Back pain surgery results may be overrated

Months following spinal surgery for back pain, patients remember their initial pain as worse than they rated it at the time, reports a recent study in the journal Spine.

A research team, headed by Dr. Ferran Pellis of Hospital Vall d'Hebron, Barcelona, Spain, concluded that studies relying on such after‑the‑fact ratings may overestimate the effectiveness of spinal surgery in relieving chronic back pain.

The researchers studied before‑and‑after ratings made by 58 patients who underwent lumbar fusion surgery for chronic low back pain. Before their operation, all patients completed standard evaluations of back pain and related disability. These prospective ("forward‑looking") ratings were compared with retrospective ("backward‑looking") ratings made an average of three years after surgery.

Patients consistently rated themselves worse than in their original questionnaires, when recalling their preoperative state. For example, on a simple 10‑point scale, the patients' original average pain rating was 7.0. On follow‑up ratings, the patients recalled their pain as being significantly worse, with average rating of 8.2.

Based on the original ratings, surgery produced an average pain reduction of 3.3 points on the 10‑point scale. Yet, if the recalled ratings were used, the average improvement would have been 4.6 points. Similar patterns were noted for other standard ratings of back pain and related disability.

Whether the time since surgery was shorter or longer, the extent of patient recall bias did not differ significantly. The ratings did not vary in any systematic way, so there was no way to adjust for them statistically.

Retrospective studies -- in which patients are asked to remember and rate their state of health before treatment -- are widely used in medical research. Few prior studies, however, have looked at how patients' recollections measure up to actual pretreatment ratings. The use of retrospective studies to assess the results of spinal surgery has increased in recent years.

Relying on such after‑the‑fact pain ratings may give the impression that surgery for back pain is more effective than it actually is, the new results suggest.

"Our study shows that relying on a patient's recall of his or her preoperative status a few months or years after surgery is not a valid method for establishing baseline status when treating low back pain," Dr. Pellis and colleagues concluded.

SOURCE:  "Reliability of Retrospective Clinical Data to Evaluate the Effectiveness of Lumbar Fusion in Chronic Low Back Pain." Pellis, Ferran MD; Vidal, Xavier MD, PhD; Hernandez, Alejandro MD; Cedraschi, Christine PhD; Bago, Joan MD; Villanueva, Carlos MD. Spine. 30(3):365‑368, February 1, 2005.