Fc. Iwuagwu et Da. Mcgrouther, EARLY CELLULAR-RESPONSE IN TENDON INJURY - THE EFFECT OF LOADING, Plastic and reconstructive surgery, 102(6), 1998, pp. 2064-2071
The effect of loading on the early cellular response to tendon injury
was studied in a partial tenotomy (window) model in the extensor digit
orum longus of the rat. Normal use of the limb was allowed, such that
tendons were either loaded (group 1) or unloaded (group 2) when a dist
al tenotomy was performed. Thirty-four male Fischer rats were used. Th
e tendons were harvested at intervals of 6 hours and 1, 3, 5, and 7 da
ys. Quantitative cell counts were performed on light microscopic cross
-sections of the window and tendon substance together with recording o
f cell orientation. Matrix changes in the tendon, window, and tendon-w
indow junction were observed on transmission electron microscopy. Ther
e was a rapid and extensive change in the tendon structure with rapid
loss of definition of the window edge, and an increase in cellularity
of the tendon substance. The loaded tendons demonstrated less cellular
ity at 5 days (window cell density 3.48 +/- 0.49 cells per 0.01 mm(2))
with better longitudinal orientation of cells and matrix than the unl
oaded tendons (8.38 +/- 1.1 cells per 0.01 mm(2)). The numbers of infl
ammatory cells in both groups were roughly comparable (5 days: loaded
0.411 +/- 0.071 cells per 0.01 mm(2); unloaded 0.554 +/- 0.11 cells pe
r 0.01 mm(2)), but the unloaded windows had more fibroblasts at 5-day
and 7-day stages (5 days: loaded 3.08 +/- 0.44 cells per 0.01 mm(2); u
nloaded 7.82 +/- 1.0 cells per 0.01 mm(2); p < 0.016). Cell counts in
the tendon substance were also higher in the unloaded (3.99 +/- 0.44 c
ells per 0.01 mm(2)) than the loaded (1.95 +/- 0.45 cells per 0.01 mm(
2)) tendons at 5 days. This study demonstrated that the cellular respo
nse after injury in this extensor tendon model is affected by tensile
loading, there being increased cell numbers in both the window and ten
don substance in the unloaded tendon.