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THE FUNCTIONAL ANATOMY OF THE KNEE JOINT Required Reading: 672 - 687 I. BONY STRUCTURES Distal Femur Lateral and Medial Condyles Articulate with tibia Intercondylar fossa Patellar articular surface Patella Sesamoid bone found within the tendon of the quadriceps femoris Articulates with the patellar surface of the femur Protects quadriceps tendon as tendon moves across knee joint Proximal End of Tibia Lateral and Medial tibial condyles Articulates with femoral condyles Intercondylar eminence Intercondylar area - anterior Found anterior to the intercondylar eminence Provides attachment for anterior cruciate ligament Intercondylar area - posterior Found posterior to the intercondylar eminence Provides attachment for posterior cruciate ligament Tibial tuberosity Point of insertion od the ligament of the patella D. Fibula - proximal end Head of fibula articulates with the lateral tibial condyle Not involved in weight bearing during standing Provides attachments for muscles II. ALIGNMENT OF THE KNEE Normal Alignment (Fig. 1) Slight valgus position Angle between longitudinal axis of femur and tibia is 1700 opened laterally Q angle ( Fig. 1) - is a measure of the axis of pull of the quadriceps tendon and that of the ligament of the patella. The former is measured by a line drawn from the ASIS to center of patella. The latter is determined by a line drawn from the tibial tuberosity to the center of the patella. The normal Q angle is between 15 -200. This angle is somewhat greater in females than males. A Q angle much greater than normal means the patella will track in a lateral direction rubbing against the lateral femoral condyle causing Patella pain. Abnormal Alignment ( Fig. 3) Genu Valgum ( Knock Knee) Tibia abducted with respect to femur Angle between longitudinal axes of bones less than 1700 Genu Varum (Bow Leg) Tibia adducted with respect to femur Angle between longitudinal axes of bones greater than 1700 III. CAPSULAR LIGAMENTS Function Strengthen the fibrous capsule Strengthening Anterior Aspect of Knee Joint Quadriceps Tendon Passes over and partially attaches to patella Continues to insert onto tibial tuberosity as the Patellar Ligament Patellar Retinacula Extensions of fascia from the quadriceps muscles Attach patella and patellar ligament to tibial and femoral condyles trengthening the Posterior Aspect of the Knee Joint Oblique Popliteal Ligament Derived from the tendon of the semimembranosus muscle Arcuate Popliteal Ligament Derived from the tendon of the biceps femoris muscle Strengthening the Medial Aspect of the Knee Joint Tibial ( Medial ) Collateral Ligament Attaches from medial femoral condyle superiorly to the media tibial condyle inferiorly Attaches to medial meniscus Forms part of the capsule and strengthens capsule medially Lateral Aspect of the Knee Joint Fibular ( Lateral ) Collateral Ligament Attaches from lateral femoral condyle superiorly to head of fibula inferiorly Does not attach to lateral meniscus Not part of the fibrous capsule Does not strengthen the fibrous capsule capsule weak laterally IV. INTRACAPSULAR LIGAMENTS Anterior Cruciate Arises from anterior intercondylar area to tibia Attaches to medial surface of lateral femoral condyle Resists anterior movement of tibia on femur or posterior movement of femur on tibia Anterior Draw Sign Integrity of anterior cruciate ligament Posterior Cruciate Arises from posterior intercondylar area to tibia Attaches to lateral surface of medial femoral condyle Resists posterior movement of tibia on femur or anterior movement of femur on tibia Posterior Meniscofemoral Ligament Continuation of lateral meniscus attaching to the posterior cruciate ligament V. MENISCI Properties Composed of fibrocartilage Cover the superior surface of the tibial condyles Adapt the shapes of the tibial condyles to provide a better fit between tibial and femoral condyles Lateral Meniscus Covers the surface of the lateral tibial condyle Oval shape Thicker, shorter and more closed shaped than medial meniscus Mobile Medial Meniscus Covers medial tibial condyle C. shaped Larger, thinner and more opened shaped than lateral meniscus Less mobile Provides attachment for medial collateral ligament More likely to be injured when medial collateral ligament is damaged Abduction injury i) Caused by lateral blow to knee ii) Stresses medial collateral ligament iii) Can lead to damage of ligament and medial meniscus Transverse Ligament of the KneeContinuation anteriorly of fibers from the lateral meniscus to the medial meniscus Coronary Ligaments Extensions of the fibrous capsule Attach the menisci to the tibial condyles VI. LOCKING OF THE KNEE JOINT Function Permits standing upright with little expenditure of energy in the form of muscle contraction Shape of the Femoral Condyles Lateral Femoral Condyle Flexion Spherical posterior part of femoral condyle in contact with tibial condyle Bones remain in contact throughout flexion Distance between femoral and tibial condyles changes little during flexion Fibular collateral ligament is lax Extension Flat anterior part is in contact with tibial condyle Less contact between bones as extension continues Distance between both bones increases as extension proceeds Fibular collateral ligament becomes taut Medial Femoral Condyle Flexion Spherical posterior part of femoral condyle in contact with tibial condyle Bones remain in contact throughout flexion Distance between femoral and tibial condyles changes little during flexion