The Importance of Increased Intraosseous Pressure in the Development of Osteonecrosis of the Femoral Head: Implications for Treatment

Simultaneous Bilateral Femoral Osteonecrosis in Gaucher Disease

Gaucher disease (GD) is one of the most common lysosomal storage disorders. Bone complications are the most critical irreversible consequence of GD. Osteonecrosis (ON) of the femoral head inevitably leads to osteoarthritis and may be managed by hip arthroplasty. The introduction and worldwide use of therapeutic agents (specifically enzyme replacement therapies (ERT)) lowered the prevalence of osteonecrosis events per patient. We present the cases of two female patients who sustained simultaneous bilateral femoral head osteonecrosis after receiving ERT for long periods while exposed to concomitant risk factors related to femoral head ON. Both patients suffered severe pain and deterioration of their daily activity capabilities, and thus, were offered bilateral hip arthroplasty. Surgery was performed in both hip joints during the same procedure. The current report highlights several key aspects of femoral head ON in young patients with GD.

Quantitative analysis of local microcirculation changes in early osteonecrosis of femoral head: DCE-MRI findings

Aim

This study aims to quantitatively analyze the changes in local microcirculation in early osteonecrosis of the femoral head (ONFH) by dynamic contrast-enhanced (DCE) MRI and to explore the pathophysiological mechanisms of early ONFH.

Patients and Methods

We selected 49 patients (98 hips) aged 21-59 years who were clinically diagnosed with early ONFH. A total of 77 femoral heads were diagnosed with different degrees of necrosis according to the Association Research Circulation Osseous (ARCO) staging system, and 21 femoral heads were judged to be completely healthy. All patients underwent DCE-MRI scanning. Pseudocolor images and time-signal intensity curves were generated by Tissue 4D processing software. The volume transfer constant (K ^trans), extracellular extravascular space, also known as vascular leakage (V _e), and transfer rate constant (K _ep) of healthy and different areas of necrotic femoral heads were measured on perfusion parameter maps. The differences and characteristics of these parameters in healthy and different areas of necrotic femoral heads were analyzed.

Results

The signal accumulation in healthy femoral heads is lower than that of necrotic femoral heads in pseudocolor images. The time-signal intensity curve of healthy femoral heads is along the horizontal direction, while they all have upward trends for different areas of necrotic femoral heads. The mean value of K ^trans of healthy femoral heads was lower than the integration of necrotic, boundary, and other areas (F = 3.133, P = .036). The K _ep value of healthy femoral heads was higher than the integration of lesion areas (F = 6.273, P = .001). The mean V _e value of healthy femoral heads was smaller than that of the lesion areas (F = 3.872, P = .016). The comparisons of parameters between different areas and comparisons among healthy areas and lesion areas showed different results.

Conclusion

ONFH is a complex ischemic lesion caused by changes in local microcirculation. It mainly manifests as increased permeability of the vascular wall, blood stasis in the posterior circulation, high intraosseous pressure in the femoral head, and decreased arterial blood flow. The application of DCE-MRI scanning to quantitatively analyze the visual manifestations of microcirculation after early ONFH is an ideal method to study the microcirculation changes of necrotic femoral heads.

Intraosseous Tibial Resuscitation After a Total Knee Arthroplasty Leading to Osteonecrosis and Loosening of the Tibial Component

A 51-year-old woman suffered cardiac arrest requiring emergent intraosseous access that abutted the tibial component of her total knee arthroplasty. She developed a wound at the site and knee pain which was concerning for deep infection. Subsequent imaging was consistent with osteonecrosis developing around the tibial component. The component eventually loosened, requiring a revision surgery. Her deep cultures remained negative throughout. Her findings are most consistent with osteonecrosis and aseptic loosening of her prosthesis. While intraosseous access may be beneficial during resuscitation, it has complications. This is the first reported case of osteonecrosis secondary to intraosseous access leading to prosthetic loosening necessitating a revision surgery.

Relationship of idiopathic femoral head necrosis with blood lipid metabolism and coagulation function: A propensity score-based analysis

Background

Nontraumatic osteonecrosis of the femoral head (ONFH) can be corticosteroid-induced, alcohol-induced, and idiopathic ONFH (IONFH). Although corticosteroid- and alcohol-induced ONFH has been investigated extensively regarding its relationship with blood lipids and coagulation factor levels. However, the effect of blood lipid metabolism and coagulation function on IONFH has rarely been studied. Therefore, this study aimed to analyse the relationship of IONFH with blood lipid and coagulation indicators.

Methods

Total 680 patients diagnosed with IONFH in our institution during January 2011-June 2019 who met the inclusion criteria composed the case group; 613 healthy persons who underwent physical examination at our institution during the same period composed the control group. Propensity scores were used for baseline feature matching, and two matching groups each with 450 patients were established. After the matching, blood lipid and coagulation factor levels of both groups were comparatively analysed.

Results

The case group showed significantly higher total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL) levels, low-density/high-density lipoprotein (LDL/HDL) ratio, and apolipoprotein B (Apo-B) levels than the control group (p < 0.05). Conversely, the HDL and apolipoprotein A (Apo-AI) levels in the case group were significantly lower than those in the control group (p < 0.05). Regarding coagulation indicators, the activated partial thromboplastin time and prothrombin time were lower in the case group than in the control group; however, the differences were insignificant (p > 0.05). Furthermore, fibrinogen (FIB) levels and thrombin time (TT) in the case group were higher than those in the control group. There were significant differences between the two groups only in terms of FIB levels (p < 0.05), while TT was not significantly different (p > 0.05).

Conclusions

IONFH has strong associations with blood lipid metabolism and coagulation function, which provide an avenue for exploring the mechanism of IONFH.

Intramedullary core decompression combined with endoscopic intracapsular decompression and debridement for pre-collapse non-traumatic osteonecrosis of the femoral head

BACKGROUND

The effect of core decompression on the treatment of pre-collapse non-traumatic osteonecrosis of the femoral head (ONFH) is still limited. This study aimed to explore the efficacy of core decompression combined with intra-articular decompression (debridement of the hip joint and incision of the hip capsule) under hip arthroscopic guidance in patients with pre-collapse ONFH.

