LUISELLAPEDROTTI, BARBARABERTANI, REDENTOMORA
Introduction
Markel and Chao [1] underlined that long bone fractures consolidate without complications in most patients. Moreover, in patients in whom the use of complex monitoring techniques of fracture healing was indicated, these tech- niques were often in an experimental stage and hardly available, and their use was limited to the study of some selected bone segments.
For these reasons the techniques most commonly employed to assess frac- ture repair until a few years ago included: subjective criteria (patient’s evalu- ation of pain), objective criteria (manual examination of the fracture stabili- ty), temporal criteria (simple passage of time), and instrumental criteria (radiographic evidence of consolidation).
In brief, if bone healing conditions are normal, traditional methods of monitoring are considered adequate. In particular, radiographic investigation is the most important method because it is the simplest, it provides continu- ous information, and it is easily used for iterative interpretations [2].
Radiographic Evaluation
Radiographic criteria of consolidation generally include these features: in the first month you can see demineralization, with broadening of the fracture line and sometimes a shadow showing the fibrous callus formation (Fig. 1). In the second month, you notice the appearance of peripheral callus and little bone bridges, whereas the solution of continuity begins to fade. In the third month (or even later) the bone trabeculae extend from one fragment to the other, the solution of continuity dissolves, and the callus formation is completed (Fig. 2).
Clearly, many variations of this scheme can be observed, according to kind and place of the fracture and the different treatments.
Fig. 1a, b.X-ray of a fresh fracture of the leg (a) after reduction and stabilization with an Ilizarov external fixation device (b)
a
b
Alternative Methods
Conversely, in cases where the consolidation process is abnormal, alternative methods of instrumental investigation can provide more useful information and are necessary to make quick decisions about treatment changes, too. To sum up, noninvasive techniques for fracture healing assessment have some important advantages [1]:
- Prediction of normal and abnormal consolidation;
- They can help make a decision about the beginning of weight bearing;
- Evaluation of timing of fixation device removal.
The ideal characteristics of these noninvasive techniques should be as fol- lows [1]:
- The ability to quantify the state of bone union and to detect abnormal bone healing early in the course of fracture treatment;
- The ability to quantify the real state of bone healing in patients with radi- ographic and clinical signs of delayed union;
- The ability to evaluate the quality of the gap tissue in patients with estab- lished nonunion.
To date, the most commonly used techniques for the noninvasive assess- Fig.2.Same case as in Fig. 1. X-ray at the end of treatment with complete formation of bone callus
ment of fracture healing are: ultrasound (US) evaluation, which provides morphological qualitative information, and extensimetric monitoring, which in contrast, provides functional-quantitative information.
US Evaluation
The US evaluation of bone callus formation has the double advantage of reducing the total amount of radiographic examinations carried out during the treatment (since US can periodically be used instead) and of indicating the early stages of the callus formation during the first 4 weeks, during which the radiographic examination cannot provide useful information [3–6].
In fact, the cortex of long bones is a linear structure which is extremely important in US images: it represents the target of the scanning and splits the echographic image into a superficial zone, which is represented by the soft tissues, and a deep zone, namely, the artifacts’ zone, in which it is possible to point out reverberations with longitudinal morphology which simulate a sec- ond cortical bone.
Some echographic phases in the evolutionary morphology of the bone callus in a long bone fracture treated by external fixation can be distin- guished [7]:
- The first phase (7–10 days): an evident gap is demonstrated between the two cortices with clear-out margins; sometimes a hypoechogenic area with shading margin may be seen related to the hematoma (Fig. 3).
Fig. 3.Ultrasonographic evaluation of bone callus: first phase
- The second phase (10–25 days): two kinds of formations can be observed related to the periostal collars that tend to meet from the two sides of the fracture filling the gap. If the fracture has an ideal strain, a global forma- tion is evident; in overstressed fractures or in inadequately fixed ones, a cuspidal structure can be observed (Fig. 4).
Fig. 4a, b.Ultrasonographic evaluation of bone callus: second phase. a Global structure.
bCuspidal structure
a
b
- The third phase (25–35 days): the echo reflected by the focus increases in intensity according to the initial callus calcification; the collars meet in one hyperecogenic convex, bridge-shaped structure on the fracture gap.
- The fourth phase (35–50 days): the hyperecogenic structure represents a clear obstacle to the ultrasounds, and an acoustic shadow appears below the new- ly formed periosteal callus according to its progressive calcification (Fig. 5a).
- The fifth phase (50–90 days): the cortex is being rebuilt. In the deep area the reverberation artifacts reappear parallel to the cortical bone which is the scanning object.
Fig. 5a, b.Ultrasonographic evalua- tion of bone callus. a Fourth phase:
progressive callus formation.
bSixth phase: the cortex is rebuilt
a
b
- The sixth phase (90–140 days): the bone callus image is clearly outlined and appears reduced in volume (Fig. 5b).
