Copyright © 2005 by The Journal of Bone and Joint Surgery, Inc.

Commentary & Perspective

Commentary & Perspective on
"Surgical Treatment of Femoroacetabular Impingement: Evaluation of the Effect of the Size of the Resection"
by Rodrigo M. Mardones, MD, et al.

Commentary & Perspective by
Reinhold Ganz, MD*,
Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich, Switzerland

The authors hypothesize that there is a potential risk of femoral neck fracture with surgical resection of the head-neck junction in the treatment of femoroacetabular impingement. To quantify this risk, they performed mechanical tests with cadaveric proximal femoral specimens. Fifteen matched pairs were divided into three groups in which 10%, 30%, or 50% of the diameter of one femoral neck was removed; the contralateral femoral neck served as an intact control. They compared peak load, stiffness, and energy to fracture among the groups.

The energy to fracture was statistically different among the 10%, 30%, or 50% resection groups. The peak load to failure in the group with 50% resection was significantly less than in the 10% or 30% resection groups. The peak load between the 10% and the 30% resections was not statistically different. The authors concluded that resection of up to 30% of the anterolateral quadrant of the head-neck junction did not significantly alter the load-bearing capacity. However 30% of neck resection decreases the amount of energy required to produce a fracture, and this amount should therefore be considered as the upper limit of resection.

Generally speaking, any article about the concept of femoroacetabular impingement as an initiator of hip pain and arthrosis is to be welcomed. However, in this manuscript, important literature on the current state of knowledge and surgical treatment is not mentioned1. Our clinical experience with trimming of the head-neck junction now encompasses more than ten years, with more than one thousand cases, and we have never experienced a case of femoral neck fracture through the area of osteochondroplasty. Therefore, the potential risk of fracture must be considered to be extremely low. This can be explained by the fact that resection of the true neck is rarely if ever performed; in most cases, the anterolateral, nonspherical extension of the head is tapered to the level of the true cortex of the neck.

A wedge-type resection like that described in this experimental model may only occur in cases with a moderate to severe slip or in neck deformity (extension or retroversion) after a healed subcapital fracture. Another potential situation in which this may occur is if treatment of both the femoral and the acetabular causes of impingement are combined through resection solely at the femoral side. This trend in treatment, in our opinion, should be avoided. In reality, one does not create a wedge resection but rather a smoothly tapered surface from the edge of the head down to the level of neck surface. The resected part of the head should be lateral to the tension trabeculi and therefore would create little important loss of strength in this area. It is likely that if the resection in the author's model was consistent with these techniques that we have used clinically, the results would show less clear difference among groups.

Nevertheless, there is interest in quantifying any induced weakness at the level of the head-neck junction. This is especially true with an apparent increase in the frequency and interest in arthroscopic treatment, as the visualization and control of the resection can be compromised. However the biomechanical approach of this study is a rather simplified protocol that deals with a rare clinical situation. There is no information on preexisting abnormalities in the cadavers, such as a pistol-grip deformity or coxa vara. In addition, only 27% of the hips were from male cadavers, whereas most of our femoral osteochondroplasties have been performed in male patients. Considering the differences that we have observed in the pathomorphology between genders, wedge resections of >10% in female hips would represent true wedge resections, whereas in the male hip, a resection of 30% may barely cut into the true neck.

In addition to the artificial nature and simplification of resection in this model, one may question whether loading of the head nearly axial to the neck is simulating the real load transmission in the hip. It is probable that the tension forces at the lateral neck are more important than the compression forces over the entire cross-section at the head-neck junction.

In summary, the test model and the applied protocol are probably not relevant to the clinical situation; therefore, this limitation should have been mentioned in the Discussion. The positive side of this paper is that it may warn of a potential problem that may become real as attempts at arthroscopic treatment of femoroacetabular impingement increase.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop. 2003;417:112-20.