Despite long-term survivorship of contemporary total knee arthroplasty (TKA) components, 1 in 5 recipients of TKA are dissatisfied with their outcomes. Possible reasons for dissatisfaction include limited function or higher pain levels. There is also a discordance between patient expectations and achievable activity levels (Noble ref). One reason for dissatisfaction is a mismatch between patient expectations and achievable activity levels.1 Instability and stiffness significantly affect activity levels and symptoms, and as a result, account for a significant proportion of early revision surgeries.2
Activities such as low-impact sports require a stable, well-balanced knee. However, techniques used to assess and achieve a balanced TKA have been simple and subjective, with no standard definition of what constitutes a “balanced” knee. The surgeon attempts to create equally spaced rectangular gaps between the tibia and the femur at 0 and 90 degrees of flexion and then tests the stability of the knee using trial implants. These methods are not reproducible or quantifiable in a reliable way, which likely accounts for a significant portion of dissatisfied patients and early revisions. Recently, sensors have been developed to quantify soft tissue tension and balance in the knee, and to attempt to establish an objective definition of balance.
Multicenter Study Results
A three-year prospective multicenter study was conducted to clinically assess patients who had received Sensor-Assisted TKA. Surgeons from 8 centers in the United States performed TKA utilizing the same implant model, with technique according to their respective training and experience. After the surgeon judged that the knee was balanced, a nanosensor trial was placed into the joint and final loading values were captured for the medial and lateral compartments at 10, 45 and 90 degrees of flexion. Analysis of early patient reported outcomes measures (PROMs) at six months revealed that patients exhibiting a mediolateral loading differential less than 15 lbf. reported statistically significantly less pain, higher activity levels, and greater function than those with differentials beyond the 15 lbf. threshold.3 Regression analysis including other potential contributing variables (preoperative function, range of motion, age, demographic or physical variables, etc.) revealed that the only significant contributing variable associated with better outcomes is the state of soft tissue balance (< 15 lbf. mediolateral load differential at all three measured flexion angles).
The same trends were reported at one and two years with the same group of patients and the same PROMs.4 Further, balanced patients were found to score significantly higher on a seven-item satisfaction survey using a five-point Likert scale at 1 year than the group of unbalanced patients, with an overall satisfaction rate of >97%, which is higher than any other published TKA study reporting on patient satisfaction to date.5
The results from this multicenter prospective study are unique, representing the first published attempts at quantifying a definition of soft tissue balance during TKA, through a range of motion. Since the time of publication of these results, independently conducted evaluations of this definition of balance have been confirmatory.6,7 Taken together, these studies demonstrate that that the clinical efficacy of TKA is highly dependent on proper soft tissue balance, defined as a mediolateral load differential of <15lbf.
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Dr. Gregory J. Golladay is a paid consultant to OrthoSensor, Inc.
1 Noble et al. The John Insall Award: Patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop Relat Res. 2006 Nov;452:35-43.
2 Fehring TK, Valadie AL (1994). Knee instability after total knee arthroplasty. Clin Orthop Relat Res. 299:157-62.
3 Gustke KA, Golladay GJ, Roche MW, Elson LC, Anderson CR (2014). A new method for defining balance: promising short-term outcomes of sensor-guided TKA. J Arthroplasty. 29: 955-960.
4 Gustke KA, Golladay GJ, Roche MW, Elson LC, Anderson CR (2014). Primary TKA patients with quantifiably balanced soft-tissue achieve significant clinical gains sooner than unbalanced patients. Adv Orthop. 2014: 628695.
5 Gustke KA, Golladau GJ, Roche MW, Elson LC, Anderson CR (2014). Increased satisfaction after total knee replacement using sensor-guided technology. Bone Joint J. 96-B(10): 1333-1338.
6 Elmallah RK, Mistry JB, Cherian JJ, Chughtai M, Bhave A, Roche MW, Mont MA (2016). Can we really “feel” a balanced total knee arthroplasty? J Arthroplasty. 31: 5102-5105.
7 Chow et al. The Use of Intraoperative Sensors Significantly Increases the Patient-Reported Rate of Improvement in Primary Total Knee Arthroplasty. Orthopedics. 2017