Changes in Bone Mineral Density of the Femur and Tibia Before Injury to 2 Years After Anterior Cruciate Ligament Reconstruction in Division I Collegiate Athletes

Background: Osteoarthritis (OA) is a significant long term concern after anterior cruciate ligament (ACL) reconstruction (ACLR). A low bone mineral density (BMD), particularly in the subchondral region, has been associated with the development of OA and is evident at the knee in patients long after ACLR. It is unknown if persistent BMD deficits are present in high level collegiate athletes. Purpose/Hypothesis: The purpose of this study was to evaluate bilateral changes in the BMD of the femur and tibia from before the injury to 24 months after ACLR in collegiate athletes. We hypothesized that the BMD of both the distal femur and the proximal tibia would be significantly reduced within the surgical limb initially postoperatively but return to preinjury levels by 24 months after ACLR. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 33 Division I collegiate athletes were identified between 2010 and 2021 (13 female) who underwent total body dual-energy X-ray absorptiometry (DXA) before sustaining an ACL injury. DXA was repeated at 6, 12, and 24 months after ACLR. Linear mixed effects models assessed differences in the BMD at 5%, 15%, and 50% of the femur's length (F 5 , F 15 , F 50 ) and at 5%, 15%, and 50% of the tibia's length (T 5 , T 15 , T 50 ) within each limb from before the injury to 24 months after ACLR, reported as Tukey-adjusted P values. Results: Compared with before the injury, the BMD at F 5 of the surgical limb was reduced by 0.15 g/cm 2 (SE, 0.02 g/cm 2 ) at 6 months ( P < .001). The BMD at F 15 of the surgical limb was reduced by 0.06 g/cm 2 (SE, 0.01 g/cm 2 ), 0.09 g/cm 2 (SE, 0.01 g/cm 2 ), and 0.09 g/cm 2 (SE, 0.01 g/cm 2 ) at 6, 12, and 24 months, respectively (all P < .001). The BMD at T 5 of the nonsurgical limb was reduced by 0.07 g/cm 2 (SE, 0.02 g/cm 2 ) at 12 months ( P = .02) and 0.10 g/cm 2 (SE, 0.02 g/cm 2 ) at 24 months ( P = .001). The BMD at T 15 of the surgical limb was reduced by 0.07 g/cm 2 (SE, 0.01 g/cm 2 ) at 6 months and 0.08 g/cm 2 (SE, 0.02 g/cm 2 ) at 12 months ( P < .001). Conclusion: BMD deficits at F 15 of the surgical limb persisted out to 24 months (–7.1%) after ACLR compared with before the injury in collegiate athletes. The BMD at F 5 and T 15 of the surgical limb was reduced at 6 and 12 months but not at 24 months compared with preinjury levels. For the nonsurgical limb, no significant differences were detected, except for the T 5 region at 12 months (–5.1%) and 24 months (–7.2%). The BMD at F 50 and T 50 of both limbs was not significantly different than preinjury levels at any time after ACLR.