Disruption of the normal thumb biomechanics by rheumatoid arthritis often leads to significant loss of the patient’s ability to carry out activities of daily living (ADLs).
Nonsurgical and surgical treatments are directed to the prevention and correction of the various thumb deformities and the restoration of function.
Evaluation should not be limited to the thumb, but instead the whole hand and upper extremity must be assessed.
When deformities are passively correctable, the goal of hand therapy is to help maintain joint mobility and to help protect the joint from the stresses of ADLs through orthotic positioning and joint protection procedures.
Surgical procedures used to treat rheumatoid thumb deformities are determined more by the joint involved than by the specific type of deformity.
Postoperative therapy is geared toward restoring functional use of the thumb, and stability is an important goal.
Rheumatoid arthritis often involves the all-important thumb, resulting in significant deformity and functional loss. Nevertheless, it is possible to understand the various deformities and to carry out nonsurgical and surgical treatment to prevent and correct them and restore function. Disruption of the normal thumb biomechanics often leads to significant loss of the patient’s ability to carry out ADLs. Such activities as buttoning clothing or manipulating small objects are difficult to accomplish if the patient lacks either control or stability of the thumb joints. Before discussing our current treatment program, we review the most common thumb deformities and determine the factors that lead to their development.
Deformities of the Rheumatoid Thumb
The deformities encountered in the rheumatoid patient are varied and are the result of changes taking place intrinsic and extrinsic to the thumb. Synovial hypertrophy within the individual thumb joints not only can lead to destruction of articular cartilage but also may stretch the supporting collateral ligaments and joint capsules. As a result, each joint can become unstable and react to the stresses applied to it. These may be functional stresses as the thumb works in opposition to the other digits, or they may be caused by the deforming forces of the extensor or flexor tendons acting on the thumb. The thumb deformity patterns are the result of imbalances occurring between the various joints of the thumb. The alteration of posture at one level has an effect on the adjacent joint. Several years ago Nalebuff proposed a classification in which the deformities to the three thumb joints were divided into six types ( Table 104-1 ).
|Type||CMC Joint||MCP Joint||IP Joint|
|I (boutonnière)||Not involved||Flexed||Hyperextended|
|II (uncommon)||CMC flexed and adducted||Flexed||Hyperextended|
|III (swan neck)||CMC subluxed, flexed, and adducted||Hyperextended||Flexed|
|IV (gamekeeper’s)||CMC not subluxed; flexed, and adducted||1°, hyperextended, ulnar collateral ligament unstable||Not involved|
|V||May or may not be involved||1°, volar plate unstable||Not involved|
|VI (arthritis mutilans)||Bone loss at any level||Bone loss at any level||Bone loss at any level|
The six patterns of thumb postures described in Table 104-1 unfortunately do not exhaust the range of deformities one encounters in rheumatoid arthritis. It is possible, for example, for the patient to stretch the supporting structures of a joint, causing a flexion, extension, or lateral deformity. However, instead of the adjacent joint assuming the opposite posture, it may assume an abnormal position secondary to a tendon rupture. Thus, a patient might have hyperextension of both the metacarpophalangeal (MCP) and interphalangeal (IP) joints or flexion at both levels. When adjacent joints are deformed in the same direction, it usually implies the influence of a combination of factors. The examiner should check each individual joint for instability and tendon function.
Type I Thumb Deformity
Type I deformity is believed to be the most common and is characterized by MCP joint flexion and distal joint hyperextension ( Fig. 104-1 ). Others have called this the boutonnière deformity of the thumb, which is confusing because the flexion deformity is at the MCP joint rather than the proximal interphalangeal (PIP) joint (as in a digit). The usual sequence of events leading to this particular deformity is as follows: Synovitis of the MCP joint stretches out the extensor mechanism made up of the extensor pollicis brevis (EPB) and extensor pollicis longus (EPL) tendons. The proximal phalanx then assumes a flexed position and tends to sublux volarly. Although the patient may maintain passive extension, he or she cannot extend the joint actively. As a compensating mechanism, the patient radially abducts the first metacarpal and hyperextends the distal joint. The hyperextension of the distal joint and the flexion of the MCP joint are accentuated when pinch forces are applied to the thumb. This particular deformity is best described as an extrinsic- minus deformity. The most common site for the initial change is at the MCP joint, and it is the lack of extrinsic extensor power that starts the sequence of events. However, a rupture of the EPL at the wrist level also can lead to a similar deformity ( Fig. 104-2 ). Although this particular deformity of the thumb most commonly originates at the MCP level with the distal joint hyperextension being a secondary factor, the reverse also can occur. As a result of stretching of the volar plate of the distal joint or rupture of the flexor pollicis longus (FPL) tendon, the distal joint hyperextension can be primary and the MCP joint flexion secondary ( Fig. 104-3 ). In these patients, the metacarpal adduction is usually not a significant factor. Therefore, when faced with a type I deformity, one should evaluate not only the extensor tendons controlling the MCP joint but also the flexor tendon controlling the distal joint to determine the primary site of imbalance. Usually, the joint with the most deformity is where the deformity was initiated.
