Complex dorsal dislocation
of the metacarpophalangeal joint
of the index finger in children:
presentation of two cases

A. Vlachos, A. Kaspiris, G. Tagaris, G. Christodoulou, G. Sdougos
Karamandanio General Children’s Hospital of Patras

SUMMARY
The irreducible dislocation of the index metacarpophalangeal joint in children is a condition that appears more often than specified in the bibliography and can require surgical intervention. We present two cases that were treated in our clinic along with a discussion of the pathological anatomy of the condition and methods of treatment.

Key words: complex dorsal dislocation, metacarpophalangeal joint, index finger, children.

INTRODUCTION
The irreducible or complex dislocation of the index metacarpophalangeal joint, which is basically dorsal, is mentioned in the bibliography as a rare condition[1,3,5,21]. However, J. Hunt reports that the injury occurs relatively often, even though few reports of such incidents have been published[18]. Most articles refer to dislocations of the metacarpophalangeal joint of the thumb.
A significant number of published cases refer to children 16 years old or younger[10]. Baldwin reports four cases, three of which refer to children[17]. Moreover, Barry and McGee published four cases of complex dislocation of the MCP joint of the index finger in children[12].
Palmar dislocation of the metacarpophalangeal joint of a finger is a rare injury. Since the first description by McLaughlin (1965), who dealt with fifteen complex dislocations of metacarpophalangeal joints that only one of which was a palmar dislocation of the middle finger, only 15 cases have been reported in English language literature. Two of them referred to the index finger in young adult patients and none of them in children[4,10].
We present two cases of complex dorsal dislocation of the index metacarpophalangeal joint in children between 9.5 and 11 years old treated in our clinic.

1a

1b
Figure 1. Radiographic appearance of the 1st case. Anteroposterior view showing ulnar displacement of the proximal phalanx and the widened joint space. The lateral radiograph completes the diagnostic appearance with displacement of the proximal phalanx dorsal to the metacarpal head.

DESCRIPTION OF CASES
Case I
This concerns a 9½-year-old boy suffering from an injury to the fingertip of his right hand, having supported his weight on his fingertips by pressing them against a wall to avoid falling. Following an X-ray examination, dorsal dislocation of the index metacarpophalanageal joint with volar displacement of the metacarpal head was ascertained (figure 1). Clinically, in addition to the deformity, there was intense skin dimpling volarly of the head. Close reduction performed in the outpatient's department was unsuccessful. The patient was transferred to the operating theater and, after general anaesthesia, a new close reduction was attempted which was also unsuccessful. Open reduction was then performed through a palmar approach. The neurovascular bundle was located directly under the skin and the index nerve was under pressure from the metacarpal head. The flexor tendons of the index were found to be displaced on the radial side of the head after the lubricalis and at the level of the neck, pressing the head volarly. The volar plate was found to interpose between the proximal phalanx and the head.
Reduction was achieved after restoration of the flexor tendons volarly of the metacarpal head and resetting of the volar plate to its normal position. Then the central ridge of the plate was restored to normal anatomy with sutures, the skin was sutured, the joint was immobilized at 45o angulation and a plaster narthex was placed on the dorsal surface (figure 2). The joint was mobilized again after a period of two weeks and was functioning normally after a period of one month.

2a

2b
Figure 2. Radiographic appearance of the 2nd case.

Case II
This concerns an 11-year-old boy who came to the Outpatient’s Department after having fallen down and injured the fingertips in his left hand. He presented with an oedema of the index metacarpophalangeal joint with volar skin dimpling. Following an X-ray examination, dislocation of the index metacarpophalangeal joint with volar and radial displacement of the metacarpal head and a fissure fracture of the first phalanx of the ring finger were ascertained (figure 3). After unsuccessful attempts for close reduction, both in the Emergency Department and the operating theater under general anaesthesia, open reduction through a palmar approach was decided. The index nerve was found, as in the previous case, to be directly under the skin and under pressure from the metacarpal head. The metacarpal neck was “locked” between the flexor tendons on the ulnar side and the lubricalis on the radial side, while the volar plate was displaced dorsally of the metacarpal head.
Reduction was successfully performed after an incision of the fibers of the superficial transversus ligament of the metacarpus was made and restoration of the volar plate volarly of the metacarpal head, on which a partial incision had previously been made, was carried out. The skin was then sutured and the joint immobilized at 45o angulation for three weeks using a dorsal plaster narthex. After a period of six weeks, total normal functioning has been restored.

3a

3b
Figure 3. Post operative radiographic appearance of the second patient.

