Biomechanical Assessment of Torsional Stiffness in a Supracondylar Humerus Fracture Model

Does Sagittal Alignment Matter? A Biomechanical Look at Pinning Pediatric Supracondylar Humerus Fractures

OBJECTIVE

Closed manipulation and percutaneous pinning is standard of care for displaced supracondylar humerus fractures, yet the optimal pin configuration, particularly in the sagittal plane, is not well defined. This study evaluates how sagittal plane pin variations affect construct strength biomechanically.

METHODS

One hundred synthetic pediatric humerus models were used to emulate supracondylar humerus fracture. The models were pinned using 4 different configurations uniformly divergent in the coronal plane with variations in the sagittal plane: (1) 2 diverging pins with the lateral pin anterior (n = 25), (2) 2 diverging pins with the lateral pin posterior (n = 25), (3) 2 parallel pins (n = 25), and (4) 3 parallel pins (n = 25). The models were tested under bending (flexion, extension, and varus) and rotational (internal and external) forces, measuring stiffness and torque. Statistical analyses identified significant differences across configurations.

RESULTS

The 2-pin parallel configuration (9.68 N/mm in extension, 8.76 N/mm in flexion, 0.14 N-m/deg in internal rotation, and 0.14 N-m/deg in external rotation) performed similarly to the 3-pin parallel setup (10.77 N/mm in extension, 7.78 N/mm in flexion, 0.16 N-m/deg in internal rotation, and 0.14 N-m/deg in external rotation), with no significant differences in stiffness. In contrast, both parallel configurations significantly outperformed the 2-pin anterior (5.22 N/mm in extension, 5.7 N/mm in flexion, 0.11 N-m/deg in internal rotation and 0.10 N-m/deg in external rotation) and posterior (9.86 N/mm in extension, 8.31 N/mm in flexion, 0.12N-m/deg in internal rotation, and 0.11 N-m/deg in external rotation) configurations in resisting deformation. No notable disparities were observed in varus loading among any configurations.

CONCLUSIONS

This study illuminates the sagittal plane's role in construct stability. It suggests that, when utilizing 2-pins, parallel configurations in the sagittal plane improve biomechanical stability. In addition, it suggests avoiding the lateral anterior pin configuration due to its biomechanical inferiority. Further research should assess ultimate strength and compare various 3-pin configurations to better delineate differences between 2-pin and 3-pin configurations regarding sagittal plane alignment.

LEVEL OF EVIDENCE

Level III-biomechanical study.

The fate of the malrotated elbow supracondylar fractures in children: is varus really a problem?

PURPOSE

To evaluate the functional and cosmetic effects of elbow supracondylar fractures (SCF) in children with residual rotational deformity.

METHODS

Retrospective review cohort of patients with evidence of malrotation after treatment for SCF. An analysis of the postoperative X-ray of 305 consecutive SCF type 3 treated surgically during five years identified 46 elbows with rotational deformity that fulfilled the selection criteria and were recalled for review; only 27 patients agreed to participate. Patients were evaluated clinically and radiographically. Clinically, the elbow and shoulder ROM were assessed. The postoperative fracture rotation (PFR) was radiologically measured using the Berdis method. Results were categorized according to Flynn criteria, and functional outcomes were evaluated with the QuickDASH questionnaire. On final assessment, a radiograph of both elbows was obtained, and measures were compared. Descriptive analysis was made calculating median, range, proportions, and confidence intervals. Non-parametric tests were used to test the association between variables.

RESULTS

The group had a median age of four years and a median follow-up of 52 months. Shoulder rotation was asymmetrical in 13 patients; six patients presented a change on carrying angle > 5° (4 varus/2 valgus). The higher the residual rotation, the higher the chances of an altered shoulder rotation (for each degree of PFR, the shoulder rotation was changed to 0.4°). However, there was a low correlation between the amount of rotation and the final carrying angle (r = 0.37). According to Flynn's criteria, over 95% had excellent or good results.

CONCLUSION

There was a weak correlation between varus and rotational malalignment. Patients with moderate residual malrotation could be expected to have a good outcome even if some shoulder rotation changes persist.

Candy box technique for the fixation of inferior pole patellar fractures: finite element analysis and biomechanical experiments

BACKGROUND

Maintaining effective reduction and firm fixation in inferior pole patellar fractures is a highly challenging task. There are various treatment methods available; although tension-band wiring combined with cerclage wiring (TBWC) is the mainstream approach, its effectiveness is limited. Herein, we propose and evaluate a new technique called candy box (CB), based on separate vertical wiring (SVW), for the treatment of inferior pole patellar fractures. Specifically, we provide biomechanical evidence for its clinical application.

