Balancing the Valgus Knee through an Arcuate Release
-Ryan Moore MD, PhD; Martin W. Roche, MD; Matthias A. Verstraete, PhD; Michael A. Conditt, PhD
While the surgical technique to obtain a balanced knee often remains challenging and the topic of much discussion, it remains clear that achieving knee stability after total knee arthroplasty (TKA) is of primary importance. As valgus knees represent only approximately 10% of TKAs performed, addressing a valgus deformity presents a particular challenge. More so since knees that present with a pre-operative valgus deformity are generally corrected to near-neutral mechanical alignment post operatively, additionally leading to a reduced bone resection on the lateral femoral condyle and distalized / posteriorized tibiofemoral joint line. With bone damage and deformity focused in the lateral compartment, it is critical to appreciate the roles of the primary anatomical structures stabilizing the lateral compartment, including the lateral collateral ligament, the popliteus and the arcuate ligament (Figure 1).
Figure 1 – anatomical description of postero-lateral corner
In this study, we performed a retrospective review of all total knee arthroplasty surgeries performed on valgus knees between April 2017 and April 2018 by a single surgeon at one institution targeting neutral mechanical alignment. Arthroplasty surgery was performed using surgical navigation with a single radius posterior stabilized design. Following the initial bone cuts, the mediolateral load distribution was quantitatively assessed using intra-operative sensors. The sensor (VERASENSE, the leading product of OrthoSensor, Inc.) is used during the trialing phase of the procedure and are dimensionally equivalent to the tibial trials. The sensor provides real-time feedback on the compartmental loads for the medial and lateral tibiofemoral joint. Based on this feedback, a number of surgical corrections (changing insert thickness, soft tissue releases or bony recuts) were performed intra-operatively to quantitatively balance the knee (differential < 15lbs). The effect of these corrections on the mediolateral load distribution was assessed at 10 and 90 degrees of flexion by comparing the load distribution before and after the correction.
When we examined the mediolateral loads after all corrections were made, we found that 75% of the knees ended in a balanced state – defined as a mediolateral load differential below 15 Lbs (Figure 2).
Figure 2 – tibiofemoral loads measured with trial sensors before and after surgical corrections to balance the knee
To obtain a balanced knee, half of the knees required two or fewer surgical corrections, with a maximum of four corrections. Apart from adjusting the insert thickness to achieve a stabile medial column and engage the medial collateral ligament, a release of the arcuate ligament was the most common surgical correction (48%) (Figure 3). On average, this arcuate release reduced the lateral loads in near-extension (10 degree flexion) by 36 lbs (Figure 4).
Figure 3 – surgical corrections required to balance the valgus knees
Figure 4 – average change in tibiofemoral load after arcuate release
The prevalence of an arcuate release scales with the degree of pre-operative deformity; with an arcuate release performed in 67% of the knees with a preoperative valgus deformity between 5-10 degrees, and 100% of the knees with a pre-operative valgus deformity of greater than 10 degrees (Figure 5).
Figure 5 – occurrence of arcuate release in the pre-operative valgus knees
This study is the first to quantitatively describe the effect of an arcuate release and its relevance in obtaining a quantitatively balanced knee. More specifically, the study showed that using sensor technology, correcting a pre-operative valgus deformity has become reproducible — and to a certain degree even predictable — particularly when dealing with pronounced pre-operative deformities.
Ryan Moore, MD, PhD, is a paid consultant to OrthoSensor Inc. | Martin W. Roche, MD serves as the chief medical officer and is a board member for OrthoSensor, Inc. Dr. Roche also receives royalty payments from OrthoSensor, Inc. | Matthias Verstraete, PhD and Michael Conditt, PhD are employees of OrthoSensor Inc.
- Coon Joint Replacement Institute, Saint Helena, California, USA
- Holy Cross Hospital, Fort Lauderdale, Florida, USA
- OrthoSensor Inc., Dania Beach, Florida, USA