Equal bony resection of distal and posterior femur in robot-
Joint imbalance has become one of the main reasons for early revision after total knee arthroplasty (TKA) and it is directly related to the surgical technique. The primary objective of this study was to analyse the amount of bone that needed to be removed from the distal and posterior femoral joint surfaces to obtain an equal flexion/extension gap in robot-assisted TKA.

The second objective of this study was to evaluate whether the size of the knee joint influenced the amount of bony resection needed to achieve an equal flexion/extension gap in robot-assisted TKA.

A retrospective analysis was performed on all patients receiving a robot-assisted TKA (Cruciate Retaining (n=268). The robot was used consecutively when available in all patients receiving Cruciate Retaining TKA. Gap assessment, bony resections, femoral implant size and hip-knee-ankle angle were evaluated with the robot. Femoral implant size was categorized into small (size 1–2), medium (size 3–5) and large (size 6–8).

--The difference between the posterior and distal resection needed to obtain equal flexion and extension gap was on average 2.0 mm (SD 1.6) and 1.5 mm (SD 2.2) for the medial and lateral compartment, respectively.

--The discrepancy was smaller in the large implant group compared to the small implant group and medium implant group.

--Varus knees required a larger differential resection compared to neutral and valgus knees (only laterally) (medial compartment.

Conclusively, removing an equal amount of bone from the distal and posterior femur will lead to flexion/extension gap imbalance in TKA. It was required to remove 1.5–2 mm more bone from the posterior femur compared to the distal femur to equalize flexion and extension gap. This effect was size dependent: in larger knees, the discrepancy between the distal and posterior resections was smaller.

Source: https://link.springer.com/article/10.1007/s00167-021-06672-y