Aims. While cementless fixation offers potential advantages over cemented fixation, such as a shorter operating time, concerns linger over its higher cost and increased risk of periprosthetic fractures. If the risk of fracture can be forecasted, it would aid the shared decision-making process related to cementless stems. Our study aimed to develop and validate predictive models of periprosthetic femoral fracture (PPFF) necessitating revision and reoperation after elective total hip arthroplasty (THA). Methods. We included 154,519 primary elective THAs from the Swedish Arthroplasty Register (SAR), encompassing 21 patient-, surgical-, and implant-specific features, for model derivation and validation in predicting 30-day, 60-day, 90-day, and one-year revision and reoperation due to PPFF. Model performance was tested using the area under the curve (AUC), and feature importance was identified in the best-performing algorithm. Results. The Lasso regression excelled in predicting 30-day revisions (area under the receiver operating characteristic curve (AUC) = 0.85), while the Gradient Boosting Machine (GBM) model outperformed other models by a slight margin for all remaining endpoints (AUC range: 0.79 to 0.86). Predictive factors for revision and reoperation were identified, with patient features such as increasing age, higher American Society of Anesthesiologists grade (> III), and World Health Organization obesity classes II to III associated with elevated risks. A preoperative diagnosis of idiopathic necrosis increased revision risk. Concerning implant design, factors such as cementless femoral fixation, reverse-hybrid fixation, hip resurfacing, and small (< 35 mm) or large (> 52 mm) femoral heads increased both revision and reoperation risks. Conclusion. This is the first study to develop machine-learning models to forecast the risk of PPFF necessitating secondary surgery. Future studies are required to externally validate our algorithm and assess its applicability in clinical practice. Cite this article: Bone Joint Res 2025;14(1):46–57

Aims. The most important complication of treatment of developmental dysplasia of the hip (DDH) is avascular necrosis (AVN) of the femoral head, which can result in proximal femoral growth disturbances leading to pain, dysfunction, and eventually to early onset osteoarthritis. In this study, we aimed to identify morphological variants in hip joint development that are predictive of a poor outcome. Methods. We retrospectively reviewed all patients who developed AVN after DDH treatment, either by closed and/or open reduction, at a single institution between 1984 and 2007 with a minimal follow-up of eight years. Standard pelvis radiographs obtained at ages one, two, three, five, and eight years, and at latest follow-up were retrieved. The Bucholz-Ogden classification was used to determine the type of AVN on all radiographs. Poor outcome was defined by Severin classification grade 3 or above on the latest follow-up radiographs and/or the need for secondary surgery. With statistical shape modelling, we identified the different shape variants of the hip at each age. Logistic regression analysis was used to associate the different modes or shape variants with poor outcome. Results. In all, 135 patients with AVN were identified, with a minimum of eight years of follow-up. Mean age at time of surgery was 7.0 months (SD 0.45), and mean follow-up was 13.3 years (SD 3.7). Overall, 46% had AVN type 1 while 54% type 2 or higher. More than half of the patients (52.6%) had a poor outcome. We found 11 shape variants that were significantly associated with a poor outcome. These shape variants were predominantly linked to AVN type 2 or higher. Conclusion. Specific morphological characteristics on pelvis radiographs of AVN hips were predictive for poor outcome, at a very young age. There was an overall stronger association to Bucholz-Ogden types 2-3-4 with the exception of two modes at age two and five years, linked to AVN type 1. Cite this article: Bone Joint J 2021;103-B(5):999–1004

Aims. The aim of this study was to compare outcomes of guided growth and varus osteotomy in treating Kalamchi type II avascular necrosis (AVN) after open reduction and Pemberton acetabuloplasty for developmental dysplasia of the hip (DDH). Methods. This retrospective study reviewed patients undergoing guided growth or varus osteotomy for Kalamchi type II AVN between September 2009 and January 2019. All children who had undergone open reduction and Pemberton acetabuloplasty for DDH with a minimum two-year follow-up were enrolled in the study. Demographic and radiological data, which included the head-shaft angle (HSA), neck-shaft angle (NSA), articulotrochanteric distance (ATD), Sharp angle (SA), and lateral centre-edge angle (LCEA) at baseline, two years, and at the extended follow-up, were compared. Revision rates were evaluated. Clinical outcomes using the Harris Hip Score were assessed two years postoperatively. Results. A total of 24 patients underwent guided growth and 19 underwent varus osteotomy, over a mean period of 3.3 years (95% confidence interval (CI) 2.8 to 3.8) and 5.2 years (95% CI 4.5 to 6.0), respectively. There were no differences in demographic and preoperative radiological data, except for a younger age at time of acetabuloplasty and larger ATD for the osteotomy group. The HSA did not differ at two years and the extended follow-up because of postoperative rebound in the osteotomy group. The NSA of the osteotomy group remained smaller postoperatively. There were no significant differences in the follow-up ATD, SA, and LCEA, except for a smaller two-year ATD of the osteotomy group. Seven patients (29.2%) in the guided growth group underwent revision surgery and none in the osteotomy group. The Harris Hip Score was similar between groups. Conclusion. Guided growth and varus osteotomy had comparable results in improving caput valgum deformity, given the rebound of lateral tilting of the physis after osteotomy correction. There were no differences in clinical outcomes at two years postoperatively. Cite this article: Bone Joint J 2022;104-B(7):902–908