METHODS

The clinical data of 101 patients with pre-collapse ONFH were analysed retrospectively. Sixty patients (80 hips) received small-diameter multi-channel core decompression alone in first half review period (group B). Forty-one patients (59 hips) were treated with small-diameter multi-channel core decompression combined with intra-articular decompression under hip arthroscopy guidance in second half review period (group A). The surgical duration; intraoperative bleeding; intra-articular pressure(IAP) before and after surgery; length of hospital stay; hospitalisation expenses; visual analogue scale (VAS) score before, 1 week, 4 weeks, 3 months and 1 year after surgery; and Harris score of the hip joint before, 3 months and 1 year after surgery were recorded and compared between group A and group B. X-ray examination was performed every month to observe the collapse of the femoral head within 2 years after surgery, which was compared using the Kaplan-Meier survival curve analysis.

RESULTS

When the two groups were compared, the surgical duration was longer and hospitalisation expenses were higher in group A than in group B (P < 0.05). However, the VAS score and the Harris score of the hip joint after surgery improved significantly compared with those before surgery (P < 0.05), which were more apparent in group A than in group B (P < 0.05). X-ray examination revealed that 6 hips in group A and 22 in group B received femoral head collapse at the 2-year follow-up. The survival rate of the femoral head in group A was significantly higher than that in group B (P < 0.05).

CONCLUSION

Small-diameter multi-channel core decompression combined with intra-articular decompression (debridement of the hip joint and incision of the hip capsule) under hip arthroscopic guidance for treating early ONFH can more effectively alleviate joint pain, improve joint function and delay ONFH progression.

CircHGF suppressed cell proliferation and osteogenic differentiation of BMSCs in ONFH via inhibiting miR-25-3p binding to SMAD7

Steroid-induced osteonecrosis of the femoral head (ONFH) is a common and devastating bone disorder, which often results in progressive collapse of the femoral head and subsequent osteoarthritis. The proliferation ability and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) play critical roles in maintaining the structural and functional integrity of the femoral head to prevent ONFH. Until now, little has been known about the underlying mechanism of BMSCs differentiation disorder during ONFH progression. Circular RNAs (circRNAs) are considered to be vital non-coding RNAs functionally involved in various human diseases. However, whether and how circRNA regulates the proliferation and osteogenic differentiation of BMSCs in ONFH remain unclear. In this study, we analyzed the circRNA expression profile of five samples of BMSCs in ONFH and five samples of control by using circRNA microarray assays. We identified 182 differentially expressed circRNAs, among which 108 circRNAs were upregulated. We further investigated the effects of a significantly upregulated circRNA, circHGF, on the proliferation and osteogenic differentiation of BMSCs in vitro. Results showed that circHGF suppressed the proliferation and osteogenic differentiation of BMSCs in ONFH by targeting miR-25-3p/SMAD7 axis. Our findings provided a potential diagnostic and therapeutic strategy for ONFH.

Relationship Between Blood Flow and Collapse of Nontraumatic Osteonecrosis of the Femoral Head

BACKGROUND

To investigate the collapse mechanism in osteonecrosis of the femoral head (ONFH), we studied the relationship between the femoral head (FH) blood circulation changes and the collapse area histomorphometry characteristics.

METHODS

A technique involving microvascular perfusion of the FH in vitro to reconstruct the vessels in the FH at different stages of nontraumatic ONFH (40 cases). In addition, we also examined the histomorphometry characteristics in the collapse area during ONFH at different stages using the hard tissue section technique. To investigate the blood supply changes in the FH on pathological involved in the FH collapse process.

RESULTS

The results showed that in all FHs, the collapse area always involved the margin of the necrotic lesion of the lateral column. Histologically, the fracture occurred between the thickened and necrotic trabeculae at the junction. We found that the collapse started at the lateral column of the FH in the necrotic lesion and that the lateral column was ischemic, which caused the FH to begin to collapse.

CONCLUSIONS

Based on the above findings, the relationship between associations of the blood circulation to the collapse showed that if a portion of the blood supply of the lateral column (the superior retinacular artery) was preserved, the prognosis of the natural progression of the diseases was improved, the collapse rate was low and collapse occurred later. The blood circulation of artery in the lateral column was good, and the FH maintained an intact shape even if the internal region was ischemic. Therefore, we can predict the collapse of the FH by measuring the blood flow in the lateral area of the FH, thus providing guidance for the selection of FH-preserving clinical therapy in young and middle-aged patients.

CLINICAL RELEVANCE

This work provides a proof of how to predict the collapse of the FH by measuring the blood flow, providing guidance for FH-preserving clinical therapy in young and middle-aged patients.

Risk factors and pathogenesis of steroid-induced osteonecrosis of femoral head - A scoping review

Steroid induced osteonecrosis of the femoral head is commonly seen in clinical practice, but yet not fully understood. It is intriguing why only some cases develop and others escape from it. We did an extensive and up to date literature review on it, with the aim to identify its incidence, associated risk factor and pathogenesis. We found that the incidence ranged from 03 to 40%, and was more with associated risk factors. Several risk factors were identified, which included higher dose and prolonged duration of steroid consumption, and underlying disease for which the steroids were given. Pathogenesis of this disease is complex and not yet fully understood. Awareness about this condition and associated risk factors should help the clinicians in identifying the cases who are prone to develop osteonecrosis with the use of steroids.

Osteonecrosis of the Femoral Head: an Updated Review of ARCO on Pathogenesis, Staging and Treatment

Non-traumatic osteonecrosis of the femoral head (ONFH) usually affects adults younger than 50 years and frequently leads to femoral head collapse and subsequent arthritis of the hip. It is becoming more prevalent along with increasing use of corticosteroids for the adjuvant therapy of leukemia and other myelogenous diseases as well as management of organ transplantation. This review updated knowledge on the pathogenesis, classification criteria, staging system, and treatment of ONFH.

Osteotomies for avascular necrosis of the femoral head

BACKGROUND

In osteonecrosis of the femoral head (ONFH), blood supply is insufficient for the metabolic requirements of the bone. The initial management is conservative, and, in case of failure, surgery is indicated. Osteotomies aim to change the spatial position of the necrotic portion of the femoral head. This systematic review evaluates the effectiveness and safety of osteotomies for ONFH.

SOURCE OF DATA

The systematic review, organized, conducted and reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, was performed on PubMed and Google Scholar. We analysed outcomes in term of Harris Hip Score, leg shortening, secondary collapse and blood loss. We also verified the percentage of patients who required total hip replacement (THR) after osteotomy for ONFH.

