Computer Hexapod-Assisted Orthopaedic Surgery for the Correction of Tibial Deformities

Fixators dynamization for delayed union and non-union of femur and tibial fractures: a review of techniques, timing and influence factors

The optimal balance between mechanical environment and biological factors is crucial for successful bone healing, as they synergistically affect bone development. Any imbalance between these factors can lead to impaired bone healing, resulting in delayed union or non-union. To address this bone healing disorder, clinicians have adopted a technique known as "dynamization" which involves modifying the stiffness properties of the fixator. This technique facilitates the establishment of a favorable mechanical and biological environment by changing a rigid fixator to a more flexible one that promotes bone healing. However, the dynamization of fixators is selective for certain types of non-union and can result in complications or failure to heal if applied to inappropriate non-unions. This review aims to summarize the indications for dynamization, as well as introduce a novel dynamic locking plate and various techniques for dynamization of fixators (intramedullary nails, steel plates, external fixators) in femur and tibial fractures. Additionally, Factors associated with the effectiveness of dynamization are explored in response to the variation in dynamization success rates seen in clinical studies.

The Relation between the Dynamization of Hexapod Circular External Fixator and Tibial Mechanical Properties

OBJECTIVE

Dynamization of the external fixator, defined as gradually decreasing construct-stability of the fixator, is widely accepted as a method for treatment during the late phase of the bone healing process. However, the dynamization is mostly based on the subjective experience of orthopaedists at present, without unified standards and a clear theoretical basis. The objective of the study is to investigate the influence of the dynamization operations on the tibial mechanical properties with a hexapod circular external fixator and standardize the dynamization process.

METHODS

A 3D-printed tibial defects model with Young's modulus of 10.5 GPa and Poisson's ratio of 0.32 simulated the clinically fractured bone. A 10 × ∅ 45 mm silicone sample with Young's modulus of 2.7 MPa and Poisson's ratio of 0.32 simulated the callus in the fracture site. Furthermore, a hexapod circular external fixator whose struts were coded from #1 to #6 was fixed on the model with six half-pins (5 mm diameter). Corresponding to the action of removing and loosening the struts, 17 dynamization operations are designed. For each construct after different dynamization operations, the mechanical environment changes in the fracture site were recorded by a triaxle forces sensor under gradually increasing external load from 0 to 500 N.

RESULTS

The results show that the bone axial load-sharing ratio of each construct in the removal group was generally higher than that in the loosening group. The ratio increased from 92.51 ± 0.74% to 102.68 ± 0.27% with the number of operated struts rising from 2 to 6. Besides, the constructions with the same number of operated struts but with different strut codes such as constructions 3-5, had similar bone axial load-sharing ratios. In addition, the proposed dynamization method of the hexapod circular external fixator can gradually increase the bone axial load-sharing ratio from 90.73 ± 0.19% to 102.68 ± 0.27% and maintain the bone radial load-sharing ratio below 8%.

CONCLUSION

The laboratory study verified the effects of the type of operations and the number of operated struts on the bone axial load-sharing ratio, as well as the slight influence of the choice of the strut code. Besides, a dynamization method of the hexapod circular external fixator was proposed to increase the bone axial load-sharing ratio gradually.

Combination of external fixation using digital six-axis fixator and internal fixation to treat severe complex knee deformity

BACKGROUND

Severe knee valgus/varus or complex multiplanar deformities are common in clinic. If not corrected in time, cartilage wear will be aggravated and initiate the osteoarthritis due to lower limb malalignment. Internal fixation is unable to correct severe complex deformities, especially when combined with lower limb discrepancy (LLD). Based on the self-designed digital six-axis external fixator Q spatial fixator (QSF), which can correct complex multiplanar deformities without changing structures, accuracy of correction can be improved significantly.

METHODS

This retrospective study included 24 patients who suffered from complex knee deformity with LLD treated by QSF and internal fixation at our institution from January 2018 to February 2021. All patients had a closing wedge distal femoral osteotomy with internal fixation for immediate correction and high tibia osteotomy with QSF fixation for postoperative progressive correction. Data of correction prescriptions were computed by software from postoperative CT scans.

