The Effects of Graduated Compression Stockings on Cutaneous Surface Pressure Along the Path of Main Superficial Veins of Lower L

Chronic venous insufficiency in the lower limb is most commonly due to varicose veins, which appear as dilated, elongated, or tortuous superficial veins. Despite the considerable number of studies conducted on the etiology of varicose veins, the cause remains elusive.^1–5 However, it is generally recognized that occupation and posture are the major associated factors^1–8 and contribute significantly to the effects of raised venous pressure and incompetence of primary structures in the vein wall and valves.^9–11 People who spend most of their working day in a standing or sedentary position (eg, nursing staff, flight attendants, teachers, sales assistants) are considered to be at a high risk for varicose vein development. The development of varicose veins usually occurs in the superficial venous system of the lower limbs, especially in the long saphenous veins (LSVs) and their tributaries.¹² The short saphenous veins (SSVs) and their tributaries can also become varicose, but this occurs less often. The reported incidence of varicose veins in adults varies from 7% to 40% in men and from 14% to 51% in women.^1,6,8 If the condition cannot be prevented or treated in a timely manner, varicose veins can lead to more serious morbidities and medical complications.
Varicose veins can lead to thrombophlebitis (due to inflammation or blockage of the vein) and subsequent bleeding of the swollen veins near the skin surface.^5,12 Other complications, such as edema, skin pigmentation, varicose eczema, and venous ulceration, are mainly a result of venous hypertension.^12–15 However, the presence of varicose veins does not indicate that complications will inevitably occur. For example, 40% of limbs with ulceration caused by superficial venous incompetence do not have varicose veins.¹² The exact mechanisms that cause venous ulceration are still not fully understood; however, overlying large varicosities, low oxygen levels, and stagnant blood are considered to be possible causes.¹⁵
Compression therapy is an essential part of the prevention and treatment of venous diseases that affect the lower limbs. Graduated compression stockings (GCSs) provide a convenient method of maintaining pressure while allowing ambulation. Many studies have demonstrated that proper compression magnitudes and gradients can provide support to the superficial venous system and accelerate lower limb blood circulation.^16–18
However, GCS therapy has not always been as effective in clinical practice as it has been in research studies.^19,20 In the authors’ previous study,²¹ the general skin pressure distribution applied by GCSs was determined and analyzed. The authors also considered it necessary to further investigate the skin pressure at the main local regions, which would help to comprehensively understand the compression performances of GCSs and improve their medical functions. Therefore, the purpose of the present study was to examine the cutaneous pressure exerted by different graduated elastic compression stockings along the main superficial veins of the lower limb and to discuss the preventive and protective effects of compression stockings on varicose veins.

Materials and Methods

Six healthy women (mean age, 33.3 ± 6.3; height, 159.7 cm ± 4.7 cm; weight, 52.6 kg ± 5.0 kg; body mass index, 20.48 kg/m² ± 1.90 kg/m²) were recruited to participate in this study. Their occupations were teachers, researchers, and laboratory technicians. The duration of standing or sitting accounted for approximately 50% to 90% of their total workday, which implied that they belonged to the high-risk group for venous insufficiency. The ethics subcommittee of The Hong Kong Polytechnic University approved this study. Written informed consent was obtained from each participant before the start of the study.
Eight different pantihose-style compression stockings were tested (Table 1). The manufacturer specified distribution of pressure gradients as 100% of pressure at the ankle level, 70% of ankle pressure at the calf level, and 40% of the ankle pressure at the thigh level.
The experiment was conducted in an environment-controlled chamber set at 23°C ± 0.5°C with a relative humidity of 65% ± 3%. The study participants were instructed to wear each stocking type in the following 7 static postures: standing; standing with knee flexion; tip-toe standing; sitting with 90-degree knee flexion, sitting with leg straight; supine resting with slight elevation of the heel; and supine with knee flexion.
FlexiForce™ interface pressure sensors with 14 mm wide and 203 mm long (Tekscan Inc., Boston, Mass) were used to determine the cutaneous pressure applied by the GCSs. The pressure sensor has a circular, flexible probe that is 9.525 mm in diameter and 0.127 mm thick at one end (Figure 1). The calibration results were shown to be satisfied linearly, and the regression coefficients (R2) were all > 0.9. The pressure signals produced by the GCSs were displayed and recorded by a multichannel monitoring system.
The clinical diagnosis found that varicose veins commonly occur in the main superficial veins (Figure 2A and 2B). Therefore, in this study, 9 individual pressure sensors were placed along the paths of the long and short saphenous veins in sequence to focus on testing the cutaneous pressure located along the target regions (Figures 3A and 3B). As shown in Figure 3A, the testing points located on the medial side of the leg were 1) thinnest ankle area (just above malleolus); 2) midway between the thinnest ankle area and widest calf area (lower calf); 3) widest calf area; 4) at the knee above the mid-patella; 5) mid-level between the knee and mid-thigh; and 6) mid-thigh. The testing points in the posterior side of the leg, as shown in Figure 3B, were 7) over the Achilles tendon; 8) widest calf area; and 9) popliteal fossa.
The statistical evaluation of the data was accomplished with variance analysis using SPSS (SPSS Inc., Chicago, Ill) software. P < 0.05 was considered statistically significant.

