MRI volume and signal intensity of ACL graft predict clinical, functional, and patient-oriented outcome measures after ACL reconstruction

Abstract

Background: Clinical, functional, and patient-oriented outcomes are commonly used to evaluate the efficacy of treatments after anterior cruciate ligament (ACL) injury; however, these evaluation techniques do not directly measure the biomechanical changes that occur with healing.

Purpose: To determine if the magnetic resonance (MR) image-derived parameters of graft volume and signal intensity (SI), which have been used to predict the biomechanical (ie, structural) properties of the graft in animal models, correlate with commonly used clinical (anteroposterior [AP] knee laxity), functional (1-legged hop), and patient-oriented outcome measures (Knee Injury and Osteoarthritis Outcome Score [KOOS]) in patients 3 and 5 years after ACL reconstruction.

Study design: Cohort study (diagnosis); Level of evidence, 3.

Methods: Based on a subset of participants enrolled in an ongoing ACL reconstruction clinical trial, AP knee laxity, 1-legged hop test, and KOOS were assessed at 3- and 5-year follow-up. Three-dimensional, T1-weighted MR images were collected at each visit. Both the volume and median SI of the healing graft were determined and used as predictors in a multiple regression linear model to predict the traditional outcome measures.

Results: Graft volume combined with median SI in a multiple linear regression model predicted 1-legged hop test at both the 3- and 5-year follow-up visits (R(2) = 0.40, P = .008 and R(2) = 0.62, P = .003, respectively). Similar results were found at the 5-year follow-up for the KOOS quality of life (R(2) = 0.49, P = .012), sport/function (R(2) = 0.37, P = .048), pain (R(2) = 0.46, P = .017), and symptoms (R(2) = 0.45, P = .021) subscores, although these variables were not significant at 3 years. The multiple linear regression model for AP knee laxity at 5-year follow-up approached significance (R(2) = 0.36, P = .088).

Conclusion: The MR parameters (volume and median SI) used to predict ex vivo biomechanical properties of the graft in an animal model have the ability to predict clinical or in vivo outcome measures in patients at 3- and 5-year follow-up.

Clinical relevance: Results from this study may enhance clinical evaluation of graft health by relating the MR parameters of volume and median SI to traditional outcome measures and could potentially aid researchers in determining the appropriate timing for athletes to return to sport.

Trial registration: ClinicalTrials.gov NCT00434837.

Keywords: ACL; MRI; biomechanics; clinical assessment; patient outcome.

© 2014 The Author(s).

Figures

Figure 1

The patient graft prediction plane for knee APlaxity difference as a function of graft volume and median SI at 5-year follow-up (R2 = 0.36, p=0.088). The grafts with the higher volume and lower SI tended to have lower APlaxity difference scores (injured minus contra-lateral).

Figure 2

The patient prediction planes for hop score as a function of graft volume and median SI at A) 3-year follow-up (R2 = 0.40, p=0.008) and B) 5-year follow-up (R2 = 0.62, p=0.003). The grafts with the higher volume and lower SI tended to have higher hop scores (% injured vs contra-lateral).

Figure 3

The patient prediction plane for KOOS-qol sub-score, as a function of graft volume and median SI at 5-year follow-up (R2 = 0.49, p=0.012). The grafts with the higher volume and lower SI tended to have higher KOOS-qol sub-scores (100 being perfect knee function). Similar plots were found for the KOOS-spt, KOOS-pain and the KOOS-sym 5-year follow-up prediction models.

Figure 4

Example A) low and B) high SI for patient grafts on one sagittal slice of the MR image stack.