Purpose Aberrant walking biomechanics after anterior cruciate ligament reconstruction (ACLR) are hypothesized to be associated with deleterious changes in knee cartilage. T1ρ magnetic resonance imaging (MRI) is sensitive to decreased proteoglycan density of cartilage. Our purpose was to determine associations between T1ρ MRI interlimb ratios (ILR) and walking biomechanics 6 months after ACLR. Methods Walking biomechanics (peak vertical ground reaction force (vGRF), vGRF loading rate, knee extension moment, knee abduction moment) were extracted from the first 50% of stance phase in 29 individuals with unilateral ACLR. T1ρ MRI ILR (ACLR limb/uninjured limb) was calculated for regions of interest in both medial and lateral femoral (LFC) and medial and lateral tibial condyles. Separate, stepwise linear regressions were used to determine associations between biomechanical outcomes and T1ρ MRI ILR after accounting for walking speed and meniscal/chondral injury (P ≤ 0.05). Results Lesser peak vGRF in the ACLR limb was associated with greater T1ρ MRI ILR for the LFC (posterior ΔR 2 = 0.14, P = 0.05; central ΔR 2 = 0.15, P = 0.05) and medial femoral condyle (central ΔR 2 = 0.24, P = 0.01). Lesser peak vGRF loading rate in the ACLR limb (ΔR 2 = 0.21, P = 0.02) and the uninjured limb (ΔR 2 = 0.27, P = 0.01) was associated with greater T1ρ MRI ILR for the anterior LFC. Lesser knee abduction moment for the injured limb was associated with greater T1ρ MRI ILR for the anterior LFC (ΔR 2 = 0.16, P = 0.04) as well as the posterior medial tibial condyle (ΔR 2 = 0.13, P = 0.04). Conclusion Associations between outcomes related to lesser mechanical loading during walking and greater T1ρ MRI ILR were found 6 months after ACLR. Although preliminary, our results suggest that underloading of the ACLR limb at 6 months after ACLR may be associated with lesser proteoglycan density in the ACLR limb compared with the uninjured limb.

Purpose To compare gait biomechanics throughout stance phase 6 and 12 months after unilateral anterior cruciate ligament reconstruction (ACLR) between ACLR and contralateral limbs and compared with controls. Methods Vertical ground reaction force (vGRF), knee flexion angle (KFA), and internal knee extension moment (KEM) were collected bilaterally 6 and 12 months post-ACLR in 30 individuals (50% female, 22 ± 3 yr, body mass index = 23.8 ± 2.2 kg·m−2) and at a single time point in 30 matched uninjured controls (50% female, 22 ± 4 yr, body mass index = 23.6 ± 2.1 kg·m−2). Functional analyses of variance were used to evaluate the effects of limb (ACLR, contralateral, and control) and time (6 and 12 months) on biomechanical outcomes throughout stance. Results Compared with the uninjured controls, the ACLR group demonstrated bilaterally lesser vGRF (ACLR, 9% body weight [BW]; contralateral, 4%BW) during early stance and greater vGRF during midstance (ACLR, 5%BW; contralateral, 4%BW) 6 months post-ACLR. Compared to the uninjured controls, the ACLR group demonstrated bilaterally lesser vGRF (ACLR, 10%BW; contralateral, 8%BW) during early stance and greater vGRF during midstance (ACLR, 5%BW; contralateral, 5%BW) 12 months post-ACLR. Compared with controls, the ACLR limb demonstrated lesser KFA during early stance at 6 (2.3°) and 12 months post-ACLR (2.0°), and the contralateral limb demonstrated lesser KFA during early stance at 12 months post-ACLR (2.8°). Compared with controls, the ACLR limb demonstrated lesser KEM during early stance at both 6 months (0.011BW × height) and 12 months (0.007BW × height) post-ACLR, and the contralateral limb demonstrated lesser KEM during early stance only at 12 months (0.006BW × height). Conclusions Walking biomechanics are altered bilaterally after ACLR. During the first 12 months post-ACLR, both the ACLR and contralateral limbs demonstrate biomechanical differences compared with control limbs. Differences between the contralateral and control limbs increase from 6 to 12 months post-ACLR.

The purpose of our study was to determine the association between biomechanical outcomes of walking gait (peak vertical ground reaction force [vGRF], vGRF loading rate [vGRF-LR] and knee adduction moment [KAM]) six months following anterior cruciate ligament reconstruction (ACLR) and biochemical markers of serum type-II collagen turnover (collagen type-II cleavage product to collagen type-II C-propeptide [C2C:CPII]), plasma degenerative enzymes (matrix metalloproteinase-3 [MMP-3]), and a pro-inflammatory cytokine (interleukin-6 [IL-6]). Biochemical markers were evaluated within the first two weeks (6.5±3.8 days) following ACL injury and again six months following ACLR in eighteen participants. All peak biomechanical outcomes were extracted from the first 50% of the stance phase of walking gait during a six-month follow-up exam. Limb symmetry indices (LSI) were used to normalize the biomechanical outcomes in the ACLR limb to that of the contralateral limb (ACLR /contralateral). Bivariate correlations were used to assess associations between biomechanical and biochemical outcomes. Greater plasma MMP-3 concentrations after ACL injury and at the six-month follow-up exam were associated with lesser KAM LSI. Lesser KAM was associated with greater plasma IL-6 at the six-month follow-up exam. Similarly, lesser vGRF-LR LSI was associated with greater plasma MMP-3 concentrations at the six-month follow-up exam. Lesser peak vGRF LSI was associated with higher C2C:CPII after ACL injury, yet this association was not significant after accounting for walking speed. Therefore, lesser biomechanical loading in the ACLR limb, compared to the contralateral limb, six months following ACLR may be related to deleterious joint tissue metabolism that could influence future cartilage breakdown.

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Relative to asymptomatic individuals, symptomatic individuals are more likely to underload the ACLR limb early following ACLR (i.e., <12 months) during both vGRF peaks, but overload the ACLR limb, during both vGRF peaks, at later time points (i.e., >24 months). We propose these differences in lower extremity loading during walking might have implications for long-term knee health, and should be considered when designing therapeutic interventions for individuals with an ACLR.