Elsevier

The Knee

Volume 10, Issue 2, June 2003, Pages 123-126
The Knee

Review
Biomechanics of anterior knee pain

https://doi.org/10.1016/S0968-0160(02)00155-2Get rights and content

Introduction

Understanding the biomechanics of the patellofemoral mechanism is one of the prerequisites towards successful treatment of patients with patellofemoral pathology.

Although most orthopaedic surgeons have a superficial understanding of patellofemoral biomechanics, many of the clinically important characteristics are not always fully appreciated.

In this review paper a clinically oriented review of patellofemoral biomechanics is presented, which differs from the traditional viewpoint of the biomechanical engineer, by focusing on the aspects that are of real importance to the clinician.

Precise knowledge of these basic biomechanics are valuable to the orthopaedic surgeon, in understanding symptoms and pathology related to the patellofemoral mechanism, as well as in the determination of operative and conservative treatment strategies.

Section snippets

General principles

The patella increases the moment arm of the quadriceps by acting as a lever arm, especially in late extension. This lever, however, is not of the typical type we usually have in mind [1]. In a classic lever, displacement is sacrificed for force. For example, lifting a weight with a lever requires a lever with a long lever arm, where the person leaning on the lever arm has to bring the arm down a considerable distance, to lift the heavy weight only a short distance.

The patellofemoral mechanism

Clinical implications

The fact that the patellofemoral mechanism is so well developed for its function and its applied loads, indicates that even subtle changes in this system may have important biomechanical and clinical implications.

The delicate situation where maximal contact area and maximal articulating cartilage thickness are obtained at highest compressive load, is easily disturbed in case of congenital, developmental, traumatic, or other conditions.

Constitutions such as patella infera or patella alta may

Therapeutical implications

The fact that this delicate patellofemoral mechanism is so easily disturbed, makes it at first sight an attractive domain for clinicians dealing with the treatment of these patients.

Treatment strategies attempting to correct or improve the observed biomechanical abnormalities or imperfections, are indeed not only logical but also have been documented with satisfactory results in numerous publications and reports in the past.

However, the above mentioned delicate biomechanical characteristics of

Conclusion

The patellofemoral mechanism is from a biomechanical standpoint remarkably well designed to act as a biological lever system. Patellofemoral contact area, patellofemoral contact stress, load sharing with the quadriceps tendon, and thickness of the cartilage layer, are all in delicate balance with the patellofemoral loads imposed during the flexion and extension range.

Any disturbance in this delicate system may lead to local cartilage overload and clinical symptoms.

Treatment strategies

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    Medial patellar tilt occurs with knee flexion angles greater than 100° until full flexion is achieved (Fulkerson, 1997; Levangie & Norkin, 2011). Patellar tilt allows for greater congruency (surface contact area) in the femoral trochlea and a progressive decrease in contact stress (Bellemans, 2003). Transverse plane patellar motion is evaluated with the patellar tilt test (Kolowich, Paulos, Rosenberg, & Farnsworth, 1990).

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    There is a constant increase in patellofemoral compressive force with increase knee flexion up to 80–90° of flexion where maximum patellofemoral contact area is reached. Contact stress area is reduced in deeper flexion [20]. Beyond 120°, contact is reduced so that only the small odd facet remains in contact with the femur [21].

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