Christin Büttner

Background: Aberrant walking biomechanics, a factor linked to knee osteoarthritis (KOA), are common after anterior cruciate ligament (ACL) injury. Although quadriceps weakness often persists after ACL reconstruction (ACLR), the extent to which strength recovery influences gait biomechanics over the first postoperative year, a critical window for implementing rehabilitation strategies, remains unclear. Hypothesis: Distinct quadriceps strength recovery trajectories will emerge after ACLR, with the lesser strength recovery group exhibiting more aberrant gait biomechanics compared with the greater strength recovery group and controls. Study Design: Prospective cohort study. Level of Evidence: Level 2. Methods: Of 62 enrolled patients with a primary ACL injury, 59 were eligible and matched with uninjured controls by sex, age, and body mass index (BMI). Quadriceps strength was assessed preoperatively and at 4, 6, and 12 months post-ACLR, and gait biomechanics, including vertical ground reaction force (vGRF), knee flexion angle (KFA), knee extension moment (KEM), and knee adduction moment (KAM), were assessed at 4, 6, and 12 months post-ACLR. Group-based trajectory modeling identified strength recovery profiles, and functional mixed effects modeling compared gait biomechanics between strength trajectory groups and controls. Results: Two distinct strength trajectories were identified. Both the weaker (N = 31) and stronger (N = 28) ACLR groups demonstrated lesser vGRF during early stance compared with controls, with maximum differences reaching −0.15 body weight (BW). Compared with the stronger group, the weaker group exhibited lesser KFA (–1.85° and −2.18° at 6 and 12 months) and KEM (0.006 BW × height at 4 and 6 months) during early stance. Compared with healthy controls, both ACLR groups exhibited lesser KFA and KEM during early stance across postoperative timepoints, with larger and more persistent differences observed in the weaker group. Only the weaker group had significantly lower KAM relative to controls (0.006 to 0.007 BW × height at 4, 6, and 12 months). Conclusion: Although the stronger group exhibited more dynamic gait waveforms than the weaker group, walking biomechanics were not fully normalized to those of healthy controls. Clinical Relevance: These findings highlight the need for complementary interventions to strength training during the first year post-ACLR to target aberrant biomechanics and potentially reduce long-term KOA risk.

Time spent in moderate-to-vigorous physical activity (MVPA) is linked to biomarkers associated with knee osteoarthritis development following anterior cruciate ligament reconstruction (ACLR). It remains unclear whether distinct MVPA trajectories exhibited during the first 12 months post-ACLR are linked to early markers of knee osteoarthritis. Purpose: To identify distinct MVPA trajectories between 2 and 12 months post-ACLR and compare tibiofemoral articular cartilage composition changes and patient-reported outcomes (PROs) between trajectory groups. Methods: Device-measured MVPA was collected at 2, 4, 6, and 12 months post-ACLR in individuals with ACLR. MVPA trajectories were identified using group-based trajectory modeling. Cartilage composition was measured preoperatively and at 12 months post-ACLR using change in T1ρ (ΔT1ρ) magnetic resonance imaging relaxation times in the lateral (lateral femoral condyle [LFC], lateral tibia) and medial (medial femoral condyle, medial tibia) femoral and tibial compartments. The Knee Injury and Osteoarthritis Outcomes Score (KOOS) was used to assess PROs preoperatively and at 2, 4, 6, and 12 months post-ACLR. Differences in KOOS subscale scores and ΔT1ρ were compared between MVPA trajectory groups. Results: We identified a consistent MVPA (74.5%) and a high-increasing MVPA trajectory (25.5%). The high-increasing trajectory group engaged in more MVPA at all time points compared with the consistent group. The high-increasing trajectory group demonstrated greater ΔT1ρ in the LFC (i.e., deleterious changes in cartilage composition, P = 0.006) and higher KOOS sport compared with the consistent MVPA group ( P = 0.037). Conclusions: Individuals between 2 and 12 months post-ACLR most commonly engage in the consistent MVPA trajectory. The high-increasing MVPA trajectory group demonstrated worsening LFC cartilage composition. These data indicate that high MVPA in the first 12 months post-ACLR may be linked to deleterious knee tissue changes but not worse PROs.

