ORIGINAL ARTICLE
How Critical is Patient Positioning in Radiographic Assessment of the Hip in Cerebral Palsy When Measuring Migration Percentage? Katie Kinch, MSc(Dist), MCSP,* Donald M. Campbell, FRCS Ed, (Tr&Orth),w James G.B. Maclean, FRCS (Tr&Orth),z Heather S. Read, BSc, FRCS Ed (Tr&Orth),y Simon L. Barker, BSc(Hons), FRCS Ed (Tr&Orth), MD,8 James E. Robb, MD, FRCS,z and Mark S. Gaston, MA, FRCS Ed(Tr&Orth), PhD#
Background: Migration percentage (MP) is an accepted method of assessing lateral displacement of the femoral head in children with cerebral palsy (CP). Difficulty in positioning of patients for pelvic radiography remains a concern for the reliability of the MP. Methods: This 2-part quantitative study examined 100 anteroposterior pelvic radiographs for children with CP. Fifty were from a region that had a positioning protocol for hip surveillance of children with CP and 50 images were from a region without. Images were assessed for acceptability of position in relation to hip abduction/adduction and/or pelvic rotation. Ten images deemed Acceptable or Borderline from the region with no protocol were then randomly selected. MP was measured on 2 separate occasions by 5 children’s orthopaedic surgeons and statistically analyzed for intrarater and interrater reliability. Results: There was no statistically significant difference in the acceptability of images between the 2 regions with 60% to 66% of the images meeting the criteria outright. When allowances were made for slight variation of abduction/adduction within 5 degrees, 74% to 80% of the images were acceptable. Reliability was variable with limits of agreement between 4.96% and 15.15%. Observers more familiar with the software measuring package had higher reliability within and between occasions. Variability within and between observers decreased as MP increased. Conclusions: Poor positioning did not appear to be the main reason for the variation in reliability of MP. Repeat measurements were reliable although standardized technique, training, and familiarity with software measuring programmes did influence outcomes.
From the *NHS Fife, Victoria Hospital, Kirkcaldy; wNinewells Hospital and Medical School, Dundee; zPerth Royal Infirmary, Perth; yRoyal Hospital for Sick Children, Glasgow; 8Royal Aberdeen Children’s Hospital, Aberdeen; zSchool of Medicine, University of St Andrews, St Andrews; and #Royal Hospital for Sick Children, Edinburgh, Scotland. The authors declare no conflicts of interest. Reprints: Katie Kinch, MSc (Dist), MCSP, Children and Young People’s Physiotherapy, Queen Margaret Hospital, Dunfermline, Fife, Scotland. E-mail: [email protected]. Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
756 | www.pedorthopaedics.com
Level of Evidence: This is a Level I diagnostic study divided into 2 parts. The first half is a retrospective study of pelvic radiographs of children with CP as part of their annual/biannual orthopaedic assessment. The second half is an interrater and intrarater reliability study of MP measurement. Key Words: migration percentage, hip surveillance program, AP pelvic radiographs, cerebral palsy, Gross Motor Functional Classification System (J Pediatr Orthop 2015;35:756–761)
H
ip displacement and dislocation are common in children with cerebral palsy (CP)1 and the clinical consequences include pain, fixed deformity, loss of function, and difficulty with personal care.2,3 Hip dislocation is potentially preventable with close surveillance and monitoring,4 but clinical examination alone is unreliable and repeat radiologic measurements are paramount to ensure a robust hip screening program (HSP).5–7 Established HSPs use a standard positioning protocol for anteroposterior (AP) pelvis images2,7,8 and the success and benefits of hip surveillance in CP to prevent displacement are well established.2,8–10 Migration percentage (MP) was proposed by Reimers11 as a means of assessing lateral displacement of the femoral head in children. MP is a widely accepted measurement of hip displacement in children with CP2,4,8,9 and the evidence supporting the accuracy of the MP is increasing.7,12,13 MP in the normal pediatric population has been established as 16% in children aged less than 4 years and 24% in children aged older than 12 years.14 Established HSPs suggest that an MP of >33% as the threshold for intervention or increased observation and recommend consideration of surgery for hips with a MP of >40%.5,8 The suggested position to achieve an acceptable AP pelvis radiograph in a HSP is the same as the routine position for AP pelvis radiographs for hips currently used in radiology departments.8,15 Modification such as elevating the legs to flatten the lumbar spine in the presence of hip flexion contracture/spasm may be required for
J Pediatr Orthop
Volume 35, Number 7, October/November 2015
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Pediatr Orthop
Volume 35, Number 7, October/November 2015
children with CP.8 Otherwise, a neutral pelvic orientation with regard to femoral abduction/adduction, internal/ external rotation, or pelvic rotation/inclination is the standard position suggested by radiology texts for AP pelvis radiographs.15 Although a national HSP did not exist in Scotland before May 2013, many children with CP did have regular (annual or biannual) hip radiographs to assess hip displacement. MP was not routinely measured on hip radiographs in some centers, as has been noted elsewhere.13 Similarly, some departments used a specific protocol for positioning for pelvic radiography, whereas others did not. We therefore wished to investigate if a specific positioning protocol for radiographic assessment of the hip in children with CP was required to achieve a reliable MP measurement. Our hypothesis was that standardized positioning of the child with CP undergoing pelvic radiography would result in more accurate MP measurements than in those children who were x-rayed in departments that did not use a standardized positioning protocol for pelvic radiography for children with CP.
