Structure and Function of the Knee Chapter 10 Structure and Function of the Knee Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 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   Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Proximal Tibia – cont’d Tibial tuberosity Protrusion of bone located on anterior aspect of proximal tibia Distal attachment for quadriceps muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 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.

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 170-175 degrees, normal genu valgum Less than 170 degrees is genu valgum, or “knock-kneed” Greater than 180 degrees is genu varum, or “bow-legged” Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Arthrokinematics at Tibiofemoral Joint – cont’d Flexion and extension are accompanied by slight rotational movements As knee nears full extension, knee rotates externally about 10-15 degrees This automatic rotation assists in “locking” knee—so- called screw-home mechanism Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc. 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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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 Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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) Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.

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.