AREAS OF AGREEMENT

A total of 16 articles were selected, including 775 patients and 852 osteotomies [curved varus osteotomy in 369 (43.3%) patients; transtrochanteric rotational osteotomy in 435 (51.05%) patients; half wedge osteotomy in 48 (5.6%) patients]. There was an overall THR conversion rate of 31.5% (268 hips on 852 osteotomies).

AREAS OF CONTROVERSY

There were no prospective randomized trials, and the outcome measures employed were often heterogeneous.

GROWING POINTS

Approximately one-third of the osteotomies performed in cases of ONFH are converted to THR over a period of ~7 years. In older patients, primary THR should be considered, especially as the conversion to THR after osteotomy is technically demanding.

AREAS TIMELY FOR DEVELOPING RESEARCH

Randomized clinical studies should be conducted in order to define the parameters of the patient that can direct towards the most suitable osteotomic technique.

ARCO Consensus on the Pathogenesis of Non-traumatic Osteonecrosis of the Femoral Head

Osteonecrosis of the femoral head (ONFH) is a devastating disease frequently leading to femoral head collapse and hip arthritis. Specifically, non-traumatic ONFH primarily affects young and middle-aged adults. Although compromised local circulation of the femoral head seems to be pathognomonic for the disease, the pathogenesis is perplexing and continues to be an area of scrutiny and research. Comprehension of the pathogenesis is of crucial importance for developing and guiding treatments for the disease. Therefore, we provide an up-to-date consensus on the pathogenesis of non-traumatic ONFH.

Aseptic osteonecrosis of the shoulder: Etiologies, diagnosis and medical management

Aseptic osteonecrosis of the humeral head is a multifactorial entity in which the final common pathway results in disrupted blood supply, increased intraosseous pressure, and bone death. It follows a pathologic and radiographic pattern of progression similar to that seen at the hip. Much of the information regarding the disease has been extrapolated from findings in the femoral head. In addition, many treatment modalities have been adapted from techniques used in the hip. The causative underlying factors seem to be multifactorial and can be traumatic or non-traumatic. Although clinical symptoms and the underlying cause of the disease influence the treatment of each patient, staging is the most objective criterion in determining the most appropriate treatment. Earlier identification of osteonecrosis should facilitate the management. MRI is important for asymptomatic humeral head osteonecrosis in patients with poor clinical symptom and risk factor. Conservative treatment can be effective in stages I and II, When symptoms persist and there are signs of collapse despite conservative treatment, surgical intervention is advocated.

Glucocorticoids decreased Cx43 expression in osteonecrosis of femoral head: The effect on proliferation and osteogenic differentiation of rat BMSCs

Glucocorticoid (GC)‐induced osteonecrosis of the femoral head (GC‐ONFH) is considered as one of the most serious side effects of long‐term or over‐dose steroid therapy. However, the underlying cause mechanisms are still not fully investigated. We firstly established a rat model of GC‐ONFH and injected lipopolysaccharide (LPS) and methylprednisolone (MPS). We found that the expressions of Cx43, Runx2, ALP and COLⅠ were more decreased than the normal group. Secondly, the isolated rat bone marrow stem cells (BMSCs) were treated with dexamethasone (Dex) in vitro, and the expressions of Cx43, Runx2, ALP and COLⅠ were decreased significantly. Moreover, the results of immunofluorescence staining, alizarin red staining, EdU assay and CCK8 showed that the osteogenic differentiation and the proliferation capacity of BMSCs were decreased after induced by Dex. A plasmid of lentivirus‐mediated Cx43 (Lv‐Cx43) gene overexpression was established to investigate the function of Cx43 in BMSCs under the Dex treatment. Findings demonstrated that the proliferation and osteogenic differentiation abilities were enhanced after Lv‐Cx43 transfected to BMSCs, and these beneficial effects of Lv‐Cx43 were significantly blocked when PD988059 (an inhibitor of ERK1/2) was used. In conclusion, the overexpression of Cx43 could promote the proliferation and osteogenic differentiation of BMSCs via activating the ERK1/2 signalling pathway, which provide a basic evidence for further study on the detailed function of Cx43 in GC‐ONFH.

BONE PERFUSION AND ADIPOSITY BEYOND THE NECROTIC ZONE IN FEMORAL HEAD OSTEONECROSIS: A QUANTITATIVE MRI STUDY

PURPOSE

To describe bone perfusion and adiposity beyond the necrotic zone with quantitative MRI techniques in osteonecrosis of the femoral head (ONFH).

METHOD

In this cross-sectional multicentre study, we recruited patients suffering from late-stage ONFH or hip osteoarthritis. Hip MRI included quantitative MRI sequences: chemical-shift imaging and dynamic contrast-enhanced MRI. We drew regions of interest inside the necrotic zone (inner necrosis and its border) and outside (femoral head, neck and greater trochanter) in ONFH. In the control group, regions of interest were drawn in the femoral head, femoral neck and the greater trochanter. For each region of interest, we measured fat fraction, and calculated semi-quantitative (area under the curve, initial slope) and pharmacokinetic perfusion parameters (K_trans and K_ep).

RESULTS

Thirty-two male adults (mean age 58 ± 9 years, range 38-74 years) were included. Sixteen patients formed the ONFH group and fifteen the control group; one was excluded. In the normal-appearing non-necrotic part of the femoral head, fat fraction was not significantly different in comparison with controls (p = 1), but _Ktrans was significantly lower than in controls (0.012 ± 0.018 vs. 0.027 ± 0.045; p = 0.05). This perfusion parameter reflects exchanges between blood microvessels and bone marrow.

CONCLUSIONS

Our results question the concept of adipose toxicity on the macroscopic scale, and bring up the concept of regional ischemic penumbra that goes beyond the visible necrotic zone. Further studies are required to test these hypotheses in larger populations and earlier disease states.

Subchondral pressures and perfusion during weight bearing

Background

Joints withstand huge forces, but little is known about subchondral pressures and perfusion during loading. We developed an in vitro calf foot model to explore intraosseous pressure (IOP) and subchondral perfusion during weight bearing.

Methods

Freshly culled calf forefeet were perfused with serum. IOP was measured at three sites in the foot using intraosseous needles, pressure transducers, and digital recorders. IOP was measured during perfusion, with and without a tourniquet and with differing weights, including static loading and dynamic loading to resemble walking.

