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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

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
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



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)
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.

Inflammatory Conditions of the Knee Joint

1. Bursitis

2. Tendonitis

3. Synovitis


Treating Inflammatory Conditions


Steroid Injections


Surgery in Severe Cases


Forms of Arthritis Affecting the Knee Joint

  • Osteoarthritis
  • Rheumatoid Arthritis
  • Post-traumatic Arthritis


Osteoarthritis in the Knee Joint


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

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


Components of the Knee Replacement

  • Metal Femoral Component
  • Metal Tibial Component
  • Plastic Patellar Component
  • Plastic Articulating Spacer


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







48 N