International clinical practice of long bones lengthening (LBL) with intramedullary distraction devices at the modern stage of development of this orthopaedic area has rather few available set of medical technologies recognized by specialists: A.I.Bliskunov (Ukraine), [1, 15], A. Betz (Fitbon device, Ger-many , Германия) [14], J.-M. Guichet (Albizzia, device, France) [9, 16], S. Hankemeier (ISKD device, USA,) [17]. Every known method has its own benefits and weak points. There are variations in distraction devices construction, implantation technologies and their application for LBL. These variations, respectively, determine the differences in clinical outcomes, in level of patients comfort during all lengthening program. Comparative analysis of methods and available results on already performed LBL provide the possibility to consider all the benefits and weak points more objectively.

Considering existent intramedullary distraction device (Fig. 1–5), one may note definite similarity in their outward appearance. In particular, every device consists of telescopic construction with two tubes. Advancing of one tube toward the other just determines lengthening effect (distraction).

Cinematic scheme of all intramedullary distraction devices operation (Fig. 1–5), has common similar series of consecutive operations that can be represented as "external effect – movement (force) > device mechanism > device internal tube advancing > - (distraction effect)". However, at this point all the similarities come to the end.

Аппарат Блискунова (Украина)
In Bliskunov devices [1] "external effect" means adducent and abdusent hip movement that activates drive 1 (Fig. 1) in femoral bone lengthening (2) and pressor effect on drive through soft tissues (3) at shin lengthening (4) (Fig. 2) [2]. Force, developed as a result of “external effect”, through the drive, is transmitted to "device racket mechanism" (it is situated in device external corpus (5) (5) for hip, (6) for shin that in its turn provides rotation moment for internal guidescrew and advancing of device internal tube (7) (Fig. 1), (8) (Fig. 2). In that way device working system could be represented as: "external effect – movement (force) > drive > device mechanism > device internal tube advancing > - (distraction effect)".

Fig. 1 Scheme of intramedullary Bliskunov device placement in femoral bone

Fig. 2 Scheme of intramedullary Bliskunov device placement in tibia

Аппарат Fitbon (Германия)
Similar principle is applied in fully-motorized implanted rod of Fitbon system that was developed by German designers [14] (Fig.3). It contains special mechanism (highly sensitive epicyclic drive) in hermetically sealed soldered corpus. (9). Electronic impulses are sent from special electric apparatus (10) (600 micro impulses correspond to 0.5 – 2 mm of distraction (one impulse - 0.0008–0.003 mm) to receiver antenna (11), which is situated under patient skin. The antenna is connected with epicyclic drive that in its turn moves telescopic rod (12) with impulse power up to 200 kg.

Fig. 3 Scheme of intramedullary Fitbone device placement in tibia

In scientists’ opinion [14], this strain is enough to counteract muscular resistance during distraction. Although practical implication of the method in clinic has shown that muscular tension and regenerate formation – all are major obstacles that limit lengthening at big magnitudes. Maximal hip or shin lengthening magnitude with Fitbon device (one program of lengthening) does not exceed 4.5 – 5 cm. If it is necessary to achieve larger result of limb elongation repeated operations in 10-12 months (osteotomy in a zone of formed regenerate or device replacement) are performed and lengthening is continued. Next stage, generally, allows elongating limb segment length up to 3 cm [14].

Important Fitbon method characteristic that distinguishes it from other distraction methods is a way of force impact transmission to device mechanism. If all distraction devices are the “pure” mechanics, the Fitbon method uses electromagnetic influence. It is clear that contact mechanical transmission of energy (force) is of high reliability. However, this is only for today. Scientific and technical developments undoubtedly will lead to new ways of noncontact energy transmission to device mechanism. In this sense Fitbon constructors made very important step that considerably broadened this development perspective in orthopedics.

However we should note several this method aspects, which in our opinion demand more detailed study and possible improvement.

1. At first place this is risky in complications sense device implantation method into femur and shinbone, where surgery access is made through knee joint [14].
2. There is an ambiguity in choice of extremity lengthening magnitude, especially in need of considerable distraction result (>4 cm).
3. It is important to clear out effect (POSITIVE AND NEGATIVE) of electronic impulses on patient organism in general, and on bone regenerate, in particular.
4. Impulse distraction effect, used in this method, demands more detailed study, namely, its effect on regeneration in osteotomy zone. In this sense it is important to check reaction of bone regenerate delicate tissues to abrupt distraction step (jerk) in response to electromagnetic impulse.
5. It is not clear if the stable “distraction step” is provided for all lengthening distance, and especially for distraction period, where there is abrupt increase in segment soft tissues resistance.

