Chronic Postsurgical Pain Likely Not Predicted by Somatosensory Processing System Signs

Authors of a systematic review published in Pain found that no consistent trends in somatosensory processing system (SPS) signs were observed after surgery and that they are likely not useful for predicting chronic postsurgical pain.

Investigators from Belgium searched publication databases through April 2022 for studies evaluating the SPS following nociceptive-targeted surgeries for musculoskeletal disorders. A total of 18 prospective cohort studies and 3 randomized controlled trials, published between 2000 and 2022, were included in this review.

Outcomes of interest included pressure pain tolerance and thresholds, cold and warmth detection thresholds, cold and heat pain thresholds, vibration detection threshold, pinprick threshold, electrical detection and pain thresholds, light-touch detection threshold, and temporal and spatial summations.

In the first 3 months after total knee arthroplasty, pain pressure thresholds generally improved. This trend was not observed in total hip arthroplasty or sequestrectomy. For pain pressure tolerance threshold, conflicting results were found following sequestrectomy and no change was observed following total knee arthroplasty. No changes in thermal thresholds were observed after total hip or knee arthroplasty, except that local cold pain threshold worsened following total knee arthroplasty. There was weak evidence that vibration detection threshold improved after sequestrectomy and that pinprick pain threshold worsened after total knee arthroplasty. Improvements in temporal and spatial summations were observed after total knee and hip arthroplasties.

At longer-term follow-up evaluation, pressure pain thresholds and pressure pain tolerance thresholds improved after sequestrectomy and total hip arthroplasty, respectively. Few changes in thermal thresholds were reported in longer-term follow-up evaluations; however, cold detection threshold had a positive change following sequestrectomy. Positive changes to pinprick pain and light-touch detection thresholds were observed after total hip arthroplasty. Results in temporal and spatial summations were similar as those observed at short-term follow-up evaluations.

In studies that used changes in SPS signs to predict postsurgical pain, some evidence suggested that changes in pain-related variables over time may predict changes in pressure pain tolerance, conditioned pain modulation, and exercise-induced analgesia over time. Similarly, changes in pressure pain tolerance, conditioned pain modulation, and exercise-induced analgesia over time predicted changes in pain-related variables over time.

The major limitations of this review were that more than half of the included studies had a high risk for bias, and many of the conclusions drawn here had weak evidence to support them.

Study authors concluded, “In general, no consistent evolution of SPS signs comparing pre- and postoperative values and predictors for this evolution in musculoskeletal disorders could be found. In most cases, static quantitative sensory testing did not change or conflicting results were found. On the other hand, dynamic quantitative sensory testing mostly improved after surgery. Worthfully mentioning is that worsening of some SPS signs was only seen at a follow-up of < 3 months after surgery, that conclusions are stronger when evaluating dynamic QST with a follow up of ≥ 3 months after surgery, and that pain improvement over time was an important predictor for improvement of SPS signs.”

This article originally appeared on Clinical Pain Advisor