John J. Walsh IV
DEFINITION
Fractures and dislocations of the carpometacarpal (CMC) joints of the index through small fingers involve intra-articular fractures at the base of the metacarpals or pure dislocations between the metacarpals and carpus. The fracture can involve the base of the metacarpal or the trapezoid, capitate, or hamate articular surface.
These fractures and dislocations can result in instability and articular incongruity (FIG 1).
ANATOMY
The CMC joints connect the metacarpals and the distal carpal row.
The shape and degree of constraint present in the joints differ from finger to finger.
The index and middle fingers have highly constrained articulations due to the shape of the index CMC articulation and supporting soft tissues.4 These include the flexor carpi radialis tendon, extensor carpi radialis longus and brevis tendons, and very strong capsular insertions. This provides for a strong radial column for the hand, and efficient force transfer to the radius (FIG 2A).
The ring and small fingers have a gliding articulation on the hamate, which allows for the closure of the hand around objects and is very important in power grip. This mobility makes them more susceptible to injury. The extensor carpi ulnaris tendon attaches to the base of the small finger metacarpal.4
The deep motor branch of the ulnar nerve crosses around the base of the hamate hook and runs along the volar surface of the CMC joints (FIG 2B). It is vulnerable at the time of injury or during fixation.
PATHOGENESIS
Injuries of the CMC joints may be divided into two broad categories.
The first, involving a load applied to a flexed metacarpal, is by far the most common mechanism. This injury usually involves the ring and small fingers displacing dorsally as a unit relative to the hamate. This may occur as a dislocation only or include a marginal fracture of the hamate.8
The second mechanism involves an axially directed force that creates a comminuted fracture of the articular surface (FIG 3A). Severe crushing injuries can cause multiple dislocations and fractures diffusely throughout the CMC region1,7
(FIG 3B,C).
NATURAL HISTORY
The natural result of an untreated fixation dislocation is progressive arthritis of the involved joints.
PATIENT HISTORY AND PHYSICAL FINDINGS
The patient's history is important to assess the mechanism of injury, which provides further clues regarding concomitant injuries in the extremity.
FIG 1 • Multiple dorsal carpometacarpal (CMC) dislocations involving the index through small fingers.
FIG 2 • A. Variable articular congruity of the various CMC joints. B. Deep motor branch of the ulnar nerve adjacent to the metacarpal bases.
Examine the hand for tenderness and local swelling.
Assess neurovascular integrity, especially function of the deep branch of the ulnar nerve (first dorsal interosseous contraction).
Examine the limb for other injuries.
Associated injuries should be detected by examination and verified by radiographs.
Preoperative notation of nerve function is important when comparing function following reduction and fixation.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Radiographs of the CMC joints require careful positioning to assess each joint.
The transverse metacarpal arch causes the CMC joints of the index and middle fingers to appear in an oblique projection when a standard PA radiograph is obtained of the ring and small finger CMC joints, and vice versa (FIG 4A).
A true frontal radiograph is most easily obtained by positioning the hand in an AP projection with the dorsum of the hand placed flat on the cassette (or image intensifier, if using fluoroscopy). The base of the affected metacarpal should lie on the cassette (FIG 4B). This will result in a far more accurate portrayal of the joint, essential for assessing the fracture as well as checking hardware position after fixation.
Visualization of the joint surfaces at the base of the ring and small fingers differs in a typical PA projection (FIG 4C) and a properly positioned film of the same patient (FIG 4D).
FIG 3 • A. Comminuted fracture of the fifth metacarpal base. B,C. Multiple fractures and dislocations involving the ulnar side of the hand.
FIG 4 • A. A conventional PA view of the hand creates an oblique view of the ring and small finger bases. B. Hand properly positioned for AP view of the ring and small finger CMC joints. C. Postoperative PA film after open reduction with internal fixation of the ring and small finger CMC joints. D. AP projection clearly shows the joint reduction in the same patient shown in C. E. CT scan of the fracture of the dorsal lip of the hamate.
The same principle holds for obtaining lateral radiographs. A semisupinated lateral view will best visualize the base of the index and middle CMC joints,5 and a semipronated lateral view will best show the bases of the ring and small finger CMC joints.2
A CT scan should be obtained in most cases to assess for articular injury. CT also is especially helpful for visualizing impacted articular surface fragments. The best visualization and determination of fracture patterns will be possible if the scan is obtained after preliminary reduction of any displaced fractures or dislocations associated with a fracture (FIG 4E).10
DIFFERENTIAL DIAGNOSIS
Metacarpal fracture
Carpal bone fracture
Carpometacarpal fracture/dislocation
Fracture associated with neurovascular injury
NONOPERATIVE MANAGEMENT
Nondisplaced fractures can be treated in a below-elbow cast that incorporates the affected digit or digits and one adjacent digit.5,9 Special attention should be paid to positioning the hand in an intrinsic-plus position. Capsular contractures of the metacarpophalangeal (MCP) joints can develop relatively rapidly in hands with the MCP joints immobilized in extension.
