CommunicationA portable monitoring system for measuring weight-bearing during tibial fracture healing
Introduction
Fracture healing is influenced by the mechanical environment prevailing at the fracture site 1, 2, 3, 4, 5. Fractures which have been accurately reduced and rigidly fixed, and in which there is minimal interfragmentary movement, heal by so called direct or primary healing 1, 2. Fractures which have been less rigidly fixed heal with the production of an external callus (this healing being termed `indirect healing'). The amount of callus produced depends on the rigidity of fixation, less rigidly fixed fractures producing more callus 1, 3, 4. For fractures treated with the same type of fixation, the daily application of a small (⩽1 mm) amount of cyclic micromovement has been shown to induce an earlier formation of periosteal callus compared with unstimulated controls 4, 5.
The rate of fracture healing, in terms of the increase of fracture stiffness and strength, can be influenced by the rigidity of the fixation system and the mechanical conditions pertaining at the fracture site, this being seen in both experimental 3, 4, 5and clinical studies 6, 7. To encourage fracture healing therefore, early weight-bearing is prescribed and encouraged to generate the strains at the fracture site necessary to promote callus formation [7]. Weight-bearing can generate significant amounts of movement at the fracture site. The largest axial movements (1–4 mm) are seen in patients treated by cast 8, 9, less movement (1–2 mm) being observed in patients treated with more rigid methods of fixation such as external skeletal fixation 10, 11, 12, 13.
The magnitude and frequency of weight-bearing will therefore determine how a fracture is loaded, how much movement (and therefore strain) is produced at the fracture site and thus should be an important influence on healing. Information on weight-bearing during healing would be invaluable is assessing the relative effects of treatment method, injury grade and patient motivation on the ability of the patient to weight-bear on the fractured leg. In previous studies of patients being treated by cast braces for femoral shaft fractures, the loading of the fractured limb during healing has been measured 14, 15and has been shown to increase with time post fracture. In patients treated with external skeletal fixation for a tibial fracture, weight bearing was found to be less than 50% of body weight during the first two months post fracture [10]. In all of these previous studies however, weight bearing was assessed from measurements made when the patient walked over a force plate, and direct inference cannot therefore be made that such weight bearing was the norm during normal patient activity.
In this study, a small portable monitoring system was developed to measure the load which a patient puts through a tibial fracture. This system was subsequently used to measure the weight-bearing achieved with time in patients being treated by a variety of fixation methods for a tibial fracture.
Section snippets
Materials and methods
The monitoring system was developed on a commercially available microprocessor system (Mini Module, PSI Systems, Essex, U.K.). Included in this system are a central processing unit (CPU) consisting of a Philips 93C100 microprocessor, erasable programmable read only memory (EPROM), random access memory (RAM) with lithium battery back-up, a real time clock, 16 digital channels, four analogue to digital converters, one digital to analogue converter, an RS485 serial interface, a keyboard adapter,
Results
During these preliminary trials, a total of 37 patients with tibial fractures were monitored at least once during the course of their treatment. Of these, nine patients had three or more consecutive measurements performed. From these, the results for three patients, two treated with an intramedullary nail and one treated with an external fixator, are given below, these having had the greatest number of measurement sessions during fracture healing. Due to the small number of consecutive
Discussion
The monitoring system developed was able to measure weight-bearing continuously during normal patient ambulation. This is an improvement over previous studies in which a single measurement or a small series of measurements of weight-bearing were obtained, often in an unfamiliar environment. As the weight-bearing data is averaged over the whole duration of the walk, it may therefore be more representative of the loading (and therefore stimulation) which the patient will give to the fracture
Conclusions
A portable system has been developed which records the magnitude and duration of weight-bearing during ambulation. This system was used to monitor changes in weight-bearing and the timing of weight-bearing in the fractured leg of a small series of patients with a tibial fracture.
Acknowledgements
This work was supported by a grant from SPARKS.
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2020, Medical Engineering and PhysicsCitation Excerpt :During the first 4 weeks after surgery, the patient is not allowed to apply body weight and advised to walk with the help of a pair of crutches [21,23]. According to the experimental study of Aranzulla et al. [25], at 6 weeks post fracture, the weight bearing load of the fractured bone was reported to be ~50% of the body weight. Gardner et al. [6] show that the callus develops drastically between 4 and 8 weeks after surgery.
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2015, Medical HypothesesCitation Excerpt :Until such technology is feasible for large scale clinical use decades of development are still needed. To recruit a large number of patients for trials and ultimately treatment a more universal surrogate parameter for healing is needed: Gait is increasingly viewed as a future surrogate parameter for fracture monitoring of the lower extremities and has shown good preliminary correlation with fracture healing [20,21]. Studies were able to show a clear correlation between the biomechanical fracture stiffness and weight bearing [22].
Gait and function as tools for the assessment of fracture repair - The role of movement analysis for the assessment of fracture healing
2014, InjuryCitation Excerpt :Another way of measuring the stage of fracture healing is the assessment of gait patterns [20,23,24]. The ability of patients to tolerate loads in fractured limb is directly proportional to the consolidation stage and the inability to bear weight can cause changes in gait patterns, resulting in antalgic gait [20,23,24]. Ambulation shows up a basic necessity for performing various daily activities, and their analysis provides important information about the functional capacity of the individual [25,26].
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2014, InjuryCitation Excerpt :In these patients it might be safer to rely on the patients’ subjective self-assessment to start and increase weight bearing. It has been shown that unrestricted weight bearing increases with time after fracture [12,13]. Joslin et al. demonstrated that patients who recovered well reached weight bearing of 90% of normal, while patients with delayed union achieved only 40% of normal at same time [14].
A novel intramedullary nail for micromotion stimulation of tibial fractures
2012, Clinical BiomechanicsCitation Excerpt :In another study, small interfragmentary displacements of approximately 0.2 mm in an external fixator of known spring rate can be correlated with a total stance-phase load of only 40 N (Kenwright and Goodship, 1989). Some authors have hypothesised that a biofeedback mechanism mediated by mecho-receptors restricts weight-bearing and prevents patients from over-loading the healing fracture (Joslin et al., 2008), a theory which is supported by observations that patients with very rigid fixators (i.e. IM nails) can bear more weight more quickly because the implant bears much of the load (Aranzulla et al., 1998). However, this has also been cited as a weakness of IM nails in that controlled callus compression does not occur and patients with full non-union may be able to fully bear weight on an IM nail (Joslin et al., 2008).