Vascular alterations in the rabbit patellar tendon after surgical incision

Open incision of the patellar tendon (PT) is thought to promote acute vascu lar responses which ultimately result in an enhanced degree of tendon repai r. Such a clinical procedure is commonly applied to patients with refractor y tendinitis. The objective of this study was to quantify the vascular adap tations (both anatomical and physiological) to longitudinal incision of the PT, and the resultant effects on tendon organisation. Fifty-four New Zeala nd White rabbits were separated into 3 experimental groups and 2 control gr oups. Experimental groups underwent surgical incision of the right PT, and were assessed 3 d, 10 d and 42 d following injury; normal unoperated contro ls were evaluated at time zero, and sham-operated controls were evaluated a t 3 d to control for the effects of incising the overlying skin. Quantitati ve measures of PT blood supply (blood how, microvascular volume) and geomet ric properties of PT substance were obtained for each PT. Histomorphology w as assessed to evaluate vascular remodelling and matrix organisation in the healing PT. Longitudinal open incision surgery of the PT led to rapid incr eases in both blood flow and vascular volume. The incision of overlying tis sues alone (sham-operated) contributed to this measurable increase, and acc ounted for 36% and 42% of the elevated blood flow and vascular volume respe ctively at the 3 d interval. In the incised PT, blood flow significantly in creased by 3 d compared with both time zero and sham-operated controls, and remained significantly elevated at the 10 d interval. Similarly, vascular volume of the incised PT increased at 3 d compared both with time zero and sham-operated controls. At the 10 d interval, the increase in vascular volu me was greatest in the central PT substance. By 42 d both blood flow and va scular volume of the incised tendon had diminished, with only blood flow re maining significantly different from controls. In the contralateral limb, a significant neurogenically mediated vasodilation was measured in the contr alateral PTs at both early time intervals, but was not seen by the later 42 d interval. With respect to PT geometric properties in the experimental an imals, a larger PT results as the tendon matrix and blood vessels remodel. PT cross-sectional area increased rapidly by 3 d to 1.3 times control value s, and remained significantly elevated at 42 d postinjury. Morphological as sessments demonstrated the disruption of matrix organisation by vascular an d soft tissue components associated with the longitudinal incisions. Substa ntial changes in matrix organisation persisted at 42 d after surgery. These findings suggest that open longitudinal incision of the PT increases the v ascular supply to deep tendon early after injury. These changes probably ar ise through both vasomotor and angiogenic activity in the tissue. Since PT blood flow and vascular volume return towards control levels after 6 wk but structural features remain disorganised, we propose that vascular remodell ing is more rapid and complete than matrix remodelling after surgical incis ion of the PT.