The ability of medial patellofemoral ligament reconstruction to correct patellar kinematics and contact mechanics in the presence of a lateralized tibial tubercle.
BACKGROUND
Tibial tubercle (TT) transfer and medial patellofemoral ligament (MPFL) reconstruction are used after patellar dislocations. However, there is no objective evidence to guide surgical decision making, such as the ability of MPFL reconstruction to restore normal behavior in the presence of a lateralized TT.


OBJECTIVE
MPFL reconstruction will only restore joint contact mechanics and patellar kinematics for TT-trochlear groove (TG) distances up to an identifiable limit.


METHODS
Controlled laboratory study.


METHODS
Eight fresh-frozen cadaveric knees (mean TT-TG distance, 10.4 mm) were placed on a testing rig. Individual quadriceps heads and the iliotibial band were loaded with 205 N in physiological directions using a weighted pulley system. Patellofemoral contact pressures and patellar tracking were measured at 0°, 10°, 20°, 30°, 60°, and 90° of flexion using pressure-sensitive film and an optical tracking system. The MPFL attachments were marked. TT osteotomy was performed, and a metal T-plate was fixed to the anterior tibia with holes at 5-mm intervals for TT fixation. The anatomic TT position was restored after plate insertion. The TT was lateralized in 5-mm intervals up to 15 mm, with pressure and tracking measurements recorded. The MPFL was transected and all measurements repeated before and after MPFL reconstruction using a double-stranded gracilis tendon graft. Data were analyzed using repeated-measures ANOVA, Bonferroni post hoc analysis, and paired t tests.


RESULTS
MPFL transection significantly elevated lateral patellar tilt and translation and reduced mean medial contact pressures during early knee flexion. These effects increased significantly with TT lateralization. MPFL reconstruction restored patellar translation and mean medial contact pressures to the intact state when the TT was in anatomic or 5-mm lateralized positions. However, these were not restored when the TT was lateralized by 10 mm or 15 mm. Patellar tilt was restored after 5-mm TT lateralization but not after 10-mm or 15-mm lateralization.


CONCLUSIONS
Considering the mean TT-TG distance in this study (10.4 mm), findings suggest that in patients with TT-TG distances up to 15 mm, patellofemoral kinematics and contact mechanics can be restored with MPFL reconstruction. However, for TT-TG distances greater than 15 mm, more aggressive surgery such as TT transfer may be indicated.


CONCLUSIONS
This provides guidance to surgeons as to the threshold at which MPFL reconstruction may satisfactorily restore patellofemoral mechanics, beyond which more invasive surgery such as TT transfer may be indicated.
Mechanical Engineering Department, Imperial College London, London, UK.
Joanna M
JM
Stephen
Mechanical Engineering Department, Imperial College London, London, UK.
Alexander L
AL
Dodds
Mechanical Engineering Department, Imperial College London, London, UK Mechanical Engineering Department, Naresuan University, Phitsanulok, Thailand.
Punyawan
P
Lumpaopong
Department of Orthopaedic Surgery, Queen Elizabeth Hospital, Gateshead, UK.
Deiary
D
Kader
Fortius Clinic, London, UK.
Andy
A
Williams
Mechanical Engineering Department, Imperial College London, London, UK Musculoskeletal Surgery Group, Department of Surgery and Cancer, Charing Cross Hospital, Imperial College London, London, UK a.amis@imperial.ac.uk.
Andrew A
AA
Amis
D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D008023:Ligaments, Articular / Q000502:physiology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D010027:Osteotomy / Q000379:methods; D010329:Patella / Q000502:physiology* / Q000601:surgery; D031222:Patellar Dislocation / Q000601:surgery; D017847:Patellar Ligament / Q000502:physiology / Q000601:surgery; D057071:Patellofemoral Joint / Q000502:physiology / Q000601:surgery; D011312:Pressure; D052097:Quadriceps Muscle / Q000502:physiology / Q000601:surgery; D016059:Range of Motion, Articular / Q000502:physiology; D013710:Tendons / Q000502:physiology / Q000637:transplantation; D013977:Tibia / Q000502:physiology / Q000601:surgery
MPFL reconstruction; contact pressures; patellar instability; patellofemoral tracking; surgery; tibial tubercle–trochlear groove (TT-TG)