Keywords
mallet finger - mallet thumb - bony mallet - complications
Traumatic injuries to the extensor mechanism at the distal interphalangeal (DIP) joint
can lead to a mallet finger with or without bony avulsion.[1] A mallet thumb refers to the avulsion of the extensor pollicis longus (EPL) tendon
from its distal phalangeal insertion, which is rare in comparison with other fingers.[2]
A mallet finger lesion is known as a variant of lesions such as skin wounds (open
mallet) and/or fractures of the distal phalanx involving more than one-third of the
articular surface or displaced fractures of the distal phalanx growth plate (Seymour
lesions).[1] Also, distal phalanx fractures can occur due to flexor digitorum profundus (FDP)
avulsion with concomitant and separated fracture of the distal phalanx dorsal base,
but basically it is an uncommon injury.[2]
A few reports have addressed thumb extensor injuries. Depending on the size of the
fragments, conservative treatment may result in satisfactory outcomes in less than
50% of the articular joints without dislocation. But surgical treatments are recommended
in patients with fragment or distal phalanx dislocations.[1]
[2]
[3] The common complications associated with conservative treatments and splint occur
in approximately 45% of the cases. The frequent complications of surgical treatments
are infection, nail deformity, joint incongruity, implant failure, nail deformity,
recurrent flexion deformity, and residual pain.[1]
[3] Here, we present a case of a patient with interposition of the nail plate in the
fracture site.
Case Presentation
A case of 30-year-old man suffering from an injury to his left thumb distal phalanx
after falling during a soccer game is presented in this report. Upon physical examination,
the left thumb was swollen and painful; moreover, he could not actively extend his
interphalangeal (IP) joint. The initial radiographs demonstrated a displaced comminuted
intra-articular fracture of the distal phalanx of the left thumb ([Fig. 1]). The dorsal fragment with a size of 4 × 5 mm comprising more than 50% of the IP
articular surface was displaced dorsally, producing a bony mallet thumb lesion.
Fig. 1 A displaced comminuted intra-articular fracture of the terminal phalanx of the left
thumb. The dorsal fragment included more than 50% of the interphalangeal articular
surface attached to the extensor pollicis longus tendon and is displaced dorsally
producing a bony mallet thumb lesion.
Under digital block, the closed reduction and percutaneous pinning were initially
attempted. However, intraoperative radiographs showed unsatisfactory reduction outcomes.
Therefore, open reduction and internal fixation were implemented. At surgery, a relatively
large dorsal osseous fragment attached to the EPL tendon lied on the proximal part
of the nail plate, and the nail plate was interposed between the dorsal and palmar
fragments ([Fig. 2]). The fragment was fixed with a 2-mm miniscrew. The thumb's IP joint was immobilized
with a spica cast for 6 weeks and then the range of motion related exercises were
initiated ([Figs. 3] and [4]). Eighteen months postsurgery, the IP joint was stable, and active range of motion
was 0 extension to 45-degree flexion without extension lag with no nail deformity
([Fig. 5]). The thumb radiographs demonstrated full extension of the IP joint with no gap
at the articular surface, and all the bone fragments were consolidated ([Fig. 6]). The patient was satisfied with the functional outcomes.
Fig. 2 Under digital block and digital tourniquet and after the skin incision, there was
a relatively large osseous fragment lying on the proximal part of the nail plate.
The nail plate was interposed between the dorsal and palmar fragments.
Fig. 3 Six months postoperative lateral radiograph.
Fig. 4 Six months postoperative anteroposterior radiograph.
Fig. 5 Eighteen months postoperative clinical photography demonstrating the active full
extension of the thumb's interphalangeal joint without nail deformity.
Fig. 6 Eighteen months postoperative lateral radiograph demonstrating the full extension
of the thumb's interphalangeal joint. There was no gap at the articular surface. All
the bone fragments were consolidated.
