Volumetric quantitative computed tomography of the proximal femur: precision and relation to bone strength

We have developed a three-dimensional computed tomography (CT) scanning and image analysis method for measurement of trabecular and integral bone mineral density (BMD) and geometry in automatically determined femoral-neck and trochanteric subregions of the proximal femur. We measured the correlation of the density and geometry variables to femoral strength assessed in vitro under loading simulating a single-limb condition and a fall to the side. While BMD alone accounted for 48%-77% of the variability in strength for the stance loading configuration, femoral neck cross-sectional area (minCSA) and femoral neck axis length (FNAL) also contributed independently to femoral strength, and a combination of BMD and geometry variables explained 87%-93% of the variance in the data. For the fall loading configuration, trochanteric trabecular BMD alone explained 87% of the variability of strength. The reproducibility in vivo of the technique was assessed in a group of seven postmenopausal women, who underwent repeat scans with repositioning. For trabecular BMD, the precision was 1.1% and 0.6% for the femoral neck and trochanteric subregions, respectively, compared to 3.3% and 1.6% for the corresponding integral envelopes. Thus, trabecular BMD measurements were reproducible and highly correlated to biomechanical strength measurements. These results support further exploration of quantitative CT for assessment of osteoporosis at the proximal femur.

Fractures of the femoral neck in patients between the ages of twelve and forty-nine years

Femoral neck fractures in young adults have a poor prognosis because the incidence of non-union and aseptic necrosis is high. We reviewed the results in twenty-seven consecutive patients with a femoral neck fracture who were younger than fifty years and who were treated with a standard protocol at Harborview Medical Center from 1975 to 1981. There were twenty-two male and five female patients, and they ranged in age from twelve to forty-nine years (mean, 32.4 years). Twenty patients were involved in high-velocity trauma and twelve of them had significant injuries to other organ systems. One of the remaining seven patients had sustained the fracture while running, and in the other six the fracture was associated with a metabolic disorder. Eight patients had a Garden Stage-II fracture; twelve, Stage-III; and seven, Stage-IV. The fractures were fixed with multiple 6.5-millimeter cancellous screws after adequate closed reduction, which was usually performed within eight hours after injury. All of the fractures united and there were no wound infections. Aseptic necrosis of the femoral head developed in five patients (20 per cent), three of whom had symptoms at the time of writing and will require surgical revision of the hip.

Diagnosis of occult fractures about the hip. Magnetic resonance imaging compared with bone-scanning

Sixty-two consecutively seen patients in whom a fracture about the hip was clinically suspected, but in whom the radiographic findings were negative, were examined with both magnetic resonance imaging and bone-scanning. The magnetic resonance-imaging studies, consisting of T1-weighted coronal sections, were done within twenty-four hours after admission to the hospital, and the bone scans, within seventy-two hours after admission. There were twenty-three men and thirty-nine women. Thirty-six patients who had evidence of a fracture on the magnetic resonance-imaging study also had a positive bone scan initially. Twenty-three patients who had a negative finding on the magnetic resonance-imaging study had a corresponding negative bone scan. Two additional patients had evidence of avascular necrosis of the femoral head on both the magnetic resonance image and the bone scan, and they were managed non-operatively. One patient had a positive magnetic resonance image and a negative bone scan twenty-four hours after admission. A repeat bone scan, which was made six days later, was positive for a fracture of the femoral neck and the patient was managed with internal fixation. Magnetic resonance imaging was as accurate as bone-scanning in the assessment of occult fractures of the hip. The magnetic resonance imaging took less than fifteen minutes to perform, and it was tolerated well by the patient. Magnetic resonance imaging provides an early diagnosis of occult fractures about the hip and may decrease the length of the stay in the hospital by expediting definitive treatment.

