Orthopaedic management of the patient with osteopetrosis

Injectable double-crosslinked bone cement with enhanced bone adhesion and improved osteoporotic pathophysiological microenvironment for osteoregeneration in osteoporosis

The osteoporotic bone defect caused by excessive activity of osteoclasts has posed a challenge for public healthcare. However, most existing bioinert bone cement fails to effectively regulate the pathological bone microenvironment and reconstruct bone homeostasis in the presence of osteoclast overactivity and osteoblast suppression. Herein, inspired by natural bone tissue, an in-situ modulation system for osteoporotic bone regeneration is developed by fabricating an injectable double-crosslinked PEGylated poly(glycerol sebacate) (PEGS)/calcium phosphate cement (CPC) loaded with sodium alendronate (ALN) (PEGS/CPC@ALN) adhesive bone cement. By incorporating ALN, the organic-inorganic interconnection within PEGS/CPC@ALN results in a 100 % increase in compression modulus and energy dissipation efficiency. Additionally, PEGS/CPC@ALN effectively adheres to the bone by bonding with amine and calcium ions present on the bone surface. Moreover, this in-situ regulation system comprehensively mitigates excessive bone resorption through the buffering effect of CPC to improve the acidic microenvironment of osteoporotic bone and the release of ALN to inhibit hyperactive osteoclasts, and facilitates stem cell proliferation and differentiation into osteoblasts through calcium ion release. Overall, the PEGS/CPC@ALN effectively regulates the pathological microenvironment of osteoporosis while promoting bone regeneration through synergistic effects of drugs and materials, thereby improving bone homeostasis and enabling minimally invasive treatment for osteoporotic defects.

Challenges of Hip and Knee Arthroplasty in Patients With Osteopetrosis

Osteopetrosis is a rare metabolic bone disease, characterized by dysfunction of osteoclasts, resulting in increased bone density and brittleness leading to pathological fractures and bone deformities. Hip and knee osteoarthritis (OA) are common long-term complications in patients with osteopetrosis. Joint arthroplasty surgery remains an effective and recommended treatment for these patients with an end-stage OA because it provides favorable outcomes. However, in osteopetrosis, joint arthroplasty surgery carries an increased risk of complications, and specific preoperative and perioperative considerations are required to deal with the technical challenges related to the disease. The aim of this article was to review some of the key aspects of osteopetrosis, provide technical recommendations, and answer clinically relevant questions related to hip and knee arthroplasty surgery.

Osteosynthesis of an intertrochanteric fracture on osteopetrosis A case report

INTRODUCTION

Osteopetrosis is a rare hereditary disease that can be transmitted in an autosomal recessive or autosomal dominant.

CASE REPORT

Here, we report a case of trochanteric fracture in an 18-year-old boy with an anatomical plate. At the last follow-up, 24 months after surgery, the fracture had healed well, and the patient was not restricted in his activities.

DISCUSSION

Osteopetrosis is a rare bone disease that is mainly caused by osteoclast dysfunction. It results from a remodelling defect that leads to hypermineralization of the skeleton, resulting in bone fragility. Both surgical and nonsurgical management have advantages and disadvantages. Thus, open reduction and anatomic plate fixation remain effective management modalities for trochanteric fractures in osteopetrosis patients.

CONCLUSION

For our patient and as described in the literature, the complication rate decreases as some principles are respected with better consolidation of the osteoporotic fracture.

Surgical outcome of distal tibia Salter Harris II fracture in osteopetrosis patient

INTRODUCTION

Osteopetrosis is a rare genetic disorder characterized by increased bone density. This condition is clinically manifested with a brittle intramedullary structure and reduced bone toughness, increasing the risk of fracture. A limited case has been reported on the management of physeal fracture in patients with osteopetrosis. The objective of this study is to report a rare osteopetrosis patient who sustains Salter-Harris II at the distal tibia with its long-term follow-up along with its literature review.

PRESENTATION OF CASE

We report a case of a four-year-old boy with an established a diagnosis of osteopetrosis brought by the parents to the emergency department after sustaining a fall while playing in the playground. Radiological examination revealed a Salter-Harris type II distal tibial fracture. The patient underwent closed reduction and fixation using the cannulated screw. 18-month postoperative patients have an uneventful healing.

DISCUSSION

Osteopetrosis is caused by impaired osteoclast function and differentiation, leading to impaired in remodelling. Salter-Harris type II distal tibial fracture can be treated by either closed reduction or open reduction. A closed reduction was performed successfully with cannulated screw in his patient.

CONCLUSION

There is a delayed union of fracture in osteopetrosis patient. This will increase the risk of displacement which will eventually resulted in growth disturbance. Delayed weight bearing and stable fixation is highly recommended.

Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

Osteopetrosis is Associated With an Increased Risk for Intraoperative Periprosthetic Fracture in Total Hip Arthroplasty but not in Total Knee Arthroplasty

BACKGROUND

Osteopetrosis is a rare, inherited disorder in which bone remodels to become pathologically dense. There has been a paucity of data evaluating medical and surgical complications following total hip arthroplasty (THA) and total knee arthroplasty (TKA) in this patient population. The objective of this study was to evaluate osteopetrosis as a potential risk factor for medical and surgical complications following THA and TKA.

METHODS

Patients who had a diagnosis of osteopetrosis and underwent THA or TKA from 2010 to 2020 were identified in a national database. A total of 534 THA and 972 TKA patients who had osteopetrosis were identified and compared with matched cohorts of 2,670 and 4,860 patients, respectively. The rates of postoperative medical and surgical complications, hospital readmissions, and emergency room visits were calculated. In addition, reimbursements and lengths of stay were determined. Osteopetrosis patients were then compared to a 5:1 matched cohort without osteopetrosis using logistic regression analyses to control for additional confounding factors.

RESULTS

The osteopetrosis THA group had a substantially higher incidence of intraoperative periprosthetic fracture compared to the matched cohort (1.12% versus 0.19%, Odds Ratio 5.88, P = .005). Patients who had a history of osteopetrosis were not found to be at a significantly increased risk for other investigated medical or surgical complications compared to matched controls following THA or TKA.

CONCLUSION

Patients who had a history of osteopetrosis undergoing elective primary THA are associated with a significantly increased risk for intraoperative periprosthetic fracture. Patients with a history of osteopetrosis undergoing elective primary TKA were not found to be at an increased risk for any of the investigated complications.