Results

Variance analysis showed that testing locations, body postural changes, and types of compression stockings all significantly influenced cutaneous pressure distributions and magnitudes along the main superficial veins (P < 0.001). Of these factors, the testing locations played a more significant role as evidenced by the highest F value (F = 47.479; P < 0.001). The interactions between testing locations and body postures and between the locations and stocking types also exerted significant influences on the cutaneous surface interface pressures (P < 0.001); that is, cutaneous pressure located in one specific location along the main superficial veins would vary with the changes in body posture and type of GCS. Analysis of variance (ANOVA) was used to investigate the influences of GCS type and body postural changes on cutaneous pressures at 9 specific locations along the 2 main superficial veins. Among the 9 tested locations, only the cutaneous pressure exerted at the posterior knee (popliteal fossa) was not significantly influenced by the GCS type (P > 0.05), while the pressure at the posterior ankle (Achilles tendon), posterior knee, medial widest calf, and midway between the medial knee and medial mid-thigh were all significantly influenced by the body postural changes (P < 0.05)—especially the first 2 points located in the path of the SSV (P < 0.001).
Cutaneous pressure distribution and variation. The average cutaneous pressure distribution exerted by 8 types of GCSs at 4 pressure levels and placed on 9 locations along the 2 main superficial veins of the lower limb (while the subjects were standing) were estimated. The pressures recorded at the medial lower calf were higher than that at the medial ankle region. For the high-compression stockings, the cutaneous pressure at medial widest calf was higher than that at other locations along the LSV. Except for the high-compression stocking, better performances in pressure gradients were found from the lower calf to mid-thigh in relation to other pressure levels. No reversed pressure gradients were found along the SSV.
When study participants changed from the standing position into other different body postures, gradual decreasing trends in cutaneous pressures along the LSV were observed from the medial lower calf to the medial mid-thigh irrespective of the new body postures. Greater changes in pressure gradients were found along the SSV. Due to the distortion of the skin, the pressure at the popliteal area was significantly increased with knee flexion (P < 0.05), especially in the supine position with full knee flexion (P < 0.001; F = 65.852). Compared with the standing position, the cutaneous pressures at all sites along the LSV were elevated when sitting with knee flexion at 90 degrees, especially at the medial lower calf, medial widest calf, and the posterior ankle regions. When the posture was changed to the sitting position with relaxed leg stretching, the pressures at the medial lower calf, medial widest calf, and posterior ankle were all decreased. A similar situation also occurred in the supine position with the leg straightened. However, the pressure at the posterior ankle (Achilles tendon) was sharply increased in the tip-toe position (P < 0.001; F = 53.348).
Cutaneous pressure magnitudes exerted on the path of main superficial veins. To investigate the cutaneous pressure magnitudes exerted on the paths of main superficial veins and the influences of leg shape, a mild pressure level GCS (A2) and a high-compression GCS (A4) were selected. The cutaneous pressures exerted by the GCSs and the corresponding girths at the 9 tested locations on the leg with the subjects in standing position were examined, respectively. The measured average cutaneous pressures at the medial ankle region exerted by stocking A2 and A4 were 1164.9 Pa and 1495.9 Pa, respectively. These measurements were nearly equal to or 17% lower than that at the medial lower calf region for the 2 types of GCSs, respectively. Furthermore, for stocking A4, the greatest pressure of 1832.6 Pa was exerted at the medial widest calf, which was 22.5% higher than that at the medial ankle region.
According to the anthropometric testing, the circumferences at the 4 tested points from the ankle to the knee level along the path of the LSV were 20.13 cm ± 0.94 cm, 26.25 cm ± 2.50 cm, 34.32 cm ± 2.60 cm, and 33.08 cm ± 2.15 cm, respectively. The above result implied that although the fabric densities of stockings decrease gradually from the level of the ankle to the knee (according to the authors’ correlative material structural testing²²), the correspondingly increasing girths of the human leg, to some extent, influenced the designed pressure gradient distribution (ie, the highest pressure was exerted at the ankle and the lowest at the knee). A bulging calf, which further increases the tension of the fabric at the calf region, would accentuate this situation.
Cutaneous pressure applied on the ankle region was found to be insufficient. The average pressures at the posterior ankle and medial ankle regions for stockings A2 and A4 were lower than the mean ankle pressures specified by the manufacturers.

