Table 1.

Theoretical Rationale for the Contribution of Different Physical Impairments to PFPS Etiology and Summary of Previous Research Findings

Factor	Theoretical Rationale for the Contribution of Physical Impairments to PFPS	Studies That Support/Refute	Theoretical Rationale and Their Findings
Muscle weakness
Quadriceps	Quadriceps is responsible for the dynamic stabilization of the patella inside the trochlear groove.65	Support	Patients with PFPS have weaker quadriceps than controls.50 and 51 Quadriceps strengthening decreases pain and increases function in short-term follow-up in patients with PFPS.22, 66 and 67
		Refute	No differences in quadriceps weakness between PFPS and controls.22 and 59
Hip abductors and ER	These muscles help maintain pelvic stability by controlling femoral IR. Weakness may increase femoral IR, valgus knee moments, and compressive forces on the PF joint.67, 68 and 69	Support	Patients with PFPS have weaker hip muscles compared with matched controls.52
		Refute	No differences in hip strength between subjects with PFPS and an age-matched and sex- matched control group.70
Soft tissue tightness
Quadriceps	Tightness may pull the patella superiorly, increasing compression of the PF joint during physical activities.68	Support	Subjects with PFPS have shorter quadriceps muscles than subjects without PFPS.22, 70 and 71
Hamstrings	Tightness may require higher quadriceps force production or cause slight knee flexion, resulting in increased PF joint reaction forces.	Support	Association between limited hamstrings tightness and PFPS.70 and 71
		Refute	No association between hamstrings tightness and PFPS.22
Plantar flexors	Tightness may result in limited ankle dorsiflexion, which can be compensated for by excessive rotation of lower leg, altered Q-angle, and increased PF stresses.	Support	Association between plantar flexor tightness and PFPS.22 and 70
		Refute	No differences in ankle dorsiflexion between runners with and without PFPS.59
ITB/TFL	Tightness may pull the patella laterally and increase the stress over the lateral surface of the trochlear groove.1	No studies.
Lateral retinaculum	Adaptive shortening of the lateral retinaculum may be a consequence of the lateral displacement of the patella and may relate to PFPS.72 and 73	Support	Manual stretch of the lateral retinaculum decreases PFPS.74
Structural and postural alterations of lower extremities
Increased foot pronation	May cause compensatory internal rotation of lower extremity, increase Q- angle, and pull patella laterally.	Support	Female overpronators who received foot orthotics to correct pronation reported less pain.75
		Refute	Foot pronation was a predictor of anterior knee pain in runners. Pronation was higher in asymptomatic runners than in symptomatic runners.50
Altered Q- angle	Both increases and decreases in Q-angle may be associated with increased PF pressures.76	Support	Runners with PFPS had significantly higher values of Q-angle than a control group without PFPS.59
		Refute	No association between Q- angle and etiology of PFPS.50, 77 and 78
Increased lateral tibial torsion	May increase the tension in the infrapatellar tendon attachment and pull the patella laterally.	Support	Increased tibial torsion in patients with PFPS compared with subjects with no PFPS.79
Increased femoral anteversion	May result in lateral displacement of the patella and increases in the PF pressure.	Support	Patients who failed to respond to a conservative treatment for PFPS had higher femoral anteversion than the group who improved with treatment.80
		Refute	No differences between an asymptomatic control group and patients with PFPS.79
Poor quality of movement
	Patients with PFPS may exhibit altered movement patterns because of muscle imbalance or different timing between synergic muscles of LE, which may result in abnormal load distribution across the PF joint.5, 81 and 82	No studies.
Psychologic factors
Anxiety	In patients with other musculoskeletal conditions, the associations among pain, disability, and psychologic factors have been widely studied29, 37 and 83 and seem to support the biopsychosocial models that explain the development of chronic musculoskeletal conditions.16 and 26	Support	Anxious patients may not respond to PFPS treatments.20
			Patients with PFPS had more anxiety and stress symptoms and higher levels of hostility than a control group.21
Fear avoidance beliefs		No studies.

Abbreviations: ER, external rotators; IR, internal rotation; PF, patellofemoral; LE, lower extremity.