Table 1 Definition of elements for measurement on preoperative plain films (Fig. 2A and B)
Elements in System | Description of computer algorithm | Function |
|---|---|---|
Femoral canal/axis (FAxis) | A line connecting the centers of two incircles located at diaphysis and metaphysis of femur, respectively | Simulating intra-medullary rod of femoral cutting jig |
Femoral cutting reference line (FRef) | A line angulating 85° laterally to femoral canal/axis (aLDFA), in contact with distal margin of lateral/medial femoral condyle (height determined by the first contact with lateral or medial margin, which means the lower one in medial and lateral contact points were counted) | Simulating distal contact of cutting jig to distal femoral articular surface |
Checkpoint for medial distal femur (FM) | Contact point of Line FRef and distal margin of medial femoral condyle | The lower point was be chosen as contact point |
Checkpoint for lateral distal femur (FL) | Contact point of Line FRef and distal margin of lateral femoral condyle | |
Initial distal femur cutting line (Line FCut) | A line parallel to Line FRef, being 9 mm apart proximally | Simulating 9-mm thickness of distal cut |
Femoral cut | True distance from FL/FM to FCut | Lower point of FL/FM was selected for calculation |
Tibial canal (TAxis) | A line along with anatomic axis of tibial shaft | Anatomic axis of tibial shaft |
Checkpoint for medial proximal tibia (TM) | Lowest point of medial tibial condylar | |
Checkpoint for lateral proximal tibia (TL) | The point located laterally at 3/8 of the total width of tibial plateau | |
Initial proximal tibial cutting line (Line TCut) | A line perpendicular to tibial anatomic axis Distance from Point TL to Line TCut was defined as 10 mm | Simulating 10-mm thickness of tibial cut |
Tibial cut | True distance from TL to Line TCut | |
Checkpoints for distal femoral osteophyte (F1 & F2) | F1: most proximal point of femoral osteophyte basement, defined as the turning point of cortex to the upper margin of femoral osteophyte F2: most protruding point of femoral osteophyte, defined as the turning point of femoral osteophyte margins | |
Checkpoints for proximal tibial osteophyte (T1 & T2) | T1: most distal point of tibial osteophyte basement, defined as the turning point of tibial cortex to the lower margin of tibial osteophyte T2: most protruding point of tibial osteophyte, defined as the turning point of tibial osteophyte margins | |
Osteophyte area (Trapeziform F1F2T2T1) | A trapeziform area formed by four check points of osteophytes |