Are Patellofemoral Pain And Anterior Knee Pain Different Populations? Comparing Measures Of Pain And Physical And Self-reported Function

Anterior knee pain (AKP) is a general term used to define all diagnoses where pain is in the anterior knee. Patellofemoral pain (PFP) is also defined by pain in the anterior knee but only after all other diagnoses have been excluded. These two populations are often referred to interchangeably; however, it is unknown to what extent these populations overlap or are independent in various outcome measures. PURPOSE: To investigate whether people with AKP and PFP differ in their pain-related outcomes, and neuromuscular and self-reported function. METHODS: We included 51 participants (PFP = 15, AKP = 13, pain-free controls = 23). For the knee pain groups, we assessed symptom duration (months), worst knee pain in the previous week (visual analogue scale), and knee pressure pain thresholds (PPT). We assessed peak knee extension torque using a dynamometer. We used the superimposed burst technique to quantify central activation ratio and transcranial magnetic stimulation to quantify active motor thresholds for quadriceps. For self-reported function, we assessed physical activity level (international physical activity questionnaire), knee-related function (anterior knee pain scale, knee osteoarthritis outcome score), and global physical and mental health. We compared groups using One-way ANOVA (or Kruskal-Wallis) or independent t-test (or Mann-Whitney U). Alpha was set to p < .05. RESULTS: We observed significantly lower PPT at the patellar tendon (p = .012) in those with AKP, as well as decreased global (p = .012) and mental (p = .002) health compared to pain-free controls (Table 1). Knee pain groups self-reported lower function compared to pain-free controls (p < .001), but no differences between them (Table 1). CONCLUSION: While most measures of physical and self-reported function were not different between those with AKP and PFP, the threshold and location of pain differed. Those with AKP also demonstrated worse physical and mental global health. - Table 1. Demographics, pain-related outcomes, neuromuscular function, and self-reported function in people with anterior knee pain (AKP) and patellofemoral pain (PFP) compared to controls PFP AKP Control p-value Sex (F/M) 7/8 9/4 13/10 Age (years)a 23.18 ± 5.6 24.82 ± 7.3 23.20 ± 3.3 .276 BMI (Kg/m 2 ) 24.7 ± 4.3 28.6 ± 7.0 24.5 ± 4.4 .060 Physical activity (IPAQ) 3673 ± 2653.1 2155.9 ± 1779.4 2722.5 ± 2660.5 .319 Pain-related Outcomes Worst pain (VAS) 45.00 ± 14.5 45.23 ± 19.7 - .972 Symptom duration (months)a 29.27 ± 33.8 44.46 ± 43.6 - .363 PPT - Vastus medialis 3.65 ± 2.1 2.91 ± 1.2 4.13 ± 1.7 .139 PPT - Vastus lateralis 3.93 ± 2.22 3.54 ± 1.3 4.11 ± 1.4 .832 PPT - Quadriceps tendona 4.82 ± 2.8 4.14 ± 2.2 5.40 ± 2.3 .055 PPT - Patellar tendon 3.63 ± 1.5 3.00 ± 1.6 4.90 ± 2.1 .012 ‡ Neuromuscular Function Knee extension peak torque (Nm/Kg)a 2.85 ± 0.7 2.49 ± 0.6 2.64 ± 0.8 .399 Central Activation Ratio (%)a 95.44 ± 4.5 94.70 ± 6.0 97.51 ± 2.0 .535 Active Motor Threshold (%) 35.09 ± 5.1 37.09 ± 8.3 32.59 ± 5.6 .149 Self-Reported Function Global Physical Health Scorea 13.20 ± 1.4 12.00 ± 1.5 13.65 ± 1.4 .012 ‡ Global Mental Health Scorea 15.40 ± 2.4 12.31 ± 2.1 15.30 ± 2.7 .002 *‡ AKPSa 76.87 ± 7.1 79.92 ± 7.0 98.13 ± 5.0 <.001 †‡ KOOS – Pain subscalea 72.77 ± 15.0 72.86 ± 12.6 99.52 ± 1.4 <.001 †‡ KOOS – Symptom subscalea 77.85 ± 15.3 78.84 ± 10.5 97.05 ± 4.1 <.001 †‡ KOOS – ADL subscalea 84.41 ± 15.3 87.21 ± 10.1 99.55 ± 1.6 <.001 †‡ KOOS – Sport subscalea 72.67 ± 18.9 74.62 ± 22.3 97.83 ± 8.4 <.001 †‡ KOOS – QOL subscalea 57.92 ± 14.8 64.90 ± 18.3 95.10 ± 8.8 <.001 †‡ KOOS – PF Subscalea 66.97 ± 17.4 69.06 ± 20.8 98.91 ± 1.92 <.001 †‡ Abbreviations: BMI=Body mass index; IPAQ = International physical activity questionnaire; VAS=Visual analogue scale; AKPS = Anterior knee pain scale; KOOS=Knee injury and osteoarthritis outcome score; ADL = Activities of daily living; QOL = Quality of life; PF=Patellofemoral; PPT = Pressure pain threshold.aNon-parametric tests; *Significant difference between PFP and AKP; †Significant difference between PFP and control; ‡Significant difference between AKP and control Supported by: This study was funded by a University of Toledo Small Grant.