Orthopedic Hardware Research Articles

Bilateral Knee Arthroplasty Infections in the Setting of Infected Spinal Hardware

Joint arthroplasty remains one of the most common elective surgeries in the United States. Orthopaedic hardware can contribute either as the primary source or as a secondary seeding site in hematogenously spread infections. Arthroplasty status should remain a focal point of history taking in both surgical and medical settings. This case details a 76-year-old woman who experienced bilateral knee arthroplasty infections after presenting with both a lumbar epidural abscess and vertebral osteomyelitis secondary to infected lumbar hardware.

MR Neurography of Peripheral Nerve Injury in the Presence of Orthopedic Hardware: Technical Considerations.

As the frequency of orthopedic procedures performed each year in the United States continues to increase, evaluation of peripheral nerve injury (PNI) in the presence of pre-existing metallic hardware is in higher demand. Advances in metal artifact reduction techniques have substantially improved the capability to reduce the susceptibility effect at MRI, but few reports have documented the use of MR neurography in the evaluation of peripheral nerves in the presence of orthopedic hardware. This report delineates the challenges of MR neurography around metal given the high spatial resolution often required to adequately depict small peripheral nerves. It offers practical tips, including strategies for prescan assessment and protocol optimization, including use of more conventional two-dimensional proton density and T2-weighted fat-suppressed sequences and specialized three-dimensional techniques, such as reversed free-induction steady-state precession and multispectral imaging, which enable vascular suppression and metal artifact reduction, respectively. Finally, this article emphasizes the importance of real-time monitoring by radiologists to optimize the diagnostic yield of MR neurography in the presence of orthopedic hardware. © RSNA, 2021.

Improving MR Image Quality in Patients with Metallic Implants.

The number of implanted devices such as orthopedic hardware and cardiac implantable devices continues to increase with an increase in the age of the patient population, as well as an increase in the number of indications for specific devices. Many patients with these devices have or will develop clinical conditions that are best depicted at MRI. However, implanted devices containing paramagnetic or ferromagnetic substances can cause significant artifact, which could limit the diagnostic capability of this modality. Performing imaging with MRI when an implant is present may be challenging, and there are numerous techniques the radiologist and technologist can use to help minimize artifacts related to implants. First, knowledge of the presence of an implant before patient arrival is critical to ensure safety of the patient when the device is subjected to a strong magnetic field. Once safety is ensured, the examination should be performed with the MRI system that is expected to provide the best image quality. The selection of the MRI system includes multiple considerations such as the effects of field strength and availability of specific sequences, which can reduce metal artifact. Appropriate patient positioning, attention to MRI parameters (including bandwidth, voxel size, and echo), and appropriate selection of sequences (those with less metal artifact and advanced metal reduction sequences) are critical to improve image quality. Patients with implants can be successfully imaged with MRI with appropriate planning and understanding of how to minimize artifacts. This improves image quality and the diagnostic confidence of the radiologist. ©RSNA, 2021.

The Contemporary Epidemiology, Microbiology and Management of Chronic Osteomyelitis in US Children.

While the majority of pediatric osteomyelitis cases are acute in nature, a significant subset present with prolonged symptoms often associated with substantial morbidity. Little data exist to guide clinicians in the management of these infections. We sought to describe the epidemiology, clinical features and management of chronic osteomyelitis (CO) in children. We reviewed hospital admissions for CO from 2011 to 2018 at Texas Children's Hospital. Cases were included if symptoms lasted ≥28 days on presentation. Cases were classified as those associated with: (1) a contiguous focus of infection; (2) penetrating trauma; (3) orthopedic hardware; (4) postacute CO (PACO, those occurring after ≥28 days of therapy for acute osteomyelitis); and (5) primary hematogenous CO. One hundred fourteen cases met inclusion criteria. The median patient age was 11.8 years and 35.9% had comorbidities. 70.2% of patients underwent ≥1 surgical procedure. A microbiologic etiology was identified in 72.8% of cases and Staphylococcus aureus was most common (39.4%). Contiguous focus of infection was more often associated with polymicrobial disease with or without Pseudomonas. Postacute CO was caused by S. aureus in 95%. The median duration of total therapy was 210 days. 26.3% of patients experienced treatment failure of which 46% underwent repeat hospital admission/surgery. There was no association between duration of intravenous therapy for CO and treatment failure. Children with CO represent a diverse group both in terms of pathogenesis and microbiology. Pathogenesis and clinical presentation can provide clues to microbiologic etiology. Prolonged intravenous therapy does not appear to improve outcomes in CO.

