A portable monitoring system for measuring weight-bearing during tibial fracture healing

Modeling age-related changes in the mechanical behavior of the fracture-fixated human tibia bone during healing

The evolutionary healing phenomenon of fractured tibia bone was investigated by comparing the bio-mechanical response of the human tibia following fracture fixation for two ranges of patient ages, when a body weight pressure (BWP) is applied. Three-dimensional finite element models have been developed by adopting the biomechanical characteristics of cortical and trabecular tibia bones, and considering the time-varying callus properties during the healing process for the two patients. The stress and strain levels generated within the fractured tibia bone by the screw tight fit during the assembly process revealed its dependence on the bone stiffness that degrades with age. They have an impact on primary stability of the implants prior to the osseointegration. The gap capacity to resist and allow a gradual BWP load transfer, through the callus for the tibia bone models, was analyzed. In fact, from 10 weeks after surgery, the callus allowed the BWP transfer for young patients, which guarantees sufficient structure stabilization of the fractured tibia. However, an insufficient load was transferred to the fracture gap for the old patient, even beyond 16 weeks, which delayed the bone consolidation.

Use of a pressure-sensing walkway system for biometric assessment of gait characteristics in goats

The purpose of this study was to quantitatively assess gait characteristics and weight-bearing forces during ambulation in goats free of lameness using a pressure-sensing walkway as a biometric tool for stride, gait, and force analysis. Forty-six non-lame adult goats ranging in age from 5 to 6 years, mixed-breeds, and with a mean body weight of 52 ± 7.1 kgs were used. Goats were trained to walk over a pressure-sensing walkway. Data for analysis was collected on 2 different days, 3 days apart. On each day, 2 to 5 walking passes, in the same direction, were captured for each goat. Data from 2 valid passes meeting the criteria for consistent walking gait on each day were averaged then used for analysis. Analysis was performed, including the day-effect, for stride, gait, and force characteristics. Of the 46 goats enrolled in the study, complete data sets were achieved in 33 (72%) goats. Gait biometrics were similar among the assessment days; therefore, all data was pooled for the purpose of characterizing data for individual limb and biometric parameter comparisons at the individual goat level. Statistical analysis revealed that no difference within the paired limbs, and that there were significant differences between the front limbs and hind limbs. Maximum force and maximum peak pressure were significantly greater for the front limbs as compared with the hind limbs (p < 0.001). Based on the results, gait and force characteristics can be consistently measured in goats using a pressure-sensing walkway during a consistent walking gait. Goats apply greater force to the forelimbs during the weight-bearing phase of stride as compared with the hind limbs. The use of objective assessment tools is expected to improve the ability of researchers and clinicians to monitor changes in weight bearing and gait and will contribute to improved animal welfare.

Development of a step counting algorithm using the ambulatory tibia load analysis system for tibia fracture patients

Introduction: Ambulation can be used to monitor the healing of lower extremity fractures. However, the ambulatory behavior of tibia fracture patients remains unknown due to an inability to continuously quantify ambulation outside of the clinic. The goal of this study was to design and validate an algorithm to assess ambulation in tibia fracture patients using the ambulatory tibial load analysis system during recovery, outside of the clinic.

Monitoring Healing Progression and Characterizing the Mechanical Environment in Preclinical Models for Bone Tissue Engineering

The treatment of large segmental bone defects remains a significant clinical challenge. Due to limitations surrounding the use of bone grafts, tissue-engineered constructs for the repair of large bone defects could offer an alternative. Before translation of any newly developed tissue engineering (TE) approach to the clinic, efficacy of the treatment must be shown in a validated preclinical large animal model. Currently, biomechanical testing, histology, and microcomputed tomography are performed to assess the quality and quantity of the regenerated bone. However, in vivo monitoring of the progression of healing is seldom performed, which could reveal important information regarding time to restoration of mechanical function and acceleration of regeneration. Furthermore, since the mechanical environment is known to influence bone regeneration, and limb loading of the animals can poorly be controlled, characterizing activity and load history could provide the ability to explain variability in the acquired data sets and potentially outliers based on abnormal loading. Many approaches have been devised to monitor the progression of healing and characterize the mechanical environment in fracture healing studies. In this article, we review previous methods and share results of recent work of our group toward developing and implementing a comprehensive biomechanical monitoring system to study bone regeneration in preclinical TE studies.

