Foot deformity correction with hexapod external fixator, the Ortho-SUV Frame™

Use of computer-assisted hexapod external fixators for complex foot and ankle reconstructions - An analysis of functional outcomes and complications

INTRODUCTION

Foot and ankle pathology can often require complex surgical reconstruction. Until recently, circular external fixators such as the Ilizarov frame have proven to be useful, yet they fall short when progressive, precise corrections are required. Computer-assisted hexapod external fixators seek to address many of the shortfalls of traditional circular fixators. However, evidence for their use is scarce. The objective of this work was to evaluate the functional and quality of life outcomes and post-operative complications of patients treated with computer-assisted hexapod external fixation.

METHODS

A retrospective, observational study was conducted. All cases were treated with either a TrueLok hex (TL-HEX) or a Taylor Spatial Frame (TSF) fixator. Primary outcomes were post-operative improvement in 12-Item Short Form Survey (SF12) and American Orthopaedic Foot and Ankle Score (AOFAS) scores, and complications following Paley's classification.

RESULTS

A total of 59 patients with complex foot and ankle conditions using 64 external fixation frames were included. The median sum of both SF12 score domains improved from a preoperative score of 63.6 to 91.3 at last follow-up (p < 0.001). Median AOFAS improved from a preoperative score of 35 to 75.5 at last follow up (p < 0.001). Functional improvement was not affected by the choice of external fixator. Complications occurred in 49 cases (77 %). The most common post-operative complications included pin tract complications in 37 (58 %) cases, joint rigidity in 24 (38 %) and axial deviation in 9 (14 %).

CONCLUSIONS

Computer-assisted hexapod external fixation is an effective technique to correct complex foot and ankle deformities and leads to a marked improvement in post-operative functional and quality-of-life outcomes with a high minor complication rate.

Developments in circular external fixators: A review

Circular external fixators (CEFs) are successfully used in orthopedics owing to their highly favorable stiffness characteristics which promote distraction osteogenesis. Although there are different designs of external fixators, how these features produce optimal biomechanics through structural and component designs is not well known. Therefore, the aim of this study was to conduct a review on CEFs following the PRISMA statement. A search for relevant research articles was performed on Scopus and PubMed databases providing the related keywords. Furthermore, a patent search was conducted on the Google Patent database. 126 records were found to be eligible for the review. Different designs of CEFs were summarized and tabulated based on their specific features. A bibliometric analysis was also performed on the eligible research papers. Based on the findings, the developments of CEFs in terms of materials, automation, adjustment methods, component designs, wire-clamping, and performance evaluation have been extensively discussed. The trends of the CEF design and future directions are also discussed in this review. Significant research gaps include a lack of consideration towards ease of assembly, effective wire-clamping methods, and CEFs embedded with online patient-monitoring systems, among others. An apparent lack of research interest from low-middle and low-income countries was also identified.

Complex rigid foot deformity correction with hexapod external fixator system

PURPOSE

Complex rigid foot deformities include three-plane deformities and usually presents with poor soft tissue coverage. In the last decades, gradual correction with computer-assisted fixator became an appropriate option for the treatment rigid foot deformities. This study aims to report our experience about treatment of complex foot deformities using Smart Correction fixator system®.

METHODS

We retrospectively analyzed 13 complex rigid foot deformities of ten consecutive patients treated with Smart Correction fixator system® from 2016 to 2020. Primary outcomes were classified as good, fair, and poor according to previously determined criteria. The outcomes were also assessed with The Manchester-Oxford Foot Questionnaire (MOXFQ). Non-parametric analysis (Wilcoxon test) for continuous variables and the Fisher's exact test for categorical variables were used.

RESULTS

Plantigrade foot was achieved in all patients after correction program. Supramalleolar osteotomy was applied in nine feet, midfoot osteotomy was applied in two feet, hindfoot osteotomy was required in one foot, and only soft tissue distraction performed in two feet. Two patients had recurrent deformity managed by further acute corrections. The mean MOXFQ scores improved from 72.7 preoperatively to 24.8 at last follow-up.

CONCLUSIONS

Present study shows that SCF the reliable option for the treatment of complex foot deformities, which also facilitates three-plane correction and concomitant lengthening with gradual soft tissue balance.

Gradual Correction of Valgus Deformities of the Tibia Using a Monolateral External Fixator

Objective

To present a review of patients subjected to gradual correction of a valgus deformity of the tibia using a monolateral external fixator.

