Diaphyseal Bone Research Articles

Glucocorticoids inhibit shaft fracture healing but not metaphyseal bone regeneration under stable mechanical conditions.

ObjectivesHealing in cancellous metaphyseal bone might be different from midshaft fracture healing due to different access to mesenchymal stem cells, and because metaphyseal bone often heals without a cartilaginous phase. Inflammation plays an important role in the healing of a shaft fracture, but if metaphyseal injury is different, it is important to clarify if the role of inflammation is also different. The biology of fracture healing is also influenced by the degree of mechanical stability. It is unclear if inflammation interacts with stability-related factors.MethodsWe investigated the role of inflammation in three different models: a metaphyseal screw pull-out, a shaft fracture with unstable nailing (IM-nail) and a stable external fixation (ExFix) model. For each, half of the animals received dexamethasone to reduce inflammation, and half received control injections. Mechanical and morphometric evaluation was used.ResultsAs expected, dexamethasone had a strong inhibitory effect on the healing of unstable, but also stable, shaft fractures. In contrast, dexamethasone tended to increase the mechanical strength of metaphyseal bone regenerated under stable conditions.ConclusionsIt seems that dexamethasone has different effects on metaphyseal and diaphyseal bone healing. This could be explained by the different role of inflammation at different sites of injury.Cite this article: Bone Joint Res 2015;4:170–175.

Metatarsal leiomyosarcoma masquerading as acute osteomyelitis – A diagnostic trap unveiled by vigilant clinical, radiologic and pathologic analysis

Due to overlapping clinical and radiological features, the differentiation between osteomyelitis and bone tumor can be challenging. A 48-year-old lady presented with intermittent left foot pain for a few months. Plain radiographs showed an osteolytic lesion affecting the proximal diaphysis of the left fourth metatarsal bone, with thinning and irregularities of the cortex and focal periosteal reaction. Ultrasonography revealed diffuse subcutaneous edema in the dorsum of the left foot, cortical irregularities along the mid-shaft of the left fourth metatarsal bone, and surrounding periosteal collection. Computed tomography showed medullary expansion along the shaft and base of the left fourth metatarsal bone with cortical irregularities and defects suggestive of cloaca, and focal mild periosteal new bone formation. The clinico-radiologic diagnosis was acute osteomyelitis with periosteal collection. During open biopsy, the finding of intramedullary fleshy tissue in the absence of significant inflammatory edema and purulent discharge, and subsequent negative culture result prompted a review of the histologic slides which was initially reported as benign fibroblastic tissue proliferation. Careful analysis of the histomorphology disclosed a spindle cell sarcoma for which ray amputation of the fourth and fifth metatarsal was performed. The final diagnosis was grade 1 leiomyosarcoma and the patient remained well 33 months after the operation.

Effect of swimming exercise on three-dimensional trabecular bone microarchitecture in ovariectomized rats.

Swimming is generally considered ineffective for increasing bone mass in humans, at least compared with weight-bearing sports. However, swimming exercise has sometimes been shown to have a strong positive effect on bone mass in small animals. This study investigated the effects of swimming on bone mass, strength, and microarchitecture in ovariectomized (OVX) rats. OVX or sham operations were performed on 18-wk-old female Fisher 344 rats. Rats were randomly divided into four groups: sham sedentary (Sham-CON), sham swimming exercised (Sham-SWI), OVX sedentary (OVX-CON), and OVX swimming exercised (OVX-SWI). Rats in exercise groups performed swimming in a water bath for 60 min/day, 5 days/wk, for 12 wk. Bone mineral density (BMD) in right femurs was analyzed using dual-energy X-ray absorptiometry. Three-dimensional trabecular architecture at the distal femoral metaphysis was analyzed using microcomputed tomography (μCT). Geometrical properties of diaphyseal cortical bone were evaluated in the midfemoral region using μCT. The biomechanical properties of femurs were analyzed using three-point bending. Femoral BMD was significantly decreased following ovariectomy. This change was suppressed by swimming. Trabecular bone thickness, number, and connectivity were decreased by ovariectomy, whereas structure model index (i.e., ratio of rod-like to plate-like trabeculae) increased. These changes were also suppressed by swimming exercise. Femurs displayed greater cortical width and maximum load in SWI groups than in CON groups. Together, these results demonstrate that swimming exercise drastically alleviated both OVX-induced decreases in bone mass and mechanical strength and the deterioration of trabecular microarchitecture in rat models of osteoporosis.

