Beveled posteromedial corner of the radial head: a three-dimensional micro-computed tomography modeling study

Microstructure of the radial head: Insights into anatomical variations and implications for advanced interventions

Appropriate management of radial head fractures is integral to prevent long-term consequences like chronic pain and loss of motion. Advanced imaging systems, like micro-computed tomography (μCT), are valuable for understanding radial head fracture patterns as they utilize micrometer scale resolution to define important parameters of bone health like cortical density and trabecular thickness. The purpose of this study was to identify and describe the structural morphology of the radial head utilizing μCT. Nine fresh-frozen cadaveric human radii were divided into four equal quadrants, based, and labeled as posteromedial, posterolateral, anteromedial, and anterolateral. Quadrants were scanned with a SCANCO MicroCT40 with both cortical and cancellous bone density measurements at a resolution of 36.0 μm. Bone density, direct trabecular number, and trabecular thickness were recorded as milligrams of hydroxyapatite/cm3. A one-way repeated measures ANOVA was performed to compare the bone densities, trabecular number, and trabecular thickness of each of the four quadrants (p < 0.05). The posteromedial quadrant contained substantially more bone than other quadrants. Significantly greater bone densities were found in the posteromedial quadrant (148.1 mg of HA/cm3) compared to the anteromedial quadrant (54.6 mg of HA/cm3), posterolateral quadrant (137.5 mg of HA/cm3) compared to the anteromedial quadrant (54.6 mg of HA/cm3), and posterolateral quadrant (137.5 mg of HA/cm3) compared to the anterolateral quadrant (58.1 mg of HA/cm3). The trabecular number was not significantly different between quadrants. Trabecular thickness was significantly lower in the anterolateral (0.1417 mg of HA/cm3) and anteromedial (0.1416 mg of HA/cm3) quadrants compared to the posteromedial (0.1809 mg of HA/cm3) quadrant. The posterior half of the radial head was found to have a higher density of columns and arches compared to the anterior half. The microstructure of trabecular bone in the distal radius forms columns, struts, and arches, which allow for efficient transmission of stress through the bone. The microstructure of the radial head has similar microarchitecture to the distal radius with the present study identifying the presence of columns and arches in the radial head. These structures, along with trabecular density, in the posterior radial head may explain the lower incidence of fractures involving the posterior half of the radial head. Furthermore, our study supports the idea that the high incidence of fractures involving the anterolateral quadrant is due to microarchitecture characteristics and the relative lack of supportive structures compared to other areas. The novel insight gained from this study will aid in the development of advanced interventions for preventative measures and better treatment of radial head fractures like more satisfactory purchase when screws are directed towards the denser posteromedial quadrant.

The Relationship between the Bevel of the Radial Head Epiphysis and the Posterior Synovial Fringe During Rotation of the Elbow: An Ultrasonography Study with Possible Implications Regarding the Pathophysiology of Nursemaid's Elbow

BACKGROUND

Nursemaid's elbow is the most common upper extremity injury in children under 5 years of age. However, the exact pathomechanism underlying the nursemaid's elbow remains elusive, and approximate one-third of patients present with a nonclassical history. Using a high-frequency ultrasound probe, we attempted to determine the relationship between the anterior edge of the posterior synovial fringe and the peripheral rim of the radial head epiphysis during rotation. It is possible that the primary reason for the nursemaid's elbow is due to the pronator position.

METHODS

Twenty-one patients had a history of nursemaid's elbow and had a successful reduction before enrollment in this study. A high-frequency linear array 6 to 24 MHz hockey stick transducer was used to detect small morphologic changes in the peripheral rim of the radial head epiphysis and the posterior synovial fringe during rotation of the capitellum-radial joint.

