Introduction. Acetabular cup positioning has been linked to dislocation and increased bearing surface wear. A previous study found correlations between patient and surgical factors and acetabular component position. The purpose of this study was to determine if acetabular cup positioning improves when surgeons receive feedback on their performance. Methods. Post-op anteroposterior (AP) pelvis and cross-table lateral radiographs were previously obtained for 2061 patients who received a total hip arthroplasty (THA) or hip resurfacing from 2004–2008. The surgeries were performed by 7 surgeons. AP radiographs were measured using Hip Analysis Suite to calculate the cup inclination and version angles. Acceptable ranges were defined for abduction (30–45 °) and version (5–25 °). The same surgeons performed a THA or hip resurfacing on 385 patients from January 2009 through June 2010. Cup inclination and version angles for this set of surgeries were compared to surgeries from 2004–2008 to determine if cup inclination and version angles improved in response to previous acetabular cup positioning studies. Improvement in accuracy was assessed by the chi-square test. Results. Time 1, from 2004 through 2008, had 1952 qualifying hips with 1845 having both version and abduction, and Time 2, from 2009 through June 2010, had 385 qualifying hips, all of which had both version and abduction angles. For Time 1, 1192 (62%) acetabular cups were within the abduction range, 1422 (79%) were within the version range, and 908 (49%) were within the range for both. For Time 2, 276 (72%) acetabular cups were within the abduction range, 250 (65%) were within the version range, and 217 (56%) were within the ranges for both. Accuracy of abduction angle improved (p<0.01) while accuracy of version angle decreased (p<0.01). Accuracy of acetabular cup positioning being within range for both abduction angle and version angle improved significantly (p=0.01), by 7%. Conclusions. Increased awareness and feedback on the resulting abduction and version measurements from THA surgery over time improves the positioning of the acetabular component. A system where objective measurements are presented to the surgeon can significantly improve cup placement which could improve the clinical outcome of THR patients

Introduction. Metal on metal articulations produce chromium (Cr) and cobalt (Co) debris, particularly when the articulations are worn in. High levels in the peripheral blood are indicative of excess wear and may cause adverse effects. The present RCT investigates metal ion levels and the relationship of Co, Cr ions and lymphocyte counts during the running-in period. Materials and Methods. Following randomization to RHA (ASRTM, DePuy) or THA we obtained whole blood (wb), and serum (s) samples at baseline, 8 w, 6 m and 1 y. We measured the Co and Cr concentrations, the total lymphocyte count as well as the CD3+, CD4+, CD8+, CD19+ and CD16+/CD56+ sub populations. Cup inclination and anteversion angles came from conventional radiographs. Activity was measured as steps by pedometer and UCLA activity. Data are presented as median (range). Results. We had 19 patients in each group. Age 57 (46–64) y (RHA) and 55 (44–64) y (THA). RHA only: head size: 51 (47 to 57)mm, cup inclination: 45.0 (40- 56)° and anteversion: 23 (7–38)°. The ion concentrations stayed below 0.2 ppb for THAs. For RHAs the Co and Cr concentrations generally rose markedly in the initial 8 weeks, followed by a slower ascent up to 1 year to wb Co: 1.0 (0.6–5.2), s Co: 1.3 (0.7–6.5), wb Cr: 1.3 (0.4–8.0) and s Cr: 1.7 (0.6–15) ppb. A high ion level was correlated to a small head size (p<0.03) and a cup inclination around 45° (p<0.04). We could not correlate the ion concentrations to the anteversion or the activity levels. The absolute lymphocyte counts were not always identical in the groups (eg. lower CD8+ for RHA) but there was no group difference when we analysed the change from baseline. We did not demonstrate any correlation between metal ion levels and lymphocyte subpopulations. Discussion. The findings of this study does not support the theory that metal ions suppress the lymphocytes or the CD8+ in particular (Hart et al., 2009). Our conclusions are limited by low numbers, but we suspect the theory could be biased by missing baseline values. Our study did not demonstrate the same 6–9 months ion peak found in other running-in studies (Back et al., 2005, Heisel et al., 2008), but rather a slow continuous rise with lower median ion concentrations. It could indicate lower wear or perhaps a longer running in period in our slightly older population. Contrary to our expectations we found that cups placed in optimal inclination displayed a higher ion level. Most of the smallest cups were found in this group, and the majority of the steep cups had very large heads. For this implant head size may be more important than cup position

