|Year : 2018 | Volume
| Issue : 2 | Page : 83-89
Spring technique for correction of multilevel deformity using hexapod external fixator
Leonid N Solomin1, Munetomo Takata2, Elena A Shchepkina3, Fanil Sabirov3, Konstantin L Korchagin3, Hiroyuki Tsuchiya4
1 Department of Orthopaedic Surgery, Vreden Russian Research Institute of Traumatology and Orthopedics, Saint Petersburg State University, St. Petersburg, Russia
2 Department of Orthopaedic Surgery, Ishikawa Prefectural Central Hospital, Kanazawa, Japan
3 Department of Orthopaedic Surgery, Vreden Russian Research Institute of Traumatology and Orthopedics, Pavlov First Saint Petersburg State Medical University, St. Petersburg, Russia
4 Department of Orthopaedic Surgery, Graduate School of Medical Science, Kanazawa University, Kanazawa, Japan
|Date of Web Publication||4-Mar-2019|
Department of Orthopaedic Surgery, Ishikawa Prefectural Central Hospital, Kuratsuki-higashi 2-1, Kanazawa City, Ishikawa Prefecture 920-8530
Source of Support: None, Conflict of Interest: None
Context: Osteotomies in several parts of one long bone are recommended for correction of a long, curved, and wide-angled deformity. Hexapod external fixators (HEFs) allow for the single-stage correction of multiplanar deformity, but they are heavy, expensive, and requires continuous management of 12 struts, if at more than one level. Aims: We proposed the use of springs with HEF to support the intermediate ring. Deformity between the proximal and distal rings is corrected using one HEF, and the intermediate fragment is automatically corrected by the tension of the springs. Settings and Design: This was a retrospective descriptive study. Subjects and Methods: We treated seven males and eight females with 17 affected limbs. Four patients with familial hypophosphatemic rickets, five posttraumatic deformities, two osteogenesis imperfectas, three fibrous dysplasias, and one neurofibromatosis were included. The mean preoperative angle between the most proximal and distal fragments was 62.5°. First, small distraction at each level was initiated with one HEF fixed to the most proximal and distal rings, and Ilizarov hinges applied between the proximal and intermediate rings. Then, a set of three springs was applied for each interval between the rings. Gradual correction using HEF was performed, considering only the axes of the proximal and distal bone fragments. Results: Good alignment was achieved in all patients without severe complications. The mean correction period was 5.5 weeks and mean fixation period was 33.8 weeks. Conclusion: Combination of HEF and springs is capable of correcting severe deformity.
Keywords: Deformity correction, hexapod external fixator, multilevel deformities, spring
|How to cite this article:|
Solomin LN, Takata M, Shchepkina EA, Sabirov F, Korchagin KL, Tsuchiya H. Spring technique for correction of multilevel deformity using hexapod external fixator. J Limb Lengthen Reconstr 2018;4:83-9
|How to cite this URL:|
Solomin LN, Takata M, Shchepkina EA, Sabirov F, Korchagin KL, Tsuchiya H. Spring technique for correction of multilevel deformity using hexapod external fixator. J Limb Lengthen Reconstr [serial online] 2018 [cited 2020 May 31];4:83-9. Available from: http://www.jlimblengthrecon.org/text.asp?2018/4/2/83/253394
| Introduction|| |
Significant deformity occurs in patients with rickets,,, osteogenesis imperfecta,, achondroplasia, postinfectious epiphysiodesis, multiple hereditary osteochondromatosis, fibrous dysplasia, and other disorders. Severe long-bone deformity can cause degeneration of the adjacent joint; therefore, its correction using osteotomy is required. Osteotomies in two or more parts of one long bone are recommended for correction of a long, curved, and wide-angled deformity because osteotomy in only one part of the bone may lead to another localized deformity. Clinical studies have shown that the healing index is significantly improved and time spent in the external fixator (EF) is shortened in bifocal procedures than that in monofocal procedures.
