Relationship between size of disc and early postoperative outcomes after lumbar discectomy

Previous studies suggest that patients with larger disc herniations (greater than 6 mm) will have better outcomes following discectomy. This has not been validated in a large series of patients.

We sought to empirically evaluate this relationship in a series of patients who had data collected prospectively as part of a randomized trial.

This retrospective review included 63 consecutive adult patients who underwent a single-level, primary lumbar discectomy. Outcomes were VAS for leg and back pain and the modified oswestry disability index (MODI). Statistical tests were used to compare patients using different cutoffs of preoperative disc diameters and disc volume removed. Regression analysis was performed to determine if there was a relationship between outcomes and the measured parameters.

While patients who achieved substantial clinical benefit (SCB) for MODI had larger disc diameters, this relationship was not found for leg or back pain for any of the measured parameters. Using 5, 6, 7, or 8 mm as a cutoff for disc diameter demonstrated no differences. Regression analysis did not demonstrate a significant relationship between disc volume removed and final MODI scores.

While patients with larger disc herniations on average might have a greater likelihood of superior clinical outcomes, the previously suggested "6 mm rule" was not supported.