Abstract
Introduction
During primary total knee arthroplasty, the surgeon may encounter excessive medial collateral ligament tension while addressing a varus knee. This may be due to medial ligament/capsular complex contractures, and/or, due to the creation of a 0 degree mechanical axis in a varus knee. This tension leads to increased loading in the medial compartment, which contributes to an unbalanced extension and flexion gap. If uncorrected, this imbalance can lead to unfavorable clinical outcomes, including: pain, accelerated polyethylene degradation, joint instability, and limited ROM. Currently, intercompartmental soft-tissue balance is obtained by a subjective surgeon's “feel”. However, this method of judging soft-tissue tension is both variable and unreliable. Most surgeons can detect gross instability, but judging ligament tension is difficult. The following technique describes the integration of intraoperative microelectronic tibial inserts to assess and modify ligament tension, utilizing real-time dynamic sensor feedback
Methods
500 TKAs were performed between September 2012 and April 2013, by three collaborating surgeons. All surgeons used the same implant system, compatible with an embedded microelectronic tibial insert with which to receive real-time feedback of femoral contact points and joint kinetics. Intraoperative kinematic data, displayed loading patterns consistent with identifiable intercompartmental imbalance through a full ROM. All mediolateral imbalance, secondary to an excessively tight medial compartment, was addressed with the technique described herein.
Results
By using the VERASENSE™ knee application, surgeons closed the medial capsule, guided the joint through dynamic motion, and received real-time feedback regarding femoral contact point position and mediolateral intercompartmental loads (measured in lbs.). Mediolateral imbalance in flexion, mid-flexion, and extension was defined as an intercompartmental loading difference of > 15 lbs.
If a surgeon encountered excessive medial tension, they utilized a “pie crusting” technique described by Bellemans, et al. This method uses a 19-guage needle to sequentially and gradually release individual fibers of the MCL (superficial and deep), and medial capsule. The surgeon directs the knee into a position of maximal tension, and elongates the defined fibers in situ. The anterior fibers were addressed for flexion gap tension, and the posterior fibers addressed the extension gap. Successful release of the MCL was defined as an intercompartmental loading difference of ≤ 15 lbs (Figure 1).
Discussion
Mediolateral intercompartmental imbalance, secondary to ligament tension or laxity, can lead to a poor functional outcome post operatively. Unfortunately with no prior data to judge this critical dimension of joint reconstruction, surgeons have based their approach on traditional methods of subjective surgeon judgment. However, by using a modified releasing technique, with real-time sensor data, the surgeon can release tension in the MCL with quantified dynamic feedback. This gradual, digitally guided ligamentous release may prove to be a safer method than traditional releases, and allows the surgeon to ensure that both compartments of the bearing surface are loading proportionately. Further follow-up will be required to evaluate the clinical outcomes of patients who have undergone release with these techniques.
