Filip Stockmans

Rapid prototyping of scaphoid and lunate bones

In this study, a novel rapid prototyping technology was used to fabricate scaphoid and lunate bone prostheses, two carpal bones that are prone to avascular necrosis. Carpal prostheses were fabricated with an Envisiontec Perfactory® SXGA stereolithography system using Envisiontec eShell 200 photocurable polymer. Fabrication was guided using 3‐D models, which were generated using Mimics software (Materialise NV, Leuven, Belgium) from patient computer tomography data. The prostheses were fabricated in a layer‐by‐layer manner; ∼ 50‐μm thick layers were observed in the prostheses. Hardness and Youngs modulus values of polymerized eShell 200 material were 93.8 ± 7.25 MPa and 3050 ± 90 MPa, respectively. The minimum compressive force required for fracture was 1360 N for the scaphoid prosthesis and 1248 N for the lunate prosthesis. Polymerized Envisiontec eShell material exhibited high human neonatal epidermal keratinocyte cell viability rate in an MTT assay. The results of this study indicate that small bone prostheses fabricated by stereolithography using eShell 200 polymer may have suitable geometry, mechanical properties, and cytocompatibility properties for in vivo use.

A technique to investigate mural thrombus formation in small arteries and veins: I. Comparative morphometric and histological analysis

Numerous clinically relevant animal models exist for thrombosis studies. Few of these are suitable for both arteries and veins. In this investigation, an established venous thrombosis model was adapted through minimal technical adjustments to allow also the study of arterial thrombosis. A standardized subintimal crush injury was performed to carotid arteries or femoral veins of hamsters. Thrombus volumes were then quantified by direct morphometric measurements from serial microscopic sections or by on-line image analysis of light intensity changes from transilluminated vessels. The platelet-rich mural thrombus, which was established within minutes of the trauma, disintegrated during the observation period. The life cycle of the thrombus was different in arteries and veins, but significant linear correlation (p<0.01) was found in both types of vessel between thrombus volumes measured by the two techniques. The model can consequently be used for comparative in vivo thrombosis studies in small (≈1-mm) arteries and veins. Stockmans F, Stassen JM, Vermylen J, Hoylaerts MF, Nyström A. A technique to investigate mural thrombus formation in small arteries and veins: I. Comparative morphometric and histological analysis. Ann Plast Surg 1997;38:56-62

Accuracy of 3D Virtual Planning of Corrective Osteotomies of the Distal Radius

Corrective osteotomies of the distal radius for symptomatic malunion are time-tested procedures that rely on accurate corrections. Patients with combined intra- and extra-articular malunions present a challenging deformity. Virtual planning and patient-specific instruments (PSIs) to transfer the planning into the operating room have been used both to simplify the surgery and to make it more accurate. This report focuses on the clinically achieved accuracy in four patients treated between 2008 and 2012 with virtual planning and PSIs for a combined intra- and extraarticular malunion of the distal radius. The accuracy of the correction is quantified by comparing the virtual three-dimensional (3D) planning model with the postoperative 3D bone model. For the extraarticular malunion the 3D volar tilt, 3D radial inclination and 3D ulnar variance are measured. The volar tilt is undercorrected in all cases with an average of -6 ± 6°. The average difference between the postoperative and planned 3D radial inclination was -1 ± 5°. The average difference between the postoperative and planned 3D ulnar variances is 0 ± 1 mm. For the evaluation of the intraarticular malunion, both the arc method of measurement and distance map measurement are used. The average postoperative maximum gap is 2.1 ± 0.9 mm. The average maximum postoperative step-off is 1.3 ± 0.4 mm. The average distance between the postoperative and planned articular surfaces is 1.1 ± 0.6 mm as determined in the distance map measurement. There is a tendency to achieve higher accuracy as experience builds up, both on the surgeons side and on the design engineering side. We believe this technology holds the potential to achieve consistent accuracy of very complex corrections.

A technique to investigate microvascular mural thrombus formation in arteries and veins: II. Effects of aspirin, heparin, r-hirudin, and G-4120.

