Tibiofemoral joint space narrowing: can dynamic joint stiffness 2 years after anterior cruciate ligament injury years predict narrowing 5 years after injury?

Abstract

Purpose: Patients with anterior cruciate ligament (ACL) injury experience higher rates of knee osteoarthritis (OA) compared with non-injured individuals. Changes in gait biomechanics are one proposed mechanism for OA development, as small changes in load bearing position shift cartilage loading to regions not adapted to ambulatory loading resulting in gradual degradation. Dynamic joint stiffness (DJS) is a biomechanical measure that captures contributions of both active muscle contraction and passive tissue tension. People with severe knee OA ambulate with higher DJS compared to healthy controls. It is unknown if DJS is predictive of radiographic changes in people after ACL injury. The purpose of this study was to evaluate if DJS measured 2 years after ACL injury predicts minimal joint space width (mJSW) 5 years after ACL injury. We hypothesized that higher DJS 2 years after injury will predict less joint space width (JSW) 5 years after injury. Methods: As part of a larger longitudinal study, 37 subjects (13 females, age 28.1 ± 11.9 yrs,) completed gait assessment 2 years after injury and radiographs at 5 years after injury. We analyzed participants' walking patterns using an eight-camera motion capture (VICON, Oxford, UK) at 120 Hz and embedded force platform (Bertec Corp, Columbus, OH) at 1080 Hz. We used 39 retroreflective markers on bilateral lower extremities and pelvis. Participants walked overground at a self-selected gait speed maintained ± 5% across trials. Data were processed using commercial software (Visual3D; C-Motion, Germantown, MD). DJS was analyzed during loading response, defined as from the first increase in external knee flexion moment to peak knee flexion. Knee flexion angle was plotted on the X-axis and an increase in the joint angle represents an increase in knee flexion. Knee extension joint moment was plotted along the Y-axis and an increase in moment represents an increase in the net external flexion moment. A larger positive slope indicates higher DJS. Weightbearing posteroanterior (PA) bent knee (30°) radiographs were read by one researcher (JLJ) for mJSW in each compartment. Tibiofemoral JSW in the medial compartment measured from plain radiographs has been shown to be a surrogate for articular cartilage thickness, of particular concern in knee OA. Linear regression was used to test if DJS at 2 years predicted mJSW at 5 years, adjusting for sex, body mass index (BMI), and meniscal involvement. Results: The median mJSW in this study was 4.6 mm and 5.7 mm in the medial and lateral compartment respectively. Using the IKDC scale for joint space narrowing, 8 subjects had mJSW of less than 4.0 mm, and 1 subject had mJSW less than 2.0 mm in the medial compartment. In the lateral compartment, 5 subjects had mJSW less than 4.0 mm and 1 subject had mJSW less than 2.0 mm. Average DJS of the involved limb at 2 years was 0.050 ± 0.009 and was not predictive of medial or lateral mJSW at 5 years, with unadjusted R2 = 0.033 and 0.022 respectively. Adjusting for sex, BMI, and meniscal involvement, the model remained not significant (R2 = 0.107 and 0.112). Conclusions: DJS was not a predictor of mJSW in subjects 5 years after ACL injury. Previous studies found a relationship only between severe OA and DJS; we had only 2 subjects with severe OA. Additionally, our cohort had a DJS range of 0.034–0.073, less stiff than previous literature. Limitations of this study included a lack of baseline DJS or JSW measurement. Additionally, our cohort had a very wide age range at time of initial injury (14.1–49.6 years old); previous research was on older adults. It is unknown what affect age has on DJS of the knee during gait. Further research at future time points (for OA progression) or with a more homogenous age sample may provide more insight to the relationship of DJS and JSW.