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Varus position does not affect short-term functional outcomes following THA with a taper-slip cemented stem

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GLASGOW – Orthopedic investigators from seven centers across the United Kingdom have found that functional outcomes and complications were unaffected by varus malalignment up to 5 years following total hip arthroplasty with a polished, double-tapered stem.

Munier Hossain, PG Cert, MSc(Orth Eng), MSc(EBHC), FRCS(Glas),FHEA, presented the findings here, at the 2010 Meeting of the Combined Orthopaedic Associations.

“We feel that it is reasonable to conclude that functional outcomes or complications were unaffected by varus position of a cemented tapered stem, and we feel that, compared to a composite beam hip, it may be more tolerant of malalignment,” Hossain said.

Cohort study

Hossain and colleagues conducted a multicenter prospective cohort study that included 1,189 patients who were consecutively recruited between 1999 and 2002. All patients received an Exeter hip stem (Stryker).

Radiographs were obtained on all patients at 1-year follow-up and for 938 patients at 5-year follow-up. For the purposes of determining functional outcome, Hossain and colleagues used the Oxford hip score as the primary outcome measure. Secondary outcomes included dislocation, revision and radiological signs of radiolucency, stem subsidence and cement fracture.

For their study, the investigators considered malalignment to be greater than 5°. They observed varus malalignment, ranging from 5° to 7.8° in 44 patients and valgus malalignment, ranging from 5° to 7.4° in 10 patients.

No significant differences

Hossain reported that there was no significant difference between patients with varus or valgus malalignment compared with those with no malalignment when considering the following baseline characteristics: gender, age, body mass index (BMI) and preoperative Oxford hip score.

Oxford hip scores at 5-year follow-up were again similar between all patients included in the study, ranging from approximately 40 in patients with neutral alignment to 42 in patients with valgus malalignment. Rates of revision and dislocation were also similar among all patients, as were the radiological results.

Hossain acknowledged such limitations to their study as a “convenient sample” and missing data. Additionally, “We do accept that we probably need longer follow-up to comment on aseptic loosening,” he said.

Reference:

• Hossain M, et al. The consequences of varus implantation of a taper-slip cemented femoral stem. Presented at the 2010 Meeting of the Combined Orthopaedic Associations. Sept. 13-17, 2010. Glasgow.
• This study was funded by Stryker Howmedica Osteonics.

The problem with looking at varus and valgus is that it automatically changes the offset of the long axis of the shaft from the center rotation of the femoral head. Varus and valgus has a much greater effect on that than any other varus and valgus per say. Varus and valgus, long-term, might have an impact on whether there is loosening in 15 years, but to look at the short-term follow-up in a huge number of people is really not going to show you anything unless you look at the impact of what the varus and valgus actually means to the biomechanics of the hip.

– Peter Devane, MD
Wellington, New Zealand

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