After a standardized trauma to carotid arteries or femoral veins of hamsters, the antithrombotic effects of two antiplatelet agents (aspirin and the glycoprotein llb/llla antagonist G4120) and two anticoagulants (heparin and the direct thrombin inhibitor rhirudin) were studied in vivo. The thrombus area volume was assessed by image analysis of the transilluminated experimental vessels. Heparin, r-hirudin, and G-4120 demonstrated a dosedependent complete inhibition of arterial and venous thrombosis. In contrast, the antithrombotic effect of aspirin was only partial in both vessel types. A significant correlation between activated partial thromboplastin time (aPTT) at the end of the experiments and the antithrombotic effect was observed with the anticoagulant agents. However, only r-hirudin inhibited thrombus formation at a therapeutical prolongation of aPTT, while heparin required supratherapeutical amounts to achieve the same inhibition. The data confirm that the inhibition of aspirin, heparin, r-hirudin, and G-4120 on the formation of platelet-rich thrombi is independent of the blood flow rate. Stockmans F, Stassen JM, Vermylen J, Hoylaerts MF, Nystrom A. A technique to investigate microvascular mural thrombus formation in arteries and veins. II. Effects of aspirin, heparin, r-hirudin, and G-4120. Ann Plast Surg 1997;38:63-68

Quantifying thumb opposition kinematics using dynamic computed tomography

Current motion capture techniques all have shortcomings when applied to the 3D quantitative evaluation of thumb base motion. Dynamic CT might overcome these shortcomings but, so far, robustness of this technique in more than one specimen has not yet been demonstrated. The aim of the current study is to further evaluate the use of dynamic CT for quantification of thumb motion in a larger cadaveric study using a protocol which is feasible in a clinical context. A dynamic CT scan was acquired from six cadaveric human forearms, while a motion simulator imposed thumb opposition. After image acquisition and segmentation, carpal bone motion was quantified using helical axes. To enable comparisons between specimens, intersection points of the instantaneous helical axis with an anatomically defined plane were determined. Precision of the dynamic CT method, measured as variation in distances between silicon nitride beads between frames of a dynamic scan, was 0.43mm (+/-0.09mm) when fixed to the skin and 0.13mm (+/-0.04mm) when embedded into the bone. Absolute deviation between known and measured distances were not larger than 0.34mm. We could demonstrate and quantify that thumb opposition is associated with motion at the trapeziometacarpal and scaphotrapezotrapezoidal joints. High consistency in motion patterns between specimen were found, while the radiation dose was limited. We conclude that dynamic CT can be used to visualize and quantify 3D thumb kinematics, making it a promising method to explore kinematics in vivo.

In vivo kinematics of the thumb during flexion and adduction motion: Evidence for a screw‐home mechanism

The thumb plays a crucial role in basic hand function. However, the kinematics of its entire articular chain have not yet been quantified. Such investigation is essential to improve our understanding of thumb function and to develop better strategies to treat thumb joint pathologies. The primary objective of this study is to quantify the in vivo kinematics of the trapeziometacarpal (TMC) and scaphotrapezial (ST) joints during flexion and adduction of the thumb. In addition, we want to evaluate the potential coupling between the TMC and ST joints during these tasks. The hand of 16 asymptomatic women without signs of thumb osteoarthritis were CT scanned in positions of maximal thumb extension, flexion, abduction, and adduction. The CT images were segmented and three‐dimensional surface models of the radius, scaphoid, trapezium, and the first metacarpal were created for each thumb motion. The corresponding rotations angles, translations, and helical axes were calculated for each sequence. The analysis shows that flexion and adduction of the thumb result in a three‐dimensional rotation and translation of the entire articular chain, including the trapezium and scaphoid. A wider range of motion is observed for the first metacarpal, which displays a clear axial rotation. The coupling of axial rotation of the first metacarpal with flexion and abduction during thumb flexion supports the existence of a screw‐home mechanism in the TMC joint. In addition, our results point to a potential motion coupling between the TMC and ST joints and underline the complexity of thumb kinematics.

