Revision after failed femoral components may be technically demanding due to loss of peri-prosthetic bone. This retrospective study evaluated the long-term results of femoral revision using the cementless Wagner Self-Locking stem. Between 1992 and 1998, 68 consecutive hips in 66 patients underwent femoral revision using this implant. A total of 25 patients died from unrelated causes without further revision; the remaining 41 hips in 41 patients (12 men and 29 women) with a mean age of 61 years (29 to 80) were reviewed at a mean follow-up of 13.9 years (10.4 to 15.8). A transfemoral approach was used in 32 hips. A total of five stems required further revision because of infection in two, progressive subsidence in two and recurrent dislocation in one. Four hips had dislocated and eight stems had subsided ≥ 10 mm. The mean Harris hip score improved from 33 points pre-operatively to 75 points at final follow-up (p < 0.001). In all, 33 stems (91.7%) showed radiological signs of stable bone fixation. The cumulative survival rates at 15.8 years with femoral revision for any reason and for stem failure as the endpoints were 92.0% (95% confidence interval (CI) 86.0% to 98.4%) and 96.6% (95% CI 92.2% to 100%), respectively. The survivorship with revision and ≥ 10 mm migration of the stem as the endpoint was 83.6% (95% CI 76.6% to 91.4%).
This study shows quite good survival and moderate clinical outcome when using a monoblock tapered titanium stem for supporting the regeneration of bone in complex revision hip surgery.
In revision hip surgery, reconstruction in the presence of mechanically compromised femoral bone stock has been addressed by several techniques and stem designs. In this situation cemented components show high failure rates1 and impaction bone grafting is technically demanding.2 Uncemented fully porous-coated cylindrical components provide a highly successful method of femoral reconstruction,3,4 but the results are adversely affected by extensive metadiaphyseal deficiency and a widened femoral canal.5,6
Another option in uncemented revision is the use of fluted, tapered, grit-blasted femoral components.7 The flutes provide rotational stability and the tapered geometry is designed to achieve axial stability. A grit-blasted rough titanium surface promotes bone ingrowth. In 1987, Wagner8,9 developed a straight, long-stemmed femoral component that gained stability in the diaphysis, bridging bone defects in the proximal femur. Excellent spontaneous bone regeneration with early restoration of bone stock was described at mid-term follow-up.10-16 The aim of this retrospective study was to present the long-term clinical and radiological results of the cementless, distally fixed Wagner Self-Locking (SL) stem (Sulzer Orthopedics Ltd, Winterthur, Switzerland) in femoral revision surgery.
Patients and Methods
Between September 1992 and March 1998, 68 consecutive femoral revisions in 66 patients were carried out using the Wagner SL stem. A total of 25 patients (27 stems) died from unrelated causes with a well-functioning total hip replacement (THR) in place, leaving 41 patients (41 hips) available for retrospective evaluation (Table I). There were 12 men and 29 women, with a mean age at surgery of 61 years (29 to 80). The main indication for revision was symptomatic aseptic loosening in 37 hips; the remaining hips were revised for fracture of the stem in two cases, peri-prosthetic fracture in one and recurrent dislocation in one. The procedure was the first revision in 24 hips, the second revision in 16 and the third revision in one. The acetabular component was replaced simultaneously in all but two patients.
The Wagner SL revision stem, made of a biocompatible TiAlNb alloy with a rough-blasted surface, has eight longitudinal flutes along the straight tapered shaft. Cementless fixation was gained by securing the stem axially in the conically reamed intact distal femoral shaft. A 32 mm diameter cobalt-chromium head was used in all cases. The assessment of femoral bone loss was based on the pre-operative radiographs and the intra-operative findings, and was documented using the criteria of Weeden and Paprosky.5 We distinguished mostly metaphyseal damage (type 2), metadiaphyseal bone deficiency with or without the reliability of a minimum 4 cm scratch-fit (type 3A and 3B, respectively), and extensive metadiaphyseal damage that precludes distal fixation (type 4). The bone defects were classified as follows: type 2 in six hips, type 3A in 19 hips, type 3B in four hips, and type 4 in 12 hips. Femoral bone resorption was also defined using the system of Böhm and Bischel,17 which divides the femur into five parts (from 0 to 4) and characterizes the distal-most extent of bone loss and proximal-most extent at which fixation is possible. There were two type 1B femora, seven type 2A, 16 type 2B, nine type 3A and seven type 3B.
All operations were performed with the patient in the supine position, through an anterolateral approach under general anaesthesia. In 32 hips exposure was achieved using a transfemoral osteotomy, as described by Wagner.8,9 Cerclage wires were used for fixation of the osteotomy. After removal of the components and any cement and intramedullary granulomatous tissue, the femur was manually reamed and the Wagner stem implanted. Supplementary bone graft was never used. Thromboprophylaxis was undertaken using low-molecular-weight heparin until the patients were fully mobile. Antibiotic prophylaxis included intravenous vancomycin administered immediately pre-operatively and continued with 1 g twice daily for two days, plus intramuscular gentamicin sulphate 80 mg twice a day for 48 hours. Passive range of movement exercises were allowed one week after the operation, but weight-bearing was delayed for eight weeks. The patients were requested to restrict loading on the revised hip for a minimum of three months, starting with 30 kg and increasing by approximately 15 kg per week. Full weight-bearing was achieved four to six months post-operatively.