Extensimetric Monitoring
The echographic controls described provide information on the morpho- logic aspects and on the biological state of the bone tissue but they allow only an indirect evaluation of its mechanical strength. Furthermore, it is often dif- ficult to choose the right moment for fixation device removal when assessing the solidity of the skeletal segment being treated. Removing the fixation device too early, in fact, represents the risk of new fracture or collapsing of the newly formed tissue, but removing it too late would be risky as well because of the excessive bone stresses by the fixation device, which may cause a new fracture.
Extensimetric monitoring has been developed to help solve this problem.
A further aim is finding out how to restore the mechanical resistance of the fracture focus and that of the bone regeneration site in order to detect any possible delay or consolidation problem beforehand.
Should external osteosynthesis be used, extensimetric monitoring quanti- fies the mechanical properties of the callus by measuring the deformities of the bone-fixator system at different moments of the consolidation [8]. During the early stages of the treatment, alterations of the fixation device, which has been too elastic or too rigid, might be indicated, whereas in the following stages it is useful to monitor the correct progress of the bone formation.
After the beginning of the rehabilitation up to weight-bearing, extensi- metric monitoring quantifies the fracture site strength some days before and after weight bearing is permitted. Determining the allowed load is, in fact, the most difficult decision in treatment with external fixation and its effect is important for the the consolidation process. Therefore, weight-bearing must be allowed at the right moment, extensimetric monitoring providing early and reliable information about the callus and regenerated bone resistance.
The principle on which the extensimetric method is based is well known:
the deformation of the external fixation device can be considered as the wit- ness of the callus or bone regenerate deformation. Progressively during treat- ment, the bone participates in the system resistance even more and the regis- tered deformations become less and less important. The machine functions on the electric resistance variation stress.
In monitoring fractures treated by circular external fixation devices, first of all, a flexion-extension test of the distal joint is carried out, then the “ bend- ing” test takes place (deformation when the limb is lifted), and at the end the marching test (regular deambulation allowing the maximum load) is per- formed [9–11].
In addition to the information about solidity of the bone union, these tests, regularly repeated during the treatment, also provide useful informa- tion about the evolutionary stage of the callus and regenerated bone consis- tency.
In fact, by analyzing the greatest deformation graphic, five stages of treat- ment, each mechanically different and corresponding to a specific biologic stage, can be identified and a “deformation curve” created (Fig. 6):
Fig.6a-c.Extensimetric monitoring. a Flexion- extension test. b Bending test. c Walking test
a
b
c
- Initial stage of solidity diminuition (of varying importance and lasting according to the kind of treatment carried out);
- Greatest deformability stage of the system (when the regenerating bone or the procallus, partially calcified, is in an extremely plastic biomechanical condition);
- Rapid reduction stage of the deformability (thanks to the progressive cal- cification of the regenerated tissue or that of the procallus osteoid trabec- ulae;
- Mechanical stability stage (with the least deformation values);
- Elasticity reestabilished stage (with deformation levels higher than those registered in the previous stage, probably related to the bone reshaping phenomenon).
If the morphologic-qualitative information (radiographic and echogra- phic tests) correspond to the functional-quantitative ones (exstensimetric data), once the fourth stage is reached, the removal of the external fixation device can usually be planned.
References
1. Markel MD, Chao EY (1993) Noninvasive monitoring techniques for quantitative description of callus mineral content and mechanical properties. Clin Orthop Relat Res 293:37–45
2. Massare C, Evrard J (1976) Critères de consolidation des fractures des os longs de l’adulte. Rev Chir Orthop 62[Suppl. 2]:177–186
3. Abendschein W, Hyatt GW (1970) Ultrasonics and selected physical properties of bone. Clin Orthop Relat Res 69:294–301
4. Gerlanc M, Haddad D, Hyatt GW et al (1975) Ultrasonic study of normal and frac- tured bone. Clin Orthop Relat Res 111:175–180
5. Dzene II, Dzenis VV, Petukhova LI et al (1980) Human tibia in the presence of coxarthrosis and fracture using exponential ultrasonic concentrators. Mekhanika Kompozitnykh Materialov 6:1081–1087
6. Carlini C, Aldegheri R (1982) Studio sperimentale del callo osseo mediante ultra- suoni. Chir Organi Mov 68:33–39
7. Ricciardi L, Perissinotto A, Dabalà M (1993) Mechanical monitoring of fracture hea- ling using ultrasound imaging. Clin Orthop Relat Res 293:71–76
8. Burny F (1968) Étude par strain gauges de la consolidation des fractures en clini- que. Acta Orthop Belg 34:917–925
9. Ceffa R, Perissinotto A (1995) Strain analysis. In: Bianchi Maiocchi A (ed) Advances in Ilizarov apparatus assembly. Medicalplastic, Milan, pp 15, 16
10. Ceffa R, Bombelli M, Boero S et al (1997) Extensimetric monitoring of healing in the treatment with the Ilizarov apparatus–a multicenter clinical trial. Bull Hosp Joint Dis 56:41–45
11. Mora R (2000) Tecniche di compressione-distrazione. Amplimedical, Milano
