Tendon healing and tendon grafting

1. TENDON HEALING AND TENDON
GRAFTING
By: Dr. Amit Kumar Choudhary

2.  ANATOMY
 HISTOLOGY AND BIOCHEMISTRY
 TENDON NUTRITION
 TENDON AND GRAFT HEALING
 CLINICAL APPLICATION
 TENDON SUBSTITUTES
 FUTURE

3. ANATOMY

4. • Tendons are glistening white
anatomic structures interposed
between muscles and bones.
• They transmit the force created in
muscle to bone and make joint
movement possible.
• Tendons may be surrounded by a
bed of loose areolar tissue called
paratenon, or they may reside
within a tunnel of dense fibrous
tissue, the tendon sheath.

5. PARATENON
• The paratenon encases the tendon
in loosely arranged connective
tissue .
• It Consist of type I and type III
collagen fibrils, some elastic fibrils,
and an inner lining of synovial cells.
• The tendon is bathed in a fluid
environment similar to synovial
fluid.

6. • Nestled within the paratenon, the
entire tendon is covered by the
epitenon (also called mesotenon),
a fine, loose connective tissue
sheath containing the vascular,
lymphatic, and nerve supply.
• The epitenon extends deeper into
the tendon between the tertiary
bundles of collagen fibrils as the
endotenon.
• Together, the paratenon and
epitenon are sometimes called the
peritendon.

7. TENDON SHEATH
• The classic two-layered synovial
tendon sheath is present only in
certain tendons as they pass areas
of increased mechanical stress.
• These sheaths span an area from
the metacarpal heads to the
midportion of the distal phalanges.
• The outer layer is the fibrotic
(ligamentous) sheath; the inner
layer is the synovial sheath,
which consists of thin visceral and
parietal sheets.

8. • The parietal layer , it allows
smooth gliding of tendon as
well as provides synovial fluid
nutrition.
• The annular and cruciate
pulleys in these fibrous sheaths
provide mechanical advantage
as they hold tendons close to the
bone while allowing acute
flexion of the interphalangeal
joints

9. BLOOD SUPPLY
• In the hand, tendons are vascularized
along the entire length in a longitudinal
pattern.
• The different sources are vessels that
enter the palm and extend down
intratendinous channels
-vessels that enter from the proximal
synovial fold in the palm,
-segmental vessels that develop from
paired digital arteries and enter tendon
sheaths as vincula,
-vessels that enter the osseous insertions
of the tendon, and
-vessels at the musculotendinous junction.
• The majority of these vessels supply the
dorsal or posterior surface of tendon.

10. • A tendon in an area of low compression is vascularized by
small vessels that enter at multiple levels from the
surrounding areolar tissue.
• Blood flow is low, averaging less than 10 mL per 100 g per
minute.
• In contrast, in compressed areas, such as across a joint space,
nutrition comes from the segmental vincula.

11. • Within the digital sheath, both profundus and sublimis
tendons have relatively avascular segments over the
proximal phalanx; the profundus has an additional short
avascular zone over the middle phalanx. In these avascular
zones, tendons must rely on synovial fluid pumping for
nutrition.

12. HISTOLOGY AND BIOCHEMISTRY
• The basic elements of tendon are collagen bundles (70%), cells, and ground
substance or extracellular matrix, a viscous substance rich in proteoglycans.
• Collagen provides tendon with tensile strength; ground substance provides
structural support for the collagen fibers and regulates the extracellular assembly
of procollagen into mature collagen. Proteoglycans regulate tissue strength
because they determine the size and packing of collagen fibrils.

13. • The collagen fibril diameter in the adult tendon typically ranges
from 100 to 200 nm, but this will vary with tissue loading.
• Tenocytes (or fibrocytes), flat tapered cells sparingly distributed
among the collagen fibrils, synthesize both the ground substance
and the procollagen building blocks of protein.
• Collagen is arranged in hierarchical levels of increasing complexity
beginning with tropocollagen, a triplehelix polypeptide chain. Each
tropocollagen is composed of helical arrangement of two α1(I) and
one Î ±2(I) collagen chains.
• These helical molecules of tropocollagen in turn unite into fibrils,
fibers (primary bundles), fascicles (secondary bundles) that spiral
into tertiary bundles, and finally the tendon itself .

14. Myotendinous and Osteotendinous
Junctions• The myotendinous junction is a highly
specialized anatomic region in the
muscle-tendon unit where tension
generated by muscle fibers is transmitted
from intracellular contractile proteins to
extracellular connective tissue proteins
(collagen fibrils).
The osteotendinous junction is a
specialized region in the muscle-tendon
unit where the tendon inserts into a bone.
In the osteotendinous junction, the
viscoelastic tendon transmits the force into
a rigid bone.