Results

IOP varied with perfusion pressure. Static loading increased subchondral IOP whether the bone was non-perfused, perfused, or perfused with a proximal venous tourniquet (p < 0.0001). Under all perfusion states, IOP was proportional to the load (R² = 0.984). Subchondral IOP often exceeded perfusion pressure. On removal of a load, IOP fell to below the pre-load value. Repetitive loading led to a falling IOP whether the foot was perfused or not.

Conclusion

Superimposed on a variable background IOP, increased perfusion and physiological loading caused a significant increase in subchondral IOP. Force was thereby transmitted through subchondral bone partly by hydraulic pressure. A falling IOP with repeat loading suggests that there is an intraosseous one-way valve. This offers a new understanding of subchondral perfusion physiology.

Increased COUP-TFII Expression Mediates the Differentiation Imbalance of Bone Marrow-Derived Mesenchymal Stem Cells in Femoral Head Osteonecrosis

Objective

Bone marrow-derived mesenchymal stem cells (BMSCs) have multilineage differentiation potential, which allows them to progress to osteogenesis, adipogenesis, and chondrogenesis. An imbalance of differentiation between osteogenesis and adipogenesis will result in pathologic conditions inside the bone. This type of imbalance is also one of the pathological findings in osteonecrosis of the femoral head (ONFH). Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) was previously reported to mediate the differentiation of mesenchymal stem cells. This study investigated the expression of the osteogenesis regulator Runx2, osteocalcin, the adipogenesis regulator PPARγ, and COUP-TFII in the femoral head tissue harvested from ONFH patients, and characterized the effect of COUP-TFII on the differentiation of primary BMSCs.

Methods

Thirty patients with ONFH were recruited and separated into 3 groups: the trauma-, steroid- and alcohol-induced ONFH groups (10 patients each). Bone specimens were harvested from patients who underwent hip arthroplasty, and another 10 specimens were harvested from femoral neck fracture patients as the control group. Expression of the osteogenesis regulator Runx2, osteocalcin, the adipogenesis regulator PPARγ, C/EBP-α, and COUP-TFII was analyzed by Western blotting. Primary bone marrow mesenchymal cells were harvested from ONFH cells treated with COUP-TFII RNA interference to evaluate the effect of COUP-TFII on MSCs.

Results

ONFH patients had significantly increased expression of the adipogenesis regulator PPARγ and C/EBP-α and decreased expression of the osteogenesis regulator osteocalcin. ONFH bone tissue also revealed higher COUP-TFII expression. Immunohistochemical staining displayed strong COUP-TFII immunoreactivity adjacent to osteonecrotic trabecular bone. Increased COUP-TFII expression in the bone tissue correlated with increased PPARγ and decreased osteocalcin expression. Knockdown of COUP-TFII with siRNA in BMSCs reduced adipogenesis and increased osteogenesis in mesenchymal cells.

Conclusion

Increased COUP-TFII expression mediates the imbalance of BMSC differentiation and progression to ONFH in patients. This study might reveal a new target in the treatment of ONFH.

An in vitro model to explore subchondral perfusion and intraosseous pressure

Background

Little is known about subchondral perfusion physiology. We developed a 3Rs (Replace, Reduce, Refine) compliant in vitro calf foot model to explore perfusion and intraosseous pressure (IOP).

Methods

Calf feet were catheterised and perfused with serum. IOP was measured at three sites, the metacarpal diaphysis (MCD), metacarpal subchondral epiphysis (MCS) and proximal phalanx diaphysis (PPD) using intraosseous needles with pressure transducers and digital recorders. Fresh (< 4 h post mortem) and old feet (> 4 h post mortem) were perfused at different pressures, with and without a proximal tourniquet.

Results

There was a wide range in basal IOP with a mean IOP of 30.0 mmHg, SD 14.4, range 7.6 mmHg to 52.7 mmHg (n = 40 records) in 15 subjects. There was no significant difference between the three sites tested (p = 0.54, 0.12 and 0.051). At each individual site IOP correlated with perfusion pressure (r = 0.993). With a proximal venous tourniquet, IOP increased from 15.1 mmHg (SD 11.3 mmHg) to 44.9 mmHg (SD 24 mmHg), p < 0.0001, n = 9. Filling and emptying curves during perfusion and with using a tourniquet were similar, indicating that the model behaves in an elastic hydrodynamic manner. In fresh feet IOP peaked after about 1 min irrespective of perfusion pressure, possibly due to auto regulation. Older feet showed a continuously rising IOP and became oedematous. There was no significant difference in IOP between fresh and old feet perfused with serum at 150 cms pressure for 1 min.

Conclusion

Though basal intraosseous pressure varies, IOP behaves predictably. IOP measurements reflect the perfusion microclimate at the individual needle tip. This 3Rs compliant model will be used for further exploration of subchondral perfusion physiology with loading.

The correlation between femoroacetabular impingement and superior retinacular artery interruption

The aim of this study was to investigate the relationship between femoroacetabular impingement (FAI) and superior retinacular artery interruption using plain radiographs and digital subtraction angiography (DSA).Sixty-one patients included in this study were divided into 2 groups based on the superior retinacular artery integrity as evaluated on DSA images. Group A included intact arteries: 33 patients (24 men, 9 women,); group B included interrupted arteries: 28 patients (21 men, 7 women). The parameters of abnormal radiographic findings thought to be associated with FAI, including positive crossover or figure-of-eight sign of acetabulum, lateral center edge angle (LCEA) >40°, Tönnis angle <0°, positive posterior wall sign, alpha angle >50°, and coxa profunda, were evaluated in all patients through plain radiographs.The cross-over sign (Group A: 0, Group B: 8, P = .0035), LCEA (Group A: 1, Group B: 7, P = .0190), Tönnis angle (Group A: 3, Group B: 13, P = .0026), and alpha angle (Group A: 7, Group B: 17, P = .0039) differed significantly between both groups. However, there were no statistically significant differences in posterior wall sign (Group A: 9, Group B: 12, P = .3143) or coxa profunda (Group A: 12, Group B: 8, P = .7096).Patients with interrupted blood supply of the superior retinacular arteries displayed more parameters of abnormal radiographic findings associated with FAI thereby indicating potential correlation between FAI and the interruption of superior retinacular arteries.

