Robert Rizza

Additive fabrication of custom pedorthoses for clubfoot correction

Purpose – The purpose of this paper is to determine the most‐practical means of transforming computer‐aided‐design models of custom clubfoot pedorthoses into functional pedorthoses for testing on patients in a clinical trial.Design/methodology/approach – The materials used in conventional orthosis fabrication are not yet available for solid free‐form fabrication; therefore, to fabricate the pedorthoses, several approaches were considered, including direct manufacturing, additive‐based moulding, laser cutting of foam and combinations of several of these approaches.Findings – The chosen approach of additively manufacturing the custom hard shell, and moulding the polyurethane‐foam insert, resulted in accurate, durable and effective pedorthoses that fit well, and could be adjusted as needed. The pedorthoses that were produced are currently being tested on the respective patients for their improvement in mobility and degree of clubfoot correction, and will continue through early 2010.Practical implications – A...

A New Method in the Design of a Dynamic Pedorthosis for Children With Residual Clubfoot

Clubfoot is a common pediatric orthopaedic deformity. Despite the popularity of Ponseti’s method and night splints such as the Denis–Browne method, there is still an 11–47% rate of deformity relapse reported in the literature. The technique to make traditional orthotics is dependent on a nonweight-bearing casting or foot imprint. These splints outdate clinical treatment trends and only apply to patients who are of nonwalking age. This study shows that a new procedure utilizing computer aided design and the finite element method can be employed to develop a customized weight-bearing dynamic orthotic. In addition, the plantar pressure distribution and the trajectory of the center of this pressure distribution are used to design the orthotic. It is shown that the trajectory of the center of pressure, traditionally used in gait analysis, can be used not only to quantify the severity of the foot deformity but to design a custom orthotic as well. Also, the new procedure allows the custom orthotic to be designed and analyzed within a day. The new orthotic design is composed of soft foam interior layers and a polymer supportive exterior layer. It is proved that rapid prototyping technologies employing selective laser sintering can be used to construct these layers to produce a custom orthotic within a 24 h time frame.

Comparison of biomechanical behavior between a cast material torso jacket and a polyethylene based jacket

BackgroundNumerous designs are used to the treatment of Early Onset Scoliosis. For example, a Thoraco-Lumbo-Sacral Orthosis (TLSO) is constructed using Polyethylene (PE). In addition, a series of castings has been implemented using cast material (3M, BSN Medical). The cast material has some significant advantages over the PE design including: growth preserving, improved compliance, decreased invasiveness, delaying or avoiding surgery, and the ability to allow the skin to breathe. However, the mechanical effectiveness of the cast material brace as compared to the TLSO is unknown, thus providing the objective of this study.MethodsA total of 23 standardized tensile tests were performed on the Delta-Cast Soft® and 3MTM ScotchcastTM Plus Casting Tape in order to obtain mechanical properties (Young’s and shear moduli and Poisson ratios). Using a radiograph of a thoracic spine, the size of twelve vertebrae and eleven intervertebral discs were measured and used to create a finite element spine model. Simulations using this model were used to establish mechanical loads which were then applied to finite element models of the TLSO and cast jacket. The thicknesses and number of material layers was varied in these models. Multiple simulations were performed.ResultsIt was found that a 6.6.mm thick cast jacket made of Delta-Cast Soft® had a maximum deformation of 4.7 mm, a maximum stress of 2.9 MPa and a structural factor of safety of 5.71. On the other hand, a 4 mm thick jacket made of PE had a maximum deformation of 2 mm, a maximum stress of 8.9 MPa and a structural factor of safety of 2.70. The cast jacket was 3.5 times lighter and had a material of cost 1/5 of the PE brace.ConclusionsBased on the results, either design will generate the proper constraint forces to maintain spinal correction. But, based on the design parameters (thickness, mechanical properties, structural factor of safety and cost) the brace made of cast material, though slightly thicker has superior structural and cost benefits. Thus, from the biomechanical point of view, the cast brace is more efficient than the PE brace.

Newly Designed Foot Orthosis for Children with Residual Clubfoot After Ponseti Casting

ABSTRACT Orthoses can be used to accommodate residual clubfoot after Ponseti casting. Traditionally, orthoses are constructed using nonweightbearing casts or foam imprints. Technological advances in pressure analysis and in three-dimensional (3D) geometry assessment by computed tomographic (CT) scans can assist in designing and fabricating orthoses. The purpose of this study was to validate the new Milwaukee Foot Orthosis (MFO) using pressure metrics. Five typically developing children (mean age of 7.2 years) and five children with residual clubfoot deformities (eight residual clubfeet and mean age of 6 years) were recruited. All children with residual clubfoot had undergone Ponseti casting as an initial treatment. Each child underwent plantar pressure measurements and acquisition of 3D foot dimensions by a CT scanner. A computer-aided design (CAD) was used to develop a customized MFO for each of the five children. The MFO was manufactured for each foot with residual deformities using a rapid prototyping system. After the use of the MFO, pressure data showed significant reduction of maximal force, peak pressure, and other measurements at the heel and the lateral forefoot. There was significant reduction of the center of pressure (CoP) deviation in the forefoot (7.9%) and the midfoot (4.0%) compared with barefoot. The new MFO is effective in reducing residual clubfoot deformities, such as supination and adduction.

