1. Bioabsorbable Fixation – The Good, the Bad, and the Ugly
Chad J. Muxlow, D.O.
Orthopedic Research of Virginia
4/30/13

2. Disclosures
No disclosures concerning bioabsorbable products

3. Objectives Basic understanding of bioabsorbable materials
Past versus current materials being used – review literature on successes and failures

4. 3. Current products- how to decipher the words of the company representatives and their brochures

5. 4. Future direction of bioabsorbable implants

6. Metallic Anchors Metallic anchors have historically performed well
Provide excellent strength and fixation
Complications such as migration, loosening, and breakage have all been described and can result in severe destruction of intra-articular structures
Unable to obtain an MRI due to scatter

7. 400 × arthrex.com
Why Bioabsorbable?
95% of patients polled said that they would prefer to have a bioabsorbable implant rather than metal if possible. 80% willing to be in study of bioabsorbable implants Mittal et al. Injury 2006
Allergies to metal
Metal implants are not perfect

9. Bioabsorbable fixation without complication…

10. Has mechanical properties that
match the application, remaining
sufficiently strong until the
surrounding tissue has healed
Cannot be too brittle (break) or too
soft (strip)
Does not invoke an inflammatory or
toxic response

11. Is metabolized in the body
after fulfilling its purpose,
leaving no trace
Is relatively easy and
affordable to manufacture
reproducibly
Demonstrates an acceptable
shelf life
Is easily sterilized (ethylene
oxide gas)

12. Catgut suture - Invented in 150AD - NOT made from cat (Kit- fiddle)
- Sub mucosal layer of intestine of goat, sheep, or cattle

13. Run with the idea…
1962 – PGA suture (Dexon) 1974 – 90/10 PGA and PLA 1980’s – biodegradable implants used in facial and cranial reconstructions Late 1980’s and 90’s – biodegradable implants used for orthopaedics
(Vicryl)

14. Bioabsorbable Materials
Currently 40 types of polymers developed for use in surgery
Most common are Polyglycolic Acid (PGA), Polylactic Acid enantiomers (PLA), and poly-D-L-lactic acid copolymer polyglycolic acid (PDLLA-co-PGA
Polymers are long chain macromolecules composed of multiple convalently bonded subunits (monomers)

15. Bioabsorbable materials 101
(Elementary organic chemistry)
Building blocks – monomer (PGA and PLLA)
Join the blocks with covalent bonds– polymer
Different types of monomers joined -copolymers

16. Amorphous Crystalline

17. Self Reinforced (SR) Usually done with same material Heat and pressure
Increases strength

18. PGA Polyglycolic Acid – obtained from opening the
ring of the dimer, glycolide

19. PGA (GONE) Loses 50% of strength in 2 weeks
Loses virtually all strength in 1 month
Completely absorbed in 6-12 months
Hydrophilic

20. PLA Polylactic acid Made from opening of ring of lactic acid/lactide
Two enantiometric isomers
L (Levo) and D (Dextro) isomer
- dextro isomer is difficult to make and maintain

21. PLLA
Crystalline
Pure PLLA tend to be crystalline and clear

22. PLLA “Long Lasting” Years before degraded…
Monomers arranged in orderly fashion
It begins to degrade around 2 years
Slow degradation secondary to its highly organized crystalline structure

23. Degradation
Polymers degrade by nonspecific hydrolytic clipping of ester bonds
Large degradation products cannot be phagocytized by marcophages, leading to an acid environment, which increases the rate of hyrolysis.
Microfractures occur within the implant, resulting in further hydrolysis until the monomers are able to by phagocytized by macrophages

24. PGA (Polyglycolic acid)
Glycolic acid monomers can be released by unspecified esterases and carboxypeptidases.
PLA (Polylactic acid)
Polymeric lactic acid oligomers degrade to monomers (lactic acid) which enter the Krebs /citric acid and get dissimilated into carbon dioxide and water.

