Dr. Matt Schmitz offers this post on a new study in JBJS.
When I was a junior resident on an arthroplasty rotation, it was hammered into me that soft-tissue balancing is critical in total knee arthroplasty (TKA). I had that in mind when I read the results of a new Level I randomized controlled trial in the current issue of The Journal. An et al. highlight an important technical detail in robotic-assisted TKA: the placement of the femoral pin tracker may affect soft-tissue balance during surgery. Read the study at JBJS.org:
In robotic-assisted TKA, trackers are attached to the femur and tibia so that the robotic system can accurately map the knee and guide bone cuts. Surgeons commonly place the femoral pin tracker in one of two ways: either intraincisionally (through the main surgical incision) or extraincisionally (outside the incision through the skin and muscle). While both methods are used in practice, their effect on knee soft tissues has remained unclear.
To investigate the impact of placement method, the authors prospectively randomized 80 patients undergoing robotic-assisted TKA to either intra- or extraincisional tracker placement. Using a sensor, they measured soft-tissue tension in the medial and lateral compartments of the knee before and after pin-tracker removal, with the knee at 10°, 45°, 90°, and 120° of flexion.
The intraincisional group had significantly greater changes in soft-tissue tension in the medial compartment at 10°, 45°, and 90° of knee flexion compared with the extraincisional group. However, there were no significant differences at 120° or in the lateral compartment at any angle.
Why does this potentially matter? Soft-tissue balance is a key factor in TKA outcomes, influencing stability, function, and patient satisfaction. If an intraincisional femoral tracker increases tension or temporarily alters the feel of the medial side of the knee, surgeons could make balancing decisions based on a distorted picture of the joint.
I’m old enough to have never used a robot for arthroplasty in my training (and subspecialized such that I don’t perform TKA), but the takeaway is simple and clinically meaningful: the method of tracker placement appears to matter. Surgeons performing robotic-assisted TKA should be aware that intraincisional placement of the femoral pin tracker may influence medial soft-tissue tension. This insight could help to refine surgical technique and improve the consistency of knee balancing in robotic procedures.
Access the study and a related video summary at JBJS.org: Impact of the Femoral Pin Tracker on Soft-Tissue Tension in Robotic-Assisted Total Knee Arthroplasty. A Prospective Randomized Controlled Trial
Additional perspective is provided in a new commentary article by Giles R. Scuderi, MD: Soft-Tissue Balance Is Still a Critical Element of Total Knee Arthroplasty
JBJS Senior Editor for Pediatrics and Social Media