Biodegradable implants, especially made from polymers like polyglycolic acid (PGA) and poly-l-lactic acid (PLLA), offer significant advantages in orthopedic procedures by gradually degrading and transferring load to healing tissues, thus reducing the need for secondary surgeries. These implants are designed to minimize foreign body reactions and have similar mechanical properties to bone, although they may cause tissue reactions and other complications. Recent advancements aim to improve the degradation characteristics and biocompatibility of these materials to enhance patient outcomes in fractures and soft tissue repairs.

1. BIODEGRADABLE IMPLANTS
JOURNAL CLUB
BY Dr.RAM GOPAL
MODERATOR – DR.V.VAMSI KRISHNA

3. INTRODUCTION
• A basic bio absorbable implant degrades in a biologic environment.
• Their breakdown products are incorporated into normal cellular
physiologic and biochemical processes.
• These implants and degraded material are well tolerated by the host with
no immunogenic or mutagenic tendency.
• For fracture fixation, these materials must have adequate strength and
should not degrade too rapidly, so that fixation is not lost before adequate
healing can occur.
• Ideally these implants should have mechanical characteristics equal to
those of standard stainless steel implants

4. • It would degrade with the healing process so that load is gradually
transferred to the healing tissue.
• But currently available polymers do not have mechanical characteristics
equal to those of metal implants.

5. • Variety of implants made from different materials is commercially
available.
• Their composition and the mode of reinforcement vary according to the
operation for which they are intended.
• Polyglycolic acid (PGA) and Poly-L-lactic acid (PLLA) implants have been
widely used, including pins, rods, screws and plates are available.
• Many other implants such as membranes, arthroscopic and spine surgery
implants are currently in use.

6. PATHOPHYSIOLOGY
• Implants modify the risk of infection by bacterial adhesion, tissue
integration, and immunomodulation.
• Bacterial adhesion to implant leads to interaction between bacteria and
implant.
• There are numerous implant-dependent factors affecting the bacterial
adherence to the surface .
• These include chemical composition, surface roughness and configuration,
and possible surface coating.
• Bacterial colony accumulates over implant which secretes biofilm slim
layer (extracelluar mucopolysaccharide), interfere with phagocytoses and
antibody function of host and promotes bacterial aggregation.

7. • This also provides a physiochemical barrier against both systemic and
implant-released antibiotic therapy, making infections difficult to treat
without implant removal.
• In addition to bacterial and implant properties, the modified immune
response of the host plays a key role in the etiological process of foreign-
body infection.

8. • All implanted devices cause a foreignbody reaction.
• The severity of which is dependent on numerous factors.
• Tissue damage caused by trauma and surgery, material of the implant, and
size and chemical composition of the debris particles present.
• The most common bacteria is coagulase negative staphylococcus .

10. • To avoid second surgical intervention, the degradation of these implant
materials is important.
• Degradation should be achieved at a rate such that partially degraded
implant should maintain their mechanical integrity until the newly formed
tissues have sufficient strength to replace them.
• Material degradation occurs by several mechanisms, including hydrolysis
and enzymatic degradation
• Most synthetic polymers are degraded by hydrolysis of their ester linkages.
• On the other hand, many natural materials and some polymers, including
degradable peptide sequences, are degraded by enzymatic mechanisms to
oligomers and monomers.

11. • The final products are excreted or used by the body.
• PGA and Poly dioxanone (PDS) degradation products can also be excreted
by the kidneys.
• It is also known that PGA degradation is partially performed by enzymes
such as esterase.
• Enzymes also seem to take part in Polylactic acid (PLA) degradation.
• Polymer breakage produces products that lower the regional pH and thus
accelerate the procedure.
• The final degradation of polymer debris is done by macrophages and
giant cells followed by mild local tissue reaction around absorbable
implants.

12. • This leads to production of a thin macrophage layer with incidentally
multinucleated giant cells surrounded by a mild connective tissue capsule.
• ] That is responsible for many adverse effects.