Fracture healing redefined

It is well established that local mechanical conditions and interfragmentary movement are important factors for successful bone healing and may vary dramatically with patient fracture-load and activity. Up until now however it was technically impossible to use these key influence parameters in the aftercare treatment process of human lower extremity fractures. We propose a theory that with state of the art sensor technology these biomechanical influences can not only be monitored in vivo, but also used for individualized therapy protocols. Local measurement systems for fracture healing are available but remain research tools, due to various technical issues. To investigate the biomechanical influences on healing right away surrogate sensor tools are needed. Various gait characteristics have been proposed as surrogate measures. Currently available sensor tools could be modified with the appropriate support structure to allow such measurements continuously over the course of a fracture healing. Interdisciplinary work between clinicians, software engineers with computer and biomechanical simulations is needed. Through such a sensor system human boundary conditions for fracture healing could not only be defined for the first time, but also used for a unique, extendible aftercare system. With this tool critical healing situations would be detected much earlier and could be prevented with easy activity modifications, reducing patient and socioeconomic burden of disease. The hypothesis, necessary tools and support structures are presented.

Return of functional mobility after an open tibial fracture: a sensor-based longitudinal cohort study using the Hamlyn Mobility Score

In this study we quantified and characterised the return of functional mobility following open tibial fracture using the Hamlyn Mobility Score. A total of 20 patients who had undergone reconstruction following this fracture were reviewed at three-month intervals for one year. An ear-worn movement sensor was used to assess their mobility and gait. The Hamlyn Mobility Score and its constituent kinematic features were calculated longitudinally, allowing analysis of mobility during recovery and between patients with varying grades of fracture. The mean score improved throughout the study period. Patients with more severe fractures recovered at a slower rate; those with a grade I Gustilo-Anderson fracture completing most of their recovery within three months, those with a grade II fracture within six months and those with a grade III fracture within nine months. Analysis of gait showed that the quality of walking continued to improve up to 12 months post-operatively, whereas the capacity to walk, as measured by the six-minute walking test, plateaued after six months. Late complications occurred in two patients, in whom the trajectory of recovery deviated by > 0.5 standard deviations below that of the remaining patients. This is the first objective, longitudinal assessment of functional recovery in patients with an open tibial fracture, providing some clarification of the differences in prognosis and recovery associated with different grades of fracture.

Haptic biofeedback for improving compliance with lower-extremity partial weight bearing

After lower-extremity orthopedic trauma and surgery, patients are often advised to restrict weight bearing on the affected limb. Conventional training methods are not effective at enabling patients to comply with recommendations for partial weight bearing. The current study assessed a novel method of using real-time haptic (vibratory/vibrotactile) biofeedback to improve compliance with instructions for partial weight bearing. Thirty healthy, asymptomatic participants were randomized into 1 of 3 groups: verbal instruction, bathroom scale training, and haptic biofeedback. Participants were instructed to restrict lower-extremity weight bearing in a walking boot with crutches to 25 lb, with an acceptable range of 15 to 35 lb. A custom weight bearing sensor and biofeedback system was attached to all participants, but only those in the haptic biofeedback group were given a vibrotactile signal if they exceeded the acceptable range. Weight bearing in all groups was measured with a separate validated commercial system. The verbal instruction group bore an average of 60.3±30.5 lb (mean±standard deviation). The bathroom scale group averaged 43.8±17.2 lb, whereas the haptic biofeedback group averaged 22.4±9.1 lb (P<.05). As a percentage of body weight, the verbal instruction group averaged 40.2±19.3%, the bathroom scale group averaged 32.5±16.9%, and the haptic biofeedback group averaged 14.5±6.3% (P<.05). In this initial evaluation of the use of haptic biofeedback to improve compliance with lower-extremity partial weight bearing, haptic biofeedback was superior to conventional physical therapy methods. Further studies in patients with clinical orthopedic trauma are warranted.