In the classic Ilizarov technique, three rings and two sets of hinges are used in bifocal correction. However, the composite frame may be complicated, and a high level of skill is required to manage the hinges. Compared with Ilizarov ring fixators, hexapod EFs (HEFs) allow for the single-stage correction of multiplanar deformity with increased precision.,,,, The correction and distraction-consolidation periods were reportedly shorter with HEF than with Ilizarov-type EF.,
Multilevel deformity in the long bone can be accurately corrected using several HEFs simultaneously. However, several shortcomings must be addressed, including different programs for each level of deformity and continuous management of 12 struts to lengthen or shorten the long bone. The weight of 12 struts is heavy and may limit daily life activities. The smallest available size for struts in the Taylor Spatial Frame (TSF) is 59 mm, which limits the distance between the rings. In addition, shorter struts require frequent adjustments and replacement. Finally, using two sets of hexapods is expensive.
Basically, the most proximal and distal bone fragments should be aligned correctly and the intermediate fragment should only be aligned with them so as to maintain bony contact for union. Therefore, strict management using HEF of all intervals between the fragments is not necessary.
We have proposed the use of springs with HEF to support the intermediate ring. Deformity between the proximal and distal rings is corrected using one HEF, and the intermediate fragment is automatically corrected by the tension of the springs. This helps in solving the problems related to heavy frame and management. Therefore, the aim of our study was to try the effectiveness of this new method in a clinical setting.
| Subjects and Methods|| |
Between April 2015 and June 2018, we treated seven males and eight females with 17 affected limbs. The mean age of the patients at the time of surgery was 30.6 (21–58) years. Five patients had deformities due to trauma, four due to rickets, three fibrous dysplasias, two osteogenesis imperfectas, and one neuromatosis combined with congenital pseudoarthrosis of the tibia. Eight femurs and nine tibias were affected [Table 1].
Assessment of deformities
Prior to surgery, all patients were radiographically evaluated. In each deformity, their apex or the center of rotation of angulation (CORA) was identified at the point where the anatomical or mechanical axes intersect [Figure 1]a. In case the CORA deviated outside the bone, another axis of the intermediate fragment was added so that the CORA would be situated along the contour of the bone. Joint orientation angle based on the joint surface line was referred in the fragment including the epiphysis. In 16 limbs, two CORAs were identified, whereas in one limb with severe deformity in the lower leg, three CORAs were detected; osteotomy was planned at each level of the CORA, with enough pins at each level to ensure stability.
|Figure 1: Staged configuration of the Spring technique. (a) An anatomical or mechanical axis of each bone fragment was drawn. The intersection point was set for osteotomy. Rings were applied orthogonally to the bone axis, at the center of the fragment. (b) Hexapod external fixator (HEF) was applied to the most proximal and distal rings. Ilizarov hinges were applied between the proximal and intermediate rings. (c) Distraction at the proximal level was performed using Ilizarov hinges and at the distal level using HEF. (d) After the first small distraction, a set of three springs for each interval was applied between the rings, and Ilizarov hinges were removed. (e) Gradual correction of deformity was achieved by HEF. (f) After lengthening, three rings were connected using simple Ilizarov rods with conical washers, instead of using HEF|
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All procedures were performed under general anesthesia. The levels of osteotomy and sites of ring application were marked on the skin prior to surgery, according to the preoperative strategy. The rings were mounted onto the bone fragment orthogonally using tensioned transosseous wires and half-pins.
After fixation, osteotomies were performed using a small osteotome through a small percutaneous incision with minimal periosteal disruption.
Staged configuration of the spring technique
Ortho-SUV Frame (OSF; Ortho-SUV Ltd, St. Petersburg, Russia) was applied. Struts were fixed to the most proximal and distal rings. In addition, Ilizarov hinges were applied between the proximal and intermediate rings [Figure 1]b. Distraction was initiated 5–7 days postsurgery at a rate of 1 mm/day at each level of osteotomy and was performed at the proximal level using Ilizarov hinges and at the distal level using hexapods. Radiographic examination was performed on days 5–7 of distraction to confirm the presence of enough distance between the bone fragments [Figure 1]c. At least 3 mm of the gap was confirmed.
Following the first small distraction, a set of three springs was applied for each interval between the rings, and Ilizarov hinges were removed. Tension coil springs made of steel were fixed orthogonally to the rings and were aligned to form an equilateral triangle in a horizontal section [Figure 1]d. The springs were made of stainless steel and had a 0.9 mm wire diameter, 8.9 mm outer diameter, and 65-mm length between both hooks without any tension. Springs were custom made especially for this project. In all cases, the increase in springs' length did not exceed 57% of the initial length of the spring.
