Serious, Often Subtle, Finger Injuries: Avoiding Diagnosis and Treatment Pitfalls

James R. Lairmore, MD; William D. Engber, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 6 - JUNE 98

In Brief: Three common finger injuries—proximal interphalangeal (PIP) injuries, mallet finger, and skier's thumb—present unique diagnostic and treatment challenges. Careful history-taking and physical examination are, of course, essential for diagnosing these injuries, but appropriate x-rays are often pivotal. For PIP joint dislocations and fracture-dislocations, extension block splinting is often appropriate, but surgery may be required for an unstable injury. Most mallet finger injuries can be treated with a Stack splint, but functional deformity may necessitate surgery. Skier's thumb can be a bony or ligamentous injury; to avoid fragment displacement, radiographs should be obtained before stressing the joint. Treatment includes a thumb spica cast for a nondisplaced fracture or stable joint, referral for a displaced fracture, and surgery for an unstable joint.

In the broad spectrum of orthopedic fractures, those involving the hand and digits may appear relatively minor. However, given the complexity of the hand and digits and their essential role in so many human tasks, these injuries require rigorous evaluation, early diagnosis, and appropriate treatment to prevent serious consequences for patients.

Physicians, therefore, need clear guidelines for managing three common, often undiagnosed or improperly treated injuries of the digits: proximal interphalangeal (PIP) joint dislocations and fracture-dislocations, mallet finger, and skier's thumb. Primary care physicians can expect excellent results if they understand the subtleties and pitfalls of these injuries.

PIP Joint Injuries

Anatomy. The PIP joint is a concentric bicondylar hinge joint, which stabilizes for rotation and lateral translation while allowing 110° of flexion and extension. The primary stabilizers of the joint are the collateral ligaments and the thick volar, or palmar, plate (figure 1). These structures combine to form a "three-dimensional ligament-box complex (1)." Injuries to the PIP joint result in various patterns of disruption to this ligamentous complex; displacement occurs when at least two sides of the box are disrupted.

Types of injury. PIP joint dislocations (figure 2) are the most common ligamentous injury of the hand (2). Fracture-dislocations of the PIP joint occur frequently and are potentially disabling. Hyperextension is the most common mechanism, but axial loading and hyperflexion are also common causes.

The usual deformity is dorsal displacement of the middle phalanx on the proximal phalanx. Fractures, when present, typically involve the volar articular portion of the middle phalanx. Displacement may also occur without fracture when a significant injury through the volar plate and collaterals occurs. Lateral and volar fracture-dislocations are less common.

Diagnosis. As with most orthopedic injuries, a careful history should include the mechanism and time of injury, associated injuries, and the degree of displacement. Knowledge of neurovascular changes as well as the history of dislocation and reduction prior to presentation is important in assessing the degree of injury and planning treatment. The physical examination should include an assessment of swelling, neurovascular status, range of motion, and presence of open injury.

The keys to accurate evaluation are true lateral and posteroanterior (PA) radiographs that show the percentage of articular arc remaining on the fracture fragment as well as joint displacement, angulation, and incongruity.

Volar dislocations, though rare, are caused by a rotatory force, usually with a flexed PIP; however, a hyperextension mechanism has also been described (1,3). They are serious injuries and normally best referred to an orthopedist. Often the condyle of the proximal phalanx is buttonholed between the central slip and the lateral band, a centrally located area between the main extensor tendon, which attaches to the base of the middle phalanx, and the more laterally positioned slips of the extensor tendon, which continue distally to attach to the base of the distal phalanx. When this occurs, reduction may be difficult or impossible by closed means.

Treatment. In the case of a dorsally dislocated joint or a fracture-dislocation, gentle traction can often achieve reduction, thus improving blood flow and decreasing traction on digital nerves. After reduction, the joint should be evaluated for active and passive stability; this assessment can be eased with the use of a local digital block (see "Anesthesia for the Injured Hand: Performing the Digital Nerve Block," November, 1994, page 75). The joint is first actively moved through its range of motion while the clinician looks for signs of instability. If displacement occurs, noting the joint angle at which it occurs can help determine an optimal splinting position. (Application of a splint just before the angle of displacement will provide enough flexion to hold the joint in a stable, reduced position, while allowing the maximum arc of motion in a stable range of motion.) Evaluation of the collateral ligaments is performed by passive stressing, using the uninjured hand for comparison.

