Purpose: A ceramic head coupled to a metal liner is a proposed new alternate bearing in THA. The authors participated in an FDA approved multicentre prospective, randomized, blinded clinical trial comparing ceramic-on-metal (CoM) to metal-on-metal (MoM) in patients receiving a THA.

Method: 390 patients received the same acetabular component and metal insert. 194 patients received a delta ceramic head (CoM) and 196 received a metal head (MoM). Metal ions were evaluated in 72 patients (36-CoM, 36-MoM). Harris Hip scores, radiographs, and metal ion levels (cobalt, chromium and titanium in serum, erythrocytes and urine) were evaluated pre-operatively and at three, 12 and 24 months.

Results: No patients were lost to follow-up. There were no differences between groups’ baseline demographics and clinical scores. At two years there were no differences in Harris Hip scores, radiographs, adverse events or postoperative complications. Both groups had overall very low median metal ion profiles with no statistically significant differences. 24 month MoM vs CoM; Serum cobalt ( g/L), mean: 1.2(+/−0.5) vs 1.1(+/−0.3), median: 0.66(range: 0.2–5.6) vs 1.0 (range: 0.3–2.7); Serum chromium ( g/L), mean: 1.1(+/−0.5) vs 1.4(+/−0.4), median: 0.86(range: 0.3–6.9) vs 1.2(range: 0.3–4.9). Urine cobalt and urine chromium ( g/day) demonstrated similar trends to serum ion levels.

Conclusion: While CoM is a new bearing surface in North America and not currently FDA or HPB approved, it has been in clinical use globally since 2006. Results of this non-inferiority RCT demonstrated no clinical outcome, metal ion, radiographic or adverse event differences between CoM and MoM cohorts.

Purpose: The purpose of this prospective blinded randomized control trial was to compare the stem migration of two cemented stem designs using radiostereometric analysis (RSA). This was essentially a safety study in which our hypothesis was that the newer design (CPCS, Smith and Nephew Inc) would demonstrate similar micro-motion to the well-established Exeter (Stryker) design.

Method: Thirty patients were consented and enrolled into a blinded RCT in which 15 patients received a dedicated RSA CPCS stem and 15 patients received a RSA Exeter stem. Both stems are collarless tapered polished cemented stems, the only difference being a slight lateral to medial taper with the CPCS design. Outcome measures were compared (Hip Society Score, WOMAC, SF-12). RSA analysis was conducted immediately postoperatively, at 6 weeks, 3 months, 6 months, 1 year and 2 years.

Results: No difference was found in any of the outcome measures pre-operatively or postoperatively. At 2 years, stem subsidence for the CPCS stem was approximately half that seen for the Exeter stem (0.565±0.189mm and 0.981±0.209mm respectively, p< 0.0001). In contrast, posterior (internal) rotation of the CPCS was approximately twice that of the Exeter stem (1.496±1.215° and 0.716±0.818° respectively, p=0.221). Other migration patterns were no different between stems.

Conclusion: As expected with this stem design, both stems showed some axial and rotational migration within the cement mantle. The subtle differences in design may explain the differences in migration patterns. Our data suggests that the newer CPCS design should perform well over the long-term.

Purpose: Metal-on-metal articulations are an increasingly popular choice as an alternate bearing surface in total hip arthroplasty (THA) and Resurfacing implants. One advantage of a metal-on-metal bearing is the use of larger diameter femoral heads with hip simulator data demonstrating reduced wear. We performed a prospective, multicentre, randomized, blinded clinical trial comparing 28mm to 36mm metal-on-metal bearings assessing multiple validated outcome measures and serum, erythrocyte and urine metal ions.

Method: Ninety-one patients were randomized to receive a metal-on-polyethylene (34), a 28mm metal-on-metal (25) or a 36mm metal-on-metal (32) insert. All patients received the same acetabular and femoral component. Patients were evaluated pre-operatively, at 6, 12 months and annually thereafter, including an evaluation of serum, erythrocyte and urine cobalt, chromium, and titanium, outcome measures (WOMAC, SF-12, Harris Hip Score) and radiographs.

Results: At a minimum two years follow-up there were no differences in WOMAC, SF-12, Harris Hip scores or radiographs. Patients receiving metal liners had significantly (p< 0.001) elevated metal ion measurements compared with the polyethylene control group, however there were no differences between the 28mm and 36mm metal-on-metal bearings (Median serum Co (mg/L): 0.14(poly), 0.77(28mm), 0.73(36mm). Median erythrocyte Co (mg/L): 0.11(poly), 0.42(28mm), 0.42(36mm). Median urine Co(mg/day): 0.44(poly), 4.55(28mm), 5.42(36mm)). (Median serum Cr(mg/L): 0.17(poly), 1.29(28mm), 0.91(36mm). Median erythrocyte Cr(mg/ L): 1.10(poly), 1.10(28mm), 1.20(36mm). Median urine Cr(mg/day): 0.27(poly), 1.92(28mm), 2.02(36mm)).

Conclusion: Both cobalt and chromium ion measurements were significantly elevated in the blood and urine of the patients randomized to receive the metal-on-metal bearings at all time intervals. There were no differences seen between the 28mm and 36mm metal-on-metal bearings, keeping all other variables identical. The larger diameter bearing therefore provides the potential clinical advantages of improved range of motion and stability, while providing a similar metal ion profile. While reduced wear is seen with larger diameter metal-on-metal bearings in-vitro, we could not demonstrate a reduction in blood or urine metal ion levels in-vivo.