Carbon-PGLA prostheses for ligament reconstruction. Experimental basis and short-term results in man

The efficiency of a pure carbon prosthesis to reconstruct intra-articular ligamentous loss of substance was evaluated on 14 sheep with an 18-month follow-up study of recent and old ACL experimental injuries. Functional results showed a correlation between a tightened implant, the stability of the knee, and the absence of severe arthritis. The rupture strength of the newly formed ligament amounts to about 300 Newtons (N). That of the normal ACL amounts to 250-550 N. The structure gives a viscoelastic behavior to the prosthesis. This tissue was made of collagen fibers surrounding the carbon fibers and running generally in the direction of the ligament. In the osseous tunnels, the newly formed lamellar bone invaded and surrounded the implant. Carbon fiber fragmentation occurred, and fibers were found in the synovia and in the homolateral, inguinal, and paraaortic lymph nodes. No degeneration, necrosis of tissue, or cellular toxicity was found. On these bases, the carbon prosthesis was modified by adding a resorbable copolymer of polyglycollic (PGA) and polylactic acid (PLA) around the fibers and a resorbable sheath of the same polymer. This carbon-PGA/PLA prosthesis was used in 23 patients with a three- to 12-month follow-up period. Patients were evaluated by clinical tests and by functional control of the ligament. The indications for prosthetic replacement were: recent mop-end tears of the ACL, cruciate ligament reconstruction in chronic knee instability, and wide rotator cuff loss of substance. Five complications occurred because of hematomas and/or sepsis and prosthesis breakage. Eighteen of 23 patients had good clinical results with good function in five. The conclusions are that PGA/PLA produces a clean and flexible ligament, thus eliminating carbon fiber articular deposits and allowing a normal function. Inflammatory postoperative reactions seem to be more frequent than with other procedures and call for operative and clinical care in order to eliminate hematoma and sepsis. The efficiency of a rehabitable carbon-PGA/PLA prosthesis in intra-articular ligamentous defects in man will be confirmed only by controlled long-term clinical observations.