Leo T. Kroonen and Eric P. Hofmeister
DEFINITION
Injuries about the distal interphalangeal joint (DIP) consist of avulsion injuries of the terminal extensor tendon or the flexor digitorum profundus (FDP) tendon, or isolated dislocations of the DIP joint.
Isolated dislocations of the DIP joint are rare injuries in which the distal phalanx is dislocated either dorsal or volar relative to the middle phalanx.
A “bony” mallet finger (ie, mallet fracture) is an intraarticular bony avulsion at the insertion site of the terminal extensor tendon on the dorsal base of the distal phalanx that results in inability to actively extend the DIP joint.
A “non-bony” mallet finger is an injury to the extensor mechanism at or near the insertion onto the distal phalanx that typically results in inability to actively extend the DIP joint.
“Jersey finger” is an avulsion of the FDP tendon, with or without its bony attachment, from the volar base of the distal phalanx. It typically results in inability to actively flex the DIP joint.
ANATOMY
The DIP joint is stabilized by the radial and ulnar collateral ligaments, the volar plate, and the firm insertions of the FDP and terminal tendons of the extensor mechanism.
The extensor mechanism terminates with the confluence of the lateral bands into a single terminal tendon, which inserts on the dorsal base of the distal phalanx. The terminal tendon is a strong, flat, thin segment that averages 10.1 mm in length and 5.6 mm in width.8
The terminal tendon insertion, on average, is 1.4 mm proximal to the germinal matrix of the fingernail.9
The volar surface of the terminal tendon usually is adherent to the dorsal capsule of the DIP joint.9
The FDP tendon inserts on the volar surface of the base of the distal phalanx. It is surrounded by the flexor tendon sheath. The A4, A5, and C3 pulleys secure the FDP tendon around the level of the DIP joint.
The vinculum longus profundus and vinculum brevis profundus are thin mesenteries providing vascular supply to the distal portion of the FDP tendon. They also provide a weak attachment of the FDP tendon to the flexor tendon sheath.4
PATHOGENESIS
Mallet finger injuries are the result of a disruption to the extensor mechanism at or near the insertion to the base of the distal phalanx. Such disruptions can occur as a result of a laceration or a sudden flexion force to an extended DIP joint. The disruption of the extensor mechanism leaves the pull of the FDP unopposed, leaving the DIP joint in a flexed posture.
Dislocations of the DIP joint are rare due to the inherent stability provided by the collateral ligaments, the volar plate, and the flexor and extensor tendon insertions. However, when a dislocation does occur, the distal end of the middle phalanx usually “buttonholes” through these structures, making reduction more difficult.
“Jersey finger” injuries occur as a result of disruption to the FDP, from either a laceration or a sudden extension force applied to a flexed DIP joint, causing an eccentric contraction. The disruption of the FDP tendon leaves the pull of the extensor mechanism unopposed, resulting in an extended posture of the DIP joint.
NATURAL HISTORY
Mallet finger injuries can occur in any finger, but most commonly are seen in the three most ulnar digits.
Left untreated, a mallet finger injury can progress to a secondary “swan neck” deformity.
With the disruption of the extensor mechanism at the DIP joint, the pull of the lateral bands adds to the extension force of the central slip at the PIP joint, thereby creating an imbalance in forces at the PIP joint and a hyperextension deformity at that joint.11
Despite treatment, residual deformity, usually in the form of a dorsal prominence, can be seen in up to 80% of cases.11
About 75% of cases of FDP avulsions involve the ring finger. Although some researchers hypothesize that this happens because the ring finger protrudes the farthest when the hand is held in a flexed position, this theory has never been proven.
Leddy and Packard3 proposed the classification system that is still widely used today for FDP avulsion injuries, based on the level of retraction of the tendon. Other authors since have made modifications, including the addition of a fourth type of injury.10
Type I FDP avulsions retract into the palm, thereby disrupting the vincular system and leading to poor blood supply. Surgery should be performed within 7 to 10 days.
Type II injuries retract to the level of the PIP joint or distal A2 pulley. An associated small bony fleck often is seen on the lateral radiograph. Because the proximal blood supply is preserved through the long vincula, these injuries can be successfully treated as late as 6 weeks from the time of injury.