14. • Biodegradable materials should be biocompatible.
• Not only it avoids eliciting inflammatory and immunogenic responses, but
also degraded materials and related chemicals should be biocompatible in
terms of both the local and the systemic response.
• The biocompatibility of a polymer depends on both its chemical structure
and the processing method that produces it.
• During a polymerization process, an initiator, a monomer, and sometimes
a catalyst are needed.
• These materials often remain in preformed implants even after
purification are also a particular concern for in situ forming implants.
• Toxicity and concentration of residual monomers or initiators should be
considered when assessing biocompatibility.

15. • Removal of these potentially toxic components is usually effected by
prolonged rinsing in aqueous solution.
• Biocompatibility of the remaining material is confirmed in vitro by
cytotoxicity assays.
• In vivo observation of the inflammatory response after implantation in
animal models is also an important step before clinical application can be
considered..
• Under in vitro conditions, PGA is an immunologically inert substance,
provoking only slight lymphocyte activation. .
• Clinically significant foreign-body reactions are far more rarely seen with
PLA than with PGA.

16. • In short-term studies, the biocompatibility has been acceptable with no
clinical manifestations of foreign-body reactions.
• There are no in vitro studies investigating the cytological immune
response of PLA.

17. • As with other biomedical implants it would be possible to sterilize
biodegradable implants without affecting their chemical or physical
properties.
• And to produce and pack them on a large scale for practical and economic
uses.
• Factors such as viscosity, curing time, and implant shape should also be
optimized for injectable scaffolds to facilitate their use during complex
surgical procedures .

18. • These implants can also be used in fractures fixation of the
• glenoid fossa ,
• radial styloid,
• patella and acetabulum;
• osteochondral fractures in the knee,
• tibial plateau,
• phalanx,
• calcaneus and talus;
• hallux valgus surgery,
• ankle surgery,

19. • radial head fixation ,
• distal radial fractures ,
• hand fractures ,
• olecranon fractures,
• distal femoral epiphyseal fractures,
• meniscal injury,
• anterior cruciate ligament and shoulder lesions repair

20. • In addition to providing physical support, they have been employed to
introduce bioactive molecules at the defect site.
• In one strategy, scaffolds can be used to control the release of bioactive
molecules, thus accelerating the healing process.
• In other cases, the effectiveness of less stable drugs may be extended by
encapsulating them inside a matrix.

22. • Biodegradable implants provide the advantages of gradual load transfer to
the healing tissue,
• reduced need for implant removal,
• and radiolucency, which facilitates postoperative radiographic evaluation
and no hinderance in second surgey.
• They can be engineered to alter their degradation characteristics and
material properties.
• These biodegradable implants are safe as they are made of biocompatible
material
• hence there is no risk of metal allergic reactions as compared to metallic
implants.

23. • These implants degrade, they lose strength and this increases pressure
over the bone, strengthening it and therefore preventing bone resorption.
• Resorption of these implants also makes revision surgery less
complicated, as there are no permanent implants inside.
• So there is no need of another surgery for implant removal.
• Hence there is reduced trauma to soft tissue thereby decreasing the cost
of surgery and reducing the risk of cross infection.
• As compared to metallic implants there is no longterm implant palpability
hence patient compliance is much better.
• There is no implant temperature sensitivity so short wave diathermy and
micro wave diathermy can be used after a period of time thus complying
increased patient satisfaction.

24. • Due to characteristic nature of these biodegradable implants there is no
growth disturbances in children after surgery as biodegradable screws or
rods can also be used for treating epiphyseal fractures.
• It facilitates fracture healing by allowing micromovements at fracture site.
• It can be used to control the release of bioactive molecules to accelerate
the healing process.
• The fixation does not disturb the anatomy as depicted on radiographs as
there is reduced radiographic scatter or obstruction and is compatible
with magnetic resonance imaging if further evaluation of the affected joint
post operatively is necessary.
• Bioabsorbable suture anchors are becoming alternative to metal staples
and screws.

