Chest surgery such as, for example, open heart surgery requires opening of the chest and rib cage in order to facilitate access to the organ to be operated. The front central part of the rib cage constitutes a longitudinal bone, the sternum, which overlies the heart and secures the ribs. A specific action performed in such surgery is longitudinal sectioning of the sternum into two halves ("median sternotomy"). After performing the heart surgery, the chest is closed as a part of a reconstitution operation, in which among other activities the sternum bone halves are brought to union and secured together by mechanical means.
Post operative complications in the healing of the sternum are not uncommon, resulting from several reasons. Especially troublesome is the constant movement associated with the breathing cycle, to which the bone is subjected, which keeps the sternum in a cyclic strain regime often accompanied by unpredicted mechanical stresses. Such strains may eventually cause nonunion or breakage of the bone. Nowadays as recuperating procedures for cardiac therapy have become more common, sternal complications have been increasing likewise. Healing disorders can be expected to occur more commonly in patients suffering from bone disorders such as excessive porosity.
None of the common traditional methods as well as the newer ones pertaining to this specific type of surgery have so far proved to insure adequate degree of sternum healing in such type of operations. A discussion of methods for sternal closure-techniques is elaborated by Cheng W. et al. (Biomechanical Study of Sternal Closure Techniques. Ann Thorac Surg. 55:737-40, 1993). Although the authors maintain that wire approximation and tensioning is the method of choice, present medical observations indicate this method to be risky with many complications which arise from inadequate fixation of the bones and interference of the artificial insertions in the physiological make up of the body. Hendrickson S. C. et al (Sternal Plating for The Treatment of Sternal Nonunion. Ann. Thorac Surg. 62:512-8, 1996), provide evidence for the superior effectivity of tension bands or plates in securing sternal fragments postoperatively. According to such technique, the bands or plates are made out of stainless steel and as such may require special care or even specific surgery for removal. The use of steel bands instead of wire for closure of sternum halves (called also hemisterna) has been shown to provide better results than wire closures also with respect to pain and duration of hospitalization (Soroff H. S. et al. Improved Sternal Closure Using Steel Bands: Early Experience With Three-Year Follow-up. Ann. Thorac Surg. 61:1172-6, 1996). Green D. T. et al. (U.S. Pat. No. 5,339,870) disclose a mechanical device for providing mechanized method and apparatus which utilizes flexible strap for retaining and securing hemisterna. The same authors disclose in a different publication (U.S. Pat. No. 5,355,913) a mechanical system for retaining and securing split tissue for surgical reconstruction. In this patent an additional feature is disclosed according to which a disengaging mechanism in the mechanical driving gear provides a means for applying an upper limit to the force applied.
Generally, the shortcomings of the present practices are a combination of all or a part of the following: infections caused by metal or plastic parts intentionally left in the bone or surrounding it, cutting effect exerted by tension stitches left intentionally in the body, pain and aesthetic aspects. The consequences of insufficient or superfluous force applied for the approximation and securing together the two hemisterna, may also be detrimental to the healing process.
Plastic materials made out of biologically benign .alpha.-hydroxy acids (Pohjonen T. and Tormala, P. In Vitro Hydrolysis of Self-Reinforced Polylactide Composites. 1996. Medical & Biological Engineering & Computing 34 Supplement 1, Part 1.) have been used in the bone fixation in the form of implants (Bostnan O. M., Curt Concepts Review: Absorbable Implants for the Fixation of Fractures. J. Bone Joint Surg. 73-A (1)148-152, 1991) or degradable sutures (Cutright D. E. et al. Fracture Reduction using a Biodegradable Material, Polylactic acid. J. Oral Surg. 29: 393-397, 1971), have revealed good potential for tissue repair and specifically bone fixation. The immune response in the body to such material is negligible, although mild, non specific reactions to the plastic do occur (Santavarita S. et al. Immune response to polyglycolic Acid Implants. J. Bone Joint Surg. [Br] 72-B:597-600, 1990).
Polydioxanone, which degrades in the body first to glycolic acid is used as a building block for production of bioabsorbable plastic (Bostman O. M., Current Concepts Review: Absorbable Implants for the Fixation of Fractures. 1991. J. Bone Joint Surg. 73-A (1)148-152.). Perkins D. J. et al (Secondary Sternal Repair Following Median Sternotomy using Interosseous absorbable Sutures and Pectoralis Major Myocutaneous Advancement Flaps. British Journal of Plastic Surgery 49:214-219, 1996), used polydioxanone sutures to achieve sternal repair with excellent therapeutic and aesthetic results.
The use of bioabsorbable plastic straps in surgery for joining split tissue was disclosed (Green D. T. et al. U.S. Pat. No. 5,355,913) as a possible alternative building material in the manufacturing of tissue repair devices. The same authors in U.S. Pat. No. 5,339,870 disclosed a device for applying a buckle assembly that secures a strap in a loop around a split tissue such as a split sternum.