Radiographs following cast immobilization should be checked carefully to ensure that no dorsal subluxation is present and should be repeated at weekly intervals for the first 2 weeks to prevent healing in a displaced position.
These injuries, especially those involving a dislocation, have a known propensity for recurrent dorsal subluxation following reduction. Most will require operative fixation.2,4,9 Some authors believe nonoperative management does have a role despite intra-articular displacement and shortening.4,13
SURGICAL MANAGEMENT
Preoperative Planning
Careful review of all imaging studies will facilitate planning of fracture fragment exposure and identify sites for internal fixation.
Positioning
The patient is positioned supine on the operating table with a standard arm table.
The surgeon often is more comfortable seated on the head side of the arm table. This avoids the neck strain that may result from looking “over the top” that happens when the arm externally rotates and the surgeon is seated on the axilla side of the table (FIG 5A).
FIG 5 • A. Positioning of the surgeon (on left) and assistant (right). B. Skin incision marked with probable course of nerve.
Approach
A dorsal extensile approach provides satisfactory exposure of any of the CMC joints.
Incisions placed between metacarpals allow access to two adjacent joints.
Cross the wrist with oblique extensions if necessary.
Marking out the anticipated locations of nearby nerve branches can be helpful (FIG 5B).
TECHNIQUES
DORSAL EXPOSURE
Following incision of the skin, careful spreading dissection should be used to locate and protect the dorsal cutaneous nerve branches in the operative field.
Ulnar sensory nerves are most commonly encountered during exposure of the CMC joints of the ring and small fingers (TECH FIG 1), and radial sensory nerves during exposure of the index and middle finger CMC joints.
Extensor tendons are mobilized and retracted.
TECH FIG 1 • Dorsal cutaneous branch of the ulnar nerve crossing the incision.
FRACTURE EXPOSURE
Careful mobilization of the fracture fragments with minimal soft tissue stripping is important.
This can be facilitated by the use of a Beaver blade, a dental pick, and a fine synovial rongeur.
The rongeur is useful because it is helpful to débride fracture callus and hematoma.
FRACTURE REDUCTION
The fracture is then reduced and held provisionally using fine K-wires (TECH FIG 2A). The surgeon must be aware of the planned location for definitive hardware placement, given the limited room available.
Pins temporarily driven across the base of an articular fragment into the corresponding carpal bone can be helpful in stabilizing any mobile pieces of bone (TECH FIG 2B).
The conventional technique of first reconstructing the articular surface, followed by securing the shaft to the reassembled joint surface, is useful.
TECH FIG 2 • A. Provisional fracture reduction using the hamate surface as a mold for articular reduction of the metacarpal base. B. Initial reduction of the shaft and stabilization of the articular surface. C.Fluoroscopic view of articular reduction. D. Dorsal hamate lip fixation with three screws.
Confirmation of the provisional reduction should be obtained with fluoroscopy before any definitive screw placement (TECH FIG 2C).
The corresponding articular surface on the uninjured bone is used as a mold for the fragments, serving as a guide to reassembly of the injured bone.
This technique works regardless of whether the injury is in the metacarpal base, as pictured in these figures, or in a distal articular injury of one of the carpal bones (TECH FIG 2D).
DEFINITIVE FIXATION
Wires can be replaced by screws if fragment size permits (TECH FIG 3A).
Placing the fragments under compression manually and inserting screws sometimes is preferable to using the lag screw technique, which requires overdrilling the near side and may risk iatrogenic comminution.
Simple K-wire fixation is satisfactory for isolated dislocations with fracture (TECH FIG 3B).
The insertion point for a percutaneous wire often is quite distant from the dislocation site in crushed and severely swollen hands.
TECH FIG 3 • A. Fracture-dislocation of the ring and small finger metacarpal bases using pins and a screw. B. Percutaneous K-wire fixation of a metacarpal shaft fracture and CMC dislocation.
ADJUNCTIVE TECHNIQUES
The construct can be protected by placing the affected metacarpal under slight distraction and pinning it to the adjacent metacarpal.
Alternatively, the proximally directed deforming force of the extensor carpi ulnaris can be reduced by detaching it from the base of the small finger metacarpal at the beginning of the procedure, and securing it to the hamate at the close, thereby avoiding proximal pull on the base of the small finger metacarpal.
I have never found it necessary to use this alternative approach, but it may be helpful in a delayed presentation, where myostatic contractures due to shortening are present.
POSTOPERATIVE CARE
Aftercare following operative fixation falls into three general phases: acute swelling control and wound healing (10–14 days), fracture consolidation and maintenance of digit range of motion (4–6 weeks), and restoration of global hand function and strength (2–6 months).
