Peri-prosthetic bone mineral density after simultaneous bilateral total knee arthroplasty under oral bisphosphonate therapy — A comparison between mobile- and fixed-bearing prostheses

Peri-prosthetic bone mineral density (BMD) decreases after total knee arthroplasty (TKA). We aimed to specifically compare peri-prosthetic BMD changes between mobile- and fixed-bearing prostheses in patients undergoing oral bisphosphonate therapy, hypothesizing that mobile-bearing components would have a favorable effect on postoperative peri-prosthetic BMD.

This prospective cohort study investigated 30 patients who underwent simultaneous bilateral TKA for primary knee osteoarthritis between December 2007 and September 2012. All patients underwent mobile-bearing TKA in one knee and fixed-bearing TKA in the other and received oral alendronate therapy at a dosage of 35 mg/week. Peri-prosthetic and lumbar spine BMDs were measured using dual X-ray absorptiometry scans, with peri-prosthetic BMD changes being compared between the two prostheses in each patient at six months and one, two, three, and five years post-operation.

Clinical results did not significantly differ between two prostheses. Relative change of lumbar spine BMD was significantly greater at five years post-operation than at one year post-operation (p = 0.01), and was significantly correlated at five years post-operation with peri-prosthetic BMD in the central femur (r = 0.39, p = 0.002), posterior femur (r = 0.39, p = 0.002), and medial tibia (r = 0.42, p = 0.007).

There was no difference in peri-prosthetic BMD changes between two prostheses in patients undergoing oral bisphosphonate therapy. Our results suggest that the influence of oral bisphosphonate therapy might offset the influence of prosthetic design. Thus, oral bisphosphonate therapy may be more effective than prosthetic design selection in preventing post-TKA peri-prosthetic BMD loss.

Level of evidence: II