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The acetabulum in Perthes' disease: inter-observer agreement and reliability of radiographic measurements
Stefan Huhnstock1, Svein Svenningsen, Are H Pripp
1Orthopaedic Department , Oslo University Hospital, Oslo.
Insights
Sharp's angle is a reliable measure for acetabular changes in Perthes' disease. Acetabular depth-width ratio is reliable with consensus, while other measures show limited agreement.
Area of Science:
- Orthopedics
- Pediatric Radiology
- Skeletal Dysplasias
Background:
- Perthes' disease causes significant radiographic changes in the hip's femoral head and acetabulum.
- Accurate assessment of acetabular remodeling is crucial for predicting outcomes in Perthes' disease.
Purpose of the Study:
- To evaluate the inter-observer agreement and reliability of four radiographic measurements for assessing acetabular changes in Perthes' disease.
- To determine the most reliable radiographic parameters for monitoring acetabular development.
Main Methods:
- 123 children with unilateral Perthes' disease, >50% femoral head necrosis, and age ≥6 years were included.
- Radiographs were taken at diagnosis, 1 year, and 5 years post-diagnosis.
- Three observers measured Sharp's angle, acetabular depth-width ratio (ADR), lateral acetabular inclination (LAI), and acetabular retroversion (ischial spine sign, ISS), with two observers having a consensus meeting prior.
Main Results:
- Sharp's angle demonstrated excellent reliability (ICC > 0.80 with consensus).
- Acetabular depth-width ratio (ADR) showed substantial reliability (ICC = 0.62–0.89) between observers with consensus.
- Lateral acetabular inclination (LAI) and ischial spine sign (ISS) exhibited only fair to good agreement (kappa = 0.20–0.52), indicating lower reliability.
Conclusions:
- Sharp's angle is the most reliable measurement for acetabular changes in Perthes' disease.
- Acetabular depth-width ratio (ADR) is reliable when landmarks are clarified and consensus is established.
- Lateral acetabular inclination (LAI) and ischial spine sign (ISS) are not recommended for routine clinical use due to poor agreement.
Background And Purpose:
Perthes' disease leads to radiographic changes in both the femoral head and the acetabulum. We investigated the inter-observer agreement and reliability of 4 radiographic measurements assessing the acetabular changes.
Patients And Methods:
We included 123 children with unilateral involvement, femoral head necrosis of more than 50%, and age at diagnosis of 6 years or older. Radiographs were taken at onset, and 1 year and 5 years after diagnosis. Sharp's angle, acetabular depth-width ratio (ADR), lateral acetabular inclination (LAI), and acetabular retroversion (ischial spine sign, ISS) were measured by 3 observers. Before measuring, 2 of the observers had a consensus meeting.
Results:
We found good agreement and moderate to excellent reliability for Sharp's angle for all observers (intra-class correlation coefficient (ICC) > 0.80 with consensus, ICC = 0.46-0.57 without consensus). There was good agreement and substantial reliability for ADR between the observers who had had a consensus meeting (ICC = 0.62-0.89). Low levels of agreement and poor reliability were found for observers who had not had a consensus meeting. LAI showed fair agreement throughout the course of the disease (kappa = 0.28-0.52). The agreement between observations for ISS ranged from fair to good (kappa = 0.20-0.76).
Interpretation:
Sharp's angle showed the highest reliability and agreement throughout the course of the disease. ADR was only reliable and showed good agreement between the observers when landmarks were clarified before measuring the radiographs. Thus, we recommend both parameters in clinical practice, provided a consensus is established for ADR. The observations for LAI had only fair agreement and ISS showed inconclusive agreement in our study. Thus, LAI and ISS can hardly be recommended in clinical practice.
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