Hrev_master Veins and Lymphatics 2013; volume 2:e5 [Veins and Lymphatics 2013; 2:e5] [page 13] Where should stiffness be measured in vivo? Jean-François Uhl,1 Jean-Patrick Benigni,2 André Cornu-Thenard3 1URDIA, research unit EA4465 – University Paris Descartes, Paris; 2HIA Bégin, Saint Mandé; 3St Antoine Hospital, Paris, France Abstract Three points in the medial aspect of the leg are routinely used to measure the interface pressure of a compression: the C point, at the largest circumference of the calf; the B point, at the smallest circumference of the leg; the anatomical B1 point, at the apex of the gas- trocnemius muscle and the manufacturer’s B1 point, computed in the midline of the line join- ing the B point to the C point). The anatomical B1 point is the most reliable point from a prac- tical point of view, and is easier to use. The underlying anatomy is the Soleus muscle. Stiffness at the anatomical B1 point seems adequate sufficient to assess stiffness of a medical device in vivo. Introduction In laboratory the stiffness of a medical com- pression device is defined as the pressure change (in mmHg) that occurs with an increase in circumference of one centimeter (ΔP/ΔC). In vivo, this is very difficult to meas- ure. For this reason the static stiffness index (SSI) proposed by Partsch et al.1 is used as a rough estimate of stiffness. By definition, SSI is calculated by substracting the interface pressure (in mmHg) in the lying position from the interface pressure (in mmHg) in standing position. Compression devices are defined as stiff if SSI is 10 mmHg or more. Another stiff- ness index has also been proposed: the dynam- ic or dorsiflexion stiffness index (DSI) calcu- lated by substracting the diastolic from the sys- tolic interface pressure (in mmHg) during dor- siflection, while lying down.2 Although slightly higher, the values of the DSI are similar to those of the SSI. Anatomical review of the venous muscular pumps The muscular pumps of the lower limb rep- resent the peripheral heart of the venous sys- tem. They push blood upward against gravity, so that downward reflux can be prevented by normally functioning valves. The main muscu- lar pump of the lower limb is the calf pump. It is divided into two parts: i) the soleus muscle pump which works at the leg level. The soleal veins are divided into two parts, lateral and medial. The lateral veins are bigger and drain, vertically, into the fibular veins. The smaller medial veins drain horizontally into the poste- rior tibial veins; ii) the gastrocnemius muscle pump which works at the popliteal level. The medial part of the muscle and the medial gas- trocnemius veins are very important. These veins originate by the gastrocnemius perfora- tors, connecting end-to end at the apex of the calf. Two or three big veins form a network inside the muscle, which join in a unique col- lector ending in the popliteal vein. The main reference points of the leg Four points in the medial aspect of the leg are routinely used to measure the interface pressure of a compression device,3 all situated at the medial aspect of the leg (Figure 1). These are: i) the C point (at the largest cir- cumference of the calf); ii) the B point (at the smallest circumference of the leg); iii) the anatomical B1 point (B1a at the apex of the gastrocnemius muscle); iv) lastly, the manu- facturer’s B1 point (B1m in the midline of the line joining the B point to the C point). Figure 2 shows a realistic 3D anatomical model, reconstructed by a multi-slice comput- ed tomography (MSCT). This medial view demonstrates that, below the apex of the medi- al gastrocnemius, the Soleus muscle is the main muscle of the underlying anatomy. This muscle represents the deeper part of the triseps suralis (calf pump muscle). Figure 3 shows that the anatomical B1 point which