Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Carpal Fractures and Ligamentous Instabilities

Carpal Fractures

Carpal Fractures

The human wrist joint is a complex arrangement of small bones and ligaments that form a mobile yet stable link from the powerful forearm to the hand. The normally functioning carpus can position the hand precisely relative to the forearm and provides remarkably stable transmission of forces. Motion and stability of the carpus provide the critical foundation for maximum hand function from precise fine motor control to power grip activities.

When the normal mechanics of the wrist are disrupted, the instability of the carpal bones results in weakness, stiffness, chronic pain, and often arthritis if not treated appropriately. Although the early clinical and radiographic findings may be subtle, an understanding of wrist kinematics and instability patterns can facilitate early diagnosis and management. Unfortunately, selecting the optimal treatment remains a difficult judgment in most cases.

Since the early reports, anatomic and biomechanical studies have provided a foundation for understanding carpal motion, stresses, and pathologic instability. Building on these studies, various models have been suggested to explain the remarkable strength and mobility of this complex joint and the predictable patterns of failure.

This article presents the current understanding of pathologic carpal instability, the common classification patterns, and early treatment options that may avoid protracted dysfunction. Appropriate hand therapy is essential to maximize recovery but requires an appreciation of the limitations of carpal instability dysfunction and the goals of various treatment options.

Carpal ligament instability is defined as any malalignment of the carpus. This may be evident on plain radiography as a static deformity; alternatively, the situation may be a dynamic one, which becomes evident only when external forces are placed on the wrist.

The malalignment may appear after a single traumatic event or may be secondary to chronic attenuation of supporting ligaments after a traumatic event or secondary to an underlying disease process (eg, rheumatoid arthritis,pseudogout).

Carpal ligament instability results from an injury to one or more ligamentous or bony constraints in the wrist. Depending on the force, rate, and point of impact and on the position of the wrist, a fall on an outstretched wrist can result in a range of injuries. This spectrum includes wrist sprains, distal radius fractures, and fractures to the scaphoid and other carpal bones. This type of trauma can also result in injury to one or more ligamentous structures in the wrist, causing carpal instability. Perilunate instability is described as progressing from the scapholunate and the capitolunate to the lunotriquetral joint.

This perilunar instability is divided into 4 stages (see image below). Stage I refers to injury to the scapholunate interosseous ligament (SLIL). Further trauma results in dorsal subluxation of the capitate relative to the lunate, or stage II. As the load increases, the lunotriquetral interosseous ligament (LTIL) is injured, causing a perilunate dislocation in stage III. Finally, stage IV is characterized by dislocation of the lunate from the radiolunate fossa.

However, if the carpus is pronated and the hypothenar area is struck first, an ulnar traumatic pattern may be observed. Specifically, disruption of the ulnotriquetral ligament complex and the LTIL occurs. As the triquetrum no longer holds the lunate, it falls into a flexed position because of pressure from the capitate and its connection with the scaphoid. With attenuation or injury to the dorsal intercarpal ligament, a volar intercalated-segment instability (VISI) pattern ensues; this can be visualized on lateral radiography. An LTIL tear most commonly results in a VISI deformity.

In addition to a direct loading type of trauma, rotational force to the wrist can also result in ligamentous injuries, eg, the forces that occur when holding a power drill while the drill bit is jammed. This type of trauma can result in injuries to the LTIL and ulnar-triquetral ligament complex and result in the lunotriquetral instability.

Some instability patterns arise after chronic attrition of supporting ligaments. One traumatic event may result in some subtle ligamentous injury but no clear instability initially. However, over time, continued normal daily loading of the wrist can result in symptomatic instability. An example is seen with scaphoid fractures, where a DISI deformity tends to appear late after the initial traumatic event.

Supporting ligaments can also be important in preventing carpal instability in the presence of other significant ligamentous injury. For example, many cadaveric studies have shown that isolated sectioning of the SLIL does not result in frank radiographic scapholunate gap or dissociation.

 

Surgical Therapy

Treatment of carpal instability is complex and usually specific to the type of instability and is certainly controversial. A full detailed review of all treatment options is beyond the scope of this article. To simplify this discussion, each treatment is summarized under specific types of instabilities: scapholunate, lunotriquetral, and midcarpal instability and also ulnar translocation.

Scapholunate instability

There is no consensus on the appropriate treatment of scapholunate instability. The treatment is usually specific to the different stages or degree of injury. Partial tears of the SLIL are thought to represent occult or predynamic instability. For these injuries, most recommend an initial trial of splinting and/or casting. Arthroscopic debridement with or without pinning can be an option in these patients in whom initial conservative treatment is unsuccessful.

A complete tear of the SLIL may not by itself lead to an acute scapholunate gap or diastasis. Biomechanical studies support the concept that additional supporting ligaments must also be injured for this gap to be apparent. In addition, attenuation of these ligaments may lead to a diastasis that is observed late with respect to the initial injury date. In either case, a complete tear of the SLIL is suggested in the presence of the significant scapholunate diastasis on static or dynamic radiography.

