DAP, Macaulay W. Longitudinal evaluation of time related femoral neck narrowing after metal-on-metal hip resurfacing

AIM: To track the short-term neck narrowing changes in Birmingham metal-on-metal hip resurfacing (MOMHR) patients.

METHODS: Since 2001, the Center for Hip and Knee Replacement started a registry to prospectively collect data on hip and knee replacement patients. From June 2006 to October 2008, 139 MOMHR were performed at our center by two participate surgeons using Birmingham MOMHR prosthesis (Smith Nephew, United States). It is standard of care for patients to obtain low, anteriorposterior (LAP) pelvis radiographs immediately after MOMHR procedure and then at 3 mo, 1 year and 2 year follow up office visits. Inclusion criteria for the present study included patients who came back for follow up office visit at above mentioned time points and got LAP radiographs. Exclusion criteria include patients who missed more than two follow up time points and those with poor-quality X-rays. Two orthopaedic residency trained research fellows reviewed the X-rays independently at 4 time points, i.e., immediate after surgery, 3 mo, 1 year and 2 year. Neck-to-prosthesis ratio (NPR) was used as main outcome measure. Twenty cases were used as subjects to identify the reliability between two observers. An intraclass correlation coefficient at 0.8 was considered as satisfied. A paired t-test was used to evaluate the significant difference between different time points with P < 0.05 considered to be statistically significant.

RESULTS: The mean NPRs were 0.852 ± 0.056, 0.839 ± 0.052, 0.835 ± 0.051, 0.83 ± 0.04 immediately, 3 mo, 1 year and 2 years post-operatively respectively. At 3 mo, NPR was significantly different from immediate postoperative X-ray (P < 0.001). There was no difference between 3 mo and 1 year (P = 0.14) and 2 years (P = 0.53). Femoral neck narrowing (FNN) exceeding 10% of the diameter of the neck was observed in only 4 patients (5.6%) at two years follow up. None of these patients developed a femoral neck fracture (FNF).

CONCLUSION: Femoral neck narrowing after MOMHR occurred as early as 3 mo postoperatively, and stabilized thereafter. Excessive FNN was not common in patients within the first two years of surgery and was not correlated with risk of FNF.

Bipolar hemiarthroplasty for femoral neck fracture using the direct anterior approach

AIM: To evaluate whether walking ability recovers early after bipolar hemiarthroplasty (BHA) using a direct anterior approach.

METHODS: Between 2008 and 2010, 81 patients with femoral neck fracture underwent BHA using the direct anterior approach (DAA) or the posterior approach (PA). The mean observation period was 36 mo. The age, sex, body mass index (BMI), time from admission to surgery, length of hospitalization, outcome after discharge, walking ability, duration of surgery, blood loss and complications were compared.

RESULTS: There was no significant difference in the age, sex, BMI, time from admission to surgery, length of hospitalization, outcome after discharge, duration of surgery and blood loss between the two groups. Two weeks after the operation, assistance was not necessary for walking in the hospital in 65.0% of the patients in the DAA group and in 33.3% in the PA group (P < 0.05). As for complications, fracture of the femoral greater trochanter developed in 1 patient in the DAA group and calcar crack and dislocation in 1 patient each in the PA group.

CONCLUSION: DAA is an approach more useful for BHA for femoral neck fracture in elderly patients than total hip arthroplasty in terms of the early acquisition of walking ability.

Unicompartmental knee prosthetization: Which key-points to consider?

Unicompartmental knee arthroplasty (UKA) has evolved into a suitable option for diseased knees that cannot be managed with arthroscopic treatment and at the same time are not good candidates for total knee replacement. Since meticulous execution of the surgical technique is essential to optimizing UKA outcome, some procedural key-points are mandatory. Templates (phantoms) are then used to size the required prosthetic component (using these radiographs. Arthritic varus (or valgus) knees with an asymptomatic patello-femoral joint are typically ideal for UKA. Metal-backed tibial components should be favourite instead of all-polyethylene tibial components to avoid polyethylene creep that may occur in fixed bearings. Moreover, a proper thickness of the polyethylene layer is mandatory, in order to avoid early failure.

