Does patellofemoral geometry in TKA affect patellar position in mid-flexion?

Mo Saffarini, Stefano Zaffagnini, Simone Bignozzi, Francesca Colle, Maurilio Marcacci, David Dejour

Research output: Contribution to journalArticlepeer-review


Purpose: This study aimed to compare the position of the patella at 90° of flexion before and after implantation of two TKA models with identical tibiofemoral geometry but different trochlear and patellar designs. The hypothesis was that the design with the deeper ‘anatomic’ trochlea could produce more natural patellar positions. Methods: Intra-operative navigation data were collected from 22 consecutive cases that received two TKA designs (9 HLS Noetos® and 13 HLS KneeTec®). Both implants were cemented postero-stabilised TKAs with mobile tibial inserts and patellar resurfacing. Operations were guided by a non-image-based system that recorded relative femoral, tibial and patellar positions pre- and post-operatively. Results: The two groups exhibited little difference in femoral internal–external rotation and anterior–posterior translation during knee flexion. The two groups exhibited significant differences in patellar position at 90° of flexion. Post-operatively, the patella was similarly shifted medially relative to the femur (Noetos 6.9 mm, KneeTec 6.0 mm, n.s.). Patellar flexion was equivalent in native knees (Noetos 18.3°, KneeTec 20.5°, n.s.), but in implanted knees, it was considerably different (Noetos 6.3°, KneeTec 23.5°, p = 0.031). Conclusions: The present study compared intra-operative navigation data from two patient series that received TKA implants with identical tibiofemoral articular geometry but different patellofemoral designs. The results confirm that tibiofemoral kinematics are unchanged, but that patellar positions at 90° of flexion offer greater mechanical advantage to the quadriceps using the KneeTec than using the Noetos. The findings raise awareness of influence of patellofemoral geometry on mid-flexion kinematics and help surgeons select the most suitable implant for patients with weak quadriceps muscles or with history of patellar instability. Level of evidence: Comparative study, Level III.

Original languageEnglish
Article number3565
Pages (from-to)1799-1807
Number of pages9
JournalKnee Surgery, Sports Traumatology, Arthroscopy
Issue number6
Publication statusPublished - Mar 13 2015


  • Component design
  • Femoral trochlea
  • Patellar height
  • Patellar kinematics
  • Patellar tendon angle
  • Postero-stabilised knee
  • Total knee arthroplasty

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Surgery
  • Medicine(all)


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