Context: Gait biomechanics and daily steps are important aspects of knee-joint loading that change after anterior cruciate ligament reconstruction (ACLR). Understanding their relationship during the first 6 months post-ACLR could help clinicians develop comprehensive rehabilitation interventions that promote optimal joint loading after injury, thereby improving long-term knee-joint health. Objectives: To compare biomechanical gait waveforms throughout stance at early time points post-ACLR in individuals with different daily step behaviors at 6 months post-ACLR and to examine how these gait waveforms compare with those of uninjured controls. Design: Case-control study. Setting: Laboratory. Patients or Other Participants: A total of 32 individuals with primary ACLR assigned to the low-step group (LSG; n = 13) or the high-step group (HSG; n = 19) based on their average daily steps at 6 months post-ACLR and 32 uninjured matched controls. Main Outcome Measure(s): Gait biomechanics were collected at 2, 4, and 6 months post-ACLR for the ACLR groups and at a single session for the control group. Knee-adduction moment, knee-extension moment (KEM), and knee-flexion angle (KFA) waveforms were calculated during gait stance and then compared via functional waveform analyses. Mean differences and corresponding 95% CIs between groups were reported. Results: Primary results demonstrated less KFA (1%–45% versus 79%–92% of stance) and greater KEM (65%–93% of stance) at 2 months and greater knee-adduction moment (14%–20% versus 68%–92% of stance) at 4 months post-ACLR for the HSG compared with the LSG. Knee-adduction moment, KEM, and KFA waveforms differed across various proportions of stance at all time points between the step and control groups. Conclusions: Differences in gait biomechanics were present at 2 and 4 months post-ACLR between step groups, with the LSG demonstrating an overall more flexed knee and more profound stepwise underloading throughout stance than the HSG. The results indicate a relation between early gait biomechanics and later daily step behaviors post-ACLR.

The purpose of this study was to compare gait biomechanics between limbs and to matched uninjured controls (i.e., sex, age, and body mass index) preoperatively and at 2, 4, 6, and 12 months following primary unilateral anterior cruciate ligament reconstruction (ACLR). Functional mixed effects models were used to identify differences in gait biomechanics throughout the stance phase between the a) ACLR limb and uninvolved limb, b) ACLR limb and controls, and c) uninvolved limb and controls. Compared with the uninvolved limb, the ACLR limb demonstrated lesser knee extension moment (KEM; within 8–37% range of stance) during early stance as well as lesser knee flexion moment (KFM; 45–84%) and greater knee flexion angle (KFA; 43–90%) during mid‐ to late stance at all timepoints. Compared with controls, the ACLR limb demonstrated lesser vertical ground reaction force (vGRF; 5–26%), lesser KEM (7–47%), and lesser knee adduction moment (KAM; 12–35%) during early stance as well as greater vGRF (39–63%) and greater KFA (34–95%) during mid‐ to late stance at all timepoints. Compared with controls, the uninvolved limb demonstrated lesser KFA (1–56%) and lesser KEM (12–54%) during early to mid‐stance at all timepoints. While gait becomes more symmetrical over the first 12 months post‐ACLR, the ACLR and uninvolved limbs both demonstrate persistent aberrant gait biomechanics compared to controls. Biomechanical waveforms throughout stance can be generally described as less dynamic following ACL injury and ACLR compared with uninjured controls.

Lesser peak vertical ground reaction force (vGRF) has been widely reported among individuals with anterior cruciate ligament reconstruction (ACLR). Peak vGRF remains less than uninjured controls and relatively stable during the first year following ACLR. However, it is unknown whether there are subgroups of individuals exhibiting consistently greater peak vGRF in the first 6‐months following ACLR and if individuals with consistently greater peak vGRF exhibit kinematic and kinetic gait differences compared to individuals with low vGRF. The purpose of this study was to determine if distinct clusters exist based upon magnitude of peak vGRF 2‐ and 6‐months post‐ACLR. Subsequently, we explored between cluster differences in vGRF, knee flexion angle, and sagittal and frontal plane knee kinetics throughout stance between clusters. Forty‐three individuals (58.1%female, 21.4 ± 4.4 years‐old, 95.3% patellar‐tendon autograft) completed five gait trials at their habitual walking speed 2‐ and 6‐months post‐ACLR. A single K‐means cluster analysis was used to identify clusters of individuals based on peak vGRF at 2‐ and 6‐months post‐ACLR. Functional waveform analyses were used to compare gait outcomes between clusters with and without controlling for gait speed and age. We identified two clusters that included a subgroup with high vGRF (n = 16) and low vGRF (n = 27). The cluster with high vGRF demonstrated greater vGRFs, knee flexion angles, and knee extension moments during early stance as compared to the low vGRF cluster 2‐ and 6‐months post‐ACLR. Individuals with peak vGRF ≥1.02 times body‐weight 2‐months post‐ACLR had 35.4 times greater odds of being assigned to the high vGRF cluster.

Continuous monitoring of knee motion can provide deep insights into patients’ rehabilitation status after knee injury and help to better identify their individual therapeutic needs. Potentiometers have been identified as one possible sensor type for continuous monitoring of knee motion. However, to verify their use in monitoring real-life environments, further research is needed. We aimed to validate a potentiometer-embedded knee brace to measure sagittal knee kinematics during various daily activities, as well as to assess its potential to continuously monitor knee motion. To this end, the sagittal knee motion of 32 healthy subjects was recorded simultaneously by an instrumented knee brace and an optoelectronic reference system during activities of daily living to assess the agreement between these two measurement systems. To evaluate the potentiometer’s behavior during continuous monitoring, knee motion was continuously recorded in a subgroup (n = 9) who wore the knee brace over the course of a day. Our results show a strong agreement between the instrumented knee brace and reference system across all investigated activities as well as stable sensor behavior during continuous tracking. The presented potentiometer-based sensor system demonstrates strong potential as a device for measuring sagittal knee motion during daily activities as well as for continuous knee motion monitoring.