Takashi Nishii

Preservation of the bone mineral density of the femur after surface replacement of the hip

We investigated the effect of the Birmingham hip resurfacing (BHR) arthroplasty on the bone mineral density (BMD) of the femur. A comparative study was carried out on 26 hips in 25 patients. Group A consisted of 13 patients (13 hips) who had undergone resurfacing hip arthroplasty with the BHR system and group B of 12 patients (13 hips) who had had cementless total hip arthroplasty with a proximal circumferential plasma-spray titanium-coated anatomic Ti6A14V stem. Patients were matched for gender, state of disease and age at the time of surgery. The periprosthetic BMD of the femur was measured using dual-energy x-ray absorptiomentry of the Gruen zones at two years in patients in groups A and B. The median values of the BMD in zones 1 and 7 were 99% and 111%, respectively. The post-operative loss of the BMD in the proximal femur was significantly greater in group B than in group A. These findings show that the BHR system preserves the bone stock of the proximal femur after surgery.

Measurements of pelvic flexion angle using three-dimensional computed tomography.

The purpose of the current study was to evaluate whether safe acetabular component position depends on differences in pelvic location between the supine, standing, and sitting positions. The subjects of the current study were 101 patients who had total hip arthroplasty. Anteroposterior radiographs of the pelvis with the patients in the supine, standing, and sitting positions were obtained preoperatively and 1 year after total hip arthroplasty. Computed tomography images of the pelvis were obtained preoperatively. Using image matching between the three-dimensional computed tomography model and anteroposterior radiograph, pelvic flexion angles with the patient in the supine, standing, and sitting positions were calculated. The mean preoperative pelvic flexion angle was 5° ± 9° (range, −37°–30°) in the supine position, 3° ± 12° (range, −46°–33°) in the standing position, and −29° ± 12° (range, −62°–10°) in the sitting position. Because there was much intersubject variability in pelvic flexion angle, it is not appropriate to determine orientation of the acetabular component from anatomic landmarks. In 90% of the cases, the difference in pelvic flexion angle between the supine and standing positions preoperatively was 10° or less. In 90% of the cases, there was 20° or greater extension of the pelvis from the supine position to the sitting position preoperatively, and the safe range of flexion of the hip from anterior prosthetic impingement in the sitting position was 20° or greater than that in the supine position. Preoperative pelvic position in each case was almost completely maintained 1 year after total hip arthroplasty. It is reasonable to regard the pelvic position in the supine position as the functional pelvic position and proper pelvic reference frame in determining optimal orientation of the acetabular component in 90% of cases before and 1 year after total hip arthroplasty, although an adjustment of orientation of the acetabular component was needed for the remaining cases.

Phase transformation of a zirconia ceramic head after total hip arthroplasty

We report two cases of surface deterioration of a zirconia ceramic femoral head associated with phase transformation after total hip arthroplasty. One head was retrieved at revision due to recurrent dislocation after six years and the other because of failure of the locking mechanism of the polyethylene liner after three years. The monoclinic content of the zirconia ceramics rose from 1% to about 30% on the surface of the heads. SEM revealed numerous craters indicating extraction of the zirconia ceramics at the surface. Surface roughness increased from an initial value of 0.006 microm up to 0.12 microm. This is the first report to show that phase transformation of zirconia ceramics causes deterioration of the surface roughness of the head in vivo after total hip arthroplasty.

Longitudinal evaluation of time related bone remodeling after cementless total hip arthroplasty.