Maiasaura, a model organism for extinct vertebrate population biology: a large sample statistical assessment of growth dynamics and survivorship

AbstractFossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological sample of 50 tibiae of the hadrosaurid dinosaurMaiasaura peeblesorumallows predictions of annual growth and ecological interpretations based on more histologic data than any previous large sample study. Tibia length correlates well (R2>0.9) with diaphyseal circumference, cortical area, and bone wall thickness, thereby allowing longitudinal predictions of annual body size increases based on growth mark circumference measurements. With an avian level apposition rate of 86.4 μm/day,Maiasauraachieved over half of asymptotic tibia diaphyseal circumference within its first year. Mortality rate for the first year was 89.9% but a seven year period of peak performance followed, when survivorship (mean mortality rate=12.7%) was highest. During the third year of life,Maiasauraattained 36% (x=1260 kg) of asymptotic body mass, growth rate was decelerating (18.2 μm/day), cortical vascular orientation changed, and mortality rate briefly increased. These transitions may indicate onset of sexual maturity and corresponding reallocation of resources to reproduction. Skeletal maturity and senescence occurred after 8 years, at which point the mean mortality rate increased to 44.4%. Compared withAlligator, an extant relative,Maiasauraexhibits rapid cortical increase early in ontogeny, whileAlligatorcortical growth is much lower and protracted throughout ontogeny. Our life history synthesis ofMaiasaurautilizes the largest histological sample size for any extinct tetrapod species thus far, demonstrating how large sample microanalyses strengthen paleobiological interpretations.

MORPHOLOGICAL STRUCTURE OF THE HUMERUS WITH IMPLANTATION INTO THE TIBIAL BONE HYDROXYAPATITE MATERIAL OC-015, ALLOYED BY MANGANESE

In the experiment on 252 albino rats with initial body weight of 135-145g it is established, that making the defect 2,2 mm in diameter on the border of proximal metaphysis and diaphysis of the tibial bone is accompanied by decrease of a mechanical strength of the humeral bones. At the same time the amplitude of deviations depends on the degree of activity of reparative regeneration processes. Implantation of biogenic hydroxylapatite ОC- 015 into the area of defect is accompanied by similar deviations which are completely leveled to the late terms of observation. Implantation of ОC-015 into the osseous defect, alloyed by manganese, substantially smoothes the deviations found.

CORR Insights(®): Is There a Benefit to Modularity in 'Simpler' Femoral Revisions?

