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Chapter 24

### Objectives

After completion of this chapter, the physical therapist should be able to do the following:

• Understand the functional biomechanics associated with normal function of the knee.

• Utilize a general rehabilitation progression when treating knee injuries.

• Integrate a comprehensive understanding of pathomechanics and mechanism of injury into the rehabilitation of ligamentous and meniscal injuries.

• Integrate a comprehensive understanding of pathomechanics and mechanism of injury into the rehabilitation of patellofemoral and extensor mechanism injuries.

• Justify the use of external supports to augment the rehabilitation process.

• Implement a functional progression to ensure safe return to activity.

### Functional Biomechanics of the Knee

The study of biomechanics, along with functional anatomy, is a cornerstone to knee rehabilitation. A complete understanding of joint articulations, arthrokinematics, and the structures responsible for controlling movement is essential for the clinician to make sound decisions in the diagnosis and treatment of musculoskeletal disorders. Despite the relative simplicity of a hinge-type joint, the knee provides an interesting biomechanical study because of the intricacies required to maintain stability without good bony support along with attenuating forces greater than 4 times the weight of the body. The patellofemoral joint and the pain syndromes often associated with the knee also present an interesting study. A solid knowledge of the supporting structures and stress placed on the patellofemoral joint provides the framework for rehabilitation program design.

#### Tibiofemoral Joint

##### Tibiofemoral Articulation: Menisci-Femoral Condyles

The condyles of the distal femur articulate with the shallow, concave tibial plateau, resulting in significant tibiofemoral joint incongruence. Tibiofemoral stability would be insufficient if left solely to the skeletal structure. The medial and lateral menisci provide additional congruency to the joint through their semicircular shape and peripheral thickness, thus forming a wedge surrounding the femoral condyles.

The contact area of the menisci varies significantly during knee range of motion (ROM). In weight bearing, the total contact area of the menisci decreases with knee flexion. Although mean surface area increases in non-weightbearing conditions, total menisci contact area also decreases during knee flexion. Following a meniscectomy, surface contact area decreases, resulting in a greater amount of stress upon the contact surface.

#### Axial Forces

The ability of the tibiofemoral joint to withstand forces imposed by the superincumbent weight of the body combined with the ground reaction force transmitted through the distal extremity requires interaction of multiple structural factors. The longitudinal axis of the femur extends laterally to medially to the tibiofemoral articulation, resulting in an oblique angle formed 5 to 10 degrees away from vertical. It would seem that this alignment would produce a greater load on the lateral femoral condyle; however, a close look at the mechanical axis that connects the head of the femur with the superior surface of the talus contradicts this. The mechanical axis, which is the true line of weight bearing and determines the ...

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