Thaddeus P. Thomas

Subchondral bone remodeling is related to clinical improvement after joint distraction in the treatment of ankle osteoarthritis

OBJECTIVE In osteoarthritis (OA), subchondral bone changes alter the joints mechanical environment and potentially influence progression of cartilage degeneration. Joint distraction as a treatment for OA has been shown to provide pain relief and functional improvement through mechanisms that are not well understood. This study evaluated whether subchondral bone remodeling was associated with clinical improvement in OA patients treated with joint distraction. METHOD Twenty-six patients with advanced post-traumatic ankle OA were treated with joint distraction for 3 months using an Ilizarov frame in a referral center. Primary outcome measure was bone density change analyzed on computed tomography (CT) scans. Longitudinal, manually segmented CT datasets for a given patient were brought into a common spatial alignment. Changes in bone density (Hounsfield Units (HU), relative to baseline) were calculated at the weight-bearing region, extending subchondrally to a depth of 8mm. Clinical outcome was assessed using the ankle OA scale. RESULTS Baseline scans demonstrated subchondral sclerosis with local cysts. At 1 and 2 years of follow-up, an overall decrease in bone density (-23% and -21%, respectively) was observed. Interestingly, density in originally low-density (cystic) areas increased. Joint distraction resulted in a decrease in pain (from 60 to 35, scale of 100) and functional deficit (from 67 to 36). Improvements in clinical outcomes were best correlated with disappearance of low-density (cystic) areas (r=0.69). CONCLUSIONS Treatment of advanced post-traumatic ankle OA with 3 months of joint distraction resulted in bone density normalization that was associated with clinical improvement.

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

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 (R2 = 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.

A computational/experimental platform for investigating three-dimensional puzzle solving of comminuted articular fractures.

Reconstructing highly comminuted articular fractures poses a difficult surgical challenge, akin to solving a complicated three-dimensional (3D) puzzle. Preoperative planning using computed tomography (CT) is critically important, given the desirability of less invasive surgical approaches. The goal of this work is to advance 3D puzzle-solving methods towards use as a preoperative tool for reconstructing these complex fractures. A methodology for generating typical fragmentation/dispersal patterns was developed. Five identical replicas of human distal tibia anatomy were machined from blocks of high-density polyetherurethane foam (bone fragmentation surrogate), and were fractured using an instrumented drop tower. Pre- and post-fracture geometries were obtained using laser scans and CT. A semi-automatic virtual reconstruction computer program aligned fragment native (non-fracture) surfaces to a pre-fracture template. The tibiae were precisely reconstructed with alignment accuracies ranging from 0.03 to 0.4 mm. This novel technology has the potential to significantly enhance surgical techniques for reconstructing comminuted intra-articular fractures, as illustrated for a representative clinical case.

A simulation trainer for complex articular fracture surgery.

BACKGROUND The purposes of this study were (1) to develop a physical model to improve articular fracture reduction skills, (2) to develop objective assessment methods to evaluate these skills, and (3) to assess the construct validity of the simulation. METHODS A surgical simulation was staged utilizing surrogate tibial plafond fractures. Multiple three-segment radio-opacified polyurethane foam fracture models were produced from the same mold, ensuring uniform surgical complexity between trials. Using fluoroscopic guidance, five senior and seven junior orthopaedic residents reduced the fracture through a limited anterior window. The residents were assessed on the basis of time to completion, hand movements (tracked with use of a motion capture system), and quality of the obtained reduction. RESULTS All but three of the residents successfully reduced and fixed the fracture fragments (one senior resident and two junior residents completed the reduction but were unsuccessful in fixating all fragments). Senior residents had an average time to completion of 13.43 minutes, an average gross articular step-off of 3.00 mm, discrete hand motions of 540 actions, and a cumulative hand motion distance of 79 m. Junior residents had an average time to completion of 14.75 minutes, an average gross articular step-off of 3.09 mm, discrete hand motions of 511 actions, and a cumulative hand motion distance of 390 m. CONCLUSIONS The large difference in cumulative hand motion distance, despite comparable numbers of discrete hand motion events, indicates that senior residents were more precise in their hand motions. The present experiment establishes the basic construct validity of the simulation trainer. Further studies are required to demonstrate that this laboratory-based model for articular fracture reduction training, along with an objective assessment of performance, can be used to improve resident surgical skills.

Computational Techniques for the Assessment of Fracture Repair

The combination of high-resolution three-dimensional medical imaging, increased computing power, and modern computational methods provide unprecedented capabilities for assessing the repair and healing of fractured bone. Fracture healing is a natural process that restores the mechanical integrity of bone and is greatly influenced by the prevailing mechanical environment. Mechanobiological theories have been proposed to provide greater insight into the relationships between mechanics (stress and strain) and biology. Computational approaches for modelling these relationships have evolved from simple tools to analyze fracture healing at a single point in time to current models that capture complex biological events such as angiogenesis, stochasticity in cellular activities, and cell-phenotype specific activities. The predictive capacity of these models has been established using corroborating physical experiments. For clinical application, mechanobiological models accounting for patient-to-patient variability hold the potential to predict fracture healing and thereby help clinicians to customize treatment. Advanced imaging tools permit patient-specific geometries to be used in such models. Refining the models to study the strain fields within a fracture gap and adapting the models for case-specific simulation may provide more accurate examination of the relationship between strain and fracture healing in actual patients. Medical imaging systems have significantly advanced the capability for less invasive visualization of injured musculoskeletal tissues, but all too often the consideration of these rich datasets has stopped at the level of subjective observation. Computational image analysis methods have not yet been applied to study fracture healing, but two comparable challenges which have been addressed in this general area are the evaluation of fracture severity and of fracture-associated soft tissue injury. CT-based methodologies developed to assess and quantify these factors are described and results presented to show the potential of these analysis methods.

