The Transcription Factor HAND1 Is Involved in Cortical Bone Mass through the Regulation of Collagen Expression.

Temporal and/or spatial alteration of collagen family gene expression results in bone defects. However, how collagen expression controls bone size remains largely unknown. The basic helix-loop-helix transcription factor HAND1 is expressed in developing long bones and is involved in their morphogenesis. To understand the functional role of HAND1 and collagen in the postnatal development of long bones, we overexpressed Hand1 in the osteochondroprogenitors of model mice and found that the bone volumes of cortical bones decreased in Hand1Tg/+;Twist2-Cre mice. Continuous Hand1 expression downregulated the gene expression of type I, V, and XI collagen in the diaphyses of long bones and was associated with decreased expression of Runx2 and Sp7/Osterix, encoding transcription factors involved in the transactivation of fibril-forming collagen genes. Members of the microRNA-196 family, which target the 3' untranslated regions of COL1A1 and COL1A2, were significantly upregulated in Hand1Tg/+;Twist2-Cre mice. Mass spectrometry revealed that the expression ratios of alpha 1(XI), alpha 2(XI), and alpha 2(V) in the diaphysis increased during postnatal development in wild-type mice, which was delayed in Hand1Tg/+;Twist2-Cre mice. Our results demonstrate that HAND1 regulates bone size and morphology through osteochondroprogenitors, at least partially by suppressing postnatal expression of collagen fibrils in the cortical bones.

A comparative evaluation of tibial metaphyseal-diaphyseal angle changes between physiologic bowing and Blount disease.

The purpose of this study was to estimate the rate of spontaneous improvement in tibial metaphyseal-diaphyseal angle (TMDA) in physiologic bowing in comparison to that in Blount disease and to provide reference values of TMDA for monitoring patients with highly suspected to have Blount disease.We retrospectively reviewed patients with physiologic bowing meeting the following criteria:(1) TMDA greater than 9° before 36 months of age at initial evaluation;(2) two or more standing long bone radiographs available; and(3) follow-up conducted up to resolution of deformity.Patients with Blount disease had(1) more than 2 standing long bone radiographs obtained before 36 months of age and(2) underwent no treatment during the period in which these images were obtained.TMDA measurements were obtained from 174 patients with physiologic bowing and 32 patients with Blount disease. Rates of TMDA improvement were adjusted by multiple factors using a linear mixed model, with sex and laterality as fixed effects and age and individual patients as the random effects.In the physiologic bowing group, TMDA improved significantly, by 3° per 6 months and by 6° per year. Changes in TMDA were not significant in the Blount disease group.Knowing the rate of TMDA change can be helpful for physicians seeking to monitor infants with suspected as having Blount disease with a high TMDA and to avoid unnecessary repeat radiographic evaluations.

Growth of the New Thumb Metacarpal After Pollicization for Thumb Hypoplasia.

PURPOSE: To investigate the radiographic length and width of the new thumb metacarpal in relation to the middle finger proximal phalanx; to assess the incidence of premature physeal closure of the new metacarpal; and to consider whether there is a relationship between growth characteristics and the presence of union or nonunion of the new trapezium to the retained index finger metacarpal base. METHODS: Forty pollicizations were assessed with preoperative or immediate postoperative radiographs and follow-up radiographs to establish the growth characteristics of the new thumb metacarpal. Functional outcomes comprising grip strength, pinch strength, and range of motion were correlated with radiological findings of presence or absence of open physes and presence or absence of union of the new trapezium to the metacarpal base. RESULTS: The new thumb metacarpal physis was open in 28 pollicizations and closed in 12. In the latter group, all physes of the hand had closed indicating skeletal maturity. The length and width indices of the new thumb metacarpal in relation to the middle finger proximal phalanx were equivalent to or greater than the perioperative growth indices. There was a reduced postoperative length ratio in those patients with nonunion of the new trapezium to the base of the metacarpal. There was no change in strength and range of motion parameters with growth other than that related to normal improvement with age. CONCLUSIONS: We are unable to demonstrate premature physeal closure following routine pollicization. The growth of the metacarpal continues in a normal manner to skeletal maturity. A failure of union of the new trapezium to the metacarpal base may compromise growth. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Differential effects of exercise on tibial shaft marrow density in young female athletes.

CONTEXT: Increased mechanical loading can promote the preferential differentiation of bone marrow mesenchymal stem cells to osteoblastogenesis, but it is not known whether long-term bone strength-enhancing exercise in humans can reduce marrow adiposity. OBJECTIVE: Our objective was to examine whether bone marrow density (MaD), as an estimate of marrow adiposity 1) differs between young female athletes with contrasting loading histories and bone strengths and 2) is an independent predictor of bone strength at the weight-bearing tibia. DESIGN: Mid-tibial MaD, cortical area (CoA), total area, medullary area, strength strain index (SSI), and cortical volumetric bone mineral density (vBMD) (total, endocortical, midcortical, and pericortical) was assessed using peripheral quantitative computed tomography in 179 female athletes involved in both impact and nonimpact loading sports and 41 controls aged 17-40 years. RESULTS: As we have previously reported CoA, total area, and SSI were 16% to 24% greater in the impact group compared with the controls (all P < .001) and 12% to 18% greater than in the nonimpact group (all P < .001). The impact group also had 0.5% higher MaD than the nonimpact and control groups (both P < .05). Regression analysis further showed that midtibial MaD was significantly associated with SSI, CoA, endocortical vBMD, and pericortical vBMD (P < .05) in all women combined, after adjusting for age, bone length, loading groups, medullary area, muscle cross-sectional area, and percent fat. CONCLUSION: In young female athletes, tibial bone MaD was associated with loading history and was an independent predictor of tibial bone strength. These findings suggest that an exercise-induced increase in bone strength may be mediated via reduced bone marrow adiposity and consequently increased osteoblastogenesis.

