A key part of kinematic alignment (KA) and functional alignment (FA) is to restore the natural femoral joint line, in particular the medial joint line. KA is known to reproduce the femoral joint line accurately; however, direct comparisons with other surgical techniques such as FA are currently lacking. The purpose of this study was to evaluate differences of alignment parameters in KA and FA techniques with a special focus given to the femoral joint line.
We performed a retrospective radiological analysis of pre- and postoperative long leg radiographs of 221 consecutive patients with varus or neutral leg alignment, who underwent primary total knee arthroplasty (TKA) procedures from 2018 to 2020. Patients were assigned to one of four groups: (1) FA: image-based robotic-assisted TKA, (2) FA: imageless robotic-assisted TKA, (3): restricted KA: 3D cutting block-assisted (patient-specific instruments, PSI) TKA, (4): unrestricted KA: calipered technique. Patients’ radiographs were (re)-analyzed for overall limb alignment, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), as well as medial and lateral femoral joint line alteration. Statistical significance was determined using unpaired t testing (FA vs. KA group) and one-way ANOVA (subgroup analyses).
Comparisons of KA vs. FA, as well as individual subgroups of KA and FA did not show any differences in the accuracy of medial joint line reconstruction (< 2 mm, p = 0.384, p = 0.744, respectively) and LDFA alteration (< 2°, p = 0.997, 0.921, respectively). Correction of MPTA (3.4° vs. 2.2°) and lateral femoral joint line (2.1 mm vs. 1.5 mm) was higher for FA and FA subgroups compared to KA and KA subgroups (both p < 0.001).
Kinematic and functional alignments showed a comparable accuracy in reconstruction of the medial femoral joint line and femoral joint line orientation. Increased correction of MPTA and lateral femoral joint line was recorded with FA techniques.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
Arithmetic hip-to-knee angle
Adductor tubercle joint line distance
Joint line obliquity
Lateral distal femoral angle
Lateral femoral joint line
Medial femoral joint line
Medial proximal tibial angle
Overall limb alignment
Robotic-assisted total knee arthroplasty
Total knee arthroplasty
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We thank Felix KF Kommoss for English language editing of the current manuscript.
This research received no external funding.
Conflict of interest
LT, PS, ME and HW are paid educational consultants for Stryker. LT, PS and ME are paid educational consultants for Smith & Nephew. HW is a paid consultant for Medacta. No funding was received for this study. MZ and DJ have no conflict of interest.
This study was approved by the local ethics committee (8403_BO_S_2019).
Informed consent was not needed due to the use of only anonymized data (radiographs) in this retrospective study.
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Tuecking, LR., Savov, P., Zander, M. et al. Comparable accuracy of femoral joint line reconstruction in different kinematic and functional alignment techniques. Knee Surg Sports Traumatol Arthrosc (2023). https://doi.org/10.1007/s00167-023-07360-9
- Kinematic alignment
- Functional alignment
- Robotic TKA
- Unrestricted KA
- Joint line
- Total knee arthroplasty