Discussion
A bony mallet finger is a consequence of an avulsion of the extensor tendon from the
distal phalanx with a bony fragment of the bone attached to the avulsed tendon.[4] The most common mechanism of injury in the mallet finger is a sudden flexion of
the DIP joint with a resistance force directed along the long the finger axis.[4] This condition may occur in athletes especially baseball players. In our patient,
the problem occurs due to direct trauma while playing soccer.
The readers may argue that our case is that of a comminuted fracture of the distal
phalanx rather than a mallet injury; however, a mallet finger lesion can be considered
a mirror lesion to an avulsion of FDP tendon.[1] We would like to compare our case with the Al-Qattan's type 5 avulsion of the insertion
of the FDP tendon.[5] Al-Qattan reviewed FDP avulsions with a significant fracture of the distal phalanx
and extended the classification. He introduced type 5 avulsion of the FDP tendon insertion
described as FDP avulsion with a comminuted intra-articular fracture of the distal
phalanx.[5]
[6]
Some authors have extended the definition of mallet finger to fractures of the distal
phalanx involving more than one or two-thirds of the articular surface or displaced
fracture of the distal phalanx growth plate (Seymour lesion).[1]
Regarding the Al-Qattan type 5 FDP avulsion with a comminuted intra-articular fracture
of the distal phalanx, we suggested a mirror concept in our case. In our opinion,
the disruption of the extensor mechanism through a significant bone lesion, where
the extensor tendon is still attached to the dorsal fragment and the patient is unable
to actively extend the thumb's IP joint, can be considered as a type of mallet lesion
rather than a comminuted intra-articular distal phalanx fracture.
Compared with a mallet finger, a mallet thumb is an uncommon lesion since the thumb
is shorter than the other fingers and its EPL is thicker than the terminal tendon
of the extensor mechanism of the other fingers.[4]
[7]
[8] The bony mallet thumb is an even rarer lesion.[3] A bony mallet finger refers to an avulsion of the extensor tendon from the distal
phalanx with a fragment of bone attached to the avulsed tendon.[1] The most common mechanism of a bony mallet finger is an axial force followed by
sudden extreme hyperextension of the DIP joint. This condition occurs in sports injuries,
in particular among baseball players.[1]
Treatments of bony mallet thumbs may vary from splinting to surgical treatment.[1] When the fragment involves more than 30 to 50% of the articular surface of the IP
joint, it is unstable and requires surgical fixation to prevent the joint subluxation.
Insufficient treatment may lead to extensor lag, early osteoarthritic changes of the
DIP joint, or even a swan-neck deformity.[9]
Only a few case reports and sporadic cases of bony mallet thumb have been described
among the large case series describing the mallet fingers or mallet thumbs. The bony
mallet thumbs can be surgically treated with tension band technique, pull-in suture,
extension block pinning with one or two Kirschner wires, hook plate, screw, external
fixation, compression pins, and biodegradable device.[9] In a recent study by Vester et al, treatment by hook plate technique was reported
as a reliable and safe method to treat bony avulsion fractures of the distal phalanx,
with high patient satisfaction.[9] But the esthetic aspects and the nail deformities are more challenging.[9] In our presented patient, however, no nail deformity occurred with the screw, which
seemed to be due to the large size of the bony fragment with stable fixation and lack
of damage to the germinal matrix.
Although these various techniques resulted in excellent functional outcomes, the authors'
successful experiences were limited to a few cases of bony mallet thumb.[3]
[4]
[6]
[7]
[8] The complication rate of surgical treatment has been reported up to 53%. The probable
serious complications are hardware-associated infections, osteoarthritis, stiffness,
nail dystrophy, and skin necrosis.[1]
Conclusion
This case report described a bony mallet thumb lesion with interposition of the nail
plate between the dorsal and volar fragments. The avulsed fragment was large enough
to receive a 2-mm miniscrew. To the best of our knowledge, the interposition of the
nail plate in the bony mallet thumb has not been described before.
