Higher revision rates were shown in varus- or valgus-positioned tibias in unicompartmental knee arthroplasty (UKA), but more than 15% of UKA prostheses are implanted with more than 5° of varus or valgus. This study aimed to analyze the wear rate in UKA when implanting the tibial component in either varus or valgus position versus a neutral placement at 90° to the tibial anatomical axis. The study hypothesized that a 5° varus or valgus positioning of the tibial plateau will generate less wear compared to a neutral alignment.
Wear was experimentally analyzed on a medial anatomical fixed-bearing unicompartmental knee prosthesis (Univation, Aesculap, Germany) in vitro with a customized, four-station, servohydraulic knee wear simulator, reproducing the walking cycle. The forces, loading and range of motion were applied as specified in the ISO 14243–1:2002, 5 million cycles were analyzed. The tibial components of the medial prostheses were inserted in a neutral position, with 5° varus, and 5° valgus (n = 3, each group).
The wear rate decreased significantly with a 5° varus positioning (6.30 ± 1.38 mg/million cycles) and a 5° valgus positioning (4.96 ± 2.47 mg/million cycles) compared to the neutral position (12.16 ± 1.26 mg/million cycles) (p < 0.01 for the varus and the valgus position). The wear area on the inlay was slightly reduced in the varus and valgus group.
A varus or valgus “malpositioning” up to 5° will not lead to an increased wear. Wear was even less because of the reduced articulating contact area between the inlay and the femur. A slight varus positioning of the tibial component (parallel to the anatomical joint line) positioning can be advocated from a point of wear.
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This study was funded in part by BBraun Aesculap, Tuttlingen, Germany by providing the prosthesis System. Beside this no further external funding was used.
Conflict of interest
VJ and PEM are advising surgeons of Aesculap, Tuttlingen, Germany. VJ, PEM and PW are advising surgeons for Medacta, Castel San Pietro, Switzerland. MW, CS and PW received research funds from Aesculap R&D projects. This did not, however, influence the study design or the collection, analysis, and interpretation of the data. It also did not influence the decision to submit the manuscript for publication.
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Woiczinski, M., Schröder, C., Paulus, A. et al. Varus or valgus positioning of the tibial component of a unicompartmental fixed-bearing knee arthroplasty does not increase wear. Knee Surg Sports Traumatol Arthrosc 28, 3016–3021 (2020). https://doi.org/10.1007/s00167-019-05761-3
- Varus valgus alignment