Dorsal avulsion of the proximal end segment

Avulsions involving the articular surface of the base of the middle phalanx are partial articular fractures and classified according to AO/OTA as 78.2–5.2.1B, where 2–5 indicates which finger is injured. The fractures may be simple or fragmentary.

An avulsion fracture may be associated with a proximal interphalangeal (PIP) joint dislocation.

Dorsal avulsion of the middle phalanx base, classified as 78.2–5.2.1B, may be simple or fragmentary, and associated with PIP joint dislocation.

Several lesions may be produced by a hyperflexion mechanism.

All of these are characterized by detachment of the central slip of the extensor apparatus. They are considered as acute boutonnière injuries.

Lesions without dislocation

Hyperflexion with detachment of the central slip (no fracture)
Simple avulsion fracture of the central slip with a small nonarticular fragment
Simple avulsion fracture of the central slip with a larger partial articular fragment

$Dorsal avulsion of the middle phalanx, hyperflexion detachment (no fracture), simple avulsion with small nonarticular or larger partial articular fragment.$

Sometimes, lesions such as these are considered minor injuries by traumatologists, and often they are confused with simple ligament sprains.

However, the boutonnière deformity and associated lesions should be addressed acutely because they are difficult to treat at a later stage.

Dorsal avulsion of the middle phalanx, often confused with ligament sprains, but boutonnière deformity needs acute treatment.

Lesions with palmar dislocation

If palmar dislocation of the proximal interphalangeal (PIP) joint is present, a rupture of the collateral ligament and detachment of the central slip are involved. In injuries of this kind, a so-called swan-neck deformity is present, and the finger can not be flexed.

Lesions with dislocations:

Detachment of the central slip without a fracture
Avulsion fracture of the central slip with a small nonarticular fragment
Avulsion fracture of the central slip with a larger partial articular fragment

$Dorsal avulsion of the middle phalanx, palmar PIP dislocation involves collateral ligament rupture and central slip detachment, causing swan-neck deformity. Lesions include central slip detachment (no fracture), avulsion fracture with small nonarticular fragment, or larger partial articular fragment$

These injuries are commonly caused during sports, eg, cricket, volleyball, basketball, etc. The middle and ring fingers are commonly involved.

Typically, hyperflexion of the finger causes an avulsion lesion of the central slip.

Often, in addition to hyperflexion, impact on the fingertips causes longitudinal compression forces through the middle phalanx proximally, leading to an additional impaction fracture of the base of the middle phalanx or proximal phalangeal head.

Boutonnière deformity

When the central slip is detached, the lateral bands are palmarly displaced and pull the DIP joint into hyperextension.

This creates a lesion like a buttonhole (“boutonnière”) in the extensor mechanism through which the head of the proximal phalanx perforates dorsally.

The flexor digitorum superficialis (FDS) pulls proximally on the middle phalanx, forcing the PIP joint into flexion.

Dorsal avulsion of the middle phalanx, central slip detachment causes boutonnière lesion, DIP hyperextension, and PIP flexion.

Swan-neck type deformity

If the middle phalanx is palmarly dislocated at the PIP joint by the energy of the trauma, the flexor digitorum profundus (FDP) pulls the DIP joint into flexion. This creates the characteristic deformity of the finger described as having the profile of a swan’s neck.

Dorsal avulsion of the middle phalanx, palmar PIP dislocation causes DIP joint flexion by FDP, creating swan-neck deformity

In the lateral view, the dorsal cortical profiles of the proximal and middle phalanges should be collinear. Any axial malalignment is a clear indication of subluxation.