A major complication and complaint regarding lower limb amputees is residual limb volume fluctuations. Many amputees are hindered by the necessity of constantly managing residual limb volume with the application of socks and volume management pads. If the residual limb volume stabilizes, it offers an increase in comfort, a reduction in tissue breakdown, and an improvement in the functional ability to perform daily activities.
A potential benefit of elevated vacuum suspension is residual limb volume stability. One study reported an average of 6.5% volume loss with suction and 3.7% volume gain with vacuum using oversized sockets.1 A second study analyzed the effects of socket fit stating that vacuum suspension reduced the amount of volume loss or resulted in a slight gain.2 Both studies used water-based measurement techniques. An additional study investigated interface pressures resulting from ambulation and hypothesized that these interface pressures are responsible for drawing fluid into the residual limb and reducing the drive of fluid outward, thereby preventing volume loss.3
An additional study4 was conducted to assess short-term residual limb volume changes; however, these patients were not using vacuum suspension. Scans of the residual limb were taken at short-time intervals over a 35-minute period. Residual limb volume increased on doffing the prosthesis. It was determined that the greatest rate of volume increase transpired immediately after socket removal with 95% of the maximum volume increase occurring in less than 10 minutes. The observed reverse movement in fluid (measured volume change) provided insight as to the amount of volume reduced during a short period of time.4 More recently, a bioimpedance device has been developed to measure extracellular fluid fluctuation to assess residual limb volume.5 This device has not been used to analyze different treatment levels.
Clinical evidence and previous research have demonstrated the potential of elevated vacuum suspension to maintain residual limb volume. However, the exact effect of elevated vacuum on residual limb volume at different vacuum pressure levels has not been quantified. The purpose of this research is to gain outcome knowledge regarding elevated vacuum suspension and the effects on lower limb amputee's residual limb volume at different vacuum pressure settings.
The single subject study focused on a K2 transtibial diabetic amputee new to elevated vacuum with a history of daily residual limb volume fluctuations (previous daily volume maintenance of 20–25 ply with a pin and lock suspension). Nine years postamputation, the patient showed no evidence of limb change before the study. The patient's dietary practices and medication were tracked for the duration of the study with patient activity remaining relatively consistent. The patient, with a signed test patient agreement, was fitted with a 0-ply total surface bearing socket using Alpha Design® liners, Alpha Flex® Suspension Sleeves, and the LimbLogic® VS (Ohio Willow Wood, Mt. Sterling, OH). For the duration of the study, vacuum suspension served as the predominant suspension system using a vacuum pressure setting between 10 and 12 in Hg. Suction suspension was achieved by turning off the vacuum system and using the one-way suction valve built into the LimbLogic VS. Residual limb volume fluctuations were measured using the OMEGA® Tracer® (Ohio Willow Wood) volume feature (accuracy of 0.5 mm on a 500-mm volume). Scans were taken over the liner because of the time sensitivity of the study.
Three treatment configurations were analyzed: absence of elevated vacuum (suction), vacuum (negative pressure) at 10 in Hg, and vacuum (negative pressure) at 15 in Hg. Vacuum pressure settings were determined according to the subject's preferred ambulation setting of 12 in Hg. All vacuum settings had a control range of 5 in Hg. The range forced the vacuum pump to activate if the pressure deceased below 5 in Hg from the designated pressure setting. A comparison between each configuration was conducted by calculating the percent change in volume from the first scan after doffing the socket and a second scan 10 minutes later. This procedure used the prior knowledge that the greatest amount of volume increase occurs less than 10 minutes after doffing a socket.4 Figure 1 illustrates the overlay of two scanned images. Measurements of each scan were in reference to the distal end of the patella. Data were collected at two time intervals: on patient arrival and 2 hr later. Activity between the time intervals was 250 steps with the last 50 steps conducted immediately before doffing the prosthesis. A total of six trials were conducted. The type of treatment and the length from the initial fitting with vacuum suspension are indicated in Table 1.
The three treatment levels were evaluated by calculating the absolute percent change in volume. Raw volume data at the 2-hr measurement for all treatments are shown in Figure 2. These data tracked the volume difference between doffing the prosthesis (time = 0 min) and the second scan (time = 10 min). The absolute percent change in volume after doffing the prosthesis is illustrated in Figure 3. The trial sequence is numerically indicated. The raw data in Figure 2 were used to calculate the absolute percent change in volume at the 2-hr time measurement (Figure 3).
