Sanjeev Kakar

BMP2 activity, although dispensable for bone formation, is required for the initiation of fracture healing

Adult bones have a notable regenerative capacity. Over 40 years ago, an intrinsic activity capable of initiating this reparative response was found to reside within bone itself, and the term bone morphogenetic protein (BMP) was coined to describe the molecules responsible for it. A family of BMP proteins was subsequently identified, but no individual BMP has been shown to be the initiator of the endogenous bone repair response. Here we demonstrate that BMP2 is a necessary component of the signaling cascade that governs fracture repair. Mice lacking the ability to produce BMP2 in their limb bones have spontaneous fractures that do not resolve with time. In fact, in bones lacking BMP2, the earliest steps of fracture healing seem to be blocked. Although other osteogenic stimuli are still present in the limb skeleton of BMP2-deficient mice, they cannot compensate for the absence of BMP2. Collectively, our results identify BMP2 as an endogenous mediator necessary for fracture repair.

Enhanced Chondrogenesis and Wnt Signaling in PTH-Treated Fractures†

Studies have shown that systemic PTH treatment enhanced the rate of bone repair in rodent models. However, the mechanisms through which PTH affects bone repair have not been elucidated. In these studies we show that PTH primarily enhanced the earliest stages of endochondral bone repair by increasing chondrocyte recruitment and rate of differentiation. In coordination with these cellular events, we observed an increased level of canonical Wnt‐signaling in PTH‐treated bones at multiple time‐points across the time‐course of fracture repair, supporting the conclusion that PTH responses are at least in part mediated through Wnt signaling.

Diminished Bone Formation During Diabetic Fracture Healing is Related to the Premature Resorption of Cartilage Associated With Increased Osteoclast Activity

Histological and molecular analysis of fracture healing in normal and diabetic animals showed significantly enhanced removal of cartilage in diabetic animals. Increased cartilage turnover was associated with elevated osteoclast numbers, a higher expression of genes that promote osteoclastogenesis, and diminished primary bone formation.

Complications of total elbow replacement: A systematic review

Total elbow arthroplasty (TEA) is becoming an increasingly popular reconstructive procedure. Improved surgical techniques, newer implant designs, and improving clinical results have each contributed to the rise in prevalence of this surgical intervention. Themost common indication remains rheumatoid arthritis (RA). However, with the advent of semiconstrained prostheses, the indications have expanded to include post-traumatic sequelae such as instability and arthritis, as well as acute comminuted distal humerus fractures in the elderly. The rate of complications following TEA, ranging from 20% to 45%, is higher than in other large joint replacements. In their review of the literature, Gschwend et al reported a complication rate of 43% including aseptic loosening, infections, ulnar nerve complications, instability, disassembly, dislocation, subluxation, intraoperative fractures, fractures of the prosthesis, and ectopic bone formation. In order to reduce these complications, a variety of technical advances have been made within the last decade in the areas of prosthetic design and surgical technique. Fully constrained prostheses have fallen out of favor due to their high rates of aseptic loosening. They have been largely replaced by linked and unlinked components. The linked prostheses are semi-constrained and utilize ‘‘sloppy hinges,’’ which both decrease the rate of aseptic

Stimulation of fracture-healing with systemic intermittent parathyroid hormone treatment.

Over the past several years, there has been an increasing interest in the biology of bone repair and potential technologies for enhancing fracture-healing. Part of this interest is derived from the growing age of the population and the recognition that increased age carries an increased risk of complications after fracture. Although use of locally implanted or injected growth factors has received the most attention, systemic treatments for the enhancement of bone repair, especially for situations in which bone repair may be diminished or delayed, are now under investigation. Since the approval of parathyroid hormone (PTH) as an anabolic treatment for osteoporosis, there has been an increasing interest in other potential clinical uses for this compound in musculoskeletal conditions. It is now widely recognized that PTH administration is an effective therapy to increase bone mineral density and prevent fractures in patients with osteoporosis. More recently, a growing body of evidence has supported the conclusion that PTH will also be an effective anabolic therapy for the enhancement of bone repair after fracture. This review focuses on the recent research demonstrating the potential of PTH in the management of bone repair in a number of fracture models and also highlights the ongoing studies into the mechanisms of PTH actions on endochondral bone repair.

