Use of Bioabsorbable Materials in Orthopedics

Introduction:

Orthopedics is a field of medicine that focuses on the prevention, diagnosis, and treatment of conditions and injuries that affect the musculoskeletal system. In recent years, there has been a growing interest in the use of bioabsorbable materials in orthopedic procedures. Bioabsorbable materials, also known as biodegradable materials, are designed to be absorbed by the body over time, which eliminates the need for a second surgical procedure to remove the implanted material.

Bioabsorbable materials have been considerably used in medicine. The use of these materials in surgery is familiar, as catgut suture (a type of surgical suture) described in the Galen writings in the second century AC. These implants are gaining popularity in orthopedic surgery and other surgical specialties, including maxillofacial surgery or plastic surgery.

The three main categories of bioabsorbable materials in trauma and orthopedic surgery are polymers, metals, and ceramics. Bioabsorbable materials were invented to address various issues with synthetic implants, including growth disturbance, migration, rigidity, radioopacity, infection, and the requirement for implant removal operations.

Despite the popularity of bioabsorbable implants, several reports of complications continue to arise in the literature. However, these complications rarely pose an adverse effect on the long-term outcome.

What Are the Advantages of Bioabsorbable Materials?

When choosing a bioabsorbable material, it is essential to consider its mechanical properties and biocompatibility. The significant advantage of bioabsorbable implants is that initial stability is adequate for healing and gradual resorption after establishing biologic fixation.

Other advantages include the following:

• They lead to less implant morbidity.

• They are radiolucent.

• They eliminate hardware removal procedures.

• They limit stress-shielding and gradually transfer the load to healing fractures.

• They facilitate postoperative radiologic imaging.

What Are the Disadvantages of Bioabsorbable Materials?

Bioabsorbable materials have three main disadvantages:

• Lower mechanical strength.

• Higher cost.

• Undesired biological response. Studies have indicated that the strength reduction during degradation is slow enough to allow tissue healing. Many studies have also shown that these implants can provide the initial strength for orthopedic application.

• The foreign body reaction to bioabsorbable ranges from the mild fluid build-up to discharging sinus formation to irreversible tissue damage. Most clinical trial reports show these reactions do not affect the long-term outcome. However, in some studies, there have been moderate to severe complications.

What Are the Different Types of Bioabsorbable Materials?

Modern bioabsorbable materials are primarily polymers of poly-alpha-hydroxy acids in the polyester family. These polymer chains have properties specific to the independent monomers that comprise them and to the bonds between them. Most orthopedic surgery materials are polyglycolic acid (PGA) and polylactic acid (PLA). PGA was introduced in 1970 as the suture material Dexon. It is more susceptible to hydrolysis and early breakdown than PLA, usually being absorbed in several months. PGA is also susceptible to gamma radiation and ethylene gas oxide sterilization.

1. Polyglycolic Acid (PGA)

Advantages:

• It is hydrophilic and crystallic.

• It has a glass transition temperature of 36 degrees Celcius.

• It becomes malleable if this temperature exceeds.

Disadvantages:

• Potential postop complications.

• Early degradation and strength loss.

• Increased intraoperative time consumption.

2. Polylactic Acid (PLA): They are more hydrophobic than PGA.

• L-isomer or Poly-L-lactic acid (PLLA)

  • Hydrophobic and crystalline.

  • Prolonged degradation time.

  • Glass transition temperature 57 degrees Celsius.

  • Late adverse reactions in the last stages of polymer degradation.

• D-isomer:

  • Amorphous, less stable.

  • Helpful in building co-polymers.

3. Co-polymers:

• P(L/D)LA Co-polymers

  • A mixture of D- and L-isomers of PLA.

  • Hydrophobic and crystallic.

  • Resistant to hydrolysis and degradation.

  • Simple and self-reinforced forms.

  • Less crystallic and more rapidly degraded than PLLA alone.

  • Adding D-isomers results in less tightly packed polymer chains.

• PLGA Co-polymers:

  • Combination of PLA and PGA.

  • Simple and self-reinforced forms.

  • Used in oral-maxillofacial surgery.

  • Low crystallinity.

4. Self Reinforcing (SR):

• Composite structure made from partially crystalline or amorphous material made of orientated fibrils and binding matrix.

• Better biomechanical properties.

• Improved rigidity and strength along the longitudinal axis.

• Malleable at room temperature.

• No need for heating-cooling.

• It can withstand four times bending.

• It can be sterilized by gamma irradiation.

What Are the Uses of Bioabsorbable Materials?

The use of bioabsorbable fixation for attaching soft tissue to bone is increasingly being utilized by orthopedic surgeons, especially in treating soft tissue lesions in the shoulder. These implants have enabled the repair of labral and rotator cuff lesions. In addition, the development of bioabsorbable tacks, pins, screws, anchors, and washers has offered surgeons more treatment alternatives.

• Repair of Shoulder Lesions: Bioabsorbable anchors have been commonly used in Bankart repairs, labral lesions, and rotator cuff lesions. The first absorbable tack utilized for such cases was constructed of PGA and has been implicated in many instances of aseptic synovitis.

• Meniscal Repair and ACL Reconstruction: The bioabsorbable screw is a safe and effective device for meniscal repair. Many case reports have published complications with the Bionx arrow for meniscal repairs. However, no infections were registered.

• Trauma Surgery: Bioabsorbable implants are used to treat calcaneal and open fractures. In a study of more than 2,500 cases of fracture fixation where bioabsorbable implants were reported, bacterial wound infection was 3.6 %. Compared with metallic fixation, absorbable fixation has shown a lower incidence of infection.

• Hand Surgery: Complications can be high, particularly in complex hand trauma. Pin infection rates range between 7 % to 15 % and have been associated with migration, osteomyelitis, pin loosening, tendon rupture, and nerve injury. Bioabsorbable implants have been suggested to reduce many of these problems.

Conclusion:

Over the years, the use of bioabsorbable implants in orthopedic surgery and other musculoskeletal procedures is gaining acceptance. Complications associated with using these materials have been reduced with the development of newer self-reinforced polymers. It is important to note that although the incidence of undesirable responses is high, most of the reactions were not accompanied by adverse clinical symptoms and did not impact the outcome.

Furthermore, the overall infection rate with biodegradable implants is not higher than with conventional metallic devices. Therefore, future work in orthopedic biomaterials can focus on foreign body reactions, the most common complication, and thus reduce the incidence of any adverse reactions, including infection.