Carly E Jones1,2, Anthony P Cooper3,4, Jonathan Doucette1,2, Lawrence L Buchan1,5, David R Wilson1,4, Kishore Mulpuri3,4, Agnes G d'Entremont6,7. 1. Centre for Hip Health and Mobility, Vancouver, BC, Canada. 2. Department of Engineering Physics, University of British Columbia, Vancouver, BC, Canada. 3. BC Children's Hospital, Vancouver, BC, Canada. 4. Department of Orthopaedics, University of British Columbia, Vancouver, BC, Canada. 5. Department of Mechanical Engineering, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, BC, V6T 1Z4, Canada. 6. Centre for Hip Health and Mobility, Vancouver, BC, Canada. agnes.dentremont@mech.ubc.ca. 7. Department of Mechanical Engineering, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, BC, V6T 1Z4, Canada. agnes.dentremont@mech.ubc.ca.
Abstract
OBJECTIVE: Slipped capital femoral epiphysis (SCFE) is a hip disorder where the femoral head slips relative to the neck at the physis. Appropriate treatment of SCFE depends on the severity of the slip, commonly categorised using the Southwick (SW) angle. The SW angle is measured in the frog-lateral leg position, which can be painful and potentially unattainable for patients. The purpose of this study is to determine how errors in frog-lateral radiograph positioning affect measured SW angles and slip classifications. METHODS: Models of SCFE hips were produced from one CT scan of a normal hip; 360 deformities were created. SW angles were measured from a simulated frog-lateral position. Femoral lateral head-neck angles (LHNA; equivalent to SW in incorrect frog-lateral plane) were measured over a range of 837 incorrect frog-lateral leg positions with positioning errors in flexion and/or internal/external rotation. RESULTS: Seventy-six per cent of all imaging position-deformity combinations had error in the reported angle (>1° difference between LHNA and SW). Of those, 70% had <5°, 24% had 5° to 10°, and 6% had >10° of error from the actual SW angle. Three per cent of LHNAs that had >10° error resulted from <10° of positioning error. CONCLUSIONS: If the patient is limited in flexion or external rotation, more diagnostic testing should be considered if error in the reported slip measurement would affect treatment decisions or if accurate severity classification is needed for research. Small positioning errors in moderate and severe slips can cause a > 10° LHNA error; additional three-dimensional imaging should be considered.
OBJECTIVE: Slipped capital femoral epiphysis (SCFE) is a hip disorder where the femoral head slips relative to the neck at the physis. Appropriate treatment of SCFE depends on the severity of the slip, commonly categorised using the Southwick (SW) angle. The SW angle is measured in the frog-lateral leg position, which can be painful and potentially unattainable for patients. The purpose of this study is to determine how errors in frog-lateral radiograph positioning affect measured SW angles and slip classifications. METHODS: Models of SCFE hips were produced from one CT scan of a normal hip; 360 deformities were created. SW angles were measured from a simulated frog-lateral position. Femoral lateral head-neck angles (LHNA; equivalent to SW in incorrect frog-lateral plane) were measured over a range of 837 incorrect frog-lateral leg positions with positioning errors in flexion and/or internal/external rotation. RESULTS: Seventy-six per cent of all imaging position-deformity combinations had error in the reported angle (>1° difference between LHNA and SW). Of those, 70% had <5°, 24% had 5° to 10°, and 6% had >10° of error from the actual SW angle. Three per cent of LHNAs that had >10° error resulted from <10° of positioning error. CONCLUSIONS: If the patient is limited in flexion or external rotation, more diagnostic testing should be considered if error in the reported slip measurement would affect treatment decisions or if accurate severity classification is needed for research. Small positioning errors in moderate and severe slips can cause a > 10° LHNA error; additional three-dimensional imaging should be considered.
Authors: Carly E Jones; Anthony P Cooper; Jonathan Doucette; Lawrence L Buchan; David R Wilson; Kishore Mulpuri; Agnes G d'Entremont Journal: J Pediatr Orthop Date: 2017-06 Impact factor: 2.324
Authors: Edward Abraham; Mark H Gonzalez; Surya Pratap; Farid Amirouche; Prasant Atluri; Patrick Simon Journal: J Pediatr Orthop Date: 2007 Oct-Nov Impact factor: 2.324
Authors: Nils Wirries; Gesche Heinrich; Alexander Derksen; Michael Schwarze; Stefan Budde; Henning Windhagen; Thilo Floerkemeier Journal: J Orthop Date: 2021-07-12
Authors: Emily S Sullivan; Carly Jones; Stacey D Miller; Kyoung Min Lee; Moon Seok Park; David R Wilson; Kishore Mulpuri; Agnes G d'Entremont Journal: J Pediatr Orthop B Date: 2022-03-01 Impact factor: 1.041