A cross-sectional nationwide survey of osteosclerotic skeletal dysplasias in Japan

BACKGROUND

The osteosclerotic skeletal dysplasias (OSSDs) are a heterogeneous group of disorders characterized by systemic bone sclerosis. Little is known about OSSDs because of their rarity. We conducted a cross-sectional nationwide survey of OSSDs and examined the incidence, epidemiology, and therapeutic interventions on these disorders.

METHODS

This study consisted of a two-step survey. The number of patients with OSSDs who had visited medical institutions between April 2017 and March 2018 was reported from a total of 341 facilities (1364 departments from pediatrics, orthopaedic surgery, neurosurgery, and otolaryngology in each facility) by the first questionnaire. In the secondary survey, their clinical features were assessed by collecting demographic data, diagnostic details, current status, family histories, therapeutic interventions, histories of bone fracture and osteomyelitis, severity assessed by the modified Rankin Scale (mRS) and recent lifestyle conditions of the patient by the EQ-5D.

RESULTS

In the first survey, 51 facilities (56 departments) reported one or more OSSDs patients, including 50 patients with osteopetrosis and 57 patients of other OSSDs. Among 87 patients eligible for inclusion in the analysis in the secondary survey, we investigated detailed information on the 42 patients with osteopetrosis. The number of initial visits of osteopetrosis patients during the surveillance period was five per year, indicating that the estimated incidence of osteopetrosis seemed to be 0.6 per 100,000 live births. Eighty-six bone fractures were reported in 22 patients (52%), and interventions of pseudarthrosis were conducted in five patients. Nine patients (23%) showed significant disabilities with the mRS of grade 3 or higher. Neurological complications and severe anemia were the factors that deteriorate patients' quality of life.

CONCLUSIONS

This is the first study to examine the detailed epidemiology of OSSDs in Japan. We demonstrated that the incidence of OSSDs is extremely rare. Bone fragility and delayed fracture healing seem to be important orthopaedic problems for patients with osteopetrosis.

Managing Osteopetrosis in the Complex Polytrauma Orthopedic Patient

Osteopetrosis is a genetic illness defined by defective osteoclasts that are incapable of absorbing adequate amounts of bone. This exceedingly rare disorder has been linked to multiple genetic mutations that have a direct impact on osteoclast function. Osteopetrosis causes bones to become brittle with large amounts of cortical bone formation making patients susceptible to pathologic fractures, pancytopenia, and cranial neuropathies among other sequelae. Known as the “marble bone disease,” this condition can range from as severe as causing death in newborn infants to as mild as an incidental finding of increased cortical thickening in a trauma patient. This case demonstrates an incidental finding of osteopetrosis in a trauma patient who suffered from significant injuries as a result of a high-velocity trauma. The patient was the pedestrian in a car vs pedestrian accident and suffered from a central cord syndrome in his cervical spine, a right humerus fracture, a left subtrochanteric femur fracture, a right tibia fracture, and a right fibula fracture. This case report illustrates the complexity of dealing with a polytrauma patient with osteopetrosis and reviews the literature on the approach to fracture fixation in osteopetrotic individuals. This paper will also discuss current medication recommendations and the current standard of care for optimizing patients with osteopetrosis as well as genetic counseling.

Total Hip Replacements in Patients with Rare Pathologic Conditions Affecting Bone

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As a result of the advances in surgical technique and implant design, total hip arthroplasty (THA) is increasingly offered for the management of osteoarthritis of the hip in patients with fragile or pathologic bone.

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Posttraumatic or congenital deformities associated with fragile or pathologic bone are frequently encountered and necessitate diligent preoperative planning.

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Surgeons should be prepared to evaluate and manage intraoperative iatrogenic fracture.

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While there is limited evidence to date, components made with computer-assisted design can be considered, given the unique and highly variable patient population.

Pediatric Scaphoid Fracture Associated with Osteopetrosis: A Case Report

CASE

A 12-year-old boy with osteopetrosis sustained a scaphoid waist fracture, which has not previously been reported with this condition. Healing was successfully achieved with percutaneous cannulated compression screw fixation, albeit with prolonged healing as is typical for this condition.

CONCLUSION

A lack of osteoclastic remodeling predisposes patients with osteopetrosis to fractures, commonly in long bones. Increased risks of infection, anesthesia, and broken hardware along with limited ability to compress bone may discourage operative management. Internal fixation should still be considered in select cases to limit displacement while allowing early range of motion.

Total Hip Arthroplasty in Patients With Osteopetrosis

BACKGROUND

Osteopetrosis is an inherited bone disease associated with high risk of osteoarthritis and fracture non-union, which can lead to total hip arthroplasty (THA). Bone quality and morphology are altered in these patients, and there are limited data on results of THA in these patients. The goals of this study were to describe implant survivorship, clinical outcomes, radiographic results, and complications in patients with osteopetrosis undergoing primary THA.

METHODS

We identified 7 patients (9 hips) with osteopetrosis who underwent primary THA between 1970 and 2017 utilizing our total joint registry. The mean age at index THA was 48 years and included two males and five females. The mean follow-up was 8 years.

RESULTS

The 10-year survivorship free from any revision or implant removal was 89%, with 1 revision and 1 resection arthroplasty secondary to periprosthetic femoral fractures. The 10-year survivorship free from any reoperation was 42%, with 4 additional reoperations (2 ORIFs for periprosthetic femoral fractures, 1 sciatic nerve palsy lysis of adhesions, 1 hematoma evacuation). Harris hip scores significantly increased at 5 years (P = .04). Five hips had an intraoperative acetabular fracture, and 1 had an intraoperative femur fracture. All postoperative femoral fractures occurred in patients with intramedullary diameter less than 5 mm at a level 10 cm distal to the lesser trochanter.

CONCLUSION

Primary THA in patients with osteopetrosis is associated with good 10-year implant survivorship (89%), but a very high reoperation (58%) and periprosthetic femoral fracture rate (44%). Femoral fractures appear associated with smaller intramedullary diameters.

