Proper rotational alignment of the tibial component in total knee arthroplasty (TKA) could be achieved using several techniques. The self adjustment methodology allows the alignment of the tibial component under the femoral component after several flexion-extension movements. Our hypothesis was that this technique allowed a posterior tibial component alignment parallel to the femoral component posterior bicondylar axis. The aim of this study was to access this hypothesis using a post-operative CT-scan study. This prospective CT-scan study involved 94 TKA. Theses TKA were divided in two groups: group1: 50 knees with a pre-operative genu varum deformity (mean HKA: 172.2°), operated using a medial parapatellar approach, and group 2: 44 knees with a preoperative valgus deformity (mean HKA: 188.7°), operated using a lateral parapatellar approach. Four measures were done on each post-operative CT-scan: angle between anatomical transepicondylar axis and femoral component posterior bicondylar axis (FCPCA), angle between FCPCA and tibial component marginal posterior axis, angle between tibial component marginal posterior axis and bony tibial plateau marginal posterior axis (BTPMPA), angle between transepicondylar axis and tibial component marginal posterior axis. Each measure was repeated, after one month by the same independent observer. Statistical evaluation used non-parametric Wilcoxon–Mann–Whitney test to compare each group of measures, and intraobserver reproducibility was assessed using ANOVA test, with an error rate of 5%.Introduction
Materials and Methods
The bare area of the humeral head is limited in front by the cartilage and backwards by the insertion of the Infra Spinatus tendon. There are few references in the current literature. The aim of this work was to precise the anatomic description of the bare area and to compare the size of this area in patients with anterior shoulder instability and patients without anterior shoulder instability. We have proceeded first to an anatomic study to precise the limit of the bare area. The second part of this study was a retrospective and prospective comparative arthro CT-scan study in two groups of patients. The first group (group 1) had 48 patients, going to have anterior instability surgery. The second group (group 2) had 38 patients, without shoulder instability. Mean age was respectively 28.2 years (range: 19–48) in group 1; and 39.3 years (16–69) in group 2. The size of the bare area was measured on the axial injected CT cut passing by the larger diameter of the humeral head, The size of the bare area was definite by the angle between the line connecting the centre of the head to the posterior limit of the cartilage and the line connecting the centre of the head to the anterior point of the Infra Spinatus tendon. The reproducibility of the measure has been evaluated by a Bland and Altman test and an intra class correlation test. The measures were realised by two independent surgeons in a blind manner. The results where compared by a Student test with a threshold at 5%. In the anatomic part of this study, the average angle of the bare area was 32.7° equal to 13.7mm wide. Mean intraobserver variability was 4° (range: 0 to 20°) (NS) and mean interobserver variability was 4° also (range: 0 to 20°) (NS). Mean size of the bare area was 49.6° eaqual to 19.8mm wide [range 25° to 70°] in group 1 and 33.2° equal to 13.5mm wide [range 21° to 60°] in group 2 (p< 0,05).Material and method
Results