Introduction. Hip wear simulation is a widely used technique for the pre-clinical evaluation of new bearing designs. However, wear rates seen in vitro can often be significantly different to those seen clinically. This can be attributed to the difference between the optimal conditions in a simulator and wide ranging conditions in real patients. This study aimed to develop more clinically relevant simulator tests, looking specifically at the effects of cup inclination angle (in vivo) and stop-dwell-start (SDS) protocols on a clinically available product. Method. Five tests using a Paul type walking cycle (ISO 14242) were carried out on two ProSim hip simulators: . 28mm MoM, standard walking, cup inclination 45°, (n = 5). 36mm MoM, standard walking, cup 45°, (n = 4). 36mm MOM, SDS: 10 walking cycles and pause of 5s with stance load of 1250N cup 45°, (n = 5). 36mm MOM, SDS: 10 walking cycles and pause of 30s with stance load of 1250N, (n = 5) cup 45°. 36mm MOM, standard walking, cup 55°(n = 5), and 65°(n = 5). All samples had matched clearances, measured using a CMM (Prismo Navigator, Zeiss, Germany). Wear was measured gravimetrically (Sartorius ME235S: 0.01mg). Results and Discussion. Metal-on-metal hip bearings are known to exhibit a bi-phasic wear pattern in-vitro (1), with the majority of wear occurring over the first 1–1.5mc, followed by lower steady state wear as the components conform to each other. Therefore bedding in wear over the first 1 million cycles was compared for each of the sample groups in this study. Bedding in wear for 36mm bearings under standard angle (45 inclination) and walking conditions was 0.16±0.15mm3/mc, while for 28mm bearings, wear was 2.67±2.06mm3/mc. Positioning the acetabular cup at an increased angle led to increased wear. At 55bedding in wear was .25±0.29mm3/mc, while at 65wear was 0.65±0.32mm3/mc. When SDS conditions were applied, no significant increase in wear was observed under either the 5s or 30s pause conditions, with bedding in wear of 0.19±0.31mm3/mc and 0.14±0.13mm3/mc respectively. Conclusion. This study illustrates the robust performance of the 36mm MoM bearing under extreme test conditions when compared with 28mm MoM. No effect was observed with the application of stop-dwell-start conditions, and only a small increase in wear was observed when the cup was inclined to a greater angle. Despite the application of extreme test conditions, the 36mm MoM still demonstrates lower wear than 28mm under all conditions. In all but the 65 inclination conditions, this difference is statistically significant. This study replicates some of the more frequently observed extreme conditions measured in real patients with THRs (2,3). Even under these more aggressive scenarios, wear of the 36mm bearing is still relatively low when compared with a commercially available 28mm THR

Introduction. One of the most common complications of ceramic on ceramic hip replacement is squeaking. The association of Accolade stem and Trident acetabular system has been reported to have squeaking incidence of up to 35,6%. There is doubt if this phenomenon occurs due to: the stem titanium alloy, the V40 femoral neck, the recessed liner of the trident cup or even the mal-seating of the trident insert on the cup. Objectives. Primary: The purpose of the present study was to determine the incidence of squeaking in association with the use of Exeter stem and Trident ceramic acetabular system. Secondary: Analysis of the correlation of the cup abduction angle and squeaking. Methods. During the period from March 2004 to December 2008, two surgeons performed 87 total hip arthroplasties in 77 patients with use of a ceramic-on-ceramic bearing (Exeter stem, alumina head, Trident ceramic acetabular system). Seventy six patients (86 THA) were available for review after at least 18 months follow-up. The incidence of squeaking and other noises was analyzed. Cup abduction angle was measured. The Pearson correlation coefficient was used to determine if a correlation existed between the cup abduction angle and squeaking. Results. The incidence of squeaking was 2,63% (2 patients). Both patients reported a “click” noise in hyperextension of the hip. The mean abduction angle was 44 degress (35–60), and 48 degrees (46 and 50) on the squeaking group. There was no statistically significant difference in the in the mean cup inclination between squeaky and quiet hips. Conclusion. The incidence of squeaking in association with the use of Exeter stem and Trident ceramic acetabular system was 2,63%. There was no correlation of the cup abduction angle and squeaking

