Instability or stiffness following total knee arthroplasty (TKA) that may result from soft tissue imbalance can impair functional activities. Whereas well-defined measures exist for the evaluation of component alignment in TKA surgery, the intra-operative assessment of soft-tissue balance has traditionally been made by surgeons’ subjective feel and operative experience rather than quantitative measures.
The introduction of sensor technology allows the quantitative assessment of soft tissue balance throughout knee range of motion using a load-sensing enabled tibial trial insert. Previous literature has shown that knees with a mediolateral load differential not exceeding 15 lbf. can be defined as “balanced,” with patients self-reporting improved functional activity levels as well as satisfaction compared to unbalanced knees.1-3 With the availability of a proven, quantitative definition of balance, the question is raised whether a surgeon, through experience, can feel this balance or instead needs sensor feedback to consistently achieve the target?
Therefore, a study was performed including 170 patients, whereby the knees were balanced in accordance to the surgeons’ subjective “feel” and routine balancing procedures. Following this balancing, sensor measurements were collected in a blinded manner at 10 and 90 degrees flexion, and the surgeon was asked if he thought the medial and lateral compartments felt loose, normal, or tight at these flexion intervals. This allowed us to correlate the surgeon-reported feel of the knee with the objective sensor readings, evaluating the surgeons’ success in predicting/feeling both balanced and unbalanced knees.
TABLE 1: A quantitatively balanced knee is achieved by obtaining a mediolateral load differential equal to or less than 15 lbf, whereas qualitative balance is confirmed based upon surgeon “feel.”
Looking at the correlation between surgeon- and sensor-defined balance, it was seen that only half of the knees that were balanced according to the surgeons’ assessment were actually quantitatively balanced (46% in extension and 58% in flexion) (Table 2). An even more pronounced discrepancy was observed for the knees that were judged medially tight by the surgeon: only 27% and 29% were quantitatively tight on the medial side in extension and flexion, respectively. The same observation was made for laterally tight knees, with a correspondence between the qualitative and quantitative assessment in 27% and 39% of cases only (extension and flexion, respectively). A final observation relates to the high number of cases where surgeons misidentified the tight compartment. As such, it was shown that in more than 23% of the cases, the knee was medially tight in extension, whereas the surgeon thought the knee was laterally tight.
TABLE 2: When a surgeon subjectively assesses a knee as imbalanced without VERASENSE, they often mis-identify the dominant compartment or identify quantifiable balance as imbalanced.
These observations indicate that the surgeon poorly feels the quantitative balance of the knee. In approximately half of the cases, surgeons incorrectly perceived that the knee was balanced while quantitative data indicated an unbalanced state. Quantitative sensor data, thus, provides the surgeon with an additional sense.4
Dr. Gregory Golladay is a paid consultant to OrthoSensor, Inc.
1. Noble PC, Conditt MA, Cook KF, et al. The John Insall Award: Patient Expectations Affect Satisfaction with Total Knee Arthroplasty. Clin Orthop Relat Res 2006;452:35.
2. Sharkey P.F., Hozack W.J., Rothman R.H., Shastri S., Jacoby S.M., Why Are Total Knee Arthroplasties Failing Today? Clin Orthop Relat Res. 2002;404;7:13.
3. Bozic K, Kurtz S, Lau E, et al. The Epidemiology of Revision Total Knee Arthroplasty in the United States. Clin Orthop Relat Res. 2010. 468: 45-51.
4. Golladay, G. Surgeon assisted balanced: Does a Surgeon Need the Extra Sense? Podium Presentation, AOA, Perth, Australia. 2018.