Transcript ESS 303 -- Biomechanics

ESS 303 – Biomechanics
Knee Joint
Knee Joint
2 convex surfaces (femur) articulating
with 2 concave surfaces (tibia)
Poor bony stability
Stability increased with cartilage and
ligaments
Up to 80% of knee stability comes from
muscles
Knee Joint
 2 semicircular menisci surround the medial
and lateral rims of the condylar facets of the
tibia
 increase depth of concavity
 stabilize femur
 medial meniscus is larger of the two and allows
slight rotation and locking mechanisms of the knee
joint
 Medial tibial condylar facet is 50% larger than
the lateral and has 3 times the articular
cartilage thickness
Knee Ligaments
 The medial collateral ligament (MCL) prevents
the knee from buckling inwards
 The lateral collateral ligament (LCL) prevents
the knee from buckling outwards
 The anterior cruciate ligament (ACL) prevents
the tibia from sliding forwards under the femur
 The posterior cruciate ligament (PCL) prevents
the tibia from sliding backwards under the
femur
ACL
PCL
MCL
LCL
Anterior View
Posterior View
Common Knee Injuries
 Popliteal tendonitis (downhill gate)
 Deep squat (weightlifting)
 Breaststroker’s knee (swimming)
 ACL injury (alpine skiing – “phantom foot fall”)
 PCL injury (clipping)
 Meniscus injuries (most common knee injury,
may case locking, )
 Hurdler’s position stretch (pry apart MCL)
Knee Ligaments
Knee Ligaments
Knee Positions
Femoral Varus
Genu Valgum
Tibial Valgus
Knock-Knee
Knee Positions
Femoral Valgus
Genu Varum
Tibial Varus
Bow Leg
Knee Positions
Genu Valgum
Knee Positions
Genu Varum
Knee Positions
Genu Recurvatum
Knee Positions - Surgical Correction
Movements and Major Muscles
 Flexion: gastrocnemius & Hamstrings
(semitendinosus, semimembranosus & biceps
femoris)
 Extension: Quadraceps (rectus femoris, vastus
lateralis, vastus medialis & vastus intermedius)
 Medial rotation (about 20° when flexed 90°):
Semitendinosus & semimembranosus
 Lateral rotation (about 30° when flexed 90°): biceps
femoris
 Medial and lateral rotation allow feet (weight bearing
and non-weight bearing) to turn without tearing knee
ligaments