A total of 37 patients were operated on for anterior cruciate ligament (ACL) insufficiency between 1980 and 1989 using two types of carbon fibre ligament substitutes. The average age of the population was 23.6 years. The carbon fibre prostheses were covered with either a strip of medial joint capsule or lyophilized dura. Follow-up averaged 8.1 years (range 4-13 years), most of the operations being done from 1983 to 1985. Evaluation included a questionnaire, physical examination, Lysholm scoring, radiographs and cruciometer testing. The operated ACLs were looser than those in the contralateral healthy knees. The Lysholm scoring system gave acceptable results (excellent and good) in 43.5%, fair in 31.4% and poor in 24.1% of cases. Acceptable results provided better stability and muscle strength. During the follow-up there was an evident deterioration in stability as well as in Lysholm score. The results between the two types of ligaments did not become statistically different. Osteoarthrosis increased in all the knees examined radiographically (28/37). The results indicate that the ACL reconstructions using these types of carbon fibre prostheses lead to unacceptable results in the long-term follow-up.
During a follow-up period of 16 weeks in 18 pigs, macroscopical and histological studies revealed invasion of fibroblasts and mesenchymal cells around the carbon fiber prosthesis inserted to replace the ACL but scarce tissue ingrowth into the prosthesis proper. There was no adherence of the carbon ligament onto the bony channels. The peak tensile strength of the reconstructed ligament was about one third of the paired normal ACL ligament during the 16 week experiment.
Connective tissue ingrowth into a carbon fiber prosthesis inserted as a substitute for the ACL was biochemically quantified in an experimental pig model with a followup of 16 weeks. During this time, the net collagen amount expressed as hydroxyproline increased to only half that of the normal control ligament. Histological studies revealed relatively few fibroblasts capable of producing collagen inside the alloplastic ligament. When these results are considered in conjunction with those of our earlier report of the disappointing mechanical strength of the carbon fiber substitutes, it seems evident that carbon fiber is not a suitable replacement for the ACL, mainly because of its failure to produce a "neoligament" before it disintegrates.
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