The exclusion of high trauma fractures may underestimate the prevalence of bone fragility fractures in the community: the Geelong Osteoporosis Study

Fractures associated with severe trauma are generally excluded from estimates of the prevalence of osteoporotic fractures in the community. Because the degree of trauma is difficult to quantitate, low bone mass may contribute to fractures following severe trauma. We ascertained all fractures in a defined population and compared the bone mineral density (BMD) of women who sustained fractures in either "low" or "high" trauma events with the BMD of a random sample of women from the same population. BMD was measured by dual-energy X-ray absorptiometry and expressed as a standardized deviation (Z score) adjusted for age. The BMD Z scores (mean +/- SEM) were reduced in both the low and high trauma groups, respectively: spine-posterior-anterior (-0.50 +/- 0.05 and -0.21 +/- 0.08), spine-lateral (-0.28 +/- 0.06 and -0.19 +/- 0.10), femoral neck (-0.42 +/- 0.04 and -0.26 +/- 0.09), Ward's triangle (-0.44 +/- 0.04 and -0.28 +/- 0.08), trochanter (-0.44 +/- 0.05 and -0.32 +/- 0.08), total body (-0.46 +/- 0.06 and -0.32 +/- 0.08), ultradistal radius (-0.47 +/- 0.05 and -0.42 +/- 0.07), and midradius (-0.52 +/- 0.06 and -0.33 +/- 0.09). Except at the PA spine, the deficits were no smaller in the high trauma group. Compared with the population, the age-adjusted odds ratio for osteoporosis (t-score < -2.5) at one or more scanning sites was 3.1 (95% confidence interval 1.9, 5.0) in the high trauma group and 2.7 (1.9, 3.8) in the low trauma group. The data suggest that the exclusion of high trauma fractures in women over 50 years of age may result in underestimation of the contribution of osteoporosis to fractures in the community. Bone density measurement of women over 50 years of age who sustain fractures may be warranted irrespective of the classification of trauma.

The superiority of magnetic resonance imaging in differentiating the cause of hip pain in endurance athletes

The accuracy of magnetic resonance imaging of the hip was prospectively evaluated in 19 military subjects engaged in endurance training. These patients had hip pain, negative radiographs, and radionuclide bone scans consistent with femoral neck stress fracture. Twenty-two hips were identified as positive for femoral neck stress fracture by bone scan. Each patient underwent magnetic resonance imaging and 6-week follow-up plain radiographs of the hips. Magnetic resonance imaging studies differentiated femoral neck stress fractures from a synovial pit, iliopsoas muscle tear, iliopsoas tendinitis, obturator externus tendinitis, avascular necrosis of the femoral head, and a unicameral bone cyst. The follow-up radiographs were used to verify the diagnosis of stress fracture. The radiographs showed healing callus in patients with stress fractures. Patients with diagnoses other than stress fractures had no changes on follow-up radiographs. Magnetic resonance imaging studies were as sensitive and much more specific than bone scan in determining the cause of hip pain. Radionuclide bone scan had an accuracy of 68% for femoral neck stress fractures with 32% false-positive results; MRI was 100% accurate. Magnetic resonance imaging proved to be superior to radionuclide bone scanning in providing an early and accurate diagnostic tool that aided in the differential diagnosis of hip pain in the young endurance athlete.

Delayed internal fixation of fractures of the neck of the femur in young adults. A prospective, randomised study comparing closed and open reduction

We have compared the results and complications after closed and open reduction with ternal fixation in young adults with displaced intracapsular fractures (Garden grades III and IV) of the neck of the femur. We also studied the risk factors which influenced nonunion and the development of avascular necrosis (AVN). A total of 102 patients aged between 15 and 50 years was randomised to receive either closed or open reduction. Both groups were compared for age, gender, time to surgery and posterior comminution as well as for union and complications. Using univariate and multivariate analysis the factors influencing nonunion and AVN were assessed. Of the 102 patients, 92 were available for review. There was no significant difference between the groups in terms of union (p = 0.93) and AVN at two years (p = 0.85). Posterior comminution, poor reduction and improper placement of the screws were the major factors contributing to nonunion. The overall incidence of AVN was 16.3% (15 of 92 patients) and it was not influenced by these factors. A delay of more than 48 hours before surgery did not influence the rate of union or the development of AVN when compared with operation within 48 hours of injury.

Optimum configuration of cannulated hip screws for the fixation of intracapsular hip fractures: a biomechanical study

The radiographs of a sample of patients who had canulated hip screw fixation for intracapsular femoral neck fractures were reviewed in our region. There were six different types of configurations used in these fixations which are divided into two groups: (I) triangular configurations, consisting of two parallel screws with a third screw placed either superiorly, inferiorly, anteriorly or posteriorly; and (II) linear configurations with two or three screws in a vertical line. In our study, we tested the relative strength of each configuration in a laboratory setting using synthetic bone models. Statistical analysis, at 5% significance level, using two-way ANOVA and post-hoc test was carried out to test the differences of the results between the configurations.Our results clearly show that the triangular configurations had a higher peak load, higher ultimate load, less displacement and more energy absorption before failure than other configurations.

