Persistent Biomechanical Alterations After ACL Reconstruction Are Associated With Early Cartilage Matrix Changes Detected by Quantitative MR

Abstract

Background: The effectiveness of anterior cruciate ligament (ACL) reconstruction in preventing early osteoarthritis is debated. Restoring the original biomechanics may potentially prevent degeneration, but apparent pathomechanisms have yet to be described. Newer quantitative magnetic resonance (qMR) imaging techniques, specifically T1ρ and T2, offer novel, noninvasive methods of visualizing and quantifying early cartilage degeneration.

Purpose: To determine the tibiofemoral biomechanical alterations before and after ACL reconstruction using magnetic resonance imaging (MRI) and to evaluate the association between biomechanics and cartilage degeneration using T1ρ and T2.

Study design: Cohort study; Level of evidence, 2.

Methods: Knee MRIs of 51 individuals (mean age, 29.5 ± 8.4 years) with unilateral ACL injuries were obtained prior to surgery; 19 control subjects (mean age, 30.7 ± 5.3 years) were also scanned. Follow-up MRIs were obtained at 6 months and 1 year. Tibial position (TP), internal tibial rotation (ITR), and T1ρ and T2 were calculated using an in-house Matlab program. Student t tests, repeated measures, and regression models were used to compare differences between injured and uninjured sides, observe longitudinal changes, and evaluate correlations between TP, ITR, and T1ρ and T2.

Results: TP was significantly more anterior on the injured side at all time points (P < .001). ITR was significantly increased on the injured side prior to surgery (P = .033). At 1 year, a more anterior TP was associated with elevated T1ρ (P = .002) and T2 (P = .026) in the posterolateral tibia and with decreased T2 in the central lateral femur (P = .048); ITR was associated with increased T1ρ in the posteromedial femur (P = .009). ITR at 6 months was associated with increased T1ρ at 1 year in the posteromedial tibia (P = .029).

Conclusion: Persistent biomechanical alterations after ACL reconstruction are related to significant changes in cartilage T1ρ and T2 at 1 year postreconstruction. Longitudinal correlations between ITR and T1ρ suggest that these alterations may be indicative of future cartilage injury, leading to degeneration and osteoarthritis.

Clinical relevance: Newer surgical techniques should be developed to eliminate the persistent anterior tibial translation commonly seen after ACL reconstruction. qMR will be a useful tool to evaluate the ability of these newer techniques to prevent cartilage changes.

Keywords: ACL; MRI; T1rho; osteoarthritis.

Figure 1.

Cloud points from the segmented tibia (T) and femur (F). Two spheres represent the femoral condyles. The red line connects the 2 most posterior ends of the tibia. Arrows indicate coordinate systems; yellow circles indicate tibial and femoral coordinate system origins.

Figure 2.

(A) Lateral side compartments (lateral femoral condyle [LF], lateral tibia [LT]) and subcompartments, patella (P), and trochlea (TrF). (B) Medial side compartments (medial femoral condyle [MF], medial tibia [MT]) and subcompartments. a, anterior; c, central; p, posterior.

Figure 3.

Mean (A) tibial position and (B) internal tibial rotation for the injured and contralateral sides at each time point. Mean side-to-side difference (SSD) for (C) tibial position and (D) internal tibial rotation at each time point are estimated with flexion angle SSD held at 0.39° and 0.45°, respectively. Error bars = standard error. *P < .05, **P < .001.

Figure 4.

Schematic illustrating the possible change in loading pattern with an anteriorly translated tibia (left) and internally rotated tibia (right). The orange areas, which did not bear load in the normal knee, bear load when biomechanics are altered. L, lateral; M, medial.