Method

This retrospective review included patients from January 2012 to May 2022 who met the following inclusion criteria: deviation of mechanical axis of the limb due to valgus deformity of the tibia; tibial deformity in the coronal plane on radiographic examination; a documented outpatient pre-operative evaluation by an orthopaedic surgeon and age between 10 and 70 years. The following exclusion criteria were applied: the presence of another tibia deformity preventing gradual correction using the proposed assembly; skin conditions incompatible with the surgical procedure; inadequate pre- or post-operative radiological evaluation; and insufficient information in the medical records.

Results

The mean age of patients with a valgus deformity of the tibia was 30.8 ± 15.9 years. These patients had a body mass index (BMI) of 26.1 ± 5.5 kg/m2. A congenital or developmental aetiology was attributed to 58.3% of the cases. Most commonly, the deformity was found in the middle third of the tibia with a mean deformity of 14.7 ± 6.6 degrees. The total external fixator time ranged from 73 to 229 days (average 149.7 ± 36.1 days). The mean medial proximal and lateral distal tibial angles differed significantly for pre- and post-operative measurements (p ≤ 0.05). There were complications in eight cases; five cases of pin site infections, two cases of medial cortical fracture and one case of peroneal nerve neuropraxia.

Conclusion

The proposed correction technique produces a satisfactory angular correction and with similar outcomes as described in the literature.

How to cite this article

Motta DP, Faria JLR, Couto A, et al. Gradual Correction of Valgus Deformities of the Tibia Using a Monolateral External Fixator. Strategies Trauma Limb Reconstr 2023;18(2):123-132.

Severe equinus cavo-varus correction through triplanar tarsectomy and posterior tibial tendon transfer based on 3D-printed biomodel

Surgery for severe equine cavo-varus is complex and must be individualized. The interindividual phenotypic variability demands a personalized planning of each foot to be operated. The study's primary goal was to evaluate the function and satisfaction of a series of patients with severe equinus cavo-varus deformity who underwent a triplanar tarsectomy and transposition of the posterior tibial tendon in a single stage surgery after a patient specific 3D biomodel planning. A series of 12 feet (5 patients bilaterally) operated with this technique was analyzed. The cohort comprised 2 females (28.5 %) and 5 males (71.4 %). The median follow-up time was 38.5 months (interquartile range: 24.75-48.75). The Foot and Ankle Disability Index pre (median 32.85; interquartile range: 20-46) and postsurgery (median 72; interquartile range: 56-75.5) were collected and statistically significant differences were observed (p < 0.002). Furthermore, the main variable evaluated was obtaining a plantigrade stable foot. This was clinically evaluated and was achieved in all patients except 1 patient who presented a residual equinus of 5º. This study shows that triplanar tarsectomy and posterior tibial tendon transfer in a single surgical procedure after patient-specific 3D biomodel planning allows for improved function in patients with severe equinus cavus varus foot deformity.

An Interference Inspection Algorithm of Limb and Hexapod Frame in the Treatment of Lower Limb Deformity

The Ortho-SUV frame is an innovative hexapod widely used in orthopedics for managing fractures and deformities. Avoidance of limb-frame interference is essential to verify the implementability of the pre-planned correction trajectory, as well as to maintain the continuity and security of the correction strategy. In this study, a novel interference inspection algorithm is developed to investigate the interaction of the limb and hexapod frame in the treatment of lower limb deformities. The algorithm is built on a minimum distance model of the cone frustum busbar and cylindrical axis using vector analysis. A pre-defined trajectory is generated by Cartesian coordinate path control. Subsequently, an interference case is performed through numerical simulation and motion simulation. The results show that the conclusion of numerical simulation and motion simulation are consistent, which prove the feasibility of the algorithm. The results also show that it is possible to identify the riskiest struts, which are prone to interfere with the limb, and the riskiest positions. The proposed algorithm can support the clinician in selecting the suitable frame configuration to avoid interference. The algorithm solves the problem that the interference can only be judged by clinical observation in the clinic.

Multiplanar correction of proximal tibial recurvatum deformity with tibial osteotomy and computer assisted fixator

BACKGROUND

Several treatment modalities including open wedge osteotomies and Ilizarov reconstruction have been described for treatment of Proximal tibial recurvatum (PTR). However, the literature lacks information regarding the multiplanar correction of PTR using the computer assisted hexapod external fixator. The aim of the study is to present the results of PTR treatment with a computer assisted fixator systems.