RESULTS

Mean discrepancy length of operative side was 2.39 ± 1.04 cm (range 0.9-4.4 cm) preoperatively. The mean difference of lower limb was 0.32 ± 0.13 cm (range 0.11-0.58 cm) postoperatively. The length of limb correction had significant difference (p < 0.05). The mean MAD and HKA decreased significantly (p < 0.05), and the mean MPTA and LDFA increased significantly (p < 0.05). There were significant increase (p < 0.05) in the AKSS-O, AKSS-F and Tegner Activity Score. The lower limb alignment was corrected (p < 0.05). The mean time of removing external fixator was 112.8 ± 17.9 days (range 83-147 days).

CONCLUSIONS

Complex knee deformity with LLD can be treated by six-axis external fixator with internal fixation without total knee arthroplasty. Lower limb malalignment and discrepancy can be corrected precisely and effectively by this approach.

Correction of severe lower extremity deformity with digital hexapod external fixator based on CT data

Purpose

Our goal was to examine the therapeutic effect of a self-designed digital six-axis external fixator technique for the correction of severe lower extremity deformities.

Patients and methods

Between January 2017 and December 2020, our institution employed self-developed digital hexapod external fixator technology (QSF), based on CT data, to gradually correct 28 severe tibial deformities, and 15 femurs underwent osteotomy and internal fixation. The mean patient age was 32.6 ± 14.3 years, and the mean follow-up duration was 27.4 ± 16.1 months. We also recoded and analyzed the values of preoperative and final follow-up MAD, mFTA, MPTA, LLD, mLDFA, LEFS, KSS, and functional score.

Results

The QSF adjustment duration was 21.4 ± 10.8 days, and the healing duration of the tibial osteotomy site was 17.6 ± 7.0 weeks. The preoperative MAD, mFTA, and MPTA were 54.1 ± 26.2 mm, 167.7 ± 15.7°, and 75.2 ± 12.0°, respectively. At the last follow-up, the MAD was 8.2 ± 9.9 mm, mFTA was 177.6 ± 3.4°, and MPTA was 87.6 ± 2.4°. Based on these data, we achieved significant improvement post operation. The preoperative LLD and mLDFA values were 13.8 ± 18 mm and 83.7 ± 10.8°, respectively, and the values were 7.6 ± 7.6 mm and 87.8 ± 2.6°, respectively, at the last follow-up. This indicated no significant difference in these values before and after the operation. Finally, the LEFS, KSS, and functional scores improved from preoperative 51.6 ± 11.2, 68.5 ± 11.7, and 67.8 ± 11.2 to postoperative 72.3 ± 6.1, 92.9 ± 3.4, and 94.2 ± 6.3, respectively.

Conclusions

Based on our analyses, the QSF technique accurately corrected severe multiplanar tibial deformities in adults. When combined with femoral osteotomy, satisfactory lower extremity alignment was obtained while correcting for femoral deformity. This technology has the advantages of simple operation, reliable fixation, less trauma, and less complications.

Outcomes of two circular external fixation systems in the definitive treatment of acute tibial fracture related infections

INTRODUCTION

Acute tibial fracture-related infection (FRI) is one of the most feared and challenging complications after a tibial fracture. The most appropriate treatment in this scenario is far from a resolved topic. Circular external fixators (CEFs) offer multiplanar control and minimize soft tissue injury using temporary implants far from the infected area. This study aimed to investigate the outcomes of two different types of CEFs (Ilizarov and hexapod) in the treatment of a series of acute tibial FRIs.

MATERIAL AND METHODS

A retrospective study at two specialized limb reconstruction centres identified all patients with an acute tibial FRI (≤4 weeks after index procedure) definitively treated with a CEF from January 2015 to December 2020.

PRIMARY OUTCOMES

fracture healing and infection eradication rate with a minimum FU of 12 months after frame removal.

