DISTAL FEMORAL MORPHOLOGY IN HINGED KNEE REPLACEMENT: VALIDATION OF THE NOVEL CITAK CLASSIFICATION

When performing arthroplasty around the hip, choice of stem fixation depends partially on proximal femoral morphology, and the Dorr classification is an important consideration in deciding on stem type. Recently, a distal femoral canal morphology classification system was proposed (the Citak Classification) and descriptive data reported in a German population. The classification system has two main components – the inner diameter of the femoral canal at 20cm proximal to the joint line, divided into Types A (narrowest), B, and C (widest), as well as an index value, calculated as the ratio of the above value to the inner diameter of the canal 2cm proximal to the adductor tubercle. Our aim was to descriptively report the classification system in a Canadian population, and analyze its impact on the risk of aseptic loosening. Data was collected for all patients who had undergone a hinged knee replacement in a prospective institutional database. Patients who did not have adequate x-rays for calculation of inner canal diameter and the Citak Index were excluded. Inner diameter of the canal 20cm proximal to the joint line and the Citak Index were calculated for each patient on the x-rays taken immediately prior to the patient undergoing hinged knee replacement. Number of patients in each category is reported descriptively, and mean age and sex distributions were compared between the groups. Revision surgery following hinged knee replacement was tracked, and all-cause revision and aseptic loosening rates were compared between the groups. A total of 59 patients underwent hinged knee replacements between 2004 and 2019 and had adequate x-rays for inclusion. Mean follow-up was 7.52 years (range 1.4 to 16.4 years). Mean age was 71.2 years (Standard Deviation: 12.6). There were 41 female and 18 male patients. For the inner diameter 20cm proximal to the joint line, 31 patients (52.5%) were in Group A, 19 patients (32.2%) in Group B, and 15.3% in Group C. Regarding the Citak Index, 26 patients (44.1%) were in Group A, 20 patients (33.9%) in Group B, and 13 (22.0%) in Group C. Patients in Group C had a significantly older mean age than Groups A or B. Proportion of male and female patients in each group were similar. Rates of all-cause revision was significantly higher in Citak Index Group C (46.2%) compared to Groups B (25.0%) or A (15.4%). There were three cases of aseptic loosening, all of which occurred in patients with a Group C Citak Index. This study has described the Citak Classification System in a Canadian population undergoing hinged knee replacement. Unlike the original descriptive study, where 50% of patients were in Group B, we found that most patients in our cohort were in Group A. As well, Group C patients were more likely to be older, to require revision surgery, and to have aseptic loosening of their hinged knee replacement. Distal femur morphology is an important consideration in selecting stemmed distal femur implants and further study of the anatomy of this region is warranted.