Introduction and Objective. Osteonecrosis of the femoral head (ONFH) is an evolving and disabling condition that often leads to subchondral collapse in late stages. It is the underlying diagnosis for approximately 3%–12% of total hip arthroplasties (THAs) and the most frequent aetiology for young patients undergoing THA. To date, the pathophysiological mechanisms underlying ONFH remain poorly understood. In this study, we investigated whether ONFH without an obvious etiological factor is related to impaired osteoblast activities, as compared to age-matched patients with primary OA. Materials and Methods. We cultured osteoblasts isolated from trabecular bone explants taken from the femoral head of patients with ONFH and from intertrochanteric region of patients with ONFH or with OA and compared their in vitro mineralisation capacity and secretion of paracrine factors. Results. Compared to patients with OA, osteoblasts obtained from the intertrochanteric region of patients with ONFH showed reduced mineralisation capacity, which further decreased in osteoblasts from the femoral head of the same patient. Lower mineralisation of osteoblasts from patients with ONFH correlated with lower mRNA levels of genes encoding osteocalcin and bone sialoprotein and higher osteopontin expression. Osteoblasts from the intertrochanteric region of patients with ONFH secreted lower osteoprtegerin levels than those from patients with OA, resulting in a higher receptor activator of NF-κB ligand (RANKL)-to-osteoprotegerin (OPG) ratio. Notably, the RANKL-to-OPG ratio, as well as the secretion of the proresorptive factors interleukin-6 and prostaglandin E. 2. , was higher in osteoblasts from the femoral head of patients with ONFH than in those from the intertrochanteric region. Conclusions. ONFH is associated with a reduced mineralisation capacity of osteoblasts and increased secretion of proresorptive factors

The cause of fracture of the femoral neck after hip resurfacing is poorly understood. In order to evaluate the role of avascular necrosis we compared 19 femoral heads retrieved at revision for fracture of the femoral neck and 13 retrieved for other reasons. We developed a new technique of assessing avascular necrosis in the femoral head by determining the percentage of empty osteocyte lacunae present. Femoral heads retrieved as controls at total hip replacement for osteoarthritis and avascular necrosis had 9% (. sd. 4; n = 13) and 85% (. sd. 5; n = 10, p < 0.001) empty lacunae, respectively. In the fracture group the percentage of empty lacunae was 71% (. sd. 22); in the other group it was 21% (. sd. 13). The differences between the groups were highly significant (p < 0.001). We conclude that fracture after resurfacing of the hip is associated with a significantly greater percentage of empty osteocyte lacunae within the trabecular bone. This indicates established avascular necrosis and suggests that damage to the blood supply at the time of surgery is a potent risk factor for fracture of the femoral neck after hip resurfacing