SECONDARY OUTCOMES

to investigate the differences between the two types of circular frames regarding final post-treatment deformity magnitude.

RESULTS

We included 31 patients with acute tibial FRIs: 18 treated with hexapod-type and 13 with Ilizarov-type CEFs. Average age was 45.5±16.56 years. Fracture healing and infection eradication were achieved in all patients (31/31) after a mean follow-up of 24.7 months (range 12.1-55.3). Patients treated with an Ilizarov-type fixator presented shorter time to fracture union (5.5±2.2 months vs. 9.2±6.0 months; p-value 0.021) and shorter duration of external fixation (p-value 0.001). Regarding residual post-treatment deformity, the hexapod system presented significantly less residual coronal translation deformity (p-value 0.034) and better callus quality. Fixator-related complications were similar when comparing the two groups. No significant differences were seen in pain (p-value 0.25), RTW rate (35% vs. 45%; p-value 0.7) or functionality (p-value 0.4).

CONCLUSIONS

Definitive circular external fixation is an excellent treatment for acute tibial FRI. Both Ilizarov and hexapod systems offer a very high rate of fracture healing and infection eradication. Although both presented very low radiological post-operative residual deformity, the hexapod system showed less residual coronal translation deformity and better callus quality.

Marker- three dimensional measurement versus traditional radiographic measurement in the treatment of tibial fracture using Taylor spatial frame

Background

The Taylor Spatial Frame (TSF) has been widely used for tibial fracture. However, traditional radiographic measurement method is complicated and the reduction accuracy is affected by various factors. The purpose of this study was to propose a new marker- three dimensional (3D) measurement method and determine the differences of reduction outcomes, if any, between marker-3D measurement method and traditional radiographic measurement in the TSF treatment.

Methods

Forty-one patients with tibial fracture treated by TSF in our institution were retrospectively analyzed from January 2016 to June 2019, including 21 patients in the marker-3D measurement group (experimental group) and 20 patients in the traditional radiographic measurement group (control group). In the experimental group, 3D reconstruction with 6 markers installed on the TSF was performed to determine the electronic prescription. In the control group, the anteroposterior (AP) and lateral radiographs were performed for the traditional parameter measurements. The effectiveness was evaluated by the residual displacement deformity (RDD) and residual angle deformity (RAD) in the coronal and sagittal plane, according to the AP and lateral X-rays after reduction.

Results

All patients achieved functional reduction. The residual RDD in AP view was 0.5 (0, 1.72) mm in experimental group and 1.74 (0.43, 3.67) mm in control group. The residual RAD in AP view was 0 (0, 1.25) ° in experimental group and 1.25 (0.62, 1.95) °in control group. As for the lateral view, the RDD was 0 (0, 1.22) mm in experimental group and 2.02 (0, 3.74) mm in control group, the RAD was 0 (0, 0) ° in experimental group and 1.42 (0, 1.93) ° in control group. Significant differences in all above comparisons were observed between the two groups (AP view RDD: P = 0.024, RAD: P = 0.020; Lateral view RDD: P = 0.016, RAD: P = 0.004).

Conclusions

The present study introduced a marker-3D measurement method to complement the current TSF treatment. This method avoids the manual measurement error and improves the accuracy of fracture reduction, providing potential advantages of bone healing and function rehabilitation.

Two-year clinical and economic burden, risk and outcomes following application of software-assisted hexapod ring fixation systems

Background

Multiplanar external fixation systems that employ software-assisted deformity correction consist of rings connected by angled struts, defined as hexapod ring fixators (HRF). Costs and outcomes associated with the application of HRFs are not well documented. This study was designed to provide a nationwide baseline understanding of the clinical presentation, risks, outcomes and payer costs, and healthcare resource utilization (HCU) of patients requiring application of an HRF, from the day of, and up to 2 years, post-application.

