The effect of semirigid dressings on below-knee amputations.

Control and reduction of edema are prerequisites for wound healing and eventual prosthetic fitting of the residuum of a person with an amputation. This is particularly true for the patient with peripheral vascular disease, who is already at risk for delayed wound healing.[1] Different techniques have been developed to control postsurgical edema in the residuum. The traditional soft dressing (elastic bandage) has proven to be ineffective in controlling edema, in part because it requires a skilled technique and numerous reapplications.[2-4] Nonremovable rigid dressings (plaster casts) have been shown to be effective in controlling swelling, thus promoting earlier healing.[5] With this dressing, however, the knee joint is immobilized, the incision cannot be easily inspected, and application requires skilled personnel and special equipment.[6] Wu et al[3] developed a removable rigid dressing that allowed inspection of the residuum and that proved effective in reducing swelling. Knee movement was allowed because the dressing did not extend above the knee. Yet, skilled personnel and special equipment are still required for application of this dressing.

Ghiulamila[4] was dissatisfied with the soft dressing (elastic bandage), and he was reluctant to use the rigid dressing because of the noted disadvantages. He developed a bandage that was flexible, lightweight, and easily removed, yet at the same time inextensible. This "semirigid dressing" (SRD) is often referred to as an "Unna boot" because it contains a zinc paste developed in the late 19th century for the treatment of ulcers by Unna, a German dermatologist.[7] This SRD is now commercially available as Dome-Paste[TM].(*) In some clinical settings, the SRD has replaced the elastic bandage for stump shrinking and shaping during the preprosthetic period.

Menzies and Newnham[6] compared the advantages and disadvantages of soft dressings, rigid dressings, and SRDs and chose the SRD as being superior to both the rigid and the soft dressings. A few clinical perspectives dating from the early to mid 1970s have been written supporting the use of the SRD alone, and in conjunction with a temporary below-knee prosthesis.[8-11] A clinical statistical study was needed to investigate the effectiveness of the SRD compared with the soft dressing in preparing the patient for the fitting of a prosthesis.

The primary question of this study was: Does the time to readiness for prosthetic fitting for patients treated with the SRD differ from that of patients treated with the soft dressing?

Method

Subjects

The subjects in this study were persons who had undergone below-knee amputations as a consequence of peripheral vascular disease. There were no exclusion criteria, which resulted in a sample consisting of subjects with complex and varied medical histories. The population of patients with amputations at our hospital is relatively small, with surgeries occurring sporadically. We did not randomize treatment to subjects; rather, we alternately assigned the subjects to one of two groups as they became available. Nineteen subjects (6 women, 13 men) with a mean age of 61.3 years (SD=9.4) were assigned to an SRD group, and 21 subjects (9 women, 12 men) with a mean age of 61.8 years (SD=11.2) were assigned to a soft dressing group. All subjects gave written informed consent before participating in the study.

Three patients were included in the study twice because they were later readmitted for amputation of the other leg. One patient received SRDs on both legs, and the other two patients received the soft dressing on one leg and the SRD on the other leg.

Several factors were recorded for each patient: sex, age, diabetes, use of insulin, anemia, smoking, hypertension, cardiac disease, presence of residuum and phantom pain, and the use of drains postoperatively. A patient was defined as a smoker if he or she had any history of smoking. A patient was considered to have pain if it was rated as moderate, severe, or agonizing. A patient was considered to have no pain if the pain was defined as none or slight.

All descriptive statistics on categorical data are shown in Table 1. All but two of the factors were distributed fairly evenly between the two groups. There were nearly twice as many patients with cardiac disease in the SRD group than in the soft dressing group. There was also an uneven distribution of drain types between the two groups.

[TABULAR DATA 1 OMITTED]

Procedure

The SRD consisted of Dome-paste [TM], which is a gauze impregnated with zinc oxide, calamine, and gelatin. The SRD was applied by the physical therapist in the operating room or in the recovery room within one-half hour after surgery. All therapists had been instructed to follow a specific protocol in applying the SRD. In a sterile field, the incision was covered with strips of Jelonet[TM].[double dagger] Three strips of Dome-Paste[TM] were then applied in a posterior-to-anterior fashion to cover the distal end of the residuum. This procedure was repeated three times. Additional overlapping strips were then applied in a figure-eight fashion proximally to the knee joint line (Fig. 1). Once completed, the dressing was covered with Kling[TM] gauze.[double dagger] This dressing was changed when the drains were removed 48 hours postoperatively. The SRD was reapplied by the physical therapist. The dressing was thereafter changed as needed (ie, if it became loose, or if the physician wanted to inspect the wound). The maximum length of time each SRD was left on was 7 days. The SRD was repeatedly reapplied until the incision was healed, at which time an elastic bandage or stump shrinker was used and girth measurements were begun.

The soft dressing consisted of a tensor bandage initially applied over the wound dressing by the surgeon in the operating room. After the 48-hour dressing change, the tensor was reapplied as needed by either a nurse or a physical therapist.

