Distal femoral fixation: a biomechanical comparison of trigen retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locking compression plate (LCP) condylar plate.

BACKGROUND: The purpose of this study was to establish if there are biomechanical differences between implants in stiffness of construct, microdisplacement, and fatigue failure in a supracondylar femoral fracture model. METHODS: A retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locked condylar plate (LCP) were tested using 33-cm long synthetic femurs. A standardized supracondylar medial segmental defect was created in the distal femur bone models. A gap away from the distal joint axis and parallel to the knee axis was created for axial testing of the specimens (Arbeitsgemeinschaft fur Osteosynthesefragen [AO] type 33-A) and a T-fracture (33-C) was created for the fatigue testing of the specimens. Peak displacements were measured, and analysis was done to determine construct stiffness and gap micromotion in axial loading. Cyclic loading was performed for fatigue testing. RESULTS: It was observed that there were statistically significant differences in micromotion across the fracture gap and overall stiffness of various implant constructs. The stiffness of the i.m. nail, DCS, and LCP were 1,106, 750, and 625 N/mm, respectively. The average total micromotion across the fracture gap for the i.m. nail, DCS, and LCP were 1.96, 10.55, and 17.74 mm, respectively. In fatigue testing, the i.m. nail distal screws failed at 9,000 cycles, the DCS did not fail (80,000 cycles completed), and the LCP failed at 19,000 and 23,500 cycles. CONCLUSIONS: When considering micromotion and construct stiffness, the i.m. nail had statistically significant higher stiffness and significantly lower micromotion across the fracture gap with axial compression. Hence, the i.m. nail tested had the greatest stability for type 33-A fractures. However, the nail demonstrated the least amount of resistance to fatigue failure with type 33-C fractures, whereas the DCS did not fail with testing in any pattern.

Impact magnitudes applied by surgeons and their importance when applying the femoral head onto the Morse taper for total hip arthroplasty.

INTRODUCTION: This study was designed to test whether the number of impacts, the experience of the surgeon or impact force made significant difference in pull off forces. MATERIALS AND METHODS: The forces applied by 10 orthopaedic surgeons (five residents and five attending staff) to impact the femoral head onto the trunnion of a femoral component were recorded. The resultant forces were then divided into four energy levels and compared to determine if the number of impacts would make a difference in pull off strength. RESULTS: No significant differences existed between the resident versus attending groups in magnitude of force applied. Through ANOVA testing, it was found that at each of the energy levels, multiple blows demonstrated a significant pull off strength difference compared to a single blow. Increased pull off force was also noted when the magnitude of force of the applied blows was increased. CONCLUSION: We recommend at least two firm, axially aligned blows to impact the femoral head onto the trunnion intra-operatively.

The effect of pilot hole size on the insertion torque and pullout strength of self-tapping cortical bone screws in osteoporotic bone.

BACKGROUND: All surgical screws can experience failure if the torsional, tensile, and flexion loads exerted on the screws are excessively high. The use of self-tapping screws (STS) results in higher insertion torques (IT) as these screws cut their own threads in the pilot hole drilled in the bone. In this study, the torque for inserting the STS into an osteoporotic bone block for different pilot hole sizes (PHS) was measured and the pullout strength (PS) for extraction of the screws was determined for different depths of insertion, 0 mm, 1 mm, and 2 mm beyond the far cortex. METHODS: Seventy-two Synthes stainless steel STS (40 mm length and 3.5 mm diameter) were inserted into pilot holes of sizes 2.55 (A: 73% OD), 2.50 (B: 71.5%), 2.45 (C: 70%), and 2.8 mm (D: 80%). Using a digital torque screwdriver, screws were inserted to 0 mm, 1 mm or 2 mm past the far cortex. Pullout tests were conducted with an Instron materials testing system. Analysis of variance and Student-Neuman-Keuls tests were performed to determine the effect of DOI and PHS on the loading energy, PS, and IT. RESULTS: Results demonstrated that IT of the screws inserted into pilot holes A, B, and C were higher than those in D. It was also observed that PS and loading energy for 1 mm and 2 mm penetration past the far cortex were higher than those for 0 mm regardless of PHS. This study also found that an increase in PHS to 2.8 mm will reduce IT but will also reduce the PS relative to a PHS of 2.5 mm, the current standard for 3.5 mm screws. CONCLUSIONS: The results of previously published studies regarding the effect of pilot hole size on PS in healthy cortical bone cannot be applied to the osteoporotic environment. The findings presented in this research support using PHS no larger than 71.5% of the screw outer diameter (i.e., pilot hole size of 2.5 mm for 3.5 mm screws) and inserting screws at least 2 mm beyond the far cortex to maximize PS and minimize iatrogenic damage in osteoporotic bone.

Pullout strength and load to failure properties of self-tapping cortical screws in synthetic and cadaveric environments representative of healthy and osteoporotic bone.