Are the etiologies of cervical and trochanteric hip fractures different?

Review of results published in the past few years indicates that there are several differences between women sustaining trochanteric fractures of cervical hip fractures. In most series women with trochanteric fractures are older, shorter, and lighter than those with cervical fractures. The bone mineral density was found to be lower in trochanteric fractures, but although in the majority of the studies the diminution was statistically significant at the level of the trochanter and spine--with predominant trabecular bone--the decrease was not uniformly significant at the level of the femoral neck or total skeleton. Previous vertebral fractures were twice as common in patients with trochanteric fractures. Ultrasound exploration of the calcaneus disclosed that the values were significantly lower in women with trochanteric fractures and this finding was independent of the diminution of the bone mineral density. On the other hand, fall biomechanics have not been found to be different in the two types of hip fractures. In summary, women with trochanteric fractures have a more severe and generalized bone loss, especially of the trabecular component. Cervical fractures seem to be more related to pelvic structure-failure of the outer diameter of the femoral neck to expand with age and increased acetabular bone width-added to a focal bone loss. The two main types of fractures should be treated separately in epidemiological or clinical studies to increase the knowledge and the possibilities of preventing hip fractures.

Ultrasound attenuation of the calcaneus: a sensitive and specific discriminator of osteopenia in postmenopausal women

Recent studies have evaluated techniques for estimating bone mass without radiation. The present study compares broadband ultrasound attenuation of the calcaneus and bone densities of the femoral neck and the lumbar spine in 17 normal women and 41 women with osteoporosis. Twenty of the osteoporotic women had spine (n = 16) or femoral neck (n = 4) fractures. There was a significant decrease in the broadband ultrasound attenuation (P less than 0.001) in women with osteoporosis compared with normal women. The osteoporotic women also showed a decrease in vertebral (P less than 0.0001) and femoral neck (P less than 0.0001) densities compared with normal women. At 63 dB/MHz, the sensitivity and specificity of broadband ultrasound attenuation for decreased bone mineral density with or without fractures were 76%. All women with fractures had a broadband ultrasound attenuation less than 72 dB/MHz. This corresponded to a specificity of 41%. To determine whether broadband ultrasound attenuation correlated with trabecular bone volume, samples of cadaver calcaneus were analyzed. The histologic determination showed a significant correlation between broadband ultrasound attenuation and trabecular bone volume (r = 0.992, P = 0.008). These results suggest broadband ultrasound attenuation of the calcaneus reflects bone mass and can be used as a safe and sensitive indicator for decreased axial bone density.

Intertrochanteric osteotomy for non-union of the femoral neck

We report a series of 50 patients under 70 years of age who had an ununited femoral neck fracture treated by a Pauwels abduction osteotomy. At an average follow-up of 7.1 years, seven patients had required prosthetic replacement and 37 others were reviewed in detail. In these patients the Harris hip score averaged 91. Twenty-two hips showed radiographic evidence of avascular femoral head necrosis, but only three of these had been replaced. For active patients with non-union of a femoral neck fracture, Pauwels osteotomy provides a high proportion of good results even in the presence of avascular necrosis of the head, providing there has been no collapse. If osteotomy fails, prosthetic replacement is still possible.

Garden's classification of femoral neck fractures. An assessment of inter-observer variation

Radiographs of 100 randomly chosen femoral neck fractures were assessed by eight observers using Garden's classification. The radiographs were classified identically by all eight in only 22 cases. Another 45 cases were classified by some observers as undisplaced fractures (Stages 1 and 2) and by others as displaced fractures (Stages 3 and 4). Between the different observers the number of displaced fractures varied from 63 to 89. These results show that observers had a relatively poor ability to delineate the various stages of Garden's classification.

A new measurement for posterior tilt predicts reoperation in undisplaced femoral neck fractures: 113 consecutive patients treated by internal fixation and followed for 1 year

BACKGROUND AND PURPOSE

Preoperative posterior tilt in undisplaced (Garden I-II) femoral neck fractures is thought to influence rates of reoperation. However, an exact method for its measurement has not yet been presented. We designed a new measurement for posterior tilt on preoperative lateral radiographs and investigated its association with later reoperation.