Both groups of subjects received identical postoperative physical therapy programs in preparation for prosthetic fitting (Tab. 2). Criteria were established to determine incision healing and readiness for prosthetic fitting. These criteria were (1) no gaping of the incision (the presence of a small adherent scab was acceptable) and (2) the absence of edema and no further changes in girth of the stump on three separate measurements taken every 2 days.

Measurements were begun when the incision no longer required a sterile dressing. Proximal and distal measurements were taken at 5-cm intervals using the medial joint line as the starting point. With no tension, the measuring tape was laid flat on the skin distal to the line of measurement. Measurements were taken three times per week on alternate days.

Two experienced therapists (having practiced physical therapy more than 3 years) examined each patient separately, and each therapist determined separately when the patient was ready for prosthetic fitting. The first therapist who measured the patients also treated the patients throughout their rehabilitation, and subsequently knew to which group each patient belonged. The second therapist who measured the patients, however, was not informed as to which group the patients belonged, nor as to the results of the measurements taken by the first therapist.

The length of time between surgery and the patients' readiness for initial prosthetic fitting was recorded. In 4 of the 24 patients who reached the stage of readiness for prosthetic fitting, the length of time differed between the two therapists, ranging from 1 to 3 days. In these cases, the "average" of the two measurements was used.

Data Analysis

To determine whether the time from surgery to readiness for prosthetic fitting for patients treated with the SRD differed from that of patients treated with the soft dressing, Kaplan-Meier survival curves were generated for, each group and the log-rank test was used to analyze the data. The Kaplan-Meier methodology provides rational estimates of the probability of lack of readiness for data such as ours in which time to readiness for prosthetic fitting was not available for all patients. Some patients left the study due to the reasons described in the "Results" section, and all we know from their experience is that the time to readiness for prosthetic fitting was at least the time when they left the study. For purposes of this analysis, the critical event was defined as readiness for prosthetic fitting.

Proportional hazards regression was used to explore the impact of variables on time to fitting. This methodology provides a generalization to the Kaplan-Meier methodology in that the researcher can study covariates somewhat analogous to the classical methods of the analysis of covariance.[12,13] We elected to use all available data, using three subjects twice. All analysis was performed using the S-plus data analysis system.[14] Fisher's Exact Test was used to explore whether pain was different in the two groups and to explore the changes in status in the two groups.[13]

Results

Six subjects in the SRD group did not complete the study. Three subjects underwent above-knee amputations, 1 subject was transferred out of town, 1 subject died, and I subject was removed at the request of the physician. In the soft dressing group, 10 subjects did not complete the study. Seven subjects underwent above-knee amputations, 2 subjects died, and we were unable to determine the time to fitting of 1 subject due to other medical problems. (The patient was very ill in the intensive care unit at the time his residuum was healed.

The Kaplan-Meier estimated survival curves are shown in Figure 2. The observed value of the log-rank test statistic was 4.97 (P=.0258). It appears that the time to readiness for prosthetic fitting in the SRD group may be less than half that of the soft dressing group.

To determine whether other factors (Tab. 1) may have influenced the time to readiness for prosthetic fitting, Cox's proportional hazards model was applied. Adjustment for covariates had no effect on the detected difference between the two groups.

Fisher's Exact Test was performed to explore the various degrees of pain between the two groups. There was no evidence to suggest that pain was significantly different between the groups. We also used Fisher's Exact Test to explore the question of whether more patients from the SRD group than the soft dressing group were dropped from the study because of revision to above-knee amputation. Again, we found no significant difference between the two groups.

Discussion

We believe our results are generalizable; however, random assignment to treatment group may have been a more rigorous approach. An examination of the two graphs reveals that in the first 40 days postsurgery, there was a similarity in the two groups' proportion of being not ready for prosthetic fitting. After this time, the difference between the two groups became greater. The curve representing the SRD group appears more consistent in time to readiness for prosthetic fitting, whereas the curve representing the soft dressing group shows a large variability in the number of days to readiness for prosthetic fitting. Patients treated with the SRD were ready for prosthetic fitting in a more consistent time frame than those treated with the soft dressing.

At the time the study was initiated, compression pump treatments were a standard part of our physical therapy program. We considered these treatments to be a useful tool in reducing edema in healed residuums, most of which had received the soft dressing postoperatively. Our study design ruled that all patients, regardless of group assignment, receive identical physical therapy programs. The compression pump, however, had little effect on the girth measurements of the residuums of those patients in the SRD group, as determined by measurements taken both before and after treatment. Unfortunately, data were not collected to compare the effect of the compression in the two groups. Since completion of the study, a protocol has been developed at our hospital that uses the SRD for all amputations, regardless of level or cause, and as a consequence the compression pump is no longer used.

