Alignment Principals in TKA

1. Chris Dowding, PGY1 University of Ottawa Orthopedics Alignment Principals in TKA • Previous Presentations by Scott McGuffin andSeyonSathiaseelan

2. 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

3. Knee Biomechanics • Knee moves in several planes: • hinge joint (ginglymus) • sliding joint (arthrodial) • Change in alignment during ROM: • Femoral rollback • Internal Rotation of Tibia

4. Ginglymus (hinge) Joint • ROM – 3 Axes • Sagittal • Extension to -10°, Flexion to 150° • Coronal • Varus/Valgus play of <5° • Axial • IR 10°, ER 30°

5. Arthrodial (gliding) Joint • Translations • Anteroposterior 5-10mm • Mediolateral 1-2mm • Compression/Distraction • 2-5mm

6. Femoral Rollback

7. Biomechanics - Flexion

8. Knee Biomechanics • Posterior translation of femoral condyles on the tibia during flexion • Medial 2mm • Lateral 20mm • Thus, internal rotation of tibia occurs during flexion

9. Alignment • Axes: • Coronal • Axial • Sagittal

10. 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°

11. Axial Alignment of Femur • Whiteside’s line • AP intercondylar line • Transepicondylar axis • Posterior condylar axis Lateral Medial

12. Sagittal Alignment • Normal radiographic posterior slope of tibial = plateau ~7-10° • Menisci correct this to about 3° of posterior slope

13. 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

14. Goals of TKA • Restore overall mechanical axis (180°) • Balance ligaments • Maintain normal Q angle • Restore joint line

15. Goals of TKA • However: • If implants are placed in varus or valgus subsidence occurs:

16. 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?

17. 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 °

18. 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

19. Tibial Cut • Tibial cut made perpendicular to mechanical axis to prevent varus subsidence of tibial component 93° 90°

20. Tibial Cut • Posterior slope 3° • Ensures adequate flexion space • Prevents anterior subsidence of tibial component

21. 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°

22. Posterior Femoral Cut • Recall the axial alignment of the distal femur Lateral Medial

23. Posterior Femoral Cut • Externally rotating the femoral component by 3° creates a symmetrical flexion gap

24. Posterior Femoral Cut

25. Flexion Gap

26. 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

27. Alignment in TKA • Malalignment may lead to: • Femorotibial instability • Patellofemoral instability • Patellar fracture • Stiffness • Accelerated polyethylene wear • Implant subsidence/loosening

28. 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

29. 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

30. 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

31. 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