Lateral Midfoot Ligaments and Peroneal Tendons
In an adult or adolescent with an inversion injury presenting with lateral mid-foot pain, swelling, and difficulty bearing weight, the calcaneocuboid ligament, calcaneofibular ligament, cervical ligament, interosseous talocalcaneal ligament, and peroneal tendons are the primary structures that may be partially torn or completely ruptured.
Primary Structures at Risk
The lateral midfoot is particularly vulnerable during inversion injuries, with specific patterns of injury:
Calcaneocuboid Ligament Complex
- This is the most commonly missed injury in lateral midfoot inversion trauma 1
- Selective rupture is extremely rare but frequently misdiagnosed 1
- Requires varus stress radiographs for proper diagnosis, as standard AP and lateral views may appear normal 1
- Classification based on calcaneocuboid angle on stress views:
- Type 1: <10° angle without bony fragment
- Type 2: >10° angle with or without small bony flake
- Type 3: >10° angle with large bony fragment
- Type 4: Complex injuries with cuboid compression fracture 1
Lateral Ankle Ligament Complex
While technically at the ankle rather than pure midfoot, these are frequently involved:
- Anterior talofibular ligament (ATFL): Most commonly torn, present in 100% of high-grade sprains 2
- Calcaneofibular ligament (CFL): Torn in 51.2% of high-grade sprains, extends into lateral midfoot region 2
- In 70% of complete disruptions, both ATFL and CFL are involved together 3
Midfoot Ligamentous Structures
- Interosseous talocalcaneal ligament: Lesions present in approximately 54% of acute inversion injuries and correlate significantly with giving way, pain, and limitation of ankle motion 4
- Cervical ligament: Lesions found in 50% of cases, correlating with giving way and pain 4
Peroneal Tendons
- Located at the base of the fifth metatarsal/peroneal tendon region, this area shows maximal tenderness in 5% of inversion injuries 5
- Peroneal tendon dislocations and peroneal retinacular injuries can occur, particularly with associated calcaneal fractures 6
- Both MRI and ultrasound are sensitive for diagnosing acute tendon rupture or dislocation 6
Clinical Pitfall: The "Supination Fracture Line"
Critical caveat: Approximately 7.4% of ankle sprains lead to injuries affecting the foot along a "supination fracture line" 3. Clinical examination must extend beyond the distal fibula to include:
- Fifth metatarsal base
- Calcaneocuboid ligament
- Ligaments of the anterior calcaneal process
- Talus
- Syndesmotic ligaments 3
Associated Injuries in High-Grade Sprains
When lateral midfoot structures are involved in high-grade injuries, expect:
- Deltoid ligament complex: Partially torn in 55.8% of high-grade lateral sprains (versus only 8.8% in low-grade) 2
- Extensor retinaculum lesions: Present in 41.9% of high-grade sprains 2
- Medial malleolus bone bruise and moderate to large articular effusions 2
Imaging Approach
MRI is the preferred modality when radiographs are noncontributory 6, with 83% sensitivity for diagnosing tendon and ligament traumatic injuries 6. For calcaneocuboid ligament injuries specifically, varus stress radiographs are essential, with CT and MRI reserved for complex cases 1. Ultrasound can effectively diagnose acute tendon rupture or dislocation when performed with focused, protocol-based examination 6.
The lateral midfoot region in inversion injuries represents a frequently underappreciated zone of injury, with 24% of all ankle inversion injuries showing maximal tenderness in the lateral midfoot ligaments 5, making thorough clinical examination of this area essential to avoid missed diagnoses.