We reviewed the results of 84 total hip replacements performed with a short metaphyseal-fitting anatomical cementless femoral component in 84 unselected consecutive patients with a mean age of 78.9 years (70 to 88). The mean follow-up was 4.6 years (4 to 5). The mean pre-operative Harris hip score was 26 points (0 to 56), which improved to 89 (61 to 100) at the final follow-up. No patient had thigh pain. The mean pre-operative Western Ontario and McMaster Universities osteoarthritis index score was 61 points (48 to 75), which improved to 21 (6 to 46). The mean University of California, Los Angeles activity score was 5.5 points (3 to 7) at the final follow-up. Osseointegration was seen in all femoral and acetabular components. All hips had grade 1 stress shielding of the proximal femur. No acetabular or femoral osteolysis was identified.
These results demonstrate that a short metaphyseal-fitting femoral component achieves optimal fixation without diaphyseal anchorage in elderly patients.
In total hip replacement (THR) it has been suggested that components fixed without cement should be reserved for young, active patients and that components fixed with cement are more appropriate for the elderly.1–7 In view of the theoretical shorter operating time and the absence of cement-related complications,8–10 cementless THR may, however, be of particular benefit in older patients. Many authors have reported that poor bone quality should not be regarded as a contraindication, and that stable fixation of porous-coated components is achievable in osteoporotic bone.11–15 Although the results of conventional cementless THR are generally good in elderly patients,11–15 pulmonary microemboli8,10 are common in those who are 65 years of age or older, and stress shielding can be pronounced.11 Complete elimination of stress shielding11 and embolic phenomena8,10 is probably impossible, but the length of the femoral stem should be minimised in order to reduce the risks to the patient. Walker et al16 and Leali et al17 suggested that extending the femoral stem below the lesser trochanter was unnecessary.
One of the main reasons for developing a new short metaphyseal-fitting porous-coated cementless femoral component (Proxima; DePuy, Leeds, United Kingdom) was to preserve bone and to provide more physiological loading. The short Proxima femoral component is designed to have a close fit within the proximal femur with the aim of maximising primary stability, particularly in torsion, thereby limiting bone resorption due to stress shielding (Fig. 1⇓). It is manufactured using titanium alloy and is entirely porous-coated with sintered titanium beads having a mean pore size of 250 mm, to which a 30 μm thick hydroxyapatite coating is applied, except for the distal tip. The design features are a longer proximomedial portion of the stem, a highly pronounced lateral flare and preservation of the femoral neck. The question arises as to whether it is possible to obtain rigid fixation of this stem without diaphyseal anchoring in the elderly patient. Such information is currently lacking.
We studied the mid-term results of THR with the Proxima femoral component in patients who were ≥70 years of age.
Patients and Methods
Between May 2004 and May 2005, 94 primary THRs were performed in 94 unselected, consecutive patients who were ≥70 years (Table I⇓). Five patients died from unrelated causes and five were lost to follow-up less than two years after the operation. A total of 12 patients who were unable to return for follow-up completed a telephone questionnaire, and were asked to send recent radiographs. There were 84 patients (84 hips) in the final clinical and radiological analysis. Of these, 51 (61%) were between 70 and 79 years of age and 33 (39%) were between 80 and 88 years of age. The indication for THR was osteoarthritis in 55 patients (65.5%), osteonecrosis in 17 (20.2%), and fracture of the femoral neck in 12 (14.3%) (Table I⇓).
All patients received a Proxima femoral component with a 36 mm Biolox delta ceramic modular head (DePuy, Warsaw, Indiana). A fully porous-coated Pinnacle acetabular component (DePuy) with a ceramic liner was used in all hips. The acetabular components were press-fitted after under-reaming by 1 mm, and in 37 hips (44%) one or two screws were used for additional fixation. The acetabular component sizes ranged from 52 mm to 58 mm. The cost of this combination (US$ 2429.98) was less than for an Exeter cemented femoral component with a contemporary acetabular component and cobalt-chrome head and conventional polyethylene bearing (US$ 2501.78). This includes the actual cost of implanting using a modern cementing technique, including two batches of cement, a distal medullary plug, the cement gun and syringe, the cement compactor and the proximal rubber seal. These costs may be different in other healthcare systems.
All the operations were performed by the senior author (YHK) using a posterolateral approach. The femoral neck was cut horizontally at the cervicocapital juncture, because preservation of the femoral neck is required for axial and torsional stability of the stem.18,19 A ‘round-the-corner’ technique20 was used for femoral broaching and insertion of the implant. The broaches and implants were inserted in a slight varus position and then rotated into the correct axial alignment (Fig. 2⇓). Adequate cancellous bone (2 mm to 3 mm) for osseointegration was left in the lateral part of the proximal femur. The size of the femoral component which was selected matched the size of the largest broach used. The dimension of the real component was 0.5 mm larger than that of the prepared metaphysis.
