Authors

  1. Schoen, Delores C.

Article Content

Eskelinen, A., Paavolainen, P., Helenius, I., Pulkkinen, P. & Remes, V. (2006). Total hip arthroplasty for rheumatoid arthritis in younger patients: 2,557 replacements in the Finnish Arthroplasty Register followed for 0-24 years.Acta Orthopaedica, 77, 853-865.

 

Little research has been reported in the literature related to young patients with rheumatoid arthritis (RA) regarding the results of THA. The purpose of this study was to investigate the outcome of THA for RA in patients under 55 years of age from the Finnish Arthroplasty Register. The study was based on patients who underwent a THA between 1980 and 2003. During the study period, 92,083 primary THAs were performed in Finland. Of those operations, 12,601 (14%) were performed on patients under 55 years of age, and RA was indicated in 20% (2,557 hips in 1,893 patients). The median duration of follow-up was 9.7 years.

 

The sex, age, personal identification number of the patient, and the side affected were recorded for all primary operations. The number and percentage of different implants used in the operations and the fixation method of each component (cemented or uncemented) were evaluated.

 

For statistical comparison, the stems and the cups used in the implants were each divided into four groups. Stems were classified as (a) uncemented proximally circumferentially porous-coated, (b) uncemented proximally circumferentially HA-coated, (c) uncemented uncoated (including isoelastic, grit-blasted, and sand-blasted uncemented stems), and (d) cemented (including polished, grit-blasted, and sand-blasted cemented stems). The cups were classified as (a) uncemented porous-coated press-fit, (b) uncemented HA-coated press-fit, (c) uncemented smooth-threaded, and (d) cemented all-polyethylene. THAs were classified into three groups as follows: (a) press-fit porous-coated uncemented (i.e., proximally porous-coated uncemented stem and press-fit porous-coated uncemented cup), (b) press-fit HA-coated uncemented (i.e., proximally HA-coated uncemented stem and press-fit HA-coated uncemented cup), and (c) cemented stem and cemented all-polyethylene cup.

 

Kaplan-Meier survival data were used to construct the survival probabilities of implants at 7, 10, and 15 years. Survival data obtained by Kaplan-Meier analysis were compared by the long-rank test. The endpoint for survival was defined as revision when either one component or the whole implant was removed or exchanged. The Cox multiple-regression model was used to study differences between groups and to adjust for potential confounding factors (implant concepts, age group, and sex).

 

Of the 2,557 THAs, 51% (1,293) were performed in patients aged 46-54 years. Fifty-two percent (1,331) were performed on the right hip. Seventy-four percent (1,889) of the patients were female. Over the study period, 71 different femoral components were used, although three quarters of them were used in fewer than 20 operations. Sixty percent of the stems were uncemented. The proportion of uncemented stems rose dramatically over the study period, and by the end of the study period the three most common brands were (a) Bi-Metric, (b) ABG II, and (c) Exeter Universal. Eighty-three different acetabular components (cups) were used, although three quarters of them were used in fewer than 20 operations. Eighty-two percent of the cups were uncemented, and the most common brands were (a) ABG II, (b) Biomet Vision, and (c) Biomet M38. The proportion of uncemented cups rose markedly over the study period. However, the authors note that cemented cups have regained popularity in the early years of the 21st century.

 

The statistical analysis showed that when the whole study period was analyzed with the endpoint defined as revision due to aseptic loosening of the stem and/or cup, all THA concepts showed <90% survival rates at 7 years. By 15 years, the survival rate had dropped to 75% for proximally porous-coated uncemented stem and press-fit porous-coated uncemented cup (PCU) and 76% for cemented stem and cemented all-polyethylene cup (CE). With the endpoint defined as any revision, the 7-year survival for PCU was 92%; for proximally HA-coated uncemented stem and press-fit HA-coated uncemented cup (HAU), 86%; and for CE, 93%. However, after 15 years, the survival proportion for PCU was down to 65%, and for CE it was down to 74%. Although the CE procedure had a higher proportion surviving, the differences were not statistically significant.

 

The results of this study show that there are sizeable differences by type of implant for both endpoints considered. Even though the current results were not statistically significantly at the .01 level, the magnitude of the differences calls out for further research. For major procedures that are extremely common, it is important to have a better appreciation of what leads to longer implant survival.