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Abstract
Angular deformities are common presentations in childhood and adolescent age group. It is important to differentiate a true deformity from a physiological deformity, this requires measurement of the intercondylar and intermalleolar distance. Once a true deformity is diagnosed, the apex of the deformity requires to be established. Lower limb frontal plane deformities are evaluated with a true AP standing radiographs of the entire lower limb from hip to ankle. Mechanical or anatomical axis calculation gives the apex (CORA) as well as the magnitude of deformity. Frontal plane deformities require surgical intervention. In younger children, growth modulation surgery allows correction of the deformity with minimal morbidity and without the need for osteotomy. Older children, adolescents and adults require corrective osteotomy. The corrective osteotomy can be closed wedge, open wedge, or a dome osteotomy. The osteotomy may be stabilized with internal fixation with plate and screws or an intramedullary implant as is dictated by the level of osteotomy and the local bony anatomy. External fixators allow gradual and precise correction of the deformity.
1. Introduction
Angular deformities of lower limb in Pediatric age group present very commonly to orthopaedic and pediatric clinics. Lower limb angulations may be physiological or may be true deformities. Normal development leads to axis alignment changes in lower limb from varus to valgus during the period of growth. This physiological angulation should be differentiated from a true angulation. A true angulation may result from a pathology of the epiphysis, the physis or the metaphysis or a malunited fracture. This if untreated, may lead to abnormal loading of the joints of the lower limb, predisposing to wear of the joints, joint instability and this eventually leads to premature degenerative arthritis.1,2
The aim of this article is to help readers provide guidelines as to which angular deformities, particularly those in the coronal plane require further evaluation and treatment. A good history, clinical examination and a knowledge of the condition is the key to identifying these patients.
2. Natural history of angular development in the lower limb
Genu varum and internal tibial torsion are normal findings in the newborn. In addition there is a physiological flexion contracture of the knees and hips, which is due to intrauterine positioning of the fetus. This varus becomes more noticeable with the gradual correction of physiological flexion contracture and maximum varus is present between 6 and 12 months of age. With growth, the lower limbs gradually straighten with a zero tibiofemoral angle around 18–24 months of age when the infant begins to stand and walk. With further development, a physiological genu valgum develops, which is maximum at around 3–4 years of age with an average lateral tibiofemoral angle of 12°. The normal adult values of physiological genu valgum with tibiofemoral angle of an average of 8° in females and 7° in males reach by 7 years of age.2
3. Evaluation of angular deformity
Deformities of the lower limb can present as the coronal (frontal)plane or as sagittal plane deformity, translational or, torsional deformity; or a combination of these. The purpose of evaluation of a deformity in the lower limb is to differentiate a physiological from true deformity, to find out the magnitude of the deformity as well as the plane of deformity. Only coronal plane deformities will be discussed in this article as sagittal, torsional and translational deformities are beyond the scope of this article.
Clinical evaluation requires measurement of intercondylar distance in genu varum and intermalleolar distance in a clinically appearing genu valgum in either standing or supine position, however since this is used as a screening tool, it is more comfortably done in supine position. To minimize the error, measurement is taken in a standard fashion with the knee facing towards the ceiling which is a patella forward position. The normal values of intercondylar distance in a patient of genu varum range from 0 to 5 cm and a measurement of more than 5 cm is considered abnormal and this requires further evaluation of the magnitude and the etiology of the deformity. Similarly, the normal values of intermalleolar distance in a child with genu valgum range from 0 to 7 cm. A measurement of more than 7 cm is considered abnormal and requires further evaluation.3,4 Fat thighs and internal femoral torsion can exaggerate the clinical appearance of genu valgum. Similarly, internal tibial torsion can clinically exaggerate genu varum and external tibial torsion a genu valgum deformity.5 Patients after the age of 3 years with persistent varus deformity and intercondylar distance of more than 5 cm; unilateral or asymmetric deformities, a positive family history of skeletal dysplasia, short stature, post traumatic or post infective deformities are always pathological and require further evaluation.3
4. Investigations when and which?
Laboratory and/or imaging studies are required if on clinical evaluation, a true deformity is recognized. The investigations should focus on the etiology, the magnitude of the deformity and the apex of deformity.
