Characterization of lateral abdominal muscle thickness in persons with lower extremity amputations

Retrospective review.

To describe bilateral thickness of the lateral abdominal muscles at baseline and during an abdominal drawing-in maneuver (ADIM) in individuals with unilateral transtibial (TTA) or transfemoral (TFA) amputations.

Although side-to-side symmetry of lateral abdominal muscle thickness has been established in healthy individuals, the degree of symmetry in those with unilateral lower extremity amputations remains unknown. Differences in lateral abdominal muscle thickness may exist based on prior findings of asymmetry and differences measured based on level of amputation in both the size and function of the iliopsoas and back extensor muscles.

Seventy patients (69 males, 1 female) with traumatic unilateral lower extremity amputations (TTA, n = 39; TFA, n = 31) received a rehabilitative ultrasound imaging examination. Absolute thickness of the transversus abdominis (TrA) and the external and internal oblique muscles combined (EO+IO) were assessed bilaterally at baseline and during the ADIM. Symmetry was assessed using relative muscle thickness values at baseline. Percent increase in muscle thickness during the ADIM was used to investigate muscle function. Separate 2-by-2 mixed-model ANOVAs were used to compare both within-group (side of amputation versus nonamputated side) and between-group (TTA versus TFA) differences for thickness and function of the TrA and the EO+IO muscles.

On the side of the amputation, the relative baseline thickness of the EO+IO measurement was greater (P < .05), while the relative baseline thickness of the TrA muscle was smaller (P < .05). But the mean differences side to side were small (1.3%) and unlikely to be clinically significant. Further, there were no differences in baseline muscle thickness between groups for the TrA (P = .95) or the EO+IO (P = .94) muscles. For thickness measurements during the ADIM, the TrA showed no side-to-side (P = .74) or group (P = .07) differences. Similarly, no side-to-side (P = .60) or group (P = .09) differences were found in the EO+IO thickness during the ADIM.

Despite the limitations of retrospective review, these findings provide an initial reference data set for future studies. Bilateral symmetry of the lateral abdominal wall muscle thicknesses at baseline and during the ADIM for those with unilateral lower extremity amputations is comparable to healthy individuals. Future studies should consider the potential influences of low back pain and gait training on symmetry of muscle thickness and muscle function based on level of amputation.