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Distribution and changes in lower limb alignment using the coronal plane alignment of the knee classification system
Takahiro Negayama1, Ken Iwata2, Masashi Shimamura3
1Faculty of Medicine, Kagawa University, Kita-gun, Japan. negayama.takahiro.1x@kagawa-u.ac.jp.
Purpose:
Total hip arthroplasty (THA) is the standard treatment for hip osteoarthritis, yet its effects on lower limb alignment remain unclear. The coronal plane alignment of the knee (CPAK) classification system, widely used in knee surgery, has not been explored in THA. We investigated CPAK classifications in patients with hip osteoarthritis and examined alignment changes following THA.
Methods:
This retrospective cohort study analyzed 110 patients (113 hips) who underwent primary THA between January 2017 and July 2019. Full-length standing radiographs were obtained preoperatively and one year postoperatively. Measured parameters included the mechanical medial proximal tibial angle (MPTA), mechanical lateral distal femoral angle (LDFA), arithmetic hip-knee-ankle angle (aHKA), and joint line obliquity for CPAK classification. Horizontal and vertical alignments were assessed to determine hip centre position.
Results:
Type II was the predominant CPAK type (47.8%) preoperatively, while types I and III were equally distributed (22.1% each). One year postoperatively, types I and II were equally prevalent (34.5% each), whereas type III decreased to 15%. LDFA and aHKA changed from 86.4 ± 2.2° to 87.9 ± 2.2° and from -0.2 ± 3.2° to -1.2 ± 3.2°, respectively, while MPTA remained unchanged. Hip center medialization was observed, with horizontal and vertical alignments changing from 43.6 ± 6.4 mm to 34.7 ± 4.9 mm and 30.2 ± 8.8 mm to 24.5 ± 6.0 mm.
Conclusion:
Japanese patients exhibit distinct CPAK patterns, with type II predominance. Post-THA alignment changes were characterized by increased LDFA and decreased aHKA due to hip center medialization, highlighting the importance of considering alignment changes during THA planning.
