PN collagen type III within tendon grafts used for anterior cruciate ligament reconstruction

Abstract

This study measured the amount of immature collagen type III present in tendon rafts obtained from anterior cruciate ligament (ACL) reconstructions. These values were compared with those obtained from control grafts typically used for reconstruction – Achilles, patellar, and fascia lata – and also to the normal ACL. Analyses were performed using a commercially available radioimmunoassay (RIA). The RIA made use of a rabbit polyclonal antibody specific to the amino terminus of procollagen type III. The specificity of the Ab was confirmed by a western blot. Fibril diameter of each of the above samples was measured by transmission electron microscopy (TEM). We thus were able to determine if there was a relationship between pN collagen III content and fibril diameter. The mean amount of pN collagen type III in the normal tendon control group was 0.8 ± 0.3 ng/μg total protein (range 0.0–2.5 ng/μg). There was significantly greater pN collagen III (16±3.7 ng/μg total protein) in the grafts containing an average fibril diameter <55 nm than in the normal tendons or ACL ( P<0.05). Grafts with an average fibril diameter >55 nm had similar levels of pN collagen III (1.0±0.79 ng/μg) as the controls. There was also significantly less pN-collagen III within the functional grafts (5.3±1.9 ng/μg) as compared to failed grafts, (21.6±5.1 ng/μg, P<0.05). These results indicate that incomplete processing of procollagen III may be responsible for some of the ultrastructural alterations seen in tendon grafts. Since ultrastructural organization is believed to influence mechanical properties of these tissues, pN collagen III levels may be a possible indicator of ligament or tendon weakness.