If reduction is not easily achieved, ligament interposition or buttonhole entrapment should be considered, and open reduction may be required. Interposition is rare in dorsal fractures and fracture-dislocations, but common in volar injuries.

Reduction of volar dislocations is achieved through slackening the extensors by slightly extending the wrist and flexing the metatarsophalangeal and PIP joints to take tension off the lateral bands. A rotation maneuver is then used to achieve reduction. If this fails, open reduction is required. A complete extensor tendon rupture may accompany this injury and cause late deformity.

Definitive treatment of PIP joint injuries, of course, depends on the type of injury (table 1). One of the most common treatments is extension block splinting (figure 3), which is an effective way to control a fracture-dislocation of the PIP joint (4,5). It allows motion through a stable range of flexion while blocking the portion of extension in which the fracture is unstable and dislocates. Extension block splinting is recommended when the fracture fragment of a stable fracture-dislocation involves less than 40% of the articular arc and when radiographs and clinical examinations demonstrate a reduced joint in flexion. Unstable injuries require surgery.

Table 1. Managing Various Types of Proximal Interphalangeal (PIP) Joint Injuries
Injury	Clinical Manifestations or Special Considerations	Treatment
Sprain	Stable joint with active and passive motion; negative radiographs; pain and swelling only	Splint for comfort; begin early ROM exercises
Open dislocation	Dislocated exposed joint	Irrigation, debridement, and antibiotics; treat as any open fracture or dislocation
Dorsal PIP dislocation
Type 1	Hyperextension, volar plate avulsion, minor collateral ligament tear	Reduction; immobilization, 3-5 days, followed by ROM exercises with buddy taping and close x-ray follow-up
Type 2	Dorsal dislocation, volar plate avulsion, major collateral ligament tear	Same as type 1
Type 3	Stable fracture-dislocation: <40% of articular arc on fracture fragment	Extension block splint; refer to hand surgeon if uncertain about stability
	Unstable fracture dislocation: >40% of articular arc on fracture fragment	Extension block splint; open reduction with internal fixation if closed treatment impossible; refer to hand surgeon if uncertain about stability
Lateral dislocation	Secondary to collateral ligament injury and avulsion and/or rupture of volar plate; angulation >20° indicates complete rupture	Same as dorsal dislocation types 1 and 2 above if joint is stable and congruous through active ROM
Volar PIP dislocation
Straight volar   dislocation	Proximal condyle causes significant injury to central extensor slip (may reduce easily, but extensor tendon may be seriously injured; requires careful examination)	Refer to a surgeon experienced in these injuries; closed reduction with traction with metatarsophalangeal and PIP flexed and extended wrist; full-extension immobilization of PIP joint if post-reduction x-rays show no subluxation; if closed reduction is not achieved or subluxation persists, surgery recommended
Ulnar or radial   volar   displacement	Condyle often buttonholes through central slip and lateral band reduction often extremely difficult	Same as straight volar PIP dislocation
ROM=range of motion

Pitfalls and Complications. Awareness of potential problems related to PIP joint injuries can help clinicians achieve good results. The most common pitfalls and complications include:

• Attempting to treat an unstable joint with splinting (figure 4),
• Failure to splint in a safe range of motion, leading to subluxation,
• Joint stiffness caused by inappropriate splinting,
• An unrecognized injury to the extensor tendon with volar dislocations, and
• Inadequate early follow-up resulting in loss of reduction and/or malunion. Fracture-dislocations of the PIP joint may be prone to redislocation. Postsplinting radiographs and close follow-up are required in the early-healing phase. Though the physician must determine the appropriate x-ray interval for each patient, weekly follow-up for the first 2 to 3 weeks is usually sufficient.

Mallet Finger

Anatomy. The distal interphalangeal (DIP) joint is extended by the medial and lateral bands of the extensor tendon, which originate in the substance of the extensor hood and insert into the dorsal base of the distal phalanx. This is thought to be a relatively avascular area of the tendon, which may account for its rupture in some cases.

