Accuracy of tibial component placement in unicompartmental knee arthroplasty performed using an accelerometer-based portable navigation system.

PURPOSE: There is a need for new devices to improve the accuracy of implantation in unicompartmental knee arthroplasties (UKAs). The accelerometer-based portable navigation system is expected to improve this accuracy. This study aimed to compare the accuracy of UKAs performed by the portable navigation system with that of the conventional method, and to investigate whether the portable navigation system can complement the surgeon's experience. METHODS: The study comprised of 80 Oxford UKAs. Knees were divided into two groups based on the method of tibial osteotomy: the conventional group (37 UKAs performed by an experienced surgeon using the extra-medullary guide) and the portable navigation group (43 UKAs performed by 2 unaccustomed surgeons using the navigation system). The absolute error from the target angle on the coronal and sagittal plane was measured on whole lower leg X-ray. The incidence of outliers (> 3°) was compared between the groups using Fisher's exact probability test. RESULTS: The incidences of outliers on the coronal plane were 41.0% (15 of 37 knees) in the conventional group and 9.3% (4 of 43 knees) in the portable navigation group (p < 0.0001). The incidences of outliers on the sagittal plane were 13.5% (5 of 37 knees) in the conventional group and 14.0% (6 of 43 knees) in the portable navigation group (p = 0.3772). CONCLUSION: This is the first report on the usefulness of an accelerometer-based portable navigation system in UKA. The use of this system improves the accuracy of implantation of the tibial component beyond the experience of the surgeon. LEVEL OF EVIDENCE: Retrospective comparative study, Level III.

Low levels of steroid-metabolizing hepatic enzyme (cytochrome P450 3A) activity may elevate responsiveness to steroids and may increase risk of steroid-induced osteonecrosis even with low glucocorticoid dose.

BACKGROUND: The main purpose of this study was to examine the relationships among osteonecrosis, steroid-metabolizing hepatic enzyme (cytochrome P450 3A; CYP3A) activity, and steroid dose to determine whether it is possible to prevent osteonecrosis in animals with low hepatic CYP3A activity by reducing exogenous steroid doses. METHODS: Japanese white rabbits (n = 103) were divided into three groups: a group with CYP3A activity induction (by intramuscular phenobarbital injection, n = 31), a group with CYP3A activity inhibition (by oral itraconazole administration, n = 30), and a control group (n = 42). Three weeks later, all rabbits received a methylprednisolone injection. Each group was divided into two subgroups by dosage of methylprednisolone (5 or 10 mg/kg body weight). Three weeks after methylprednisolone injections, the animals were killed and histological examination was performed to determine the incidences of osteonecrosis in the six subgroups. RESULTS: Incidence in the inhibition subgroup with 5 mg/kg steroid was higher than that in the induction subgroup receiving 10 mg/kg steroid. Thus, suppression of CYP3A activity significantly increased vulnerability to steroid-induced osteonecrosis, while increased CYP3A activity reduced this vulnerability. CONCLUSIONS: These findings suggest that low CYP3A activity may be vulnerable to the effect of steroids and increase risk of osteonecrosis, even with a low dose of steroid.

Effect of simvastatin on steroid-induced osteonecrosis evidenced by the serum lipid level and hepatic cytochrome P4503A in a rabbit model.

OBJECTIVE: This study was designed to investigate the efficacy of lipid-lowering agents in preventing steroid-induced osteonecrosis and the mechanism by which they do so in a rabbit model. METHODS: Female Japanese white rabbits were randomly allocated to receive probucol (group P), pravastatin (group PS), simvastatin (group SS), or saline (group C) for 6 weeks (n = 15 in groups P, PS, and SS; n = 30 in group C). Methylprednisolone (20 mg/kg) was injected at 3 weeks after starting treatment, and the femurs were histologically examined bilaterally 3 weeks after methylprednisolone injection. Midazolam clearance was measured before treatment and before methylprednisolone injection to determine hepatic cytochrome P4503A (CYP3A) levels. RESULTS: The incidence of osteonecrosis in the proximal metaphysis of the femurs in groups PS and SS was significantly lower than in group C (P < 0.05 and P < 0.0001, respectively), whereas it did not differ between groups P and C. It was significantly lower in group SS than in group PS (P < 0.05). Plasma concentrations of lipids (low-density lipoprotein, triglyceride, free fatty acid, and total cholesterol) in groups P, PS, and SS were significantly lower than in group C; and hepatic CYP3A levels were significantly higher in group SS than in groups P or PS after treatment (P < 0.005 for both). CONCLUSIONS: Simvastatin and pravastatin significantly reduced the incidence of steroid-induced osteonecrosis in rabbits. Simvastatin was more effective in reducing the incidence of the disease, and increased CYP3A activity is a possible mechanism for this effect.

