Ankle lateral ligament injury is one of the most common musculoskeletal injuries, typically caused by an inversion mechanism. The lateral ligament complex consists of three components: anterior talofibular ligament (ATFL — most commonly injured, 70-85%), calcaneofibular ligament (CFL — 50-75% combined with ATFL), and posterior talofibular ligament (PTFL — most rarely injured). On MRI, acute injury shows ligament thickening, irregularity, T2 signal increase, and surrounding soft tissue edema. In chronic instability, ligaments appear thickened but with heterogeneous signal mixed with scar tissue. Clinical significance: recurrent injuries can lead to chronic ankle instability requiring surgical reconstruction (Brostrom procedure).
Age Range
15-45
Peak Age
25
Gender
Equal
Prevalence
Very Common
The lateral ligament complex provides lateral stability of the ankle and protects against inversion stress. ATFL is the weakest ligament and is under maximum tension in neutral-plantar flexion — making it the first structure injured in inversion. CFL is stronger than ATFL and also contributes to subtalar joint stability. PTFL is strongest and isolated injury is extremely rare. Sequential damage in inversion mechanism: ATFL → CFL → PTFL. In acute ligament injury, collagen fiber disruption, hemorrhage, and inflammatory response occur → T2 signal increase on MRI (edema, hemorrhage = increased free water), ligament morphologic disruption, and surrounding soft tissue edema. In complete tear, ligament continuity is lost with fluid-filled gap. In chronic instability, healing ligament is replaced by scar tissue — weaker and less organized than original → predisposition to recurrent injuries.
Thickened (>2mm), irregular ATFL showing hyperintense signal on axial T2 fat-sat images is the most common and reliable MRI finding of lateral ankle sprains. ATFL is the most commonly injured lateral ligament and the first structure damaged in inversion mechanism.
On axial T2 fat-sat images, ATFL appears thickened, irregular, and shows T2 hyperintense signal. In complete tear, ligament continuity is lost with fluid-filled gap. In partial tear, ligament is thickened but continuity is partially preserved. Normal ATFL appears as a 2mm homogeneous low signal band. In acute injury, surrounding soft tissue edema (around lateral malleolus) accompanies.
Report Sentence
The anterior talofibular ligament appears thickened with T2 signal increase on axial images, consistent with acute ligament injury.
On coronal and axial T2 fat-sat images, CFL appears thickened with signal increase. CFL extends from the fibular tip to the lateral calcaneal surface and passes deep to the peroneal tendons. CFL injury usually accompanies ATFL injury (Grade II-III sprains). Isolated CFL injury is rare.
Report Sentence
The calcaneofibular ligament is thickened and irregular with T2 signal increase, consistent with Grade II-III lateral ligament injury combined with ATFL injury.
On B-mode US, ATFL is evaluated as the structure extending from anterior lateral malleolus to talar neck. In acute injury, the ligament appears thickened (>2mm), irregular, and hypoechoic. In complete tear, ligament continuity is lost. Dynamic stress US showing increased anterior talar translation during anterior drawer test demonstrates instability.
Report Sentence
The anterior talofibular ligament is thickened and hypoechoic on US, consistent with acute injury.
On T2 fat-sat/STIR images, soft tissue edema is seen around the lateral malleolus, sinus tarsi, and peroneal tendon sheath. Accompanying bone marrow edema (bone bruise) may be seen in the lateral talar dome and/or distal fibula — related to contusion mechanism. These findings are indirect evidence of ligament injury.
Report Sentence
Soft tissue edema around the lateral malleolus and sinus tarsi with bone contusion in the lateral talar dome is noted, consistent with lateral ligament injury.
On axial and coronal T2 images, increased fluid in the peroneal tendon sheath is seen. This is indirect evidence of lateral ligament injury because CFL passes deep to the peroneal tendon sheath and CFL injury can lead to sheath effusion. May also be part of the general traumatic inflammatory response.
Report Sentence
Increased fluid is noted in the peroneal tendon sheath, consistent with reactive effusion in the setting of lateral ligament injury.
Criteria
Ligament fibers stretched but no macroscopic tear. MRI shows ligament slightly thicker than normal, mild signal increase, surrounding edema.
Distinct Features
Ligament continuity preserved. Clinical: mild swelling, minimal joint laxity. Conservative treatment sufficient.
Criteria
Partial disruption of ligament fibers. ATFL ± CFL involvement. MRI shows significant thickening, heterogeneous signal, partial continuity.
Distinct Features
Moderate swelling, ecchymosis, mildly positive anterior drawer. Brace + rehabilitation usually sufficient.
Criteria
Complete ATFL + CFL disruption ± PTFL. MRI shows complete discontinuity, fluid-filled gap.
Distinct Features
Significant swelling, ecchymosis, inability to bear weight. Markedly positive anterior drawer. Surgical reconstruction in recurrent cases.
Distinguishing Feature
Achilles rupture shows tendon discontinuity at posterior calcaneus level, while lateral ligament injury shows ligament pathology at lateral malleolus level
Distinguishing Feature
Fibular stress fracture shows bone marrow edema and T1 linear fracture line, while lateral ligament injury shows ligament signal abnormality without bone pathology
Distinguishing Feature
Plantar fasciitis shows fascial pathology on plantar calcaneal surface, while lateral ligament injury shows ligament pathology in the lateral ankle compartment
Urgency
urgentManagement
conservativeBiopsy
Not NeededFollow-up
6-monthThe vast majority (85%+) of acute lateral ligament injuries heal with conservative treatment using a stepwise approach. Acute phase (first 72 hours): PRICE protocol (protection — short-term immobilization/aircast brace, rest — weight restriction, ice — 15-20 minutes every 2-3 hours, compression — elastic bandage, elevation — above heart level). Rehabilitation phase (1-6 weeks): early functional mobilization (better outcomes than immobilization), proprioceptive exercises (balance board — recurrence prevention), peroneal strengthening (evertor muscles — dynamic stabilization), ROM exercises. Full return to sport in 4-6 weeks for Grade I-II. Surgical reconstruction considered for Grade III injuries and chronic instability (symptoms >6 months, recurrent sprains, mechanical instability — positive anterior drawer and talar tilt): Brostrom-Gould procedure (anatomic ATFL repair + inferior extensor retinaculum augmentation — most common, 85-95% success), allograft reconstruction (when Brostrom fails or advanced bony deformity). Recurrent sprains can lead to chronic ankle instability, osteochondral lesions (talar dome — 40-50% association), and early osteoarthritis — aggressive rehabilitation is critical. Early MRI is valuable to exclude osteochondral lesion (talus), peroneal tendon pathology (peroneus brevis tear), syndesmosis injury (high ankle sprain), and fifth metatarsal avulsion fracture.
Grade I and II injuries heal with conservative treatment (RICE protocol, brace, physical therapy). Grade III (complete tear) carries risk of recurrent instability and surgical ligament reconstruction may be needed if chronic instability develops. Chronic lateral instability predisposes to osteochondral lesion development.