The purpose of this study was to investigate neuroma formation and the impact of distal
stump factors on this process in a rat median nerve model. In three different groups,
the median nerve was exposed in the axilla and a gap was created.
In the first group, a short gap of 1 cm (short-gap group) was created, while in the
second group, a long gap of 2 cm (long-gap group) was made between the proximal and
distal nerve stump. A further group of animals was used to analyze the formation of
neuroma while burying the proximal stump into adjacent muscle, with the presence of
a long gap of 2 cm (muscle-covered group). The use of different gap lengths between
the proximal and distal stump should allow one to gain more information about the
possible dilution effects of distal nerve stump factors that may contribute to the
extent of neuroma formation. To completely exclude distal nerve stump influences,
burying the proximal stump into the pectoral muscle in the muscle-covered group was
used in combination with a long defect of 2 cm.
Nine months post operation, the animals were sacrificed and histologic analysis was
performed. The area of the neuromas in cross-section was measured, and the neural-to-connective-tissue
ratio was estimated. The results of the investigation of cross-sectional area demonstrated
that neuroma formation was significantly higher in the short-gap group (5.33 mm2, 95%-confidence interval (CI) 4.77 to 5.88 mm2), than in the long-gap group (4.05 mm2, CI 3.5 to 4.6 mm2), with the smallest neuroma formation found in the muscle-covered group (2.53 mm2, CI 1.97 to 3.08 mm2). The percentage of neural tissue was highest in the muscle-covered group (55.6%,
CI 46.99 to 64.27%) and the long-gap group (42.3%, CI 33.62 to 50.9%) and lowest in
the short-gap group (34.1%, CI 25.5 to 42.78%), indicating neural tissue increasing
with increasing distance and muscular covering of the proximal stump.
The results of this study demonstrated a strong correlation between proximal stump
neuroma formation and distal stump distance, indicating the direct impact of distal
stump factors on the proximal stump. These factors coming from the distal nerve stump
were best blocked when the proximal nerve stump was completely isolated when buried
into the adjacent muscle. For clinical applications, the authors recommended not only
burying the proximal stump into a skeletal muscle but, in addition, surgical augmentation
of the gap between the proximal and distal portions.