As surgeons continue to grapple with persistent issues of patient dissatisfaction post-TKA, the literature has focused on the coronal plane when considering alignment strategies but has largely ignored the sagittal and axial planes. The purpose of this retrospective observational cohort study is to evaluate variability in knee anatomy and alignment beyond the coronal plane and rationalise how this relates to existing arthroplasty alignment philosophies.
4116 knee CTs from 360 Knee Systems© database of arthritic pre-operative TKA patients were evaluated. Standardised bony landmarks were used in each CT to determine the hip–knee angle, medial proximal tibial angle, lateral distal femoral angle, medial plateau posterior tibial slope, lateral plateau posterior tibial slope, trochlea angle (TA) to distal femoral angle (TA–DFA) and TA to posterior condylar angle (TA–PCA). Analysis was performed to determine the distributions of each measure across the cohort population.
Both the medial and lateral PTS ranged from 5° anterior to 25° posterior. 22.6% of patients had differential PTS greater than 5°. 14.5% have greater lateral PTS (mean difference to medial PTS of 4.8° ± 5.0°), whilst 31.0% have greater medial PTS (mean difference to lateral PTS of 5.7° ± 3.2°). 14% of TA–DFAs and 5.2% of TA–PCAs vary greater than 10°.
This study demonstrates a wide variation in tibial slope, differential slope between the medial and lateral tibial plateau as well as variation in the trochlear geometry. There has been an overemphasis in the literature on coronal alignment, ignoring the considerable variability present in tibial and patellofemoral morphology. Existing arthroplasty techniques are based on assumptions that may not adequately address the anatomy of morphologic outliers and could lead to dissatisfaction.
Level of evidence
III—retrospective cohort study.
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The authors acknowledge Andrea Grant-Administration and Clinical Research Governance support. 360 Knee Group—Andrew Shimmin, Bede O'Connor, Brad Miles, Brett Fritsch, David Dickison, David Liu, David Parker, Jonathan Baré, Joshua Twiggs, Justin Roe, Michael Solomon, Richard Boyle, and Stephen McMahon.
Conflict of interest
ORIQL members of the research team have no financial association with 360 Knee Systems Pty Ltd. Shilpa Dhariwal is an employee of 360 Knee Systems Pty Ltd and has provided the study data and statistical analysis pro-bono for interpretation.
No institutional or commercial funding was obtained for this study.
Bellberry Human Research Ethics Committee, approval number 2012-03-710.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
360 Knee Systems© Knee CT Protocol:
Slice increment—1.25 mm.
Slice thickness—1.25 mm.
The estimated effective dose for the protocol was determined to be a Category IIb (2 mSv to 20Msv) risk.
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Hazratwala, K., O’Callaghan, W.B., Dhariwal, S. et al. Wide variation in tibial slopes and trochlear angles in the arthritic knee: a CT evaluation of 4116 pre-operative knees. Knee Surg Sports Traumatol Arthrosc (2021). https://doi.org/10.1007/s00167-021-06725-2
- Kinematic alignment
- Mechanical alignment
- Total knee arthroplasty
- Total knee replacement
- Posterior tibial slope
- Trochlear angles
- Alignment strategies