Trajectories in severe persistent pain after groin hernia repair: a retrospective analysis.
Objectives Severe persistent post-surgical pain (PPSP) remains a significant healthcare problem. In the third most common surgical procedure in the U.K., groin hernia repair, including 85,000 surgeries, estimated 1,500-3,000 patients will annually develop severe PPSP. While the trajectory of PPSP is generally considered a continuation of the acute post-surgery pain, recent data suggest the condition may develop with a delayed onset. This study evaluated pain-trajectories in a consecutive cohort referred from groin hernia repair-surgeons to a tertiary PPSP-center. Potential explanatory variables based on individual psychometric, sensory, and surgical profiles were analyzed. Methods Patients completed graphs on pain trajectories and questionnaires on neuropathic pain, pain-related functional assessments, and psychometrics. Surgical records and quantitative sensory testing profiles were obtained. Pain trajectories were normalized, and pre- and post-surgical segments were analyzed by a normalized area-under-the-curve (AUC) technique. Principal component analysis (PCA) was applied to the explanatory variables. Significant PCA-components were further examined using multiple logistic regression models. Results In 95 patients, the AUC identified groups of post-surgical pain trajectories (p<0.0001): group I (n=48), acute high-intensity pain progressing to PPSP; group II (n=28), delayed onset of PPSP; group III (n=7), repeat-surgery gradually inducing PPSP. Data from groups IV (n=3) and V (n=9) were not included in the statistical analysis due to small sample size and data heterogeneity, respectively. The PCA/logistic analyses indicated that neuropathic pain scores, composite pain scores, and pain-related functional assessments were explanatory variables for groups I and II. Conclusions Pain trajectories in PPSP after groin hernia repair are heterogeneous but can be classified into meaningful groups. Examination of pain trajectories, mirroring the transition from acute to severe persistent post-surgical pain, has the potential of uncovering clinically relevant pathophysiological mechanisms.