Predictors of recurrent instability after acute patellofemoral dislocation in pediatric and adolescent patients.

BACKGROUND: Patellofemoral instability is common in the pediatric and adolescent population, yet prognosis after the first dislocation has been difficult to determine. PURPOSE: To describe the demographics of pediatric and adolescent patients with a first-time patellofemoral dislocation and to determine predictors of recurrent instability. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A search of the Mayo Medical Index database between 1998 to 2010 was performed, and 2039 patients were identified. Inclusion criteria were (1) age 18 years or younger, (2) no history of patellofemoral subluxation/dislocation of the affected knee, (3) radiographs within 4 weeks of the initial instability episode, and (4) a dislocated patella requiring reduction or convincing history/findings suggestive of acute patellar dislocation (effusion/hemarthrosis, tenderness along medial parapatellar structures, and apprehension with lateral patellar translation). Radiographs were evaluated for trochlear dysplasia (Dejour classification) and patella alta (Caton-Deschamps and Insall-Salvati indices). Skeletal maturity was graded based on the distal femoral and proximal tibial physes (open, closing, or closed). RESULTS: A total of 222 knees (120 male [54.1%] and 102 female [45.9%]) in 210 patients with an average age of 14.9 years (range, 9-18 years), met the inclusion criteria. Twenty-four patients (10.8%) underwent early surgery. All others were initially treated nonoperatively. Of the 198 patients in this group, 76 (38.4%) had recurrent instability, and 39 (51.3%) of these required surgical treatment. Recurrent instability was associated with trochlear dysplasia (P < .01). Patients with both immature physes and trochlear dysplasia had a recurrence rate of 69% (33/48), with a hazard ratio of 3.3. Age, sex, body mass index, and patella alta were not statistically associated with recurrent instability. CONCLUSION: Nonoperative treatment for first-time patellofemoral dislocation resulted in a 62% success rate. However, skeletally immature patients with trochlear dysplasia had only a 31% success rate with nonoperative management. Nearly half of patients with recurrent instability required surgical intervention to gain stability.

Increasing participation of sclerostin in postnatal bone development, revealed by three-dimensional immunofluorescence morphometry.

Confocal immunofluorescence tiling imaging revealed the spatio-temporal distributions of osterix and sclerostin in femurs from 3-day-old, 2-week-old and 4-week-old rats to be reciprocally exclusive at the tissue level. Further quantitative three-dimensional immuno fluorescence morphometry demonstrated the increasing distribution of sclerostin in the osteocytic lacuno-canalicular system specifically in diaphysis, which paralleled the cooperative participation and depletion of osterix and ß-catenin in adjacent periosteum cells. Treating MC3T3-E1 cells with BIO (a GSK3 inhibitor) induced the stabilization of ß-catenin and nuclear translocation of osterix, and negatively regulated osteocalcin/BGLAP and Dmp1. These results collectively demonstrate that the increasing distribution of sclerostin in diaphyseal cortical bone appears to be involved in the attenuation of osterix and ß-catenin in adjacent periosteum cells, thus possibly contributing to osteoblast maturation and reducing the osteoblast formation at this bone site. Our confocal microscopy-based imaging analyses provide a comprehensive and detailed view of the spatio-temporal distribution of sclerostin, ß-catenin and osterix at the tissue to subcellular level in a coherent manner, and uncovered their spatio-temporal cooperation in postnatal bone development, thus providing evidence that they link skeletogenic growth and functional bone development.

Growth potential of different zones of the growth plate-an experimental study in rabbits.

Despite clinical efforts to treat growth disturbances only little is known about the growth potential of the different zones of the growth plate. The aim of this study was to investigate the growth potential of different zones of the growth plate. A total of 20 New Zealand White rabbits were used for this experiment. The right and left ulna of each animal were used resulting in a total of 40 ulnae. Animals were assigned into five groups. In groups I and II resection of the metaphyseal (n = 12) or the epiphyseal (n = 6) segment of the growth plate was performed. In group III resection of the growth plate and re-implantation was performed (n = 6). In group IV the growth plate was resected and re-implanted after a 180° rotation (n = 6). Animals in group V served as controls. Histologic and radiologic examinations were performed to evaluate the growth process at 1, 2, 4, and 12 weeks following surgery. In group I, III, and IV temporary growth disturbance which was compensated within a short time was observed. Resection of the epiphyseal part resulted in growth arrest of the distal ulna in combination with normal growth of the radius which led to and valgus deformity of the limb. The results of this study indicate the importance of the reserve zone for the functioning of the growth plate.

