Stemmed implants improve stability in augmented constrained condylar knees.

We previously combined experimental and computational measures to ascertain whether tibial stem augmentation reduces bone strains beneath constrained condylar implants. Using these same integrated approaches, we examined the benefit of a stem when a wedge is used. Implants were removed from the eight paired cadaver specimens from our previous experiment, and oblique defects created that were restored with 15 degrees metallic wedges cemented in place. We applied a varus moment and an axial load and monitored relative motion between implant and bone. Specimen-specific 3-D finite element models were constructed from CT scans and radiographs to examine bone stress in the proximal tibia. Implants with a wedge but no stem had greater motion than the previous control with no stem or wedge. Use of a modular stem with a wedge maintained the same level of motion as the primary case, suggesting that a stem is preferable when a wedge is utilized. The computational models confirmed this conclusion with a 30% reduction in bone stress compared to 17% in the primary case without a wedge. The wedge carried more axial load compared to the primary implant due to its support on stiff metaphyseal bone.

Measuring improvement following total hip and knee arthroplasty using patient-based measures of outcome.

BACKGROUND: Patient-derived outcome scales have become increasingly important to physicians and clinical researchers for measuring improvement in function after surgery. The goal of the present study was to evaluate the ability of health-status instruments to measure early functional recovery after total hip and total knee arthroplasty. METHODS: Four hundred and six patients undergoing total hip arthroplasty and 266 patients undergoing total knee arthroplasty completed health-status questionnaires preoperatively and six months postoperatively to determine the standardized response mean. In the second phase of the study, a group of patients undergoing knee and hip arthroplasty were evaluated with several instruments before and after surgery to test for postoperative ceiling effects. RESULTS: The standardized response mean at six months was 1.7 for the MODEMS Hip Core, 1.2 for the MODEMS Knee Core, and 1.5 and 1.1 for the Physical Component Summary of the SF-36 for patients managed with hip and knee replacement, respectively. A standardized response mean of 1.0 is generally satisfactory for measuring improvement in orthopaedic surgery. In Phase 2 of the study, the vast majority of patients who had a score of 95 to 100 (that is, a maximum or near-maximum score) on the joint-specific scales generally believed that the hip or knee was normal and could not be better. CONCLUSIONS: The MODEMS, Oxford, and WOMAC scales all demonstrated a ceiling effect following total knee and total hip arthroplasty. These scores likely reflected the patients' perception of the status of the knee or hip rather than an inability to measure their improvement beyond the highest possible score. The Physical Component Summary score of the SF-36 had similar standardized response means when compared with hip and knee-specific instruments, and, therefore, consideration should be given to using this scale without a joint-specific scale for the measurement of improvement following total knee and total hip replacement, as a way to decrease responder burden (that is, the time required to complete the questionnaires).

Role of magnetic resonance imaging in the assessment of pediatric cervical spine injuries.

The purpose of this study was to determine the role of magnetic resonance imaging (MRI) in the evaluation of children with suspected cervical spine injury (CSI). The authors studied 237 consecutive children, 74 of whom were evaluated by MRI based on a trauma protocol of the authors' institution. The criteria for MRI were: (1) an obtunded or nonverbal child suspected of having CSI, (2) equivocal plain films, (3) neurologic symptoms without radiographic findings, or (4) an inability to clear the cervical spine within 3 days, based on testing. The average age of the evaluated children was 8 years. MRI confirmed the plain radiography diagnosis in 66% of children and altered the diagnosis in 34%. MRI is valuable in the evaluation of potential CSI, especially in obtunded children or children with equivocal plain radiographs.