Factors affecting intraosseous pressure measurement

BACKGROUND

Although a raised intraosseous pressure (IOP) has been found in osteoarthritis and osteonecrosis, the normal physiology of subchondral circulation is poorly understood. We developed an animal model and explored the physiology of normal subchondral perfusion and IOP.

METHODS

In 21 anaesthetised rabbits, 44 intraosseous needles were placed in the subchondral bone of the femoral head (n = 6), femoral condyle (n = 7) or proximal tibia (n = 31). Needles were connected to pressure transducers and a chart recorder. In 14 subjects, the proximal femoral artery and vein were clamped alternately. In five subjects, arterial pressure was measured simultaneously in the opposite femoral artery.

RESULTS

The average IOP at all 44 sites was 24.5 mmHg with variability within SD 6.8 and between subjects SD 11.5. IOP was not significantly influenced by gender, weight, site or size of a needle. Needle clearance by flushing caused a prolonged drop in IOP whereas after clearance by aspiration, recovery was rapid. IOP recordings exhibited wave patterns synchronous with the arterial pulse, with respiration and with drug circulation time. There was a correlation between IOP and blood pressure (13 sites in 5 subjects, Pearson correlation 0.829, p < 0.0005). There was a correlation between IOP and the associated pulse pressure (PP) in 44 sites among 21 subjects (Pearson correlation 0.788, p < 0.001). In 14 subjects (31 sites), arterial occlusion caused a significant reduction in IOP and loss of PP (p < 0.0001). Venous occlusion significantly raised IOP with preservation of the PP (p < 0.012).

CONCLUSION

Our study shows that subchondral cancellous bone behaves as a perfused tissue and that IOP is mainly a reflection of arterial supply. A single measure of IOP is variable and reflects only perfusion at the needle tip rather than being a measure of venous back pressure. Alternate proximal vessel clamping offers a new means of exploring the physiology of subchondral perfusion. We describe a model that will allow further study of IOP such as during loading.

Superimposition of maximal stress and necrosis areas at the top of the femoral head in hip aseptic osteonecrosis

INTRODUCTION

Recent reports described possible mechanical factors in the development and aggravation of osteonecrosis of the femoral head (OFH), but these have yet to be confirmed on dedicated mechanical study. We therefore developed a 3D finite element model based on in-vivo data from patients with incipient OFH, with a view to determining whether the necrosis area was superimposed on the maximal stress area on the femoral head.

HYPOTHESIS

The location of the necrosis area is determined by stress on the femoral head.

MATERIAL AND METHOD

All patients from the rheumatology department with early stage OFH in our center were investigated. Analysis of CT scans showed stress distribution on the head by 3D finite elements models, enabling determination of necrosis volume within the maximal stress area and of the percentage intersection of necrosis within the stress area (%I n/s: necrosis volume in stress area divided by total stress area volume and multiplied by 100) and of stress within the necrosis area (%I s/n: stress volume in necrosis area divided by total necrosis area volume and multiplied by 100).

RESULTS

Nineteen of the 161 patients assessed retrospectively for the period between 2006 and 2015 had incipient unilateral OFH, 10 of whom (4 right, 6 left) had CT scans of sufficient quality for inclusion. Mean age was 52 years (range, 37-81 years). Mean maximal stress was 1.63MPa, mean maximal exported stress volume was 2,236.9 mm³ and mean necrosis volume 6,291.1 mm³. Mean %I n/s was 83% and mean %I s/n 35%, with no significant differences according to gender, age, side or stress volume. There was a strong inverse correlation between necrosis volume and %I s/n (R²=-0.92) and a strong direct correlation between exported stress volume and %I s/n (R²=0.55). %I s/n was greater in small necrosis (<7,000mm³).

CONCLUSION

OFH seems to develop within the maximal stress area on the femoral head. The present results need confirmation by larger-scale studies. We consider it essential to take account of these mechanical parameters to reduce failure rates in conservative treatment of OFH.

LEVEL OF EVIDENCE

IV.

Avascular necrosis of the humeral head following bilateral upper extremity vascular composite allotransplantation: a case report

Vascularised composite allotransplantation (VCA) represents an exciting and emerging field in plastic and reconstructive surgery. Despite the generally good functional and psychosocial outcomes, multiple complications can be associated with the procedure. The authors describe a case of avascular necrosis of the humeral head following successful upper extremity VCA.

Anatomical Findings in Patients Undergoing Total Hip Arthroplasty for Idiopathic Femoral Head Osteonecrosis

BACKGROUND

Osteonecrosis of the femoral head has a host of etiologies. However, in 30% of the cases, no underlying etiology is identified and the process is considered "idiopathic." Our hypothesis was that osseous anatomical abnormalities might be frequently found in patients with femoral head osteonecrosis.

METHODS

A retrospective, 1:2 matched, case-control study was undertaken to compare ninety patients with idiopathic osteonecrosis who had undergone lower-limb computed tomography (CT) prior to undergoing total hip arthroplasty with 180 control patients matched for age, sex, and body mass index (BMI) who had undergone lower-limb computed tomography scanning at our radiology department for any reason except articular or bone disease. Preoperative CT scans were performed for all patients to evaluate femoral offset, femoral neck-shaft angle, femoral neck version, femoral head diameter, acetabular coverage estimated with use of the lateral center-edge angle, acetabular version, and acetabular diameter. The mean age was forty-five years, 69% of the patients were men, and the mean BMI was 26 kg/m2.

RESULTS

Anatomical "abnormalities" associated with osteonecrosis were determined to be a femoral neck-shaft angle of <129° (likelihood ratio [LR] = 3.6), femoral neck version of >17° (LR = 3.8), a lateral center-edge angle of <32° (LR = 5.7), and acetabular version of <19° (LR = 1.38). A combination of three of the four anatomical "abnormalities" was found in 73% of the patients with osteonecrosis but only 11% of the control cases (LR = 6).

CONCLUSIONS

This 1:2 matched, anatomical study suggests that acetabular and femoral anatomical factors, in isolation or combination, can be found in a large percentage of cases of "idiopathic" osteonecrosis.

CLINICAL RELEVANCE

In this study, isolated or combined abnormalities of the hip were observed in the group of patients with osteonecrosis. Those elements may help surgeons to understand the process underlying idiopathic osteonecrosis and thus require further investigation.