Methods

Patients with HRF application (“index”) between 2007 and 2019 within the IBM Marketscan® Commercial Claims database were identified and categorized based on diagnosis: acquired deformity, arthropathy, congenital deformity, deep infection, nonunion, fracture, and other post-operative fracture sequelae. Demographics, comorbidities at index, complications post-index, HCU, and payments were analyzed. Payments were estimated using a generalized linear model and were adjusted for inflation to the 2020 consumer price index. Rates of deep infection and amputation were estimated up to 2 years post-index using Poisson regressions, and risk factors for each were estimated using logistic regression models.

Results

Six hundred ninety-five patients were included in our study (including 219 fractures, 168 congenital deformities, 68 deep infections, 103 acquired deformities). Comorbidities at index were significantly different across groups: less than 2% pediatrics vs 18% adults had 3 or more comorbidities, < 1% pediatric vs 29% adults had diabetes. Index payments ranged from $39,250–$75,350, with 12-months post-index payments ranging from $14,350 to $43,108. The duration of the HRF application ranged from 96 days to 174 days. Amputation was observed in patients with deep infection (8.9, 95% confidence interval (CI): 3.2–23.9%), nonunion (5.0, 95%CI: 1.6–15.4%) or fracture (2.7, 95%CI: 0.9–7.6%) at index. Complicated diabetes was the main predictor for deep infection (odds ratio (OR): 5.14, 95%CI: 2.50–10.54) and amputation (OR: 5.26, 95%CI: 1.79–15.51).

Conclusions

Findings from this longitudinal analysis demonstrate the significant heterogeneity in patients treated with HRF, and the wide range in treatment intensity, payments, and outcomes. Risks for deep infection and amputation were primarily linked to the presence of complicated diabetes at the time of HRF application, suggesting a need for careful management of comorbid chronic conditions in patients requiring HRF for orthopedic care.

Accuracy and Efficacy of Software-guided Bony Realignment in Periarticular Deformities of the Lower Limb

Aim and objective

Software-guided realignment is proposed as an easy and accurate method of achieving simultaneous multiaxial correction. The accuracy and efficacy in periarticular problems have not been investigated fully. This study investigates the results and possible clinical benefits.

Materials and methods

A retrospective review was performed in 24 patients with 27 periarticular deformities of the lower limb treated by the Ilizarov technique. Bony realignment was achieved by a software-guided hexapod realignment device. The deformity category, deformity severity score (DSS) and individual deformity component scores were measured for objective quantification of each deformity. The periarticular level, number of manoeuvres, correction period and any difficulties in the execution of the correction manoeuvre were noted. Pre-procedure and post-procedure values of deformity parameters were analysed to estimate the accuracy and efficacy of the realignment device.

Results

The correction manoeuvre was accomplished successfully in all patients except two. The mean correction period was 14.9 days (range, 5–38 days). The mean pre-procedure DSS was 18.7 (range 6.3–27.3), which reduced to a mean post-procedure value of 1.5 (range, 0–7.9) with a 92.0% deformity correction (p-value < 0.001)). There was a significant reversal of individual deformity components. DSS values were achieved to an excellent level (< 3.5) in 25 deformities and to good and poor levels in one deformity, respectively.

Conclusion

Software-guided realignments are effective for accurate realignment of periarticular deformities using Ilizarov fixators. These devices offer simultaneous multidimensional corrections even in complex multiplanar deformities and simplify the task of deformity correction.

Clinical significance

The present study assesses the accuracy and efficacy of software-guided realignments using novel concepts of deformity category, DSS and individual deformity component scores, which may overcome some of the shortcomings of conventional assessment methods.

How to cite this article

Singh P, Sabat D, Dutt S, et al. Accuracy and Efficacy of Software-guided Bony Realignment in Periarticular Deformities of the Lower Limb. Strategies Trauma Limb Reconstr 2021;16(2):65–70.

Correction outcomes of the postoperative malalignment salvaged by the temporary application of the hexapod external fixator in tibial diaphyseal fractures treated by monolateral external fixation

BACKGROUND

Postoperative malalignment in fractures treated by monolateral external fixation is not uncommon in clinical practice. Accurate reduction without excessive tissue disruption caused by surgical intervention and sequentially manage the fractures using monolateral external fixation for definitive treatment is still a challenge for surgeons. The purpose of our study was to evaluate the feasibility and effectiveness of the temporary application of the hexapod external fixator (HEF) for the postoperative malalignment correction in tibial diaphyseal fractures treated by monolateral external fixation.

