Richard Y. Kim and Robert J. Strauch
DEFINITION
Thumb carpometacarpal (CMC) joint instability can occur as a result of ligament laxity or trauma.
Regardless of the cause, injury to the stabilizing ligaments surrounding the CMC joint leads to instability and dorsoradial subluxation or dislocation of the thumb metacarpal.
ANATOMY
The thumb CMC joint is a biconcave-convex joint similar to a horseback rider's saddle.4
The base of the thumb metacarpal has a prominent volar styloid process (beak) that articulates with a recess in the volar trapezium when in flexion.
There are 16 ligaments that provide stability to the thumb CMC joint.1 Of these ligaments, the two that provide the most restraint against dorsoradial subluxation of the thumb metacarpal are the dorsoradial and volar beak ligaments (FIG 1).1,4,12,15
The volar beak ligament (deep anterior oblique ligament, palmar ligament, ulnar ligament) originates from the volar central apex of the trapezium and inserts onto the volar beak of the thumb metacarpal.1 It lies immediately under a more widely based superficial anterior oblique ligament, which is located immediately deep to the thenar musculature and has a broad insertion across the base of the thumb metacarpal.
The dorsoradial ligament originates from the dorsoradial tubercle of the trapezium and inserts onto the dorsal base of the thumb metacarpal. It is the thickest, widest, shortest, and strongest of the CMC ligaments.4
PATHOGENESIS
The biconcave-convex nature of the thumb CMC joint allows for a wide range of thumb motion but is inherently unstable.7 Laxity or incompetence of the supporting ligaments, especially the volar beak or dorsoradial ligaments, will cause instability of the thumb CMC joint.10,12 Especially in middleaged women, the cause of the laxity is often idiopathic.
In addition, there is a population of patients who have inherent ligament laxity, such as those with collagen disorders like Ehlers-Danlos syndrome.
In the setting of trauma, acute thumb CMC joint dislocation occurs with axial loading and flexion of the thumb metacarpal. In all reported cases, the dislocation occurs in a dorsoradial direction.11,12
NATURAL HISTORY
Ligamentous laxity at the thumb CMC joint may cause degenerative changes to the joint cartilage and lead to arthritis, corresponding to higher stages in the Eaton–Littler staging system.2
If the ligamentous laxity is symptomatic and causing pain, ligament reconstruction can be successful in reducing pain in over 90% of patients. Ligament reconstruction has also been shown to potentially halt the progression of arthritis.5
FIG 1 • The stabilizing ligaments of the thumb carpometacarpal joint. Of these, the dorsoradial and volar beak ligaments are the most important in preventing dorsoradial subluxation of the thumb metacarpal.
For traumatic dislocations, a stable reduction is important for thumb function. If the thumb CMC joint remains unstable, functions such as key pinch and grasp may be compromised.
Open ligament reconstruction of these unstable thumb CMC joint dislocations may decrease the incidence of recurrent instability and joint degeneration compared to closed reduction and pinning.11
PATIENT HISTORY AND PHYSICAL FINDINGS
Nontraumatic Ligamentous Laxity
The history should include questions about ligament laxity involving other joints. Metabolic diseases such as Ehlers-Danlos syndrome are notable.
Radiographic findings often do not correlate with symptomatology. Therefore, it is important to elicit from the patient the exact symptoms and their severity.
Any history of previous nonoperative treatments should be noted. If splinting and steroid injections have not been attempted, it may be beneficial to attempt these treatment modalities before discussing surgery.
The physical examination should determine the degree of subluxation and reducibility of the thumb CMC joint.
The thumb metacarpophalangeal (MCP) joint should also be examined for possible hyperextension laxity.
Pinch strength and opposition should be tested and compared to the contralateral side.
The hand should also be evaluated for concomitant carpal tunnel syndrome, flexor carpi radialis tunnel syndrome, and DeQuervain tenosynovitis, as these may also need to be addressed.
Traumatic Injuries
In addition to the evaluation cited for nontraumatic laxity, the history and physical examination should include the following:
Time and nature of the injury
Status of the thumb before injury
Stability of joint reduction: This is of major concern in the physical examination because assessment of stability will determine the treatment path.