A metabolic profile is required in those patients where the deformity is suspected to be as a result of rickets.6 These include serum Calcium, Phosphorus and alkaline phosphatase. In patients with rickets, phosphorous levels are low and alkaline phosphatase levels high. In hypophosphatemic rickets, phosphorous levels remain low unless phosphate supplementation is given. Serum Vitamin D levels are useful when there is a strong suspicion of subclinical vitamin D deficiency with normal phosphorous and alkaline phosphatase levels.6 Other frequently done lab investigations include parathormone levels. Imaging studies to rule out skeletal dysplasia is usually required in patients with short stature or a positive family history.
The magnitude of the frontal or coronal plane deformities of the lower limb is calculated by a standing full length Hip-Knee-Ankle X-ray with Knee forwards (Patella-Forwards) radiographs. The frontal plane measurements include the mechanical and the anatomical axis calculations, joint line congruence angle of the knee.7 A mechanical axis line of the limb is drawn from center of femoral head to center of ankle. In a normal mechanical alignment, the line should pass through the center of knee. A 3 mm deviation on either side is considered as normal (Fig. 1). A deviation of mechanical axis line medial to medial tibial spine indicates varus alignment of the lower limb. Similarly, deviation of mechanical axis line lateral to lateral tibial spine is considered valgus alignment of the lower limb.
Outline of full length x ray of lower limb in a patient of genu valgum. The mechanical axis of the limb is calculated by a line drawn from center of hip to center of ankle. In this patient the line is passing lateral to the center of knee indicating a medial mechanical axis deviation of the lower limb (Dashed line). Also note that the valgus in the femur with abnormal mechanical lateral distal femoral angle.
Once a deformity is established in the lower limb, the next step is to find out the source of deformity which can be from the femur, knee joint line or the tibia. Calculations are then done to find the mechanical axis of femur, tibia and the joint line congruence angle of the knee. To calculate the deformity in femur, the center of femoral head is marked. A second point is marked at tip of greater trochanter and joined with a line. This marks the hip joint orientation line. A 900 angle is drawn from this line from center of femoral head towards knee. The distal femoral joint line is marked as most convex points on the distal femur and joined with a line. The center of distal femur is marked on this line and a lateral distal femoral angle of 870 is drawn. The angle of intersection of these lines drawn denotes the level and magnitude of varus or valgus in femur as the case may be (Fig. 2a). This represents the apex of the deformity which is also called center of rotation of angulation (CORA), that is the axis on which the deformity has occurred (Table 1).8
a. Outline of full length x ray of lower limb in a patient of genu varum. After drawing the normal mechanical axis of hip and knee, the magnitude of deformity is 55° in diaphyseal region of femur. b. Outline of full length x ray of lower limb in a patient of genu varum. After drawing the normal mechanical axis of knee and ankle, the magnitude of deformity is 49° in diaphyseal region of tibia.
Table 1
| MECHANICAL (m) JOINT ORIENTATION ANGLES | NORMAL VALUES IN DEGREES (POPULATION AVERAGE) | ANATOMICAL (a) JOINT ORIENTATION ANGLES | NORMAL VALUES IN DEGREES (POPULATION AVERAGE) |
|---|---|---|---|
| Lateral proximal femoral angle (m LPFA) | 84-93 (90) | Medial proximal femoral angle (a MPFA) | 81-87 (84) |
| Lateral distal femoral angle (m LDFA) | 84-90 (87) | Lateral distal femoral angle (a LDFA) | 78-84 (81) |
| Medial proximal tibial angle (m MPTA) | 84-90 (87) | Medial proximal tibial angle (a MPTA) | 84-90 (87) |
| Lateral distal tibial angle (m LDTA) | 85- 94 (89) | Lateral distal tibial angle (a LDTA) | 85- 94 (89) |
| Joint line convergence angle (JLCA) | 0–2 |
To calculate the deformity in tibia, proximal tibial joint line is marked by a line joining the most concave points on the proximal tibial condyles. Its center is marked and a medial proximal tibia angle of 870 is drawn. The distal tibia joint line is marked with 2 points on the distal tibia articular surface and its center point is marked. A lateral 890 angle is drawn from the center of this ankle joint line. The center of ankle may be taken as the center of articular surface of talus or center of ankle mortise. The angle of intersection of these lines drawn denotes the level and magnitude of varus or valgus in tibia as the case may be (Fig. 2b).
