Arithmetic hip knee angle measurement on long leg radiograph versus computed tomography-inter-observer and...

Area of Science:

• Orthopedic surgery
• Radiology
• Biomedical engineering

Background:

• Accurate pre-operative coronal alignment is crucial for total knee arthroplasty (TKA).
• The arithmetic Hip Knee Angle (aHKA) measures coronal alignment using medial proximal tibial (MPTA) and lateral distal femoral angles (LDFA).
• Traditionally, aHKA is measured using long leg radiographs (LLR), with potential limitations.

Purpose of the Study:

• To assess the reproducibility of aHKA measurements on LLR versus CT scans.
• To compare intra-observer and inter-observer reliability for these measurements across modalities.
• To evaluate CT as a potential alternative to LLR for pre-operative knee alignment assessment.

Main Methods:

• Sixty-eight TKA patients with pre-operative LLR and planning CT scans were analyzed.
• Three observers repeatedly measured MPTA, LDFA, and aHKA on both LLR and CT data.
• Intra-observer and inter-observer reliability were calculated using Pearson's r and Bland-Altman analysis.

Main Results:

• CT measurements showed higher intra-observer and inter-observer reproducibility (lower Coefficient of Repeatability) for MPTA, LDFA, and aHKA compared to LLR.
• Pearson's r values indicated strong correlation (0.90-0.97) between LLR and CT measurements for all parameters.
• CT measurements demonstrated superior reliability, particularly for MPTA (intra-observer COR 1.73° vs. 3.50°, inter-observer COR 1.28° vs. 2.74°).

Conclusions:

• CT measurements of MPTA, LDFA, and aHKA are more reproducible and correlate well with LLR measurements.
• CT overcomes limitations associated with LLRs, such as patient positioning, rotation, habitus, and contractures.
• Pre-operative CT may obviate the need for LLRs in assessing coronal plane alignment for TKA.