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Biomechanics of the Knee. Meagan Carnes, Kevin Chico, John Paul Dumas, Tanner Jones and Amy Loya. Learning Objectives. Identify the bones of the knee and describe their characteristics which facilitate joint function Name the ligaments in the knee joint and describe their function in the knee

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Biomechanics of the Knee

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Biomechanics of the knee

Biomechanics of the Knee

Meagan Carnes, Kevin Chico, John Paul Dumas, Tanner Jones and Amy Loya

Learning objectives

Learning Objectives

  • Identify the bones of the knee and describe their characteristics which facilitate joint function

  • Name the ligaments in the knee joint and describe their function in the knee

  • Identify the major flexor and extensor muscles in the knee

  • Describe molecular structure of tendons and apply these properties to the various functions of a tendon

  • Differentiate between osteoarthritis and rheumatoid arthritis as they relate to the knee joint

Bones of the knee

Bones of the knee

  • tibia

  • femur

  • fibula

  • patella

Knee joints

knee joints

  • tibiofemoral joint – femur and tibia

  • patellofemoral joint – patella and femur



  • specific structural characteristics of the posterior end of the femur allow it to successfully articulate with both the tibia and the patella

  • important characteristics:

    • medial & lateral condyles

    • patellar surface

    • intercondylar fossa

Femoral condyles

Femoral Condyles

  • medial and lateral condyles

  • the condyles’ round nature allow them to articulate smoothly with the tibial plateau

posterior view of right femur

Intercondylar fossa

Intercondylar fossa

  • posterior, deep notch between the two condyles

inferior view of right femur

Patellar surface

Patellar Surface

  • the central, anterior portion between condyles is grooved

inferior view of right femur



  • triangular shaped, sesamoid bone

  • anterior surface is convex, while the posterior surface is divided into a medial and lateral facets for articulation with the femur

posterior surface of right patella

Patella as a pulley

Patella as a pulley

  • a pulley changes the direction of an applied force

  • the patella helps to support the work of the quadricep muscles during the contraction of the quadricep that allows for extension of the knee



  • the portion of the tibia proximal to the femur plays a significant role in the knee joint

  • important characteristics:

    • medial and lateral condyles/plateaus

    • intercondyloid eminence

    • tibial tuberosity





Tibial plateau

Tibial Plateau

  • medial and lateral plateaus

  • oval and concave in shape

Intercondyloid eminence

Intercondyloid eminence

  • located between the plateaus, near the posterior end

  • tubercles on either side of the eminence

  • above and below are the intercondyloid fossa

Tibiofemoral joint

Tibiofemoral joint

  • due to the oblique nature of the femur, the angle at which the femur and tibia come in contact is not 180°, but rather 185°

  • deviation of more than 5° from this creates varied stresses on the medial and lateral components of the femur and tibia





Cartilage of the knee

Cartilage of the Knee

  • Menisci

    • lateral meniscus and medial meniscus

  • Articular Cartilage

    • located on femur, tibia,

      and patella

Articular cartilage

Articular Cartilage

  • hyaline cartilage on the articular surface of bone

  • located on the tibial and femoral condyles and the posterior portion of the patella

  • smooth, slippery surface that allows for minimal friction of the joint



  • lateral meniscus and medial meniscus are c-shaped fibrocartilage located on top of the tibial condyles

  • both together form a depression in which the femoral condyles sit

Meniscus distributes stress

Meniscus distributes stress

Synovial membrane

Synovial Membrane

  • blood vessels begin to diminish in the meniscus over time, which limits the nutrition required to keep it healthy

  • the inner portion of the meniscus relies on the synovial fluid to gain nutrients

  • also useful in maintaining joint motion

Ligaments in the knee




Ligaments in the Knee




ACL – Anterior Cruciate Ligament

PCL- Posterior Cruciate Ligament

LCL – Lateral Collateral LigamentMCL-Medial Collateral Ligament



Acl tear in mri test

ACL Tear In MRI test

Actual acl tear

Actual ACL Tear

Ligament injuries

Ligament Injuries

  • Three Classes of tendon injury(1, 2, 3)

  • Injuries to any of the ligaments are cause by

    • Twisting your knee with the foot planted.