Gait and function as tools for the assessment of fracture repair - the role of movement analysis for the assessment of fracture healing

Assessment of gait and function might be as sensitive tool to monitor the progress of fracture healing. Currently available assessment tools for function use instrumented three dimensional gait analysis or pedobarography. The analysis is focused on gait or movement parameters and seeks to identify abnormalities or asymmetries between legs or arms. The additional inclusion of muscle function by electromyography can further elucidate functional performance and its temporal development. Alternative approaches abstain from directly assessing function in the laboratory but rather determine the amount of activities of daily living or the mere ability to perform defined tasks such as walking, stair climbing or running. Some of these methods have been applied to determine recovery after orthopaedic interventions including fracture repair. The combination of lab-based functional measurements and assessment of physical activities in daily live may offer a valuable level of information about the gait quality and quantity of individual patients which sheds light on functional limitations or rehabilitation of gait and mobility after a disease or injury and the respective conservative, medical or surgical treatment.

Biomechanical methods for the assessment of fracture repair

The progress of fracture healing is directly related to an increasing stiffness and strength of the healing fracture. Similarly the weight bearing capacity of a bone directly relates to the mechanical stability of the fracture. Therefore, assessing the progress of fracture repair can be based on the measurement of the mechanical stability of the healing fracture. However, fracture stability is difficult to assess directly due to various obstacles of which shielding of the mechanical properties by the fracture fixation construct is the most relevant one. Several assessment methods have been proposed to overcome these obstacles and to obtain some sort of mechanical surrogate describing the stability of the fracture. The most direct method is the measurement of the flexibility of a fracture under a given external load, which comprises the challenge of accurately measuring the deformation of the bone. Alternative approaches include the measurement of load share between implant and bone by internal or by external sensors. A direct 3 dimensional measurement of bone displacement is provided by radiostereometric analysis which can assess fracture migration and can detect fracture movement under load. More indirect mechanical methods induce cyclic perturbations within the bone and measure the response as a function of healing time. At lower frequencies the perturbations are induced in the form of vibration and at higher frequencies in the form of ultrasonic waves. Both methods provide surrogates for the mechanical properties at the fracture site. Although biomechanical properties of a healing fracture provide a direct and clinically relevant measure for fracture healing, their application will in the near future be limited to clinical studies or research settings.

Comparison of the plantar pressure distributions at different degrees of tilting: a preliminary report

[Purpose] The purpose of this study was to investigate the amount of plantar pressures on the lower limb during tilt table standing and to indicate the ideal degree of tilting for partial weight bearing. [Subjects and Methods] Fifteen healthy subjects between the ages of 20 and 30 were recruited as volunteers for this study. All the measurements were taken while standing on a tilt table according to different inclination angles. [Results] The plantar pressures for 60° tilt table standing were lower by 7–9% of total body weight than the pressures during tilt table standing at 90°, and the pressures for 30° tilt table standing were lower by 18–20% of total body weight than the pressures for tilt table standing at 90°. [Conclusion] Standing training on a 60° tilt table might be equivalent to 80% of full weight bearing training, and tilt table standing training at 30° might be equivalent to 60% of full weight bearing training.

Orthopedic inpatients’ ability to accurately reproduce partial weight bearing orders