The angle between distal femoral and proximal tibia line as drawn above gives the knee joint convergence angle which ranges from 0-20.8
The above given mechanical axis angles represent the population average. To remember the range of normal angles in a simplified way, a difference of ±3 may be taken, otherwise the range remains specific for specific angles.8 Contralateral limb may be taken as a template in situations when it is normal.8
Anatomical axis angles are drawn using the mid-diaphyseal lines. Acute angular deformities are easier to calculate by this method, however deformities without a sharp angulation require anatomical axis lines of proximal and distal joints. The joint line orientation of proximal femur is drawn as a line joining the center of femoral head to tip of greater trochanter. The proximal mechanical axis line is 840 medial, drawn to this line at the level of pyriformis fossa. The distal femur joint line is drawn by joining the most convex parts of distal femur. The distal femur anatomical axis line is drawn at 810 lateral to this line at the level corresponding to the medial tibial spine. The anatomical axis of tibial is parallel to the mechanical axis with a distance of 3 mm so for all practical purposes they are taken as same.8
MRI and CT Imaging is helpful in evaluation of physeal bony bars leading to angular deformity. CT scan also used for calculation of torsional component of the deformity9 (Fig. 3a and b).
a. CT scan showing physeal bar in the region of distal femur physis. (Arrow). b. MRI images of the same patient showing physeal bar in the region of distal femur physis. (Arrow).
5. Management
The goal of correcting a lower limb deformity is to restore the normal mechanical alignment and to improve function. Once surgical correction of the deformity is decided, the next issue remains as to how to correct the deformity; by guided growth or corrective osteotomy using either acute or gradual correction.
5.1. Observation
Patients with clinically diagnosed physiological angulation require only monitored observation for evaluation of an undiagnosed pathological deformity. Routine radiographic assessment is not recommended for clinically evaluated physiological deformities. Use of external bracing has no role in their treatment and in fact spontaneous correction of the ‘physiological deformity' is sometimes attributed to the use of brace.1
5.2. Guided growth
The correction of angular deformity is possible by retarding the growth on the longer or convex side in growing children. The prerequisites to guided growth include minimum of 2 years of growth remaining and where the CORA is at or near to the growth plate, and an angular deformity of less than 200,10,11 . Though, it is possible to correct any plane of deformity by guided growth by tethering the growth plate at appropriate site, local anatomy usually prevents this technique to be used effectively in sagittal plane deformities, and is most commonly used around the knee for coronal plane deformities.10,11 The guided growth can be achieved with a less invasive temporary hemi epiphyseal arrest using staples or specially designed plates. This traditionally has been done by staples, usually 3 staples are required for appropriate temporary arrest of growth. Staples compress the growth plate and have a potential for permanent closure of growth plate, so it is recommended remove them no later than 2 years of insertion. Recently figure of 8 plates have been used, where a single plate is sufficient for guided growth (Fig. 4). The eight-Plate is placed extra-periosteal across the physis in the frontal plane and should be in center in the sagittal plane to prevent a secondary deformity.11 A transphyseal screw may be used in areas like the medial or lateral malleolus.12 It is important to remove the hardware at appropriate time otherwise reverse deformity may occur. Rebound phenomenon of about 50in the opposite direction may occur, and this should be factored in with a mild overcorrection before removing the hardware, if sufficient growth remaining is there.10,11 Permanent epiphysiodesis, is usually used near to skeletal maturity, by ablation of the appropriate side of growth plate by open or percutaneous technique.10,13
Follow up case of Figure of 8 plate for genu valgum. Note the divergence of screws indicating that guided growth has happened.
5.3. Corrective osteotomy
Corrective osteotomy is indicated in those patients where the CORA is far away from growth plate, a deformity in 2 planes, multi-apical deformity, a deformity presenting in patients near to or after skeletal maturity, if the deformity is greater than 200 or in a condition of sick physis which can result from trauma and infection. If limb alignment is planned using a corrective osteotomy, then the nature of osteotomy should be decided. Similarly, the hardware required to stabilize the osteotomy should be decided.8
Correction can be achieved acutely with an osteotomy and stabilization using internal fixation or be gradually corrected with the help of external fixation device.
