Outcomes in Free-hand Versus Sensor-guided Balancing in Total Knee Arthroplasty: a Randomized Controlled Trial

Total knee arthroplasty (TKA) is one of the most successful surgical procedures performed worldwide, and if conducted properly, has proven to improve pain, knee range of motion, and ultimately quality of life. Approximately 700,000 TKAs are performed annually in the United States, and this number is projected to increase to 3.48 million annually by 2030. Unfortunately, roughly 20% of patients who undergo TKA are dissatisfied with their outcome and this number has remained stagnant for the past decade.Patient satisfaction after TKA is predominantly driven by postoperative pain and function.

Outcomes in TKA are influenced by multiple factors, stemming from patient-specific factors and surgically modifiable factors. Patient specific factors include body mass index (BMI), preoperative range of motion (ROM), psychological status, and other comorbidities; examples of surgically modifiable factors include the type of prosthesis utilized, posterior condylar offset, posterior tibial slope, and soft tissue balancing. Knee arthritis is a disease not only of the condylar surfaces, but of the soft tissues as well. As such, the success of a TKA depends on the ultimate restoration of the integrity of the knee articular surfaces,necessitating two critical elements, beginning with precise osteotomies and ending with soft tissue balancing to realign the lower extremity to a neutral mechanical axis.

In the last three decades, this first element has been addressed by major technological advances to perform precise and reproducible osteotomies, most recently with the development of computer-assisted navigation and validation techniques and modalities that allow osteotomies based on anatomical jigs created by CT imaging of the patient's knee.

Despite these advances, little advancement has been appreciated by the second element-soft tissue balancing.While precise osteotomies are critical to the success of a TKA, they do not address ligamentous stability and balance, which if absent, leads to knee instability, stiffness, accelerated prosthetic wear, aseptic loosening, and premature implant failure. Soft tissue imbalance accounts for 35% of early TKA revisions in the United States. Soft tissue balancing in TKA has traditionally been more of an art than a science, relying exclusively on the surgeon's subjective assessment based on nebulous tactile feedback after completion of the osteotomies. The diseased soft tissues (i.e. ligaments) may be lengthened, tightened, or released to achieve balance, range of motion, and functional stability. However, these methods are numerous, variable, and above all, highly subjective. The individual experience of the surgeon, including fellowship training and procedural volume play a role in their ability to balance a knee properly.

Typically, it is only after many years of experience does the surgeon develop the ability to accurately assess stability in varus, valgus, anterior and posterior planes.Objective balancing of soft tissues in TKA may contribute to a decrease in pain, improve function, patient satisfaction, and ultimately decrease the rate of revision. The need for the transformation of TKA soft tissue balancing from an art to a science has been realized by a technology that allows surgeons to objectively quantify ligament balance by offering real-time, evidence-based data during TKA. The Verasense (Orthosensor Inc., Dania, FL) is a disposable wireless device embedded with force sensors and inserted into the tibial component during the trialing phase of surgery after gross balancing, allowing real-time loading values in the medial and lateral compartments of the knee and fine-tuning of the end result by further soft tissue releases to improve balance and stability.