Type III injuries usually are associated with a bony avulsion, and as a result, do not retract proximal to the A4 pulley. These injuries are treated as bony injuries with open reduction and internal fixation and can be treated late if required.
Type IV injuries are bony avulsion injuries in which the tendon also has separated from the avulsed bony fragment. Time to treatment depends on the level of tendon retraction.
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The views expressed in this chapter are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government.
PATIENT HISTORY AND PHYSICAL FINDINGS
As with all hand injuries, patients should be questioned about their hand dominance and occupational requirements so the surgeon can better understand individual needs and goals.
The following examinations should be performed to determine possible injuries:
FDP function
Inability to flex at the DIP joint implies disruption of the FDP tendon.
Limited, weak, or painful flexion may indicate a partial injury or a complete disruption with intact vinculae or pseudotendon.
DIP joint extensor mechanism function
Inability to extend at the DIP joint implies disruption of the terminal extensor tendon. Weak extension implies a partial or less severe injury. Loss of passive extension indicates a possible fracture or dislocation.
Axial injuries to an extended DIP joint often are the culprit in mallet finger injuries.
The history often reveals an axial blow to the fingertip, such as when catching a ball.
The patient will be unable to actively extend at the DIP joint.
“Jersey finger” injuries often are the result of a sudden extension force on a flexed DIP joint, such as when grabbing for another player's shirt while playing football.
These patients will be unable to actively flex through the DIP joint.
Active PIP flexion will be present but may be moderately diminished due to pain or stiffness.
Most dislocations of the DIP joint are the result of sporting injuries.7,8
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs of the affected hand (PA, lateral, and oblique) and dedicated views of the affected finger (PA, lateral, and oblique) should be obtained, and usually are sufficient for making the diagnosis in association with a thorough clinical examination.
Mallet finger injuries can be associated with a bony avulsion. Any joint subluxation should be noted, and the size of the avulsed fragment should be estimated (FIG 1).
In FDP avulsion injuries, the location of the retracted flexor tendon often can be appreciated by finding a bony fragment on the lateral radiograph of the affected digit (FIG 2A).
FIG 1 • Lateral radiographs usually are the most helpful in identifying a mallet fracture. Note that in this image, the avulsed fragment includes more than 50% of the articular surface. There is no significant volar subluxation in this case.
FIG 2 • A. Flexor digitorum profundus (FDP) avulsion in which a bony fragment has been caught up at the A4 pulley. B. Lateral radiograph of a finger demonstrates chronic dorsal dislocation of the DIP joint, with associated arthrosis. C. Axial cut MRI at the level of the proximal phalanx shows both FDP and flexor digitorum superficialis (FDS) tendons are present. D. At the level of the middle phalanx, only the FDS tendon can be seen. (B-D: Copyright Thomas R. Hunt III, MD.)
Ultrasound sometimes can be helpful in determining continuity of the flexor tendon or identifying the location of the retracted proximal flexor tendon stump.
MRI also is valuable in determining flexor tendon continuity and level of tendon retraction (FIG 2C,D).
DIFFERENTIAL DIAGNOSIS
Osteoarthritis
Inflammatory arthropathy
FDP rupture
FDP laceration
Terminal extensor tendon rupture (mallet finger)
Mallet fracture
NONOPERATIVE MANAGEMENT
For tendinous mallet fingers and mallet fractures involving less than one third of the articular surface and without joint subluxation, a variety of splints are available.
We prefer immobilizing the DIP joint with a prefabricated polyethylene extension splint.
Casting of the DIP joint also has been described.
Full-time splinting in extension is recommended for 6 weeks, followed by 6 weeks of part-time splinting. During this second 6 weeks, we advise our patients to wear the splint for any heavy activity and at night, and we emphasize the inclusion of gentle DIP joint flexion, not exceeding 20 degrees in the first 2 weeks, and then gradually increasing to full flexion over the course of 6 weeks. If any loss of extension is experienced during this time, we advise the patient to return immediately to full-time splinting and to follow up in our clinic.
Nonoperative treatment of acute FDP lacerations or ruptures at the DIP joint is not recommended unless the patient is unwilling to comply with postoperative splinting or rehabilitation.
In subacute and chronic FDP lacerations or avulsions, the functional necessity of DIP joint motion should be carefully considered, and nonoperative treatment should be considered.
