Patellofemoral pain syndrome (PFPS) is also known as chondromalacia patella, anterior knee pain, and extensor mechanism malalignment.


  • Accounts for 25-40% of all knee problems seen in sports medicine centers (Chesworth et al, 1993; Insall, 1982; Rubin and Collins, 1980)
  • Nearly 10% of all sports medicine center visits by physically active individuals are attributed to patellofemoral pain syndrome (Kannus et al, 1987)
  • The most prevalent disorder involving the knee (Baquie and Brukner, 1997; Hilyard, 1990; Malek and Mangine, 1981)
  • The second most common musculoskeletal complaint presenting to physical therapists (Tobin and Robinson, 2000)
  • Constitutes 16-25% of all injuries in runners (Taunton et al, 2002; Garrick, 1989; Clement et al, 1981)

Etiology and Risk Factors

The primary cause of PFPS is poorly understood and is likely multifactorial. The most commonly accepted hypothesis is that of patellar maltracking. Maltracking of the patella can cause increased load or stress to the underlying articular cartilage, resulting in wear and pain. 

Risk factors can be divided into anatomical and physiological. 

Anatomical Risk Factors

  • Femoral anteversion
  • Trochlear notch sulcus angle
  • Tibial torsion
  • Patella alta or baja
  • Foot and ankle alignment

Physiologic Risk Factors

  • Muscle performance (strength, endurance, motor control)
  • Range of motion or flexibility  

Strength and Endurance

  • Hip abductors: The hip abductors provide pelvic stability during weight bearing and control adduction moments. Adduction creates a larger Q-angle, allowing a greater lateral pull on the patella, leading to increased compressive forces
    • Ireland et al (2003) revealed decreased hip abduction strength (26%) in females with PFPS compared to controls
    • Piva et al (2005) showed no significant differences between groups of those with and without PFPS
    • Robinson (JOSPT 2007) showed decreased hip strength in females (12-35) with unilateral PFPS compared to control subjects, whereby the symptomatic leg with PFPS had less strength for abduction (27%) and ER (30%). Limb symmetry index (LSI) ranged from 71-79% vs 93-101% (weak compared to strong leg).
  • Hip Extensors
    • Robinson (JOSPT 2007) showed decreased hip strength in females (12-35) with unilateral PFPS compared to control subjects. The symptomatic leg with PFPS had less strength for extension (52% less than CL side)
  • Hip External Rotators: Hip external rotators contribute to pelvic stability and leg alignment by eccentrically controlling femoral internal rotation during weight-bearing activities, resulting in an increased Q-angle and subsequently altering the tracking of the patella and increasing compressive forces of the patellofemoral joint
    • Ireland et al (2003) revealed decreased hip external rotation strength (36%) in females (ages 15-21) with PFPS compared to controls


  • Quadriceps: Limited flexibility of the quadriceps may pull the patella superiorly, thus increasing compression of the patella femoral joint during physical activities (Hertling, 1996)
    • In a young, athletic population, Witvrouw et al (2000) found that subjects who developed PFPS over time had less quadriceps flexibility than subjects without PFPS
    • Smith et al (1991) showed decreased quadriceps flexibility in adolescent elite figure skaters with PFPS
    • Piva et al (2005) demonstrated decreased flexibility in those with PFPS (mixed gender, ages 20-42) compared to controls
  • Hamstrings: Theorized either to require higher quadriceps force production to overcome the passive resistance offered by the hamstrings or to cause a slight knee during physical activities, both of which may result in increased patellofemoral joint reaction forces (Hertling, 1996)
    • Smith et al (1991) found limited hamstring flexibility associated with PFPS
    • Witvrouw et al (2000) found no relationship between decreased hamstring flexibility and PFPS (SLR PFPS 91 degrees, controls 94 degrees)
    • Piva et al (2005) showed decreased flexibility in those with PFPS (mixed gender, ages 20-42) compared to controls
  • Gastroc/Soleus: Decreased flexibility is associated with limited ankle dorsiflexion. Lack of ankle dorsiflexion can result in increased pronation during stance phase of gait, leading to increased tibial internal rotation, increased femoral internal rotation, and subsequent increase in the Q-angle, which consequently increase patellofemoral stresses
    • Witvrouw et al (2000) reported decreased gastroc flexibility in those with PFPS compared to controls
    • Piva et al (2005) revealed increased tightness in both the gastroc and soleus compared to controls
    • Messier et al (1991) found no difference in ankle dorsiflexion with knees extended between runners with and without PFPS. Both groups had a mean of 6.5 degrees of dorsiflexion
    • Duffey et al (2000) found no difference between those with PFPS and controls
  • Iliotibial Band: Because the distal fibers of the ITB/TFL comlex attach to the lateral aspects of the patella via the ITB, tightness may theoretically pull the patella laterally, leading to increased pressure over the patella (Barber-Westin et al, 1997; Rubin and Collins, 1980)
    • Smith et al (1991) reported no significant association between tightness of the ITB/TFL and patellofemoral pain ** Piva et al (2005) reveled no significant difference between groups of those with and without PFPS
    • Three other authors found ITB tightness in athletes with PFPS (Winslow et al, 1995; Kibler, 1987; Puniello, 1993)
  • Patellar Glide: Tight lateral structures on the patella would result in limited medial glide and could cause increased compression laterally on the patella. This could also cause increased lateral glide and potential overloading of the lateral tissue or subluxation/dislocation of the patella.
    • Punillo et al (1993) revealed that 82% (14/17) of individuals with PFPS exhibited decreased medial patellar mobility
    • Ota et al (2008) showed no difference in medial or lateral patellar mobility between those with PFPS and controls

Outcomes and Interventions

  • VMO Strengthening vs General Quadriceps strengthening
    • Syme et al (2008): Both the selective and general groups displayed statistically significant and "moderate" and "large" effect size improvements in subjective function and quality of life compared to the control group (no intervention)
  • Weight Bearing vs. Non-weight bearing exercises
    • Herrington et al (2007): In a randomized controlled trial, individuals in both exercise groups demonstrated a statistically significant decrease in pain and an increase in muscle strength and functional performance, as compared to the control group (p <.05). All measures showed no significant differences in outcome between the two exercise groups (p >.05).
  • Weight Bearing vs Control
    • Boling et al (2006): Subjects diagnosed with PFPS responded favorably to a therapeutic exercise program that incorporated quadriceps and hip musculature strengthening.
  • Orthotic Interventions