Sample size for prospective studies of hip joint space width narrowing in osteoarthritis by the use of radiographs.

OBJECTIVE: To determine the number of participants required in controlled clinical trials investigating the progression of osteoarthritis (OA) of the hip as evaluated by the joint space width (JSW) on radiographs and to evaluate the reproducibility of the JSW measurement methods. MATERIALS AND METHODS: Anteroposterior radiographs of hip were taken from 13 healthy volunteers and from 18 subjects with radiographic hip OA. The reproducibility of the JSW was determined from four segments using digital caliper measurements performed on film radiographs and using semiautomatic computerized image analysis of digitized images. Pearson correlation coefficient, coefficient of variability [CV (%)], and sample size values were calculated. RESULTS: It was found that 20 was a typical number of patients for a sufficiently powered study. The highest sample size was found in subjects with OA in the lateral segment. The reproducibility of the semiautomatic computerized method was not significantly better than the digital caliper method. CONCLUSION: The number of study subjects required to detect a significant joint space narrowing in follow-up studies is influenced by the baseline hip joint OA severity. The JSW measurements with computerized image analysis did not improve the reproducibility and thus performing JSW measurements with a digital caliper is acceptable.

Comparison of DXA and MRI methods for interpreting femoral neck bone mineral density.

The aim of the study was to improve the practical implementation of the dual X-ray absorptiometry (DXA) by converting the areal bone mineral density BMD (BMD(areal)) to volumetric BMD using magnetic resonance (MR) imaging (MRI) because a failure to control for the femoral neck size can lead to erroneous interpretation of BMD values. We also evaluated the feasibility of MR T2* relaxation time in assessing bone mineral status of the femoral neck. Twenty-eight randomly selected 47- to 64-yr-old healthy men were studied. The men had neither unilateral nor bilateral hip osteoarthritis according to radiographs. Bone width, mineral content (BMC), BMD(areal), and apparent volumetric BMD (BMD(vol)) of the right femoral neck were measured with DXA. The BMD(vol) was calculated by approximating the femoral neck to be cylindrical with a circular cross-section (Vol(dxa)). Volumetric measurements from MR (Vol(mri)) images of the femoral neck were also used to create a BMD measure that was corrected for the femoral neck volume (BMD(mri)). T2* measurements were performed with a 1.5-T scanner (Siemens Magnetom 63SP, Erlangen, Germany). A single 10-mm-thick coronal slice was generated on the femur with a repetition time of 60 ms, and nine echo times (4-20 ms) were used to derive T2* values. Vol(mri) correlated positively (r = 0.828, p < 0.001) with Vol(dxa). However, the Vol(mri) of the femoral neck was 18% lower than the Vol(dxa). Similarly, the BMD(mri) was related to the BMD(vol) (r = 0.737, p < 0.001). Because of the difference in the volumetric measures, the BMD(mri) of the femoral neck was 21% higher than the BMD(vol) (p < 0.001). T2* relaxation time showed a significant negative correlation with BMC, BMD(areal), BMD(vol), and BMD(mri) (r = -0.423 to -0.757, p < 0.05-0.001). In conclusion, these results are evidence that DXA-derived volume approximations by the cylinder with circular cross-section geometry may lead to lower DXA-derived BMD(vol) values, as compared to true MRI-derived volumetric bone mineral density. Thus, the BMD(vol) may not be an accurate method to calculate the true volumetric BMD in the femoral neck. Our results also suggest that the MRI-derived T2* method may be used to approximate the BMD in the proximal femur.

Hip muscle strength and muscle cross sectional area in men with and without hip osteoarthritis.

OBJECTIVE: To study the hip muscle strength and cross sectional area (CSA) in men with hip osteoarthritis (OA) compared to age and sex matched healthy controls. METHODS: Based on the American College of Rheumatology criteria regarding classification of hip OA, 27 men (aged 47-64 yrs) with unilateral or bilateral hip OA and 30 age matched randomly selected healthy male controls were studied. The maximal isometric hip abductor, adductor, flexor, and extensor strength (Nm) at 0 degree of hip flexion in the supine position was determined with a dynamometer. The isokinetic hip flexion and extension strength (peak torque, Nm) was determined using angular velocities of 60 degrees /s and 120 degrees /s. The subjective severity of hip pain was rated by visual analog scale prior to the muscle strength test. CSA of the pelvic and thigh muscles was measured from magnetic resonance images. RESULTS: The reliability of intraclass correlation coefficients for repeated measures of muscle strength varied from 0.70 to 0.94 in controls and from 0.84 to 0.98 in subjects with OA. Hip isometric adductor and abductor strength was 25% and 31% lower (p < 0.001) in OA subjects than in controls, respectively. The hip isometric and isokinetic flexion strength was 18-22% lower (p < 0.01) in OA subjects than in controls, but extension strength did not differ between groups. In OA subjects, the hip flexion and extension isometric and isokinetic strength values were 13-22% lower (p < 0.05) on the more deteriorated side compared to the better side. CSA of the pelvic and thigh muscles did not differ between the groups. However, in OA subjects, the CSA of the pelvic and thigh muscles was 6-13% less (p < 0.05 to < 0.001) on the more severely affected hip compared to the better hip. CONCLUSION: Men with hip OA have significantly lower abduction, adduction, and flexion muscle strength than controls. The decrease of muscle size and hip pain may contribute to the decrease of muscle strength in hip OA. Other possible underlying causes of the muscle weakness need to be studied.