J.H. Waarsing

Renal Ca2+ wasting, hyperabsorption, and reduced bone thickness in mice lacking TRPV5

Ca2+ ions play a fundamental role in many cellular processes, and the extracellular concentration of Ca2+ is kept under strict control to allow the proper physiological functions to take place. The kidney, small intestine, and bone determine the Ca2+ flux to the extracellular Ca2+ pool in a concerted fashion. Transient receptor potential (TRP) cation channel subfamily V, members 5 and 6 (TRPV5 and TRPV6) have recently been postulated to be the molecular gatekeepers facilitating Ca2+ influx in these tissues and are members of the TRP family, which mediates diverse biological effects ranging from pain perception to male aggression. Genetic ablation of TRPV5 in the mouse allowed us to investigate the function of this novel Ca2+ channel in maintaining the Ca2+ balance. Here, we demonstrate that mice lacking TRPV5 display diminished active Ca2+ reabsorption despite enhanced vitamin D levels, causing severe hypercalciuria. In vivo micropuncture experiments demonstrated that Ca2+ reabsorption was malfunctioning within the early part of the distal convolution, exactly where TRPV5 is localized. In addition, compensatory hyperabsorption of dietary Ca2+ was measured in TRPV5 knockout mice. Furthermore, the knockout mice exhibited significant disturbances in bone structure, including reduced trabecular and cortical bone thickness. These data demonstrate the key function of TRPV5 in active Ca2+ reabsorption and its essential role in the Ca2+ homeostasis.

An Improved Segmentation Method for In Vivo μCT Imaging

Image segmentation methods for μCT can influence the accuracy of bone morphometry calculations. A new automated segmentation method is introduced, and its performance is compared with standard segmentation methods. The new method can improve the results of in vivo μCT, where the need to keep radiation dose low limits scan quality.

Cam impingement causes osteoarthritis of the hip: a nationwide prospective cohort study (CHECK)

Objective To determine the association between cam impingement, which is hip incongruity by a non-spherical femoral head and development of osteoarthritis. Methods A nationwide prospective cohort study of 1002 early symptomatic osteoarthritis patients (CHECK), of which standardised anteroposterior pelvic radiographs were obtained at baseline and at 2 and 5 years follow-up. Asphericity of the femoral head was measured by the α angle. Clinically, decreased internal hip rotation (≤20°) is suggestive of cam impingement. The strength of association between those parameters at baseline and development of incident osteoarthritis (K&L grade  2) or end-stage osteoarthritis (K&L grades 3, 4, or total hip replacement) within 5 years was expressed in OR using generalised estimating equations. Results At baseline, 76% of the included hips had no radiographic signs of osteoarthritis and 24% doubtful osteoarthritis. Within 5 years, 2.76% developed end-stage osteoarthritis. A moderate (α angle >60°) and severe (α angle >83°) cam-type deformity resulted in adjusted OR of 3.67 (95% CI 1.68 to 8.01) and 9.66 (95% CI 4.72 to 19.78), respectively, for end-stage osteoarthritis. The combination of severe cam-type deformity and decreased internal rotation at baseline resulted in an even more pronounced adjusted OR, and in a positive predictive value of 52.6% for end-stage osteoarthritis. For incident osteoarthritis, only a moderate cam-type deformity was predictive OR=2.42 (95% CI 1.15 to 5.06). Conclusions Individuals with both severe cam-type deformity and reduced internal rotation are strongly predisposed to fast progression to end-stage osteoarthritis. As cam impingement might be a modifiable risk factor, early recognition of this condition is important.

The Development of Cam-Type Deformity in Adolescent and Young Male Soccer Players

Background: Cam impingement is a well-recognized cause of hip pain and might cause osteoarthritis of the hip. Clinically, cam impingement is mostly observed in young, active male patients, but only a few studies have focused on the manifestation of cam-type deformities during skeletal development. Purpose: To determine the age of onset and prevalence of cam-type deformities in young male soccer players versus controls. Study Design: Cross-sectional study; Level of evidence, 3. Methods: In this study, 89 elite preprofessional soccer players and 92 controls aged 12 to 19 years were included. In the soccer players, range of motion and impingement tests were performed. Both an anteroposterior (AP) pelvic radiograph and a frog-leg lateral radiograph of the hip were obtained according to a standardized protocol. Controls with both an AP pelvic and a frog-leg lateral radiograph and no hip disorders were obtained from radiology databases. The α angle was automatically determined in all radiographs, using a threshold value of 60° to define a cam-type deformity. Further, all radiographs were scored using a 3-point scoring system. The anterosuperior head-neck junction was classified as (1) normal, (2) flattened, or (3) having a prominence. Differences in prevalence were tested using logistic regression. Differences in range of motion were calculated using generalized estimating equations. Results: An α angle >60° was already found at the age of 12 years in some soccer players and controls. A cam-type deformity defined by α angle tended to be more prevalent in soccer players (26%) than in controls (17%; P = .31). In 13% of soccer players, a prominence was visible on radiographs and was first seen at the age of 13 years. The anterosuperior flattening (56% vs 18%, P = .0001) and prominence (13% vs 0%, P < .03) were more prevalent in soccer players than in controls. Conclusion: Cam-type deformities were recognizable and present from the age of 13 years and were more prevalent in soccer players than in their nonathletic peers. Cam-type deformity develops during adolescence and is likely to be influenced by high-impact sports practice.