Where Are We Now? Cementless distal fixation for femoral revision is an established and effective surgical technique [1, 3]. Failure of these femoral revisions at 10 years is typically less than 10%. However, the failure rate is correlated with the extent of femoral bone loss. When the femoral diaphyseal bone is damaged or of poor quality, failure of distal fixation increases [3]. Modular body femoral stems were developed to facilitate reconstruction of the most difficult femoral revisions. The modular construct allows surgeons to improve distal fixation with a wide range of distal implant sizes and shapes. After the distal segment is secured, the modular proximal body is attached; this step typically offers the surgeon many options in terms of lengths as well as the ability to control rotation independently from the distal stem portion. Potential advantages of modular-body revision stems include easier surgery, better restoration of leg length, and a lower likelihood of hip dislocation. The disadvantages include the potential for mechanical failure of the modular junction and increased cost. Some surgeons use modular body stems for femoral revisions that show only mild or moderate femoral bone loss. We must recognize that the present healthcare environment places a major emphasis on value-based care. In light of that, and given the disadvantages of modular body stems, should surgeons continue to use these components for milder femoral bone loss when nonmodular body stems have been proven to be effective for these defects? The authors addressed this question with a retrospective multicenter study. In their study, the authors also determined the relative value of modular and monoblock femoral components. While rerevisions were less common in patients treated with modular stems, intraoperative fractures were more common in this group. Modular stems also failed to show benefits in terms of the risk of dislocation or the likelihood of osseointegration. Because the authors could not conclude superiority of one technique they recommended avoidance of unnecessary modularity in patients that have lesser degrees of femoral bone loss. Where Do We Need To Go? The addition of patient satisfaction, function, and quality of life scores would be an important topic to address in future studies comparing these two techniques. This is illustrated in a similar retrospective single-center study that compared tapered modular body implants to extensively porous coated implants for femoral revision [2]. In that study, all patients were retrospectively administered WOMAC, SF-12, Oxford-12, UCLA activity score, and satisfaction scores. Richards and colleagues found that the tapered fluted modular body stems had better patient scores that supported the authors’ recommendation for these stems. Studies about our reconstructive techniques should measure and present patient-reported outcomes whenever possible; without those, an important angle in the value equation—the patient's perspective—cannot be inferred. How Do We Get There? As researchers, we should look for funding to perform prospective randomized trials. Specialty societies might be able to fund studies of this type. One of the main expenses of a prospective randomized study is the cost and time it takes to complete enrollment. This topic may be easier than some to investigate in the context of a randomized trial because a number of important elements already are in place: The implants are approved for use, most revision hip surgeons are facile with both approaches, and the patterns of bone loss that we are most interested in here (namely, mild to moderate bone loss) are common. The fact that the study by Huddleston and colleagues could not determine superiority of one implant over the other illustrates the need for a prospective randomized trial and provides much of the data for the power analysis, which is needed to design such a study. Although the current study has a lower level of evidence, it was the first to ask an important question regarding modular body stems: Should surgeons continue to use these components for milder femoral bone loss when nonmodular body stems are proven to be effective for these defects? Future researchers inspired by the current study—and “empowered” by it, as it were—now can design a study that will be able to answer the question more definitively.

Thrombospondin-2 deficiency in growing mice alters bone collagen ultrastructure and leads to a brittle bone phenotype.

Thrombospondin-2 (TSP2) is a matricellular protein component of the bone extracellular matrix. Long bones of adult TSP2-deficient mice have increased endosteal bone thickness due to expansion of the osteoblast progenitor cell pool, and these cells display deficits in osteoblastic potential. Here, we investigated the effects of TSP2 deficiency on whole bone geometric and mechanical properties in growing 6-wk-old male and female wild-type and TSP2-knockout (KO) mice. Microcomputed tomography and mechanical testing were conducted on femora and L2 vertebrae to assess morphology and whole bone mechanical properties. In a second series of experiments, femoral diaphyses were harvested from wild-type and TSP2-KO mice. Detergent-soluble type I collagen content was determined by Western blot of right femora. Total collagen content was determined by hydroxyproline analysis of left femora. In a third series of experiments, cortical bone was dissected from the anterior and posterior aspects of the femoral middiaphysis and imaged by transmission electron microscopy to visualize collagen fibrils. Microcomputed tomography revealed minimal structural effects of TSP2 deficiency. TSP2 deficiency imparted a brittle phenotype on cortical bone. Femoral tissue mineral density was not affected by TSP2 deficiency. Instead, transmission electron microscopy revealed less intensely stained collagen fibrils with altered morphology in the extracellular matrix assembled by osteoblasts on the anterior surface of TSP2-KO femora. Femoral diaphyseal bone displayed comparable amounts of total collagen, but the TSP2-KO bones had higher levels of detergent-extractable type I collagen. Together, our data suggest that TSP2 is required for optimal collagen fibrillogenesis in bone and thereby contributes to normal skeletal tissue quality.

Abstract 2272: A novel epigenetic regulator histone demethylase NO66 promotes prostate cancer bone metastasis

