Dynamic CT Assessment of Distal Radioulnar Instability

Transcription

1 Dynamic CT Assessment of Distal Radioulnar Instability Poster No.: P-0114 Congress: ESSR 2016 Type: Educational Poster Authors: S. Dumonteil, M. A. Shah, A. Srikanthan, V. Ejindu, N. Papadakos; London/UK Keywords: Trauma, Education and training, Diagnostic procedure, CT, Musculoskeletal joint DOI: /essr2016/P-0114 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 24

2 Learning objectives To understand and apply the different radiological techniques for assessing Distal Radioulnar Joint instability using standard radiographs, MRI, ultrasound and dynamic CT imaging. Page 2 of 24

3 Background Distal radioulnar joint (DRUJ) instability is an important cause of ulnar sided wrist pain, often associated with distal radial fractures. DRUJ instability can also manifest as an isolated injury and is occasionally seen in the context of DRUJ arthritis. DRUJ instability is often underappreciated both clinically and radiologically, leading 1 potentially to long-term morbidity if the diagnosis is missed. By convention, the stability of the DRUJ is described by the relationship of the distal ulnar to the radius with dorsal subluxation being more common than volar. Several radiological techniques exist to assess the stability of the DRUJ, including plain radiographs, ultrasound and dynamic CT. Multiple different evaluation methods using dynamic CT have been proposed to measure the degree of dorsal or volar translation of the distal 2 ulnar relative to the radius. The technical details of these different techniques and lack of a standardised methodology can be confusing for both radiologists and clinicians when assessing patients suspected of having DRUJ instability. In this review, we look at the main radiological techniques used to assess for DRUJ instability with the aim of clarifying the technical details and increasing the reliability of using the different methods available. Page 3 of 24

4 Imaging findings OR Procedure Details Radiography Plain radiographs can be helpful in identifying features suggestive of DRUJ subluxation secondary to DRUJ instability. Dorsal subluxations are most common and result from a fall onto a pronated hand, while volar subluxations occur less frequently, usually from forced supination. Radiographic features suggestive of instability include widening of the radioulnar joint on the AP view, significant shortening of the radius, fracture at the base of the ulnar styloid 3 or obvious dislocation on the lateral view. On a true lateral view of the wrist, a radiolunar distance, as measured by the dorsal projection of the distal ulnar beyond the dorsal cortex of the radius should not measure 4 more than 6mm (Fig. 1 on page 9). MRI MRI findings in DRUJ instability are dependent on the relevant mechanism involved and include an abnormal relationship of the distal ulnar with the sigmoid notch. Other findings may include ligamentous and capsular injuries such as disruption of the radioulnar 8 ligaments (Fig. 2 on page 9). Dynamic Computed Tomography Dynamic CT evaluation performed with the wrist in supination, neutral and pronation can be used to diagnose subluxation of the DRUJ. A number of different methods have been proposed, each of which have been reported to demonstrate or quantify DRUJ instability 2,5,6,7. Park et al. evaluated these methods in normal subjects to quantify the normal 2 range. We describe the dynamic CT protocol and use example cases to demonstrate the different calculation methods used to assess DRUJ instability. Page 4 of 24

5 Dynamic CT Protocol At our local institution patients are scanned prone with both arms overhead (superman position) in the pronated (Fig. 3 on page 10), supinated (Fig. 4 on page 11) and neutral position (Fig. 5 on page 12). 0.63mm axial slices are acquired with no reformats required (pronated and supinated at approximately 70 ) (Fig. 6 on page 13). Measurement methodology 1. The Subluxation Ratio Method A line is drawn through the dorsal and volar margins of the sigmoid notch. Two perpendicular lines are drawn though the dorsal and volar margins of the sigmoid notch. The distance that the ulnar head lies either dorsal or volar to these lines is measured with the ratio of this distance to the distance of the sigmoid notch calculated 2. Dorsal displacement is recorded as positive and volar translation as negative. Comment on method: Selection of the dorsal and volar sigmoid notch points are relativley consistent with lines perpendicular to the sigmoid notch used to assess the presence of subluxation. This allows for a more reproducible method with lower interobserver variation is the method we use in our unit. 2. As such, this The normal values for measuring translation of the DRUJ are shown in table 1 2 Table 1: Subluxation Ratio Wrist Position Mean 95% Confidence Interval Neutral to 0.26 Pronation to 0.39 Supination to 0.03 Page 5 of 24

