Abstract
Purpose
The undulating pattern of the distal femur is well recognized. Radiographs do not always represent the full extent of the undulations. With recent increasing use of guided growth technique in the distal femur, it is important to define safe zones for screw placement.
Method
We performed an anatomical study on 26 cadaveric distal femoral epiphyses, ages 3–18 years. High resolution three-dimensional surface scans were obtained with a laser scanner, and were analyzed to determine the absolute height of the central physeal ridge, and the central physeal ridge height with respect to the highest points medially and laterally.
Results
The average height of the central physeal ridge was 5.5mm (range 2.9–9.8mm) with respect to the lowest point on the physis. When normalized to the size of the physis, both the height and surface area of the central physeal ridge decreased with increasing age. The amount that the central peak protruded superior to a line from the medial to lateral physeal edges is shown. In all specimens ages 13 years and older the central peak was below the medial-lateral line, in specimens ages 8–12 years it was no more than 4mm above the line, and in specimens under 8 years it was no more than 8mm above the line.
Conclusion
The central physeal ridge is the major structure within the distal femoral physis. In patients 13 years and older the medial-lateral physeal line defines a safe zone one should stay above to avoid screw penetration into the central physis. In patients ages 8–12 years one should stay 4mm above the medial-lateral line, and in patients 8 years and under one should stay 8mm above the line.