Paget’s Disease of Bone Affecting Site With Orthopedic Hardware

Introduction: Paget’s disease of bone is a focal disorder of accelerated bone remodeling which leads to bone hypertrophy, cortical expansion and abnormal bone architecture. Either a single bone (monostotic) or multiple bones (polyostotic) can be affected. Although it has been suggested to be caused by a chronic slow viral infection of the bone, a cause and effect relationship has not been clearly established. Therefore, the etiology of Paget’s disease remains an uncertain and controversial topic of discussion. Case Description: A 62-year-old African American male with a past medical history of a left tibial fracture presented with worsening left leg pain for the past 6 months. He denied any recent traumatic events, falls or strenuous physical activity. Since the pain started, his ambulation had been significantly affected requiring the use of a cane for gait stability. His left tibial fracture occurred over 20 years ago after landing on another person’s foot while playing basketball. It was surgically treated with intramedullary nailing and metal rod insertion into the canal of the tibia. Since then, he remained an active person with no physical limitations or ailments until the recent developments that brought him to clinic. A left leg CT-Scan ordered for evaluation of the tibial hardware revealed cortical thickening, marrow expansion and coarse trabeculae throughout the majority of the tibia consistent with Paget’s disease. The hardware was intact with no peri-hardware lucency to suggest loosening or infection. His laboratory workup showed a normal alkaline phosphatase level (94 U/L; normal range 40 - 115 U/L) and low 25-OH Vitamin D level of 14. A Radionuclide Bone Scan done for evaluation of location and extent of bone disease resulted in diffusely abnormal uptake present in the left tibia with no other locations of suspicious uptake. After his 25-OH Vitamin D levels were replenished, a dose of Zoledronic acid IV infusion was given with significant improvement of pain several months after. Discussion: Paget’s disease of bone is the second most common bone disease after osteoporosis. Affected skeletal sites develop a disorganized mosaic of woven and lamellar bone more susceptible to deformities and fractures than normal bone. It is often asymptomatic, but classical features include bone pain experienced either at rest or with motion, cutaneous erythema and warmth. The goal of medical therapy is to relieve symptoms and to prevent future complications with high potency bisphosphonates. Although it is well known that Paget’s disease increase the risk of fractures, this case brings up an interesting take about the possibility of fractures managed with hardware placement increasing the risk of Paget’s disease in the involved site.

