Comparative Biomechanical Analysis of Stress-Strain State of the Elbow Joint After Displaced Radial Head Fractures

Biomechanical comparison of different internal fixation devices for transversely unstable Mason type II radial head fractures

Background: The integrity of the radial head is critical to maintaining elbow joint stability. For radial head fractures requiring surgical treatment, headless compression cannulated screw fixation is a less invasive scheme that has fewer complications. The aim of this study was to compare the mechanical stability of different fixation devices, including headless compression cannulated screws and mini-T-plates, for the fixation of transversely unstable radial head fractures. Methods: Forty identical synthetic radius bones were used to construct transverse unstable radial head fracture models. Parallel, cross, and tripod headless compression cannulated screw fixation and mini-T plate fixation were applied. The structural stiffness of each group was compared by static shear loading. Afterward, cyclic loading was performed in each of the three directions of the radial head, and the shear stability of each group was compared by calculating the maximum radial head displacement at the end of the cycle. Findings: The mini-T plate group had the lowest structural stiffness (51.8 ± 7.7 N/mm) and the highest relative displacement of the radial head after cyclic loading (p < 0.05). The tripod headless compression cannulated screw group had the highest structural stiffness among all screw groups (p < 0.05). However, there was no significant difference in the relative displacement of the radial head between the screw groups after cyclic loading in different directions (p > 0.05). Interpretation: In conclusion, the biomechanical stability of the mini-T plate for fixation of transverse unstable radial head fractures is lower than that of headless compression cannulated screws. Tripod fixation provides more stable fixation than parallel and cross fixation with headless compression cannulated screws for the treatment of transversely unstable radial head fractures.

Finite Element Analysis of Elbow Joint Stability by Different Flexion Angles of the Annular Ligament

Objective

The injury of the annular ligament can change the stress distribution and affect the stability of the elbow joint, but its biomechanical mechanism is unclear. The present study investigated the biomechanical effects of different flexion angles of the annular ligament on elbow joint stability.

Methods

A cartilage and ligament model was constructed using SolidWorks software according to the magnetic resonance imaging results to simulate the annular ligament during normal, loosened, and ruptured conditions at different buckling angles (0°, 30°, 60°, 90°, and 120°). The fixed muscle strengths were 40 N (F1), 20 N (F2), 20 N (F3), 20 N (F4), and 20 N (F5) for the triceps, biceps, and brachial tendons and the base of the medial collateral ligament and lateral collateral ligament. The different elbow three‐dimensional (3D) finite element models were imported into ABAQUS software to calculate and analyze the load, contact area, contact stress, and stress of the medial collateral ligament of the olecranon cartilage.

Results

The results showed that the stress value of olecranon cartilage increased under different conditions (normal, loosened, and ruptured annular ligament) with elbow extension, and the maximum stress value of olecranon cartilage was 2.91 ± 0.24 MPa when the annular ligament was ruptured. The maximum contact area of olecranon cartilage was 254  mm² with normal annular ligament when the elbow joint was flexed to 30°, while the maximum contact area of loosened and ruptured annular ligament was 283 and 312 mm² at 60° of elbow flexion, and then decreased gradually. The maximum stress of the medial collateral ligament was 6.52 ± 0.23, 11.51 ± 0.78, and 18.74 ± 0.94 MPa under the different conditions, respectively.

Conclusion

When the annular ligament ruptures, it should be reconstructed as much as possible to avoid the elevation of stress on the surface of the medial collateral ligament of the elbow and the annular cartilage, which may cause clinical symptoms.

Comparison of two surgical techniques for the treatment of transverse olecranon fractures: A finite element study

BACKGROUND

In this study, we aimed to compare the stability of traditional tension band wiring (TBW) and screw combined TBW (SC-TBW) fixation methods performed for a transverse olecranon osteotomy-fracture during different degrees of elbow movement by using finite element analysis.

METHODS

Three-dimensional solid modeling of the olecranon was obtained by computed tomography images. Transverse olecranon fracture was created and fixed by TBW and SC-TBW with respect to triceps muscle force. Opening angle, twisting angle and interplanar translation occurring on the fracture line were evaluated at 45° and 90° elbow flexion.

RESULTS

Opening angle: 0.71°, 0.87° at 45° and 0.64°, 0.67° at 90° elbow flexion for TBW and SC-TBW, respectively. Twisting angle: -0.01°, -0.19° at 45° flexion and 0.19°, 0.30° at 90° flexion for TBW and SC-TBW, respectively. Interplanar translation: 1.93 mm, 4.65 mm at 45° flexion and 1.78 mm, 3.95 mm at 90° flexion for TBW and SC-TBW, respectively.

CONCLUSION

TBW fixation provides more stability than SC-TBW fixation model.

Finite Element Analysis of Insertion Angle of Absorbable Screws for the Fixation of Radial Head Fractures

Objective

To investigate the biomechanical effects of different insertion angles of absorbable screws for the fixation of radial head fractures.

Methods

The finite element models used to simulate the fractures were created based on CT scans. Two absorbable screws were used to fix and maintain the stability of the fracture, and the angles between the screws were set to 0°, 15°, 30°, 45°, 60°, 75°, and 90°. A downward force of 100 N was applied at the stress point, which was coupled with the surface, and the distal radius was limited to six degrees of freedom. The direction and location of the applied force were the same in each model. The values of the von Mises stress and peak displacements were calculated.

Results

Under the applied load and different screw angles, the maximum von Mises stress in the screws was concentrated on the surface contacting the fracture surfaces. The maximum von Mises equivalent stress in the screw decreased when the angle increased from 0° (19.54 MPa) to 45° (13.11 MPa) and increased when the angle further increased to 90° (24.63 MPa). The peak displacement decreased as the angle increased from 0° (0.19 mm) to 45° (0.15 mm) and increased when the angle further increased to 90° (0.25 mm).

Conclusion

The computational stress distribution showed that fixation with absorbable screws is safe for patients. Moreover, the minimum von Mises stress and displacements were generated when the angle between the screws was 45°; hence, this setting should be recommended for Mason type II radial fractures.

Prediction and Potential Preventions for the Development of Posttraumatic Osteoarthritis after the Terrible Triad Injury: A Multicenter Risk Factors Study

Objective

A multicenter study to evaluate risk factors for the development of moderate or severe posttraumatic osteoarthritis (PTOA) and to find potential preventions.

Methods

We conducted a retrospective multicenter study including the terrible triad injury (TTI) patients with surgical treatment from January 2007 to November 2014. Demographics, injury information, and treatment history were obtained retrospectively. According to the Broberg and Morrey criterion, 198 included patients were sorted into two groups: the mild or no PTOA and moderate or severe PTOA. Uni- and multivariate logistic regression analyses were used to identify risk factors for moderate or severe PTOA.

Results

Moderate or severe PTOA was present in 64 patients (32.3%). Significant risk factors were Mason III radial head fracture (OR 4.049, 95% CI 1.877-8.736, p < 0.001), medial collateral ligament injury (OR 5.120, 95% CI 1.261-20.790, p = 0.022), and heavy use of elbow (OR 2.333, 95% CI 1.060-5.136, p = 0.035). Besides, patients suffered subluxation (p = 0.007) and those with more risk factors had a higher risk to develop moderate or severe PTOA.

Conclusions

Moderate or severe PTOA was common after the TTI. Patients need to be counseled about avoiding heavy use of the elbow, especially for those with Mason III radial head fractures. Surgeons should be aware of the recurrent instability of the elbow.