Session III - Combined Meeting with AAST

*The Insensate Foot: An Indication for Amputation?

Alan L. Jones, MD; Melissa L. McCarthy, ScD; Lawrence X. Webb, MD; Stephen H. Sims, MD; Roy W. Sanders, MD; and the LEAP Study Group, University of Maryland Medical Center ­ R. Adams Cowley Shock Trauma Center, Baltimore, MD (all authors - a-NIH-NIAMS Grant)

Purpose: The insensate foot has been identified, perhaps wrongly, as an indicator for amputation when associated with a high-energy lower extremity injury. Absence of plantar sensation is included as a major component of several predictive index scores. However, in many cases, reversible ischemia and neuropraxic injuries of peripheral nerves make determination of ultimate sensation in the foot impossible at the time of admission. Despite the belief that an insensate foot precludes successful treatment of an injured lower extremity, the insensate foot associated with other conditions, such as diabetes and spinal cord injury, is routinely managed without amputation. The purpose of this investigation was to evaluate the outcome of patients with absent plantar sensation in association with high-energy lower extremity trauma.

Methods: In a prospective, longitudinal study, we analyzed 601 patients (633 limbs) with high-energy lower extremity trauma at 8 level-I trauma centers. High-energy lower extremity injuries were defined as those resulting in a traumatic amputation below the distal femur or injuries associated with some risk of amputation, including: (1) Gustilo grade IIIB & IIIC tibia fractures, (2) selected grade IIIA tibia fractures, (3) traumatic dysvascular limbs (4) major soft tissue injuries to the tibia, and (5) severe ankle and hind-foot injuries. A subgroup of 100 patients (101 limbs) had an absence of plantar sensation at the time of admission. Of those 100 patients, 45 were excluded from the study. Seven patients (8 insensate feet) were excluded because their contralateral lower extremity injury would have affected outcome. Thirty-eight patients (38 limbs) were excluded because their more severe lower extremity injuries mandated immediate (within 24 hours) amputation. Therefore, the study group consisted of 55 patients (49 men, 6 women) with unilateral injuries and absent plantar sensation. The mechanism of injury was vehicular trauma in 27 (49%), gunshot in 10 (18%), machinery-related in 6 (11%), falls in 4 (7%), and other in 8(15%) patients. The 26 patients who underwent delayed amputation (>24 hours after injury but during the initial hospitalization) formed group I. The 29 patients who were managed without amputation formed group II. Four group II patients (14%) went on to have late amputations (after the first hospitalization). We collected and analyzed data on demographics, Injury Severity Score (ISS), length of initial hospital stay, bone loss, contamination, skin injury, ipsilateral foot injury, limb ischemia, vein injury, and muscle injury. Patient-reported outcome was evaluated with Sickness Impact Profile (SIP) scores (overall and selected components) at 12 and 24 months and compared with pre-injury SIP scores of a similar group of patients (norms) with lower extremity fractures.¹ Data were analyzed with the chi square test and Student's t-test. Significance was set at P £0.05.

Results: Comparing the 2 groups, there were no significant differences in age, sex, mechanism of injury, or injury characteristics (Table 1), and mean ISS and length of initial hospital stay were comparable (Table 2).

Table 1

Parameter	Group I  (Amputation, N = 26)	Group II (No Amputation; N=29)
Severe bone loss	6 (23%)	1(3%)
Severe muscle injury	10 (38%)	7 (24%)
Severe skin injury	6 (23%)	7 (24%)
Massive contamination	10 (38%)	6 (21%)
Limb ischemia	15 (58%)	17 (58%)
Vein injury	9 (35%)	5 (17%)
Foot injury	5 (19%)	8 (28%)

Table 2

Parameter	Group I (Amputation, N = 26)	Group II (No Amputation, N = 29)
Mean ISS (range)	10.2 (4 - 41)	11.2 (4 - 34)
Length of hospital stay in days (range)	18.3 (4 - 54)	19.7 (4 - 79)

SIP scores were available for 43 patients (78%) at 12 months and for 37 patients (68%) at 24 months. There were no significant differences between individual or overall SIP scores between groups I and II (Table 3), but both groups I and II differed significantly from the published norms.

Table 3

Parameter	Group I (Amputation)		Group II (No Amputation)		Norms*
SIP Score	12-Month	24-Month	12-Month	24-Month
Overall	14.9	12.3	12.3	11.6	2.5
Physical	14.2	9.1	9.7	8.8	1.3
Psychosocial	12.1	12.3	15.1	10.9	2.5
Work	37.4	45.2	33.6	35.0	8.8

* Pre-injury SIP scores for patients with lower extremity injuries.¹

Discussion: Many factors affect the decision regarding whether or not to amputate a severely injured lower extremity. The absence of plantar sensation at the time of admission has been used as a highly weighted indicator for amputation. However, this position is not supported by prospective data. High-energy lower extremity trauma in association with an insensate foot at the time of admission results in substantial impairment at 12 and 24 months, independent of treatment with or without amputation. In the current analysis, outcome was not adversely affected by treatment without amputation, despite the presence of an insensate foot.

Conclusion: The validity of using the insensate foot as an indicator for amputation should be questioned.

Reference

¹ MacKenzie EJ, Burgess AR, McAndrew MP, Swiontkowski MF, Cushing BM, DeLateur BJ, Jurkovich GJ, Morris JA, Jr.: Patient-oriented functional outcome after unilateral lower extremity fracture. J Orthop Trauma 7:393-401, 1993.