Kinesiology of the Musculoskeletal System Chapter 13

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Kinesiology of the Musculoskeletal
SystemChapter 13

• The Knee

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Knee Joint

• One of the largest joint complexes of the body
• Condyloid joint tibiofemoral roll and slide
  kinematics
• Patellofemoral joint planar joint
• Positioned between two long bones increasing
  vulnerability to torque forces
• Controlled largely by large two joint muscles
• Stability based primarily on its soft tissue
  constraints
• Moves in two planes
• Sagittal Flexion/Extension
• Horizontal Internal/External Rotation

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Anatomical Structures of the Knee

• Femoral Condyles medial and lateral
• Articular Cartilage
• Tibial Plateau
• Patella
• Menisci medial and lateral
• Ligaments ACL, PCL, MCL, LCL
• Musculotendinous structures
• Fibular head
• Joint Capsule

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Anatomy of the Knee
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Anatomy of Knee
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Patella

• Largest sesamoid bone in the body
• Free floating bone attached chiefly by quadriceps
  tendon and patellar ligament
• Chief function is to increase the IMA of knee
  extension mechanism
• Undersurface articulates with the intercondylar
  region of the femur and has a thick articular
  cartilage layer to disperse large compression
  forces of this patellofemoral joint
• Patellofemoral pain is one of the most common
  knee ailments in athletes and the general
  population

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Tibiofemoral Patellofemoral Joints
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Knee Joint Capsule

• Fibrous capsule reinforced by muscles, tendons,
  ligaments and fascia
• No bony block against hyperextension muscles and
  capsule limits hyperextension

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Knee Alignment

• Normal alignment is in slight genu valgum
  170-174 degrees due to angle of inclination of
  the femoral head
• Excessive Genu Valgum lateral angle of knee is
  less than 170 degrees, aka Knock Knees
• Genu Varum lateral angle of knee is greater
  than 180 degrees, aka Bow Legs
• Longitudinal or Vertical axis of rotation line
  connecting femoral head with the center of the
  knee joint Mechanically links horizontal plane
  movements of the major lower limb joints
  horizontal plane movement of any lower limb joint
  can directly affect the other lower limb joints

Genu Valgum
Genu Varus
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Menisci

• Menisci crescent shaped fibrocartilagenous
  discs located within the knee joint
• Medial C shaped Lateral O shaped
• Loose ligamentous attachment to tibia and joint
  capsule allows menisci to pivot/slide during knee
  movement
• Shock absorption reduces
• compressive stress
• Deepens articular surface
• of tibia for femoral condyles
• increases joint contact 3X
• Guides femoral motion

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Menisci (cont.)

• Increases joint surface contact 3X
• During walking, menisci deform peripherally with
  each step
• Joint Reactive Force approximates 3X body weight
  with each step
• Menisci support 50 of load across the knee
• Removal of lateral meniscus increases peak
  contact pressures 230
• Extreme compression (high impulse) can fracture
  menisci and underlying bone

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Menisci (cont.)

• Poorly vascularized
• only outer edges
• of the menisci
• have a blood supply
• Poor repair
• Poor nerve supply
• often non-painful

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Cadaver Tibiofemoral Joint
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Cadaver Menisci
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Tibiofemoral Arthrokinematics

• Flexion/Extension Internal/External rotation
• Menisci follow tibia
• Roll Slide

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Tibiofemoral Flexion/Extension

• Flexion to 130-140 degrees
• Extension to 5-10 degrees of hyperextension
• Axis of Rotation varies or migrates through F/E
  termed evolute alters IMAs and may have
  clinical and training implications

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Tibiofemoral Internal/External Rotation

• Axial rotation in the horizontal plane
• Near zero degrees of I/E rotation with knee fully
  extended
• Up to 50 degrees of total I/E rotation with knee
  in 90 degrees of flexion
• External Internal 2 1
• Tibial on Femoral
• Femoral on Tibial

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Tibiofemoral Internal/External Rotation
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Femoral on Tibial Rotation

• Femoral rotation on a relatively fixed tibia
• Requires some
• degree of knee
• flexion
• High level of
• vulnerability
• especially when
• coupled with
• muscular force
• production

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Screw Home Mechanism

• 10 degrees of coupled external rotation during
  the final 30 degrees of knee extension
• T on F Screw Home is more evident but F on T SHM
  does occur
• SHM caused by
• Shape of medial femoral condyle
• Passive tension of the ACL as knee is extended
• Lateral pull of the quadriceps muscle group

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Active Flexion of the Knee

• From full extension, the Screw Home Mechanism is
  reversed
• Knee joint is unlocked by popliteus muscle
  creating knee flexion and internal rotation
• T on F or F on T

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Ligaments of the Knee

• Medial Collateral Ligament (MCL) primarily
  checks valgus stress has attachment to meniscus
• Lateral Collateral Ligament (LCL) primarily
  checks varus stress blends with biceps femoris
  tendon

MCL
LCL
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Ligaments of the Knee (cont.)

