The Knee: Anatomy and Injuries
2 Joints at the Knee Tibiofemoral Joint – formed between tibia and femur A HINGE JOINT Patellofemoral joint – formed between the patella and the femur A GLIDING JOINT
Skeletal Anatomy Femur proximal – head and neck of femur, greater trochanter distal – medial and lateral condyles and epicondyles
Patella – largest sesamoid bone in body Tibia – tibial plateau forms knee joint with femur The fibula is not a part of the knee joint
http://uwmsk.org/RadAnatomy.html
Muscles that move the knee and thigh The Quadriceps – Knee Extension 1. Vastus Medialis 2. Vastus Lateralis 3. Vastus Intermedius 4. Rectus Femoris – 2 joint muscle that also acts as a hip flexor http://www.bodybuilding.com/exercises/detail/view/name/leg-extensions
The Hamstrings- knee flexion 3 muscles: 1. Biceps Femoris 2. Semimembranosus 3. Semitendinosus http://www.bodybuilding.com/exercises/detail/view/name/lying-leg-curls
The Adductors (Groin) Adduct the thigh 1. Adductor Longus 2. Adductor Magnus 3. Adductor Brevis 4. Gracilis http://www.5min.com/Video/Adductor-exercise-1924
The Sartorius: - flexes, abducts, and laterally rotates thigh - longest muscle in the body, “tailor’s muscle” - Crosses hip and knee joint
The Iliotibial Tract (IT Band) - neither a muscle or tendon, but a long, thick band of tissue that inserts into the lateral tibia (Gerdy’s Tubercle)
What muscles can you identify?
The Major Knee Ligaments 1. ACL – Anterior Cruciate Ligament prevents anterior motion of tibia 2. PCL – Posterior Cruciate Ligament prevents posterior motion of tibia 3. MCL – Medial Collateral Ligament 4. LCL – Lateral Collateral Ligament
ACL and PCL run from femur to tibia and form an X inside the knee
The Collateral Ligaments MCL: Medial Collateral Ligament Runs from medial femur to medial tibia LCL: Lateral Collateral Ligament Runs from lateral femur to head of fibula
The Meniscus A “c”-shaped piece of fibrocartilage located in the knee joint between the femur and attached to the top of the tibia Cartilage = meniscus
Differences between medial and lateral - larger and more C-shaped - more firmly attached to tibia - has attachments to MCL Lateral - smaller and more round or O-shaped - not firmly attached to tibia and LCL
Blood Supply to the Meniscus Mostly avascular – little or no blood supply Only the outer 20% has a blood supply * Does not have the ability to heal itself unless there is a small tear in the outer 20%
Functions of Meniscus Stability Shock absorption Lubrication and nutrition Allows adequate weight distribution
Normal Torn
Total Knee Joint Replacement Surgery to replace a painful damaged or diseased knee joint with an artificial joint (prosthesis) Artificial hip invented 1962 1969 – first artificial knee in USA
The Knee Surgery Thin layer of bone removed from femur – thin metal replaces it Upper layer of tibia replaced with plastic Back of patella replaced with plastic Parts fastened with “bone cement”
Risks of Knee Joint Replacement Blood clots in large veins Infection Stiffness Implant Loosening/Failure - more of a problem in younger patients
Knee Injuries and Conditions
Genu Valgum: “knock knees”
Genu Varum: “bowlegs”
Genu Recurvatum: hyperextension of the knee joint
Patellofemoral Disorders Problems with patella – most common cause of knee pain Anatomy: - Patella is a sesamoid bone formed in Quad tendon - Patellofemoral joint – patella and femur - Compression forces – <body weight during walking 2.5 x body weight during stairs
Patellar Tendonitis “Jumper’s Knee” Inflammation and degeneration of the tendon that connects the kneecap (Patella) to the shin bone (Tibia).
Chondromalacia Damage to the cartilage under the kneecap Causes: abnormal patellar tracking Most Common Symptom: Knee pain when walking up and down stairs Prevention: strengthen quads Minimize squats, downhill running, biking with low seat
Chondromalacia
Patellar Dislocation Involves the patella sliding out of its position on the knee. Caused by direct blow or abnormal twisting of the knee Usually lateral
Osgood-Schlatter Disease 1. Painful swelling over tibial tuberosity (patellar tendon insertion) 2. Usually occurs between 9-13 years of age 3. Pain increases with activity
The Chopat Strap
Iliotibial Band Friction Syndrome Occurs where IT Band rubs over femur at the knee joint Common in running (esp. downhill) or any activity with repetitive flexion Hills or stairs increase pain Lots of IT Band stretching
Popliteal Cyst “Baker’s Cyst” Fluid accumulation in posterior knee (popliteal space) Patient usually complains of a mass behind the knee
Prepatellar Bursitis “Housemaid’s Knee” Tender swelling over the kneecap (prepatellar bursa)
Pes Anserine Bursitis Inflammation of a bursa in your knee. The pes anserine bursa is located on the inner side of the knee just below the knee joint. Tendons of three muscles attach to the shin bone (tibia) over this bursa SGT: Sartorius, Semitendinosis, Gracilis
Knee Sprains
ACL Sprain >200,000 injuries/year >100,000 reconstructions/year Higher incidence in females Males = contact Females = noncontact http://www.youtube.com/watch?v=PzpOEdUdoM4
ACL Sprain 1. MOI: twisting of knee forced hyperextension lateral blow to knee *foot must be firmly anchored to playing surface 2. 50% of people describe a “pop” in knee 3. Knee fills with blood quickly Hemarthrosis 4. Usually immediate loss of motion Knee feels unstable http://www.youtube.com/watch?v=uuoj_HFG5Z0&feature=fvst
Anterior Drawer Test: examiner attempts to slide the tibia forward which may indicate a torn ACL ligament http://www.youtube.com/watch?v=1iWqUsd1aqY
ACL Sprain Who needs surgery? - Activity level? - Level of Competition - Age?
ACL Surgery Arthroscopic Graft options Patellar Tendon Semitendinosus Gracilis Cadaver Synthetic http://www.youtube.com/watch?v=Xsq0sQp6DwU http://www.youtube.com/watch?v=dZiDd6e4drc
PCL Sprain MOI: excessive hyperextension hyperflexion tibia forced posteriorly (blow to front of knee) “dashboard knee” Possibly 90% of all PCL injuries due to motor vehicle accidents?
Mild hemarthrosis Posterior knee pain Walk with knee slightly flexed, avoid full extension Posterior sag of tibia Surgery?
MCL Sprain MOI: Blow to the outside of the knee = Valgus Force Possible overuse – breaststroke in swimmers Commonly associated with meniscal injuries – attached to medial meniscus No surgery
MCL Sprain
Valgus Stress Test: tests for injury to the MCL ligament
LCL Sprain MOI: Blow to inside of the knee – Varus force Grade III tear may require surgery
Varus Stress Test: tests for injury to the LCL ligament
Injuries to the Meniscus MOI: Rotation of the knee as the knee extends during rapid cutting or pivoting
Signs and Symptoms: - pain - joint line tenderness - catching or locking - knee buckling or giving way - swelling - incomplete flexion - clicking on stair climbing
Surgery? Meniscectomy: removal of the meniscus - Total meniscectomy = osteoarthritis Depends on location of tear, type of tear, and blood supply
Types of Meniscal Tears bucket handle Flap tear Transverse tear Horn tear
Tests for Meniscal Tears Apley’s Compression
“The Unhappy Triad” Tear of the medial meniscus, anterior cruciate ligament (ACL), and medial collateral ligament (MCL)