Various systems of computer-assisted orthopaedic surgery (CAOS) in total hip arthroplasty (THA) were reviewed. The first clinically applied system was an active robotic system (ROBODOC), which performed femoral implant cavity preparation as programmed preoperatively. Several reports on cementless THA with ROBODOC showed better stem alignment and less variance in limb-length inequality on radiographic evaluation, less incidence of pulmonary embolic events on transesophageal cardioechogram, and less stress shielding on the dual energy X-ray absorptiometry analysis than conventional manual methods. On the other hand, some studies raise issues with active systems, including a steep learning curve, muscle and nerve damage, and technical complications, such as a procedure stop due to a bone motion during cutting, requiring re-registration and registration failure. Semi-active robotic systems, such as Acrobot and Rio, were developed for ease of surgeon acceptance. The drill bit at the tip of the robotic arm is moved by a surgeon's hand, but it does not move outside of a milling path boundary, which is defined according to three-dimensional (3D) image-based preoperative planning. However, there are still few reports on THA with these semi-active systems. Thanks to the advancements in 3D sensor technology, navigation systems were developed. Navigation is a passive system, which does not perform any actions on patients. It only provides information and guidance to the surgeon who still uses conventional tools to perform the surgery. There are three types of navigation: computed tomography (CT)-based navigation, imageless navigation, and fluoro-navigation. CT-based navigation is the most accurate, but the preoperative planning on CT images takes time that increases cost and radiation exposure. Imageless navigation does not use CT images, but its accuracy depends on the technique of landmark pointing, and it does not take into account the individual uniqueness of the anatomy. Fluoroscopic navigation is good for trauma and spine surgeries, but its benefits are limited in the hip and knee reconstruction surgeries. Several studies have shown that the cup alignment with navigation is more precise than that of the conventional mechanical instruments, and that it is useful for optimizing limb length, range of motion, and stability. Recently, patient specific templates, based on CT images, have attracted attention and some early reports on cup placement, and resurfacing showed improved accuracy of the procedures. These various CAOS systems have pros and cons. Nonetheless, CAOS is a useful tool to help surgeons perform accurately what surgeons want to do in order to better achieve their clinical objectives. Thus, it is important that the surgeon fully understands what he or she should be trying to achieve in THA for each patient.

Background and purpose

It is controversial whether the transverse acetabular ligament (TAL) is a reliable guide for determining the cup orientation during total hip arthroplasty (THA). We investigated the variations in TAL anatomy and the TAL-guided cup orientation.

Methods

80 hips with osteoarthritis secondary to hip dysplasia (OA) and 80 hips with osteonecrosis of the femoral head (ON) were examined. We compared the anatomical anteversion of TAL and the TAL-guided cup orientation in relation to both disease and gender using 3D reconstruction of computed tomography (CT) images.

Results

Mean TAL anteversion was 11° (SD 10, range –12 to 35). The OA group (least-square mean 16°, 95% confidence interval (CI): 14–18) had larger anteversion than the ON group (least-square mean 6.2°, CI: 3.8 – 7.5). Females (least-square mean 20°, CI: 17–23) had larger anteversion than males (least-square mean 7.0°, CI: 4.6–9.3) in the OA group, while there were no differences between the sexes in the ON group. When TAL was used for anteversion guidance with the radiographic cup inclination fixed at 40°, 39% of OA hips and 9% of ON hips had more than 10° variance from the target anteversion, which was 15°.

Interpretation

In ON hips, TAL is a good guide for determining cup orientation during THA, although it is not a reliable guide in hips with OA secondary to dysplasia. This is because TAL orientation has large individual variation and is influenced by disease and gender.

Background

Many studies that analyzed bone mineral density (BMD) and skeletal factors of hip fractures were based on uncalibrated radiographs or dual-energy xray absorptiometry (DXA).

Questions/purposes

Spatial accuracy in measuring BMD and morphologic features of the femur with DXA is limited. This study investigated differences in BMD and morphologic features of the femur between two types of hip fractures using quantitative computed tomography (QCT).

Patients and Methods

Forty patients with hip fractures with normal contralateral hips were selected for this study between 2003 and 2007 (trochanteric fracture, n = 18; femoral neck fracture, n = 22). Each patient underwent QCT of the bilateral femora using a calibration phantom. Using images of the intact contralateral femur, BMD measurements were made at the point of minimum femoral-neck cross-sectional area, middle of the intertrochanteric region, and center of the femoral head. QCT images also were used to measure morphologic features of the hip, including hip axis length, femoral neck axis length, neck-shaft angle, neck width, head offset, anteversion of the femoral neck, and cortical index at the femoral isthmus.

Results

No significant differences were found in trabecular BMD between groups in those three regions. Patients with trochanteric fractures showed a smaller neck shaft angle and smaller cortical index at the femoral canal isthmus compared with patients with femoral neck fractures.

