Targeted intervention for patellofemoral pain (TIPPS): psychosocial characteristics of clinical subgroups

Background: Patellofemoral pain (PFP) is a specific musculoskeletal disorder that causes significant pain and dysfunction around the knee cap and knee joint leading to long term limitation in societal participation and physical activity. PFP is a condition commonly referred for physiotherapy intervention, however long term outcomes are poor. We have undertaken a study to explore the presence of clinical subgroups within the PFP population based on the scores of 6 tests that could be used within routine clinical practice. Our research study identified 3 clinical subgroups: Strong subgroup; Weak and Tight subgroup; Pronated feet subgroup. Purpose: There is mounting evidence that factors such as gender and activity levels influence development and outcome in PFP. There is also interest in whether psychosocial factors and different pain mechanisms play a role in determining potential subgroups. Therefore the main objective of this study was to explore interactions between demographic, clinical and psychosocial characteristics and clinical subgroups. Methods: Observational study, at one time point (commencement of physiotherapy). Demographic (Age; Body Mass Index (BMI)), clinical (Time since onset; Patellar skin fold; Tibialis anterior/patella temperature index; Cold Knees questions), and psychosocial characteristics (numeric pain rating scale (NPRS); International physical activity questionnaire (IPAQ); Modified functional index questionnaire (MFIQ); Short Leeds assessment neuropathic sign and symptoms (SLANSS); EQ-5D-5L; Hopkins symptoms check list (HSCL); Movement specific reinvestment scale (MSRS)) were assessed. Differences between the three clinical subgroups were explored using ANOVA, with post hoc tests, or chi-squared tests. Results: Of 127 participants, 66% were female and the mean age was 26 years (SD 5.7), BMI 25.5 (SD 5.8), time since onset 45 months (SD 55) and MFIQ was 34 (SD 17). The strong subgroup had significant higher function, quality of life and there were proportionally more males in this subgroup. The weak and tight subgroup significantly had the highest BMI, and there was a trend towards the lowest levels of activity. The pronated feet subgroup was significantly younger at time of first assessment and there was a trend for higher mean scores for neuropathic pain (SLANSS). There was no difference in mean scores of other characteristics across the subgroups. Conclusion(s): This study, the largest on PFP subgrouping, provides data on other characteristics of PFP patients and suggests significant differences in non-clinical factors between clinical subgroups. The latter provides support for the existence of clinical subgroups and possible insight into potential intervention strategies. For example, higher function and quality of life in the strong subgroup may suggest a focus on movement control is required whereas the higher BMI in the weak and tight subgroup may suggest adjunct weight management strategies may be needed. The neuropathic pain in the pronated feet subgroup may warrant desensitisation interventions. Implications: Demographic and psychosocial characteristics may be important factors to consider in addition to clinical factors in PFP patients. Such factors are increasingly important in managing patients with other musculoskeletal problems. The next step is to understand the relationship between these factors and treatment outcome. Keywords: Patellofemoral pain; Psychosocial; Subgrouping