25. • In this, sutures don’t have to pass through bone tunnels.
• Pullout strengths for bioabsorbable suture anchors are comparable to
those of their metallic counterparts.
• Bioabsorbable suture anchor fixation has several advantages.
• The anchor undergoes reabsorption so no need for removal of implant as
compared to metallic implants which need to removed because of
osteopenia, corrosion and irritation of adjacent tissues.
• Improperly placed anchors may simply be drilled out rather than
unscrewed or pushed through due to which stress is gradually transferred
to the healing soft tissue as the anchor degrades.

26. • These are more expensive, have less strength than metals.
• Complications with the use of these materials include tissue reactions
including mild fluid accumulation,
• painful erythematous fluctuating papule over the implant track,
• the papule, if left untreated, bursts within a few days and revealed a sinus
draining liquid remnants of the implant leading sterile sinus tract
formation,
• osteolysis around the implants,
• synovitis when implanted intra articularly,
• and hypertrophic fibrous encapsulation.

27. • Adverse effects such as migration of implant,
• growth disturbance,
• rigidity,
• radio-opacity,
• infection,
• effects on cellular level and implant removal operations, often accompany
the use of these materials.
• Similarly improper insertion of the anchor too deep in the bone can cause
suture failure.
• l

28. • Superficial insertion of the anchor can lead to cartilage wear on the
opposing articular surface.
• There may be pullout from bone and become an intra-articular loose
body.
• Due to its radiolucent nature, diagnosis can be difficult to make
postoperatively in a persistently painful joint.

29. • The use of PGA is now limited, since materials and copolymers with better
degradation properties.
• As per Bostman et al and Tuompo et al, a total of 2037 and 1879 patients
respectively were included in study, adverse reaction ranged from 2.8% to
60%in a series of paediatric fractures and wrist fractures respectively.
• Tissue reactions included fluid accumulation, sinus formation and
osteolysis that was apparent 2 to 17 months postoperatively.
• PLLA has a low degradation rate because of this, adverse reaction tend to
appear late, even 4-5 years postoperatively.
• This renders many studies weak regarding the presentation of true
adverse reaction rate in procedures where PLLA implants have been used,
since the follow-up of these studies is shorter than the complete
absorption time of the material.

30. • . A review of the first clinical trials where PLLA implants were used
presents 14 series that were performed from 1990 to 1996.
• A wide variety of reaction rates was reported, from no adverse reactions
to swelling in 47% of the patients.
• Advances in material science, such as self-reinforcement technique and
elimination of factors that were considered responsible for reaction .
• Enantiomeric isomers of PLA were mixed to develop a material less
crystallic and more hydrophilic than PLLA, in order to accelerate the
degradation process and avoid late tissue reactions.
• Latjai et al used P(L/D)LA-PGA copolymer screws in ACL reconstruction
procedures.
• No material-related tissue reactions were reported in the mean follow-
up time of 5.2 years in the 28 patients that were included in the study.

31. • Clearly, future work in the area of orthopaedic biomaterials should be
focused on the reduction of the foreign-body response.
• Reducing the crystallinity of the polymer or controlling the pH in the
degrading implants may help reduce the incidence of the foreign-body
response.

33. INTRODUCTION
• Bone is one of the most important components of the human body, and
functions in a supportive and protective role.
• Damage to bone may result from external impact, or from diseases such
as tuberculosis or tumor invasion.
• It is estimated that more than 3 million individuals in China develop bone
complications such as fractures, or diseases such as tuberculosis or tumors
annually .
• Non-degradable metal implants have good mechanical properties and can
achieve early stable fxation, so have often been used for treatment.
• However, the elastic modulus of the implants is far greater than that of
human bone , which often leads to stress shielding and subsequent
osteoporosis, osteolysis and secondary fractures .