is easily found by a simple clinical exam during the muscular contraction of the calf. Objectives The aims of this studies were: i) to verify if these reference points are reliable; ii) to assess their variability; iii) to assess the opti- mal site for calculating stiffness: at the anatomical B1 point, the C point, or both; iv) to compare stiffness with two different short stretch bandages. Materials and Methods We performed three different studies: a clin- ical study on 22 healthy subjects to localize ref- erence points, a radiological computed tomog- raphy venography (CTV) study with MSCT was performed on 19 patients to assess the anatomical landmarks of the leg, and a study assessing stiffness by two compression devices applied on ten legs. Clinical study to localize reference points: measurements of the legs of 22 healthy sub- jects (17 women and five men) were done in the standing position. The evaluations includ- ed the measure of the distance of the B and C points from the ground, the distances of the anatomical B1 and manufacturer’s B1 points from the ground, and the height of the subject. Study by CT venography to assess the anatomical landmarks of the leg:4 MSCT scan- ning was performed with a Siemens SOMATOM® Definition Flash 64 slice CT scan- ner, with contrast injection into a dorsal foot vein. The CT parameters were acquisition from feet to head, 120 KV, and 150 mAs. Reconstruction parameters: slice width 1 mm, slice increment 0.75, matrix 512¥512, zoom factor 1.7. Post processing was performed with the volume rendering technique by OsiriX 64- bit, version 5 (Pixmeo company, www.osirix. foundation.com) Nineteen patients (thirteen women and six men) were investigated in the lying position before varicose vein surgery. Measurements were made using the OsiriX software on the 3D reconstructed images. Localization of the C, B, B1a, and B1m points were made and the distances between the points were computed, as well. The length of the tibia was considered to be equal to the dis- tance from knee joint to the apex of the medi- al malleolus. Clinical study to assess the stiffness of two compression devices: the stiffness of two com- pression devices was assessed in 23 healthy legs. Rosidal K™ (Lohmann & Rauscher), was applied to eleven legs and Coban™2 (3M™) to twelve. Rosidal K™ (Lohmann & Rauscher) is a short stretch bandage (5 m ¥ 10 cm). The bandage was applied in a circular way with full Correspondence: Jean-François Uhl, URDIA, research unit EA4465 – University Paris Descartes, Paris, France. E-mail: jeanfrancois.uhl@gmail.com Key words: compression, stiffness index. Conference presentation: part of this paper was presented at the International Compression Club (ICC) Meeting on Stiffness of Compression Devices, 2012 May 25, Vienna, Austria (http://www.icc-compressionclub.com/). Received for publication: 29 September 2012. Revision received: 2 November 2012. Accepted for publication: 15 November 2012. This work is licensed under a Creative Commons Attribution 3.0 License (by-nc 3.0). ©Copyright J.-F. Uhl et al., 2013 Licensee PAGEPress, Italy Veins and Lymphatics 2013; 2:e5 doi:10.4081/vl.2013.e5 No n- co mm er cia l u se on ly stretch. Coban™2 is a two layer bandage con- sisting in a padding layer (10 cm ¥ 2.7 m) and a short stretch bandage (10 cm ¥ 4.7 m). The two bandages were applied according to the recommendations of the manufacturer. Each bandage being overlapped by 65%. Bandages were applied so that a target pressure of 40 mmHg at the anatomical B1 and C points could be achieved. The interface pressure was meas- ured with a Kikuhime® device (Makoto TAKA- HASHI and Sanae, Biomedical Systems Engineering, Graduate School of Engineering, Hokkaido University, Japan), using the small probe, in the lying position, at rest and during muscular contraction, and