ANATOMY

The palmar arcuate ligament complex comprises a radial arm, which is confluent with and distal to the radioscaphocapitate ligament, and an ulnar arm, the triquetrohamate-capitate ligament (TCL) (Fig. 25-1). In the normal situation, the proximal carpal row moves smoothly, from a flexed position when the wrist is in radial deviation to extension when the wrist is in ulnar deviation. This is possible because of the progressive tightening effect of the arcuate ligament as it stretches out to length, incrementally pulling the midcarpal row into extension, and the carpal bone geometry, which causes the triquetrum to translate dorsally along the helicoidal facet of the hamate. If the arcuate ligament is attenuated, this synchronous motion is lost.³

FIGURE 25-1 A, Line drawing of the volar ligaments. Ligaments: TCL, triquetrohamate-capitate ligament; RSC, radioscaphoid ligament; LRL, long radiolunate ligament; SRL, short radiolunate ligament; UL, ulnolunate ligament; UC, ulnocapitate ligament; UT, ulnotriquetral ligament; SC, scaphocapitate ligament; STT, scaphotrapezial trapezoidal ligament; TH, triquetrohamate ligament; IC, intercarpal ligament. Bones: R, radius; U, ulna; S, scaphoid; L, lunate; C, capitate; T, triquetrum; H, hamate; P, pisiform; Tm, trapezium; Td, trapezoid. B, Arthroscopic view of the arcuate ligament from the midcarpal ulnar portal. C, capitate; RSC, radioscaphocapitate ligament; S, scaphoid; TCL, triquetrohamate-capitate ligament.

Studies by Trumble and colleagues⁴ and Viegas and coworkers⁵ showed that sectioning of the TCL or the dorsal radiocarpal ligament (DRCL), also known as the dorsal radiotriquetral ligament, could produce a volar intercalated segmental instability (VISI) deformity and simulate PMCI. Lichtman and colleagues showed in vivo that tightening the DRCL alone can stabilize the proximal carpal row and eliminate the clunk of PMCI, emphasizing the potential importance of dorsal ligament laxity in the pathogenesis of this disorder.⁶ Lichtman believed that PMCI is caused by laxity of the TCL and DRCL, which allows an excessive palmar sag of the heads of the capitate and hamate at the midcarpal joint. This produces a VISI pattern of the proximal row in the nonstressed wrist. This sag results in a loss of joint contact across the midcarpal joint, which manifests clinically as a loss of the smooth transition of the proximal row from flexion to extension as the wrist deviates ulnarward. The proximal carpal row stays in a flexed position until the terminal extent of ulnar deviation, when the helicoidal shape of the hamate facet suddenly forces the triquetrum to move dorsally. This snaps the lunate, and subsequently the scaphoid, into extension, causing a sudden reversal of the VISI. This sudden proximal row extension is responsible for the painful and rapid catch-up clunk that occurs. As the wrist moves back to neutral position, the triquetrum translates down the hamate facet, allowing the proximal row to drop back into VISI while the distal row again settles palmarly into its slightly subluxated starting point (Fig. 25-2).

FIGURE 25-2 Dorsal exposure of the midcarpal joint in a left wrist. H, hamate, T, triquetrum. A, Triquetrohamate joint with the proximal row reduced. B, Subluxed triquetrohamate joint with volar sag of the proximal row. H, hamate, T, triquetrum.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

The dorsal pattern of MCI has not been studied as extensively. It appears that laxity of the radial arm of the palmar arcuate ligament permits the capitate and hamate to translate dorsally to an excessive degree, especially with ulnar deviation of the wrist.^7,8 In the palmar and dorsal patterns, the proximal row always moves into extension, and the distal row translates dorsally with ulnar deviation. It is the timing and force of this movement that differentiates the two patterns. In PMCI, the distal carpal row starts out in palmar subluxation with the wrist in neutral position. As the wrist moves into ulnar deviation, the subluxation suddenly corrects. In DMCI, the wrist starts out in a reduced position in neutral. Dorsal subluxation of the distal row then occurs with ulnar deviation. In either case, the instability is caused primarily by laxity of the selected extrinsic carpal ligaments that support the proximal row, which prevents them from controlling the complex kinematic relationships among the articular surfaces across the midcarpal joint.

