Although cementless total hip replacement (THR) has become the standard in the US and has dramatically increased as compared with cemented fixation in Europe over the last decade, the data of the Scandinavian registries do not support this evolution. Indeed, the data from the Swedish register1 clearly indicates that uncemented components have not performed as well as cemented components in terms of survival. The outcome of the historical cohort from the paper McLaughlin and Lee are in accordance with these results showing a high incidence of thigh pain, osteolysis and loosening requiring revision on both the femoral and acetabular side.2 From the mid 90’s, refinements in uncemented components included the addition of surface treatment to the acetabular components using porous or hydroxy-apatite coating, the absence of screws or the use of screw-holes obturators, and a highly polished inner surface of the metal-back shell along with an improved locking mechanism of the liner within the shell to decrease the incidence of backside wear. The results in terms of fixation demonstrated that these modifications led to a significant improvement with 10 to 15-year survival being comparable to the gold standard all-cemented implants. The paper of McLaughlin and Lee including 172 primary THAs using second generation component is important as the initial cohort at a minimum of 12-year follow-up had no patient lost to follow-up, and the 47 deceased patients had a known outcome with regard to component fixation. This paper outlines the value of introducing limited new variables when modifying an implant to allow comparison with historical data. The survival at 16 years with revision for aseptic loosening as the endpoint was 100% for the femoral component and 98% (CI 95%, 93 to 99) for the acetabular component. No additional femoral or acetabular component was radiologically loose. Localised osteolysis was observed around two femoral and four acetabular components. Thigh pain was present in only four hips. Other similar series using second generation cementless implants have shown similar results as indicated by the authors. Interestingly, the wear rate of the polyethylene insert in the current series was very low with a mean of 0.036 mm/year. Although the polyethylene was not highly cross-linked with gamma radiation dose limited to 2.5 to 4 Mrads in an inert environment, the inserts were made from Himont 1900 which is a calcium stearate free isostatic compression moulded resin. To the best of my knowledge, Himont 1900 is no longer available, and current polyethylene is made of GUR 1020 or GUR 1050, either from moulded sheet or extruded bar. These latter processes, as indicated in the paper by McLaughlin and Lee, using a conventional radiation dose have resulted in higher wear rates when compared with Himont 1900. The current standard for polyethylene is highly cross-linked and the results now reaching ten years have confirmed the in vitro investigations. Further improvements with the addition of vitamin E to the material seem promising in vitro, and clinical investigations are being currently performed in the form of randomised trials.
In conclusion, second generation cementless implants have now come of age, and they seem to perform similarly to all-cemented components. The main limitation to the survival of THR is no longer the method of fixation whether cemented or cementless, whereas wear of the polyethylene continues to limit the long term performance. The choice of the type of fixation should be guided by the surgeons’ practice, as both cemented and cementless fixation needs a satisfactory technique. We, as surgeons, should use what we have been trained to perform best.
1. Swedish hip arthroplasty register. Annual report 2008. Shortened Version. Available at: http://www.jru.orthop.gu.se/archive/AnnualReport-2008-eng.pdf. Accessed December 12, 2010.
2. Mc Laughlin JR, Lee KR. Total hip arthroplasty with an uncemented tapered femoral component. J Bone Joint Surg [Am] 2008;90-A:1290-6.
Hamadouche M, Professor, MD, PhD
Department of Orthopaedic Surgery, Hôpital Cochin, Paris, France