Summary

Postoperative hamstring tendon autograft signal intensities and interface zones on MR imaging do not determine functional clinical outcomes, or re-rupture.

Abstract

Background

Magnetic Resonance (MR) imaging is an accurate method to assess the postoperative healing process following anterior cruciate ligament (ACL) reconstruction using hamstring tendon autografts. However, it remains unclear to what extent postoperative MR imaging findings determine clinical outcomes, such as functional outcomes or re-rupture rates.

Purpose

To determine to what extent MR imaging signal intensities of specific regions of the hamstring tendon autograft predict clinical outcomes, such as functional outcomes and re-rupture rates in the first and second year following ACL reconstruction in a prospective follow-up study.

Methods

Of the 154 patients who were included in a prospective follow-up study, 61 underwent reconstruction of the ACL entailing the hamstring tendons and met the following inclusion criteria: (1) ACL rupture diagnosed by physical examination and MR imaging, (2) initial MR imaging within 6 months after trauma, (3) age between 18 and 45 years, and (4) follow-up MR imaging data available at one and two years after reconstruction. Signal intensity at the proximal, mid-portion and distal region along the ACL graft was measured and compared to the signal intensity of the posterior cruciate ligament, resulting in a signal intensity ratio (SIR) . In addition, signal intensities of the interface zone between graft and bone were measured. Clinical evaluation was performed at 1 and 2 years after enrollment, including International Knee Documentation Committee (IKDC) subjective knee form score, Lysholm knee scoring scale, Tegner activity score, one leg hop test, and anterior tibial translation using the KT-1000. In addition, re-ruptures that occurred in the two years following reconstruction were documented.

Results

The entire graft showed a significant decrease in SIR over time (1.58 to 1.29, p= 0.003). The distal region showed a higher median SIR (1.40) compared to the SIR in the proximal (1.26, p= 0.012) and mid-substance (1.19, p= 0.010) region two years after reconstruction. The grade of fibrous interface zone decreased significantly over time at the proximal tibial (3 to 2, p< 0.001) and distal femoral region side (4 to 3, p< 0.001), with the tibial side superior to the femoral side (p< 0.001). Only one patient (1.6%) sustained an ACL re-rupture. No correlation was found between the SIR of the graft or interface zone and functional clinical outcomes, or re-rupture. Also, the outliers in functional outcomes showed no potential correlations with the SIR of the graft.

Conclusion

The ACL autograft undergoes a continuous healing process in the two years following reconstruction. However, no correlation could be found between the extent of graft healing and functional outcome scores or re-rupture rate. Based on the current work, graft signal intensity assessed by MR imaging is not an accurate measure to determine functional outcomes and re-rupture rates.