METHODS

Five fixation models were built: SVW combined with cerclage wiring (SVWC); TBWC; modified SVW with the middle (MSVW-A) or upper (MSVW-B) 1/3 of the steel wire reserved, and CB. A finite element analysis was performed to compare the displacement and stress under 100-N, 200-N, 300-N, 400-N and 500-N force loads. Three-dimensional printing technology was utilized to create fracture models, and the average displacement of each model group was compared under a 500-N force.

RESULTS

The results of the finite element analysis indicate that CB technology exhibits significantly lower maximum displacement, bone stress, and wire stress compared to that with other technologies under different loads. Additionally, in biomechanical experiments, the average force displacement in the CB group was significantly smaller than that with other methods under a 500-N force (P < 0.05).

CONCLUSIONS

CB technology has the potential to overcome the limitations of current techniques due to its superior biomechanical characteristics. By incorporating early functional exercise and ensuring strong internal fixation, patient prognosis could be enhanced. However, further clinical trials are needed to fully evaluate the therapeutic effects of CB technology.

Extra Lateral Pin or Less Radiation? A Comparison of Two Different Pin Configurations in the Treatment of Supracondylar Humerus Fracture

BACKGROUND

Closed reduction and percutaneous fixation are the most commonly used methods in the surgical treatment of supracondylar humerus fractures. The pin configuration changes stability and is still controversial. The aim of this study was to investigate the relationship between surgical duration and radiation dose/duration for different pinning fixations.

METHODS

A total of 48 patients with Gartland type 2, 3, and 4 supracondylar fractures of the humerus were randomized into two groups-2 lateral and 1 medial (2L1M) pin fixation (n = 26) and 1 lateral 1 medial (1L1M) pin fixation (n = 22). A primary assessment was performed regarding surgical duration, radiation duration, and radiation dose. A secondary assessment included clinical outcome, passive range of motion, radiographic measurements, Flynn's criteria, and complications.

RESULTS

There were 26 patients in the first group (2L1M) and 22 patients in the second group (1L1M). There was no statistical difference between the groups regarding age, sex, type of fracture, or Flynn's criteria. The overall mean surgical duration with 1L1M fixation (30.59 ± 8.72) was statistically lower (p = 0.001) when compared to the 2L1M Kirschner wire K-wire fixation (40.61 ± 8.25). The mean radiation duration was 0.76 ± 0.33 s in the 1L1M K-wire fixation and 1.68 ± 0.55 s in the 2L1M K-wire fixation. The mean radiation dose of the 2L1M K-wire fixation (2.45 ± 1.15 mGy) was higher than that of the 1L1M K-wire fixation (0.55 ± 0.43 mGy) (p = 0.000).

CONCLUSIONS

The current study shows that although there is no difference between the clinical and radiological outcomes, radiation dose exposure is significantly lower for the 1L1M fixation method.

Spontaneous humeral torsion deformity correction after displaced supracondylar fractures in children

BACKGROUND

After displaced supracondylar humerus fractures (SCHF) in children, residual deformities are common with cubitus varus (CV) being the clinically most visible. Distal fragment malrotation may lead to instability, fragment tilt and subsequent CV. Detection and assessment of malrotation is difficult and the fate of post-traumatic humeral torsion deformity is unknown. The aim of this study was to evaluate the incidence of humeral torsion differences in children with surgically treated SCHF and to observe spontaneous changes over time.

METHODS

A cohort of 27 children with displaced and surgically treated SCHF were followed prospectively from the diagnosis until twelve months after trauma. Clinical, photographic, sonographic and radiological data were obtained regularly. Differences in shoulder and elbow motion, elbow axis, sonographic humeral torsion measurement and radiological evaluation focusing on rotational spur were administered.

RESULTS

Six weeks after trauma, 67% of SCHF children had a sonographically detected humeral torsion difference of > 5° (average 14.0 ± 7.6°). Of those, 44% showed a rotational spur, slight valgus or varus on radiographs. During follow-up, an average decrease of the difference from 14° (six weeks) to 7.8° (four months) to 6.5° (six months) and to 4.9° (twelve months) was observed. The most significant correction of posttraumatic humeral torsion occurred in children < 5 years and with internal malrotation > 20°.

CONCLUSION

After displaced and surgically treated SCHF, most children had humeral torsion differences of both arms. This difference decreased within one year after trauma due to changes on the healthy side or correction in younger children with severe deformity.