Aneurysmal bone cysts recur at juxtaphyseal locations in skeletally immature patients.

Aneurysmal bone cysts are associated with a high rate of recurrence. Many aneurysmal bone cysts arise near open physes or articular cartilage in skeletally immature patients. Fear of damaging these structures could cause surgeons to curette the tumors less aggressively. We hypothesized location of an aneurysmal bone cyst in a periarticular or juxtaphyseal location would increase the risk of recurrence. We retrospectively studied 53 patients with aneurysmal bone cysts treated between 1989 and 2004. All patients had primary disease, and all patients underwent curettage of the lesion. Ten patients (18.9%) had local recurrence. Gender, race, and size did not predict recurrence; however 12 years of age or younger was associated with recurrence. Of the 19 juxtaphyseal cysts directly adjacent to an open physis, eight developed recurrence. Of the five periarticular cysts, two developed recurrence. The data suggest the risk of recurrence is highest in pediatric patients with juxtaphyseal or periarticular aneurysmal bone cysts. Meticulous treatment of these cysts is necessary, but we believe an overly aggressive approach that destroys the physis or articular cartilage is not warranted. Preservation of these structures remains a high priority of treatment.

[Formation of ossification nucleus in the femoral head in hamsters exposed to laser radiation].

The purpose of the study was to detect the relation between the formation of ossification nucleus in the epiphysis and the ingrowth of vessels into it, using laser radiation of femoral heads. The study was performed in 30 golden hamsters, 20 of them starting at 10 days after birth were exposed to daily irradiation of the right hip joint (during 3-80 days). The left joint was used as control. The radiation was performed with Agnis laser device (radiation power--2 mW, impulse frequency--2500 Hz, exposure duration--8 min, optical fiber diameter--4 mm). Femoral bones of experimental and control animals were histologically studied at days 13 till 90. Laser radiation was found could delay vessel growth from diaphysis into epiphysis for up to 13 days, and the beginning of ossification nucleus formation in the femoral head--for up to 5 days. This suggests the direct relation of the development of bone ossification nucleus in the epiphysis and growing of vessels into its cartilage, since no other factors retarding the vessel growth and formation of bone nucleus were used.

Evidence for overgrowth after midfemoral fracture via increased RNA for mitosis.

Middiaphyseal femoral fractures in children and young rats stimulate linear femoral growth, a phenomenon commonly attributed to increased vascularity. To test for changes in mRNA expression of genes related to blood vessels, nerve fibers, cartilage, bone, and cell metabolism, we measured mRNA gene expression for all known rat genes in the physis at various times after diaphyseal fracture. Female Sprague-Dawley rats, 4 weeks of age at surgery, were subjected to a unilateral, simple, transverse, middiaphyseal femoral fracture stabilized with an intramedullary rod. At 0 (intact), 0.1, 0.4, 1, 2, 3, 4, and 6 weeks after fracture, the femoral head with the proximal physis was collected from fractured and intact femora. The RNA was extracted, processed to biotinlabeled cRNA, and hybridized to Affymetrix Rat 230 2.0 GeneChip microarrays. Transcripts from fracture-induced lengthening of the injured femora were compared to those of the intact contralateral femur. In the proximal physis, transcripts related to blood vessels and cartilage formation were down-regulated by fracture. Transcripts related to bone remodeling, nerve axon elongation, cell division, and protein synthesis were up-regulated by fracture. The data support increased mitotic activity in the physis after a midshaft fracture and not increased vascularity.

Interstitial growth of bone revisited.

The distance between two or more metallic implants placed within the same flat bones (mandible, nasal, frontal, hyoplastron, hypoplastron) of young pigs, rabbits, and turtles followed by means of serial radiographs, remained the same for periods as long as 546 days. Thus, it is concluded that there is no interstitial growth. In 1743, Duhamel demonstrated that long bones grow at their ends and that there is no interstitial growth. This report is unique in that it demonstrates by use of radiopaque implants and serial radiographs that there is no interstitial growth of flat bones, which grow by apposition and resorption, and not endochondrally, such as occurs in long bones.

An assessment of ADAMs in bone cells: absence of TACE activity prevents osteoclast recruitment and the formation of the marrow cavity in developing long bones.

ADAMs (A Disintegrin And Metalloprotease domain) are metalloprotease-disintegrin proteins that have been implicated in cell adhesion, protein ectodomain shedding, matrix protein degradation and cell fusion. Since such events are critical for bone resorption and osteoclast recruitment, we investigated whether they require ADAMs. We report here which ADAMs we have identified in bone cells, as well as our analysis of the generation, migration and resorptive activity of osteoclasts in developing metatarsals of mouse embryos lacking catalytically active ADAM 17 [TNFalpha converting enzyme (TACE)]. The absence of TACE activity still allowed the generation of cells showing an osteoclastic phenotype, but prevented their migration into the core of the diaphysis and the subsequent formation of marrow cavity. This suggests a role of TACE in the recruitment of osteoclasts to future resorption sites.