Impact of the patella height on the strain pattern of the medial patellofemoral ligament after reconstruction: a computer model-based study.
OBJECTIVE
Medial patellofemoral ligament (MPFL) reconstruction is a key procedure for treating patellofemoral instability. However, controversy exists regarding the correct graft placement in different patellar heights. Therefore, our study aimed to investigate the influence of patellar height on MPFL insertion points.


METHODS
Strain patterns of the reconstructed MPFL were calculated using a dynamic musculoskeletal multibody simulation. Numerous patellar (proximal, central, distal) and femoral attachment sites (around the radiological point according to Schöttle) were analysed in the presence of different patella heights [Insall-Salvati (IS) indices 0.74, 1.0, 1.5] during dynamic knee flexion from 0° to 120°.


RESULTS
The reconstructed MPFL showed an almost isometric behaviour at the anatomic insertion (IS 1.0). Slight variation (<5 mm) around the ideal femoral insertion point resulted in only small changes in MPFL tension. However, a displacement of 10 mm led to a significant increase in MPFL tension, especially in the more anteriorly/proximally located femoral attachment points. Depending on the patella height, there exists an area of absolute isometry of the MPFL (length change <3 %) on the femoral condyle, which did not necessarily coincide exactly with the radiological point, but was located within a radius of 5 mm around it.


CONCLUSIONS
When reconstructed in the radiological femoral insertion point, MPFL strain patterns were only slightly affected by different patella heights (IS 0.74-1.5) suggesting that MPFL reconstruction could be safely performed using the radiological insertion. However, in case of a patella alta (IS 1.5), a slightly more proximal femoral insertion is beneficial for the biomechanical behaviour of the reconstructed MPFL.
Department of Orthopaedics, University of Rostock, Doberaner Strasse 142, 18057, Rostock, Germany. thomas.tischer@med.uni-rostock.de.
Thomas
http://orcid.org/0000-0002-3942-0235
T
Tischer
Department of Orthopaedics, University of Rostock, Doberaner Strasse 142, 18057, Rostock, Germany.
Andreas
A
Geier
Department of Orthopaedics, University of Rostock, Doberaner Strasse 142, 18057, Rostock, Germany.
Robert
R
Lenz
Chair of Technical Dynamics, University of Rostock, Rostock, Germany.
Christoph
C
Woernle
Department of Orthopaedics, University of Rostock, Doberaner Strasse 142, 18057, Rostock, Germany.
Rainer
R
Bader
D003201:Computers; D006801:Humans; D008023:Ligaments, Articular / Q000601:surgery*; D008297:Male; D008953:Models, Anatomic; D010329:Patella / Q000033:anatomy & histology*; D031222:Patellar Dislocation / Q000601:surgery; D057071:Patellofemoral Joint / Q000502:physiology* / Q000601:surgery*; D019651:Plastic Surgery Procedures
Biomechanics; Insertion point; Medial patellofemoral ligament; Patella height; Patella kinematics