Discussion

The long and short saphenous veins are 2 main superficial veins located in the subcutaneous tissue. The LSVs extend up the medial side of the leg from the foot to the groin, and the SSV run up the back of the calf from the foot to the knee. Their venous walls are thin and not supported by the skeletal muscles.^23,24 Normally, to ensure adequate venous return from the lower limb, the superficial veins, deep veins, perforating veins, bicuspid valves, and the calf muscle must all work together.²⁵
However, when people sit or stand still for prolonged periods of time, the venous walls cannot withstand the hydrostatic pressure due to the local high pressure and lack of the pumping action of the leg muscles. As a result, the venous valves become incompetent and the venous blood gradually accumulates in the leg, thus forming tortuous varicose veins. GCSs are designed to provide the greatest pressure on the ankle region and gradually decrease pressure toward the thigh. The external pressure will support the superficial venous systems during increased venous pressure.
The level of applied pressure and the steepness of the ankle/calf/thigh pressure gradient are 2 important parameters that will dictate the effectiveness of the compression stocking. In this study, the results of cutaneous pressure distribution and magnitude along the LSV while in the standing position reveal 3 noteworthy issues.
First, according to the manufacturers’ recommendations, 18.4–21.2 mmHg (2453.12–2826.43 Pa) at the ankle area are suitable for relieving the symptoms of varicose veins at the early stage. The test data show that the mean pressure at the medial and posterior sides of the ankle is 1372.9 Pa, which is 52% less than the stated lower limit of 2453.12 Pa. That is, the cutaneous pressures exerted at the ankle area are insufficient. Second, the results of this study demonstrate that the pressure at the medial ankle region is less than that at the lower calf region among all tested stockings, which fails to follow the design principle of the pressure gradient exerting the highest pressure at the ankle region. Third, for high-compression stockings, the greatest pressure along the LSV is observed at the most prominent position of the calf muscle. Inadequate pressure exerted by these compression stockings cannot provide effective support for the LSVs.
Obviously, these experimental results are not consistent with the specifications provided by the manufacturers. One possible reason is the discrepancy between the testing models. The pressure recommendations from the manufacturers are normally generated by placing the stockings on a round cylinder and do not account for the irregular shape of human legs. For example, the outlines of the cross-section at the ankle region are shaped like an ellipse. According to Laplace’s Law, more pressure will be distributed on the prominent areas with larger curvature, such as the anterior tibial bone and Achilles tendon.
In addition, the authors considered that the practical course of the LSVs tends to pass through the hollow (valley) places between the anterior tibia and prominent medial gastrocnemius. The pressure exerted on the LSV here, perhaps, would be zero or lower than the measured pressure values; that is, the LSV could not obtain effective pressure and support from GCSs. Several auxiliary methods were suggested by some researchers, such as wearing GCSs with a higher pressure class than required or adding foam pads on the medial ankle (just above the medial malleolus) to increase curvature at the local site. Tazellaar et al obtained satisfactory effectiveness by fixing a “long cotton wool roll” over the course of the entire vein to increase local compression.^26,27
Body posture also has an important effect on the cutaneous pressure applied by stockings. When subjects flexed the knees in knee-flexion standing, sitting with knee flexion at a 90-degree angle, or in a supine position with maximum knee flexion, most of the cutaneous pressures exerted on the regions along the 2 saphenous veins were raised compared to the tip-toe position. This situation became more prominent at the popliteal fossa due to the local wrinkles of knitting fabric and deformation of the skin. The increased pressure at popliteal fossa can reverse the regular pressure gradient along the SSVs, producing a tourniquet effect.
Similar situations also occurred in the Achilles tendon area. When study participants were in the tip-toe posture, the Achilles tendon would tighten. The GCSs exert the most pressure at the ankle region where the fabric density is relatively higher. The somewhat small change in the cross-sectional shape of the ankle in this region can cause relatively higher cutaneous pressure. The markedly raised pressure exerted on the Achilles tendon area should have a negative effect on posterior tibial artery blood circulation.
The authors also found that when study participants extended their legs in a relaxed manner, irrespective of being in the sitting or supine position, most of the cutaneous pressures exerted at the areas along the LSVs were reduced, implying that the knee joint flexion exercise and the muscle activity of the lower limbs can contribute to provide more support and compression on the superficial venous system. Based on the aforementioned analysis, the authors suggest that proper lower-extremity exercises, such as ankle and knee flexions, are still necessary even if the subject is wearing a GCS. This not only will help avoid sustained high pressure exerted at the local regions but also will assist the skeletal muscle pump in preventing the backflow of blood.

Conclusion

The present study investigated the effects of GCSs with different pressure levels on the cutaneous pressure along the course of main saphenous veins and discussed the pathology of varicose veins and their prevention and protection.
The authors concluded the following:
1) Tested locations, body postures, and types of GCS significantly influenced the cutaneous pressure recorded along the main superficial veins
2) The pressure gradients along the SSV were enhanced when participants were in the standing position; however, the pressures along SSV were significantly influenced by the various body postures, especially at the posterior knee (popliteal fossa) and posterior ankle (Achilles tendon)
3) Insufficient pressure and reversed pressure gradients existed on the regions along the LSV
4) The flexion exercise of joints and muscle activity of the lower limbs provided more support and compression on the superficial venous system
5) Proper lower limb exercises when wearing GCSs should still be recommended.

Acknowledgements

The authors gratefully acknowledge the Research Grant Council through the project PolyU 5157/02E and Central Research Grant of the Hong Kong Polytechnic University through the project A188 and YD31 for their support of this research. The authors also thank JY Hu, YF Mao, SX Wang, and the study participants for their help with this study.