Genetic Disorders of Bone or Osteodystrophies of Jaws-A Review

Bone is a specialized form of connective tissue, which is mineralized and made up of approximately 28% type I collagen and 5% noncollagenous matrix proteins. The properties of bone are very remarkable, because it is a dynamic tissue, undergoing constant renewal in response to mechanical, nutritional, and hormonal influences. In 1978, "The International Nomenclature of Constitutional Diseases of Bone" divided bone disorders into two broad groups: osteochondrodysplasias and dysostoses. The osteochondrodysplasia group is further subdivided into two categories: dysplasias (abnormalities of bone and/or cartilage growth) and osteodystrophies (abnormalities of bone and/or cartilage texture). The dysplasias form the largest group of bone disorders, hence the loose term "skeletal dysplasia" that is often incorrectly used when referring to a condition that is in reality an osteodystrophy or dysostosis. The word "dystrophy" implies any condition of abnormal development. "Osteodystrophies," as their name implies, are disturbances in the growth of bone. It is also known as osteodystrophia. It includes bone diseases that are neither inflammatory nor neoplastic but may be genetic, metabolic, or of unknown origin. Recent studies have shown that bone influences the activity of other organs, and the bone is also influenced by other organs and systems of the body, providing new insights and evidencing the complexity and dynamic nature of bone tissue. The 1,25-dihydroxyvitamin D3, or simply vitamin D, in association with other hormones and minerals, is responsible for mediating the intestinal absorption of calcium, which influences plasma calcium levels and bone metabolism. Diagnosis of the specific osteodystrophy type is a rather complex process and various biochemical markers and radiographic findings are used, so as to facilitate this condition. For diagnosis, we must consider the possibility of lesions related to bone metabolism altered by chronic renal failure (CRI), such as the different types of osteodystrophies, and differentiate from other possible neoplastic and/or inflammatory pathologies. It is important that the dentist must be aware of patients medical history, suffering from any systemic diseases, and identify the interference of the drugs and treatments to control them, so that we can able to perform the correct diagnosis and propose the most adequate treatment and outcomes of the individuals with bone lesions.

Bilateral Posterior-Stabilized Total Knee Arthroplasty in a Patient With Osteopetrosis and Literature Review

We present a case report of a patient with osteopetrosis and refractory bilateral knees osteoarthritis who underwent bilateral total knee arthroplasties (TKAs). After conservative management has failed, surgical treatment with arthroplasty is an excellent alternative with satisfactory outcomes. TKA in patients with osteopetrosis has only been described in 6 other case studies, none of which underwent bilateral TKA. To perform this procedure, additional attention should be directed toward the presurgical planning because of the amplified difficulty of the procedure and the altered bone biology that increases the risks of intraoperative fractures and markedly extends the time of surgery. This report describes a case of osteopetrosis with refractory osteoarthritis managed with bilateral TKA, the surgical technique and special considerations, complications, and future recommendations.

Skeletal Changes After Hematopoietic Stem Cell Transplantation in Osteopetrosis

Osteopetrosis is a rare skeletal dysplasia resulting from an osteoclast defect leading to increased bone mass and density. Hematopoietic stem cell transplantation can rescue the disease phenotype and prevent complications. However, little is known about the skeletal changes hematopoietic stem cell transplantation induces in patients with this disease. The purpose of this study was to describe the skeletal changes after hematopoietic stem cell transplantation in a retrospective cohort of patients diagnosed with osteopetrosis in one medical center over 13 years. For this purpose, all available epidemiological, hematological, biochemical, and radiographic data were collected and quantitatively analyzed. We found a significant early change in bone metabolism markers coinciding with hematopoietic recovery after stem cell transplantation. Hematopoietic stem cell transplantation induced a later significant improvement in both skeletal mineral distribution and morphology but did not lead to complete radiological normalization. Presumably, changes in bone metabolism, skeletal mineral distribution, and morphology were the result of renewed osteoclast function enabling bone remodeling. We propose that biochemical bone metabolism markers and radiological indices be routinely used to evaluate response to hematopoietic stem cell transplantation in patients with osteopetrosis. © 2020 American Society for Bone and Mineral Research.

Genetic testing is useful in adults with limited phenotypes of genetic skeletal conditions

We show the value of genetic screening in 3 adults with limited phenotypes of three bone sclerosing genetic disease (GD): osteopetrosis (OPT), Camurati-Engelmann disease (CED) and pycnodysostosis.

INTRODUCTION

OPT, CED and pycnodysostosis are three rare bone diseases often diagnosed in childhood. However, some atypical phenotypes raise the problem of delayed diagnosis in adults. Genetic tests may then be useful to establish a formal diagnosis.

METHODS

We report 3 cases of adult patients with symptomatic or asymptomatic bone sclerosing lesions for whom the clinical, radiological and biological explorations were atypical and did not allow a formal diagnosis. These unusual descriptions led to the search for genetic mutations.

RESULTS

These 3 cases of limited phenotypes were associated with unknown or poorly described variants of 3 rare bone genetic diseases.

CONCLUSIONS

Genetic tests proved useful to establish the diagnosis and manage the condition of adults with rare bone sclerosing GD.

Management of early-onset hip osteoarthritis in an adolescent patient with osteopetrosis tarda: a case report

Osteopetrosis (OP) is a group of rare sclerosing bone dysplasia characterized by increased bone density. The benign autosomal dominant form is the most common type. It typically carries a full life expectancy, despite increased propensity for fractures and other musculoskeletal problems, particularly hip osteoarthritis. In the current literature, the youngest OP patient having hip osteoarthritis is 16 years of age and treated with total hip arthroplasty. Within the present study, a 16-year-old female patient with early-onset hip osteoarthritis treated with hip joint debridement and femoral head reshaping is presented. The pain relieved and hip joint movements recovered to almost normal range. At the final follow-up at 2 years after the surgery, the patient was still free of pain and ambulating without restriction. Hip joint debridement and femoral shaping may be beneficial in hip osteoarthritis secondary to OP in adolescents, and may delay hip arthroplasty in a young age.

Lessons Learned from Long-Term Management of Hip Fracture in Patients with Osteopetrosis: A Report of Nine Hips in Five Patients

Background

Treating patients with osteopetrosis is very challenging even in very skilled surgeons with many experiences. We present an account of 5 patients treated for hip fracture related problems occurring throughout their life due to this disease. Difficulties encountered during their treatment prompted us to present some general management principles.

Methods

From January 2003 to December 2016, 5 patients with osteopetrosis (9 hips; 3 men, 2 women), who underwent operative or conservative treatment were retrospectively reviewed. We evaluated their clinical features and rate of union, malunion and post-operative infection.

