Scanning Skeletal Remains for Bone Mineral Density in Forensic Contexts

Podsumowanie

Bone mineral density (BMD) is an important factor in understanding nutritional intake. For human skeletal remains, it is a useful metric to assess quality of life in both juveniles and adults, particularly in fatal starvation and neglect cases. This paper provides guidelines for scanning human skeletal remains for forensic purposes.

Streszczenie

The purpose of this paper is to introduce a promising, novel method to aid in the assessment of bone quality in forensically relevant skeletal remains. BMD is an important component of bone's nutritional status and in skeletal remains of both juveniles and adults, and it can provide information about bone quality. For adults remains, it can provide information on pathological conditions or when bone insufficiency may have occurred. In juveniles, it provides a useful metric to elucidate cases of fatal starvation or neglect, which are generally difficult to identify. This paper provides a protocol for the anatomical orientation and analysis of skeletal remains for scanning via dual-energy X-ray absorptiometry (DXA). Three case studies are presented to illustrate when DXA scans can be informative to the forensic practitioner. The first case study presents an individual with observed longitudinal fractures in the weight bearing bones and DXA is used to assess bone insufficiency. BMD is found to be normal suggesting another etiology for the fracture pattern present. The second case study employed DXA to investigate suspected chronic malnutrition. The BMD results are consistent with results from long bone lengths and suggest the juvenile had suffered from chronic malnutrition. The final case study provides an example where fatal starvation in a fourteen-month infant is suspected, which supports autopsy findings of fatal starvation. DXA scans showed low bone mineral density for chronological age and is substantiated by traditional assessments of infant health. However, when dealing with skeletal remains taphonomic alterations should be considered before applying this method.

Wprowadzenie

The objective of forensic anthropological analyses relies on the practitioner's understanding of bone as a complex tissue with multiple units and variation. Bone is a hierarchical, composite tissue with both organic and inorganic components organized into a matrix of collagen and carbonated apatite^1,2,3,4. The inorganic component, or bone mineral is organized in a nanocrystalline structure to provide stiffness and framework for the organic portion^1,2,5. The mineral aspect comprises approximately 65% of bone by weight and its' mass is influenced by both genetic and environmental factors^1,2,4,6. Because bone mineral occupies a three-dimensional space, it can be measured as bone mineral density (BMD), or a function of the mass and the volume occupied⁷. The bulk density of bone mineral varies with age from birth into adulthood^8,9,10,11,12 and has been used extensively in clinical settings as an indicator of osteoporosis and fracture risk^{4,13,14,15,16,17,18}. Dual-energy X-ray absorptiometry (DXA) has been a widespread tool for the assessment of bone health since its introduction in 1987, particularly scans performed in the lumbar spine and hip regions^11,13,19. Validation of DXA scans has been shown as the gold standard when investigating changes in BMD^{13,19,20,21,22,23}. Subsequently, the World Health Organization (WHO) has created normative standards including t- and z-score definitions for juvenile and adult lumbar spine (L1-L4) and hips as these are the regions easily captured volumetrically^11,13,19,24.

The increasing reliance on forensic anthropology in medicolegal casework has encouraged the investigation of novel techniques to better assess skeletal remains in a variety of circumstances. Among these potential techniques is the application of DXA scans to assess BMD as an indicator of bone quality in cases involving fatal starvation and neglect in juveniles^25,26, identification of metabolic bone diseases, and estimating survivability of skeletal elements in taphonomic research^7,27.

In the 2015 U.S. Department of Health and Human Services Child Maltreatment Report, 75.3% of the reported child abuse cases were some form of neglect with ~1,670 fatalities resulting from fatal starvation and neglect in 49 states²⁸. Most juvenile victims of neglect fail to show signs of external physical abuse, but failure-to-thrive is seen in all cases^29,30. Failure-to-thrive is defined as the inadequate nutrition intake to support growth and development. These can have different factors, one of which is neglect resulting from nutritional deprivation^25,31 (see Ross and Abel³² for a more comprehensive review). Deliberate starvation that results in the death of a child or infant is much rarer and considered as the most extreme form of maltreatment^25,33,34. These nutritional deficiencies have a significant effect on bone growth, particularly longitudinal growth in children as an immediate consequence of malnutrition³⁵. Skeletal growth and mineralization primarily depend on vitamin D and calcium, and their supplementation has been linked to increased BMD^25,35,36.

