Implant for soft tissue reconstruction

Abstract

Implant for reconstructing tissue of the musculo-skeletal apparatus selected by the group consisting of tendon, fascia, periosteum, ligament, muscle, includes a porous matrix or scaffold of a polymeric material having a tensile stiffness lower by 50% or more than the tensile stiffness of the native tissue it is intended to reconstruct.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a surgical implant or graft for soft tissue reconstruction.BACKGROUND OF THE INVENTION[0002]Surgical treatment of injury to soft tissues of the muscular-skeletal system of mammals caused by trauma, sudden overload, fatigue, sickness or other degenerative medical condition may in some cases benefit from or even require structural support to start healing. An example of such a situation is injuries to structures that do not heal spontaneously such as the intraarticular crucial ligaments. A text book or review paper on sports medicine in general starts out with a phrase stating that “ . . . anterior cruciate ligament (ACL) rupture is the most common chronically incapacitating injury . . . ” stresses the importance to find a cure for this condition. The golden standard surgical therapy for ACL reconstruction is to put a biological graft where the native ACL used to be. Biological grafts can be either of auto or allogenic origi...

AI Technical Summary

Benefits of technology

[0009]According to the present invention is disclosed an implant for reconstructing soft tissues of the musculo-skeletal apparatus, in particular tendon, fascia, periosteum, ligament, muscle but excluding bone and articular cartilage having an initial tensile stiffness that is significantly lower than that of the tissue to be reconstructed. In this application “initial stiffness” is the tensile stiffness at the time of implantation. The implant of the invention has a porosity and texture capable of accommodating matrix producing cells to form a functional tissue. Furthermore, the implant material of the invention is capable of resisting long term stress relaxation and creep thereby avoiding plastic deformation of the implant. Stress relaxation that rapidly levels off (within, for instance, one minute) is acceptable while plastic deformation (elongation) is not. Plastic deformation or creep ruins the implant's ability to template the healing tissue to its desired dimensions ensuring correct kinematics. The ability to support an applied load with an initial stress relaxation that rapidly levels off asymptotically to a finite value is beneficial to the implant for two reasons. Firstly, the residual load generated from the prestretch procedure can reapproximate retracted tissues, a clinical condition often seen, for instance, in tendon injuries such as rotator cuff tears or in avulsion injuries. Secondly, the residual pre-stretch force of a pre-stretched implant used in joint surgery provides active joint stabilization. This kind of active joint stabilization is important for intra-articular ligament reconstruction according to the invention. The nature of stress relaxation of fabrics is two-fold. There are contributions both from the textile design and from the material itself. Depending on fiber interlocking the fibers slide in respect of each other; with an elastic material this sliding will be gradual and appear as a rapid stress relaxation. The material's resistance to stress relaxation is strongly dependent on inherent limitation of molecular mobility by cross-links that may be chemical or physical. Chemical cross-links are found in e.g. rubbers while physical cross-links of permanent character are found in e.g. poly(urethane urea). The limited molecular mobility also offers the ability to orient the molecular network by simply stretching the implant and thereby modulate its stiffness. The molecules orient along the direction of the applied pre-stretch. Thereby the implant is stiffened in the pre-stretch direction.

[0014]The present invention additionally discloses an implant made of the material of the invention manufactured into a porous matrix, a template, an added synthetic extracellular matrix, but most often referred to as a scaffold. The implant has a tensile stiffness significantly lower than that of the native tissue it is intended to reconstruct, for instance lower by at least 50% or at least 80% or 85% and even as much as 90% or more. The material of the invention has elastomeric characteristics, which ensures that the implant can be deformed without permanent elongation. The implant may be manufactured by processes with inherent ability to accomplish porosity such as foaming, porogen extraction from molded block, textile confection or non-woven structures made out of fibers. It is also possible to manufacture it from combinations of these processes such as a porous matrix reinforced by fibers or a fabric.

Problems solved by technology

Hence, loads cause larger deformations of a healing soft tissue than of the corresponding uncompromised native tissue.

Firstly, the residual load generated from the prestretch procedure can reapproximate retracted tissues, a clinical condition often seen, for instance, in tendon injuries such as rotator cuff tears or in avulsion injuries.

Secondly, the residual pre-stretch force of a pre-stretched implant used in joint surgery provides active joint stabilization.

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