Treatment of intra-articular fractures with shape memory compression staples

Augmented Fixation in Transverse Midshaft Humerus Fractures Using a Nitinol Staple: Surgical Technique and Case Series

Maintaining the reduction of a transverse humeral shaft fracture can be particularly challenging while applying a compression plate for definitive fixation. Nitinol compression staples are being increasingly utilized in orthopedic surgery due to their unique ability to apply continuous compression between staple legs at body temperature. We have found them to be particularly useful in the maintenance of the reduction of transverse humeral shaft fractures before compression plate application. This simple technique allows for the removal of reduction clamps and precise plate placement. We describe our technique for using nitinol compression staples to augment fracture fixation in transverse humeral shaft fractures as well as our experience using this technique in a case series of 4 patients.

Staple Technology for Fracture Fixation and Joint Arthrodesis

The use of staple technology in the upper extremity has continued to evolve with the development of shape-memory alloys (SMAs) such as Nitinol that display superelastic properties that can be exploited for persistent compression. Clinical and biomechanical studies support the use of SMA staples for upper extremity fracture fixation and joint arthrodesis. To optimize biomechanical strength and clinical outcomes, it is recommended to place two staples, if possible, at the site of interest as well as to trough the staples to prevent hardware prominence.

Scaphoid waist fractures fixation with staple. Retrospective study of a not widespread procedure

INTRODUCTION

In carpal scaphoid fractures, the surgical treatment with screw is considered the gold standard; shape memory staple however presents substantial advantages. The authors report a study on unstable fractures of the scaphoid waist (type B1, B2, B5, according to Herbert classification) treated with shape memory staple on a large sample of patients, with the aim to confirm the usefulness of this method, the quality of reduction and fixation, the functional results, the time of union and the possible complications.

MATERIALS AND METHODS

A retrospective analysis of 131 patients with scaphoid waist fractures with minimum follow-up 1 year was performed. Staples were used in all cases; technical details are discussed. Outcome measures were: postoperative pain, flexion-extension wrist range, hand grip strength, radiographic consolidation, work absence. Herbert and Fisher Grading System was used to assess subjective, objective and radiographic results.

RESULTS

Consolidation was achieved in all cases of primary fractures (0-30 days) within three months after surgery, and within eight months in all but two cases of delayed unions (operated within 6 months of the injury). Pain was absent at follow-up in 79% of cases, never severe or unbearable, the average flexion-extension range achieved was 112°. Handgrip strength values were comparable to those of contralateral wrist in 75% of cases. Mean time lost at work was 7.4 weeks. No algo-distrophy or malunion were observed. Discussion CONCLUSIONS: Scaphoid waist fractures' treatment with shape memory staple should be considered as an excellent alternative to screw fixation.

Outcomes of Nitinol Compression Staples in Tarsometatarsal Fusion

BACKGROUND

Tarsometatarsal (TMT) arthrodesis is commonly performed in the management of midfoot arthritis, trauma, or deformity. The purpose of this study was to collect aggregate data (demographic, surgical, and perioperative outcomes) on patients who previously had a TMT fusion with BME compression staples.

METHODS

Sixty-six patients underwent TMT fusion with BME compression staples. Outcomes included demographics, surgical information, the Veterans Rand VR-12 Health Survey, Foot and Ankle Ability Measure (FAAM), visual analog scale (VAS), Revised-Foot Function Index (FFI-R), Ankle Osteoarthritis Scale (AOS), patient satisfaction survey scores, radiographic fusion rate, level of pain reduction, and complications. Sixty-six patients (68 feet) were analyzed (59 females) with an average age of 64 years (range, 18-83). The mean latest follow-up was 35.9 (range, 6-56.6 months).

RESULTS

The average surgical time was 38.1±14.3 minutes (range, 11-75). All outcomes improved significantly (P < .001) from preoperative to latest follow-up except for the VR-12 Mental and Physical score. The average time to fusion determined by radiographs was 8.4 weeks (range, 6.1-46.1 weeks). Wound complications were not seen. Indications for subsequent surgeries (26.5%, 18/68 feet) in this current study included pain (n = 14), broken staples, and nonunion (n = 3).