While correcting the deformity, one must follow the osteotomy principles as described by Paley for optimal correction of the deformity.8 If the osteotomy is planned at the site of CORA, then no translation of the fragments is required. However when the osteotomy site is different from the site of CORA, a translation is necessary to obtain mechanical axis correction.7,8
If acute correction is planned, accurate preoperative wedge calculation is essential otherwise under or overcorrection may occur.7 The various types of osteotomy usually done include open wedge, closed wedge, reverse wedge or dome osteotomy with each procedure having its own advantages and disadvantages. Opening wedge osteotomy requires a single bone cut keeping the opposite cortex intact followed by spreading of the osteotomy. This makes the procedure easier and more accurate as it offers better control of the fragments. The drawbacks include concomitant lengthening of the limb, increased chances of non-union at osteotomy site and the need for bone grafting at osteotomy site if used in acute correction mode.15 In closing wedge osteotomy, a pre calculated wedge of bone is removed at the CORA and bone ends are opposed and fixed. Closing wedge osteotomy does not require additional bone grafting, is more stable. The disadvantages include shortening of the limb, and though the osteotomy is technically simple, the difficulty arises in inadvertent wrong calculation of the wedge removed which can result in less than optimal correction of the deformity.14 It is important to prevent a secondary deformity in sagittal plane by keeping a hinge of bone intact. Dome Osteotomy is a cylindrical osteotomy with corresponding bone cuts, which rotate around the central axis of a circle. Focal Dome Osteotomy is when the osteotomy level corresponds to CORA; the correction can be achieved without translation of the bone fragments.15,16 The advantages of focal dome osteotomy include no change in limb length and early partial weight-bearing; major disadvantage includes technical difficulty and a longer learning curve.16 Acute correction of the deformity is usually fixed internally with plate and screws especially so in the metaphyseal region, or locked intramedullary nails which are usually preferred in the diaphyseal region (Fig. 5a and b). K wire fixation can be occasionally done in metaphysis of younger children. Internal fixation does not permit any post-operative correction if desired, therefore it is very important that pre-operative planning is done accurately and execution is very precise.7,8
a. Radiographs of a 14 years old girl with bilateral genu valgum and CORA in distal femur. b. Radiographs of the same child after bilateral corrective osteotomy.
External fixator has the advantage of holding the fragments before the osteotomy thus preventing a secondary deformity in other plane. External fixators also allow to fine tuning the mechanical axis to the desired position in the post-operative period, using gradual correction, and simultaneous lengthening if required. This obviates the need for any bone graft as well as the gap is filled with new bone by the process of distraction osteogenesis. External fixators also allow translation of the fragments without the fear of secondary deformity in the second plane should this be required especially in those cases where the CORA is at the joint level or at the level of physis. The major disadvantage of external fixators remains less patient-acceptability. The most popular and versatile external fixators include the circular Ilizarov fixator Taylor's spatial frame and the monolateral Rail fixator System7,8 (Fig. 6a,b,c).
a. Radiographs of a 12 years old girl with left sided genu varum following malunited fracture of proximal tibia and CORA in proximal tibia. b. Radiographs of same patient with Ilizarov and SUV 6 axis correction system in place. c. Radiographs of same patient after correction of the deformity.
The fixator assisted correction and then internal fixation utilizes an external fixator to achieve acute correction, assessment of accuracy of correction on operating table with possibility of intraoperative adjustments using appropriate imaging. This is followed by internal fixation of the osteotomy, and removal of fixator. Initial fixator and then internal fixation at an interval is useful for patients requiring additional limb lengthening.16,17
6. Summary
Physiological angulation of limbs is frequently seen during growth period and requires only observation. True deformities should be evaluated by screening the children clinically by intercondylar or intermalleolar distance. The magnitude and plane and apex of deformity require a full length standing radiograph in patella forward position. Deformity correction in younger children with minimum of 2 years of growth remaining and angulation of less than 200 can be carried out using growth modulation surgery. Deformities more than 200, those in older children, adolescents, adults require corrective osteotomy and stabilization with an internal fixation device or an external fixator for appropriate limb alignment.
Declaration of competing interest
The Authors declare that they have no conflict of interest with regards to the article titled.
References
Abstract
Purpose
In this study, the correction accuracy of Smart Correction spatial fixators and of Ilizarov-type external fixators are compared in terms of deformity complexity.
Methods
Seventy-seven (40 male, 37 female) bone segments of 57 patients treated with a Smart Correction device were compared with 94 (51 male, 43 female) segments of 68 patients treated with an Ilizarov fixator. Mean age of the Smart Correction group was 20.69 ± 12.94 years, and or the Ilizarov group 22.45 ± 12.18 years. Patients were categorised according to limb lengthening and the number of deformity planes.