METHODS A total of 100 pelvic radiographs were obtained from 2 regions in Scotland where neither had specialist pediatric radiology departments. One region used a radiographic positioning protocol specifically for hip surveillance of children with CP and one did not. Focal film distance and centering of the beam were not specified in
How Critical is Patient Positioning
the positioning protocol as variations in magnification would not affect the measurement of the MP which, being a ratio, does not rely on absolute measurements. Inclusion criteria were children with a diagnosis of CP who had AP pelvis images taken in 2011. One postoperative pelvic radiograph from a child who had had a hip reconstruction was excluded. Approval from the Caldicott Guardians of both regions with regard to patient confidentiality was obtained. Images were accessed according to the Community Heath Index number (a unique patient identification number) to eliminate bias of where the image was obtained. No bias in terms of additional attention to positioning occurred as this was a retrospective study.
RADIOGRAPHIC MEASUREMENTS Part 1: Acceptability of Images In the first part of this study, images were assessed based on the following criteria to ensure acceptable pelvic orientation (Figs. 1A, B): (1) Femoral shaft angle: the angle between the femoral shaft and Hilgenreiner’s line had to be
How Critical is Patient Positioning in Radiographic Assessment of the Hip in Cerebral Palsy When Measuring Migration Percentage? Katie Kinch, MSc(Dist), MCSP,* Donald M. Campbell, FRCS Ed, (Tr&Orth),w James G.B. Maclean, FRCS (Tr&Orth),z Heather S. Read, BSc, FRCS Ed (Tr&Orth),y Simon L. Barker, BSc(Hons), FRCS Ed (Tr&Orth), MD,8 James E. Robb, MD, FRCS,z and Mark S. Gaston, MA, FRCS Ed(Tr&Orth), PhD#
Background: Migration percentage (MP) is an accepted method of assessing lateral displacement of the femoral head in children with cerebral palsy (CP). Difficulty in positioning of patients for pelvic radiography remains a concern for the reliability of the MP. Methods: This 2-part quantitative study examined 100 anteroposterior pelvic radiographs for children with CP. Fifty were from a region that had a positioning protocol for hip surveillance of children with CP and 50 images were from a region without. Images were assessed for acceptability of position in relation to hip abduction/adduction and/or pelvic rotation. Ten images deemed Acceptable or Borderline from the region with no protocol were then randomly selected. MP was measured on 2 separate occasions by 5 children’s orthopaedic surgeons and statistically analyzed for intrarater and interrater reliability. Results: There was no statistically significant difference in the acceptability of images between the 2 regions with 60% to 66% of the images meeting the criteria outright. When allowances were made for slight variation of abduction/adduction within 5 degrees, 74% to 80% of the images were acceptable. Reliability was variable with limits of agreement between 4.96% and 15.15%. Observers more familiar with the software measuring package had higher reliability within and between occasions. Variability within and between observers decreased as MP increased. Conclusions: Poor positioning did not appear to be the main reason for the variation in reliability of MP. Repeat measurements were reliable although standardized technique, training, and familiarity with software measuring programmes did influence outcomes.