CONCLUSIONS

The fusion rate in this study, 89.7%, was similar to values reported in the literature. The patient satisfaction score of 81.9 at latest follow-up is consistent with patient satisfaction for other methods of fusion.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Miniplate osteosynthesis in fracture surgeries: Case series with review of concepts

PURPOSE

Miniplates were initially developed as targets for foot and hand fractures, but they have been used in the treatment of fixation of small bone fragments, reduction of long bone fractures and non-union treatment, which have been difficult to treat. In this study, the authors used miniplates to treat fractures of the upper extremities, lower extremities, and pelvis obtained good outcomes. Herein, the authors report these good outcomes and review the current concept of miniplates.

PATIENTS AND METHODS

Forty-two patients treated with miniplates between March 2012 and March 2017 who attended follow-up for > 1 year were included in this retrospective study. Miniplates were selected according to purpose, which was classified into three categories: fixation, reduction, and stability enhancement. For fixation, miniplates were used to fix distal fibular fractures occurring distal to the syndesmosis and treat patellar and olecranon fractures with severe comminution. For reduction, miniplates were used to reduce the tibia during intramedullary nailing in tibiofibular shaft fractures, while reduction was performed in advance of definitive plating fixation in patients with humeral and pelvic fractures. To enhance stability, the miniplate was inserted after autobone graft for atrophic nonunion at the humeral shaft following nail insertion. The validity of a miniplate was analyzed by reviewing the published literature on the use of miniplates in orthopedic fracture surgeries.

RESULTS

Bony union was achieved in all cases. No specific postoperative complications were observed; however, mild pain and limited range of motion observed in two patients were resolved after implant removal. Sixteen studies on fracture treatment using miniplates reported clinically fair outcomes.

CONCLUSION

Miniplates are not just small metal plates. Depending on the location and treatment of the fracture, the miniplate can effectively fix small bone fragments, help the main plate to maintain the reduction of large bone fragments, and increase the fixation force for nonunion treatment.

Analysis of One-Dimensional Ivshin-Pence Shape Memory Alloy Constitutive Model for Sensitivity and Uncertainty

Shape memory alloys (SMAs) are classified as smart materials due to their capacity to display shape memory effect and pseudoelasticity with changing temperature and loading conditions. The thermomechanical behavior of SMAs has been simulated by several constitutive models that adopted microscopic thermodynamic or macroscopic phenomenological approaches. The Ivshin–Pence model is one of the most popular SMA macroscopic phenomenological constitutive models. The construction of the model requires involvement of parameters that possess inherent uncertainty. Under varying operating temperatures and loading conditions, the uncertainty in these parameters propagates and, therefore, affects the predictive power of the model. The propagation of uncertainty while using this model in real-life applications can result in performance discrepancies or failure at extreme conditions. In this study, we employed a probabilistic approach to perform the sensitivity and uncertainty analysis of the Ivshin–Pence model. Sobol and extended Fourier Amplitude Sensitivity Testing (eFAST) methods were used to perform the sensitivity analysis for simulated isothermal loading/unloading at various operating temperatures. It is evident that the model’s prediction of the SMA stress–strain curves varies due to the change in operating temperature and loading condition. The average and stress-dependent sensitivity indices present the most influential parameters at several temperatures.

Fracture Fixation Using Shape-Memory (Ninitol) Staples

Shape-memory alloy (SMA) staples are a recent innovation in fracture fixation. These staples have inherent compressive properties that create a stable fracture environment that promotes primary bone healing. They have been used successfully for osteotomies, arthrodesis, and fracture fixation. Understanding where SMA staple compression can be optimized and using proper indications are important for obtaining consistent success and minimizing failures. SMA staples are not a substitute for lag screw fixation or traditional plate and screw constructs.

Biomechanical Properties of Nitinol Staples: Effects of Troughing, Effective Leg Length, and 2-Staple Constructs

PURPOSE

Nitinol memory compression staples are a recent addition to carpal bone fixation. Compared with traditional staples, they have been shown to have superior compression at the far cortex relative to standard and traditional compression staples. The purpose of this study was to (1) determine the effective leg length of different nitinol staples, (2) confirm the effect of 1 versus 2 staples on biomechanical compression, and (3) determine the effect of troughing (countersinking the staple into bone) the bone on staple biomechanical properties.

METHODS

Three commonly used nitinol staples of various bridge and leg lengths were used in a bicortical sawbones block construct. There were 3 separate constructs tested, which included single staple, double staple, and troughed. We measured compression force, stiffness, and bending strength for each construct before and after cyclical 4-point bending. Compression mapping was used to determine the effective leg length of each staple, which included the distance that compression extended beyond the tips of the staple legs.

