Biomechanics  of knee and implant design
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Biomechanics of knee and implant design

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  • 1. BIOMECHANICS OF KNEE AND IMPLANT DESIGN
  • 2. KINEMATICS OF KNEE
  • 3. VARYING TRANSVERSE AXIS OF KNEE
  • 4. EACH GAIT CYCLE • Flexion and extension -70 * swing 20 * stance • Abduction and adduction 10 * • internal and external rotation - 10 to 15* • 67* flexion for swing phase • 83* flexion for climbing stairs • 90* flexion for descending stairs • 93* flexion for rise from chair
  • 5. NORMAL POST TRANSLATION OF KNEE IN FLEXION • Medial condyle = 2mm • Lateral condyle = 21 mm • Medial based pivoting of the knee • In flexion - tibia undergoes internal rotation • In extension - tibia undergoes ext rotation
  • 6. • MA is 3 degrees of valgus from vertical axis of body. • AA is in 6 * of valgus from MA •9 degrees of valgus vertical axis of body.
  • 7. • The tibial articular surface is in 3* of varus. • The distal femur is in 9* of valgus • So in order to get the neutral mechanical axis in TKR we insert the femoral component in 5-7* of valgus.
  • 8. • Proximal tibial cut is perpendicular to the mechanical axis • Posterior condylar axis is 3* • In order to create a rectangular flexor space the femoral component should be in 3* ER
  • 9. PATELLO FEMORAL JOINT
  • 10. Q ANGLE
  • 11. JOINT REACTION FORCE • It’s the force experienced by the trochlea due to posterior displacement of the patella during flexion • JRF increases with flexion • Normal ADL it is 2-5 times • Squatting and 120* flexion 8 times
  • 12. EVOLUTION OF KNEE PROSTHESIS • Interpositional • Mold arthroplasty • Hinged knee implants- they did not account for the complex knee motion. • Bi-compartmental prosthesis- 1. Gunston- polycentric knee
  • 13. ARGUMENTS IN FAVOUR PCL RETAINING • > range of motion with effective femoral roll- back • restraint to translational displacement • more symmetrical gait. • less bone resection • improved function of the patellofemoral joint • proprioceptive role of the PCL
  • 14. PCL substituting design the displacement must be resisted by the prosthetic articular geometry ↓ Inc stress on the prosthesis ↓ Inc stress transfer to the bone cement interphase
  • 15. GAIT • SYMMETRICAL GAIT more so in stair climbing • PCL substituting 1. decreased knee flexion 2. tendency to lean forward in a quadriceps- sparing posture • Contradicting studies both in favor of and against PCL retaining.
  • 16. • The patella to the joint line is less altered with PCL-R • Improved patello-femoral joint function • Patellar clunk syndrome with PCL-S.
  • 17. ARGUMENTS IN FAVOUR PCL SUBSTITUTION • PCL is diseased with arthritis and contracture • Technically surgery is less demanding • No problems related to a too loose or a too tight PCL • Better deformity correction • No problems with excess femoral rollback • Less polyethylene wear.