In our hospital, patients are not fitted with a temporary prosthesis. Once the edema in the residuum has stabilized (no changes in girth measurement after three measurements over a 6-day period), the prosthetists choose to fit patients with a definitive socket (polyester resin) that is "unfinished"; that is, the pylon is exposed to allow for changes in alignment. The prosthesis is only finished when the residuum appears to be remaining stable and the patient's gait is optimal. If it appears that the residuum will continue to change, the prosthesis will not be completed until the patient is recasted for another socket. Thus, the sooner a residuum can reach that stable state, the sooner a patient can be ambulated on a prosthesis. This underscores the importance of decreasing the time between surgery and readiness for prosthetic fitting. The SRD appears to be a more effective dressing than the soft dressing in achieving this goal.

Most of our patients with amputations are elderly, with multiple medical problems. Often, they are ambulatory and living at home independently when they are admitted to the hospital. These patients often cannot return to their home environments until after they receive their prostheses and regain their former levels of function. The SRD, therefore, not only could be a benefit to the patient, but also could provide cost benefits.

Soft dressings are changed daily. In the early postsurgical period, there is usually considerable drainage onto the tensors and they are discarded. The soft dressing is a mobile dressing that has to be reapplied several times throughout the day (and often in the absence of skilled personnel). Considering the fact that the SRD can be left on for a period of up to 7 days, one could assume that there would be additional savings in the cost of dressing materials and personnel time.

Conclusion

We conclude, from the results of our study, that a patient may be ready for prosthetic fitting sooner if treated with the SRD. Benefits for both patient and hospital could be assumed when the SRD effects a decrease in the length of time between surgery and readiness for prosthetic fitting. Earlier prosthetic fitting could result in decreased rehabilitation time and earlier discharge.

Acknowledgments

We give special thanks to Dr Cy Frank, Dr Gary Hughes, Peggy Wilson, BScP'T, Ann McKenna, MSc Statistics, and Barb McLaughlin, BScPT, for their support and assistance in the development and completion of this research project.

References

[1] Horne G, Abramowicz J. The management of healing problems in the dysvascular amputee. Prosthet Orthot Int. 1982;6:38-40. [2] Mueller MJ. Comparison of removable rigid dressings and elastic bandages in preprosthetic management of patients with below-knee amputations. Phys Ther. 1982;62:1438-1441. [3] Wu Y, Keagy R, Krick N, et al. An innovative removable rigid dressing technique for below-the-knee amputation. J Bone Joint Surg [Am]. 1979;61:724-729, [4] Ghiulamila RI. Semi-Rigid dressing for postoperative fitting of below-knee prosthesis. Arch Phys Med Rehabil. 1972;53:186-190. [5] Mooney Y. Comparison of postoperative stump management: plaster vs soft dressings. J Bone Joint Surg [Am]. 1971;53:241-248. [6] Menzies H, Newnham J. Semi-rigid dressings for lower extremity amputees. Physiotherapy Canada. 1978;30:225-227. [7] Skinner HA. The Origin of Medical Term. New York, NY: Hofner Publishing Co; 1970:41-56. [8] LaForest NT, Regon LW. Physical therapy program after an immediate semirigid dressing and temporary below-knee prosthesis. Phys Ther. 1973;53:497-502. [9] Sterescu LE. Semi-rigid (Unna) dressing for amputations. Arch Phys Med Rehabil. 1974;55: 433-434. [10] Kay S. Wound dressings: soft, rigid, or semi-rigid, Orthot Prosthet, 1975;2:59-68. [11] Fish SL. Semirigid dressing for stump shrinkage: suggestion from the field. Phys Ther. 1976;56:1376. [12] Armitage P, Berry G. Statistical Methods in Medical Research, Cambridge, Mass: Blackwell Scientific Publications. Inc; 1987:14. [13] Matthews DE, Farewell VT. Using and Understanding Medical Statistics Basel, Switzerland: S Karger AG, Medical and Scientific Publishers; 1988:67. [14] Becker RA, Chambers JM, Wilks AR. The New S Language: A Programming Environment for Data Analysis and Graphics. Pacific Grove, Calif Wadsworth Inc., 1988.

N MacLean, DipPT, is Part-time Joint Clinical Lecturer, Faculty of Rehabilitation Medicine, Univer of Alberta, and Physiotherapist, Department of Physical Medicine and Rehabilitation, Foothills Hospi 1403-29 St NW, Calgary, Alberta, Canada T2N 2T9. Address all correspondence to Ms MacLean.

GH Fick, PhD, is Associate Professor, Faculty of Medicine, University of Calgary, Calgary, Alberta Canada T2N 4N1.

This study was approved by the Conjoint Ethics Committee of the Faculty of Medicine, University of Calgary. It was also approved and funded by the Research and Development Committee of Foothills Hospital.

This article was submitted December 29, 1992 and was accepted January 24, 1994.

(*) Miles Inc, Pharmaceutical Division, 400 Morgan Ln, West Haven, CT 06516.

[dagger] Smith and Nephew Inc, Lachine, Quebec, Canada H8T 2Y5.

[double dagger] Kendall Canada Inc, 1100 Curity Ave, Box 570, Peterborough, Ontario, Canada K9J 6Z