Orthosensor vs Conventional Total Knee Arthroplasty

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 2030.1
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.2

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.3,4,5Knee 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.6

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.6

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.6,
7,8 Soft tissue imbalance accounts for 35% of early TKA revisions in the United States.9,10
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.11
However, these methods are numerous, variable, and above all, highly subjective.9, 12 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.2 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.

Balance in TKA is defined as stability in the sagittal plane and less than 15 pounds
difference in the medial and lateral compartments of the knee.9, 13 In a multicenter study,
intraoperative sensors were utilized to define balance and to correlate it with improved
clinical outcomes. TKAs that had undergone said balancing were compared to unbalanced TKAs,
with results showing improved Knee Society Score (KSS) and Western Ontario and McMaster
Universities Osteoarthritis Index (WOMAC) between balanced (172, 14.5 points) and unbalanced
(145.3, 23.8 points), respectively.9 The authors concluded that a well-balanced TKA was the
most significant contributing factor to improved postoperative outcomes.

Similarly, Chow et al. investigated six-month patient-reported outcomes in a small
retrospective cohort study with short-term follow up of six months comparing sensor-assisted
to non-sensor-assisted TKA balancing. They reported that the KSS, Oxford Knee Score, and knee
range of motion was significantly higher in the sensor-assisted cohort and that the rate of
arthrofibrosis was lower in the sensor-assisted group, however, not statistically
significant.2

Further, Geller et al. retrospectively compared the incidence of arthrofibrosis before and
after the implementation of the Verasense technology to assist with ligament balancing and
reported a 5% rate of arthrofibrosis prior to implementation versus 1.6% after.14 In this
same report, median length of surgery was 83 minutes before implementation compared to 115
minutes after. The authors reported that while the implantation of the sensor increased
operative time, this additional time does not have a clinical impact and that the benefits
outweigh this potential increase in operative time.14Multiple reports in the literature have
suggested that a well-balanced TKA, which leads to increased activity levels may be part of a
cascade effect, which ultimately results in higher patient-reported outcome scores.

Unfortunately, soft tissue balancing is one of the only remaining aspects of TKA that has not
benefited from a consensus based on quantitative measures and objective data. As the economic
environment changes in medicine, coupled with a five-fold increase in TKAs performed and the
subsequent need for less experienced surgeons to perform TKAs, it is imperative that the
traditional subjectivity once relied upon be replaced by more empirical and clinical data to
construct a scientific consensus of what balance is. In so doing, clinical outcomes may be
improved, with a resultant decrease in the rate of early revisions, and ultimately
significant savings in healthcare expenditures.While the literature has demonstrated a clear
advantage by technology like the Verasense, previous studies have predominantly been
underpowered, with short-term follow up, and unstandardized TKAs, including surgical
approach, prosthetic designs, manufacturer, and above all, not randomized and controlled.

Inclusion Criteria:

- Primary total knee replacement

Exclusion Criteria:

- Revision knee surgery

- Prior knee surgery