While successful surgical treatments to confer DRUJ stability were well-documented, most of these treatments comprised either prolong immobilization or intrinsic TFCC repair or extrinsic ligament reconstruction following internal fixation of DRF (13–19), which may result in joint stiffness and delayed functional recovery for prolong immobilization, and the steep learning curve of repair or reconstruction of soft-tissue stabilizers for the DRUJ may hinder the application of these treatments to the setting of acute injury.
From biomechanical perspective of DRUJ stability, TFCC served as the primary static stabilizer while DIOM, though with some debate in recent biomechanical study (20), served as the secondary static stabilizer, and Arimitsu et al had been proved that the osteotomy performed proximal to the ulnar origin of the DIOM during ulnar shortening has better DRUJ stability compared to the distal osteotomy, especially in the coexistence of the DOB (8). The origin of the DOB was located at the distal ulnar proximal to the ulnar head while the insertion of the DOB was located at the sigmoid notch of the radius (21). Therefore, it is possible to tighten the DOB by moving the distal fracture fragment of DRF containing the insertion of the DOB distally, thereby resembling the biomechanical effect of the DOB in stabilizing DRUJ during proximal ulnar shortening. On the other hand, previous anatomy and biomechanics review had suggested that DRUJ instability in Galeazzi type fracture could be managed by anatomical reduction of radius fracture due to regain of the DOB’s tension (22). Hence, we hypothesized that radius distraction could treat intraoperative DRUJ instability during volar plating of DRF by further DOB tightening, and our previous preliminary study (9) demonstrated the stabilizing effect of radius distraction to treat intraoperative DRUJ instability following volar plating fixation of acute DRF. However, it was unknown whether radius distraction could ameliorate this DRUJ instability in long-term follow-up. Therefore, we conduct this retrospective study to check long-term outcome of radius distraction on stabilizing DRUJ, and the results of our case series showed that radius distraction could not only prevent DRUJ from symptomatic instability necessitating revision surgery in long term follow-up, but also provide compatible functional outcome compared with other surgical technique dealing with DRF-related DRUJ instability (13, 15).
For ulnar variance measurement, we measured the ulnar variance at post-operative 1 month rather than post-operative immediately to ensure that the radiograph of injured wrist was taken in the same neutral position to avoid change of ulnar variance by different pronation-supination (23). There were 30 patients with negative ulnar variance in our case series at the final follow-up, and none of them suffered from avascular necrosis of lunate bone or other radiocarpal arthritis; this result also corresponds to the finding of the recent biomechanical study that radius distraction beyond native ulnar variance may not cause excessive loading of the radial-lunate contact stress (24), which may affect the metaphyseal bony purchase of volar locking plate, leading to distal screw migration and shortening of radial length as well as increase of ulnar variance. Although there was a statistical difference comparing the ulnar variance at post-operative 1-month follow-up and at the final follow-up, the significant statistical difference of ulnar variance between the injured wrists and the uninjured wrists at the final follow-up had proved the promising longevity of radius distraction. On the other hand, the distraction distance judging from ulnar variance seems to be too small to make the stabilizing effect feasible. However, the biomechanics study by Arimitsu et al(8) had found that significantly stability of the DRUJ could obtained with even 1 mm of proximal ulnar shortening, and the anatomy study by Moritomo et al(25) had found that the DOB acts as isometric stabilizer and its average length was about 25.4mm to 26mm, and typical load-deformation curve from tendons and ligaments had revealed that tendons and ligaments can be strained to between 5 and 7 % without damage(26). Therefore, we could find that the mean distracted length of the DOB without damage should be 1.3mm ~ 1.8mm, which corresponded with the results of radius distraction in terms of the difference of ulnar variance, mean 1.4mm at the final follow-up, from both hands in our case series.
For long-term DRUJ stability, all the patients got firm endpoint from the radioulnar stress test at the final follow-up. Although none of the patients suffered from symptomatic DRUJ translation or subluxation from the radioulnar stress test, there were still two cases with Grade 1 of DRUJ instability. Both patients with Grade 1 of DRUJ instability had increase of ulnar variance (2.2 mm and 1.2 mm, in each) at the final follow-up compared to the ulnar variance (0.5 mm and 0 mm, in each) at 1 month after the surgery. We assumed that the loss of ligamentotaxis by fracture subsidence could cause loosening of the DOB, which may lead to instability of DRUJ if initial DRUJ stabilizers other than the DOB were not fully healed. Meanwhile, since the prevalence of TFCC injuries increases with age (27), it is possible that their injured wrist might have suffered from inherent degenerative TFCC injuries as their contralateral uninjured wrist, which was not uncommon in our case series.
The role of fixation for ulnar styloid fracture in volar plating of DRFs is still a controversial issue. Traditionally, ulnar styloid fractures with concomitant DRFs were treated conservatively (28). There have been some studies suggesting that the outcome of DRFs was not significantly affected by fixation of ulnar styloid fracture (29–35). Fixation of ulnar styloid fracture after distal radius volar plating is generally not suggested if no DRUJ instability is detected (29, 36). Therefore, none of our cases with ulnar styloid fracture got internal fixation since intraoperative DRUJ stability was successfully achieved after radius distraction. Moreover, these 24 cases had Grade 0 of DRUJ instability at the final follow-up, and there was no significant difference in NRS of pain score, DASH, or MMWS between the cases of ulnar styloid nonunion and other cases with ulnar styloid fracture in our series at the final follow-up. Although ulnar styloid fracture could lead to DRUJ instability and hinder the outcome of DRFs with concomitant ulnar styloid fracture in some literature review (2, 37), it seems that the stabilizing effect of DIOM tightening in radius distraction could confer long term DRUJ stability even in the presence of ulnar styloid fracture, thereby achieving satisfactory functional outcomes no matter ulnar styloid is healed or not.
There are several limitations to mention in our study. First, our study was retrospective and the final case volume for cohort study was relatively small due to long-term follow-up. Second, we do not have a control group without radius distraction for comparison since it always needs surgical intervention for persisted DRUJ instability after fixation of DRFs to avoid prolong immobilization, and therefore we compared our results with the results in existing literature about DRF-related DRUJ instability. Third, there was no direct radiographic evidence of radius distraction due to lack of radiographic image prior to injury as comparator, and some radiographic parameters such as radial inclination, volar tilt, radial shift, and are not recorded, which may affect functional scores of the wrist joint and the relative stability of the DRUJ. Forth, the radioulnar stress test is not objective; since the radioulnar stress test has been proved to possess high inter-rater agreement (38) and we added two blinded evaluators to determine the DRUJ stability during the clinic visit. Although we didn’t perform reliability test in this study, we considered it as a practical examination to detect DRUJ instability following the fixation of DRF. Fifth, we didn’t explore the pathogenesis of DRUJ instability such as TFCC injury and DRUJ ligament injury by either arthroscopy or magnetic resonance imaging. Sixth, there were only plain film radiograph for pre/post-operative evaluation, and it would be better to evaluate the presence of osteoarthritis of DRUJ or degree of DRUJ subluxation from computed tomography scan or magnetic resonance imaging. Lastly, there was no direct biomechanical evidence to prove that tightened DOB alone in DRFs with intraoperative DRUJ instability could help the DRUJ to regain stability, and further biomechanical study focusing on the DOB’s role in DRUJ stability should be considered to make this inference more persuasive.