Purpose: While abnormal knee kinematics observed after ACL injury and reconstruction are thought to contribute to increased osteoarthritis (OA) risk, the affects of altered kinematics on in vivo cartilage contact mechanics have not been well characterized. The purpose of this study was to investigate whether alterations in cartilage strain and contact area during functional tasks (walking, running; assessed 6 months after ACLR) would predict clinical outcomes and changes in cartilage morphology 2 years after surgery. Methods: Anatomic ACL reconstructions were performed usingquadriceps tendon autografts on 50 patients (mean age 22 ± 7.5 years). Patientreported outcomes (PRO; IKDC and KOOS) and kinematics (gait/running) were assessed 6 and 24months after reconstruction. 3TMRI (3DDESS)was acquired 6 and 24 months after ACLR to assess changes in cartilage thickness over time, using previously described subregions of the tibial and femoral articulating surfaces. Tibiofemoral kinematics and cartilage contact mechanics (contact area and cartilage strain/deformation) were determined using a previously validated method (Figure 1) combining dynamic stereo x-ray (for bone motion) and CT/MRI (for bone and cartilage morphology). Strain and contact area side-to-side (SSD) differences between limbs were evaluated via repeated-measures ANOVA and post-hoc t-tests. Relationships between patient-reported outcomes, contact area and cartilage thickness changes were explored using Pearson correlations. Results: Contact area in the medial compartment was smaller in ACL-R knees than contralateral limbs (Figure 1). Strain was slightly decreased in ACL-R medial weight-bearing regions, while lateral femoral strain differences were mixed (Figure 2). Tibial cartilage strains decreased in the anterior-medial region of the medial tibia and the posterior region of the lateral tibia, where as ACLR strains increased in the posterior-lateralmedial and anterior-lateral tibial plateaus (Figure 3). As shown in Figure 4, there were significant correlations between higher strains (SSD, 6 months) and increased cartilage thickness from6 to 24months after ACLR in the central weight bearing region of the medial tibial plateau (p=0.024) and subregions of the medial femur in contactnear fullknee extension(p=0.008& p=0.028). Decreased lateral compartment (R=0.38, p=0.01) and medial compartment (R=0.36, p=0.017) contact area was associated with reductions in the KOOS Activities of Daily Living scores in the medial (r=0.36, p=0.017) and lateral (r=0.38, p=0.010) compartments, and poorer KOOS Pain Scores in the medial compartment (R=0.31, p=0.04). There were no significant correlations between SSD strain at 6months and any patient-reported outcomes at 2 years after surgery. Conclusions: These results indicate relationships between altered joint contact mechanics and cartilage morphological response, particularly in the medial compartment where OA is most likely to occur after ACL injury/reconstruction. Regional shifts in cartilage strain are consistent with external tibial rotation in ACLR knees, as previously reported. All significant correlations between increased strain/deformation and cartilage thickening were positive, suggesting that abnormal loading may be contributing to early cartilage hypertrophy and/or softening. Moderate correlations of contact area changes and PRO suggest there are short-term clinical implications of altered contact mechanics as well. Longer follow-up is needed to assess the long-term impact of these early changes on cartilage health. (Figure Presented).
Tashman, S., Thorhauer, E., Fu, F., & Irrgang, J. (2016). Alterations in in vivo knee cartilage contact mechanics after anterior cruciate ligament reconstruction and correlations to clinical outcomes and regional changes in cartilage thickness. Osteoarthritis and Cartilage, 24, S409–S410. https://doi.org/10.1016/j.joca.2016.01.738