Associated MCP joint collateral ligament injury and stability
Other associated hand injuries are important to note as well.
Tests to perform include the ballottement test and the grind test.
Tenderness associated with dorsal pressure indicates symptomatic subluxation.
Crepitance and pain are positive indicators of CMC pathology.
IMAGING AND OTHER DIAGNOSTIC STUDIES
AP, lateral, and oblique views of both thumbs should be obtained.
A true AP (Robert) view is taken with the forearm in maximal pronation and the dorsum of the thumb resting on the imaging table. The beam is then angled 15 degrees from distal to proximal.4
A true lateral film of the thumb is one in which the sesamoids volar to the thumb MCP joint overlap each other.
A 30-degree oblique stress view of the thumb CMC joint is performed by pressing the radial side of the thumb tips together. This maneuver will subluxate the thumb metacarpal base radially, thereby demonstrating the degree of laxity in the radial direction.14
DIFFERENTIAL DIAGNOSIS
De Quervain tenosynovitis
Flexor carpi radialis tunnel syndrome
C6 radiculopathy
Trigger thumb
NONOPERATIVE MANAGEMENT
For symptomatic ligament laxity and stage I or II basal joint disease, conservative management should first be attempted. This includes thumb spica splint immobilization and anti-inflammatory medications.6,13
If the symptoms do not improve, a steroid injection into the CMC joint can be attempted. The number of injections should be limited to a maximum of three; theoretically more than three injections increases joint morbidity.
In the scenario of acute trauma, reduction of the CMC joint should be performed by applying axial traction and palmardirected pressure to the base of the thumb metacarpal, along with pronation of the thumb metacarpal. After reduction, if the joint remains reduced, the injury can be treated with cast immobilization.
If the joint is unstable at all after an attempt at closed reduction, surgical management is indicated.11
SURGICAL MANAGEMENT
Freedman et al5 have demonstrated that ligament reconstruction for symptomatic thumb CMC joint laxity can halt or slow the progression to degenerative arthritis. By providing joint stability, shear forces on the CMC joint and translation of the metacarpal on the trapezium can be minimized.
In the presence of articular pathology, arthroplasty may be the treatment of choice, depending on the degree of chondromalacia.
If greater than 20 degrees of MCP hyperextension is present with lateral pinch, MCP capsulodesis or arthrodesis may also need to be considered.14
If carpal tunnel syndrome or De Quervain tenosynovitis is present, carpal tunnel release or first dorsal compartment release may be need to be addressed at the time of surgery.
For traumatic thumb CMC joint dislocations, Simonian and Trumble have shown that ligament reconstruction was superior to percutaneous pinning of unstable joints.11
When the injury pattern results in fracture-dislocations such as unstable Bennett and Rolando fractures, percutaneous pinning or open reduction and internal fixation may be the treatment of choice.
Preoperative Planning
Plain films should be reviewed.
In the case of acute trauma, associated fractures and hand injuries should be addressed.
A preoperative Allen test should be performed since all procedures involving the thumb CMC joint are in close vicinity to the radial artery, and iatrogenic injury may occur.
Positioning
The procedure is performed with the patient supine and the arm on a standard hand table.
The operating table should be turned away from the anesthesia machines to allow the surgeon and assistant to sit across from each other at the hand table.
Approach
A number of techniques have been described for ligament reconstruction of the thumb CMC joint using a variety of different tendons, including the flexor carpi radialis, palmaris longus, extensor carpi radialis longus, extensor pollicis brevis, and abductor pollicis longus (APL).
The technique presented here is the classic volar ligament reconstruction described by Eaton and Littler.3 This method effectively reconstructs both the volar and dorsal ligaments using the flexor carpi radialis.
TECHNIQUES
MODIFIED WAGNER APPROACH TO THE THUMB CMC JOINT
The incision is started longitudinally along the radial side of the thenar mass, at the junction between the glabrous and nonglabrous skin. The distal extent of the incision is near the midportion of the thumb metacarpal (TECH FIG 1A).
Proximally at the wrist crease, the incision is brought transversely across the wrist to the ulnar side of the flexor carpi radialis tendon.
Once through the skin, care should be taken to avoid transection of superficial radial sensory nerve branches that may be crossing the operative field.
