Abstract
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.