Literature directing treatment in cases of delayed diagnosis is scarce.
If the patient does not have any functional limitations as a result of the injury, we prefer to defer surgical management.
If the patient is troubled by a tender mass in the palm but the hand is functional, we recommend excision of the tendon alone.
Instability and weakness of pinch can become problematic. In such cases, we recommend tenodesis or arthrodesis.
Only if the function of the DIP is crucial to the performance of daily activities do we recommend a staged reconstruction of the flexor tendon.
Closed reduction of isolated DIP joint dislocations can be attempted under a digital block.
For dorsal dislocations, the FDP tendon or the volar plate can be interposed, blocking the reduction as the head of the middle phalanx buttonholes through the interval between the FDP tendon and the collateral ligament.8
For dorsal dislocations, gentle traction and extension through the DIP joint can assist in reducing the interposed volar plate.
In volar dislocations, the head of the middle phalanx can buttonhole through the interval between the terminal extensor tendon and the collateral ligament.7
For volar dislocations, gentle traction can be used while guiding the condyle of the middle phalanx back through the interval between the terminal extensor tendon and the collateral ligament.
In either case, a gentle reduction maneuver should be attempted, keeping in mind the structures that are likely to be interposed in the joint. Care should be taken to avoid excessive traction, which may tighten the tendon and ligament, preventing reduction.
SURGICAL MANAGEMENT
Surgical treatment of mallet fractures is reserved for those fractures associated with joint subluxation.
Operative treatment is recommended for all acute flexor tendon avulsions at the DIP joint and selected subacute or chronic cases.
The level of retraction of the tendon on the flexor side determines the urgency with which the injury needs to be addressed (see Table 1). Although Type I and II injuries can be treated up to 6 weeks with good results, we recommend treating these injuries sooner when possible to optimize recovery and function.
For isolated dislocations of the DIP joint, surgical management is indicated in those cases where closed reduction is unsuccessful. Generally, no surgical stabilization is required.
Preoperative Planning
All images should be reviewed.
For isolated dislocations, a review of the relevant anatomy, including the volar plate, flexor and extensor tendons, and collateral ligaments, is essential to understand which structures might be interposed in the DIP joint.
Positioning
The patient is placed supine on the operating room table with the affected arm outstretched on an arm board. When treating a flexor tendon injury, a flexible aluminum hand-holder can be useful for positioning the hand during the exploration.
A well-padded tourniquet is placed high on the arm.
Approach
Mallet fingers
We prefer to treat mallet fingers with percutaneous techniques.
Percutaneous treatment is more likely to succeed if the injury is treated within the first 3 to 5 days after the injury, although we have successfully treated cases at as late as 6 weeks.
If open treatment is to be attempted, a variety of incisions can be used, including straight longitudinal, lazy-S type, Htype, and Bruner incisions. Meticulous soft tissue handling is vital to minimize trauma to the skin. Great care must be taken to avoid injury to the germinal matrix proximal to the nail fold.
“Jersey fingers”
A volar Bruner incision is used and is extended proximal enough to identify or retrieve the proximal tendon stump.
In type I injuries, one oblique limb of the Bruner incision over the A1 pulley region often is used to retrieve the retracted tendon.
Care is taken to preserve the A2 and A4 pulleys.
For open reduction of isolated DIP dislocations, the approach is dictated by the direction of the dislocation.
Dorsal dislocations are approached volarly, and volar dislocations are approached dorsally.
TECHNIQUS
TREATMENT OF MALLET FINGERS
Extension-Block Pinning of Mallet Fractures
The DIP joint is flexed initially, pulling the avulsed fragment volarly.
A dorsal block pin is inserted obliquely from distal to proximal under fluoroscopy. A 0.045-inch K-wire usually is ideal, although 0.035-inch K-wires are sometimes preferred if the finger is small.
The pin should enter at the dorsal edge of the articular surface of the middle phalanx, and bicortical purchase should be obtained (TECH FIG 1A,B). The dorsal blocking pin should not actually engage the fracture fragment, because this may result in comminution of the bone.
Anteroposterior and lateral views on fluoroscopy should be obtained to ensure appropriate positioning (TECH FIG 1C).
The distal phalanx is then extended, reducing and compressing the fracture.
