Midcarpal Instability

Midcarpal instability (MCI) is a non-dissociative carpal instability pattern characterised by abnormal motion between the proximal and distal carpal rows. The pathognomonic finding is a painful "catch-up clunk" during ulnar deviation, caused by sudden shift from VISI (palmar flexion) to neutral alignment as lax palmar midcarpal ligaments are overcome. It is associated with generalised ligamentous laxity (Beighton score positive in 60-70%) and predominantly affects young females. Diagnosis requires the midcarpal shift test, dynamic fluoroscopy, and arthroscopy (Lichtman classification). Treatment ranges from conservative strengthening to dorsal capsulodesis or limited arthrodesis for refractory cases.

Lichtman Classification of Midcarpal Instability:

• Grade I: Mild laxity with positive shift test, easily reducible
• Grade II: Moderate laxity with significant subluxation, reducible
• Grade III: Severe laxity with fixed subluxation, partially reducible
• Grade IV: Fixed instability, not reducible, cartilage damage

Treatment Based on Classification:

• Grade I-II: Conservative management, consider capsulodesis if refractory
• Grade III: Capsulodesis or ligament reconstruction
• Grade IV: Limited arthrodesis (four-corner fusion)

Incidence and Demographics

Carpal Kinematics

Midcarpal instability (MCI) is a non-dissociative carpal instability pattern characterised by abnormal motion between the proximal and distal carpal rows. The pathognomonic finding is a painful "catch-up clunk" during ulnar deviation, caused by sudden shift from VISI (palmar flexion) to neutral alignment as lax palmar midcarpal ligaments are overcome. It is associated with generalised ligamentous laxity (Beighton score positive in 60-70%) and predominantly affects young females. Diagnosis requires the midcarpal shift test, dynamic fluoroscopy, and arthroscopy (Lichtman classification). Treatment ranges from conservative strengthening to dorsal capsulodesis or limited arthrodesis for refractory cases.

In MCI, the carpal alignment is typically VISI in neutral wrist position, with a scapholunate angle less than 30 degrees and capitolunate angle greater than 15 degrees with palmar angulation. However, this VISI pattern is dynamic and reducible, disappearing with radial deviation or grip. This distinguishes MCI from static VISI patterns seen with lunotriquetral dissociation.

History

Patients typically present with ulnar-sided wrist pain that is activity-related and associated with a painful clunk or snap. The clunk is often audible to others and may be accompanied by a sensation of the wrist "giving way" or feeling unstable. Symptoms are exacerbated by activities requiring forceful grip with ulnar deviation (tennis, golf, weight lifting, push-ups) or repetitive wrist motion.

Many patients report difficulty with daily activities including opening jars, lifting heavy objects, pushing up from chairs, and keyboard use. Pain is typically intermittent and mechanical in nature, rather than constant. Swelling is usually mild if present. A subset of patients can voluntarily reproduce the clunk and may have developed a habit of self-manipulation (similar to knuckle cracking).

Physical Examination

Inspection: Look for swelling (usually minimal), asymmetry, muscle atrophy (rare), and signs of generalized laxity

Palpation: Midcarpal joint tenderness (dorsal and palmar), no discrete mass, capitate prominence dorsally in VISI position

Range of Motion: Typically full or near-full ROM; document flexion, extension, radial deviation, ulnar deviation

Provocative Tests: Midcarpal shift test (key test), catch-up clunk with ulnar deviation, reduction with radial deviation

Strength: Often reduced grip strength on affected side (20-40% reduction common)

Ligamentous Laxity: Beighton score assessment (thumb to forearm, finger hyperextension, elbow/knee hyperextension, spine flexion)

The midcarpal shift test is the most specific clinical maneuver for diagnosing MCI. The examiner stabilizes the patient's forearm with one hand while placing the thumb of the other hand on the dorsal capitate, applying a palmar-directed force. The patient then actively ulnarly deviates the wrist. A positive test reproduces the painful clunk and sensation of instability as the proximal row suddenly shifts from palmar flexion to neutral.