in the standing position (Figures 4 and 5). Statistical methods We used StatView, version 5 (Copyright 1998 SAS institute inc., USA), to compute the mean and standard deviation (σ) of the sam- ples and to determine the median for interface pressures. Results Clinical measurement The height from the ground was measured for the C point (at the largest circumference of the calf), the B1a point (at the apex of the gas- trocnemius muscle), and the B1m point (in the midline of the line joining the B point to the C point), and distances between these points were all measured on 22 healthy sub- jects. Results are shown in Table 1. The mean distance B1a-C was 5.66 cm [standard devia- tion (SD) 1.76] and the mean distance B1a-m was 3.95 cm (SD 1.87). There was no correla- tion between the distances observed and the height of the subject. Computed tomography venography anatomical measurement The same parameters were measured by CTV on 19 patients before varicose vein sur- gery. By CTV, the average distance from B1a to Conference presentation [page 14] [Veins and Lymphatics 2013; 2:e5] Table 1. Values of the heights of B1a, B1m, C points above the ground. Distance between B1m, B1a and C points on 22 healthy subjects (in centimeters, single values, means±stan- dard deviation). Height from ground Distance between points B1m B1a C B1 a-m B1a-C 19 23 30 4 7 22 26 32 4 6 18 22 27 4 5 19 23 30 4 7 19 24 29 5 5 20 22 28 2 6 22 27 32 5 5 22 25.5 30 4 4.5 20 26 29 6 3 21 28 31 7 3 16 19.5 26 4 6.5 20 28 31 8 3 19 22.5 27.5 4 5 21 21 30 0 9 21 24.5 30 4 5.5 19 22 28 3 6 20 23.5 30 4 6.5 24 29 34.5 5 5.5 23 23 33 0 10 25 28 32 3 4 22 27.5 32.5 6 5 22 26 33 4 7 Mean SD 20.64±2.06 24.59±2.65 30.25±2.16 3.95±1.87 5.66±1.76 SD, standard deviation. Figure 1. The main reference points of the leg commonly used to measure the inter- face pressure of a compression device. Figure 2. Study of the anatomical land- marks of the reference points by 3D recon- struction with multi-slice computed tomography. Arrow shows the apex of the medial gastrocnemius muscle (B1a). MG, medial gastrocnemius muscle; Sol, soleus muscle; B1m, half distance measured between C and B. Figure 3. Clinical assessment of the B1 point at the apex of the calf. No n- co mm er cia l u se on ly Conference presentation [Veins and Lymphatics 2013; 2:e5] [page 15] B1m was 3.6 cm (SD 1.63), average distance from B1a to C was 9.3 cm (SD 1.69). There was a significant correlation with tibial length (r=0.4, Table 2). A comparison between the two measure- ment methods shows: i) there was a signifi- cant difference in the distance from the C point to the ground between the two measure- ment methods. The C point required repeated measurements and so appears to be difficult to locate clinically; ii) the manufacturer’s B1 point is in the middle of the BC line and is not easy to locate; iii) the anatomical B1 point is the easiest to identify in clinical practice because it is located at the apex of the medial gastrocnemius muscle. As a result, it is easy to assess clinically and, if necessary, to verify by ultrasound. It is also the most reproducible; iv) the distance between the anatomical B1 and the manufacturer’s B1 points are closer than the anatomical B1 and C points according to either calculation method. Calculation of stiffness Calculation of the median stiffness index on 11 legs with a Rosidal K™ (Lohmann & Rauscher, Table 3) shows that the SSI and the DSI were very similar at the B1a and C points; this is considered stiff. Median SSI was 14 mmHg at B1 vs 19 mmHg at C. Median DFSI was 29 mmHg at B1 vs 31 mmHg at C. Stiffness index measurement on 12 legs with a Coban™2 (3M™) (Table 4) also shows that SSI and DSI were very close at the B1a and C points; they are also considered stiff. Median SSI was 13.7 mmHg at B1 vs 14.3 mmHg at C. Median