knee

Definitions of Components Involved in the Knee

  • Femur: The distal end of the femur forms part of the knee joint, critical for its function.
  • Tibia: The proximal end of the tibia is also integral to the knee joint structure.
  • Patella: A sesamoid bone that serves an important role in knee articulation.
  • Knee: Defined as a joint that connects the thigh to the leg and lacks bony stability, which means it is held together entirely by ligaments and muscles.
  • Fibular Head: Though it does not participate directly in the knee joint, it acts as a bony attachment for muscles that support the knee.

Bones of the Thigh and Leg

Femur

  • Long bone located in the thigh.
  • Anatomical Features:
    • Medial and Lateral Condyles: Rounded prominences at the distal end that articulate with the tibia.
    • Medial and Lateral Epicondyles: Projections above each condyle that serve as attachment sites for ligaments.
    • Trochlea: Smooth groove for the patella to glide in during joint movement.
    • Adductor Tubercle: A bony prominence that serves as an attachment point for muscles.
    • Popliteal Region: Area behind the knee joint.
    • Linea Aspera: A ridge on the posterior surface of the femur where muscles attach.

Tibia

  • Long bone of the shin.
  • Anatomical Features:
    • Plateau: Upper surface that forms the joint with the femur.
    • Medial and Lateral Condyles: Articulating surfaces that receive the femoral condyles.
    • Tibial Tuberosity: Bump on the anterior surface for attachment of the patellar ligament.
    • Popliteal Area: Same region as previously mentioned regarding the femur.
    • Pes Anserinus: Area on the medial tibia for muscle attachment.

Patella

  • Sesamoid bone encased in the quadriceps tendon/ligament.
  • Anatomical Features:
    • Base: The top part of the patella.
    • Apex: The bottom point of the patella.
    • Posterior Surface: Contains medial and lateral articular facets for contact with the femur.

Supporting Structures of the Knee

Pelvis

  • Although not part of the knee structure, the muscles that move the knee have attachments in the pelvis.
  • Major Landmarks:
    • ASIS (Anterior Superior Iliac Spine)
    • AIIS (Anterior Inferior Iliac Spine)
    • Ischial Tuberosity: Site for muscle attachments related to knee function.

Fibula

  • Also not a part of the knee but serves as an attachment site for muscles that support the knee.
  • Anatomical Features:
    • Styloid Process
    • Head: The top part of the fibula.
    • Neck: Part below the head.

Articulations in the Knee

Tibio-Femoral Joint

  • Articulation between the tibia and femur.
  • Type: Synovial hinge joint.
  • Motions Allowed:
    • Flexion/Extension: Bending and straightening movements.
    • Roll and Glide: Describes how the bones move during these actions.
    • Slight Rotation: Rotation permitted within the range of movement.
    • Hyperextension: Extension beyond the normal range.

Patellar-Femoral Joint

  • Articulation between the patella and femur.
  • Not classified as a “true” joint due to the nature of its connection.
  • Motions Allowed:
    • Patella glides within the trochlear groove, moving:
      • Superiorly: During knee extension.
      • Inferiorly: During knee flexion.
    • The patella enhances quadriceps' ability to generate force as it acts like a pulley, improving the line of force application.

Tibio-Fibular Joint

  • Articulation that occurs at the superior tibiofibular joint, allowing for slight gliding motions.

Planes of Motion

Sagittal Plane

  • Permits Extension and Flexion of the knee.

Transverse Plane

  • Permits Medial (Internal) Rotation and Lateral (External) Rotation of the knee.

Knee Motions and Mechanisms

Flexion

  • Definition: Movement where the posterior surfaces of the thigh and leg come closer.
  • Motion: The patella moves inferiorly during flexion.
  • Concept Check: Identify the direction of the roll and glide during open-chain extension.

Extension

  • Definition: The tibia and femur align during this movement.
  • Motion: The patella moves slightly superior within the trochlea.
  • Concept Check: Identify the direction of roll and glide during open-chain extension and during closed-chain conditions.

Screw Home Mechanism

  • Explanation: Due to anatomical differences, the medial condyle is longer than the lateral condyle.
  • This length difference creates slight rotational movement during flexion and extension.
  • The last portion of this rotation is termed the “screw home” mechanism.
  • Specifics:
    • Open Chain: Tibia moves on femur with slight lateral rotation at the end of extension.
    • Closed Chain (Weight Bearing): Femur moves on tibia with slight medial rotation at the end of extension.

Cartilage in the Knee

General Function

  • Cartilage serves to protect bony surfaces and absorbs shock within the weight-bearing joint structure of the knee.
  • Types:
    • Fibrocartilage: Found in the menisci.
    • Articular Cartilage: Found on the surfaces of the bones.

Menisci

  • Two C-shaped rings attached to the tibial plateau, providing stability.
  • Features:
    • More thickness laterally compared to medially.
    • Concave surfaces shape to accommodate femoral condyles, enhancing joint stability.
Medial Meniscus
  • Has a more open C shape.
  • Connections:
    • Attached to the Medial Collateral Ligament (MCL) and hamstring tendon fibers.
  • More frequently injured compared to the lateral meniscus.
Lateral Meniscus
  • Has a closed O shape.
  • Rarely sustains injuries on its own, often associated with other structures.

Meniscal Tears

  • Common types of tears include:
    • Horizontal Tear
    • Radial Tear
    • Oblique Tear
    • Longitudinal Tear
  • Zones of Repair:
    • White Zone: Contains no blood supply; poor healing potential.
    • Red Zone: Has a rich blood supply; higher healing potential.