Introduction. The objective of the work is construction of a multi-bioactive scaffold based on that allows a space/time control over the regeneration of damaged bones by Medication-Related Osteonecrosis of the Jaw using a minimal invasive approach based on the injection of the fast-degrading pro neuro and angiogenic ELR (Elastin-Like Recombinamers) based hydrogels. Method. Chemical crosslinking facilitated the creation of multi-bioactive scaffolds using ELRs with reactive groups. Cell-loaded multi-bioactive scaffolds, prepared and incubated, underwent evaluation for adhesion, proliferation, angiogenic, and neurogenic potential. In vitro assessments utilized immunofluorescence staining and ELISA assays, while live-recorded monitoring and live-dead analysis ensured cytocompatibility. In rat and rabbit models, preformed scaffolds were subcutaneously implanted, and the regenerative process was evaluated over time. Rabbit models with MRONJ underwent traditional or percutaneous implantation, with histological evaluation following established bone histological techniques. Result. A 3D scaffold using ELR that combines various peptides with different degradation rates to guide both angiogenesis and neurogenesis has been developed. Notably, scaffolds with different degradation rates promoted distinct patterns of vascularization and innervation, facilitating integration with host tissue. This work demonstrates the potential for tailored tissue engineering, where the scaffold's bioactivities and degradation rates can control angiogenesis and neurogenesis. In an animal model of medication-related osteonecrosis of the jaw (MRONJ), the scaffold showed promising results in promoting bone regeneration in a necrotic environment, as confirmed by histological and imaging analyses. This study opens avenues for novel tissue-engineering strategies where precise control over vascularization and nerve growth is crucial. Conclusion. A groundbreaking dual approach, simultaneously targeting angiogenesis and innervation, addresses the necrotic bone in MRONJ syndrome. Vascularization and nerve formation play pivotal roles in driving reparative elements for bone regeneration. The scaffold achieves effective time/space control over necrotic bone regeneration. The authors are grateful for funding from the Spanish Government (PID2020-118669RA-I00)

Osteonecrosis of the femoral head after femoral neck fracture (ONFHpoFNFx) poses challenges in children, particularly at Ficat III stage. Limited effective treatments are available. This study explores basicervical femoral neck rotational osteotomy (BFNRO) for ONFHpoFNFx in children and adolescents and evaluates its outcomes. Children and adolescents with ONFHpoFNFx (Ficat stage III) underwent BFNRO at our center from June 2017 to September 2022 were included. Follow-up exceeded 1 year, with data on modified-Harris-hip-score (mHHS), range of motion (ROM), patient satisfaction, femoral head collapse, necrotic area repair, leg-length, and osteoarthritis progression recorded. This study included 15 cases (15 hips), with 8 males and 7 females, averaging 12.9 years in age (range: 10–17 years). Nine cases had BFNRO alone, and six had combined PAO. Rotation angles varied from 70° to 90° for anterior rotation and 110° to 135° for posterior rotation. Nine patients had femoral neck fixation in a varus position (10° to 30°). The postoperative contour of the weight-bearing area of the femoral head has significantly improved in all patients. With an average follow-up of 28.6 months (range: 12.2–72.7 months), mHHS significantly improved (65.2 to 90.2, P<0.001). Only one patient showed femoral head collapse. Patients experienced no/mild hip pain (VAS=0-3), slight restriction in range of motion, and mild limb shortening. Two patients showed osteoarthritis progression. No infections, joint replacements, or nerve injuries were observed. Even in cases of ONFHpoFNFx in the late stage, BFNRO in children and adolescents can still yield positive early to mid-term results by relocating the necrotic area and restoring the integrity of the anterior-lateral column of the femoral head, thereby preventing femoral head collapse and delaying the onset of severe osteoarthritis

Avascular necrosis of the scaphoid following a fracture in children is rare and there is no established treatment protocol in the literature. We present two boys with nonunion and avascular necrosis of the scaphoid treated by simple immobilisation. Both cases healed with painless wrists and full movements. Our cases confirm that an ununited scaphoid fracture in children may heal with conservative treatment, even when an MRI scan suggests avascular necrosis. Unlike in adults, operative treatment need only be considered in children when conservative treatment fails

The use of bisphosphonates in the treatment of avascular necrosis of the femoral head is an encouraging but relatively new option with most published data being derived from small trials with limited follow-up. We present a clinicoradiological analysis of 395 hips with avascular necrosis which were treated with oral alendronate for three years with a mean follow-up of four years (1 to 8). Our results show an improvement in the clinical function, a reduction in the rate of collapse and a decrease in the requirement for total hip replacement, compared with the findings of other studies in which no treatment was given. This improvement is particularly marked if the treatment is begun in the pre-collapse stages of the disease. Even in Ficat stage-III hips some benefit was obtained from treatment with alendronate by at least a delay in the need for total hip replacement

Whereas avascular necrosis of the scaphoid after a fracture is well-documented, idiopathic avascular necrosis of the scaphoid (Preiser’s disease) is rare. Little is known of the aetiology of the condition and even less about the best course of management. We describe a rare case of bilateral Preiser’s disease. Possible aetiological factors and a summary of the current concepts of management are discussed