Partial weight bearing is often prescribed for patients with orthopedic injuries. Patients’ ability to accurately reproduce partial weight bearing orders is variable, and its impact on clinical outcomes is unknown. This observational study measured patients’ ability to reproduce partial weight bearing orders, factors influencing this, patients’ and physiotherapists’ ability to gauge partial weight bearing accuracy, and the effect of partial weight bearing accuracy on long-term clinical outcomes. Fifty-one orthopedic inpatients prescribed partial weight bearing were included. All received standard medical/nursing/physiotherapy care. Physiotherapists instructed patients in partial weight bearing using the hand-under-foot, bathroom scales, and/or verbal methods of instruction. Weight bearing was measured on up to 3 occasions during hospitalization using a force-sensitive insole. Factors that had the potential to influence partial weight bearing accuracy were recorded. Patients and their physiotherapists rated their perception of partial weight bearing accuracy. Three-month clinical follow-up data were retrieved from medical records. The majority of patients (72% or more) exceeded their target load, with mean peak weight bearing as high as 19.3 kg over target load (285% of target load). Weight bearing significantly increased over the 3 measurement occasions (P<.001) and was significantly associated with greater body weight (P=.04). Patients and physiotherapists were unable to accurately gauge partial weight bearing accuracy. The incidence of clinically important complications at 3 months was 9% and not significantly associated with partial weight bearing accuracy during hospitalization (P≥.45). Patients are unable to accurately reproduce partial weight bearing orders when trained with the hand-under-foot, bathroom scales, or verbal methods of instruction.

Development and preliminary validation of a Function IndeX for Trauma (FIX-IT)

BACKGROUND

Assessing fracture healing in clinical trials is subjective. The new Function IndeX for Trauma (FIX-IT) score provides a simple, standardized approach to assess weight-bearing and pain in patients with lower extremity fractures. We conducted an initial validation of the FIX-IT score.

METHODS

We conducted a cross-sectional study involving 50 patients with lower extremity fractures across different stages of healing to evaluate the reliability and preliminary validity of the FIX-IT score. Patients were independently examined by 2 orthopedic surgeons, 1 orthopedic fellow, 2 orthopedic residents and 2 research coordinators. Patients also completed the Short Form-36 version 2 (SF-36v2) questionnaire, and convergent validity was tested with the SF-36v2.

RESULTS

For interrater reliability, the intraclass correlation coefficients ranged from 0.637 to 0.915. The overall interrater reliability for the total FIX-IT score was 0.879 (95% confidence interval 0.828-0.921). The correlations between the FIX-IT score and the SF-36 ranged from 0.682 to 0.770 for the physical component summary score, from 0.681 to 0.758 for the physical function subscale, and from 0.677 to 0.786 for the role-physical subscale.

CONCLUSION

The FIX-IT score had high interrater agreement across multiple examiners. Moreover, FIX-IT scores correlate with the physical scores of the SF-36. Although additional research is needed to fully validate FIX-IT, our results suggest the potential for FIX-IT to be a reliable adjunctive clinician measure to evaluate healing in lower extremity fractures.

LEVEL OF EVIDENCE

Diagnostic Study Level I.

Validation of a standardised gait score to predict the healing of tibial fractures

There is no absolute method of evaluating healing of a fracture of the tibial shaft. In this study we sought to validate a new clinical method based on the systematic observation of gait, first by assessing the degree of agreement between three independent observers regarding the gait score for a given patient, and secondly by determining how such a score might predict healing of a fracture.

We used a method of evaluating gait to assess 33 patients (29 men and four women, with a mean age of 29 years (15 to 62)) who had sustained an isolated fracture of the tibial shaft and had been treated with a locked intramedullary nail. There were 15 closed and 18 open fractures (three Gustilo and Anderson grade I, seven grade II, seven grade IIIA and one grade IIIB). Assessment was carried out three and six months post-operatively using videos taken with a digital camera. Gait was graded on a scale ranging from 1 (extreme difficulty) to 4 (normal gait). Bivariate analysis included analysis of variance to determine whether the gait score statistically correlated with previously validated and standardised scores of clinical status and radiological evidence of union.

An association was found between the pattern of gait and all the other variables. Improvement in gait was associated with the absence of pain on weight-bearing, reduced tenderness over the fracture, a higher Radiographic Union Scale in Tibial Fractures score, and improved functional status, measured using the Brazilian version of the Short Musculoskeletal Function Assessment questionnaire (all p < 0.001). Although further study is needed, the analysis of gait in this way may prove to be a useful clinical tool.

