Aims

Spontaneous osteonecrosis of the knee (SONK) mainly affects the medial femoral condyle, would be a good indication for UKA. The primary aim of this study was to assess the clinical, functional and radiographic outcomes at middle to long-term follow-up, of a consecutive series of fifty UKA used for the treatment of SONK. The secondary aim was to assess the volume of necrotic bone and determine if this influenced the outcome.

In previous congress of ISTA in Hawaii, we reported the results about accuracy of the cup center position in our image-free navigation system. In the new version of our navigation system, leg elongation and offset change as well as cup center position can be navigated. In this study, we therefore investigated the accuracy of cup center position, leg elongation and offset change.

Twenty four THA operations were performed with using the image-free OrthoPilot THA3.1 dysplasia navigation system (B. Braun Aesculap, Tuttlingen, Germany) between August 2009 and December 2009 by three experienced surgeons. In this system, cup center height was shown as the distance from tear drop, and cup medialization was shown as horizontal distance from inner wall of acetabulum. Leg elongation and offset change were navigated by comparing the two reference points in femur between registration before neck resection and that after inserting the trial implant. After operation, the cup angles were measured on CT image, and cup center position, leg elongation and offset change were measured on plain radiography. We compared these values that indicated by the navigation system to those measured on the CT image and the plain radiography.

The average cup inclination was 37.5 ± 7.0 degree and anteversion was 22.2 ± 4.7 degree. The average absolute difference between navigation and measured angles were 5.2 ± 4.0 degree in inclination, 5.9 ± 4.0 degree in anteversion. The difference of cup height was 5.8 ± 3.9 mm, cup medialization was 3.8 ± 2.7 mm, leg elongation was 4.3±3.3mm, and offset was 5.4±4.1mm, respectively.

By using this new version navigation system, we can plan the cup center position and navigate it within smaller error of vertical and horizontal direction than the previous system. Moreover, leg elongation and offset change can be satisfactory navigated during operation. However surgeon's skill and learning curve might have influence the accuracy. We have to continue to evaluate this system and make effort to further improvement.

Introduction: In total hip arthroplasty, the angle of acetabular component is a critical factor for the postoperative dislocation and the longevity of prostheses. The angle is principally determined in relation to anterior pelvic plane. It is reported that the pelvis tends to tilt posteriorly along with aging. Furthermore, the pelvic tilt might change after THA. The changes might be infiuenced by the hip condition and lumbar lordosis. We measured the pelvic tilt and the lumbar lordosis, and evaluated the effects of contralateral hip and lumbar lordosis on pelvic tilt after THA.

Materials and Methods: Fifty-one unilateral patients and 30 bilateral patients were enrolled in this study. The diagnosis was dysplastic osteoarthritis in all patients. In unilateral patients, the hip was affected in one side and the other hip was normal or acetabular dysplasia without symptoms. In bilateral patients, THAs in both hips were done within two months.

Pelvic inclination angle (PIA) and lumbar lordotic angle (LLA) were measured on the standing lateral X-rays before operation and 1-month, 6-month and 1-year post-operation. The effects of patient age, BMI, ROM of the hip, preoperative PIA and LLA on the changes of PIA were statistically investigated using multiple linear regression analysis. We divided the patients into three groups with regard to pre-operative PIA (anterior group: PIA < 0, intermediate group: 0 < PIA < 10, posterior group: PIA > 10) and with regard to pre-operative LLA (insufficient group: LLA < 20, moderate group: 20 < LLA < 40, severe group: LLA > 40).

Results: Overall, significant factor was only preoperative PIA. In bilateral cases, preoperative PIA and patient age affected the changes of PIA after THA. In patients with severe lordosis, preoperative PIA and LLA were significant factors. PIA increased in anterior tilt group and PIA did not change in intermediate group, while PIA gradually decreased in posterior group. In insufficient lordosis group, PIA remarkably increased after THA compared with that in severe group.

Discussion: Pelvic tilt after THA has been reported without considering the conditions of contralateral hip and lumbar spine. By categorizing patients with regard to the conditions of hips and lumbar spine, we can prospect the tendency of the direction of PIA changes. These results indicated that pre-operative PIA was related the changes of PIA in bilateral group. PIA slightly increased in all bilateral patients, PIA tended to close each other in unilateral patients. Further investigation is necessary to prospect the estimated PIA value after THA.

Cup orientation of total hip arthroplasty (THA) is critical for dislocation, range of motion, polyethylene wear, pelvic osteolysis, and component migration. But, substantial error under manual technique has been reported. Therefore, various navigation systems were introduced to reduce outliers. CT based navigation (CTN) was reported to reduce outliers in cup orientation. Recently, a noble technique, fluoroscopy-CT-based navigation (FCTN), has recently been developed using 2D-3D matching technique. Because of much less registration points, FCTN might be friendly to MIS THA and cases with sever bone deformity. Between October 2006 and April 2008, 33 THAs were performed through MIS approach with navigations.

We prospectively randomized those into two groups, CTN and FCTN groups. We implanted cementless hemispherical cups in 18 hips using CTN (VectorVision CT Hip 3.1) and in 15 hips using FCTN (VectorVision CT Hip 3.5). For all the patients, volumetric post-operative CT scan was performed to measure 3D cup orientation. using 3D image-processing software (JMM, Japan). The difference from target angles of anteversion was 2.7 ± 2.4 degrees in FCTN group, and 12.1 ± 5.7 degrees in CTN group (p < 0.001). The absolute value of difference from target angles of inclination was 2.7 ± 2.4 degrees in FCTN group, and 6.5 ± 4.5 degrees in CTN group (p = 0.006). FCTN does not need surface registration around acetabulum, which is great advantage to MIS THA. Our study clearly showed that FCTN significantly improved a cup orientation to CTN.