Osteotomy in the newborn classic bladder exstrophy patient: A comparative study

Pelvic osteotomy is indicated in classic bladder exstrophy (CBE) patients with a wide pubic diastasis or non-malleable pelvis. While the safety of pelvic osteotomy in delayed and failed closures is established, there remains less clarity on their safety in newborns. The authors herein sought to present their experience with CBE patients who underwent pelvic osteotomy for assistance with bladder closure during both the newborn and delayed time periods. The authors hypothesize that pelvic osteotomy during exstrophy closure may be performed safely in newborns with few perioperative or post-operative negative sequelae. A prospectively maintained IRB-approved database was reviewed for CBE patients who underwent osteotomy during primary closure. Patient demographics, performing institution (authors' or outside), closure outcome, diastasis width, and post-operative complications were noted. Patient subgroups included newborn and delayed (>28 days of life) closures. Failure was defined as bladder dehiscence, prolapse, outlet obstruction, or vesicocutaneous fistula requiring reoperation. Orthopedic complications included nerve palsies, superficial pin-site infection, and bladder neck erosion by orthopedic hardware. Analyses were performed using a Chi-square test. 286 patients were included: 186 newborn and 100 delayed closures. The authors' institution performed 109 cases (44 newborn and 65 delayed). Within the overall newborn closure cohort, no significant differences were found in outcomes among the osteotomy types with success rates of 80%, 60.8%, and 71.4% in the combined, posterior iliac, and anterior innominate groups, respectively (p=0.24). In the delayed group, success rates were significantly different with rates of 100%, 72.4%, and 93.8% in the combined, posterior iliac, and anterior innominate groups, respectively (p<0.001). Febrile urinary tract infection (UTI) was the most common complication at 8% (23/286). Only 1.7% (5/286) of patients had orthopedic complications with 3 patients in the newborn cohort, 2 patients in the delayed cohort, and only one patient requiring reoperation. Orthopedic complications are rare in CBE patients who undergo osteotomies regardless of the closure period. No clinically significant difference in orthopedic complication rate was found between newborn and delayed closure periods. While current trends have moved toward delayed primary closures, there remains a role for osteotomy during exstrophy closure in select newborn patients and can be performed safely with few complications.

Magnetic resonance imaging in children with implants.

As access to MRI in pediatrics increases, the radiologist needs to become acquainted with the basic principles of MRI safety. As part of the image acquisition, the static magnetic field, gradient system, and the radiofrequency transmit-receive coil interact with medical and non-medical implants and can result in serious injury. The main stage of risk triage is based on the determination of whether the implant is MRI-safe, conditional, unsafe or unknown. Guiding principles include the strict adherence to manufacturer specifications for MRI-conditional implants and the assumption that an unknown implant is MR-unsafe. In this article we review considerations for common medical implants encountered in pediatrics including ventriculoperitoneal shunts, orthopedic hardware, orthodontic hardware, pacemakers, vascular stents, vagal nerve stimulators and cochlear implants. Finally, we review a set of high-yield considerations, including the non-communicative patient (sedated or non-verbal), susceptibility artifacts from unclear source, and the approach to an unknown implant.

Usage of External Fixation in the Treatment of Adult Patients with Knee Joint Stiffness: Review

Relevance. Knee contractures have an impact on quality of life and are also a common cause of disability. The use of external fixation devices has a certain place in the treatment of this pathology.Purpose. Using the world literature, to identify the modern position, problems, and prospectives of external fixation in the treatment of knee flexion and extension contractures in adult patients.Methods. EMBASE, Medline, Google Scholar, PubMed, e-LIBRARY, and Cyber resources were used. The analysis included publications relative treatment of knee joint stiffness using external fixation in patients over 18 years old, regardless of gender. At analysis several criterial were used: frame ability to provide movements in the knee joint according with its natural kinematics (biomechanics), stable fixation of the femur and tibia, and possibility inserting wires and halfpins in projection of Reference Positions (RP).Results. The devices used in the treatment of knee joint contractures in adult patients were conditionally divided, depending on the type of hinge, into 4 groups: non-hinged, uniaxial, reproducing, and virtual. It has been established that only orthopedic hexapods, based on virtual hinge, can meet all of the criteria mentioned above. However the technology of any orthopedic hexapod hardware and software usage for the treatment of contractures of the knee joint, was not developed till now.Conclusion. The necessity of developing hex-based technology for treatment patients with knee joint contractures was justified by world literature review. Hexapod hardware must provide possibilities of any inclination angle of any ring, and struts fixation not only to base and mobile rings, but to stabilizing as well. Software should be equipped with multi-total residual option. Ortho-SUV Frame (OSF) meets these requirements.

