at final follow-up. All participants had normal findings on neurological examination at final follow-up.Two trials compared posterior instrumentation with fracture level screw incorporation ('including' group) versus posterior instrumentation alone ('bridging' group). Investigators reported no differences between the two groups in patient-reported function, quality of life, or pain at final follow-up. One trial confirmed that all participants had normal findings on neurological examination at final follow-up.One trial comparing monosegmental pedicle screw instrumentation versus short-segment pedicle instrumentation found no significant differences between the two groups in Oswestry Disability Index results or in pain scores at final follow-up. No neurological deterioration was reported.Three trials compared posterior instrumentation with fusion versus posterior instrumentation without fusion. Researchers found no differences between the two groups in function and quality of life or pain. No participants showed a decline in neurological status in any of the three trials, and no significant difference was reported between groups in the numbers whose status had improved at final follow-up. Two trials stated that patients in the fusion group frequently had donor site pain. Other reported complications included deep vein thrombosis and superficial infection. AUTHORS' CONCLUSIONS: This review included only eight small trials and five different comparisons of methods of pedicle fixation in various participants while looking at a variety of outcomes at different time points. Overall, evidence is insufficient to inform the selection of different methods of pedicle screw fixation or the combined use of fusion. However, in the absence of robust evidence to support fusion, it is important to factor the risk of long-term donor site pain related to bone harvesting into the decision of whether to use this intervention. Further research involving high-quality randomised trials is needed.

[Efficacy analysis of intermediate screws technique plus injectable calcium sulfate for thoracolumbar fracture in postmenopausal patients].

OBJECTIVE: To explore the clinical efficacies of intermediate screws plus injectable calcium sulfate MIIGX3 for thoracolumbar fracture in postmenopausal patients. METHODS: A total of 21 postmenopausal patients with vertebral compression fractures reconstructed with posterior internal fixation of intermediate screws technique and anterior vertebral augmentation of MIIGX3 technique in three dimension were retrospectively analyzed. The changes of fracture vertebral height and Cobb's angle were compared.Visual analogue scale (VAS) was performed to evaluate their symptoms. All patients were followed up. RESULTS: Intermediate screws surgical technique plus MIIGX3 was successfully performed. The average injection dose was 4.6 ml.Leakage occurred intraoperatively in two cases. The average follow-up period was 15 (6-36) months. The VAS system demonstrated that pain decreased significantly (preoperative:7.8, postoperative:2.2). The height and Cobb's angle of fractured vertebra improved greatly. The preoperative values were 45.0 ± 6.4% and 19.4 ± 4.5° and postoperative ones 15.4 ± 3.9% and 8.64 ± 3.18° respectively. There was no occurrence of severe complications related with treatment.Except for 2 patients with a loss of 15% of vertebral height, the average heights of fractured vertebra in other 19 patients recovered to 85% of normal ones. CONCLUSION: Thoracolumbar fracture in postmenopausal patients may be managed satisfactorily by intermediate screws and injectable calcium sulfate technique.Such a technique is both safe and effective. And its stable and durable reduction offers significant improvement.