A.B. Weiss

Ligament replacement with an absorbable copolymer carbon fiber scaffold--early clinical experience.

Eighty-two patients, average age 29 years, were surgically treated (during the period from April 1981 to July 1983) for both acute (8%) and chronic (92%) knee ligament instabilities. An absorbable copolymer-carbon fiber ligament prosthesis was used as a tissue scaffold. Seventy-five percent had anterior cruciate ligament reconstructions, 6% had anterior cruciate and posterior cruciate ligament reconstructions, 6% had just posterior cruciate ligament reconstructions, and 9% had other combinations of anterior cruciate ligament, medical collateral ligament, and lateral collateral ligament reconstructions. Preoperative and postoperative evaluation, consisting of questionnaires, physical examinations, and isoskinetic testing, revealed significant improvements in categories of stability, pain, function, and strength persisting to the end of the study at 24 months. Arthroscopic examination and histologic studies of retrieved specimens demonstrated well-vascularized reconstructions with collagenous tissue ingrowth into the carbon-copolymer implants.

DEVELOPMENT OF NEW METHODS FOR PHALANGEAL FRACTURE FIXATION

Abstract Surgical intervention is warranted in the fixation of finger fractures only if it results in high mechanical stability. This allows early motion and avoids loss of range of motion and stiffness often associated with immobilization. To facilitate the rational design of finger fracture fixation devices an analytical and experimental program is presented to establish appropriate design criteria. The analytical scheme uses composite beam theory treating the device and bone as components of a system contributing to the strength and rigidity of fixation. The experimental program uses the pig metacarpal as an animal model for the proximal phalanx. K-wire fixation and intramedullary fixation with a polylactic acid polymer (PLA)-carbon fiber composite device are considered. Fixation rigidity is found to be limited by device slippage and device-bone hardness mismatch. However, both techniques are shown to be capable of sustaining the bending moments expected in normal pinch hand function. A method of fixation using four 0.712-mm ( 28 1000 - in. ) wires is shown to increase the maximum bending moment by 170% and bending rigidity by 300% over the conventional two crossed K-wire method. Its maximum bending moment capability provides a safety factor of 2.01 over expected tip pinch moments. A method using a 3.5-mm square cross-section PLA-carbon intramedullary (IM) device is shown to increase the maximum bending moment by 240% and bending rigidity by 297% over the two-wire method with a maximum bending moment safety factor of 2.53.

Achilles Tendon Repair with an Absorbable Polymer-Carbon Fiber Composite:

Twenty-seven patients were surgically treated for Achilles tendon rupture using a composite implant. The implant is ribbon-like in configuration and composed of filamentous carbon fiber coated with an absorbable polymer. When used to secure an Achilles repair, the implant acts as a scaffold for the regrowth of collagenous tissue. Rapid attachment of host tissue assures good, early repair strengths which allows for a more vigorous rehabilitation program. Fourteen patients have at least 9 months of follow-up (average follow-up, 14.4 months) and have been objectively and subjectively evaluated on a temporal basis for return of function. To date, complications have been minimal. Results have been very encouraging with 90% return of function at 18 months.

INTERNAL FRACTURE FIXATION WITH PARTIALLY DEGRADABLE PLATES

Bone plates have been produced of a composite material of carbon fiber reinforced polylactic acid polymer (PLA). Since PLA is an absorbable polymer, the device is mechanically degradable in-vivo. As the fracture heals, the fixation device degrades, avoiding stress protection osteoporosis and the necessity for device removal. The usefulness of this concept has been demonstrated in a canine animal experimental study.

ATTACHMENT OF A PARTIALLY ABSORBABLE TENDON AND LIGAMENT TO SOFT TISSUE

The attachment to living soft tissues of a partially degradable tendon and ligament replacement was investigated in a rabbit model. The replacement tendon was a composite of filamentous carbon-polylactic acid (PLA) polymer. Biological fixation of the synthetic material to the tendinous and myotendinous tissues of the rabbit gastrocnemius system was achieved. This occurs by ingrowth of soft tissues into the composite network. The carbon fibers provide mechanical strength and act as a scaffold for tissue ingrowth while the absorbable PLA polymer protects the fibers upon implantation (Alexander, Weiss, Parsons and colleagues, 1979; Jenkins, Forster, McKibbin and colleagues, 1977). The attachment strengths were tested in tension over a twelve week period. After four weeks, the systems with implants had strengths equivalent to those of unoperated controls. Histologically, the ingrown tissue was found to be highly cellular with collagen oriented longitudinally to the tendon.

MEDIAL COLLATERAL LIGAMENT REPLACEMENT WITH A PARTIALLY ABSORBABLE TISSUE SCAFFOLD

Dammage to the ligaments of the knee is a serious clinical problem. Instability in this joint is debilitating and often leads to chronic, progressive osteoarthritis if left unchecked. In this study, the medial collateral ligaments of canines were replaced with a carbon fiber-polylactic acid polymer tissue scaffold. After four weeks, eight weeks and twelve weeks in-vivo, the stability of the knees was quantitatively evaluated and the mechanical properties of the regrown structures were determined.