Results

Four of 5 patients (80%) suffered bilateral fracture, and 8 of 9 fractures (89%) are transverse and occurred at subtrochanteric area resulted from minor trauma. Among 9 hips, surgery was performed in seven hips. Nonunion were found in 3 hips (33%), malunion in 1 hip (11%) and oteomyelitis was developed in 2 hips (22%) at a median of 8.1 years.

Conclusions

Clinical features of hip fracture in osteopetrosis are very similar to atypical subtrochanteric femoral fractures. Patients should be informed of the possibilities of several anticipated complications including the risk of nonunion and infection after surgery.

Osteopetrosis-Anesthetic Considerations for Total Knee Arthroplasty: A Case Report

Autosomal dominant or benign osteopetrosis is a rare genetic disorder of osteoclasts that results in dense but brittle bone structures. Patients with osteopetrosis may be scheduled for total knee arthroplasty to treat painful and functionally limiting osteoarthrosis. A search of the published literature produced no citation concerning anesthesia for patients with autosomal dominant osteopetrosis undergoing total knee arthroplasty. We present a case report detailing our experience and discuss considerations for the care of future patients with autosomal dominant osteopetrosis.

The Use of Distraction Osteogenesis and a Taylor Spatial Frame in the Treatment of a Tibial Shaft Nonunion and Deformity in a Pediatric Patient with Osteopetrosis: A Case Report

CASE

Osteopetrosis is a heritable disease that causes brittle bones that are prone to fracture. Furthermore, these brittle bones have a poor healing response and a high risk of subsequent refracture. Many treatment strategies have been described for initial fracture stabilization; however, there is a paucity of literature describing treatment of refractures and subsequent deformity. We present the long-term results of a unique case in which we used a circular external fixator, the TAYLOR SPATIAL FRAME (Smith & Nephew), to correct a deformity in a patient with osteopetrosis who suffered multiple refractures of the tibia.

CONCLUSION

We propose the potential use of distraction osteogenesis as an option for fracture and deformity treatment in patients with osteopetrosis.

Anterior cervical arthrodesis for chronic hangman's fracture in a patient with osteopetrosis: a case report

INTRODUCTION

Osteopetrosis is a clinical syndrome characterized by the failure of osteoclasts to resorb bone. Affected patients usually suffer from repetitive fractures due to this pathological state. Surgical treatment of these fractures is often complicated by the difficulty of working with the extremely hard and brittle bones. The purpose of this study was to report a case of chronic hangman's fracture in a patient with osteopetrosis who underwent surgery for cervical anterior interbody fusion.

MATERIALS AND METHODS

A 76-year-old woman visited our institute 1 month after injury. Radiographs revealed a type II hangman's fracture with severe translation according to the Levine-Edwards classification. We performed anterior spinal arthrodesis from C2 to C3.

RESULTS

We obtained successful anterior C2-C3 arthrodesis without major complications, but encountered some surgical difficulties in treatment due to hard and brittle bones.

CONCLUSIONS

Anterior cervical arthrodesis can be considered an effective treatment for chronic unstable hangman's fracture in patients with osteopetrosis. However, great care must be taken when performing surgery and continued follow-up is warranted.

Cervical spine fractures in osteopetrosis: a case report and review of the literature

While management of appendicular fractures has been well described in the setting of osteopetrosis, there is limited information on managing fractures of the axial spine. Here we present an osteopetrotic patient with multiple traumatic multiple, comminuted, unstable cervical spinal fractures managed with non-operative stabilization, and provide a review of the pathophysiology, genetic characteristics, and special considerations that must be explored when determining operative versus non-operative management of spinal injury in osteopetrosis. A PubMed query was performed for English articles in the literature published up to June 2016, and used the following search terms alone and in combination: "osteopetrosis", "spine", "fractures", "osteoclasts", and "operative management". Within four months after initial injury, treatment with halo vest allowed for adequate healing. The patient was asymptomatic with cervical spine dynamic radiographs confirming stability at four months. On four-year follow up examination, the patient remained without neck pain, and CT scan demonstrated partially sclerotic fracture lines with appropriate anatomical alignment. In conclusion, external halo stabilization may be an effective option for treatment of multiple unstable acute traumatic cervical spine fractures in patients with osteopetrosis. Given the challenge of surgical stabilization in osteopetrosis, further research is necessary to elucidate the optimal form of treatment in this select patient population.

Diagnosis and Management of Osteopetrosis: Consensus Guidelines From the Osteopetrosis Working Group

BACKGROUND

Osteopetrosis encompasses a group of rare metabolic bone diseases characterized by impaired osteoclast activity or development, resulting in high bone mineral density. Existing guidelines focus on treatment of the severe infantile forms with hematopoietic cell transplantation (HCT) but do not address the management of patients with less severe forms for whom HCT is not the standard of care. Therefore, our objective was to develop expert consensus guidelines for the management of these patients.

METHODS

A modified Delphi method was used to build consensus among participants of the Osteopetrosis Working Group, with responses to an anonymous online survey used to identify areas of agreement and conflict and develop a follow-up survey. The strength of recommendations and quality of evidence was graded using the Grading of Recommendations Assessment, Development and Evaluation system.

RESULTS

Consensus was found in the areas of diagnosis, monitoring, and treatment. We recommend relying on characteristic radiographic findings to make the diagnosis and found that genetic testing adds important information by identifying mutations associated with unique disease complications. We recommend ongoing monitoring for changes in mineral metabolism and other complications, including cranial nerve impingement, anemia, leukopenia, and dental disease. We suggest that calcitriol should not be used in high doses and instead recommend symptom-based supportive therapy for disease complications because noninfantile osteopetrosis has no effective treatment.

CONCLUSIONS

Scarcity of published studies on osteopetrosis reduce the ability to develop evidence-based guidelines for the management of these patients. Expert opinion-based guidelines for this rare condition are nevertheless important to enable improved care.

Successful open reduction and internal fixation for displaced femoral fracture in a patient with osteopetrosis: Case report and lessons learned

RATIONALE

Osteopetrosis is a rare disease that predominantly occurs in descendants of inbreeding families. In the case of fractures happen in patients with osteopetrosis, the choice between operative or conservative treatment is still controversial. Open reduction and internal fixation (ORIF) is a conventional treatment for fractures, and it possesses more applicability than conservative treatment. During this surgical treatment, ensure that bone union in the right way is pivotal to success and simultaneously prevents refracture and displacement after the operation. Herein, we present a case of femoral fracture of a patient with osteopetrosis via open reduction and internal fixation. To illustrate successful factors during the treatment process, we discuss experience combined with literature review following case report.