MicroRNA Functions in Osteogenesis and Dysfunctions in Osteoporosis

MicroRNAs (miRNAs) are critical post-transcriptional regulators of gene expression that control osteoblast mediated bone formation and osteoclast-related bone remodeling. Deregulation of miRNA mediated mechanisms is emerging as an important pathological factor in bone degeneration (eg, osteoporosis) and other bone-related diseases. MiRNAs are intriguing regulatory molecules that are networked with cell signaling pathways and intricate transcriptional programs through ingenuous circuits with remarkably simple logic. This overview examines key principles by which miRNAs control differentiation of osteoblasts as they evolve from mesenchymal stromal cells during osteogenesis, or of osteoclasts as they originate from monocytic precursors in the hematopoietic lineage during osteoclastogenesis. Of particular note are miRNAs that are temporally upregulated during osteoblastogenesis (eg, miR-218) or osteoclastogenesis (eg, miR-148a). Each miRNA stimulates differentiation by suppressing inhibitory signaling pathways (‘double-negative’ regulation). The excitement surrounding miRNAs in bone biology stems from the prominent effects that individual miRNAs can have on biological transitions during differentiation of skeletal cells and correlations of miRNA dysfunction with bone diseases. MiRNAs have significant clinical potential which is reflected by their versatility as disease-specific biomarkers and their promise as therapeutic agents to ameliorate or reverse bone tissue degeneration.

Open fractures of the tibia treated by immediate intramedullary tibial nail insertion without reaming: a prospective study.

Objective: Does immediate tibial nail insertion without reaming as part of protocol-driven management provide a safe and effective treatment for open tibia fractures? Study Design: Prospective cohort. Setting: Level 1 trauma center. Patients: A consecutive series of 161 patients with Gustilo grade I-IIIb open tibia fractures. Intervention: Emergent incision and debridement of the wound with immediate tibial nail insertion without reaming, repeat incision and debridement, and soft-tissue coverage within 14 days. Main Outcome Measurements: Time to union, number of secondary procedures performed to obtain union, implant failures, and the type and incidence of complications. Results: One hundred and forty-three fractures were followed to union. Follow up averaged 2.2 years (0.6-5.5 years). Seventy-six fractures united in less than 6 months, 35 took between 6 and 9 months, and 32 took longer than 9 months. Twenty-five additional procedures were needed to obtain union in 16 of the delayed unions (12 nail exchanges, 4 bone grafts, 9 dynamizations). Complications included 3 patients with cellulitis, 1 superficial infection, 4 deep infections (1 grade I, 2 grade II, 1 grade IIIb), 3 loose screws, 2 broken screws, 5 malunions greater than 5 degrees, and 30 patients with decreased ankle motion when compared with the uninjured side. Not counting the ankle loss of motion, 18 complications occurred in 143 fractures (13%). Twenty-nine patients (20%) had complaints of minor knee pain and 30 (21%) had occasional fracture site pain after activity despite clinical and radiographic evidence of union. Eleven patients (8%) considered themselves completely disabled. Five patients were not treated by the standard protocol and are not included in the previously listed statistics; 3 were grade IIIB that did not have adequate coverage by 14 days, and 2 were grade II injuries that did not have a second debridement. Four of these 5 patients developed a complication. Conclusions: Protocol-driven management emphasizing meticulous soft-tissue management and the use of immediate tibial nailing without reaming appears to be safe and effective in the treatment of open tibia fractures. The deep infection rate for the patients who were treated by protocol was 3% and the implant failure rate was lower than has been previously reported, most likely attributable to attempts to obtain cortical contact and avoid fracture gaps. Overall satisfaction was good, but approximately 41% of the patients had complaints of knee or fracture site pain or both well after union.

High-Resolution Molecular Validation of Self-Renewal and Spontaneous Differentiation in Clinical-Grade Adipose-Tissue Derived Human Mesenchymal Stem Cells

Improving the effectiveness of adipose‐tissue derived human mesenchymal stromal/stem cells (AMSCs) for skeletal therapies requires a detailed characterization of mechanisms supporting cell proliferation and multi‐potency. We investigated the molecular phenotype of AMSCs that were either actively proliferating in platelet lysate or in a basal non‐proliferative state. Flow cytometry combined with high‐throughput RNA sequencing (RNASeq) and RT‐qPCR analyses validate that AMSCs express classic mesenchymal cell surface markers (e.g., CD44, CD73/NT5E, CD90/THY1, and CD105/ENG). Expression of CD90 is selectively elevated at confluence. Self‐renewing AMSCs express a standard cell cycle program that successively mediates DNA replication, chromatin packaging, cyto‐architectural enlargement, and mitotic division. Confluent AMSCs preferentially express genes involved in extracellular matrix (ECM) formation and cellular communication. For example, cell cycle‐related biomarkers (e.g., cyclins E2 and B2, transcription factor E2F1) and histone‐related genes (e.g., H4, HINFP, NPAT) are elevated in proliferating AMSCs, while ECM genes are strongly upregulated (>10‐fold) in quiescent AMSCs. AMSCs also express pluripotency genes (e.g., POU5F1, NANOG, KLF4) and early mesenchymal markers (e.g., NES, ACTA2) consistent with their multipotent phenotype. Strikingly, AMSCs modulate expression of WNT signaling components and switch production of WNT ligands (from WNT5A/WNT5B/WNT7B to WNT2/WNT2B), while upregulating WNT‐related genes (WISP2, SFRP2, and SFRP4). Furthermore, post‐proliferative AMSCs spontaneously express fibroblastic, osteogenic, chondrogenic, and adipogenic biomarkers when maintained in confluent cultures. Our findings validate the biological properties of self‐renewing and multi‐potent AMSCs by providing high‐resolution quality control data that support their clinical versatility. J. Cell. Biochem. 115: 1816–1828, 2014.