Types of injury. A mallet finger injury results from loss of bony or ligamentous attachment of the extensor mechanism into the distal phalanx (figure 5). This loss of extensor continuity results in incomplete extension of the DIP joint or extensor lag. The mechanism is commonly hyperflexion, but occasionally hyperextension and axial loading will result in this injury.

Fracture and rupture through the tendon are both commonly seen. Fractures involving large portions of the articular arc may be unstable, and subluxations may occur acutely or late, leading to malunion and arthrosis.

Diagnosis. A patient who has mallet finger has typically had a blow to a digit and subsequent extensor lag in the DIP joint. A history should include the mechanism of injury, associated injuries, and neurovascular complaints.

The physical examination should include a careful evaluation of active and passive range of motion, an assessment of collateral stability, extensor lag, and rotation, a neurovascular examination, and inspection of the nail. The PIP joint should also be inspected, since concomitant injury, although uncommon, has been described (6).

Lateral and PA radiographs should be obtained initially to assess injury and also after splinting to determine joint congruity.

Treatment. Treatment for mallet finger varies according to the type of injury (figure 6: not shown), but the Stack splint (figure 7) is often used. This splint is very effective if the joint is stable and the patient follows instructions on the use of the splint for the entire treatment period. The Stack splint should be worn for 6 weeks for a fracture and 8 weeks for tendon failure.

The patient should understand that the splint must be worn 24 hours a day. He or she should also be told how to maintain the DIP joint in extension when the splint is removed for skin care. Compliance with these measures can be bolstered if the patient knows that treatment must recommence if the DIP joint is allowed to flex during the treatment period.

Clinicians often wonder what to do with a patient who presents late or has residual lag after treatment in a splint. A Stack splint is probably helpful as late as 6 months after injury. Patients who have residual lag should be observed for up to 6 months following splinting, because considerable improvement can occur. Surgical intervention may be considered if residual functional deformity exists beyond this period.

Pitfalls and Complications. For mallet finger, these include:

• Splinting an incongruent joint (7),
• Improper splinting,
• Stack splinting a subluxated joint (figure 8),
• Splint complications, such as ulcers, maceration, and noncompliance, and
• Residual lag.

Skier's Thumb

Anatomy. As with the PIP joint, the thumb metacarpophalangeal (MCP) joint has a volar plate and stout collateral ligaments. The unique feature of this joint is the relationship of the ulnar collateral ligament (UCL) to the adductor aponeurosis; the UCL is located deep to the tightly overlying adductor aponeurosis (figure 9a).

Types of injury. Skier's thumb, also called gamekeeper's thumb, is a UCL rupture of the thumb MCP joint, causing instability and a weak, ineffective pinch. This injury may be bony and/or ligamentous.

Whether skiing, ball handling, or wringing the neck of a game bird is the mechanism, this injury is the outcome of a radially directed stress at the MCP joint of the thumb. With sufficient force, UCL rupture or bony avulsion occurs (figure 9). The rupture of the ligament can be proximal or distal to the joint line. If sufficient angulation and distal disruption occur, the ligament can be trapped outside the adductor aponeurosis (a Stener lesion) and, if the ligament is not relocated and surgically repaired, the injury can result in chronic instability. A similar injury may occur on the radial side of this joint—the "reverse gamekeeper's thumb"—but it does not produce a Stener lesion and is treated in a spica cast.

Diagnosis. Accurate diagnosis requires a high index of suspicion when a patient has ulnar-sided pain and swelling at the thumb MCP. Much has been written about what position allows the most effective stress test of the injury and what criteria allow the most accurate identification of a Stener lesion. Our approach is to first evaluate tenderness and swelling over the ligament. If these are present and the mechanism of injury is suspicious for skier's thumb, PA, lateral, and oblique radiographs should be obtained prior to stressing the involved joint.

If no fracture is seen, the examiner should flex the joint maximally (a digital block is occasionally required) and apply radially directed stress and compare with the opposite side (8,9). The joint is considered stable if it opens less than 35° and unstable if it opens more.