PATIENT CONCERNS

A 67-year-old man who has diagnosed with osteopetrosis over 20 years ago suffered from pain in the left hip last for more than 1 month and he was incapable of walking recently. Before this incident, he had sustained 4 femoral fractures that treated insufficiently by open reduction surgery.

DIAGNOSIS

Physical, radiological, and biological examinations indicated a femoral subtrochanteric fracture that was overlapping displacement between fracture ends.

INTERVENTIONS AND OUTCOMES

Treated with surgery by open reduction with internal fixation and osteotomy, the fracture united in 12 months, and he returned to walk with full weight bearing, during which no complication occurred.

LESSONS

Open reduction and internal fixation is also suitable for the patient with osteopetrosis, and they have similar union ability to the normal. To guarantee successful treatment, specific strategies of operation and rehabilitation program are necessary.

Guided growth for valgus deformity correction of knees in a girl with osteopetrosis: a case report

Autosomal dominant osteopetrosis (Albers-Schönberg disease) classically displays the radiographic signs of osteosclerosis. The main ADO complications involve the skeleton: low-impact bone fractures, scoliosis and hip osteoarthritis. Management of osteopetrosis-related orthopedic problems is a surgical challenge due to increased bone density. The healing process is very slow in these patients because of bone remodeling defects related to osteoblast function failure. In case of bone deformities, a realignment method should be appropriated to osteopetrosis conditions. This article presents a case report of operative treatment of an 11-year-old girl affected with ADO, who underwent a simultaneous valgus knee deformity correction of both limbs with medial eight-plate epiphysiodesis. Simultaneous correction of valgus deformity on both limbs using an extraperiosteal tension plate technique for medial tibial hemiepiphysiodesis was performed in a girl of 11.5 years old with autosomal dominant osteopetrosis. The treatment duration from surgery to complete deformity correction and removal of plates was 18 months. The final aMPTA was 86° on the right side and 85° on the left side. The correction rate was 0.61°/month (right tibia) and 0.67°/month (left tibia). The MAD correction rate was evaluated as 1.5 mm/month for the right limb and 1.6 mm/month for the left limb. At the moment of plate removal, one screw was broken because of tight fixation in osteopetrotic bone. But it did not compromise the final result. The latest follow-up visit at the age of 14 years 6 months revealed excellent realignment without any deformity relapse. There was no any functional impairment. We consider the guided growth by tension band technique as very interesting and promising solution for treatment of pediatric angular deformity in patients with OP. This method allows to avoid osteotomy and related important risk of delayed union or nonunion frequently observed in osteopetrosis.

Level of evidence: Level IV.

Retrograde locked intramedullary nailing for aseptic supracondylar femoral nonunion following failed locked plating

PURPOSE

To review the outcome of retrograde locked nailing for aseptic supracondylar femoral nonunions following failed locked plating.

METHODS

Records of 20 men and 4 women aged 20 to 57 (mean, 39) years who underwent retrograde locked intramedullary nailing for aseptic supracondylar femoral nonunion following failed locked plating were reviewed. There were 20 closed and 4 open Gustilo type II or IIIA fractures secondary to motor vehicle accidents (n=21) or falls (n=3). Patients had undergone one to 3 operations. The mean time from injury to the present revision surgery was 1.3 years. No patient had a flexion contracture. The locked plate was removed and replaced with a retrograde dynamic locked nail (with or without buttress plate augmentation) followed by bone grafting.

RESULTS

17 men and 4 women were followed up for a mean of 3.4 years. The rest were lost to follow-up. The 21 patients achieved bone union after a mean of 4.3 months. The mean maximal knee flexion improved from 97.1º to 107.6º (p=0.03). Knee function was excellent in one, good in 15, and fair in 5 knees. The fair outcome was due to extension contracture, varus knee deformity, or knee pain. There were 3 malunions with varus deformity of 7º, 8º, and 9º each. No patient had deep infection causing a nonunion. All 21 patients could walk without aids.

CONCLUSION

Retrograde locked intramedullary nailing for aseptic supracondylar femoral nonunions following failed locked plating achieved a high union rate.

Non-total body irradiation myeloablative conditioning with intravenous busulfan and cyclophosphamide in hematopoietic stem cell transplantation for malignant infantile osteopetrosis

HSCT is the only curative treatment for MIOP. We prospectively investigated the outcome of HSCT using intravenous busulfan-based conditioning regimen from 2008 to 2013. Nineteen patients (median age = 17 months) underwent transplantation from HLA-matched related donors (n = 14), HLA-haploidentical related donors (n = 2), partially matched cord blood donors (n = 2), and HLA-matched unrelated donor (n = 1). Bone marrow (n = 9), peripheral blood (n = 8), and cord blood (n = 2) were used as stem cell sources. All but one patient demonstrated primary engraftment. Two patients experienced secondary graft failure. During the follow-up period, three patients showed mixed chimerism (45%, 45%, and 70% of donor cells were engrafted in each one of these patients) but are disease free. Two-yr OS and DFS were 84.2% and 73.7%, respectively. Improvement of visual acuity and partial reversal of mild conductive hearing loss occurred in two and four patients, respectively. The causes of death among three patients were infection, GvHD, and disease progression. In conclusion, due to major side effects of MIOP such as visual and hearing loss, early treatment using myeloablative conditioning without irradiation HSCT is suggested. The use of an HLA-matched related donor seems to be highly successful in this regard. Also, according to results of our study, mixed chimerism may be sufficient to resolve symptoms of disease.

