Aims

Obesity is associated with an increased risk of hip osteoarthritis, resulting in an increased number of total hip arthroplasties (THAs) performed annually. This study examines the peri- and postoperative outcomes of morbidly obese (MO) patients (BMI ≥ 40 kg/m²) compared to healthy weight (HW) patients (BMI 18.5 to < 25 kg/m²) who underwent a THA using the anterior-based muscle-sparing (ABMS) approach.

Objectives. The setting angle of the cup is important for achieving the stability and avoiding the dislocation after total hip arthroplasty (THA). It is difficult to set the cup at correct angle in minimally invasive THA by modified Watson-Jones approach. So we use CT-based navigation system. We evaluated the accuracy of with post-operative CT data. Materials and Methods. We treated 30 hips in 30 patients (7 male and 23 females) by navigated THA. 26 osteoarthritis hips, 2 rheumatoid arthritis hips and 2 idiopathic osteonecrosis hips were performed THA with VectorVision Hip 3.5.2 navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Kyocera Medical, Osaka). Appropriate angles and positions of cups were decided on the 3D model of hip joint before operation. According to the preoperative planning, we put the cups with navigation system and stems without navigation system. We measured the anteversion angle with post-operative CT data and 3-dimensional template software. Results. The average angle of cup inclination was 35.2 degrees on navigation system in operation. The average angle was 37.4 degrees in post-operative CT data. We calculated the deference between the inclination angle of intra-operative navigation data and the angle of post-operative CT data. The average of error was 2.2 degrees. The average angle of cup anteversion was 24.2 degrees on navigation system in operation. The average angle was 27.5 degrees in post-operative CT data. The average of error was 3.5 degrees. Conclusions. There are some reports of complications in minimally invasive THA by modified Watson-Jones approach. Anteversion angle of cup are tend to insert from relative anterior direction with this approach. We could make the error of cup setting minimize with CT-based navigation system

Introduction. Venous thromboembolism (VTE) is one of the common complications after total hip replacements (THRs). To reduce the risk of VTE, early rising, active movement of the foot, the use of a foot pump or graduated compression stockings and prophylactic administration of anticoagulant drugs are important. Further, intraoperative factors should be taken intoãζζconsideration. Objective. The objective of this study is to assess the influence of surgical approaches, which are a modified Watson-Jones approach and a posterolateral approach, on the frequency of VTE after primary THRs. Materials and Methods. One hundred seventy-five patients underwent 199 primary total hip replacements by a single surgeon using modified Watson-Jones approach between gluteus medius muscle and tensor fascia lata (AL Group). The average age at the operation was 63.4 ±12.5 years old. The average BMI was 23.6±3.6. The original diagnosis consisted of 151 cases of osteoarthritis of the hip, 34 cases of avascular necrosis of the femoral head, 7 cases of rheumatoid arthritis and two cases of rapidly destructive coxopathies. Control group was 159 primary total hip replacements by a single surgeon using posterolateral approach (PL Group). The average age at the operation was 63.0±11.3 years old. The average BMI was 22.8±3.6. The original diagnosis consisted of 130 cases of osteoarthritis of the hip, 17 cases of avascular necrosis of the femoral head, 7 cases of rheumatoid arthritis and four cases of rapidly destructive coxopathies. VTE was detected by contrast computed tomography or ultrasound, and soluble fibrin monomer complex (SF) was measured on the first day after surgery. Results. The frequency of VTE was thirty three of 199 cases (16.6%) in the AL Group. On the other hand, the frequency of VTE was sixty three of 159 cases (39.6%) in the PL Group. The average value of SF on the first day after surgery was 16.1±28.1 in the AL Group, 15.4±20.6 in the PL Group, respectively. In each group, the SF values showed a significant difference between VTE detected cases (41.7±55.3 in the AL Group; 24.2±26.4 in the PL Group) and VTE non-detected ones (10.9±13.6 in the AL Group; 9.4±12.4 in the PL Group) by Mann-Whitney U test. Conclusion. Modified Watson-Jones approach is useful to reduce the risk of VTE, compared with posterolateral approach. The foot position to obstruct blood flow during THRs using poterolateral approach may be the risk factor for VTE

