Thirteen year follow-up of a cementless femoral stem and a threaded acetabular cup in patients younger than fifty years of age.

PURPOSE

Compared to older patients undergoing total hip arthroplasty (THA) younger patients are considered to be more active, thereby exposing the implant to significantly higher loads over a much longer period of time. Additionally, cases of secondary osteoarthritis caused by hip dysplasia, femoral head necrosis or rheumatic diseases are much more frequent than among the average patient population. Therefore, durable implant fixation and low wear rates are extremely important to achieve good long-term implant survival in this group of patients.

OBJECTIVE

The aim of this retrospective study was to evaluate the mid- to long-term survival of a cementless femoral stem (Zweymüller® SL stem) and a threaded cup (Bicon SL®) in patients younger than 50 years of age.

METHODS

Therefore, a consecutive series of 100 patients (111 hips) aged 50 years or younger (range: 30 to 50 years) was analysed at a mean follow up of 13.5 years. Follow-up assessment included physical examination and radiographic workup. Hip disability osteoarthritis and outcome score (HOOS) and Harris hip score (HHS) were used to evaluate the pre- and post-operative functional outcome, respectively. Patient satisfaction with the surgical result was assessed by standardized questionnaires.

RESULTS

The overall survival rate with any revision as endpoint was 96.8 % (95 % CI: 90.5 % to 98.9 %) at ten years. Gender, operation time and the occurence of osteolyses had no influence on joint function or patient satisfaction. We recorded an overall failure rate of 7.4 % (six cases). In four cases (5 %) the prosthesis had to be revised due to aseptic loosening of the cup after 12 years, eight years, 12 years and 11 years, in one case (1.2 %) recurrent luxation led to a revision operation (acetabular cup and head) after three years of primary implantation. In one case an implant failure was recorded (acetabular cup breakage after eight years of implantation). We recorded the occurence of asymptomatic radiolucent lines of the cup in 21 % and of the stem in 35 % in our series. The HOOS was influenced by the presence or abscence of radiolucent lines of the stem. Patients with radiolucent lines of the stem had a median HOOS score of (74 points) compared to those without radiolucent lines (89 points). Other factors, such as "diagnosis led to operation" and "previous operations" had no influence on the HHS and HOOS.

CONCLUSION

Our study demonstrates excellent long-term survival of cementless femoral stem in combination with a threaded cup in young patients undergoing total hip arthroplasty.