Types II and III Thumb Deformity
In the classification of thumb deformities presented in Table 104-1 , deformities of types II and III were described. In each type, the original alteration was at the carpometacarpal (CMC) joint level with subluxation of the first metacarpal, which then assumed an adducted position. In the type II deformity, the MCP joint and IP joint assumed positions identical to the type I deformity, in that the MCP joint was flexed and the distal joint hyperextended. This particular combination of metacarpal adduction with MCP joint flexion and distal joint hyperextension (type II) ( Fig. 104-4 ) is not common and assumes importance only in that it should be recognized as different from the type I deformity because of the CMC involvement and subsequent metacarpal adduction. A much more common sequence of events after CMC joint subluxation and metacarpal adduction is MCP joint hyperextension and distal joint flexion (type III) ( Fig. 104-5 ). This deformity is the opposite of the common type I deformity in all respects. It has been called a swan-neck deformity of the thumb, but because the hyperextension is at the MCP joint rather than the PIP joint, this term is confusing and, we believe, should therefore be avoided in classifying thumb deformities. At first, the MCP joint hyperextension is passively correctable. In fact, with time the range of MCP joint flexion diminishes and ultimately the joint is fixed in either a straight or hyperextended position. Any attempt to correct the type III deformity requires the first metacarpal adduction to be corrected. If the CMC joint is subluxed, abduction often can be accomplished only by salvage surgery. With restoration of metacarpal abduction, the MCP joint hyperextension deformity may correct itself. However, if hyperextension persists, this joint also must be treated (by capsulodesis, sesamoidesis, tenodesis, or arthrodesis [if fixed deformity or minimal active flexion is present]) in a flexed position.
Type IV Thumb Deformity
Since types I, II, and III thumb deformities were first described, we have encountered a number of patients with deformities that at first glance appear similar to the type III deformity but originate at the MCP joint level. The most common of these, which we call type IV ( Fig. 104-6 ), is the result of stretching out of the ulnar collateral ligament of the MCP joint as a result of synovitis. As the proximal phalanx deviates laterally at the MCP joint level, the first metacarpal secondarily assumes an adducted position. After this, the first dorsal interosseous and adductor muscles are shortened and the webspace between the thumb and index finger becomes contracted. Although the first metacarpal is adducted in these patients, there is no subluxation at the CMC joint. The key to treatment of this deformity is to restore stability to the MCP in a corrected position and, if needed, to release the first webspace contracture. A Z -plasty of the skin in the first webspace may also be needed. Surgery is ordinarily not necessary at the CMC joint level.
Type V Thumb Deformity
Another thumb deformity, type V, also should be recognized. In these patients the major deforming factor is instability or stretching of the volar plate of the MCP joint of the thumb. As a result, the MCP joint hyperextends and the distal joint assumes a flexed position ( Fig. 104-7 ). However, the first metacarpal need not assume an adducted position, and the CMC joint is usually not involved. This particular deformity is best treated by stabilizing the MCP joint by a capsulodesis, sesamoidesis, or fusion (if the deformity is fixed or there is minimal active flexion) in a flexed position.
Type VI Thumb Deformity
In another type of thumb deformity, type VI ( Fig. 104-8 ), the major element is a collapse or loss of bone substance. Patients with arthritis mutilans develop thumbs that become short and are characteristically unstable, with what appears to be redundant skin in relation to the underlying skeleton. Although this condition can be isolated at the thumb, it is ordinarily associated with similar difficulties in the other digits.
Evaluation of the Thumb
Although recognizing the various thumb deformities and understanding their development is valuable, one still must examine the individual joints of the thumb to determine appropriate therapy. One should, of course, not limit the examination to the thumb, but instead assess the whole hand and upper extremity, because the thumb does not act in isolation in hand function.
Our examination ordinarily includes a recording of the active (AROM) and passive range of motion (PROM), pinch strength, and grip strength, as well as a functional status of the hand. Range of motion (ROM) is recorded with a goniometer. Grip strength is recorded with a standard dynamometer, and pinch strength with a standard pinch meter. It is rarely necessary to use a blood pressure cuff to measure strength.
Normal grip strength varies with age and sex; normal grip strength for a man is around 100 pounds. We have found that grip strength of at least 20 pounds is necessary to perform most daily activities. One must keep in mind that many people with rheumatoid arthritis have grip strengths far below this functional level.
Pulp, lateral, and three-jaw chuck pinch also are tested. Although grip strength is important, pinch strength has a particular application when one is assessing self-care skills. These include holding eating utensils, buttoning clothing, writing, and manipulating small objects for precision grip. Normal pinch strength ranges between 15 and 20 pounds. We have found that a pinch strength of 5 to 7 pounds is necessary to accomplish most daily activities. Many rheumatoid patients have less than this, and therefore encounter considerable difficulty accomplishing even simple activities.
Functional assessment is also done as part of our examination. We use the Moberg Picking-Up Test to evaluate dexterity ( Fig. 104-9 ). We also may use other objective tests, such as the Purdue Pegboard Test, if the situation merits additional testing. In more complex cases, we may use the Jebsen Hand Function Test.