PATIENTS AND METHODS

A consecutive series of 113 patients, > or = 60 years of age with undisplaced (Garden I-II) femoral neck fractures treated with two parallel implants, was assessed regarding patient characteristics, radiographs, and rate of reoperation within the first year. In a subgroup of 50 randomly selected patients, reliability tests for measurement of posterior tilt were performed.

RESULTS

Intra- and interclass coefficients for the new measurement were > or = 0.94. 23% (26/113) of patients were reoperated and increased posterior tilt was an accurate predictor of failure (p = 0.002). 14/25 of posteriorly tilted fractures > or = 20 degrees were reoperated, as compared to 12/88 of fractures with less tilt (p < 0.001). In multiple logistic regression analysis including sex, age, ASA score, cognitive function, new mobility score, time from admission to operation, surgeon's expertise, postoperative reduction, and implant positioning, a preoperative posterior tilt of > or = 20 degrees was the only significant predictor of reoperation (p < 0.001).

INTERPRETATION

The new measurement for posterior tilt appears to be reliable and able to predict reoperation in patients with undisplaced (Garden I-II) femoral neck fractures.

Biomechanical study of the resurfacing hip arthroplasty: finite element analysis of the femoral component

Finite element analysis was performed using 3-dimensional models to examine the biomechanical characteristics of the femoral component in resurfacing hip arthroplasty. Stress concentration was observed in the cortical bone adjacent to the rim of the prosthesis. Stress shielding was observed in the anterosuperior regions on the cancellous bone cross-sections near the cup rim. These biomechanical characteristics may lead to complications such as femoral neck fractures in patients with osteopenic bone and long-term loosening.

Femoral neck stress fractures

Fifty-four femoral neck stress fractures were studied prospectively to evaluate treatment methods. Fifty-four fractures in 49 patients were identified in a 4 year prospective study that included 1,049 stress fractures of all types. From our evaluation of treatment methods, a modification of existing classification systems was developed based on radiographic findings and treatment. Differences from earlier studies were noted in racial diversity, in nonprogression of tension-side fractures, and in return to function.

Cortical thickness mapping to identify focal osteoporosis in patients with hip fracture

Background

Individuals with osteoporosis are predisposed to hip fracture during trips, stumbles or falls, but half of all hip fractures occur in those without generalised osteoporosis. By analysing ordinary clinical CT scans using a novel cortical thickness mapping technique, we discovered patches of markedly thinner bone at fracture-prone regions in the femurs of women with acute hip fracture compared with controls.

Methods

We analysed CT scans from 75 female volunteers with acute fracture and 75 age- and sex-matched controls. We classified the fracture location as femoral neck or trochanteric before creating bone thickness maps of the outer ‘cortical’ shell of the intact contra-lateral hip. After registration of each bone to an average femur shape and statistical parametric mapping, we were able to visualise and quantify statistically significant foci of thinner cortical bone associated with each fracture type, assuming good symmetry of bone structure between the intact and fractured hip. The technique allowed us to pinpoint systematic differences and display the results on a 3D average femur shape model.

Findings

The cortex was generally thinner in femoral neck fracture cases than controls. More striking were several discrete patches of statistically significant thinner bone of up to 30%, which coincided with common sites of fracture initiation (femoral neck or trochanteric).

Interpretation

Femoral neck fracture patients had a thumbnail-sized patch of focal osteoporosis at the upper head-neck junction. This region coincided with a weak part of the femur, prone to both spontaneous ‘tensile’ fractures of the femoral neck, and as a site of crack initiation when falling sideways. Current hip fracture prevention strategies are based on case finding: they involve clinical risk factor estimation to determine the need for single-plane bone density measurement within a standard region of interest (ROI) of the femoral neck. The precise sites of focal osteoporosis that we have identified are overlooked by current 2D bone densitometry methods.

Hip fractures in children: a long-term follow-up study

University of Iowa Hospital records from 1926 to 1988 were searched for cases of hip fractures in otherwise healthy children aged between 1 and 16 years. Twenty-six cases were identified. Nineteen patients were available for clinical and radiographic follow-up evaluation. The average follow-up was 16 years postinjury. There were four type I (transepiphyseal), nine type II (transcervical), three type III (cervicotrochanteric), and three type IV (intertrochanteric) femoral fractures. Avascular necrosis (AVN) of the femoral head complicated nine of the 19 fractures (47%). Seventy-eight percent of patients who developed AVN required additional surgical intervention to obtain acceptable hip function.