34. • The need for a second fracture surgery to remove the implants is complex
and carries the risk of surgical complications,
• increased physical pain and fnancial burden for patients .
• To avoid these issues there has been a surge in availability of degradable
orthopedic implants over the past two decades.
• These implants have good biocompatibility, bone conduction and
biodegradability, and have gradually gained acceptance by most clinicians
and patients.
• To date, biodegradable implant materials used domestically and
internationally are mainly polymers and magnesium alloys.
•

36. • Polymer implants have good mechanical features, physical properties and
biodegradability, as well as having an elastic modulus similar to human
bone.
• Therefore, they are often used to treat human fractures.
• Polymer implants can efectively prevent stress shielding and the need for
a second operation to remove the implant.
• Common orthopedic polymer implants used clinically include polylactide
(PLA), poly-l/dl-lactide (PLDLA) and poly-l-lactic

37. • PLA has been used as an internal fixator for more than 30 years, and can
effectively cure cancellous bone fractures.
• PLA was the first degradable implant to be used as bone and cartilage
tissue engineering scaffold materials .
• . Zeng et al.compared the ability of different materials to fix maxillofacial
fractures after initial curative effects.
• Postoperatively, PLA micro plate treatment was better than steel wire or
titanium plates .

38. • Treatment of mandibular fractures with PLDLA and poly (dl-lactide)
(PDLLA) screws and plates, can promote bone healing based on
biomechanical principles.
• However, PDLLA has high crystallinity, and slow degradation and
absorption rates.
• Thus, it is unlikely that it would assist with fracture healing, and it may
increase the incidence of infammatory reactions.
• PLDLA due to the addition of amorphous PLDLA in PLLA, lessens the
crystallinity of PDLLA, and increases molecular chain mobility.
• This can result in greater hydrophilicity, leading to accelerated
degradation

39. • . Compared to PDLLA, PLDLA has a higher mechanical strength, which
improves fracture fxation safety .
• When PLDLA implants were used to treat mandibular fractures, PLDLA
screws provided the same fixation strength as titanium screws and patients
recovered well .
• In addition, only 16 of 281 patients with facial fractures treated with PLDLA
screws had complications, supporting satisfactory treatment overall .
• Tiihonen et al. attempted to use PLDLA implants to treat patients with soft
tissue and bone defects.
• In these patients, PLDLA implants relieved pain but did not enable them to
return to their preoperative state.
• Therefore, patients with soft tissue and bone defects should not be treated
with PLDLA implants.

40. • In 1966, PLLA sutures were frst used as an implant in animals and were
found to be non-toxic and to degrade gradually .
• Eppley et al.retrospectively analyzed the clinical curative efects of
craniofacial reconstruction with poly-l-lactic-polyglycolic implants.
• The results showed that postoperative implants can stabilize the affected
area, while having low propensity for foreign body reactions and good
patient recovery .
• In anterior cruciate ligament (ACL) injury there is a change in
metalloproteinase (MMPs) secretion by cartilage tissue, synovial
membrane and the intra-articular ligament that increases matrix
metalloproteinase-2 in synovial fuid, thus hindering self-healing of the
ligament [20]. If not treated in time, it may lead to premature
degeneration of the knee .

41. • Animal experiments showed that use of PLLA/hydroxyapatite
(HA)/αFe2O3 and PLLA–PEG/HA for ACL reconstruction can meet
biomechanical requirements .
• Arama et al. used PLLA–HA screws and titanium screws for ACL
reconstruction, and observed no statistical diferences in their
mechanical properties.
• However, patients treated with PLLA–HA screws were less likely to
experience surgical complications, and did not have bone tunnel
enlargement.
• Robinson et al further proved that PLLA–HA screws for ACL
reconstruction can reduce the probability of bone tunnel enlargement.
• The weakest part of the ACL reconstruction is the tibia fxation of
grafts.

42. • Use of PLLA–HA screws for grafting was associated with reduced implant
degradation postoperatively.
• They were also associated with good mobilization recovery for the
patient .
• The ankle is composed of the talus, and the lower ends of the tibia and
fbula, and is commonly injured orthopedically.
• Approximately 187 of every 100,000 individuals experience a fractured
ankle every year .
• Rangdal et al.followed 16 patients whose ankle fractures were treated
using PLLA screws.

