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Keywords:

  • hip fracture;
  • cervical;
  • trochanteric;
  • geometry;
  • neck/shaft angle

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The geometry of the upper femur has been reported to associate with the hip fracture risk in postmenopausal women. However, these associations seem to be partly conflicting, probably because of differences in measurement setup. Here, we compared the upper femur and pelvic geometries of 70 hip fracture patients (46 cervical and 24 trochanteric fractures) and 40 age-adjusted controls based on plain anteroposterior radiographs, eliminating the possible sources of inaccuracy as far as possible by using a standardized patient position and calibrated dimension measurements by digital image analysis. The femoral neck/shaft angle (NSA) was larger in the fracture patients compared with the controls (p < 0.001). The fracture group had thinner cortices in the upper femur than the controls (p < 0.001). The femoral shaft diameter (FSD; p < 0.001), trochanter width (TW; p < 0.01), and the pelvic dimensions, that is, the smallest outer pelvic diameter (SOPD; p < 0.01) and the largest inner pelvic diameter (LIPD; p < 0.05) were smaller in the fracture group. Comparing the fracture types, we found NSA larger in the cervical hip fracture patients than in the patients with a trochanteric fracture (p < 0.01). The femoral neck/shaft cortex ratio was lower and the FSD was smaller in the cervical hip fracture group (p < 0.05). Acetabular width (AW) was greater and the SOPD was wider in the cervical fracture patients (p < 0.01). We concluded that the upper femur and pelvic dimensions as defined from calibrated and position-standardized plain radiographs are useful in the evaluation of hip fracture risk and fracture type.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

HIP FRACTURE is the most serious age-related osteoporotic fracture.(1–4) Its incidence has been rising,(5–7) although this tendency has been suggested to have changed.(8) The femoral skeletal geometry has been presented to be predictive of hip fracture.(9–17) Particularly, a long hip axis length (HAL) has been considered an independent risk factor when evaluating the hip fracture risk of osteoporotic women.(9, 11 12 14) There also are findings that challenge the significance of HAL(18, 19) and even a report of shorter HAL in fracture groups.(19) In the recent article by Michelotti and Clark(20) it was concluded that the measurement of femoral neck length (NL) is sensitive to the patient's position during imaging, which may explain the conflicting findings in dual-energy X-ray absorptiometry (DXA) and pelvic X-ray measurements and, consequently, the measured values of HAL. Moreover, in the previous studies the data concerning the accuracy and reproducibility of the dimension measurements generally are lacking, which also may explain some of the conflicting results.

In most of the geometrical hip fracture studies,(9–11, 16) the fracture group has been considered a single group without differentiating between the two main fracture types, cervical and trochanteric fractures. On the other hand, it also has been postulated that the etiologies of cervical and trochanteric fractures are different(21–23) and cortical thickness, trabecular structure, and bone size in the upper femur and pelvis are important in the pathogenesis of these main hip fracture types.(13)

We carried out a study to determine the upper femur and pelvic geometrical dimensions from plain anteroposterior radiographs attempting to avoid typical inaccuracies in the measurement procedure. The geometrical parameters that associate with hip fracture and any geometrical difference between cervical and trochanteric fractures were defined.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Subjects

Ninety-three consecutive postmenopausal females with nonpathologic cervical (Garden 1-4)(24) or trochanteric (two-fragment or multifragment)(25) hip fractures without previous hip fractures or hip surgery who were admitted to Oulu University Hospital between January 1998 and October 1998 formed the basis for the study group. Inclusion criteria and the ambulation at fracture were assessed by a trained nurse at admission. The roentgenograms were inadequate in nine cases (missing calibration scale or inability to maintain the required position on the X-ray table), and they were excluded from the study. Further, 14 patients were excluded because of a failure to find suitable controls with regard to age (patients aged over 85 years were excluded). Thus, 70 patients (fracture group: mean age, 74.9 years; range, 53-85 years) constituted the final study group. Forty-six of them had a cervical fracture (cervical group: mean age, 73.7 years; range, 53-85 years) and 24 had a trochanteric fracture (trochanteric group: mean age, 77.3 years; range, 60-85 years). Sixty-seven percent of the patients were fully ambulatory (able to walk outdoors without help) and all were ambulatory indoors with or without support. Fifty-five percent of the patients did not use any walking aids.

