Abstract
We report the long-term results of revision total hip replacement using femoral impaction allografting with both uncemented and cemented Freeman femoral components. A standard design of component was used in both groups, with additional proximal hydroxyapatite coating in the uncemented group. A total of 33 hips in 30 patients received an uncemented component and 31 hips in 30 patients a cemented component. The mean follow-up was 9.8 years (2 to 17) in the uncemented group and 6.2 years (1 to 11) in the cemented group. Revision procedures (for all causes) were required in four patients (four hips) in the uncemented group and in five patients (five hips) in the cemented group. Harris hip scores improved significantly in both groups and were maintained independently of the extent of any migration of the femoral component within the graft or graft–cement mantle.
When using impaction bone grafting in revision total hip replacement (THR), both cemented and uncemented techniques with various designs of femoral component have been reported.1-3 Which technique is superior and where precisely the subsidence of the femoral component occurs, however, remains unclear.4
We present two groups of patients who underwent femoral impaction grafting at revision THR using the same generic type of femoral component with either an uncemented or a cemented technique. All the operations were performed by a single surgeon (GS) over a 17-year period.
Patients and Methods
Between 1992 and 2009, 60 consecutive patients with a mean age of 52 years (31 to 78) underwent 64 revision THRs with impaction femoral bone grafting. The initial technique used an uncemented Freeman femoral component coated proximally with hydroxyapatite (HA) (Finsbury, Leatherhead, United Kingdom) in 30 patients (33 hips) and the preliminary results for these patients were communicated to the British Hip Society,5 but the failure to incorporate cement in the reconstruction was not generally endorsed. This persuaded the senior author to reconsider the technique and add cement. Subsequently, 30 patients (31 hips) had impaction allografting with a cemented version of the Freeman component without HA.
Patient demographics and diagnoses are shown in Table I; the distribution of pathologies and age ranges were similar across the two groups.
Table I
Patient demographics and pre-operative diagnoses for both groups
| Uncemented | Cemented | |
|---|---|---|
| Hips (n) | 33 | 31 |
| Mean age (yrs) (range) | 49 (33 to 62) | 54 (31 to 78) |
| Male : Female | 21:12 | 13:18 |
| Diagnosis (n, %) | ||
| Osteoarthritis | 22 (66.7) | 25 (80.6) |
| Rheumatoid arthritis | 2 (6.1) | 4 (12.9) |
| Post-traumatic | 3 (9.1) | 1 (3.2) |
| Other | 6 (18.2) | 1 (3.2) |
In the uncemented group 21 hips (21 patients) were being revised for the first time, and three patients had undergone previous revision of the acetabular component only. In nine hips (eight patients) the femoral component was being revised for the second time. In the cemented group 20 hips (20 patients) were being revised for the first time; three patients had undergone previous revision of their acetabular component only. In eight hips (seven patients) the femoral component was being revised for the second time. There was one bilateral case in each group.
All hips were being revised for aseptic loosening associated with loss of proximal femoral bone stock. Pre-operatively the bone deficiency was classified according to the American Association of Orthopaedic Surgeons (AAOS) scale6 (Table II). A similar distribution of defects was present in both groups.
Table II
The American Association of Orthopaedic Surgeons (AAOS) grading6 of femoral bone loss for both groups
| Femoral bone loss (AAOS grade) | Uncemented | Cemented |
|---|---|---|
| 1 | 0 | 0 |
| 2 | 30 | 27 |
| 3 | 3 | 4 |
| 4 to 6 | 0 | 0 |
Implants
The uncemented Freeman femoral component has longitudinal 1 mm ridges along its anterior, lateral and proximal surfaces and 1 mm ‘stipples’ which stand proud on the anterior and posterior faces of the neck.7 Distally it is circular in cross-section, tapered and polished to prevent ongrowth of bone and distal fixation. Proximally it has a shot-blasted cobalt–chrome (CoCr) surface (roughness 7.6 μRa), which in the uncemented version is HA coated to a thickness of 80 µm to 120 µm with a crystallinity > 75%. The cemented version is identical except that the longitudinal ridges are machined flat and there is no HA coating (Fig. 1).
Fig. 1
Photograph of the two Freeman femoral components: uncemented with proximal ridges and hydroxyapatite coating (A), and cemented without proximal ridges and machined flat proximal section (B).
