Microarchitecture of the radial head and its changes in aging

Patient-specific finite element analysis of four different fixation methods for transversely unstable radial head fractures

Plate fixation is a common treatment option for radial head fractures (RHFs). Due to the benefits of less invasiveness and fewer complications of internal fixation, the application of small-diameter headless compression screws (HCSs) to treat RHFs has become a new trend. This study aimed to compare the mechanical stability of four distinct internal fixation protocols for transversely unstable RHFs via finite element analysis. Using computed tomography data from 10 patients, we developed 40 patient-specific FE models of transversely unstable RHFs fixed by parallel, crossed, and tripod HCSs and mini-T plate (MTP). Under simulated physiological loading of the elbow joint, the construct stiffness, displacement, and von Mises stresses were evaluated and verified by a biomechanical experiment. Under shear loading, the MTP group exhibited lower construct stiffness, larger displacement, and higher Von Mises stress than the HCSs group. The stiffness of tripod HCSs was greater than parallel and crossed screw fixation techniques. There was a strong relationship between apparent bone density and construct stiffness (R = 0.98 to 0.99). In the treatment of transversely unstable RHFs, HCSs have superior biomechanical stability than MTP. The tripod technique was also more stable than parallel and crossed fixation.

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.

Investigation of distal femur microarchitecture and factors influencing its deterioration: An ex vivo high-resolution peripheral quantitative computed tomography study

While fractures of the distal femur are often considered as fragility fractures, detailed knowledge of the bone microarchitecture at this skeletal site is largely unavailable. Initial evaluation of a patient cohort with distal femur fractures showed a markedly increased occurrence in elderly women. The purpose of this study was to determine the extent to which demographic characteristics of distal femur fractures are reflected by general age- and sex-specific variations in local microarchitectural parameters. Fifty cadaveric femora were collected from 25 subjects (12 females, 13 males, age 25-97 years). A volume of interest within 3 cm proximal to the condyles was analyzed using high-resolution peripheral quantitative computed tomography (HR-pQCT), which revealed impaired trabecular and cortical bone microarchitecture in women compared to men as well as in osteoporotic compared to normal or osteopenic subjects, as classified by dual-energy X-ray absorptiometry (DXA) T-score. Linear regression analyzes showed negative associations between age and HR-pQCT parameters in women (e.g., cortical thickness -14 µm/year, 95% CI: -21 to -7 µm/year), but not in men (e.g., cortical thickness 1 µm/year, 95% CI: -12 to 14 µm/year). HR-pQCT parameters showed strong positive associations with areal bone mineral density (aBMD) determined by DXA at the hip in both sexes. Taken together, our findings suggest that female sex, advanced age, and low aBMD represent major risk factors for impaired microarchitecture at the distal femur. Both the diagnostic value of DXA for predicting distal femur fractures and the efficacy of bone-specific agents on fracture risk reduction should be investigated in the future.

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.

Involvement of the proximal radial ulnar joint in partial radial head fractures: a novel three-dimensional computed tomography scan evaluation method

BACKGROUND

Partial radial head fractures (PRHF) can involve the proximal radioulnar joint (PRUJ) or be restricted to the 'safe zone' (SZ) during forearm rotation. The objective of the present study was to develop an assessment method for PRUJ involvement in radial head fractures using axial computed tomography (CT) scans.

METHODS

The area of the radial head in contact with the PRUJ zone was identified, and defined on 18 cadaveric elbows CT scans; the quantitative relationship between PRUJ zone and radial tuberosity was established. Then, four evaluators validated it on PRHF CT scan axial views, classifying the fractures as involving the PRUJ or not.

RESULTS

Using the radial tuberosity as the 0° of a 360° circle, the SZ was within 108° to 212° clockwise for a right elbow and counter clockwise for the left elbow. Fifty-five consecutive (30 men, 25 women, mean age of 49 years) partial radial head fracture CT scans were classified: four in the SZ only, three in the PRUJ zone and 48 in both the PRUJ and SZ. The kappa for the inter- and intra-observer agreement was 0.517 and 0.881, respectively.