The control group (40 females, mean age, 73.7 years, and range, 63-84 years) was selected from the females who had bone densitometry in a private clinic during the years 1998-1999. The excluding criteria for the controls were hip fracture; any metabolic bone disease; or treatment with sex hormones, calcitonin, or bisphosphonates. All but one was fully ambulatory and 90% did not use any walking aids.

Body weight, height, and body mass index (BMI) were recorded for both the fracture patients and the controls. Written informed consent was obtained from all the patients and controls, and the study protocol was approved by the institutional ethical committee.

Radiographs

Anteroposterior pelvic roentgenograms of the fracture patients were taken within a few days postoperatively, and those of the controls were taken using the same X-ray equipment. A standard position was used in all cases: supine with the pelvis and both legs straight forward and the big toes touching each other, resulting slight internal rotation of the femur. The beam was centered on symphysis pubis in the midline, and the focus-to-film distance was always 1 m. The 43-cm × 38-cm cassette was placed under the patient. A calibration scale was fixed at the level of the greater trochanter of the noninvolved hip for calibrating the dimension measurements (Fig. 1).

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Figure FIG. 1.. Calibration scale (arrow) fixed at the trochanteric level during the radiographic imaging.

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The X-rays were digitized with a CCD camera (Dage MTI 72E; Dage-MTI, Michigan City, IN, USA) on a light table (Northern Light Desktop Illuminator; Imaging Research, Inc., Ontario, Canada), using an objective Canon CI-TV 16-mm lens (Canon, Tokyo, Japan), and digitally stored in a PC computer. The images were calibrated using the calibration scale, and the dimensions were measured by a digital image analysis system MCID M4 with software version 3.0, revision 1.1 (Imaging Research, Inc.). Several dimensions of the uninjured hip and pelvis were measured (Fig. 2):

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Figure FIG. 2.. Definition of the parameters measured from the anteroposterior (AP) roentgenograms of the pelvis and the upper femur. L-LL, largest inner pelvic diameter (LIPD); M-MM, smallest outer pelvic diameter (SOPD); A-H, hip axis length (HAL); A-B and A-C, femoral neck axis length (FNALa and FNALb, respectively, measured in two ways); B-H, acetabular width (AW); D-DD, femoral head diameter (HD); E-EE, femoral neck diameter (ND); F-FF, trochanteric width (TW); G-GG, femoral shaft diameter (FSD); I, femoral neck cortex width (FNC); J, medial calcar femoral cortex (CFC) width; K, femoral shaft cortex width (FSC); P, neck/shaft angle (NSA). O shows the calibration scale and N is a 3-cm bar generated with the software.

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(1) Pelvic dimensions: largest inner pelvic diameter (LIPD) and smallest outer pelvic diameter (SOPD)

(2) Upper femur dimensions: HAL, femoral neck axis length (measured in two ways; FNALa and FNALb), acetabular width (AW), femoral head diameter (HD), femoral neck diameter (ND), trochanteric width (TW) and femoral shaft diameter (FSD; measured 3 cm below the center of trochanter minor)

(3) Cortical thickness: femoral neck cortex width (FNC), medial calcar femoral cortex (CFC) width, and femoral shaft cortex width (FSC; measured 3 cm below the center of trochanter minor)

(4) femoral neck/shaft angle (NSA)

All the measurements were made by a single observer.