Pathophysiology and risk factors for osteonecrosis

Osteonecrosis, also known as avascular necrosis or AVN, is characterized by a stereotypical pattern of cell death and a complex repair process of bone resorption and formation. It is not the necrosis itself but rather the resorptive component of the repair process that results in loss of structural integrity and subchondral fracture. Most likely, a common pathophysiological pathway exists involving compromised subchondral microcirculation. Decreased femoral head blood flow can occur through three mechanisms: vascular interruption by fractures or dislocation, intravascular occlusion from thrombi or embolic fat, or intraosseous extravascular compression from lipocyte hypertrophy or Gaucher cells. In this review, we emphasize etiologic relationships derived mostly from longitudinal cohort studies or meta-analyses whose causal relationships to osteonecrosis can be estimated with confidence. Understanding risk factors and pathophysiology has therapeutic implications since several treatment regimens are available to optimize femoral head circulation, interrupt bone resorption, and preserve the subchondral bone.

Avascular necrosis in pediatric systemic lupus erythematosus: a brief report and review of the literature

Avascular necrosis (AVN) occurs in several chronic illnesses, including systemic lupus erythematosus (SLE), but can also occur in healthy children. There are multiple theories to explain why and how AVN occurs, but an exact mechanism has yet to be unraveled. AVN in the pediatric lupus population is understudied. The Atherosclerosis Prevention in Pediatric Lupus Erythematosus (APPLE) trial, provides an excellent venue to conduct an exploratory analysis to assess associations between AVN and demographics, SLE disease activity and vitamin D deficiency. Herein we present a brief report describing our findings, as well as reviewing the literature on AVN in SLE and other entities.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00065806.

Complete resolution of avascular necrosis of the human femoral head treated with adipose tissue-derived stem cells and platelet-rich plasma

We report a case of a 43-year-old man with early stage (stage 1) avascular necrosis (AVN) of the femoral head treated with adipose tissue-derived stem cells (ASCs) and platelet-rich plasma (PRP). ASC-containing stromal vascular fraction was mixed with PRP and hyaluronic acid. This mixture was then injected into the diseased hip under ultrasound guidance. The affected hip was reinjected weekly with additional PRP for 4 weeks. The patient was followed-up with sequential magnetic resonance imaging (MRI) scans at 3, 18, and 21 months after treatment, together with Visual Analogue Scale (VAS) Walking Index, Functional Rating Index, Harris Hip Score, and Range of Motion (ROM) assessments. The patient's severe hip pain was considerably improved at 3 months after treatment, with pain scores, ROM and MRI showing near complete resolution of AVN. Pain scores, ROM and MRI at 18 and 21 months after treatment indicated complete resolution of AVN. This case represents the first evidence of complete resolution of early stage AVN of the hip following treatment with ASCs/PRP.

Preventive effects of siRNA targeting PPARγ gene on steroid-induced osteonecrosis in rabbits

PURPOSES/AIM: Glucocorticoid steroids can induce expression of PPARγ gene and enhance adipogenesis by bone marrow mesenchymal stem cells (BMSCs), which may result in osteonecrosis of the femoral head. Currently, there are no medications available to prevent steroid-induced osteonecrosis. We hypothesized that siRNA targeting PPARγ gene may prevent steroid-induced adipogenesis and osteonecrosis in rabbit. The purpose of this study was to evaluate the preventive effects of siRNA targeting PPARγ gene on steroid-induced adipogenesis and osteonecrosis.

METHODS

Forty-eight healthy New Zealand rabbits were randomized into four groups with Group M treated with dexamethasone only, Group S with dexamethasone and a recombinant adenovirus shuttle vector carrying siRNA targeting PPARγ gene, Group Con with dexamethasone and a vector carrying irrelative sequence, and Group N with no treatment serving as control. Expressions of the PPARγ, osteocalcin and Runx2 genes, as well as histopathologic changes were evaluated.

RESULTS

The levels of PPARγ gene expression were decreased while the levels of osteocalcin and Runx2 gene expression were increased in rabbits treated with dexamethasone and recombinant adenovirus shuttle vector carrying siRNA targeting PPARγ gene (Group S), compared to rabbits treated either with dexamethasone alone (Group M) or with both dexamethasone and a vector carrying irrelative sequence (Group Con). The marrow necrosis, adipocyte hypertrophy and proliferation, diminished hematopoiesis, thinner and sparse trabeculae, and increased empty osteocyte lacunae in the femoral head were observed in Group M and Group Con rabbits. However, no such changes were seen in Group S rabbits that were treated with dexamethasone and a recombinant adenovirus shuttle vector carrying siRNA targeting PPARγ gene.

CONCLUSION

siRNA targeting PPARγ gene can inhibit adipogenic differentiation of BMSCs and prevent steroid-induced osteonecrosis in rabbit. The inhibition of bone-marrow adipogenesis and concomitant enhancement of osteogenesis with RNAi may provide a novel approach to the prevention of steroid-induced osteonecrosis.

Reduced head-neck offset in nontraumatic osteonecrosis of the femoral head

INTRODUCTION

Risk factors for nontraumatic osteonecrosis of the femoral head have in common that they trigger intravascular coagulation and thus lead to devascularization of the femoral head. In part of the patients, however, no risk factors seem to be evident. Mechanical reasons contributing to nontraumatic osteonecrosis have not been discussed so far. We hypothesized that recurrent traumatization of the vessels supplying the femoral head by a cam-type mechanism as in femoroacetabular impingement could add to intravascular coagulation. We, therefore, asked whether structural abnormalities at the femoral head-neck junction indicative of such a mechanism could be observed in radiographs of patients with osteonecrosis of the femoral head.

MATERIALS AND METHODS

The preoperative anteroposterior and lateral radiographs of 77 patients who underwent surgery because of osteonecrosis of the femoral head were retrospectively screened for a reduced head-neck offset by measuring the α-angle. For comparison, the α-angle was measured on anteroposterior and lateral radiographs of 339 control subjects without evident underlying hip pathology.

RESULTS

The mean α-angle was 62.8° (SD 18.7°) for anteroposterior and 67.6° (SD 13.2°) for lateral radiographs in patients with nontraumatic osteonecrosis of the femoral head, whereas in control subjects, the mean α-angle was 47.2° (SD 9.6°) (p < 0.0001) and 47.6° (SD 10.3°) (p < 0.0001), respectively.

CONCLUSIONS

A reduced head-neck offset in patients with nontraumatic osteonecrosis of the femoral head may act as a mechanical (co-)factor in developing osteonecrosis of the femoral head.

