Midcarpal Instability

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Definition/Description

Midcarpal Instability (MCI) is characterized by a lack of support of the proximal carpal row and the midcarpal joint and loss of normal joint forces between proximal and distal carpal rows. Midcarpal instability can be palmar less common dorsal and extrinsic.  [1]

Clinically Relevant Anatomy

The arcuat ligament complex is the most important stabilizer of the midcarpal joint and exist of an ulnar arm, the triquetrohamatecapitate ligament and a radial arm who extends distal of the radioscaphocapitate ligament. The dorsal radiolunotriquetral ligament is also an important stabilizer of the proximal carpal row. 

Epidemiology /Etiology

Palmar midcarpal instability (PMC) is due to the laxity of the ulnar arm of the arcuat ligament and an increased laxity of the dorsal radiolunotriquetral ligament. A dynamic flexion deformity occurs in the proximal row as the distal row translates volarly due the ligament laxity.There is no longer the coupled rotation of the carpus with the gradual transition of the proximal row from volar to dorsal intercalated segment instability. Instead the proximal row remains flexed and the distal row remains volarly subluxed for a prolonged period, Until extreme ulnar deviaton when the distal row abruptly reduces on the proximal row and the proximal row jumps into a DISI configuration and we hear  a painful  catch–up clunk.[2]
Dorsal midcarpal instability is due to a laxity of the palmar radioscapocapitate ligament. There is a dorsal subluxation of the midcarpal joint.You hear also a clunk, but more a subluxation clunk
Extrinsic midcarpal instability is mostly caused by malalignment of a distal radius malunion. There is a dorsal displacement and angulation of the distal radius and an adaptive z-deformity of the carpus. [3]

Characteristics/Clinical Presentation

The patients often have no history of traumatic events. The patients have complaints in the form of loss of strength, laxity, impaired prehension, uncomfortable feeling and clicking and/or snapping sounds with an ulnar deviation.

Differential Diagnosis

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Diagnostic Procedures

Radiology

MCI is a dynamic instability, so X-rays, wrist arthrography or magnetic resonance imaging aren’t really helpful in the diagnosis of MCI. But they are helpful  to exclude other pathology, in particular lunotriquetral dissociation, and to assess the joint surfaces before reconstructive surgery. However RM images of PMCI shows a VISI pattern.

Fluoroscopy

Fluoroscopy is the imaging method to diagnose MCI. [4]

 - A lateral view of radioulnar deviation of the wrist shows the typical jump of the proximal row from flexion to extension by patiens with PMCI
- Under fluoroscopy, dorsal subluxation of the capitate on the lunate could be shown by pushing the capitate dorsally by patients with DMCI. This caused apprehension, and the patients recognized the click caused by the sudden movement of the lunate dorsal and ulnar.  [5][6]

Outcome Measures

add links to outcome measures here (also see Outcome Measures Database)

Examination 

Patients have a painful clunk on the ulnar side of the wrist during active ulnar deviation. If the wrist is in neutral deviation a palmar sag can be seen on the ulnar side of the carpus, this sag can be disappear with extreme ulnar deviation of the wrist. If the wrist is in a neutral position, we can see a prominent ulnar head.There can be a localized synovitis,There is often tenderness over the ulnar carpus especially the triquetrohamate joint and there is a positive midcarpal shift test.

Medical Management

Stabilization of the midcarpal joint can be achieved by soft tissue procedures (ligament reconstruction or capsular tightening) or a limited midcarpal arthrodesis. If ligament laxity can be traced to a specific place, specific ligament augmentation is indicated

We can use soft tissue procedures like distal advancement of the palmar ulnar arm of the volar arcuat ligament, dorsal radiocarpalcapsulodesis and dorsal reefing; this procedure is indicated in patients with mild to moderate MCI. For the severe cases a midcarpal arthodesis is performed, like 4 quadrant fusions or radial fusions or triquetrohamate fusion.  For extrinsic MCI we use radial shortening or radial osteotomy or ulnar lengthening. For Dorsal MCI the treatment exist of closing the space of Poirier by imbricating the palmar radioscaphocapitate ligament to the palmar radiolunotriquetral ligament.  [1], [2], [6]

Physical Therapy Management

Nonsurgical treatment:

This starts with nonsteroidal anti-inflammatory drugs (NSAIDs), steroid injections are also used for patients with a substantial midcarpal synovitis and advice. The therapist alerts you of compensatory movements and the importance to avoid pain provocative activities.

Splint immobilization is indicated: we use gutter splint, frequently combined with a pisiform boost pad. This pisiform boost pad is often combined with a dorsal pressure pad over the ulnar head. If a neutral wrist support splint or a pisiformis boost splint does not control the subluxation a modification of the perilunate stabilizing splint may work. This forearm based wrist support splint controls the scaphoid and the scaphotrapezial trapezoid joint by exerting dorsally directed pressure on the scaphoid tuberosity and the trapezoid ridge. This controls flexion tendency of the proximal carpal row by dorsally directed pressure on the pisiformis. [6]

When there is a reduction of symptoms we can start with dynamic strengthening and re-education of the M. flexor carpi ulnaris, M. flexor carpi radialis, M. extensor carpi radialis longus and brevis and M. extensor carpi ulnaris.

Dynamic strengthening exercises:

Palmairflexion and dorsalflexion:

1. the underarm is being fixed on the table in pronation for dorsiflesion and in supination for palmairflexion ,with a theraband, a weight or tubing in your hand you slowly bring your hand upwards. We can make this exercise more difficult by adding more weight or a more powerful theraband. We can also do this exercise with a power web.

2.Wrist roll .
You are standing with your arms extended in front of you and the roller in both hands. Now you slowly roll the chain up with palmairflexion and dorsiflexion of the wrist. Keep the rest of your body stationary.When the chain has reached the top, slowly lowering using the same motion. You can add a weight to the chain to make it more difficult.

Ulnar and radialdeviation:
We hold our arm extended beside our body with a weigh in our hand. We are going to move our hand with the weight forwards ( radial deviation) and backwards (ulnar deviation) .

References

1. Lichtman DM, Wroten ES. Understanding Midcarpal Instability. Journal of Hand Surgery [AM]. 2006; 31A:491–498. Level of evidence: 1A
2 . Buchler U. Wrist instability. Ln: Gaenslen ES, Lichtman DM. Midcarpal instability: description, classification, and treatment. First ed. UK; The livery house, 1996. pg 163-168 level of evidence: 2B
3. Stoller DW. Midcarpal instabilities. Magnetic resonance imaging in orthopaedics and sports medicine.3rd ed. Baltimore US: wolters kluwer health, 2007. Pg 1729 level of evidence: 5
4. Braunstein EM et al. Fluoroscopic and arthrographic evaluation of carpal instability. AJR Am J. Roentgenol.. 1985 Jun;14(6):1259-62. Level of evidence: 1B
5. Slutsky D, Osterman A. Fractures and Injuries of the Distal Radius and Carpus. Ln: Carlos Heras-Palou MD. Midcarpal instability. First ed. Philadelphia: Saunders Elsevier, 2008. Level of evidence 5
6. Cooney WP. The wrist: Diagnosis and operative treatment. 2nd ed. Philadelphia, PA,:Lippincott Williams & Wilkins; 2010.pg 655-666.level of evidence: 1A