Abstract
Introduction
Modern acetabular shells have many liner options from which the surgeon can choose to most appropriately reconstruct the arthritic hip. Lateralised liners are one option that is available to the surgeon and these liners have potential benefits over “standard” polyethylene liners. Benefits include decreased Von Mises stresses which may lead to decreased polyethylene wear, lateralisation of the femur away from the pelvis which can decrease impingement / increase ROM and having the ability to use larger femoral heads in a smaller shell improving stability of the THA. Despite these benefits, lateralised liners are not routinely used by surgeons as there is concern over lateralisation of the centre of rotation of the hip with increased joint reaction forces, unsupported polyethylene that could lead to liner failure, and a slightly increased torque moment to the shell which could lead to micromotion and failure of the shell to obtain bony ingrowth. This study reports on 5-year minimum clinical and radiographic F/U of a prospective series of lateralised, moderately crosslinked polyethylene liners.
Methods
102 consecutive patients who were to have a THA with a polyethylene liner were enrolled prospectively in an acetabular shell study. Two patients that had standard thickness liners were excluded from this analysis. The remaining 100 patients all had +4 lateralised liners of the same construct (Marathon polyethylene / Pinnacle Cup, DePuy, Warsaw, Indiana). All surgeries were performed by the same surgeon via a posterior approach. A neutral or 10 degree face changing liner was chosen based on shell position and stability of the THA construct. Patient data including the Harris Hip Score (HHS), WOMAC and ROM was collected at 3, 6 and 12 months and yearly thereafter. Radiographs were obtained at each visit.
Results
87 patients with minimum 5-year clinical and radiographic F/U were evaluated. Average age was 68.7 years with an average BMI of 27.3. Average F/U was 7.5 years (5–10.1). Sixty-one liners were neutral and 26 were 10° face changing. HHS improved from 44 pre-op (18–71) to 95 at latest F/U (68–100). Kaplan-Meier survivorship was 97% at an average of 7.5 yr. Three liners were revised – one during revision of a femoral stem, one for sepsis, and one for instability. There were no mechanical failures or liner dissociations. Radiographic F/U revealed no obvious polyethylene wear or osteolysis. All cups were radiographically ingrown.
Conclusions
Lateralised liners can provide advantages with respect to wear, ROM and stability of the THA construct when compared to standard thickness liners. Concerns of increased polyethylene wear, failure of the cup to ingrow and potential liner dissociation or failure were not seen. At midterm F/U this particular lateralised liner/shell construct appears to be performing well clinically and radiographically with excellent survivorship. Although further F/U is required to evaluate long-term performance, these results should allow surgeons to use this construct on a routine basis without fear of early or mid-term complication.