Tibial collateral ligament is lax Extension Flat anterior part is in contact with tibial condyle Less contact between bones as extension continues Distance between both bones increases as extension proceeds Tibial collateral ligament becomes taut Length of the Femoral Condyles Articular surface of the medial femoral condyle is longer than the surface on the lateral femoral condyle Moving into extension from a flexed position Articular surface of lateral femoral condyle stops Surface for articulation still exposed on medial condyle Medial Rotation accompanies final stages of extension Accommodates remainder of exposed articular surface on medial femoral condyle Promotes greater contact between articular surfaces of femoral and tibial condyles Tightens collateral and cruciate ligaments 4. Locked Position Brought about by medial rotation of the femur on the tibia during final stages of extension Promotes maximum contact between articular surfaces of femoral and tibial condyles Renders ligaments taut Ligaments maintain the joint in the stable ( extended) position VII. UNLOCKING OF THE KNEE JOINT Properties Lateral rotation of the femur on the tibia Brought about by action of the Popliteus Muscle Arises from lateral femoral condyle Inserts into the posterior part of the tibia Pulls the lateral condyle posteriorly laterally rotating the femur Necessary to loosen the tension on the ligaments Collateral ligaments Cruciate ligaments VIII. MOVEMENTS OF THE KNEE Properties of the Knee Joint Uniaxial modified hinge joint Weight bearing (fixed) - foot in contact with ground and the limb is supporting weight of body Femur moves on a fixed tibia Deep knee bends Non Weight bearing (free) - foot free of ground and the limb is unable to support weight of body Tibia free to move on a fixed femur Movements at the Knee Flexion / Extension Occurs in sagittal plane Coronal ( side to side) axis through knee joint Inward / Outward Rotation Occurs only when the knee is flexed b. Vertical axis through tibial shaft Muscle Actions The movements that can occur at the knee joint and the muscles acting as prime movers for each motion are outlined in Chart 1 IX. CLINICAL CONSIDERATIONS Actions of the Knee Joint During Gait (Review the video "The Anatomical Gait Cycle") Acceleration and Heel Strike The knee is in a flexed position when the heel comes in contact with the ground. Flexion enables the knee to help absorb impact resulting from heel contacting ground. In addition, the mass of body behind knee joint forcing it into flexed position Quadriceps femoris contract eccentrically to restrict flexion Skiing position Heel Strike to Midstance The movement of the torso that results when the non reference limb swings forward carries the torso over the reference limb. The knee joint of the reference limb assumes an extended position. This lengthens the limb facilitating the ability of the limb to support the weight of the torso. Concentric contraction of quadriceps femoris assists in knee extension Midstance to Toe Off The knee joint is flexed by the concentric contraction of the gastrocnemius muscle. This shortens the limb enabling it to clear the ground in order to swing forward during the following interval. Toe Off to Acceleration The reference limb goes from a weight bearing to a non weight bearing position. The gastrocnemius along with the soleus muscle contracts concentrically during this phase with the gastrocnemius causing the knee joint to actively flex. The Effect of Nerve Lesions on the Hip Joint During Gait Femoral nerve Wasting of muscles in anterior compartment of thigh Extending knee against resistance very difficult. The patient will not be able to rise from a seated position without the use of the upper limbs for support because the quadriceps muscles are not capable of the concent contraction necessary to put the knee in an extended position. The quadriceps muscles will not be able to contract in an eccentric manner. Thus, the patient will not be able to sit from a standing position without using the upper limbs for support. Patient will walk with an abnormal gait since the quadriceps muscles will not be able to contract in an eccentric manner during the interval between swing and heel strike. Without the ability to restrain the amount of knee flexion during this interval, normal gait is impossible. The patient compensates by taking very small steps and having the foot come down in midstance rather than heel strike. L3,4 nerve root damage will effect result in weak action of the quadriceps femoris. To test for damage of these roots, have the patient sit and have them try and extend their knee against resistance. Patients with L3,4 damage will have very weak knee extension. Ligament or Meniscal Damage The muscles and ligaments stabilize the knee under usual conditions. However, many activities such as sports can damage the knee. Assessing the knee for ligament damage or cartilage tears is something most physicians should be able to do. Anterior Cruciate Ligament - is very susceptible to tears becuase it is stressed whenever a forward movement is suddenly stopped such as occurs during tennis, basketball skiing, etc. To asses damage to this ligamnent, the patient is asked to lie supine and the knee is placed is a position of slight flexion. The femur is stabilized with 1 hand while the leg is pulled forward with the other. Anterior movement of the leg on the thigh is a positive anterior draw sign indicative of anterior cruciate damage. Posterior Cruciate Ligament - is