The soft tissue is bluntly dissected until the thenar musculature is identified (TECH FIG 1B). The radial border of the thenar muscle mass is incised and the muscles are elevated extraperiosteally to expose the CMC joint capsule. The capsule is incised and the thumb metacarpal base, the CMC joint, and the trapezium exposed (TECH FIG 1C).
Blunt dissection is continued dorsally toward the extensor pollicis longus and brevis tendons. The dorsal metacarpal cortex is exposed between these tendons.
TECH FIG 1 • A. Modified Wagner incision. B. Thenar musculature. C. The radial border of the thenar muscles is incised and elevated, exposing the thumb carpometacarpal joint.
FLEXOR CARPI RADIALIS GRAFT HARVEST
The flexor carpi radialis tendon is identified just radial to the palmaris longus tendon at the wrist crease. The tendon sheath is then opened.
A transverse incision is made proximally in the forearm overlying the flexor carpi radialis musculotendinous junction, about 8 to 10 cm proximal to the wrist crease (TECH FIG 2A,B).
The soft tissue is bluntly dissected until the tendon sheath is identified and opened. The flexor carpi radialis tendon is then exposed.
A longitudinal split is made in the midline of the tendon just proximal to its insertion onto the trapezium. A 0 Prolene suture is then passed through the longitudinal split (TECH FIG 2C).
A pediatric feeding tube is now passed from the proximal wound into the distal wound, just underneath the flexor carpi radialis tendon sheath but superficial to the flexor carpi radialis tendon fibers. The tip of the feeding tube is cut off, and the two ends of the Prolene suture are passed through the end of the feeding tube from distal to proximal. Once the suture is seen in the proximal wound, the feeding tube can be removed, leaving the ends of the Prolene suture in the proximal wound site (TECH FIG 2D–F).
TECH FIG 2 • A. Flexor carpi radialis harvest incision is made 8 to 10 cm proximal to the wrist crease. B. Flexor carpi radialis musculotendinous junction. C. A longitudinal split is made through the flexor carpi radialis distally and a 0 Prolene suture is passed through it. D. A pediatric feeding tube is passed from the proximal to the distal wound. E. The Prolene suture is then passed through the feeding tube from distal to proximal. F. The feeding tube is removed, leaving the Prolene suture ends in the proximal wound. G. The two suture ends are pulled, thereby dividing the flexor carpi radialis tendon in half until the proximal wound is reached. The flexor carpi radialis tendon spirals, so the distal radial half corresponds to the proximal ulnar half of the tendon. H. The split flexor carpi radialis tendon is delivered into the distal wound.
The two suture ends in the proximal wound are now pulled so that the rest of the suture is delivered from the distal to the proximal wound. In so doing, the suture will divide the flexor carpi radialis tendon in half along its course into the proximal wound (TECH FIG 2G).
At this time, the ulnar half of the tendon is transected proximally just after the musculotendinous junction. The fibers of the flexor carpi radialis tendon spiral, so the ulnar half of the tendon will continue to become the radial half of the tendon distally at the wrist. Before transection, traction should be applied to the proximal ulnar half of the tendon to ensure that it corresponds to the distal radial half of the tendon.
The split flexor carpi radialis tendon is finally delivered into the distal wound (TECH FIG 2H).
METACARPAL TUNNEL PLACEMENT AND FLEXOR CARPI RADIALIS GRAFT PASSAGE AND FIXATION
A tunnel is made from dorsal to volar in the thumb metacarpal, 1 cm distal to the articular base. The tunnel should start dorsal to the APL insertion and then course parallel to the articular surface, exiting volarly just distal to the insertion of the volar beak ligament onto the metacarpal base.
The tunnel is started by first drilling a 0.045 Kirschner wire from dorsal to volar in the manner described. The tunnel is enlarged by drilling a 0.062 Kirschner wire, followed by a 3.5-mm drill (TECH FIG 3A,B).
Once completed, a nylon whipstitch is placed in the end of the flexor carpi radialis graft. The ends of the stitch are passed through the metacarpal tunnel from a volar to dorsal direction. The stitch is pulled dorsally, delivering the flexor carpi radialis graft through the metacarpal tunnel to the dorsum (TECH FIG 3C).
