Background: Lumbar canal and foraminal stenosis are common degenerative conditions causing neurogenic claudication and radiculopathy. Indirect decompression via pedicle screw distraction, utilizing ligamentotaxis, has emerged as an alternative to direct decompression. However, the quantitative relationship between the magnitude of rod distraction and the resulting canal and foraminal opening has not been defined in Nigerian patients.

Methods: A retrospective cohort study of 63 patients who underwent pedicle screw insertion and rod distraction alone for lumbar canal and foraminal stenosis at the National Orthopaedic Hospital Dala, Kano, from January 2021 to June 2025 was conducted. Preoperative and postoperative MRI was used to measure the anteroposterior canal diameter and foraminal diameter from L2 to L5. Intraoperative pedicle distance at insertion and after distraction was recorded. Correlation and linear regression analyses were performed to determine the relationship between distraction magnitude and canal/foraminal opening.

Results: The mean distraction achieved was 3.2±1.1 mm per level. The mean increase in anteroposterior canal diameter was 2.4±0.8 mm (range 1.2–4.2 mm). The mean increase in foraminal diameter was 2.1±0.7 mm (range 1.0–3.8 mm). There was a strong positive correlation between rod distraction and canal opening (r=0.84, p<0.001) and between rod distraction and foraminal opening (r=0.81, p<0.001). The derived predictive equations were: Canal opening (mm) = 0.68 + 0.54 × Distraction (mm) and Foraminal opening (mm) = 0.52 + 0.50 × Distraction (mm).

Conclusions: Rod distraction produces predictable, measurable increases in lumbar canal and foraminal dimensions. The derived equations provide a practical tool for estimating the expected decompression effect and guiding the magnitude of distraction during surgery.