It is exceedingly difficult to identify or prosecute these cases even following a complete autopsy^31,37,38 and special consideration to methods employed must be used. Thus, in cases where fatal starvation or malnutrition is suspected, a multidisciplinary approach is needed particularly in cases involving remains in advanced states of decomposition²⁶. When skeletal remains are involved, bone densitometry is a useful tool in conjunction with other skeletal indicators such as dental development, measurement of the pars basilaris of the skull, and long bone lengths²⁶. Without using the skeletal indicators mentioned above for infants and juveniles, it would not be possible to discern if low BMD is the result of an inherent metabolic disorder, malnutrition, or taphonomic process. Another concern is the estimation of body size (weight and stature) in infant or juvenile skeletal remains. Most normative data sets require information about height or weight for comparison purposes as bone growth in children is size and age dependent¹². When the remains being assessed are unidentified, estimation methods should be employed. For infants under one, normative DXA data is age matched only. In juveniles over the age of 1, Ruff³⁹ or Cowgill⁴⁰ are recommended for estimating body size in skeletal remains as they are based on the Denver Growth Study sample including ages 1 - 17^39,40. When age and body size are estimated, confidence intervals vary and comparison of the mean to the Center for Disease Control (CDC) produced growth curves⁴¹ should be included in the report as well as the confidence interval for the estimated body size. It is important to note that in most cases, information regarding ancestry and sex cannot be determined from juvenile skeletal remains prior to puberty, which is particularly important for adolescents as ancestry and sex are known to significantly impact BMD in adults. In these circumstances, the DXA method may not be applicable. In identified cases, biological information regarding ancestry, sex, and body size, should be obtained prior to analysis.

Bone densitometry in pediatrics has increased with the development of normative data^42,43 with DXA being the most widely available technique⁴⁴. Malnourished children show significantly lower levels in BMD than healthy children with mineralization correlated with severity of malnutrition⁴⁵. DXA scans of the lumbar spine and hips are the most appropriate areas to assess for juveniles according to The American College of Radiology⁴⁶. Reproducibility has been shown for spine, whole hip, and whole body in children throughout the growth period⁴⁷. However, the lumbar spine is preferred as it is primarily composed of trabecular bone, which is more sensitive to metabolic changes during growth and has been found to be more precise than whole hip assessments^25,47,48. Using DXA scans is common in pediatric assessment. However, since DXA is two-dimensional, it does not capture true volume and produces a BMD based on bone area¹³. In children, this is an important distinction as body and bone size vary within and between age groups in children¹². Most normative data available is for comparison with DXA measurements, but care should be exercised to choose an appropriate reference population (see Binkovitz and Henwood¹³ for a list of commonly used DXA normative databases).

Following the scan, a z-score is calculated using an age-matched and population specific reference sample. Z-scores are more appropriate for juveniles since t-scores compare the measured BMD to a young adult sample¹². A z-score between -2 to 2 indicates normal BMD for chronological age while any score below -2 indicates low BMD for chronological age⁴⁹. The -2 to 2 range for both the t- and z-score represent up to two standard deviations from the mean. Plainly, if a measured BMD score is within two standard deviations above or below their reference population mean, they are considered clinically normal.

The reliance on morphological variation for the forensic anthropologist comes from many sources. One of which is the skeletal variation that arises from disease processes, including metabolic bone disorders⁵⁰. The ability to identify specific disorders in skeletal remains has a two-fold advantage: 1) adding information to the biological profile making it more robust and 2) identifying if fractures are pathological or the result of inflicted trauma. There are a variety of metabolic bone disorders^51,52,53, but the most relevant for BMD measures of contemporary remains is osteoporosis. Osteoporosis develops when the rate of trabecular bone loss is greater than the rate of cortical bone loss with a net loss in bone density^53,54,55. Trabecular bone loss is correlated to an increased risk of fracture, especially in bones that have greater trabecular bone content (e.g., the os coxa)^4,55.

Numerous studies on osteoporosis and bone mineral density in skeletal remains have been conducted on archaeological assemblages using both DXA^56,57,58,59 and other methods^60,61,62. However, when assessing osteoporosis in the adult skeleton from archaeological contexts, practitioners disregard that diagnosing osteoporosis clinically requires the mean of a younger reference sample contemporaneous with the individuals being assessed^55,63,64. This is not an issue in forensic anthropology contexts since individuals are age- and sex- matched to modern populations with developed reference samples for both the hip and the lumbar spine, although changes in BMD through diagenesis should be considered for forensic remains. However, taphonomy is the likely factor affecting the ability to obtain legitimate BMD measures from archaeological samples. This is a consideration in forensic contexts as well, where remains recovered from burial conditions with potential postmortem intervals beyond a few months. While still of forensic interest, sufficient doubt could be raised for any BMD scores obtained from remains found in these circumstances.

