PubMed · 8478754
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R E Marx. 1993. Mandibular reconstruction.. https://doi.org/10.1016/s0278-2391(10)80501-4
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STUDY DESIGN: This experimental study used synthetic spine models to compare the effect of the angle of kyphosis, rod diameter, and hook number on the biomechanical stiffness of a long-segment posterior spinal construct. OBJECTIVE: To examine the biomechanical effects of incremental kyphosis on variously instrumented long-segment posterior spinal constructs. SUMMARY OF BACKGROUND DATA: Euler's formula for loading of curved long columns would suggest that kyphosis has a profound impact on the biomechanical behavior of long-segment posterior spinal constructs. The effects of sagittal contour on the mechanical properties of long-segment posterior spinal constructs have not been well documented. METHODS: Kyphotic and straight synthetic spine models were used to test long-segment posterior instrumentation constructs biomechanically while varying rod diameter and the number of hook sites. The synthetic spines, composed of polypropylene vertebral blocks and isoprene elastomer intervertebral spacers, were fabricated with either 0 degrees, 27 degrees, or 53 degrees of sagittal contour. The models were instrumented with 5.5- or 6.35-mm titanium rods, and with either 8 or 12 hooks. The models were loaded from 0 to 300 N in a cyclical ramp fashion using an MTS 858 Bionix testing device testing device. Construct stiffness (force and displacement) during axial compression was determined. RESULTS: Straight model: Changing the hook number from 8 to 12 caused a 32% increase in construct stiffness with the 5.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 36% increase in construct stiffness with the 8-hook pattern. Changing both the rods and hooks caused the stiffness to increase 44%. 27 degrees MODEL: Changing the hook number from 8 to 12 caused a 20% increase in construct stiffness with the 6.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 29% increase in construct stiffness with the 12-hook pattern. Changing both the rods and hooks caused the construct stiffness to increase 26%. 53 degrees MODEL: Changing the hook number from 8 to 12 caused a 14% increase in construct stiffness with the 6.35-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 17% (P<0.0005) increase in construct stiffness with the 12-hookpattern. Changing both rods and hooks caused the stiffness to increase 21%. Summary data on angular kyphosis: Using the same rod diameter and the same number of hooks, and progressing from a straight alignment to 27 degrees of sagittal contour decreased construct stiffness 32%. Going from straight alignment to 53 degrees decreased the stiffness 59.6%. All reported values were statistically significant (P < 0.0005). CONCLUSIONS: The biomechanical stiffness of the straight spine was sensitive to both an increase in hook fixation sites and an increase in rod diameter. The kyphotic spines, however, were more sensitive to variations in rod diameter. Although with increasing kyphosis, the optimum instrumentation strategy will maximize both rod diameter and the number of hook sites, instrumented kyphotic spines remain biomechanically "disadvantaged" as compared with nonkyphotic instrumented spines.
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BACKGROUND: Cephalocondylic intramedullary nails which are inserted proximally to distally (cephalocondylic) have been used for the surgical treatment of extracapsular hip fractures. OBJECTIVES: To update and expand our review comparing the Gamma nail with the sliding hip screw (SHS) by comparing all cephalocondylic intramedullary nails with extramedullary implants for the surgical treatment of extracapsular hip fractures in adults. SEARCH STRATEGY: We searched the Cochrane Musculoskeletal Injuries Group trials register, Medline, select orthopaedic journals and conference proceedings, and reference lists of relevant articles. We contacted trialists, colleagues and implant manufacturers. Date of the most recent search: June 1998. SELECTION CRITERIA: All randomised and quasi-randomised trials comparing cephalocondylic nails with extramedullary implants for extracapsular hip fractures. DATA COLLECTION AND ANALYSIS: Both reviewers independently assessed trial quality and extracted data. Additional information was sought from all trialists. Wherever appropriate and possible, results were pooled. MAIN RESULTS: The one trial of 230 patients comparing the Kuntscher-Y nail with the SHS, reported no major difference the outcome aside from a significantly increased number of patients with leg shortening, and a tendency for poorer recovery of mobility in the Kuntscher-Y nail group. Fourteen trials comparing the Gamma nail with the SHS were included, with data available for 1977 patients. The Gamma nail was associated with an increased risk of operative and later fracture of the femur and an increased re-operation rate. There were no major differences in the incidence of wound infection, mortality or medical complications between implants. Data were inadequate to determine if there were differences for other outcomes. Two trials involving 231 patients compared the intramedullary hip screw (IMHS) with the SHS. Fracture fixation complications were more common in the IMHS group: all cases of operative and later fracture of the femur and haematoma occurred in this group. Results for post-operative complications, mortality and functional outcomes were similar in the two groups. REVIEWER'S CONCLUSIONS: Further evidence is required before any conclusions can be drawn on the relative merits of the Kuntscher-Y nail and the SHS. Given the lower complication rate of the SHS in comparison with the Gamma nail, it appears that for trochanteric fractures the SHS is superior. Further evidence is still required to confirm this, as well as to determine if the Gamma nail, or modifications of the Gamma nail, have advantages for selected fracture types (for example, subtrochanteric fractures). From the limited evidence available, IMHS appears to have the same problems as the Gamma nail, but other theoretical advantages of the IHMS can not be ruled out.