Medullary decompression of the radius as treatment for lameness in a horse

Increased intraosseous pressure (IOP) is a well-characterized source of pain in humans that can be successfully treated by medullary decompression. This report describes the clinical and diagnostic findings, treatment and successful outcome of a horse with a four week long, non-weight bearing lameness secondary to suspected traumatically-induced increased IOP in the left radius. Scintigraphic examination characterized by severe increase in radiopharmaceutical uptake within the affected radius aided in the initial localization of the source of lameness. Decompression of the affected radius was performed by drilling two 3.2 mm tracts through the lateral bone cortex into the medullary cavity. Intramedullary pressure in the radius was measured (37-39 mmHg). Dramatic clinical improvement was observed after surgical decompression of the affected bone and the horse showed full recovery and returned to previous exercise use by 12 months after treatment. Gradual decrease in radial radiopharmaceutical uptake was observed during the following year. Increased IOP should be considered as a cause of lameness in horses and scintigraphic examination may aid in its diagnosis. Medullary decompression may be a successful treatment in some cases.

The pathogenesis of nontraumatic osteonecrosis

Nontraumatic osteonecrosis continues to be a challenging problem causing debilitating major joint diseases. The etiology is multifactorial, but steroid- and alcohol-induced osteonecrosis contribute to more than two thirds of all cases with genetic risk factors playing an important role in many other cases, especially when they contribute to hypercoagulable states. While the exact mechanisms remain elusive, many new insights have emerged from research in the last decade that have given us a clearer picture of the pathogenesis of nontraumatic osteonecrosis of the femoral head. Progression to end stage osteonecrosis of the femoral head appears to be related to four main factors: interactions involving the differentiation pathway of osteoprogenitor cells that promote adipogenesis, decreased angiogenesis, direct suppression of osteogenic gene expression and proliferation of bone marrow stem cells, and genetic anomalies or other diseases that promote hypercoagulable states.

Osteocyte apoptosis and lipid infiltration as mechanisms of alcohol-induced bone loss

AIMS

We carried out an in vivo study to assess the relationship between increase in adiposity in the marrow and osteocyte apoptosis in the case of alcohol-induced bone loss.

METHODS AND RESULTS

After alcohol treatment, the number of apoptotic osteocytes was increased and lipid droplets were accumulated within the osteocytes, the bone marrow and the cortical bone micro-vessels. At last, we found an inverse correlation between bone mineral density and osteocyte apoptosis and strong significant correlations between the osteocyte apoptotic number and lipid droplet accumulation in osteocyte and bone micro-vessels.

CONCLUSION

These data show that alcohol-induced bone loss is associated with osteocyte apoptosis and lipid accumulation in the bone tissue. This lipid intoxication, or 'bone steatosis', is correlated with lipid accumulation in bone marrow and blood micro-vessels.

The use of joint-specific and whole-body MRI in osteonecrosis: a study in patients with juvenile systemic lupus erythematosus

OBJECTIVE

This study aimed to estimate the prevalence of osteonecrosis (ON) in juvenile systemic lupus erythematosus (SLE) patients using joint-specific and whole-body MRI; to explore risk factors that are associated with the development of ON; and to evaluate prospectively patients 1 year after initial imaging.

METHOD

Within a 2 year period, we studied 40 juvenile SLE patients (aged 8-18 years) with a history of steroid use of more than 3 months duration. Risk factors including disease activity, corticosteroid use, vasculitis, Raynaud's phenomenon and lipid profile were evaluated. All patients underwent MRI of the hips, knees and ankles using joint-specific MRI. Whole-body STIR (short tau inversion recovery) MRI was performed in all patients with ON lesions.

RESULTS

Osteonecrosis was identified in 7 patients (17.5 %) upon joint-specific MRI. Whole-body STIR MRI detected ON in 6 of these 7 patients. There was no significant difference between the ON and non-ON groups in the risk factors studied. One patient had pre-existing symptomatic ON. At 1 year follow-up, the ON lesions had resolved in one patient, remained stable in four and decreased in size in two. No asymptomatic patients with ON developed clinical manifestations.

CONCLUSION

Whole-body STIR MRI may be useful in detecting ON lesions in juvenile SLE patients but larger studies are needed to define its role.

Effects of an anticoagulant and a lipid-lowering agent on the prevention of steroid-induced osteonecrosis in rabbits

This study was designed to evaluate the effects of the combined treatment with an anti-coagulant (enoxaparin) agent and a lipid-lowering agent (lovastatin) on prevention or decrease in the occurrence of steroid-induced osteonecrosis in rabbits. A total of 112 rabbits, which were injected intramuscularly with 20 mg/kg of methylprednisolone acetate were divided into four groups and treated as follows: one group received enoxaparin combined with lovastatin (EL; n = 30), another received enoxaparin alone (EA; n = 28), another received lovastatin alone (LA; n = 28) and the last received no treatment (non-prophylactic; NP, n = 26). Haematological examination for serum lipid levels and prothrombin time was carried out and both femora and humeri were examined histopathologically for the presence of osteonecrosis (ON) before injection and at 2, 4, 8 and 12 weeks after the injection. The incidence of ON in the EL group (15%) was significantly lower than that observed in the NP group (68%). The incidence in the EA and LA groups was also significantly lower than that in the NP group (31%, 35%vs. 68%). The fat cell sizes of the bone marrow in both EL (46.49 +/- 1.27 microm) and LA (50.8 +/- 2.31 microm) groups were lower than in the NP group (59.89 +/- 6.33 microm). The prothrombin time was prolonged and plasma lipid levels were reduced in the EL group during the study. Combination treatment with an anti-coagulant agent and a lipid-lowering agent can reduce the incidence of steroid-induced ON in rabbits. Future evaluation in clinical practice is necessary.

Hemiarthroplasty and total shoulder arthroplasty for avascular necrosis of the humeral head

The purpose of this study was to review the outcome of patients with osteonecrosis of the humeral head, based on etiology and treatment with either hemiarthroplasty or total shoulder arthroplasty (TSA). Sixty-four shoulders, with an average age of 57 years, were evaluated at a mean of 4.8 years. Outcomes included L'Insalata and American Shoulder and Elbow Surgeons (ASES) scores, as well as range of motion (ROM). The overall ASES score was 67, average flexion was 127 degrees, and external rotation was 49 degrees. Outcomes did not differ based on etiology, but ROM was decreased with post-traumatic osteonecrosis. There was no difference in outcome or ROM between hemiarthroplasty and TSA. The complication rate was significantly higher with TSA (22%) than with hemiarthroplasty (8%). Achieving ROM in patients with post-traumatic osteonecrosis remains difficult. TSA was associated with a higher complication rate and decreased mobility and should be reserved for patients with stage V osteonecrosis.