PATIENT EVALUATION

History and Physical Examination

In PMCI, the patient presents with a history of clunking of the wrist. Patients can often reproduce the clunk on both sides, because generalized ligamentous laxity frequently coexists. The patient may have a trivial injury that accentuates this normal laxity, resulting in a painful clunk. On physical examination, close inspection reveals a sag of the midcarpal joint with the wrist in radial deviation, which is reduced with active or passive ulnar deviation (Fig. 25-3). The clunk may be reproduced by performing the midcarpal shift test.³ This test is performed by placing the patient’s wrist in neutral position with the forearm in pronation. A palmar force is then applied to the hand at the level of the distal capitate. The wrist is simultaneously loaded and deviated ulnarly. The test result is positive if a painful clunk occurs that reproduces the patient’s symptoms.

FIGURE 25-3 Palmar midcarpal instability. A, Notice the sag in the midcarpal joint with the wrist in radial deviation. B, The carpus is reduced in ulnar deviation and the sag disappears.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

In DMCI, a history of an extension injury may be present. Patients complain of post-traumatic chronic pain, weakness, and wrist clicking. Tight grasping, especially in supination, aggravates the symptoms. The physical examination also reveals palmar sagging of the ulnar wrist. A dorsal capitate displacement test is performed by applying dorsal pressure to the scaphoid tuberosity while longitudinal traction and flexion are applied to the wrist. There is an associated painful click as the lunate is abruptly shifted dorsally and ulnarly.

Diagnostic Imaging

Static radiographs are typically normal but occasionally reveal a mild VISI pattern with the wrist in the neutral position. Arthrograms are normal unless there are associated intracarpal or triangular fibrocartilage complex tears. Magnetic resonance imaging findings are nonspecific. Videofluoroscopy provides the hallmarks for diagnosis of this condition. With normal wrist kinematics, the proximal carpal row rotates synchronously from flexion to extension as ulnar deviation of the wrist is achieved. With PMCI, the proximal row maintains a volar-flexed position until terminal ulnar deviation is reached, at which time it suddenly snaps into extension (see MCI video).

In dynamic DMCI, the radiographs are usually normal. In chronic cases, they often show a VISI pattern (Fig. 25-4). The capitolunate displacement test shows dorsal subluxation of the proximal carpal row in addition to dorsal subluxation of the capitate from the lunate (Fig. 25-5).⁹ This effect led Louis and colleagues to coin the term capitolunate instability pattern (i.e., CLIP wrist).¹⁰

FIGURE 25-4 Volar intercalated segmental instability. A, Lateral radiograph shows volar tilting of the lunate and extension of the scaphoid. B, The same view is shown with the lunate and scaphoid outlined for clarity.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

FIGURE 25-5 Capitolunate displacement test. A, Lateral radiograph demonstrates dorsal subluxation of the capitate on the lunate. B, The same view is shown with the lunate and capitate outlined for clarity.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

Nonoperative Management

Nonsurgical treatment consists of activity modification, nonsteroidal anti-inflammatory medication (NSAIDs), and splinting.¹¹ Various pisiform support splints have been described. They are based on the observation that application of dorsally directed pressure under the pisiform reduces the carpal sag along with the VISI position of the carpal row. Applying this principle, a three-point dynamic splint may maintain the reduction while permitting wrist motion in milder cases (Fig. 25-6). The splint may be worn full time for 6 to 8 weeks to reduce the midcarpal synovitis and then as needed.

FIGURE 25-6 Three-point fixation with a dynamic splint.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

Lichtman and Wroten observed that active co-contraction of the extensor carpi ulnaris, flexor carpi ulnaris, and hypothenar muscles can reduce the sagging of the midcarpal joint. Some patients can eliminate the catch-up clunk by contracting these muscles before ulnar deviation of the wrist. Patients are taught this isometric muscle contraction as a part of the therapy program.¹ However, definitive treatment of this condition ultimately requires surgical treatment.