Abstract Epigenetic changes by histone methylation that affect expression of key genes linked to progression and metastasis of androgen-independent prostate cancer (PCa) cells remain elusive. Histone demethylase NO66 is a JumonjiC-domain containing histone demethylase specific for H3K4me3 and H3K36me3 and acts as an inhibitor of bone formation. NO66 interacts with EZH2 (enhancer of zeste homolog 2) containing PRC2 (polycomb-repressor complex 2), which has histone K27 methyl transferase activity. EZH2 is amplified and upregulated in advanced and metastatic prostate cancer (PCa). High levels of NO66 are present in several cancers, but the role of NO66, particularly in PCa, is still unknown. We hypothesize that NO66 and EZH2 interactions at the chromatin are critical in the deregulation of key gene expression that promotes PCa progression and metastasis to bone. We found that NO66 levels are increased in prostate cancer patient samples, cell lines and xenografted samples. Our data indicate that forced expression of NO66 in prostate cancer cell lines PC3 and DU-145 promoted proliferation, colony formation, anchorage-independent growth, and invasion of these cells. In contrast, knocked-down of NO66 had reverse effects in those cells. NO66 depletion in DU145 and PC3 resulted in a two- to threefold decrease in colony formation and anchorage-independent growth. We observed that [[Unsupported Character - Symbol Font β]]-Catenin expression at both mRNA and protein levels were decreased in NO66-depleted DU145 cells. RNAseq analysis between DU145 and DU145-NO66shRNA cells revealed that tumor suppressor genes including IRX4, IL32, and the proapoptotic gene NOXA among several candidates are upregulated in DU145-NO66-shRNA. However, expression levels of proliferation/adhesion-associated genes including IGFBP5, FGF5, Wnt pathway genes-WNTs, sFRP, AXIN, TRIB2 are decreased in DU145-NO66shRNA cells. These biochemical and cellular data suggest that NO66 has oncogenic activity to PCa cells. In xenograft studies, femurs of 6 weeks old male SCID mice implanted with PC3 cells that overexpress NO66 (PC-NO66) showed significant femoral bone loss compared with mice that received control PC3 cells. Bone shaft volume and bone mineral density were also decreased in PC-NO66 xenografted femur. Gene expression analysis in xenograft femurs showed that expression of DKK1- a Wnt inhibitor, NFkB, and Cathespin K (CstK), known markers for osteolysis were indeed stimulated in femur of PC3NO66 xenograft. These cell-based and animal studies indicate that NO66 plays an important role in cell proliferation, cell invasion and bone metastasis in prostate cancer. Our data provide several avenues to distinguish aggressive form of prostate cancer from indolent stage based on levels of NO66 and to develop effective treatments by testing epigenetic inhibitors of NO66 and EZH2 for drug therapies. Citation Format: Rozita Bagheri-Yarmand, Sharmistha Lahiri, Xinhai Wan, Nora Navone, Christopher J. Logothetis, Robert F. Gagel, Krishna M. Sinha. A novel epigenetic regulator histone demethylase NO66 promotes prostate cancer bone metastasis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2272. doi:10.1158/1538-7445.AM2015-2272

Skeletal Pathology of Eastern Grey Kangaroos (Macropus giganteus) Exposed to High Environmental Fluoride Levels in South-Eastern Australia

Significantly elevated bone fluoride concentrations have been reported in a population of eastern grey kangaroos (Macropus giganteus) resident near a fluoride-emitting aluminum smelter in southeastern Australia. This paper describes the skeletal and synovial joint lesions observed post mortem in the same sample of kangaroos (n=76). The prevalence and severity of skeletal lesions, specifically the formation of multiple, large, smooth exostoses over the diaphysis of long bones (especially, but not exclusively, on the tibia, fibula and metatarsi), were positively associated with bone fluoride concentration. So too were lesions of degenerative joint disease, including periarticular osteophytosis, articular cartilage erosion/ulceration, synovial hyperplasia and joint capsular fibrosis. Joint lesions were most commonly seen in the knee, hock and metatarsophalangeal joints. This is the first study to describe in detail the full range of lesions induced by chronic fluorosis in a marsupial species.

Morphological Variations of Nutrient Foramina in Lower Limb Long Bones

Background: The major blood supply to long bone is from the nutrient arteries, which enter through nutrient foramina. Nutrient foramen is an opening into the bone shaft which give passage to the blood vessels of the medullary cavity of a bone The direction of the nutrient foramen of all bones is away from growing end and has a particular position for each bone. Objective: The aim of the present study was to study the topographic anatomy and morphology of the nutrient foramina in human adult lower limb long bones. Material and Method: The study was performed on 150 lower limb long bones which included 50 femora, 50 tibiae and 50 fibulae. The bones were obtained from department of anatomy, Punjab Institute of Medical Sciences, Jalandhar. Results: The variations were found in number and location of nutrient foramen in different lower limb long bones. In femur double and triple foramina were observed. Absence of nutrient foramen was observed in femur and fibula. Conclusion: The topographical knowledge of these foramina is useful in certain operative procedures, in orthopedics as well as in plastic and reconstructive surgery, to avoid damage to the nutrient vessels.