Results
A longer correction period was found with Ilizarov (66.53 ± 47.7 days) compared with Smart Correction (49.05 ± 35.6 days) devices. The bone healing index of the Ilizarov group was significantly better compared with the spatial group. Residual deformity after treatment was significantly lower with the Smart Correction device; however, this relationship could not be shown between subgroups. Although there was no significant difference between subgroups, mean residual deformity was higher with the increasing number of planes of the deformity.
Conclusions
The Smart Correction fixator is an accurate device that allows ease of application and planning. It demonstrates higher accuracy for correcting deformities compared with an Ilizarov external fixator. With an increasing number of planes, the difference between the two devices becomes even more pronounced. The relationship between the complexity of the deformity and residual deformity may possibly be significantly greater in favour of the Smart Correction fixator in a study with a larger sample size.
Introduction
External fixators are one of the oldest devices used in orthopaedic surgery, dating back to Hippocrates [1]. Until Hoffman and Ilizarov performed methodological studies, many orthopaedic biological and mechanical principles were not fully understood, and many devastating complications were encountered [–4]. With the introduction of spatial fixators, simultaneous six-axis and one-step correction of complex deformities became possible. With a traditional Ilizarov circular fixator, the precise calculation of clinical and radiological parameters, along with precise mounting, is essential. Minor deviations may lead to major residual deformities and increase the treatment period. For complex deformities consisting of translational, rotational and angular deformities, it is not possible to perform a one-step correction. Various components, such as hinges and translation devices connected to rods, are used to achieve correction. In addition, it may be necessary to delay the required lengthening due to deformity correction. Carrying out these steps usually requires changing components, which can be painful for the patient and exhausting for both the patient and surgeon.
Spatial fixators are used to treat the deformity as a combined vector, and correction is performed according to it over a so-called virtual hinge. Pre-operative calculation and mounting errors do not affect postoperative planning. This one-step correction will eventually lead to a much shorter correction period, which may decrease external fixator period. More precise correction of deformities is possible []. The mechanical properties of the frame require more studies; however, Paley reports that the Taylor spatial frame is stiffer in all directions [6].
In this study, we hypothesised that spatial fixators provide more accurate deformity correction in a shorter period of time. For this reason, we compared our deformity correction cases that received spatial fixators with cases traditional Ilizarov circular external fixator cases.
Patients and methods
One hundred and thirteen patients operated using a Smart Correction (SC)spatial fixator and 1,116 patients who received a traditional Ilizarov-type circular external fixator (CEF; Tasarim Med, Istanbul, Turkey) were retrospectively evaluated to form the SC and CEF groups. Inclusion criteria were as follows: (1) The patient was operated with an SC or CEF. (2) Adequate documentation with sufficient clinical notes was available, and the patient was appropriate for radiological measurements. (3) The patient was followed up for three months following fixator removal. The following aetiologies were excluded due to inferior bone healing potential and altered bone quality: (1) Congenital tibial pseudoarthrosis; (2) applications due to joint contracture; (3) lengthening over nail or fixator-assisted nailing; (4) applications performed immediately following malignant tumor resection; (5) acute or chronic osteomyelitis; (6) internal segment transports.
Patients in both groups were operated in the same clinic by three senior surgeons using the same surgical techniques. Fixator-to-bone fixation for all patients was performed; both half pins and wires were used. To evaluate the accuracy of deformity correction and contribution of limb-length discrepancy (LLD) to the final results, both main groups were divided into subgroups according to the number of planes of deformity (sagittal, coronal, rotational) and existence of lengthening. Segments with lengthening were tagged as A. Segments without lengthening were tagged as B. The number of planes was noted: from 0 = no deformity to three = sagittal, coronal and rotational deformity.
Following application of inclusion and exclusion criteria, 77 SC and 255 CEF cases remained for further matching. Initial statistical analysis of both device groups consisted of age, sex, aetiological distribution and deformity groups (subgroups). To create a similarly matched CEF group, stratification was used, which returned 94 CEF cases. Pre-operative deformity magnitude was also similar for each SC subgroup with its respective CEF subgroup. Distribution of each subgroup and their demographic data are listed in Table 1. To avoid creating a selection bias regarding learning curve when using the CEF device, only patients operated in the last decade were included in the study. We believe spatial fixators have a significantly shorter period of learning, therefore do not require excluding first applications.
