John A. Cardea

Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty

The presence of a femoral prosthesis superior to a shaft fracture severely complicates fixation and treatment. This study uses two-dimensional, multithickness, plane stress finite-element models of a femur with prosthesis to investigate the stresses developed with the application of three popular fixation techniques: revision to a long stem prosthesis, lateral plating with a cortical bone allograft strut and cerclage wires, and custom plate application with proximal Parham band fixation with distal cortical screws (Ogden plate). The plate and bone contact as well as the fracture site contact were modelled by using orthotropic elements with custom-fit moduli so that only the normal stress to the interface was significant. A thermal analogy was used to model the cerclage and Parham band preloads so that representative preloads in the proximal fixation of the two types of plate treatments could be modelled. A parametric study was performed with the long-prosthesis model to show variations in stem lengths of one, two and three femoral diameters distal to the fracture site. The Ogden plate model showed a transfer of tensile stress near the proximal-most band, with the highest tensile stress being at the fracture site with evidence of stress shielding of the proximal lateral cortex. The cortical bone strut model showed a transfer of tensile stress to the bone strut but showed less shielding of the proximal cortex. The cerclage wires at the base of the bone strut showed the highest changes in load with the distalmost wire increasing to almost four times its original preload.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of high-energy shock waves for bone cement removal

The revision rate of total hip arthroplasty has increased dramatically over recent years, leading to different methods of extraction of the femoral cement mantle to reduce operative time and surgical risks. The use of high-energy shock waves produced by the Dornier HM.3 Lithotripter to interrupt the cement-bone interface and to reduce the material properties of the cement is investigated. Tests were conducted to measure the pull-out strength of cemented treated rods versus untreated rods, from the medullary canal of canine femurs. The treated femurs showed an average reduction in pull-out strength of 43%. An investigation involving the material properties of acrylic bone cement was also conducted. The properties tested were the compressive modulus of elasticity, the ultimate compressive strength, the ultimate tensile strength, and fracture toughness. The scanning electron microscope aided in determining whether microfractures in the cement resulted from the shock wave treatment. A theoretical study utilizing the finite element method was used to investigate areas of select shock wave treatment about the femoral prosthesis. Analysis of the results showed that the lithotripter treatment had no significant effect on the compressive properties but reduced the tensile properties and fracture toughness significantly. Scanning electron microscopy uncovered definite areas of induced microfractures not present in the control specimens. This study supports the concept of clinically noninvasive, preoperative shock wave treatment prior to total hip revision.

Treatment of Femoral Shaft Fractures with the Brooker-Wills Interlocking Intramedullary Nail

Fifty femur fractures were treated with the Brooker-Wills intramedullary locking nail. The indications included subtrochanteric, subisthmal, segmental or comminuted acute fractures or nonunions, and intramedullary shortening procedures. Eighteen technical problems in 13 (26%) patients were encountered during insertion of the nail. The incidence of technical problems was high early in the series and in procedures done with the patient in the supine position. Adverse clinical results from technical errors occurred in two patients. Most technical errors seem avoidable with careful technique. The mean healing time was only 12.1 weeks and there were four nonunions (8%). One patient had a 10 degrees malunion, four patients had 1-2 cm of shortening, and there were two late device fractures. No patients had rotational malalignment or deep infections. The results and complication rate are comparable to those reported for other interlocking systems. The Brooker-Wills nail is useful for treatment of complex femur fractures and has been effective in preventing malrotation, angulation, and excessive shortening.