METHODS

There were three female and three male patients (10 lower extremities) with a mean age of 20.6 years (7.3 to 25.2y) in the study group. The angle of genu recurvatum (aGR), the tibial plateau tilt angle (aTP), the mechanical posterior proximal tibial angle (mPPTA) and sagittal mechanical axis deviation (MADs) was measured for the sagittal plane assessment.

RESULTS

Preoperative sagittal assessment showed that the mean aGR was 28.9°±6.8°, mean aTP was 64.5°±10.2° and mean mPPTA was mPPTA was 114.1° ±10.3°. At the final follow-up there was a significant correction (p < 0.05 for aGR, aTP and mPPTA). Mean MADs was improved from 66.1 ± 14.2 mm to 16.6 ± 5.1 mm (p:0.005). Mean A:B ratio was 0.92 ± 0.13 preoperatively and 0.89 ± 0.14 postoperatively (p:0.37). Nine out of 10 knees had valgus deformity and mean preoperative tibiofemoral anatomic angle (TFA) was improved from 10.8°±3.7° valgus to 6.5°±1.7° valgus.

CONCLUSION

The treatment of PTR deformity with a computer-assisted hexapod external fixator is safe and effective. It provides multiplanar correction of the deformity with a high precision and the patellar alignment remains stable during the correction.

Influence of parameter deviation on the closeness of the tibial limb and external fixator based on a novel collision detection algorithm

The Ortho-SUV frame (OSF) is a hexapod external fixator widely applied in orthopedics deformity correction. The possibility of collision between OSF's struts and the soft tissue is an essential but overlooked issue. To avoid the issue, a novel collision detection algorithm is established based on a cone-cylinder model of the tibial limb-strut interaction for detecting the closeness of the tibial limb and external fixator. The algorithm is constructed using the vector analysis based on the model of the minimum distance between the truncated cone generatrix and the cylinder axis. The motion simulation is performed on the overall alignment through the Solidworks-motion module to verify the feasibility of the algorithm. Subsequently, the installation parameter deviations of the bone-fixator system are described to investigate the influence of orientation and position deviation on the closeness of the tibial limb and external fixator through the numerical method. The investigation results show that the orientation deviation γ (around the z-axis), the position deviation τ₁ and τ₂ (along the x and y-axes, respectively) have greater sensitivity to closeness and the influence of multiple deviations on the closeness has the property of superposition. The proposed algorithm can assist clinicians to strictly design and appraise frame configurations prior to their application to avoid the collision between the external fixator and the limbs during the correction. It has great application significance in the development of computer-aided correction software.

Comparison of three different correction trajectories for foot and ankle deformity treated by supramalleolar osteotomy using a novel external fixator

Based on the principle of distraction osteogenesis, external fixators are widely used in deformity correction of the foot and ankle. In this study, a novel ankle external fixator is proposed to correct complex multiplane deformities, especially for supramalleolar osteotomy to correct distal tibia deformities. The relatively simple structure and fewer struts in the proposed fixator reduce the complexity of adjusting the external fixator. Based on two existing adjustment strategies, a new strategy taking into account the orientation and shortest path of the ankle joint center is proposed, which is named joint adjustment for equal bone distraction. By proposing the inverse kinematic solutions of the novel external fixator, mathematical derivations of the bone trajectory and modelling of the bone shape for the three distraction strategies are performed. The results obtained by comparative analysis indicate that a uniformly spaced path of the ankle joint center can be acquired, and a smooth and uniform correction trajectory of the distal tibia end can be obtained using the new adjustment strategy. It can avoid bone end interference and only generates a maximum deviation 0.66% greater than the currently optimal 1 mm/day. The new strategy can perform multiplane corrections simultaneously, which shortens the correction time and reduces the patient's pain.

Treatment of complex foot deformities with hexapod external fixator in growing children and young adult patients

BACKGROUND

Treatment of complex foot deformities in growing children and young adult patients is challenging. The traditional approach consists of extensive soft tissues releases, osteotomies and/or arthrodesis. More recently, distraction osteogenesis has been proposed as an alternative strategy. The aim of this study was to describe our treatment strategy and report clinical outcomes of the patients affected from complex foot deformities treated by distraction osteogenesis and hexapod external fixator.