In Figure 2, the data for suction (trial 1, 2, 3, and 5) demonstrated a greater slope increase indicating a greater volume change. The maximum amount of change occurred in trial 1 with a volume difference of 100.29 cm3. Both vacuum trials (trial 4 and 6) displayed a slight change in volume (little slope) with a difference of approximately 16 cm3. Trial 4, vacuum at 15 in Hg, actually produced a decreasing slope. This decreasing slope might indicate a physiological change in the residual limb, that is, an increase in cellular fluid (hydration). Furthermore, this occurrence supports previous research, which states that the application of vacuum causes an increase in negative pressure during swing phase and the decrease in pressure during stance phase, suggesting an increase of fluid in the residual limb.3
Vacuum suspension significantly (95% criteria level) decreased the absolute percent change in volume compared with suction (Figure 3). The suction suspension trials displayed a decreasing trend with each sequential trial. Therefore, an improvement in volume retention was correlated (r = 0.91) to the length of vacuum suspension usage during the testing period of 3.5 months. The two vacuum pressure settings (10 and 15 in Hg) produced similar absolute percent volume changes; however, the vacuum treatment of 15 in Hg at the 2-hr measurement displayed a negative percent volume change as explained earlier. Vacuum suspension displayed 0.8% absolute percent change in volume compared with 4.9% displayed by suction in trial 1. In addition, the patient stated that there was no need for volume management with the use of vacuum suspension system. Conclusions regarding vacuum's effect on absolute limb volume were not drawn in this study because of the usage of a liner during measurement and the repeatability of the placement of reference landmarks between trial visits.
As an additional observation, the patient began the study with a wound on the distal end of the residual limb. Before the study, the patient battled the healing of the wound for several months without success, which is typical for many diabetic amputees. Figures 4 and 5 visually document the wound's healing during the course of the study. The wound appeared to heal quickly per weekly visual inspections. The healing occurred in weeks compared with months for other diabetic amputees of the same physical condition. After 2 weeks in vacuum suspension, the wound decreased in size and improved in color. Within 2 months, the wound was completely closed, and at 3 months, the coloration was returning to normal. The wound continued to show signs of improvement poststudy, and skin tones appeared healthier than prestudy.
Vacuum suspension with a resulting 0.8% change in volume significantly improved volume retention compared with suction, which produced 4.9% change in volume. Vacuum settings at 10 and 15 in Hg generated similar absolute percent changes in volume; however, 15 in Hg demonstrated a decreasing rate of change potentially suggesting a physiological alteration in the residual limb. During the duration of the study (3.5 months), an improvement was seen in volume retention with the length of vacuum suspension usage. In addition, the progressive healing of a distal wound was observed.
Future research is necessary to investigate any physiological changes to the residual limb because of vacuum pressure settings. Stronger evidence is required to fully understand the mechanisms associated with the ability to retain residual limb volume with elevated vacuum suspension. Furthermore, an extensive investigation is essential to determine whether an optimal vacuum pressure setting exists for each individual patient to reap maximum benefits. Ideally, a real-time measurement device would provide the most constructive information.
As lower limb amputees continue to contend with residual limb volume fluctuations, it is important to understand the benefits the elevated vacuum can provide. The results of this study demonstrated the ability of elevated vacuum to maintain residual limb volume including the effect of different vacuum pressures. This research has increased patient outcome knowledge and provided direction for future research regarding elevated vacuum suspension.
1. Board WJ, Street GM, Caspers C. A comparison of transtibial amputee suction and vacuum socket conditions. Prosthet Orthot Int
2. Goswami J, Lynn R, Street G, Harlander M. Walking in a vacuum-assisted socket shifts the stump fluid balance. Prosthet Orthot Int
3. Beil TL, Street GM, Covey SJ. Interface pressures during ambulation using suction and vacuum-assisted prosthetic sockets. J Rehabil Res Dev
4. Zachariah SG, Saxena R, Fergason JR, Sanders JE. Shape and volume change in the transtibial residuum over the short term: preliminary investigation of six subjects. J Rehabil Res Dev
5. Sanders JE, Rogers EL, Abrahamson DC. Assessment of residual-limb volume change using bioimpedence. J Rehabil Res Dev
KEY INDEXING TERMS: elevated vacuum suspension; lower limb prosthesis; residual limb volume; amputee outcome studies© 2010 American Academy of Orthotists & Prosthetists