Operative technique
Using a modified anterolateral approach,8 existing components and the interface membrane were removed. Acetabular revision was usually undertaken but does not form part of this report. Impaction allografting was performed as described elsewhere9,10 using thawed fresh-frozen femoral heads which were milled to create chips 3 mm to 5 mm in diameter, before being rinsed with warm saline to remove excess fat. Generally the equivalent of two or three femoral heads was required for each procedure. The impaction tools were specific to the implant design, which enabled grafting until a new canal was fashioned, generally to an internal proximal diameter of 14 mm, but occasionally 16 mm. A trial prosthesis of the same size as the cavity was used as a template to graft the femoral neck. If the original neck had been destroyed a structural graft was used to retain the cancellous graft, as the design of this component is based on femoral neck retention.
For the uncemented group, once a tight fit had been obtained, the trial prosthesis was removed and replaced with a definitive component that was 2 mm larger in diameter. The ridges and stipples provided additional proximal over-sizing. The component was driven home with slow hammer blows using a force based on experience. If it could not be advanced before it was fully seated it was withdrawn and a little graft was cautiously removed, before the component was re-impacted until stable.
In the cemented group allograft was impacted as above, but the definitive component was the same diameter as the prepared cavity in order to allow retrograde cementing with low-viscosity CMW cement (DePuy, Blackpool, United Kingdom) introduced using a cement gun.
The post-operative regime was similar in both groups: physiotherapy was undertaken to regain abductor control in bed for three to four days, followed by non-weight-bearing mobilisation using crutches. After six weeks 25% of body weight was permitted, increasing by 25% each six weeks until full weight-bearing at 26 weeks. One crutch or a stick was retained for the rest of the first post-operative year. However, in the cemented group the progression from partial weight-bearing at six weeks to full weight-bearing occurred by three months. Thereafter, the patients underwent annual clinical and radiological review.
Clinical outcome
The functional outcome of the patients was measured using the Harris hip score (HHS).11
Radiological assessment
At each visit a standardised anteroposterior (AP) radiograph was taken. The beam was centred on the greater trochanter and contained the whole of the component to allow vertical downward migration to be measured. Lateral views were also often obtained but were not used for study assessments because of their inherent variability.12 The AAOS grading of the pre-operative radiographs was performed independently by two of the authors (SM and SL), who were not involved in the surgery. Assessments were subsequently repeated for consistency of results, and a consensus was obtained. Similarly, the post-operative AP radiographs of the proximal femur were assessed. The thickness of the allograft was measured from the immediate post-operative radiographs. This varied along the length of the femur; therefore, for standardisation, the medial and lateral widths of the graft were measured at the distal end of the neck of the component. The mean thickness in the uncemented group medially was 6 mm (0 to 15) and laterally 9 mm (3 to 20). The mean thickness in the cemented group medially was 3 mm (0 to 9) and laterally 5 mm (2 to 15). Subsequent radiographs were examined for changes in bone quality, radiolucent lines and lytic lesions.
Measurement of migration
Migration measurements of the femoral component were performed by SM and SL using a calibrated Vernier micrometer (Mitutoyu, Kawasaki, Japan) on the standardised AP radiographs, correcting for magnification by reference to the known size of the modular femoral head. Migration was assessed from the tip of the greater trochanter to the pointed superior lateral marker, which is integral to the design of the component as previously described, to an accuracy of ± 1 mm.12
Survival analysis
Survival analysis was undertaken using the life-table method,13 and the 95% confidence interval (CI) was calculated using the Rothman formula as recommended in other reports,14,15 with aseptic loosening as the end-point. Any patient lost to follow-up was treated as a failure. The log-rank test was performed to compare outcomes between the two series.
Statistical analysis
The statistical significance of any change between the pre-operative mean HHS and the mean at final review was compared using the paired t-test. The final mean HHSs of the two groups were compared using the unpaired t-test. The mean cumulative migration rates after one year for the two groups were compared using the t-test. A p-value ≤ 0.05 was considered statistically significant.