Clinical examination included grading of pain, mobility and movement of the hip according to the Harris hip score (HHS).18
Standard anteroposterior and lateral radiographs of the pelvis and the involved hip were obtained pre-operatively, immediately after surgery, at six weeks, at three, six and 12 months, and annually thereafter. Radiological assessment was performed by a single observer (IB). Despite some difficulties in interpretation, related to the design of the stem and the presence of the flutes, osseo-integration was estimated as proposed by Engh, Bobyn and Glassman.19 Fixation of the stem was graded as stable (implant with no progressive migration and minimal or no radio-opaque line formation around the stem), fibrous stable (no progressive migration of the stem and extensive radio-opaque line formation), or unstable (progressive subsidence or migration and divergent radiolucent lines surrounding the stem).
The immediate post-operative and follow-up radiographs were compared to assess bone regeneration. Remodelling in the proximal femur was classified according to Kolstad et al20 as A (increasing defects), B (stable defects) or C (osseous restoration), and the cortical index as described by Callaghan et al21 was also evaluated. Bone mass at the femoral diaphysis was quantitatively assessed by measuring cortical and cancellous bone thickness, and the external diaphyseal diameter at two levels.15 The transfemoral osteotomy site was considered healed radiologically if callus was seen bridging the site in both the anteroposterior and the lateral planes, in the absence of any pain in the femur.22 The occurrence of peri-prosthetic fractures was classified according to the system of Greidanus et al,23 which updated the Vancouver classification.24 The progression of intra-operative fractures was followed using the criteria of Tadross et al.25 Migration was assessed by measuring the subsidence of the femoral component according to the method of Callaghan et al.21 Subsidence was not considered significant unless it exceeded 10 mm.20 Heterotopic ossification was graded using the classification of Brooker et al.26
The cumulative survival rate was evaluated according to the method of Kaplan-Meier, using three endpoints for the entire series of 68 hips: removal of the stem because of aseptic loosening, removal of the stem for any cause, and revision of the stem for any reason and ≥ 10 mm migration of the femoral component. Survival analysis was reported with 95% confidence intervals (CI).27
The pre-operative and HHSs at final follow-up were compared using Wilcoxon’s signed-ranks test as data were not normally distributed according to the skewness-kurtosis test. The level of significance was set at p < 0.01.
The mean follow-up of the 36 living patients who did not have further revision of the stem was 13.9 years (10.4 to 15.8), with no patient lost to follow-up. The 36 surviving hips were available for clinical and radiological assessment (Table I).
The mean pre-operative HHS was 33 points (1 to 81), which improved to a mean of 75 at the final follow-up (46 to 97) (p < 0.001). The mean age of the patients at the time of follow-up was 75 years (49 to 94), and only 18 obtained an HHS > 80 points. Five patients underwent a further revision.
A complete radiological assessment was undertaken for all the remaining 36 patients (36 hips). Evidence of bone ingrowth was present in 33 hips (91.7%) (Fig. 1) and three demonstrated stable fibrous fixation with partially radiolucent, non-progressive lines around the stem. At final follow-up, no unrevised stem was judged to be unstable or definitely loose. Radiological signs of bone restoration in the proximal femur were seen in 23 hips (63.9%). In 34 hips (94.4%) the thickness of the diaphyseal cortical bone had not diminished at final follow-up compared with the immediate post-operative radiographs (Fig. 2). However, increasing defects occurred in two patients, one in a woman aged 90 at the latest follow-up who had previously undergone a revision and plating for the management of a diaphyseal peri-prosthetic fracture. In one man with a pre-operative type 3B femoral defect there was failure of osseo-integration. He had previously undergone two revisions, and although marked subsidence occurred, his final HHS was 93 points.
All 32 femoral osteotomies healed: in 23 hips (71.9%) healing occurred between two and six months after the operation. The mean time to union of the osteotomy was 5.5 months (2 to 15). There was heterotopic ossification in 17 hips (41.5%), being responsible for painless functional impairment only in one patient.
There were seven intra-operative fractures of the greater trochanter, all of which were treated with cerclage wires and healed without any further complications. The mean time to union was 17.6 weeks (12 to 23). One patient suffered a deep-vein thrombosis, with no lasting sequelae. A 72-year-old woman developed a permanent palsy of the sciatic nerve.
