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Transtibial Amputation: Preoperative Vascular Assessment and Functional Outcome

Elaine K. NgDavid Berbrayer, MD, FRCPC
Gordon A. Hunter, MB, FRCS,FRCSC
David Berbrayer, MD, FRCPC

ABSTRACT

An eight-year retrospective outcomes study of 135 transtibial amputees was undertaken in which patient charts were reviewed and survivors were interviewed. The authors found the ankle-brachial index to be of limited value in determining the level of amputation. Transcutaneous oxygen pressure of >30 mmHg was a good indicator of successful healing, whereas that of 20-30 mmHg warrants further consideration. Ambulatory status after at least six months of follow-up care was found to be dependent on the etiology of limb loss, the state of the other limb, and the general health and age of the patient.

Introduction

In the lower extremities, peripheral vascular disease (PVD) and diabetes account for the majority of amputations in the adult population. Other causes of amputation include trauma, osteomyelitis, tumor and congenital deformity (1,2).

Level of amputation is determined from the results of the clinical examination of the patient and from noninvasive arterial bloodflow studies. Serum albunim level and total lymphocyte count have been correlated with wound healing (3).

The authors investigated the values of the ankle-brachial index (ABI), which is the ratio of the systolic pressure in the ankle to that in the arm as determined by Doppler flow studies, and transcutaneous oxygen pressure (TcPO2) as predictors of wound healing (4). Generally, an ABI greater than 0.35 in nondiabetics or greater than 0.45 in diabetics and a TcPO2 of 40 mmHG or greater indicates proper healing will occur (4).

The transtibial operations were carried out as described elsewhere; using proper techniques promotes successful residual-limb healing and prosthetic fit (1,5,6). The authors recognized that preservation of the knee joint greatly improves the functional outcome of the amputee and lowers the energy expenditure necessary for ambulation (1,7,8) and that adequate bloodflow is essential for the residual limb to heal.

Following amputation, most patients are discharged to a rehabilitation unit to be fitted with a custom-made prosthesis. Over a period of three to six months, transtibial amputees progress through several devices, including an above-the-knee cast with pylon and a temporary transtibial prosthesis, before final fitting with a permanent prosthesis. Use of a prosthesis is limited by the mental and physical health of the patient (6). Nonprosthesis wearers generally rely on wheelchairs, walkers or crutches.

An amputee's outcome depends on a number of factors. Scremin et al. concluded age alone determines the progress of wound healing as indicated by temporary prosthetic fittings (9). However, the etiology of limb loss may be important as well since the survival rate of diabetics is lower than that of PVD patients due to the severity of diabetes-associated disease (10,11). Others have suggested a multifactorial basis to rehabilitation outcomes, including wound healing, level of amputation, the status of the other limb, the general health of the patient and postoperative care (7,12).

The present study was undertaken to determine the functional outcome of transtibial amputees and to investigate the pre- and postoperative factors that determine their eventual outcomes.

Method

A retrospective study was carried out on 135 patients at Toronto's Sunnybrook Health Science Centre (SHSC) and Sunnybrook Centre for Independent Living (SCIL). The patients had undergone transtibial amputations between January 1986 and December 1993. Information was obtained from patients' hospital charts, and semistructured interviews were conducted either in person or by telephone. In other cases, patients were followed to the time of death or the last entry in the clinic files, with a minimum follow-up of six months.

Information on general demographics, cause of amputation, past medical history, and results from Doppler studies and transcutaneous oxygen measurements was collected. The data were analyzed by student t-tests where p <0.05 was regarded as significant. The patients' ambulatory statuses were assessed based on the scale used by Volpicelli et al. (8) shown in Table A .

Subjects

The authors studied 135 patients with transtibial amputations; 94 (70 percent) were male, and 41 (30 percent) were female. Eighty percent were unilateral amputees; 20 percent were bilateral amputees. The sample of bilateral amputees included 20 bilateral transtibial amputees, one transtibial/Syme, one transtibial/transmetatarsal, two transtibial/toes, one transtibial/transfemoral and two patients who eventually became bilateral transfemoral amputees. Of the 162 amputations, 15 (9 percent) required revision of the transtibial amputation to the transfemoral level.

