Description
BACKGROUND: Anterior knee pain (AKP), defined as pain around or behind the patella, is the most frequent reason why active young people consult a knee surgeon. The pathogenesis of AKP is still debated despite its high prevalence and the abundance of research on this matter. Chronic pain ethiology is multifactorial and psychological factors have been shown to play a role in the course of AKP. One of the mechanisms that might explain chronification in AKP, and therefore, non-satisfactory outcomes after treatment, is the phenomenon of central sensitization (CS). It is defined as the increased responsiveness of nociceptive neurons in the central nervous system. There is evidence that CS can contribute to the development and persistence of chronic pain, which might be explained by an alteration of the facilitating and inhibiting mechanisms at the medullary and cerebral levels.
OBJECTIVES: Define the prevalence of CS in AKP female patients. Analyze if there is an association between CS and the magnitude of pain, disability, quality of life and psychological impairment.
METHODS: The data of a total of 44 AKP female patients aged between 15 and 50 (mean 27.7 years) recruited consecutively from hospital outpatient knee clinics were prospectively included in this study. The patients had no antecedents of knee trauma or surgery and no history of injury or disease of the nervous system. There were also 50 healthy female controls aged between 16 and 46 (mean 26.1 years). CS was evaluated using the Central Sensitization Inventory (CSI). Quality of life was evaluated using EuroQoL-5D questionnaire. Self-reporting of clinical pain intensity was obtained on a Visual Analogue Scale. The Kujala Knee Scale and IKDC form used to evaluate disability. Anxiety and depression were evaluated using the Hospital Anxiety and Depression Subscale (HAD). Kinesiophobia was measured with the Tampa Scale for Kinesiophobia (TSK) and catastrophizing by means of the Pain Catastrophizing Scale (PCS).
RESULTS: 36% of the AKP patients and only 4% of the healthy controls presented a centralization phenomenon (p<0.01). AKP patients with CS have a higher level of disability according to the Kujala Scale and higher levels of anxiety and depression than AKP patients without CS. The score on the CSI in AKP patients correlated weakly with disability and quality of life, moderately with anxiety and depression. However, no association was observed between CSI score and pain intensity, nor with catastrophizing and kinesiophobia. A multivariate logistic regression analysis demonstrated that only depression was statistically significant in the prediction of the presence of CS (odds ratio 1.45; 95% CI 1.07 to 1.96).
CONCLUSION: AKP patients have a significantly higher prevalence of CS in comparison to what has been reported for the general population. This finding suggests the presence of an altered pain modulation in a subgroup of these patients, and its identification could help to select a multimodal treatment plan.