The Japan National Register (JAR) for total hip arthroplasty (THA) was launched in 2006. The JAR office accumulates and processes all the data and reports annually. The comparative studies among the annual data from 2013 to 2016 reveal the current trend of THA in Japan. Up to March 2016, 1,188 hospitals have participated in the JAR. Registration ratio of THA is supposed to be about 50% in 2016. From 2006 to 2016, 88.146 data collection forms were submitted for THA. More than 65% of the patients are diagnosed with Developmental Dysplasia of the Hip in Japan. Recently, the anterior approaches, direct Anterior approach and anterolateral modified Watson-Jones approach, have increased. About 80% of implants are cementless, while 8.7% are cement. The major reasons for revision THA are aseptic loosening, osteolysis, and infection, while periprosthetic fracture and implant dislocation/instability increase currently. A brief summary of the annual report of the JAR is available from The Japanese Society for Replacement Arthroplasty website at . http://jsra.info/.

Purpose. Various approaches have been reported for the total hip replacement (THR). In recent years, a muscle sparing approach with low postoperative muscle weakness and low dislocation risk has been frequently selected. However, such surgery has a learning curve. Thus, at the time of switching from the conventional approach to such approaches, invasion or infection risk may increase with the operation time extension. The purpose of this study is to clarify the change of invasiveness or latent infection rate with the change in approach in order to select the cases safely at the beginning of introducing a new approach in THR. Methods. In facility A, THR was performed with Dall's approach (Dall), but 1 surgeon changed Dall to anterolateral modified Watson-Jones approach (OCM) and another surgeon changed Dall to direct anterior approach (DAA). In facility B, all 3 surgeons changed posterolateral (PL) approach to OCM. The subjects are 150 cases in total, including the each last 25 cases operated with the conventional approach and the each first 25 cases operated with a new approach (Dall to OCM: 25 + 25, Dall to DAA: 25 + 25, PL to OCM: 25 +25 cases). And, differences in operative time, intraoperative bleeding volume, postoperative hospital stay, and postoperative hemoglobin, white blood cell count, lymphocyte count, creatine kinase (CK), C-reactive protein (CRP) were investigated. Results. The average age of subjects was 64 years (31–87 years old), and there were 27 male subjects and 123 female subjects. In the change from Dall to OCM, only the postoperative hospital stay decreased significantly. In the change from Dall to DAA, the length of hospital stay and postoperative CRP significantly decreased, but the intraoperative bleeding volume increased. In the change from PL to OCM, the operation time, postoperative CRP and CK decreased, but postoperative Hb decreased. Cases with lymphocytes less than 1000/µL or less than 10% after surgery on day 4 are latent infection cases, and in such cases the operation time was significantly longer, the postoperative Hb was significantly lower, and the postoperative CK was significantly higher. However, such cases were not significantly increased by the change of operation approach. Conclusion. Introduction of the muscle sparing approach improved many items on surgical invasion, but some items deteriorated especially at the beginning of a new approach. In the early stages of introduction of the new approach, choosing cases without obesity and without lots of muscle volume may reduce latent infection