We performed 96 Birmingham resurfacing arthroplasties of the hip in 71 consecutive patients with avascular necrosis of the femoral head. A modified neck-capsule-preserving approach was used which is described in detail. The University of California, Los Angeles outcome score, the radiological parameters and survival rates were assessed. The mean follow-up was for 5.4 years (4.0 to 8.1). All the patients remained active with a mean University of California, Los Angeles activity score of 6.86 (6 to 9). Three hips failed, giving a cumulative survival rate of 95.4%. With failure of the femoral component as the endpoint, the cumulative survival rate was 98.0%. We also describe the combined abduction-valgus angle of the bearing couple, which is the sum of the inclination angle of the acetabular component and the stem-shaft angle, as an index of the optimum positioning of the components in the coronal plane. Using a modified surgical technique, it is possible to preserve the femoral head in avascular necrosis by performing hip resurfacing in patients with good results

Aims. The aim of this study was to clarify the factors that predict the development of avascular necrosis (AVN) of the femoral head in children with a fracture of the femoral neck. Patients and Methods. We retrospectively reviewed 239 children with a mean age of 10.0 years (. sd. 3.9) who underwent surgical treatment for a femoral neck fracture. Risk factors were recorded, including age, sex, laterality, mechanism of injury, initial displacement, the type of fracture, the time to reduction, and the method and quality of reduction. AVN of the femoral head was assessed on radiographs. Logistic regression analysis was used to evaluate the independent risk factors for AVN. Chi-squared tests and Student’s t-tests were used for subgroup analyses to determine the risk factors for AVN. Results. We found that age (p = 0.006) and initial displacement (p = 0.001) were significant independent risk factors. Receiver operating characteristic (ROC) curve analysis indicated that 12 years of age was the cut-off for increasing the rate of AVN. Severe initial displacement (p = 0.021) and poor quality of reduction (p = 0.022) significantly increased the rate of AVN in patients aged 12 years or greater, while in those aged less than 12 years, the rate of AVN significantly increased only with initial displacement (p = 0.048). A poor reduction significantly increased the rate of AVN in patients treated by closed reduction (p = 0.026); screw and plate fixation was preferable to cannulated screw or Kirschner wire (K-wire) fixation for decreasing the rate of AVN in patients treated by open reduction (p = 0.034). Conclusion. The rate of AVN increases with age, especially in patients aged 12 years or greater, and with the severity of displacement. In patients treated by closed reduction, anatomical reduction helps to decrease the rate of AVN, while in those treated by open reduction, screw and plate fixation was preferable to fixation using cannulated screws or K-wires. Cite this article: Bone Joint J 2019;101-B:1160–1167

Avascular necrosis is a serious complication of slipped capital femoral epiphysis and is difficult to treat. The reported incidence varies from 3% to 47% of patients. The aims of treatment are to maintain the range of movement of the hip and to prevent collapse of the femoral head. At present there are no clear guidelines for the management of this condition and treatment can be difficult and unrewarding. We have used examination under anaesthesia and dynamic arthrography to investigate avascular necrosis and to determine the appropriate method of treatment. We present 20 consecutive cases of avascular necrosis in patients presenting with slipped capital femoral epiphysis and describe the results of treatment with a mean follow-up of over eight years (71 to 121 months). In patients who were suitable for joint preservation (14), we report a ten-year survivorship of the hip joint of 75% and a mean Harris hip score of 82 (44 to 98)

Avascular necrosis is an iatrogenic complication of the treatment of congenital dislocation of the hip. In order to assess the incidence of this and other complications, we have reviewed a consecutive series of 211 children treated at some stage with the modified Denis Browne splint used in Adelaide. In 173 children treated with this splint alone for 238 subluxed or dislocated hips which were stable when reduced, six hips (2.5%) developed radiographic avascular necrosis, though there was progressive growth deformity in only one. There was a much higher incidence among cases treated for unstable reduction by tenotomy, plaster spica and then the splint, 20 of 33 hips (60.6%) showing radiographic signs, though only one led to progressive abnormality. Of seven patients treated by adductor tenotomy and the splint no case of avascular necrosis was encountered. In the whole series the incidence of significant long-term growth disturbance in children treated in this splint was 0.7%. The great majority of our cases of avascular necrosis were attributable to manipulation and plaster, not to the subsequent use of a splint

