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 (F5, F15, F50) and at 5%, 15%, and 50% of the tibia's length (T5, T15, T50) 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 F5 of the surgical limb was reduced by 0.15 g/cm2 (SE, 0.02 g/cm2) at 6 months ( P < .001). The BMD at F15 of the surgical limb was reduced by 0.06 g/cm2 (SE, 0.01 g/cm2), 0.09 g/cm2 (SE, 0.01 g/cm2), and 0.09 g/cm2 (SE, 0.01 g/cm2) at 6, 12, and 24 months, respectively (all P < .001). The BMD at T5 of the nonsurgical limb was reduced by 0.07 g/cm2 (SE, 0.02 g/cm2) at 12 months ( P = .02) and 0.10 g/cm2 (SE, 0.02 g/cm2) at 24 months ( P = .001). The BMD at T15 of the surgical limb was reduced by 0.07 g/cm2 (SE, 0.01 g/cm2) at 6 months and 0.08 g/cm2 (SE, 0.02 g/cm2) at 12 months ( P < .001). Conclusion: BMD deficits at F15 of the surgical limb persisted out to 24 months (–7.1%) after ACLR compared with before the injury in collegiate athletes. The BMD at F5 and T15 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 T5 region at 12 months (–5.1%) and 24 months (–7.2%). The BMD at F50 and T50 of both limbs was not significantly different than preinjury levels at any time after ACLR.
Purpose Reduced bone mineral density of the distal femur (BMDDF) can persist long term after anterior cruciate ligament reconstruction (ACLR), even in athletes who return to high levels of competition. These deficits may have implications for the onset and progression of knee osteoarthritis. It is unknown if clinically modifiable factors are associated with losses in BMDDF. This study evaluated the potential influence of knee extensor peak torque (PT), rate of torque development (RTD), as well as peak knee flexion (PKF) angle and peak knee extensor moment (PKEM) during running, on longitudinal changes in BMDDF post-ACLR. Methods After ACLR, 57 Division I collegiate athletes underwent serial whole-body dual-energy x-ray absorptiometry (DXA) scans between 3 and 24 months post-ACLR. Of these, 43 athletes also had isometric knee extensor testing (21 female, 105 observations), and 54 had running analyses (26 female, 141 observations). Linear mixed-effects models, controlling for sex, assessed the influence of surgical limb quadriceps performance (PT and RTD), running mechanics (PKF and PKEM), and time post-ACLR on BMDDF (5% and 15% of femur length). Simple slope analyses were used to explore interactions. Results Athletes with RTD less than 7.20 (N·m)·kg−1·s−1 (mean) at 9.3 months post-ACLR demonstrated significant decreases in 15% BMDDF over time (P = 0.03). Athletes with PKEM during running less than 0.92 (N·m)·kg−1 (−1 SD below mean) at 9.8 months post-ACLR demonstrated significant decreases in 15% BMDDF over time (P = 0.02). Significant slopes were not detected at −1 SD below the mean for PT (1.75 (N·m)·kg−1, P = 0.07) and PKF (31.3°, P = 0.08). Conclusions Worse quadriceps RTD and running PKEM were associated with a greater loss of BMDDF between 3 and 24 months post-ACLR.
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