EXCLUSIVE CONSECUTIVE USE OF RECTANGULAR STRAIGHT STEMS IN PRIMARY THA OUTCOME AT 10 YEARS PLUS

Abstract

Introduction: Cementless tapered straight stems of the first generation were introduced in 1979, those of the second generation in 1986. For further perfection SL-PLUS stems were introduced in early 1993. These were redesigned proximally and featured slimmer necks for a larger range of motion, a central trochanteric pull-out thread and a larger surface area in the proximal stem third.

Method: Between 01/01/1993 and 31/03/1994 339 patients were implanted with these cementless new-generation stems. In the period under review no stems other than these, e.g. cemented implants or other implant systems, were used in primary THAs.

Of the 339 patients, 218 were available for follow-up, 72 had died, 38 without revision surgery were contacted by phone and 11 were lost to follow-up.

The underlying pathology was idiopathic degenerative joint disease (153 pts.), dysplastic OA (37 pts.), femoral head necrosis (12 pts.), posttraumatic OA (6 pts.) and OA of other origins (5 pts.). To evaluate changes in stem position, radiolucent lines, osseointegration and revision, clinical and monitor-controlled radiographic follow-ups were conducted at 10 years plus.

Results: 5 patients were revised within the follow-up time because of: one aseptic loosening, one low-grade infection, two periprosthetic fractures, one traumatic subsidence.

At the 10 year follow-ups (10,0 to 11,1, mean 10,2 years) the stem position was unchanged in all of the 213 patients. The stems had been implanted in proper anatomical alignment in 196 patients, in varus in 16 and in valgus in one patient. 93 patients showed no changes of the peri-implant bone. In 96 peri-implant bone apposition was recorded in one or more zones (Gruen). 20 patients presented with radiologic evidence of both peri-implant bone apposition and some atrophy. None of these patients showed abnormalities clinically (HHS: 95.2; 76–100). At the 10-year follow-ups 2 stems had worked loose. Another 2 patients presented with intertrochan-teric osteolyses with definite progression versus the 5-year follow-up. On analysis, radiolucent lines (RLs) were seen in zone 1 in 28.6% of cases, in zones 2 and 6 in 3.3%, in zones 3, 4 and 5 in 0.5% and in zone 7 in 22.1%.

The Kaplan-Meier survival rate was 98.2% (CI 95.3 to 99.2) with revision of the stem for any reason as the end point (N = 339).

Conclusion: The outcome of this quality control study showed the stem to be universally applicable in all primary THAs so that its continued use in the indications listed is well justified.