Mechanically aligned total knee arthroplasty carries a risk of bony gap changes and flexion–extension axis displacement



The flexion–extension axis (FEA) of the femur is substantially changed after mechanically aligned total knee arthroplasty (TKA) due to a discrepancy in bone cut thickness between the posterior and distal femoral regions. This study assessed the bony gap changes and FEA displacement caused by this problem in osteoarthritis patients.


The study enrolled 60 knees from 60 patients for whom primary TKA was planned due to medial knee osteoarthritis. All patients underwent computed tomography, and 3-dimensional (3D) bone models were reconstructed on 3D-planning software. Bone cuts of the distal femur and proximal tibia were simulated to be perpendicular to each mechanical axis. Bony gap change was computed as the difference in bone cut thickness between medial and lateral compartments. Each femoral condyle was assessed for potential FEA displacement, as the difference in bone cut thickness between posterior and distal femoral regions.


The mean magnitude of bony gap discrepancy necessary for mediolateral balancing was 1.6 ± 3.3 mm (range −7 to 8.2 mm) at 0° extension and −0.2 ± 2.6 mm (range −6.4 to 4.3 mm) at 90° flexion. At least 2 mm of bony gap discrepancy at 0° extension and 90° flexion was found in 40 patients (67%) and 26 patients (43%), respectively. In terms of femoral bone cut, posterior bone cut thickness was significantly larger than distal bone cut thickness in the medial compartment (p < 0.001). Bony gap discrepancy between distal and posterior regions of the femoral condyle was ≥2 mm in 28 patients (47%).


This study focused on two flaws of mechanically aligned TKA in OA patients. Substantial numbers of patients inevitably required >2 mm of medial collateral ligament release at 0° extension and showed a bone cut discrepancy between distal and posterior regions, carrying a risk of FEA displacement and subsequent unnatural knee motions during knee extension and flexion.

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  1. 1.

    Bellemans J, Colyn W, Vandenneucker H, Victor J (2012) The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res 470:45–53

    Article  PubMed  Google Scholar 

  2. 2.

    Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, Faris GW, Davis KE (2004) Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res 428:26–34

    Article  Google Scholar 

  3. 3.

    Chauhan SK, Clark GW, Lloyd S, Scott RG, Breidahl W, Sikorski JM (2004) Computer-assisted total knee replacement. A controlled cadaver study using a multi-parameter quantitative CT assessment of alignment (the Perth CT Protocol). J Bone Joint Surg 86B:818–823

    Article  Google Scholar 

  4. 4.

    Choong PF, Dowsey MM, Stoney JD (2009) Does accurate anatomic alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty 24:560–569

    Article  PubMed  Google Scholar 

  5. 5.

    Churchill DL, Incavo SJ, Johnson CC, Beynnon BD (1998) The transepicondylar axis approximates the optimal flexion axis of the knee. Clin Orthop Relat Res 356:111–118

    Article  Google Scholar 

  6. 6.

    Colle F, Lopomo N, Bruni D, Visani A, Iacono F, Zaffagnini S, Marcacci M (2014) Analysis of knee functional flexion axis in navigated TKA: identification and repeatability before and after implant positioning. Knee Surg Sports Traumatol Arthrosc 22:694–702

    Article  PubMed  Google Scholar 

  7. 7.

    Dossett HG, Estrada NA, Swartz GJ, LeFevre GW, Kwasman BG (2014) A randomised controlled trial of kinematically and mechanically aligned total knee replacements: two-year clinical results. Bone Joint J 96B:907–913

    Article  Google Scholar 

  8. 8.

    Eckhoff DG, Bach JM, Spitzer VM, Reinig KD, Bagur MM, Baldini TH, Flannery NM (2005) Three-dimensional mechanics, kinematics, and morphology of the knee viewed in virtual reality. J Bone Joint Surg Am 87(Suppl 2):71–80

    PubMed  Google Scholar 

  9. 9.

    Fang DM, Ritter MA, Davis KE (2009) Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty 24(6 Suppl):39–43

    Article  PubMed  Google Scholar 

  10. 10.

    Gu Y, Roth JD, Howell SM, Hull ML (2014) How frequently do four methods for mechanically aligning a total knee arthroplasty cause collateral ligament imbalance and Change Alignment from Normal in White Patients? AAOS Exhibit Selection. J Bone Joint Surg Am 96:e101

    Article  PubMed  Google Scholar 

  11. 11.

    Howell SM, Papadopoulos S, Kuznik KT, Hull ML (2013) Accurate alignment and high function after kinematically aligned TKA performed with generic instruments. Knee Surg Sports Traumatol Arthrosc 21:2271–2280

    Article  PubMed  Google Scholar 

  12. 12.

    Hungerford DS, Kenna RV, Krackow KA (1982) The porous-coated anatomic total knee. Orthop Clin North Am 13:103–122

    CAS  PubMed  Google Scholar 

  13. 13.

    Iacono F, Bruni D, Bignozzi S, Colle F, Marcacci M (2014) Does total knee arthroplasty modify flexion axis of the knee? Knee Surg Sports Traumatol Arthrosc 22:1728–1735

    CAS  Article  PubMed  Google Scholar 

  14. 14.

    Jeffery RS, Morris RW, Denham RA (1991) Coronal alignment after total knee replacement. J Bone Joint Surg Br 73:709–714

    CAS  PubMed  Google Scholar 

  15. 15.

    Markolf KL, Mensch JS, Amstutz HC (1976) Stiffness and laxity of the knee—the contributions of the supporting structures. A quantitative in vitro study. J Bone Joint Surg Am 58:583–594

    CAS  Article  PubMed  Google Scholar 

  16. 16.

