We hypothesised that the removal of the subchondral bone plate (SCBP) for cemented acetabular component fixation in total hip arthroplasty (THA) offers advantages over retention by improving the cement-bone interface, without jeopardising implant stability. We have previously published two-year follow-up data of a randomised controlled trial (RCT), in which 50 patients with primary osteoarthritis were randomised to either retention or removal of the SCBP. The mean age of the retention group (n = 25, 13 males) was 70.0 years (sd 6.8). The mean age in the removal group (n = 25, 16 males) was 70.3 years (sd 7.9). Now we have followed up the patients at six (retention group, n = 21; removal group, n = 20) and ten years (retention group: n = 17, removal group: n = 18), administering clinical outcome questionnaires and radiostereometric analysis (RSA), and determining the presence of radiolucent lines (RLLs) on conventional radiographs. RSA demonstrated similar translation and rotation patterns up to six years. Between six and ten years, proximal acetabular component migration and changes of inclination were larger in the retention group, although the mean differences did not reach statistical significance. Differences in migration were driven by two patients in the SCBP retention group with extensive migration versus none in the SCBP removal group. The significant difference (p < 0.001) in the development of radiolucent lines in the retention group, previously observed at two years, increased even further during the course of follow-up (p < 0.001). While recognising SCBP removal is a more demanding technique, we conclude that, wherever possible, the SCBP should be removed to improve the cement–bone interface in order to maximise acetabular component stability and longevity.

Cite this article: Bone Joint J 2015;97-B:35–44.

Progressive retroversion of a cemented stem is predictive of early loosening and failure. We assessed the relationship between direct post-operative stem anteversion, measured with CT, and the resulting rotational stability, measured with repeated radiostereometric analysis over ten years. The study comprised 60 cemented total hip replacements using one of two types of matt collared stem with a rounded cross-section. The patients were divided into three groups depending on their measured post-operative anteversion (< 10°, 10° to 25°, >  25°). There was a strong correlation between direct post-operative anteversion and later posterior rotation. At one year the < 10° group showed significantly more progressive retroversion together with distal migration, and this persisted to the ten-year follow-up. In the < 10° group four of ten stems (40%) had been revised at ten years, and an additional two stems (20%) were radiologically loose. In the ‘normal’ (10° to 25°) anteversion group there was one revised (3%) and one loose stem (3%) of a total of 30 stems, and in the > 25° group one stem (5%) was revised and another loose (5%) out of 20 stems. This poor outcome is partly dependent on the design of this prosthesis, but the results strongly suggest that the initial rotational position of cemented stems during surgery affects the subsequent progressive retroversion, subsidence and eventual loosening. The degree of retroversion may be sensitive to prosthetic design and stem size, but < 10° of anteversion appears deleterious to the long-term outcome for cemented hip prosthetic stems.

Cite this article: Bone Joint J 2013;95-B:23–30.

Collarless, polished and tapered cemented stems are nowadays commonly used in hip surgery. Normally, a hollow centralizer is applied to the stem tip to allow the prosthesis to sink in the cement mantel in the event of creep and loosening between stem and cement. It is believed that in this way the stem will stabilize and regain its tight bond with the cement. The prosthesis MS-30 (Zimmer) is collarless, polished and triple tapered and has a hollow centralizer, but was previously used with a solid centralizer. We hypothesised that these types of stems, exemplified by the MS-30, used with a hollow centralizer would sink more but stabilize better, become more stable in the important rotational migration and retrovert less than with a solid centralizer. In a prospective, controlled clinical study we randomised 60 patients with primary coxarthrosis into either hollow or solid centralizer used with the MS-30 stem. The effect was evaluated for a 2-year follow up period by repeated RSA examinations, conventional radiographs and clinical follow-ups with the questionnaires WOMAC, SF-12 and Harris Hip Score.

The RSA results showed small early migration in both groups and almost all of it occurred within the cement mantle, i.e. between stem and cement. The group with hollow centralizers migrated distally significantly more than the group with solid centralizers (p< 0.0001) (1.40 mm vs 0.28 mm). In rotation, however, there was no difference (retroversion 0.99° and 0.94°). Neither was there any difference regarding clinical outcome and questionnaires.