Hypertrophic osteopathy in a cat with a concurrent injection-site sarcoma

Case summary An 11-year old neutered female domestic shorthair cat presented for investigation of a large, partially ulcerated skin mass in the area of the left scapula. The cat had been vaccinated 6 weeks previously in the same area. Haematology showed a marked neutrophilia and monocytosis. Tru-cut biopsies were taken and histopathology was consistent with a high-grade soft tissue sarcoma. Thoracic radiographs and abdominal ultrasound revealed no abnormalities. Moderate mixed (palisading, brush border and smooth) periosteal reaction was seen on the diaphysis of long bones at the time of the radiographic examination. Magnetic resonance imaging of the mass showed infiltration within deeper tissues and the owners elected euthanasia. Post-mortem examination confirmed the presence of hypertrophic osteopathy with a concurrent injection-site sarcoma. No evidence of intra-thoracic or intra-abdominal disease was found.Relevance and novel information To our knowledge, this is the first report where hypertrophic osteopathy has been described in a cat with a soft tissue sarcoma, most likely an injection-site sarcoma.

Osteosclerotic Bone Dysplasia of the Craniofacial Bones

Melorheostosis is a rare sclerosing bone dysplasia which is characterized by a localized, diffuse thickening of the cortical bone mainly affecting diaphysis of long bones, and bones of hand and feet unilaterally. Involvement of the maxillofacial region is rare and the diagnosis is mainly based on radiographic features. We report a rare case of a 5 year old girl with Osteosclerotic Bone Dysplasia (Melorheotosis) of multiple craniofacial bones.

Foreign-Body Granuloma after Metacarpal Fracture Treatment with Absorbable Implants.

Foreign-Body Granuloma after Metacarpal Fracture Treatment with Absorbable Implants.

The Management of Bone Loss of Diaphyseal Tibial Long Bones

The management of segmental defects within the diaphysis of long bones is one of the most challenging problems that the surgeon confronts in his practice. The procedures traditionally used to bridge bone gaps include autogenous bone grafting (1), posterolateral bone grafting (2), transplantation of allograft bone & tibialization of fibula procedures (3,4). All the above traditional methods of management of bone defects sometimes require multiple surgical interventions. The treatment period is long & weight bearing may not be possible while the functional results are often less than satisfactory. Recent studies showed that the G.A. llizarov Technique is a more popular than vascularised bone grafts especially for big bone defects (5).

Did Homo erectus kill a Pelorovis herd at BK (Olduvai Gorge)? A taphonomic study of BK5

New research and excavations at Bell Korongo (BK, Olduvai Gorge, Upper Bed II) have uncovered a dense concentration of megafauna that contributes to our understanding of Homo erectus subsistence strategies around 1.34 Ma. Recent work has yielded clear taphonomic evidence for the exploitation of large-sized animals. The frequency and distribution of cut marks, for example, indicates that hominins enjoyed early access to substantial amounts of meat. This degree of carcass processing, particularly megafauna, suggests that the human group(s) exploiting them were large and had significant nutritional needs. Here, we build upon this work by presenting the first comprehensive taphonomic analysis of the faunal material excavated by the Leakeys at BK between 1952 and 1957 corresponding to 24 Pelorovis oldowayensis. Leakey’s assemblage was biased due to selective collection of the most readily identifiable specimens, among which long bone shafts were not included. The recent assemblage reflects the relevance of using long bone shafts to overcome the equifinality of the alternative scenarios proposed to explain the accumulation of Pelorovis. The analysis of The Olduvai Paleoanthropology and Paleoecology Project’s (TOPPP) recent assemblage sheds light on the reconstruction of hominin strategies of carcass acquisition at BK.

