Summary

Quantitative MRI appearances are better at 6 years following ACL repair compared to reconstruction

Abstract

Anterior cruciate ligament (ACL) repair with internal bracing is emerging as a viable alternative to traditional reconstruction. Previous studies have demonstrated satisfactory patient-reported outcome measures (PROMs) and superior proprioception and strength outcomes with ACL repair. While MRI is commonly used to evaluate graft integrity and maturation following ACL reconstruction, its application in assessing ACL repair remains underreported. This study employs quantitative MRI (qMRI) to compare radiological outcomes of ACL repair with internal bracing to those of ACL reconstruction.

A cohort of 29 patients was retrospectively analysed, with 15 undergoing primary ACL repair with internal bracing and 14 receiving ACL reconstruction using a hamstring autograft. MRI scans were conducted at a mean follow-up of six years postoperatively, utilizing a 3 Tesla scanner and a standardised protocol. Two experienced musculoskeletal radiologists, blinded to treatment type, independently assessed the images. ACL integrity and maturation were evaluated using the Figueroa score, while secondary signs of re-rupture, such as Blumensaat’s angle (>15° or <0°), empty notch, anterior tibial translation, and PCL buckling, were also examined. Morbidity was assessed via the MRI Osteoarthritis Knee Score (MOAKS) and compared to preoperative scans. Tunnel position and dimensions were quantitatively analysed.

The mean age of patients was 30(±10) years, with a median Tegner score of 6 (4.5-7.0), and both groups were well-matched. All ACL repairs achieved a Figueroa score of 5/5, indicating normal radio-intensity. In contrast, one reconstruction (7%) had a score of 2/5, suggestive of graft rupture, while the remainder scored 5/5. The median Blumensaat’s angle was 6° (4.5-7.5°), with no significant difference between the groups; one case in each group displayed an angle indicative of re-rupture. No additional secondary signs of re-rupture were observed. Tunnel diameters were significantly larger in the reconstruction group compared to the repair group (femoral: 9 mm vs. 4 mm; tibial: 11 mm vs. 4 mm, p<0.001). Oedema around the pes anserinus was noted in five reconstructions and one repair. MOAKS indicated significant progression of degenerative changes in both groups (repair 7.1 to 12.3, reconstruction 5.6 to 15.9, p<0.001), with a greater deterioration in the reconstruction group (p=0.03). Bone marrow lesions worsened more in the reconstruction group, while cartilage lesions progressed similarly in both groups. Osteophyte formation increased in the reconstruction group but remained stable in the repair group, with no significant change in meniscal pathology in either group. Inter-rater reliability was high, with an ICC of 0.97 (0.77 - 0.99).

In conclusion, qMRI findings confirm that ACL repair with internal bracing results in a healed ligament with normal radiological appearance, demonstrating equivalence to reconstruction in terms of ACL integrity. The smaller tunnel size observed in the repair group may be beneficial for preserving bone stock, potentially facilitating future revision surgery. Additionally, the slower progression of osteoarthritis in the repair group suggests a protective effect, possibly due to improved proprioception. However, longer-term follow-up is needed to fully understand the implications of these findings. These qMRI results contribute to the growing evidence supporting ACL repair as a viable alternative to reconstruction in selected cases.