Bone remodeling after cementless total hip arthroplasty was evaluated by dual energy xray absorptiometry in a longitudinal study of 32 hips. After insertion of a fully porous surface anatomic stem made of cobalt chromium, bone mineral density was analyzed until at least 2 years postoperatively. Bone remodeling was evaluated in terms of regional bone density changes in the seven adjacent periprosthetic zones as well as the global change in bone density distribution over the entire periprosthetic area. At 12 months after the operation, the averaged regional bone mineral density in all seven zones showed a rapid decrease, ranging from 9% to 24% of the bone mineral density present at 2 weeks postoperatively. Thereafter, the bone density change appeared to be stabilized. The global change in the bone density distribution was expressed as two summarizing statistical indexes derived from principal component analysis: the first index represents the change of average bone mineral density over the entire periprosthetic area, and the second represents the severity of bone mineral density decrease in the proximal area versus the distal area. The second index proved that more bone density reduction occurred in the proximal area, but this was variable among patients and correlated significantly with the stem size and the initial bone mineral density in the distal part of the periprosthetic area. This longitudinal dual energy xray absorptiometry study suggests that a large part of the bone remodeling after cementless hip arthroplasty ceases within 1 year postoperatively, and stem size and the initial bone density around the distal portion are important considerations for predicting the proximal bone density decrease during the early rapid remodeling period.

Does alendronate prevent collapse in osteonecrosis of the femoral head

Progression of collapse in osteonecrosis of the femoral head is related to the repair response, especially bone resorption around the necrotic region. A preliminary clinical study was done to determine whether systemic alendronate would prevent collapse and lead to pain relief in patients with osteonecrosis of the femoral head. Fourteen patients (20 hips) with osteonecrosis of the femoral head received daily administration of 5 mg alendronate (alendronate group) for 1 year. Eight patients (13 hips) with osteonecrosis of the femoral head did not receive alendronate (control group). All patients had measurements of biochemical markers of bone turnover at entry into the study, and the patients in the alendronate group repeated the measurements at 3 months, 6 months, and 12 months. All patients had clinical and plain radiographic examinations at entry into the study and at 3 months, 6 months, and 12 months. The alendronate group showed a greater decrease of biochemical marker of bone resorption than biochemical marker of bone formation. The alendronate group showed a lower frequency of collapse of the femoral head and reported less hip pain than the control group. Our results suggest alendronate has the potential to prevent collapse of the femoral head, even with extensive necrosis, presumably by inhibiting bone resorption in the necrotic region. Level of Evidence: Therapeutic study, level II (prospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Automated segmentation of acetabulum and femoral head from 3-d CT images

This paper describes several new methods and software for automatic segmentation of the pelvis and the femur, based on clinically obtained multislice computed tomography (CT) data. The hip joint is composed of the acetabulum, cavity of the pelvic bone, and the femoral head. In vivo CT data sets of 60 actual patients were used in the study. The 120 (60 /spl times/ 2) hip joints in the data sets were divided into four groups according to several key features for segmentation. Conventional techniques for classification of bony tissues were first employed to distinguish the pelvis and the femur from other CT tissue images in the hip joint. Automatic techniques were developed to extract the boundary between the acetabulum and the femoral head. An automatic method was built up to manage the segmentation task according to image intensity of bone tissues, size, center, shape of the femoral heads, and other characters. The processing scheme consisted of the following five steps: 1) preprocessing, including resampling 3-D CT data by a modified Sine interpolation to create isotropic volume and to avoid Gibbs ringing, and smoothing the resulting images by a 3-D Gaussian filter; 2) detecting bone tissues from CT images by conventional techniques including histogram-based thresholding and binary morphological operations; 3) estimating initial boundary of the femoral head and the joint space between the acetabulum and the femoral head by a new approach utilizing the constraints of the greater trochanter and the shapes of the femoral head; 4) enhancing the joint space by a Hessian filter; and 5) refining the rough boundary obtained in step 3) by a moving disk technique and the filtered images obtained in step 4). The above method was implemented in a Microsoft Windows software package and the resulting software is freely available on the Internet. The feasibility of this method was tested on the data sets of 60 clinical cases (5000 CT images).

Change in knee cartilage T2 in response to mechanical loading.

To assess the clinical feasibility of magnetic resonance (MR) imaging with a mechanical loading system for evaluation of load‐bearing function in knee joints using cartilage T2 as a surrogate of cartilage matrix changes.

Gender differences in 3D morphology and bony impingement of human hips.