CONCLUSIONS

Ninety-three percent of partial radial head fractures will involve the PRUJ and the geometric model developed allows their classification, potentially helping surgeons decide on optimal treatment.

LEVEL OF EVIDENCE

Retrospective basic science study. Level III: anatomic study, imaging.

Trabecular architecture in the forelimb epiphyses of extant xenarthrans (Mammalia)

Background

Bone structure has a crucial role in the functional adaptations that allow vertebrates to conduct their diverse lifestyles. Much has been documented regarding the diaphyseal structure of long bones of tetrapods. However, the architecture of trabecular bone, which is for instance found within the epiphyses of long bones, and which has been shown experimentally to be extremely plastic, has received little attention in the context of lifestyle adaptations (virtually only in primates). We therefore investigated the forelimb epiphyses of extant xenarthrans, the placental mammals including the sloths, anteaters, and armadillos. They are characterised by several lifestyles and degrees of fossoriality involving distinct uses of their forelimb. We used micro computed tomography data to acquire 3D trabecular parameters at regions of interest (ROIs) for all extant genera of xenarthrans (with replicates). Traditional, spherical, and phylogenetically informed statistics (including the consideration of size effects) were used to characterise the functional signal of these parameters.

Results

Several trabecular parameters yielded functional distinctions. The main direction of the trabeculae distinguished lifestyle categories for one ROI (the radial trochlea). Among the other trabecular parameters, it is the degree of anisotropy (i.e., a preferential alignment of the trabeculae) that yielded the clearest functional signal. For all ROIs, the armadillos, which represent the fully terrestrial and fossorial category, were found as characterised by a greater degree of anisotropy (i.e., more aligned trabeculae). Furthermore, the trabeculae of the humeral head of the most fossorial armadillos were also found to be more anisotropic than in the less fossorial species.

Conclusions

Most parameters were marked by an important intraspecific variability and by a size effect, which could, at least partly, be masking the functional signal. But for some parameters, the degree of anisotropy in particular, a clear functional distinction was recovered. Along with data on primates, our findings suggest that a trabecular architecture characterised by a greater degree of anisotropy is to be expected in species in which the relevant epiphyses withstand a restricted range of load directions. Trabecular architecture therefore is a promising research avenue for the reconstruction of lifestyles in extinct or cryptic species.

Electronic supplementary material

The online version of this article (10.1186/s12983-017-0241-x) contains supplementary material, which is available to authorized users.

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

The posteromedial quadrant of the radial head is known to be different from the other quadrants. However, the explanation of this unique anatomical feature remains elusive. Hence, this study was designed to address this unique anatomical variance using three-dimensional μCT (micro-computed tomography) analysis. Nine fresh cadaveric radial heads were scanned using μCT. Three-dimensional subchondral bone and cartilage models were rendered. Both models were separated into the four quadrants at both the periphery (rim) and the articulating dish (fovea): anteromedial (AM), posteromedial (PM), posterolateral (PL), and anterolateral (AL). Each quadrant was analyzed in terms of (1) subchondral bone porosity (SBP), (2) mean subchondral bone thickness (MSBT), and (3) mean cartilage thickness (MCT). There was a significant difference between the fovea and the rim in terms of its microarchitectural features. Although within the fovea, the PM quadrant did not differ significantly from the other quadrants, a significant difference was found within the rim. In terms of SBP, PM, AM, PL and AL were calculated as 33, 37, 36 and 35%, respectively. In terms of MSBT, PM, AM, PL and AL were calculated as 0.11, 0.10, 0.09, and 0.09 mm, respectively. In terms of MCT, PM, AM, PL and AL were calculated 1.09, 0.81, 0.84 and 0.83 mm, respectively. The PM corner of the radial head between the 8 and 9 o'clock positions, was beveled. This might explain why the PM quadrant of the rim differed significantly from the other quadrants in terms of its microarchitectural features.

Fracture mapping of displaced partial articular fractures of the radial head

BACKGROUND

Recognition of patterns of traumatic elbow instability helps anticipate specific fracture characteristics and associated injuries. The objective of this study was to assess the association of fracture line distribution and location of displaced partial articular radial head fractures with specific patterns of traumatic elbow instability using fracture mapping techniques.

