Osteoporosis Int (1994) 4:283-285 © 1994 European Foundation for Osteoporosis

Osteonorosis

International

Letters SIR-

I read with considerable interest the recent excellent article by Glfier et al. on quality assurance for bone densitometry research studies [1]. Certainly, control of machine variations is an essential factor in longitudinal studies of D X A determination of BMD. On the other hand, reproducibility of patient positioning is a major element in the final outcome of any study. Far less attention has been paid to this issue than to machine error. Having an interest in femoral neck responses to controlled, mild-impact loading, I have found the standard devices provided with Lunar and Hologic scanners to be inadequate in assuring a reproducible position of the hip. Ideally, the femoral neck should always be parallel to the scanner table. For the average patient 15° of internal rotation will approach this condition. In my experience, however, the current positioning devices invert the foot, and do not necessarily internally rotate the hip to a standard position. Furthermore, only the scanned extremity is placed in the holder. An attempt has been made to overcome these disadvantages by designing a bilateral ' A ' frame splint which abducts both hips 15° , locks the knees in full extension and captures both feet firmly in holders which can be internally rotated 15°, without inverting the foot through the subtalar joint. The 15° of hip abduction makes it possible, in most patients, to position the region of interest in the femoral neck so it does not impinge on the ischium, unless a patient has a high degree of anteversion or an exceedingly short neck. Pilot experience with this splint suggests that inter-operator and longitudinal hip positioning errors can be significantly reduced.

C. Andrew L. Bassett, MD, ScD, L H D

2600 Netherland Avenue Suite 103 Riverdale New York NY 10463-4889 USA

References 1. Glfier C-C, Faulkner KG, Estilo MJ, Engelke K, Rosin J, Genant HK. Quality Assurance for bone densitometry research: concept and impact. Osteoporosis Int 1993;3:227-35.

Hologic's Response to Dr Bassett's Letter SIR-Dr Bassett correctly points out that instrument quality control is not the only important component to quality control programs in multi-center bone densitometry research studies. The paper by Gliier et al. [1] points out that scan review for

verification of correct positioning and analysis is required; however, no results of such a review process are given. In the Study of Osteoporotic Fractures 7659 subjects had a complete set of spine and hip scans. Of these, 1231 spine and 655 hip scans were reviewed based on criteria similar to those suggested by Glfier et al. In that study, 815 scans had to be reanalyzed, primarily for the removal of artifacts [2]. We disagree with Dr Bassett that the standard hip scanning procedures provided by the manufacturers of D X A equipment are inadequate for assuring reproducible hip positioning. In fact, the positioning device and procedure he suggests closely resembles what Hologic distributes with its scanners and describes in its operator's manuals [3,4]. The manual states: 'Ensure that the leg to be examined is rotated inwards: abduct the patient's leg, rotate the patient's leg by turning the leg and foot, and then place the foot against the positioning fixture. Adjust the strap to snugly hold the foot of the side to be examined in the correct position. Fasten the second strap over the patient's leg to keep the knee close to the table.' As Dr Bassett notes, the knee must be fully extended in order for the internal foot rotation to result in a corresponding rotation of the proximal femur. The second strap of the Hologic knee positioning fixture is used to maintain the knee in a fully extended and locked position. The use of a hip positioning aid is indicated for two reasons. First, it optimizes the projected length of the femoral neck. However, due to anatomical variation, no single rotation angle will result in optimal projection for all patients. Second, when a patient is followed prospectively, the positioning device ensures reproducible patient positioning. A study of Wilson et al. [5] demonstrated that a significant error can be introduced by gross carelessness in foot and leg positioning. Scan quality is determined not only by instrument quality but also by operator diligence. Numerous studies have demonstrated that, even on osteopenic subjects, the precision error of the femoral neck on Hologic scanners ranges from 0.8% to 1.7% [6-10] when standard operating procedures are followed. Hologic recognizes the need for careful operator training and provides such training to all new customers free of charge. However, operator turnover results in many D X A scanners being operated by personnel not formally trained by the manufacturers and often unfamiliar with proper patient positioning and scan analysis. Centralized quality assurance programs in multi-center trials can correct inappropriate scan analysis. However, false patient positioning can lead to sub-optimal precision which cannot be corrected. Therefore, careful operator training is mandatory for multi-center trials where optimal D X A precision has a direct impact on the power of the results. In conclusion, while we agree with Dr Bassett that attention must be given to patient positioning, we feel that this can be achieved with the standard procedures already in use. We