RESULTS

Effective leg length for each staple construct extended 2 mm distal to the tip of the shortest staple leg. Two staple constructs more than doubled compressive force and increased bending strength by greater than 90% in all staple types. There was no loss of compressive force before or after loading for single, double, or troughed constructs with any staple type.

CONCLUSIONS

This study supports that nitinol staples do not have to be placed bicortically to achieve adequate compression; placing staples 2 mm short of the far cortex has the same compression as bicortical placement; and troughing of the bone will not significantly diminish the biomechanical properties of the construct.

CLINICAL RELEVANCE

Better understanding of the effective leg length of nitinol staples provides support that bicortical placement is not necessary for adequate compression. This study supports troughing bone to minimize implant prominence.

Sensitivity and Uncertainty Analysis of One-Dimensional Tanaka and Liang-Rogers Shape Memory Alloy Constitutive Models

A shape memory alloy (SMA) can remember its original shape and recover from strain due to loading once it is exposed to heat (shape memory effect). SMAs also exhibit elastic response to applied stress above the characteristic temperature at which transformation to austenite is completed (pseudoelasticity or superelasticity). Shape memory effect and pseudoelasticity of SMAs have been addressed by several microscopic thermodynamic and macroscopic phenomenological models using different modeling approaches. The Tanaka and Liang-Rogers models are two of the most widely used macroscopic phenomenological constitutive models for describing SMA behavior. In this paper, we performed sensitivity and uncertainty analysis using Sobol and extended Fourier Amplitude Sensitivity Testing (eFAST) methods for the Tanaka and Liang-Rogers models at different operating temperatures and loading conditions. The stress-dependent and average sensitivity indices have been analyzed and are presented for determining the most influential parameters for these models. The results show that variability is primarily caused by a change in operating temperature and loading conditions. Both models appear to be influenced by the uncertainty in elastic modulus of the material significantly. The analyses presented in this paper aim to provide a better insight for designing applications using SMAs by increasing the understanding of these models’ sensitivity to the input parameters and the cause of output variability due to uncertainty in the same input parameters.

The incidence of nonunion after Lapidus arthrodesis using staple fixation

Today's foot and ankle surgeon has multiple options when choosing a fixation device for Lapidus arthrodesis, many of which have well-documented nonunion rates. The present study aimed to fill a void in the current foot and ankle literature by establishing a nonunion rate for staple fixation for the Lapidus procedure. The present retrospective analysis of the medical record focused on nickel-titanium staples that were inserted in a delta configuration to yield a stable construct for first metatarsal-cuneiform fusion. The patients were kept strictly non-weightbearing for the first 6 weeks postoperatively. Weightbearing progressed at that point according to the radiographic findings of each case. The data from 35 consecutive patients were analyzed (25 females, 10 males; mean age 43.1 [range 15 to 72] years in whom a Lapidus arthrodesis was performed using staple fixation in 36 feet. The patients were followed until fusion was noted and pain had resolved. Pain resolution occurred at 6 weeks in the earliest cases and several years in others. The incidence of nonunion was 3 (8.3%) of 36 when staple fixation was used for first metatarsal-medial cuneiform arthrodesis.

Adjustable patella grapple versus cannulated screw and cable technique for treatment of transverse patellar fractures

BACKGROUND

Although the cannulated screw and cable (CSC) tension band technique is an effective method for fixation of transverse patellar fractures, it has shortcomings, such as extensive soft tissue damage, osseous substance damage, and complex manipulation. We conducted a retrospective comparison of the adjustable patella grapple (APG) technique and the CSC tension band technique.

PATIENTS AND METHODS

We retrospectively reviewed 78 patients with transverse patellar fractures (45 in the APG group and 33 in the CSC group). Follow-up was 18 months. Comparison criteria were operation time, fracture reduction, fracture healing time, the knee injury and osteoarthritis outcome score for knee function, and complications.

RESULTS

The APG group showed shorter operation time and equal fracture reduction, fracture healing time, and knee function compared with the CSC group. Eleven patients in the APG group experienced skin irritation generated by implants. There was no complication in the CSC group.

CONCLUSIONS

The APG technique should be considered as an alternative method for treatment of transverse patellar fractures.

