2015 ISAKOS Biennial Congress ePoster #1924
How Does Patellofemoral Arthroplasty (PFA) Alter Trochlea Anatomy? A Comparison of 5 Commercially Available Systems
Rael Salkinder, MBChB, FC Orth (SA),, Cape Town, Western Cape SOUTH AFRICA
Kyung-Jin Cho, MSc, Stellenbosch, Western Cape SOUTH AFRICA
Pieter J. Erasmus, MBChB, MMed, FCS(Orth), Stellenbosch, Western Cape SOUTH AFRICA
University of Stellenbosch, Stellenbosch, Western Cape, SOUTH AFRICA
FDA Status Not Applicable
Summary: A wide discrepancy in trochlea geometry among different PFA's with none recreating normal anatomy
Abstract:
Introduction
The results of PFA compare inferiorly to that of TKR. Implant design is considered one of the critical factors in order to recreate a functional articulation and in turn allow for a successful outcome. We have noticed a wide variation in geometry of the commercially available trochlea components. In order to define these differences as well as ascertain whether the normal trochlea parameters were recreated with a PFA, we virtually implanted 5 off-the-shelf PFA’s in two 3D reconstructed knees.
Method
We 3D reconstructed two trochleas from full lower limb CT’s and knee MRI images of a normal trochlea and a dysplastic trochlea (Dejour Type D). Five commercially available PFA’s were implanted in these models taking care to ensure that they were anatomically aligned with no overhang, placed at the level of the anterior femoral cortex, and inserted with a smooth prosthesis-articular-cartilage transition.
The following static parameters were measured: AP height as a ratio to the medial-lateral width and trochlea groove alignment. The following parameters were measured at 0°, 15°, 30°, 45°, 60° and 75° flexion: radius of curvature, trochlear depth, sulcus angle, lateral trochlear inclination (LTI), trochlea facet asymmetry (TFA), and lateral and medial AP height.
Results
There was a wide variation in the measured parameters between the tested implants. None restored the trochlea to normal geometry in the normal or dysplastic models. Trochlea groove alignment was altered post PFA from varus and internal rotation in relation to the coronal and axial planes respectively, to that of valgus and external rotation. There was a wide variation in trochlea groove orientation among the different implants. Only one prosthesis maintained the preoperative trochlea groove in relation to the mechanical and anatomical axes. There was a trend towards increasing the medial AP: ML ratio while decreasing the lateral AP: ML ratio in both the normal and dysplastic knees; normal ratios were altered to abnormal values in the non-dysplastic knee. After PFA in the normal knee, the sulcus angle was altered to lie within the dysplastic range in 2 of the prostheses. The sulcus angle was not normalized post replacement in 3 prostheses in the dysplastic knee.
Discussion
A possible explanation for the wide discrepancy in the trochlea geometry among the implants could be that the designs are based on widely different values, which are all considered normal in the literature. Our results, suggest that there is no common ground among the various designs to produce patellofemoral implants according to set standards. Further concern is that some of the implants created a dysplastic type trochlea in the non-dysplastic knees and failed to restore the dysplastic trochlea’s, in the abnormal knees, to accepted normal values
Conclusion
We suggest that in future attention needs to be given to reach a consensus on prosthesis design. With such a wide variation in the patellofemoral joint morphology in the population as well as with current advanced computer technology, it may be more appropriate to create patient specific type patellofemoral implants based on the suggested reached consensus.