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Letters

always welcome improvements and are looking forward to reviewing the results of a controlled study which demonstrates that the method Dr Bassett is proposing performs better than current practice and is tess dependent on operator skill. However, we doubt that new positioning aids will replace the need for careful operator training and operator performance monitoring. Peter Steiger, PhD

Scientific Director, Hologic Inc. 590 Lincoln Street Waltham, M A 02154 USA

References 1. Gltier CC, Faulkner KG, Estito MJ, Engelke K, Rosin J, Genant HK. Quality assurance for bone densitometry research studies: concept and impact. Osteoporosis Int 1993;3:227-35. 2. Steiger P, Cummings S, Black DM, et aI. Age-related decrements in bone mineral density in women over 65. J Bone Miner Res 1992;7:625-32. 3. Hologic. QDR-1000 and QDR-1000/W operator's manual. Waltham, MA: Hologic Inc., 1992. 4. Hologic. QDR-2000 Operator's Manual. Waltham, MA: Hologic Inc., 1992. 5. Wilson CR, Fogelman I, Blake GM, et al. The effect of positioning on dual energy x-ray bone densitometry of the proximal femur. Bone Miner 1991;13:69-78. 6. Duboeuf F, Braillon P, Chapuy MD, et al. Bone mineral density of the hip measured with dual energy x-ray absorptiometry in normal elderly women and in patients with hip fracture. Osteoporosis Int 1991;1:242-9. 7. Estilo MJ, Glfier CC, Faulkner KG, et al. Long-term precision and longitudinal sensitivity in-vivo of quantitative computed tomography and dual x-ray absorptiometry. J Bone Miner Res 1991;6 (Suppl 1):$167. 8. Laksey MA, Flaxman ME, Barber RW, et al. Comparative performance in vitro and in vivo of Lunar DPX and Hologic QDR-1000 dual energy x-ray absorptiometers. Br J Radiol 1991 ;64:1023-9. 9. Devogeleer JP, Baudoux C, Nagant de Deuxchaisnes C. Reproducibility of BMD measurements on the Hologic QDR-2000. In: Ring, editor. Bath Conference on Osteoporosis and Bone Mineral Measurement, Bath, England. British Institute of Radiology, 1992:20. 10. Kelly TL, Stelger P, van Stetten E, et al. Performance evaluation of a multi-detector DXA device. J Bone Miner Res 1991;6 (Suppl 1):S168.

Lunar's Response to Dr Bassett's Letter SIR-Quality control for D X A densitometers can ensure early attention to possible technical malfunctions. However, most of the precision error at a single facility, and the variation among research sites, is due to operator influences, particularly (1) analysis of spine and femur scans, and (2) positioning of the patient for femur scans. Careful operators can obtain precision errors of 0.5%, 1% and 1.5% for total body BMD, spine BMD (L2-4) and femur neck BMD, respectively [1]. There is considerably more possibility for variation in femur neck BMD. A recent multicenter clinical trial using both DPX and Q D R densitometers showed precision errors ranging from 1.5% to 4.3% for femoral neck BMD [2]. Trevisan et al. [3] and Wilson et al. [4] point out that small variations in

