A Study of Bone Mineral Density in Lower Limb Amputees at a National Prosthetics Center E ´ imear Smith, MD, MRCPI, Catherine Comiskey, PhD, A ´ ine Carroll, MD, MRCP, FRCPI, Nicola Ryall, FRCPI ABSTRACT The objective of this study was to examine the prevalence of low bone mineral density, based on World Health Organization diagnostic criteria, in patients with lower limb amputation. This is a cross-sectional study of 52 lower limb amputees in a national prosthetics center. All completed a questionnaire and had laboratory investigations and dual- energy x-ray absorptiometry assessment of lumbar spine and both hips. Study participants were 24 transtibial amputees (46.2%), 19 (36.5%) transfemoral amputees, 8 (15.4%) bilateral amputees, and 1 (1.9%) with a hip disarticulation. Six (11.5%) were unable to walk at all, 26 (50%) were only indoor walkers, and 20 (38.5%) were outdoor walkers. Thirty-three patients (68.8%) were vitamin D deﬁcient, 25-hydroxyvitamin D level less than 50 nmol/L, and ﬁve (10.4%) had insufﬁciency, level between 50 and 72 nmol/L. Based on T-scores, 26 (50%) had osteopenia and 20 (38.5%) had osteoporosis at either lumbar spine or hip. Z-score -1 but -2 occurred in 25 (48.1%), and Z-score -2 occurred in 10 (19.2%) at a minimum of one site. Negative correlation was found between duration of disability and bone mineral density (BMD) at the neck of femur (r =-0.447, p = 0.002) and total proximal femur (r =-0.391, p = 0.009) on the amputated side. There was a signiﬁcant difference between BMD of the sound and amputated sides at the neck of femur (t = 6.17, df = 43, p  0.001) and total proximal femur (t = 7.79, df = 43, p  0.001). BMD was not affected by amputation level or ambulatory status. Osteopenia and osteoporosis occur frequently in lower limb amputees. Hip BMD on the amputated side is correlated with duration since amputation. Bone health monitoring should form part of the long-term follow-up in this patient population. (J Prosthet Orthot. 2011;23:14 –20.) KEY INDEXING TERMS: osteoporosis, bone mineral density, lower limb amputation, dual energy x-ray A mong lower limb amputees, 52.4% have reported at least one fall in the previous year. 1 Therefore, it is surprising that lower limb fracture rates in this pop- ulation have been reported at just 2.35% and 3%, although these recordings were taken more than 20 years ago when life expectancy after amputation was possibly shorter than it is now. 2,3 It was suggested in one of these publications that fracture rate was likely to increase among amputees with improving life expectancy among dysvascular patients. 3 There are reports of a decline in bone mineral density (BMD) at the hip of the amputated limb. This was initially suspected on plain x-rays 4,5 and later conﬁrmed by dual-energy x-ray absorptiometry (DXA). 6 On the amputated limb, BMD has been reported to be an average of 10.4% to 12% less than the sound side, greater trochanter 14.9% less, and proximal tibia 45% less. 7–9 When comparisons were drawn between BMD on the amputated side and controls, the mean differences at the neck of femur ranged between 10% and 28%, at the greater trochanter 8.8%, and at the proximal tibia 24%. 7–9 It was also observed that the reduction in femoral neck BMD was signif- icantly greater in transfemoral than in transtibial amputees. 6 After fracture, a decline in mobility status has been re- ported in this patient population. 2,3,10 In a population with such a high rate of falls and signiﬁcantly lower BMD at the hip of the amputated leg, fracture prevention should form a part of long-term medical follow-up. Fracture prevention ﬁrst entails ﬁnding patients who are at risk of fracture. BMD measurement using DXA at any speciﬁc site is the single best predictor of fracture at that site and provides the measures on which World Health Organization (WHO) diagnostic catego- ries are based; the hip represents the site with greatest predictive power. 11 In calculating fracture risk based on BMD, actual BMD measurements (gram per square centime- ter) are expressed as relative values, T-score, and Z-score, T-score representing a comparison with the young adult reference mean and Z-score representing a comparison with the age-matched mean. According to WHO criteria, a T-score of less than or equal to 1 standard deviation (SD) below the young adult mean is normal, a T-score greater than 1 but less than 2.5 SD below the young adult mean is osteopenia, and a T-score of 2.5 or more SD below the young adult mean is classiﬁed as osteoporosis. Every SD in BMD below the age- matched mean correlates to an approximate doubling of fracture risk, a relationship best proven in postmenopausal women and men older than 50 years. 11–14 To date, there is no E ´ IMEAR SMITH, MD, MRCPI, A ´ INE CARROLL, MD, MRCP, FRCPI, AND NICOLA RYALL, FRCPI, are afﬁliated with the Department of Rehabilitation Medicine, National Rehabilitation Hospital, Du ´n Laoghaire, Dublin, Ireland. CATHERINE COMISKEY, PhD, is afﬁliated with the School of Nurs- ing and Midwifery, Trinity College Dublin, Dublin, Ireland. Disclosure: The authors declare no conﬂict of interest. This work was supported by the National Medical Rehabilitation Trust Ltd. (Ireland). Copyright © 2010 American Academy of Orthotists and Prosthetists. Correspondence to: E ´ imear Smith, MD, MRCPI, Department of Rehabilitation Medicine, National Rehabilitation Hospital, Roch- estown Avenue, Du ´ n Laoghaire, Dublin, Ireland; e-mail: eimear. smith@nrh.ie 14 Volume 23 • Number 1 • 2011