6 Example cases: 2 Example cases are shown using the Subluxation Ratio Method (Fig. 7 on page 14 & Fig. 8 on page 15) 2. The Radioulnar Line Method The distance that the ulnar head lies either dorsal or volar to lines drawn through the dorsal and volar aspects of the ulnar and radial borders of the radius is measured with the 5 ratio of this distance to the distance of the sigmoid notch calculated. Initially described as abnormal if the position of the ulna crossed these lines, but the degree of displacement has subsequently been quantified 2,5. Dorsal displacement is recorded as positive and volar translation as negative. Comment on method: Whilst this method is the simplest, selection of the position of the dorsal and volar lines is subjective, resulting in potential false positives and interobserver variability 2,5 The normal values for measuring translation of the DRUJ are shown in table 2 2 Table 2: Radioulnar Line Wrist Position Mean 95% Confidence Interval Neutral to 0.26 Pronation to 0.35 Supination to 0.00 Example cases: 2 Example cases are shown using the Radioulnar Line Method (Fig. 9 on page 16 & Fig. 10 on page 17) Page 6 of 24

7 3. The Epicentre Method The halfway point between the centre of the styloid process to the centre of the ulnar head is marked. A line is drawn from this point perpendicular to a line drawn through the dorsal and volar margins of the sigmoid notch. The ratio of the distance between this perpendicular line and mid point of the sigmoid to the length of the sigmoid notch 6 is calculated. Dorsal displacement from the midpoint is recorded as positive and volar translation as negative. Comment on method: This method relies on the identification of the axis of rotation of the DRUJ, which has the advantage of minimising the effect of normal translation of the ulnar head during rotation of the forearm. However, this method is dependent on the subjective selection of discreet reference points on the ulna head with the potential for error and variation in results The normal values for measuring translation of the DRUJ are shown in table 3 2,6. 2 Table 3: Epicentre Wrist Position Mean 95% Confidence Interval Neutral to 0.23 Pronation to 0.18 Supination to 0.21 Example cases: 2 Example cases are shown using the Epicentre Method (Fig. 11 on page 18 & Fig. 12 on page 19) 4. The Radioulnar Ratio Method Page 7 of 24

8 Using concentric circles, the centre of the ulnar head is found. A perpendicular line is drawn from this point to a line drawn through the dorsal and volar margins of the sigmoid notch. The ratio of the distance from this point to the volar aspect of the sigmoid notch 7 to the length of the sigmoid notch is calculated. Comment on method: This method has the advantage of eliminating the reliance on more subjective reference points such as the centre of the ulnar styloid and whilst sensitive in demonstrating early subluxation this is the most technically challenging method, making it less reliable The normal values for measuring translation of the DRUJ are shown in table 4 2,7. 2 Table 4: Radioulnar Ratio Wrist Position Mean 95% Confidence Interval Neutral to 0.69 Pronation to 0.86 Supination to 0.52 Example cases: 2 Example cases are shown using the Radioulnar Ratio Method (Fig. 13 on page 20 & Fig. 14 on page 21) Ultrasound DRUJ instability and associated surrounding soft tissue injuries can also be assessed using dynamic ultrasound with comparison to the normal contralateral side. However this method is highly subjective and potentially technically challenging. In addition, a clear objective measure of the degree of subluxation can be difficult to quantify. Page 8 of 24

9 Images for this section: Fig. 1: Lateral radiograph of the wrist, which demonstrates 7mm of dorsal subluxation of the distal ulnar, suggestive of DRUJ instability. Page 9 of 24

10 Fig. 2: Axial T1-weighted fat suppressed MR of the right wrist shows dorsal displacement of the ulnar head, capsular high signal soft tissue thickening, extensor compartment tenosynovitis and a DRUJ effusion. Page 10 of 24

