CHAPTER 12 Structure and Function of the Knee Knee flexed 135° Fat pad


Quadriceps Femur


265


A Knee flexed 90° B Knee flexed 20° Medial 60° epicondyle 90° 135° C D E Lateral epicondyle Knee flexion


Figure 12.22 (A) The patella functions like a cable on a pulley as it moves up and down in the trochlear groove. (B) During 135° of knee flexion, the patella is in its most inferior position with minimal contact with the femur. (C) As the knee extends, the patella moves superiorly and has greater contact with the femoral surface at 90° of flexion. (D) As the knee approaches terminal knee extension, the patella moves superior to the trochlear groove. (E) The path and contact areas of the patella on the trochlear groove of the femur.


Patellar tendon Fibula Tibia


Clinical Connection 12.2


Patellofemoral pain syndrome (PFS) is a condition that manifests with symptoms of anterior or retropa- tellar discomfort and pain that are often exacerbated during functional activities such as squatting, running, jumping, negotiating stairs, kneeling, and even pro- longed sitting with the knees fl exed. The causes of PFS are multifactorial but appear to be most likely related to patellar malalignment and maltracking in the femoral trochlear groove. The faulty kinematics can be the result of hip abductor and lateral rotator muscle weakness resulting in dynamic genu valgum and excessive femoral medial rotation, often seen when landing from a jump. Faulty patellar kinematics can


also result from quadriceps weakness, foot malalign- ment, and structural abnormalities of the patellofemo- ral joint.


Evidence supports the effectiveness of strengthen- ing hip abductors and lateral hip rotators in reducing abnormal patellar kinematics and PFS symptoms. To minimize patellofemoral joint stresses while perform- ing quadriceps strengthening exercises, squat exercises should be performed from 45° to 0° of knee extension. Patellar taping has been shown to reduce pain, alter patellofemoral kinematics, and improve knee joint proprioception.


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