Patients were allowed to stand on the second postoperative day and progressed to full-weight-bearing with crutches as tolerated. They were advised to use crutches for six weeks and to use a cane thereafter if needed.
The patients were reviewed at three months, one year, and yearly thereafter. Radiographs were taken one week after surgery and at each follow-up evaluation. The Harris hip score (HHS)21 was determined before surgery and at each follow-up, as was the Western Ontario and McMaster Universities osteoarthritis index (WOMAC) score.22 Thigh pain was scored on a 10-point visual analogue scale23 where 0 = no pain and 10 = severe pain, and activity was assessed using the University of California, Los Angeles (UCLA) score.24 All the data were obtained by one observer (SML), who was not part of the surgical team. Any clicking or squeaking from the ceramic-on-ceramic bearing was recorded.
A supine anteroposterior (AP) radiograph of the pelvis with both hips in 15° internal rotation and no abduction, and a cross-table lateral radiograph of each, were obtained immediately after operation and at follow-up visits. The femoral morphology was determined pre-operatively using Dorr’s system of classification.25 The position of the femoral component in the AP and lateral planes was assessed as shown in Figure 3⇓.
The radiographs were analysed by a research associate (SML) for stability of the components. They were classified as osseointegrated, fibrous stable or unstable.26 Components that showed spot welds were considered osseointegrated. Those that lacked definite ingrowth but had no progressive lucency or change in position were designated as fibrous stable, and those with clear signs of loosening, including axial or angular migration, were classified as unstable. Subsidence of the femoral component was evaluated by measuring the distance between the tip of the greater trochanter and the upper margin of the lateral flare of the stem, and the distance between the most proximomedial part of the porous-coated surface of the stem and the upper border of the lesser trochanter. These values in the AP radiographs taken one week after operation were compared with those taken at the final follow-up to define the subsidence. The intra-observer error for this measurement was determined by the intraclass correlation coefficient after the measurements were repeated three times at intervals of three days. This was 0.96 (0.95 to 1.0), indicating excellent reproducibility. A linear change of 2 mm or an angular change of 5°, bead-shedding and increased circumferential lucency were considered to be signs of loosening of the acetabular component. The vertical change in its position was measured between its inferior margin and the inferior margin of the ipsilateral teardrop, and horizontal change was measured between the Köhler line and the centre of the outer shell. The intraclass correlation coefficient was 0.97 (0.95 to 1.0).
Stress shielding was graded on the radiographs at the final follow-up according to the classification of Engh and Bobyn.27 Measurement of linear wear of the ceramic liner was attempted, but was below the level detectable by the method used.
The size and location of osteolytic lesions were assessed using the technique described by Zicat, Engh and Gokcen.28 The prevalence of heterotopic ossification was determined, and lesions were classified according to the criteria of Brooker et al.29
The changes in HHS were evaluated with two-tailed Student’s t-tests. The chi-squared test with Yates’ correction was used to analyse complication rates and the radiological data. All statistical analyses were performed using the Statistical Package for the Social Sciences, version 14.0 (SPSS Inc., Chicago, Illinois) and statistical significance was set at p < 0.05.
The mean follow-up was 4.6 years (4 to 5). The mean HSS, WOMAC score, patient activity level and level of thigh pain improved significantly (p ≤0.001). The mean HHS was 26 points (0 to 56) before surgery and 89 points (61 to 100) at final follow-up. The mean WOMAC score was 61 points (48 to 75) before surgery and 21 points (6 to 46) at the final follow-up, at which time 68 patients (81%) had no pain, 11 (13%) had mild pain that did not limit activity, and five (6%) had discomfort around the greater trochanter. No patient had thigh pain. The mean UCLA activity score at the final follow-up was 5.5 points (3 to 7). Even though the mean age was 83 years at the most recent follow-up, all but seven patients were active, with the others walking only indoors. All patients reported improved function, and were satisfied with the outcome. No hip had clicking or squeaking.
The morphology of the proximal femur was Dorr type A in 26 hips (31%), type B in 21 (25%) and type C in 37 (44%). In the AP view 80 femoral components (95%) were in a neutral position and four (5%) were in varus, and in the lateral view all were in an anatomical position. We found no significant difference between the normal hips and the operated hips in terms of the centre of rotation and the femoral offset. The mean leg-length discrepancy was 3.1 mm longer (5 mm shorter to 5 mm longer) in the operated hip (Table II⇓) (Fig. 4⇓). Osseointegration was seen in all the femoral and acetabular components. No acetabular or the femoral component migrated by > 1 mm. There was no evidence of a radiolucent line around the porous-coated surface of either component on the AP or the lateral radiographs. All hips had grade 1 stress shielding.27 No acetabular or femoral osteolysis was identified (Fig. 4⇓).