Stress radiographs and arthrograms are suggested for evaluation of this injury by some authors; however, we feel that these studies add little and do not routinely order them.

Treatment. Nondisplaced fractures and stable joints are treated with a thumb spica cast for 6 weeks. A displaced fracture should be referred to an orthopedist, and an unstable joint requires surgery. For a more complete list of specific injuries and treatments, see table 2.

Table 2. Conservative vs Surgical Management of 'Skier's Thumb' Treatment in Thumb Spica Cast for 6 Wk Nondisplaced fracture of proximal phalanx No fracture, joint stable Volar plate avulsion fracture from proximal phalanx, without ulnar collateral ligament injury Surgical Treatment Displaced fracture of proximal phalanx No fracture, joint unstable, ulnar collateral ligament displaced and trapped outside adductor aponeurosis (Stener lesion)

Some investigators have suggested that palpation of a mass proximal to the joint confirms a Stener lesion and, in its absence, conservative therapy is appropriate (10). We feel that instability with or without a mass mandates surgical intervention because of the potential for chronic instability and the difficulty of delayed surgery that results from the missed diagnosis of a Stener lesion.

Pitfalls and Complications. Common problems in managing skier's thumb include:

• Treating a Stener lesion with immobilization. These injuries will not heal or function well without surgical correction.
• Displacing a nondisplaced fracture through a stress test (figure 10).
• Misdiagnosing a volar avulsion as a UCL tear. A volar avulsion is confirmed by noting a volar, rather than an ulnar, fracture on the lateral radiograph and volar tenderness and swelling. This injury may be treated in a cast or splint and does not require surgery.
• Examining the injury in full extension. The volar plate adds to stability, and the injury can be diagnosed as stable when it is actually unstable.

Positive Results for Patients

Primary care physicians frequently see patients who have PIP joint injuries, mallet finger, or skier's thumb. Clinicians who recognize the features and complexities of these serious, often subtle injuries can avoid diagnostic and treatment pitfalls and improve the results for their patients.

References

1. Crenshaw AH (ed): Campbell's Operative Orthopedics, ed 8. St Louis, Mosby Year Book, 1992
2. Green DP (ed): Operative Hand Surgery, ed 3. New York City, Churchill Livingstone, 1993
3. Bowers WH: The proximal interphalangeral joint volar plate II: a clinical study of hyperextension injury. J Hand Surg (Am) 1981;6(1):77-81
4. McElfresh EC, Dobyns JH, O'Brien ET: Management of fracture-dislocation of the proximal interphalangeal joints by extension-block splinting. J Bone Joint Surg (Am) 1972;54(8):1705-1711
5. Damron TA, Lange RH, Engber WD: Mallet fingers: a review and treatment algorithm. Int J Orthop Trauma 1991;1(2):105-111
6. Strong ML: A new method of extension-block splinting for the proximal interphalangeal joint: preliminary report. J Hand Surg (Am) 1980;5(6):606-607
7. Lange RH, Engber WD: Hyperextension mallet finger. Orthop 1983;6(11):1426-1431
8. Louis DS, Julius J, Hankin FM: Rupture and displacement of the ulnar collateral ligament of the metacarpophalangeal joint of the thumb: preoperative diagnosis. J Bone Joint Surg (Am) 1986;68(9):1320-1326
9. Palmer AK, Louis DS: Assessing ulnar instability of the metacarpophalangeal joint of the thumb. J Hand Surg (Am) 1978;3(6):542-546
10. Abrahamsson SO, Sollerman C, Lundborg G, et al: Diagnosis of displaced ulnar collateral ligament of the metacarpophalangeal joint of the thumb. J Hand Surg (Am) 1990;15(3):457-460

Dr Lairmore is an orthopedic surgery resident and Dr Engber an associate professor in the Division of Orthopedic Surgery in the Department of Surgery at the University of Wisconsin Hospital and Clinics in Madison. Address correspondence to James R. Lairmore, MD, Division of Orthopedic Surgery, Dept of Surgery, University of Wisconsin, 600 Highland Ave, Madison, WI 53792.

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