Causes of Amputation

Of patients who lost a limb as a result of peripheral vascular disease (77 percent), 58 percent had diabetes. Transtibial amputation as a result of trauma accounted for 19 percent of the amputations. Other causes included septic neuroarthropathy, spina bifida, tumor and neurofibromatosis (see Table B ).

Average Age at Amputation

The average age at first amputation was 58 years (range 16-90 years). Trauma patients were younger than those who had an amputation due to vascular disease (34 versus 65 years). For the 27 bilateral amputees, the average age of first amputation was 60 years, and the mean duration between the first and second amputations was 3.0 (± 3.6) years.

Death

At the time of review, 36 people (27 percent) were deceased, of which 10 (28 percent) were bilateral amputees. Average time from first amputation to death was 2.50 years (range 0-14 years). The average survival of diabetics postamputation was 3.42 years; mean age at death was 65.6 years. The average survival of those with nondiabetic vascular disease was 1.75 years; mean age at death was 75.4 years. Twelve of these patients did not survive more than a year following their amputation, and the majority (92 percent) of deceased patients had died within five years of their first amputation.

Results

Preoperative Assessment

Table C compares the levels of ABI and TcPO2 for amputation at the transtibial level. A failed residual limb was defined as one that requires revision to a proximal level; a healed residual limb was defined as one that remains at the transtibial level even though debridement or revision may have been necessary. There was no difference between the ABI for nondiabetic and diabetic patients.

The mean transcutaneous oxygen pressure was 41.8 for the healed residual limbs (range 12-78) mmHg and 20.7 (range 4-44) mmHg for the failed residual limbs. No difference between the TcPO2 for diabetics and nondiabetics was apparent. A significant difference was noted between the healed and the failed residual limbs.

Outcomes of Transtibial Amputees

The following groups of patients were excluded from the outcomes part of the study: patients who had a revision from a transtibial to a higher level, those who were deceased (except for one person who died during the period of review) and 26 people who were not available for follow-up consultation. The functional outcomes of 59 patients were evaluated.

Average age of evaluated patients was 59 years (range 22-85 years). Trauma patients were significantly younger than those whose amputations were caused by vascular disease. The average age at their first amputation was 56 years (range 16-82 years).

Of the transtibial subjects, 38 (64 percent) were male, and 21 (36 percent) were female. Eleven subjects (18 percent) were bilateral amputees, including six transtibial/transtibial, one transtibial/Syme, one transtibial/transmetatarsal and two transtibial/toes. Peripheral vascular disease accounted for 73 percent of the amputations, of which 70 percent were due to diabetes. Twenty-two percent of the patients lost their limb(s) as a result of trauma. Other causes included spina bifida, septic neuroarthropathy and neurofibromatosis.

Use of Prosthesis

Ninety-three percent of the patients were prosthesis users; 83 percent used their prosthesis regularly; 10 percent were partial users; and the remaining 6 percent were not fitted with a prosthesis.

Employment, Accommodation and Mobility

Twenty-nine of the 59 patients (49 percent) were younger than 65 years; eight (28 percent) were employed part- or full-time, and two worked as volunteers. Eighteen (62 percent) were not in the workforce. The study included one student.

Forty-three of the subjects (73 percent) lived with their families, relatives or roommates; 10 people (17 percent) were able to live alone with help from friends, family members or homecare services; and five lived alone without aid. One person resided in a senior citizens' home.

In terms of mobility and independence, 27 subjects (46 percent) could drive a car, four (7 percent) relied on trains and buses for transportation, and 28 (47 percent) were dependent on other people to get around.

Ambulatory Status

The ambulatory statuses of the patients and the causes of amputation are shown in Figure 1 . Overall, 25 (42 percent) were community ambulators, 27 (46 percent) were household ambulators, one required supervision for limited household ambulation, three were wheelchair bound, and three were bedridden. Most trauma patients were able to attain a higher ambulation level than were dysvascular patients. The bedridden patient in this group was paraplegic as a result of an accident.