Pathophysiology, diagnosis, and treatment of discogenic low back pain

Discogenic low back pain is a serious medical and social problem, and accounts for 26%-42% of the patients with chronic low back pain. Recent studies found that the pathologic features of discs obtained from the patients with discogenic low back pain were the formation of the zones of vascularized granulation tissue, with extensive innervation in fissures extending from the outer part of the annulus into the nucleus pulposus. Studies suggested that the degeneration of the painful disc might originate from the injury and subsequent repair of annulus fibrosus. Growth factors such as basic fibroblast growth factor, transforming growth factor β1, and connective tissue growth factor, macrophages and mast cells might play a key role in the repair of the injured annulus fibrosus and subsequent disc degeneration. Although there exist controversies about the role of discography as a diagnostic test, provocation discography still is the only available means by which to identify a painful disc. A recent study has classified discogenic low back pain into two types that were annular disruption-induced low back pain and internal endplate disruption-induced low back pain, which have been fully supported by clinical and theoretical bases. Current treatment options for discogenic back pain range from medicinal anti-inflammation strategy to invasive procedures including spine fusion and recently spinal arthroplasty. However, these treatments are limited to relieving symptoms, with no attempt to restore the disc's structure. Recently, there has been a growing interest in developing strategies that aim to repair or regenerate the degenerated disc biologically.

Polymethylmethacrylate bone cements and additives: A review of the literature

Polymethylmethacrylate (PMMA) bone cement technology has progressed from industrial Plexiglass administration in the 1950s to the recent advent of nanoparticle additives. Additives have been trialed to address problems with modern bone cements such as the loosening of prosthesis, high post-operative infection rates, and inflammatory reduction in interface integrity. This review aims to assess current additives used in PMMA bone cements and offer an insight regarding future directions for this biomaterial. Low index (< 15%) vitamin E and low index (< 5 g) antibiotic impregnated additives significantly address infection and inflammatory problems, with only modest reductions in mechanical strength. Chitosan (15% w/w PMMA) and silver (1% w/w PMMA) nanoparticles have strong antibacterial activity with no significant reduction in mechanical strength. Future work on PMMA bone cements should focus on trialing combinations of these additives as this may enhance favourable properties.

Combined distal tibial rotational osteotomy and proximal growth plate modulation for treatment of infantile Blount’s disease

Infantile Blount’s disease is a condition that causes genu varum and internal tibial torsion. Treatment options include observation, orthotics, corrective osteotomy, elevation of the medial tibial plateau, resection of a physeal bar, lateral hemi-epiphysiodesis, and guided growth of the proximal tibial physis. Each of these treatment options has its disadvantages. Treating the coronal deformity alone (genu varum) will result in persistence of the internal tibial torsion (the axial deformity). In this report, we describe the combination of lateral growth modulation and distal tibial external rotation osteotomy to correct all the elements of the disease. This has not been described before for treatment of Blount’s disease. Both coronal and axial deformities were corrected in this patient. We propose this combination (rather than the lateral growth modulation alone) as the method of treatment for early stages of Blount’s disease as it corrects both elements of the disease and in the same time avoids the complications of proximal tibial osteotomy.

Distinguishing erosive osteoarthritis and calcium pyrophosphate deposition disease

Erosive osteoarthritis is a term utilized to describe a specific inflammatory condition of the interphalangeal and first carpal metacarpal joints of the hands. The term has become a part of medical philosophical semantics and paradigms, but the issue is actually more complicated. Even the term osteoarthritis (non-erosive) has been controversial, with some suggesting osteoarthrosis to be more appropriate in view of the perspective that it is a non-inflammatory process undeserving of the “itis” suffix. The term “erosion” has also been a source of confusion in osteoarthritis, as it has been used to describe cartilage, not bone lesions. Inflammation in individuals with osteoarthritis actually appears to be related to complicating phenomena, such as calcium pyrophosphate and hydroxyapatite crystal deposition producing arthritis. Erosive osteoarthritis is the contentious term. It is used to describe a specific form of joint damage to specific joints. The damage has been termed erosions and the distribution of the damage is to the interphalangeal joints of the hand and first carpal metacarpal joint. Inflammation is recognized by joint redness and warmth, while X-rays reveal alteration of the articular surfaces, producing a smudged appearance. This ill-defined, joint damage has a crumbling appearance and is quite distinct from the sharply defined erosions of rheumatoid arthritis and spondyloarthropathy. The appearance is identical to those found with calcium pyrophosphate deposition disease, both in character and their unique responsiveness to hydroxychloroquine treatment. Low doses of the latter often resolve symptoms within weeks, in contrast to higher doses and the months required for response in other forms of inflammatory arthritis. Reconsidering erosive osteoarthritis as a form of calcium pyrophosphate deposition disease guides physicians to more effective therapeutic intervention.

