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Postural coronal alignment shift after total knee arthroplasty diminishes with age and becomes negligible in elderly
Komson Plangsiri1, Bhumin Chotiwatanadilok1, Pruk Chaiyakit2
1Department of Orthopedics, Faculty of Medicine, Srinakharinwirot University, Ongkharak, Nakhon Nayok, Thailand.
Purpose:
To investigate whether patient age moderates the change in coronal hip-knee-ankle (HKA) alignment between supine and standing positions following total knee arthroplasty (TKA).
Methods:
In this cross-sectional study, 113 consecutive patients after primary TKA for osteoarthritis underwent standardized full-length radiographs in both supine and standing positions. The postural shift (ΔHKA) was defined as standing minus supine alignment. Associations between age and ΔHKA were examined using a linear mixed-effects model with restricted cubic splines, adjusting for body mass index (BMI), sex, preoperative alignment and time since surgery. Equivalence testing (±1° margin) was performed in patients aged ≥60 years.
Results:
Younger patients demonstrated a standing varus drift of approximately 2-3°, whereas the effect progressively diminished with advancing age. The age-position interaction was significant (p = 0.011), while BMI, sex, preoperative alignment and time since surgery were not. In patients ≥60 years, the mean ΔHKA was -0.01° (90% confidence interval = -0.55° to +0.53°), meeting statistical equivalence to 0 (p = 0.008). Collateral ligament laxity on stress radiography showed no association with ΔHKA.
Conclusion:
Postural coronal alignment change after TKA is strongly age dependent. Younger patients show a measurable varus drift, whereas older patients demonstrate negligible change within radiographic error. Age should be considered when tailoring intraoperative alignment strategies to ensure durable functional outcomes.
Level Of Evidence:
Level III.
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