Morphological variation in proximal femur anatomy and its implication in metaphyseal fit femur prosthesis in total hip arthroplasty: A dry bone study

Total hip replacement is the most common procedure done by orthopedic surgeons which restores the hip joint function. The most commonly used cementless femoral stems in primary hip arthroplasty are metaphyseal fit stems (CORAIL). We found that in certain patients the metaphyseal stem tips comes in contact with the medial cortex and valgus orientation. In this context, there might be variation in metaphyseal fit in type 2 stems, which might lead to stress shielding and thigh pain. So, we decided to do a simple measurement in dry bones and to look for this variation in the proximal femur anatomy which will help to predict preoperatively the implications of metaphyseal fit stems.

Methodology

This is a dry bone study done in the department of orthopedics, MGMCRI. In 65 femurs following measurements were done directly and digitally in PACS after obtaining a templating radiograph.

The proximal femur mediolateral shaft diameter was measured at the lower border of the lesser trochanter. Medial cortex to greater trochanter -Distance between lines drawn along the lateral most border of the greater trochanter to a vertical line drawn along the medial cortex of the femur. Lateral cortex to greater trochanter- Distance between a lines drawn along the lateral most border of greater to a vertical line drawn along the lateral cortex of the femur. The total length of the femur using the infant meter. The statistical analysis was done.

Result

Among the 65 femurs, the distance between the tips of the stem to the innermost aspect of the medial cortex was less than 50% of the canal diameter in 24 femurs; among them the distance was closest almost touching the medial cortex in nine femurs. In these femurs, the distance between the lateral cortex line to an outermost aspect of the greater trochanter was high which was significant (p value=0.045). Three of them were Dorr type I femur and six were Dorr type II.

Conclusion

Our study demonstrates a simple radiological preoperative measurement which will help in choosing an alternative to the metaphyseal fitting stems (CORAIL) in certain population with this varied anatomy. This varied anatomy we describe as proximal femur metaphyseal valgus.