A second K-wire is inserted in a retrograde manner from the distal tip of the distal phalanx to the level of the DIP joint (TECH FIG 1D).
While holding the digit extended with the fracture and DIP joint reduced, the second smooth K-wire is advanced retrograde across the DIP joint into the middle phalanx (TECH FIG 1E,F).
The K-wires are cut, and protective plastic caps are placed over the exposed ends.
The finger is then placed in a protective dressing.
TECH FIG 1 • A With the DIP joint flexed, a K-wire is inserted at the dorsal edge of the articular surface of the middle phalanx. B. Bicortical purchase is obtained. C. PA fluoroscopic image confirms good bony purchase in both the dorsal and volar phalanx. D. With the DIP joint extended, a retrograde K-wire is introduced through the tip of the distal phalanx. E. Once reduction is confirmed, this retrograde pin is advanced into the middle phalanx. F. A final PA image confirms good placement of pins.
Pinning of Non-Bony Mallet Fingers
For patients whose compliance is in doubt, or to assist with occupational requirements, a single 0.045-or 0.062-inch Kwire can be inserted in a retrograde manner through an extended DIP joint.
The pin can be left either protruding through the skin and covered with a pin cap, or under the skin.
Pull-Through Button Technique for Flexor Digitorum Profundus Avulsions
The fingers are held in an extended position using an aluminum hand.
The volar surface of the injured finger is exposed through a Bruner incision, and the edges of the avulsed tendon are identified (TECH FIG 2A).
The proximal segment of the tendon is retrieved, pulled out to length, and secured using a small-gauge needle directed transversely across the tendon (TECH FIG 2B).
Using a 2-0 monofilament nonabsorbable suture (or other permanent suture appropriate for tendon repair), the proximal segment of the avulsed tendon is captured using a Krakow or Bunnell suture technique (TECH FIG 2C).
The proximal segment of tendon is then threaded through the flexor pulley system.
The volar base of the distal phalanx is prepared with a rongeur to expose bleeding bone.
Two straight Keith needles are introduced into the volar wound and, using a wire driver, driven from the volar base of the distal phalanx, through the nailbed, and exiting through the center of the fingernail on the dorsal side (TECH FIG 2D,E).
A small square of sterile felt and a plastic sterile button are placed over the exposed tips of the Keith needles (TECH FIG 2F).
The two free ends of suture are threaded through the eyelets of the Keith needles, and the needles are advanced through the nailbed, felt, and button.
The distal end of the avulsed tendon is pulled into its prepared footprint at the volar base of the distal phalanx, and the suture is then carefully tied over the button (TECH FIG 2G,H).
Additional fixation is obtained by securing the tendon to tendon remnants at the insertion site.
As an alternative to tying over the nail and a button, the Keith needles may be advanced through the proximal portion of the distal phalanx, avoiding the germinal matrix. A 3-mm transverse incision is then made over the exiting Keith needles, and the suture is tied down on bone.
The wound is closed in standard fashion, and the hand is secured in a dorsal extension blocking splint (TECH FIG 2I).
Suture Anchor Technique for Flexor Digitorum Profundus Avulsions
The approach, identification, and suture of the avulsed profundus tendon are the same as in the pull-through button technique.
Two small suture anchors are introduced into the volar base of the distal phalanx in a trajectory from proximalvolar to distal-dorsal, or, as recently described by McAllister et al,6 may be placed in a distal-volar to proximal-dorsal direction, taking special care not to violate the dorsal cortex. This placement ensures maximum bony purchase in the thickest portion of the distal phalanx and ensures maximum pullout strength.
TECH FIG 2 • A. A volar Bruner incision is planned. B. The avulsed tendon is identified and held in the wound with a small-gauge needle. C. The avulsed tendon is captured with a Krakow technique. D.Keith needles are advanced through the volar wound to exit in the center of the fingernail. (continued)
TECH FIG 2 • (continued) E. A side view shows the Keith needles exiting through the fingernail. F. Sterile felt and a plastic button are threaded over the needles. G. The finger is flexed down, and the sutures are pulled through. H. The suture is securely tied over the button. I. The patient is immobilized initially in an extension block splint.
Fluoroscopic imaging can be used to ensure proper anchor placement and document that the suture anchors have not violated the dorsal cortex or the joint.
