2015 ISAKOS Biennial Congress ePoster #1918

Orientation of The Trochlear Groove

Pieter J. Erasmus, MBChB, MMed, FCS(Orth), Stellenbosch, Western Cape SOUTH AFRICA
University of Stellenbosch, Stellenbosch, Western, SOUTH AFRICA

FDA Status Not Applicable

Summary: There is a wide variation in the orientation of the trochlear groove among iindividuals and PFR prosthessis




We believe that the correct trochlear groove alignment is important when performing a patellofemoral replacement as it affects the tracking of the patella and soft tissue balance. Looking at the trochlear groove angle in five commercially available PFR’s we found that the angle varied from 0° to 13° valgus. This wide inbuilt variation in the groove alignment is further influenced by the rotational orientation of the anterior femoral cut and distal fit of the prosthesis to allow a smooth prosthesis-articular-cartilage transition. When performing a PFR, only the distal femur is visualized. Our aim was to develop a simple accurate way of measuring the groove orientation using the distal femur as reference for planning and intra operative orientation


3D reconstructions were done on 36 femurs in people with asymptomatic knees. Twenty had at least one sign of trochlear dysplasia.
The posterior condylar line and distal condylar line were used as axial and coronal reference planes. The distal border of the groove was defined as the deepest point on a coronal view, the proximal border as the highest point on the lateral condyle on an axial view. Nine axial cuts were performed, parallel to the distal condylar plane and between the defined borders. From these slices the groove line could be determined in both axial and coronal planes.
The coronal groove angle was defined as the angle between the groove line and a line perpendicular to the distal condylar line. The axial groove angle was defined as the angle between the groove line and a line perpendicular to the posterior condylar line. The angle between the groove line and the anatomical axis was also measured to define the coronal orientation.
The difference in the orientation of the groove line in normal trochlea and those with at least one sign of dysplasia was also evaluated.


The mean coronal groove angle was 5.9°valgus (Range: 12.6° varus to 13.3° valgus). The mean axial groove angle was 4.3° external rotation to the posterior condylar line (Range: 8.4° internal rotation to 10.6° external rotation). There was a better correlation between our coronal groove line angle and the anatomical axis than between the groove line angle and the mechanical axis. In dysplastic trochleas the groove was in less valgus and external rotation compared to normal trochleas


The fact that there is a better correlation between our groove line angle and anatomical axis than with the mechanical axis might indicate that the angle is influenced by muscle action rather than mechanical factors. Changing the natural groove line angle post PFR might have a negative effect on soft tissue balance. Our study showed wide individual variation in the groove line orientation in the coronal and axial alignment. Available commercial PFR shows a similar variation in the groove line angles and we suggest that a prosthesis should be selected that has a similar trochlea groove orientation to that of the patient. Our technique can be used for preoperative planning and for correct positioning of the prosthesis intraoperatively.