SLR - January 2021 - Rebecca Van Dyke

The Added Diagnostic Value of the Bright Rim Sign to Conventional MRI Assessment of Anterior Talofibular Ligament Disruption

Reference: Basha MAA, Eldib DB, Zaitoun MMA, Ghandour TM, Aly T, Mostafa S, Atta DS, Algazzar HY. The Added Diagnostic Value of the Bright Rim Sign to Conventional MRI Assessment of Anterior Talofibular Ligament Disruption. Acad Radiol. 2020 Jun 10:S1076-6332(20)30281-6. 

Scientific Literature Review

Reviewed By: Rebecca Van Dyke, DPM
Residency Program: University Hospital – Newark, NJ

Podiatric Relevance: Ankle sprains are the most common ligamentous injury encountered in the podiatric field, accounting for up to 90 percent of sports-related injuries. An accurate diagnosis of ATFL disruption is paramount to prevent sequelae of lateral ankle instability and post-traumatic ankle arthritis. Therefore, a through knowledge of radiologic interpretation plays a major role to the evaluation and treatment course of an ankle injury. MRI is a valuable tool due to its soft-tissue resolution and visualization of soft tissue pathology. This study examined the addition of the bright rim sign (BRS) as a reliable indicator of ATFL disruption. This sign, not adequately discussed in current literature, represents a foci of bright signal intensity at the talar or fibular attachment site of the ATFL on the axial T2-weighted image attributed to chemical-shift artifact produced with exposure of subcortical fat marrow to joint fluid. 

Methods: This prospective study of 62 patients with a mean age of 36.9 years diagnosed with an ankle sprain was performed between May 2019 and January 2020. Inclusion criteria included those with persistent pain, swelling or instability after conservative treatment and positive clinical findings indicating an ATFL rupture (e.g. positive talar tilt test and/or anterior drawer test). All study participants underwent both MRI and arthroscopic examinations of the affected ankle. Two radiologists with over 10 years of experience in musculoskeletal imaging evaluated the images for positive BRS, a dot-like or curvilinear signal overlying the attachment sites, and ligament disruption sign (LDS), which would appear as torn or absent ligament. Arthroscopy was performed in addition in order to confirm the diagnosis.

Results: After grouped into one of three groups based on time lapse between injury and treatment (acute lateral sprain, chronic ankle instability, and recurrent ankle sprain), MRI findings determined that 36/62 patients were positive for LDS (nine complete and 27 partial tears) with 27 positive for BRS (fibular side in 15 patients, talar side in four patient and both sides in eight patients). Arthroscopic evaluation demonstrated that 60/62 patient had ATFL disruption with 12 showing complete tear and 48 with partial tearing. In regards to diagnostic value of LDS and BRS compared to arthroscopy, the greatest sensitivity for an ATFL rupture was noted when both signs were present. 

Conclusions: The use of MRI for evaluation and treatment of ATFL disruption is a valuable tool in determining the positive predictive value by assessing for LDS and BRS. With the presence of both signs, the sensitivity increases. This is due to the production of new formation of scar tissue and/or granulation tissue which can obscure the tear gap in those with chronic and recurrent ankle sprains. Without better evidence for reproducibility, the study results are not yet ascertained for clinical practice. However, there is an importance of understanding the MRI protocol, which should include T2 or PD axial when assessing ATFL disruption, because same-slice STIR images failed to show the BRS. It’s paramount for the podiatric physician to become well-versed with interpretation of MRI for these ligamentous disruptions as well as associated injury such as bone marrow edema and cortical disruption. 

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