Sizing and Seating of the Tibial Tray





- Sizing of the Tibial Component:
    - generally, the tibial component is either larger or at least the same size as the femoral component;
           - femoral overhang is a significant source of postoperative TKR pain;
           - ref:  Overhang of the Femoral Component in Total Knee Arthroplasty: Risk Factors and Clinical Consequences
    - generally, the surgeon chooses the largest tibial component which allows for appropriate tibial rotation.
           - ref: Maximizing Tibial Coverage Is Detrimental to Proper Rotational Alignment

    - rotation of tibial component:
           - avoid internal rotation of the tibial component:
           - medially rotated tibial & femoral components have a high incidence of assoc postop patellar dislocation;
           - if there is tendency for lateral subluxation, position of tibial component can be adjusted to more external rotation, producing
                   relative IR of tibial tubercle, lessening angle between quadriceps & patellar tendon, & thus lessening tendency of patella
                   to dislocate laterally; (see Q angle);
           - note that too much external rotation of the tibial component can overhang laterally and cause impingement on the popliteus tendon;
    - medial lateral translation:
           - goal is to provide maximum coverage &, when possible, have component extend to the cortical margins;
           - laterally dislocated soft tissues tend to push trial component medially, which is resolved by adequate retraction;
           - overhang:
                   - medial overhang is usually avoided but the literature shows that overhang by itself does not correlate with pain;
                   - slight lateral translation of the tibial component helps to centralize patellar tracking;
                   - note that too much external rotation of the tibial component can overhang laterally and cause impingement on
                          the popliteus tendon;
                   - of note, femoral overhang has been shown to be a much more important cause of pain than tibial overhang.  
                   - references:
                          - Tibial component overhang in total knee replacement: incidence and functional outcomes.
                          - The effect of tibial component sizing on patient reported outcome measures following uncemented total knee replacement.
                          - The impact of tibial component overhang on outcome scores and pain in total knee replacment.
                          - Overhang of the femoral component in total knee arthroplasty: risk factors and clinical consequences.

    - anterior posterior translation:
           - goal is to provide maximum coverage;
           - if symmetric component is sized to fit AP length of medial plateau, comonent will either overhang posteriorly on the lateral
                   plateau or have a tendency to internally rotate;
                   - the solution is to compromise in AP coverage, rather than allow overhang or internal rotation;
           - appropriately sized component is then placed as posteriorly as possible;
                   - this will in effect shift the tibial tubercle anteriorly, which will decrease patello-femoral contact pressures
           - ref: Anteroposterior positioning of the tibial component and its effect on the mechanics of patellofemoral contact.




 



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Monday, March 28, 2016 10:18 am