Arithmetic hip knee angle measurement on long leg radiograph versus computed tomography—inter-observer and intra-observer reliability
Open accessAbstract
Background: Pre-operative alignment is important for knee procedures including total knee arthroplasty (TKA), especially when considering alternative alignments. The arithmetic Hip Knee Angle (aHKA) is a measure of coronal alignment calculated using the medial proximal tibial (MPTA) and lateral distal femoral angles (LDFA). Traditionally, aHKA is measured on long leg radiographs (LLR). This study assesses the reproducibility of aHKA measurement on LLR and robotic-assisted TKA planning CT. Methods: Sixty-eight TKA patients with pre-operative LLR and planning CTs were included. Three observers measured the LDFA, MPTA and aHKA three times on each modality and intra-observer and inter-observer reliability was calculated. Statistical analysis was undertaken with Pearson’s r and the Bland–Altman test. Results: Mean intra-observer coefficient of repeatability (COR) for LLR vs. CT: MPTA 3.50° vs. 1.73°, LDFA 2.93° vs. 2.00° and aHKA 2.88° vs. 2.57° for CT. Inter-observer COR for LLR vs. CT: MPTA 2.74° vs. 1.28°, LDFA 2.31° vs. 1.92°, aHKA 3.56° vs. 2.00°. Mean intra-observer Pearson’s r for MPTA was 0.93 for LLR and 0.94 for CT, LDFA 0.90 for LLR and 0.91 for CT and aHKA 0.92 for LLR and 0.94 for CT. Inter-observer Pearson’s r for LLR compared to CT: MPTA 0.93 vs. 0.97, LDFA 0.91 vs. 0.90, aHKA 0.91 and 0.95. Conclusion: When compared to LLR, CT measurements of MPTA, LDFA and aHKA are more reproducible and have a good correlation with LLR measurement. CT overcomes difficulties with positioning, rotation, habitus and contractures when assessing coronal plane alignment and may obviate the need for LLRs.
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A 1° difference was determined clinically sufficient to power the study, and similar patient numbers have been used in other studies comparing LLR to CT for CPAK.
“However, a 1° difference was determined clinically sufficient to power our study and similar patient numbers have been used in other studies comparing LLR to CT for CPAK [16, 18].”
From Imageless robotic total knee arthroplasty determines similar coronal plane alignment of the knee (CPAK) parameters to long leg radiographs (2024) · cites this paper as [18]
The source’s Results report 68 patients, with 64 CT scans and 68 LLRs assessed, supporting its use as an example of a similarly sized LLR–CT comparison. Its Introduction specifies that the comparison concerned aHKA measurements, not CPAK classification. The 1° threshold and power calculation refer to the citing authors’ own study, not this source. (LLM, conf=0.83)
Experimental — accuracy not yet measuredThe ability of CT-based robotics to define constitutional alignment and CPAK has been established.
“The ability of CT-based robotics to define constitutional alignment and CPAK has been established [16–18], yet it remains unknown if imageless intraoperative robotic data can accurately describe CPAK parameters [19–23].”
From Imageless robotic total knee arthroplasty determines similar coronal plane alignment of the knee (CPAK) parameters to long leg radiographs (2024) · cites this paper as [18]
The Conclusion (page unavailable) reports that CT measurements of MPTA, LDFA, and aHKA are more reproducible than long-leg radiograph measurements and correlate well with them, supporting CT assessment of alignment using scans obtained for robotic planning. But the Discussion (page unavailable) does not establish that CT-based robotics itself defines CPAK: it describes CPAK as incorporating aHKA and joint-line obliquity, and says CT-based aHKA measurement may be integrated into robotic planning software in the future. (LLM, conf=0.87)
Experimental — accuracy not yet measured
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Cited by
Sorted by citations
Edelstein, A. I., Orsi, A. D., Plaskos, C., Coffey, S., & Suleiman, L. I. (2024) · Arthroplasty · doi:10.1186/s42836-024-00231-9 · Cited by 11 · see citing works
“The ability of CT-based robotics to define constitutional alignment and CPAK has been established [16–18], yet it remains unknown if imageless intra-operative robotic data can accurately describe CPAK parameters [19–23].”
BackgroundResult
- Authors
- Gieroba, T. J., Marasco, S., Babazadeh, S., Di Bella, C., & van Bavel, D.
- Affiliations
- Flinders University (AU)
- St Vincent's Hospital Melbourne (AU)
- The University of Melbourne (AU)
- Corresponding author
- Gieroba, Tom Jan
- Venue
- Arthroplasty
- Published
- 2023-08-02
- Volume
- 5
- Issue
- 1
- Pages
- 35-35
- ISSN
- 2524-7948 (ISSN-L)
- PMC
- PMC10394810
- OpenAlex
- W4385448478
- Cited by
- 28
- References
- 2
- Citations by year
- 2026: 8 · 2025: 12 · 2024: 6 · 2023: 2
- FWCI
- 7.50
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- Arthroplasty (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Topics
- Health Sciences › Medicine › Surgery › Total Knee Arthroplasty Outcomes
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Reliability and Agreement in Measurement
- Health Sciences › Medicine › Surgery › Knee injuries and reconstruction techniques
- Keywords
- total knee arthroplasty, coronal alignment, long-leg radiographs, computed tomography, inter-rater reliability, intra-rater reliability, medial proximal tibial angle, lateral distal femoral angle, measurement reproducibility
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