The value of computed tomography in detecting distal radio ulnar   joint instability after a distal radius fracture

This study evaluated the value of computed tomography scans for the diagnosis of distal radioulnar joint instability. A total of 46 patients, conservatively treated for a unilateral distal radius fracture, were evaluated. Clinical instability was tested using the stress test and clunk test. A computed tomography scan of both wrists was performed in pronation and supination. Two independent observers reviewed the computed tomography scans using: the radioulnar line, subluxation ratio, epicentre and radioulnar ratio methods. Radiological distal radioulnar joint instability was assessed by comparing the measurements of the injured wrist with those of the contralateral uninjured wrists. A total of 22 patients had clinical instability of whom 12 suffered from pain in the injured wrist. Distal radioulnar joint instability was diagnosed on computed tomography in 29 patients. Reliability analysis between clinical and radiological evaluations showed at best moderate, but generally poor agreement. The diagnostic ability of computed tomography for identifying distal radioulnar joint instability seems limited. Introduction Distal radius fractures are common and comprise 17% of all adult fractures (Court-Brown and Caesar, 2006). In the Netherlands, the incidence is 400 fractures per 100,000 people per year (Oskam et al., 1998) and is increasing due to the ageing population. In the literature, distal radioulnar joint (DRUJ) instability, due to or in combination with, a distal radius fracture has been recognized as a potential complication (Lindau et al., 2000) that may cause long-lasting pain and restricted range of motion. The incidence of DRUJ instability after a distal radius fracture is reported to be between 10%–40% (Geissler et al., 1996; Lindau et al., 2000; Stoffelen et al., 1998). Clinical determination of the diagnosis of DRUJ instability remains a challenge (Pickering et al., 2016), due to the low sensitivity, specificity and reproducibility of available clinical tests (Wijffels et al., 2012). Despite these deficiencies, the stress test and clunk test are generally accepted clinical tests for evaluation of DRUJ instability (Jupiter, 2009; Nakamura et al., 1997). Various radiological modalities may be used if physical examination is inconclusive, although these all have limitations (Lindau et al., 2000; May et al., 2002; Szabo, 2006). Conventional radiography of the wrist has a low sensitivity for detecting DRUJ pathology (Pan et al., 2003). Arthrography was of limited direct value and has been replaced by magnetic resonance imaging (Levinsohn et al., 1991). The role of magnetic resonance imaging in detecting DRUJ translation is unclear (Anderson et al., 2008). Computed tomography (CT) seems promising for evaluating DRUJ translation (Kim and Park, 2008; Mino et al., 1985), but the most reliable measuring method is still a matter of debate. Several methods for diagnosing DRUJ translation using CT have been proposed. Mino et al. (1985) were the first to describe CT criteria for DRUJ translation. These were later modified by Nakamura et al. (1996) and supplemented by Lo et al. (2001) and Wechsler et al. (1987). Different guidelines for diagnosing DRUJ instability, based on their measurement techniques, were suggested, all lacking hard criteria for standardization. The absence of pre-determined normal values renders definite statements concerning CT-diagnosed DRUJ instability even more difficult. The agreement between clinical findings and DRUJ translation on CT has not been evaluated in detail. To date, only Kim and Park (2008) studied this in a small group of patients after a short period of follow-up. In this study, we therefore aimed to evaluate the value of CT scans for the diagnosis of DRUJ instability, comparing post-traumatic to contralateral, normal wrists. In addition, the level of agreement between CT findings regarding DRUJ dislocation and clinical DRUJ instability tests was analysed. Materials and methods Patients The institutional medical ethics review board approved this study. All adults that had been conservatively treated for a unilateral distal radius fracture in our hospital between May 2008 and February 2010 were identified from the hospital records. Patients with unstable triangular fibrocartilage complex (TFCC) lesions were not excluded. No further analysis was done regarding the TFCC status. Patients with systemic diseases affecting bones and/or joints, patients with contralateral wrist injury and patients who were unable to give informed consent were excluded. Eligible patients received an invitation letter for a study visit in our clinic and were included for analysis after they had provided written informed consent. Clinical evaluation The patients’ wrists were clinically evaluated for DRUJ instability by an experienced trauma surgeon, who had not been involved in the initial treatment and was blinded for the injured side. Clinical instability was determined using both the stress test and clunk test. Clinical DRUJ instability can be defined as static or dynamic, both to be diagnosed by individual tests. Static DRUJ instability was defined as the existence of pathological movement in the DRUJ when stressed without rotation of the forearm. This can be determined using the stress test. To perform the stress test, the wrist is held in supinated and pronated positions, while the physician attempts to manipulate the distal ulna in dorsal and volar directions. A positive stress test is defined by more laxity when compared with the uninjured side (Kleinman, 2007). Dynamic instability is defined as pathologic movement of the ulna relative to the radius during pronosupination and is tested using the clunk test (Jupiter, 2009). During the clunk test the distal ulna is compressed to the radius between thumb and index finger of the physician, with simultaneous passive pronosupination. The clunk test is considered positive if a ‘clunk’ is palpable for either the patient or examiner (Jupiter, 2009). Pain at rest and during movement was scored on a visual analogue scale (VAS) ranging from 0 (no pain) to 100 (worst imaginable pain) (Huskisson, 1974). Radiological evaluation First, an experienced trauma surgeon (MW) classified the distal radius fractures on the trauma radiographs according to the AO Comprehensive Classification of Fractures (Müller et al., 1991). For further radiological evaluation, CT scans of both wrists were obtained using an Aquilion One (Toshiba Medical Systems) CT-scanner with the patient in prone position with both arms above the head and extended elbows, and with both wrists first in maximal pronation and, during the second run, in maximal supination. Trained radiology assistants subsequently performed postprocessing, which included 2 mm coronal and sagittal reformats, as well as 2mm axial reformats perpendicular to the axis of the styloid process, for each wrist separately. Finally, two trained observers (MW and WS), who were blinded for the clinical results, independently assessed DRUJ translation on the CT scans according to the radioulnar line method, subluxation ratio method, epicentre method and radioulnar ratio method (Kim and Park, 2008; Lo et al., 2001; Park and Kim, 2008). All methods quantify radio-ulnar translation by evaluating the position of the ulna relative to the radius resulting in a ratio (Figures 1 to 4). Prior to the study measurements, the two observers scored and discussed 10 CT-scans of wrists of patients not included in this study, for training purposes. For each method, the mean of the observers’ measurements was calculated for both the injured and the uninjured side. DRUJ instability on the CT scan was defined in two ways. First, the mean translation measurement of the injured wrist was compared with the mean measurements of all the uninjured wrists. The result was determined to show ‘no instability’ when the mean measurement was within two standard deviations of the normal range for the specific method. Second, the results of the injured wrist were compared specifically with the measurements of the patient’s non-injured wrist. DRUJ instability was considered present if the mean measurement for the injured wrist was outside the range of mean measurements (of the two observers) for that patient’s own non-injured wrist. Statistical analysis Agreement on presence of DRUJ instability between the clinical test and CT measurements was evaluated using Cohen’s Kappa. Kappa values were interpreted according to Landis and Koch (1977) with values below 0 indicating no agreement; 0.01 to 0.20, slight agreement; 0.21 to 0.40, fair agreement; 0.41 to 0.60, moderate agreement; 0.61 to 0.80, substantial agreement; and more than 0.81, almost perfect agreement.