1. Structure and Function of the Knee
Chapter 10
Structure and Function of the Knee
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Distal Femur
Medial and lateral condyles
Projections of distal femur articulating with medial and lateral condyles of tibia
Intercondylar groove
Smooth, rounded area between femoral condyles articulating with posterior surface of patella
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Distal Femur – cont’d
Intercondylar notch
Located on posterior-inferior aspect of distal femur, separating medial and lateral condyles
Forms passageway for anterior and posterior cruciate ligaments
Medial and lateral epicondyles
Bony projections on medial and lateral femoral condyles, serving as attachments for medial and lateral collateral knee ligaments
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Proximal Tibia
Tibial medial and lateral condyles articulate with condyles of femur; flattened superior surfaces of condyles are often called tibial plateau
Intercondylar eminence
Double-pointed projection of bone separating medial and lateral tibial condyles; attachment for anterior and posterior cruciate ligaments and medial and lateral meniscus  
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5. Proximal Tibia – cont’d
Tibial tuberosity
Protrusion of bone located on anterior aspect of proximal tibia
Distal attachment for quadriceps muscles
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6. Proximal Fibula – cont’d
Long slender bone that courses along lateral shaft of tibia
Fibular head
Rounded superior portion of fibula that articulates with tibia, forming proximal tibiofibular joint
Distal attachment of lateral collateral ligament and biceps femoris muscle
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Patella
Small sesamoid bone embedded within quadriceps tendon
Superior pole accepts quadriceps tendon; inferior pole accepts proximal side of patella ligament
The posterior articular surface articulates with intercondylar groove of femur through medial and lateral facets
Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

8. Arthrology: Normal Alignment
Angle of inclination
125-degree angle of proximal femur directs shaft toward midline, to articulate with tibia at knee
Femur usually meets tibia to form lateral angle of degrees, normal genu valgum
Less than 170 degrees is genu valgum, or “knock-kneed”
Greater than 180 degrees is genu varum, or “bow-legged”
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9. Supporting Structures: Anterior and Posterior Cruciate Ligaments
Cruciate describes X shape of anterior and posterior cruciate ligaments as they interconnect tibia with femur
These cruciate ligaments are most important stabilizers of knee in sagittal plane
Anterior cruciate ligament is frequently injured during sporting events that generate a combination of rotational, valgus, and hyperextension-producing forces through knee
Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

10. Supporting Structures: Medial and Lateral Collateral Ligaments
Strengthen medial and lateral sides of knee capsule; protect against excessive genu varus or genu valgus
Medial collateral ligament
Spans medial side of knee and resists valgus-producing forces
Become taut at full extension, useful for locking extended knee while standing
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11. Supporting Structures: Medial and Lateral Meniscus
Crescent-shaped fibrocartilaginous discs at top of tibial medial and lateral condyles
Absorb compressive forces across knee caused by muscular contraction and body weight
Reduce pressure across knee
“Deepen” socket of knee, further stabilizing joint
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12. Supporting Structures: Posterior Capsule
Prevents hyperextension of knee
Includes two major ligaments: arcuate popliteal ligament and oblique popliteal ligament  
Knee demonstrating marked hyperextension (genu recurvatum) has strain on most knee structures including posterior capsule
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13. Osteokinematics of Tibiofemoral Joint
Allows 2 degrees of freedom
Flexion and extension occur in sagittal plane about a medial-lateral axis of rotation
Internal and external rotation of knee occurs within horizontal plane about a vertical or longitudinal axis of rotation
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14. Arthrokinematics at Tibiofemoral Joint
Open-chain arthrokinematics is based on concave tibial condyles rotating around convex condyles of femur
Closed-chain extension is based on a roll-and-slide pattern occurring in opposite directions
Arthrokinematics for knee flexion are reversed for knee extension
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15. Arthrokinematics at Tibiofemoral Joint – cont’d
Flexion and extension are accompanied by slight rotational movements
As knee nears full extension, knee rotates externally about degrees
This automatic rotation assists in “locking” knee—so- called screw-home mechanism
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Patellofemoral Joint
Articulation formed between posterior surface of patella and intercondylar groove of femur
Patella enhances torque-producing capability of quadriceps by about 25%
Following patellectomy, quadriceps must produce 25% more force
This increased muscle force may cause fatigue, or damage to patellofemoral joints
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17. Innervation to Knee Muscles
Femoral nerve
Supplies sole source of innervation to quadriceps
