Repeated early failure of a newly designed hinged knee system.

We report a case of acute and recurrent accelerated wear of the polyethylene bushings of the hinge mechanism in the Zimmer Segmental Knee System. This resulted in an unacceptable recurvatum deformity leading to multiple revision knee operations, which was unexpected in a modern design hinged knee system. A custom modification of the original design was used to prevent further recurvatum deformity. The current design of the hinge post mechanism in this system appears to be inadequate, which led to the development of a significant recurvatum deformity in our patient. Surgeons should be aware of this potential complication when considering the use of this revision knee system.

Rare presentations of delayed radiation injury: a lobar hematoma and a cystic space-occupying lesion appearing more than 15 years after cranial radiotherapy: report of two cases.

OBJECTIVE AND IMPORTANCE: Radiation vasculopathy and radionecrosis, constituting delayed radiation injury, are rare but recognized complications of radiation therapy occurring at a peak incidence of 3 years after treatment. Little information is available about these complications occurring more than 15 years after radiotherapy and presenting as other than solid intracranial masses. CLINICAL PRESENTATION: We describe two patients who presented with space-occupying cerebral lesions. Patient 1 presented as an emergency with a sudden loss of consciousness. Computed tomography revealed a large left intracerebral hemorrhage; cerebral angiography disclosed nothing abnormal, and a primary spontaneous hemorrhage was presumed. Twenty-seven years earlier, this patient had received adjuvant whole-brain and spine radiotherapy and concomitant chemotherapy after excision of a vermis medulloblastoma. Patient 2 presented with a left frontal cystic lesion (presumed malignant glioma) as the cause of personality and behavioral changes for some months. She had previously received external beam radiation for a basal cell epithelioma, which had been excised from her left forehead 19 years earlier. INTERVENTION: Both patients recovered well after undergoing craniotomies and removal of their lesions; they were discharged home with no neurological deficit. CONCLUSION: Even after long intervals after radiotherapy, it is important to consider radiation vasculopathy and radionecrosis as differential diagnoses of more common conditions. Histological confirmation of a delayed radiation injury in the absence of any evidence of neoplasia or vascular abnormality has allowed appropriate prognosis and management to be formulated with confidence in each of these patients.

Cup version can be accurately measured on the false profile view radiograph.

INTRODUCTION: Accurate measurement of cup version on plain radiographs remains difficult due to the two-dimensional projection of an ellipse and difficulty obtaining reproducible radiographs. PURPOSE: Determine: 1) if the cup angle measured on the false profile view (FPV) could be used to determine radiographic cup version; 2) how patient positioning would affect cup angle measurement on the FPV; 3) if implant cup design affects cup angle measurement. MATERIALS AND METHODS: Three cup version positions were assessed in a sawbone: 13° (normal); 28° (excessive anteversion) and -2° (retroversion). Cup angle was measured on the FPV at five different degrees of pelvic rotation within each cup version group. Pelvic rotation was quantified using the ratio of the inter-femoral head distance measured on the FPV versus the anteroposterior radiographs (FP/AP ratio). Eighty patients (40 metal-on-polyethylene, 40 metal-on-metal) post-total hip were also assessed. Cup version was assessed with Einzel-Bild-Roentgen-Analysis software (EBRA). R2 was calculated to assess correlation between both measurement methods. RESULTS: For the sawbone model, an R2 of 0.95 was obtained. For patients, overall R2 was 0.56 with an FP/AP ratio of 0.3-0.49 having an R2 of 0.72. The EBRA anteversion versus cup angle scatterplot had an R2 of 0.72 (95%CI: +/-7.8°). Subgroup analysis revealed no differences between the metal-on-poly and metal-on-metal for cup angle measurements. The intra-class coefficient for intra- and inter-observer reliability for all cases (individual and combined FP/AP groups) was 0.98 to 0.99. CONCLUSION: The FPV cup angle measurement value provides an accurate measurement of radiographic cup anteversion with well-defined patient position parameters.

Cobalt and chromium levels in blood and urine following hip resurfacing arthroplasty with the Conserve Plus implant.

BACKGROUND: The purpose of the present study was to determine cobalt and chromium ion levels in the blood and urine of patients in whom a modern-generation metal-on-metal hip resurfacing device had been implanted. METHODS: A total of ninety-seven patients with a Conserve Plus metal-on-metal hip resurfacing implant were followed prospectively for two years. Cobalt and chromium levels in erythrocytes, serum, and urine were measured preoperatively as well as three, six, twelve, and twenty-four months postoperatively. RESULTS: The median serum cobalt and chromium ion levels were 1.04 µg/L (range, 0.31 to 7.42 µg/L) and 2.00 µg/L (range, 0.28 to 10.49 µg/L), respectively, at one year after surgery and 1.08 µg/L (range, 0.44 to 7.13 µg/L) and 1.64 µg/L (range, 0.47 to 10.95 µg/L), respectively, at two years after surgery. The corresponding mean levels (and standard deviations) of serum cobalt and chromium were 1.68 ± 1.66 µg/L and 2.70 ± 2.22 µg/L, respectively, at one year after surgery and 1.79 ± 1.66 µg/L and 2.70 ± 2.37 µg/L, respectively, at two years after surgery. CONCLUSIONS: These levels compare favorably with other published ion results for metal-on-metal hip resurfacing and replacement implants. No pseudotumors or other adverse soft-tissue reactions were encountered in our study population. Further research is needed to determine the clinical importance of increased cobalt and chromium ion levels in serum and urine following metal-on-metal hip resurfacing.

Increased force simulator wear testing of a zirconium oxide total knee arthroplasty.

Total knee replacements provide cost effective treatment for debilitating conditions such as osteoarthritis. Their long term performance is governed by ultra-high molecular weight polyethylene (UHMWPE) wear which produces wear debris leading to osteolysis and aseptic loosening of the implant. An oxidised zirconium alternative to cobalt chrome is being used to reduce wear debris formation in the younger patients. Two TKRs of cobalt chrome and two of zirconium oxide coated zirconium were tested in a six degrees of freedom of motion, Stanmore-Instron force controlled knee wear simulator over 4 million increased force cycles. Oxidised zirconium was demonstrated to be more scratch resistant than CoCr. Increases in Ra (mean average roughness) of 12-fold compared to 1.9 fold rise for ZrO. The differences in roughness were accompanied by a 78%, statistically significant, reduction in wear of UHMWPE with the ZrO femoral components compared to the CoCr (p=0.037). Long term clinical results from the use of oxidised zirconium femoral components are awaited. However, it shows potential to reduce the wear rate.