Rotation of the Tibial Component : Wheeless' Textbook of Orthopaedics

- Discussion:
- ultimate effects of rotation of TKR components:
- internal rotation of tibial component w/ respect to tibia will cause external rotation of tibia when knee is reduced, resulting in lateral
           displacement of the tibial tubercle;
- medial rotatation of the tibial & femoral components will both contribute to lateral patellar subluxation;
- if there is tendency for lateral patellar subluxation, position of tibial component can be adjusted to more external rotation,
                  producing relative internal rotation of tibial tubercle, lessening Q angle;
- taken to excess, this may internally rotate the leg and may cause incongruenty in the femoral-tibial articulation;
- rotational constraint is an early important factor in tibial loosening;
   - rotational stresses are most effective means of inducing tibial component micromotion in vivo;
   - hence, more constrained components, cause more rapid loosening as compared to unconstrained components;
- in the report by Barrack et al, the authors sought to correlate anterior knee pain with TKR component malrotation;
- significant anterior knee pain rating at least 3 of 10 on the visual analog scale was present in 16 knees (13 patients);
- 11 patients with 14 symptomatic knees had CT to accurately determine the rotation of tibial and femoral components;
- epicondylar axis and tibial tubercle were used as references using a previously validated technique;
- there was a highly significant difference in tibial component rotation between the two groups w/ the patients w/
anterior knee pain averaging 6.2° internal rotation compared with 0.4° external rotation in the control group;
- there also was a significant difference in combined component rotation with the patients w/ anterior knee pain avg
4.7° internal rotation compared with 2.6° external rotation in the control group;
- there was no significant difference in the degree of radiographic patellar tilt or patellar subluxation between the two groups;
- patients with combined component internal rotation were more than five times as likely to experience anterior knee pain after
                   TKR compared with those with combined component external rotation
           - ref: Component Rotation and Anterior Knee Pain After Total Knee Arthroplasty.
    - consequences of external rotation of tibial component:
   - in the report by Nicoll et al 2010, there were no negative consequences to excessive external rotation;
           - in the report by Bell et al 2012, there were no consequences to external rotation of the tibial component;

- Rotational Alignment of the Extramedullary Jig:
- there is often a tendency to internally rotate tibial cut because of:
- jig systems fitted to anterior surface of proximal tibia will have tendency to align in excessive internal rotation because of
                   everted patella tendon laterally;
- external rotation of the flexed tibia;
- internal rotation of cut should be avoided particularly in systems that incorporate a significant posterior slope, becuase this will
           produce a lateral tilt;
- in the study by Dalury DF, et al, the authors showed that a line drawn 1 mm medial to the medial border of the tibial tubercle and
           going through the midsulcus of the tibial spines (the midsulcus line) provided a reproducible landmark for the tibia, and when
           a perpendicular cut was made relative to this line, 46 of 50 knees were cut in appropriate alignment;

- Trial Component Positioning:
   - alignment based off of the tibial tubercle:
- rotational alignment of the tibial component can be achieved by aligning center of tibial component w/ medial 1/3 of tibial tubercle;
- in this case, moving the tibial component will change the rotation of the leg (rotating it internally);
- theoretical disadvantages:
- placing the tibial component in what appears to be the correct alignment (as based off the tibial tubercle), may result in a
                         posterior capsular twisting force which acts upon the joint and upon the bone cement interface leading to early
                         loosening of the tibial component;
           - references:
                  - Rotational alignment of the tibial component in total knee arthroplasty is better at the medial third of tibial tuberosity than at the medial border.
                  - Variability of the tibial tubercle affects the rotational alignment of the tibial component in kinematically aligned TKR
   - posterior capsular - rotational alignment of the component:
- alignment determined by the posterior capsule;
- in full extension, posterior capsular ligament may dictate tibio-femoral rotation;
- in this case, femoral component can twist matching tibial polyethylene into correct position as the knee is extended;
- technique is limited by how the foot is held when the knee is flexed and extended;
- if patellar tracking is optimal, then it is acceptable to allow the tibial component to seek its own rotation (with the knee in
                  extension) as long as there is no component overhang;
- use cautery to mark out the center of component on the tibia, so that its rotation can be reproduced when the tibial trial
                            stem is inserted;
- in the study by Dalury DF, et al, the authors showed that a line drawn 1 mm medial to the medial border of the tibial tubercle
                  and going through the midsulcus of the tibial spines (the midsulcus line) provided a reproducible landmark for the tibia;
- they showed that when the tibia is allowed to float in a functional position relative to the femoral implant, the tibial
                         external rotation was only 2 mm lateral from the medial edge of the tibial tubercle (ie internal rotation)
- this is far less than the medial 1/3 of the tubercle and close to the starting point of the midsulcus line;
           - in the study by Ikeuchi et al 2007, noted that ROM technique tends to place the component in internal ration;
           - references:
                 - Observations of the Proximal Tibia in Total Knee Arthroplasty.
                 - Determining the rotational alignment of the tibial component at total knee replacement: a comparison of two techniques.
                 - Maximizing tibial coverage is detrimental to proper rotational alignment.