Background

The purpose of this study was to investigate the effect of notching depth of the femoral neck on the compressive load required to cause a femoral neck fracture.

Methods

Thirty 4th generation composite femurs, with an alpha angle of 61°, were divided into 5 groups: 1) intact, 2) resection of the femoral head-neck junction, reducing the alpha angle to 45°, 3) as in group 2 with 2 mm notching depth achieved with a 5.5 mm diameter spherical burr 4) as in group 2 with 4 mm notching depth, 5) as in group 2 with 6 mm notching depth. The specimens were loaded in the position of mid-stance during gait and tested until failure using a dynamic tensile testing machine with loading applied under displacement control at a rate of 6 mm/min.

Results

The energy absorption and ultimate load to failure required to fracture the femoral neck was significantly lower between specimens with 4 mm notching and specimens with 6 mm notching versus the intact state (p < 0.05). For both metrics, there was also a significant difference between specimens with 6 mm notching and a cam resection alone (p<0.05). In the deeper notching groups, the fracture line occurred more lateral as compared to groups without notching, propagating through the notch in 50% (3/6) and 83% (5/6) specimens in the 4 mm and 6 mm groups, respectively.

Conclusion

Notching of the femoral neck influences a change in fracture pattern as compared to the intact state. Notching depths of 4 and 6 mm have a significant impact on ultimate load to failure and energy absorption as compared to the intact state.

Clinical Relevance:
Our results indicate that notching of the femoral neck during an arthroscopic cam resection while treating FAI can lead to an increased risk of a femoral neck fracture. If notching occurs during arthroscopy, extra post-operative precaution should be considered to avoid excessive forces on the weakened bone structure with prolonged limited weightbearing.