Association between 3D knee kinematics and clinical phenotypes in people with Patellofemoral Pain Syndrome: a prospective comparative study

Background : Patellofemoral pain syndrome (PFPS) includes static and dynamic lower limb dysfunctions. We used a pragmatic classification differentiating 3 main clinical phenotypes: PFPS with 1) objective patellar displacement, 2) altered extra-patellar alignment, and 3) no altered alignment. Objective : To compare kinematic gait parameters associated with the 3 main clinical phenotypes. Method : Prospective comparative study. We used the KneeKG® device (EMOVI) to assess 3D femoro-tibial (FT) rotations during gait. We assessed static FT alignment using EOS imaging, foot posture and knee function using clinical tests, neuromuscular activity using EMG and an isokinetic device, and single-leg stability using posturography. Joint angle time series were compared between phenotypes using Statistical Parametric Mapping. We used the Kruskall-Wallis test (Dwass-Steel test for post-hoc analyses) for group comparisons, p<0.05. Results We included 45 participants: 29 (64.4%) females, mean (SD) age 36.3 (13.7) years, BMI: 22.9 (3.8) kg.m ² , symptom duration: 8.1 (9.6) years. Four (9%) participants were classified as Phenotype 1, 25 (56%) as Phenotype 2 and 10 (22%) as Phenotype 3. Six (13%) participants fitted both Phenotypes 1 and 2; thus, we added Phenotype 4. Knee valgus angle during the gait loading phase differed significantly between phenotypes (p=0.03); Phenotypes 2 and 4 had the highest value (2.1 [1.9]° and 2.1 [2.3]°, respectively). Static knee valgus angle also differed (p=0.014), with Phenotype 4 having the highest value (3.6 [2.0]°). No other parameters differed between groups. Conclusion Increased knee valgus during the gait loading phase was the only kinematic parameter that differed significantly between the phenotypes. Knee valgus may differentiate PFPS phenotypes. Trial registration : NCT05441332 (ClinicalTrials.gov). Date of registration 14/06/2022, date of first publication 2022-07-01, date of last modification 2023-09-07. https://clinicaltrials.gov/study/NCT05441332?cond=Patello%20Femoral%20Syndrome&term=PHENOPAT&rank=1