Elevated intraosseous pressure in the intertrochanteric region is associated with poorer results in osteonecrosis of the femoral head treated by multiple drilling

Multiple drilling is reported to be an effective treatment for osteonecrosis of the head of femur, but its effect on intra-osseous pressure has not been described. We undertook multiple drilling and recorded the intra-osseous pressure in 75 osteonecrotic hips in 60 patients with a mean age of 42 years (19 to 67). At a mean follow-up of 37.1 months (24 to 60), 42 hips (56%) had a clinically successful outcome. The procedure was effective in reducing the mean intra-osseous pressure from 57 mmHg (SD 22) to 16 mmHg (SD 9). Hips with a successful outcome had a mean pressure of 26 mmHg (SD 19). It was less effective in preventing progression of osteonecrosis in hips with considerable involvement and in those with a high intra-osseous pressure in the intertrochanteric region (mean 45 mmHg (SD 25)). This study is not able to answer whether a return of the intra-osseous pressure to normal levels is required for satisfactory healing.

Preventive effects of puerarin on alcohol-induced osteonecrosis

Alcohol can induce adipogenesis by bone marrow stromal cells and may cause osteonecrosis of the femoral head. Currently, there are no medications available to prevent alcohol-induced osteonecrosis. We hypothesized puerarin, a Chinese herbal medicine with antioxidative and antithrombotic effects, can prevent alcohol-induced adipogenesis and osteonecrosis. Both bone marrow stromal cells (in vitro) and mice (in vivo) were treated either with ethanol or with ethanol and puerarin, with an untreated group serving as a control. In the in vitro study, the number of adipocytes, contents of triglycerides, and levels of PPAR gamma mRNA expression were decreased and alkaline phosphatase activity, contents of osteocalcin, and levels of osteocalcin mRNA expression were increased in cells treated with both alcohol and puerarin, compared with cells treated with alcohol only. In the in vivo study, marrow necrosis, fat cell hypertrophy and proliferation, thinner and sparse trabeculae, diminished hematopoiesis, and increased empty osteocyte lacunae in the subchondral region of the femoral head were observed in mice treated with alcohol. However, no such changes were seen in femoral heads of mice treated with alcohol and puerarin. The data suggest puerarin can inhibit adipogenic differentiation by bone marrow stromal cells both in vitro and in vivo and prevents alcohol-induced osteonecrosis in this model.

Ethanol may suppress Wnt/beta-catenin signaling on human bone marrow stroma cells: a preliminary study

Ethanol and glucocorticoids are risk factors associated with osteonecrosis. Previous reports suggest ethanol and glucocorticoids induce adipogenesis, decrease osteogenesis in bone marrow stroma cells, and produce intracellular lipid deposits resulting in death of osteocytes. The Wnt/beta-catenin signal pathway is involved in the regulation of homeostasis of bone and we presume glucocorticoids and ethanol may induce osteonecrosis in humans through a similar mechanism as in rodents. We hypothesized (1) ethanol, like glucocorticoids, decreases osteogenesis and increases adipogenesis through the Wnt/beta-catenin signaling pathway in human bone marrow stromal cells; and (2) ethanol decreases intranuclear translocation of beta-catenin. We found both dexamethasone and ethanol decrease the gene and protein expression of osteogenesis and increase that of adipogenesis through Wnt signaling-related genes by semiquantitative and quantitative polymerase chain reaction and Western blot. Ethanol hampered intranuclear translocation of beta-catenin by immunofluorescence analysis. The data suggest the Wnt/beta-catenin signaling pathway may be associated with ethanol-induced osteonecrosis.

Avascular necrosis of the femoral head: vascular hypotheses

Vascular hypotheses provide compelling pathogenic mechanisms for the etiology of avascular necrosis of the femoral head (ANFH). A decrease in local blood flow of the femoral head has been postulated to be the cause of the disease. Several studies in human and animal models of ANFH have shown microvascular thrombosis. Endothelial cell damage could be followed by abnormal blood coagulation and thrombus formation with any resulting degeneration distal to the site of vascular occlusion. Other studies suggest that thrombophilia, particularly impaired fibrinolysis, plays a potential role in thrombus formation in ANFH. Reduction in shear stress due to decreased blood flow could lead to apoptosis of endothelial cells, which can ultimately contribute to plaque erosion and thrombus formation. Dysregulation of endothelial cell activating factors and stimulators of angiogenesis or repair processes could also affect the progression and outcome of ANFH. Likewise, regional endothelium dysfunction (RED), referred to as a potential defect in endothelial cells located in the feeding vessels of the femoral head itself, may also have a crucial role in the pathogenesis of ANFH. Molecular gene analysis of regional endothelial cells could also help to determine potential pathways important in the pathogenesis of ANFH.

Results of multiple drilling compared with those of conventional methods of core decompression

We performed multiple drilling as a femoral head-preserving procedure for osteonecrosis of the femoral head thinking the therapeutic effects of core decompression could be achieved by this simpler procedure than core decompression. We retrospectively reviewed 136 patients (163 hips) who had multiple drilling using 9/64-inch Steinmann pins for treatment of nontraumatic osteonecrosis of the femoral head. The mean followup for patients who did not require additional surgery (113 hips) was 87 months (range, 60-134 months). We defined failure as the need for additional surgery or a Harris hip score less than 75. After a minimum 5-year followup, 79% (31/39) of patients with Stage I disease and 77% (62/81) of patients with Stage II disease had no additional surgery. All (15/15) small lesions (<25% involvement) and 84% (37/44) of medium-sized lesions (25-50% involvement) were considered successful. Survival rates of patients with Ficat Stages I or II lesions were greater than survival rates for patients with Stage III lesions. Hips with a large necrotic area had poor results. We had one instance of subtrochanteric fracture through drill entry holes. Multiple drilling is straightforward with few complications and produces results comparable to results of other core decompression techniques.