Improving inter-fragmentary alignment for virtual 3D reconstruction of highly fragmented bone fractures

This article describes two new algorithms that, when integrated into an existing semi-automatic virtual bone fragment reconstruction system, allow for more accurate anatomic restoration. Furthermore, they spare the user the painstaking task of positioning each fragment in 3D, which can be extremely time consuming and difficult. The virtual interactive environment gives the user capabilities to influence the reconstruction process and that allows idiosyncratic geometric surface reconstruction scenarios. Coarse correspondences specified by the user are refined by a new alignment functional that allows geometric surface variations such as ridges and valleys to more heavily influence the final alignment solution. Integration of these algorithms into the system provides improved reconstruction accuracy, which is critical for increasing the likelihood of satisfactory clinical outcome after the injury.

Virtual 3D bone fracture reconstruction via inter-fragmentary surface alignment

This paper presents a system for virtual reconstruction of comminuted bone fractures. The system takes as input a collection of bone fragment models represented as surface meshes, typically segmented from CT data. Users interact with fragment models in a virtual environment to reconstruct the fracture. In contrast to other approaches that are either completely automatic or completely interactive, the system attempts to strike a balance between interaction and automation. There are two key fracture reconstruction interactions: (1) specifying matching surface regions between fragment pairs and (2) initiating pairwise and global fragment alignment optimizations. Each match includes two fragment surface patches hypothesized to correspond in the reconstruction. Each alignment optimization initialized by the user triggers a 3D surface registration which takes as input: (1) the specified matches and (2) the current position of the fragments. The proposed system leverages domain knowledge via user interaction, and incorporates recent advancements in surface registration, to generate fragment reconstructions that are more accurate than manual methods and more reliable than completely automatic methods.

ASB Clinical Biomechanics Award Paper 2010 Virtual pre-operative reconstruction planning for comminuted articular fractures.

BACKGROUND Highly comminuted intra-articular fractures are complex and difficult injuries to treat. Once emergent care is rendered, the definitive treatment objective is to restore the original anatomy while minimizing surgically induced trauma. Operations that use limited or percutaneous approaches help preserve tissue vitality, but reduced visibility makes reconstruction more difficult. A pre-operative plan of how comminuted fragments would best be re-positioned to restore anatomy helps in executing a successful reduction. METHODS In this study, the methods for virtually reconstructing a tibial plafond fracture were developed and applied to clinical cases. Building upon previous benchtop work, novel image analysis techniques and puzzle solving algorithms were developed for clinical application. Specialty image analysis tools were used to segment the fracture fragment geometries from CT data. The original anatomy was then restored by matching fragment native (periosteal and subchondral) bone surfaces to an intact template, generated from the uninjured contralateral limb. FINDINGS Virtual reconstructions obtained for ten tibial plafond fracture cases had average alignment errors of 0.39 (0.5 standard deviation) mm. In addition to precise reduction planning, 3D puzzle solutions can help identify articular deformities and bone loss. INTERPRETATION The results from this study indicate that 3D puzzle solving provides a powerful new tool for planning the surgical reconstruction of comminuted articular fractures.

3D reconstruction of highly fragmented bone fractures

A system for the semi-automatic reconstruction of highly fragmented bone fractures, developed to aid in treatment planning, is presented. The system aligns bone fragment surfaces derived from segmentation of volumetric CT scan data. Each fragment surface is partitioned into intact- and fracture-surfaces, corresponding more or less to cortical and cancellous bone, respectively. A user then interactively selects fracture-surface patches in pairs that coarsely correspond. A final optimization step is performed automatically to solve the N-body rigid alignment problem. The work represents the first example of a 3D bone fracture reconstruction system and addresses two new problems unique to the reconstruction of fractured bones: (1) non-stationary noise inherent in surfaces generated from a difficult segmentation problem and (2) the possibility that a single fracture surface on a fragment may correspond to many other fragments.

Utility of double-contrast multi-detector CT scans to assess cartilage thickness after tibial plafond fracture

The pathophysiology of post-traumatic osteoarthritis (PTOA) after intra-articular fractures is poorly understood. Pursuit of a better understanding of this disease is complicated by inability to accurately monitor its onset, progression and severity. Common radiographic methods used to assess PTOA do not provide sufficient image quality for precise cartilage measurements. Double-contrast MDCT is an alternative method that may be useful, since it produces high-quality images in normal ankles. The purpose of this study was to assess this techniques performance in assessing cartilage maintenance in ankles with an intra-articular fracture. Thirty-six tibial plafond fractures were followed over two years, with thirty-one MDCTs being obtained four months after injury, and twenty-two MDCTs after two years. Unfortunately, clinical results with this technique were unreliable due to pathology (presumed arthrofibrosis) and technical problems (pooling of contrast). The arthrofibrosis that developed in many patients inhibited proper joint access and contrast infiltration, although high-quality images were obtained in eleven patients. In this patient subset, in which focal regions of cartilage degeneration could be visualized, thickness could be measured with a high degree of fidelity. While thus useful in selected instances, double-contrast MDCT was too unreliable to be recommended to assess these particular types of injuries.