Background. Accurate acetabular cup positioning is considered to be essential to prevent postoperative dislocation and improve the long-term outcome of total hip arthroplasty (THA). Recently various devices such as navigation systems and patient-specific guides have been used to ensure the accuracy of acetabular cup positioning. Objectives. The present study evaluated the usefulness of CT-based three-dimensional THA preoperative planning for acetabular cup positioning. Methods. This study included 120 hips aged mean 68.3 years, who underwent primary THA using CT-based THA preoperative planning software ZedHip® (LEXI, Tokyo Japan) and postoperative CT imaging (Fig.1). The surgical approach adopted the modified Watson-Jones approach in the lateral decubitus position and Trident HA acetabular cups were used for all cases. Preoperatively the optimum cup size and position in the acetabular were decided using the ZedHip® software, taking into consideration femoral anteversion and to achieve the maximum range of motion in dynamic motion simulation. Radiographic inclination (RI) was selected in the range between 40°∼45° and radiographic anteversion (RA) in the range between 5°∼25°. Three-dimensional planning images of the cup positioning were obtained from the ZedHip® software, and the distances between the edge of the implant and anatomical landmarks such as the edge of the anterior or superior acetabular wall were measured on the three-dimensional images and recorded (Fig.2). Intraoperatively, the RI and RA were confirmed by reference to these distances and the acetabular cup was inserted. Relative positional information of the implant was extracted from postoperative CT imaging using the ZedHip® software and used to reproduce the position of the implant on preoperative CT imaging with the software image matching function. The difference between the preoperative planning and the actual implant position was measured to assess the accuracy of acetabular cup positioning using the ZedHip® software. Results. Actual cup size corresponded with that of preoperative planning in 95% of cases (114 hips). Postoperative mean RI was 42.3° ± 4.2° (95% confidence interval (CI), 41.5° ∼ 43.0°) and mean RA was 16.1° ± 5.9° (95%CI, 15.0° ∼ 17.1°). Deviation from the target RI was 4.2° ± 3.7° (95%CI, 3.5° ∼ 4.9°) and deviation from the target RA was 4.0° ± 3.6° (95%CI, 3.4° ∼ 4.7°). Overall 116 hips (96.7%) were within the RI safe zone (30° ∼ 50°) and 108 hips (90.0%) were within the RA safe zone (5° ∼ 25°), and 105 hips (87.5%) were within both the RI and RA safe zones (Fig.3). Mean cup shift from preoperative planning was 0.0mm ± 3.0mm to the cranial side in the cranio-caudal direction, 2.1mm ± 3.0mm to the anterior side in the antero-posterior direction, and 1.7mm ± 2.1mm to the lateral side in the medio-lateral direction. Conclusion. The accuracy of acetabular cup positioning using our method of CT-based three-dimensional THA preoperative planning was slightly inferior to reported values for CT-based navigation, but obviously superior to those without navigation and similar to those with portable navigation. CT-based three-dimensional THA preoperative planning is effective for acetabular cup positioning, and has better cost performance than expensive CT-based navigation. For any figures or tables, please contact the authors directly

Anterior surgical approaches for total hip arthroplasty (THA) have increased popularity due to expected faster recovery and less pain. However, the direct anterior approach (Heuter approach which has been popularised by Matta) has been associated with a higher rate of early revisions than other approaches due to femoral component loosening and fractures. It is also noted to have a long learning curve and other unique complications like anterior femoral cutaneous and femoral nerve injuries. Most surgeons performing this approach will require the use of an expensive special operating table. An alternative to the direct anterior approach is the anterior-based muscle-sparing approach. It is also known as the modified Watson-Jones approach, anterolateral muscle-sparing approach, minimally invasive anterolateral approach and the Röttinger approach. With this technique, the hip joint is approached through the muscle interval between the tensor fascia lata and the gluteal muscles, as opposed to the direct anterior approach which is between the sartorius and rectus femoris and the tensor fascia lata. This approach places the femoral nerve at less risk for injury. I perform this technique in the lateral decubitus position, but it can also be performed in the supine position. An inexpensive home-made laminated L-shaped board is clamped on end of table allowing the ipsilateral leg to extend, adduct, and externally rotate during the femoral preparation. This approach for THA has been reported to produce excellent results. One study reports a complication rate of 0.6% femoral fracture rate and 0.4% revision rate for femoral stem loosening. In a prospective randomised trial looking at the learning curve with new approach, the anterior-based muscle-sparing anterior approach had lower complications than a direct anterior approach. The complications and mean operative time with this approach are reported to be no different than a direct lateral approach. Since this surgical approach is not through an internervous interval, a concern is that this may result in a permanent functional defect as result of injury to the superior gluteal nerve. At a median follow-up of 9.3 months, a MRI study showed 42% of patients with this approach had fat replacement of the tensor fascia lata, which is thought to be irreversible. The clinical significance remains unclear, and inconsequential in my experience. A comparison MRI study showed that there was more damage and atrophy to the gluteus medius muscle with a direct lateral approach at 3 and 12 months. My anecdotal experience is that there is faster recovery and less early pain with this approach. A study of the first 57 patients I performed showed significantly less pain and faster recovery in the first six weeks in patients performed with the anterior-based muscle-sparing approach when compared to a matched cohort of THA patients performed with a direct lateral approach. From 2004 to 2017, I have performed 1308 total hip replacements with the anterior-based muscle sparing approach. Alternatively, I will use the direct lateral approach for patients with stiff hips with significant flexion and/or external rotation contractures where I anticipate difficulty with femoral exposure, osteoporotic femurs due to increased risk of intraoperative trochanteric fractures, previously operated hips with scarring or retained hardware, and Crowe III-IV dysplastic hips when there may be a need for a femoral shortening or derotational osteotomy. Complications have been very infrequent. This approach is a viable alternative to the direct anterior approach for patients desiring a fast recovery. The anterior-based muscle-sparing approach is the approach that I currently use for all outpatient total hip surgeries