Biofouling of surgical power tools during routine use

Surgical power tools (SPTs) are frequently used in many surgical specialties such as dentistry, orthopaedics, ophthalmology, neurology, and podiatry. They have complex designs that may restrict access to cleaning and sterilization agents and frequently become contaminated with microbial and tissue residues following use. Due to these challenges, surgical power tools can be considered the weak link in the decontamination cycle and present a potential for iatrogenic transmission of infection. We aimed to review the existing literature on the decontamination of surgical power tools and associated iatrogenic transmission of infection. A search of the medical literature was performed using Ovid online using the following databases: Ovid Medline 1950-2014, Embase 1980-2014, and EBM Reviews Full Text--Cochrane DSR, ACP Journal Club, and Dare. Despite challenges to decontamination processes, reported episodes of iatrogenic infection directly linked to SPTs appear rare. This may reflect a true picture but more likely represents incomplete reporting, failure to investigate power tools, or lack of surveillance linking surgical site infections (SSIs) to power tools. Healthcare professionals should be aware of the complexities associated with the decontamination of different SPTs, and should review manufacturers' reprocessing instructions prior to purchase. More clarity is required in the manufacturers' validation of these reprocessing instructions. This particularly applies to the emerging surgical robot systems that present extreme challenges to decontamination between uses. Investigation of cross-infection incidents or SSI surveillance should include an element of assessment of SPT decontamination to further elucidate the contribution of SPTs to skin and soft tissue infections.

Recommendations for fracture management in patients with osteopetrosis: case report

INTRODUCTION

Osteopetrosis is caused by general increase in bone density and obliteration of the medullary canal. Fractures are a frequent complication and their management is considered a challenge due to increased resistance to reaming and screw positioning; reduction maneuvers have to be done more carefully to avoid intraoperative fractures, and there is an increased risk of drill breakage. There is also a higher risk of infection and malunion, which increases the incidence of surgical revisions in this population.

CASE REPORT

55-year-old male with osteopetrosis and a history of two previous proximal femur fractures, who sustained an oblique supracondylar fracture of the left humerus and a simple, intra-articular, rotated fragment with capitelum involvement, as well as a fracture in the base of the coronoid process was admitted in our hospital. We performed an open reduction and internal fixation (ORIF) and 12 months after surgery, the patient's bone has healed and he recovered flexion (110˚) and extension (-10˚) without complications.

DISCUSSION

During ORIF, two drill bits were broken and screw fixation was challenging due to the strength required. Bone overheating was also present during drilling, evidenced by smoke production and increased temperature of both bone and drill bits. Recommendations to avoid these problems include continuous cold saline irrigation, frequent drill bit changing, and spaced cycles with low-speed drilling. Additionally, high-resistance and high-speed electric drill bits can also be effective. Finally, patients should be closely followed postoperatively due to the high incidence of refracture, infection and malunion.

CONCLUSIONS

Fracture fixation in patients with osteopetrosis requires strategies to overcome the technical difficulties found during the procedure. Preoperative planning must include the availability of multiple metal drill bits, electric drills, and bone substitutes, having in mind drilling techniques, drilling speed, and temperature control. Patients should be closely followed to evidence any complications such as infections and malunions.

Osteopetrosis: genetics, treatment and new insights into osteoclast function

Osteopetrosis is a genetic condition of increased bone mass, which is caused by defects in osteoclast formation and function. Both autosomal recessive and autosomal dominant forms exist, but this Review focuses on autosomal recessive osteopetrosis (ARO), also known as malignant infantile osteopetrosis. The genetic basis of this disease is now largely uncovered: mutations in TCIRG1, CLCN7, OSTM1, SNX10 and PLEKHM1 lead to osteoclast-rich ARO (in which osteoclasts are abundant but have severely impaired resorptive function), whereas mutations in TNFSF11 and TNFRSF11A lead to osteoclast-poor ARO. In osteoclast-rich ARO, impaired endosomal and lysosomal vesicle trafficking results in defective osteoclast ruffled-border formation and, hence, the inability to resorb bone and mineralized cartilage. ARO presents soon after birth and can be fatal if left untreated. However, the disease is heterogeneous in clinical presentation and often misdiagnosed. This article describes the genetics of ARO and discusses the diagnostic role of next-generation sequencing methods. The management of affected patients, including guidelines for the indication of haematopoietic stem cell transplantation (which can provide a cure for many types of ARO), are outlined. Finally, novel treatments, including preclinical data on in utero stem cell treatment, RANKL replacement therapy and denosumab therapy for hypercalcaemia are also discussed.

Simple reproducible technique in treatment for osteopetrotic fractures

Osteopetrosis is a rare skeletal condition first described by German radiologist Heinrich Albers-Schonberg. The most important technical difficulty is drilling due to hard bone in patients with osteopetrosis; recommendations have been made to use high-speed electric drill bits. But, the unavailability of this special drill bit in most of the centres makes the job more difficult. The study was conducted from 2009 to 2012; the cases are selected from Outpatients Department of Postgraduate Institute of Medical Education and Research. The patients were in the age group of 10-50 years with a mean age of 26 years. Five cases were included in the study: four patients had subtrochanteric fractures, and one had segmental fracture of the humerus. Open reduction and internal fixation was done in all the fractures using metal-cutting drill bit. The use of metal-cutting drill bit in osteopetrosis not only made our job easy but also prevented thermal necrosis of the bone to a large extent. The union rate was 100 % in our series, and there was no infection in any of our cases. In the treatment for fractures in osteopetrosis, the use of a metal-cutting drill bit along with careful attention to drilling technique can help avoid bit breakage and thermal bone injury that may produce ring sequestrum or destroy the already scant osteogenic cells.

Case report of LCP pediatric hip osteosynthesis of a proximal femoral fracture in a child with marble bone disease

We present a case report demonstrating the experience of the department of pediatric orthopaedics of the University Orthopedic Hospital at Sofia Medical University in the treatment of an intertrochanteric proximal femoral fracture in a child with osteopetrosis. We performed open fracture reduction with stable 120° LCP (Locking Compression Plate) Pediatric hip osteosynthesis. Fracture consolidation and ability to walk without crutches was achieved in a half a year. The presented case is the first for Bulgaria. There are still no publications in the world literature on application of such osteosynthesis in marble bone disease.

Metachronous bilateral subtrochanteric fracture of femur in an osteopetrotic bone: A case report with technical note

Osteopetrosis is a rare inherited skeletal disorder characterized by increased density. The increased fragility of such dense bone results in a greater incidence of fractures, especially around hip and proximal femur. The surgical treatment of such fractures is difficult due to hard but brittle structure of bone. Herein we report a case of bilateral subtrochanteric fracture in an osteopetrotic patient. It was fixed using a dynamic hip screw with plate.

