Objective CT-based metrics of articular fracture severity to assess risk for posttraumatic osteoarthritis

Abstract

Objectives: Intra-articular fractures predispose patients to posttraumatic osteoarthritis (PTOA) with associated chronic joint pain and decreased function. The success of articular fracture management is dependent on how the fracture is treated and on fracture type and severity. The purpose of the present study was to correlate objective computed tomography (CT)-based indices of intra-articular fracture severity with subsequent joint degeneration. It was hypothesized that an injury severity metric that included objective measures of articular disruption, of fracture energy, and of fragment displacement/dispersal would be a useful predictor of PTOA.

Methods: Novel CT-based image analysis techniques were used to quantify acute injury characteristics in a prospective series of 20 tibial plafond fractures managed by articulated external fixation with later definitive surgical fracture reduction performed after soft tissue swelling had sufficiently resolved. PTOA severity was assessed 2 years postinjury using the Kellgren-Lawrence radiographic grading scale. A predictive model was developed by linearly regressing these 2-year Kellgren-Lawrence outcomes on the CT-based severity metrics.

Results: A combined acute severity score involving articular disruption and fracture energy successfully predicted PTOA severity (R2 = 0.70), whereas fragment displacement/dispersal and surgeon opinion correlated much less well with degeneration (R = 0.42 and 0.47). The concordance between the combined metric and PTOA severity was 88%.

Conclusions: The findings of this study indicate that objective CT-based metrics of acute injury severity can reliably predict intermediate-term PTOA outcomes in this challenging class of articular fractures. Quantitative biomechanical assessment of injury characteristics provides new possibilities to improve fracture management and to guide PTOA research.

Figures

Figure 1

The surface area for the fractured (red) and intact contralateral (green) are plotted along the length of the tibia. The total inter-fragmentary surface area is graphically represented by the blue area between the intact and fractured curves. The severe disruption and fragmentation visible in the fractured metaphysis illustrates comminution.

Figure 2

Method for quantifying fragment displacement[4]. Segmented intact and fractured bones (a) were circumscribed by convex hulls (b). The difference in area between convex hulls estimated in-plane tissue displacement (c). A volumetric quantity was formed by stacking the slices along the limb (d).

Figure 3

Linear regression modeled arthrosis scores as a function of measured severity characteristics. The combined severity score was formulated from the statistically significant characteristics, fracture energy and articular involvement.

Figure 4

Agreement between measures of acute injury severity and long term outcomes are evaluated using their rates of concordance. Severity of arthrosis had excellent agreement with the combined severity score (88% concordance). Acute severity measures agreed less well with functional outcomes (68% concordances).

Figure 5

Cases were grouped according to their PTOA status at 2 years post injury (OA absent: KL

Figure 6

CT-based measures of injury severity are shown for each patient. Cases are ordered according to their combined severity score. Moderate to severe OA developed in patients with a combined severity score greater than 40, suggesting the existence of a severity threshold.