What is a left ankle/foot avulsion fracture, and what are the typical patient profile, clinical presentation, imaging findings, and recommended management?

Left Ankle/Foot Avulsion Fracture Overview

An avulsion fracture of the left ankle/foot occurs when a ligament or tendon pulls off a fragment of bone from its attachment site, most commonly affecting the lateral malleolus at the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) insertions, typically following inversion injuries.

Definition and Mechanism

An avulsion fracture results from tensile force applied to a musculoskeletal unit or ligament, causing a bone fragment to separate at the attachment site 1. In the ankle/foot, this occurs when the force of injury exceeds the bone's strength before the ligament fails, pulling off a piece of bone rather than tearing the ligament itself 2.

Typical Patient Profile

Age Distribution

• Children and adolescents: More susceptible due to apophyseal weakness 1
• Adults over 40 years: Increased incidence, particularly with osteoporotic bone 3, 1
• Mean age in surgical series: 34 years (range 15-64 years) 2

Activity Level and Mechanism

• Sedentary patients: 77% of avulsion fractures occur in low-activity individuals 3
• Low-energy injuries: 68% involve low-energy mechanisms rather than high-impact trauma 3
• Sports-related: Can occur during athletic activities, particularly those involving twisting or inversion forces 4

Clinical Presentation

Acute Symptoms

• Point tenderness over the lateral malleolus, specifically at ligament attachment sites 5
• Swelling inferior to the lateral malleolus 5
• Inability to bear weight immediately after injury 5
• Inability to ambulate for 4 steps in the emergency department 5
• Increased displacement of the fragment under varus stress 2

Chronic Presentation (Missed Diagnosis)

• Persistent posteromedial ankle pain when medial tubercle of posterior talus is involved 4
• Chronic instability if untreated, with inferior functional outcomes 6, 3

Imaging Findings

Initial Radiography

Standard three-view ankle radiographs (AP, lateral, mortise) are the first-line imaging study for patients meeting Ottawa Ankle Rules criteria 5.

Detection Challenges

• 40-50% of lateral talar process avulsions are missed on routine radiographs 5
• 26% of lateral ankle sprains have occult fibular avulsion fractures not visible on standard views 5

Specialized Radiographic Views

• ATFL view: Identifies distal fibular avulsion fractures in 26% of lateral ankle sprain patients with negative standard radiographs 5
• CFL view: Improves detection of calcaneofibular ligament avulsion fractures 6, 3
• Broden view: 30-45° internal rotation for lateral talar process fractures 5
• Gravity stress view: More reliable than manual stress for detecting deltoid ligament disruption 5

Fragment Characteristics

• Average size: 6.3 mm width (anterior-posterior) × 5.2 mm length (superior-inferior) 2
• Range: 4-9 mm width, 4-7 mm length 2
• Ligament attachment: Both ATFL and CFL remain attached to the avulsed fragment 2

Advanced Imaging

CT is the first-line study after radiographs to determine extent, displacement, comminution, and intra-articular extension 5.

MRI without contrast is indicated for:

• Occult fractures with bone marrow edema in patients with persistent pain and negative radiographs 5
• Associated soft tissue injuries: Ligament tears, tendon abnormalities, cartilage damage 5
• Bone contusions: 70% of ankle fractures and 50% of ankle sprains show cartilage injury on MRI 5

Ultrasound can detect superficial occult fractures at the lateral malleolus and assess for chondral avulsion fractures in children, but is not first-line 5.

Management Recommendations

Conservative Treatment

Casting or stirrup splint immobilization is the initial treatment approach 6, 3.

Treatment Outcomes by Modality

Nonoperative treatment of avulsion fractures yields satisfactory results comparable to ligament ruptures when properly diagnosed 3:

• Mean Karlsson score: 89.1 points for avulsion fractures vs 88.4 points for ligament ruptures 3
• Osseous union achieved in 65% of conservatively treated avulsion fractures 3

Surgical Indications

Primary screw fixation of the avulsed fragment to the fibula is indicated for:

• Displaced fragments that increase under varus stress 2
• Fragments with attached ATFL and CFL, as motion between fragment and fibula prevents spontaneous healing 2
• Prevention of rotational instability 2

Surgical timing: Mean 7.7 days (range 2-17 days) after injury 2

Surgical outcomes: All patients clinically and radiographically stable at mean 2.4-year follow-up with high satisfaction 2

Delayed/Missed Diagnosis Management

Late operative excision is indicated for:

• Persistent pain after missed acute diagnosis 4
• Chronic instability symptoms 4

Outcomes of delayed excision: Significant functional and symptomatic improvement, though inferior to acute treatment 4.

Critical Clinical Pitfalls

Diagnostic Errors

• High suspicion required in children due to high incidence and difficulty of detection 3
• Misdiagnosis as lateral ankle sprain when lateral talar process avulsion is present, especially with swelling inferior to lateral malleolus 5
• Standard radiographs miss 26-50% of avulsion fractures; obtain specialized views (ATFL/CFL) when clinical suspicion is high 5, 6

Treatment Errors

• Untreated avulsion fractures predictably do poorly, unlike ligament sprains which heal well conservatively 4
• Functional treatment outcomes for avulsion fractures are inferior to ligament injuries when fragments remain displaced 6
• Motion between fragment and fibula prevents healing, necessitating fixation consideration 2

Stability Assessment

Weight-bearing radiographs provide critical stability information 5:

• Medial clear space <4 mm confirms stability 5
• Increased instability with: medial tenderness, fibular fracture above syndesmosis, bi/trimalleolar fractures 5

Associated Injuries

• 2 of 10 patients (20%) with lateral avulsion fractures had concomitant lateral talus cartilage lesions 2
• Evaluate for osteochondral injury when fracture is identified 5