Mechanical comparison of a distal femoral side plate and a retrograde intramedullary nail.

OBJECTIVE: To compare quantitatively the axial and torsional stiffness of a retrograde intramedullary nail and a fixed angle screw side plate in treating a supracondylar femur fracture in osteopenic femora. To determine the modes of failure of an intramedullary nail and a side plate under axial loading. DESIGN: Matched pair cadaveric study. SETTING: Orthopaedic biomechanics laboratory. PATIENTS AND OTHER PARTICIPANTS: Eleven matched pairs of preserved human femora were selected. The cadaveric specimens were harvested from relatively elderly donors with an average age of 75.6 years, which represents the principal population at risk for poor fracture fixation. INTERVENTION: The eleven matched pairs were osteotomized to simulate segmental structural defects in the supracondylar region. One femur of each matched pair was fixed with an intramedullary nail, and the contralateral femur was fixed with a side plate. MAIN OUTCOME MEASURES: Axial and torsional stiffness values. Axial modes of failure. RESULTS: The intramedullary nail axial stiffness was 14 percent (p = 0.04) less and torsional stiffness was 17 percent (p = 0.05) less than that provided by the side plate. The axial failure of the intramedullary nail occurred distally, allowing the hardware to protrude into the articular space. The side plate also failed distally by displacing the condylar screw into a varus angulation. CONCLUSION: The mechanical advantages favor the use of the side plate if fixation stiffness is essential. The axial mode of failure occurs distally for both fixation devices.

Combined limited internal fixation with circular frame external fixation of intra-articular tibial fractures.

High-energy intra-articular fractures of the tibial plateau and plafond cause ongoing management problems for the orthopedic surgeon. This study retrospectively evaluated 37 such fractures treated with limited internal fixation and circular frame external fixators. Seventeen plateau fractures (5 open) and 20 plafond fractures (9 open) were treated. Time to union, number of procedures, complications, and functional outcomes were evaluated. All tibial plateau fractures healed within an average of 3.8 months. Eighteen of 20 plafond fractures healed at an average of 4.8 months. There was a high complication rate as is common with these injuries, but most of the complications were minor and easily treated.

Effect of nicotine on the rate and strength of long bone fracture healing.

Empirical clinical observation suggests that cigarette smoking had an inhibitory effect on long bone fracture healing, but this has not been proven scientifically. Forty female New Zealand White rabbits had midshaft tibial osteotomies performed and plated. These were divided randomly into two groups receiving either systemic nicotine or saline (placebo). Lateral radiographs were taken at 4, 6, and 8 weeks that showed a 17.2% average difference in callus formation between the two groups and a significant lag in formation of cortical continuity in the nicotine group. The rabbits were sacrificed 8 weeks after fracture, and healing was compared biomechanically. Three (13%) fractures showed no clinical evidence of union in the nicotine group, whereas all fractures in the control group healed. Biomechanical testing showed the nicotine exposed bones to be 26% weaker in three-point bending than were those exposed to placebo.

Bilateral brachial plexus compressive neuropathy (crutch palsy).

Brachial plexus compressive neuropathy following the use of axillary crutches (crutch palsy) is a rare but well-recognized entity. Most reported cases involve the posterior cord of the brachial plexus in children and have resolved spontaneously within 8-12 weeks. We recently treated a 36-year-old man who was using axillary crutches for mobilization after a supracondylar femoral fracture. Bilateral posterior cord (predominantly radial nerve) compressive neuropathy subsequently developed, with lesser involvement of the ulnar and median nerves. The patient had little to no improvement clinically 8 weeks after the estimated onset of the palsy, and an electromyogram at that time confirmed the presence of a severe axonotmesis lesion of the radial, median, and ulnar nerves bilaterally. The patient was treated with static cock-up wrist splinting and discontinuation of the axillary crutches. Return of sensory and motor function was delayed but occurred within 9 months.

Differences in patellofemoral joint cartilage material properties and their significance to the etiology of cartilage surface fibrillation.

OBJECTIVE: To determine if differences in biomechanical properties and biochemical composition exist between human patellar articular cartilage and the opposing femoral articular cartilage. DESIGN: The biomechanical properties and biochemical composition of the articular cartilage of 17 knees from 13 donors were determined for four sites on the patella and three sites on the femur representing regions of contact at 30 degrees and 90 degrees of flexion. The material properties were determined by biphasic indentation testing, yielding the compressive aggregate modulus, HA, permeability, k, and Poisson's ratio, vs. The thickness of the cartilage at the indentation site, h, was also measured using a needle probe. Full-thickness samples of cartilage adjacent to each indentation site were used for wet weight, sulfated glycosaminoglycan content and hydroxyproline content determinations. RESULTS: The patellar cartilage was found to have a lower compressive aggregate modulus by 30% (P < 0.001), higher permeability to fluid flow by 66% (P < 0.001) and greater thickness by 23% (P = 0.017) than that of the opposing femoral cartilage. The Poisson's ratios for both surfaces were found to be nearly zero. The water content of the patella was higher by 5% (P = 0.031) and the proteoglycan content lower by 19% (P = 0.030) than that of the femur. However, no differences were found between the collagen contents of the cartilages. CONCLUSIONS: Significant differences were found between the intrinsic material properties of the patellar cartilage and those of the femoral-trochlear cartilage. This variability of cartilage material properties with the patellofemoral joint may help explain why patellar cartilage has been frequently observed clinically to exhibit earlier and more severe fibrillation changes than the opposing femoral cartilage.

Total hip arthroplasty after acute displaced femoral neck fractures.

Displaced femoral neck fractures have three treatment options; reduction and fixation, hemiarthroplasty, and total hip arthroplasty. Total hip arthroplasty is often avoided; this is commonly owing to its assumed increased risk of dislocation. A careful and critical review of the literature reveals that it does offer certain advantages in selected patients. If acute dislocations (less than 4 months) are prevented, the dislocation rates after a fracture appear to be the same, regardless of whether a hemiarthroplasty or total hip arthroplasty is used.