Total knee arthroplasty in osteopetrosis using patient-specific instrumentation

Osteopetrosis is an uncommon endocrine disease characterized by defective osteoclast resorption of bones. This causes a hard, sclerotic, and brittle bone throughout the skeleton. Fractures and unforgiving subchondral bone are common in this condition, both of which can lead to osteoarthritis. Total knee arthroplasty is often the treatment of choice but presents challenges due to the hard and sclerotic bone present throughout the metaphysis and diaphysis of the femur and the tibia. We present a case of knee osteoarthritis in a patient with osteopetrosis who underwent total knee arthroplasty using patient-specific instrumentation. This technique eliminates intramedullary alignment and minimizes drilling, reaming, and saw passes, making it attractive in the setting of diseases such as osteopetrosis to decrease operative time and potential complications.

Successful staged hip replacement in septic hip osteoarthritis in osteopetrosis: a case report

BACKGROUND

Osteopetrosis is a rare, inherited, bone disorder, characterized by osteosclerosis, obliteration of the medullary cavity and calcified cartilage. The autosomal dominant form is compatible with a normal life span, although fractures often result from minimal trauma, due to the pathologic nature of bone. Osteomyelitis is common in patients with osteopetrosis because of a reduced resistance to infection, attributed to the lack of marrow vascularity and impairment of white cell function. Only one case of osteomyelitis of the proximal third of the femur has been previously reported, treated with several repeated debridements and finally with femoral head resection. Here we present for the first time a case of a staged implant of a cementless total hip prosthesis for the treatment of a septic hip in femoral neck nonunion in osteopetrosis.

CASE PRESENTATION

A 36-years-old woman, affected by autosomal dominant osteopetrosis was referred to our department because of a septic hip arthritis associated with femoral neck septic non-union, with draining fistulas. The infection occurred early after a plate osteosynthesis for a closed perthrocanteric fracture of the femur and persisted in spite of osteosynthesis removal, surgical debridement and external fixation. In our hospital the patient underwent accurate debridement, femoral head and greater trochanter resection, preparation of the diaphyseal intramedullary canal and implant of an antibiotic-loaded cement spacer. The spacer was exchanged after one month, due to infection recurrence and four months later, a cementless total hip arthroplasty was implanted, with no clinical and laboratory signs of infection recurrence at two years follow-up.

CONCLUSIONS

In case of hip septic arthritis and proximal femur septic non-union, femoral head resection may not be the only option available and staged total hip arthroplasty can be considered.

Meox2Cre-mediated disruption of CSF-1 leads to osteopetrosis and osteocyte defects

CSF-1, a key regulator of mononuclear phagocyte production, is highly expressed in the skeleton by osteoblasts/osteocytes and in a number of nonskeletal tissues such as uterus, kidney and brain. The spontaneous mutant op/op mouse has been the conventional model of CSF-1 deficiency and exhibits a pleiotropic phenotype characterized by osteopetrosis, and defects in hematopoiesis, fertility and neural function. Studies to further delineate the biologic effect of CSF-1 within various tissues have been hampered by the lack of suitable models. To address this issue, we generated CSF-1 floxed/floxed mice and demonstrate that Cre-mediated recombination using Meox2Cre, a Cre line expressed in epiblast during early embryogenesis, results in mice with ubiquitous CSF-1 deficiency (CSF-1KO). Homozygous CSF-1KO mice lacked CSF-1 in all tissues and displayed, in part, a similar phenotype to op/op mice that included: failure of tooth eruption, osteopetrosis, reduced macrophage densities in reproductive and other organs and altered hematopoiesis with decreased marrow cellularity, circulating monocytes and B cell lymphopoiesis. In contrast to op/op mice, CSF-1KO mice showed elevated circulating and splenic T cells. A striking feature in CSF-1KO mice was defective osteocyte maturation, bone mineralization and osteocyte-lacunar system that was associated with reduced dentin matrix protein 1 (DMP1) expression in osteocytes. CSF-1KO mice also showed a dramatic reduction in osteomacs along the endosteal surface that may have contributed to the hematopoietic and cortical bone defects. Thus, our findings show that ubiquitous CSF-1 gene deletion using a Cre-based system recapitulates the expected osteopetrotic phenotype. Moreover, results point to a novel link between CSF-1 and osteocyte survival/function that is essential for maintaining bone mass and strength during skeletal development.

Infection, inflammation, and bone regeneration: a paradoxical relationship

Various strategies have been developed to promote bone regeneration in the craniofacial region. Most of these interventions utilize implantable materials or devices. Infections resulting from colonization of these implants may result in local tissue destruction in a manner analogous to periodontitis. This destruction is mediated via the expression of various inflammatory mediators and tissue-destructive enzymes. Given the well-documented association among microbial biofilms, inflammatory mediators, and tissue destruction, it seems reasonable to assume that inflammation may interfere with bone healing and regeneration. Paradoxically, recent evidence also suggests that the presence of certain pro-inflammatory mediators is actually required for bone healing. Bone injury (e.g., subsequent to a fracture or surgical intervention) is followed by a choreographed cascade of events, some of which are dependent upon the presence of pro-inflammatory mediators. If inflammation resolves promptly, then proper bone healing may occur. However, if inflammation persists (which might occur in the presence of an infected implant or graft material), then the continued inflammatory response may result in suboptimal bone formation. Thus, the effect of a given mediator is dependent upon the temporal context in which it is expressed. Better understanding of this temporal sequence may be used to optimize regenerative outcomes.

Diseases affecting bone quality: beyond osteoporosis

BACKGROUND

Bone quantity, quality, and turnover contribute to whole bone strength. Although bone mineral density, or bone quantity, is associated with increased fracture risk, less is known about bone quality. Various conditions, including disorders of mineral homeostasis, disorders in bone remodeling, collagen disorders, and drugs, affect bone quality.

QUESTIONS/PURPOSES

The objectives of this review are to (1) identify the conditions and diseases that could adversely affect bone quality besides osteoporosis, and (2) evaluate how these conditions influence bone quality.

METHODS

We searched PubMed using the keywords "causes" combined with "secondary osteoporosis" or "fragility fracture." After identifying 20 disorders/conditions, we subsequently searched each condition to evaluate its effect on bone quality.