Shape Memory Alloy Expandable Pedicle Screw to Enhance Fixation in Osteoporotic Bone: Primary Design and Finite Element Simulation

The properties of shape memory alloys, specifically the equiatomic intermetallic NiTi, are unique and significant in that they offer simple and effective solutions for some of the biomechanical issues encountered in orthopedics. Pedicle screws, used as an anchoring point for the implantation of spinal instrumentations in the spinal fracture and deformity treatments, entail the major drawback of loosening and backing out in osteoporotic bone. The strength of the screw contact with the surrounding bone diminishes as the bone degrades due to osteoporosis. The SMArtTM pedicle screw design is developed to address the existing issue in degraded bone. It is based on the interaction of bi-stable shape memory-superelastic elements. The bi-stable assembly acts antagonistically and consists of an external superelastic tube that expands the design protrusions when body temperature is attained; also an internal shape memory wire, inserted into the tube, retracts the assembly while locally heated to above the body temperature. This innovative bi-stable solution augments the pull-out resistance while still allowing for screw removal. The antagonistic wire-tube assembly was evaluated and parametrically analyzed as for the interaction of the superelastic tube and shape memory wire using a finite element model developed in COMSOL Multiphysics®. The outcomes of the simulation suggest that shape memory NiTi inserts on the SMArtTM pedicle screw can achieve the desired antagonistic functionality of expansion and retraction. Consequently, a parametric analysis was conducted over the effect of different sizes of wires and tubes. The dimensions for the first sample of this innovative pedicle screw were determined based on the results of this analysis.

Biomedical Applications of Shape Memory Alloys

Shape memory alloys, and in particular NiTi alloys, are characterized by two unique behaviors, thermally or mechanically activated: the shape memory effect and pseudo-elastic effect. These behaviors, due to the peculiar crystallographic structure of the alloys, assure the recovery of the original shape even after large deformations and the maintenance of a constant applied force in correspondence of significant displacements. These properties, joined with good corrosion and bending resistance, biological and magnetic resonance compatibility, explain the large diffusion, in the last 20 years, of SMA in the production of biomedical devices, in particular for mini-invasive techniques. In this paper a detailed review of the main applications of NiTi alloys in dental, orthopedics, vascular, neurological, and surgical fields is presented. In particular for each device the main characteristics and the advantages of using SMA are discussed. Moreover, the paper underlines the opportunities and the room for new ideas able to enlarge the range of SMA applications. However, it is fundamental to remember that the complexity of the material and application requires a strict collaboration between clinicians, engineers, physicists and chemists for defining accurately the problem, finding the best solution in terms of device design and accordingly optimizing the NiTi alloy properties.

Corrosion Kinetics of Laser Treated NiTi Shape Memory Alloy Biomaterials

NiTi shape memory alloy presents interesting mechanical properties as surgical implants. However, due to its high amount of Ni which may dissolve and release toxic ions in human fluids, the medical use of this material is a great concern. We have developed a laser treatment which modifies the oxide layer and enhances uniform and localised corrosion resistance of NiTi alloy.

In this paper we further analysed the effect of this treatment with potentiostatic and AC impedance measurements in physiological Hank's solution. We conclude that the laser treatment creates a stable passive film which results in improved corrosion resistance of this alloy.

A biomechanical comparison of shape memory compression staples and mechanical compression staples: compression or distraction?

Compression staples are a popular form of fixation for osteotomy and arthrodesis. "Mechanical compression" or "shape memory" designs are commercially available. We performed a biomechanical study comparing these designs. A load cell measured compression across a simulated fusion site. The two designs available were tested and compared. The effect of altering staple limb length was also assessed. The limbs of all mechanical compression staples diverged causing inconsistent compression and distraction. Shape memory staples all achieved consistent compression across the fusion site with significantly greater maximum force when compared to mechanical compression staples (P < 0.001). Staple limb length did not appear to alter compression force generated. Mechanical compression staples cause a distractive force, and we therefore suggest alternate forms of fixation for arthrodesis. Shape memory staples do provide compression and may be suitable for arthrodesis and osteotomy.

Skin wound closure with a novel shape-memory alloy fixator

BACKGROUND

Previously, we have described novel, thermally deployable tissue fixators based on the shape-memory properties of nickel titanium. The present study reports on the in vivo wound closure with these fixators as a preliminary to evaluating their use for bowel anastomoses.

METHODS

Twenty adult Sprague-Dawley rats had 2.0-cm dorsal skin incisions approximated either with shape-memory alloy (SMA) fixators or conventional skin staples on a random basis. Electrical resistance heating was used to transform and deploy the SMA fixators into the wound. The rats were killed on day 14 or day 28 and wound specimens were harvested for force distraction studies and histologic examination.

