Trajectory modelling techniques have been developed to determine subgroups within a given population and are increasingly used to better understand intra- and inter-individual variability in health outcome patterns over time. The objectives of this narrative review are to explore various trajectory modelling approaches useful to epidemiological research and give an overview of their applications and differences. Guidance for reporting on the results of trajectory modelling is also covered. Trajectory modelling techniques reviewed include latent class modelling approaches, ie, growth mixture modelling (GMM), group-based trajectory modelling (GBTM), latent class analysis (LCA), and latent transition analysis (LTA). A parallel is drawn to other individual-centered statistical approaches such as cluster analysis (CA) and sequence analysis (SA). Depending on the research question and type of data, a number of approaches can be used for trajectory modelling of health outcomes measured in longitudinal studies. However, the various terms to designate latent class modelling approaches (GMM, GBTM, LTA, LCA) are used inconsistently and often interchangeably in the available scientific literature. Improved consistency in the terminology and reporting guidelines have the potential to increase researchers’ efficiency when it comes to choosing the most appropriate technique that best suits their research questions.

Background: The goals of this study were to examine the trajectory of pediatric chronic postsurgical pain (CPSP) over the first year after surgery and to identify acute postsurgical predictors of CPSP. Methods: Eighty-three children aged 8–18 years (mean 13.8, standard deviation 2.4) who underwent major orthopedic or general surgery completed pain and pain-related psychological measures at 48–72 hours, 2 weeks (pain anxiety and pain measures only), and 6 and 12 months after surgery. Results: Results showed that 1 year after surgery, 22% of children developed moderate to severe CPSP with minimal functional disability. Children who reported a Numeric Rating Scale pain-intensity score ≥ 3 out of 10 two weeks after discharge were more than three times as likely to develop moderate/severe CPSP at 6 months and more than twice as likely to develop moderate/severe CPSP at 12 months than those who reported a Numeric Rating Scale pain score < 3 (6-month relative risk 3.3, 95% confidence interval 1.2–9.0 and 12-month relative risk 2.5, 95% confidence interval 0.9–7.5). Pain unpleasantness predicted the transition from acute to moderate/severe CPSP, whereas anxiety sensitivity predicted the maintenance of moderate/severe CPSP from 6 to 12 months after surgery. Conclusions: This study highlights the prevalence of pediatric CPSP and the role played by psychological variables in its development/maintenance. Risk factors that are associated with the development of CPSP are different from those that maintain it.

This study was designed to determine whether a 4 day perioperative regimen of gabapentin added to celecoxib improves in-hospital rehabilitation and physical function on postoperative day 4 and 6 weeks and 3 months after total knee arthroplasty (TKA). After Research Ethics Board approval and informed consent, 212 patients were enrolled in a randomized, double-blinded, placebo-controlled study. Two hours before surgery, patients received celecoxib 400 mg p.o. and were randomly assigned to receive either gabapentin 600 mg or placebo p.o. Two hours later, patients received femoral, sciatic nerve blocks, and spinal anaesthesia. After operation, patients received gabapentin 200 mg or placebo three times per day (TID) for 4 days. All patients also received celecoxib 200 mg q12 h for 72 h and i.v. patient-controlled analgesia for 24 h. Pain and function were assessed at baseline, during hospitalization, on postoperative day 4 (POD4), and 6 weeks and 3 months after surgery. The gabapentin group used less morphine in the first 24 h after surgery [G=38.3 (29.5 mg), P=48.2 (29.4 mg)] (P<0.0125) and had increased knee range of motion compared with the placebo group in-hospital (P<0.05). There were no differences between groups in favour of the gabapentin group for pain or physical function on POD 4 [95% confidence interval (CI): pain: −1.4, 0.5; function: −6.3, 2.0], 6 weeks (95% CI: pain: 0.1, 1.9; function: −0.2, 6.5) or 3 months (95% CI: pain: −0.2, 1.7; function: −2.2, 4.3) after TKA. In the context of celecoxib, spinal anaesthesia, femoral and sciatic nerve blocks, a dose of gabapentin 600 mg before operation followed by 4 days of gabapentin 200 mg TID decreased postoperative analgesic requirements and improved knee range of motion after TKA. Gabapentin provided no improvement in pain or physical function on POD4 and 6 weeks or 3 months after surgery.

The goal of this study was to follow a cohort of patients undergoing total knee arthroplasty over time to: (1) identify and describe the various pain trajectories beginning preoperatively and for up to 12 months after surgery, (2) identify baseline predictors of trajectory group membership, and (3) identify trajectory groups associated with poor psychosocial outcomes 12 months after surgery. One hundred seventy-three participants (female = 85 [49%]; mean age [years] = 62.9, SD = 6.8) completed pain and psychological questionnaires and functional performance tests preoperatively and 4 days, 6 weeks, and 3 and 12 months after total knee arthroplasty. Using growth mixture modeling, results showed that a 4-group model, with a quadratic slope and baseline pain data predicting trajectory group membership, best fit the data (Akaike information criterion = 2772.27). The first 3 pain trajectories represent various rates of recovery ending with relatively low levels of pain 12 months after surgery. Group 4, the constant high pain group, comprises patients who have a neutral or positive pain slope and do not show improvement in their pain experience over the first year after surgery. This model suggests that preoperative pain levels are predictive of pain trajectory group membership and moderate preoperative pain, as opposed to low or high pain, is a risk factor for a neutral or positive pain trajectory postoperatively. Consistent with previous studies, these results show that postoperative pain is not a homogeneous condition and point to the importance of examining intraindividual pain fluctuations as they relate to pain interventions and prevention strategies.

Background: The goal of this longitudinal study was to examine the associations among psychological factors and pain reports of children and their parents over the 12 month period after pediatric surgery. Materials and methods: Included in the study were 83 children aged 8–18 years undergoing major surgery. In each case, the child and one of their parents completed measures of pain intensity and unpleasantness, psychological function, and functional disability at 48–72 hours, 2 weeks (child only), 6 months, and 12 months after surgery. Results: The strength of the correlation coefficients between the psychological measures of the parent and their child increased significantly over time. There was a fair level of agreement between parent ratings of child acute and chronic pain (6 months after surgery) and the child's actual ratings. Parent and child pain anxiety scores 48–72 hours after surgery interacted significantly to predict pain intensity, pain unpleasantness, and functional disability levels 2 weeks after discharge from hospital. Parent pain catastrophizing scores 48–72 hours after surgery predicted child pain intensity reports 12 months later. Conclusion: These results raise the possibility that as time from surgery increases, parents exert greater and greater influence over the pain response of their children, so that by 12 months postsurgery mark, parent pain catastrophizing (measured in the days after surgery) is the main risk factor for the development of postsurgical pain chronicity.