Aims: Minimal invasive total hip replacement is supposed to allow a quicker rehabilitation in the immediate post-operative period due to reduced soft tissue damage. The aim of this study is to compare gait kinematics after total hip arthroplasty using a one incision minimal invasive approach to a traditional approach. Matarial and Methods: 21 patients were available for a complete analysis. In 12 patients (MIS group) a minimal invasive, modified Watson-Jones approach was used, in 9 patients (Standard group) a transgluteal approach as described by Bauer was used. All operations were performed by a single surgeon with the patient in supine position. In all cases the same cementless implant (Alloclassic® VariallTM system) with standard instruments was used. 3D gait analysis was carried out pre-operatively, 10 days postoperatively and after 3 months. The variables analysed in this study were velocity, step length, range of hip extension, range of pelvic tilt, Trendelenburg’s sign and Duchenne limp, pelvic rotation and symmetry. Results: There were no significant differences between the MIS and the Standard group in any of the evaluated variables. In both groups of the patients presented a decrease in the hip extension at the end of stance phase 10 days postoperatively. About half of these patients compensated with an increased sagital pelvic tilt during maximal hip extension. At the 3 months follow-up all patients in both groups had an increased hip extension compared to the preoperative values, reached normative values. The velocity was reduced in both groups at the 10 days follow-up, ¼ reached normative values after 3 months. Conclusion: Our data show no significant improvement of gait kinematics in patients who underwent a total hip arthroplasty using a minimal invasive approach (modified Watson-Jones) compared to a standard approach (Bauer) during the early postoperative period

AIM: Total hip replacement is the most successful procedure since 3 decades. In the last years a lot of new helpful implants were introduced to the market, minimal invasive procedures are presented in increasing numbers and the technique of navigation is introduced. On the other hand there is no scientific proof of the benefit of these procedures. The objective of this study was to collect data about the different procedures and the common used implants. METHOD: In a countrywide anonymous survey, 250 German trauma surgery and orthopaedic surgery departments were asked about their MIS procedures and their treatment strategies.(August 2006). RESULTS: 112 of the questionnaires have been returned so far. We found 82% of the surgeons doing minimal invasive THR, 18% are doing more than 50% of all procedures in MIS technique, while 45% of the colleagues report, that the patients never ask for the procedure. Most of the surgeons (58%) define “minimal invasive” as the preservation of muscle, tendons and soft tissue, 1% as the preservation of bone and 41% as the length of skin incision (6–12cm). The most common MIS approach is the lateral (45%), followed by the anterior approach (25%) and the modified Watson-Jones approach (21%) and the MIS dorsal approach (19%) (Some use more than 1 approach). For standard procedure (not minimal invasive) there is most used the Kocher approach (51%), followed by Bauer approach (29%) and Smith-Petersen/Watson-Jones (19%). 23% use navigation and 51% are convinced, there is no sense in that. 66% do not use articular resurfacing, 33% are using short implants. 49% are using cellsaver regular, 99% are using wounddrains. CONCLUSION: While the technique of MIS in THR is whidespread in Germany, an exact definition is still missing. Patients don’t expect MIS as much as surgeons perform it. Out of the variety of approaches a standard still has to be defined. For minimal invasive procedure there is most used a lateral approach, for standard procedure the Kocher approach. New implants are used by every third surgeon, navigation by every fourth surgeon

