PHYSIOLOGICAL AND MECHANICAL ADAPTATIONS OF RABBIT MEDIAL COLLATERAL LIGAMENT AFTER ANTERIOR CRUCIATE LIGAMENT TRANSECTION

Progressive physiological and mechanical changes in the medial collate ral ligament of the adult rabbit were investigated for as long as 48 w eeks after disruption of the anterior cruciate ligament. Eighty-one Ne w Zealand White rabbits were separated into experimental, sham-operate d control, and normal control groups The experimental group underwent unilateral transection of the right anterior cruciate ligament, sham-o perated animals served as controls for comparison, and normal animals were evaluated as age-matched, undisturbed (no surgery) controls. Bloo d flow to the medial collateral ligament (as a physiological measure) and mechanical function (structural and material properties) were asse ssed at 6, 14, and 48 weeks. The results indicated that loss of the an terior cruciate ligament leads to early mechanical deterioration of th e medial collateral ligament with a corresponding loss of physiologica l homeostasis. Six to 14 weeks after the transection, values for cross -sectional area of the medial collateral ligaments rapidly increased t o 1.5 times control values. The ligament became twice as large as the control ligament by 48 weeks. Concomitantly, medial collateral ligamen t stress at failure of the medial collateral ligament complex decrease d rapidly 6-14 weeks after the transection and eventually fell to one- half that of controls by 48 weeks. In terms of Low-load behaviour. lax ity and load relaxation were significantly greater than that of contro ls 6 weeks after transection and were further increased by 14 weeks. B y 48 weeks, laxity values had recovered somewhat and load-relaxation m easures had recovered to near control values. At both 6 and 14 weeks, a statistically significant elevation in blood flow was demonstrated c ompared with controls By 38 weeks, however, blood flow was no differen t from that of the sham-operated control. Thus, early after transectio n of the anterior cruciate ligament, both low-load and high-load mecha nical properties of the medial collateral ligament deteriorated and th e rate of blood flow was temporarily elevated. By 38 weeks, blood flow declined to near control values, with a corresponding recovery in vis coelastic behaviour. These findings suggest that, after transection of the anterior cruciate ligament, viscoelastic behaviour of the medial collateral ligament may be related to changes in blood flow and that r estoration of normal flow patterns and vascular responses may be linke d to the recovery of some low-load mechanical properties in the anteri or cruciate ligament-deficient medial collateral ligament.