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Knee biomechanics


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Knee biomechanics

  1. 1.  Articulation:  Posterior surface of the patella  Femoral sulcus or patellar surface of femur
  2. 2.  Triangular with apex downwards divided by a vertical ridge into medial and lateral facets. a second vertical ridge toward the medial border separates the medial facet from an extreme medial edge, known as the odd facet of the patella
  3. 3.  The femoral sulcus has a groove that corresponds to the ridge on the posterior patella it divides the sulcus into medial and lateral facets. The lateral facet of the femoral sulcus is slightly moreconvex than the medial facet and has a more highlydeveloped lip than does the medial surface
  4. 4.  Changes with knee position Extension:only the inferior Pole is in contact with the femur. along the inferior margin of both the medial and lateral facets of the patella at 10 to 20 of knee flexion. At 45 degree covers middle of patella and spreads outward to cover the medial and lateral facet. At 90 superior pole beyond 90 the area of contact begins to migrate inferiorly. smaller odd facet makes contact with the medial femoral condyle for the first time. At full flexion, the patella is lodged in the intercondylar groove, and contact is on the lateral and odd facets, with the medial facet completely out of contact.
  5. 5.  Muscles crossing knee are basically flexors or extensors, and have additional function of rotation/ abdn addn
  6. 6.  7 muscles flex the knee:3Hamstrings:the semimembranosus, semitendinosus, biceps femoris(long and short heads) sartoriusgracilis popliteusgastrocnemius musclesPlantaris also flexes the knee when present
  7. 7. Other than short head of biceps femoris and popliteus all other are two joint muscles, thus their flexing ability depends on angle of the other joint where it is attached.
  8. 8.  Rotation:the popliteus, gracilis, sartorius, semimembranosus, and semitendinosus are also medial rotatorsBiceps femoris is a lateral rotator
  9. 9.  Varus & valgus moment: The lateral muscles (biceps femoris, lateral head of the gastrocnemius, and the popliteus) are capable of producing valgus moments Muscles on the medial side of the joint (semimembranosus, semitendinosus, medial head of the gastrocnemius, sartorius, and gracilis) can generate varus moments.
  10. 10.  Popliteus is known as the unlocking muscle although without it also locking will take place. active assistance of the semimembranosus and popliteus muscles ensures that tibio femoral congruence is maximized throughout the range of knee flexion by acting on menisci
  11. 11.  RF, VI pull upwards. pull of vastus lateralis muscle is 35 degree laterally, whereas the pull of the vastus medialis muscle is 40degree medially. The combined action produces a force directly upwards.
  12. 12.  the patella lengthens the MA of the quadriceps by increasing the distance of the patellar tendon from the axis of the knee joint. The patella, as an anatomic pulley, deflects the action line of the quadriceps femoris muscle away from the joint center, increasing the angle of pull
  13. 13.  at semi flexion, the patella is primarily responsible for increasing the quadriceps angle of pull. In full knee flexion, the patella is fixed firmly inside the intercondylar notch of the femur, which reduces the pulley action of patella. Still the quadriceps maintains a fairly large MA because the rounded contour of the femoral condyles deflects the muscle’s action line and because the axis of rotation has shifted posteriorly into the femoral condyle.
  14. 14. in the final stages of knee extension, patella’s effect on the quadriceps’ MA is diminished but the small improvement in joint torque provided by the patella is important. because near end range extension, the quadriceps is in a shortened position, which reduces its ability to generate active tension.
  15. 15.  If there is substantial quadriceps weakness or if the patella has been removed because of trauma (a procedure known as a patellectomy), the quadriceps may not be able to produce adequate torque to complete the last 15degree of non–weight-bearing knee extension. This is called as “quadriceps lag” or “extensor lag.”
  16. 16.  The Q-angle (or "quadriceps angle) is formed in the frontal plane by two line segments: from tibial tubercle to the middle of the patella from the middle of the patella to the ASIS The q-angle in adults is typically 15 degrees. Increases or decreases in the q-angles are associated in cadaver models with increased peak patellofemoral contact pressures (Huberti & Hayes, 1984). Insall, Falvo, & Wise (1976) implicated increased q-angle, along with patella alta, in a prospective study of patellofemoral pain.
  17. 17.  Oblique fibers of vastus medialis. Credited to locking of knee joint and terminal knee extension.
  18. 18. Soleus and gmax can produce knee extension although they do not have any attachment in knee.