title: Does patellofemoral geometry in TKA affect patellar position in mid-flexion?
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Comparative study, Level III.
authors.affiliation: Accelerate Innovation Management SA, 1 Rue de la Navigation, 1201, Geneva, Switzerland, saffarini@icloud.com.
authors.forename: Mo
authors.initials: M
authors.lastname: Saffarini
authors.forename: Stefano
authors.initials: S
authors.lastname: Zaffagnini
authors.forename: Simone
authors.initials: S
authors.lastname: Bignozzi
authors.forename: Francesca
authors.initials: F
authors.lastname: Colle
authors.forename: Maurilio
authors.initials: M
authors.lastname: Marcacci
authors.forename: David
authors.initials: D
authors.lastname: Dejour
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery; D010329:Patella / Q000503:physiopathology* / Q000601:surgery; D017847:Patellar Ligament / Q000502:physiology; D011474:Prosthesis Design; D011897:Random Allocation; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D025321:Surgery, Computer-Assisted