Reconstruction of Chronic Radial and Ulnar Instability of the Thumb Metacarpophalangeal Joint



Reconstruction of Chronic Radial and Ulnar Instability of the Thumb Metacarpophalangeal Joint


Steven Z. Glickel





ANATOMY



  • The MCP joint of the thumb has characteristics of both a condyloid and a ginglymus joint. The radial condyle is taller in the dorsovolar dimension than the ulnar condyle.


  • The dorsoulnar and dorsoradial digital nerves are terminal branches of the superficial sensory branch of the radial nerve and invariably cross the operative field in the plane immediately superficial to the adductor and abductor aponeuroses, respectively.



    • They are at risk during reconstruction of the collateral ligaments. During the exposure of the joint, the nerve should be mobilized and gently retracted. Forceful retraction may cause a neurapraxia and hypesthesia distal to the nerve on the dorsum of the thumb on the involved side.


  • The adductor aponeurosis is an extension of the tendon of the adductor pollicis muscle, which contributes obliquely oriented fibers to the extensor mechanism distal to the vertical fibers.


  • The abductor aponeurosis is an extension of the tendon of the abductor pollicis brevis muscle, which contributes obliquely oriented fibers to the extensor mechanism distal to the vertical fibers.


  • The proper UCL and RCL originate from fossae of the condyle of the metacarpal head on the radial and ulnar sides and pass obliquely from dorsal-proximal to volar-distal to insert on the volar third of the base of the proximal phalanx. The ligament widens as it goes from its metacarpal origin to its proximal phalangeal insertion.



    • The proper collateral ligaments are tight in MCP joint flexion and lax in extension.


  • The accessory collateral ligaments originate on the metacarpal head contiguous with but just volar to the proper collateral ligament and extend obliquely across the MCP joint, inserting on the sesamoid and volar plate.



    • The accessory collateral ligaments are tight in extension and lax in flexion.


  • By definition, to have a complete ligament rupture, both the proper and the accessory collateral ligaments must be torn.


  • The Stener lesion is a palpable soft tissue mass on the ulnar aspect of an injured MCP joint. It results from a tear of the UCL caused by forceful radial deviation of the proximal phalanx, angulating the MCP joint 70 degrees or more. The ligament tears distally at or near its insertion on the volar ulnar base of the proximal phalanx. As the proximal phalanx deviates radially, the ruptured UCL remains attached to its metacarpal origin. As the proximal phalanx returns to its resting, neutral position, the UCL stump comes to lie proximal and superficial to the adductor aponeurosis. Hence, the avulsed ligament is separated from its deep insertion by the aponeurosis, preventing ligament healing.


  • The abductor aponeurosis is wider than the adductor aponeurosis. When the RCL tears, the ends of the torn ligament remain deep to the abductor aponeurosis. Hence, a Stener type of lesion rarely occurs on the radial side.


  • Tears of the collateral ligaments result in rotatory deformities of the MCP joint. When one ligament is torn and the other is intact, the metacarpal head subluxates volarly on the injured side, rotating around the axis of the intact ligament. The metacarpal head on the injured side appears to be prominent due to the volar translation of the base of the proximal phalanx on that side.


PATHOGENESIS



  • The UCL of the MCP joint of the thumb is usually torn by forceful abduction and extension of the thumb, as in a fall on the outstretched hand with the thumb abducted. The proximal phalanx deviates radially and, if there is sufficient force, the UCL either avulses from its insertion on the base of the proximal phalanx or, less commonly, tears in its midsubstance or from its origin on the metacarpal head.19


  • There are four primary causes of chronic instability of the UCL.



    • Failure to diagnose an acute, complete tear resulting in no treatment


    • Failure to diagnose a Stener lesion resulting in inadequate, nonoperative treatment of a recognized acute, complete, and displaced tear


    • Inadequate treatment or insufficient immobilization of a recognized, acute tear without a Stener lesion


    • Progressive attenuation of the ligament due to repetitive trauma


  • Tears of the RCL typically result from forceful ulnar deviation and extension of the MCP joint.