    • Getting hit on the knee.

    • Extending the knee too far.

    • Jumping and landing on a flexed knee.

    • Stopping suddenly when running.

    • Suddenly shifting weight from one leg to the other.

Symptoms of injured ligaments

Symptoms of Injured Ligaments

  • Swelling

  • Severe Pain

  • Instability in Joint

  • Inability to load the joint

  • Hearing a pop sound when injured

  • Decreased Range of motion

  • Diminished Strength

Testing knee ligaments

Testing Knee Ligaments

  • Lachman Test (ACL)

  • Piviot Shift Maneuvor (ACL)

  • Opposite of Lachman Test (PCL)

  • Valgus Stress Test (MCL)

  • Varus Stress Test (LCL)

  • MRI

  • Xrays

  • Testing Range of Motion

  • Testing Strength of Quad

Treatment options

Treatment Options

  • Physical Therapy-rebuild knee strength, allow for ligament to heal on its own

  • Arthroscopic Surgery- Remove torn tissue, and stitch ligament back together

  • Orthopedic Surgery – Removal of torn ligament(s) and replaced by a new one.

    • Patella Tendon

    • Hamstring Tendon

    • Cadaver

Orthopedic surgery for the acl

Orthopedic Surgery For The ACL

  • First the knee is probed to check knee joint

  • Torn ACL is removed by an electric shaver

  • Remove some femoral bone

    • Place graph in the correct position

  • Drill to create the Femoral Tunnel

  • Drill Tibial Tunnel into the joint

  • ACL graft is then passed through Tibial tunnel up through the femoral tunnel using a suture



Muscles of the knee

Muscles of the Knee

  • Considered a mechanically weak joint

  • Multiple muscles cross the knee joint but we are primarily concerned with the main flexors/extensors.

  • Extensors – Quadriceps

  • Flexors – Hamstrings

  • Secondary functions are rotation and adduction/abduction leg

  • Two joint muscles

Major muscle groups

Major Muscle Groups

Extensors quadriceps

Extensors (Quadriceps)

Quadriceps cont

Quadriceps (cont.)

Rectus Femoris

Force modeling

Force Modeling

  • For modeling these 4 muscles (RF, VL, VI, VM) can be represented by a single upward force

  • All 4 are controlled by the femoralnerve

Additional extensors

Additional Extensors

  • Muscles do not need to cross a joint to be involved in joint motion

  • The soleus (calf) and gluteus maximus can help extend when foot is on the ground

Flexors hamstrings

Flexors (Hamstrings)


Hamstrings cont

Hamstrings (cont.)

Additional flexors

Additional Flexors

  • Satorius

    • Longest muscle in the body

    • Responsible for rotating knee after flexion

  • Gracilis

    • Most superficial muscle on medial side of the knee

  • Popliteus

    • Responsible for locking the knee

  • Sit to stand motion

    Sit-to-Stand Motion

    • Lombard’s Paradox

      • What is it?

      • How is it explained?

    • Muscles cannot develop different amounts of force in their different parts


    Quad and hamstring injuries

    Quad and Hamstring Injuries

    • Rectus Femoris is most susceptible because it is in contact with the femur throughout its length

    • The muscle is more resistant to injury if it is struck while in a contracted non-fatigued state.

    • Hamstring injuries often caused by abrupt stops or starts


    What are tendons

    What are Tendons?

