The difference between weight-bearing and non-weight-bearing alignment in patient-specific instrumentation planning.
OBJECTIVE
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).


CONCLUSIONS
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.


METHODS
IV.
University Hospital Saint Luc, Av. Hippocrate 10, 1200, Brussels, Belgium.
Frederic
F
Paternostre
Pierre-Emmanuel
PE
Schwab
Emmanuel
E
Thienpont
D000368:Aged; D000843:Ankle Joint / Q000000981:diagnostic imaging / Q000502:physiology; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery; D007720:Knee Prosthesis; D035002:Lower Extremity / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery*; D011859:Radiography; D012189:Retrospective Studies; D025321:Surgery, Computer-Assisted / Q000379:methods*; D054159:Torsion, Mechanical; D016474:Weight-Bearing