Osteonecrosis of the femoral head (ONFH) is an ischemic disorder that causes bone and bone marrow necrosis. In spite of many studies, the primary cause of ischemia is still unknown. The purpose of this study is to identify the susceptibility genes in ONFH. We performed a genome-wide association study (GWAS) in 1,602 ONFH cases and 60,000 controls. Stratified GWASs based on the 3 subgroups of ONFH (corticosteroids, alcohol, idiopathic) were also performed. We then evaluated the candidate gene in silico using public databases. Two loci in 12q24.11–12 and 20q12 showed significant association with ONFH. A stratified analysis suggested that the 12q24 locus was associated with ONFH through the drinking capacity. In the 20q12 locus, LINC01370 was the only gene, which functions were related to the plausible biological pathway for the development of ONFH. A novel ONFH locus was identified at chromosome 20q12, and LINC01370 was the best candidate gene in this locus

Osteonecrosis of the femoral head is a complex pathologic process with many aetiological factors. Factors most often mentioned in the literature are mechanical disruption (hip trauma or surgery), steroid use, smoking, haemoglobinopathies and hyperlipidaemia. 1. Our case depicts a rare association of crack cocaine related to osteonecrosis of the femoral head which has never been reported in the available literature. Case Report: A 32 year old man was referred to our Orthopaedic clinic with right hip pain. He had a 9 pack-year history of cigarette smoking and had also smoked crack cocaine between ages 20 to 28; shortly after this the hip pain started. He denied antecedent injury. He had undergone a steroid injection into his right ankle abroad for swelling one year before referral, which was after onset of hip pain. MRI of his hip previously performed abroad had been normal. The patient had an indoor job and was otherwise fit and well. On examination he had reduced of movement in his right hip with 5–10 degrees of fixed flexion deformity. Plain radiography demonstrated cyst formation and sclerosis of both femoral heads. Repeat MRI confirmed bilateral osteonecrosis, worse on the right with risk of head collapse. The patient underwent bilateral core decompressions. Subsequent follow-up demonstrated a mobile patient with no need for arthroplasty and he was discharged after two years. Osteonecrosis is caused by the coagulation of the intra-osseous microcirculation leading to thrombosis formation and eventual reduction in osseous blood supply. Steroid use is associated with increased risk of osteonecrosis to the femoral head, however in these cases the patients often undergo either direct local or systemic infiltration of steroid. In this case steroid was administered after symptoms began to a far distant site and therefore cannot be the cause. Cigarette smoking is also known to cause osteonecrosis. Our patient had smoked cigarettes for fourteen years without problems, and it was after he ceased to smoke crack cocaine that his symptoms began. Cocaine blocks voltage-gated sodium-channels causing vasospasm. It is known to cause nasal and facial bone osteonecrosis due to its common intranasal method of delivery. We postulate that in this case crack cocaine was a synergistic factor towards development of femoral head osteonecrosis

Summary Statement. Osteonecrosis of the femoral head (ONFH) is a multifactorial skeletal disorder. S100A9 represseses angiogenesis and vessel integrity in ONFH. It also may function as a marker of diagnosis in ONFH. Introduction. Osteonecrosis of the femoral head (ONFH) is a multifactorial skeletal disorder characterised by ischemic deterioration, bone marrow edema and eventually femoral head collapse and joint destruction. Several surgical, pharmaceutical and non-invasive biophysical modalities have been employed to alleviate this joint disorder. Our proteomic analysis showed that ONFH patients displayed increased expression of S100A9 protein when compared with healthy volunteers. This study is designed to evaluate the pathogenesis of S100A9 on the patients of ONFH. Patients & Methods. We collected 56 patients with ONFH including stage I, II, III and IV and 14 health volunteers. 20 ml of peripheral venous blood is drawn from each subject or prior to general anesthesia for hip arthroplasty. We compared the ELISA of S100A9, Osteocalcin, TRAP-5b, sVCAM-1. Immunohistochemistry of S100A9, vWF and VEGF are compared using femoral head harvested from late stages of ONFH and femoral neck fracture when received hip arthroplasty. In vitro angiogenic assay was performed by tube formation assay. Results. There were significant elevation of S100A9 in the serum of ONFH patients then in healthy volunteers. sVCAM-1 and TRAP-5b were increased and Osteocalcin was decreased in ONFH patient when comapred with healthy volunteers. The expression of S100A9 protein in ONFH tissue was significantly higher than femoral neck fracture tissue. In tube formation assay, we found S100A9 and the serum of ONFH patient supressed angiogenesis in vascular endothelial cell culture. Discussion/Conclusion. The expression of S100A9 significantly increased in the serum and femoral head tissue of patients with ONFH. S100A9 also supressed angiogenesis expression. The results indicated that S100A9 represseses angiogenesis and vessel integrity in ONFH. It also may function as a marker of diagnosis in ONFH