For the proper diagnosis or treatment of hip joint disorders caused by anatomical abnormalities, the normal hip joint morphology must be studied to understand its influence on the maximum range of motion (ROM) until bony impingement by focusing on gender differences. Acetabular and femoral morphologies were analyzed from 3D CT images of 106 normal hip joints from elderly men (n = 36 joints) and women (n = 70 joints), and measurements of ROM until bony impingement were made in four directions (flexion, extension, and external and internal rotation at 90° flexion) using surface models of the pelvis and femur reconstructed from the CT data. Gender differences were found not only in joint orientation, including anteversion and inclination of the acetabulum and femoral neck anteversion, but also in the shape around the joint, including the acetabular rim and the femoral neck. This ROM study also showed gender differences in all four standard directions. In conclusion, significant gender differences were observed in the acetabular and femoral morphology, which led to significant gender differences in ROM until bony impingement.

Significance of lesion size and location in the prediction of collapse of osteonecrosis of the femoral head: a new three-dimensional quantification using magnetic resonance imaging

Size and location of a necrotic lesion are considered important factors predicting collapse of the femoral head in the early stages of osteonecrosis. However, few analytical studies have performed a three‐dimensional quantification of lesions to clarify how these two morphological factors are related to the occurrence of collapse. We evaluated the relevance of lesion size and location for prediction of collapse quantitatively using new three‐dimensional indexes. Magnetic resonance (MR) imaging was performed in 65 hips in a consecutive series of 47 patients with osteonecrosis without radiological evidence of collapse. Lesion volume as well as latitude and longitude of the center of gravity of the lesion within the femoral head were calculated. Thirty‐three hips developed radiological collapse, while in the remaining 32 hips collapse did not occur over 2 years. Multiple logistic regression analysis showed a significant relationship between lesion volume and radiological collapse. In 35 hips in which the lesion volume was less than 30% of the femoral head, only 9 collapsed. In comparison with non‐collapsed hips, collapsed hips had a significantly higher combined value for latitude and longitude of the lesion, corresponding to the anterosuperior portion of the femoral head. Quantitative analysis of lesion morphology demonstrated that lesion volume is strongly correlated with risk of collapse, and that lesion location is an important prognostic indicator of collapse in small necrotic lesions.

Computed-Tomography-Based Computer Preoperative Planning for Total Hip Arthroplasty

For precise preoperative planning in total hip arthroplasty (THA), we developed a technique of computed tomography (CT)-based computer preoperative planning and compared this technique with the single X-ray and template method generally used. The subjects of this study were 42 hips in 38 patients who underwent THA using a cementless total hip system. Preoperatively, a standard anteroposterior X-ray of the hip was taken, and conventional preoperative planning was done with a template of the total hip system. Transverse images were obtained using a helical CT scanner, and a CT-based computer preoperative plan was performed on true coronal slice images of the proximal femur reconstructed from CT data. Postoperatively, 29 hips (69%) showed good proximal fit of the femoral component to the medial endosteal line. Of the 20 hips with good proximal fit on preoperative X-ray planning, 12 hips had good proximal fit on postoperative X rays. Sensitivity and specificity of the proximal fit on X-ray templating were 41 and 23%, respectively. In 27 of 28 hips with good proximal fit on reconstructed CT images preoperatively, the postoperative X ray revealed good proximal fit. Sensitivity and specificity of the proximal fit on computer planning were 93 and 86%, respectively. Twelve hips with good proximal fit on preoperative templating, the reconstructed images, and the postoperative X ray had 20 degrees or less of combined femoral neck anteversion and external rotational contracture of the hip on the X-ray table. Eight hips with good proximal fit on preoperative templating and proximal poor fit on the reconstructed images had 17-65 degrees of combined version and rotational contracture. In 16 hips with poor proximal fit on preoperative templating and good proximal fit on the reconstructed images, the combined version and rotational contracture ranged from 17 to 69 degrees. When combined femoral neck anteversion and external rotational contracture of the hip is less than 15 degrees, the simple X-ray and template method might be sufficient for THA planning. Otherwise, the CT-based method of preoperative planning is recommended.