Ligaments of the Knee

General Function of Ligaments

  • Ligaments attach bone to bone and provide stability to the knee joint, which is crucial for optimal function.

Patellar Ligament

  • Continuation of the patellar/quadriceps tendon extending from the patella to the tibial tuberosity.
  • Function: Stabilizes the patella while transmitting the quadriceps' force to the leg.

Anterior Cruciate Ligament (ACL)

  • Location: Deep within the knee, extending from the medial side of the tibia to the lateral side of the femur.
  • Functional Properties:
    • More anterior than the Posterior Cruciate Ligament (PCL).
    • Taut during knee extension.
  • Prevents:
    • Tibia sliding anteriorly on femur.
    • Hyperextension of the knee joint.

Posterior Cruciate Ligament (PCL)

  • Location: Deep within the knee, from the lateral side of the tibia to the medial side of the femur.
  • Functional Properties:
    • More posterior than the ACL.
    • Taut during knee flexion.
  • Prevents:
    • Tibia from sliding posteriorly on the femur.

Lateral Collateral Ligament (LCL)

  • Also known as the fibular collateral ligament.
  • Structural Characteristics:
    • Cord-like in shape.
    • Extends from the lateral femur to the fibular head.
  • Prevents varus stress (a force pushing laterally through the knee).

Medial Collateral Ligament (MCL)

  • Also known as tibial collateral ligament.
  • Structural Characteristics:
    • Broad and flat ligament.
    • Connects from the medial condyle of the femur to the medial condyle of the tibia.
  • Prevents valgus stress (a force pushing medially through the knee).

Joint Capsule and Bursae

Joint Capsule

  • Made up of wide, lax fibrous tissue that encloses all bony structures of the knee joint.
  • The MCL forms part of the medial portion of the capsule, while other ligaments and tendons remain separate.

Bursae

  • Description: Small, fluid-filled sacs situated in areas of friction.
  • Function: Cushion and prevent irritation of tendons during knee movement.
  • Total Count: 13 bursae within the knee structure.

Muscles Associated with the Knee

Quadriceps Muscle Group

  • Location: Anterior thigh.
  • Components:
    • Rectus Femoris
    • Vastus Lateralis (VLO)
    • Vastus Intermedius
    • Vastus Medialis (VMO)
  • Common Action: Extension of the knee joint.
  • Common Innervation: Femoral nerve.
  • Concept Check: Identify which of these muscles has an action at the hip and what that action is.

Hamstring Group

  • Location: Posterior thigh.
  • Components:
    • Biceps Femoris (long and short heads)
    • Semimembranosus
    • Semitendinosus
  • Common Action: Flexion of the knee and hip extension (the short head of biceps femoris is an exception).
  • Common Innervation: Sciatic nerve.

Additional Muscles with Actions at the Knee

  • Other muscles worthy of note (primarily acting elsewhere):
    • Gastrocnemius
    • Plantaris
    • Popliteus
    • Gracilis
    • Sartorius
    • Tensor Fascia Lata (TFL)
    • Iliotibial Band (ITB)

Important Landmarks

Popliteal Area

  • Definition: A region at the posterior aspect of the knee.
  • Borders: Defined by muscular structures surrounding the area.
  • Contains:
    • Tibial Nerve
    • Common Peroneal Nerve
    • Popliteal Artery
    • Popliteal Vein

Pes Anserine

  • Description: A common attachment point for three muscles:
    • Sartorius
    • Gracilis
    • Semitendinosus
  • Location: Medial, anterior surface of the tibia.
  • Associated Structure: Pes anserine bursa, provides cushion and decreases friction.

Innervation

Dermatomes

  • Thigh: L3
  • Anterior Knee: L4
  • Posterior Knee: S1-S2

Myotomes

  • Motor Control: Muscles originating from the lumbar portion of the lumbosacral plexus (L3-S2).
  • Innervation:
    • Knee Movement: L3, L4, L5, S1

Innervation of Muscles of the Leg

  • Femoral Nerve: Formed from branches exiting from L2-L4; innervates the quadriceps group and sartorius.
  • Sciatic Nerve: Brushes off lumbar plexus (L4-S3); primarily innervates hamstrings (knee flexors).
  • Obturator Nerve: (L2-L4) innervates gracilis.
  • Superior Gluteal Nerve: (L4-S1) innervates TFL.

Posture and Abnormalities at the Knee

Q-angle

  • Also known as the patellofemoral angle.
  • Defined as the angle between the long axis of the femur and the patellar tendon.
  • Noted Differences:
    • Females tend to have a greater Q-angle compared to males.
    • This angle can serve as a predictor for knee injuries.

Abnormalities

Genu Valgus
  • Also known as knock-knees, where the knees angle inward.
Genu Varus
  • Also known as bow-legged, where the knees angle outward.
Genu Recurvatum
  • Refers to knee hyperextension, where the knee extends beyond its normal straight position.

Laboratory Component

Key Identification Skills

  • Palpation of bones and landmarks associated with the knee.
  • Review of muscles concerning origin, insertion, action (O, I, A).

Key Concepts Summary

  1. Identification of bony landmarks and their attachment points.
  2. Understanding the tibiofemoral, patellofemoral, and tibiofibular joints, including components involved.
  3. Examination of motions, axes, and planes associated with these joints.
  4. Study of muscles regarding origin, insertion, action, and innervation.
  5. Review of ligaments and the motions they prevent.
  6. Location and function of menisci.
  7. Understanding the mechanisms leading to knee joint stability.
  8. Insight into various postural abnormalities and their implications on performance.