Vol.:(0123456789) 1 3 Knee Surgery, Sports Traumatology, Arthroscopy https://doi.org/10.1007/s00167-019-05417-2 KNEE Native non-osteoarthritic knees have a highly variable coronal alignment: a systematic review Lukas B. Moser 1,2  · Silvan Hess 1,3  · Felix Amsler 4  · Henrik Behrend 5  · Michael T. Hirschmann 1,2 Received: 29 December 2018 / Accepted: 13 February 2019 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2019 Abstract Purpose Coronal alignment of the knee is defned by the hip–knee–ankle angle (HKA), the femoral mechanical angle (FMA), the tibial mechanical angle (TMA), and the joint line convergence angle (JLCA). To date, there is still a lack of knowledge about the variability of native coronal knee alignment. The purpose of this paper is to present a systematic review of the current literature about the variability of coronal knee alignment (HKA, FMA, TMA, and JLCA) in non-osteoarthritic knees. Methods The electronic databases MEDLINE, EMBASE, and Google Scholar were searched from database inception to search date (November 1, 2018) and screened for relevant studies. The PRISMA guidelines were followed. Inclusion criteria were studies that reported the coronal alignment of the native, non-osteoarthritic knee. Results A total of 15 studies met the inclusion criteria. Thirteen studies performed the measurements on weight-bearing long-leg standing radiographs (LLR), one study used MRI, and one study used the EOS imaging system. The mean HKA ranged from 176.7° ± 2.8° (male) to 180.7° (female). The mean FMA ranged from 92.08° ± 1.78° (female) to 97.2° ± 2.7° (female). The mean TMA ranged from 84.6° ± 2.5° (female) to 89.6° (female). The mean JLCA ranged from − 0.47° ± 0.98° (male) to − 1.9° ± 1.4° (female). Conclusion This systematic review provides a detailed overview about the variability of the coronal knee alignment in non- osteoarthritic knees. The broad variability of all coronal alignment parameters highlights the necessity for a more anatomic and individualized approach in knee arthroplasty. It also ofers the fundament to understand the changes in osteoarthritic knees. Level of clinical evidence Systematic review, Level IV. Keywords Knee · Alignment · Anatomy · Functional knee phenotypes · Hip knee ankle angle · Femoral mechanical angle · Tibial mechanical angle · Osteoarthritis Abbreviations HKA Hip–knee–ankle angle FMA Femoral mechanical angle TMA Tibial mechanical angle JLCA Joint line convergence angle LLR Long-leg radiographs MRI Magnet resonance imaging CT Computed tomography Introduction The coronal alignment of the knee is defined by the hip–knee–ankle angle (HKA) [18], and can be measured as the angle between the mechanical axes of the femur and the tibia [4, 9]. A mean native coronal knee alignment of 180° is regarded as physiological in non-osteoarthritic knees and referred to as being neutral [2, 30]. If the HKA is larger than 180°, the knee alignment is classifed as valgus and lower than 180° as varus [3]. However, studies have shown that the mean HKA tends to be slightly in varus [2, 9, 18]. This * Lukas B. Moser lukas_b_moser@yahoo.de 1 Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laufen), 4101 Bruderholz, Switzerland 2 University of Basel, Basel, Switzerland 3 University of Bern, Bern, Switzerland 4 Amsler Consulting, Basel, Switzerland 5 Department of Orthopaedic Surgery, Kantonsspital St. Gallen, 9007 St. Gallen, Switzerland