Genetic Variation in the Patterns of Skeletal Progenitor Cell Differentiation and Progression During Endochondral Bone Formation Affects the Rate of Fracture Healing

These studies examined how genetic differences that regulate architectural and bone material properties would be expressed during fracture healing and determine whether any of these features would affect rates of healing as defined by regain of strength. Controlled fractures were generated in three inbred strains of mice: A/J, C57Bl/6J (B6), and C3H/HeJ (C3H). Both the A/J and B6 strains showed faster healing than the C3H strain based on regains in strength and stiffness. Strain‐specific architectural features such as moment of inertia, cross‐sectional area, and cortical thickness were all recapitulated during the development of the callus tissues. None of these traits were directly relatable to rates of fracture healing. However, rates of healing were related to variations in the temporal patterns of chondrogenic and osteogenic lineage development. The B6 strain expressed the highest percentage of cartilage gene products and had the longest period of chondrocyte maturation and hypertrophy. The slowest healing strain (C3H) had the shortest period of chondrogenic development and earliest initiation of osteogenic development. Although the A/J strain showed an almost identical pattern of chondrogenic development as the C3H strain, A/J initiated osteogenic development several days later than C3H during fracture healing. Long bone growth plates at 28 days after birth showed similar strain‐specific variation in cartilage tissue development as seen in fracture healing. Thus, the B6 strain had the largest growth plate heights, cell numbers per column, and the largest cell size, whereas the C3H columns were the shortest, had the smallest number of cells per column, and showed the smallest cell sizes. These results show that (1) different strains of mice express variations of skeletal stem cell lineage differentiation and (2) that these variations affect the rate of fracture healing.

Risk factors for surgical site infection after posterior cervical spine surgery: an analysis of 5,441 patients from the ACS NSQIP 2005–2012

BACKGROUND CONTEXT The incidence of surgical site infection (SSI) following posterior cervical surgery has been reported as high as 18% in the literature. Few large studies have specifically examined posterior cervical procedures. PURPOSE The study aims to examine the incidence, timing, and risk factors for SSI following posterior cervical surgery. DESIGN This is a retrospective cohort study of prospectively collected data in a national surgical outcomes database. PATIENT SAMPLE The sample includes patients who underwent posterior cervical spine surgery between 2005 and 2012 identified in the American College of Surgeons National Surgical Quality Improvement Project (ACS NSQIP) Participant Use Data File. OUTCOME MEASURES The 30-day rate of postoperative SSI, timing of diagnosis, and associated risk factors were determined. METHODS The ACS NSQIP was used to identify 5,441 patients who underwent posterior cervical spine surgery by Current Procedural Terminology codes from 2005 to 2012. Thirty-day readmission data were obtained for 2011-2012. The incidence and timing of SSI were determined. Multivariable logistic regression analysis was then performed to identify significant risk factors. RESULTS Of the 5,441 patients identified as having undergone posterior cervical surgery, 3,724 had a posterior cervical decompression, 1,310 had a posterior cervical fusion, and 407 underwent cervical laminoplasty. Surgical site infection within 30 days was identified in 160 patients (2.94%), with 80 of those cases being superficial SSI. There was no significant difference in SSI rate among the three procedure groups. The average time for diagnosis of SSI was over 2 weeks. In 2011-2012, 36.9% of patients with SSI were readmitted within 30 days. Several significant predictors of SSI were identified in univariate analysis, including body mass index (BMI) >35, chronic steroid use, albumin <3, hematocrit <33, platelets <100, higher American Society of Anesthesiologists class, longer operative time, and longer hospital admission. Independent risk factors, including BMI >35 (odds ratio [OR]=1.78, p=.003), chronic steroid use (OR=1.73, p=.049), and operative time >197 minutes (OR=2.08, p=.005), were identified in multivariable analysis. CONCLUSIONS Optimization of preoperative nutritional status, serum blood cell counts, and operative efficiency may lead to a reduction in SSI rates. Obese patients and patients on chronic steroid therapy should be counseled on elevated SSI risk.