Epoxy putty external skeletal fixation in a tibiotarsal fracture of a wild choroy parakeet (Enicognathus leptorhynchus)

Tibiotarsal fractures are common in birds because in most birds this is the longest, most exposed bone in the leg. Transverse fractures are most common and rotational and shear forces must be stabilized in order to achieve good bone regeneration. A 230g male Slender-billed Parakeet or Choroy parakeet (Enicognathus leptorhynchus), with more than five years of age, was received with non-weight bearing lameness with 24 hours duration. X-rays were taken, and these revealed a closed, complete, non-comminuted transverse fracture of the distal diaphysis of the left tibiotarsal bone. Fixation was planned with 10-minute fast-setting epoxy putty. In order to assess the temperature of polymerization of the epoxy dough and the possibility of heat-bone necrosis, the temperature was recorded every 30 seconds for 12 minutes with three different amounts of the epoxy material in an ex vivo test. The temperature of the pieces reached a peak of 50-60ºC, where the highest peak corresponds to the highest amount of material. When approximately 6g of putty were used, the peak temperature reached only 51ºC. This peak changed to 58ºC when 4 times more epoxy was mixed and measured. If the temperature of the pins inserted in the bone exceeds 70ºC, bone necrosis could occur. In light of these results, the fracture was treated with 6 g of epoxy putty that was allowed to polymerize over a 1A 2/2 external skeletal fixation, with 1-mm pins bent at 90º and joined together with cerclage wire. At 6 weeks after surgery the bird had formed a good primary bone callus, and the external fixators were therefore removed. With this approach a satisfactory recovery of the patient was achieved with normal use of the affected limb.

Ewing's sarcoma of proximal phalanx of the hand with skip metastases to metacarpals.

Ewing's sarcoma is the second most common malignant primary bone tumor of childhood and adolescence affecting mainly the diaphysis of long bones and flat bones. This tumor is extraordinarily rare in small bones of the hand and presents as a swelling with atypical radiological features of cystic and lytic lesion with scant periosteal reaction. The common differential diagnosis include osteomyelitis, tuberculosis, enchondroma and benign tumors. Moreover, skip metastasis to adjacent bones is even rarer. The prognosis of this condition is greatly influenced by the presence of metastasis at presentation, further emphasizing the importance of early diagnosis. Multimodality treatment using surgery, radiotherapy and chemotherapy is currently recommended though no consensus exists. We report a case of Ewing's sarcoma of the little finger proximal phalanx which was initially missed and developed skip metastasis to several metacarpals within 4 months.

Limb bone loading in swimming turtles: changes in loading facilitate transitions from tubular to flipper-shaped limbs during aquatic invasions.

Members of several terrestrial vertebrate lineages have returned to nearly exclusive use of aquatic habitats. These transitions were often accompanied by changes in skeletal morphology, such as flattening of limb bone shafts. Such morphological changes might be correlated with the exposure of limb bones to altered loading. Though the environmental forces acting on the skeleton differ substantially between water and land, no empirical data exist to quantify the impact of such differences on the skeleton, either in terms of load magnitude or regime. To test how locomotor loads change between water and land, we compared in vivo strains from femora of turtles (Trachemys scripta) during swimming and terrestrial walking. As expected, strain magnitudes were much lower (by 67.9%) during swimming than during walking. However, the loading regime of the femur also changed between environments: torsional strains are high during walking, but torsion is largely eliminated during swimming. Changes in loading regime between environments may have enabled evolutionary shifts to hydrodynamically advantageous flattened limb bones in highly aquatic species. Although circular cross sections are optimal for resisting torsional loads, the removal of torsion would reduce the advantage of tubular shapes, facilitating the evolution of flattened limbs.

High Survivorship With Cementless Stems and Cortical Strut Allografts for Large Femoral Bone Defects in Revision THA.

