During knee replacement surgery, orthopaedic surgeons use different approaches to quantify and balance soft-tissue tension in the joint.
Why is soft-tissue balancing important?
Traditionally, they have relied on a conventional jig-based sensor (which uses mechanical cutting guides called jigs, plus alignment rods and the surgeon’s skill) to assess whether or not the soft-tissue tension balance was correct. However, this could produce inconsistent results.
By contrast, intraoperative sensors fit inside the joint space and measure exact pounds or units of pressure across the medial (inner) and lateral (outer) compartments in real time. The surgeon can see where pressure is uneven on the digital readout, enabling them to make precise soft tissue adjustments, ligament releases and minor bone resections. This ensures the joint is evenly loaded through a full range of movements which is important for reducing instability of the knee joint.
A well-balanced knee joint helps to prevent stiffness and uneven wear after a knee replacement, minimising the chances of needing early joint revision surgery to replace a worn-out implant.
Comparing jig-based and robotic arm-assisted partial knee replacements
A team from The Fourth Medical Center of PLA General Hospital in Beijing published an article in the Bone & Joint Journal[1]. As part of the study, the researchers developed a novel pressure sensor designed to measure pressure within the medial compartment of the knee. In its study, the team set out to compare the results of robotic arm-assisted partial knee replacement surgery with conventional jig-based surgery. They used the new pressure sensor to assess the effect and impact on soft tissue balance of these two approaches.
They carried out a retrospective evaluation of 80 patients who’d undergone a partial knee replacement to the medial compartment of their knee between November 2022 and June 2023. Forty of these patients had received conventional jig-based measurement (mobile bearing) and 40 had undergone robotic arm-assisted surgery (fixed bearing).
After interoperative soft tissue balancing, the researchers measured pressure at 10 degrees, 45 degrees and 90 degrees of knee flexion using the new unicompartmental pressure sensor. The knee range of motion, Numerical Rating Scale and American Knee Society scores were recorded at three months and one-year post-surgery.
They found robotic arm-assisted partial knee replacement achieved more balanced pressure, compared to a conventional jig-based approach which failed to achieve consistent pressure within the medial compartment. Robotic arm-assisted partial knee replacements also showed better outcome scores and range of motion at three months, although there was no significant difference at one-year post-surgery.
The team concluded that its unicompartmental pressure sensor demonstrated that a robotic arm-assisted partial knee replacement was able to achieve more consistent pressure within the joint compared with conventional jig-based surgery and may also improve early postoperative rehabilitation.
What is unicompartmental knee arthroplasty?
Unicompartmental knee arthroplasty – also called unicompartmental knee replacement or partial knee replacement – is a surgical procedure that involves resurfacing only one portion of the knee using metal and plastic components.
The knee joint is made up of three compartments – the medial compartment is the inner part of the knee, the lateral compartment is the outer part, and the patellofemoral compartment is the front area of the knee between the kneecap and the thighbone. In patients with osteoarthritis, sometimes only one compartment of the knee is damaged, usually the medial compartment. In such cases, they may be offered a unicompartmental (or partial) knee replacement rather than a total knee replacement which is where the entire joint is replaced with a prosthetic implant.
During a unicompartmental knee replacement, the orthopaedic surgeon removes worn cartilage and a small amount of bone from the affected compartment only. These are replaced with a medical grade plastic insert. Healthy bone, cartilage and ligaments are left intact.
If you are interested in finding out more about robotic arm-assisted partial and total knee replacement, download our Patient Guide and contact us to discuss your requirements.
Sources
[1] Bone Joint J 2026;108-B(3):302–309 ‘Robotic arm-assisted versus convenventional jib-based unicompartmental knee arthroplasty achieves better soft-tissue balance