Osteoporosis is clinically assessed using t-scores of BMD measures that are derived from the individuals’ BMD measures in the hip or lumbar spine relative to a young adult reference sample using DXA^65,66,67,68. This reference sample can be employed for identifying the occurrence of osteoporosis in the skeleton. In forensic contexts, this is useful for two reasons: 1) differentiating between fractures related to abuse-inflicted trauma in the elderly and those from increased bone fragility in osteoporotic individuals⁶⁹, and 2) as a possible personal identification feature⁵⁰.

Bone density has long been considered an indicator that reflects the activity and nutrition of an animal^70,71. More recently it has been noted that bone density, as an intrinsic property of bone, affects its survivability during taphonomic processes⁷.  A consequence of decomposition is the differential survivability of skeletal elements (i.e., discrete, anatomically complete units of the skeleton) and bone density can be used as a predictor of survivability, or bone strength^{7,70,71,72,73,74,75}. This is important in forensic contexts as well as archaeological and paleontological environments in that it affects the practitioners’ ability to adequately employ methods to estimate a biological profile (or age, sex, stature, and ancestry) if only certain skeletal elements are represented.

Bulk density (bone density with pore space included in the measurement) is the appropriate measurement in this situation, considering it is precisely the porous structure of bone that influences its susceptibility to taphonomic processes⁷. Many methods of assessing bone density have been employed including single-beam photon densitometry^27,75, computed tomography^76,77,78, photodensitometry^72,79, and DXA^80,81,82. DXA scans may be preferable to other methods as it is relatively inexpensive, whole body scans can be performed, and individual skeletal elements can be assessed separately or together during analysis. Using BMD scans before and after taphonomic research studies provides useful information on bone survivability resulting from different taphonomic factors and environments⁸².

This paper outlines a protocol for obtaining DXA scans of skeletal remains. The method employs the common, clinical positioning of individuals when performing lumbar spine and hip scans. This allows practitioners to compare the skeletal remains with the appropriate normative standards. The protocol outlined is applicable to both juvenile and adult remains with limitations discussed later.

Protokół

The protocol herein adheres to the North Carolina State University's ethics guidelines for human research.

1. Machine Preparing

NOTE: The following protocol can be broadly applied to any whole body, clinical DXA and BMD scanner.

1. Perform calibration once daily prior to scanning any individuals to ensure quality control. After calibration prompts appear upon start-up of the systems' software, scan a lumbar spine phantom of known density to ensure correct reading of the BMD scanner.
2. If the scanner being utilized does not have a quality control feature in the software, compare the lumbar spine results with those recorded on the spine phantom to ensure the correct measurements.
   NOTE: The spine phantom, should be placed in the center of the scan table and lumbar spine should be selected for quality control.
3. Perform additional tests (e.g., radiographic uniformity) as needed. Perform radiographic uniformity every ten scans maximum to ensure that the entire scanning surface is detected by the scanner.
4. If the scanner being utilized does not have a radiographic uniformity test in the quality control menu, select whole body scan to ensure the scanner can read the entire scanning surface.
   NOTE: Always center the exam table following quality control and before performing exams.