Аппараты Аlbizzia (Франция) и ISKD (США)
Аlbizzia [9, 16] (Fig. 4), and ISKD [17] devices (Fig. 5) work by the principle: "external effort – movement (force) > device mechanism > internal device tube prolongation – (distraction effect)".

Fig. 4 Scheme of intramedullary Albizzia device placement in tibia

Fig. 5 Scheme of intramedullary ISKD device placement in tibia

We should note that Bliskunov device (see. Fig. 1, 2) works with longer transmission chain from external force to distraction effect.

Is this an advantage or drawback? In order to answer this question it is necessary to "consider" all "positive" and "negative" aspects of such additional link as drive.

We may notice at once that “drive” presence in construction means additional surgical manipulations for its implantation and removal (device switching off). We may also state that the "drive" in Bliskunov device is additional link in construction, because it is situated not inside the device. For “drive” positioning inside the body "anatomic place" should be foreseen. At first glance the “drive” presence may be classi-fied as the method drawback. However this view is eliminated if we consider all functional advantages that Bliskunov method acquires due to this drive in construction.

"Drive" (1) (see Fig. 1), and "drive" (3) (see Fig. 2) creates lifting jack effect, where external force is smoothly transmitted to leader with step-up ration. On the one hand, internal tube prolongation (5) (see Fig. 1) and (6) (see Fig. 2) goes smoothly, without jerks, and on the other hand this tube protracts strictly by the device axis (this means according to bone growth vector) without "additional", "side", and rotational movements.

Thus, it is very important that Bliskunov device construction (see Fig. 1, 2) with the "drive" (1) and (3) does not demand large external force to achieve lengthening effect. This allows a patient actually during the whole lengthening program to activate the device (to make LBL) independently (without help of doctor, assistant and special equipment) outside medical institution, at home. Painlessness distraction process and patient comfort during the device work are all evidences of sparing regimen, caused by Bliskunov device construction.

"Drive" absence in Аlbizzia devices (see Fig. 4), and ISKD devices (see Fig. 5) – is an advantage. However, this link absence in kinematical system makes external force transmission into distraction mechanism more direct and hard. External effect in Аlbizzia (see Fig. 4) and ISKD (see Fig. 5) devices – are rotational movements of extremity segment. Doctor or assistant holds patient lower extremity by shin/foot and make rotational movements (till characteristic click), trying to make the device to work.

Such rotation leads to unscrewing of one device tube out from other with back movement blocking, which provides for telescopic distraction effect. However, it is necessary to note that dissected bone is situated on the device rod (apparatus), which is in unstable condition (rotation/tubes unscrewing with further inner tube prolongation). The device distraction effect is rotational movement of one apparatus tube with respect to other. In other words, one device part with fixed in it corresponding bone part is rotated with respect to other construction (the second tube with bone part). As the result geometrical space parameters (volume parameters) between bone margins in osteotomy zone are changed, there is regenerate tissue screwing in space between bone margins, which is especially pronounced at the beginning of distraction.

Every operation of ratchet gear in Аlbizzia device (see Fig. 4) lengthens the system by 0.07 mm (15 ratchet gear operations correspond to 1 mm of lengthening). Authors [9, 16] note that distal fragment rotation shift (17) in respect to proximal (18) by 20°, which prevents regeneration, looses its negative effect as bone fragments separate further. Experimental evidence shows [9] that their shifting during rod mechanism turn becomes smaller in comparison with diastasis magnitude. However, as bone fragments separate and paraosseous tissues are stretched the device mechanism work becomes harder. In this connection the author [9] had to complete single-stage hip lengthening in patients by several stages under general or transdural anesthetics (such distraction steps number sometimes reached 30). At that the single-stage lengthening was 4-10 mm. The author [9] described the case, when one patient could tolerate only 13 such procedures, after which lengthening program was stopped. The distraction process was complicated by the device fracture and false joint formation in hip.

ISKD device with identical construction (see Fig. 5) – the skeletal kinetic distractor [17], also provides for distraction effect at distant fragment rotation (19) with respect to proximal (20) (device movement in respect to external (15) and internal (16) tubes) from 3 to 9°. In authors’ opinion [17], rotational oscillations are physiological part of human walking process. Distraction 1 mm is achieved with 160 rotational extremity movements. Actual distraction magnitude is controlled by special external manual monitor. Patients change daily distraction minimum 5 times a day. If the distraction length is insignificant the lower extremity is rotated under monitor control till desired length.