MATERIALS AND METHODS

We retrospectively reviewed 10 consecutive patients with complex foot and ankle deformities treated from 2014 to 2016 at our unit. A TrueLok external fixator system was used in all patients. Final outcome was classified as good, fair and poor according to the criteria indicated by Paley and Ferreira. The results were also evaluated by the pre-operative and post operative American Orthopedic Foot and Ankle Score (AOFAS) and The Manchester-Oxford Foot Questionnaire (MOXFQ).

RESULTS

A plantigrade foot was obtained in eight patients at the end of treatment, while in two patients a recurrence of the deformity was noted. Result was classified as good in 6 patients, fair in 2 patients, and poor in 2 patients. The AOFAS score improved from 33.9±21.2 pre-operatively to 67.25±15.1 post-operatively (p=0.005). A statistically significant improvement was observed for the MOXFQ score as well (from 60.6±23.3 to 33.0±25.2, p=0.020).

CONCLUSIONS

Our study shows that the TrueLok hexapod external fixator is a safe and effective tool in treatment of complex rigid foot deformities. Nevertheless, deformity recurrence can be observed in some cases and treatment remains challenging. Distraction osteogenesis should be reserved as a salvage solution for particularly complex cases and should be performed at dedicated specialized centers.

Treatment Strategies and Frame Configurations in the Management of Foot and Ankle Deformities

To provide standardized nomenclature for various hexapod frame configurations for foot and ankle deformity correction, a unique classification of the hexapod external fixators was proposed. This classification is based on number of correction levels, secured anatomic blocks, and direction of the strut attachment. It allows the combination of all different foot and ankle frame assemblies into a few standard hexapod configurations, irrespective of which external fixator is used.

Strategies of enhancing bone regenerate formation in distraction osteogenesis

Distraction osteogenesis (DO) is a commonly used technique in multiple orthopedic sub-specialties, including trauma, oncology and pediatrics. This technique aims to produce new bone formation in the distraction gap in a controlled manner. The issue with this technique has been the high risk of complications, one of which is poor regenerate formation during the distraction process. Although several factors (including patient and operative factors) and techniques (including surgical, mechanical and pharmacological) have been described to ensure successful regenerate formation during the process of DO, these factors are sometimes difficult to control clinically. Our aim from this review is to highlight the different factors that affect DO, modalities to assess the regenerate and review treatment options for poor regenerate in the distraction gap. In addition, we propose a management protocol derived from the available literature that can be used to facilitate the management of inadequate regenerate formation.

A comparative study of the correction of femoral deformity between the Ilizarov apparatus and Ortho-SUV Frame

PURPOSES

This study compared the six-axis external fixator Ortho-SUV Frame (OSF) and the Ilizarov apparatus (IA) in femoral deformity correction. Our specific questions were: (1) which of the fixators (OSF or IA) provides shorter period of femoral deformity correction, and (2) which of the fixators (OSF or IA) provides better accuracy of correction.

METHODS

We retrospectively analysed 123 cases of femoral deformities (127 femora): 45 (47) treated with OSF (20 male and 27 female) and 78 (80) with IA (53 male and 27 female). The average age in the OSF group was 34.6 (range, 18-66) and in the IA group 35.8 (range, 18-76). All the deformities were categorized according to the number of planes and deformity components as simple, middle and complex deformities.

RESULTS

Elimination of simple deformities in the IA group took 58.3 ± 21.4 days, EFI 58.8 ± 39.8 days/cm, and lengthening was 4.6 ± 1.98 cm. Middle deformities were 71.3 ± 26.2, 61.9 ± 30.3 and 4 ± 2, respectively. In complex deformities we had 105.2 ± 21.8, 79.3 ± 35.4 and 3.2 ± 1.45, respectively. Normal alignment was achieved in 55.0% of cases in IA. In 45.0% of cases we had residual deformity. Elimination of simple deformations in the OSF group took 55.3 ± 12.8 days, EFI 47.5 ± 23 days/cm, and lengthening 4.5 ± 1.1 сm. Middle deformities were 43.6 ± 18.9, 59 ± 14.6 and 3.6 ± 2, respectively. In complex deformities we had 44.9 ± 11.5, 57.5 ± 9.4 and 3.6 ± 1.7, respectively. In the OSF group normal alignment was achieved in 85.1%. In 14.9% there was residual deformity.

CONCLUSION

Using OSF simplifies deformity correction and reduces its period by 2.3 times in complex deformities and by 1.6 times in middle deformities. Accuracy of correction with OSF was significantly higher than correction with IA.