METHODS

Fracture line distribution and location of 66 acute displaced partial articular radial head fractures were identified using quantitative 3-dimensional computed tomography reconstructions that allowed reduction of fracture fragments and a standardized method to divide the radial head into quadrants with forearm in neutral position. Based on qualitative and quantitative assessment of fracture maps, the association between fracture characteristics of displaced partial articular radial head fractures and specific elbow fracture patterns was determined.

RESULTS

In partial articular radial head fractures, the highest fracture line intensity was located in the anterolateral quadrant near the center of the radial head. Fracture location corresponded with fracture line distribution; most fractures involved the anterolateral quadrant (n = 65; 98%), whereas parts of the posteromedial quadrant were involved in a minority of the fractures (n = 10; 15%). The association of fracture line distribution and location with overall fracture patterns of the elbow, as depicted on fracture maps, was not statistically significant.

CONCLUSION

Fracture maps demonstrated no association between fracture line distribution and location of displaced partial articular fractures of the radial head and overall specific patterns of traumatic elbow instability, suggesting a common fracture mechanism that involves the anterolateral part of the radial head in most patients.

Mason Type I Fractures of the Radial Head

Mason type I fractures are the most common fractures of the radial head. The fractures have a benign character and often result in good, pain-free function. Nevertheless, up to 20% of patients with a Mason type I fracture report loss of extension and residual pain. Currently, there is a lack of consensus concerning diagnosis and treatment of these fractures. The goal of this study was to systematically review incidence, diagnosis, classification, treatment, and outcome of Mason type I radial head fractures in adults and establish an evidence-based treatment guideline. A search of the MEDLINE, EMBASE, and Cochrane databases was conducted for English titles without restrictions on publication date. The authors included titles that addressed Mason type I radial head fractures and covered incidence, diagnostics, treatment, or functional or patient-related outcome. Included were randomized controlled trials; case-control studies; comparative cohort studies; case series with more than 10 patients; and expert opinions. Reference lists were cross-checked for additional titles. The search yielded 1734 studies, of which 95 met the inclusion criteria. Seven studies showed that the elbow extension test has a high sensitivity (88.0-97.6) to rule out Mason type I radial head fractures. If radiography is required, antero-posterior and lateral radiographs suffice. For pain relief, hematoma aspiration seems safe and effective. Mason type I fractures are best treated with 48 hours of rest with a sling, followed with active mobilization. Cast immobilization should be avoided. Mobilization should be encouraged and if needed supported by physical therapy.

The effect of trauma and patient related factors on radial head fractures and associated injuries in 440 patients

Background

Radial head fractures are commonly interpreted as isolated injuries, and it is assumed that the energy transferred during trauma has its influence on the risk on associated ipsilateral upper limb injuries. However, relationships between Mason classification, mechanism of injury, and associated injuries have been reported only once before in a relatively small population. The purpose of this study was to define whether trauma mechanism and patient related factors are of influence on the type of radial head fracture and associated injuries to the ipsilateral upper limb in 440 patients.

Methods

The radiographs and medical records of 440 patients that presented with a fracture of the radial head were retrospectively analyzed. The medical records of all patients were searched for (1) the trauma mechanism and (2) associated injuries of the ipsilateral upper limb. The mechanism of injury was classified as being low-energy trauma (LET) or high-energy trauma (HET).

Results

Associated injuries to the ipsilateral upper limb were present in 46 patients (11 %). The mean age of patients with associated injuries (52 years) was significantly higher compared to patients without associated injuries (47 years) (P = 0.038), and female patients with a radial head fracture were older than males. Injury patterns were classified as LET in 266 patients (60 %) and as HET in 174 patients. HETs were significantly more common in young men. Associated injuries were not significantly different distributed between HET versus LET (P = 0.82).

Conclusions

Injuries concomitant to radial head fractures were present in 11 % of patients and the risk for these associated injuries increases with age. Trauma mechanism did not have a significant influence on the risk of associated injuries. Complex elbow trauma in patients with a radial head fracture seems therefore to be suspected based on patient characteristics, rather than mechanism of injury.