Functional Properties of Low-Modulus PMMA Bone Cements Containing Linoleic Acid.

Acrylic bone cements modified with linoleic acid are a promising low-modulus alternative to traditional high-modulus bone cements. However, several key properties remain unexplored, including the effect of autoclave sterilization and the potential use of low-modulus cements in other applications than vertebral augmentation. In this work, we evaluate the effect of sterilization on the structure and stability of linoleic acid, as well as in the handling properties, glass transition temperature, mechanical properties, and screw augmentation potential of low-modulus cement containing the fatty acid. Neither 1H NMR nor SFC-MS/MS analysis showed any detectable differences in autoclaved linoleic acid compared to fresh one. The peak polymerization temperature of the low-modulus cement was much lower (28–30 °C) than that of the high-modulus cement (67 °C), whereas the setting time remained comparable (20–25 min). The Tg of the low-modulus cement was lower (75–78 °C) than that of the high-stiffness cement (103 °C). It was shown that sterilization of linoleic acid by autoclaving did not significantly affect the functional properties of low-modulus PMMA bone cement, making the component suitable for sterile production. Ultimately, the low-modulus cement exhibited handling and mechanical properties that more closely match those of osteoporotic vertebral bone with a screw holding capacity of under 2000 N, making it a promising alternative for use in combination with orthopedic hardware in applications where high-stiffness augmentation materials can result in undesired effects.

Successful Microsurgical Reconstruction for Limb Salvage in a COVID-19-Positive Patient: A Case Report

Abstract Background Although the novel 2019 coronavirus (COVID-19) pandemic delayed elective microsurgical reconstruction cases, traumatic injuries requiring microsurgical reconstruction for limb salvage still presented to our hospital. Recent data suggests a link between COVID-19 and increased venous and arterial thromboembolic events, theoretically increasing the risk of microvascular anastomotic thrombosis and flap failure. Methods We provide a single case report of microsurgical limb salvage in a COVID-19-positive patient with a Gustilo IIIb open tibial-fibular fracture. Results A free latissimus dorsi muscle flap was used to successfully cover a Gustilo IIIb open tibial-fibular fracture with exposed orthopedic hardware and large soft tissue defect, with 5-month follow-up demonstrating a well-healed flap allowing for preserved ambulation. Conclusion Although there is a theoretical increased incidence of venous and arterial thrombotic microvascular failure in COVID-19-positive patients, microsurgical reconstruction is occasionally the lone option for salvage. Microsurgical reconstruction in this population must be carefully considered, meticulously executed, and closely monitored.

1369. The Spectrum of Chronic Osteomyelitis in Children

BackgroundWhile the majority of pediatric osteomyelitis cases are acute in nature, a significant subset present with prolonged symptoms often associated with substantial morbidity. Little data exist to guide clinicians in the management of these infections. We sought to describe the epidemiology, clinical features and management of chronic osteomyelitis in children.MethodsWe reviewed hospital admissions with an ICD10 code for chronic osteomyelitis from 2011-2018 at Texas Children’s Hospital. Cases were included if symptoms lasted >28 days on presentation. Patients diagnosed with chronic recurrent multifocal osteomyelitis were excluded. Cases were classified as those 1) associated with a contiguous focus (CoF), 2) penetrating or open trauma, 3) orthopedic hardware (OH), 4) post-acute chronic osteomyelitis (PACO, those occurring after >28 days of therapy for acute osteomyelitis) and 5) primary hematogenous chronic osteomyelitis (PHCO, those with 28 days of symptoms without other clear risk factors).Results114 cases met inclusion criteria. The median patient age is 11.8 years and 35.9% patients had underlying comorbidities. 83% of patients underwent a surgical procedure. Cases were diverse in terms of pathogenesis (Figure 1). A microbiologic etiology was identified in 72.8% of cases and was polymicrobial in 20.2% of cases; Staphylococcus aureus was the single most common etiology (Figure 2). CoF infection was more often associated with polymicrobial etiology with or without Pseudomonas (P< 0.001) and disease of the foot. PACO was caused by S. aureus in 95% of cases (p< 0.001, Figure 3). The overall median duration of total therapy was 210 days. 41% were discharged from hospital on OPAT with or without later transition to oral antibiotics. 26.3% of patients had persistent functional limitations at time of last follow-up of which 46% experienced repeat hospital admission/surgery. There was no association between duration of intravenous therapy and persistent functional limitations.Figure 1. Categories of Chronic Osteomyelitis Figure 2. Microbiology of Pediatric Chronic Osteomyelitis Figure 3. Clinical Features of Pediatric Chronic Osteomyelitis ConclusionChildren with chronic osteomyelitis are diverse both in terms of pathogenesis and microbiology. Pathogenesis and clinical presentation can provide clues to microbiologic etiology. Prolonged intravenous therapy does not appear to improve functional outcomes in chronic osteomyelitisDisclosures Jonathon C. McNeil, MD, Allergan (Research Grant or Support, Allergan provided ceftaroline powder for use in studies described in this abstract)