Biepicondylar fracture dislocation of the elbow joint concomitant with ulnar nerve injury

In this article, we present a case of humeral biepicondylar fracture dislocation concomitant with ulnar nerve injury in a seventeen year-old male patient. Physical examination of our patient in the emergency room revealed a painful, edematous and deformed-looking left elbow joint. Hypoesthesia of the little finger was also diagnosed on the left hand. Radiological assessment ended up with a posterior fracture dislocation of the elbow joint accompanied by intra-articular loose bodies. Open reduction-Internal fixation of the fracture dislocation and ulnar nerve exploration were performed under general anesthesia at the same session as surgical treatment of our patient. Physical therapy and rehabilitation protocol was implemented at the end of two weeks post-operatively. Union of the fracture lines, as well as the olecranon osteotomy site, was achieved at the end of four months post-operatively. Ulnar nerve function was fully restored without any sensory or motor loss. Range of motion at the elbow joint was 20-120 degrees at the latest follow-up.

Best approach for the repair of distal biceps tendon ruptures

The preferred treatment of distal biceps tendon ruptures is by operative repair. However, the best approach for repair (single vs double incision) is still subject of debate. Grewal and colleagues recently presented the results of a randomized clinical trial evaluating two different surgical approaches for the repair of distal biceps tendon ruptures. Despite the fact that this article currently presents the highest level of evidence for the surgical repair of distal biceps tendon ruptures, we have some comments on the study that might be interesting to discuss. We think that some of the results and conclusions presented in this study need to be interpreted in the light of these comments.

Incidence and analysis of radial head and neck fractures

AIM: To investigate several complications like persistent radial head dislocation, forearm deformity, elbow stiffness and nerve palsies, associated with radial head fractures.

METHODS: This study reviewed the clinical records and trauma database of this level I Trauma Center and identified all patients with fractures of the radial head and neck who where admitted between 2000 and 2010. An analysis of clinical records revealed 1047 patients suffering from fractures of the radial head or neck classified according to Mason. For clinical examination, range of motion, local pain and overall outcome were assessed.

RESULTS: The incidence of one-sided fractures was 99.2% and for simultaneous bilateral fractures 0.8%. Non-operative treatment was performed in 90.4% (n = 947) of the cases, surgery in 9.6% (n = 100). Bony union was achieved in 99.8% (n = 1045) patients. Full satisfaction was achieved in 59% (n = 615) of the patients. A gender related significant difference (P = 0.035) in Mason type distribution-type III fractures were more prominent in male patients vs type IV fractures in female patients-was observed in our study population.

CONCLUSION: Mason type I fractures can be treated safe conservatively with good results. In type II to IV surgical intervention is usually considered to be indicated.

Anterior muscle sparing approach for total hip arthroplasty

The purpose of this review is to examine the validity of positive claims regarding the direct anterior approach (DAA) with a fracture table for total hip arthroplasty. Recent literature regarding the DAA was searched and specific claims investigated including improved early outcomes, speed of recovery, component placement, dislocation rates, and complication rates. Recent literature is positive regarding the effects of total hip arthroplasty with the anterior approach. While the data is not definitive at present, patients receiving the anterior approach for total hip arthroplasty tend to recover more quickly and have improved early outcomes. Component placement with the anterior approach is more often in the “safe zone” than with other approaches. Dislocation rates tend to be less than 1% with the anterior approach. Complication rates vary widely in the published literature. A possible explanation is that the variance is due to surgeon and institutional experience with the anterior approach procedure. Concerns remain regarding the “learning curve” for both surgeons and institutions. In conclusion, it is not a matter of should this approach be used, but how should it be implemented.

Regulation of bone destruction in rheumatoid arthritis through RANKL-RANK pathways

Recent studies have demonstrated that osteoclasts, the primary cells responsible for bone resorption, are mainly involved in bone and joint destruction in rheumatoid arthritis (RA) patients. Recent progress in bone cell biology has revealed the molecular mechanism of osteoclast differentiation and bone resorption by mature osteoclasts. We highlight here the potential role of the receptor activator of nuclear factor κB ligand (RANKL)-RANK pathways in bone destruction in RA and review recent clinical trials treating RA by targeting RANKL.

