• Based on the mean prediction error for single leg, legs, and total body BMD, the following
correction factors were developed to correct for artifact error in the event of automated /
non-manually corrected DEXA scans:
Single Leg BMD BMD x (1-0.127)
Legs BMD BMD x (1-0.066 [per implant])
Total body BMD BMD x (1-0.030 [per implant])
• To validate the correction factor for in situ knee implants, forty-five additional patients were
recruited from the same population and underwent the same analysis using DEXA (m=30,
64±6yr, 176.8±7.4cm, 102.0±19.2kg, BMI 32.6±6.1 kg·m2 | f=15, 67±8yr, 163.1±6.0cm,
84.1±16.2kg, BMI 31.5±5.2 kg·m2). A Bland-Altmon analysis for instrument agreement was
used to detect proportional measurement bias between the BMD values corrected using the
correction factor compared to MAC. Type I error was set as α = 0.05 for all analyses.
FIGURE: Data plots representing the results of a Bland-Altman analysis for instrument agreement between adjusted BMD
corrected by either by either manual artifact correction (MAC) or application of correction factors. Significance for the
initial detection of disagreement and post hoc regression to detect proportional bias was set at α = 0.05.
• KEY FINDING: Bland-Altman analysis revealed no proportional bias between BMD values
adjusted using the calculated correction factors (Limb BMD = 1.316 ± 0.028 | Total body
BMD = 1.315 ± 0.024) compared to MAC (Limb BMD = 1.321 ± 0.017 | Total body BMD =
1.324 ± 0.025). Similarly, the linear relationship between observed between predicted and
MAC also indicated instrument agreement for limb (R2=0.96), and total body (R2=0.99) BMD
Total Body & Limb Specific
Results & Follow-up Analysis
Correction Factor For Knee Implants
DEXA Model Specific?
• Standard software based artifact removal typically used in DEXA analysis results in an
overestimation of BMD in patients with joint implants that may result in misclassification of bone
health and risk for low BMD, and osteoporosis.
• Therefore, those with total-joint replacements who may stand to benefit from intervention may
remain at an elevated risk for fragility fractures.
• Importantly, manual artifact correction / removal can successfully overcome software based BMD
• Therefore, it is critical that technicians screen for patients who have joint replacements and take
appropriate image correction measures. It is also critical that physicians take note of regional limb
measures (example: right leg, left leg, etc) as well as total body measures to ensure that BMD
overestimation and misdiagnosis does not occur in this population.
• On the occasion that a patient presents with a DEXA report whereby manual artifact correction was
not properly performed for one or more implants, the correction factors generated here may be of
use for approximating a corrected BMD value.
• However, we caution the reader that these findings are limited to primary knee implants. Further
research will be required to determine the degree to which other types of joint replacements result in
overestimations of BMD by standard automated software analysis.
DEXA Overestimates Bone Mineral Density in Patients with Total Joint Replacements:
The Critical Importance of Correcting Automated Error for Improved Screening Accuracy
Bradley S. Lambert, Ph.D; Katharine D. Harper, M.D.; Terry A. Clyburn, M.D.; Stephen J. Incavo, M.D.
Orthopedic Biomechanics Research Laboratory, Department of Orthopedics and Sports Medicine, Houston Methodist Hospital;
REFERENCES:  Wright NC, Looker AC, Saag KG, Curtis JR, Delzell ES, Randall S, Dawson-Hughes B. The
Recent Prevalence of Osteoporosis and Low Bone Mass in the United States Based on Bone Mineral Density at
the Femoral Neck or Lumbar Spine. J Bone Miner Res. 2014 Nov; 29(11): 2520–2526.  El Maghraoui A, Roux C.
DXA scanning in clinical practice. QJM. 2008 Aug;101(8):605-17.  Kanis JA. Assessment of fracture risk and its
application to screening for postmenopausal osteoporosis: synopsis of a WHO report. WHO Study
Group, Osteoporos Int, 1994, vol. 4 (pg. 368-81).  United States Census Bureau. 2017. https://www.census.gov/.
Accessed 2018 Apr 11.  Sloan M, Premkumar A, Sheth NP. Projected Volume of Primary Total Joint
Arthroplasty in the U.S., 2014 to 2030. J Bone Joint Surg Am. 2018;100:1455-60
• Osteopenia and osteoporosis are important modifiable health factors.
In 2010, it was estimated that 10.2 million adults were diagnosed with
osteoporosis and that 43.4 million adults had low bone mass (1).
• Dual energy x-ray absorptiometry (DEXA) allows for accurate
screening for osteoporosis, estimation of fracture risk, and monitoring
of patients undergoing treatment (2).
• The World Health Organization has established DEXA as the
standard densitometric technique for assessing bone mineral density
(BMD) in postmenopausal women and based the definitions of
osteopenia and osteoporosis on its results (3).
• In the same population group that osteoporosis and osteopenia
present, patients are also most likely to receive a total joint
replacement. Most patients who receive a total hip arthroplasty (THA)
or total knee arthroplasty (TKA) are between 65 and 85 years of age.
Current total THA and TKA volume in the United States is
approximately one million / year, and is expected to grow to ~1.5
million/year by the year 2030 (4,5).
• Typically, automated software is relied upon to remove image artifact
of non-tissue origin (such as implant materials).
