Influence of TFCC foveal tear on the location of lunate chondromalacia in ulnar impaction syndrome

Objective: The purpose of this study was to identify the location of lunate chondromalacia and to compare the difference in location according to presence or absence of triangular fibrocartilage complex (TFCC) foveal tear, which induces distal radioulnar joint (DRUJ) instability. Methods: We performed a retrospective study of 97 patients (102 wrists) who were diagnosed with and treated for idiopathic ulnar impaction syndrome (UIS) between 2014 and 2018. Subjects were divided into two groups according to presence or absence of TFCC foveal tear with DRUJ instability. Group I had UIS without a TFCC foveal tear (52 wrists, mean age of 43.2 years), while Group II had UIS with a TFCC foveal tear (50 wrists, mean age of 45.3 years). There was no significant difference in age, sex, or duration of symptoms between the two groups. All patients underwent wrist MR Arthrography (MRA) in the same gantry, and all scanned coronal sections of the lunate were standardized into 10 slices, including the whole anteroposterior width of the lunate. Each slice was sequentially numbered from dorsal to volar side, and the location of chondromalacia was marked in each numbered section. Radiological parameters including ulnar variance and ulnolunate distance (ULD), which indicated the distance between the ulnar head and lunate, were measured in the wrist series. Results: The most frequent location of lunate chondromalacia was slightly to the volar side of the lunate in both groups. Group I showed a higher frequency of chondromalacia in the volar side of the lunate. In Group II, chondromalacia was identified with high frequency not only on the volar side of the lunate but also on the dorsal side. In other words, Group II showed broader chondromalacia in the lunate. There was no significant difference in ulnar variance (Group I, 3.19 ± 1.42 mm; Group II, 2.76 mm ± 1.67 mm) or ulnolunate distance (Group I, 1.66 ± 0.94 mm; Group II, 2.05 mm ± 0.87 mm). The average ULD decreased during radial deviation but increased during ulnar deviation. Conclusion: This study showed that lunate chondromalacia associated with idiopathic ulnar impaction syndrome occurs more frequently on the volar side of the lunate. Also, TFCC foveal tear, which causes DRUJ instability, leads to broader lunate chondromalacia in idiopathic ulnar impaction syndrome. Therefore, further analysis of the pattern of lunate chondromalacia can provide a clue for DRUJ instability.