MIS techniques in hip arthroplasty above all have the objective to shorten the rehabilitation period by suitable preparation. A modified Watson-Jones approach through the muscle interval between the middle gluteus and the tensor muscle of fascia latae via a 6 – 8 cm anterolateral skin incision provides a good overview to the preparation. The risk of damaging the lateral femoral cutaneous muscle is relatively low when a suitable incision technique is employed. The use of special instruments decisively decreases the risk of preparation errors, extension damage of the skin nerve and misimplantation of prosthesis components. Back-positioning of the patient on the operating table has clear advantages compared to lateral positioning. When the stem is prepared the proximal femur can be brought into the surgery area by re-positioning the leg under the contralateral leg without overstretching the leg which in turn might lead to extension damage of the femoral nerve. When the implant is chosen, short stems provide minimum bone loss and the advantage of a varic access to the bone, which makes the preparation substantially easier and additionally spares the soft parts. Straight stem prostheses may also be implanted using this method, however, here the danger of an extension damage of the femoral nerve is given by the hyperextension of the leg during preparation. A further common minimal invasive approach is ventral access between the tensor muscle of fascia latae and the sartorious muscle. Here in particular with muscular patients the danger of damaging the rectus femoris by post-operative bleeding is given. The skin is incised in alignment with the lateral femoral cutaneous muscle, which is to be displayed imperatively to be spared. For stem preparation an even more disadvantageous hyperextension of the leg is required. The two-incision-technique where the straight stem is implanted by a gluteussnip – comparable with femur nailing – only provides a very bad view at the proximal femur. Here there is a greater risk of an unnoticed bone fissure when cement-free pressfit stems are used. The advantage of this technique lies in minor hyperextension of the leg for preparation. Minimal invasive hip arthroplasty provides advantages for the patients above all in the early rehabilitation stage. However, the total concept is to be “minimal invasive” and skin incision, sparing of soft parts, choice of prosthesis and duration of surgery are to be considered

Total hip arthroplasty (THA) using minimally invasive surgeries (MIS) now become popular operative procedures. It is not easy to understand geometric information of pelvis and femur in the restricted operative fields during MIS-THA. Recently, THA in supine position comes into the limelight again to place acetabular cups in an optimum position because we can minimise the intra-operative pelvic motion during THA in supine position. To verify the usefulness of supine position, we measured the angels of acetabular trial cups intra-operatively using the CT-based navigation system. The trial cup positions were placed according to a conventional acetabular cup alignment guide. We compared the angles of acetabular trial cups between supine and lateral positions through the same MIS antero-lateral (AL) surgical approach. Thirty eight hips underwent THA in lateral position (the AL group; average age: 63.9 years old, female: 29 cases, 33 hips, male: 5 cases, 5 hips) and 40 hips underwent THA in supine position (the AL Supine group; average age: 62.2 years old, female 40 cases, 40 hips) were subjected in this study. The single surgeon (the first author) performed all surgeries. We used the Roettinger's modified Watson-Jones approach in both groups. The pelvic registration for navigation was carried out using the CT-fluoro matching procedure with VectorVision Hip (BrainLAB, Germany). After acetabular reaming, the acetabular trial cups were placed into the reamed acetabulum to be at 45 degrees of operative inclination (OI) and at 20 degrees of operative anteversion (OA) using a conventional acetabular cup alignment guide. These angles of the trial cups were measured intra-operatively using the CT-based navigation system, VectorVision Hip. After removing the acetabular trial cup, the acetabular cups were placed using the navigation system. Trilogy cups (Zimmer, USA) and AMS HA shells (JMM, Japan) were used in this study. The average angles of OI were 45.7 degrees (SD 5.5 degrees) in the AL group and 46.3 degrees (SD 4.6 degrees) in the AL Supine group. The average angles of OA were 30.0 degrees (SD 13.5 degrees) in the AL group and 23.5 degrees (SD 8.2 degrees) in the AL Supine group. The hip numbers whose errors were less than 10 degrees were 13 hips in the AL group and 26 hips in the AL Supine group, respectively. There was significant difference in hip numbers whose errors of angles were less than 10 degrees between the AL and Supine groups. The hip numbers whose errors were less than 5 degrees were 7 hips in the AL group and only 6 hips in the AL Supine group, respectively. There was no significant difference in hip numbers whose errors of angles were less than 5 degrees between the AL and Supine groups. The error values of OI were less than 10 degrees except one hip in both groups. However, the error values of 25 hips in the AL group were more than 10 degrees. In lateral position, the pelvis easily rotated when the affected lower extremity was extended, externally rotated, and adducted during the femoral preparation in the AL group, which resulted in malalignment of acetabular OA. In contrast, most hips could be set with the error values less than 10 degrees in the AL Supine position because the pelvis could be stabilised on the operative table. In addition, landmarks, such as bilateral antero-superior iliac spines and the symphysis pubis, were palpable in supine position. However, the hips with error values less than 5 degrees were only 6 out of 40 hips even though in supine position. Using MIS techniques, we can provide more stable hip joint just after surgery since the muscles surrounding hip joints can be preserved. We have to place acetabular cups in an optimum position to achieve wide range of hip motion to prevent dislocation and to provide limitation-free daily activities for patients. These data suggests that we should use more accurate guide systems for acetabular cup replacement such as navigation systems, patient specific templates, and patient specific mechanical instruments to place acetabular cups in an optimum position