Detecting late infected hip prosthesis via ultrasonography: A case report

The case of a 64 year old female, who has had a septic prosthesis, is presented. She came to the Accident and Emergency Department complaining of a right hip pain after a minimal injury. She referred a right hip fracture ten years ago, treated with a hemi-arthroplasty having no problem ever since. The past medical history was clear. Roentgenograms were negative for fracture or gross loosening. She was sent home. After a couple of days the pain insisted and she has had a computed tomography scan which showed a hematoma. The symptoms worsened and then she underwent an ultrasound examination which revealed a large fluid collection and a snowstorm appearance around the prosthesis. The ultrasound findings and the elevated CRP set the diagnosis of a septic prosthesis. The operation confirmed these findings and a large amount of pus evacuated. The Orthopaedic hardware was removed as well.

Foreign-body reaction to orthopedic hardware a decade after implantation.

Foreign-body reaction to orthopedic hardware a decade after implantation.

Spectrum of microarchitectural bone disease in inborn errors of metabolism: a cross-sectional, observational study

BackgroundPatients diagnosed with inborn errors of metabolism (IBEM) often present with compromised bone health leading to low bone density, bone pain, fractures, and short stature. Dual-energy X-ray absorptiometry (DXA) is the current gold standard for clinical assessment of bone in the general population and has been adopted for monitoring bone density in IBEM patients. However, IBEM patients are at greater risk for scoliosis, short stature and often have orthopedic hardware at standard DXA scan sites, limiting its use in these patients. Furthermore, DXA is limited to measuring areal bone mineral density (BMD), and does not provide information on microarchitecture.MethodsIn this study, microarchitecture was investigated in IBEM patients (n = 101) using a new three-dimensional imaging technology high-resolution peripheral quantitative computed tomography (HR-pQCT) which scans at the distal radius and distal tibia. Volumetric BMD and bone microarchitecture were computed and compared amongst the different IBEMs. For IBEM patients over 16 years-old (n = 67), HR-pQCT reference data was available and Z-scores were calculated.ResultsCortical bone density was significantly lower in IBEMs associated with decreased bone mass when compared to lysosomal storage disorders (LSD) with no primary skeletal pathology at both the radius and tibia. Cortical thickness was also significantly lower in these disorders when compared to LSD with no primary skeletal pathology at the radius. Cortical porosity was significantly greater in hypophosphatasia when compared to all other IBEM subtypes.ConclusionWe demonstrated compromised bone microarchitecture in IBEMs where there is primary involvement of the skeleton, as well as IBEMs where skeletal complications are a secondary outcome. In conclusion, our findings suggest HR-pQCT may serve as a valuable tool to monitor skeletal disease in the IBEM population, and provides insight to the greatly varying bone phenotype for this cohort that can be used for clinical monitoring and the assessment of response to therapeutic interventions.

