Flexor Carpi Radialis Involvement in Extension-Type Supracondylar Humerus Fractures
The flexor carpi radialis (FCR) is not typically involved in extension-type supracondylar humerus fractures, as nerve injuries in these fractures predominantly affect the anterior interosseous branch of the median nerve rather than the branches innervating the FCR. 1, 2
Nerve Injury Patterns in Supracondylar Fractures
Extension-Type Fractures (97-98% of cases)
- In extension-type supracondylar humerus fractures, the anterior interosseous nerve (a branch of the median nerve) is the most commonly injured nerve, representing 34.1% of associated neurapraxias 3
- Median nerve injuries in extension-type fractures typically affect the anterior interosseous branch, which innervates the flexor pollicis longus, flexor digitorum profundus to the index finger, and pronator quadratus - not the FCR 2
- When median nerve injuries occur in extension-type fractures, they present with a clinical syndrome showing "predominant but not exclusive affection of AIN innervated muscles" 2
Flexion-Type Fractures (2-3% of cases)
- Flexion-type supracondylar fractures most commonly involve ulnar nerve injuries (91.3% of associated neurapraxias) 3
- These injuries typically affect the ulnar nerve, which does not innervate the FCR 4
Anatomical Considerations
- The FCR is innervated by the median nerve proper, not by the anterior interosseous branch that is commonly injured in extension-type fractures 2
- Nerve injuries in supracondylar fractures occur in approximately 11% of pediatric extension-type cases, with the majority (62%) affecting the median nerve 1
- However, detailed neurological examinations show that even in median nerve injuries, the clinical pattern predominantly affects anterior interosseous nerve-innervated muscles rather than the FCR 2
Management Implications
- The American Academy of Orthopaedic Surgeons (AAOS) guidelines recommend closed reduction with pin fixation for displaced supracondylar fractures 5
- The AAOS does not provide specific recommendations for nerve exploration in patients with nerve injuries associated with pediatric supracondylar fractures 5
- Most nerve injuries associated with pediatric extension-type supracondylar fractures recover within 6 months without acute nerve decompression 1
- Conservative management with careful neurological follow-up is appropriate for most nerve injuries, as complete functional recovery is expected in the majority of cases 2
Prognosis of Nerve Injuries
- Median nerve injuries have a better prognosis compared to radial nerve injuries, with 70% of isolated median nerve injuries recovering within 3 months versus 42% of radial nerve injuries 1
- Multiple nerve injuries take 54% longer to recover than single median nerve injuries 1
- If there is no clinical or electromyographic evidence of neural function return by 5 months post-injury, exploration and neurolysis should be considered 6
In conclusion, while nerve injuries do occur in extension-type supracondylar humerus fractures, the FCR function is typically preserved as the injuries predominantly affect the anterior interosseous branch of the median nerve rather than the branches innervating the FCR muscle.