• Anterior Cruciate Ligament (ACL) primarily
  checks posterior to anterior shear forces
• Posterior Cruciate Ligament (PCL) primarily
  checks anterior to posterior shear forces
• AP and PA shear forces commonly seen in sagittal
  plane motion, i.e. walking, running, jumping,
  squatting

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Ligaments of the Knee (cont.)

• Acting together
• ACL and PCL
• limit extremes
• of knee motions
• in all directions
• Intracapsular
• Extrasynovial

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ACL Injury

• Most frequently injured ligament of the knee
  especially with high velocity stretch while
  ligament is under tension
• Often seen in cutting
• and jumping sports,
• i.e. football, soccer,
• skiing, volleyball,
• basketball
• Up to 80 of
• ACL injuries are
• non-contact injuries

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PCL Injury

• Slightly thicker and stronger
• than ACL
• Less vulnerable to injury
• Injured due to hyperflexion falling on
  hyperflexed knee contact injury to proximal
  tibia with planted foot (dashboard injury)
  landing from a jump with slightly flexed knee or
  rapid descent into full squat

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ACL / PCL Assessment
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ACL Kinesiopathology

• Partial or complete tear of the ACL will likely
  result in hamstring spasm in the short term or
  hamstring facilitation (increased activity) in
  the long term
• Hamstring muscles can
• help stabilize knee by limiting
• anterior tibia translation on
• the femur
• Increased hamstring muscle
• activity will Reciprocally Inhibit
• the quadriceps
• This reciprocal inhibition is
• based on the same neurology as
• the facilitation/inhibition found
• in many faulty postural muscle
• patterns

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ACL Rehab

• Early phase must limit tension on ACL
• Avoid open chain T on F exercises through full
  ROM
• Emphasize closed kinetic chain exercises loading
  quadriceps muscle in the final 45 degrees of F on
  T extension
• Mini-squats, terminal knee extension exercises

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T on F Extension
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Muscular Function at the Knee

• Knee Extensor Mechanism
• Isometric Contraction stabilizes knee and
  patella
• Eccentric Contraction decelerates the lower leg
  (ie. walking, running), absorbs shock, controls
  rate of descent of the bodys center of mass
  (i.e. sitting)
• Concentric Contraction accelerates the tibia (T
  on F) or the femur (F on T) raise the bodys
  center of mass (i.e. standing up, jumping)

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Knee Extensor Mechanism (cont.)
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Patellofemoral Mechanics

• Describes the position and movement of the
  patella within the inter-condylar groove
• Patellofemoral joint compressive forces may
  reach 3.3X BW while climbing stairs or 7.8X BW
  during deep knee bends
• Anatomical considerations (widening intercondylar
  groove, thickened articular cartilage, underlying
  soft tissue structures) help minimize the effect
  of these large compressive forces
• Patellofemoral compressive forces increase as
  knee flexion increases, and as quadriceps force
  production increases

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Patellofemoral Mechanics (cont.)
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Patellofemoral Tracking

• Describes the path taken by the patella through
  the intercondylar groove
• Contributing structures include the overall line
  
• 
  of force of the
• 
  quadriceps group,
• 
  pull of the vastus
• 
  medialis oblique
• 
  (VMO), patellar
  
• 
  retinacular fibers,
• 
  ilitotibial band

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Patellofemoral Tracking (cont.)

• Aberrant or abnormal tracking can
• lead to painful conditions including
• patellofemoral pain, chondromalacia
• patella, degenerative arthritis,
• subluxing or dislocating patella

Dislocated Patella
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Q Angle

• The degree of lateral pull exerted by the
  quadriceps, on the patella
• Formed between line representing the pull of the
  quadriceps (ASIS to patella) and a line
  connecting the tibial tuberosity with the patella
• Female Average 15.8 degrees, Male 11.2 degrees
• Contributing factors Width of pelvis degree of
  adduction of femur hip extensor and abductor
  strength patellar stability degree of tibial
  rotation foot, ankle stability degree of
  pronation

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Knee Flexor / Rotator Mechanism

• Except for the gastrocnemius, all muscles that
  cross the knee joint posteriorly function to flex
  rotate the knee (hamstrings, sartorius,
  gracilis, popliteus)
• Medial hamstrings (semimembranosus and
  semitendinosus flex and internally rotate the
  knee
• Lateral hamstrings (biceps femoris) flex and
  externally rotate the knee

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Knee Flexor / Rotator Mechanism (cont.)

• Flexor / Rotator muscles best perform their
  actions during walking and running, both
• T on F F on T
• T on F Flexor / Rotator muscles decelerate the
  tibia during walking or running
• F on T stabilize and/or rotate knee during
  walking or running

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References

• Neumann, D. Kinesiology of the Musculoskeletal
  System. 2002. Human Kinetics.