Increased hepatic cytochrome P4503A activity decreases the risk of developing steroid-induced osteonecrosis in a rabbit model.

Low hepatic cytochrome P4503A (CYP3A) activities might play an important role for inducing osteonecrosis of the femoral head (ONFH) by corticosteroids. However, the relationship between hepatic CYP3A activity and steroid-induced ONFH is unknown. We have examined the relationship between hepatic CYP3A activity and the inducibility of ONFH in a rabbit model. Sixty rabbits were divided into three groups. Hepatic CYP3A inducer (phenobarbital, group P; n = 15), inhibitor (itraconazole, group I; n = 15), or saline (group C, n = 30) was administrated for 3 weeks before intramuscular methylprednisolone. In groups P and I, hepatic CYP3A levels were measured by midazolam clearance before treatment (baseline) and before methylprednisolone injection. All animals were sacrificed 3 weeks after methylprednisolone injection and both femurs were harvested and examined histologically for osteonecrosis. Midazolam clearance was significantly increased and decreased, compared with baseline in groups P and I respectively (p < 0.0005, p < 0.002). The incidence of osteonecrosis in group P (33%) was significantly lower than in group I (100%) and group C (83%; p < 0.001 for both). The percentage necrotic area to whole bone marrow area on cross sections in group P (8.2 +/- 5.9%) was significantly lower than in group I (69.8 +/- 20.8%) and group C (51.5 +/- 30.7%; p < 0.005 for both). Hepatic CYP3A activity inversely correlated with the incidence of osteonecrosis and extent of the necrotic area caused by the same dose of corticosteroids, suggesting possible prevention of the steroid-induced osteonecrosis by reducing steroid dose in poor corticosteroid metabolizers.

Low hepatic cytochrome P450 3A activity is a risk for corticosteroid-induced osteonecrosis.

BACKGROUND: Osteonecrosis of the femoral head (ONFH) is one of the major side effects of corticosteroid therapy. Because corticosteroids are metabolized by hepatic cytochrome P450 (CYP) 3A, a low endogenous activity of this enzyme may contribute to the pathogenesis of ONFH. The purpose of this study was to examine the possible association of hepatic CYP3A activity and the susceptibility to ONFH in patients treated with corticosteroids. METHODS: In this prospective controlled study we measured the clearance of intravenous midazolam (0.25 mg/kg) to estimate hepatic CYP3A activity in patients with steroid-induced ONFH (n = 26), patients with alcohol-related ONFH (n = 29), and non-ONFH control patients (n = 75) undergoing orthopedic surgery. Midazolam clearance was compared between the groups, and the relationship between the level of hepatic CYP3A activity and the prevalence of ONFH was evaluated by multivariate analysis. RESULTS: Midazolam clearance in patients with steroid-induced ONFH was significantly lower than that in control patients and patients with alcohol-related ONFH (7.7 +/- 1.8 mL x kg(-1) x min(-1) versus 11.4 +/- 3.5 mL x kg(-1) x min(-1) and 10.5 +/- 2.8 mL x kg(-1) x min(-1), respectively; P < .001). Patients with low midazolam clearance (<9.5 mL x kg(-1) x min(-1)) had a 9-fold greater risk for steroid-induced ONFH (adjusted odds ratio, 9.08 [95% confidence interval, 2.79-29.6]; P < .001). Midazolam clearance did not show a significant correlation with the prevalence of alcohol-related ONFH. CONCLUSIONS: Low hepatic CYP3A activity may significantly contribute to the risk for steroid-induced ONFH.

Transient osteoporosis of the femoral condyle: a case report.

In this paper, we describe a patient with transient osteoporosis of the femoral condyle. A differential diagnosis should be made for osteonecrosis, infectious disorders, and infiltrative neoplasms based on the normal laboratory findings and diffuse bone edema pattern in MRI. Since this disorder is self-limiting, both the surgeon and clinician should be aware of this condition and must avoid unnecessary intervention.