As expected the group with hollow centralizers migrated more distally, in the same magnitude as reported in earlier RSA studies for the conceptually similar prostheses Exeter and C-stem. Interestingly, there was no difference regarding the rotational behaviour, and both groups showed less retroversion than reported in the earlier reports. MS-30 seems to have a design that regardless of centralizer type well withstands rotational motion within the cement mantle. This study cannot fortify the need for a hollow centralizer for this collarless, polished and triple tapered prosthesis.

Introduction: Progressive retroversion of the stem within the femur has been suggested to be an important initial mode of hip prosthesis failure. We have assessed the relationship between postoperative stem anteversion angle, measured with CT, and the rotational stability as measured with repeated radiostereometric analysis (RSA) with 5 years follow up.

Patients and methods: 57 patients were operated on with THA using a cemented, matt and collared stem. The achieved stem anteversion angles were measured postoperatively with 3-D CT-examinations. The patients were divided into three groups depending on their ante-version angle: ≤10°, 11°–25° and ≥25°. They were followed with repeated RSA examinations for 5 years to determine the stem migration pattern.

Results: The mean postoperative anteversion angle was 20.5° (range 1°–43°). At 5 years, all except one stem had rotated into retroversion. There was a strong correlation between the postoperative anteversion angle and later rotation into retroversion (p=0.007). The group with ≤10° of stem anteversion rotated significantly more into retroversion, seen as early as 3 months (p=0.02), but more obvious at 5 years (p=0.002) with a mean of 9.9° of retroversion compared to 3.8° in the 11°–25° group and 2.4 ° in the ≥25° group. The distal stem migration results were accordant with more migration at 5 years (p=0.008) for the ≤10° anteversion group (1.6 mm subsidence compared to 0.5 and 0.3 mm respectively). Two stems have been revised because of aseptic loosening, both with a low initial anteversion angle (7° and 1°) and large retroversion at 5 years (7 ° and 31° respectively).

Conclusion: Measured by RSA, rotation into retroversion of the femoral stem was a regular finding in this study using a conventional prosthesis design. We propose that such rotation is a common finding in hip arthroplasty, but the degree may be design sensitive. Our results strongly suggest that the initial rotational position of the femoral component during surgery is decisive for the degree of later retroversion and probably prosthetic longevity; the less anteverted position the more the stem will migrate into a more retroverted position after the operation. This rotational migratory pattern is correlated to subsidence and eventual loosening. Hence, meticulous attention should be paid to the rotational position of the femoral stem during surgery, with less than 10° of anteversion appearing deleterious. However, too much anteversion will risk impingement and possibly other unwanted biomechanical effects, and an upper limit still remains to be established.

In a prospective, controlled clinical study we randomised 50 patients with primary coxarthrosis into either removal or retention of the subchondral bone plate during ace-tabular preparation in cemented total hip arthroplasty. The effect was evaluated for a 2-year follow up period by repeated RSA examinations, analyses of radiolucent lines on conventional radiographs and clinical follow-ups with WOMAC, SF-12 and Harris Hip Score. Removal of the subchondral bone plate resulted in an improvement in radiological appearance of the bone-cement interface. For the retention group the extent of radiolucent lines as measured on pelvic and AP-view, had increased from a direct postoperative average level of 3.4% to a 2-year level of 28.8%. For the group with removal of the subchondral bone plate, the direct postoperative radiographs revealed no radiolucency, and at 2 years it only occupied a mean of 4.1 % of the interface. With the classification according to Hodgkinson the retention group had 10 out of 25 patients remaining in grade 0 (no demarcation) at 2years, whereas the removal group had 23 out of 25 patients in grade 0 at 2 years. The RSA results showed small early migration in both groups, but a tendency towards better stability and less scatter of the results in the removal group. The retention group tilted from 6 months onwards slightly but continuously towards a more horizontal position, whereas the removal group stabilized in a slightly vertical position after 1 year. The mean proximal migrations for all cups taken together were 0.09 mm at 2 years with no significant difference between groups. No differences were found in clinical outcome neither pre- nor postoperatively. To optimize the bone-cement interface and thereby increase the long time cup survival, removal of the subchondral bone plate where possible appears to be advantageous, but it is a more demanding surgical technique.