43. • One patient developed localized pain and swelling at 14 weeks after
surgery, but responded well to antimicrobial treatment.
• The remaining patients recovered favorably.
• It has also been reported that use of PLLA screws to repair meniscus
injuries can efectively reduce the risk of neurovascular damage .
• Anterior cervical decompression with PLLA screw fxation for bone grafting
can successfully treat cervical spondylosis.
• The screws were absorbed as predicted, grafts fused well with adjacent
vertebrae, and only a few complications ensued [29].
•

44. • Wendelstein et al.conducted a three-year follow-up investigation of 34
patients with lesser toe deformities treated with PLLA.
• Of these patients, 84.6% healed well following surgery, while three had
misaligned toes and two had recurrent deformity .

45. • Use of a degradable poly (l-lactic acid)/poly (glycolic acid) screw to treat
patients with osteochondritis dissecans was associated with adequate
stability to area postoperatively without development of infammatory
reactions like recurrent effusion, warmth or erythema during screw
degradation .
• Park et al used poly (lactic-co-glycolic acid) screws and plates to treat
rabbit mandibles, and reported that all fractured sites had new bone
formation without infammation at 8 and 10 weeks postoperatively.
• Wang et al. retrospectively analyzed the clinical efficacy and complication
rate of degradable INION [synthesized from PLLA, PLDLA, polyglycolic acid
(PGA) and trimethylene carbonate (TMC)] screws and metal screws, which
were all used to treat elderly patients with tibial plateau fractures
complicated by osteoporosis.

46. • The observation group had biodegradable screw fxation plus external
fixation treatment,
• while the control group was treated with metal cancellous bone screw
fixation and external fixation .
• Degradable screws not only promoted fracture healing and reduced pain
postoperatively,
• but also shortened the time for fracture healing and for disappearance of
the fracture.
• However, it is essential to prevent infection during fracture treatment .

47. • A principle of magnesium alloy as an orthopedic implant is that
magnesium is an essential element for the human body.
• The total body content of magnesium is 21–25 g, with 53% contained in
bones, 27% in muscle, 19% in soft tissue, 0.5% in erythrocytes and 0.3% in
serum.
• Further advantages of magnesium alloy include the ability of magnesium
to promote new bone formation and bone metabolism.
• It also has an elastic modulus that is close to that of human bone , so it
avoids the efects of stress shielding.

48. • Magnesium alloy has favorable properties like biocompatibility,
osteoconductivity and biodegradability, which avoids secondary
operational implant removal.
• Magnesium is also abundant in nature.
• Collectively, these features mean that it is often used to treat fractures.
• Commonly used magnesium alloys include high-purity magnesium alloy,
MgCa0.8 alloy, MgYREZr alloy and AZ series alloy.

49. • High-purity magnesium avoids second phase and microgalvanic corrosion
and is, therefore, nontoxic.
• It also has a low degradation rate.
• Various tests (impregnation, cytotoxicity and biological activity) showed
that high-purity magnesium screws possess uniform corrosion behavior.
• This can improve cell activity and the genes that are related to osteogenic
diferentiation such as alkaline phosphatase, osteopontin (OPN), human
bone marrow mesenchymal stem cells and RUNX2.

50. • All of these genes contribute to mRNA expression .
• Animal experiments showed that high-purity magnesium screws had good
osseointegration properties, which increased bone mass and density.
• Thus, in addition to not compromising fracture site healing, it also
promoted new bone formation .
• By increasing anti-bending bone performance, the bone can nearly
recover to the pre-fracture state .
• High purity magnesium can also stimulate expression of bone
morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor
(VEGF) to promote reconstruction of the ACL .

51. • In addition, use of vascularized bone grafts with high-purity magnesium
screws after fixation can significantly improve hip joint function in
osteonecrosis patients .
• Implanting MgCa0.8 screws into rabbit tibia was well tolerated and had
good biocompatibility postoperatively.
• However, it degraded fast, which potentially contributed to its lack of
mechanical properties (Fig. 6) [40].
• Thomann et al. [41] implanted MgCa0.8 implants coated with MgF2 into
the tibia bone marrow cavity of New Zealand white rabbits.