Figure 2 shows the ambulatory statuses attained by patients in different age groups. Younger patients (<50 years) were able to attain a higher level of ambulation than those over age 65.

Ambulation of nine bilateral amputees was assessed. Six subjects were transtibial/transtibial, one was transtibial/Syme, one was transtibial/toe and one was transtibial/transmetatarsal; the latter achieved Grade A on the ambulatory scale. Two of the bilateral amputees were not included as their second amputations were carried out after the chosen period of review.

Many patients had concomitant illness. Of the 59 patients, 19 people had cardiorespiratory diseases, including myocardial ischemia, congestive heart failure and chronic obstructive pulmonary disease; four people had suffered a stroke; and 12 had musculoskeletal disorders-mostly arthritis in the other limb.

The ambulatory statuses achieved by these patients and the bilateral amputees are shown in Table D . One subject with Alzheimer's disease and another with Parkinson's disease were classified as Grade E and Grade G, respectively.

A large percentage of patients with cardiorespiratory diseases (63 percent) or musculoskeletal disorders (58.3 percent) achieved Grade C or Grade D on the ambulatory status scale. Stroke patients also had limited ambulation. Three of four patients in this group were household ambulators, and one person was bedridden. The distribution of patients who had previously undergone vascular surgery is similar to the total study group.

Discussion

A retrospective review of 135 transtibial amputees was conducted. The male-to-female ratio, the proportion of unilateral and bilateral amputees, and the diagnoses leading to amputation are consistent with those reported in other studies (2,13). The mean age at amputation in this study (58 years) was lower than those in other studies (10,13,14). A relatively large proportion of trauma patients from the SHSC Regional Trauma Unit was included. These patients were younger than those whose amputations were caused by vascular disease, which may explain the lower age at amputation in comparison with other studies.

The survival of amputees has increased significantly from the 1970s to the 1980s, but the lifespan of a patient with vascular disease is severely limited when compared to that of amputees without the disease. The prognosis is even worse for diabetics (10,11). Stewart et al. (10) reported a longer mean survival of PVD patients (4.17 years) than diabetic patients (3.67 years). This finding is contrary to our results; however, the diabetics died at an earlier age (65.6 years) than did the nondiabetic patients (75.4 years). The overall mortality rates are comparable to those reported elsewhere.

Some studies have shown that if a patient survives more than three years after the first amputation, there is a significant chance the other limb will be lost during that three-year period (10). Similarly, in our series, the major cause of amputation of bilateral amputees was diabetes. On average, the other limb was lost within three years. Others also have reported a similar interval between the first and second amputations (6,8).

Clinical examination and laboratory tests are essential in determining the level of amputation. The ankle-brachial index has been used as a preoperative assessment tool to determine postoperative wound healing. Such pressures are dependent on the compliance of blood vessels and therefore may be artificially high in diabetics with calcified vessels. Some research suggests a value of 0.35 or greater in nondiabetics and 0.45 or higher in diabetics is an accurate indicator of successful wound healing (4).

Our results indicate no difference between the indices in diabetic and nondiabetic patients. A valid comparison could not be made between the healed and the failed residual limbs since no flow was detected in a large number of cases. Hence the ankle-arm ratio has limited application and is not a reliable indicator for the determination of level of amputation.

Transcutaneous oxygen pressure measurements have been advocated as a simple and accurate method of predicting residual-limb healing (15). They are dependent on skin perfusion pressures and not on the state of arterial walls. Therefore, there should be no difference in the TcPO2 values of diabetic and nondiabetic patients; our results support this notion. The mean TcPO value of 41.8 (± 15.8) mmHG for healed amputations is consistent with that of other studies (15).

Variability in the results could be due to the oximeter used in the study (16). Comparison with failed transtibial amputations showed a significant difference. Therefore, TcPO2 is a more reliable predictor of wound healing than is the ankle brachial index and is a valuable tool in selecting the level of amputation. A TcPO2 value of 30 mmHg or greater suggests a successful transtibial amputation. For a patient who is a potential prosthetic candidate for a transtibial prosthesis, has a TcPO2 pressure between 20 and 30 mmHg, and has a healthy and mobile knee joint and a calf musculature that is not indurated, transtibial amputation can be attempted with a reasonable chance of success.