25. Rates of Degradation Affected by:
1. Material – hydrophilic/phobic, amorphous, crystal
2. Size and shape/surface area
3. Mechanical stress (load=microfracture?)
4. Metabolic activity of tissue/blood flow

26. Rates of Degredation
Mechanical properties of bioabsorbable implants change over time as determined by the molecular weight (MW) and degree of crystallinity
PGA implants have a degradation time of 3 to 4 months
PLLA implants have a degredation time between months (depending upon stereoisomers or self-reinforcement)
MW and crystallinity can alter the implant
Polymers with a higher degree of crystallinity are stronger and degrade slower than amourphous polymers with the same chemistry

27. Complications Inflammatory reaction Sterile abscess
Fibrous encapsulation
Implant migration
(not visible on radiographs)
Osteolysis
Synovitis

28. PGA
G= GONE

29. Adverse tissue reactions to bioabsorbable fixation devices
Bostman OM, Pihlajakmaki HK.
Clin Orthop Rel Res 2000 Feb; (371):
2528 pts – malleolar fracture, chevron
osteotomy for hallux valgus, and radial
head fractures
108 significant sterile tissue reactions
107 from PGA (5.3%) - 11 weeks

30. Self Reinforced PGA rods

31. PGA failures
Accumulation of monomer in tissue causes lowering of pH, which can increase osmotic pressure
Expansion of implant cavity and possible sterile fluid accumulation
Pain and swelling
anti-inflammatory recommended-
removal if necessary

32. CT scan 24 months after
implantation of PGA
pin in a distal sheep
femur.

33. Biodegradable Implants in Sports Medicine
Weiler et al. The Journal of Arthroscopic and Related Surgery
Vol 16 No3, 2000 pp
PGA particles in lymph nodes of sheep 6 months after implant in knee

34. Back to the drawing board…
PGA alone in amounts necessary to make fixation devices causes an unacceptable amount of soft tissue reaction and bone osteolysis
Purely PGA devices were abandoned in the early 2000’s and attention was turned to PLLA.

35. PLLA
LL-Long Lasting
Crystalline

36. 2528 pts – malleolar fracture, chevron osteotomy for
Adverse tissue reactions to bioabsorbable fixation devices
Bostman OM, Pihlajakmaki HK.
Clin Orthop Rel Res 2000 Feb; (371):
2528 pts – malleolar fracture,
chevron osteotomy for
hallux valgus, and radial
head fractures
108 significant sterile tissue reactions
1 from PLA (0.2%) years

37. Progressive osteolysis of the radius after distal biceps tendon repair with the bioabsorbable screw
Potapov A, Laflamme YG, Gagnon S, Canet F, Rouleau DM.
 J Shoulder Elbow Surg Jul;20(5): May 24.
* 19 consecutive distal biceps repairs with PLLA biotenodesis screw
* Average 22 month follow up
* 49% post operatively
to 61% of radius at follow up
1 tunnel filled completely at 5 year follow up
(Many surgeons fear creep and stress
relaxation with these implants)

38. Transcutaneous Migration of a Tibial Bioabsorbable Interference Screw After Anterior Cruciate Ligament Reconstruction
Greg Sassmannshausen, M.D., and Charles F. Carr, M.D.
Arthroscopy: The Journal of Arthroscopic and Related SurgeryVol 19, No 9 (November), 2003: E79

39. 27 year old female 1 year status post revision of ACL with
Severe cartilage damage by broken poly–L–lactic acid (PLLA) interference screw after ACL reconstruction
Burkhard Lembeck and Nikolaus Wulker
Knee Surg Sports Traumatol Arthrosc (2005) 13: 283–286
27 year old female 1 year status post revision of ACL with
No history of trauma, but pain and effusions

40. Intra-articular migration of broken PLLA screw.
Grade 3 and 4 chondral damage.

41. The authors of this case compared metal screw migration cases in the literature vs bioabsorbable and noted that all bioabsorble screws were broken when migrated and none of the metallic ones were. They also noted that metallic screw migration was typically diagnosed within weeks where as bioabsorbable ones usually took months before they were diagnosed.
The authors of this case compared metal screw migration cases in the literature vs bioabsorbable and noted that all bioabsorble screws were broken when migrated and none of the metallic ones were. They also noted that metallic screw migration was typically diagnosed within weeks where as bioabsorbable ones usually took months before they were diagnosed.