METHODS

We carried out a retrospective analysis of 23 trauma patients with tibial diaphyseal fracture treated by the monolateral external fixation at our institution from January 2016 to May 2019. There were 21 males and 2 females with a mean age of 38 years (range 18-60 years). The hexapod external fixator was temporarily applied due to postoperative malalignment within two weeks and who unwilling to undergo a secondary surgical intervention. For patients with postoperative malalignment requiring correction, the HEF components were installed on the original existing half pins of the monolateral external fixator after removing the connecting rod. The standard anteroposterior and lateral X-rays of the injured limb combined with the temporary HEF were conducted to measure the hexapod external fixator parameters. Any residual deformities were corrected by gradual struts adjustment with the aid of computer-based software. When satisfactory alignment was achieved, the HEF was removed, and the monolateral external fixator was sequentially used as the definitive structure.

RESULTS

All patients acquired functional reduction, which was evaluated by radiographs. The mean correction time was 4 days (range 2 to 8 days). The mean coronal plane translation (1.3±1.0 mm), coronal plane angulation (0.9±0.7°), sagittal plane translation (1.4±1.1 mm), and sagittal plane angulation (0.7±0.7°) after correction were all less than those (7.0±4.9 mm, 4.7±2.3°, 5.6±3.6 mm, 3.2±2.5°) before correction.

CONCLUSIONS

The temporary application of the hexapod external fixator is an alternative and feasible method for the postoperative malalignment correction in tibial diaphyseal fractures treated by monolateral external fixation.

Long bone fracture reduction and deformity correction using the hexapod external fixator with a new method: a feasible study and preliminary results

Background

The hexapod external fixator (HEF), such as the Taylor spatial frame (TSF), offering the ability of multidirectional deformities correction without changing the structure, whereas there are so many parameters for surgeons to measure and subjective errors will occur inevitably. The purpose of this study was to evaluate the effectiveness of a new method based on computer-assisted three-dimensional (3D) reconstruction and hexapod external fixator for long bone fracture reduction and deformity correction without calculating the parameters needed by the traditional usage.

Methods

This retrospective study consists of 25 patients with high-energy tibial diaphyseal fractures treated by the HEF at our institution from January 2016 to June 2018, including 22 males and 3 females with a mean age of 42 years (range 14–63 years). Hexapod external fixator treatments were conducted to manage the multiplanar posttraumatic deformities with/without poor soft-tissue that were not suitable for internal fixation. Computer-assisted 3D reconstruction and trajectory planning of the reduction by Mimics were applied to perform virtual fracture reduction and deformity correction. The electronic prescription derived from the length changes of the six struts were calculated by SolidWorks. Fracture reduction was conducted by adjusting the lengths of the six struts according to the electronic prescription. Effectiveness was evaluated by the standard anteroposterior (AP) and lateral X-rays after reduction.

Results

All patients acquired excellent functional reduction and achieved bone union in our study. After correction, the mean translation (1.0 ± 1.1 mm) and angulation (0.8 ± 1.2°) on the coronal plane, mean translation (0.8 ± 1.0 mm) and angulation (0.3 ± 0.8°) on the sagittal plane were all less than those (6.1 ± 4.9 mm, 5.2 ± 3.2°, 4.2 ± 3.5 mm, 4.0 ± 2.5°) before correction (P < 0.05).

Conclusions

The computer-assisted three-dimensional reconstruction and hexapod external fixator-based method allows surgeons to conduct long bone fracture reduction and deformity correction without calculating the parameters needed by the traditional usage. This method is suggested to apply in those unusually complex cases with extensive soft tissue damage and where internal fixation is impossible or inadvisable.

