Biodegradable implants

biodegradable implants

1. BIODEGRADABLE IMPLANTS

2. The implants which undergo gradual degradation by biological process and absorbed and excreted by the body are called Biodegradable Implants.

3. Why biodegradable implants? There will be need for a second operation for removal of metallic implants,with considerable additional inconvenience,expense and at some risk of operative complication. This led to the development of so called biodegradable/ bioabsorbable /biologically inert implants which undergo gradual degradation after their purpose is being served .

4. HISTORY The history of absorbable implants in the repair of bone tissue began in late 1960’s. The first studies were performed in the field of maxillofacial and mandibular surgery. Implants of more complex design,such as screws and small plates became possible in late 1970’s and early 1980’s.

5. Types of materials Polyglycolic acid Polylactic acid Polyparadiaxonone Chemically these compounds are Alpha polyesters.

6. Structure, strength and properties Polyglycolic acid (PGA) is a hard, tough, crystalline polymer with an average molecular weight of 20,000 to 145,000 and a melting point of 224-230°C. Polylactic acid (PLA)is a polymer with initial molecular weights of 180,000 to 530,000 and a melting point of about 174°C. In orthopaedic implants Poly-L-lactic acid (PLLA) has been used more extensively because it retains its initial strength longer than Poly-D-lactic acid (PDLA). PGA belongs to the category of fast degrading polymers, and intraosseously implanted PGA screws have been shown to completely disappear within 6 months. PLLA on the other hand has a very long degradation time and has been shown to persist in tissues for as long as 5 years post implantation.

7. Polyglycolic acid and polylactic acid copolymers in a ratio of 90:10 and polydiaxonose are used as absorbable sutures world wide.

8. The most important characteristic which determines the behaviour of these polymers is the glass transition temperature at which the polymer becomes rigid and brittle. This ranges from 58 degree celsius for polylactic acid and 16 degree celsius for polypara diaxonone .

9. The commercially available resorbable polymers include pure polyglycolic ( PGA) acid in the form of PINS and SCREWS. Pure poly-l-lactic acid (PLLA) and a co-polymer of PLLA and PGA . They maintain most of their strength for 8 weeks and will completely resorb in the body in 12–15 months.

10. BIODEGRADABLE CERAMICS(CALCIUM PHOSPHATE) Uses : • Repair material for bone damaged with trauma or disease. • Void filling after resection of bone tumours • Repair and fusion of vertebrae • Repair of herniated discs • Repair of maxillofacial and dental defects • Drug-delivery

11. KNEE It is used extensively for ACL reconstruction in the form of interference screws and transfixation screws. Osteochondral fractures can be well fixed by using arthroscopic techniques and biodegradable pins. Meniscal tacks and biodegradable suture anchors have opened new avenues for soft tissue reconstruction in complex knee injuries. At 5 years, this bioaborbable interference screw appeared clinically safe and MRI showedcomplete absorption and replacement with new bone.

12. Shoulder Biodegradable implants provide viable options for the repair and reconstruction of rotator cuff tears, shoulder instability, and biceps lesions that require labrum repair or biceps tendon tenodesis . In a study of arthroscopic Bankart reconstruction using either PGA polymer or PLA polymer implants the overall clinical results.

13. Spine Coe and Vaccaro published the first clinical series using bioresorbable implants as interbody spacers in lumbar interbody fusion. The clinical and radiographic results allowed them to recommend the use of bioresorbable devices in structural interbody support in the TLIF procedure. B ioabsorbable polymer-calcium phosphate composite cages were implanted in cervical spines ; the latter showed significantly better distractive properties, a significantly higher biomechanical stiffness, and an advanced interbody fusion. .

14. FOOT and ankle S elf reinforced absorbable implants in medial malleolar fractures. Brunetti et al used bioresorbale implants in the fixation of osteotomies for hallux valgus. Bioabsorbable implants offer specific advantages in the foot where removal of the hardware is mandatory in some fixations like syndesmotic disruptions and Lisfranc’s dislocations. .

15. Cipro -screw World’s first antibiotic releasing bioabsorbable fixation device

16. FEATURES OF IMPLANTS Tensile and flex strength are comparable to titanium plating system ,Plates are easy to adapt with aid of heat pack; A wide selection of implant sizes an shapes are available A convenient hex-drive breakaway delivery system simplifies screw placement;

17. Eliminates growth restriction and implant migration for paediatric craniofacial reconstruction ; Resorbs completely and may eliminate the need for second operation; Does not induce late stage inflammatory Mreaction .