Selective laser melting-produced porous titanium scaffolds regenerate bone in critical size cortical bone defects.

Porous titanium scaffolds have good mechanical properties that make them an interesting bone substitute material for large bone defects. These scaffolds can be produced with selective laser melting, which has the advantage of tailoring the structures architecture. Reducing the strut size reduces the stiffness of the structure and may have a positive effect on bone formation. Two scaffolds with struts of 120‐µm (titanium‐120) or 230‐µm (titanium‐230) were studied in a load‐bearing critical femoral bone defect in rats. The defect was stabilized with an internal plate and treated with titanium‐120, titanium‐230, or left empty. In vivo micro‐CT scans at 4, 8, and 12 weeks showed more bone in the defects treated with scaffolds. Finally, 18.4 ± 7.1 mm3 (titanium‐120, p = 0.015) and 18.7 ± 8.0 mm3 (titanium‐230, p = 0.012) of bone was formed in those defects, significantly more than in the empty defects (5.8 ± 5.1 mm3). Bending tests on the excised femurs after 12 weeks showed that the fusion strength reached 62% (titanium‐120) and 45% (titanium‐230) of the intact contralateral femurs, but there was no significant difference between the two scaffolds. This study showed that in addition to adequate mechanical support, porous titanium scaffolds facilitate bone formation, which results in high mechanical integrity of the treated large bone defects.

A Cam Deformity Is Gradually Acquired During Skeletal Maturation in Adolescent and Young Male Soccer Players A Prospective Study With Minimum 2-Year Follow-up

Background: A cam deformity is a major risk factor for hip osteoarthritis, and its formation is thought to be influenced by high-impact sporting activities during growth. Purpose: To (1) prospectively study whether a cam deformity can evolve over time in adolescents and whether its formation only occurs during skeletal maturation and (2) examine whether clinical or radiographic features can predict the formation of a cam deformity. Study Design: Cohort study (prognosis); Level of evidence, 2. Methods: Preprofessional soccer players (N = 63; mean age, 14.43 years; range, 12-19 years) participated both at baseline and follow-up (mean follow-up, 2.4 ± 0.06 years). At both time points, standardized anteroposterior and frog-leg lateral radiographs were obtained. For each hip, the α angle was measured, and the anterosuperior head-neck junction was classified by a 3-point visual system as normal, flattened, or having a prominence. Differences between baseline and follow-up values for the α angle and the prevalence of each visual hip classification were calculated. Additionally, the amount of internal hip rotation, growth plate extension into the neck, and neck shaft angle were determined. Results: Overall, there was a significant increase in the prevalence of a cam deformity during follow-up. In boys aged 12 and 13 years at baseline, the prevalence of a flattened head-neck junction increased significantly during follow-up (13.6% to 50.0%; P = .002). In all hips with an open growth plate at baseline, the prevalence of a prominence increased from 2.1% to 17.7% (P = .002). After closure of the proximal femoral growth plate, there was no significant increase in the prevalence or increase in severity of a cam deformity. The α angle increased significantly from 59.4° at baseline to 61.3° at follow-up (P = .018). The amount of growth plate extension was significantly associated with the α angle and hip classification (P = .001). A small neck shaft angle and limited internal rotation were associated with cam deformities and could also significantly predict the formation of cam deformities (α angle >60°) at follow-up. Conclusion: In youth soccer players, cam deformities gradually develop during skeletal maturation and are probably stable from the time of growth plate closure. The formation of a cam deformity might be prevented by adjusting athletic activities during a small period of skeletal growth, which will have a major effect on the prevalence of hip osteoarthritis.

Osteoarthritis Induction Leads to Early and Temporal Subchondral Plate Porosity in the Tibial Plateau of Mice An In Vivo Microfocal Computed Tomography Study