Regional variations in radial head bone volume and density: implications for fracture patterns and fixation

BACKGROUND

Fractures of the radial head are common with most partial articular fractures resulting in an anterolateral fragment. The exact mechanism of radial head fracture is unknown; however, forces transmitted and variations in local bone density are believed important. This study quantifies the regional variations in bone density and volume of the radial head to better understand the pathomechanics of fracture patterns.

METHODS

Computer tomography scan data of 18 cadaver elbows were imported into imaging analysis software. The radial head was divided into quadrants based on neutral forearm rotation. Bone density and volume were calculated and compared between quadrants.

RESULTS

The regional densities of bone expressed in Hounsfield units (HU) were posteromedial quadrant (PM) 496 ± 87 HU, anteromedial quadrant (AM) 443 ± 72 HU, anterolateral quadrant (AL) 409 ± 60 HU, and posterolateral quadrant (PL) 406 ± 57 HU. The volume of bone in descending order was PM 1138 ± 179 mm(3), PL 1013 ± 213 mm(3), AM 1010 ± 210 mm(3), and AL 938 ± 175 mm(3). The PM quadrant was significantly denser than the AM, AL, and PL quadrants, (P = .001) and the AM quadrant was significantly denser than the AL and PL quadrants (P = .006 and .009). The PM quadrant had significantly more bone volume when compared to the AM, AL, and PL (P = .001). The AM and PL quadrants had significantly greater bone volume compared to AL quadrant (P = .023 and .018, respectively).

CONCLUSION

Radial head bone volume and density is highest in the posteromedial quadrant and lowest in the anterolateral quadrant where fractures occur more frequently.

Osteoporosis and radial head fractures in female patients: a case-control study

BACKGROUND

Identifying radial head fractures as fragility fractures may improve case-findings for osteoporosis and thus be an indicator other fragility fractures.

MATERIALS AND METHODS

Thirty-five women aged ≥ 50 years with a radial head fracture and 57 controls were retrospectively selected and matched for age in strata of 5 years. Peripheral bone mineral density (BMD) measurement was performed at the calcaneus. A T score of less than -2.7 was considered osteoporosis. If the T value was between -1.4 and -2.7, an additional dual energy X-ray (DXA) scan was performed.

RESULTS

The patients were a median age of 60 years compared with 58 years for the control patients (P = .33). The mean T score of the patients was -1.8 (standard deviation [SD], 1.0; range, -2.2 to -0.3) compared with -1.2 (SD, 1.2; range, -4.0 to 1.3) for the control patients (P = .04). Osteoporosis was diagnosed in 11 patients and in 5 control patients. The patients had an increased risk of osteoporosis compared with the control patients (odds ratio, 3.4; P = .027).

CONCLUSIONS

This study confirms that radial head fractures in women aged ≥ 50 years are potentially osteoporotic fractures. Offering these patients a BMD measurement may prevent future osteoporotic fractures, such as hip and spine fractures.

Direct visualization and quantification of bone growth into porous titanium implants using micro computed tomography

The utility of porous metals for the integration of orthopaedic implants with host bone has been well established. Quantification of the tissue response to cementless implants is laborious and time consuming process requiring tissue processing, embedding, sectioning, polishing, imaging and image analysis. Micro-computed tomography (μCT) is a promising three dimensional (3D) imaging technique to quantify the tissue response to porous metals. However, the suitability and effectiveness of μCT for the quantification of bone ingrowth remains unknown. The purpose of this study was to evaluate and compare bone growth within porous titanium implants using both μCT and traditional hard-tissue histology techniques. Cylindrical implants were implanted in the distal femora and proximal tibiae of a rabbit. After 6 weeks, bone ingrowth was quantified and compared by μCT, light microscopy and backscattered electron microscopy. Quantification of bone volume and implant porosity as determined by μCT compared well with data obtained by traditional histology techniques. Analysis of the 3D dataset showed that bone was present in the pores connected with openings larger 9.4 μm. For pore openings greater than 28.2 μm, the size of the interconnection had little impact on the bone density within the porosity for the titanium foams.