Review of Knee Joint Function

Ligaments and menisci

  • Tibiofemoral: primary motion is between the distal femur and proximal tibia is flexion and extension with accessory motion of internal and external rotation.
    • Ligaments, menisci and the joint capsule are the primary static stabilizers
      • LCL and MCL excessive motion laterally and medially, respectively (side-to-side)
      • ACL and PCL control motion anterior and posteriorly, respectively (back and forth)
      • Menisci distribute the weightbearing forces from the femur onto the tibia; wedge shape provide additional stability
  • The medial meniscus is attached to: both cruciate ligaments, the medial collateral ligament, and the semimembranosus tendon. Any injury to these structures often creates a meniscal injury as well.

     

Muscles

Knee muscles function to produce movement and provide dynamic stability

  • gastroc provides soft tissue resistance preventing hyperextension; secondary knee flexor
  • popliteus muscle initiates open chain lateral tibal rotation to allow knee to flex from full extension
  • pes anserine (gracilis, sartorius, semitendinosus) are medial stabilizers for tibia rotation in closed chain
  • quadriceps, hamstrings, gastrocnemius produce motion and control motion at the knee
  • peak quadriceps function occurs at 70-50 degrees of flexion and is nearly exhausted at 15 degrees of flexion ( hence extensor lags)
  • The soleus assists with maintaining extension in standing.
  • hamstring strength is greatest when it is stretched by hip flexion (common to 2 joint muscles) and poor hamstring function can cause genu recurvatum due to poor posterior  instability.
  • the gastrocnemius can assist in protecting against hyperextension in closed chain activities.
  • the pes anserinus group help with medial knee stability.In regard to the pes anserine, recall that one of the members is attached to medial collateral ligament and an injury to this ligament can cause some pain referrals and dysfunctions in all the muscles due to their common attachment. A helpful memory device about the order of attachment and palpation is Say Grace before Tea. This is important to remember because medial collateral ligaments are often managed conservatively, and due to the extensive attachments, it is difficult to treat all the possible sequelae.

Patellofemoral joint

 

Patellofemoral: lies anterior to the distal femur and articulates in the intertrochlear groove. Primary motions are:

  • superior/cephalad (toward the head) with knee extension
  • inferior/caudad (toward the feet) knee flexion
  • Function is to increase the advantage of the quadricep for knee extension motion
    • Patella alta: describes a patella that sits too high on the femur; typically due to laxity in the quadriceps tendon and increases risk for patellar dislocation
    • Patella baja: describes a patella that sits too low on the femur; typically due to a tight quadriceps tendon or a tight quadriceps muscle
  • The Quadriceps Angle ("Q Angle") describes the angle between the hip and the patella and the patella with the tibial tubercle
    • the larger the Q angle the higher the risk for lateral knee pain and lateral patella dislocation due to increase lateral forces
  • Primary factors that influence patella femoral motion:
    • size of Q angle (larger = more lateral forces)
    • Tight muscles and fascia
      • IT band
      • lateral retinaculum
      • quadriceps
    • Quadriceps weakness, especially vastus medialis oblique (VMO)
    • Quadriceps imbalance (lateral quadricep is stronger than medial quadricep)
    • Hip muscle weakness: weak abductors, weak external rotators
  • Compression forces at the patellofemoral joint are high in mid-range flexion:
    • In the closed kinetic chain, patellar compression is maximum at 90 degrees of flexion, and rapidly rises at 30-60 degrees of flexion.
    • In the open kinetic chain, patellar compression is maximum at 30 degrees of flexion.
  • Patellofemoral dysfunction syndrome (PFDS) is most often attributed to faulty, excessive lateral tracking of the patella. This can be affected by Q-angle, tight iliotibial (IT) bands/tensor fascia lata (TFL), tight gluteus maximus, weak hip abductors and tight lateral retinaculum.Additionally, the patella is attached to the tibial tubercle by the ligamentum patella. A tight gastrocnemius will laterally rotate the tibial tubercle.  Are there any foot positions that cause ER of the tibia? Keep this in mind for next week.

 

  • The "screw home" mechanism describes the motion between the femur and tibia in the terminal extension (0-30 degrees)
    • occurs because the medial femoral condyle is larger, so lateral structures (femoral condyle, meniscus) are congruent sooner with extension
      • open chain: tibia externally rotates on femur in terminal extension
      • closed chain: femur internally rotates on the tibia in terminal extension
    • popliteus - unlocks knee with open chain motions
    • hip external rotation - unlocks knee with closed chain motions
    • Medial tibial condyle is longer than lateral tibial condyle. The medial femoral condyle will be moving longer than lateral condyle and will slide further posterior. This is responsible for the screw home mechanism of the knee or functional locking of the knee. The femur rotates internally to lock into extension (closed kinetic chain) The function of the popliteus muscle is to unlock the knee when standing. Adding to this concept is the fact that hip extension pulls the iliofemoral ligament tight, which can cause the last 20 degrees of knee extension, in absence of quadriceps action. A hip joint that is lacking extension will significantly impair knee extension/locking.

 Functional range of motion

The functional knee ROM of the knee is full extension for maximally efficient weight bearing, 60 degrees of flexion for swing phase of gait, 90 degrees or greater for getting into bath tubs, automobiles, and rising from sit to stand.

Postion of ease

Position of comfort is defined as 20-25 degrees of flexion, as this is the range that will accomodate the most joint effusion, post injury. Be sure to let this guide you in exercise selection for people with patellofemoral dysfunction syndrome (PFDS).

A tight IT band is commonly understood to contribute to lateral knee pain due to its connection to the lateral retinaculum. A tight TFL obviously can contribute to this process. A tight gluteus

maximus is often overlooked and will also contribute to tight IT band problems.