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. We reviewed 50 knees who were treated for SONK. Patients included ten males and 38 females. The mean age was 73 years (range, 57 to 83 years). The mean height and body weight were, respectively 153 cm (141 ∼171 cm) and 57 kg (35 ∼75kg). All had been operated on using the Oxford mobile-bearing UKA (Zimmer-Biomet, Swindon, United Kingdom) with cement fixation. The mean follow-up period was 8.4 years (range, 4 to 15years). We measured the size (width, length and depth) and the volume to be estimated (width x length x depth) of the necrotic bone mass using MRI in T1-weighted images. The clinical results were evaluated using the Knee Society Scoring System (KSS) and Oxford Knee Score (OKS). The flexion angle of the knee was evaluated using lateral X-ray images in maximum flexion.Aims
Patients and Methods
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.