Additional provocative maneuvers include the catch-up clunk test (passive motion from radial to ulnar deviation reproduces the clunk), the supination lift test (inability to lift weight while forearm is supinated due to pain and instability), and the shear test (applying dorsal-palmar shear force across the midcarpal joint elicits pain).

Functional Impact

Functional deficits vary with activity level and symptom severity. Common limitations include reduced grip strength (typically 50-80% of contralateral side), difficulty with activities requiring wrist extension and ulnar deviation, avoidance of weight-bearing on the affected extremity, and compensatory movement patte

rns. Athletes may be unable to participate in their sport, particularly in gymnastics, racquet sports, golf, and weight training.

Radiographic Evaluation

Standard radiographs (posteroanterior, lateral, oblique views) are often normal or show subtle findings. The lateral view may demonstrate VISI alignment in neutral position with a capitolunate angle greater than 15 degrees (palmar angulation) and scapholunate angle less than 30 degrees. However, these findings may be absent on static radiographs if the patient is not relaxed or if the technologist inadvertently positions the wrist in slight radial deviation.

Dynamic fluoroscopic examination with video recording is the gold standard radiographic study for diagnosing MCI. The examination is performed with the patient seated and the forearm resting on the fluoroscopy table. Real-time imaging captures the wrist as it moves from full radial to full ulnar deviation. The catch-up clunk is visualized as a sudden shift of the proximal carpal row from palmar flexion (VISI) to neutral or slight extension.

Stress radiographs may be helpful, including ulnar deviation views (may accentuate VISI deformity), grip compression views (assess for dynamic instability), and comparison views of the contralateral wrist. Quantitative measurements include the capitolunate angle (normal less than 15 degrees), scapholunate angle (normal 30-60 degrees), and radiolunate angle (normal 0 plus or minus 15 degrees).

Advanced Imaging

Magnetic resonance imaging (MRI) is typically normal in isolated MCI, as the ligamentous laxity represents attenuation rather than complete rupture. MR arthrography may show increased capacity of the midcarpal joint or contrast extravasation into the radiocarpal joint with midcarpal injection, suggesting ligamentous communication. However, MRI is primarily useful for excluding other pathology such as triangular fibrocartilage complex (TFCC) tears, lunotriquetral dissociation, or occult fractures.

Computed tomography (CT) is rarely indicated for MCI evaluation unless there is concern for subtle carpal coalition, malunion, or arthritis. CT arthrography has been described but is not commonly used in current practice given the superiority of MRI and arthroscopy for soft tissue assessment.

Wrist Arthroscopy

Wrist arthroscopy is both diagnostic and potentially therapeutic for MCI. The examination is performed under regional or general anesthesia with the wrist in traction. Standard portals (3-4, 4-5, 6R radiocarpal; midcarpal radial and ulnar) are established. The midcarpal joint is examined for excessive laxity between the proximal and distal rows, assessed using a probe (trampoline test or bounce test). The palmar midcarpal ligaments are visualized and assessed for attenuation, thinning, or disruption.

Arthroscopic classification systems have been proposed based on the degree of laxity and reducibility. Grade I shows mild laxity with easy manual reduction, Grade II demonstrates moderate laxity with manual reduction required, Grade III exhibits severe laxity that is difficult to reduce, and Grade IV shows severe laxity with associated midcarpal arthritis or other structural damage.

Lichtman Classification of Palmar Midcarpal Instability

Conservative management is the initial treatment for most patients with MCI, particularly those with mild symptoms (Lichtman Grade I-II) and those with generalized ligamentous laxity. The mainstay of treatment is wrist strengthening and proprioceptive training, focusing on dynamic stabilizers (flexor carpi ulnaris, extensor carpi ulnaris, wrist extensors and flexors). A structured hand therapy program should include progressive resistance exercises, proprioceptive training (balance board, closed kinetic chain activities), and activity-specific training.

Splinting may provide symptom relief, particularly for acute exacerbations. Options include cock-up wrist splints maintaining the wrist in slight radial deviation and extension (prevents VISI position), custom molded splints for activities, and taping techniques to support the wrist during provocative activities. Splints are typically worn during aggravating activities and at night for 6-12 weeks during the rehabilitation program.