    • Tendons are bundles or bands of strong fibers that attach muscles to bones

    Knee tendoncies

    Knee Tendoncies

    Tendons associated with the knee joint include:

    Patellar Tendon

    Lateral Retinaculum

    Pes Anserine Tendons

    Biceps Tendon

    Popliteal Tendon

    Hamstring Tendon

    Quadriceps Tendon


    Illiotibial Tendon

    Medial Retinaculum

    Anterior view

    Anterior View

    Quadriceps Tendon

    Illiotibial Tendon

    Medial Retinaculum

    Lateral Retinaculum

    Patellar Tendon

    Posterior view

    Posterior View

    Popliteal Tendon

    Biceps Tendon

    Medial view of right knee

    Medial View of Right Knee

    Quadriceps Tendon


    Patellar Tendon

    Pes Anserine Tendons

    Lateral view of right knee

    Lateral View of Right Knee

    Illiotibial Tendon

    Quadriceps Tendon

    Hamstring Tendon

    Lateral Retinaculum

    Patellar Tendon

    Tendon injuries and disorders

    Tendon Injuries and Disorders

    • The three main types of tendon injuries and disorders are:

      • Tendinitis and ruptured tendons

      • Osgood-Schlatter disease

      • Iliotibial band syndrome

    • Treatment for tendon injuries and disorders include:

      • Rest

      • Ice

      • Elevation

      • Medicines such as aspirin or ibuprofen to relieve pain and reduce swelling

      • Limiting sports activity

      • Exercise for stretching and strengthening

      • A cast, if there is a partial tear

      • Surgery for complete tears or very severe injuries.

    Tendinitis and jumper s knee

    Tendinitis and Jumper’s Knee

    Osgood schlatter disease

    Osgood-Schlatter Disease

    Biomechanics of the knee

    Inflammatory Conditions of the Knee Joint

    1. Bursitis

    2. Tendonitis

    3. Synovitis

    Biomechanics of the knee

    Treating Inflammatory Conditions


    Steroid Injections


    Surgery in Severe Cases

    Biomechanics of the knee

    Forms of Arthritis Affecting the Knee Joint

    • Osteoarthritis

    • Rheumatoid Arthritis

    • Post-traumatic Arthritis

    Biomechanics of the knee

    Osteoarthritis in the Knee Joint

    Biomechanics of the knee

    Rheumatoid Arthritis


    Treating arthritic conditions

    Treating Arthritic Conditions

    • Osteoarthritis

      • Rest

      • Analgesics

      • Steroid Injections

      • Decreased Use

      • Knee Replacement surgery as a last resort

    • Rheumatoid Arthritis

      • Analgesics

      • Physical Exercise

      • Surgery to remove damaged synovial fluid when caught early

      • Knee Replacement surgery as a last resort

    Biomechanics of the knee

    Knee Replacement- Knee Arthroscopy

    • “96% of Knee Replacements are due to osteoarthritis”

    • “Osteoarthritis was the 4th most frequent principal diagnosis for hospital stays in 2009.”

    • “Approximately 12% of adults over 60 have symptoms of knee osteoarthritis.”

      • Natalie Fawzi, July 2012

    Biomechanics of the knee

    Components of the Knee Replacement

    • Metal Femoral Component

    • Metal Tibial Component

    • Plastic Patellar Component

    • Plastic Articulating Spacer

    Biomechanics of the knee

    Components of the Knee Replacement

    Different types of materials used

    Different Types of Materials Used

    • Stainless Steel

    • Cobalt-chromium Alloys

    • Titanium and Titanium Alloys

    • Uncemented implants

    • Tantalum

    • Polyethylene

    • Zirconium

    Pros and cons

    Pros and Cons

    • Minimally invasive

    • 80% of current knee replacements last for up to 20 years

    • Greatly improve knee functioning and restore a good quality of life

    • 90% of patients experience a radical decrease in pain

    • 6.1% of patients experience a complication during the hospital stay

    • 7.5% experience a complication within 90 days of the procedure

    • Revision rates

      • 0.2% within 90 days

      • 3.7% within 18 months

      • 6% after 5 years

      • 12% after 10 years



    • Givens: Quadriceps tendon is inserted on the tibia 5 cm from the knee joint, and is at a 30deg angle. Weight of the lower leg Is 48 N. Center of gravity of the lower leg is 0.20 m from the knee joint.

    Determine Fquad required to hold the lower leg in static equilibrium

    Determine the joint reaction force of the femur

    Biomechanics of the knee






    48 N

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