We have studied the concept of posterior condylar offset and the importance of its restoration on the maximum range of knee flexion after posterior-cruciate-ligament-retaining total knee replacement (TKR). We measured the difference in the posterior condylar offset before and one year after operation in 69 patients who had undergone a primary cruciate-sacrificing mobile bearing TKR by one surgeon using the same implant and a standardised operating technique. In all the patients true pre- and post-operative lateral radiographs had been taken.

The mean pre- and post-operative posterior condylar offset was 25.9 mm (21 to 35) and 26.9 mm (21 to 34), respectively. The mean difference in posterior condylar offset was + 1 mm (−6 to +5). The mean pre-operative knee flexion was 111° (62° to 146°) and at one year postoperatively, it was 107° (51° to 137°).

There was no statistical correlation between the change in knee flexion and the difference in the posterior condylar offset after TKR (Pearson correlation coefficient r = −0.06, p = 0.69).

The aim of this study was to evaluate the risk factors for dislocation of the bearing after a mobile-bearing Oxford medial unicompartmental knee replacement (UKR) and to test the hypothesis that surgical factors, as measured from post-operative radiographs, are associated with its dislocation

From a total of 480 UKRs performed between 2001 and 2012, in 391 patients with a mean age of 66.5 years (45 to 82) (316 female, 75 male), we identified 17 UKRs where bearing dislocation occurred. The post-operative radiological measurements of the 17 UKRs and 51 matched controls were analysed using conditional logistic regression analysis. The post-operative radiological measurements included post-operative change in limb alignment, the position of the femoral and tibial components, the resection depth of the proximal tibia, and the femoral component-posterior condyle classification.

We concluded that a post-operative decrease in the posterior tibial slope relative to the pre-operative value was the only significant determinant of dislocation of the bearing after medial Oxford UKR (odds ratio 1.881; 95% confidence interval 1.272 to 2.779). A post-operative posterior tibial slope < 8.45° and a difference between the pre-operative and post-operative posterior tibial slope of > 2.19° may increase the risk of dislocation.

Cite this article: Bone Joint J 2014; 96-B:914–22.

Medium-term survivorship of the Oxford phase 3 unicompartmental knee replacement (UKR) has not yet been established in an Asian population. We prospectively evaluated the outcome of 400 phase 3 Oxford UKRs in 320 Korean patients with a mean age at the time of operation of 69 years (48 to 82). The mean follow-up was 5.2 years (1 to 10). Clinical and radiological assessment was carried out pre- and post-operatively. At five years, the mean Knee Society knee and functional scores had increased significantly from 56.2 (30 to 91) pre-operatively to 87.2 (59 to 98) (p = 0.034) and from 59.2 (30 to 93) to 88.3 (50 to 100) (p = 0.021), respectively. The Oxford knee score increased from a mean of 25.8 (12 to 39) pre-operatively to 39.8 (25 to 58) at five years (p = 0.038). The ten-year survival rate was 94% (95% confidence interval 90.1 to 98.0). A total of 14 UKRs (3.5%) required revision. The most common reason for revision was dislocation of the bearing in 12 (3%). Conversion to a total knee replacement was required in two patients who developed osteoarthritis of the lateral compartment.

This is the largest published series of UKR in Korean patients. It shows that the mid-term results after a minimally invasive Oxford phase 3 UKR can yield satisfactory clinical and functional results in this group of patients.

Between April 2004 and July 2007, we performed 241 primary total knee replacements in 204 patients using the e.motion posterior cruciate-retaining, multidirectional mobile-bearing prosthesis. Of these, 100 were carried out using an image-free navigation system, and the remaining 141 with the conventional technique. We conducted a retrospective study from the prospectively collected data of these patients to assess the early results of this new mobile-bearing design.

At a mean follow-up of 49 months (32 to 71), 18 knees (7.5%) had mechanical complications of which 13 required revision. Three of these had a peri-prosthetic fracture, and were removed from the study. The indication for revision in the remaining ten was loosening of the femoral component in two, tibiofemoral dislocation in three, disassociation of the polyethylene liner in four, and a broken polyethyene liner in one. There were eight further mechanically unstable knees which presented with recurrent disassociation of the polyethylene liner. There was no significant difference in the incidence of mechanical instability between the navigation-assisted procedures (8 of 99, 8.1%) and the conventionally implanted knees (10 of 139, 7.2%).

In our view, the relatively high rate of mechanical complications and revision within 30 months precludes the further use of new design of knee replacement.