Femoral impaction grafting

Femoral impaction grafting is a reconstruction option applicable to both simple and complex femoral component revisions. It is one of the preferred techniques for reconstructing large femoral defects when the isthmus is non-supportive. The available level of evidence is primarily derived from case series, which shows a mean survivorship of 90.5%, with revision or re-operation as the end-point, with an average follow-up of 11 years. The rate of femoral fracture requiring re-operation or revision of the component varies between several large case series, ranging from 2.5% to 9%, with an average of 5.4%.

Access related complications during anterior exposure of the lumbar spine

The new millennium has witnessed the emergence of minimally invasive, non-posterior based surgery of the lumbar spine, in particular via lateral based methodologies to discectomy and fusion. In contrast, and perhaps for a variety of reasons, anterior motion preservation (non-fusion) technologies are playing a comparatively lesser, though incompletely defined, role at present. Lateral based motion preservation technologies await definition of their eventual role in the armamentarium of minimally invasive surgical therapies of the lumbar spine. While injury to the major vascular structures remains the most serious and feared complication of the anterior approach, this occurrence has been nearly eliminated by the use of lateral based approaches for discectomy and fusion cephalad to L5-S1. Whether anterior or lateral based, non-posterior approaches to the lumbar spine share certain access related pitfalls and complications, including damage to the urologic and neurologic structures, as well as gastrointestinal and abdominal wall issues. This review will focus on the recognition, management and prevention of these anterior and lateral access related complications.

Finger movement at birth in brachial plexus birth palsy

AIM: To investigate whether the finger movement at birth is a better predictor of the brachial plexus birth injury.

METHODS: We conducted a retrospective study reviewing pre-surgical records of 87 patients with residual obstetric brachial plexus palsy in study 1. Posterior subluxation of the humeral head (PHHA), and glenoid retroversion were measured from computed tomography or Magnetic resonance imaging, and correlated with the finger movement at birth. The study 2 consisted of 141 obstetric brachial plexus injury patients, who underwent primary surgeries and/or secondary surgery at the Texas Nerve and Paralysis Institute. Information regarding finger movement was obtained from the patient’s parent or guardian during the initial evaluation.

RESULTS: Among 87 patients, 9 (10.3%) patients who lacked finger movement at birth had a PHHA > 40%, and glenoid retroversion < -12°, whereas only 1 patient (1.1%) with finger movement had a PHHA > 40%, and retroversion < -8° in study 1. The improvement in glenohumeral deformity (PHHA, 31.8% ± 14.3%; and glenoid retroversion 22.0°± 15.0°) was significantly higher in patients, who have not had any primary surgeries and had finger movement at birth (group 1), when compared to those patients, who had primary surgeries (nerve and muscle surgeries), and lacked finger movement at birth (group 2), (PHHA 10.7% ± 15.8%; Version -8.0°± 8.4°, P = 0.005 and P = 0.030, respectively) in study 2. No finger movement at birth was observed in 55% of the patients in this study group.

CONCLUSION: Posterior subluxation and glenoid retroversion measurements indicated significantly severe shoulder deformities in children with finger movement at birth, in comparison with those lacked finger movement. However, the improvement after triangle tilt surgery was higher in patients who had finger movement at birth.

Current concepts in management of femoroacetabular impingement

Femoroacetabular impingement (FAI) is an increasingly recognized condition, which is believed to contribute to degenerative changes of the hip. This correlation has led to a great deal of interested in diagnosis and treatment of FAI. FAI can be divided into two groups: cam and pincer type impingement. FAI can lead to chondral and labral pathologies, that if left untreated, can progress rapidly to osteoarthritis. The diagnosis of FAI involves a detailed history, physical exam, and radiographs of the pelvis. Surgical treatment is indicated in anatomic variants known to cause FAI. The primary goal of surgical treatment is to increase joint clearance and decrease destructive forces being transmitted through the joint. Treatment has been evolving rapidly over the past decade and includes three primary techniques: open surgical dislocation, mini-open, and arthroscopic surgery. Open surgical dislocation is a technique for dislocating the femoral head from the acetabulum with a low risk of avascular necrosis in order to reshape the neck or acetabular rim to improve joint clearance. Mini-open treatment is performed using the distal portion of an anterior approach to the hip to visualize and to correct acetabular and femoral head and neck junction deformities. This does not involve frank dislocation. Recently, arthroscopic treatment has gained popularity. This however does have a steep learning curve and is best done by an experienced surgeon. Short- to mid-term results have shown relatively equal success with all techniques in patients with no or only mild evidence of degenerative changes. Additionally, all techniques have demonstrated low rates of complications.