Results
Clinical outcome
The mean follow-up for the uncemented group was 9.8 years (2 to 17) and for the cemented group was 6.2 years (1 to 11). At latest follow-up, the mean HHS had improved significantly from 45 (25 to 73) to 82 (61 to 97) (t-test, p < 0.001) in the uncemented group, and from 45 (27 to 62) to 80 (54 to 100) (t-test, p < 0.001) in the cemented group. There was no significant difference in the final HHS between the groups (unpaired t-test, p = 0.76).
Complications
Overall there were nine complications in the uncemented group of 33 hips. There were three intra-operative fractures, one peri-prosthetic fracture, two dislocations and three hips that required revision for loosening. In the cemented group of 31 hips there were six complications. Two hips required revision for aseptic loosening, two developed infection and two had a peri-prosthetic fracture.
Survival analysis
The survival rate at ten years for the uncemented component with aseptic loosening as the end-point was 79.2% (95% CI 63.5 to 95) when 20 hips were at risk, and for the cemented component was 72.6% (95% CI 45.5 to 99.6) when nine hips were at risk. There was no significant difference in these results (log rank, p = 0.81). Longer-term data are available to 17 years for the uncemented component, but the numbers are too small for statistical analysis (Table III and Fig. 2).
Table III
Life-table for survival of cemented Freeman stem with aseptic loosening as the end-point (CI, confidence interval)
| Years since operation | Number at start | Failed | Died | Lost | Not completed the year | At risk | Cumulative survival (%) (95% CI) |
|---|---|---|---|---|---|---|---|
| 0 to 1 | 31 | 1 | 0 | 1 | 0 | 30.5 | 96.7 (90.5 to 100) |
| 1 to 2 | 29 | 0 | 0 | 1 | 3 | 27 | 96.7 (90.1 to 100) |
| 2 to 3 | 25 | 0 | 0 | 0 | 0 | 25 | 96.7 (89.9 to 100) |
| 3 to 4 | 25 | 1 | 1 | 0 | 1 | 24 | 92.7 (82.7 to 100) |
| 4 to 5 | 22 | 1 | 0 | 0 | 1 | 21.5 | 88.4 (75.7 to 100) |
| 5 to 6 | 20 | 1 | 0 | 0 | 2 | 19 | 83.7 (68.6 to 98.8) |
| 6 to 7 | 17 | 0 | 0 | 0 | 2 | 16 | 83.7 (67.3 to 100) |
| 7 to 8 | 15 | 0 | 1 | 0 | 1 | 14 | 83.7 (66.1 to 100) |
| 8 to 9 | 13 | 0 | 0 | 0 | 4 | 11 | 83.7 (63.9 to 100) |
| 9 to 10 | 9 | 1 | 0 | 0 | 3 | 7.5 | 72.6 (45.5 to 99.6) |
| 10 to 11 | 5 | 0 | 0 | 0 | 2 | 4 | 72.6 (35.5 to 100) |
| 11 to 12 | 3 | 0 | 0 | 0 | 0 | 3 | 72.6 (29.8 to 100) |
Fig. 2
Implant survival rates for both uncemented and cemented groups. Error bars denote 95% confidence intervals.
Migration data and radiological results
The migration data for the two groups are presented in Figure 3. In both series individual bone chips became progressively less identifiable, producing a more homogeneous appearance. A trabecular pattern emerged and the sclerotic lines of the pre-revision endocortex faded. Thin cortical areas gradually thickened, even distally, where early in this series no great emphasis had been placed on graft impaction. In the early radiographs these bone changes were subtle, but by the end of the first post-operative year they were obvious, although the process occurred at varying rates. Remodelling continued into the third post-operative year, but after the second year changes were slow. In general, the final appearance of the graft was denser than seen after initial impaction, with a trabecular pattern but less abundant than that in the host bone.
Fig. 3
Bar chart showing the overall subsidence rates at the final follow-up for uncemented and cemented groups.