2. Performing Exam

1. Create patient profiles
   1. Create new patient profiles for each new individual scanned to maintain chain of custody and to ensure scans are correctly associated with individual remains. If the individual being scanned is identified, proceed to step 2.1.2. If the individual is unidentified, establish the biological profile prior to scanning to employ the most accurate database references.
   2. Enter demographic information into the patient profile including estimated stature if unknown. Ensure that you select the most appropriate equation for the remains being investigated.
   3. Select scan type. For steps 2.2, select Anterior-Posterior (AP) Lumbar Spine. For step 2.3, select Left or Right Hip scans.
2. AP Lumbar Spine scan
   NOTE: Require lumbar vertebrae (L) one to four.
   1. Select Perform Exam | choose patient | Select scan type |AP Lumbar Spine | Next. Select an open container at least as large as the articulated segment of L1-L4.
      NOTE: The one used in this study is 48.26L X 26.85W X 8.89D in cm (19 in. L X 10.57 in. W X 3.5 in. D).
   2. Fill the bottom of the container with rice as a soft tissue proxy.
      NOTE: Any kind of rice can work as a soft tissue proxy.
   3. Place L1-L4 in anatomical position (spinous processes should be oriented downwards) in the rice with approximately 0.7 cm (0.28 in.) between each vertebral body as shown in Figure 1A. Ensure that the superior and inferior articular facts are articulated, but the vertebral bodies are not in contact with one another.
   4. Center the scanning table and place the container with L1 is oriented towards top (head) of scanning table and L4 is placed 1 cm superior to the intersecting crosshairs. The vertical laser line should be bisecting the vertebrate bodies of all four vertebrae (Figure 1B).
   5. Cover the exposed bone with rice.
   6. Select Start Scan.
   7. Proceed to analysis (step 3.1), If scanned properly (Figure 2). Repeat the scan if not all vertebrae are captured.
3. Left or Right Hip scans
   NOTE: Figure 3 is from a left hip exam, if performing a right hip exam, positioning is mirrored.
   1. Select Perform Exam | choose patient | Select scan type | Left Hip (or Right Hip) | Next. Select an open container at least as large as the articulated os coxa and femur being scanned.
      NOTE: The one used in this study is 88.5L X 41.5W X 13.9D in cm (34.85 in. L X 16.35 in. W X 5.47 in. D).
   2. Fill the bottom of the container with rice (any kind of rice will work as a soft tissue proxy).
   3. Place the os coxa with the acetabulum and obturator foramen facing laterally with the pubic bone oriented medially. Position the ischial tuberosity beneath the femoral head as it articulates with the acetabulum (Figure 3A).
      NOTE: Positioning of the ischial tuberosity is most important because if it extends laterally below the femoral neck it will inflate BMD estimates.
   4. Place the femur with the femoral head in the acetabulum and with the greater trochanter and femoral head in line parallel to the scanning table (i.e., in the same plane). Ensure that the femoral shaft is medially rotated with the distal condyle rotated medially and slightly higher than the medial condyle (Figure 3B).
   5. Center the scanning table, then move the position of the scanning arm and table until the laser crosshairs are oriented so that the center is directly above the subtrochanteric area of the femur with the vertical line bisecting the top-half of the femoral shaft (Figure 3A). Do not move the remains once they have been positioned. Move the table ensures that bones remain in proper anatomical position.
   6. Cover the remaining visible portion of the femoral-acetabular joint with rice.
   7. Select Start Scan.
   8. Proceed to analysis in step 3.2 if scanned properly (Figure 4).
      NOTE: Scans should capture the alignment of the joint such that the midline of the proximal femur is in one plane. The midline should lie from the center of the femoral head to just under the greater trochanter.

3. Analyzing Exams

1. Analyze AP Lumbar Spine scan
   1. Following the scan, an Exit Exam prompt box will appear. Select Analyze Scan.
      NOTE: Software will separate each vertebra into their own regions to assess individual elements and total BMD when scanned properly as shown in Figure 5.
   2. Select Results in the Scan Analysis window. Select vertebral lines If the vertebrae are not properly separated for minor adjustments or directly reposition vertebrae for rescanning.
   3. Obtain both age-matched and population specific BMD reference measures to calculate a z-score when performing juvenile BMD scans.
   4. Collect results graph for visualization of the individual relative to the reference population.
      NOTE: Figure 6 shows scan results for AP Lumbar Spine of a 31-year-old female.
2. Analyze hip scan.
   1. Following the scan, an Exit Exam prompt box will appear. Select Analyze Scan.
      NOTE: Software will automatically capture the femoral neck, Ward's triangle, and trochanteric area as shown in Figure 7, if scanned properly.
   2. Select the bone map tool to add or delete areas that are not part of the femoral neck and trochanteric region when not read exactly by the software due to slight malposition. Make midline adjustments directly on scan by selecting the neck tool and repositioning the midline.
   3. Reposition and rescan if these small adjustments do not allow the proper alignment shown in Figure 7.
   4. Select Results in the Scan Analysis window. Compare to reference data for femoral neck, trochanteric region, and the intertrochanteric region in the software for adults.
   5. Compare results with the appropriate age- and population-matched references when assessing juveniles.
   6. Use the t-score for adults as it is the most appropriate to differentially assess pathological conditions.
      NOTE: Figure 8 shows the ideal scan results for the left hip analysis of a 31-year-old female.

Wyniki

The methodology proposed here is commonly used in living patients and consideration of its novelty to deceased individuals should be noted. Figure 6 and Figure 8 present the results of an AP lumbar spine and left hip scan, respectively. The individual assessed in these scans is a deceased white, female, 31 years of age that is housed at the Forensic Analysis Laboratory of North Carolina State University. This individual had a tot...

Dyskusje

The results presented in this paper are illustrative of the applicability of BMD metrics in forensic contexts. As Figure 6 and Figure 8 show, the scanning position of living individuals for clinical BMD scans is reproducible with skeletal remains, but care must be taken to ensure proper positioning. This is especially critical for the hip examination where identifying the midline of the femoral neck require the proper angle of the femur and overestimation of BMD...

Materiały

Name	Company	Catalog Number	Comments
QDR Discovery 4500W system	Hologic	Discovery W	All inclusive DXA whole body scanner that includes APEX software for visualization and analysis of scans. Incorporates FRAX reference data developed by WHO to provide both t- and z- scores.
APEX 3.2	Hologic	APEX	Software used by the DXA PC connected to the bone desitometer (QDR Discovery 4500W system) to acquire the BMD data and analyze results.