Activity modification involves avoiding or modifying activities that provoke symptoms, particularly those requiring forceful grip with ulnar deviation. Anti-inflammatory medications (NSAIDs) may provide short-term pain relief but do not address the underlying instability. Corticosteroid injections are generally not recommended as they do not provide lasting benefit and may contribute to ligamentous weakening.

Indications for Surgery

Surgery is considered when conservative management fails after 3-6 months of appropriate therapy, symptoms significantly limit function or quality of life, patients are unable to participate in work or sports activities, or there is documented progression of instability on dynamic imaging. Relative contraindications include severe generalized ligamentous laxity (Beighton score greater than 7 out of 9), workers' compensation claims or litigation (poorer outcomes reported), psychiatric comorbidities, and unrealistic patient expectations.

Surgical Options

Dorsal Capsulodesis Technique

Dorsal capsulodesis is the most commonly performed procedure for MCI. The technique involves creating a dorsal wrist incision, typically between the third and fourth extensor compartments. The extensor retinaculum is incised and the extensor tendons are retracted to expose the dorsal capsule. A distally based capsular flap is created, preserving the attachment to the distal carpal row. The flap is then advanced proximally and secured to the dorsal lip of the radius, effectively tightening the dorsal structures and limiting palmar flexion of the proximal carpal row.

Multiple capsulodesis techniques have been described, including the Ritt capsulodesis (radially based flap), the Lichtman capsulodesis (ulnarly based flap), and the dorsal radiocarpal ligament advancement. All techniques share the goal of preventing excessive palmar flexion while preserving wrist motion. The capsule is secured with suture anchors or transosseous sutures. Postoperative immobilization in a short arm cast for 6 weeks is typical, followed by progressive range of motion and strengthening.

Palmar Ligament Reconstruction

Palmar ligament reconstruction attempts to directly restore the deficient palmar midcarpal ligaments. The procedure uses tendon graft (palmaris longus, plantaris, or toe extensor) passed through bone tunnels in the capitate and triquetrum to recreate the triquetrohamate-capitate ligament. The technique is technically demanding and requires accurate tunnel placement and appropriate graft tension. Long-term outcomes are variable, with some studies reporting good results and others showing high failure rates. This procedure is less commonly performed than dorsal capsulodesis.

Limited Wrist Arthrodesis

Four-corner fusion (capitate-hamate-lunate-triquetrum arthrodesis with scaphoid excision) is reserved for salvage situations, particularly Lichtman Grade IV MCI with established midcarpal arthritis. The procedure provides reliable pain relief and stability but sacrifices approximately 50% of wrist motion (particularly flexion-extension arc). The technique involves excision of the scaphoid, preparation of the articular surfaces of the four remaining bones, and fixation with a circular plate, dorsal plate, or compression screws. Scaphoid excision prevents impingement and allows settling of the carpus.

Total wrist arthrodesis is considered only for failed prior procedures or severe symptomatic arthritis affecting multiple carpal articulations. This salvage procedure eliminates all wrist motion but provides stable pain-free support for activities of daily living.

Surgical Complications

Recurrent Instability: Most common complication after capsulodesis (15-25%); consider revision versus salvage fusion

Stiffness: Expected loss of 10-20 degrees flexion-extension after capsulodesis; aggressive therapy if excessive

Pain: Persistent pain suggests inadequate stabilization, nerve injury, or unrecognized pathology; investigate thoroughly

Dorsal Ganglion: May form at capsulodesis site; often asymptomatic, excise if symptomatic

Neurovascular Injury: Rare but possible; protect terminal branches of radial and ulnar nerves during dissection

Early complications include wound infection (1-2%), hematoma formation, and iatrogenic nerve injury (dorsal sensory branch of radial nerve or ulnar nerve most vulnerable). Nerve injury typically presents as numbness or dysesthesia over the dorsal hand and may be temporary (neurapraxia) or permanent (nerve division).