42. Pretibial Cyst Formation after Anterior Cruciate Ligament
Reconstruction with a Hamstring Tendon Autograft
Eiichi Tsuda et al. Arthroscopy: The Journal of Arthroscopic and Related Surgery
Vol 22, No 6 (June), 2006 p 691
20 year old with anterior knee pain and swelling
2 years after reconstruction

43. Complications after meniscal arrows with bioabsorbable
arrows: two cases and analysis of literature
Knee Surg, Sports Traum, Arthros (2002) 10:
Resulted in granuloma formation and articular cartilage wear.

44. Glenoid osteolysis after arthroscopic labrum repair
with a bioabsorbable suture anchor
Acta Orthop. Belg., 2007, 73,
Marco Spoliti from S. Camillo-Forlanini Hospital, Rome, Italy
25 year old female professional volley ball player 8 months after SLAP lesion repair
With PLLA suture anchors

45. Severe osteolysis 3 years after RC repair with bioabsorable suture anchor fixation

46. Mayo study

47. Review
The first bioabsorbable anchors were composed of PGA, which resulted in rapid loss of fixation strength due to rapid absorption.
Resulting in loose bodies, synovitis, and osteolysis
The result was PLLA anchors
The concern became the excessively long period of degradation resulting in incomplete or partial osseous replacement
The can result in replacement with fibrous or fatty-fibrous tissue, a sterile abscess, and potential for microfracture of implant
PLLA was further refined to alter the amorphous nature by using copolymers of the levo- and dextro-steroisomers affecting the rate of degradation

48. What other options or combinations could yield better results?
347 × collegeboundacademy.com
What other options or combinations could yield better results?
The Search Continued……

49. But Is There A Clear Solution?
                

50. PEEK Polyetheretherketone (PEEK)
PEEK is exceptionally strong thermoplastic polymer
Mechanical properties (tensile yield, strength, shear strength and modulus) closely match bone
PEEK is relatively inert, radiolucent, and can be drilled out during revision cases
Eg: PEEK Corkscrew, PEEK SutureTak, PEEK SwivelLock, Healix PEEK, VersaLok, TwinFix PK, BioRaptor PK
Permanent implant

51. Not bioabsorbable
PEEK (Polyether-Etherketone) hard radiolucent plastic
JuggerKnot (Biomet) – anchor composed of suture
Obviously PEEK does not absorb
JuggerKnot has tested well; however, also does not absorb and questions remain regarding fixation strength

52. Composites
TCP- Alpha tricalcium phosphate Ca3(PO4)2 TCP- Beta tricalcium phosphate Ca3(PO4)2 HA- Hydroxyapatite Ca5(PO4)3

53. Composite Anchors
Composite anchors are composed of a blend of tricalcium phosphate (TCP) and PLA
Biocryl Rapide (DePuy Mitek): 30% TCP and 70% PLGA
PLGA is a copolymer composed of 15% PGA and 85% PLLA
BioComposite SutureTak (Arthrex): 15% TCP and 85% PLA
Composite anchors were shown to have minimal tissue reaction with complete absorption follow by bone ingrowth

54. Composite Anchors
Studies have showed resorption between 18 and 24 months and bone ingrowth by 24 months

56. Biomet/Arthrotek Lactosorb L15 PLLA – 85% PGA – 15%
Retains 80% of strength at 8 weeks
Resorbed by 12 months

57. Depuy/Mitek Milagro BR (biocryl rapide) 70% biocryl rapide – PLGA
30% beta tricalcium phosphate
Absorbs and allows for ossification
of implant site in as little as 3
years.

59. Bioabsorbable implants in orthopaedics?
Room for improvement Know implant, complications, and when to look for them But is there a bright future?

60. Future Possibilities - Allow for elution of BMPs
(cardiovascular stents)
- PEEK Composites
- Allow for elution of anti-inflamatories/steroids in area of synostosis
Many possibilities

61. Thank You