The dislocation risk could be higher if cup anteversion was not between 10° and 30°. Greater combined anteversion could be a risk factor of anterior dislocation, and posterior dislocation could be more common in smaller combined anteversion.
Aims Cementless unicompartmental knee arthroplasty (UKA) has advantages over cemented UKA, including improved fixation, but has a higher risk of tibial plateau fracture, particularly in Japanese patients. The aim of this multicentre study was to determine when cementless tibial components could safely be used in Japanese patients based on the size and shape of the tibia. Methods The study involved 212 cementless Oxford UKAs which were undertaken in 174 patients in six hospitals. The medial eminence line (MEL), which is a line parallel to the tibial axis passing through the tip of medial intercondylar eminence, was drawn on preoperative radiographs. Knees were classified as having a very overhanging medial tibial condyle if this line passed medial to the medial tibial cortex. They were also classified as very small if a size A/AA tibial component was used. Results The overall rate of fracture was 8% (17 out of 212 knees). The rate was higher in knees with very overhanging condyles (Odds ratio (OR) 13; p < 0.001) and with very small components (OR 7; p < 0.001). The OR was 21 (p < 0.001) in those with both very overhanging condyles and very small components. In all, 69% of knees (147) had neither very overhanging nor very small components, and the fracture rate in these patients was 1.4% (2 out of 147 knees). Males had a significantly reduced risk of fracture (OR 0.13; p = 0.002), probably because no males required very small components and females were more likely to have very overhanging condyles (OR 3; p = 0.013). 31% of knees (66) were in males and in these the rate of fracture was 1.5% (1 out of 66 knees). Conclusion The rate of tibial plateau fracture in Japanese patients undergoing cementless UKA is high. We recommend that cemented tibial fixation should be used in Japanese patients who require very small components or have very overhanging condyles, as identified from preoperative radiographs. In the remaining 69% of knees cementless fixation can be used. This approach should result in a low rate of fracture. Cite this article: Bone Joint J 2020;102-B(7):861–867.
Unicompartmental knee arthroplasty (UKA) is a less invasive method for treating monocondylar arthritis of the knee than total knee arthroplasty (TKA). The use of UKA is gaining popularity and has shown excellent long-term results. 1,2) The survivorship of medial mobile bearing Oxford UKA (OUKA; Zimmer Biomet, Warsaw, IN, USA) is as high as 98% at 10 years 3) and 91% through the second decade. 4) One of the most serious complications of UKA is tibial fracture. It has been described as a result of technical errors, such as the creation of an improper pin site for the fixation of the tibial cutting block, 5) vertical overcutting of the medial plateau, 6) use of an excessive force with a heavy hammer, 7) and breach of the posterior tibial cortex during preparation of the tibial plateau for the implant. 8) Although rarely reported as a complication in Europe (less than 1%), 7,9,10) tibial fracture is reported more frequently in Asian countries. 11) Yoshida et al. 12) described that the 10-year survival rate of >1,000 cases of OUKA in a Japanese population was 95.4%, with good clinical results. However, fractures after UKA were reported to occur in 7.2% of cases in spite of good technical skill. 13) It may indi-
To assess the accuracy of cup orientation and learning curve of the disposable accelerometer-based portable navigation system for total hip arthroplasty (THA) in the supine position. Methods: A total of 75 patients who underwent THA through the anterolateral supine approach (ALS) with an accelerometer-based portable navigation system for the supine position (HipAlign ®) between July 2017 and October 2018 were analyzed in this study. We compared the intraoperative cup angles using navigation records with the postoperative angles using postoperative computed tomography (CT) data. All patients were categorized into the following groups according to the course of three discrete, sequential operative time periods: 1-25 (initial group), 26-50 (intermediate group), and 51-75 (recent group). We compared the accuracy of cup inclination and anteversion among the three groups. The time required for navigation and the operative time of all patients were measured. Results: The average absolute error in measurement (postoperative CT-navigation record) was 2.6 + 2.7 (inclination) and 2.8 + 2.7 (anteversion). There were no significant differences among the three groups. The average time required for navigation and the operative time were 365.1 + 90.3 s and 76.1 + 1.6 min, respectively. The required time for HipAlign ® navigation and operative time were constant in most patients, except for those of the initial five cases. Conclusion: The accelerometer-based portable navigation system provides good accuracy of cup orientation, has a short learning curve, and requires a minimal surgical time for THA in supine position.
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