Avascular necrosis of the femoral head after femoral neck fracture

Trauma-induced avascular necrosis of the femoral head represents the most common femoral head aseptic necrosis. An alteration in blood supply to the femoral head is the cause of the vascular necrosis. Another mechanism in the genesis of femoral head necrosis is the tamponade effect. Femoral head necrosis may be asymptomatic for a long time, even in patients in whom late segmental collapse already is present. Radiography does not allow diagnostic reliability until 6 months after fracture. The presence of a low signal intensity band away from the fracture line on magnetic resonance images clearly delimits the necrotic area. Once segmental collapse has developed, the diagnosis becomes simple using plain radiographs. The treatment of established femoral necrosis complicating fractures of the upper end of the femur is approached as a therapeutic problem lacking an optimal solution. The main therapeutic options are femoral head-preserving procedures and joint reconstruction. Among the procedures that preserve the femoral head are joint unloading, femoral head core decompression, electric stimulation, osteotomy, and bone grafting. Joint reconstruction procedures including cup arthroplasty, hemiresurfacing, total hip resurfacing, femoral head replacement, femoral head endoprosthesis, and total arthroplasty will be reviewed.

Osteoarthritis of the hip: the patient behind the disease

Previous epidemiological studies suggested that patients with osteoarthritis (OA) of the hip might constitute a definable subset of the population with characteristics that predispose them to joint failure. To investigate this possibility a comparative study of somatotype, bone density, disc degeneration, polyarticular joint degeneration, and soft-tissue calcification was carried out in 3 groups of individuals: (1) patients presenting with OA of the hip; (2) patients with acute femoral neck fracture; (3) healthy controls. OA of the hip was rare in patients with femoral neck fracture; conversely, patients with coxarthrosis did not have the low values for bone density seen in the fracture group. There were significant differences in somatotype in the 2 patient groups; 94% of those with OA were endomorphic mesomorphs. Polyarticular OA occurred with the same prevalence in the 2 groups of women, but among males there was a significantly greater involvement of knees and hands in the OA group than in the fracture group. The highest incidence of joint calcification was found in the fracture group and the lowest in the OA group. It was concluded that patients with OA of the hip form a definable subset of the general population. Within this group the appearances of hip OA are determined by 3 interacting factors: mechanical stress, cartilage degeneration, and bone response.

The complications of displaced intracapsular fractures of the hip

We have studied the placement of three screws within the femoral head and the degree of angulation of the screws in 395 patients with displaced intracapsular fracture of the hip to see if either was related to the risk of failure of the fracture to unite. No relationship between nonunion of the fracture was found regarding the position of the screws on the anteroposterior radiograph. However, we found that a reduced spread of the screws on the lateral view was associated with an increased risk of nonunion of the fracture.

Complications associated with fracture of the neck of the femur in children

We reviewed 16 children with 16 displaced fractures of the femoral neck associated with complications. One was a transepiphyseal fracture, 12 were transcervical fractures, and three were basocervical fractures. The mean age at time of fracture was 11 years 7 months (range, 4 years 6 months to 16 years), and the mean length of follow-up after fracture was 6 years 11 months (range, 2-24 years). Complications in this series were avascular necrosis (AVN) (14 patients), nonunion (seven patients), premature physeal closure (15 patients), chondrolysis (seven patients), and coxa vara (two patients). Avascular necrosis, nonunion, and chondrolysis were associated with a poor outcome. Coxa vara or premature physeal closure alone was not responsible for a poor result.

Relevance of osteoporosis in women with fracture of the femoral neck

A prospective study of fractures of the femoral neck was conducted over 12 months in order to ascertain the relevance of generalised osteoporosis as determined by metacarpal morphometry. A series of some 200 women sustaining a fracture of the femoral neck after minor trauma had bone mass measurements similar to those of a control population of normal women, and 16% were not osteoporotic. A history of previous fractures was documented in one third of the women, but this was unrelated to the presence or severity of osteoporosis, although over half of the fractures had occurred within the previous four years. Trochanteric fractures were seen more commonly in severely osteoporotic women (p less than 0.005), whereas cervical fractures predominated in those who were not osteoporotic. These findings support the hypothesis that postural instability is the major determinant for femoral neck fracture and that generalised osteoporosis, rather than being a prerequisite for fracture, merely determines the type of fracture sustained.