Successful Use of Recombinant Factor VIIa for Hemostasis During Total Knee Replacement in a Severe Hemophiliac with High-Titer Factor VIII Inhibitor

A 32-year-old male patient with severe factor VIII (FVIII) deficiency had developed a high-titer FVIII inhibitor at age 13. Recurrent hemarthroses caused bony destruction in both knees, significantly impairing his ability to walk. Knee examination revealed 20 degrees of varus, destruction of the medial joint line, and flexion contracture. Total knee arthroplasty was performed using recombinant factor VIIa (rFVIIa, NovoSeven) for hemostatic control. rFVIIa (85 μg/kg given intravenously over 3-5 minutes) was given just prior to surgery. The dose was repeated every 2 hours during and for the first 48 hours after surgery. When the tourniquet was removed, rFVIIa had not been infused for 1.5 hours, and significant hemorrhage was noted. The hemorrhage responded promptly to rFVIIa infusion. The infusion interval was extended to every 4 hours for an additional 48 hours, and subsequent doses were given every 6 hours until the patient returned to the clinic 2 days postdischarge. Hemoglobin levels dropped from 16.9 gm/dL on admission to 9.1 gm/dL at discharge. After 2 months, the patient returned to work. We recommend that tourniquet release be performed immediately after rFVIIa administration and that aggressive physical therapy be considered in the early postoperative period when rFVIIa infusions are frequent.

Penetration of Moxalactam and Cefazolin into Bone Following Simultaneous Bolus or Infusion

The penetration of cefazolin and moxalactam into bone was studied in 20 adults scheduled for total hip arthroplasty. Patients randomly received both moxalactam and cefazolin (10 mg/kg of each) by either a rapid bolus or a 30-minute infusion. Serum and bone-extract concentrations were measured by HPLC. Serum concentrations of cefazolin were significantly greater than those of moxalactam at 15 minutes, 30 minutes, and at the time of bone removal for both rates of injection. Bone concentrations of cefazolin were significantly greater than those of moxalactam for both the bolus study (7.7 +/- 4.8 micrograms/g versus 5.4 +/- 3.4 micrograms/g) and the infusion study (5.6 +/- 3.4 micrograms/g versus 4.3 +/- 2.6 micrograms/g, respectively). There was no significant difference in the bone levels for the two drugs when penetration was expressed as a function of the simultaneous serum concentration (18% for each drug), and there were no significant differences in bone concentrations between the two rates of administration.

Evaluation of oral ketorolac, oxycodone plus acetaminophen, and placebo for pain relief after orthopedic surgery

Abstract This multicenter, randomized, controlled study evaluated the analgesic effects and safety profile of a single oral dose of ketorolac 10 mg (KET), oxycodone 5 mg plus acetaminophen 325 mg (OXY), and placebo (PLA) in patients with at least moderate pain after orthopedic surgery. Two hundred forty-two patients were enrolled. The three groups were demographically similar; mean age was 41.7 years. Pain intensity difference scores were greater in the OXY group at hour 2 postdose ( P =0.52) but were greater in the KET group at hours 5 and 6 ( P ≤0.032). Summed pain intensity difference (SPID) scores were similar for both OXY and KET and significantly better than PLA at hours 3 and 6 ( P P

Total hip arthroplasty complicated by mismatched implant sizes: Report of two cases

Abstract Numerous alternative types and sizes of implants for total hip arthroplasties are currently available. Two cases are reported in which the head size of the femoral component inserted was larger than the corresponding inner diameter of the acetabular cup. These are the first reported cases of this technical complication. The error can be avoided with careful preoperative planning and proper selection of implants. At 12- and 30-month follow-up evaluation, however, neither of these hips had dislocated or required revision. Immediate revision is not recommended, unless the hip dislocates or has symptomatic subluxations.

Polymethylmethacrylate fixation of osteochondral fragments in dog knees.

The usefulness of polymethylmethacrylate (PMMA) to secure small osteochondral fragments was investigated in canine knees. Small osteochondral free fragments were osteotomized from the medial femoral condyle of 16 dog knees. The fragments were then bonded back in place with various amounts of PMMA. After 13 months, the animals were killed and each knee was examined for healing and arthritis. All of the fragments revascularized and healed. Poor reduction and PMMA extending to the articular surface universally led to arthritis. Small localized spot bonds of PMMA seemed to yield better results than large amounts of surface attachments.