Effect of cold weather on patients with orthopedic implants

ObjectiveWe conducted this study to examine the prevalence of pain in patients with orthopedic implants, placed to stabilize a fracture or for arthroplasty, when exposed to cold weather in the Saudi Arabia MethodsWe asked 100 patients with orthopedic implants to complete a pretested questionnaire. These patients visited the Orthopedic Clinic at King Fahad Medical City, Saudi Arabia, for follow-up. ResultsOf 100 patients, 49 (49%) experienced pain from implants related to cold temperatures (8 °C–10 °C) during winter. The remaining 51 patients (51%) did not experience pain due to cold weather. ConclusionThe current study showed a statistically significant relationship between cold weather and pain in patients with implanted orthopedic hardware.

A Dual-Motor Drill Reduces Plunge, Simultaneously Gauges Depth, and Saves Time When Placing Orthopedic Screws

The technique for placement of orthopedic hardware remains unchanged despite technological advances. The surgeon controls drill bit speed and advancement, which risks drill bit overpenetration, or plunge. Measurement is performed as an additional step, introducing measurement error and increasing operative time. A dual-motor drill was created to control drill variables and combine drilling and measurement into a single step. The purpose of this study was to determine whether a dual-motor drill could reduce drilling and measurement errors while increasing the speed of placement of orthopedic hardware. Five orthopedic surgeons drilled and measured 10 holes with a standard drill and a dual-motor drill in randomized bicortical bone blocks. The bone blocks were placed on standard ballistic gels, which left a defect from drill bit overpenetration that could be measured with a calibrated gauge. The accuracy of drilling was determined by the depth of the defect in the ballistic gel and was compared between groups. Finally, time for drilling and measurement was collected and compared between groups. Overpenetration for the dual-motor drill (0.5±0.3 mm) was significantly less than for the standard drill (8.4±1.9 mm) (P<.0001). Depth measurement error for the dual-motor drill (0.6±0.3 mm) was significantly less than for the standard drill (2.6±0.5 mm) (P<.0001). Drilling and measurement time for the dual-motor drill (6.0±2.2 seconds) was significantly less than for the standard drill (13.4±3.9 seconds) (P<.0001). Use of a dual-motor drill reduced overpenetration, improved measurement accuracy, and reduced time spent during placement of orthopedic hardware. [Orthopedics. 2020;43(5):e465-e470.].

The use of negative pressure therapy for the treatment Of lower-extremity wounds.

Abstract Background: lower extremity wounds with exposed bone, tendon or orthopedic hardware present a difficult treatment challenge. Objective: The purpose of this study is to assess the role of the vacuum assisted closure (VAC) therapy in the management of lower extremity wounds. Material and methods: A prospective analytic cohort study was conducted among 15 patient referred for reconstruction of lower extremity wounds. The study was conducted between January 2019 to June 2019. The wounds were inspected, surgical debridement was done if needed, and the VAC dressings were changed every 72 hours. Primary outcome was wound healing and granulation tissue formation. Secondary outcome was wound infection and wound size. Results: Vacuum- assisted closure therapy greatly decrease the surface area of the wound. Profuse granulation tissue formed rapidly, covering the bone and hardware. There was no statistically significant difference between the included patients regarding the pattern of wound infection pre and after negative pressure therapy (p=0.655). Results were both functionally and aesthetically satisfactory. Conclusion: VAC therapy appears to be a simple and more effective than conventional dressings for the management of difficult wound in terms of reduction in wound volume, depth, treatment duration and cost minimize the number of local and free-flap transfers.

