The difference between weight-bearing and non-weight-bearing alignment in patient-specific instrumentation planning
Paternostre, F., Schwab, P. & Thienpont, E.Knee
Purpose
Retrospective study to analyse the difference between weight-bearing and non-weight-bearing alignment in osteoarthritic knees planned for patient-specific instrumented (PSI) total knee arthroplasty (TKA). The aim of the study is to observe whether a difference in alignment can be linked to arthritis staging or zone mechanical axis.
Methods
Full-leg standing radiographs and non-weight-bearing MRI of the whole leg were compared for hip–knee–ankle (HKA) angle, measured according to Moreland criteria, in seventy osteoarthritic patients. Kellgren–Lawrence (KL) staging and classification according to zone mechanical axis with Kennedy zones was done.
Results
A mean preoperative HKA angle on standing radiographs of 176.4° ± 7.2° was measured compared to 176.4° ± 6.9° for the MRI whole-leg HKA angle. A difference of 0°–1° was observed in 54 % of patients when comparing the weight-bearing with the non-weight-bearing HKA angle. Twenty-three per cent had a difference of 2° and another 23 % a difference of 3° or more. In female patients, the dynamic load pattern of weight-bearing increases the HKA angle due to convex side soft tissue laxity both in varus and valgus knees. More important differences were observed in the KL stage 3 and 4 patients (P < 0.05) and with a load-bearing axis outside of the articular surface (P < 0.05).
Conclusion
Surgeons should be aware that there is a difference between weight-bearing and non-weight-bearing alignment in patients with Kellgren–Lawrence 3 and 4 with a load-bearing axis outside of the articular surface (Kennedy 0 or 1 or 5). According to this study, these changes seem related to the amount of articular wear and the load-bearing axis. This is important for the preoperative planning process in PSI-assisted TKA. More concave side ligamentous release or more constraint can be necessary than imagined based on the PSI alignment result. Full-leg standing radiographs should be performed for PSI-assisted TKAs to analyse the position of the load-bearing axis.
Level of evidence
IV.
Link to article