Late complications include recurrent instability (most common, occurring in 15-25% after capsulodesis), wrist stiffness (expected to some degree but may be excessive), chronic pain (may indicate inadequate correction or progression to arthritis), and dorsal ganglion formation at the capsulodesis site. Hardware complications (loosening, prominence, irritation) may occur after four-corner fusion.

Outcomes and Prognosis

Outcomes after surgical treatment for MCI are generally favorable for appropriately selected patients. Dorsal capsulodesis results in resolution or significant improvement of the catch-up clunk in 75-85% of patients, with pain improvement in 70-80% and satisfaction scores of 7-8 out of 10. However, recurrence occurs in 15-25% of cases, particularly in patients with severe generalized laxity or those who return to high-demand activities prematurely.

Functional outcomes include return to work in 85-90% of patients at 3-6 months postoperatively, return to sports in 60-70% (often with some activity modification), and grip strength recovery to 80-90% of the contralateral side. Range of motion is typically reduced by 10-20 degrees in flexion-extension arc compared to the contralateral wrist, which is an expected and generally well-tolerated tradeoff for stability.

Factors associated with poorer outcomes include severe generalized ligamentous laxity (Beighton score greater than 7), workers' compensation or litigation involvement, late presentation with established arthritis (Grade IV), bilateral involvement, and unrealistic patient expectations. Careful patient selection and thorough preoperative counseling are critical to achieving satisfactory outcomes.

Midcarpal instability represents one pattern within the broader spectrum of carpal instability. Familiarity with the classification of carpal instabilities (dissociative versus non-dissociative, VISI versus DISI patterns) is essential for accurate diagnosis and treatment planning. MCI must be distinguished from lunotriquetral dissociation (which can also present with VISI), scapholunate dissociation (DISI pattern), and other wrist pathology.

Australian Specific Considerations

Midcarpal instability is managed by hand surgeons with expertise in wrist pathology, typically in metropolitan centres with access to fluoroscopy and wrist arthroscopy capabilities. Public hospital hand clinics provide assessment and treatment, with surgical procedures performed at major teaching hospitals. Private hand surgery practices offer alternative pathways for assessment and operative management.

Imaging is readily available through public and private radiology services, with dynamic fluoroscopy requiring coordination between the hand surgeon and radiologist to ensure appropriate views are captured. Wrist arthroscopy is performed in both public and private hospital settings with appropriate arthroscopic equipment and expertise.

Hand therapy is a critical component of both conservative and postoperative management, with certified hand therapists (CHT) available in major centres. Medicare rebates apply for hand therapy services with appropriate referral. Occupational therapy services may provide functional assessment and work-related rehabilitation for patients with MCI affecting employment.

Examination Techniques and Tips

Clinical examination for suspected MCI should be systematic and include comparison to the contralateral wrist. The midcarpal shift test must be performed correctly with appropriate force application and patient positioning. Video recording the provocative maneuver can be valuable for documentation and patient education.

Dynamic fluoroscopy requires clear communication with the radiology technologist regarding the specific views and maneuvers needed. Real-time video capture during the examination from radial to full ulnar deviation is essential. Side-by-side comparison with the contralateral asymptomatic wrist can be helpful in subtle cases.

Wrist arthroscopy for MCI evaluation requires familiarity with both radiocarpal and midcarpal portals and systematic examination of all carpal articulations. The trampoline test (applying pressure with the probe on the palmar midcarpal ligaments to assess laxity) should be performed in multiple locations. Comparison to the expected normal resistance is subjective and improves with experience.

Future Directions

Research into the molecular basis of ligamentous laxity may identify genetic markers or predisposing factors for MCI, potentially allowing preventive strategies. Improved arthroscopic techniques including thermal capsular modification and ligament reconstruction are being refined. Biomechanical studies using computational modeling may optimize capsulodesis techniques and predict outcomes. Long-term outcome studies with validated patient-reported measures are needed to better compare surgical techniques and guide treatment algorithms.

This topic provides comprehensive coverage of midcarpal instability aligned with FRACS examination requirements, emphasizing clinical diagnosis, dynamic imaging assessment, and evidence-based surgical management of this challenging carpal instability pattern.