Osteoclast fusion and regulation by RANKL-dependent and independent factors

Osteoclasts are the bone resorbing cells essential for bone remodeling. Osteoclasts are formed from hematopoietic progenitors in the monocyte/macrophage lineage. Osteoclastogenesis is composed of several steps including progenitor survival, differentiation to mono-nuclear pre-osteoclasts, fusion to multi-nuclear mature osteoclasts, and activation to bone resorbing osteoclasts. The regulation of osteoclastogenesis has been extensively studied, in which the receptor activator of NF-κB ligand (RANKL)-mediated signaling pathway and downstream transcription factors play essential roles. However, less is known about osteoclast fusion, which is a property of mature osteoclasts and is required for osteoclasts to resorb bone. Several proteins that affect cell fusion have been identified. Among them, dendritic cell-specific transmembrane protein (DC-STAMP) is directly associated to osteoclast fusion in vivo. Cytokines and factors influence osteoclast fusion through regulation of DC-STAMP. Here we review the recently discovered new factors that regulate osteoclast fusion with specific focus on DC-STAMP. A better understanding of the mechanistic basis of osteoclast fusion will lead to the development of a new therapeutic strategy for bone disorders due to elevated osteoclast bone resorption. Cell-cell fusion is essential for a variety of cellular biological processes. In mammals, there is a limited number of cell types that fuse to form multinucleated cells, such as the fusion of myoblasts for the formation of skeletal muscle and the fusion of cells of the monocyte/macrophage lineage for the formation of multinucleated osteoclasts and giant cells. In most cases, cell-cell fusion is beneficial for cells by enhancing function. Myoblast fusion increases myofiber size and diameter and thereby increases contractile strength. Multinucleated osteoclasts have far more bone resorbing activity than their mono-nuclear counterparts. Multinucleated giant cells are much more efficient in the removal of implanted materials and bacteria due to chronic infection than macrophages. Therefore, they are also called foreign-body giant cells. Cell fusion is a complicated process involving cell migration, chemotaxis, cell-cell recognition and attachment, as well as changes into a fusion-competent status. All of these steps are regulated by multiple factors. In this review, we will discuss osteoclast fusion and regulation.

Male osteoporosis: A review

Osteoporosis in men is a heterogeneous disease that has received little attention. However, one third of worldwide hip fractures occur in the male population. This problem is more prevalent in people over 70 years of age. The etiology can be idiopathic or secondary to hypogonadism, vitamin D deficiency and inadequate calcium intake, hormonal treatments for prostate cancer, use of toxic and every disease or drug use that alters bone metabolism.Risk factors such as a previous history of fragility fracture should be assessed for the diagnosis. However, risk factors in men are very heterogeneous. There are significant differences in the pharmacological treatment of osteoporosis between men and women fundamentally due to the level of evidence in published trials supporting each treatment. New treatments will offer new therapeutic prospects. The goal of this work is a revision of the present status knowledge about male osteoporosis.

Single row rotator cuff repair with modified technique

Rotator cuff tear is a common medical condition. We introduce various suture methods that can be used for arthroscopic rotator cuff repair, review the single row rotator cuff repair method with modified technique, and introduce the Ulsan-University (UU) stich. We compare the UU stitch with the modified Mason-Allen (MA) suture method. The UU stitch configuration is a simple alternative to the modified MA suture configuration for rotator cuff repair.

Do osteoporosis-related vertebral fractures precede hip fractures?

AIM

To evaluate the relationship between a vertebral fracture and a hip fracture in Saudi Arabians with osteoporosis.

METHODS

In this retrospective study, 154 Saudi Arabian patients with osteoporosis-related hip fractures were analyzed for the presence of a vertebral fracture. Radiographs were retrieved from the IPAC (Image Picture Archiving and Computing) System, an imaging retrieval system, and were reviewed independently by two of the authors, Abid Hussain Gullenpet, and Mir Sadat-Ali, and later reviewed jointly. Patients admitted with proximal hip fracture who were ≥ 50 years and had undergone Thoraco-lumber imaging and a dual energy X-ray absorptiometry (DEXA) scan were included in the study. Patients with a history of significant trauma to the spine and those with a malignancy or connective tissue disorder were excluded from the analysis.

