Structural response and relative strength of a laminated composite hip prosthesis: effects of functional activity.

To obtain a better appreciation for the structural performance of a laminated composite hip prosthesis (CP), we examined in situ prosthesis structural response and relative strengths as a function of walking and stair climbing using our previously developed analysis guidelines. Accordingly, we examined overall prosthesis structural response utilizing a global continuum level modeling approach and prosthesis relative strengths using a local microstructural (or ply-level) modeling approach. As a reference and control, we examined the structural performance of the intact natural femur (NAT) and a titanium alloy (Ti) based hip prosthesis. In terms of the overall structural response, i.e., the femur/prosthesis deformational response, stem/bone interfacial stress transfer, and calcar strain energy density restored, the performance of the CP prosthesis was moderately improved over that of the control Ti prosthesis and better approximates the NAT response. In terms of relative strength, we found that the neck of the CP prosthesis failed for all activities with the exception of the mid-stance phase of level walking. However, the prosthesis appears to have sufficient relative strength for function at positions distal to the neck of the prosthesis. While these results dampen enthusiasm for consideration of laminated composite hip prostheses designed with a shape based on a metal alloy implant, they indirectly support consideration of alternate hip prosthesis structural designs such as using a better supported prosthesis neck or utilizing metal/composite hybrid constructions. Importantly, our simulation and analysis approach could be utilized in the design of other laminated composite biomedical structural components.

Baseline hemoglobin as a predictor of risk of transfusion and response to Epoetin alfa in orthopedic surgery patients.

A multicenter, double-blind, placebo-controlled, parallel-group study was undertaken to determine whether Epoetin alfa can reduce perioperative transfusion requirements. Twenty-six medical centers enrolled 316 patients who were scheduled for major orthopedic surgery and were expected to require > or = 2 units of blood. Patients were stratified according to baseline hemoglobin levels and randomly assigned to receive either Epoetin alfa (300 IU/kg or 100 IU/kg) or placebo for 15 consecutive days starting 10 days prior to, on the day of, and for 4 days after surgery. Epoetin alfa (300 IU/kg) resulted in significantly less exposure to allogeneic blood transfusion compared with placebo (16%) versus 45%) in patients whose baseline hemoglobin level was > 10 to < or = 13 g/dL (P = 0.024). Mean number of units transfused per patient was also lower among those treated with Epoetin alfa (overall, P = 0.027). Epoetin alfa was safe and well tolerated in this population.

Integrated analysis of thrombotic/vascular event occurrence in epoetin alfa-treated patients undergoing major, elective orthopedic surgery.

Data from four prospective, multicenter, randomized studies involving 869 major, elective orthopedic surgery patients were examined by means of a retrospective integrated analysis to evaluate whether perioperative Epoetin alfa use was associated with the occurrence of thrombotic/vascular events. The incidence of thrombotic/vascular events was similar between 619 patients treated with Epoetin alfa and 250 patients receiving placebo (7.4% versus 8.0%, respectively). Regression analyses identified age, cardiac history, hypertension, and cardiac medications, but not Epoetin alfa, as risk factors for thrombotic/vascular events. The analysis did not implicate an increase in the rate of rise in hematocrit or maximum hematocrit obtained prior to surgery as contributors to thrombotic events. Thus, Epoetin alfa, which enhances preoperative erythropoiesis and increases hematocrit, did not affect the probability of thrombotic/vascular events.

Staged versus simultaneous bilateral total knee replacement.

Bilateral total knee replacements were reviewed to determine whether any difference exists in the perioperative course between procedures done under one anesthetic (simultaneous) and those done under two anesthetics (staged). There were 29 staged and 18 simultaneous cases, therefore 76 separate procedures and 94 knees done. The total operative time, blood loss, and complications were similar between the two groups. However, the staged replacements had more than twice the hospital days (34.6 +/- 7.7 vs. 16.8 +/- 5.6, P less than .001) and 18% greater hospital bills. In fact, for a given patient, the hospital bill may be greater than 50% higher if a staged rather than simultaneous replacement is done. Therefore, simultaneous replacement is recommended for appropriate patients.

Comparison of oral ketorolac, intramuscular morphine, and placebo for treatment of pain after orthopedic surgery.

Using a randomized, double-blind, placebo-controlled, parallel, single-dose, single-center, 6-hour study, we compared the analgesic response and tolerability of oral ketorolac tromethamine and intramuscular morphine sulfate and placebo. The study group comprised 176 patients with moderate, severe, or very severe pain after hip or knee surgery at a teaching hospital. Patients received either 10 mg of ketorolac orally, 10 mg of morphine intramuscularly, 5 mg of morphine IM, or placebo. Patients rated pain intensity at baseline and pain intensity and pain relief at 30 minutes, 1 hour, and hourly thereafter for 6 hours. At study completion, we evaluated overall patient ratings of pain relief and occurrence of adverse events. Summed pain intensity difference scores and total pain relief scores showed the active medications to be significantly superior to placebo and not significantly different from each other. The 10-mg dose of morphine showed a small advantage over ketorolac in peak analgesic effect, but the onset of pain relief was comparable among the active agents. The incidence of adverse events among the active-treatment groups was similar, though there was a numerical trend favoring ketorolac over 10 mg of morphine. We found oral ketorolac to be an effective alternative to parenteral opioids for the treatment of pain after hip or knee surgery in patients who can tolerate oral medication.