The reproducibility of the measurements was evaluated by three blind repeat measurements of the geometrical parameters from 10 radiographs. The root mean square CV (CVrms) was used as a measure of reproducibility, being 0.9, 1.5, 2.5, 2.5, 3.3, 1.5, 0.7, 1.2, 1.1, 1.2, 1.5, 5.2, and 9.9% for FNALa, FNALb, FSD, TW, AW, ND, HD, HAL, NSA, SOPD, LIPD, FSC, and FNC, respectively. These values indicate that the method was highly reproducible for all the other parameters except cortical thickness.

The accuracy of dimension measurements was evaluated from the radiographs of 18 patients with a hip prosthesis (Austin Moore). The diameter of the spherical head of the prosthesis was measured from the radiographs with image analysis and compared with the known head size of the prosthesis. The root mean square accuracy error was 2.3%.

Statistical analysis

The data organization and statistical analyses were performed by a statistician using the SPSS statistical software (version 8.0; SPSS, Inc., Chicago, IL, USA). Pearson's linear correlation coefficients were calculated between age, body size, and radiographic parameters. Student's t-test was used to compare the fracture group with the control group and the cervical fracture group with the trochanteric fracture group. Mann-Whitney U test was used whenever the material was not normally distributed. A value of p < 0.05 was considered significant.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The upper femur and pelvis measures correlated poorly with body weight but more significantly with height (Table 1). Most of the different pelvis size and upper femur size parameters were strongly positively intercorrelated. NSA had a negative relationship with cortical indices, TW, and FSD.

Table Table 1.. Bivariate Linear Correlation Coefficients Between Age, Height, Weight, and Pelvic and Upper Femur Geometrical Dimensions (n = 109)
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There was a remarkable difference in body size between the fracture and control groups. BMI was significantly lower (p < 0.01) in the hip fracture patients, the explanation being their lower weight (Table 2). The cortical thickness values were significantly lower in the fracture group (p < 0.001). FSD (p < 0.001) and TW (p < 0.01) also were significantly lower in the fracture group than in the control group. NSA, SOPD, and LIPD were significantly different between the fracture and control groups. The fracture group had a higher NSA than the controls (p < 0.001), and the pelvic dimensions SOPD and LIPD were smaller in the fracture group than in the control group (p < 0.01 and p < 0.05, respectively; Table 2).

Table Table 2.. Pelvic and Upper Femur Geometrical Dimensions from Postmenopausal Hip Fracture Patients and Controls
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There was no significant difference in BMI between the cervical and trochanteric fractures, but weight and height were lower in the trochanteric fracture patients (p < 0.05). There were no differences in cortical thickness, but the ratio of FNC/FSC was significantly lower in the cervical fracture patients (p < 0.05). NSA was significantly greater in the cervical hip fracture patients (p < 0.01). SOPD and AW were significantly wider in the cervical fracture patients (p < 0.01 and p < 0.05, respectively). FSD was significantly narrower in the cervical fracture group than in the trochanteric group (p < 0.05; Table 3).

Table Table 3.. Pelvic and Upper Femur Geometrical Dimensions from Postmenopausal Cervical and Trochanteric Hip Fracture Patients
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DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

We measured the geometrical parameters of the pelvis and the proximal femur from plain pelvic radiographs. To reduce the variability of the data, we standardized the patients' positions and calibrated the dimension measurements. Accuracy and reproducibility also were improved by using digital image analysis, which has been shown to be more accurate than the human eye.(26)

The magnitude of the bone dimensions in this study differs from those presented in many previous works.(9, 10, 12, 13), (16, 20) Apparently, the previously reported values are straight measurements from pelvic radiographs without any calibration at the bone level, whereas our measurements were calibrated against a scale at the level of the greater trochanter. In a radiographic setup, the X-ray beam is sectorial, which may introduce magnification errors and variation of the measured geometrical dimensions because of body size. Thus, the conflicting findings might be explained partly by the difference in the measurement setup. Generally, the accuracy of noncalibrated measurements of pelvic radiographs as well as fan beam DXA measurements might be limited because of variation in patient size and bone projection.(13, 20, 27) On the other hand, NSA as an angular parameter is comparable between different measurement setups if the patient position is similar.

