Aetiology

Many theories have been proposed to explain the cause of patellofemoral pain.[4] The exact aetiology is unknown, but it is likely to be multi-factorial with contributing factors including:[5][6]

  • Abnormal patellofemoral joint mechanics

    • Bony and structural abnormalities

    • Tightness of soft tissue structures

    • Decreased patellar mobility

    • Quadriceps muscle weakness

  • Altered lower-extremity alignment and/or motion

    • Subtalar joint pronation

    • Excessive hip internal rotation

    • Hip abductors weakness

    • Gait deviations

  • Overuse

    • Training errors.

Pathophysiology

The pathophysiology of patellofemoral pain is not well understood.

Normal patellar tracking requires a balance of forces acting on the patella. If any force is too large or too small, the movement of the patella may be altered, thereby placing additional stresses on joint soft tissue. As the stress exceeds the tissue's mechanical strength, microdamage, inflammation, and pain result.[7] Delayed onset of vastus medialis activity compared with that of vastus lateralis may lead to an imbalance in muscle forces and subsequent patellar maltracking. A statistically significant correlation has been found between measures of patellar maltracking (patellar tilt and bisect offset) and delay in vastus medialis activation in patients with patellofemoral pain.[8]

Excessive stress or normal stress applied in an abnormal direction to the cartilage, with resultant deformation, can transmit abnormal shear stress to the subchondral bone. Patients with patellofemoral pain exhibit elevated bone metabolic activity at the patellofemoral joint.[9] Nerves are associated with a blood supply to the subchondral bone, and the increase in pressure between the patella and femur is likely to be transmitted to these nerve receptors and perceived as patellar pain.

The lateral retinaculum also plays an important role in patellofemoral pain. The chronic lateral subluxation of the patella can lead to shortening of the retinaculum with secondary nerve damage, resembling the histopathological picture of a Morton neuroma.[10][11]

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