Abstract
INTRODUCTION
The role of soft tissue balancing in optimizing function and is gaining interest. Consistent soft tissue balancing has been aided by novel technologies that can quantify loads across the joint at the time of surgery. In theory, compressive load equilibrium should be correlated with ligamentous equilibrium between the medial and lateral collateral ligaments.
The authors propose to use the Coronal Angular Deviation Ratio (CADR) as a functional tool to quantify and track surgical changes in laxity of the collateral ligaments over time and correlate this ratio to validated functional scores and patient reported outcomes.
MATERIALS AND METHODS
The study is a prospective IRB approved clinical study with three cohorts: (1) a surgical prospective study group (n=112 knees in101 patients) with balanced compartmental loads (2) a matched control group of non-operated high function patients (n=50); (3) a matched control group of high function knee arthroplasty recipients (n=50). Standard statistical analysis method is applied. The testing is performed using a validated angular deviation measuring device. The output variables for this report consist of the maximum numerical angular change of the knee in the coronal plane at 10 degrees of flexion produced by a controlled torque application of 10 Nm in the varus and valgus (VV) directions. This is reported as a ratio (CADR=Varus deviation / Total deviation). The New Knee Society Score is used to track outcomes.
RESULTS
Pre-operative scatter graphs demonstrate a wide distribution of absolute VV values, reflecting the spectrum of pathological states. The relative distribution of angular deviation after surgery demonstrates clustering. The range is from 0–5 degrees. The median CADR creeps from 0.50 pre-operatively to 0.58 at 6 months. Scatter graphs of angular deviation (valgus:varus) (Fig. 1) and frequency distribution histograms (Fig. 2) demonstrate post-operative clustering similar to that reported by the authors for kinetic loads after soft tissue balancing. The clustering effect appears to gradually dissipate over the ensuing 5 months, demonstrating a wider distribution width but with a median value distinctly favoring a tighter medial soft tissue envelope.
DISCUSSION
The angular deviation changes form testing under standardized torque are similar to previously reported linear displacement values. The observed shift toward a tighter medial side in this series, with a median CADR in extension of 0.58 at 6 months is similar to previous laxity studies. In a separate report the authors of this study have presented the concept of a safe target zone for balancing of knee arthroplasties. In this series, there is noteworthy reproducibility in angular deviation produced by standardized varus/valgus load testing outcome with greater than 75% of values falling within the boundaries of the defined target zone. This report specifically focuses on the apparent preferential stiffening of the medial side of the knee over time. A second and equally interesting finding is the departure from a tight cluster in the early post-operative period to a broader distribution, possibly reflecting individual ligamentous properties and activity levels.