In the uncemented group only, a thin radiodense line was sometimes present around the more distal uncoated portion of the component after two years. A similar radiodense line may be found in successful primary THR with this prosthesis, usually forming about one to two years after operation.17
Those components that migrated > 4 mm in the first year were examined as a subgroup. This threshold was chosen as approximately 20% of the cases reported by Gie et al9 migrated more than this, and it is slightly less than the maximum migration in a series studied by radiostereometric analysis (RSA) by Franzén et al.10 In the uncemented group nine components (27%) subsided by > 4 mm in the first year, the mean being 8 mm (4 to 16). In seven of these components subsidence was < 2 mm in the second year. The other two continued to subside rapidly and required revision, one after two years with a total migration of 21 mm, the other after four years with 15 mm of subsidence. In contrast, the third case, which required revision at five years, did not show initial rapid migration. The cemented group had two early cases of rapid migration of 4 mm and 20 mm, respectively, both requiring early revision. The mean cumulative migration after one year in the uncemented group was 4.4 mm (1 to 16) and in the cemented group was 1.85 mm (0 to 20) (t-test, p = 0.05).
Discussion
In the uncemented group with a mean follow-up of 9.5 years further revision was necessary for femoral problems in four cases, one for fracture and three for pain associated with migration. These results differ little from the outcomes reported in other series using cement, which describe further revision for fractures and components with excessive subsidence.10,18-20 It has been noted that in order to produce consistent results, experience in performing approximately 100 cases is required.21
The rehabilitation regime in our series, which was decided empirically, was quite prolonged in terms of progressive weight-bearing. This conservative approach was thought necessary to provide adequate time for initial healing of the impacted bone graft.
The functional outcome is not well reported in the literature. In 21% of the patients described by Eldridge et al22 there was some residual thigh pain and 32% needed a walking aid at least part of the time. Elsewhere, broadly similar findings were noted when patients were evaluated using a self-administered questionnaire.18 Our functional outcomes with or without cement were not dissimilar to the reports for cemented cases. In another series, which included cemented and uncemented impaction allografting,23 there was no significant difference in the HHS.
The migration results of both our uncemented and cemented components resemble those of other series, most of which have used cement in conjunction with allograft.4 Among these other series, four included cases where the follow-up did not exceed one year.10,20,22,24 In one series using cement with a double polished tapered stem at a mean follow-up of 30 months, 38% of cases (13 of 34) displayed rapid initial migration.18 Elting et al19 concluded that the initial stability of the reconstruction seemed to be important for a successful outcome. However, we found that neither the presence nor the absence of initial migration of > 4 mm reliably predicted the outcome. Elsewhere it has also been noted that early migration does not predict the late outcome.18 Nevertheless, it would seem sensible to impact bone graft as much as possible to produce initial stability, and to be cautious about early weight-bearing so as to restrict micromovement as graft incorporation commences. This approach appears justified, given the finding of rapid migration of an uncemented femoral component in an in vitro study.24 The presence of cement might facilitate a more rapid return to weight-bearing.
It is not clear from the literature where the distal migration occurs. In some cemented series9,18-20 distal migration of the femoral component within the cement mantle has been recorded, as well as migration of the whole cement/component construct into the graft. A recent RSA study on impaction allografting with the Exeter stem (Stryker, Newbury, United Kingdom) at long-term follow-up did not investigate whether the stem migrated within the cement mantle or in the graft bed in isolation.25 In our series where cement was not included, any distal migration must have been due to settlement into the graft bed or possibly some distal migration of the graft material itself. Experimental work with goats using an HA-coated femoral component placed into impacted allograft without cement gave good mechanical and histological results in the short term.26 In a non-randomised comparison of impaction allografting, where the first 20 cases received HA-coated components and the subsequent 12 cases received cemented components, the cemented ones migrated less.27 However, in our study this migration differed only in the first 12 months, but afterwards there was no significant difference in the subsidence (p = 0.1) or hip scores (p = 0.76) between the two groups.
In conclusion, the overall results obtained in our series are comparable to those of others. The similarity in the design of the uncemented and cemented versions suggests that the migration identified would appear to involve principally the graft itself, with more subsidence in the uncemented group. However, the addition of cement to the impaction technique does not seem to influence the outcome with regard to revision rates or HHS.
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The authors would like to thank J. Houghton for her assistance with the data collection, and L. Masterson and H. Pandit for their contributions to statistical analysis.
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.
Supplementary material. Two tables detailing i) the complications in patients in both the cemented and uncemented groups and ii) a life-table for survival of uncemented Freeman hydroxyapatite-coated stem with aseptic loosening as the end-point are available with the electronic version of this article on our website www.jbjs.org.uk
