Mechanical properties of primate vascularized vs. nonvascularized patellar tendon grafts; changes over time

Abstract

Summary: Mechanical properties of patellar tendon autografts used to replace the anterior cruciate ligament (ACL) in the cynomolgus monkey were measured at four time periods up to l year. The ACL was replaced in each knee with the medial half of the patellar tendon: as a vascularized graft (VG) on one side and as a nonvascularized or free graft (FG) on the other. Postoperative care consisted of 4 weeks of cast immobilization at 30" flexion followed by unrestricted activity in a large cage. Both grafts showed low stiffness and maximum force at 7 weeks (24% and 16% of ACL control values, respectively), increasing to 57% of control ACL stiffness and 39% of control maximum force by 1 year. Corresponding material properties, modulus and maximum stress, also increased over time, but at 1 year were only 34% and 26% of ACL values, respectively. The results indicate that retaining vascularity does not prevent significant reduction in graft properties that occur postoperatively, nor does it accelerate the return in strength and stiffness. Tissue stiffness, which returns earlier than maximum force and joint anteroposterior (AP) force displacement data, should be routinely reported in any healing study. Finally, in studies of this kind, the large variation in the results makes sampling only one or two animals from each time period unreliable. Key Words: Patellar tendonAnterior cruciate ligament replacement-Mechanical properties-PrimatesCynomolgus monkey.The anterior cruciate ligament (ACL) is frequently injured during both contact and noncontact sports. Clinical studies (12,27) indicate that the ACL is torn in over 72% of patients who present with an acute knee hemarthrosis. Laboratory studies (7,21) have shown that the anterior cruciate is the ll Deceased.

Effects of combined administration of transforming growth factor‐β1 and epidermal growth factor on properties of the in situ frozen anterior cruciate ligament in rabbits

“…The mechanical properties of tendon autografts are reduced after surgery, and the properties remain abnormal even a year post-operatively [5,6]. Therefore, a goal in ligament reconstruction is to prevent graft deterioration *Corresponding author Tel ' +81-11-706-7211, fax +81-11-706-1822.…”

The effects of graft width and graft laxity on the outcome of caprine anterior cruciate ligament reconstruction

“…Repositioning the ACL tibial insertion posterior [3] or into the joint [16] reduced ligament strength and increased joint AP translation postoperatively. No study has investigated if increased initial graft laxity also affects the subsequent graft strength and joint stability of ACL reconstructions.…”

Recent advances following anterior cruciate ligament reconstruction: rehabilitation perspectives

“…An overall concern during this phase is evidence that the autograft itself is reaching its weakest point structurally during the 6 to 8 week time frame postoperatively [16]. Additional evidence states that the actual graft may only reach between 11 and 50% failure loads of the native ACL at the 1-year point [17].…”

“…Following early necrosis the process of revascularization begins. This usually starts at approximately weeks 6-8 at which time animal studies have shown that the graft is at its weakest point in the post reconstruction process [16]. Some studies indicate that the graft may only reach failure loads of 11 to 50% at 1 year post-operative [17].…”