Introduction. The prosthetic impingement occurs if the range of motion of the hip exceeds implant mobility or in case of component malorientation. This retrieval study was designed to assess the frequency and the risk factors of this phenomenon. Material and Methods. The frequency and the severity of the impingement were calculated from a continuous series of 311 cups retrievals collected between 1989 and 2004 by a single surgeon. The reason for retrieval was loosening (131 cases), infection (43 cases), instability (56 cases), osteolysis (28 cases), unexplained pain (48 cases) and prosthetic impingent (5 cases all with hard bearings). The notching at the cup rim was assessed twice by two examiners with optic magnification. The risk factors were analyzed from clinical charts by univariate and cox multihazard. Results. Among the 311 cups explants, the frequency of impingement was 59.2% (it was severe in 11%, the notching exceeding 3 millimeters). The impingement was the reason for removal in only 1.6%, meaning that it was mainly unexpected (98.4 percent). The impingement was more frequent when revisions were performed because of instability (notching 80%), when the sum of hip motion exceeded 200 degrees (sum of motion in the 6 degrees of freedom of the hip) (notching 66%). The other risk factors were: use of heads with skirts, liner with an elevated rim, and head-neck ratio below 2, younger age at surgery. The multivariate analysis identified only two independent factors: 1) the use of skirted heads (Odd ratio 3.2 (1.2–15.3)), 2) and revision because of instability (Odd ratio 4.2 (1.1–16.2)). In contrast different classical factors were not correlated with impingement on retrieval: cup inclination, the duration before retrieval, the indication for primary prosthetic replacement. Discussion and Conclusion. This study underlines the impingement is common when assessing cup retrievals (over 50 percent). One should be aware of impingement when performing hip replacement in patients having a high range of motion. This situation may require prostheses with a high head-neck ratio, as well as use of computer-assisted surgery. One should avoid liners with elevated rim as well as heads with skirts to prevent dislocation, particularly when other risk factors are detected

Introduction. Large wear rate reductions have been shown for crosslinked PE in simulators and short- to mid-term clinical wear studies. However, concerns persist about long-term in-vivo oxidation (especially with annealed PE), late accelerating wear and the possibly higher osteolytic potential of crosslinked PE particle debris. This is the first long-term study comparing conventional to crosslinked PE investigating whether the wear reduction is maintained in the long-term and if reduced osteolysis becomes evident. Materials & Methods. In a prospective study 48 primary THA patients (Stryker ABG-II, 28mm CoCr heads) were randomized to either receive a first generation crosslinked PE (Stryker Duration: 3MRad gamma irradiation in N2, annealed) or then conventional, now “historic” PE (3MRad gamma irradiation in air). Both groups were statistically non-different (p>0.1) regarding age (63.9 years), gender, BMI, stem and cup size, cup inclination, liner thickness or pre- and post-op HHS leaving the insert material as the only variable. Patients were followed-up annually using the Harris Hip score, AP and lateral radiographs and digital wear measurements using Roman V1.70 [1, 2]. Wear and radiographic signs of osteolysis were analysed at a mean follow-up of 12.9 years (12.0–13.3). Groups were compared using the t-test (means) or the Fisher Exact test (proportions). Results. Thirty-one patients (18 conventional, 13 Duration) were left for analysis (8 deaths, 9 lost to FU). At 13yrs the total linear head penetration was sign. lower with Duration (0.70 ±0.36mm, range: 0.3–1.2mm) than conventional PE (1.56 ±0.83, range: 0.4–3.3mm, p=0.015). Also the annual wear rate was sign. lower (p=0.005) for Duration (0.063 ±0.027mm/yr) than conventional PE (0.122 ±0.065mm/yr). This reduction (−48%) compared well to the original simulator prediction (−45%) and even increased with time (−30% at 5yrs, −38% at 8yrs, −42% at 10yrs). In the Duration group only 1 patient had a wear rate >0.1mm/yr (osteolysis threshold) compared to 10 in the Conventional group (p=0.007). Patients with radiographic signs of acetabular osteolysis (cysts) on the AP x-ray were less frequent in the Duration (4/13=31%) than in conventional group (13/18=72%, p=0.023). This difference became even more pronounced when also the lateral view was evaluated and the affected DeLee-Charnley zones were counted (7 vs 22, p=0.017). Only in the conventional group a revision was performed (cup for wear). Discussion & Conclusions. At long-term FU the absolute wear rate of Duration crosslinked PE did not increase but decrease and the wear relative reduction did not deteriorate but increased. The incidence of osteolysis was sign. less. Thus No clinical evidence of degradation or elevated osteolytic potential for this annealed first generation crosslinked PE debris was found