Patellofemoral kinematics in patellofemoral pain syndrome: The influence of demographic factors.

Due to the multifactorial nature of patellofemoral pain, it is often difficult to identify an individual patient's exact cause of pain. Understanding how demographic variability influences these various factors will support improved consensus in regards to the etiology of PF pain. Thus, in this retrospective study, we tested the hypothesis that sex, height, weight, body mass index (BMI), and age influence the determination of between-groups differences in PF kinematics. We included 41 skeletally mature patients with patellofemoral pain and 79 healthy controls. Three-dimensional patellofemoral kinematics were quantified from dynamic magnet resonance images. We ran multiple regression analyses to determine the influence of demographic covariates (age, sex, height, weight, and BMI) on patellofemoral kinematics. Patellar shift was significantly influenced by weight (p = 0.009) and BMI (p = 0.009). Patellar flexion was influenced by height (p = 0.020) and weight (p = 0.040). Patellar tilt and superior displacement were not influence by demographic variables. Age and sex did not influence kinematics. This study supports the hypothesis that demographic parameters influence PF kinematics. The fact that weight, a modifiable measure, influences both patellar shift and flexion has strong implications for future research and clinical interventions. Clinically, weight loss may have a dual benefit of reducing joint stress and maltracking in patients who are overweight and experiencing patellofemoral pain. The influence of key demographics on patellofemoral kinematics, reinforces the clear need to control for population characteristics in future studies. As such, going forward, improved demographic matching between control and patient cohorts or more advanced statistical techniques that compensate for confounding variables are necessary.

Adolescents and adults with patellofemoral pain exhibit distinct patellar maltracking patterns.

BACKGROUND: Chronic idiopathic patellofemoral pain is associated with patellar maltracking in both adolescents and adults. To accurately target the underlying, patient-specific etiology, it is crucial we understand if age-of-pain-onset influences maltracking. METHODS: Twenty adolescents (13.9 ± 1.4 years) and 20 adults (28.1 ± 4.9 years) female patients with idiopathic patellofemoral pain (age-of-pain-onset: < 14 and > 18 years of age, respectively) formed the patient cohort. Twenty adolescents and 20 adults (matched for gender, age, and body mass index) formed the control cohort. We captured three-dimensional patellofemoral kinematics during knee flexion-extension using dynamic MRI. Patellar maltracking (deviation in patient-specific patellofemoral kinematics, relative to their respective age-controlled mean values) was the primary outcome measure, which was compared between individuals with adolescent-onset and adult-onset patellofemoral pain using ANOVA and discriminant analysis. FINDINGS: The female adolescent-onset patellofemoral pain cohort demonstrated increased lateral (P = 0.032), superior (P = 0.007), and posterior (P < 0.001) maltracking, with increased patellar flexion (P < 0.001) and medial spin (P = 0.002), relative to the adult-onset patellofemoral pain cohort. Post-hoc analyses revealed increased lateral shift [mean difference ± 95% confidence interval = -2.9 ± 2.1 mm at 10° knee angle], posterior shift [-2.8 ± 2.1 mm, -3.3 ± 2.3 mm & -3.1 ± 2.4 mm at 10°, 20°& 30°], with greater patellar flexion [3.8 ± 2.6 mm & 5.0 ± 2.8 mm, at 20°& 30°] and medial spin [-2.2 ± 1.7 mm & -3.4 ± 2.3 mm at 20°& 30°]. Axial-plane maltracking accurately differentiated the patient age-of-pain-onset (60-75%, P < 0.001). INTERPRETATION: Age-of-pain-onset influences the maltracking patterns seen in patients with patellofemoral pain; with all, but 1, degree of freedom being unique in the adolescent-onset-patellofemoral pain cohort. Clinical awareness of this distinction is crucial for correctly diagnosing a patient's pain etiology and optimizing interventional strategies.

A Word of Caution for Future Studies in Patellofemoral Pain: A Systematic Review With Meta-analysis.