15. Light Microscopic Appearance of Tendon
• Normal tendon consists of dense,
clearly defined parallel and slightly
wavy collagen bundles.
• Collagen has a characteristic
reflective appearance under
polarized light. Between the collagen
bundles, there is a fairly even sparse
distribution of cells with thin wavy
nuclei.
• There is an absence of stainable
ground substance and no evidence
of fibroblastic or myofibroblastic
proliferation. Tendon is supplied by a
network of small arteries oriented
parallel to the collagen fibers in the
endotenon, which is a continuation
and invagination of the outer
epitenon.
Cross section of a tendon showing the arrangement of the fasciculi
and vascular bundles

16. TENDON NUTRITION
• Tendons receive nutrition from both vascular and synovial
systems.
• Synovial fluid diffusion provides rapid delivery of nutrients by
imbibition, whereby fluid is pumped into small conduits in the
tendon surface during digital flexion and extension.
• In the absence of vascular inflow, diffusion alone can provide
adequate nutrition for tendon healing.
• However, for rapid tendon healing and functional gliding to
be achieved, it is important to preserve the integrity of these
two nutritional sources. Compromise to either vincula or
digital sheath will result in less than optimal healing.

17. TENDON AND GRAFT HEALING

18. The healing of tendon grafts may include three phases
(1) Cellular phase: the space between the graft and host tissue is
filled with blood clot, inflammatory cells, and granulation
tissue. Epitenon cells may proliferate and invade to
participate in the repair.
(2) Collagen synthesis phase, beginning at the first week and
lasting for several weeks with extracellular matrix production
along with ongoing revascularization process.
(3) Remodeling phase: during this phase, transplanted graft
gains strength and peritendinous adhesions become loose and
filmy and lose their strength, allowing the graft to glide.
However, it may need 9 months to remodel the collagen
fibers to a relatively normal pattern.

19. • The stages of tendon and graft healing model normal wound
healing.
STAGE OF INFLAMMATION
- lasts 48 to 72 hours after repair. The strength of the tendon
repair is almost entirely supplied by the suture.
- A fibrin clot fills the space between tendon, or between
tendon and graft, while macrophage and inflammatory cells
join the repair site.
- Cells originating from the extrinsic peritendinous tissue, the
epitenon, and the endotenon migrate to the wound, and the
morphologic appearance changes to that of fibroblasts. These
cells proliferate and begin collagen production.

20. PROLIFERATION STAGE
• The fibroblastic or collagen- proliferation stage lasts 5
days to 4 weeks, when scar is deposited.
• The scar tissue is composed of random collagen fibrils, with
type I and type III collagen, along with increased water,
DNA, and glycosaminoglycan content.
• Fibroblast numbers peak at 2 to 3 weeks, then decrease. At this
time, there is relative weakness in the healing tendon ends, and
strength of repair is dependent on the construct and strength of
the holding suture.

21. MATURATION OR REMODELING STAGE
• During the maturation or remodeling stage, the parallel,
longitudinally oriented collagen fibers merge with the
disorganized scar and impart a portion of their normal
physiologic stress through the scar.
• Cross-linking of fibers also imparts an increase in tensile
strength. By 3 to 4 months, the remodeling process is
complete.

22. Extrinsic Versus Intrinsic Healing
• Controversy used to exist in determining whether the extrinsic
cells (coming from peritendinous tissue) or intrinsic cells
(coming from within the tendon, such as tenocyte, endotenon,
or epitenon) produced new collagen.
• Numerous authors have now shown that intrinsic healing is
indeed a pathway to tendon healing.The relative contribution
of extrinsic and intrinsic cells to tendon healing is dependent
on level of initial injury, quality of surgical repair, and
postoperative regimen.
• As a rule, intrinsic cellular healing results in less adhesion
formation

23. Modulators of Tendon Healing
• In the hope of enhancing tendon healing, investigators are
looking at the role of soluble polypeptides in the cellular
events of tendon healing.
• The agents under study include growth factors, hormones, and
chemotactic factors such as fibronectin.
• Nessler and Fujita examined the effect of direct current
electrical stimulation.
• Nelson and Greenough looked at pulsed electromagnetic
fields, with some positive effects on an experimental model.
• Ultrasound may also limit adhesions, assisting in ultimate
functional outcome.

24. • Nonsteroidal anti-inflammatory agents may decrease
adhesion formation.
• Use of hyaluronic acid in decreasing tendon adhesions.
Hyaluronic acid's efficacy is affected by both the concentration
and the molecular weight of the preparation.

25. CLINICAL APPLICATION

26. Repair of Tendon Laceration
• To achieve tendon healing and to attain effortless gliding to
allow full joint motion.
• The challenge has been to repair both flexor tendon and the
surrounding sheath, which is 1 mm away, and have both heal
without being encased in a single scar mass.
GOALS

27. • Bunnell's original principle of
avoiding primary repair of zone II
injuries, between the distal palmar
crease and insertion of the
sublimis tendon, has given way to
immediate primary repair.
• Particular indications for primary
tendon repair are tendon
lacerations in clean wounds with
intact soft tissue, digital
replantation, and tendon injury
with concomitant bone fractures
in which fixation is stable enough
to allow immediate motion of
joints.
INDICATIONS