As the graft exits the dorsal hole in the metacarpal, the thumb is extended and abducted. The graft is pulled tightly and then allowed to relax 2 to 3 mm to set the appropriate tension.
Once the graft tension is set, the graft is sutured to the metacarpal periosteum where it exits the dorsal hole using nonabsorbable 3-0 suture material.
The flexor carpi radialis graft is then passed under the APL tendon radially toward the volar side of the wrist. The graft is sutured to the APL with similar nonabsorbable 3-0 suture material as it is passed underneath it.
The graft is then passed underneath and around the ulnar portion of the flexor carpi radialis tendon that has remained intact. The graft is also sutured to the flexor carpi radialis tendon as it is looped around it.
If there is additional length to the graft, it is brought back dorsally and again passed underneath and sutured to the APL (TECH FIG 3D).
A 0.045-inch Kirschner wire is drilled from the radial thumb metacarpal base into the trapezium to immobilize the CMC joint. The wire is removed after 5 weeks once adequate soft tissue healing has occurred (TECH FIG 3E).
TECH FIG 3 • A. The tunnel is drilled from dorsal to volar, staying parallel and 1 cm distal to the metacarpal articular base. B. A curette is shown in the metacarpal tunnel to illustrate its size and direction. C.The flexor carpi radialis graft is passed through the tunnel from volar to dorsal. D. The flexor carpi radialis graft is passed underneath and sutured to the abductor pollicis longus, the remaining flexor carpi radialis, and back dorsally to the abductor pollicis longus if the graft length permits. E. A 0.045 Kirschner wire is drilled from the thumb metacarpal into the trapezium to protect the ligament repair.
WOUND CLOSURE
The thenar muscle mass is reapproximated and sutured using synthetic absorbable 3-0 suture material.
The proximal and distal skin incisions are closed with 5-0 nylon sutures (TECH FIG 4).
The hand is then placed in a short-arm thumb spica splint.
TECH FIG 4 • Final wound closure with nylon sutures.
POSTOPERATIVE CARE
AP, lateral, and oblique films or fluoroscopic mini C-arm views are obtained intraoperatively to evaluate CMC joint congruency and Kirschner wire placement.
The thumb spica splint is left in place for 2 weeks. At 2 weeks of follow-up, the dressings are taken down, sutures are removed, and a new thumb spica splint is applied.
At 5 weeks of follow-up, the Kirschner wire is removed and a removable thumb splint is used for protection. The splint can be removed for therapy, which can be started at this time.
Therapy should start with active range-of-motion exercises of the wrist, thumb CMC, MCP, and interphalangeal joints. Thumb abduction, flexion, and opposition are emphasized.
Strengthening exercises can be started at 2 months after surgery, and full activity without restrictions can begin at 3 months.
OUTCOMES
When performed for stage I basal joint disease, ligament reconstruction has been shown to improve pain and establish joint stability.
In a number of long-term follow-up studies of over 5 years, 87% to 100% of patients demonstrated joint stability against stress testing, 29% to 67% of patients reported no pain, and 83% to 100% reported marked improvement in pain. Interestingly, only 0% to 37% of patients progressed to a higher stage of arthritis.5,8
Freedman et al5 reviewed their long-term results of 24 thumbs that underwent ligament reconstruction for stage I or II disease. After a minimum of 10 years of follow-up, 29% of patients reported no pain, 54% reported pain with strenuous activity only, and 17% of patients had pain during activities of daily living. When tested against stress, 87% demonstrated joint stability.
Simonian and Trumble11 found that 89% of patients who underwent ligament reconstruction after traumatic thumb CMC dislocation had no pain with work at 2 years of followup. Also, none of the patients in this treatment group had any evidence of joint instability, and no revision procedures were required. This is in contrast to 50% of patients who had residual joint instability and pain after closed reduction and percutaneous pinning. Of this treatment group, 38% required revision surgery and underwent ligament reconstruction. 12% of these patients required CMC arthrodesis.
COMPLICATIONS
Residual joint instability
Residual pain, likely due to untreated arthritis involving surrounding joint articulations, such as the scaphotrapezial joint
Radial artery injury
Superficial radial nerve or lateral antebrachial cutaneous nerve injury
Pin tract infection
REFERENCES
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