title: The influence of medial patellofemoral ligament on patellofemoral joint kinematics and patellar stability.
abstract: OBJECTIVE
  Retinacular restraints have a critical role in patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is probably the main stabilizer against lateral displacement; few studies are focused on MPFL role on patellofemoral kinematics and patellar stability. The main goal of this in vitro study was to analyse the influence of the MPFL on the kinematics of the patellofemoral joint and patellar stability.
  
  
  METHODS
  Using a non-image-based navigation system, kinematics and anatomical data of six fresh-frozen specimens were collected. A passive flexion-extension from 0° to 90° and static acquisitions at 0°, 30°, 60° and 90°, with and without 25 N of lateral load, were performed with intact and resected MPFL with a 60 N axial force applied to the isolated quadriceps tendon. Patellar tilt and shift were analysed.
  
  
  RESULTS
  The MPFL intact state showed a shift in medial direction during the first degrees of knee flexion-that disappeared in MPFL resected condition-followed by a lateral shift, similar to that of MPFL resected condition. Tilt analysis showed that patella rotated laterally until 85° of knee flexion for intact MPFL condition and until 70° for resected MPFL condition and after rotated medially. Static tests showed that patellar stability was significantly affected by MPFL resected condition in particular at 30° and 60°.
  
  
  CONCLUSIONS
  The MPFL has an aponeurotic nature. It works as a restraint during motion, with an active role under high stress on lateral side, but with a small contribution during neutral knee flexion. Its biomechanical behaviour under loading conditions should be kept into account when performing surgical reconstruction of this ligamentous structure.
authors.affiliation: Laboratorio di Biomeccanica ed Innovazione Tecnologica, Istituto Ortopedico Rizzoli, via di Barbiano, 1/10, 40136, Bologna, Italy. s.zaffagnini@biomec.ior.it
authors.forename: Stefano
authors.initials: S
authors.lastname: Zaffagnini
authors.forename: Francesca
authors.initials: F
authors.lastname: Colle
authors.forename: Nicola
authors.initials: N
authors.lastname: Lopomo
authors.forename: Bharat
authors.initials: B
authors.lastname: Sharma
authors.forename: Simone
authors.initials: S
authors.lastname: Bignozzi
authors.forename: David
authors.initials: D
authors.lastname: Dejour
authors.forename: Maurilio
authors.initials: M
authors.lastname: Marcacci
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005269:Femur / Q000033:anatomy & histology; D006801:Humans; D066298:In Vitro Techniques; D007593:Joint Instability / Q000503:physiopathology; D007719:Knee Joint / Q000502:physiology* / Q000503:physiopathology; D008297:Male; D017888:Medial Collateral Ligament, Knee / Q000502:physiology*; D008875:Middle Aged; D010329:Patella / Q000033:anatomy & histology; D017847:Patellar Ligament / Q000502:physiology*; D013977:Tibia / Q000033:anatomy & histology