positioning of the patient, and in location of the region of interest (ROll), can cause potential problems. While their studies focused on the Q D R device, similar errors can occur with the DPX. Mayo Clinic researchers found substantial analysis problems in 30% of Q D R femur scans [5]. The initial precision error for femoral neck BMD of 3.4% was reduced to 2.4% after central review and re-analysis, but the precision error for Ward's triangle was 5 % - 6 % , even after review. The precision error for Ward's triangle can be halved to 3% by use of a fixed R O I position [6]; a larger R O I (3 cm 2 versus 1 cm 2) can further reduce errors. These findings suggest the need for careful analysis. Bassett expresses a legitimate concern with minimizing patient positioning problems. However, the positioning devices now supplied by the manufacturers are n o t deficient. As noted above, technicians carefully trained in use of these positioning aids can obtain a precision error of 1.5% for femur neck BMD [1,2]. The recent multicenter STOPIT study in 70year-old women maintained a long-term precision error of ~ 1 % by careful attention to both positioning and analysis (Gatlagher, personal communication). A new femur positioning device introduced by Norland, that lifts the upper leg to overcome femural anteversion, can facilitate precision by providing greater comfort. Similarly, the E X P E R T densitometer, which rotates the C-arm rather than the leg to overcome femoral anteversion, could potentially enhance precision. Our limited experience with the Bassett positioning device did not show advantages in precision, and there were problems in accommodating patients with differing build. This device, and other new approaches, should be carefully evaluated in large-scale studies with trained operators to see whether then can significantly reduce positioning problems, Densitometry users should give careful attention to training of operators. Clinical results must be monitored long term to ensure both optimal positioning and analysis. Richard B. Mazess, PhD Professor Emeritus of Medical Physics

President, Lunar Corporation 313 W Beltline Hwy Madison, W I 53713 USA

References 1. Mazess RB, Chesnut CH III, McClung M, Genant H. Enhanced precision with dual-energy x-ray absorptiometry. Calcif Tissue Int 1992;51:14-7. 2. Bendavid EJ, Young KC, Gliier CC, Grampp HK. Frequency and magnitude of analysis errors of bone density results assessed by dual x-ray absorptiometry. J Bone Miner Res 1993;8 (Suppl 1):S345. 3. Trevisan C, Gandolini GG, Sibilla P, Penotti M, Caraceni MP, Ortolani S. Bone mass measurement by DXA: influence of analysis procedures and interunit variation. J Bone Miner Res 1992;7:1373-82. 4. Wilson CR, Fogelman I, Blake GM, Rodin A. The effect of positioning on dual energy x-ray bone densitometry of the proximal femur. Bone Miner 1991;13:69-76. 5. Wahner HW, Looker A, Dunn WL, Wakers L, Hauser MF. Precision of bone mineral measurements (BMD) at the proximal femur in a multi-center study using three mobile examination centers (Nhanes III). J Bone Miner Res 1993;8 (Suppl 1):$354. 6. Burnham WH, Sharpe JR, Schulz EE. Hip densitometry: improvements in Ward's triangle measurements. Presented at Fourth International Symposium on Osteoporosis, Hong Kong, 1993:60.

Letters

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Fractures of the Femoral Neck and Arterial Disease of the Lower Limbs SIR-We demonstrated in an earlier study that the bone mineral density (BMD) of the femoral neck is lower in patients with ischemic atherosclerotic disease ( I A D ) of the lower limbs than in control subjects [1]. Some publications have shown structural anomalies, decreased bone mineral content and loss of bone resistance after inadequate blood supply [2,3]. These observations led us to suspect that there is a relationship between arteriosclerosis and osteoporosis, between arterial occlusive disease of the lower limbs and fragility of the femur. The aim of our study was to evaluate by Doppler ultrasonography the incidence of ischemic atherosclerotic disease of the lower limbs in aged patients admitted to hospital for fracture of the femoral neck (FFN), compared with age- and sexmatched control subjects.