RESULTS

Out of 154 patients with hip fractures, 78 had a fracture of the femoral neck while 76 had an intertrochanteric hip fracture. Of the 111 patients who were finally included in the study, after applying inclusion and exclusion criteria, 76 patients with an average age of 67.28 ± 12 years had no fractures of the spine. Thirty-five patients with an average age of 76.9 ± 14.5 years (31.53%) had a total of 49 vertebral fractures. Patients with vertebral fractures were significantly older than those without fractures P < 0.001. Overall, 24.7% of these patients had an asymptomatic vertebral fracture. Further analysis showed that 11 males (18.96%) and 24 females (45.28%) had suffered a previous asymptomatic vertebral fracture. Interestingly, all women who participated in this study and who presented with a femoral neck fracture had experienced a prior asymptomatic vertebral fracture.

CONCLUSION

We recommend that all elderly patients who go to the radiology department for a chest X-ray also have a DEXA scan and a lateral thoracic spine radiograph.

Strategy for prevention of hip fractures in patients with Parkinson's disease

Hypovitaminosis D and K due to malnutrition or sunlight deprivation, increased bone resorption due to immobilization, low bone mineral density (BMD) and an increased risk of falls may contribute to an increased risk of hip fractures in patients with Parkinson's disease. The purpose of the present study was to clarify the efficacy of interventions intended to prevent hip fractures in elderly patients with Parkinson's disease. PubMed was used to search the literature for randomized controlled trials (RCTs) regarding Parkinson's disease and hip fractures. The inclusion criteria were 50 or more subjects per group and a study period of 1 year or longer. Five RCTs were identified and the relative risk and 95% confidence interval were calculated for individual RCTs. Sunlight exposure increased serum hydroxyvitamin D [25(OH)D] concentration, improved motor function, decreased bone resorption and increased BMD. Alendronate or risedronate with vitamin D supplementation increased serum 25(OH)D concentration, strongly decreased bone resorption and increased BMD. Menatetrenone (vitamin K(2)) decreased serum undercarboxylated osteocalcin concentration, decreased bone resorption and increased BMD. Sunlight exposure (men and women), menatetrenone (women), alendronate and risedronate with vitamin D supplementation (women) significantly reduced the incidence of hip fractures. The respective RRs (95% confidence intervals) according to the intention-to-treat analysis were 0.27 (0.08, 0.96), 0.13 (0.02, 0.97), 0.29 (0.10, 0.85) and 0.20 (0.06, 0.68). Interventions, including sunlight exposure, menatetrenone and oral bisphosphonates with vitamin D supplementation, have a protective effect against hip fractures elderly patients with Parkinson's disease.

New roles of osteoblasts involved in osteoclast differentiation

Bone-resorbing osteoclasts are formed from a monocyte/macrophage lineage under the strict control of bone-forming osteoblasts. So far, macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor-κB ligand (RANKL), and osteoprotegerin (OPG) produced by osteoblasts play major roles in the regulation of osteoclast differentiation. Recent studies have shown that osteoblasts regulate osteoclastogenesis through several mechanisms independent of M-CSF, RANKL, and OPG production. Identification of osteoclast-committed precursors in vivo demonstrated that osteoblasts are involved in the distribution of osteoclast precursors in bone. Interleukin 34 (IL-34), a novel ligand for c-Fms, plays a pivotal role in maintaining the splenic reservoir of osteoclast-committed precursors in M-CSF deficient mice. IL-34 is also able to act as a substitute for osteoblast-producing M-CSF in osteoclastogenesis. Wnt5a, produced by osteoblasts, enhances osteoclast differentiation by upregulating RANK expression through activation of the non-canonical Wnt pathway. Semaphorin 3A produced by osteoblasts inhibits RANKL-induced osteoclast differentiation through the suppression of immunoreceptor tyrosine-based activation motif signals. Thus, recent findings show that osteoclast differentiation is tightly regulated by osteoblasts through several different mechanisms. These newly identified molecules are expected to be promising targets of therapeutic agents in bone-related diseases.

