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The Knee Complex

Functions of the Knee
Joint Structure of the Knee
Kinematics of the knee
Muscle Actions Around the Knee
Knee Stability
Mechanism of Injury at the Knee

Objectives： After studying this topic, the students will be able to

1. to identify the structures of the knee complex, including joint type, articular shape, and the surrounding tissues
2. to describe joint motions occurring at the knee complex, including physiological and accessory movements, muscle actions, and factors checking knee motions
3. to understand the stability mechanism of the knee complex and the possible mechanisms of injury
4. to understand functions of the meniscus and the ligaments surrounding the knee complex
5. to explicate functions of the sesamoid bone such as the patella as well as its significance in biomechanics

1. Neumann DA (2002).  Knee.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 13, pp. 434-476.
2. Smith LK, Weiss EL, Don Lehmkuhl L (1996). Brunnstrom's Clinical Kinesiology, 5th ed.  Philadelphia, F.A. Davis.  Chapter 9, pp. 301-331.
3. Nordin M & Frankel VH (2001).  Biomechanics of the knee.  In Nordin M & Frankel VH: Basic Biomechanics of the Musculoskeletal System.  Philadelphia: Lippincott Williams & Wilkins. Chapter 7, pp.176-201.

Functions of the Knee

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Joint Structure of the Knee Complex

Joints at the knee complex

tibiofemoral joint (knee joint)： principal joint at the knee complex patellofemoral joint NOTE： In Neumann's book, the tibiofemoral joint was divided into medial and lateral tibiofemoral joints

Tibiofemoral joint (TF joint)

proximal components： femur convex femoral condyles distal components： tibia concave superior surface of the tibial plateau C-shaped medial meniscus and O-shaped lateral meniscus joint type： hinged joint DOF = 2 because of the menisci between the articular surfaces motions： concave on convex knee flexion/ extension with posterior/ anterior glide of the tibial plateau on the femoral condyles tibia inward/ outward rotation： only occurs at the knee flexed position resting position： slight knee flexion (10º) closed-packed position： full knee extension

Joints at the Knee Complex
Knee Flexion/ Extension
Tibial Rotation

Patellofemoral joint (PF joint)

Joints at the Knee Complex
Knee Flexion/ Extension

Patella

largest sesamoid bone in the body location： embedded in quadriceps tendon function： to increase mechanical leverage of the quadriceps patellar compression force： to pull the patella against the anterior surface of the femur increased with knee flexion

medial meniscus： C-shaped lateral meniscus： O-shaped functions to deepen the tibial plateau for knee stability to absorb the ground reaction forces： carrying 40-70% of loads across the knee joint
removal of menisci increases the magnitude of stresses on the cartilage of the tibia plateau changes the size and location of tibiofemoral contact area
movements of meniscus Both menisci distorted and moved posteriorly during knee flexion and anteriorly during knee extension In rotation, both menisci follow the motions of the femoral condyles Movements significantly greater in weight-bearing conditions

Tibiofemoral Joints

Q angle

full name： quadriceps angle the angle formed by the line of pull of the quadriceps and the line representing patellar tendon male： 12º female： 15º

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Kinematics of the Knee

Knee flexion and extension

joint involved tibiofemoral joint patellofemoral joint plane of motion： sagittal plane (not really) axis of rotation a frontal axis passing through the center of the medial and lateral epicondyles of the femur instant center of rotation (IAR)： axis of rotation changes through the range of motion (not a fixed point) path of IAR forms a semi-circle from lateral view
osteokinematic movements range of motion (ROM) 0-140º for knee flexion some for knee hyperextension closed kinematic chain motions deep squatting standing up from sitting stance phase of the gait cycle supine lying with the leg pushing against the wall functional range walking: 0-67º climbing stairs: 0-83º descending stairs: 0-90º sitting in a chair: 0-93º tying a shoe: 0-106º lifting an object from the floor: 0-117º
arthrokinematic movements tibiofemoral joint： concave on convex 　 Tibia on Femur Patella on Femur Menisci relative to tibia Knee Flexion posterior glide inferior glide posterior displacement Knee Extension anterior glide superior glide anterior displacement screw-home mechanism synonym： knee locking mechanism continuous inward rotation of the femur that accompanies the completion of knee extension during the closed kinematic chain motions patellar tracking movement： dictated by quadriceps contraction medial/lateral shift： c-curve pattern from knee flexion to extension meidal/lateral tilt： The patella tilts medially from knee flexion to extension, but the patella is still in the laterally tilt position even the knee is in the fully extended position. factors checking knee flexion mass of the hamstrings passive tension of the quadriceps tension of the posterior cruciate ligament factors checking knee extension bony contact passive tension of the hamstrings tension of the anterior cruciate ligament

Tibia inward and outward rotation

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Muscles Actions Around the Knee

Knee extensors

quadriceps femoris rectus femoris： two-joint muscle knee extensor hip flexor vastus medialis vastus medialis longus vastus medialis obliquus vastus lateralis vastus intermedialis Efficiency of quadriceps depends on the patella Maximum isometric force occurs at 60º of knee flexion
No quadriceps activity required to keep knee extension at erect stance isokinetic strength： H/Q ratio= 0.7:1

Knee flexors

Tibia inward rotation at 90º of knee flexion

popliteus： knee flexion + inward rotation semitendinosus semimembranosus

Tibia outward rotation at 90º of knee flexion

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Knee Stability

Factors affecting stability of the tibiofemoral joint

Factors affecting patella stability

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Mechanism of Injury at the Knee

Direct stress

Repeated stresses

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