Tibial portion of sciatic nerve
Innervates semitendinosus, semimembranosus, and long head of biceps femoris
Peroneal portion of sciatic nerve
Innervates short head of biceps femoris
Obturator nerve
Innervates most of hip adductor muscles
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Knee Muscles
Divided into extensors and flexor-rotators
Although these muscles have important individual actions, they often work in teams to maximize movement control
e.g., standing from a seated position requires simultaneous activation of quadriceps and hamstrings
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19. Knee Extensors: Quadriceps
Rectus femoris
Proximal attachment: anterior-inferior iliac spine
Distal attachment: tibial tuberosity
Actions: knee extension, hip flexion
Vastus medialis
Proximal attachment: medial lip of linea aspera and intertrochanteric line of femur
Actions: knee extension
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20. Knee Extensors: Quadriceps – cont’d
Vastus lateralis
Proximal attachment: linea aspera’s lateral lip, intertrochanteric line, gluteal tuberosity’s lateral region
Distal attachment: tibial tuberosity
Vastus intermedius
Proximal attachment: upper two thirds of anterior femoral shaft
Action of both muscles: knee extension
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21. Functional Considerations: Lateral Tracking of Patella
Lateral tracking of patella increases pressure and friction within patellofemoral joint
May result in pain, inflammation, joint degeneration, and dislocation
Classifying factors contributing to laterally tracking as intrinsic or extrinsic helps determine more effective treatment strategies
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22. Functional Considerations: Patellofemoral Joint and Deep Squats
Patellofemoral joint pain is characterized by inability of patellofemoral joint to tolerate large compression forces
Often, clinicians recommend that patients avoid “squatting” motions to limit excessive compression and damage to patella
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23. Knee Flexor-Rotators: Hamstrings
Semitendinosus, semimembranosus, and biceps femoris (long and short heads)
Span posterior thigh, perform knee flexion, and most perform hip extension
Most hamstrings cross hip, and hip position affects their operational length
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24. Knee Flexor-Rotators: Gracilis and Sartorius
Provide stability to medial aspect of knee
Assist with flexion and internal rotation of knee
Both muscles attach proximally to pelvis
Distally, they course posterior to medial-lateral axis of rotation of knee
Tendons of gracilis, sartorius, and semitendinosus join for collective insertion at pes anserinus
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25. Knee Flexor-Rotators: Gastrocnemius and Plantaris
Powerful two-headed muscle
Produces large plantar flexion torques across ankle
Knee flexor
Plantaris
Relatively small
Crosses posterior knee
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26. Knee Flexor-Rotators: Popliteus
Proximal attachment
Posterior aspect of lateral femoral condyle
Distal attachment
Posterior surface of proximal tibia
Innervation
Tibial nerve
Actions
Knee internal rotation
Knee flexion
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27. Functional Considerations: Tight Hamstrings
Often due to spasticity, muscle irritability, or spending extended time in a flexed-knee position
Tightness of hamstrings is often visibly observed by inability to fully extend knee
Extreme hamstring tightness may also lead to chronically flexed hips or posterior pelvic tilt and flattened lumbar spine
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28. Functional Considerations: Tight Hamstrings – cont’d
Passive tension in hamstrings may posteriorly tilt pelvis
Pelvis should be stabilized as stretch is being performed
Excessive posterior tilting may produce an unwanted overstretching of connective tissues within lumbar region
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29. Functional Considerations: Rectus Femoris and Hamstrings
Most lower extremity activities combine hip flexion and knee flexion or hip extension and knee extension
During combined hip and knee extension, both rectus femoris and semitendinosus avoid maximum shortening across hip and knee to prevent muscles from becoming actively insufficient
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30. Internal and External Rotators of Knee
Hamstrings, gracilis, popliteus, and sartorius control active rotation of knee within transverse plane
Medial hamstrings, gracilis, and sartorius internally rotate knee, whereas lateral hamstrings externally rotate knee
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31. Functional Considerations: Activation of Internal Rotators
Internal rotator muscles of knee far outweigh strength of external rotator muscles
This disparity likely reflects need to either accelerate knee into internal rotation (by concentric contraction) or decelerate external rotation of knee (by eccentric activation)
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32. Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Summary
Stability of knee maintained largely by ligaments and surrounding musculature
Combination of large forces and lack of bony constraint may account for high incidence of knee joint injuries
Rehabilitation approaches usually involve knee itself, as well as surrounding joints and muscles
Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.