Insall–Salvati ratio stabilizes one year after mobile-bearing total knee arthroplasty and does not correlate with mid-to-long-term clinical outcomes

  • Yoshinori IshiiEmail author
  • Hideo Noguchi
  • Junko Sato
  • Hana Ishii
  • Nobukazu Ezawa
  • Shin-ichi Toyabe



It has not been established whether changes in the length of the patellar tendon (LPT) after total knee arthroplasty (TKA) affect clinical outcomes. Therefore, this prospective cohort study aimed to evaluate changes in the LPT over time postoperatively and clarify their impact on clinical outcomes after bilateral TKA, performed with differently designed mobile-bearing (meniscal-bearing and rotating-platform) implants on contralateral knees.


51 patients who required staged bilateral mobile-bearing TKA were recruited. LPT was evaluated by measuring the Insall–Salvati ratio (ISR) preoperatively and at 1 week, 6 months, and 1, 2, and ≥ 5 years postoperatively. Hospital for Special Surgery score and range of motion were assessed at the final follow-up.


Based on the ISR, there were no differences in the patterns of change between the two types of implant (n.s.). At the 6-month follow-up, the ISRs of both implants had significantly decreased (p = 0.002). Throughout the follow-up, the ISR was significantly lower (p < 0.001) for the meniscal-bearing knees than for the rotating-platform knees. After the 1-year follow-up, there were no further substantial changes in the ISR in either group. There was also no significant correlation between the ISR and clinical outcomes.


LPT decreased after both mobile-bearing TKAs for up to 1 year postoperatively, although the decrease was more significant for the meniscal-bearing knees than the rotating-platform knees. After 1 year postoperatively, however, these conditions had stabilized, with no further changes. Thus, LPT plays a minimal role in mid-to-long-term clinical outcomes after TKA.

Level of evidence

Therapeutic prospective study, Level II.


Mobile-bearing TKA Patellar tendon length Insall–Salvati ratio Hospital for Special Surgery score Range of motion 



We thank Nancy Schatken, BS, MT (ASCP), from Edanz Group (, for editing a draft of this manuscript.


No external funding was used.

Compliance with ethical standards

Conflict of interest

All authors declare that they have no conflicts of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.


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Copyright information

© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2018

Authors and Affiliations

  • Yoshinori Ishii
    • 1
    Email author
  • Hideo Noguchi
    • 1
  • Junko Sato
    • 1
  • Hana Ishii
    • 2
  • Nobukazu Ezawa
    • 1
  • Shin-ichi Toyabe
    • 3
  1. 1.Ishii Orthopaedic and Rehabilitation ClinicGyodaJapan
  2. 2.Kouseiren Takaoka HospitalToyamaJapan
  3. 3.Niigata University Crisis Management Office, Niigata University Graduate School of Medical and Dental SciencesNiigata University HospitalNiigataJapan

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