Table 1
Distribution of patients among groups and subgroups: demographic data and aetiologies Dental smile design software, free download.
| Smart correction (SC) | Circular external fixator (CEF) | |||||
|---|---|---|---|---|---|---|
| No. segments (patients) | 77 (57) | 94 (68) | p = 0.764; χ2 0.09 | |||
| Sex (M/F) | 40/37 | 51/43 | ||||
| Average age | 20.69 ± 12.94 | 22.45 ± 12.18 | t:−0.92; p = 0.361 | |||
| Aetiologies | Acquired | 18 | 24.30 % | 20 | 21.30 % | χ2 1.18; p = 0.882 |
| Developmental | 6 | 8.10 % | 12 | 12.80 % | ||
| Nonunion | 9 | 12.20 % | 11 | 11.70 % | ||
| Congenital | 35 | 47.30 % | 42 | 44.70 % | ||
| Trauma | 6 | 8.10 % | 9 | 9.60 % | ||
| Subgroups | A-0 | 16 | 20.80 % | 20 | 21.30 % | χ2 2.27; p = 0.943 |
| A-1 | 11 | 14.30 % | 13 | 13.80 % | ||
| A-2 | 10 | 13.00 % | 16 | 17.00 % | ||
| A-3 | 3 | 3.90 % | 6 | 6.40 % | ||
| B-1 | 11 | 14.30 % | 14 | 14.90 % | ||
| B-2 | 7 | 9.10 % | 5 | 5.30 % | ||
| C | 9 | 11.70 % | 11 | 11.70 % | ||
| D | 10 | 13.00 % | 9 | 9.60 % |
Numbers indicating complexity of the deformity: 0 for only lengthening without deformity, 1 for only one plane, 2 for two plane deformity and 3 for deformities with sagittal, coronal and rotational deformity
A segments with lengthening, B segments without lengthening, C with nonunion, D with trauma
Deformity analysis was performed with the method suggested by Paley et al. [–]. Frontal and sagittal deformities were measured with X-rays using mechanical axis. Rotational deformity measurements were obtained from clinical photos. Center of rotation of angulation (CORA) was measured for each plane, and resultant deformity vector was calculated to be used for pre- and postoperative accuracy comparisons. Total external fixator time (days), latent period (days), correction period (days), consolidation period (days) and bone-healing index as suggested by Paley et al. (days/cm) [, ] were calculated and compared. The follow-up period was calculated as months from fixator removal to last visit. Complications were grouped as problems, obstacles and sequelae []. The accuracy of deformity correction was measured using residual deformity at the final follow-up. Each subgroup's average residual deformity was noted and compared with their respective opposites. Statistical analyses were performed with Number Cruncher Statistical System (NCSS) 2007 Statistical Software (Utah, USA) and MedCalc Statistical Software (Mariakerke, Belgium). In addition to descriptive statistical methods (average, standard deviation), chi-square test for qualitative data, stratification for CEF sampling and Mann–Whitney U test to compare two samples were also used. Results were evaluated according to a p < 0.05 significance level.
Results
The two main groups (SC and CEF) were compared, as were the subgroups with their respective opposite. The average correction period for the CEF group was significantly longer than for the SC group. The average consolidation period was similar between the two groups. The bone-healing index of the CEF group was better than that of the SC group. All results are summarized in Table 2.
Table 2
Results of two main groups: Smart Correction (SC) and Ilizarov circular external fixator (CEF)
| SC | Ilizarov | P value | |
|---|---|---|---|
| Correction period (days) | 49.05 ± 35.6 | 66.53 ± 47.7 | 0.011 |
| Lengthening performed (mm) | 29.01 ± 32.06 | 31.81 ± 31.59 | 0.982 |
| Total fixator period (days) | 214.21 ± 98.07 | 211.93 ± 83.05 | 0.911 |
| Consolidation period (days) | 159.26 ± 77.85 | 141.44 ± 63.01 | 0.177 |
| Bone-healing index (d/cm) (A subgroups) | 64.61 ± 37.58 | 50.79 ± 39.77 | 0.001 |
| Follow-up (days) | 281.08 ± 169.73 | 516.97 ± 531.33 | 0.02 |
Number of days spent for deformity correction and lengthening was better for patients treated with SC device. However, bone healing index was superior for Ilizarov
The consolidation periods for all patients with and without derotation were also compared. The average periods were 135.79 ± 66.25 and 149.89 ± 68.31, respectively, for the SC and CES groups. This difference was statistically insignificant (p = 0.530). In addition, there was no difference between groups regarding derotation.
