The Patulous Proximal Femur

Abstract

Patients with patulous proximal femurs who have hip revision surgery can be treated with reduction osteotomies or with large ingrowth sleeves used with proximally modular stems. Three hundred nine patients had hip revision with >5-years’ follow-up (mean 8.6 years). Reduction osteotomies were performed in six patients, all of whom have done well. The overall re-revision rate of 1.7% suggests that either of these methods produces reasonable results in patients with expanded proximal femurs.

In failed total hip replacement, the proximal femur often appears expanded due to loss of metaphyseal cancellous bone. In the absence of vertical stress fractures, it is unlikely that the cortex of the proximal femur expands.

Various methods of treating the patulous proximal femur are available. One method is to ignore the proximal femur and use a distally fixed implant. Some regeneration of the proximal femur occurs by removing the toxins, but the proximal femur is stress shielded and loaded only by muscle pull, so recovery must be incomplete. Impaction grafting the femur is another method, although this method is expensive because it may require a considerable amount of bone graft and has a steep learning curve and variable reported outcomes.

With the proximally modular ingrowth S-ROM stem (DePuy Orthopaedics Inc., Warsaw, Ind), a large sleeve can be used to obtain medial and lateral contact and overhang the calcar, providing resistance to sinkage. Because a gap may persist anteriorly and posteriorly, it is intuitive to graft these areas. However, the author does not graft these areas and recovery of the proximal femur still occurs.


Figure 1: A total hip replacement was performed in this patient. The cemented stem was the largest available in the original hospital but is still small. The canal measures 21 mm distally (A). After 2 years, the stem is loose and the distal canal measures 23 mm in diameter (B).

When the proximal femur is abnormally expanded, a reduction osteotomy can be performed.¹ If only the metaphysis must be reduced, then a series of vertical cuts are made and cerclage wires are used to sequentially tighten down or close the proximal femur to a normal diameter. If the diaphysis must also be reduced in size, then a long anterior wedge of bone is removed down to the required level. The metaphysis closes easily, but the diaphysis is stiffer and requires the use of a cable plate to reduce the femoral diameter (Figures 1 and 2).


Figure 2: The distal canal has been reduced to 19 mm (A). The metaphysis could be closed by the cerclage wires. A cable plate was required to close the diaphysis (B).

For the purposes of this article, all patients with revisions treated by the author using the S-ROM stem have been examined to determine the effectiveness of the large sleeve and/or reduction osteotomy. The failure point accepted was that of the Swedish Hip Registry, ie, re-revision.

Materials and Methods

The S-ROM stem is a proximally modular stem. The distal stem is circular and canal filling and has thin, sharp 0.6-mm flutes to engage the distal endosteal cortex to provide rotational control. The technique is to obtain full distal canal fill >5 cm providing angular stability. The long stems are bowed 7° to 10° at the 200-mm level. Because a bowed stem can be inserted in only one version, a 15° anteverison twist has been given to the proximal femur, requiring lefts and rights. Porous-coated sleeves of varying geo-metries are coupled to the proximal stem by a taper lock. The sleeve can be coupled in any version with respect to the stem.

All patients treated by the author with an S-ROM stem have been followed annually when possible. If a patient has not been seen in 3 years, then attempts are made to bring him or her back for review.

Three hundred nine patients with revisions with >5-years’ follow-up were observed. In 105 patients, a primary stem was used. The mean patient age was 61, with a mean follow-up of 8.5 years. In 204 patients, a long stem was used. The mean patient age was 75, with a mean follow-up of 8.6 years. Reduction osteotomies were performed in six patients. Patients have been rated clinically using the Harris hip score² and radiologically following Gruen’s example.³

In five patients, structural allografts were performed, two of which were re-revisions. The sleeve was cemented to the allograft, and the stem/sleeve/allograft composite press fitted into the residual bone. No re-revisions have been required in this group.

Results

No patients with measurable sinkage have been noted in the primary stem group. Two patients with subsidence were present in the long-stem group. One patient subsided 5 mm but stabilized at 6 months and has remained stable. One patient subsided 2.5 cm but does not have sufficient symptoms to request revision at present. No re-revisions were required in the primary stem group, but five re-revisions were required in the long stem series with re-revision at 4, 6, and 7 years. The two patients who were revised at 7 years and required proximal femur structural allografts at re-revsion are doing well.

Harris hip scores for the primary stems were 61.6% excellent, 22.2% good, 10% fair, and 6.7% poor. In the long-stem group, the Harris scores were 58.6% excellent, 18.8% good, 8.3% fair, and 14.3% poor. In the primary stem group, 88.9% showed no lucency, 10% showed low-grade lucency, and 1.1% showed high-grade lucency. In the long-stem group, 75.9% showed no lucency, 21.8% showed low-grade lucency, and 2.3% showed high-grade lucency.

Distal osteolysis occurred in only one patient. In this patient, a radiolucent line between the sleeve and the bone was present the first few years and eventually became obliterated, probably by sinkage, although this could not be measured. Sinkage <3 mm cannot be measured on clinical radiographs.

Grafting of the obvious gap between the sleeve and bone has not been performed because the proximal femur regenerates rapidly when the toxins are removed and a stable proximally off-loading stem is inserted.

The overall re-revision rate of 1.7% suggests that the use of a large sleeve and/or reduction osteotomy provides a satisfactory method of dealing with the expanded proximal femur.

Although distal fixation and impaction grafting are other possible forms of treatment, the low re-revision rate suggests that the proximally modular S-ROM stem is a useful implant in hip revision surgery.

References

Cameron HU. The Technique of Total Hip Replacement. Toronto: Mosby Year Book; 1992:378.
Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. J Bone Joint Surg Am. 1969; 51:737-755.
Gruen TA, McNeice GM, Amstutz HC. "Modes of failure" of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop Relat Res. 1979; 141:17-27.

Author

Dr Cameron is from The Orthopedics and Arthritic Institute of Sunnybrook and Women’s College Health Sciences Centre and The University of Toronto, Toronto, Canada.