Intraobserver and Interobserver Measurement Variability of the Rib-Vertebral Angle Difference

Area of Science:

• Orthopedics
• Radiology
• Pediatric Medicine

Background:

• The rib-vertebral angle difference (RVAD) is crucial for distinguishing progressive from resolving infantile idiopathic scoliosis (IIS).
• RVAD measurements <20 degrees often indicate spontaneous resolution, while >20 degrees suggest progression requiring intervention.
• Understanding RVAD measurement variability is essential to differentiate true curve changes from observer error.

Purpose of the Study:

• To mathematically determine the intraobserver and interobserver measurement variability of the RVAD in patients with IIS.
• To quantify the reliability of RVAD measurements in the context of infantile idiopathic scoliosis.

Main Methods:

• A convenience sample of 50 patients with IIS was analyzed.
• Seven observers (orthopaedic residents, pediatric radiologist, pediatric orthopaedic surgeons) measured the RVAD twice, with a minimum 3-week interval.
• Intraobserver and interobserver variability were calculated using three statistical methods with 95% prediction/confidence limits.

Main Results:

• Three statistical methods yielded consistent results for measurement variability.
• Intraobserver variability for RVAD measurements was approximately 24 degrees.
• Interobserver variability for RVAD measurements was approximately 23 degrees.

Conclusions:

• The significant measurement variability of the RVAD necessitates caution when used alone for medical decision-making and patient counseling in IIS.
• Clinical utility of RVAD in isolation for infantile idiopathic scoliosis management is limited by substantial observer error.