One hip had a fracture of the calcar. Open reduction and internal fixation was performed with a Dall-Miles cable (Howmedica, Rutherford, New Jersey) one week after operation. The period of protected weight-bearing was extended by three months, with no additional precautions. It healed satisfactorily with osseointegration at the final follow-up. One patient with a fracture of the femoral neck had recurrent dislocation. The position of the acetabular component was revised at a further operation. No hip had heterotopic ossification.
This study showed gratifying results after cementless THR using a Proxima femoral component in elderly patients. We found that poor bone quality was not a contraindication and stable fixation of the femoral component was achievable in osteoporotic bones, as was observed by McAuley et al11 with their extensively porous-coated diaphyseal femoral component. We believe that the satisfactory results using this femoral component in this group of patients can be attributed to optimal preparation of the proximal femur with preservation of the femoral neck, the lateral flare of the femoral component, a reduced load transfer to the component due to reduced daily activities, the potential for osseointegration even in this age group, and the improved quality of the ceramic-on-ceramic bearing.
There are only two reports describing the results in a similar unselected consecutive series of patients who were aged ≥65 years.11,30 It is useful to compare their results with ours. In one study, the rate of revision or radiological loosening was 12% (125 of 1041 hips) for the femoral component and 27% (281 of 1041) for the acetabular component.30 In another study,11 the rate of failure of theanatomical, medullary locking prosthesis (AML; DePuy, Warsaw, Indiana) was 2% (3 of 142 hips with radiological follow-up) for the femoral components and 6% (9 of 142 hips) for the acetabular components. We had no failures in our study.
In the study with the AML,11 five of 152 patients had thigh pain. Oishi, Walker and Colwell31 found that three of their 88 patients had thigh pain when hybrid fixation was used with a third-generation cementing technique. The absence of thigh pain in our study may be attributable to the rigid axial and torsional stability of the femoral component in the proximal femur and an absence of contact between the distal stem and the femoral cortex.
A potential concern with the use of short metaphyseal-fitting anatomical cementless femoral components in elderly patients is loss of stability of the component and failure of osseous ingrowth. Walker et al16 suggested that extending the femoral component beyond the lesser trochanter would be unnecessary for a cementless anatomical femoral component with a lateral flare, and that a short stemless implant would suffice. Leali and Fetto32 found that a proximally fixed cementless femoral component with a lateral flare provided significant initial stability. Santori et al33,34 and Santori and Santori20 reported solid fixation of their custom-made short metaphyseal-fitting stem (DePuy, Leeds, United Kingdom). Their findings validated the assumption that torsional loads can be controlled without diaphyseal anchorage by preservation of the femoral neck and the lateral flare of the femoral component. In our study, the fixation was successful in all hips and stability of the femoral component did not deteriorate at mid-term follow-up and the performance of the Proxima femoral component in this consecutive series of elderly patients was comparable to that of other conventional cementless femoral components.26,27,35–37
Santori et al33 observed mild stress shielding with rounding off of the calcar in 70 of 131 femora after using their custom-made short femoral component. This did not progress after one year. Leali and Fetto32 also demonstrated that the bone content was preserved after one year. All hips in our series had mild stress shielding at the final follow-up, which we think is due to physiological loading of the proximal femur.
McAuley et al11 noted in a series of older lower-demand patients, that 13 of 142 hips showed evidence of at least 2 mm of wear of the polyethylene liner. They suggested that the generation of debris and the resulting osteolysis remain unresolved issues. They considered using a 32 mm head in older, lower-demand patients if the larger diameter head improves stability of the hip and the thickness of the poly-ethylene liner is adequate. In our series, we used a 36 mm Biolox delta liner and a Biolox delta femoral head to improve stability and to potentially reduce wear and osteolysis.
Several studies38–40 have shown that the perceived cost differential between cemented and cementless systems is not necessarily an issue. Barrack et al39 also found that the actual cost of implanting a modern cemented femoral component was greater than for a corresponding cementless one. In our series, the Proxima stem with a Biolox delta ceramic head and liner was cheaper than a modern cemented femoral component with a contemporary acetabular component and cobalt-chrome head and polyethylene liner. The Proxima femoral component was 4% cheaper than other conventional cementless components.
It has been suggested that the use of conventional cementless components may increase the prevalence of intra-operative peri-prosthetic fracture and heterotopic ossification. None of these problems were of concern in our series.
Our study has some limitations. Although we collected all the data prospectively, the study was not randomised and we had no control group in which we used a different component or a different surgical technique to compare outcomes. For analysis of femoral component migration we did not use the more precise methods of radiostereophoto-grammetric analysis. The duration of follow-up was short and hence insufficient to allow us to draw significant conclusions. However, there is strong evidence that the early stability of the cementless femoral component produces good clinical results.41,42
The authors would like to thank S.-M. Lee for her assistance with the collection and analysis of data.
The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund, foundation, educational institution, or other nonprofit organisation with which one or more of the authors are associated.
- Received September 29, 2010.
- Accepted December 17, 2010.
- © 2011 British Editorial Society of Bone and Joint Surgery