OBJECTIVE In osteoarthritis (OA), changes occur in both cartilage and subchondral bone. The subchondral bone plate facilitates normal cross-talk between articular cartilage and trabecular subchondral bone, and adaptive changes in the plate due to OA may therefore disturb cross-talk homeostasis. To investigate these changes over time, we examined the cartilage-subchondral bone interface using a combined approach of histologic analysis and in vivo microfocal computed tomography. METHODS Sixteen-week-old male C57BL/6 mice (n=32) received intraarticular injections of collagenase in 1 joint to induce instability-related OA and received saline injections in the contralateral knee joint (control joint). At 2, 4, 6, 10, and 14 weeks after injection, changes in the tibial subchondral bone plate and subchondral trabeculae were analyzed. RESULTS Two weeks after injection, collagenase-injected joints had significantly more cartilage damage and osteophytosis than did control joints. Osteoclast activity directly underneath the subchondral bone plate was significantly elevated in collagenase-injected joints compared to control joints (mean±SEM osteoclast surface/bone surface 11.07±0.79% versus 7.60±0.81%), causing the plate to become thinner and creating a large increase in subchondral bone plate porosity (mean±SEM cumulative porosity volume 0.05±0.04×10(-3) mm3 in control joints versus 2.52±0.69×10(-3) mm3 in collagenase-injected joints). Four weeks after injection, the previously formed perforations disappeared, coinciding with a significant rise in osteoblast activity in the subchondral trabecular bone in collagenase-injected joints compared to control joints (mean ± SEM bone formation rate/bone surface 0.62±0.13 μm3/μm2 per day versus 0.30±0.03 μm3/μm2 per day). CONCLUSION The current study is the first to provide quantitative longitudinal data on the dynamic changes in the subchondral bone plate after OA induction. The development of plate perforations may enhance mutual interaction between subchondral trabeculae, bone marrow cells, and the articular cartilage in OA.

In vivo imaging of cartilage degeneration using μCT-arthrography

OBJECTIVE In vivo imaging of cartilage degeneration in small animal models is nowadays practically impossible. In the present study, we investigated the use of micro-computed tomography (microCT) in combination with a negatively charged ionic iodine dimer (ioxaglate) for in vivo assessment of cartilage degeneration in a small animal model. METHODS Cartilage degeneration was induced in the right knee of rats by injection of mono-iodoacetate (MIA). We imaged the rat knees with ioxaglate enhanced microCT-arthrography at 4, 16 and 44 days after MIA injection. Subsequently, microCT-arthrographic findings were evaluated and compared with quantitative histology of the patellar cartilage. RESULTS In vivo microCT-arthrography clearly detected cartilage degeneration in the rat knee-joints, in which the ioxaglate diffused into the degenerated cartilage layer. Higher microCT-attenuation values and smaller total volumes of the cartilage layer were detected at longer time periods after MIA injection, which is quantitatively confirmed by histology. CONCLUSION In vivo microCT-arthrography is a valuable tool for detection of minor cartilage alterations and distinguishes different stages of cartilage degeneration in a small animal model. Since microCT, at the same time, also visualizes osteophyte formation and changes in the underlying subchondral bone structures, the technique will be very useful for longitudinal overall assessment of the development of (osteo)arthritis and to study interventions in small animal models.

Osteoarthritis Susceptibility Genes Influence the Association Between Hip Morphology and Osteoarthritis

OBJECTIVE The identified osteoarthritis (OA) susceptibility genes are mainly active in skeletal development and could thus affect joint geometry. Because nonoptimal joint geometry is a risk factor for the development of OA, we investigated if and how the path that leads from nonoptimal joint geometry to OA of the hip is influenced by these genes. METHODS The shape of the hips of subjects in the Genetics, Osteoarthritis and Progression Study, consisting of sibling pairs with symptomatic OA at multiple joint locations, was quantified by applying a statistical shape model to radiographs. Shape aspects (modes) were correlated to OA characteristics. We then tested for the association of shape modes with OA susceptibility single-nucleotide polymorphisms (SNPs) of GDF5, FRZB, and DIO2. RESULTS Four of 23 shape modes (mode 1, mode 17, mode 18, and mode 21) were strongly associated with OA characteristics. We observed a significant interaction between carrier status of DIO2 rs12885300 and hip OA characteristics for mode 1 (P = 0.005). This indicates that this specific aspect of hip shape correlates with OA characteristics only in carriers of the susceptibility allele. CONCLUSION Our results suggest that it is more likely that the rs12885300 SNP of DIO2 increases the vulnerability of cartilage to nonoptimal bone shapes rather than directly influencing the formation of these shapes.

Cam impingement of the hip—a risk factor for hip osteoarthritis

Femoroacetabular impingement (FAI) is characterized by abnormal contact between the proximal femur and the acetabulum. Two subtypes have been described: pincer impingement, caused by an overcovered acetabulum; and cam impingement, which occurs as a result of an aspherical femoral head (cam abnormality). A strong correlation exists between cam impingement and the subsequent development of hip osteoarthritis (OA). Major cam abnormalities confer a high risk of OA. However, the association between cam abnormalities and the pathology of OA has been difficult to compare between studies, as different methods have been used to define the abnormality. Cam abnormalities are acquired during skeletal growth and could be influenced by high impact sporting activities. Preventative treatments aiming to reduce the incidence of cam abnormalities and subsequent OA could, therefore, be developed. In this Perspective, we discuss the current understanding of FAI, focusing on cam abnormalities and their association with OA.