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.

Background: The role of polyethylene (PE) wear in relation to synovitis and elevated hydrostatic pressure in the loosening process after THA has gained increased attention. The aim of our study was to investigate the correlation between prosthetic head size, PE wear and sonographic capsular distention, reflecting the degree of intracapsular synovitis/synovia/hydrostatic pressure.

Patients and methods: In 2005 we analyzed 60 randomly selected and unrevised OA patients 10 years after surgery with 32 or 28mm femoral heads. We evaluated radiographic signs of loosening, linear and volumetric PE wear. Sonographic examination was performed to measure the “capsular distance”, i.e. the capsular distension, defined as the distance between the metallic echo from the anterior surface of the prosthetic femoral neck, and the echo from the anterior surface of the anterior capsule.

Results: The linear wear was 0.2 mm per year and 0.1 mm per year in the 32 mm and 28 mm head size group respectively (p< 0.001), the volumetric wear was 139 mm3/year and 48 mm3/year (p< 0.001), and the capsular distention was 17 mm and 13 mm respectively (p< 0.001). There was also a significant positive correlation between PE volumetric wear and capsular distension (r=0.63, p< 0.001).

Interpretation: We conclude that 32 mm femoral heads were associated with almost three times higher volumetric wear as compared to 28 mm heads, and increased “capsular distension”, reflecting increased synovitis/synovia/hydrostatic pressure in prosthetic hip.

Introduction. Since the early days of total hip arthroplasty (THA) the choice of the proper diameter of the femoral head has been debated with respect to its effect on wear. The most widely accepted theory explaining aseptic loosening of THA is that of polyethylene particles induced osteolysis. In a previous study concerning 1,660 ScanHip THA’s that were followed for up to 12 years the cumulative revision rate was not found to be dependent on if a 22 mm or a 32 mm head size had been used1. We have reexamined these patients to see whether a longer follow-up time (9–21 years) would disclose an effect of head size on the revision rate.

Patients and Methods. We analyzed the CRR for 1,720 Scan Hip^® Classic I THA implanted in 1,550 patients, with 22 and 32mm heads, performed at Lund University Hospital during 1983 to 1995. Patients with the 3 most common diagnoses were included in the analysis, i.e. osteoarthritis, rheumatoid arthritis and femoral neck fracture. The end-point was defined as revision of any component for aseptic loosening before the end of 2004.

Results. Using the life table method analyzed cumulative revision rate for osteoarthritis, femoral neck fracture and rheumatoid arthritis patients and found that the 32 mm head had higher cumulative revision rate (p=0.04 (Wilcoxon)). Further analysis with Cox regression adjusting for age and sex showed that the 32 mm head had 2.8 times greater risk of revision (CI 1.7–4.6), p< 0.001. For each year increase in age the risk of revision was reduced 0.96 times (CI 0.95 – 0.97), p< 0.001, males had 1.5 times (CI 1.1 – 2.1), p=0.01 greater risk of revision than females.

Discussion. The reason that we did not find any significant difference in cumulative revision rates when followed up to 12 years, depending on head size in previous study (Kesteris et al. 1998) may be the time it takes for wear particles to induce the chain of events, eventually ending up in loosening. However extended follow-up up to 21 years after THA revealed significant differences in cumulative revision rates depending on head size.

Different resurfacing implants offer different kinds of positioning instruments. As it is of outmost importance to position the components within rather narrow limits to diminish the risk of femoral notching or impingement we decided to measure the position achieved in 72 hips resurfaced with the Durom^® resurfacing hip and instruments.

There were 38 males and 27 females with 72 hips (7 bilateral). The indication was OA in 51 cases, RA in 12 and ON in 2. We compared 2 groups, 26 hips operated with an antero-lateral approach (A) and 46 with a postero-lateral approach (B).

The acetabular cup anteversion angle was 22±11° in group A and 15±9° in group B. The abduction angle was 38±9 ° in group A and 44±7° in group B. The acetabular gap was 2±1 mm, resp. 2±2 mm. The stem-shaft angle was 140±5° resp. 141±6°. Retroverted cups averaged 7±4°.

The difference between pre- and postoperative acetabular size was 3 mm in group A (mostly RA patients) and 5 mm in group B (mostly OA patients).

Conclusions: We have obtained a fairly good implant position. The only significant differences between the two groups were decreased acetabular cup abduction angle compared to the preoperative angle in the antero-lateral group, but increased angle in the postero-lateral group, and that less acetabular bone was removed in the antero-lateral group (patients with RA included) compared to the postero-lateral group.

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.