11 Fig. 3: Dynamic CT protocol: Pronated position Page 11 of 24

12 Fig. 4: Dynamic CT protocol: Supinated position Page 12 of 24

13 Fig. 5: Dynamic CT protocol: Neutral position Page 13 of 24

14 Fig. 6: Axial CT images demonstrating the different positions acquired during dynamic CT evaluation of the DRUJ Page 14 of 24

15 Fig. 7: Subluxation Ratio calculation in the neutral position = CD/AB. Distance AB = 14.4mm Distance CD = -1.5mm. Ratio = -1.5/14.4 = This degree of volar displacement is within normal limits for the neutral position. Page 15 of 24

16 Fig. 8: Subluxation Ratio calculation in the pronated position = CD/AB. Distance AB = 14.7mm Distance CD = +7.3mm. Ratio = +7.3/14.7 = This degree of dorsal displacement is outside normal limits for the pronated position. Page 16 of 24

17 Fig. 9: Radioulnar line calculation in the neutral position = CD/AB. Distance AB = 14.4mm Distance CD = -1.2mm. Ratio = -1.2/14.4 = This degree of volar displacement is within normal limits for the neutral position. Page 17 of 24

18 Fig. 10: Radioulnar line calculation in the pronated position= CD/AB. Distance AB = 14.7mm Distance CD = +6.3mm. Ratio = +6.3/14.7 = This degree of dorsal displacement is outside normal limits for the pronated position. Page 18 of 24

19 Fig. 11: Epicentre calculation in the neutral position = CD/AB. Distance AB = 14.4mm Distance CD = +1.6mm. Ratio = +1.6/14.4 = This degree of dorsal is within normal limits for the neutral position. Page 19 of 24

20 Fig. 12: Epicentre line calculation in the pronated position = CD/AB. Distance AB = 14.7mm Distance CD = +3.5mm. Ratio = +3.5/14.7 = This degree of dorsal displacement is outside normal limits for the pronated position. Page 20 of 24

21 Fig. 13: Radioulnar Ratio calculation in the neutral position = AD/AB. Distance AB = 14.4mm Distance AD = 7.2mm. Ratio = 7.2/14.4 = This is within normal limits for the neutral position. Page 21 of 24

22 Fig. 14: Radioulnar Ratio calculation in the pronated position = AD/AB. Distance AB = 14.7mm Distance AD = 13.7mm. Ratio = 13.7/14.7 = This degree of dorsal displacement is outside normal limits for the pronated position. Page 22 of 24

23 Conclusion Radiological assessment of DRUJ instability can be assessed using different methods. Familiarity with the different techniques is important to confidently make this frequently missed and important diagnosis. Page 23 of 24

24 References Squires JH, England E, Mehta K, Wissman RD. The role of imaging in diagnosing diseases of the distal radioulnar joint, triangular fibrocartilage complex, and distal ulna. American Journal of Roengenology 2014: 203(1): Park MJ, Kim JP. Reliability and Normal Values of Various Computed Tomography Methods for Quantifying Distal Radioulnar Joint Translation. J Bone Joint Surg Am, 2008: Wheeless' Textbook of Orthopaedics [Online]. Available at: [Accessed: 1 May 2016]. Nakamura R, Horii E, Imaeda T, Tsunoda K, Nakao E. Distal radioulnar joint subluxation and dislocation diagnosed by standard roentgenography. Skeletal Radiol 1995; 24:91-94 Mino DE, Palmer AK, Levinsohn EM. The role of radiography and computerized tomography in the diagnosis of subluxation and dislocation of the distal radioulnar joint. J Hand Surg Am 1983; 8:23-31 Wechsler RJ, Wehbe MA, Rifkin MD, Edeiken J, Branch HM. Computed tomography diagnosis of distal radioulnar subluxation. Skeletal Radiol. 1987;16:1-5. Lo IK, MacDermid JC, Bennett JD, Bogoch E, King GJ. The radioulnar ratio: a new method of quantifying distal radioulnar joint subluxation. J Hand Surg [Am].2001;26: Saifuddin, AS, Musculoskeletal MRI. 2nd ed. Boca Raton: Taylor & Francis Group. Page 24 of 24