In the first and second cases there is necessity to carry out extremity rotational movements under constant doctor control. At that general, transdural anesthetics and other anesthetic methods are not excluded. Especially evident rotational distraction drawbacks are during shin lengthening (see Fig. 4, 5). Here one of the problems is “behavior” of dissected fibula free ends during distraction device activation. Danger of soft tissues and fibular nerve damage considerably hampers shin lengthening by ISKD and Аlbizzia methods, which is indirectly supported by "poor" statistical data of general completed programs number of these segments lengthening [16, 17].

Of special interest is bone regeneration in this distraction osteosynthesis conditions. If we consider how axial instability in distraction movements affects bone regeneration conditions, we may note that here periostal reaction is major component [9, 16, 17], which is noticed both at diastasis level, and in adjacent bone fragments. At that distraction regenerate “growth zone” is absent.

Thus, "considering" all "pro et contra" of various distraction methods we can not fail to notice that by today “drive” is rather Bliskunov device advantage. Drawbacks of temporary (only for lengthening period) “drive” presence in the device construction are compensated by exceeding benefits of its application.

Speaking about stability in regenerate zone we mean, at first place, strong bone parts fixation as necessary condition for qualitative bone healing. However, as for bone lengthening, the stability should be interpreted not only as good bone fixation outside distraction process, but also clearly defined by axis advancing and dosed bone fragments “separation” during distraction. Such stability is the proper very important precondition for good final clinical result of long bones lengthening.

In case of instability in osteotomy (future regenerate) zone the disturbances of bone tissue reparation are possible. This is supported by experimental research of V.I.Stetsul (1965) [12] of bones consolidation in long bones diaphysial fractions after operative osteosynthesis by interstitial constructions. General regularity was discovered: regenerate volume and its cartilage tissue content progressively decrease with increase of bone fragments stability. In case of bone fragments incomplete fixation (mobility in osteotomy zone) large bone-cartilage or bone-fibrous regenerate is formed that leads to bone cross-section growth and excessive periosteal callus as a bone “keloid” variety.

We can not disagree with J.-M. Guichet [9, 16], А. Betz [14], and S. Hankemeier [17] also in choosing osteotomy level. It is known [11] that long bone blood supply normally is made predominantly through main nutritious artery that divides itself in bone-marrow cavity into ascending and descending branches with predominance of capillary net longitudinal-radial orientation. Osteotomy (21) (see Fig. 3), (22) (see Fig. 4), (23) (see Fig. 5) at the level of upper margin of one-third or at one-third of long bone diaphysis always damages main artery, and the necessary bone-marrow cavity milling for distraction device even more damages intraosseous blood vessels and leads to wide-spread bone microcirculatory disturbances. The larger the device diameter, the more pronounced is traumatic effect on endosteum, and, respectively, more prolonged is bone circulation restoration, which decreases bone tissue reparative processes [5, 8].

Osteotomy level, proposed by the authors [9, 14, 16, 17] in our opinion is forced choice. The point is that during technological channel milling there is danger of cutter perforation of the anterior wall (on physiological curve top) of femur (24) (Fig. 6а) in sagittal plane. At the point, where cutter (25) sets against anterior bone wall the transverse bone osteotomy takes place (26) (Fig. 6б) with the help of centro-medullary saw. Further milling of distal fragment is completed from the physiological curve top (medium one-third of bone diaphysis), and the bigger the bone curve, the more angle ? is increased to the front (27) between proximal (28) and distal (29) fragments after intraosseous device implantation (рис. 6б); that means load axis changing for lower extremity.

Fig. 6 Implantation scheme of intraosseous devices Albizia, ISKD, and Fitbon into femur: а – the moment, where cutter sets against frontal femur wall; b – condition after intraosseous device implantation and changing of femur angle á

Why this does not take place in Bliskunov method? Technological channel (30) (Fig. 7) for distraction device in femur (31) should be direct in respect to physiological curve, and should be completed by special conductive device (32) [1, 2]. At that future channel direction in frontal and sagittal planes is determined through preliminary radiograms, as well as through special anatomical formations on the bone, which have constant coordinates. The conductive device association (32) (Fig. 7) with concrete coordinates with the help of special restrictive elements (33–36) allows obtaining necessary special position of the proper conductive device, and respectively, its elements strict position that determine milling instrument direction. After the conductive device (32) is placed on the bone (31) technological channel is formed (30) with strictly determined direction that provides for minimal cutter cutting into bone-marrow cavity walls, and which excludes bone damage along all its length.

