Sports Medicine and Orthopaedic


Running Biomechanics Before Injury and 1 Year After Anterior Cruciate Ligament Reconstruction in Division I Collegiate Athletes

After anterior cruciate ligament (ACL) reconstruction (ACLR), athletes demonstrate significant alterations in surgical limb running biomechanics as compared with the nonsurgical limb and healthy controls. These changes include decreased peak knee flexion angle and knee flexion excursion, decreased peak knee extensor moment, decreased patellofemoral joint force, increased initial impact forces, and decreased peak vertical ground reaction force (GRF). Compensatory loading strategies, particularly at the hip, have also been observed, indicating changes extend beyond the knee joint. Running asymmetries have been observed up to 5 years postoperatively, despite rehabilitation typically ending 6 to 12 months after surgery.

Previous studies of running mechanics after ACLR have used cross-sectional designs where the nonsurgical limb or healthy controls are used for comparison. The appropriateness of this approach is questionnable, owing to the potential for bilateral neuromuscular and biomechanical performance deficits to be present after injury and/or surgery.

To this end, one must compare longitudinal postoperative data with preinjury data, allowing for bilateral assessment of within-limb changes over time. Baseline preinjury data are not commonly available given the unpredictable nature of ACL injuries. To date, only a few case studies have been published comparing preinjury and postoperative running mechanics, with limited generalizability.

The purpose of this study was to assess the longitudinal changes in running biomechanics throughout the first year after ACLR as compared with the preinjury state among National Collegiate Athletic Association Division I collegiate athletes.

This study was based on 6 years (2015-2020) of routinely collected pre-season performance data and post-ACLR testing. Thirteen Division I collegiate athletes were identified (7 male, 6 female; age, 20.7 ± 1.3 years old) who had whole body kinematics and ground-reaction forces recorded during treadmill running (3.7 ± 0.6 m/s) before sustaining an ACL injury. All athletes underwent ACLR with bone–patellar tendon–bone autograft. After ACLR, athletes underwent a standardized testing protocol that included running gait analyses performed at 4, 6, 8, and 12 months.

Whole body kinematics were collected using 42 reflective markers placed on the body segments, 23 of which were located on anatomic landmarks. Marker kinematics were collected at 200 Hz using an 8-camera passive marker system. GRFs were recorded at 2000 Hz using an instrumented treadmill and synchronized with the kinematic marker data. The body was modeled as a 14-segment articulated linkage, and body segments were scaled using the athlete’s height, mass, and segment lengths.

Fifteen strides were analyzed on both limbs from each athlete and included the following biomechanical variables: peak knee flexion during stance; peak knee extensor moment during stance; rate of knee extensor moment during stance; hip, knee, ankle, and total negative work during stance (summation of hip, knee, and ankle negative work); vertical GRF impulse; and braking impulse.

Linear mixed effects models were used to assess the influence of time point and limb, as well as a potential interaction effect, on each biomechanical variable of interest. For variables in which a significant interaction was detected, Tukey-adjusted P values were used for pairwise comparisons between preinjury and postoperative time points for the surgical and nonsurgical limbs.

When compared with preinjury, the surgical limb displayed significant deficits at all postoperative assessmentsfor peak knee flexion angle, peak knee extensor moment, rate of knee extensor moment, and knee negative work. No significant changes in the nonsurgical limb knee biomechanics as compared with preinjury were identified throughout the first 12 months postoperatively (P values >0.88). The following largest deficits in the surgical knee mechanics versus the preinjury mechanics were observed at 4 months and did not return to preinjury levels by 12 months: peak knee flexion angle, 4 months (–13.2o [1.4o]; P<0.001) and 12 months (–9.0o [1.5o]; P <0.001); peak knee extensor moment, 4 months (–1.32 [0.13] N.m/kg; P<0.001) and 12 months(–0.87 [0.15] N.m/kg; P<0.001); rate of knee extensor moment, 4 months (–22.7 [2.4] N.m/kg/s; P<0.001) and 12 months (–16.1 [2.6] N.m/kg/s; P<0.001), which corresponds to 46% and 33% deficit, respectively. Knee negative work was significantly reduced at all follow-up time points within the surgical limb: 4 months (–0.33 [0.04] J/kg; P<0.001), 6 months (–0.27 [0.04] J/kg; P<0.001), 8 months (–0.25 [0.04] J/kg; P<0.001), and 12 months (–0.22 [0.05] J/kg; P=0.002).

Surgical limb vertical GRF and braking impulses were significantly reduced shortly after ACLR but were restored to within preinjury levels by 6 and 8 months, respectively. In contrast, the nonsurgical limb showed a significant increase in vertical GRF impulse at 8 months (P=0.04) and braking impulse at all time points (all P values <0.004).

The authors concluded that athletes after ACLR demonstrate substantial deficits in running mechanics as compared with preinjury. These deficits persist beyond the typical return-to-sport time frame. The findings confirm the substantial reductions in knee flexion angle, extensor moment, and negative work during running in the surgical limb throughout the first 12 months after ACLR when compared with preinjury. The nonsurgical limb appears to be a valid reference of recovery for the surgical knee–specific running mechanics after ACLR but not for GRF variables.


Knurr KA et al. (2021) Running Biomechanics Before Injury and 1 Year After Anterior CruciateLigament Reconstruction in Division I Collegiate Athletes. The American Journal of Sports Medicine.

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