Quantitative computed tomography assessment of bone mineral density after 2 years' oral bisphosphonate treatment in postmenopausal osteoarthritis patients who underwent total knee arthroplasty.

OBJECTIVES

To identify the effects of two years' oral bisphosphonate (alendronate) treatment in patients who underwent total knee arthroplasty (TKA); to determine whether significant responses seen after the first year of treatment changed during the second year. Additionally, the study tried to identify factors relating to bone mineral density (BMD) changes.

METHODS

This was a prospective 2-year follow-up study of a previous 1-year report of postmenopausal women with knee osteoarthritis who underwent primary unilateral or staged bilateral TKA, after which they received 70 mg alendronate orally once-weekly. BMD was measured using quantitative computed tomography (QCT) on lumbar vertebrae at baseline (pre-TKA) and at 12 and 24 months. Factors associated with BMD changes were determined by regression analysis.

RESULTS

Sixty-one patients entered the second year and continued treatment for ≥ 24 months. Mean vertebral QCT BMDs at baseline and after 12 and 24 months' alendronate treatment were 71.8 mg/ml (41.9-97.5 mg/ml), 69.3 mg/ml (31.4-103.9 mg/ml), and 72.7 mg/ml (33.1-136.1 mg/ml), respectively. Patients undergoing bilateral TKA and who had more severe OA at baseline (bilateral severe [grade 4] OA) had a lower BMD response after 2 years' bisphosphonate treatment, compared with patients with less severe unilateral knee OA who underwent unilateral TKA. Improvements were, however, seen compared with year 1 levels. Low BMI was associated with BMD nonresponse.

CONCLUSIONS

Patients with bilateral severe OA (grade 4) requiring bilateral knee replacement are at greater risk of nonresponse after 2 years' oral alendronate treatment. A longer duration of treatment may be necessary in these patients.