Fig. 7 Scheme of conductive device installation on femur: а – frontal view; б – side view

Experimental modeling of long bone damages at its various levels with further lengthening and distraction regenerate morphological assessment demonstrated good bone tissue reparative capacity in osteotomy not in diaphysis, but in metaphysis zone [8]. This is exactly what is foreseen by Bliskunov technology [1, 2].

It is known that bone tissue reparation quality in distraction osteosynthesis depends on several factors, namely:

1. bone osteotomy level;
2. fragments stable fixation and their gradual, smooth distraction;
3. blood flow preservation in extremity;
4. adjacent joints function preservation.

Prof. A. I. Bliskunov already back in 1987 refused from stainless steel (12Х18N9T) in favor of titanium alloy, caused by cases of negative organism reaction – metallosis – in some patients [13]. Unique combination of titanium alloy properties, namely, its mechanical strength, load resistance and light weight allowed decreasing the device diameter considerably – from 15 to 12 mm, without compromising its reliability.

The table below summarizes basic characteristics of intraosseous distraction methods.

Device diameter, mm	Methods
	Albizzia	ISKD	Fitbon	Bliskunov
	13	13	14	12
Osteotomy level	Medium diaphysis one-third	Medium diaphysis one-third	Medium diaphysis one-third	Metadiaphysis
Average segment lengthening, mm	Hip – 55 Shin – 35	Hip – 31 Shin – 31	Hip – 40 Shin – 40	Hip – 94 Shin – 55
Device working principle (how distraction step is obtained)	Rotation extremity movements (15 rotations – 1 mm) in osteotomy zone up to 20°	Rotation extremity movements (160 rotations – 1 mm) in osteotomy zone up to 9°	Magnetic-impulse distraction (axial) (600 microimpulses correspond to 0.5–2 mm of distraction a day)	Hip diversion (for femur) and pressure movements on clicker (for tibia). Mechanical distraction through tooth-hook mechanism (axial) (18 mechanism clicks (1 mm) – hip; 55 mechanism clicks (1 mm) – shin)
Material of the device	Stainless steel	Stainless steel	Stainless steel	Titanium alloy (ВТ-16)

Other important aspect – is organism reaction level to foreign material, including the devices "mas-sive" implantation (into 2 or 4 extremities segments). Distraction device situates inside human body for a long period (up to 1 year and more) till complete bone healing. In this aspect titanium alloys do not have competitors. Virtually neutral organism reaction to this metal due to its increased corrosion resis-tance in oxidative environment is the best evidence.

Morphological examinations [4] of tissue biopsy materials that surround intraosseous device after its extraction testify that the material – titanium-vanadium alloy (ВТ-16), is biologically inert and does not produce pathological changes in bone tissue and bone marrow.

With the purpose to determine possible foreign material effect on immunity we completed titanium alloy immune response for several parameters, namely:

1. lymphocytes number of different populations – T (CD3), B (CD20), NK (CD16);
2. T- и NK blood cells functional activity;
3. phagocytes activity in latex particles capturing;
4. immunoglobulins levels for classes A, M, G, and E;
5. relative content of "young" lymphoid blood cells and their rosettes formation with xenogenenic tissue basophiles.

We discovered that during the whole period of titanium device stay in human organism neither quantita-tive nor functional characteristics of basic immunity cells were changed significantly comparing to baseline. We also received interesting results from patient, in whose body titanium alloy device rested for 5 years. Even in this case the patient organism did not develop aggressive reaction to foreign body.

The obtained results testify on absence of negative titanium alloy effect on immune system. These data are also consistent with studies results on immunity factors determination in titanium carriers implantation in dentistry [6, 7].

The completed research allows concluding that internal distraction osteosynthesis as orthopedic field gained much development during recent years. It is important to note that implementation into clinical practice of “internal” bones lengthening methods allowed us to approach significantly to keeping patient best interests, the most important from them is distraction comfort and adequate clinical results.

Distraction devices multi-functionality, namely, intraosseous osteosynthesis as long and adequate consolidating bone protection together with distraction effect possibility that does not demand connection to external environment provided the opportunity to minimize quantity of “submersible” into organism material (actually it is, predominantly, only device corpus) with high efficiency.

Basing on completed research results we may name the main priorities on the way of methods improvement in intraosseous distraction:

1. further optimization of devices work for distraction effect production with maximal sparing conditions for bone regenerate;
2. decrease of linear devices size due to new materials, saving and even increasing devices reliability at distraction loads;
3. decrease of general traumatization for organism tissues due to development of more optimal devices implantation methods and increase of appearance (aesthetic qualities) of surgical routes;
4. searching for new scientific and technical achievements that may be of use for such orthopedic goals as internal distraction osteosynthesis.

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