Numerous studies have investigated the clinical and radiographic results of revision THAs with use of cementless stems and cortical strut allografts. However, to our knowledge, no long-term followup studies have evaluated patients undergoing revision THA with use of cortical strut allografts where the allografts provided the primary stability for extensively coated femoral stems in the presence of extensive femoral diaphyseal bone defects. We performed this study to determine (1) validated outcomes scores; (2) radiographic signs of fixation and allograft healing; (3) frequency of complications; and (4) survivorship of the components after use of cortical strut onlay allografts in Types IIIB and IV femoral diaphyseal bone defects. Between 1994 and 2003, we performed 140 revision THAs in 130 patients with Paprosky Types IIIB and IV femoral diaphyseal defects. The patients were treated using extensively coated femoral stems and cortical strut allografts because primary axial or rotational stability could not be achieved without grafting. Ten of the patients (10 hips; 7.7%) were lost to followup or died before 10 years; the remaining 120 patients (130 hips) represent the study group in this retrospective study. There were 66 men and 54 women. Their mean age at the time of index surgery was 59 ± 18 years (range, 36-67 years). The primary diagnosis was predominantly osteonecrosis of the femoral head (53%). The most common reason for revision was aseptic loosening (97%), followed by periprosthetic fracture (3%). The mean time from primary to revision THA was 12 years (range, 8-27 years). The mean duration of followup was 16.1 years (range, 12-20 years). The mean Harris hip score was 39 ± 10 points before revision and improved to 86 ± 14 points at 16 years followup (p = 0.02). The mean preoperative WOMAC score was 62 ± 29 (41-91) points and improved to 22 ± 19 (11-51) points at 16 years followup (p = 0.003). Of the 130 stems, 113 (87%) had bone ingrowth, five (4%) had stable fibrous ingrowth, and 12 (9%) were unstable. All allografts were incorporated. Four hips (3%) had a displaced femoral shaft fracture at the stem tip; four (3%) had a postoperative dislocation; and six (5%) had early postoperative infection. Kaplan-Meier survivorship analysis, with revision or radiographic failure as the endpoint, revealed that the 16-year rate of survival of the components was 91% (95% CI, 0.88%-0.96%). Supportive cortical strut onlay allografts provided high survivorship beyond 12 years of followup in revision THAs. Future studies might compare this approach with allograft-prosthesis composites, proximal femoral replacement, or modular fluted, tapered stems. Level IV, therapeutic study.

Accumulation of type VI collagen in the primary osteon of the rat femur during postnatal development.

In rodents, the long bone diaphysis is expanded by forming primary osteons at the periosteal surface of the cortical bone. This ossification process is thought to be regulated by the microenvironment in the periosteum. Type VI collagen (Col VI), a component of the extracellular matrix (ECM) in the periosteum, is involved in osteoblast differentiation at early stages. In several cell types, Col VI interacts with NG2 on the cytoplasmic membrane to promote cell proliferation, spreading and motility. However, the detailed functions of Col VI and NG2 in the ossification process in the periosteum are still under investigation. In this study, to clarify the relationship between localization of Col VI and formation of the primary osteon, we examined the distribution of Col VI and osteoblast lineages expressing NG2 in the periosteum of rat femoral diaphysis during postnatal growing periods by immunohistochemistry. Primary osteons enclosing the osteonal cavity were clearly identified in the cortical bone from 2 weeks old. The size of the osteonal cavities decreased from the outer to the inner region of the cortical bone. In addition, the osteonal cavities of newly formed primary osteons at the outermost region started to decrease in size after rats reached the age of 4 weeks. Immunohistochemistry revealed concentrated localization of Col VI in the ECM in the osteonal cavity. Col VI-immunoreactive areas were reduced and they disappeared as the osteonal cavities became smaller from the outer to the inner region. In the osteonal cavities of the outer cortical regions, Runx2-immunoreactive spindle-shaped cells and mature osteoblasts were detected in Col VI-immunoreactive areas. The numbers of Runx2-immunoreactive cells were significantly higher in the osteonal cavities than in the osteogenic layers from 2 to 4 weeks. Most of these Runx2-immunoreactive cells showed NG2-immunoreactivity. Furthermore, PCNA-immunoreactivity was detected in the Runx2-immunoreactive spindle cells in the osteonal cavities. These results indicate that Col VI provides a characteristic microenvironment in the osteonal cavity of the primary osteon, and that differentiation and proliferation of the osteoblast lineage occur in the Col VI-immunoreactive area. Interaction of Col VI and NG2 may be involved in the structural organization of the primary osteon by regulating osteoblast lineages.