52. • The implants were well tolerated in vivo and had slower degradation
postoperatively.
• Compared with uncoated implants, coated implants were stronger at
6 months after surgery.
• Adam et al. [42] further proved that use of MgCa0.8 implants was non-
toxic to animal

53. • Due to presence of the element, rare earth (RE), MgYREZr has a high yield,
tensile strength and elongation along with other favorable mechanical
properties.
• RE also stabilizes the corrosion layer. Additionally, reasonable heat
treatment of MgYREZr alloy can reduce its degradation rate .
• In 2013, Syntellix Company used the MgYREZr screw to treat hallux
valgus, with good therapeutic effect.
• Indeed, MgYREZr alloy was the world’s frst certifed biodegradable
magnesium alloy bone implant product, and became available
commercially in Europe .
• Diekmann et al implanted MgYREZr alloy screws and titanium screws into
the left tibia of rabbits to experiment with ACL reconstruction.

54. • The results of micro-computer tomography (µCT) scans showed that
obvious bubbles appeared 4 weeks after implantation, but these
decreased in number by 24 weeks.
• All magnesium screws had bonded well with tendons at 24 weeks
postoperatively, and had good synostosis ability .
• Histological evaluation showed that neither infammation nor tendon
necrosis occurred.
• Further, blood concentration of Y and Zr were both within the normal
range.

55. • Some patients who had acute scaphoid fractures treated with MgYREZr
compression screws showed severe osteolysis and cyst phenomenon after
surgery.
• None of the patients’ fracture sites were fxated at 6 months
postoperatively.
• Therefore, such patients should not be treated with MgYREZr compression
screws .

56. • Witte et al. [47] conducted in vitro and in vivo experiments using two
magnesium alloy implants.
• This group found that the implant corrosion rate in vivo was four orders of
magnitude less than observed in vitro.
• Thus, this study showed that the conclusions drawn from in vitro corrosion
tests of magnesium alloys cannot be used to predict the in vivo corrosion rate .
• Three months after removal of magnesium alloy screws that had been
diferences between groups (Table 10).
• Tensile experiments showed that anti-pull-out and tensile strengths of
magnesium alloy intramedullary nail were better than PLLA intramedullary nail
(Table 11).
• The animal experiments showed that use of fuoride to coat the magnesium
alloy screw not only enhanced the biocompatibility and corrosion resistance of
the screw, but also stimulated new bone formation (Fig. 8) [50].

57. • Yan et al used the three-point bending experiment and further proved
that AZ31B magnesium alloy implants containing fuoride on the surface,
had mechanical properties that met bone implantation requirements in
terms of the degradation process.
• One study reported improved biocompatibility when magnesium alloy
(AZ31) porous scafolds with MgF2 surface-coating were used to repair the
New Zealand white rabbit femoral condylar bone defect, compared with a
magnesium alloy stent without surface coating.
• Additionally, surface-coated scafolds induced more bone formation
in vivo .

58. • Biodegradable implants have good biocompatibility, osteoconductivity and
biodegradability in their application for fracture treatment.
• However complications may occur in some patients with these implants,
as summarized in Table 12.
• The research showed that composites should not only function as a
delivery vehicle but also provide a proper framework to achieve
appropriate bone formation .

59. • Degradable implants can effectively avoid stress shielding, and have good
biocompatibility, osteoconductivity and biodegradable properties.
• They also enable avoidance of a second surgical procedure to remove the
implant.
• However, some shortcomings exist in the clinical application of these
implants.
• A small number of patients treated with biodegradable screws may
develop bone surface infections , bone tunnel enlargement , cysts , screw
movement , a rapid degradation rate or other complications.
• Commonly used magnesium alloy and polymer implants also have these
problems

60. • . One survey found that patients who smoked tobacco and those with
diabetes or immunodefciency had a longer bone healing time.
• Too fast a degradation of the implant will compromise its mechanical
properties, resulting in failure of the surgical intervention.
• Use of PLLA screws to conduct ACL reconstruction is advantageous
compared with surgical steel or titanium screws [11, 14].
• However, some patients will develop cyst phenomenon, which may
result from a foreign body reaction caused by screw damage [18, 26],
tibial tunnel caused by synovial joint fuid leakage [57], failure of the
implant to match the diameter of the bone tunnel, placement of the
implant in the eccentric position of the bone tunnel [58] or uneven
torsional force on the screw [59].