DSI was 26 mmHg at B1 vs 25.6 mmHg at C. Wherever the calculation of the stiffness is performed, the values at the C point and the anatomical B1 points were very close for both compression devices. Table 2. Distances between the C point and B1a, B and B1m points. Distance B1a to B1m and the tibial length measured in centimeters measured on the 3D model of 19 legs prior to varicose vein surgery with OsiriX software (Pixmeo company, www.osirix.foun- dation.com). Tibial length Distance between points C-B1a C-B C-B1m B1a-m 33 9 22 11 2 46 13 36 18 5 46 12.8 34.4 17.2 4.4 34 8.3 22.7 11.35 3.05 36 9 23.2 11.6 2.6 39 10.7 24.8 12.4 1.7 38 7.8 21.3 10.65 2.85 37 10.4 23 11.5 1.1 39 9.4 27 13.5 4.1 37 8.5 25.4 12.7 4.2 38 8.5 26 13 4.5 35 7.1 25.7 12.85 5.75 36 10.8 24.4 12.2 1.4 34.6 7.5 20.8 10.4 2.9 43.6 8.3 26 13 4.7 32.8 7.3 19.5 9.75 2.45 39 9 31 15.5 6.5 45.6 8.2 29 14.5 6.3 40 10.2 25.2 12.6 2.4 Average 38.4 9.3 25.7 12.8 3.6 SD 4.21 1.69 4.37 2.18 1.63 SD, standard deviation. Figure 4. Pressures at rest, with dorsiflexions, during standing and stiffness indices under a Rosidal K (Lohman & Rauscher) on 11 legs. Ranges of 95% confidence interval. Rest, at rest; Contr, with dorsiflexion; Stand, standing; SSI, static stiffness index; DSI, dorsiflexion stiffness index. Figure 5. Pressures at rest, with dorsiflexions, during standing and stiffness indices under Coban™2 (3M™) on 12 legs. Ranges of 95% confidence interval. Rest, at rest; Contr, with dorsiflexion; Stand, standing; SSI, static stiffness index; DSI, dorsiflexion stiff- ness index. Table 3. Interface pressure (mmHg) at B1 and C points under a Rosidal K (Lohman & Rauscher) bandage (11 legs). B1 point C point Rest Contr Stand Rest Contr Stand Average 41.4 74.5 58.3 36 61.5 51.5 SD 4.4 15 11.4 9.4 24 14.3 Median 41 70 55 35 67 54 Rest, at rest; Contr, with dorsiflexion; Stand, standing; SD, standard deviation. No n- co mm er cia l u se on ly Conference presentation [page 16] [Veins and Lymphatics 2013; 2:e5] Discussion The distance between the C and anatomical B1 points was found to be significantly different by clinical and CT measurement (average 9.3 vs 5.6 cm; P<0.1). The possible explanation for this result could be the different position of the subjects, supine when submitted to CT and standing during the clinical examination. In fact, the C point varies according to positioning due to isometric contraction, lying or standing. Conclusions The C point is difficult to locate in prac- tice. The anatomical B1 point is the most reliable point from a practical point of view, and is easier to use. The underlying anatomy is the Soleus muscle. Stiffness at the anatomical B1 point seems adequate sufficient to assess stiffness of a medical device in vivo. References 1. Partsch H, Clark M, Mosti G, et al. Classification of compression bandages: practical aspects. Dermatol Surg 2008; 34:601-8. 2. Partsch H, Clark M, Bassez S, et al. Measurements of lower leg compression in vivo: recommendations for the perform- ance of measurements of interface pres- sure and stiffness. Dermatol Surg 2006; 32:224-33. 3. Benigni JP, Cornu-Thenard A, Uhl JF, Blin E. Superimposition of medical compres- sion stockings: interface pressure meas- urements in normal legs and calculation of the stiffness indices. Phlébologie 2009; 62:67-74. 4. Uhl JF. 3D modeling of the venous system by direct multi-slice helical CT venography (CTV): technique, indications and results. Phlebology 2012;27:270-88. Table 4. Interface pressure (mmHg) in B1 and C points under a Coban™2 bandage (12 legs). B1 point C point Rest Contr Stand Rest Contr Stand Average 43.3 70.9 57.6 43.9 68.8 58.4 SD 5.4 13.1 10.2 10.8 21.8 13.8 Median 42 68 55.7 45.7 71.3 60 Rest, at rest; Contr, with dorsiflexion; Stand, standing; SD, standard deviation. No n- co mm er cia l u se on ly