A total of eight stems (19.5%) showed subsidence ≥ 10 mm, up to a maximum of 30 mm. In six of these the migration occurred within the first 12 months after operation and persisted unchanged at the final follow-up. Local complications included four dislocations within the first 24 days of surgery (9.7%). All were managed successfully by a closed reduction followed by four weeks’ immobilisation using a plaster hip spica.
Five patients (12.2%) underwent further femoral revision. Two developed deep infection requiring excision arthroplasty, which in one patient occurred after revision of the acetabular component performed five years after Wagner stem implantation. One patient developed recurrent dislocation due to severe wear of the polyethylene acetabular component and underwent a further revision 15 years after femoral revision. Two hips were revised for progressive subsidence of the stem in the medullary canal leading to recurrent dislocation and head-neck disassembly, at five and eight years respectively after implantation. Both operations were successfully completed using a tapered modular stem.
With failure defined as removal of the stem for any reason, five of the 68 stems had to be further revised during the follow-up period, giving a cumulative survival of 92.0% (95% CI 86.0% to 98.4%) at 15.8 years. No additional hips were found to be at risk (Fig. 3a).
The survival rate of the Wagner stem with removal for aseptic loosening as the endpoint was 96.6% (95% CI 92.2% to 100%) at 15.8 years, and no additional hips were found to be at risk of failure (Fig. 3b). The survivorship with revision of the stem for any reason and ≥ 10 mm migration of the femoral component as the endpoint was 83.6% (95% CI 76.6% to 91.4%). No additional hips were found to be at risk (Fig. 3c). After the seventh year there was no deterioration in the survival rate with all endpoints.
Impaction bone grafting with cement has shown good results in revision THR,28,29 but it must be recognised that the technique is demanding.2 Some less good results have also been reported.30 A cemented allograft composite may also be used.31 An alternative is uncemented revision.32 Extensively porous-coated stems providing stable initial fixation in the diaphysis show encouraging results,3,4 but proximal stress shielding has been a cause for concern.3,32 Computer assisted designed components can be used.33 In more extensive bone deficiency, especially with a wide diaphyseal canal, fully coated cylindrical femoral components have insufficient stability.5,6
The Wagner Self-Locking stem was the first fluted, tapered stem designed to bypass the areas of proximal bone loss and secure uncemented fixation in the remaining distal, well-preserved femur.8 Spontaneous bony regeneration has been reported after cementless implantation of this stem.8,9 Subsequent studies reported comparable signs of femoral reconstruction, with survival rates of > 90% after five to ten years (Table II).10-17,20,34-39 New bone formation is promoted by numerous factors, including a low modulus of elasticity and mechanical stability, careful removal of peri-prosthetic cement and granulation tissue, and the use of a trochanteric osteotomy.10,14-16 In difficult cases, the transfemoral approach helps gain access to the femur for easier removal of the component and retained cement, creating a fracture-like situation in the proximal femur while keeping the fragments well vascularised to stimulate healing.10,20,36 Signs of bony consolidation were detected within six months after surgery in 71.9% of our osteotomies. However, extensive remodelling of bone defects was seen with the Wagner SL stem, even when a transfemoral approach was not used. We observed proximal bone regeneration in 23 of the 36 hips. Our results are the same as those in other series.10,12,15-17,20,34-36,40-45 The clinical results could be open to question, because at the latest examination only 18 patients obtained an HHS > 80 points. However, these were generally elderly, and some had severe bone defects that could not have been adequately dealt with using conventional prostheses. In accordance with Böhm and Bischel14 and Gutiérrez del Alamo et al,15 we consider that stable distal anchoring of the stem acts like an intramedullary nail bridging the site of fracture, and is necessary for peri-prosthetic bone growth. Impressive signs of osseo-integration of the stem were detected, and radiologically stable fixation was found in 33 of our 36 surviving implants.
Despite a reasonably successful outcome, most previous reports of fluted tapered monoblock stems have shown a high rate of complications, including subsidence and dislocation (Table II),7 with significant subsidence reported in over 10% of hips.10,12-15,20,35,37,38,42,46-50 Our experience was similar, with 19.5% of the stems showing a high rate of migration, but most stabilised after 12 months. However, in two hips the subsidence was progressive and further revision was necessary. Dislocation was another common complication, as also reported by many authors, with rates ranging from 12% to 21%.15,20,34,36,38,44,51 The inadequate offset of the Wagner SL design was primarily responsible for this problem,36 which has since been addressed with the development of proximally modular, distally fluted tapered components.6,7,52 These newer stems have been reported to have high survival rates at medium-term follow-up.53-55
We recognise the limitations of our study, which include its retrospective nature, the small number of patients and the lack of a control group undergoing an alternative treatment.
Nevertheless, we have found that the Wagner SL femoral stem proved reliable in enabling restoration of the bone stock. However, because of the unacceptably high rate of complications, modular tapered stems are now preferable.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
- Received October 1, 2010.
- Accepted June 2, 2011.
- © 2011 British Editorial Society of Bone and Joint Surgery