    • Proximal and distal avulsions of the ligament occur with roughly equal frequency.


    • Intrasubstance tears occur infrequently.



  • Chronic instability of the RCL has three primary causes.



    • Most commonly, chronic laxity is due to failure to recognize an acute tear resulting in no treatment or inadequate or late treatment.


    • Even when the pathology is recognized, conservative management may fail because surgeons tend to be less aggressive about treatment of radial compared to ulnar-sided collateral ligament injuries.


    • Chronic attenuation due to repetitive trauma is uncommon but does occur.


NATURAL HISTORY



  • Over time, chronic tears of the collateral ligaments of the thumb MCP joints cause progressive weakness of pinch and grip due to instability and pain. There may also be increasing deformity as the proximal phalanx on the injured side translates volarly causing dorsal prominence of the metacarpal head on that side. Occasionally, the proximal phalanx deviates in the coronal plane away from the side of the injured ligament resulting in a static deformity.



    • Incompetence of the UCL diminishes the thumb’s ability to act as a stable post against which to pinch with the index finger. Patients often have difficulty holding large objects that require counterpressure by a stable thumb.


    • Patients with chronic RCL instability often have pain with torsional motions such as unscrewing jar tops.


  • Chronic laxity may cause incongruity and asymmetric wear of the MCP joint, which may progress to posttraumatic osteoarthritis of the joint.



    • Arthritis of the joint causes increasing pain, stiffness, and weakness.


PATIENT HISTORY AND PHYSICAL FINDINGS



  • Obtaining a relevant history from patients with chronic instability of the thumb MCP joint includes eliciting a history of trauma to the thumb in the recent or distant past.


  • Patients are questioned about pain in the thumb, particularly if it is exacerbated by forceful pinch and grasp and torsional activities such as turning keys in locks, turning doorknobs, or unscrewing jar tops.



    • The examiner should establish the chronicity of the symptoms and whether they are increasing in severity.


  • Assessment of instability of the thumb MCP collateral ligaments is primarily clinical.


  • Clinical examination begins with observation.



    • The resting posture of the thumb at the MCP joint is occasionally indicative of pathology. The joint may be angulated or rotated in its resting posture if the collateral ligament is grossly incompetent and the instability is chronic.


    • In thumbs with chronic RCL instability, there is often a dorsal prominence on the radial aspect of the metacarpal head. Such a prominence is generally less apparent in cases of chronic UCL instability.


  • The involved side of the joint is often tender to palpation.


  • Palpation of a fullness or soft tissue mass on the ulnar side of the metacarpal head is strongly suggestive of a Stener lesion.


  • Stability of the collateral ligament is tested in extension and 30 degrees of MCP joint flexion (under local anesthesia if needed but that is rarely required). There is no consensus in the literature concerning the degree of instability that is diagnostic of a complete tear.



    • Valgus stress of the MCP joint in flexion is used to assess the stability of the proper UCL, whereas stress with the joint in extension is used to assess the accessory UCL as well.


    • The criteria for diagnosis of a complete ligament disruption that are most accurate were described by Heyman et al3 and include 30 to 35 degrees of laxity of the ulnar side of the MCP joint when stressed in extension and 15 degrees more laxity than the contralateral thumb when stressed in 30 degrees of flexion.


    • Laxity in extension suggests that the accessory and proper collateral ligaments are both torn.


    • A more subtle, but often very helpful, finding is the presence or absence of a discrete end point to joint opening when stressed. Absence of a solid end point is strongly suggestive of a complete ligament tear.


  • To test for joint degeneration, the MCP joint is passively moved in extension and flexion radially and ulnarly deviated. The joint is axially loaded as it is moved. Crepitus and pain strongly suggest the presence of osteoarthritis, a contraindication to reconstruction of an unstable MCP joint.


IMAGING AND OTHER DIAGNOSTIC STUDIES



  • Radiographic evaluation includes posteroanterior (PA), lateral, and oblique radiographs of both thumbs.



    • Fractures should be ruled out.