RESULTS

There was no incidence of wound dehiscence. 14- and 28-day wounds from both groups showed no significant difference in breaking force or energy. Histology revealed appropriate stages of wound healing for both SMA-closed and control wounds.

CONCLUSIONS

The results confirm the efficacy and safety of tissue-edge approximation with SMA fixators.

Le traitement des fractures du corps du scaphoïde carpien par agrafes à mémoire de forme. Étude rétrospective de 60 cas opérés

OBJECTIVES

In carpal scaphoid fractures, treatment with screws is considered the gold standard: ostheosynthesis with mini-staples is not the usual choice of treatment. The authors report a study on fractures of the middle third of the scaphoid treated by mini shape memory staples, in order to test the quality of reduction and ostheosynthesis, functional results, time of union and complications.

MATERIALS AND METHODS

A retrospective analysis of 60 patients, with average age 39 years old and follow-up 36 months, was performed. Evaluation criteria were: the grade of pain, flexion-extension and pronation-supination wrist range, hand grip strength, radiographic consolidation of fractures and lateral intrascaphoid angle of flexion as described by Amadio.

RESULTS

Pain was absent in 86% of the cases, the average flexion-extension range achieved was 107 degrees and the average pronation-supination range 171 degrees. Hand grip strength values achieved were comparable to those of the controlateral wrist in 85% of cases. Radiographic consolidation of the fracture was achieved in all patients within three months of surgery and the average value of the lateral intrascaphoid angle of flexion was 37 degrees. No cases of algodystrophy were observed.

CONCLUSIONS

Our results show the safety and the practicality of ostheosynthesis with mini shape memory staples in fresh unstable fractures of the middle third of the scaphoid. Stable fixation, continuous compressive force on fragments and the ability to allow early active movement, are the main advantages.

Computational Studies of Shape Memory Alloy Behavior in Biomedical Applications

Background: Nowadays, shape memory alloys (SMAs) and in particular Ni–Ti alloys are commonly used in bioengineering applications as they join important qualities as resistance to corrosion, biocompatibility, fatigue resistance, MR compatibility, kink resistance with two unique thermo-mechanical behaviors: the shape memory effect and the pseudoelastic effect. They allow Ni–Ti devices to undergo large mechanically induced deformations and then to recover the original shape by thermal loading or simply by mechanical unloading. Method of approach: A numerical model is developed to catch the most significant SMA macroscopic thermo-mechanical properties and is implemented into a commercial finite element code to simulate the behavior of biomedical devices. Results: The comparison between experimental and numerical response of an intravascular coronary stent allows to verify the model suitability to describe pseudo-elasticity. The numerical study of a spinal vertebrae spacer, where the effects of different geometries and material characteristic temperatures are investigated, allows to verify the model suitability to describe shape memory effect. Conclusion: the results presented show the importance of computational studies in designing and optimizing new biomedical devices.

First metatarsophalangeal joint arthrodesis: a new technique of internal fixation by using memory compression staples

A prospective clinical study of first metatarsophalangeal joint arthrodesis using memory compression staples is presented. In 27 patients, 30 feet underwent surgery. There were 24 women and 3 men, with a mean age of 61.2 years. Two memory compression staples were used at right angles to each other to achieve compression at the fusion site. Postoperatively, patients were allowed full weightbearing in a rigid-soled shoe. Subjective assessment was performed with a standard questionnaire, which included questions regarding level of pain, ambulation, and patient satisfaction. Objective assessment was performed by a clinical and included a radiographic examination. There was a postoperative reduction in the pain score from 4.6 to 1.6 (P < .0001). Ambulation ability improved from 4 to 2.5 (P < .0001). Patients reported 86.6% excellent to good results, and 96.7% achieved radiographic fusion at an average 8.2 weeks. The only significant postoperative complication was a single nonunion. The authors advocate memory compression staples for the internal fixation of first metatarsophalangeal joint arthrodesis. The implant is low profile, and postoperative cast immobilization is not required. The use of this device has a predictable success rate comparable to previously reported methods.

