Chris dowding pgy1 university of ottawa orthopedics
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Alignment Principals in TKA PowerPoint PPT Presentation


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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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Alignment Principals 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


Femoral rollback

Femoral Rollback


Biomechanics flexion

Biomechanics - Flexion


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


    Posterior femoral cut2

    Posterior Femoral Cut


    Flexion gap

    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


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