Application of elliptic registration and three-dimensional reconstruction in the postoperative measurement of Taylor spatial frame parameters

BACKGROUND

The Taylor spatial frame offered the ability of simultaneous correction of the multidirectional deformities without the need to change the frame, and it was widely used for limb lengthening, deformity correction, and fracture reduction in recent years. There are still some inherent limitations that can affect the accuracy of correction, especially for the measurement of the mounting and rotational parameters. The purpose of our study was to propose some more precise postoperative measurement of Taylor spatial frame (TSF) parameters by application of elliptic registration and three-dimensional reconstruction.

METHODS

This retrospectively study included 28 trauma patients who suffered tibial fracture treated by the TSF at our institution from January 2016 to January 2018, including 25 males and 3 females with a mean age of 43 years (range 14-70 years). We conducted standard full-length anteroposterior and lateral X-rays of the injured extremity and the computed tomographic scans of the bilateral extremities after the operation. Elliptic registration and 3D reconstruction were used to calculate the parameters by two types of software Mimics and CorelDRAW. Correction of the deformity was conducted by adjusting the struts of the TSF according to the electronic prescription. The standard anteroposterior and lateral X-rays after correction were taken to evaluate the effectiveness.

RESULTS

All patients acquired functional reduction, which was evaluated by digital radiography. The mean coronal plane translation(1.9±2.2 mm), coronal plane angulation(1.2±1.0°), sagittal plane translation(2.7±2.1 mm), and sagittal plane angulation(1.2±1.0°) after correction were all less than those(5.5±4.6 mm, 4.9±3.9°, 4.7±4.0 mm, 2.7±2.3°) before correction.

CONCLUSIONS

The TSF system can correct the 6-axis deformities simultaneously with the accurate parameters. Elliptic registration and three-dimensional reconstruction are alternative methods to precisely measure the parameters needed by the TSF system, especially for the mounting and rotational parameters of unusually complex cases.

What's New in Pediatric Limb Lengthening and Deformity Correction?

Over the past 5 years, published literature regarding treatment of pediatric limb deformity and limb length discrepancy demonstrates much interest in better understanding, categorizing and treating these challenging problems. Many studies explore expanding and refining indications for traditional treatment methods like guided growth techniques. Other studies have evaluated the results of new techniques such as lengthening via mechanized intramedullary nails. Additionally, series comparing older and newer techniques such as lengthening with external devices versus mechanized nails are becoming increasingly available.

Effectiveness of Treatment for Distal Tibial Nonunions With Associated Complex Deformities Using a Hexapod External Fixator

OBJECTIVE

To determine the efficacy of a hexapod external fixator (TSF) and its ability to perform 6-axis correction in restoring deformities associated with distal tibial nonunions.

DESIGN

Consecutive retrospective case review.

SETTING

St. Louis University Hospital. Level 1 Trauma Center.

PATIENTS/PARTICIPANTS

Thirty-seven patients with distal tibial nonunion with greater than 5 degrees of deformity in any plane. Patients were excluded who were less than 18 years of age, had tibial deformities less than 5 degrees, had proximal or middle tibial deformities, or had less than 1 year of follow-up.

INTERVENTION

Patients with distal tibial nonunions with combined deformities were treated by the senior author with a hexapod device. Preoperative mechanical axis deviation and union status were assessed. Postoperative parameters evaluated included anatomic and mechanical axis determination and adequacy of union. Metrics include long alignment films with routine clinical follow-up.

MAIN OUTCOME MEASUREMENTS

Assessment of deformity correction in 6 axes, restoration to union, and mechanical axis correction.

RESULTS

Average combined preoperative deformity was greater than 17.7 degrees. Average mechanical axis was restored within 5 degrees of the desired goal in all categories except in patients with severe preoperative valgus deformities. The complex nonunion group had a 94% union rate. Average time in the hexapod was 106.7 days. Average follow-up time was 2 years.

CONCLUSIONS

Hexapod external fixators can be used as an accurate modality to heal complex distal tibia nonunions with multifocal deformities and significant mechanical axis deviation. These difficult reconstructions are accomplished with minimum complications using these devices.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.