Gradual correction of deformity was initiated immediately after mounting of the springs. At calculations in software, only the axes of the proximal and distal bone fragments were taken into consideration. The rate of movement required to provide 1 mm of correction at each level was 2 mm/day for two-level deformities [Figure 1]e. During the movement of the distal fragment, the intermediate fragments occupied the correct position automatically.
After deformity correction, all rings were connected using simple Ilizarov rods with conical washers, instead of OSF struts. Axial compression was applied to reduce excess length and improve stability to promote bone consolidation and union. The frame remained in the consolidation phase until sufficient bone regeneration was seen clinically and radiographically [Figure 1]f.
| Results|| |
As expected, good alignment was achieved in all patients. The mean angle of the deformity was improved from 62.5° (30°–95°) before treatment to 1.0° (0°–5°) after treatment. Lengthening was performed in 11 cases, and the mean amount of lengthening was 21.7 (5–50) mm. The mean correction period was 5.5 (2–9) weeks and mean fixation period was 33.8 (1–59) weeks. In congenital diseases, fixation period was tended to be longer. Seven patients, who lived far away from the hospital, could not come in time for frame removal, despite the signs of bone fragment union. The fixation period of patient 13 was 59 weeks, which was the longest; however, the bone consolidation was gained at the 12 weeks after the operation [Table 1].
During fixation of the springs, none complained of severe pain which could occur with flexible fixation. The springs during deformation correction were lengthened and shortened in accordance with the distance changing between the rings. None of the springs loosened, detached, broke or deformed irreversibly.
A patient with posttraumatic deformity had premature consolidation at one level and required a re-osteotomy, followed by correction using two hexapods. Two pin-tract infections occurred in the femur, in which one required removal and re-insertion, and one was dealt conservatively with antibiotics. Another patient with deformity in tibia had wire breakage, which required removal and insertion of additional wires. Two neuropathies occurred and recovered conservatively.
There was no apparent difference in bone regeneration between the proximal and distal osteotomy sites, and no additional correction was required. Observations in a 21-year-old male patient with osteogenesis imperfecta are shown in [Figure 2].
|Figure 2: The preoperative front (a) and lateral (b) view of the right tibia of a 21-year-old male patient with a severe valgus deformity. He was diagnosed with osteogenesis imperfecta in childhood, and had sustained multiple fractures. When he presented to us, he was unable to walk because both femora and tibia had severe deformities. (c) The anatomical axes were drawn. The angle between the most proximal and distal fragments was 105°, requiring three osteotomies. (d) There was also a 102° deformity in the lateral projection. (e) A front view of the leg shows Ortho-SUV Frame (OSF) and the set of three springs at each interval between the rings. (f) An AP radiograph obtained 11 weeks after surgery shows good alignment of the most proximal and distal fragments, and good bony contact of each osteotomy site. An anterior (g) and lateral (h) radiographs obtained after removal of the frame shows bone union. (i) Ipsilateral femoral correction with two osteotomies using OSF was started after correction in the lower leg. (j) During the consolidation period in the femur, the patient could walk using crutches. (k) A bipedal long AP radiograph shows no mechanical axis deviation on the treated side. Further correction would be performed on the left side|
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| Discussion|| |
This is the first report that demonstrates the effective correction of severe long bone deformity using HEF in combination with springs instead of two or three sets of hexapods.
The premature consolidation requiring re-osteotomy occurred in one patient early during treatment, which was most likely due to an insufficient lengthening during the first osteotomy [Figure 1]c.
Spring technique could reduce the burden on patients: since one OSF strut weighs 120 g, the total weight reaches approximately 1 kg including other connecting parts. Moreover, it is a well-known disadvantage that price of a set of HEF is high. However, weight and cost of the springs are negligibly small. Furthermore, surgeon could avoid the trouble of making several programs during correction of severe deformity.