Deformity correction and accuracy
Overall initial deformity of the SC and CEF groups was statistically similar (18.68 ± 14.48 and 21.22 ± 15.78, respectively; p = 0.516). The measured residual deformity at the end of the treatment was significantly higher for the CEF group (11.96 ± 11.12) compared with the SC group (7.73 ± 8.19; p = 0.012). Accuracy of deformity correction with increasing complexity and the effect of lengthening over accuracy were evaluated using subgroups. Subgroups with nonunion (C) and trauma (D) patients were excluded, as it is not possible to compare results in a similar manner with patients with deformity. Table 3 lists pre-operative and residual deformity measurements.
Table 3
Pre-operative and final residual deformity for each subgroup
| Subgroup | SC | CEF | P value | |
|---|---|---|---|---|
| Preoperative deformity | A-0 | 4.49 ± 8.3 | 4.84 ± 5.39 | 0.457 |
| A-1 | 21.28 ± 13.06 | 22.2 ± 11.63 | 0.839 | |
| A-2 | 29.29 ± 13.79 | 34.95 ± 14.03 | 0.282 | |
| A-3 | 25.91 ± 17.77 | 43.45 ± 10.54 | 0.302 | |
| B-1 | 22.94 ± 10.6 | 23.05 ± 12.23 | 0.784 | |
| B-2 | 23.64 ± 12.1 | 24.98 ± 13.9 | 0.935 | |
| Residual deformity | A-0 | 6.19 ± 6.57 | 8.59 ± 8.98 | 0.501 |
| A-1 | 7.4 ± 8.84 | 13.26 ± 12.93 | 0.218 | |
| A-2 | 11.31 ± 9.43 | 13.42 ± 11.15 | 0.61 | |
| A-3 | 16.67 ± 9.57 | 26.6 ± 13.41 | 0.302 | |
| B-1 | 7.37 ± 4.3 | 7.61 ± 7.56 | 0.762 | |
| B-2 | 5.92 ± 10.99 | 15.97 ± 5.67 | 0.056 |
There was no difference between each SC subgroup regarding final residual deformity (p > 0.05). However, residual deformity in the A-0, A-1 and A-2 CEF groups were statistically lower than the A-3 CEF group (p = 0.002, p = 0.028, p = 0.015, respectively). Residual deformity of the B-1 CEF group was statistically lower than that of the B-2 CEF group (p = 0.014). Bone-healing index for lengthened segments (A groups) were superior for CEF patients (50.79 ± 39.77 days/cm),compared with SC patients (64.61 ± 37.58 days/cm). The average number of re-evaluations and replanning performed for deformity at the outpatient clinic was 1.6 ± 0.7 for SC patients. No data were available for CEF patients.
We encountered 46 problems, 11 obstacles and seven sequelae for SC patients and 76 problems, 20 obstacles and five sequelae for CEF patients. Most complications were pin-tract problems and joint stiffness, which resolved by the end of treatment (74.6 % for SC and 69.7 % for CEF). For both SC and CEF patients, lengthening did not create any significant difference in the complication rate when the A and B groups were compared.
Discussion
Spatial fixators are based on identical biological properties and host response as those of a traditional Ilizarov fixator, with possibly better mechanical properties and ease of use [6]. With the introduction of hexagonal strut geometry, the precise displacement of the proximal and distal fragments relative to each other is achieved. However, this improvement comes with a price: increased cost. Spatial fixator costs are six- to ten-times higher than traditional Ilizarov circular external fixators. For this reason, it is essential to identify patient groups for which spatial fixators would play a significantly effective role.
Various studies have been performed with spatial fixators, mostly case reports or case series [–]. Few comparative studies have been published [, ]. In this study, Ilizarov CEF and spatial fixators were compared in similar patient groups. Our main purpose was to reveal criteria for which spatial fixators allowed a significantly more accurate correction than CEF. For this purpose, corrected segments were distributed among subgroups, according to deformity complexity and existence of lengthening.