A modified Kessler pattern of suturing can then be used to secure the FDP tendon in place at the base of the distal phalanx.
The wound is closed and the splint applied in the manner described.
Treatment Technique for Flexor Digitorum Profundus Disruption With Bony Avulsion
If the avulsed fragment is large enough, some authors recommend open reduction and internal fixation using small screws or wires.
It is recommended that the fragment have a diameter at least 2 ½ times the diameter of the screw to avoid comminution of the bony fragment.5
Intraoperative radiographs are imperative to confirm reduction.
POSTOPERATIVE CARE
Mallet fractures
The patient is allowed nearly full activity immediately postoperatively, including PIP joint and MCP joint motion.
An antibiotic ointment may be applied to the pin sites twice daily.
The patient should be counseled thoroughly on keeping pin sites clean.
The patient is seen for follow-up around postoperative day 10, and as needed for 4 weeks.
Pins are removed in the office setting when there is no tenderness to palpation at the fracture site and there is evidence of bridging trabeculae at the fracture site (usually about 4 to 5 weeks).
FDP avulsions/lacerations
The patient is evaluated 3 to 5 days postoperatively, and if a strong repair has been accomplished and the patient is deemed compliant, a forearm-based dorsal extension block splint is fitted and the patient is enrolled into a directed hand therapy rehabilitation protocol with immediate edema control.
In the compliant patient, place-and-hold exercises, initially in the splint and then with the wrist in slight extension, are started between postoperative days 5 and 7.
Further progression is based on the protocol described by Cannon and Strickland,1 and typically includes tendon glides and wrist tenodesis activities at 5 weeks, and progressive strengthening at 7 to 8 weeks.
OUTCOMES
For extension block pinning of mallet fractures, one study by the primary author reported average time to bony union of 35 days.
At an average follow-up time of 74 weeks, range of motion averaged 4 to 78 degrees.2
For isolated dislocations of the DIP joint, case studies suggest that active range of motion at the DIP joint from 0 to 65 degrees is regained by 4 to 12 months postreduction.7,8
Most patients with FDP avulsions treated acutely are able to work between 8 and 18 weeks after the surgery, with some studies suggesting that an earlier return to work is seen with a suture anchor repair.
An 8-to 10-degree flexion contracture and a similar lack of terminal flexion at the DIP joint often are encountered.6
COMPLICATIONS
Pin tract infection
Migration of pins
Loss of reduction
Nail deformity
Dorsal skin necrosis from splinting
Joint stiffness
Loss of grip strength
Tendon adherence
Tendon rupture
REFERENCES
1. Cannon NM, Strickland JW. Therapy following flexor tendon surgery. Hand Clin 1985;1:147–165.
2. Hofmeister EP, Mazurek MT, Shin AY, et al. Extension block pinning for large mallet fractures. J Hand Surg Am 2003;28:453–459.
3. Leddy JP, Packer JW. Avulsion of the profundus tendon insertion in athletes. J Hand Surg Am 1977;2:66–69.
4. Leversedge FJ, Ditsios K, Goldfard CA, et al. Vascular anatomy of the human flexor digitorum profundus tendon insertion. J Hand Surg Am 2002;27:806–812.
5. Lubahn JD, Hood JM. Fractures of the distal interphalangeal joint. Clin Orthop Relat Res 1996;327:12–20.
6. McCallister WV, Ambrose HC, Katolik LI, et al. Comparison of pullout button versus suture anchor for zone I flexor tendon repair. J Hand Surg Am 2006;31:246–251.
7. Morisawa Y, Ikegami H, Izumida R. Irreducible palmar dislocation of the distal interphalangeal joint. J Hand Surg Br 2006;31:296–297.
8. Pohl AL. Irreducible dislocation of a distal interphalangeal joint. Br J Plas Surg 1976;29:227–229.
9. Schweitzer TP, Rayan GM. The terminal tendon of the digital extensor mechanism: Part I, anatomic study. J Hand Surg Am 2004;29: 898–902.
10. Smith JH. Avulsion of the profundus tendon with simultaneous intraarticular fracture of the distal phalanx—case report. J Hand Surg Am 1981;6:600–601.
11. Wehbe MA, Schneider LH. Mallet fractures. J Bone Joint Surg Am 1984;66A:658–669.