Osteonecrosis is a pathologic bone condition caused by a disruption in the osseous circulation and impairment of normal cellular function which ultimately leads to bone infarction, osteocyte death, and joint degeneration. The incidence of osteonecrosis in the general population has been reported to be approximately 3 per 100,000 people. Up to 20,000 new cases are diagnosed each year and this condition is the indication for surgery in approximately 10% of all total hip arthroplasties performed in the United States. The hip is the most common joint affected, with approximately 75% of cases occurring in this joint, although multifocal osteonecrosis (defined as involvement of more than 3 joints) can also occur. Other commonly observed locations for osteonecrotic lesions include the knee, shoulder, wrist, and ankle. Joint preserving procedures may be performed for early stages without evidence of collapse, while intermediate lesions (e.g. femoral head collapse < 2 mm) may be candidates for joint preserving procedures such as bone grafting and rotational or proximal femoral varus osteotomies. However, total hip arthroplasty is usually required in advanced cases where there are large lesions, deformation of the femoral head, or acetabular involvement. Osteonecrosis has been traditionally associated with poor outcomes following total hip arthroplasty. However, recent studies using newer implant designs and surgical techniques have demonstrated outcomes comparable to the general total hip arthroplasty population. Johansson and colleagues, in a systematic reviewed of the literature, observed a decrease in the revision rate from 17% to 3% for arthroplasties performed later than 1990. The clinical outcomes were also comparable between patients who had osteoarthritis and those who had osteonecrosis. The young age at which these patients often present makes bearing surface choice challenging. Bearings that have low liner wear rates, such as ceramic bearings, had concerns with implant durability following reports of chipping and fracture of the ceramic. However, recent studies evaluating ceramic bearings in young patients with osteonecrosis have demonstrated that newer third and fourth generation ceramics have solved many of these issues. Byun et al. evaluated the clinical outcomes of ceramic bearings in patients younger than 30 years who had osteonecrosis and observed that at six year follow-up, none of the bearings had failed and that 95% of patients were able to continue with their prior occupation. Similar results at even longer follow-up periods were reported by Kim and colleagues who observed no failures in 93 ceramic hips at a mean follow-up of 11 years. Polyethylene wear continues to be a concern for these younger, more active patients. Early studies with non-highly cross linked polyethylene demonstrated high wear rates in these patients. Although newer polyethylene designs have become available which have demonstrated substantially lower wear than the traditional ultra high molecular weight polyethylene cups of the recent past, further studies are needed with these newer polyethylene bearings in the osteonecrosis population. The goal of treatment for femoral head osteonecrosis remains early diagnosis and joint preservation. For patients who present with femoral head collapse or acetabular involvement, total hip arthroplasty often is the only treatment option left. Although clinical outcomes for these patients were initially poor in earlier reports, the advent of modern cementless arthroplasty components, refined surgical techniques, and newer bearing designs have greatly improved the outcomes of this procedure

Introduction

Femoral head osteonecrosis (FHO) is a condition in which the inadequate blood supply disrupts osteogenic-angiogenic coupling that results in diminishment of femoral perfusion and ends up with FHO. The insufficient knowledge on molecular background and progression pattern of FHO and the restrictions in obtaining human samples bring out the need for a small animal trauma model to research FHO aetiology. Hence, this study aims to develop a mouse trauma model to elucidate the molecular mechanisms behind FHO.

Much of the current confusion and contradiction on the treatment of avascular necrosis of the femoral head is caused by the lack of an agreed efficient, quantitative system for evaluation and staging. We have used a new system to evaluate over 1000 hips with avascular necrosis during a period of 12 years; it has proved to be very valuable. The system is based on the sequence of pathological events known to take place. It allows accurate quantification in both early and later stages, does not use older, invasive diagnostic procedures, and incorporates the newer techniques of bone scanning and MRI. Clinical records of pain and reduced function are not a specific part of the system, although they help to determine treatment and outcome. Hips are first placed into one of seven stages from 0 to VI, based upon the type of radiological change. The extent of involvement is then measured. This allows more accurate evaluation of progression or resolution and better comparison of different methods of management. The system also helps to provide a prognosis and to decide on the best available method of treatment