1.05+_0 16

p = 0.0003

Fig. 1. Comparison of the systolic indexes of patients with fracture of the femoral neck (FFN; dark column) and control subjects without FFN (light column). Values are the mean _+ SD. Materials and Methods Thirty patients (27 women and 3 men) admitted to the traumatology department for FFN between 1 September 1992 and 31 January 1993 and with a mean age of 82.4 + 8.4 years were included in the study. Inclusion criteria were age over 65 years and FFN sustained after minimal trauma (fall from a standing position). Exclusion criteria were major injury (road traffic accident), pathological fracture (i.e. metastases, primary bone tumours, myelomas) or bedridden condition. The controls comprised 30 subjects with a mean age of 82 + 7.6 years admitted during the same period to the departments of rheumatology, internal medicine and geriatrics who were agematched (within 2 years) and sex-matched to the patients, not bedridden and had never sustained FFN. In both patients and controls, smoking consumption and physical activity were recorded. The clinical signs of I A D of the lower limbs were sought. Doppler ultrasound was used for the assessment of the distal systolic index (DSI) of the lower limbs. Arterial systolic pressure was measured by a Doppler probe in the two humeral arteries (HA) and in the two tibial posterior arteries (TPA). DSI is equal to the ratio of T P A mean pressure to H A mean pressure. A DSI value lower than 0.9 means I A D ; DSI greater than 1.2 means mediacalcinosis [4]. A t-test was used for statistical comparisons.

Results The age of the patients was comparable to that of the control subjects (p=0.4). On clinical examination 10 patients with FFN had symptomatic I A D of the lower limbs, compared with 4 control subjects. Only 4 patients in the F~N group and 3 patients in the control group were smokers. The physical activity level was similar in the F F N group and the controls (1.6 + 0.4 (mean + SD) v 1.8 _+ 0.7; p = 0 . 2 ) . On Doppler investigation 3 patients with FFN and 3 controls had mediacatcinosis. Mean DSI values were significantly lowered in patients with F F N compared with control subjects (0.9 + 0.23 v 1.05 _+ 0.16;p=0.0003) (Fig. 1). In 20 lower limbs of the patients with F F N the DSI value was below 0.9, indicating the presence of arterial disease. Only 9 limbs were affected by arterial disease in control subjects.

Discussion Our study demonstrates that arterial disease of the lower limbs is more frequent in aged patients with FFN than in age- and sex-matched control subjects without FFN. Correlations between the bone mineral content of the femoral neck and risk of fracture have been clearly established, but other factors contribute to the risk of FFN: loss of muscle tone, propensity to lose balance, posturaI hypotension. These troubles could complicate generalized ischemic arterial disease involving brain arteries, but correlations have been established between intraosseous blood flow and bone apposition [5], so arterial occlusive disease of the lower limbs could directly cause disturbances of bone remodelling, and increase femur fragility. We hope that our work will encourage the systematic search for arterial disease of the lower limbs in epidemiological studies of fractures of the femoral neck; this does not appear to have been done previously. M. Laroche 1, P. Chiron 2, P. Bendayan 3, M. Degeilh 4, L. Moulinier 1, B. Vellas 5, D. Adoue 5, H. Boccalon 3, J. Puget 2, J.-L. Albarede 5, G. Utheza 2 and B. Mazieres 1. 1Service de Rhumatologie; 2Service d'Orthop6die et Traumatologie; and 3Service de M6decine Interne et Explorations Vasculaires, CHU Rangueil, Toulouse, and 4Service d'Angiologie and SService de G6riatrie, C H U Purpan, Toulouse, France

References 1. Laroche M, Pnech JL, Pouilles JM, et at. Arteriopathie des membres inf6rieurs et ost6oporose masculine. Rev Rhum Mal Osteoartic 1992;59:95--101. 2. Sherman MS, Sekalovitch WG. Bones changes in chronic circulatory insufficiency. J Bone Joint Surg [Am] 1957;39:892-901. 3. Ramseier E. Arteriosclerosis in the arteries of bone. Virchows Arch Pathol Anat 1962;336:77-86. 4. Carter SA. Clinical mesurements of systolic pressure in the limbs with arterial occlusive disease. JAMA 1969;207:1869-74. 5. Reeve J, Arlot M, Wootton R, et al. Skeletal blood flow, iliac histomorphometry and strontium kinetics in osteoporosis: a relationship between blood flow and corrected apposition rate. J Clin Endocrinol Metab 1988;66:1124-31.