To the Editor:

Thank you for your insightful comments regarding the contributing factors to femoral neck fracture in resurfacing arthroplasty. We acknowledge that disruption of the blood supply to the femoral head would be one possible means of initiating a process of osteonecrosis which may, in turn, contribute to neck fracture, particularly following trauma and, in fact, we believe that in one of our reported cases this occurred. The low incidence of avascular necrosis in failed resurfaced femoral heads inserted through the posterior approach (3 out of 25 in our series to date), as judged by histological examination of retrievals, does not appear to support devascularization as an inevitable consequence of that approach. Those 3 cases had atypically much deeper penetration of cement into the trabecular bone, but we cannot be sure if this, or vessel damage, caused the avascular necrosis. Similarly, we previously reported only 3 of 25 failed resurfacings from an earlier generation resurfacing had any evidence of necrotic bone (2 with a pre-operative diagnosis of AVN and 1 with a previous resurfacing that was revised) (1) and none appeared to be the cause of loosening Rarely, avascular necrosis leading to femoral neck fracture has been observed after resurfacing with the anterior approach. (2,3)

Freeman (4) reported that an intraosseous blood supply is predominant in arthritic femoral heads, which makes the contribution of the retinacular vessels less important. The anatomic area where the retinacular vessels enter the femoral head described in anatomy books or the paper you quote by Gautier et al (5) is generally altered and obscured by the osteophytic process. I routinely remove the posterior-superior osteophytes (not those present anteriorly) and the soft tissue at the head/neck junction in order to make certain that all available bone is optimally prepared for acrylic cementation. I have often observed tiny holes devoid of any vessels presumably the entry points of those former vessels. Probably the best evidence for head viability is that the bone surfaces bleed, often quite vigorously after bone preparation for resurfacing. It is my belief that osteoarthritic process is accompanied by diaphyseal neovasculature which, even though some may be destroyed by reaming, appears to be ample to keep the head viable.

It was, and remains, a common misconception that femoral failure and resorption of bone after cup arthroplasty and resurfacing with metal- polyethylene bearings was due to surgically induced osteonecrosis. From our histologic observations, the resorption process has always been accompanied by vascularity.

If a surgeon performs resurfacing on a hip with minimal evidence of osteoarthritis then the surgeon should be aware of those retinacular vessels and avoid notching the neck where there may be subchondral vessels.

Harlan C Amstutz, MD, Joint Replacement Institute, Orthopaedic Hospital, Los Angeles

1. Campbell P, Mirra J, Amstutz HC. Viability of femoral heads treated with resurfacing arthroplasty. J. Arthroplasty.2000;15:120-122.

2. Howie DW, Cornish BL, Vernon-Roberts B. The viability of the femoral head after resurfacing hip arthroplasty in humans. Clin. Orthop.1993;171- 184.

3. Bell RS, Schatzker J, Fornasier VL, Goodman SB. A study of implant failure in the Wagner resurfacing arthroplasty. J. Bone and Joint Surg.1985;67A:1165-1175.

4. Freeman MA. Some anatomical and mechanical considerations relevant to the surface replacement of the femoral head. Clin. Orthop.1978;19-24.

5. Gautier E, Ganz K, Krugel N, Gill T, Ganz R. Anatomy of the medial femoral circumflex artery and its surgical implications. J. Bone and Joint Surg.2000;82:679-683.

To the Editor:

The article published by Amstutz et al.(1) reporting on the fracture of the femoral neck after resurfacing arthroplasty in five patients highlights an important point. Fracture of the femoral neck after resurfacing arthroplasty is a recognized and feared complication. Dr Amstutz, with extensive experience in resurfacing arthroplasty, and his coauthors attribute this complication mostly to structural and/or technical factors. Although no one will dispute the author’s conclusion in that technical errors can lead to such complication after resurfacing arthroplasty, I would urge the authors to consider an additional possibility.

A detailed cadaveric study has described the vascular anatomy around femoral neck. (2) That study observed that the critical branch of the medial femoral circumflex artery lies under the protection of obturator externus. The retinacular vessels supplying blood to the femoral head penetrate the neck at the posterosuperior region, an area that is usually rife with osteophytes. One therefore wonders if it is possible that the blood supply to the femoral head, with an already tenuous circulation, is compromised further during posterior approach to the hip or during aggressive capsulotomy or osteophyte resection. This in turn might initiate or propagate the process of osteonecrosis of the femoral head resulting in biomechanically weak pillar of bone supporting the resurfacing component.

Although fracture of the femoral neck in experienced hands is very low (0.8% in this series),I wonder if the osteonecrosis of the femoral head observed in one of their patients may have occurred as a result of disruption of the blood supply to the femoral head and erroneously attributed to excessive cement penetration.

1. Amstutz HC, Campbell PA, Le Duff MJ. Fracture of the neck of the femur after surface arthroplasty of the hip. J Bone Joint Surg Am. 2004 Sep;86-A(9):1874-7.

2. Gautier E, Ganz K, Krugel N, Gill T, Ganz R. Anatomy of the medial femoral circumflex artery and its surgical implications. J Bone Joint Surg Br. 2000 Jul;82(5):679-83.