Lunotriquetral Instability

64 Lunotriquetral Instability

Loryn P. Weinstein and Allen T. Bishop

History and Clinical Presentation

A 48-year-old right hand dominant mechanic presented for evaluation of right ulnar-sided wrist pain. Two weeks earlier he had slipped in his shop and landed on a dorsiflexed wrist. The primary impact was to the hypothenar eminence. Subsequently, he developed intermittent ulnar-sided wrist pain, exacerbated by radialulnar deviation. Grip strength was diminished, and he felt his wrist give way when torquing heavy tools. These symptoms reduced his work productivity and prevented him from participating in his weekly bowling league.

Physical Examination

No wrist swelling or obvious deformity was noted. There was point tenderness dorsally over the triquetrum. Range of motion was diminished in all planes. A painful clunk was palpable with radialulnar deviation. Compression of the triquetrum with a radially directed force elicited pain. Excessive laxity was present with lunotriquetral (LT) ballottement when compared with the contralateral wrist. Grip strength was reduced 20% compared with the contralateral, nondominant side. He was neurovascularly intact.

Diagnostic Studies

Anteroposterior, lateral, and oblique radiographs of the wrist were normal. An arthrogram was obtained (Fig. 64–1).

Relative malalignment between the lunate and the triquetrum may be apparent on lateral radiographs. Bisectors of the lunate and triquetrum intersect to form an LT angle (normal = 14 degrees, range −3 to +31 degrees). Patients with LT dissociation will exhibit a negative angle (mean value = − 16 degrees). A volar intercalated segmental instability (VISI) pattern is present in some (chronic) cases.

Radial deviation and clenched-fist anteroposterior views can be useful. Palmar flexion of the scaphoid and lunate without movement of the triquetrum confirms the loss of proximal row integrity.

Arthrography is a useful imaging tool for LT instability. Passage of dye through the LT interspace documents the presence of a perforation, tear, or dissociation. Age-related LT perforations and tears have been frequently demonstrated in asymptomatic individuals. Therefore, arthrogram findings require clinical correlation. A videotaped arthrogram with motion sequences demonstrating abnormal dye pooling associated with abnormal proximal row kinetics is useful as a confirmatory study.

Bone scans, tomograms, and magnetic resonance imaging (MRI) have limited utility in the setting of LT instability. Standards for MRI of LT ligaments are not yet available.

PEARLS

A standardized PA wrist radiograph yields useful information about ulna variance and impaction.
LT and TFCC pathology often coexist.
Dynamic imaging is useful to confirm the presence of LT pathology.

PITFALLS

Beware of false-positive and false-negative arthrograms Clinical correlation is required.
Viewing the LT articulation from the midcarpal joint is important to exclude nondissociative midcarpal instability.

Figure 64–1. Patient arthrogram.

Differential Diagnosis

Nondissociative midcarpal instability

Lunotriquetral instability

Ulnar impaction syndrome

Triangular fibrocartilage complex (TFCC) injury

Pisotriquetral injury

Extensor carpi ulnaris (ECU) subluxation

The differential diagnosis of ulnar-sided wrist pain is broad (Table 64–1). However, a history of a specific injury with subsequent instability and “clunking” during radial-ulnar deviation suggests relatively few diagnoses. These include LT instability, nondissociative midcarpal instability, TFCC injury, ulnar impaction syndrome, pisotriquetral injury, and ECU subluxation.

**Table 64–1** **Differential Diagnosis**
Diagnosis	Differentiating Findings
Triquetrohamate instability	Antecedent trauma, hyperextension mechanism
TFCC tear	Painful radial-ulnar deviation and clunk
Ulna impaction syndrome	Focal tenderness
Pisotriquetral injury	Positive LT provocative tests
ECU instability	Positive radiograph findings
	Positive arthrogram or arthroscopic exam