• Therefore the purpose of this study was to evaluate the analysis of
DEXA scans in patients with total knee arthroplasty to determine if
there are irregularities noted in the measurement of BMD and the
diagnosis of low BMD, osteoporosis, or osteopenia in patient’s with in
• Thirty-eight older patients (m=15, 61±7yr,
178.1±7.7cm, 103.5±24.1kg, BMI 32.3±5.7 kg·m2 |
f=23, 67±6yr, 163.0±6.2cm, 82.7±19.4kg, BMI
31.0±6.2 kg·m2) who previously underwent total knee
arthroplasty (TKA) for a single limb within the past year
consented to have their total body and regional bone
mineral density assessed by DEXA scan (iDXA, GE®;
commonly used in radiology clinics for assessment of
• To determine the regional effect of TKA implants on
BMD analysis of the legs by DEXA, BMD was
recorded as an average of both legs and individually
for the CONTROL (no implant) and TKA (with implant)
• The impact of implants on automated T-scores were
then calculated as a common metric for diagnosis of
osteopenia and osteoporosis using enCORE software
and standardized national norms for bone
• Within the analysis software, implant materials were
automatically detected and removed as artifact by the
software (typical analysis). To examine the
effectiveness of the software of detecting and
removing implant artifact from the analysis, additional
measures were taken and scored when implant artifact
was manually removed from the images.
• Finally, a correction factor was calculated for
application in scenarios where adequate artifact
removal did not occur via automated software or
• Statistical Analysis: A mixed-model ANOVA was used
to compare BMD and t-scores between the control
limb, the TKA limb, and the TKA limb following manual
artifact correction (TKA- MAC) as well as for
comparing total-body BMD, total-body BMD-MAC, and
BMD assessed from the non-TKA side only. All
detected significant interactions were followed by a
Tukey’s post hoc test for pairwise comparisons.
Houston Methodist OBRL
5505 W. Loop South Freeway, Houston, TX 77081
Phone: (___) ___-____
Statistically 68% of repeat scans fall within 1SD (± 0.010 g/cm² for Total Body Total); USA (NHANES 1999-2004) Total Body, Male Reference Population (v100); Matched for Age, Sex, Ethnic
Date created: 09/25/2018 3:27:02 PM 16 [SP 2]; Filename: 00hkfp4ilb.meb; Total Body; 100:0.19:153.85:15.6 0.00:-1.00 2.40x3.04 13.2:%Fat=34.0%; 0.00:0.00 0.00:0.00; Scan Mode: Standard; 3.0
GE Healthcare Page: 1 of 1 Lunar iDXA
Patient: INC1-058, INC1-058 Referring Physician: (not specified)
Birth Date: 11/30/1953 Age: 64.8 years Patient ID: INC1-058
Height: 72.0 in. Weight: 187.0 lbs. Measured: 09/24/2018 10:49:17 AM (16 [SP 2])
Sex: Male Ethnicity: White Analyzed: 09/25/2018 3:26:37 PM (16 [SP 2])
Total Body Bone Density
Densitometry: USA (NHANES 1999-2004) (Enhanced Analysis)
Head 2.200 - -
Arms 0.841 - -
Legs 1.227 - -
Trunk 0.936 - -
Ribs 0.841 - -
Spine 1.104 - -
Pelvis 0.926 - -
Total 1.146 29 -0.6
FIGURE: Data are presented as mean±SEM for BMD (g·cm2) of the legs and total body measured using DEXA (A & B) with corresponding T-scores
calculated for each measure (C & D). Regional limb comparison (A&C): CONTROL, limb with no implant present; TKA, limb with TKA implant
assessed using standard iDXA software analysis; TKA-MAC, limb with TKA implant following manual artifact removal. Total-Body Comparison (B&D):
Total Body, total-body BMD with implant included assessed using standard iDXA software analysis; Non-TKA Side Only, BMD assessed from the
lateral side of the body with no implant; Total Body – MAC, total body BMD analyzed following manual artifact removal. Individual patient data are
also shown for those classified as normal, osteopenic (T < -1), or osteoporotic (T < -2.5) regionally (E) and for the total-body across each analysis
• Those with TKA implants had significantly higher BMD (~15% difference, p<0.01) compared to control limbs when
standard automated artifact removal was used.
• This resulted, on average, in a 2.7% (range 0.8-6%) overestimation of total body BMD (for a single implant).
• When analyzing the individual limbs, 7 of the 38 patients (18.4%) were found to have low BMD falling into the
osteopenic (T-score < -1) or osteoporotic (T-score < -2.5) categories. This was masked in the TKA limb whereby
0/38 (0%) patients were observed to have a T-score below 1 indicating that the implant resulted in an overestimation
• With regards to the impact of a single knee implant on the total body analysis (Figure 2F), 2 of 38 patients (5.3%)
were observed to be osteopenic when analyzing the non-TKA side only compared to the actual total body
measurement (including the TKA implant) where 0/38 (0%) patients were observed to be osteopenic.
• Manual artifact correction (MAC) was found to successfully ameliorate the overestimation of BMD for both regional
and total-body measures (Figure 2A – 2F).
• All patients in this study
underwent DEXA analysis
from the same model of
• However, we did observe this
error to be present in a single
case scan performed using a
separate DEXA model
(Horizon, Hologic, San Diego,
CA) where the overestimation
of BMD was present similar to
the scans in this investigation.
• Therefore, more research is
needed to determine the
extent that other software
designs have issue with
Discussion & Conclusions