The loss of a limb often is viewed by patients as a disaster, but modern prostheses and successful rehabilitation can restore patients' independence and improve their outlook. The quality of life can be evaluated by considering the patient's functional, social and vocational status. The functional outcome was assessed only in patients with whom a personal or telephone interview was conducted. Obviously, only the survivors were selected for this part of the study, but this limitation might have influenced the results. The ages, male-to-female ratio and causes of amputation of the 59 patients were consistent with the rest of the study group.

Several methods of evaluation may be used to determine the functional outcome of amputees. The International Classification of Impairments, Disabilities and Handicaps (17) is extremely comprehensive but was too detailed for this study. The ambulatory status scale was satisfactory in assessing patients' mobility.

The scale is simple to use, and it classifies patients according to ambulatory capabilities. The evaluation showed a majority of patients could walk (Grades A to E), and 42 percent were able to walk at least one to two blocks (Grades A and B). These results are not surprising since more than 90 percent of the subjects were fitted with prostheses, and the majority used them regularly. The success rate of prosthetic fittings reported in this study was higher than those reported in other studies (3,10,18).

Approximately half of the patients were independent and either were able to drive themselves or relied on public transportation. Though approximately half of the patients were under age 65, more than 60 percent were unemployed. Only 27 percent were employed full- or part-time. This is another indication of the severity of disease and the toll it has on patients' lives. This situation also could be partially due to the unemployment rate in Canada at the time of the study.

The authors found trauma patients generally had better outcomes than other patients. While Scremin et al. (9) concluded the age of an amputee was the only determinant in wound healing, this notion ignores the function of the amputee; wound healing is only one aspect of rehabilitation.

Figure 2 shows some of the patients in the oldest age group were level A ambulators. The absolute age of patients in this study could not be regard- ed as a significant predictor. Coexisting illness, including stroke, cardiorespiratory disease and poor status of the other limb, might impede function.

Vascular amputees die from heart disease more often than do members of the general population (19). Diabetes also leads to complications such as neuropathy, retinopathy, nephropathy and coronary artery disease. Attention to the management of these diseases should not be overlooked. Some controversy exists as to whether vascular surgery prior to amputation has an adverse effect on a patient's outcome (2022). The amputees in this study who had previous vascular surgery achieved ambulatory statuses comparable to those of the other patients. Thus, it does not appear vascular surgery had a significant deleterious effect on the functional outcome of these patients.

A loss of data due to death, loss of records or inconsistency in reporting limited the number of patients whose functional outcomes could be assessed. In addition, patients' denial of their apparent preoperative and postoperative functional statuses may have influenced the results. Future prospective studies can control some of these variables.

Consideration of physical and social rehabilitation is necessary for successful management of amputees (23,24). This study showed the functional outcome of transtibial amputees is dependent on a number of factors. Perhaps limb loss may be prevented by good diabetic control, better foot care and attention to the risk factors for vascular disease.

Conclusion

In this study, the ankle-brachial index proved of limited value in the preoperative assessment of the level of transtibial amputation. On the other hand, transcutaneous oxygen pressure proved reliable as an indicator of residual-limb healing.

The functional outcome of transtibial amputees was evaluated by the ambulatory status scale. Results revealed the prognosis of patients is determined by a number of factors, including the patient's age and general health along with the etiology of the amputation and the status of the other limb.

Acknowledgments

The authors are indebted to the staff members at SHSC for their support and assistance in conducting this study.

ELAINE K. NG is a medical student at the University of Toronto, Ontario, Canada.

GORDON A. HUNTER, MB, FRCS, FRCSC, is professor of orthopaedic surgery in the division of orthopaedics at the Sunnybrook Health Science Centre.

DAVID BERBRAYER, MD, FRCPC, is assistant professor in the division of rehabilitation medicine at the Sunnybrook Health Science Centre, University of Toronto, Ontario, Canada.

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