Age / Sex : 33 / M

Age / Sex : 33 / M

Chief complaint : Painful swelling of left ring finger for 2 months

Distal avulsion of flexor digitorum profundus tendon

Discussion

Findings:

Sagittal PD-weighted, sagittal fat suppression T2-weighted and axial PD-weighted FSE MR images show distal avulsion of the FDP tendon of the ring finger with a torn tendon retracted to the proximal interphalangeal joint level. On axial PD-weighted image at middle phalanx, the empty digital canal mimics a remnant tendon, the FDS tendon is intact.

Differential Diagnosis: Partial tear of flexor digitorum profundus tendon

Diagnosis: Distal avulsion of the flexor digitorum profundus tendon of the ring finger (chronic)

Discussion:

Injuries to the flexor tendons are not as common as injuries to the extensor apparatus, and are classified as either open or closed. Closed injuries of the flexor tendon are generally of two types. First, disruption of non-insertional sites of the tendon, especially the musculotendinous junction, is observed in cases of tenosynovitis. Second, avulsive injury of the flexor digitorum profundus (FDF) tendon or less commonly, the flexor digitorum superficialis (FDS) tendon is observed, particularly in athletes.

Avulsion of the FDP tendon is the most frequent type of closed rupture and is caused by a sudden hyperextension during active flexion. Ring finger is most commonly injured, although any finger or multiple fingers may be affected. Our patient had a history of ring finger dislocation. When occurring in American fooball, the avulsive injury is sometimes called “jersey finger” or even “sweater finger”. This injury is often neglected initially as there is no typical deformity or alignment abnormality associated with it on physical examination, and the combination of pain and soft tissue swelling may mask the pathognomonic sign of loss of active flexion at the DIP joint. This lesion is classified according to the degree of tendon retraction and the presence or absence of a bony fragment. Type I is characterized by retraction of the tendon into the palm. Type II shows tendon retraction at the PIP joint with or without a small osseous avulsion at the joint. Type II lesion may convert to type I lesion over a period of time if treatment is delayed. In type III there is a large bony fragment incarcerated in the A4 pulley. Type IV is a type III injury with an associated avulsion of the flexor tendon from the bone fragment.

Imaging is important because it can be easily overlooked in the acute context. Ultrasonography and MRI are useful for displaying the zone of rupture and the proximal and distal tendons and accurately measure the gap between the torn tendon ends. On T2-weighted image the empty digital canal lined by a synovial sheath may appear as a low signal intensity structure that mimics a flexor tendon but is thinner than a normal tendon. Primary repair of the tendon is usually needed, and trans-osseous reinsertion of the tendon is frequently possible, even with large gap.

References:

1. Resnick D, Kang HS, Pretterklieber ML. Internal derangements of joints. 2^nd ed. Philadelphia: Saunders Elsevier,2007:1335-1344

2. Drape J-L, Viet DL. MR imaging of the fingers. In Stoller DW. Magnetic resonance imaging of orthopaedics and sports medicine. 3^rd ed. Philadelphia: Lippincott Williams & Wilkins,2007:1868-1873 

3. Cerezal L, Llopis E, Canga A, Abascal F, Rolon A. Soft tissue injuries of the hand and wrist. In Pope LT, Bloem H, Beltran J, Morrison WB, Wilson DJ. Imaging of the musculoskeletal system. 1^st ed. Philadelphia: Saunders Elsevier,2008:392-394