I have pain under my lateral malleolus; what are the possible causes and how should I manage it?

Pain Under the Lateral Malleolus: Differential Diagnosis and Management

Pain under the lateral malleolus most commonly results from lateral ankle ligament injury (particularly ATFL tears), but peroneal tendon pathology must be actively excluded, especially if pain persists beyond 6 weeks or is located posterolaterally.

Initial Diagnostic Approach

Immediate Assessment (Day 0-3)

Apply the Ottawa Ankle Rules to determine if radiographs are needed 1, 2:

• Order X-rays if you find point tenderness at the posterior edge or tip of the lateral malleolus 1, 2
• Also order if unable to bear weight immediately after injury and walk four steps 2
• These rules have 86-99% sensitivity and 97-99% negative predictive value for excluding fractures 2

Standard three-view ankle radiographs (AP, lateral, mortise) should be weight-bearing when possible to assess dynamic instability and medial clear space (normal <4mm) 3.

Delayed Physical Examination (Day 4-5)

Do not perform definitive ligament testing acutely - the anterior drawer test has optimal sensitivity (84%) and specificity (96%) when performed 4-5 days post-injury, not immediately 3, 2. This timing allows acute swelling and guarding to subside.

Key Differential Diagnoses

1. Lateral Ankle Ligament Injury (Most Common)

• The ATFL is the most commonly torn ligament in inversion injuries 1
• These injuries account for 25% of all musculoskeletal injuries and 50% of sports-related injuries 1
• Immediate treatment: Apply a lace-up ankle brace and begin early mobilization - functional treatment is superior to immobilization for reducing morbidity and improving quality of life 2

2. Peroneal Tendon Pathology (Often Missed)

This is an under-appreciated source of lateral hindfoot pain that can be difficult to distinguish from ligament injuries 4. Suspect peroneal tendon injury when:

• Pain is specifically posterolateral or retromalleolar rather than directly over the malleolus 5, 6
• Pain persists beyond 6 weeks despite appropriate ligament treatment 7
• Patient has recurrent "giving way" combined with retromalleolar pain 6

Peroneal pathology includes three categories 4:

• Tendinitis and tenosynovitis
• Tendon subluxation and dislocation
• Tendon splits and tears (particularly longitudinal splits of peroneus brevis) 6

Up to 40% of patients with ankle sprains experience chronic ankle pain, and peroneal tendon injury should be considered in every patient with chronic lateral ankle pain 5.

3. Other Causes of Persistent Pain (>6 weeks)

If pain persists beyond 6 weeks, consider 7:

• Inadequate rehabilitation
• Soft tissue impingement
• Occult osteochondral or chondral lesions
• Syndesmosis injury
• Chronic ankle instability (develops from inadequately treated initial injuries) 3

Physical Examination Specifics

Examine for:

• Foot type: cavus or planovalgus deformity (associated with peroneal pathology) 4
• Palpate the peroneal tendons in the retromalleolar groove during resisted ankle dorsiflexion and eversion 4
• Check for medial tenderness, bruising, or swelling (suggests associated deltoid ligament injury) 2
• Assess lateral ankle ligaments with anterior drawer test at 4-5 days post-injury 3, 2

Advanced Imaging Algorithm

When Radiographs Are Negative

MRI without IV contrast is the study of choice for 1, 3:

• Assessment of ligament injuries when radiographs show no fracture
• Chronic ligamentous injuries
• Occult bone pathology
• Peroneal tendon evaluation

Ultrasound can also diagnose peroneal tendon lesions 6.

CT scan is reserved for determining exact extent of malunion and planning corrective osteotomy 3.

Treatment Algorithm

Acute Phase (Stable Injury, No Fracture)

1. Apply lace-up ankle brace immediately 2
2. Begin early mobilization - functional treatment is superior to immobilization 2
3. Delay definitive ligament assessment until day 4-5 3, 2
4. Address pain level, workload, and sports participation early 2

Persistent Pain (>6 weeks)

If ligament injury: Supervised rehabilitation and home exercise 7

If peroneal tendon injury:

• Low-demand patients: Conservative treatment with physical therapy 5
• High-demand patients: May benefit from surgery 5
• Concomitant peroneal tendon tear and ligament injury: Repair both simultaneously with superior peroneal retinaculum reconstruction, side-to-side tendon sutures, and anatomical lateral ligament reconstruction 6

If impingement syndrome: Surgery for refractory cases 7

If osteochondral lesions: Usually require arthroscopic excision or repair 7

Critical Pitfalls to Avoid

• Do not assume all lateral ankle pain is a simple sprain - 5-33% of patients have persistent pain at 1 year, and 3-34% experience recurrent sprains 2
• Do not overlook peroneal tendon injury, especially when pain is posterolateral or persists beyond 6 weeks 4, 5
• Do not miss occult malunion or associated deltoid ligament injury 3
• Do not immobilize when functional treatment is indicated - this increases morbidity 2