Preserving the femoral neck in hip replacement: a concept for the future?

A number of new hip prostheses have shown initial success using the preserved femoral neck.

Issue: Issue 6 2004

ByHans Jürgen Refior, MD

Hans Jürgen Refior, MD [photo] ---Hans Jürgen Refior, MD

The historical development of total hip arthroplasty led to the concept that the femoral neck should be the weight-bearing structure for the implant.

Brothers Robert and Jean Judet developed a short-stemmed hemiarthroplasty in 1947, which found a wide acceptance within a short time. This implant consisted primarily of a metal stem and an acrylic head. This hemiarthroplasty was anchored in the femoral neck after resection of the femoral head. The Judet brothers performed a broad follow-up study of this prosthesis in 1952.

In the beginning, the results seemed quite successful. This had a strong influence on the development of numerous similar models by Anderson, Townley, Zanoli and others. But despite the various modifications of the “head-neck prosthesis” invented by Judet, this implant had one major defect: The lack of stability and the advanced technical development of hip prostheses led to a decreasing interest in this type of prosthesis.

A different type of hip replacement anchored in the femoral shaft following head and neck resection had a worldwide breakthrough under the influence of Moore, Charnley and others. With the increasing rate of hip replacements worldwide, the rate of complications rose. In response to this trend, Freeman, in 1986, described the advantages of preserving the femoral neck during hip replacement.

The transfer of force

Meanwhile, various authors, as well as our own biomechanical experiments, proved that forces developed under weight-bearing were transferred more homogeneously into the proximal femur when the femoral neck was preserved, as opposed to an implant that made a head and neck resection necessary. Furthermore, the rotation stability increased, and it was possible to anatomically reconstruct the femoral antetorsion by preserving the femoral neck. Another advantage was the improvement of the “second line of defense” for possible changes of the implants, which required only minor resections of the femur.

Pipino and colleagues showed a drastic reduction in muscle and soft tissue destruction and guaranteed an almost physiological offset when preserving the femoral neck. Over time, the increase in knowledge, combined with more clinical experience, led to the development of new implants that were able to preserve the femoral neck.

In this context, it is necessary to mention the thrust plate endoprosthesis designed by Huggler and Jacob, which was first implanted in 1978. This prosthesis is able to transfer the resulting force developed by the hip joint directly into the cortical bone of the femoral neck stump. The central prosthesis stem is stabilized from the lateral side with a connection rod, leading the force over a mounting link on the opposite corticalis. This link is fixed with two screws to the femur, thus neutralizing the traction force.

New results which were recently published (Ishaque et al, 2004) have shown a cumulative survival rate of 91.7% over eight years. This prosthesis seems to be an alternative implant to that used in cementless standard arthroplasty.

More implants

Another noteworthy type of implant is the CUT 2000 femoral neck endoprosthesis by ESKA Implants GmbH & Co. in Germany. This implant is fixed in the metaphysis and is supposed to guarantee a physiological proximal force transfer. The oval shape is completely formed to fit the femoral neck. The cancellous bone-metal surface structure is supposed to ensure the osseous integration. So far, the follow-up has not been long enough to fully interpret the clinical test results of the prosthesis.

On the other hand, there are more than four years of good clinical experience with the broadly propagated CFP implant by Waldemar Link in Germany. This type of femoral neck-preserving implant is a new development of the Pipino concept. The prosthesis is able to adapt to the individual anatomical needs of the patient by offering a left and right stem, different curvatures and various neck and head angles and length. This “collum femoris-preserving” stem, as it is labeled, can be combined with a special cementless acetabulum. Due to the surface structure of the stem reaching into the diaphysis of the femur, this implant enables a good osseous integration, though it is still necessary to test its long-term stability in follow-up studies.

The Mayo Conservative Prosthesis has been described as the ideal implant for young patients. The reason is that it offers a secure anchorage with its short multipoint contact stem, and it is only necessary to resect marginally in the area of the femoral neck and in the intertrochanteric region.

This implant guarantees a safe proximal transfer of force. B.F. Morrey first published details of this type of prosthesis in 1989. In a prospective study, the survival rate of the implant without mechanical loosening after five and 10 years was 98%. Due to the surface structure, the osseous integration is very stable.

A two-step option

A new concept recently emerged from Italy. F.S. Santori and colleagues recently described the “two-step-solution” prosthesis. The first step includes the implantation of a titanium stem through the cortical bone from the lateral side. After three months and the osseous integration of the stem, the second step involves resection of the femoral head and connection of a steel or ceramic head to the stem in the femoral neck.

In the first 21 patients treated with this two-step process, only one loosening was reported, according to the Italian investigators. The initial clinical results seem to be excellent, but as in the other cases, we have to wait for the long-term results.

The different concepts of implants show that there is great interest in developing new forms and types of prostheses concerning form, bone preservation and physiological force transfer into the proximal femur. However, it is not yet possible to distinguish which procedure will be a solution for the future. It has become clear, though, that only a high quality of bone structure will guarantee primary and long-term stability of the implant.

Considering the growing interest in minimally invasive techniques of hip replacement, we might want to take a closer look at femoral neck preservation. Further developments will be evaluated and overseen quite extensively in the future.

Hans Jürgen Refior, MD, of Munich, is an editor of Orthopaedics Today.