Safe, simple, and valid position for obtaining flexion-extension radiographs to assess instability in patients with lumbar spondylolisthesis: one specific instruction can make a difference.

Objective: In lumbar spondylolisthesis, conventional standing flexion-extension radiography can yield varying results depending on the patient's effort and cooperation. Previous research suggested that assisted flexion radiography provides larger flexion with a significantly greater change in lumbar lordosis (ΔLL) and increased sagittal translation (ST), posterior opening (PO), segmental angulation (SA), and instability detection rates. In this study, the authors aimed to identify a safe, simple, and valid position for obtaining functional radiographs to evaluate abnormal instability in lumbar spondylolisthesis.

Methods: Consecutive patients diagnosed with L4-5 degenerative lumbar spondylolisthesis were included. The patients underwent upright and extension radiography and three different flexion radiography positions: conventional flexion (CF), hand-knee (HK), and hand-ankle (HA). Measurements included ΔLL, ST, PO, and SA, with instability rates compared between the three flexion techniques.

Results: This study included 117 patients (81 women, mean age of the study sample 76.8 years). The median ΔLL values were 10.8° (interquartile range [IQR] 5.2°-18.2°) in the CF position, 30.0° (IQR 21.0°-41.1°) in the HK position, and 32.1° (IQR 23.0°-42.4°) in the HA position, with significant differences noted (p < 0.05). For PO and SA, significant differences were observed between the techniques (p < 0.05). ST medians were CF 5.5% (IQR 3.6%-8.1%), HK 9.5% (IQR 7.7%-11.1%), and HA 9.7% (IQR 7.4%-11.4%), with HK and HA positions differing significantly from the CF position (p < 0.001), but not the HK from the HA position (p = 0.15). Instability detection rates were 29.1% in the CF position, 76.1% in the HK position, and 76.9% in the HA position, with significant differences between the HK, HA, and CF positions (p < 0.001), but not between the HK and HA positions (p > 0.99).

Conclusions: The study showed that HK and HA flexion radiographs provided greater ΔLL, ST, PO, SA, and better instability detection than the CF position. Given its safety and simplicity, the HK position is suitable for detecting abnormal lumbar mobility in degenerative lumbar spondylolisthesis.