Toward an Improved Wrist View: Qualitative and Quantitative Investigation of the 20° Axial Lateral Wrist X-Ray

AimIn standard lateral wrist radiographs, the radiocarpal joint is often obscured because of the angulation of the radial styloid process. A modified lateral projection at a 20° angle has been shown to demonstrate the distal radius in profile in postoperative patients without superimposing of the orthopedic hardware used in open reduction and internal fixation procedures over the wrist joint. We assessed whether this 20° axial-lateral view is advantageous in a wider patient group. Materials and MethodsConsenting adults receiving wrist radiographs in a tertiary hospital radiology department for any indication underwent posteroanterior, posteroanterior-oblique, 0° lateral, and 20° lateral views. A musculoskeletal radiologist and a radiology technologist, blinded to clinical data and to which view was 0°/20°, both evaluated 0°/20° images in random order for whether the radiocarpal joint was obscured by radial styloid, radiocarpal articular margins, or ulnar styloid process, and which view was preferred. ResultsIn 124 cases, the radiocarpal joint was shown clearly on more 20° than 0° views (75/124 vs. 23/124, P < .001). Orthopedic hardware obscured joint lines in fewer 20° than 0° views (12/124 vs. 28/124, P < .001). There was a trend to the ulnar styloid process obscuring part of the radiocarpal joint less in 0° view (28/124 vs. 78/124 in 20°; P = .088), primarily in 20° laterals of wrists with positive ulnar variance. The 20° view was preferred by the radiologist in 76% (95/124) and preferred by the technologist in 83% (104/124). ConclusionThe 20° lateral view was superior to the current 0° lateral view in a wide range of patients, with the radiocarpal joint obscured significantly less by hardware or adjacent anatomy, and preferred by both the blinded radiologist and technologist.

Ultrasound of local complications in hand surgery: a pictorial essay.

Early detection of local complications (venipuncture complications, nerve lesions, infections, arthritis, and tenosynovitis, tendon adhesions and re-tears, complications related to orthopaedic hardware) after hand surgery is required for prompt treatment. Ultrasound has proven to be a valuable imaging modality for detecting and assessing a variety of disorders of the wrist and hand. The purpose of this pictorial essay is to present a wide range of complications after wrist and hand surgery assessed by ultrasound.

Periosteum: The forgotten source of osteoprogenitors

Bone is one of the few tissues capable of authentic regenerative repair. However, despite advances in surgical technique, orthopaedic hardware and our understanding of fracture biology, inadequate bone repair remains a major concern in both veterinary and human medicine. Cell-based technologies provide opportunities to utilize the osteogenic capacities of Mesenchymal Stem Cells (MSC) to augment bone repair. Much of the research on MSC biology has focused on cells derived from the bone marrow/endosteal compartment; however, osteoprogenitor cells (OPC) also reside in the periosteum. Periosteum develops as a fibro-cellular envelope surrounding developing skeletal elements. The inner, or cambium layer of periosteum, includes committed OPCs directly adjacent the bone surface, and a distinct sub-population of progenitors within the periosteal mid-substance that retain both chondrogenic and osteogenic capacities. During skeletogenesis, periosteal OPCs are responsible for appositional intramembranous bone formation that increases the radial diameter of long bones. Of critical importance, periosteal stem cells are the predominant cell population responsible for generating the cartilaginous or ‘soft’ callus that provides intermediate stabilization and a scaffold for subsequent callus ossification by endochondral ossification; the primary mechanism of bone repair. In recent experiments using isolates from ‘donor-matched’ periosteum and bone marrow, we have found that the basal osteogenic capacity of equine OPCs is considerably less than that of bone marrow-derived MSCs. Periosteal OPCs require exogenous Bone Morphogenetic Protein (BMP) for robust osteogenesis, a finding consistent with the clinical responses of bone to recombinant BMP protein. Perhaps more surprising, the osteogenic capacity of adult (2-10 years of age) OPCs is comparable to those of young foals’, although the cell yield is considerably greater from foal specimens. In light of the vital importance of callus formation for successful fracture healing of most, further research on the biology and clinical manipulation of periosteal OPCs is highly warranted.