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Chris Dowding, PGY1 University of Ottawa Orthopedics. Alignment Principals in TKA. Previous Presentations by Scott McGuffin and Seyon Sathiaseelan. Objectives. Review “Normal” Knee Biomechanics Review “Normal” Knee Alignment Discuss How Alignment is Restored/Maintained in TKA

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chris dowding pgy1 university of ottawa orthopedics
Chris Dowding, PGY1

University of Ottawa Orthopedics

Alignment Principals in TKA

  • Previous Presentations by Scott McGuffin andSeyonSathiaseelan
objectives
Objectives
  • Review “Normal” Knee Biomechanics
  • Review “Normal” Knee Alignment
  • Discuss How Alignment is Restored/Maintained in TKA
  • Identify the Consequences of Poor Alignment in TKA
  • Brief review of New Literature
knee biomechanics
Knee Biomechanics
  • Knee moves in several planes:
    • hinge joint (ginglymus)
    • sliding joint (arthrodial)
  • Change in alignment during ROM:
    • Femoral rollback
    • Internal Rotation of Tibia
ginglymus hinge joint
Ginglymus (hinge) Joint
  • ROM – 3 Axes
    • Sagittal
      • Extension to -10°, Flexion to 150°
    • Coronal
      • Varus/Valgus play of <5°
    • Axial
      • IR 10°, ER 30°
arthrodial gliding joint
Arthrodial (gliding) Joint
  • Translations
    • Anteroposterior 5-10mm
    • Mediolateral 1-2mm
  • Compression/Distraction
    • 2-5mm
knee biomechanics1
Knee Biomechanics
  • Posterior translation of femoral condyles on the tibia during flexion
      • Medial 2mm
      • Lateral 20mm
  • Thus, internal rotation of tibia occurs during flexion
alignment
Alignment
  • Axes:
    • Coronal
    • Axial
    • Sagittal
coronal alignment
Coronal Alignment
  • Proximal tibia in 3° of varus from AAT/MAT
  • Distal femur in 9° of valgus from AAF
  • Thus, anatomical and mechanical axes of the femur diverge at 6° (femorotibial angle of 174°)

81°

93°

axial alignment of femur
Axial Alignment of Femur
  • Whiteside’s line
    • AP intercondylar line
  • Transepicondylar axis
  • Posterior condylar axis

Lateral

Medial

sagittal alignment
Sagittal Alignment
  • Normal radiographic posterior slope of tibial = plateau ~7-10°
  • Menisci correct this to about 3° of posterior slope
q angle
Q Angle
  • The angle between the extensor mechanism axis and a line joining the centre of the patella with the tibialtuberosity
    • Divergence = poor tracking of patella
goals of tka
Goals of TKA
  • Restore overall mechanical axis (180°)
  • Balance ligaments
  • Maintain normal Q angle
  • Restore joint line
goals of tka1
Goals of TKA
  • However:
    • If implants are placed in varus or valgus subsidence occurs:
goals of tka2
Goals of TKA
  • Subsidence is bad because it defeats the purpose of TKA in the first place
  • How to prevent subsidence but retain overall joint alignment in order to maintain balanced ligament tension and proper gait mechanics?
native alignment
Native Alignment
  • Recall:
    • 6 degrees of valgus
    • 3 degrees of posterior tibial slope
    • Internal rotation of tibia relative to femur during flexion
    • Q-angle 14 deg for males and 17 deg for females

°

tibial cut
Tibial Cut
  • Goal is to have the joint line perpendicular to the mechanical axis
  • By placing implants perpendicular to mechanical axis of each bone, it ensures that mechanical axis of limb goes through center of new joint
tibial cut1
Tibial Cut
  • Tibial cut made perpendicular to mechanical axis to prevent varus subsidence of tibial component

93°

90°

tibial cut2
Tibial Cut
  • Posterior slope 3°
  • Ensures adequate flexion space
  • Prevents anterior subsidence of tibial component
distal femoral cut
Distal Femoral Cut
  • Increased lateral joint space with a perpendicular tibial cut
  • This is corrected by making a distal femoral valgus cut angle of 6° relative to the AAF, instead of the anatomic 9°
  • Distal femur now perpendicular to mechanical axis

81°

84°

90°

90°

posterior femoral cut
Posterior Femoral Cut
  • Recall the axial alignment of the distal femur

Lateral

Medial

posterior femoral cut1
Posterior Femoral Cut
  • Externally rotating the femoral component by 3° creates a symmetrical flexion gap
patellofemoral tracking
Patellofemoral Tracking
  • Increased Q angle:
    • IR of femoral component
    • Valgus knee
    • Medialization of femoral component
    • IR of tibial component (medial 1/3 of TT)
    • Lateralization of the patellar dome
alignment in tka
Alignment in TKA
  • Malalignment may lead to:
    • Femorotibial instability
    • Patellofemoral instability
    • Patellar fracture
    • Stiffness
    • Accelerated polyethylene wear
    • Implant subsidence/loosening
research in knee alignment
Research in Knee Alignment
  • Most new publications evaluate methods of obtaining and maintaining what we think is ideal alignment, rather than challenging or testing what ideal alignment is
  • Many publications deal with the use of navigation
    • Due to the importance of alignment with respect to positive outcomes navigation may become more and more popular
    • However it is expensive and potentially time consuming, so research is being done to determine whether it can be used to provide a significantly better outcome over traditional methods
research in knee alignment1
Research in Knee Alignment
  • The advantages of computer assistance in total knee arthroplasty, Bar et. Al, AOTT 2011.
    • Retrospective case review 175 cases
    • Coronal alignment, incision length, hospital stay all favoured computer assisted TKA
research in knee alignment2
Research in Knee Alignment
  • A computed tomography based study on rotational alignment accuracy of the femoral component in total knee arthroplasty using computer-assisted orthopaedic surgery, van der Linden-van der Zwaag et al, SICOT 2011
    • Prospective analysis of 20 TKA using navigation
      • Significant difference in rotation of femoral implant when measured by navigation vs. post op CT
research in knee alignment3
Research in Knee Alignment
  • Anterolateral approach with tibial tubercle osteotomy versus standard medial approach for primary total knee arthroplasty: does it matter?, Hirschmann et al, Muskoloskeletal Disorders 2011.
    • Prospective multicenter study
    • Medial parapatellar vs. lateral patellar with tibial tubercle ostetomy
    • Comparison
      • Flexion and pain at two years
        • Lateral patellar gave more flexion (4 degrees), less pain (using scale)
      • However Medial parapatellar shorter OR time and less post-op complications
ad