Conclusions

We conclude that severe osteoporosis with thinner cortical bone of the femoral diaphysis is seen more often in patients with trochanteric fracture than in patients with femoral neck fracture.

Levels of Evidence

Level IV, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Background

The Japanese Orthopaedic Association Hip Score is widely used in Japan, but this tool is designed to reflect the viewpoint of health-care providers rather than that of patients. In gauging the effect of medical therapies in addition to clinical results, it is necessary to assess quality of life (QOL) from the viewpoint of patients. However, there is no tool evaluating QOL for Japanese patients with hip-joint disease.

Methods

With the aim of more accurately classifying QOL for Japanese patients with hip-joint disease, we prepared a questionnaire with 58 items for the survey derived from 464 opinions obtained from approximately 100 Japanese patients with hip-joint disease and previously devised evaluation criteria. In the survey, we collected information on 501 cases, and 402 were subjected to factor analysis. From this, we formulated three categories—movement, mental, and pain—each comprising 7 items, for a total of 21 items to be used as evaluation criteria for hip-joint function.

Results

The Cronbach’s α coefficients for the three categories were 0.93, 0.93, and 0.95, respectively, indicating the high reliability of the evaluation criteria. The 21 items included some related to the Asian lifestyle, such as use of a Japanese-style toilet and rising from the floor, which are not included in other evaluation tools.

Conclusions

This self-administered questionnaire may become a useful tool in the evaluation of not only Japanese patients, but also of members of other ethnic groups who engage in deep flexion of the hip joint during daily activities.

Background

The clinical importance of asymptomatic deep venous thrombosis in elective hip surgery is not clearly known.

Questions/purposes

We determined the preoperative and postoperative incidences of asymptomatic deep venous thrombosis, identified preoperative factors associated with postoperative deep venous thrombosis or pulmonary embolism, and established its natural course in patients who underwent elective hip surgery without receiving pharmacologic thromboprophylaxis.

Patients and Methods

We reviewed 184 patients who underwent consecutive elective hip surgeries with a mechanical thromboprophylaxis regimen including combined general and epidural anesthesia, intraoperative calf bandaging, early mobilization, and postoperative intermittent pneumatic compression with additional use of elastic stockings. Duplex ultrasonography was performed routinely to diagnose deep venous thrombosis in all patients before surgery and on Postoperative Days 3 and 21. All patients with postoperative deep venous thrombosis underwent additional ultrasonography at 3-month intervals, and all patients were followed postoperatively for 6 months or more.

Results

Preoperatively, we found asymptomatic deep venous thrombosis in two patients (1%); both thromboses had completely and spontaneously resolved by Postoperative Day 21. Postoperatively, no patients had a fatal or symptomatic pulmonary embolism or proximal deep venous thrombosis, but nine patients (5%) had asymptomatic distal deep venous thrombosis develop, with no preoperative associated factors. These nine patients were followed closely without anticoagulant drugs, and all thromboses had disappeared without pulmonary embolism or thrombophlebitis by 6 months.

Conclusions

The incidence of preoperative and postoperative deep venous thrombosis was low in an Asian population having elective hip surgery and a nonpharmacologic thromboprophylaxis regimen. There were no preoperative factors associated with postoperative deep venous thrombosis, and all asymptomatic deep venous thromboses resolved spontaneously without associated pulmonary embolism or thrombophlebitis.

Level of Evidence

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Background

The benefits of robotic techniques for implanting femoral components during THA are still controversial.

Questions/Purposes

The purpose of this study was to prospectively compare the results and complications of robotic-assisted and hand-rasping stem implantation techniques.

Method

The minimum followup was 5 years (mean, 67 months; range, 60–85 months). One hundred forty-six primary THAs on 130 patients were included in this study. Robot-assisted primary THA was performed on 75 hips and a hand-rasping technique was used on 71 hips.

Results

At 2 and 3 years postoperatively, the Japanese Orthopaedic Association (JOA) clinical score was slightly better in the robotic-assisted group. At 5 years followup, however, the differences were not significant. Postoperative limb lengths of the robotic-milling group had significantly less variance than the hand-rasping group. At 2 years postoperatively, there was significantly more stress shielding of the proximal femur in the hand-rasping group; this difference was more significant 5 years postoperatively.

Conclusions

Substantially more precise implant positioning seems to have led to less variance in limb-length inequality and less stress shielding of the proximal femur 5 years postoperatively.

Level of Evidence

Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Malalignment of the cup in total hip arthroplasty (THA) increases the risks of postoperative complications such as neck cup impingement, dislocation, and wear. We asked whether a tailor-made surgical guide based on CT images would reduce the incidence of outliers beyond 10° from preoperatively planned alignment of the cup compared with those without the surgical guide. We prospectively followed 38 patients (38 hips, Group 1) having primary THA with the conventional technique and 31 patients (31 hips, Group 2) using the surgical guide. We designed the guide for Group 2 based on CT images and fixed it to the acetabular edge with a Kirschner wire to indicate the planned cup direction. Postoperative CT images showed the guide reduced the number of outliers compared with the conventional method (Group 1, 23.7%; Group 2, 0%). The surgical guide provided more reliable cup insertion compared with conventional techniques.