A novel intramedullary nail for micromotion stimulation of tibial fractures

BACKGROUND

Animal studies and clinical trials have suggested that early application of controlled axial micromotion can accelerate healing of long bone fractures compared to rigid fixation. However, experimental investigations of micromotion constructs have been limited to external fixators, which have a higher incidence of complications than intramedullary nails. The purpose of this study was to assess whether a novel intramedullary nail design can generate stimulatory micromotion under minimal weight-bearing loads typical of the early healing period.

METHODS

Eight cadaver tibiae were reamed, osteotomised, and implanted with commercially-available IM nails fitted with a custom insert that allowed 1mm of axial micromotion after proximal/distal interlocking. Specimens were mounted in a materials testing machine and subjected to cyclic axial loading while interfragmentary motion was measured using an extensometer. Implants were also tested in standard statically-locked mode.

FINDINGS

The average force required to cause distraction of the fracture gap in micromotion mode was 37.0 (SD 21.7) N. The mean construct stiffness was 1046.8 (SD 193.6) N/mm in static locking mode and 512.4 (SD 99.6) N/mm in micromotion mode (significantly different, P<0.001).

INTERPRETATION

These results support the development of a micromotion-enabled IM nail because the forces required to cause interfragmentary movements are very low, less than the weight of the hanging shank and foot. In contrast to rigid-fixation nails, which require significant weight-bearing to induce interfragmentary motion, the micromotion-enabled nail may allow movement in non-weight-bearing patients during the early healing period when the benefits of mechanical stimulation are most critical.

Simulation of fracture healing in the tibia: mechanoregulation of cell activity using a lattice modeling approach

In this study, a three-dimensional (3D) computational simulation of bone regeneration was performed in a human tibia under realistic muscle loading. The simulation was achieved using a discrete lattice modeling approach combined with a mechanoregulation algorithm to describe the cellular processes involved in the healing process-namely proliferation, migration, apoptosis, and differentiation of cells. The main phases of fracture healing were predicted by the simulation, including the bone resorption phase, and there was a qualitative agreement between the temporal changes in interfragmentary strain and bending stiffness by comparison to experimental data and clinical results. Bone healing was simulated beyond the reparative phase by modeling the transition of woven bone into lamellar bone. Because the simulation has been shown to work with realistic anatomical 3D geometry and muscle loading, it demonstrates the potential of simulation tools for patient-specific pre-operative treatment planning.

When is a fracture healed? Radiographic and clinical criteria revisited

Selecting the most appropriate outcome measures can be especially burdensome in trials studying fracture healing, because the process of fracture healing is subjective and without a gold standard. Although a wide variety of radiographic modalities are available, plain radiography remains the most common approach for healing assessment. Radiographic criteria, however, do not correlate well with fracture strength and stiffness. Additional challenges include a lack of consensus in what radiographic measures are most appropriate in the assessment of healing. In this article, we provide an overview of the most commonly used radiographic and clinical criteria for defining fracture healing. The validity and reliability of alternative approaches is also discussed.

Weight bearing after tibial fracture as a guide to healing

BACKGROUND

Judging when it is safe to remove an external fixator or plaster cast requires clinical and radiological assessment, both of which are subjective. Weight bearing has been shown to increase with time post-fracture and we hypothesised that it could be used as an objective measure of fracture healing.

METHODS

Ground reaction force (and hence weight bearing) and fracture stiffness were measured serially in a group of 12 patients with tibial fractures treated by external fixation. Ground reaction force was measured for both fractured and non-fractured limbs using a force plate and the fracture stiffness was measured using the Orthometer, a commercially produced device for measuring the stiffness of fractures treated by external fixation.

FINDINGS

In 10 patients who made good recoveries, prior to fixator removal, weight bearing though the injured leg was seen to approach 90% of that through the uninjured leg and the fracture stiffness exceeded 15 Nm/deg. Two patients with delayed union achieved weight bearing of 40% of normal and a fracture stiffness of less than 5 Nm/deg at 20 weeks.

