Biomechanics of the Knee

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

Learning Objectives1. Identify the bones of the knee and describe their

characteristics which facilitate joint function2. Name the ligaments in the knee joint and describe

their function in the knee3. Identify the major flexor and extensor muscles in

the knee4. Describe molecular structure of tendons and apply

these properties to the various functions of a tendon

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

Bones of the knee

1. tibia2. femur3. fibula4. patella

knee joints

•tibiofemoral joint – femur and tibia

•patellofemoral joint – patella and femur

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• medial and lateral condyles• the condyles’ round nature allow them to

articulate smoothly with the tibial plateau

posterior view of right femur

Intercondylar fossa

• posterior, deep notch between the two condyles

inferior view of right femur

Patellar Surface• the central, anterior portion between

condyles is grooved

inferior view of right femur

Patella• 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

• 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

Tibia• 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

anteriorview

posteriorview

Tibial Plateau• medial and lateral plateaus• oval and concave in shape

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

• 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

anatomicalaxis

mechanicalaxis

Cartilage of the Knee• Menisci– lateral meniscus and medial meniscus

• Articular Cartilage– located on femur, tibia, and patella

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

Menisci• 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

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

ACL – Anterior Cruciate Ligament

PCL- Posterior Cruciate Ligament

LCL – Lateral Collateral Ligament

MCL-Medial Collateral Ligament

ACLFemur

PCL

MCLLCL

Tibia

LCL

Fibula

ACL Tear In MRI test

Actual ACL Tear

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

• 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• 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• 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• 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• http://www.youtube.com/watch?v=PjL7-tIsQhw• http://www.youtube.com/watch?v=q96M0jRqn7

k

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

http://www.medicalook.com/human_anatomy/organs/Muscles_involved_in_knee_motion.html

Extensors (Quadriceps)

http://www.floota.com/quadricepsstretch.html

Quadriceps (cont.)

Rectus Femoris

Force Modeling

http://www.slideshare.net/SubhanjanDas/knee-biomechanics

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

• All 4 are controlled by the femoral nerve

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)

• http://wavesport.ning.com/profiles/blogs/a-paddler-s-pelvis

Hamstrings (cont.)

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

• Lombard’s Paradox– What is it?– How is it explained?

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

THE ACTION OF TWO-JOINT MUSCLES: THE LEGACY OF W. P. LOMBARD

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

A

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

Knee Tendoncies

Tendons associated with the knee joint include:

Anterior View

Posterior View

Medial View of Right Knee

Lateral View of Right Knee

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

Osgood-Schlatter Disease

http://www.aidmybursa.com/bursitis/bursitis-information.php

Inflammatory Conditions of the Knee Joint

http://www.eorthopod.com/sites/default/files/images/knee_prepatellar_intro01.jpg

1. Bursitis2. Tendonitis3. Synovitis

Treating Inflammatory Conditions

http://www.kelseypro.com/Vaso/Synovectomy_knee_dyn.jpg http://www.eorthopod.com/sites/default/files/images/knee_prepatellar_intro01.jpg

R.I.C.E.Steroid InjectionsAnalgesicsSurgery in Severe Cases

http://www.barc.org.uk/arthritis/rheumatoid/index.html

Forms of Arthritis Affecting the Knee Joint1. Osteoarthritis2. Rheumatoid Arthritis3. Post-traumatic Arthritis

http://orthoinfo.aaos.org/topic.cfm?topic=a00389

Osteoarthritis in the Knee Joint

http://www.lurj.org/article.php/vol2n1/arthritis.xml http://orthoinfo.aaos.org/topic.cfm?topic=a00389

Rheumatoid Arthritis Osteoarthritis

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

http://orthoinfo.aaos.org/topic.cfmtopic=a00389

Knee Replacement- Knee Arthroscopy

http://www.healthline.com/health/total-knee-replacement-surgery/statistics-infographic

http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/health_tools/knee_replacement_slideshow/agefoto_rf_photo_of_knee_replacement_compnents.jpg

Components of the Knee Replacement

1. Metal Femoral Component2. Metal Tibial Component3. Plastic Patellar Component4. Plastic Articulating Spacer

http://www.hss.edu/conditions_arthritis-of-the-knee-total-knee-replacement.asp

http://orthoinfo.aaos.org/topic.cfmtopic=a00389

Components of the Knee Replacement

Different Types of Materials Used

• Stainless Steel• Cobalt-chromium Alloys• Titanium and Titanium Alloys• Uncemented implants• Tantalum• Polyethylene• Zirconium

http://bonesmart.org/knee/knee-replacement-implant-materials/

Pros and Cons

http://sentarainfo.com/today/2012/02/the-sounds-of-caring/http://arthritiskerala.com/disease-treatment.php?id=7

•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

http://www.healthline.com/health/total-knee-replacement-surgery/statistics-infographic

•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

Problem!• 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.

1.Determine Fquad required to hold the lower leg in static equilibrium

2.Determine the joint reaction force of the femur

48 N

T30°

Fquad

Rx

Ry