Level of Evidence: Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

We investigated whether the vertical-center-anterior (VCA) angle measured on the false-profile view of the hip represents true anterior coverage by computer simulation using three-dimensional (3-D) computed tomography (CT) in 100 hips without osteoarthritic changes. True anterior coverage angle on the sagittal plane was measured in the pelvic coordinate system. Two types of VCA angle were measured on the digital reconstructed radiographs: the anterior point of the VCA angle was defined as the foremost aspect of the acetabulum, denoted VCA-1, whereas the anterior edge of the dense shadow of the subchondral bone of the acetabulum was defined as VCA-2. In the normal hips, VCA-1 was consistent with anterior coverage angle (r = 0.88, Spearman rank test), whereas VCA-2 underestimated the anterior coverage (r = 0.72). In the dysplastic hips, VCA-2 did not always indicate true anterior coverage (r = 0.64), whereas VCA-1 overestimated the anterior coverage (r = 0.002). Although VCA-1 in normal hips shows true anterior coverage, the VCA angle does not indicate true anterior coverage in dysplastic hips, and VCA angle measurement in dysplastic hips should be used carefully.

Level of Evidence: Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

In revision surgery with proximal femoral bone loss, progressive bone atrophy due to stress shielding remains a concern. We compared 2-year radiological results between two types of cementless long titanium stems with different configurations and surface coatings. Of 17 hips implanted with a wholly hydroxyapatite-coated stem, 12 (71%) exhibited stress shielding of the second degree or higher according to Engh’s criteria, and the mean relative bone mass index decreased from 22.1% pre-operatively to 14.6% at 2 years post-operatively. In 23 hips implanted with a sand-blasted, conically shaped stem, no hip showed stress shielding of the second degree or higher. The mean relative bone mass index increased from 21.6% to 31.4%. These results indicate that the configuration and surface coating of the stem have a significant influence on proximal bone remodelling after revision surgery.

Although MRI is useful for predicting progression of osteonecrosis (ON) of the femoral head or femoral condyle, predicting outcome of atraumatic osteonecrosis of the humeral head using MRI has not been previously examined. We asked whether the prognosis was related to the extent and location of necrotic lesions on MRI. We investigated 46 radiographically noncollapsed humeral heads in 27 patients, 24 steroid-related and three alcohol-related, using MRI and serial radiographs. The minimum followup was 24 months (mean, 84.9 months; range, 24–166 months). The necrotic lesion was typically located at the medial and superior aspect of the humeral head. The necrotic angle, which expressed the extent of the necrotic lesion, was measured on midoblique-coronal plane (range; 0°–134.7°) and on midoblique-sagittal plane (range; 0°–150.6°). Of the 46 lesions, 34 were less than 90° and did not collapse, whereas 11 of the other 12 lesions of more than 90° (92%) collapsed within 4 years. Of these 11 collapsed lesions, four of less than 100° did not progress, followed by reparative reaction on plain radiographs, whereas the other seven of more than 100° progressed to osteoarthritis. The extent of a necrotic lesion on MRI is useful to predict collapse of the humeral head.

Level of Evidence: Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Registration is a critical and important process in maintaining the accuracy of CT-based image-guided surgery. The aim of this study was to evaluate the effects of the area of intraoperative data sampling and number of sampling points on the accuracy of surface-based registration in a CT-based spinal-navigation system, using an optical three-dimensional localizer. A cadaveric dry-bone phantom of the lumbar spine was used. To evaluate registration accuracy, three alumina ceramic balls were attached to the anterior and lateral aspects of the vertebral body. CT images of the phantom were obtained (1-mm slice thickness, at1-mm intervals) using a helical CT scanner. Twenty surface points were digitized from five zones defined on the basis of anatomical classification on the posterior aspects of the target vertebra. A total of 20 sets of sampling data were obtained. Evaluation of registration accuracy accounted for positional and rotational errors. Of the five zones, the area that was the largest and easiest to expose surgically and to digitize surface points was the lamina. The lamina was defined as standard zone. On this zone, the effect of the number of sampling points on the positional and rotational accuracy of registration was evaluated. And the effects of the additional area selected for intraoperative data sampling on the registration accuracy were evaluated. Using 20 surface points on the posterior side of the lamina, positional error was 0.96 mm±0.24 mm root-mean-square (RMS) and rotational error was 0.91°±0.38°RMS. The use of 20 surface points on the lamina usually allows surgeons to carry out sufficiently accurate registration to conduct computer-aided spine surgery. In the case of severe spondylosis, however, it might be difficult to digitize the surface points from the lamina, due to a hypertrophic facet joint or the deformity of the lamina and noisy sampling data. In such cases, registration accuracy can be improved by combining use of the 20 surface points on the lamina with surface points on other zones, such as on the both sides of the spinous process.