INTERPRETATION

Weight bearing correlates reasonably well with fracture stiffness. It is quicker and easier to measure than fracture stiffness and potentially has relevance to other fracture fixation methods.

Gait evaluation: a tool to monitor bone healing?

BACKGROUND

Current clinical methods for monitoring fracture healing are often invasive and inaccurate. This paper evaluates the use of a pressure sensitive platform to improve monitoring.

METHODS

Standardised 3 mm diaphyseal bone defects were created in the right tibia of 64 female sheep and stabilised with either a rigid monolateral external fixator or a more flexible variant. Over a nine week healing period gait parameters were measured using a pressure sensitive platform and interfragmentary movements at the fracture site were monitored. Frequency spectra were calculated for the ground reaction forces. The tibiae were tested biomechanically after sacrifice and callus sections were analysed histomorphometrically.

FINDINGS

All animals unloaded the operated and overloaded the contralateral hindlimb. Callus mineralisation and stiffness, as well as limb loading increased during healing whilst interfragmentary movements were reduced. Larger interfragmentary movements resulted in a slower fracture healing rate as documented histologically and biomechanically. Frequency analysis showed upto 14 dB loss of power at frequencies associated with bone mechanotransduction at four weeks postoperatively, reducing to a 3 dB loss at nine weeks.

INTERPRETATION

Gait analysis is a valuable tool for monitoring the course of fracture healing. Different fixation stiffnesses caused different initial interfragmentary movements leading to different healing rates. Ground reaction forces were strongly related to the course of callus mineralisation and thus directly reflected the recovery of stiffness at the fracture site. Reduced levels of loading frequencies that may affect bone healing persist to nine weeks postoperatively.

Comparison of biophysical stimuli for mechano-regulation of tissue differentiation during fracture healing

Most long-bone fractures heal through indirect or secondary fracture healing, a complex process in which endochondral ossification is an essential part and bone is regenerated by tissue differentiation. This process is sensitive to the mechanical environment, and several authors have proposed mechano-regulation algorithms to describe it using strain, pore pressure and/or interstitial fluid velocity as biofeedback variables. The aim of this study was to compare various mechano-regulation algorithms' abilities to describe normal fracture healing in one computational model. Additionally, we hypothesized that tissue differentiation during normal fracture healing could be equally well regulated by the individual mechanical stimuli, e.g. deviatoric strain, pore pressure or fluid velocity. A biphasic finite element model of an ovine tibia with a 3mm fracture gap and callus was used to simulate the course of tissue differentiation during normal fracture healing. The load applied was regulated in a biofeedback loop, where the load magnitude was determined by the interfragmentary movement in the fracture gap. All the previously published mechano-regulation algorithms studied, simulated the course of normal fracture healing correctly. They predicted (1) intramembranous bone formation along the periosteum and callus tip, (2) endochondral ossification within the external callus and cortical gap, and (3) creeping substitution of bone towards the gap from the initial lateral osseous bridge. Some differences between the effects of the algorithms were seen, but they were not significant. None of the volumetric components, i.e. pore pressure or fluid velocity, alone were able to correctly predict spatial or temporal tissue distribution during fracture healing. However, simulation as a function of only deviatoric strain accurately predicted the course of normal fracture healing. This suggests that the deviatoric component may be the most significant mechanical parameter to guide tissue differentiation during indirect fracture healing.

How accurate is partial weightbearing?

The accuracy of partial weightbearing was assessed in six healthy volunteers and 23 patients who had sustained either a fracture of a lower limb or surgery. They were trained to weightbear partially using the conventional bathroom scale method and were assessed in a gait laboratory using force platforms. The amount of weight exerted on the involved limb during three-point crutch walking was determined. Four of six volunteers exerted a mean of 27% of body weight more than required. The remaining two volunteers exerted a mean of 8.5% of body weight less than required. Of the 23 patients, 21 exerted a mean of 35.3% of body weight more than that prescribed and two patients exerted a mean of 11.97% of body weight less than that prescribed. In both groups there was little relationship between the weightbearing prescribed and actual weightbearing. None of the patients or volunteers was able to reproduce the extent of partial weightbearing for which they were trained using the bathroom scale method, confirming that this technique of instructing patients in partial weightbearing is inaccurate.