BACKGROUND: Patellar maltracking is widely accepted as an underlying mechanism of patellofemoral pain. However, methodological differences in the literature hinder our ability to generate a universal quantitative definition of pathological patellofemoral kinematics (patellar maltracking) in patellofemoral pain, leaving us unable to determine the cause of patellofemoral pain. PURPOSE: To systematically review the literature to provide evidence regarding the influence of confounding variables on patellofemoral kinematics. STUDY DESIGN: Systematic review and random effects meta-analysis of control-case studies. METHODS: A literature search of case-control studies that evaluated patellofemoral kinematics at or near full extension and were written in English was conducted using Embase, PubMed, Scopus, and Web of Science up to September 2019. Cases were defined as patients with patellofemoral pain. Studies were eliminated if they lacked quantitative findings; had a primary aim to assess therapy efficacy; or included participants with osteoarthritis and/or previous trauma, pathology, or surgery. A quality assessment checklist was employed to evaluate each study. Meta-analyses were conducted to determine the influence of confounding variables on measures of patellofemoral kinematics. RESULTS: Forty studies met the selection criteria, with quality scores ranging from 13% to 81%. Patient characteristics, data acquisition, and measurement methods were the primary sources of methodological variability. Active quadriceps significantly increased lateral shift (standardized mean difference [SMD]shift = 0.33; P = .0102) and lateral tilt (SMDtilt = 0.43; P = .006) maltracking. Individuals with pain secondary to dislocation had greater effect sizes for lateral maltracking than had those with isolated patellofemoral pain (ΔSMDshift = 0.71, P = .0071; ΔSMDtilt = 1.38, P = .0055). CONCLUSION: This review exposed large methodological variability across the literature, which not only hinders the generalization of results, but ultimately mitigates our understanding of the underlying mechanism of patellofemoral pain. Although our meta-analyses support the diagnostic value of maltracking in patellofemoral pain, the numerous distinct methods for measuring maltracking and the limited control for cofounding variables across the literature prohibit defining a single quantitative profile. Compliance with specific standards for anatomic and outcome measures must be addressed by the scientific and clinical community to establish methodological uniformity in this field.

Patellofemoral Pain in Adolescents: Understanding Patellofemoral Morphology and Its Relationship to Maltracking.

BACKGROUND: Developing bone is highly adaptable and, as such, is susceptible to pathological shape deformation. Thus, it is imperative to quantify if changes in patellofemoral morphology are associated with adolescent-onset patellofemoral pain, as a pathway to improve our understanding of this pain's etiology. PURPOSE: To quantify and compare patellofemoral morphology in adolescent patients with patellofemoral pain with matched healthy adolescent controls and determine if a relationship exists between patellofemoral shape and kinematics (measured during active flexion-extension). STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Using 3-dimensional static magnetic resonance images acquired during a previous study, we measured patellar, trochlear, and lateral patellar width; trochlear and patellar depth; Wiberg index; patellar-height ratio; lateral trochlear inclination; cartilage length; and lateral femoral shaft length. Student t test was used to compare shape parameters between adolescents with patellofemoral pain and controls. Pearson correlations and stepwise linear regression models were used to explore the relationship among morphology, kinematics (medial-lateral shift/tilt), and pain. RESULTS: Relative to controls, adolescents with patellofemoral pain had larger sulci (mean ± SD, 6.6 ± 0.7 vs 6.0 ± 1.1 mm; 95% CI, 0.6 mm; P = .043; d = 0.66), lateral patellar width (23.1 ± 2.4 vs 21.4 ± 2.6 mm; 95% CI, 1.6 mm; P = .033; d = 0.70), and patella-trochlear width ratio (1.2 ± 0.1 vs 1.1 ± 0.1; 95% CI, 0.1; P < .001; d = 1.26). Shape correlated with kinematics in both cohorts and in the entire population. In the patellofemoral pain group, lateral shaft length (r = 0.518; P = .019), Wiberg index (r = 0.477; P = .033), and patellar-height ratio (r = -0.582; P = .007) were correlated with medial shift. A moderate correlation existed between patellar-height ratio and lateral patellar tilt (r = 0.527; P = .017). Half of the variation in patellar shift in the patellofemoral pain cohort was explained by the patellar-height ratio and Wiberg index (R2 = 0.487; P = .003). Linear correlations with pain were not found. CONCLUSION: This study provides direct evidence that patellofemoral morphology is altered and influences maltracking in adolescents with patellofemoral pain, highlighting the multifactorial etiology of this pain. Neither morphology nor kinematics (measured during active flexion-extension) correlated with pain. Both increases and decreases in these parameters likely lead to pain, negating a direct linear correlation.