DISCUSSION
The mechanism that causes the dorsal dislocation injury is a sudden extensive strain of the joint, usually after a fall on the fingertips and the detachment of the volar plate from its normal position in the metacarpal neck[10,16]. Although dorsal dislocations of the metacarpophalangeal joint are well documented, palmar’s dislocations pathogenesis remains uncertain[4,6,8]. According to Betz et al and Murase - Moritomo, the main cause of the injury in our case is probably a hyperextension force applied during strong active flexion of the digit. The chondral defect at the dorsoulnar aspect of the metacarpal head and the rupture of the palmar plate also suggest that a hyperextension injury was the mechanism of dislocation. The rapture of the collateral ligaments may indicate that forceful rotation occurred during the dislocation[4].
Early diagnosis is the first and perhaps the most critical step in the management of this injury. The clinical presentation can be very helpful. The index finger is held in an attitude of extension at the MCP joint and the interphalangeal (IP) joints are held in mild flexion. The finger is usually held in mild ulnar deviation toward the middle finger. Motion is painful. A visible clinical sign, which Kaplan says is pathognomic of complex dislocation, is the puckering of the palmar skin overlying the head of the metacarpal. This is caused by the intimate connections between the skin and the fascial fibres which lie under the dislocated metacarpal head. If recognized, this may avoid prolonged, unsuccessful and harmful attempts at reduction[1,5,7,20].
In 1957, Kaplan was the first to describe the pathological anatomy of this condition through detailed reference to the factors that obstruct reduction[20]. Understanding the pathoanatomy is extremely important in the treatment of the injury. A hyperextension force leads to rupture of the weaker membranous portion of the volar plate from its metacarpal attachment. Then, the volar plate is displaced dorsally of the metacarpal head and is interposed between the head and the base of the proximal phalanx. The flexor tendons of the index are displaced on the ulnar side of the head, the lumbricalis on the radial side of the head and the superficial transversus ligament volarly of the metacarpal neck. In the first case, the flexor tendons were found to be displaced on the radial side of the metacarpal head, as was the lumbricalis.
Many doctors believe that the volar plate is the most important anatomical obstruction to close reduction[10,12,16]. The unimpaired collateral ligaments of the joint obstruct the sideways movement of the plate, resulting in its becoming “locked” dorsally of the metacarpal head[10,22].
In 1876, Farabeuf was the first to use the dorsal approach for the treatment of this condition[12,16]. Later, Kaplan considered the palmar approach to be more reasonable as it ensures the immediate visibility of all factors obstructing reduction[20]. Bacton et al believe the dorsal approach has several advantages over the volar approach. The dorsal approach provides full exposure of the volar plate the most common structure blocking reduction. Also possible osteochondrous fragments in the metacarpal head can be detected and removed and injury to the neurovascular bundle can be avoided[12,13,15]. Contrariwise, in the palmar approach, the neurovascular bundle is at direct risk and the volar plate is not completely visible[12,13,15]. The main advantage of volar approach is that allows anatomical restoration of the joint and the attachments of the volar plate may be repaired, decreasing the possible risk of late instability[12]. Moreover, visualizing the neurovascular bundle is a constant reassuring factor, which in a dorsal approach is lacking. On the contrary, while cutting the volar plate to reduce the dislocation in the dorsal approach, the neurovascular bundle lying deep to the volar plate could inadvertently be damaged[3].
Although Kaplan’s classic paper does not comment on the displacement of the digital nerve and artery, we must highlight the fact that the radial digital neuromuscular bundle of the index finger is displaced to lie directly over the head of metacarpal, in a majority of patients with dorsal dislocation of the second metacarpophalangeal joint. In the Chadha’s and Dhal’s paper, it was mentioned that in six out of nine patients (66,67%), the neurovascular bundle was tented across the displaced metacarpal head and was very close to the surface of the skin[3]. Similar observations have been reported by Stowell and Rennie in their case reports[5]. Moreover, in both of the cases that were treated in our hospital through the palmar approach, the radial index nerve was directly under the skin and under pressure volarly from the metacarpal head. So, any transverse volar incision has to be made very carefully since this neurovascular bundle lies just under the skin, which is puckered and with almost negligible subcutaneous tissue[3].
Dislocation reduction can be achieved through resetting the volar plate from its pathological position to its normal position, which can be facilitated by a partial or full incision in the plate. It may be necessary to make an incision in the fibers of the superficial transversus ligament of the metacarpus and an oblique incision in the transverse fibers of the palmar fascia[11]. In children, however, large incisions in soft molecular matter are not necessary because the increased flexibility of their ligaments facilitates reduction.
After reduction, the joint is stable but a narthex should be put in place for a few days to prevent hyperextension of the joint16. The dressing and splints usually removed after 10-14 days. Complete extension of the MCP joint is allowed after a further 10 days. Recovery of a full range of motion is seen within 4 to 6 weeks1.
The longer a dorsal dislocation remains unreduced, the more likely the development of degenerative arthritis and the less satisfactory the results of surgery will be in terms of pain and ultimate range of motion. A delay diagnosis is often seen and is usually accompanied by multiple attempts at achieving a closed reduction. This may be associated with greater soft tissue trauma and ensuing stiffness1,5,11,16. Other complications of this condition have been reported as ischemic necrosis of the metacarpal epiphysis and damage to the growth plate10. Such complications were not observed in our cases.
As a conclusion, irreducible dislocation of the index metacarpophalangeal joint in children is not a rare injury, despite what is mentioned in the bibliography, and can be surgically treated. Identifying the anatomical obstructions to reduction during an operation is a necessary prerequisite for easy reduction and the avoidance of further injuries. A desirable outcome is almost always achieved.

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Mailing address:
Α. Κaspiris
Karamandanio General Children’s Hospital of Patras
Erithrou Stavrou 40, 263 31, Patras