What is the appropriate diagnosis and treatment for a patient with a hyperextended wrist injury experiencing pain with supination, extension with ulnar deviation, and paresthesias in the second through fifth digits?

Extensor Carpi Ulnaris (ECU) Tendon Subluxation with Possible Ulnar Nerve Involvement

This clinical presentation—pain with supination and extension with ulnar deviation following wrist hyperextension, combined with paresthesias in digits 2-5—most likely represents extensor carpi ulnaris (ECU) tendon subluxation or injury, potentially with concurrent ulnar nerve trauma at the wrist.

Clinical Diagnosis

The specific mechanism and symptom pattern are highly suggestive:

• Pain with supination is the hallmark of ECU pathology, as this motion stresses the ECU tendon and its subsheath 1
• Extension with ulnar deviation further provokes ECU tendon instability by forcing the tendon to subluxate from its groove over the ulnar styloid 1
• Paresthesias in digits 2-5 indicate ulnar nerve involvement (digits 4-5) with possible median nerve contribution (digits 2-3), which can occur from direct trauma during hyperextension injury 2, 3

Key Physical Examination Findings to Elicit

• Dynamic subluxation test: Palpate the ECU tendon during forced supination from pronation—you should feel the tendon snap or subluxate over the ulnar styloid 1
• Point tenderness over the ulnar styloid and ECU groove 4
• Sensory testing in ulnar nerve distribution (palmar and dorsal aspects of digits 4-5) and median nerve distribution (digits 2-3) 5, 2
• Tinel's sign at Guyon's canal and carpal tunnel to localize nerve involvement 5

Diagnostic Imaging Algorithm

Initial Study: Plain Radiographs

• Obtain standard wrist radiographs first to exclude fractures and gross dislocations 1
• These are widely available and rule out bony pathology that would change management 1

Definitive Study: Ultrasound with Dynamic Maneuvers

• High-frequency ultrasound is the optimal next study because it can directly visualize ECU tendon subluxation during dynamic supination maneuvers 1
• US can show the tendon displacing from its groove in real-time, which static MRI may miss unless specifically performed in pronation and supination 1
• US also allows assessment of the ulnar nerve at Guyon's canal 1

Alternative: MRI with Dynamic Sequences

• If US is unavailable or inconclusive, obtain MRI with sequences performed in both pronation and supination 1
• Standard MRI without dynamic positioning may miss ECU subluxation 1
• MRI better evaluates associated soft tissue injuries including ligamentous tears 1

Treatment Approach

Acute Management (First 2-3 Weeks)

• Immobilize the wrist in pronation and slight flexion to reduce the ECU tendon into its groove and allow subsheath healing 1
• Apply ice for 10-20 minutes with a thin towel barrier to control swelling 6, 7
• Avoid supination and ulnar deviation movements that provoke subluxation 1

Definitive Treatment Decision

If dynamic instability is confirmed on imaging:

• Surgical repair of the ECU subsheath is indicated for complete tears or persistent subluxation after 4-6 weeks of immobilization 1
• Delayed surgical intervention may be necessary if conservative management fails 1

For ulnar nerve symptoms:

• If paresthesias persist beyond 2-3 weeks despite immobilization, obtain electrodiagnostic studies to localize and quantify nerve injury 5
• Surgical neurolysis may be required for nerve entrapment, particularly if there is anatomic variation or direct nerve trauma 2, 3

Critical Pitfalls to Avoid

• Do not obtain static MRI without dynamic sequences—this will miss ECU subluxation in up to 50% of cases 1
• Do not assume all paresthesias are from carpal tunnel syndrome—this distribution (digits 2-5) suggests both median and ulnar nerve involvement, requiring broader evaluation 5, 2
• Do not delay imaging if symptoms persist beyond 1-2 weeks—chronic ECU subluxation becomes progressively harder to treat conservatively 1
• Avoid wrist injections in this acute setting—direct nerve injection can cause permanent damage, and the diagnosis must be confirmed first 8

Follow-Up and Prognosis

• Re-evaluate at 2 weeks to assess symptom improvement with immobilization 6, 7
• If unremitting pain or progressive neurologic symptoms develop, immediate surgical referral is warranted 6, 7
• Most ECU subluxations respond to 4-6 weeks of proper immobilization if treated acutely, but chronic cases typically require surgery 1