RESULTS

In complete pronation, the anterior edge of the posterior synovial fringe contacts the beveled articular surface of the radial head peripheral rim in all 21 patients. In neutral and complete supination, the anterior edge of the posterior synovial fringe contacts the convexly nonarticular surface of the radial head peripheral rim and extends deep into the foveal radius. The posterior synovial fringe and the capsule-aponeurotic membrane were tightened in passive pronation in all 21 cases. The posterior synovial fringe and the capsule-aponeurosis membrane were all loose in the neutral and supination positions.

CONCLUSION

The anterior edge of the posterior synovial fringe touches the beveled peripheral rim of the radial head epiphysis during complete pronation, and the tension of the lateral collateral ligament complex during pronation may further cause unstable conditions of the anterior edge of the posterior synovial fringe. We hypothesized that the beveled peripheral rim of the radial epiphysis and its relationship with the anterior edge of the posterior synovial fringe could be the reason why nursemaid's elbow only occurs while the elbow is in the pronator position.

Regional differences in the three-dimensional bone microstructure of the radial head: implications for observed fracture patterns

INTRODUCTION

A characterization of the internal bone microstructure of the radial head could provide a better understanding of commonly occurring fracture patterns frequently involving the (antero)lateral quadrant, for which a clear explanation is still lacking. The aim of this study is to describe the radial head bone microstructure using micro-computed tomography (micro-CT) and to relate it to gross morphology, function and possible fracture patterns.

MATERIALS AND METHODS

Dry cadaveric human radii were scanned by micro-CT (17 μm/pixel, isotropic). The trabecular bone microstructure was quantified on axial image stacks in four quadrants: the anterolateral (AL), posterolateral (PL), posteromedial (PM) and anteromedial (AM) quadrant.

RESULTS

The AL and PL quadrants displayed the significantly lowest bone volume fraction and trabecular number (BV/TV range 12.3-25.1%, Tb.N range 0.73-1.16 mm^-1) and highest trabecular separation (Tb.Sp range 0.59-0.82 mm), compared to the PM and AM quadrants (BV/TV range 19.9-36.9%, Tb.N range 0.96-1.61 mm^-1, Tb.Sp range 0.45-0.74 mm) (p = 0.03).

CONCLUSIONS

Our microstructural results suggest that the lateral side is the "weaker side", exhibiting lower bone volume faction, less trabeculae and higher trabecular separation, compared to the medial side. As the forearm is pronated during most falls, the underlying bone microstructure could explain commonly observed fracture patterns of the radial head, particularly more often involving the AL quadrant. If screw fixation in radial head fractures is considered, surgeons should take advantage of the "stronger" bone microstructure of the medial side of the radial head, should the fracture line allow this.

The contact area of the radiocapitellar joint under pronation and supination with axial load using a 3-dimensional computed tomography: an in vivo study

OBJECTIVE

To evaluate the contact area of the radiocapitellar joint with forearm pronation and supination under axial loading.

MATERIALS AND METHODS

Six healthy volunteers (2 males and 4 females, mean age: 44.6 years) were included in the study. A computed tomography scan of the extended elbow joints was obtained at 4 positions of forearm: full pronation with or without load and full supination with or without load. Mimics, 3-matic Medical, Geomagic, and Photoshop were used to reconstruct 3-dimensional models. The contact area of the radiocapitellar joint was measured. Shifting of the center of the contact area of the radiocapitellar joint was measured.

RESULTS

The axial load added 8.6% and 10.5% contact area to pronation and supination without load, respectively. From pronation without load, the center of contact area significantly shifted 2.4 ± 1.1 mm anteromedially to supination without load and shifted by 1.0 ± 0.5 mm to the center of the radial head compared with the pronation with load. The center of the contact area significantly shifted 2.4 ± 1.5 mm anteromedially from the pronation to the supination under loading. The contact area of the tuberosity anterior in the radial head significantly increased by 14% (without load) and 8% (with load) from pronation to supination.

CONCLUSION

Axial loading increases the contact area of the radiocapitellar joint. The center of the contact area of the radiocapitellar joint changed according to loading and shifted to the anterior tuberosity of the radial head from forearm pronation to supination.