Introduction/Aim:
High grade varus osteoarthrosis (OA) is characterized by a pronounced intra-articular varus deformity and associated insufficiency of the lateral ligamentous complex. When performing a total knee arthroplasty (TKA) in such a knee, traditionally the alignment is restored to neutral, and the medial soft tissue structures are released to balance the joint and to compensate for lateral laxity. However, another option is to leave the medial soft tissues untouched and accept the lateral laxity, but to compensate for it using a ML stabilized Constrained-Condylar-Knee (CCK) design. It was our hypothesis that such knees would demonstrate better clinical stability and better functional as well as subjective outcome scores.

Methods

We searched our bicenter database of 912 primary TKAs (from 2016 to 2019) for primary TKA patients with a preoperative varus alignment of >8° and a documented lateral laxity. 60 patients were included and divided into three groups by implant design: CCK (n=21), Posterior-Stabilized (PS)(n=20) and Cruciate-Retaining (CR)(n=19). Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Knee Society Score (KSS), UCLA-activity score, ML instability scores and both radiographic and clinical data were compared between groups.

Results

ML stability was significantly better in CCK designs (86% grade 0) compared to CR (37% grade 0) (p=0.004) but not PS (70% grade 0) designs. No grade II instability was present in CCK and PS implants compared to 16% of CR implants.
KSS and UCLA-activity score were higher in CCK designs compared to PS (p=0.027, p=0.041) and CR designs (p<0.001, p=0.007). OKS and FJS were higher in CCK designs compared to CR (p=0.025, p=0.008).

Conclusion

Leaving the medial soft tissues untouched and compensate the lateral laxity by using a CCK design in high grade varus OA knees results in improved clinical stability and better functional as well as subjective outcome scores compared to less-constrained designs.