Our main findings indicate that women with thin cortices have an increased risk of sustaining a hip fracture. This is in good agreement with the other studies.(9, 13) Here, the pelvic dimensions FSD, TW, and body weight being greater in the controls also were related to the occurrence of hip fractures. However, contrary to this, Karlsson et al.(16) failed to see any differences in the pelvic dimensions between their control and fracture groups. Here, the smaller TW in the fracture patients differs from the finding of Glüer et al.,(13) who observed wider TW in the fracture group. These differences might be explained partly by the differences in the measurement setup.

Some studies have shown HD and ND to be larger(10, 20) and HAL and FNAL to be longer(9) in the fracture group, but we did not find any significant differences between the groups in these parameters. Here again, the conflicting findings might be explained partly by the difference in the measurement setup.

In this study, NSA was significantly larger in the fracture group compared with the controls, which is in good accordance with the previous studies.(13, 16) Ferris et al.(28) found smaller NSA in both cervical and trochanteric fracture patients compared with patients with osteoarthritis (OA), which is a pathological condition. They adjusted hip rotation to the minimum value for NSA by using an image intensifier, which also may make some differences in the results, because OA patients have limitations on hip rotation. We used slight internal rotation in positioning the patient, which makes NSA less dependent on the rotation angle.(20) Glüer et al.(13) also found a higher fracture risk in patients with larger NSA, also using a slight (15-30°) internal rotation.

Here, the main differences between cervical and trochanteric fractures are the greater NSA, SOPD, and AW; the narrower FSD; and smaller FNC/FSC in cervical fracture patients. Glüer et al.(13) reported similar findings for FNC/FSC and AW, but they did not report the pelvic diameters or FSD. However, we did not find any significant difference in HD or cortical thickness, as Glüer et al.(13) did. Ferris et al.(28) reported a shorter femoral NL in patients with trochanteric fractures but no differences in HD, FSD, or NSA. However, they did not differentiate between women and men, their cervical fracture patients were significantly younger than those with a trochanteric fracture, and the group size (n = 10) was relatively small.

The contribution of NSA to the occurrence of hip fracture and fracture type might be caused by variations in the biomechanical environment.(29, 30) Rafferty(31) studied the structural design of the femoral neck in primates, including humans, observing that primates with greater NSA had relatively lower cortical thickness in the inferior than in the superior part of the neck when compared with the primates with lower NSA. The inferior femoral neck cortex will attain less bending stress if the NSA is higher and cortex will remain thinner,(31) predisposing the neck to a greater fracture risk. This loading effect also may explain the negative relationship between NSA and cortical dimensions found here. It has been reported that NSA tends to decrease during aging.(32, 33) It remains to be seen if this age-related diminution is altered in the individuals with hip fracture or do they have a congenitally higher NSA. This question could be clarified with a population study by measuring the NSA in connection with routine DXA.

Falling mechanics, a low hip bone mineral density (BMD), and impairment in mobility have all been found as independent risk factors for hip fracture.(34–36) Here, we found that also geometry plays a role in the occurrence of fracture. In the future, it would be useful to combine the geometric measurements with the analysis of falling mechanics, BMD, and mobility.

According to this study, the geometry of the upper femur, especially high NSA, thin cortices, low FSD and TW, and the pelvic dimensions, associate strongly with the fracture risk and fracture type in postmenopausal women. These upper femur and pelvic measures defined from calibrated and position-standardized plain radiographs might be useful in the clinical evaluation of hip fracture risk.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The authors thank Mrs. Eila Haapakoski for practical assistance and Mr. Pasi Ohtonen for statistical analysis. This work was partly supported by the Ministry of Social Affairs and Health of Finland and by the Finnish Office for Health Care Technology Assessment.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES
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