Ulnocarpal impaction syndrome and ulnar styloid impaction syndrome

Relevant anatomy and biomechanics

Ulnar impaction can produce ulnar-sided wrist pain and can be related to ulnocarpal impaction (UCI) due to an ulnar-positive variance ( Fig. 5.1 ). Palmer et al. demonstrated that there was an inverse relationship between the thickness of the triangular fibrocartilage (TFC) and the ulnar variance: The more positive the ulnar variance, the thinner the TFC. Hara et al. found that the force-transmission ratio was 50% through the scaphoid fossa, 35% through the lunate fossa, and 15% through the TFC in the neutral position. Werner et al. demonstrated that lengthening the ulna by 2.5 mm increased the force borne by the ulna from 18.4% to 41.9% of the total axial load. Shortening of the ulna by 2.5 mm decreased the axial load borne by the ulna to 4.3%. Removal of the articular disk portion of the triangular fibrocartilage complex (TFCC) decreased the load on the intact ulna from 18.4% to 6.2%. The peak pressure at the ulnolunate articulation increased from 1.4 N/mm2 for the unaltered wrist to 3.3 N/mm2 when the ulna was lengthened by 2.5 mm.

Degenerative central tears of the articular disk occur more frequently with advancing age. In a cadaver study of 180 wrist joints, Mikic noted an incidence of 53% over age 60 compared with 7% in the third decade. Clinical experience has shown, however, that not all of these tears are symptomatic. Most symptomatic degenerative tears of the TFCC are related to chronic overloading of the ulnocarpal joint. Primary ulnar impaction is related to an increased ulnar variance. Viegas and Ballantyne dissected 100 cadaver wrists and found a 73% incidence of TFCC tears in specimens with an ulnar-positive variance versus 17% when there was a negative-ulnar variance. Acquired ulnar-positive deformities can occur with distal radius fractures that heal with radial shortening, distal radial growth arrest, and Essex-Lopresti and Galeazzi fractures. Ulnar impaction may also be dynamic and occur with power grip in the pronated position. This is because of the approximate 1.95 cm of radial shortening that occurs as the radius rotates across the ulna during pronation, which leads to a dynamic impingement. UCI syndrome consists of the triad of a TFCC tear, a lunotriquetral (LT) ligament tear, and an ulnar-positive variance ( Video 1-12 ). There is often chondromalacia of the proximal ulnar aspect of the lunate (i.e., a kissing lesion) and there may be chondromalacia of the ulnar head ( Fig. 5.2 A–E).

Mechanism and classification

Acquired ulnar-positive deformities can occur with distal radius fractures that heal with radial shortening, distal radial growth arrest, and Essex-Lopresti and Galeazzi fractures. Deformities can also occur following a radial head excision, due to congenital causes of ulnar-positive variance such as Madelung’s deformity, or due to a premature closure of the distal radius growth plate and following a wrist fusion. Ulnar impaction may also be dynamic and even occur in patients with an ulnar neutral or negative variance during power grip in the pronated position. Friedman et al. noted that a maximum grip effort resulted in an average increase in ulnar variance of 1.95 cm in asymptomatic volunteers. This is because of the approximate 1.95 cm of radial shortening that occurs as the radius rotates across the ulna during pronation which leads to a dynamic impingement. In Palmer’s classification, degenerative TFCC tears are subdivided into five categories: Type IIA: wearing of the TFCC without perforation or chondromalacia. Type IIB: wearing of the TFCC with chondromalacia of the lunate or ulna. Type IIC: true perforation of the TFCC with lunate chondromalacia. Type IID: TFCC perforation plus lunate and/or ulnar chondromalacia and lunotriquetral interosseous ligament (LTIL) tears without carpal instability. Type IIE: TFCC perforation with an LTIL tear and ulnocarpal arthritis.

Diagnosis

Patients with UCI syndrome present with chronic ulnar-sided wrist pain that may be increased by power grip, ulnar wrist deviation, and/or forearm rotation. They may complain of intermittent clicking localized to the ulnar carpus and post-activity swelling, decreased strength, and a loss of wrist and forearm motion. They may experience tenderness over the fovea and possibly the triquetrum and ulnar head. Passive and active ulnar deviation produces pain. The ulnocarpal stress test diagnoses UCI syndrome and is performed by applying axial stress to a maximally ulnar-deviated wrist during pronation and supination. Ulnar styloid triquetral impingement (USTI) occurs in supination and may be confused with UCI (discussed later). Extensor carpi ulnaris (ECU) tendonitis may mimic USTI. The ECU synergy test was found to be highly specific and exploits an isometric contraction of the ECU during resisted radial abduction of the thumb with the wrist in neutral position and the forearm supinated. Recreation of pain along the dorsal ulnar aspect of the wrist is considered to be a positive test result for ECU tendonitis. Diagnostic local anesthetic injections may also help identify the pain generator.

Standard wrist radiographs are obtained to assess for arthritis involving the carpus and distal radioulnar joint (DRUJ) and to measure the ulnar variance. When evaluating ulnar-sided wrist pathology, a zero rotation PA view is essential. This is performed with the shoulder abducted 90 degrees, the elbow flexed 90 degrees, and the wrist in neutral. Because ulnar variance is dynamic, stress PA views can help. A pronated grip view may reproduce a dynamic increase in the ulnar variance. Osteoarthritis changes such as joint space narrowing, sclerosis, and cystic changes or osteophytes can be seen along the ulnocarpal joint.

MRI is the method of choice for diagnosing UCI syndrome. Degenerative tears of the TFCC may be seen as well as focal cartilage defects. Magnetic resonance with intravenous contrast is better for visualizing bone marrow pathology. Marrow edema typically affects the ulnar aspect of the lunate, with or without involvement of the radial aspect of the triquetrum and ulnar head. Subchondral cystic changes appear as low signal intensity on T1-weighted images and high signal intensity on T2-weighted images ( Fig. 5.3 ). If sclerosis is present, low signal intensity on both T1- and T2-weighted images will be seen. A measurement of the ulnar variance using MRI is, however, not accurate because it is difficult to obtain a true anatomic position in the magnet gantry. MR arthrography can be performed by injecting gadolinium in the DRUJ to detect TFCC tears. A dedicated 23-mm wrist coil and 3.0 T magnet can improve the accuracy. One study found that the presence of MRI signs of UCI is a predictor of a good outcome following an arthroscopic wafer resection.

Arthroscopic wafer resection

Wnorowski et al. examined the biomechanical effects of an arthroscopic wafer resection in 9 ulnar-positive cadaver forearms. Each specimen was evaluated biomechanically using axial load cells and pressure-sensitive film to evaluate the effect of serial resection of the TFCC and distal ulna on axial load and ulnar carpal pressures. There was a statistically significant unloading of the ulnar aspect of the wrist after excision of the centrum of the TFCC and resection of the radial two-thirds width of the ulnar head to a depth of subchondral bone resection.