Good results were obtained with these custom-made springs. Unless it is a simple system, it becomes unusable clinically. Moreover, careful management of the spring is not necessary, considering several aspects of dynamics. Basically, a spring is an elastic body that deforms according to the Hooke's law, which states that the force is proportional to the extension. Although the distance between the rings varies depending on the part of the ring, and the length changes during correction, the force works to restore them to the same length when three springs are installed in a place that forms a balanced triangle, and finally the two rings become parallel. If three rings are connected by the three springs respectively without the core rod of the bone, none of them inclines in an unintended direction. Considering the number of springs, three springs are sufficient to create a stable three-dimensional structure, and any additional springs would only the weight and hinder the X-ray evaluation. Surgeons should be careful to prevent it from deflecting or stretching out during the correction so as not to lose its effect as a spring, and to make the distances between the rings equal, to deliver the same force at both proximal and distal rings. At the same time, we understand that the spring characteristics should have “stiff” and “loose” borders. We admit that we need to perform further research to determine ideal properties of the springs.
It is difficult to align all the axes of the bone fragments in the same cross-sectional position of the ring, and there is a possibility that translation may occur along the ring deviation. Internal biological springs, such as periosteum, muscle, and fibrous interzone in lengthening site, could have prevented the translation.
Limb lengthening using EF is usually difficult, time-consuming, and susceptible to various complications. Simultaneous lengthening in multiple segments can reduce the duration of treatment for patients with severe deformity. It has been reported that the lengthening index is significantly reduced in the bifocal osteotomy and lengthening group compared with that in the monofocal group. External fixation-assisted nailing and consecutively using external and internal fixation (deformity correction and then nailing) could also reduce the fixation period.,,, However, only in two cases (patients 11 and 15), the shape and diameter of the bone canal were acceptable for nailing.
In a previous study, a patient with fibrous dysplasia was treated with a double-level correction using a TSF and achieved a 60° correction of the rotational deformity. He medially shifted the middle segment to maximize the bony contact between the fragments. If different amounts of correction are required at two levels, then two hexapods would be required.
Some authors have reported patients treated with bifocal osteotomy using a set of two hexapod fixators, although they did not specifically mention the method. Photographs of a double-level TSF have been published; a postinfection epiphysiodesis for a varus deformity of the knee, a patient with arrested growth of the proximal tibia who underwent double lengthening, patients with multiple hereditary osteochondromatosis, and patients with osteogenesis imperfecta have also been reported.
Although there was no apparent difference in bone formation between the proximal and distal sites in our series, Choi et al. suggested that to minimize external fixation time, the distraction rate or amount of length gain of the distal osteotomy site should be approximately three-fourth of that of the proximal site in double-level tibial lengthening. Although there was no apparent instability, it is possible that micromotion at the osteotomy site induced by the spring had a favorable effect. In a study in which experiments of fracture healing models were performed using sheep metatarsus, it was reported that 2 mm of interfragmentary movement showed the greatest amount of callus formation. Stabilization is necessary to promote the consolidation of callus; therefore, we replaced the springs with rigid rods after the correction period.
With the spring technique, OSF has several advantages over TSF. First, the adjustment range of the strut length is wider, which avoids the need for frequent changes, even in the case with large deformity. The connecting plates between the ring and struts can be placed at any part of the ring, which allows for free assembly of the frame and transformation during correction. In addition, a Z-shaped plate is useful for attaching struts to the protruded part of the ring and for avoiding collisions among the parts. Using the spring technique, struts should be mounted beyond the intermediate rings [Figure 3]. The direction of the X-ray beam is based on the bone axis, which enables to assess the deformity accurately with OSF software. However, if a TSF is used, the X-ray beam should be parallel to the ring, even when it is not right angled to the bone axis.
|Figure 3: There are two kinds of connection plates between a strut and a ring, (a) normal standard and Z-shaped. A normal standard connection plate (b) has a projected part that can be inserted into the hole anywhere in the ring, and is fixed with a bolt at the adjacent hole. (c) A Z-shaped connection plate is fixed in the same way and allows for the changing of the distance, both in axial and vertical directions to the ring, (d) which is useful for avoiding collisions between the parts|
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Our study had two limitations. First, the patients were retrospectively reviewed. Second, the number of patients was less. Future reports will be more refined by increasing the number of patients, comparing to an alternative cohort managed purely with multiple HEF methods.
| Conclusion|| |
We used a combination of HEF and springs to correct a wide-angled severe deformity with multiple osteotomies successfully. Although the study was preliminary with small number of patients, this novel technique could be less burdensome for patients and easier for surgeons.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]