    • The lateral view may show volar subluxation of the MCP joint, which is fairly common and may be the result of extension of the collateral ligament tear to involve the dorsal capsule. This may occur with both UCL and RCL tears. An isolated tear of the dorsal joint capsule very rarely causes volar subluxation without an associated collateral ligament injury.


    • A comparison lateral radiograph of the contralateral thumb is very helpful if volar subluxation is suspected.


  • Stress views of the MCP joint have been recommended to demonstrate instability radiographically.



    • Most experienced clinicians rely almost exclusively on physical examination and static plain radiographs to make the diagnosis. Stress views done by the treating surgeon can be used to confirm the diagnosis and provide documentation for the medical record.


  • Magnetic resonance imaging (MRI), ultrasound, and arthrography are rarely indicated to assess completeness of the UCL tear, particularly in the setting of a chronic injury. MRI and ultrasound can show the presence of a Stener lesion, but in the setting of a chronic injury, the presence or absence of a Stener lesion does not substantially alter the treatment plan.


  • The use of arthroscopy as a diagnostic and treatment modality in the setting of chronic UCL instability remains investigational. Although the ligament and joint pathology may be able to be visualized, reconstruction using the arthroscope is a challenge, which has not yet yielded reportable results.




NONOPERATIVE MANAGEMENT



  • Customized hand-based thermoplastic splints, nonsteroidal anti-inflammatory medication, and corticosteroid injections may improve the synovitis and pain resulting from chronic instability and early degenerative arthritis. The duration of pain relief is unpredictable but usually in the range of a few weeks to months.


SURGICAL MANAGEMENT



  • The indication for reconstruction of chronic UCL or RCL disruption is failure of conservative treatment, with persistent pain and instability of the MCP joint.


  • Instability alone is a soft indication for surgery.



    • Theoretically, the asymmetric wear of the articular cartilage resulting from chronic laxity causes degeneration of the articular cartilage. This can be used as an argument for prophylactic reconstruction.


    • However, most patients without pain are hesitant to consider surgery and the prolonged rehabilitation required thereafter.


  • Contraindications to reconstruction of UCL or RCL tears include osteoarthritis, “multidirectional” instability, and fixed subluxation of the joint.



    • Mild chondromalacia is not a contraindication to reconstruction but more significant cartilage degeneration is better treated by MCP arthrodesis.



      • If an arthritic joint is stabilized by reconstruction, pain is likely to persist and increase over time, necessitating conversion to an arthrodesis.


    • Fixed instability of the MCP joint is an uncommon contraindication to ligament reconstruction.


    • Reconstruction of the incompetent ligament in this scenario would require an extensive joint release, creating multidirectional instability.


    • Failure to release the joint adequately would preclude anatomic realignment or result in rapid recurrence of the preoperative deformity and instability.


  • Reconstruction of chronic instability may involve mobilization of the disrupted ligament, mobilization of local tissues, or ligament replacement using a tendon graft.



    • The decision is made at the time of surgery.


    • The more chronic the injury and the more dramatic the laxity and deformity, the more likely the need for replacement of the ligament with a graft. The prevailing wisdom is that if an MCP collateral ligament has been torn for more than 6 weeks, it cannot be used for secondary repair or reconstruction. I have not found that to be the case. I have used ligaments torn for as much as several months for secondary repair but the tissue has to be supple and able to be mobilized. Significantly, fibrotic ligament should be excised and reconstructed.


Preoperative Planning



  • The patient is asked to actively bring all five digits together and simultaneously flex the wrist against resistance. The volar wrist is inspected for the presence of a palmaris longus (PL) tendon.


  • Examination under anesthesia may show even greater joint laxity than anticipated based on an awake examination with the patient guarding.


Positioning



  • The patient is supine on the operating room table with the arm on a hand table at an angle slightly less than perpendicular to the torso.


Approach



  • Lazy S incision centered over the MCP joint


  • Midaxial incision


  • Chevron-shaped incision centered over the midaxial point of the MCP joint


Jul 22, 2016 | Posted by in ORTHOPEDIC | Comments Off on Reconstruction of Chronic Radial and Ulnar Instability of the Thumb Metacarpophalangeal Joint

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