From the *NHS Fife, Victoria Hospital, Kirkcaldy; wNinewells Hospital and Medical School, Dundee; zPerth Royal Infirmary, Perth; yRoyal Hospital for Sick Children, Glasgow; 8Royal Aberdeen Children’s Hospital, Aberdeen; zSchool of Medicine, University of St Andrews, St Andrews; and #Royal Hospital for Sick Children, Edinburgh, Scotland. The authors declare no conflicts of interest. Reprints: Katie Kinch, MSc (Dist), MCSP, Children and Young People’s Physiotherapy, Queen Margaret Hospital, Dunfermline, Fife, Scotland. E-mail: [email protected]. Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
756 | www.pedorthopaedics.com
Level of Evidence: This is a Level I diagnostic study divided into 2 parts. The first half is a retrospective study of pelvic radiographs of children with CP as part of their annual/biannual orthopaedic assessment. The second half is an interrater and intrarater reliability study of MP measurement. Key Words: migration percentage, hip surveillance program, AP pelvic radiographs, cerebral palsy, Gross Motor Functional Classification System (J Pediatr Orthop 2015;35:756–761)
H
ip displacement and dislocation are common in children with cerebral palsy (CP)1 and the clinical consequences include pain, fixed deformity, loss of function, and difficulty with personal care.2,3 Hip dislocation is potentially preventable with close surveillance and monitoring,4 but clinical examination alone is unreliable and repeat radiologic measurements are paramount to ensure a robust hip screening program (HSP).5–7 Established HSPs use a standard positioning protocol for anteroposterior (AP) pelvis images2,7,8 and the success and benefits of hip surveillance in CP to prevent displacement are well established.2,8–10 Migration percentage (MP) was proposed by Reimers11 as a means of assessing lateral displacement of the femoral head in children. MP is a widely accepted measurement of hip displacement in children with CP2,4,8,9 and the evidence supporting the accuracy of the MP is increasing.7,12,13 MP in the normal pediatric population has been established as 16% in children aged less than 4 years and 24% in children aged older than 12 years.14 Established HSPs suggest that an MP of >33% as the threshold for intervention or increased observation and recommend consideration of surgery for hips with a MP of >40%.5,8 The suggested position to achieve an acceptable AP pelvis radiograph in a HSP is the same as the routine position for AP pelvis radiographs for hips currently used in radiology departments.8,15 Modification such as elevating the legs to flatten the lumbar spine in the presence of hip flexion contracture/spasm may be required for
J Pediatr Orthop
Volume 35, Number 7, October/November 2015
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Pediatr Orthop
Volume 35, Number 7, October/November 2015
children with CP.8 Otherwise, a neutral pelvic orientation with regard to femoral abduction/adduction, internal/ external rotation, or pelvic rotation/inclination is the standard position suggested by radiology texts for AP pelvis radiographs.15 Although a national HSP did not exist in Scotland before May 2013, many children with CP did have regular (annual or biannual) hip radiographs to assess hip displacement. MP was not routinely measured on hip radiographs in some centers, as has been noted elsewhere.13 Similarly, some departments used a specific protocol for positioning for pelvic radiography, whereas others did not. We therefore wished to investigate if a specific positioning protocol for radiographic assessment of the hip in children with CP was required to achieve a reliable MP measurement. Our hypothesis was that standardized positioning of the child with CP undergoing pelvic radiography would result in more accurate MP measurements than in those children who were x-rayed in departments that did not use a standardized positioning protocol for pelvic radiography for children with CP.
METHODS A total of 100 pelvic radiographs were obtained from 2 regions in Scotland where neither had specialist pediatric radiology departments. One region used a radiographic positioning protocol specifically for hip surveillance of children with CP and one did not. Focal film distance and centering of the beam were not specified in
How Critical is Patient Positioning
the positioning protocol as variations in magnification would not affect the measurement of the MP which, being a ratio, does not rely on absolute measurements. Inclusion criteria were children with a diagnosis of CP who had AP pelvis images taken in 2011. One postoperative pelvic radiograph from a child who had had a hip reconstruction was excluded. Approval from the Caldicott Guardians of both regions with regard to patient confidentiality was obtained. Images were accessed according to the Community Heath Index number (a unique patient identification number) to eliminate bias of where the image was obtained. No bias in terms of additional attention to positioning occurred as this was a retrospective study.
RADIOGRAPHIC MEASUREMENTS Part 1: Acceptability of Images In the first part of this study, images were assessed based on the following criteria to ensure acceptable pelvic orientation (Figs. 1A, B): (1) Femoral shaft angle: the angle between the femoral shaft and Hilgenreiner’s line had to be
