Mallet finger refers to an injury affecting the fingertip, preventing it from straightening. This condition often arises from a forceful impact that causes the extensor tendon at the distal interphalangeal (DIP) joint, the joint closest to the fingertip, to tear or pull away from the bone. The affected fingertip will droop, resembling a mallet or hammer. Prompt medical evaluation is recommended, as early diagnosis and appropriate intervention can help restore function and prevent long-term complications.
Why Imaging is Crucial
Medical imaging, particularly X-rays, is an important step in assessing a suspected mallet finger injury. While a physical examination can suggest the presence of a mallet finger, X-rays provide internal details not visible externally. Imaging helps confirm the diagnosis, determine injury severity, and rule out other finger injuries with similar symptoms.
X-rays determine if a bony component is involved, such as an avulsion fracture. An avulsion fracture occurs when the tendon pulls a small piece of bone away from the main bone. This distinction between a purely soft tissue injury and one involving bone fragments significantly influences the treatment approach.
Identifying Mallet Finger on X-rays
When examining X-ray images for a suspected mallet finger, radiologists look for specific signs. Standard X-ray views include posteroanterior (PA), lateral, and oblique views of the affected finger. The lateral view is particularly informative as it clearly shows the characteristic flexion deformity of the DIP joint, where the fingertip is noticeably bent downwards.
A small bone fragment, often triangular, pulled away from the dorsal (back) base of the distal phalanx (the bone at the fingertip) indicates an avulsion fracture. Soft tissue swelling around the injured joint may also be observed on the X-ray.
Distinguishing Injury Types through Imaging
Imaging differentiates between the two primary types of mallet finger injuries: soft tissue and bony. A soft tissue mallet finger involves a rupture or tear of the extensor tendon without bone involvement, meaning the X-ray will not show a fracture. In contrast, a bony mallet finger is characterized by an avulsion fracture where a piece of the distal phalanx is pulled off with the tendon’s attachment.
The X-ray reveals the size of the bone fragment, its displacement, and whether the DIP joint is subluxed (partially dislocated). For instance, a small, non-displaced fragment may be managed differently than a larger, significantly shifted fragment. In children, X-rays also assess if the injury affects the growth plate.
How Imaging Guides Treatment
X-ray findings directly influence mallet finger treatment. The presence or absence of a fracture, along with the size and displacement of any bone fragment, determines whether non-surgical or surgical management is appropriate. Injuries without a fracture or with a small, non-displaced avulsion fracture (less than 30% of the joint surface) are managed non-surgically with continuous splinting of the DIP joint in extension for 6 to 8 weeks. Consistent splinting is important for successful healing, as any flexion during this period may require restarting treatment.
Surgical intervention may be considered for larger, displaced avulsion fractures (involving more than 30% of the joint surface) or if there is subluxation of the distal phalanx that cannot be corrected with splinting. Surgery might involve using pins to hold bone fragments in place and realign the joint while it heals. For purely tendinous injuries with proper joint alignment, surgery is not recommended due to the thin nature of the tendon, making repairs challenging.