Ensuring correct rotation of the femoral component is a challenging aspect of patellofemoral replacement surgery. Rotation equal to the epicondylar axis or marginally more external rotation is acceptable. Internal rotation is associated with poor outcomes. This paper comprises two studies evaluating the use of the medial malleolus as a landmark to guide rotation.
We used 100 lower-leg anteroposterior radiographs to evaluate the reliability of the medial malleolus as a landmark. Assessment was made of the angle between the tibial shaft and a line from the intramedullary rod entry site to the medial malleolus. The femoral cut was made in ten cadaver knees using the inferior tip of the medial malleolus as a landmark for rotation. Rotation of the cut relative to the anatomical epicondylar axis was assessed using CT. The study of radiographs found the position of the medial malleolus relative to the tibial axis is consistent. Using the inferior tip of the medial malleolus in the cadaver study produced a mean external rotation of 1.6° (0.1° to 3.7°) from the anatomical epicondylar axis. Using the inferior tip of the medial malleolus to guide the femoral cutting jig avoids internal rotation and introduces an acceptable amount of external rotation of the femoral component.
The authors wish to thank the staff of the Bristol University Anatomy Department and M. Snow in the Bristol Royal Infirmary radiology department. Without their enthusiasm and expertise this research would not have been possible.
This work was supported by institutional funding from the Department of Orthopaedics at the Bristol Royal Infirmary.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
- Received March 6, 2012.
- Accepted August 13, 2012.
- ©2012 British Editorial Society of Bone and Joint Surgery