Recommended Initial Imaging for Sudden Lockjaw After Fall with Lower Chin Wound
CT maxillofacial without IV contrast is the recommended initial imaging study for this patient, as it provides superior detection of mandibular fractures that are causing the lockjaw (trismus) while also evaluating the extent of soft tissue injury from the chin wound. 1, 2
Primary Imaging Rationale
CT maxillofacial without contrast is nearly 100% sensitive for detecting mandibular fractures with improved interobserver agreement, and excels at identifying subtle nondisplaced fractures that could be causing the lockjaw. 1
This modality provides multiplanar and 3D reconstructions that are critical for characterizing complex fractures and surgical planning, which will likely be needed given the clinical presentation of trismus (lockjaw). 1, 2
CT is superior to plain radiography for evaluating mandibular fractures, particularly posterior mandibular fractures, ramus fractures, and condyle fractures where displacement can be subtle but clinically significant. 1
Why Not Plain Radiographs First?
While panoramic radiographs (OPG) have 86-92% sensitivity for simple mandibular fractures, 82.1% of patients who receive plain films require a subsequent CT scan for diagnosis and treatment planning. 1, 3
Plain films can miss nondisplaced and minimally displaced anterior fractures when there is overlap with the cervical spine, and may mistake complex fractures for isolated fractures. 1
In patients requiring surgical management (70% of those with mandibular trauma), CT should be obtained from the outset to avoid delays in diagnosis and reduce cumulative radiation burden. 3
Critical Clinical Considerations
Mandibular Fracture Patterns to Anticipate
The mandible forms an incomplete ring, so 67% of mandibular fractures involve two separate fracture sites—after identifying one fracture, actively search for a second. 1
Common patterns include: mandibular angle or subcondylar fracture with contralateral parasymphyseal fracture, or bilateral subcondylar fractures with symphyseal fracture (flail mandible). 1
Condylar and subcondylar fractures are particularly associated with lockjaw and are better visualized on CT than radiography. 1
Associated Injuries Requiring Complementary Imaging
Approximately 39% of patients with mandibular fractures have coexisting intracranial injuries, so consider complementary CT head without contrast if there are any signs of head trauma beyond the isolated chin wound. 1
In high-velocity trauma, 11% of patients with mandibular fractures have cervical spine injuries, though this is less likely with a simple fall mechanism. 1
If the fall was from significant height or high-energy mechanism, CT head should be obtained complementary to the maxillofacial CT to fully characterize the injury pattern. 1, 2
When Contrast Would Be Indicated
IV contrast is NOT needed for initial fracture evaluation in this trauma scenario. 4, 2
However, if there is concern for deep space infection, abscess formation, or neoplasm (unlikely in acute trauma but relevant if symptoms persist), then CT with IV contrast would be appropriate for soft tissue characterization. 4
Important Pitfall to Avoid
Do not order both CT with and without contrast, as this doubles radiation dose with minimal additional diagnostic benefit in the trauma setting. 4
The chin wound location raises concern for mandibular symphysis or parasymphyseal fracture, which combined with lockjaw suggests possible bilateral injury pattern requiring comprehensive mandibular imaging. 1