Unipolar versus bipolar hemiarthroplasty: functional outcome after femoral neck fracture at a minimum of thirty-six months of follow-up

OBJECTIVES

This investigation was undertaken to compare a series of elderly individuals who sustained a displaced femoral neck fracture treated with either a cemented bipolar prosthesis or a cemented modular unipolar prosthesis.

DESIGN

A retrospective review of prospectively collected data.

SETTING

Hospital-based tertiary care orthopaedic trauma practice.

PATIENTS AND PARTICIPANTS

Two hundred eighty-one community dwelling elderly patients sixty-five years of age or older who sustained a displaced femoral neck fracture (Garden Types III-IV) and underwent primary prosthetic replacement.

INTERVENTION

One hundred one patients received a cemented bipolar prosthesis and 180 received a cemented modular unipolar prosthesis.

MAIN OUTCOME MEASUREMENTS

The study was designed to determine whether there were any significant differences in: (a) the rate of prosthetic dislocation, postoperative medical and wound complications, or need for revision surgery, and (b) the functional outcome, including the incidence of hip pain and recovery of preinjury levels of ambulatory status and activities of daily living, at a minimum of thirty-six months of follow-up.

RESULTS

The two groups of patients did not differ in preinjury characteristics (age, sex, American Society of Anesthesiologist rating of operative risk, number of comorbidities, fracture type, activities of daily living, ambulatory status). There were no significant differences in the rates of postoperative medical or wound complications or dislocation. Ninety-two patients died during the period of study. Forty patients were lost to follow-up or refused to participate. Consequently, 149 patients were followed for a minimum of thirty-six months. Functional ability was compared between both groups with regard to recovery of ambulatory status and activities of daily living, as well as the incidence of hip pain at a minimum of thirty-six months of follow-up. No significant differences were found between the unipolar and bipolar groups.

CONCLUSION

Based on the results of this study, there does not appear to be any advantage to the use of a bipolar endoprosthesis in the management of displaced femoral neck fractures in the elderly. Furthermore, the extra cost of bipolar endoprostheses does not seem to warrant its use.

Is bone microarchitecture status of the lumbar spine assessed by TBS related to femoral neck fracture? A Spanish case-control study

Bone mineral density (BMD) as assessed by dual energy X-ray absorptiometry (DXA) constitutes the gold standard for osteoporosis diagnosis. However, DXA does not take into account bone microarchitecture alterations.

INTRODUCTION

The aim of our study was to evaluate the ability of trabecular bone score (TBS) at lumbar spine to discriminate subjects with hip fracture.

METHODS

We presented a case-control study of 191 Spanish women aged 50 years and older. Women presented transcervical fractures only. BMD was measured at lumbar spine (LS-BMD) using a Prodigy densitometer. TBS was calculated directly on the same spine image. Descriptive statistics, tests of difference and univariate and multivariate backward regressions were used. Odds ratio (OR) and the ROC curve area of discriminating parameters were calculated.

RESULTS

The study population consisted of 83 subjects with a fracture and 108 control subjects. Significant lower spine and hip BMD and TBS values were found for subjects with fractures (p < 0.0001). Correlation between LS-BMD and spine TBS was modest (r = 0.41, p < 0.05). LS-BMD and TBS independently discriminate fractures equally well (OR = 2.21 [1.56-3.13] and 2.05 [1.45-2.89], respectively) but remain lower than BMD at neck or at total femur (OR = 5.86 [3.39-10.14] and 6.06 [3.55-10.34], respectively). After adjusting for age, LS-BMD and TBS remain significant for transcervical fracture discrimination (OR = 1.94 [1.35-2.79] and 1.71 [1.15-2.55], respectively). TBS and LS-BMD combination (OR = 2.39[1.70-3.37]) improved fracture risk prediction by 25 %.

CONCLUSION

This study shows the potential of TBS to discriminate subjects with and without hip fracture. TBS and LS-BMD combination improves fracture risk prediction. Nevertheless, BMD at hip remains the best predictor of hip fracture.