Aims

The aim of this study was to compare the pattern of initial fixation and changes in periprosthetic bone mineral density (BMD) between patients who underwent total hip arthroplasty (THA) using a traditional fully hydroxyapatite (HA)-coated stem (T-HA group) and those with a newly introduced fully HA-coated stem (N-HA group).

Aims

Dislocation of the hip remains a major complication after periacetabular tumour resection and endoprosthetic reconstruction. The position of the acetabular component is an important modifiable factor for surgeons in determining the risk of postoperative dislocation. We investigated the significance of horizontal, vertical, and sagittal displacement of the hip centre of rotation (COR) on postoperative dislocation using a CT-based 3D model, as well as other potential risk factors for dislocation.

Purpose: Many surgeons are now performing hip arthroplasty using a minimally invasive technique with the aim of reducing muscle damage and improving rehabilitation. We compared the learning curve of two MIS THA approaches: the two-incision mini and a modified Watson-Jones (G3) approach. Methods: A retrospective review of 47 consecutive patients who underwent a THA using an MIS approach was conducted. All patients received an uncemented acetabular cup (Trilogy–Zimmer) fixed with 1 or 2 screws, and an uncemented femoral stem (ML taper, fiber metal taper, fully porous coated–Zimmer). Note was made of BMI, surgical time, incision length, blood loss, component positioning, hospital stay and perioperative complications. Results: Twenty-one patients received a G3 and 26 received a 2 incision mini approach. The average BMI was 29.7 and 26.1 respectively. Average acetabular inclination was 37 for the G3 and 42 for the 2-incision mini. On average, the femoral component was positioned in neutral in the coronal plane for both approaches. Average surgical time was 121minutes for the G3 and 166 minutes for the 2-incision which also includes fluoros-copy time. Hospital stay averaged 5.4 and 6.8 days respectively. The skin incision averaged 8.9 cm for G3 a total of 9.8cm for 2-incision. Perioperative complications for the G3 included 1 lateral femoral cutaneous nerve palsy, 1 DVT, 1 PE and 1undisplaced intraoperative acetabular fracture. Complications for the 2-incision mini included 5 intraoperative fractures, 7 nerve injuries, 1 wound infection, 1 infection requiring revision and 1 PE. Conclusions: The G3 minimally invasive approach for THA has advantages over the 2-incision mini: shorter operative time, no need for fluoroscopy, fewer days in hospital, shorter total incision length and lower complication rate. The G3 approach also offers the opportunity to bail out to a traditional approach, by extending the incision, should this be necessary

Prophylaxis against venous thromboembolism after elective total hip replacement is routinely recommended. Our preference has been to use mechanical prophylaxis without anticoagulant drugs. A randomised controlled trial was performed to evaluate whether the incidence of post-operative venous thromboembolism was reduced by using pharmacological anticoagulation with either fondaparinux or enoxaparin in addition to our prophylactic mechanical regimen. A total of 255 Japanese patients who underwent primary unilateral cementless total hip replacement were randomly assigned to one of three postoperative regimens, namely injection of placebo (saline), fondaparinux or enoxaparin. There were 85 patients in each group. All also received the same mechanical prophylaxis during and after the operation, regardless of their assigned group. The primary measurement of efficacy was the presence of a venous thromboembolic event by day 11, defined as deep-vein thrombosis detected by ultrasonography, documented symptomatic deep-vein thrombosis or documented symptomatic pulmonary embolism. The duration of follow-up was 12 weeks.

The rate of venous thromboembolism was 7.2% with the placebo, 7.1% with fondaparinux and 6.0% with enoxaparin (p = 0.95 for the comparison of all three groups). Our study confirmed the effectiveness and safety of mechanical thromboprophylaxis without the use of anticoagulant drugs after total hip replacement in Japanese patients.