Energy metabolism and the skeleton: Reciprocal interplay

The relation between bone remodelling and energy expenditure is an intriguing, and yet unexplained, challenge of the past ten years. In fact, it was only in the last few years that the skeleton was found to function, not only in its obvious roles of body support and protection, but also as an important part of the endocrine system. In particular, bone produces different hormones, like osteocalcin (OC), which influences energy expenditure in humans. The undercarboxylated form of OC has a reduced affinity for hydroxyapatite; hence it enters the systemic circulation more easily and exerts its metabolic functions for the proliferation of pancreatic β-cells, insulin secretion, sensitivity, and glucose tolerance. Leptin, a hormone synthesized by adipocytes, also has an effect on both bone remodelling and energy expenditure; in fact it inhibits appetite through hypothalamic influence and, in bone, stimulates osteoblastic differentiation and inhibits apoptosis. Leptin and serotonin exert opposite influences on bone mass accrual, but several features suggest that they might operate in the same pathway through a sympathetic tone. Serotonin, in fact, acts via two opposite pathways in controlling bone remodelling: central and peripheral. Serotonin product by the gastrointestinal tract (95%) augments bone formation by osteoblast, whereas brain-derived serotonin influences low bone mineral density and its decrease leads to an increase in bone resorption parameters. Finally, amylin (AMY) acts as a hormone that alters physiological responses related to feeding, and plays a role as a growth factor in bone. In vitro AMY stimulates the proliferation of osteoblasts, and osteoclast differentiation. Here we summarize the evidence that links energy expenditure and bone remodelling, with particular regard to humans.

Management of postoperative spinal infections

Postoperative surgical site infection (SSI) is a common complication after posterior lumbar spine surgery. This review details an approach to the prevention, diagnosis and treatment of SSIs. Factors contributing to the development of a SSI can be split into three categories: (1) microbiological factors; (2) factors related to the patient and their spinal pathology; and (3) factors relating to the surgical procedure. SSI is most commonly caused by Staphylococcus aureus. The virulence of the organism causing the SSI can affect its presentation. SSI can be prevented by careful adherence to aseptic technique, prophylactic antibiotics, avoiding myonecrosis by frequently releasing retractors and preoperatively optimizing modifiable patient factors. Increasing pain is commonly the only symptom of a SSI and can lead to a delay in diagnosis. C-reactive protein and magnetic resonance imaging can help establish the diagnosis. Treatment requires acquiring intra-operative cultures to guide future antibiotic therapy and surgical debridement of all necrotic tissue. A SSI can usually be adequately treated without removing spinal instrumentation. A multidisciplinary approach to SSIs is important. It is useful to involve an infectious disease specialist and use minimum serial bactericidal titers to enhance the effectiveness of antibiotic therapy. A plastic surgeon should also be involved in those cases of severe infection that require repeat debridement and delayed closure.

Molecular mechanisms of triggering, amplifying and targeting RANK signaling in osteoclasts

Osteoclast differentiation depends on receptor activator of nuclear factor-κB (RANK) signaling, which can be divided into triggering, amplifying and targeting phases based on how active the master regulator nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) is. The triggering phase is characterized by immediate-early RANK signaling induced by RANK ligand (RANKL) stimulation mediated by three adaptor proteins, tumor necrosis factor receptor-associated factor 6, Grb-2-associated binder-2 and phospholipase C (PLC)γ2, leading to activation of IκB kinase, mitogen-activated protein kinases and the transcription factors nuclear factor (NF)-κB and activator protein-1 (AP-1). Mice lacking NF-κB p50/p52 or the AP-1 subunit c-Fos (encoded by Fos) exhibit severe osteopetrosis due to a differentiation block in the osteoclast lineage. The amplification phase occurs about 24 h later in a RANKL-induced osteoclastogenic culture when Ca(2+) oscillation starts and the transcription factor NFATc1 is abundantly produced. In addition to Ca(2+) oscillation-dependent nuclear translocation and transcriptional auto-induction of NFATc1, a Ca(2+) oscillation-independent, osteoblast-dependent mechanism stabilizes NFATc1 protein in differentiating osteoclasts. Osteoclast precursors lacking PLCγ2, inositol-1,4,5-trisphosphate receptors, regulator of G-protein signaling 10, or NFATc1 show an impaired transition from the triggering to amplifying phases. The final targeting phase is mediated by activation of numerous NFATc1 target genes responsible for cell-cell fusion and regulation of bone-resorptive function. This review focuses on molecular mechanisms for each of the three phases of RANK signaling during osteoclast differentiation.