RESULTS

Many disorders or conditions have an effect on bone metabolism, leading to fragility fractures. These disorders include abnormalities that disrupt mineral homeostasis, lead to an alteration of the mineralization process, and ultimately reduce bone strength. The balance between bone formation and resorption is also essential to prevent microdamage accumulation and maintain proper material and structural integrity of the bone. As a result, diseases that alter the bone turnover process lead to a reduction of bone strength. Because Type I collagen is the most abundant protein found in bone, defects in Type I collagen can result in alterations of material property, ultimately leading to fragility fractures. Additionally, some medications can adversely affect bone.

CONCLUSIONS

Recognizing these conditions and diseases and understanding their etiology and pathogenesis is crucial for patient care and maintaining overall bone health.

Characterization of the bone phenotype and fracture repair in osteopetrotic incisors absent rats

Osteopetrotic patients possess a genetic condition that leads to a deficiency in osteoclast number or function. Patients have a high bone density and suffer from an increased risk of fracture. The lack of normal osteoclast activity has the potential to impede repair by complicating orthopedic fixation and/or by affecting the biology of fracture healing. The naturally occurring incisors absent (ia/ia) rat was adopted as a rodent model of congenital osteopetrosis. A detailed phenotypic analysis of the ia/ia rat indicated that some functional recovery occurred between 7 and 9 weeks. Consequently a fracture repair study was undertaken using 5-week-old rats. Closed femoral fractures were generated in ia/ia rats and control ia/+ and +/+ rats using an Einhorn apparatus. Fracture healing was examined radiologically and histologically at 1-3 weeks. No difference was seen in bridging between ia/ia and control rats at any time point. The ia/ia rats showed no delay in cartilage removal but showed a significant delay in hard callus remodeling. This is consistent with an essential role for osteoclasts in only the latter stages of endochondral bone repair. This delay in hard callus remodeling was offset by an increase in moment of inertia.

Total joint arthroplasty in a patient with osteopetrosis: 10-year follow-up

Total joint arthroplasty may be considered as a last option to treat osteopetrosis associated with osteoarthritis. However, many intraoperative and postoperative challenges need to be overcome when performing arthroplasty in patients with osteopetrosis, and few studies have focused on the longer-term outcomes.This article describes a case of a 22-year-old woman with osteopetrosis who presented with osteoarthritis and underwent right total hip arthroplasty 10 years prior. A smaller and shorter femoral component was chosen for the patient, special tungsten steel drill bits were used to create the femoral canal, and the drilling process was under fluoroscopic guidance. In the second postoperative week, her Harris Hip Score increased to 82.15 points from 40.25 points preoperatively. No postoperative complications were seen, and radiographs illustrated the components were in good position. At 10-year follow-up, her Harris Hip Score was still 82 points, the components were in good position radiographically, and the patient could walk freely and perform activities of daily living with no pain. The success of the treatment lies in suitable selection of prosthesis components, extra caution during surgery, adequate perioperative antibiotic administration, postoperative functional exercise, and a low-calcium diet.

Osteopetrosis

Osteopetrosis ("marble bone disease") is a descriptive term that refers to a group of rare, heritable disorders of the skeleton characterized by increased bone density on radiographs. The overall incidence of these conditions is difficult to estimate but autosomal recessive osteopetrosis (ARO) has an incidence of 1 in 250,000 births, and autosomal dominant osteopetrosis (ADO) has an incidence of 1 in 20,000 births. Osteopetrotic conditions vary greatly in their presentation and severity, ranging from neonatal onset with life-threatening complications such as bone marrow failure (e.g. classic or "malignant" ARO), to the incidental finding of osteopetrosis on radiographs (e.g. osteopoikilosis). Classic ARO is characterised by fractures, short stature, compressive neuropathies, hypocalcaemia with attendant tetanic seizures, and life-threatening pancytopaenia. The presence of primary neurodegeneration, mental retardation, skin and immune system involvement, or renal tubular acidosis may point to rarer osteopetrosis variants, whereas onset of primarily skeletal manifestations such as fractures and osteomyelitis in late childhood or adolescence is typical of ADO. Osteopetrosis is caused by failure of osteoclast development or function and mutations in at least 10 genes have been identified as causative in humans, accounting for 70% of all cases. These conditions can be inherited as autosomal recessive, dominant or X-linked traits with the most severe forms being autosomal recessive. Diagnosis is largely based on clinical and radiographic evaluation, confirmed by gene testing where applicable, and paves the way to understanding natural history, specific treatment where available, counselling regarding recurrence risks, and prenatal diagnosis in severe forms. Treatment of osteopetrotic conditions is largely symptomatic, although haematopoietic stem cell transplantation is employed for the most severe forms associated with bone marrow failure and currently offers the best chance of longer-term survival in this group. The severe infantile forms of osteopetrosis are associated with diminished life expectancy, with most untreated children dying in the first decade as a complication of bone marrow suppression. Life expectancy in the adult onset forms is normal. It is anticipated that further understanding of the molecular pathogenesis of these conditions will reveal new targets for pharmacotherapy.

Foxo3a is essential for maintenance of the hematopoietic stem cell pool

The mobilization of hematopoietic stem cells does not require osteoclasts, which may even have an inhibitory effect.

Hematopoietic stem cells (HSCs) are maintained in a specific bone marrow (BM) niche in cavities formed by osteoclasts. Osteoclast-deficient mice are osteopetrotic and exhibit closed BM cavities. Osteoclast activity is inversely correlated with hematopoietic activity; however, how osteoclasts and the BM cavity potentially regulate hematopoiesis is not well understood. To investigate this question, we evaluated hematopoietic activity in three osteopetrotic mouse models: op/op, c-Fos-deficient, and RANKL (receptor activator of nuclear factor kappa B ligand)-deficient mice. We show that, although osteoclasts and, by consequence, BM cavities are absent in these animals, hematopoietic stem and progenitor cell (HSPC) mobilization after granulocyte colony-stimulating factor injection was comparable or even higher in all three lines compared with wild-type mice. In contrast, osteoprotegerin-deficient mice, which have increased numbers of osteoclasts, showed reduced HSPC mobilization. BM-deficient patients and mice reportedly maintain hematopoiesis in extramedullary spaces, such as spleen; however, splenectomized op/op mice did not show reduced HSPC mobilization. Interestingly, we detected an HSC population in osteopetrotic bone of op/op mice, and pharmacological ablation of osteoclasts in wild-type mice did not inhibit, and even increased, HSPC mobilization. These results suggest that osteoclasts are dispensable for HSC mobilization and may function as negative regulators in the hematopoietic system.