Purpose: Flexion deformity after total knee arthroplasty (TKA) is associated with poor function and dissatisfaction and should, therefore, be avoided. In the case of preoperative flexion deformity, an increased distal resection of the femur may be necessary. The degree of resection required has only been determined for cruciate-retaining (CR) prostheses to date and varies considerably from study to study. Although, for many surgeons, the algorithm for the treatment of a flexion deformity includes the resection of the posterior cruciate ligament (PCL) before additional distal resection, the degree of resection necessary for posterior-stabilized (PS)-type prostheses is not known.
Methods: Fifty consecutive patients (50 knees) who were due to undergo navigated TKA were included in this prospective study. At the end of the operation, the flexion deformity resulting from different sizes of distal femoral augmentations on the trial implants (0-8.5 mm) was determined using the navigation system.
Results: A linear relationship of 2.2° ± 0.3° flexion deformity per mm distal femoral augmentation was found. This was not dependent on age, sex, the preoperative coronal alignment, or the preoperative flexion deformity.
Conclusions: In conclusion, after the removal of posterior osteophytes and posterior capsule release, around 5 mm of the distal femur must be further resected in the case of 10° flexion deformity and 9 mm in the case of 20° flexion deformity.
Level of evidence: II (Prospective cohort study).
Keywords: Distal femoral resection; Flexion deformity; Joint line; Posterior stabilized; Total knee arthroplasty; Total knee replacement.