Surgeons have many options when facing a femoral revision. Although proximal ingrowth and impaction grafting are appealing because they maintain or even restore bone stock, they have limitations. Proximal ingrowth requires bone stock present in the proximal femur that is strong enough to support body weight. Impaction grafting requires an intact tube of femoral bone that can hold the allograft and femoral component. In contrast, distal fixation devices can be used for a wide array of revision cases. Distal fixation is in essence an extensile technique in much the same sense that we think of different surgical approaches as extensile. The success of the technique is dependent on having an accessible 4 to 6 cm of healthy cortical bone that can be prepared for a distally fixed stem. If a fracture or a perforation occurs, the technique is just extended to a more distal segment of cortical bone by using a longer stem. Other than a longer stem, additional implants or allografts are rarely needed. It is this extensile nature of distal fixation that allows surgeons to use the same technique for routine revisions, for complex revisions, and when intraoperative complications occur.
The classic publications from multiple centers document the success in a wide range of cases. Lawrence and Engh reported on 81 patients at a mean follow-up of 9 years. There was a femoral rerevision rate of 10% and a mechanical loosening rate of 11%. Moreland and Bernstein published even better results in 175 patients at a mean follow-up of 5 years. The femoral rerevision rate and the mechanical loosening rate were 4% each. One of the largest consecutive series of patients treated with distal fixation involved 297 femoral revisions reported by Paprosky. At a mean of 8 years, the femoral rerevision and mechanical loosening rates were each 2%.
Although the indications are virtually any femur that has 4 to 6 cm of healthy cortical bone, the results are influenced by the extent of femoral bone loss. Paprosky was able to obtain osseointegration in 34 of 38 cases in which varying degrees of metaphyseal bone loss and little, if any, diaphyseal bone loss (type I and type II defects) were present.1 In contrast, in cases in which extensive metaphyseal bone loss and some damage of diaphyseal bone were present, osseointegration was obtained in 24 of 30 cases (type III femoral defects). In the three cases with a completely unsupported and widened diaphysis, osseointegration could not be obtained. The same author in another article had eight revisions in 69 cases with a type III defect and two revisions in eight cases with type IV defects.2 The influence of bone stock on the outcome has been corroborated in a survivorship analysis from another institution.3,4
Two additional articles have been published on cases with extensive bone loss. Engh published a report on a group of 26 hips with extensive metaphyseal and cortical bone loss.5 In this series, 190-mm or longer stems were used to bypass cortical defects that existed 10 cm or more below the lesser trochanter. The femoral aseptic loosening rate was 15% at a minimum 10-year follow-up, and 10-year femoral survivorship was 89% in this series of cases involving extensive proximal bone loss. More recently Nadaud and Griffin published a report on a group of patients who had cortical bone loss extending below the lesser trochanter.6 Of their distally fixed stems, 94% were functioning well at a mean 77-month follow-up.
Based on this review, the indications cover most femoral revision cases. Surgeons may need to consider an alternative technique when no femoral cortical bone is available for support (Paprosky type IV). In addition, the technique is contraindicated in patients with a very small femoral diameter. If the femoral canal is smaller than 10.5 mm for an 8-inch stem or smaller than 13.5 mm for a 10-inch stem, then there is a risk of stem breakage if there is no proximal bone support.
Although the applications of distal fixation cover a wide range of cases, there remain additional relative contraindications to the technique. These contraindications are not specific to distal fixation but are more general and apply to most femoral revision techniques. Patient noncompliance is a relative contraindication to cementless fixation. The ability to comply with postoperative weight-bearing restrictions is essential to obtain the results quoted. Whereas patients who undergo simple revisions may be weight bearing as tolerated, more complex procedures with extensive proximal bone loss may require protective weight bearing for up to 3 months. Therefore patients must be mentally and physically capable of following their weight-bearing precautions.
In addition to these concerns, the surgeon must ensure that patient goals are realistic. A stable bone ingrown femoral component alone does not ensure a satisfied patient. Issues of leg length and nerve and abductor function that has been compromised by previous surgeries are not always curable. Likewise, surgeons should be reticent to recommend femoral revision for unexplained thigh or hip pain.