With complete SLIL tears, cast immobilization does not reduce or prevent scapholunate diastasis. Significant force occurs at the scapholunate interval on wrist loading. Options for acute management of these tears include direct repair with or without dorsal capsulodesis or arthroscopic debridement, reduction, and pinning. Some recommend the latter treatment for acute (< 3 mo) tears that have evidence of instability on static radiography (gap < 3 mm or DISI).

A retrospective study by Weiss et al showed that 33% of patients who underwent arthroscopic debridement, reduction, and pinning of complete SLIL tears had persistent pain and required further surgery. Most reconstructive wrist surgeons recommend direct repair for acute (< 6 wk) tears if a sufficient SLIL remnant is present. Lavernia et al reported on dorsal capsulodesis to augment a direct repair and demonstrated good results in 81% of their patients. Satisfactory results were seen in patients, even as long as 3 years after injury.

In patients with unrepairable SLIL but with a reducible scapholunate interval and without degenerative changes, an indirect or direct ligament reconstruction has been advocated. Typically, the presentation is chronic, and the SLIL is usually not repairable. Indirect ligament reconstruction is based on stabilizing the scaphoid to prevent the rotatory subluxation that often occurs in scapholunate instability.

Some indirect ligament reconstructions also attempt to close the scapholunate gap. The most widely used indirect ligament reconstruction is the Blatt dorsal capsulodesis.[45] This technique uses a flap of dorsal capsule to tether the scaphoid tuberosity to retard scaphoid flexion. Because the flap is attached to the distal radius, wrist flexion is significantly reduced by 20% on average.

More recent techniques attempt to avoid limitation of flexion by not tethering the scaphoid to the radius. Several techniques have been described. As Berger et al initially proposed a strip of dorsal intercarpal ligament detached from the triquetrum can be used to tether the distal scaphoid pole to the lunate or radius . Slater et al described the use of a portion of the dorsal intercarpal ligament that attaches to the distal scaphoid and trapezoid and reinserts it to the distal pole of scaphoid tuberosity. These authors believe that this technique not only serves to limit scaphoid flexion but also reduces the scapholunate gap more effectively than the Blatt capsulodesis.

Direct ligament reconstruction is indicated when the SLIL is not directly repairable, when the scapholunate dissociation is reducible, and when no evidence of degenerative arthritis is observed. Some also believe that evidence of carpal instability (DISI) should be absent. Techniques for this approach involve either a tendon to reconstruct the SLIL or a bone-ligament-bone construct. All of these techniques have had some degree of success, but they are not universally durable. They require a long period of wrist immobilization and result in some loss of final wrist motion.When arthritic change (advanced scapholunate collapse) or a wide, irreducible scapholunate gap is present, options include a proximal row carpectomy or scaphoid excision and fusion of the lunate, triquetrum, capitate, and hamate (4-corner fusion). Significant degenerative changes at the proximal hamate or of the lunate fossa are a contraindication to proximal row carpectomy. Once pancarpal arthritis involves the lunate fossa, the best surgical option may be total wrist fusion.

Lunotriquetral instability

There is no consensus on the appropriate treatment of lunotriquetral instability. Treatment algorithm can probably be based on the type and age of the injury. A partial tear of the LTIL may be clinically suspected and should not have the associated VISI deformity. Reagan et al recommend a period of immobilization for acute injuries. Others have recommended arthroscopic evaluation and percutaneous pinning.

For patients in whom conservative treatment fails, lunotriquetral dissociation direct repair with or without augmentation has been advocated. Repairing the LTIL by using an open technique to reattach it back to the site of its avulsion (usually from the triquetrum) has good results. Augmentation is usually in the form of a capsulodesis. The goal of capsulodesis is to prevent excessive flexion of the proximal row by imbricating the dorsal radiotriquetral ligament.

For patients who present late after their initial injury, surgical management includes techniques of capsulodesis, ligament reconstruction, arthrodesis, or ulnar shortening.  Because some patients with symptomatic lunotriquetral instability also have ulnar impaction syndrome, Ruby treats these patients with chronic lunotriquetral tears with ulnar shortening alone, especially if they have positive or neutral ulnar variance. Ulnar shortening is believed to tighten the volar ulnotriquetral and ulnolunate ligaments, indirectly improving lunotriquetral stability. However, this treatment may be ill advised in the patient with a VISI deformity because tightening of these volar ligaments may exacerbate their deformity.

Instead of lunotriquetral fusion, others have recommended lunotriquetrohamate or triquetrohamate fusions. Further studies are needed to fully evaluate these fusions.

Midcarpal instability

Carpal instability that results from distal radius malunion can be effectively treated by correcting the malalignment of the radius. Opening wedge osteotomy of the radius at the location of the deformity to correct radial malalignment usually also corrects the carpal instability.

Ulnar translocation

In the rheumatoid wrist, ulnotranslocation is usually effectively treated with radiolunate fusion. Significant arthritis at the radioscaphoid joint may also require radioscaphoid fusion. Total wrist fusion is probably the best option significant midcarpal arthrosis is present as well.

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