Abaloparatide Increases Distal Femur Bone Mineral Density Post-Total Knee Arthroplasty

Osteoporosis is common in joint replacement patients and increases adverse outcome risk. Data indicate that total knee arthroplasty (TKA) causes distal femur bone loss. We hypothesized that abaloparatide (ABL) would mitigate this loss. The study's purpose was to evaluate the effect of ABL initiated before TKA on distal femur bone mineral density (BMD) in osteoporotic patients.

TKA candidates age ≥55 years were enrolled in this open-label, prospective, observational 18-month study. Those with clinical osteoporosis, defined as lowest T-score ≤ -2.5 or < -1.0 if prior low-trauma fracture, received daily ABL. TKA patients with osteopenia without fracture comprised an untreated control group. BMD was measured by dual energy x-ray absorptiometry at the L-spine, hip, radius and 2 distal femur regions of interest (ROIs) placed at 15% and 25% of femur length at screening (∼3 months pre-TKA), 1 week pre-TKA, and 6 months and 15 months post-TKA. Patient-reported outcomes were obtained at the same time points. Groups were compared at screening by t-test. Between group outcomes over time were evaluated by repeated measures mixed modelling.

At screening (n = 58; 29 ABL/29 control) sex, mean age and mean BMI did not differ between groups. ABL group screening BMD was lower (p ≤ 0.05) at all sites except the L-spine. ABL was dosed for a mean (SD) of 96 (60) days before TKA. Control group distal femur BMD was statistically unchanged, -1.0% and -2.4% at the 15% and 25% ROIs, respectively, at 15 months post-TKA, (p ≥ 0.34). ABL group distal femur BMD increased at the 15% and 25% ROIs and differed from control by 4.6% to 7.6% (all p < 0.01) at 6 and 15 months post-TKA. Knee injury and Osteoarthritis Outcome Score for Joint Replacement demonstrated significantly worse (<0.05) function at baseline in the osteoporotic group and greater improvement over time compared with controls.

ABL increases distal femur BMD in osteoporotic patients undergoing TKA. Unlike prior reports distal femur BMD did not decrease after TKA among controls; further study to clarify the effect of TKA on distal femur BMD is needed.

Clinical trial status-open-label prospective trial registered at ClinicalTrials.gov: NCT04167163.

Level II, Therapeutic. See Instructions for Authors for a complete description of levels of evidence.