2002 - University of Washington Bone and Joint Sources

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Accuracy and Reproducibility of Step and Gap Measurements from Plain Radiographs After Intra-Articular Fracture of the Distal Radius WREN V. MCCALLISTER, M.D., JEFFREY M. SMITH, M.D., JEFF KNIGHT, B.S., AND THOMAS E. TRUMBLE, M.D. Recent reports have highlighted the important relationship between residual intra-articular displacement and the long-term outcome of distal radius fractures. There appears to be a general consensus that accelerated development of arthritis and worsened severity of degenerative changes is associated with residual step-off displacements greater than 1 to 2 millimeters. Therefore, to improve clinical outcome after intraarticular fracture of the distal radius, many reports in the literature strongly advocate surgical reduction of fragments with articular incongruities greater than 1 to 2 millimeters. In each of these studies, the intra-articular stepoff and gap displacements were measured in millimeters using plain radiographs. Definitive standards for describing and quantifying articular surface incongruity do not exist. Kreder et al. in 1996 attempted to standardize the technique for measuring intra-articular displacement of distal radius fractures. Sixteen observers examined six radiographs of healed intra-articular distal radius fractures and found that, “…even experienced clinicians did not readily agree on the size of step and gap deformity.” Specifically, they found that two experienced observers chosen at random to measure step-off and gap displacement would differ by 3 millimeters or more at least 10% of the time, while the same observer making repeat measurements would be expected to differ by 2 millimeters at least 10% of the time. Singer also demonstrated significant interobserver variability in the measurement of intraarticular distal radius fracture fragment displacement using plain radiographs. To date, the accurate and reliable measurement of intra-articular fracture displacements of less than 2 millimeters from plain radiographs has not been established. The purpose of this study was to determine the accuracy and reproducibility of measured step-off and gap displacements involving the articular surface of the distal radius. Our hypothesis was that step-off and gap displacements of 2 millimeters or less would show poor accuracy and reproducibility for both intra- and inter-observer measurements. This study differs from others in that by using cadaver specimens, we have created a gold standard for the fracture displacements. Earlier studies, lacking such a gold standard, were limited to comparisons among observers and could not comment on the accuracy of measurement. Further, our cadaver model mimics intra-articular fracture in the acute setting. As Kreder et al. acknowledge, “It may well be that some parameters (such as step and gap deformity) are more readily quantified in the acute setting, since fracture lines have not been obscured by the healing process.” Finally, by computing tolerance limits, we attempt to define a reliable threshold for the accuracy and reliability of plain film radiography in the setting of intra-articular distal radius fractures. Such information has value to the clinician in the decisionmaking process regarding the use of CT imaging. METHODS A Melone three-part fracture was created in cadaver forearms to generate a total of 12 combinations of step and gap displacement (Figure 1). The range of step deformity was 3.5mm (0.5 min, 4.0 max) and the range of gap deformity was 3.9mm (0.1 min, 4.0 max). The radiographs were examined by 22 physicians (divided into three groups based on skill level: Group 1: six R1 and R2 level orthopaedic surgery residents; Group 2: four R4 senior orthopaedic surgery residents on the Hand service, five Hand Fellows; Group 3: six experienced Attending hand surgeons and one musculoskeletal radiologist) in a blinded, randomized fashion using a standardized technique. Twice each physician (range 3 weeks to Step-off Gap Inter Intra Inter Intra ICC * 0.78 0.81 0.85 0.89 κκ ** 0.64 0.65 0.65 0.76 Tolerance (mm) 2.58 1.76 2.51 1.61 Table 1: Results for inter- and intra-observer measurements (see Methods for explanation). * Landis & Koch agreement criteria: 0.80 almost perfect. 2002 ORTHOPAEDIC RESEARCH REPORT 25
RESULTS Table 1 shows the overall results for this study. For all data in this study, there were no statistically significant differences based upon skill level. The overall average observation was accurate to within .62 ± .53 millimeters (95% C.I. .59 to .65). Radiographs in which the beam was parallel to the plane of fracture had an observer accuracy of .58 ± .47 millimeters. For radiographs of specimens number two, four and six, which did not have the x- ray beam parallel to the plane of fracture, observer accuracy decreased to .72 ± .70 millimeters (p 2mm). Tolerance limits were calculated to describe the value x for which 95% of all measurements will be within ± x 90% of the time. The accuracy of raters was determined by calculating the accuracy of measurement, mean and standard deviation for each observer. Fernandez DL, Geissler WB. Treatment of displaced articular fractures of the radius. J Hand Surg [Am]. 1991 May;16(3):375-84. Knirk JL, Jupiter JB. Intra-articular fractures of the distal end of the radius in young adults. J Bone Joint Surg Am. 1986 Jun;68(5):647-59. Kreder HJ, Hanel DP, McKee M, Jupiter J, McGillivary G, Swiontkowski MF. X- ray film measurements for healed distal radius fractures. J Hand Surg [Am]. 1996 Jan;21(1):31-9. Trumble TE, Schmitt SR, Vedder NB. Factors affecting functional outcome of displaced intra-articular distal radius fractures. J Hand Surg [Am]. 1994 Mar;19(2):325-40. 26 2002 ORTHOPAEDIC RESEARCH REPORT
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