Fixation Strength of Polyetheretherketone Sheath-and-Bullet Device for Soft Tissue Repair in the Foot and Ankle

ABSTRACT Tendon transfers are often performed in the foot and ankle. Recently, interference screws have been a popular choice owing to their ease of use and fixation strength. Considering the benefits, one disadvantage of such devices is laceration of the soft tissues by the implant threads during placement that potentially weaken the structural integrity of the grafts. A shape memory polyetheretherketone bullet‐in‐sheath tenodesis device uses circumferential compression, eliminating potential damage from thread rotation and maintaining the soft tissue orientation of the graft. The aim of this study was to determine the pullout strength and failure mode for this device in both a synthetic bone analogue and porcine bone models. Thirteen mature bovine extensor tendons were secured into ten 4.0 × 4.0 × 4.0‐cm cubes of 15‐pound per cubic foot solid rigid polyurethane foam bone analogue models or 3 porcine femoral condyles using the 5 × 20‐mm polyetheretherketone soft tissue anchor. The bullet‐in‐sheath device demonstrated a mean pullout of 280.84 N in the bone analog models and 419.47 N in the porcine bone models. (p = .001). The bullet‐in‐sheath design preserved the integrity of the tendon graft, and none of the implants dislodged from their original position. Level of Clinical Evidence: 5

Effectiveness of a New Dynamic Pedorthosis with Wedge on the Clubfoot

INTRODUCTION: Ponsetis method, which implements a series of castings and physical therapy, has become popular in the treatment of clubfoot. Although this non-surgical procedure has found wide clinical use and there are significant improvement of clubfoot deformities and foot function, residual clubfoot deformities with a range of 11% to 47% still occur [1]. To those that have residual clubfoot and ambulation, there is a lack of effective modality to continually correct the foot deformity. For patients with abnormal foot rotation, an orthotic wedge has the effect of shifting the abnormal center of pressure (COP) of patients with clubfoot and hence changes the foot orientation. Finite element analysis (FEA) has the unique ability to predict the effectiveness of the orthotic and wedge design based on geometry and material properties. Thus, the purpose of this research was to: 1) develop a FEA model to predict this effectiveness, 2) assess the impact of different wedge angles on the COP, and 3) validate clinically the pressure metrics between barefoot in regular shoes and the new dynamic Pedorthosis design.

A Custom Contoured Surgical Pillow to Reduce Soring

Commercial donut pillows are used during lengthy surgical operations. With the patient anesthetized, the multiple pressure points on the head and wrinkling of the skin cut off blood circulation in the face, which leads to facial decubitus ulcers [1].Cellular type materials such as foam, which are used in these pillows, are very effective in reducing pressure points by transferring pressure into shear forces [2]. In a similar way to surgical pillows, these materials are used to reduce foot pain due to plantar pressure in foot orthotics [3].However, these same shear forces lead to wrinkling of the skin which generates sores. These shear forces are related to shear stress in the pillow. Pressure normal to the pillow surface is related to normal stress in the pillow, which also leads to soring. Thus, the optimal pillow design, which reduces sores due to pressure points and wrinkling, would be characterized by the design where optimal values of the normal and shear stress are obtained [2].In a previous study [2], a surgical pillow design was developed which implemented foam wedges. The angle these foam wedges made with the transverse plane was determined to be the angle that gave minimal values of the normal and shear stresses. Thus this new pillow design reduced pressure sores as well as sores due to wrinkling of the skin.The use of foam wedges has some fundamental disadvantages. Chief among these disadvantages is that the wedges have planar surfaces which do not match the curvature of the human body well. This tends to make the wedges uncomfortable and ineffective. In addition, the manufacturing of small wedges which then have to be connected to the main pillow structure is cumbersome and inefficient.In this study, a new pillow design was developed which is based on the contour of the patient’s body to generate supportive surfaces that not only match the patient’s shape exactly but which minimizes normal and shear stresses.Copyright

Effect of implant stiffness on spinal growth in the pig spine

Introduction According to the ‘vicious cycle’ hypothesis proposed by Dr Stokes, sensitivity to load has been implicated in the progression of spinal deformity during growth due to the reaction of vertebrae to mechanical loads on their growth plate. Mechanical loads on the vertebrae are altered by the mechanical stiffness of the spinal implant. Unfortunately , the relationship between the implant stiffness and the modulation of spinal growth is not quantified. This review aims to analy se the study investigating the effect of implant stiffness on this growth using experimental and finite element techniques. Materials and methods In vitro and finite element studies involving multiple pig spines and segments (T1–T4, T5–T8, and T9–T12) were used. Springs of varying length (320 N/m stiffness) and a metal link (64.5 × 10 6 N/m stiffness) were attached to adjacent vertebrae and the spines distracted to model growth. Discussion It is shown that the addition of an implant to the spinal column will increase the stiffness of the spine. Furthermore, as the stiffness increases, the distraction of the spine decreases. In addition, asymmetric placement of the implant leads to r otation of the spine segment during distraction. Conclusion Spinal devices with different mechanical properties yield variable stiffness of the spine segments, as well as displacement and rotations, which will further affect the longitudinal growth of the spine.

Changes in the COP Trajectory After Use of a CAD and FEA Designed Orthotic

Following Ponseti casting, a new modality has been successfully developed to prevent clubfoot from recurrence in ambulating children. The new modality utilizes a non-traditional approach in the design and construction of customized dynamic pedorthtoses [1]. This approach implements dynamic plantar pressure data, as well as computer aided design (CAD) and finite element analysis (FEA).Copyright

Validation of Finite Element Models for Plantar Pressure in an Orthotic for Clubfoot

Ponseti’s method, which implements a series of castings, has become popular in the treatment of clubfoot. Although this non-surgical procedure has found wide clinical use and there are significant improvement of clubfoot deformities and foot function, residual clubfoot deformities with a range of 11% to 47% still occur [1].© 2010 ASME