Immediate measures following surgery include strict elevation and range-of-motion exercises through a full arc of motion.4 This limits swelling, reduces pain, and prevents accumulation of protein-rich edema fluid that will slow rehabilitation.
The relative speed at which the hand can be mobilized during the weeks after surgery depends on a number of factors, including the magnitude of the original injury, stability of fixation, reliability of the patient, and specific occupational or athletic needs.
The radiograph in Tech Fig 2D shows the hand of a physician with stable fixation of a dorsal hamate injury who was mobilized and given a 1-pound lifting restriction shortly after surgery to allow continuation of his residency training.
In contrast, unreliable patients require immobilization for 6 weeks in a cast (see TECH FIG 3B).
Patients should be warned that full grip strength is the last thing that will recover and may take months.2 It is not uncommon for patients to report pain with a handshake for an extended period of time.
OUTCOMES
Opinions on outcomes vary with regard to overall success. A dichotomy exists between recommendation for operative and nonsurgical treatment. Kjaer-Petersen and colleagues11 found that, regardless of treatment, long-term symptoms were present in 38% of patients at 4.3 years of follow-up.
Petrie and Lamb,13 who used immediate, unrestricted motion, reported on results at 4.5 years. Even with metacarpal shortening and irregularities in the articular surface, only one patient had work limitations.
Another study found that pain was related to the degree of posttraumatic arthritis secondary to articular incongruity and advocated anatomic reductor and internal fixation.12
Multiple CMC dislocations were reviewed by Lawliss and Gunther, and poor results were noted in dislocations of the second and third CMC joints (which require higher energy for dislocation) and in those patients with an ulnar nerve injury.7
COMPLICATIONS
Complications include those common to any periarticular surgery:
Failure of wound healing
Hematoma formation
Neurovascular injury
FIG 6 • Radiograph taken several months following K-wire fixation of a fracture-dislocation of the fifth CMC joint. Fragments were too small for screw fixation and were resorbed.
Neuroma formation
Tendon adhesions
Posttraumatic arthritis
Nonunion or malunion
Joint stiffness
Weakness
Occasionally small fragments may resorb, leading to collapse and articular incongruity (FIG 6).
Long-term arthritis can be treated with fusion of the affected joint.4
Alternatively, an interposition “anchovy” using the palmaris longus as a biologic spacer can be inserted after resection of the arthritic joint surfaces, analogous to that performed for thumb basal joint arthritis.3
REFERENCES
1. Bergfield TG, DuPuy TE, Aulicino PL. Fracture-dislocations of all five carpometacarpal joints: a case report. J Hand Surg Am 1985;10:76–78.
2. Bora FW Jr, Didizian NH. The treatment of injuries to the carpometacarpal joint of the little finger. J Bone Joint Surg Am 1974;56A: 1459–1463.
3. Gainor BJ, Stark HH, Ashworth CR, et al. Tendon arthroplasty of the fifth carpometacarpal joint for treatment of posttraumatic arthritis. J Hand Surg Am 1991;16:520–524.
4. Glickel SZ, Barron OA, Catalano LW. Dislocations and ligament injuries in the digits. In Green DP, Hotchkiss RN, Pederson WC, et al, eds. Green's Operative Hand Surgery, ed 5. Philadelphia: Churchill Livingstone, 2005:364–366.
5. Hsu JD, Curtis RM. Carpometacarpal dislocations on the ulnar side of the hand. J Bone Joint Surg Am 1970;52:927–930.
6. Kjaer-Petersen K, Jurik AG, Petersen LK. Intra-articular fractures at the base of the fifth metacarpal: a clinical and radiographical study of 64 cases. J Hand Surg Br 1992;17:144–147.
7. Lawliss JF III, Gunther SF. Carpometacarpal dislocations. J Bone Joint Surg Am 1991;73A:52–58.
8. Lilling M, Weinberg H. The mechanism of dorsal fracture dislocation of the fifth carpometacarpal joint. J Hand Surg Am 1979;4:340–342.
9. Lundeen JM, Shin AY. Clinical results of intraarticular fractures of the base of the fifth metacarpal treated by closed reduction and cast immobilization. J Hand Surg Br 2000;25:258–261.
10. Marck KW, Klasen HJ. Fracture-dislocation of the hamatometacarpal joint: A case report. J Hand Surg Am 1986;11:128–130.
11. Niechajev I. Dislocated intra-articular fracture of the base of the fifth metacarpal: a clinical study of 23 patients. Plast Reconstr Surg 1985; 75:406–410.
12. Papaloizos MY, Le Moine PH, Prues-Latour V, et al. Proximal fractures of the fifth metacarpal: a retrospective analysis of 25 operated cases. J Hand Surg Br 2000;25:253–257.
13. Petrie PWR, Lamb DW. Fracture-subluxation of the base of the fifth metacarpal. Hand 1974;6:82–86.