Smart intramedullary rod for correction of pediatric bone deformity: a preliminary study

We were interested in determining if a smart intramedullary rod made of nitinol shape-memory alloy is capable of correcting deformed immature long bones. Because of limitations in our study design the process was reversed in that we examined the smart rod's ability to create a deformity rather than to correct one. Smart rods of different lengths and diameters were heat-treated to resume a radius of curvature of 30 to 110 mm. The low and high temperature phases of the smart rods were set, respectively, at 0 degrees C to 4 degrees C and 36 degrees C to 38 degrees C. The preshaped smart intramedullary rods were implanted in the cooled martensite phase in the medullary canal of the tibia in eight rabbits, where they restored their austenite form, causing a continuous bending force. On a weekly basis anteroposterior and lateral radiographs of the surgically treated tibia and the contralateral tibia were obtained for comparison. Rabbits were euthanized 6 weeks after surgery and computed tomography scans of both tibias were used for image analysis. Smart rods with a larger radius of curvature showed only minimal signs of remodeling; however, rods with a radius of curvature of 50 and 70 mm generated enough force history to create bone remodeling and deformation. The amount of bone deformation was highly magnified when unicortical corticotomy on the tension side was done. Based on this preliminary study the technology of the smart intramedullary rod may provide a valuable alternative method to correct pediatric skeletal deformities.

Unicoronal Suture Immobilization in the Fetal Rabbit

Pre-clinical evaluation of surgical procedures aimed to correct craniosynostosis is ideally performed in species of small animals characterized by perinatal brain development, early skeletal maturation, and genuine synostosis in all newborns. It would be nearly impossible to breed such a colony to homozygosity, so most researchers have resorted to artificial postnatal suture immobilization. Our aim was to test the hypothesis that artificial immobilization of a unicoronal suture in the fetal rabbit (25 days of gestation) would result in neurocranial growth alterations similar to those seen in the 9-day postnatally immobilized or congenital synostotic rabbit models. The advantages of prenatal immobilization are that rabbits can undergo the tested corrective procedure at postnatal day 9. This age corresponds to a human age of 6 months and allows the deformity and the effects of its correction to be more readily detected. The heads of 25-day-old fetuses of five time-dated pregnant New Zealand white rabbits were exposed by hysterotomy. The left unicoronal suture of 4 fetuses in each litter was immobilized with a polyglactin suture piercing the frontal and parietal bone plates. The remaining two fetuses were sham-operated. Nine days after spontaneous delivery, all rabbits were marked with four titanium screws close to the sagittal and coronal sutures. Growth was recorded with dorsoventral cephalograms at 9 and 90 days. The group with the immobilized suture showed a small increase in growth across the sagittal sutures. However, the decreases in growth at the unicoronal suture in both the immobilized (5.41-mm difference with sham-treated group) and nonimmobilized (1.17-mm difference with sham-treated group) were significant. Fetal immobilization results in growth alterations similar to those observed after postnatal immobilization.

Porous titanium-nickel for intervertebral fusion in a sheep model: part 2. Surface analysis and nickel release assessment

Porous titanium-nickel (PTN) devices represent an alternative to traditional cage implants. PTN materials possess an interconnecting network of pores with capillarity properties that may promote bone ingrowth, long-term fixation, and intervertebral fusion without the need for bone grafting. However, their considerable surface area and nickel content may elicit concerns over sensitization potential. Therefore, PTN surface corrosion and nickel release resistance must be carefully studied. To evaluate this possibility, a PTN interbody fusion device (IFD) was compared to a conventional nonporous cage made of TiAlV, a well-known biocompatible biomaterial, in a sheep model. PTN and TiAlV IFDs were inserted at two non-contiguous lumbar sites for 3, 6, and 12 months postsurgery. Their surface was then evaluated by scanning electron microscopy (SEM) combined with backscattered electron analysis (BSE). No evidence of surface corrosion was observed either pre- or postimplantation, regardless of device type. Dosage of nickel ions was also performed with the use of inductively coupled plasma-mass spectrometry (ICP-MS). Blood nickel levels were observed to be within acceptable levels at all postinstrumentation times. Nickel content in PTN-adjacent tissue, as well as in detoxification and remote organs, was equivalent both in PTN-treated and control sheep. Therefore, porous titanium-nickel demonstrated resistance to both in vivo surface corrosion and nickel ion release and compared very well with a conventional titanium implant in the course of a 12-month sheep study.