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Evaluation of the overall SC and CEF group data reveals a significantly more accurate deformity correction with lower residual deformity (7.73 ± 8.19 to 11.96 ± 11.12, respectively; p = 0.012) in a shorter period (49.05 ± 35.6 to 66.53 ± 47.7 days, respectively; p = 0.011) for the SC group. However, faster simultaneous correction did not provide a lower fixator period for SC as expected.; total consolidation and fixator time was similar. The bone healing index is used to evaluate the total fixator time required to gain length (days for each cm in this study) [, ]. This value is an indirect method of assessing both correction and consolidation efficiency of a device. Although a faster correction with a faster consolidation improves scores, the opposite leads to a decreased result. As spatial fixators have a stiffer structure and perform correction and lengthening simultaneously, it was expected that they would have an improved bone healing index. On the contrary, our average bone healing index was lower for CEF patients (50.79 ± 39.77) than SC patients (64.61 ± 37.58). Kristiansen et al. compared spatial fixator with CEF in terms of lengthening index (months/cm, which is identical to the bone healing index in our study). Lengthening indices and amounts were statistically similar for both groups. However, number of segments with reduced callus formation requiring bone grafting was higher in the spatial fixator group []. Additional evaluation of bone quality for lengthening cases with and without deformity, with a higher number of cases, is necessary to fully verify these results.
Increasing deformity leads to a higher residual deformity at the end of treatment. This difference tends to be even higher for cases with more complex deformities and existence of lengthening, as shown in Fig. 1. CEF cases with lengthening (A groups) tended to complete treatment with increased deformity compared with SC cases in all subgroups, regardless of deformity complexity. On the other hand, in patients without lengthening (B groups), there was no difference between groups for one- and two-plane deformities. However, due to an insufficient number of patients, the average difference calculated between the respective subgroups was not statistically significant.
Increase in residual deformity with increasing deformity complexity. Horizontal line (X axis) represents the number of planes of the deformity, from A-0 to A-3 and B-1 to B-3. The Y axis is residual deformity at the end of treatment
Simultaneous correction is one of the major advantages of spatial fixators. Traditional Ilizarov-type external fixators require the sequential correction of each component of the deformity due to the limited mobility of the device. Some spatial fixators require an initial correction based on mounting following residual deformity correction [, ]. Smart Correction software is intended to correct all deformities in one step, regardless of the mounting parameters. The average planning number was 1.6 ± 0.7 for the SC group, and only seven cases required three. There were no planning data available for the CEF group to make a comparison. A sample case with a multiplanar deformity correction achieved with a one-step correction is shown in Fig. 2.
Eight-year-old male patient with a posttraumatic distal tibial deformity with limb-length discrepancy (a–c). Proximal osteotomy was planned for lengthening, and a distal osteotomy for deformity correction. For this purpose, a preshaped frame was mounted (d) and correction performed simultaneously with lengthening (e). As seen in the postoperative X-rays and clinical photo of the patient, distal tibial deformity is corrected and plantigrade foot achieved. A slight shortening still exists, requiring a further, simple lengthening procedure (f, g)
It is generally accepted that derotation during lengthening and deformity correction has an adverse effect on regenerate quality and leads to an increased consolidation period and increased number complications, such as plastic deformation and regenerate fracture. In our study, no group or subgroup with derotation presented increased consolidation or complication rates compared with cases without derotation (p > 0.05).
The main weakness of this study is patient distribution and number of patients in each subgroup. Assessing all deformity groups together creates a wide deformity distribution with a high standard deviation. Focusing on a small group would give more accurate results. We had a heterogeneous patient population regarding aetiology, which was necessary to increase the number of patients. Also, a prospective randomised study design would provide more valuable results than a retrospective study.
Conclusion
The SC fixator demonstrates higher deformity correction accuracy than an Ilizarov external fixator. With an increasing number of planes, the differences between the two devices become more pronounced. The relationship between deformity complexity and residual deformity may be statistically more significant in favour of the SC fixator in a study with a larger sample size. In contrast to severl advantages of a spatial fixator, inferior bone healing index score suggests a possible low-quality regenerate, which requires further studies.
Contributor Information
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References
Paley Principles Of Deformity Correction Pdf Free Apps
Paley Principles Of Deformity Correction Pdf Free Apps Download