TREATMENT

Arthroscopic Technique

Arthroscopic Capsular Shrinkage

Although thermal capsular shrinkage has not enjoyed great success in the shoulder, its role in the treatment of wrist disorders remains promising. Thermal energy unwinds the collagen triple helix in capsular and ligamentous structures, with subsequent healing in a shortened or tightened position. The temperature required to achieve the effect is about 70 to 80 degrees; to avoid tissue ablation, the temperature should not exceed 100 degrees. Tissue repair occurs by vascular invasion and fibroblastic activity. In vitro, capsular tissue has been shown to shrink by 9% to 50%, depending on the probe and the type of tissue. After shrinkage, collagen stiffness is reduced to approximately 20% of normal; it returns to normal by about 2 months.¹⁴ This concept has led to the use of these techniques as a treatment option for MCI of the wrist.

The patient is placed in a supine position on the operating table. After exsanguination of the limb, the tourniquet is inflated to 250 mm Hg. A 2.7-mm, 30-degree angle arthroscope, along with a fiberoptic light source and camera setup, are used. Some type of diathermy unit is used to create the thermal shrinkage. Large-bore outflow cannulas are desirable to provide rapid joint irrigation and minimize the risk of chondral damage through heat necrosis. With the use of a tower, 10 pounds of traction is applied to the index and long fingers. The radiocarpal joint is inflated 1 cm distal to Lister’s tubercle at the 3-4 portal, and the 2.7-mm arthroscope is introduced. Outflow is established through the 6-R portal. The standard dorsal portals, including a 3-4 and a 4-5 portal, are used for an arthroscopic survey. Any associated triangular fibrocartilage tears or lunotriquetral ligament tears are identified and treated by débridement or repair. The ulnar extrinsic ligaments are assessed for laxity. If laxity is observed, a 1.5-mm electrothermal probe (Arthrocare, Sunnyvale, CA; or Oratec, Menlo Park, CA) is introduced through the 6-R portal. The ulnolunate and ulnotriquetral ligaments are painted with the probe using a stripe technique, leaving sections of untouched ligament in between. The correction of any associated VISI deformity is assessed with a combination of arthroscopy and fluoroscopy.

A midcarpal radial portal is then established. The scapholunate and lunotriquetral joints are inspected and probed for laxity. The TCL is identified as it runs obliquely from the triquetrum, across the proximal corner of the hamate, to the palmar neck of the capitate. A midcarpal ulnar portal is established and used for introduction of the thermal probe. The TCL is then shrunk while the tension is again adjusted with correction of any VISI deformity (Fig. 25-7).

FIGURE 25-7 A, Shrinkage of the arcuate ligament (asterisks) as viewed from the midcarpal radial portal. L, lunate; S, scaphoid.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

A volar radial portal is established by making a 2-cm longitudinal incision in the proximal wrist crease, exposing the flexor carpi radialis tendon sheath. The sheath is divided, and the tendon is retracted ulnarly. The radiocarpal joint space is identified with a 22-gauge needle, and the joint is inflated with saline. A blunt trocar and cannula are introduced through the floor of the flexor carpi radialis sheath, which overlies the interligamentous sulcus between the radioscaphocapitate ligament and the long radiolunate ligament. A 2.7-mm, 30-degree arthroscope is inserted through the cannula. The DRCL can be seen ulnar to the 3-4 portal and underneath the lunate. If laxity is present, the electrothermal probe is introduced through the 3-4 and 4-5 portals and used to shrink the DRCL (Fig. 25-8). The tension of the DRCL can be adjusted by correcting any VISI deformity with a Kirschner wire in the lunate under fluoroscopic control. At the end of the procedure, 0.045-mm Kirschner wires are used to pin the triquetrum to the capitate and hamate in a neutral and reduced position.