18. The headed bioabsorbable tissue anchor has a large thread surface per turn of thread . As the anchor is turned into bone for engaging cancellous bone, the disk-shaped head engages and anchors the tissue to the bone.

19. DEGRADATION AND ELIMINATION The implants of polyglycolic acid,polylactic acid or polydiaxonone are completely absorbable within the bone tissue and the new bone is deposited on or within the implant as the degradation proceeds. The degradation of these polymers occurs 1.Mainly by hydrolysis 2.And to lesser extent through non specific enzymatic action.

20. Factors which influence the degradation process 1.molecular weight 2.crystallinity 3.Thermal history 4.Geometry Poly-lactic acid copolymers have the slowest rate of degradation(half-life 6months) The co-polymers of polyglycolyic acid and poly paradiaxonone are much more rapid. The principal route of elimination is respirationand to lesser exent in urine and faeces .

21. DO U KNOW? The fact that the interfragmentary compression cannot be achieved with polyester pins or rods should be recognized when the indications for the use of these implants are being considered. Polyester screws do provide compression of the fracture but are more difficult to insert than the comparable metallic screws.

22. Only fractures affecting the cancellous bone can be managed effectively with the array of implants currently available. At the moment the INDICATIONS for the biodegradable implants are  1.Radial head Fracture  2.Wedge fractures of the patella  3.Fractures of the proximal and distal ends of the metatarsals and metacarpals  4.osteochondrosis Dessicans or Osteochondral fractures of the femur condyle.

23.  5.Ankle Fracture  6.Adult capitellum Fracture  7.Displaced elbow fractures in children  8.Distal radius fracture  9.Pediatric fracture  10.Small fractures or osteotomies.

24. Bioabsorbable meshes are available for acetabular reconstructions . Bioabsorbable implants are also variously used in cranio maxillo facial surgery and dental surgery.

25. ADVANTAGES  1.No irritation of soft tissue  2.No Osteopenia  3.No need of secondary operation to remove the implants .  4.Useful in pediatric fracture fixation.  5.No interference with the callus formation and fracture healing.  6.Anti-biotic releasing Bioabsorbable screws to reduce implant related infecion .

26. COMPLICATIONS The unique complication of these implants is the delayed inflammatory reaction or sterile inflammatory foreign body reaction. The other complications include  1.Failure of fixation  2.Postoperative wound infection

27. CLINICAL PRESENTATION The clinical presentation of the delayed sterile inflammatory reaction is…… The patient has no local or systemic signs of the problems with the wound in the immediate post-op period.,then a painfulerythematous,fluctuant swelling suddenly develops about the healed wound. The mean interval between the fixation of fracture and clinical manifesation of reaction is twelve weeks.

28. A sinus draining t he liquid remnants of the implant material often form. Bacterial cultures of the drainage from the sinuses are negative.

29. DRAWBACKS 1.Fixation achieved with these type of implants is often neither rigid not stable enough to hold the fracture with motion or weight bearing force before union. 2.Cast support and use of cruchtes for lower extremity fractures has been recommended,which limits their further use. 3.Bioabsorbable Implants have excessively low moduli resulting in backing out of screws 4.Poor handling characteristics when compared to metals.

30. 5.The price of 45/50 mm fibre reinforced rod is approximately 15 times that of a metallic cancellous screw. 6.The treatment of diaphyseal fractures of long bones however would necessitate a larger device such as a long plate and intramedullary nail,that has a slow rate of degradation. Nevertheless the unsolved problem of irritation of soft tissue and of osteopenia beneath metallic plates will continue to simulate research on absorbable implants .

31. FUTURE Resorbable plates can be covalently linked with compounds such as HRP , IL-2, and BMP-2 and represents a novel protein delivery technique . BMP-2 covalently linked to resorbable plates has been used to facilitate bone healing. Covalent linking of compounds to plates represents a noveL method for delivering concentrated levels of growth factors to a specific site and potentially extending their half-life. An area for future development would have to focus developing implants that degrade at the “medium term”. Since the screw that persists in its track for 5 years or more does not offer the advantage of bioresorbability .

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