LEVEL OF EVIDENCE/CLINICAL RELEVANCE

Therapeutic Level IV.

Modified Closed Reduction and Percutaneous Kirschner Wires Internal Fixation for Treatment of Supracondylar Humerus Fractures in Children

OBJECTIVE

Supracondylar humerus fractures are the most frequent fractures of the paediatric elbow. The present study introduced a modified surgical procedure for treatment of supracondylar humerus fractures in children.

METHODS

From February 2015 to August 2019, 73 patients with Gartland's type II and III supracondylar fractures were treated with this modified method. Totally, 68 of all patients were followed up for 3-12 months (mean 8.25 months). The evaluation results included fracture nonunion, ulnar nerve injury, pin track infection, carrying angle and elbow joint Flynn score.

RESULTS

The results showed that bone union was observed in all children, one case had an iatrogenic ulnar nerve injury, and the symptoms were completely relieved in 4 months after removing of the medial-side pin. All children had no cubitus varus deformity and no pin track infection, and the rate of satisfactory results according to Flynn's criteria score was 100%.

CONCLUSION

The modified closed reduction and Kirschner wires internal fixation could effectively reduce the rate of open reduction, the risk of iatrogenic ulnar nerve injury, and the incidence of cubitus varus deformity in treatment of supracondylar humerus fractures in children.

Biomechanical Analysis of Sagittal Plane Pin Placement Configurations for Pediatric Supracondylar Humerus Fractures

Anterior to posterior (AP) pinning is the recommended sagittal pin configuration in divergent lateral entry coronal pinning of pediatrics supracondylar fractures. However, there was still a lack of evidence regarding alternative sagittal pins configurations. We aimed to compare the construct stiffness of alternative sagittal pin configurations by using synthetic bone models. Sixty synthetic pediatric humeri were osteotomized to create a supracondylar fracture. After the fracture reduction, all specimens were fixed in the coronal plane with divergent lateral entry pin configurations in four different patterns in the sagittal plane: AP, crossed, divergent and parallel sagittal pin configuration. Each configuration was tested with five loading patterns. The AP sagittal pin had significantly lower construct stiffness than the divergent (p = 0.003) and the parallel sagittal pin configuration (p = 0.005) in external rotation loading tests. The divergent sagittal pin had the highest construct stiffness in extension, valgus, and external rotation loads, but the parallel sagittal pin had lower construct stiffness under extension load than the divergent and crossed sagittal pin configurations. The divergent sagittal pin configuration provides greater construct stiffness than other sagittal pin configurations due to the maximal pin spreading distance at the fracture site and the pin angle lock mechanism.

Manejo da fratura supracondiliana do úmero na criança

Supracondylar humeral fracture represents ∼ 3 to 15% of all fractures in children. It is the fracture that most requires surgical treatment in the pediatric population. Advances in treatment and care have contributed to a reduction in the most dramatic complication: Volkmann ischemic contracture. Nevertheless, the risks inherent to the fracture remain. Absence of palpable pulse in type-III fractures is reported in up to 20% of the cases. Careful sensory, motor, and vascular evaluation of the affected limb is crucial in determining the urgency of treatment. Older children, male patients, floating elbow, and neurovascular injury are risk factors for compartment syndrome. Medial comminution can lead to varus malunion, even in apparently innocent cases. The recommended treatment of displaced fractures is closed reduction and percutaneous pinning. Technical errors in pin placement are the main cause of loss of reduction. There is enough evidence for the addition of a third lateral or medial Kirschner wire in unstable fractures (types III and IV). Medial comminution may lead to cubitus varus even in mild displaced fractures. Based on current concepts, a flowchart for the treatment of supracondylar humeral fracture in children is suggested by the authors.

[Supracondylar humeral fractures in childhood]

The classification of supracondylar humeral fractures in German-speaking areas is carried out according to von Laer, which has been appropriated from the AO system and has the advantage that it can be used to derive the treatment. When indicated immediate surgery is given preference over a delayed treatment. The result is controlled by functional tests directly during the operation. Instability of the fracture and correct placement of the Kirschner (K) wires are challenging. Alternatives are an external fixator and elastically stable intramedullary nailing (ESIN). Concomitant injuries initially affect the median nerve and the brachial artery and secondarily the radial nerve. Lesions of the ulnar nerve are mostly a postoperative complication. The bony consolidation is achieved after 3-4 weeks and afterwards implant removal can be safely carried out. Embedded K‑wires and ESIN are removed after 3-6 months, depending on the surgical capacity and complaints of the patient.