61. • In addition, ACL repair and the regenerative process are not independent.
In both of these processes, all tissues within the joint cavity play an
important role.
• This is especially so early in the time course of ACL injury, where
regulation of the intra-articular environment is of great importance for the
ligament’s repair.

62. • Use of magnesium alloy implants for fracture treatment also has some
shortcomings.
• Too rapid a degradation of the magnesium alloy implant leads to
insufcient mechanical properties and poor bone healing around the
fracture [61].
• During implant degradation a considerable quantity of degradation
products attach to the fracture and slow healing.
• Further, the corrosion resistance of magnesium alloy is poor, with fast
corrosion producing a large amount of harmful hydrogen.
• Additionally, if the magnesium ion content in the body exceeds normal
physiological levels, it may lead to respiratory diseases, muscle paralysis,
hypotension and other symptoms of hypomagnesaemia .

63. • . The reactive pathways for magnesium alloy implants in the body are
shown as follows:
• Excessive corrosion of magnesium alloy limits its clinical application. Argo
et al. found that adding Sr to the Mg–Al alloy reduces its corrosion rate.
• Addition of Sr to Mg–Zn–Ca screws can improve mechanical properties,
and enhance and regulate corrosion resistance .
• Use of Sr as an orthopedic implant element has advantages.
• Sr is a trace element necessary for the human body, with 99% existing in
bone .
• Sr can stimulate bone growth, increase bone mass and reduce the
incidence of fractures .

64. • These advantages have prompted us to focus our research on the
relationship of Sr with mechanical and corrosion properties, and
biocompatibility with magnesium alloys.
• In addition, coating the screw surface with Sr can efectively reduce the
degradation rate .
• In addition to the clinical and biochemical applications mentioned
previously, the numerical simulation method represented by fnite element
has been used widely to predict the behavior of biodegradable vascular
stents .

65. • For the degradable screws and plates mentioned in this article, the
numerical simulation method can be used to predict the control of factors
such as degradation rate, boundary load and boundary constraints.
• This can optimize the structural design of the screw, and the clinical and
surgical plan.
• Therefore, with efective promotion of computer hardware and calculation
methods, numerical simulation will be widely applied to the study of
biodegradable implants in orthopedic fractures.

66. • The use of magnesium alloy or polymer implants to treat fractures results
in good therapeutic effect.
• However, degradable implants have some drawbacks. Their degradation
rate is too fast, which can lead to rapid loss of initial strength.
• It remains unclear how the degradation rate can be controlled to align
with the growth rate of bone.

67. • Therefore, future research needs to focus on how to slow the degradation
rate, as well as identifying strategies to enhance abrasion and corrosion
resistance.
• Additional investigations should be undertaken to develop other non-
toxic, and degradable implants containing multiple nutrients.
• As science progresses, further improvement to the mechanical properties
and biological performance of degradable implants is necessary.
• Development of more efficient biodegradable implants would have a very
promising future in the treatment of orthopedic fractures.

68. • When patients with syndesmosis injury were treated with PLA screws,
there was sufficient fatigue and failure strength to repair the syndesmosis
injury postoperatively [11]. Zhao et al. [12] used PLA screws and titanium
alloy lag screws in patients with ankle fractures, and observed no
significant difference in treatment effect or healing time compared with
the metal group (Tables 5 and 6). Patients treated with PLA screws had
good outcomes. The callus grew well, the fracture ends accorded well,
there was no delayed union or nonunion of bones, and ankle function
restored effectively.

69. • THANK YOU