In vivo contact biomechanics in the trapeziometacarpal joint using finite deformation biphasic theory and mathematical modelling

The assessment of the contact biomechanics in the trapeziometacarpal (TMC) joint during functional tasks represents a relevant way to obtain a better understanding of the onset of osteoarthritis (OA). CT scans of the hand region of 20 female volunteers were taken in relaxed neutral, lateral key pinch and power grasp configuration. 3D models of the first metacarpal (MC1) and the trapezium were created. The articular area of each bone was quantified and a mathematical model was developed in Matlab to evaluate the projected contact area and stress distribution of each bone. The articular areas of the MC1 and the trapezium presented no significant difference. A slightly smaller projected contact area was calculated for the trapezium compared to the MC1. Similar amounts of stress were reported in the neutral and lateral pinch configurations. The highest stress levels were observed during power grasp. Very consistent results for high stress location on the volar/radial articular sub-region were found in the neutral and power grasp configurations. More variation was reported during lateral pinch. The mathematical model presented in this paper offers the possibility to predict contact patterns within the TMC joint based on in vivo CT images.

Endoscopic Ankle Lateral Ligament Graft Anatomic Reconstruction.

Chronic instability is a common complication of lateral ankle sprains. If nonoperative treatment fails, a surgical repair or reconstruction may be indicated. Today, endoscopic techniques to treat ankle instability are becoming more popular. This article describes an endoscopic technique, using a step-by-step approach, to reconstruct the ATFL and CFL with a gracilis graft. The endoscopic technique is reproducible and safe with regard to the surrounding anatomic structures. Short and midterm results confirm the benefits of this technique.

Arthroscopic Subtalar Arthrodesis after a Calcaneus Fracture Covered with a Forearm Flap

Surgical treatment of intraarticular calcaneal fractures is often associated with postoperative wound problems. Soft tissue necrosis, bone loss and uncontrollable infection are a challenge for the surgeon and amputation may in some cases be the ultimate solution. A free flap can be very helpful to cover a significant soft tissue defect and help in fighting the infection. However, the free flap complicates the surgical approach if subtalar arthrodesis and bone reconstruction are needed. This study demonstrates the value of an arthroscopic technique to resect the remaining articular cartilage in preparation for subtalar arthrodesis and bone grafting. This approach avoids compromising the soft tissues and minimizes damage to the free flap.

In vivo biomechanical behavior of the trapeziometacarpal joint in healthy and osteoarthritic subjects

Background: The contact biomechanics of the trapeziometacarpal joint have been investigated in several studies. However, these led to conflicting results and were mostly performed in vitro. The purpose of this study was to provide further insight on the contact biomechanics of the trapeziometacarpal joint by in vivo assessment of healthy and osteoarthritic subjects. Methods: The hands of 16 healthy women and 6 women with trapeziometacarpal osteoarthritis were scanned in positions of maximal thumb extension, flexion, abduction and adduction during three isometric tasks (lateral key pinch, power grasp and jar twist) and in thumb rest posture (relaxed neutral). Three‐dimensional surface models of the trapezium and first metacarpal were created for each thumb configuration. The articular surface of each bone was measured in the neutral posture. A computed tomography‐based proximity mapping algorithm was developed to calculate the distance between opposing joint surfaces, which was used as a surrogate for intra‐articular stress. Findings: Distinct proximity patterns were observed across tasks with a recurrent pattern reported on the volar aspect of the first metacarpal. The comparison between healthy and arthritic subjects showed a significantly larger articular area, in parallel with a significant joint space narrowing and an increase in proximity area in arthritic subjects. We also observed severe articular deformations in subjects with late stage osteoarthritis. Interpretation: This study has increased our insight in the contact biomechanics of the trapeziometacarpal joint during tasks and positions of daily life in healthy and arthritic subjects, which might contribute to a better understanding of the occurrence mechanisms of degenerative diseases such as osteoarthritis. HIGHLIGHTSAn approach based on joint proximity is proposed to assess the contact biomechanics of the thumb.Proximity patterns of healthy and late stage osteoarthritic subjects were compared.Healthy group: distinct proximity patterns were observed between tasks.Osteoarthritic group: severe morphological changes were observed.Findings suggest an association between proximity patterns and osteoarthritis development.