Flexor tendon repair using shape memory alloy suture: a biomechanical evaluation

The purpose of the current study was to test in vitro a new shape memory alloy suture for flexor tendon repair. Forty fresh-frozen human anatomic flexor superficialis and profundus tendons were divided and repaired via the cruciate four-strand technique using one of two suture materials (the shape memory alloy suture and the 4-0 Ethibond suture). The forces required to cause a 1, 2, and 3 mm gap, ultimate load to failure, and repair stiffness were compared. Twenty specimens of each suture material also were tensile tested for load to failure, tensile strength, and elongation at failure. The shape memory alloy suture had a significantly higher mean resistance force to 1, 2, and 3 mm gap formation than the 4-0 Ethibond suture (47 N versus 31 N, 51 N versus 36 N, and 57 N versus 41 N, respectively). The shape memory alloy suture repair was 40% stronger than the 4-0 Ethibond suture (61.9 +/- 8.8 N versus 44.3 +/- 10.6 N). Repair with the shape memory alloy suture was significantly stiffer than repair with the 4-0 Ethibond suture (8.1 +/- 1.0 N/mm versus 6.1 +/- 0.9 N/mm). The load to failure and tensile strength of the shape memory alloy suture were significantly higher than that of the 4-0 Ethibond suture. The values of elongation for the two materials were not significantly different. The results of the current study suggest that the shape memory alloy suture may be superior to the 4-0 Ethibond suture in resisting gap formation in the range of forces generated in the early rehabilitation protocol and may be the future material of choice for tendon repairs.

Bone modeling controlled by a nickel-titanium shape memory alloy intramedullary nail

Nitinol (NiTi) shape memory metal alloy makes it possible to prepare functional implants that apply a continuous bending force to the bone. The purpose of this study was to find out if bone modeling can be controlled with a functional intramedullary NiTi nail. Pre-shaped intramedullary NiTi nails (length 26 mm, thickness 1.0-1.4 mm) with a curvature radius of 25-37 mm were implanted in the cooled martensite form in the medullary cavity of the right femur in eight rats, where they restored their austenite form, causing a bending force. After 12 weeks, the operated femurs were compared with their non-operated contralateral counterpairs. Anteroposterior radiographs demonstrated significant bowing, as indicated by the angle between the distal articular surface and the long axis of the femur (p = 0.003). Significant retardation of longitudinal growth and thickening of operated femurs were also seen. Quantitative densitometry showed a significant increase in the average cross-sectional cortical area (p = 0.001) and cortical thickness (p = 0.002), which were most obvious in the mid-diaphyseal area. Cortical bone mineral density increased in the proximal part of the bone and decreased in the distal part. Polarized light microscopy of the histological samples revealed that the new bone induced by the functional intramedullary nail was mainly woven bone. In conclusion, this study showed that bone modeling can be controlled with a functional intramedullary nail made of nickel-titanium shape memory alloy.

Arthrodesis of the first metatarsophalangeal joint: a biomechanical study comparing memory compression staples, cannulated screws, and a dorsal plate

Arthrodesis of the first metatarsophalangeal joint of 21 matched pairs of cadaver toes was performed in order to compare the strength of three methods of internal fixation: 1. two crossed cannulated screws, 2. a dorsal plate with an oblique 0.062 K-wire, and 3. two compression staples with an oblique 0.062 K-wire. Biomechanical testing with plantar force was carried out, and gapping across the fusion site was measured. Stiffness, load to 1-mm displacement, and force to failure was determined for each specimen. Both the plate and screw constructs were statistically stronger in force to failure and initial stiffness than the compression construct. Compression staples have an advantage in their ease of insertion and theoretical continuous compressive force across an arthrodesis site, but should be supplemented with a cast or other external immobilization until union is achieved.

Fixation of a frontozygomatic fracture with a shape-memory staple

A simple method using a staple was successfully used to treat a 74-year-old lady with a fractured frontozygomatic suture.

Customized staple fixation in hand and wrist surgery

Fixation of small bones in the adult and the child's hands remains a challenge. The authors present a technique of bone fixation using customized staples made intraoperatively from K-wires (0.9-1.6 mm in diameter). Their specific purpose was to provide axial alignment and rotational stability for carpal bone fixation and for epiphysiodesis in phalanges. This technique was used in 14 cases (11 adult and three paediatric). No bone shattering, implant breakage, implant loosening or infection occurred. As K-wires are quite malleable, custom sized and shaped staples which follow the bone contours could be made to give a more exact fixation. All cases had satisfactory outcomes, achieving the preoperative objectives of bony fixation. This method is safe, precise and technically easy. It is also relatively cheap and only requires simple, standard instruments.