BACKGROUND: The parameters of self-tapping screw (STS) performance in normal and osteoporotic bone have been defined in representative environments, but the question remains as to the clinical application of such findings. The goal of this study was to analyze the biomechanical performance of STSs in cadaveric and synthetic environments representative of healthy and osteoporotic bone. METHODS: Ninety-six Synthes STSs were inserted into cadaveric and synthetic models representative of osteoporotic and healthy bone. Screws were inserted to depths of 1 mm short of the far cortex, flush and 1 mm and 2 mm beyond the far cortex. Screws were tested with an Instron 8511 material testing system utilizing axial pullout forces. A SAS procedure was used to conduct analysis of variance for unbalanced datasets. RESULTS: Substantial differences were appreciated with respect to screw performance between osteoporotic and healthy bone specimens. Although a similar pattern of increased pullout strength and loading energy with increasing depth of insertion was demonstrated, absolute values were lower in osteoporotic specimens. Although performance trends were similar in cadaveric and synthetic testing models for both osteoporotic and healthy bone, values obtained during testing were different. Incomplete insertion of STSs resulted in a 21.5% and 37% reduction of biomechanical properties in osteoporotic and normal bone, respectively. CONCLUSIONS: These results indicate that previously published findings on the performance of STSs in synthetic models cannot reasonably be applied to the clinical realm. Although trends may be similar, screw performance in synthetic, as compared with cadaveric, models is markedly different.

Valgus osteotomy of the proximal femur with sliding hip screw for the treatment of femoral neck nonunions: the technique, a case series, and literature review.

Femoral neck nonunions are a difficult complication in the treatment of femoral neck fractures and have traditionally been managed using an intertrochanteric valgus osteotomy and blade plate. We propose an alternative method, a proximal femoral valgus osteotomy using a sliding hip screw instead of a blade plate. This technique eliminates many of the difficulties experienced with the valgus osteotomy and blade plate by employing a device and instrumentation that is more familiar to orthopedic surgeons. The technique is reproducible and has been used successfully in a series of 4 patients.

Fixation of femoral head fractures using the modified heuter direct anterior approach.

Large displaced fractures of the femoral head require open reduction and internal fixation. If the displaced fragments are small, open reduction may not be possible and excision of the fragment or nonoperative care may be the treatment of choice. Surgical approaches that have been used for open reduction and internal fixation include the Smith-Petersen approach, Watson-Jones approach, Kocher-Langenbeck approach, a posterior approach with a trochanteric flip osteotomy, and surgical dislocation of the hip. Here, we describe the use of the modified Heuter direct anterior approach for open reduction and internal fixation of femoral head fractures in 2 patients.

Outcomes of modular proximal femoral replacement in the treatment of complex proximal femoral fractures: a case series.

BACKGROUND: The treatment of complex femur fractures poses a significant challenge. Even with current advancements and the various implements available for the fixation of femoral fractures, results are often disappointing. This study sought to identify problems associated with and examine results of modular proximal femoral replacement. Outcomes were evaluated in two groups of patients: those receiving primary modular proximal femoral replacement for fractures and those treated with salvage arthroplasty for failed internal fixation. METHODS: Twelve patients who had received modular proximal femoral replacement as primary treatment for proximal femoral fractures were evaluated along with nine patients treated with salvage proximal femoral replacement for failed internal fixation. After the surgical procedure, patients were evaluated at regular follow-up intervals and contacted by phone at the conclusion of this study. Patient functional results were evaluated using the Merle D'Aubigne hip rating scale, which measures pain, motion and ambulatory status. Routine radiographs were also obtained at each patient visit. RESULTS: On average, patients who received modular proximal femoral replacement as the primary surgery for their femoral fractures enjoyed a high-level functional result and had few complications. Subjects who received salvage femoral replacement had a less optimal outcome and experienced more complications. Nonetheless, final post-operative MDA score was significantly increased from pre-operative levels. CONCLUSION: Modular proximal femoral replacement is a viable option in the primary fracture or revision setting, and has been shown to have a reasonable outcome, especially when the nature of initial injury is taken into account.

Preinjury warfarin and geriatric orthopedic trauma patients: a case-matched study.

BACKGROUND: This study examined the hypothesis that patients on warfarin before sustaining orthopedic injuries will have increased morbidity and mortality compared with matched control patients not on warfarin. METHODS: Records of consecutive trauma patients on warfarin with orthopedic fractures who presented from January 1997 to June 2002 to a Level I trauma center were retrospectively analyzed. Data were evaluated using the chi and Student's t tests and nonparametric tests when appropriate; values of p < 0.05 were considered significant. RESULTS: A study group of 53 patients was available for review. In comparison with the control group, significant differences were found in time delay from admission to surgery (p = 0.005), hospital length of stay (p = 0.03), total units of blood transfused (p = 0.03), and discharge disposition (p < 0.0003). No difference was found in number of intensive care unit days, complications, or mortality. CONCLUSION: Preinjury warfarin impacts outcomes of geriatric trauma patients sustaining orthopedic injuries.