FIGURE 25-8 A, View of a dorsal radiocarpal ligament tear (asterisks) from the volar radial portal. B, View of a dorsal radiocarpal ligament tear after shrinkage. L, lunate; R, radius.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

Arthroscopic Findings

There are no arthroscopic findings that are diagnostic of MCI. Inspection of the radiocarpal joint may reveal a nonspecific synovitis. I have seen an associated tear of the DRCL (see Fig. 25-8). In this case, an arthroscopic DRCL repair failed to correct the MCI.¹⁵ Inspection of the midcarpal row may demonstrate erosive lesions along the triquetrum (Fig. 25-9) and the hamate, or both. Laxity of the lunotriquetral ligament may be seen though this is not invariable. Midcarpal arthroscopy may reveal laxity of the TCL (Fig. 25-10).

FIGURE 25-9 Erosion of the triquetrum (asterisk) is seen from the midcarpal ulnar portal. L, lunate; T, triquetrum.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

FIGURE 25-10 Laxity of the triquetrohamate-capitate ligament (asterisks). C, capitate; H, hamate.

(Courtesy of David J. Slutsky, MD, Torrance, California.)

PEARLS& PITFALLS

PEARLS

• Examine the opposite wrist for MCI.

• Examine for a painful midcarpal clunk.

• Videofluoroscopy demonstrates loss of the normal synchronous motion from physiologic dorsal intercalated segmental instability to VISI.

• Perform arthroscopy to assess and treat any associated intercarpal ligament pathology.

• Perform capsular shrinkage for milder forms of MCI.

PITFALLS

• Use rapid fluid irrigation to prevent thermal chondral damage during shrinkage.

• Perform a scaphoid shift test to differentiate the wrist clunk from scapholunate instability.

• A fixed VISI seen on radiography results from other causes.

• No arthroscopic findings are characteristic of MCI.

• Severe MCI is treated with open methods.

CONCLUSIONS

There is a paucity of literature on the use of arthroscopy for MCI. In 2003, Lichtman and associates reported their experience of five patients who underwent an arthroscopic capsular shrinkage.⁶ The average age was 33 years (range, 29 to 57 years). Follow-up averaged 9 months (range, 3 to 18 months). The midcarpal clunk resolved in six of the eight patients with pain resolution. Range of motion decreased by 20% in the flexion/extension plane, whereas grip strengths increased by an average of 15%.

Mason and Hargreaves¹⁶ reported the results of a prospective study of 13 patients (15 wrists) with painful wrist clunking due to PMCI who underwent arthroscopic thermal capsulorrhaphy after at least 6 months of failed conservative treatment. The mean duration of symptoms was 5 years (range, 8 months to 20 years). Preoperatively, patients were evaluated clinically and by fluoroscopic examination, which confirmed a positive ulnar shift test. A thermal probe was applied to the ulnar arm of the arcuate ligament (i.e., the ulnocapitate, ulnotriquetral, and triquetrocapitate ligaments) and to the radial arm (i.e., radioscaphocapitate, long and short radiolunate ligaments, and accessible parts of the dorsal capsule in the radiocarpal and midcarpal joints). Postoperatively, the patients’ wrists were splinted for 6 weeks. Patients were evaluated at a mean follow-up of 42 months (range, 14 to 67 months) by means of the ulnar shift test; grip strength; range of motion; the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire; and a structured questionnaire that included a question on their ability to pour a heavy kettle without wrist clunking. Complete resolution of symptoms occurred in 4 patients and almost complete resolution in the remaining 11 patients. Functional improvement was confirmed by an improvement in the mean DASH score from 34 (range, 13-67; SD 16) preoperatively to 12 (range, 0-48; SD 14) at final follow-up. The ulnar shift test was negative in 12 of 14 wrists that were available for examination. Wrist movement was reduced by a mean of 16 degrees in flexion and 10 degrees in extension in 9 wrists compared with the opposite side, but there was no reduction in grip strength.