    Mochizuki T, Tanifuji O, Koga Y, Sato T, Kobayashi K, Nishino K, Watanabe S, Ariumi A, Fujii T, Yamagiwa H, Omori G, Endo N (2016) Sex differences in femoral deformity determined using three-dimensional assessment for osteoarthritic knees. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-016-4166-2

    Google Scholar 

  17. 17.

    Mullaji AB, Sharma A, Marawar S, Kanna R (2009) Quantification of effect of sequential posteromedial release on flexion and extension gaps: a computer-assisted study in cadaveric knees. J Arthroplasty 24:795–805

    Article  PubMed  Google Scholar 

  18. 18.

    Nakano N, Matsumoto T, Hashimura M, Takayama K, Ishida K, Araki D, Matsushita T, Kuroda R, Kurosaka M (2016) Coronal lower limb alignment in normal knees-a radiographic analysis of 797 normal knee subjects. Knee 23:209–213

    Article  PubMed  Google Scholar 

  19. 19.

    Nielsen S, Kromann-Andersen C, Rasmussen O, Andersen K (1984) Instability of cadaver knees after transection of capsule and ligaments. Acta Orthop Scand 55:30–34

    CAS  Article  PubMed  Google Scholar 

  20. 20.

    Niki Y, Harato K, Nagai K, Suda Y, Nakamura M, Matsumoto M (2015) Effects of reduction osteotomy on gap balancing during total knee arthroplasty for severe varus deformity. J Arthroplasty 30:2116–2120

    Article  PubMed  Google Scholar 

  21. 21.

    Niki Y, Nagai K, Sassa T, Harato K, Suda Y (2016) Comparison between cylindrical axis-reference and articular surface-reference femoral bone-cut for total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-016-4251-6

    Google Scholar 

  22. 22.

    Ritter MA, Davis KE, Davis P, Farris A, Malinzak RA, Berend ME, Meding JB (2013) Preoperative malalignment increases risk of failure after total knee arthroplasty. J Bone Joint Surg Am 95:126–131

    Article  PubMed  Google Scholar 

  23. 23.

    Ritter MA, Davis KE, Meding JB, Pierson JL, Berend ME, Malinzak RA (2011) The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am 93:1588–1596

    Article  PubMed  Google Scholar 

  24. 24.

    Sharkey PF, Hozack WJ, Rothman RH, Shastri S, Jacoby SM (2002) Why are total knee arthroplasties failing today? Clin Orthop Relat Res 404:7–13

    Article  Google Scholar 

  25. 25.

    Tang WM, Zhu YH, Chiu KY (2000) Axial alignment of the lower extremity in Chinese adults. J Bone Joint Surg Am 82:1603–1608

    Article  PubMed  Google Scholar 

  26. 26.

    Tei K, Ishida K, Matsumoto T, Kubo S, Sasaki H, Shibanuma N, Akisue T, Nishida K, Kurosaka M, Kuroda R (2012) Novel image-matching software for postoperative evaluation after TKA. Orthopedics 35:e1711–e1715

    Article  PubMed  Google Scholar 

  27. 27.

    Thienpont E, Cornu O, Bellemans J, Victor J (2015) Current opinions about coronal plane alignment in total knee arthroplasty: a survey article. Acta Orthop Belg 81:471–477

    CAS  PubMed  Google Scholar 

  28. 28.

    Urabe K, Mahoney OM, Mabuchi K, Itoman M (2008) Morphologic differences of the distal femur between Caucasian and Japanese women. J Orthop Surg 16:312–315

    CAS  Article  Google Scholar 

  29. 29.

    Vanlommel L, Vanlommel J, Claes S, Bellemans J (2013) Slight undercorrection following total knee arthroplasty results in superior clinical outcomes in varus knees. Knee Surg Sports Traumatol Arthrosc 21:2325–2330

    Article  PubMed  Google Scholar 

  30. 30.

    Wang JW, Wang CJ (2002) Total knee arthroplasty for arthritis of the knee with extra articular deformity. J Bone Joint Surg Am 84:1769–1774

    Article  PubMed  Google Scholar 

  31. 31.

    Wolff AM, Hungerford DS, Pepe CL (1991) The effect of extra articular varus and valgus deformity on total knee arthroplasty. Clin Orthop Relat Res 271:35–51

    Google Scholar 

  32. 32.

    Yin L, Chen K, Guo L, Cheng L, Wang F, Yang L (2015) Identifying the functional flexion-extension axis of the knee: an in-vivo kinematics study. PLoS One 10:e0128877

    Article  PubMed  PubMed Central  Google Scholar 

  33. 33.

    Young SW, Walker ML, Bayan A, Briant-Evans T, Pavlou P, Farrington B (2016) No difference in 2-year functional outcomes using kinematic versus mechanical alignment in TKA: a randomized controlled clinical trial. Clin Orthop Relat Res. doi:10.1007/s11999-016-4844-x

    PubMed  Google Scholar 

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Corresponding author

Correspondence to Yasuo Niki.

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Conflict of interest

Niki, Y, Sassa T, Nagai K, Harato K, Kobayashi S, and Yamashita T declare that they have no conflict of interest.

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Niki, Y., Sassa, T., Nagai, K. et al. Mechanically aligned total knee arthroplasty carries a risk of bony gap changes and flexion–extension axis displacement. Knee Surg Sports Traumatol Arthrosc 25, 3452–3458 (2017).

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  • Total knee arthroplasty
  • Mechanical alignment
  • Bony gap change
  • Flexion–extension axis