Techniques for measuring weight bearing during standing and walking

OBJECTIVE

To classify and assess techniques for measuring the amount of weight bearing during standing and walking.

BACKGROUND

A large variety of weight bearing measuring techniques exists. This review describes their advantages and limitations to assist clinicians and researchers in selecting a technique for their specific application in measuring weight bearing.

METHODS

A literature search was performed in Pubmed-Medline, CINAHL, and EMBASE. Measurement techniques were classified in 'clinical examination', 'scales', 'biofeedback systems', 'ambulatory devices' and 'platforms', and assessed on aspects of methodological quality, application, and feasibility.

RESULTS

A total of 68 related articles was evaluated. The clinical examination technique is a crude method to estimate the amount of weight bearing. Scales are useful for static measurements to evaluate symmetry in weight bearing. Biofeedback systems give more reliable, accurate and objective data on weight bearing compared to clinical examination and scales, but the high costs could limit their use in physical therapy departments. The ambulatory devices can measure weight bearing with good accuracy and reliability in the hospital and at home. Platforms have the best methodological quality, but are mostly restricted to a gait laboratory, need trained personnel, and are expensive.

CONCLUSIONS

The choice of a technique largely depends upon the criteria discussed in this review; however the clinical utilisation, the research question posed, and the available budget also play a role. The new developments seen in the field of 'ambulatory devices' are aimed at extending measuring time, and improved practicality in data collection and data analysis. For these latter devices, however, mainly preliminary studies have been published about devices that are not (yet) commercially available.

A mechano-regulation model for tissue differentiation during fracture healing: analysis of gap size and loading

Bone has a capability to repair itself when it is fractured. Repair involves the generation of intermediate tissues, such as fibrous connective tissue, cartilage and woven bone, before final bone healing can occur. The intermediate tissues serve to stabilise the mechanical environment and provide a scaffold for differentiation of new tissues. The repair process is fundamentally affected by mechanical loading and by the geometric configuration of the fracture fragments. Biomechanical analyses of fracture healing have previously computed the stress distribution within the callus and identified the components of the stress tensor favouring or inhibiting differentiation of particular tissue phenotypes. In this paper, a biphasic poroelastic finite element model of a fracture callus is used to simulate the time-course of tissue differentiation during fracture healing. The simulation begins with granulation tissue (post-inflammation phase) and finishes with bone resorption. The biomechanical regulatory model assumes that tissue differentiation is controlled by a combination of shear strain and fluid flow acting within the tissue. High shear strain and fluid flows are assumed to deform the precursor cells stimulating formation of fibrous connective tissue, lower levels stimulate formation of cartilage, and lower again allows ossification. This mechano-regulatory scheme was tested by simulating healing in fractures with different gap sizes and loading magnitudes. The appearance and disappearance of the various tissues found in a callus was similar to histological observation. The effect of gap size and loading magnitude on the rate of reduction of the interfragmentary strain was sufficiently close to confirm the hypothesis that tissue differentiation phenomena could be governed by the proposed mechano-regulation model.

A do-it-yourself membrane-activated auditory feedback device for weight bearing and gait training: a case report

An augmented auditory feedback device comprised of a thin membrane switch mini-buzzer, and battery is described as a modification of a previously described feedback device. The membrane switch can be customized for the patient and is designed to fit inside a patient's shoe without altering the heel height. Its appeal lies in its simplicity of construction, low cost, and ease of implementation during a patient's training for weight bearing and gait. An ever-present source of information, it provides performance-relevant cues to both patient and clinician about the occurrence, duration, and location of a force component of motor performance. The report includes suggested applications of the device, instructions to construct it, and a case report in which the device was used to improve weight bearing and gait in a cognitively healthy person with spina bifida.