less often damaged. To test its integrity, the opposite is done. With a stabilized thigh, the leg is pulled posteriorly. To great a movement indicates damage to this ligament. Medial Collateral Ligament - is more commonly injured that the lateral (fibula) collateral ligment because it resists valgus stresses. A valgus stress is one in which a force applied to the outside ( lateral) aspect of the knee joint. This forces the knee in a medial direction causing the the tibia and femur to separate on the medial side. The medial collateral ligament resists such a force. To test for the integrity of the Medial Collateral Ligament, place the limb in an extended position. Place one hand on the medial side of the ankle and the other on the lateral side of the knee. Pull the ankle laterally (outward) with one hand while stabilizing the knee with the other. Laxity indicates medial collateral ligament damage. Lateral Collateral Ligament - resists varus stresses A varus stress is one in which a force applied to the inside ( medial) aspect of the knee joint. This forces the knee in a lateral direction causing the the tibia and femur to separate on the lateral side. The lateral collateral ligament resists such a force. To test for the integrity of the Lateral Collateral Ligament, place the limb in an extended position. Place one hand on the lateral side of the ankle and the other on the medial side of the knee. Pull the ankle medially (inward) with one hand while stabilizing the knee with the other. Laxity indicates medial collateral ligament damage. Meniscus- The menisci are cartilagenous plates that help adapt the shape of the femur to the tibia and also act as shock absorbers. Continued pounding, as occurs with road running on playing on a hard surface ( basketball) can result in tears of the menisci. Damage to the medial collateral ligament can also result in injury to the medial meniscus because to the attachment of the medial collateral ligament to this meniscus. The lateral collateral ligament has no attachment to the lateral meniscus so it is very moveable and less like to be injured. To test for the integfrity of the menisci, have the patient lie supine with the knee flexed. Push down on the knee with one hand. The other hand grasps the heel and rotates the leg in either a medial or lateral direction. Pain caused by rotating the knee in a medial direction indicates damage to the lateral meniscus. Eliciting pain from rotating the leg in a lateral direction indicates damage to the medial meniscus. Chart 1 -PRIME MOVERS OF THE KNEE MOVEMENT MUSCLES NERVE SEGMENT Extension Rectus femoris* Femoral L 2, 3, 4 Vastus Medialis* Femoral L 2, 3, 4 Vastus Lateralis* Femoral L 2, 3, 4 Vastus Intermedius* Femoral L 2, 3, 4 Flexion Semimembranosus+ Sciatic L 5 S 1 Semitendinosus + Sciatic L 5 S 1 Biceps Femoris+ Sciatic L 5 S 1,2 Sartorius Femoral L 3, 4 Gracilis Obturator L 3, 4 Gastrocnemius Tibial S 1,2 Unlocking Popliteus Sciatic (T) L 4, 5 S 1 Outward Rotation1 Biceps Femoris Sciatic L 5 S 1,2 Inward Rotation1 Sartorius2 Femoral L 3, 4 Gracilis2 Obturator L 3, 4 Semitendinosus Sciatic L 5 S 1 * = Quadriceps Femoris Muscles + = Hamstring Muscles 1 = Inward and Outward rotation are possible only if the knee is in a flexed position 2 = Pes anserinous muscles Figure 1 - Knee Alignment 1. Normal Alignment - Notic that the tibia (2) is abducted with respect to the femur (1) imparting a valgus position to the knee joint. 2.Q Angle - a line connecting the ASIS (A) with the center of the patella (B) indicates the pull of the quadriceps tendon. A line theough the center of the patella to the tibial tuberosity indicates the pull of the ligament of the patella. The distance between these lines equals the Q angle Figure 2 1.Genu Valgum - A force is applied to the lateral side of the knee forcing the knee to bend in a medial direction. This abducts the tibia with respect to the femur. 2. Genu Varum - A force is applied to the medial side of the knee forcing the knee to bend in a lateral direction. This adducts the tibia with respect to the femur. Objectives: Know the bony , ligamentous and cartilaginous structures the comprise the knee joint Understand the role each plays in supporting and strengthening the knee joint Know the proper alignment of the knee Be able to distinguish genu valgum from genu varus Understand how these conditions might occur. Understand the anatomical basis of the Q angle and how it could lead to joint pain Understand the mechanisms involved with locking and unlocking of the knee Know how the shape of the femoral condyles determines how the knee locks Know the role of the popliteus muslce in unlocking the knee. Know the attachments, actions, segmental and peripheral innervation of the muscles acting on the knee Be able to asses the function(s) of these muscles during the normal range of motion of the knee Be able to localize the site of appropriate nerve lesion by defecits in knee movement Be able to differentiate between how peripheral nerve lesions effect the knee from that of a lesion of the roots of the lumbosacral plexus. Understand the factors responsible for the position of the knee joint during each interval of the gait cycle. Be able to determine the site of a nerve lesion by defecits produced at the knee joint during gait. Understand the functions of thye ligaments and cartilages of the knee joint. Be able to test for the integrity of the muscles,ligaments and cartilages of the knee.

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