Measurement Variability in the Evaluation of the Proximal Junction in Distraction-based Growing Rods Patients

Proximal junctional kyphosis (PJK) is a known complication of spinal fusion and has been shown to occur in the setting of growing rod instrumentation. Previous studies have shown good reliability in measuring PJK in adolescent idiopathic scoliosis.

Four pediatric orthopaedic spine surgeons measured the proximal junction in 10 patients with growing rod instrumentation using 2 methods. In method 1, measurements were made from the inferior endplate of the upper instrumented vertebrae (UIV) to the superior endplate of 1 level above the UIV. In method 2, measurements were made from the inferior endplate 2 levels below the UIV to the superior endplate 2 levels above the UIV. These measurements were repeated 1 week later.

Method 1 had an intraobserver variability of ±13.2 degrees and interobserver variability of ±21.6 degrees, whereas method 2 had an intraobserver variability of ±18.3 degrees and interobserver variability of ±20.7 degrees.

Interobserver variability of PJK is >20 degrees. As PJK is commonly defined as >10 degrees of kyphosis above the UIV, measurement of PJK in patients with distraction-based growing rods on lateral radiographs has too much variability to be useful.

Level III-diagnostic studies.