Volar Avulsion Fracture of Middle Phalanx Base: Tendon Involvement
Yes, an avulsion fracture at the volar base of the middle phalanx can involve tendon structures, but it typically involves the volar plate rather than the flexor digitorum profundus (FDP) tendon. The FDP tendon inserts on the volar base of the distal phalanx, not the middle phalanx, making direct FDP involvement anatomically impossible at this location 1.
Anatomical Clarification
The key distinction here is anatomical:
- Flexor Digitorum Profundus (FDP): Inserts exclusively on the volar base of the distal phalanx, approximately 3.5 mm distal to the volar articular line, often marked by a characteristic volar spur on radiographs 1
- Flexor Digitorum Superficialis (FDS): Inserts on the middle phalanx shaft (not the base)
- Volar Plate: Attaches to the volar base of the middle phalanx at the proximal interphalangeal (PIP) joint
What Structure Is Actually Involved
A volar avulsion fracture at the base of the middle phalanx represents a volar plate avulsion injury, not a flexor tendon avulsion 1. The volar plate is a fibrocartilaginous structure that stabilizes the PIP joint and prevents hyperextension.
Clinical Implications
This distinction matters significantly for management:
- Volar plate avulsions at the middle phalanx base may require operative fixation if the fragment is large or if there is joint instability
- FDP avulsions (jersey finger) occur at the distal phalanx and represent a completely different injury pattern requiring urgent surgical repair to prevent tendon retraction 2, 3
Diagnostic Approach
According to ACR guidelines, standard 3-view radiographs of the hand are sufficient for initial evaluation 4. The guidelines specifically note that radiographs effectively detect fracture fragments associated with tendon injuries and help determine if operative fixation is needed.
When to Consider Advanced Imaging
MRI is ideal for evaluating volar plate injuries that don't involve underlying bone 4. This is particularly important because untreated volar plate tears can result in contractures or joint laxity, affecting long-term function and quality of life.
MRI should be considered when:
- Clinical examination suggests soft tissue injury beyond what radiographs show
- There is persistent pain or instability despite appropriate fracture fragment size
- Surgical planning requires detailed assessment of the volar plate integrity
Common Pitfall to Avoid
Do not confuse middle phalanx base avulsions with FDP injuries. The literature describes rare cases of FDS avulsion with middle phalanx fractures 2, but these involve the phalangeal shaft, not the base. If you suspect flexor tendon involvement at the middle phalanx base, you're likely dealing with a volar plate injury instead, which has different treatment implications and prognosis.
The volar spur visible on lateral radiographs at the distal phalanx base can help differentiate true FDP avulsions from volar plate injuries 1, serving as a useful radiological landmark during evaluation.