28. Primary flexor tendon repairs
Indications
 Clean-cut tendon injuries
 Tendon cut with limited peritendinous damage, no defects in soft-tissue
coverage
 Regional loss of soft-tissue coverage or fractures of phalangeal shafts are
borderline indications
 Within several days or at most 3 or 4 weeks after tendon laceration
Contraindications
 Severe wound contamination
 Bony injuries involving joint components or extensive soft-tissue loss
 Destruction of a series of annular pulleys and lengthy tendon defects
 Experienced surgeons are not available

29. • Matev, Schneider, and others have shown that primary repair
of tendon injury within the flexor sheath may be performed in
a delayed fashion without compromise to outcome.
• Gelberman's review, however, suggested that better
biomechanical results can be achieved with immediate repair
of tendon injury compared with repairs delayed 7 or 21 days.
TIMING OF REPAIR

30. GUIDELINES FOR REPAIR
 Surgical technique and tissue handling are critical to the
quality of the result after tendon repair.
 Meticulous atraumatic technique is necessary to avoid
tendon or tendon sheath injury and injury to the blood supply.
Because the blood supply to tendons in the sheath lies dorsally,
strangulation is avoided by placement of core sutures in the
relatively avascular, anterior portion of the tendon.
 Repeated efforts to retrieve a retracted tendon may result in
trauma to the tendon or sheath, and one should not hesitate to
extend the exposure.

31.  Several suture materials for flexor tendon repairs of that 4-0
monofilament polypropylene or braided polyester sutures
are reasonable choices.
 Barrie et al recommended that 3-0 suture be considered for
tendon repairs when early active motion is planned.
 Suture method for tendon repair should not be unduly
complex, and there should be a smooth edge between cut
ends

32.  The repaired tendon must not bulge outside the confines of the
tendon sheath.
 The circumferential, epitendinous suture performs two functions.
It avoids exposing the cut ends of
tendons, minimizing extrinsic healing by
adhesions and the development of gap
formation, and adds to the tensile
strength of the repair.
 Several authors have advocated the placement of the epitenon
suture first, as a technique to align the tendon ends, to provide
stability during repair and to keep the free ends from fraying.
 Papandrea compared two methods of Kessler suture repair of
tendons and reported a 22% increase in tensile strength when the

33. Variables That Affect the Outcome of
Tendon Repair

34. • Vascularity is a critical factor determining the final result after
tendon repair. Hypovascularity is reflected in decreased matrix
synthesis in the tendon, decreased tensile strength and motion,
and greater adhesion formation.
• In cases of severe injury, with damage to vincula or when
sublimis tendon was excised, the results of tendon repair were
worse.
BLOOD SUPPLY

35. • The critical elements that
must be preserved within
the flexor sheath are the
A2 and A4 pulleys.
PRESERVATION AND RECONSTRUCTION
OF THE FLEXOR SHEATH

36. • They provide the moment arm
for digit flexion and inhibit
bowstringing .
• Repair of the fibrous flexor
sheath restores the closed
synovial space for nutrition and
lubrication.
• With sheath repair, there are
additional pitfalls, including
excessive scarring, loss of
vascularity, and limitation of
tendon gliding.

37. EARLY MOTION AND TENSILE STRESS
• Early controlled postoperative motion improves tendon tensile
strength and excursion.
• This salutary effect is thought to be secondary to increased
intrinsic healing, increased collagen formation, facilitated
pumping of synovial fluid, and possible disruption of early
vascular budding and adhesion formation.
• The tensile stress initiated by early motion has been shown to
increase the rate and organization of collagen synthesis

38. Improvements in Suture Technique
• Myriad core suture techniques have been developed to
minimize gap formation and to avoid rupture with early
postoperative motion, especially active motion.
• Biomechanical testing in numerous four-strand and six-strand
repairs attests that the strength of a flexor tendon repair is
roughly proportional to the number of suture strands that cross
the repair site.
• The advantages of achieving greater tensile strength and
decreased gap formation with multistrand repairs must be
weighed against possible increase in bulk of the tendon,
increased gliding resistance within the sheath, potential
compromise of vascularity, and increased operating time.

40. • Uncontrollable factors that affect outcome are the extent of
soft tissue and flexor sheath injury and the vascular supply to
the injured tendon ends.
• Controllable factors that affect the outcome of tendon repair
are the amount of stress placed on the repair (postoperative
regimen), surgical technique, and type of suture repair.

41. Tenolysis
• When tendon adhesions inhibit motion of the digit, better
function may be gained through tenolysis.
• Tenolysis may be performed after primary tendon repair, after
tendon grafting, or after two-staged tendon grafting.
• This should not be attempted until tissue equilibrium, that is,
suppleness of soft tissue as well as of joints, is achieved.
• The patient's passive motion should exceed his or her active
motion, but regardless, surgery should be considered when
there is a plateau in therapy.
• The optimal time may be 3 to 4 months after initial tendon
repair.

42. • Tenolysis is optimally performed under initial local anesthesia
to allow the patient to actively flex the digits and to confirm
adequate release of all adhesions tethering the tendon.
• If tenolysis fail, it may become necessary to remove the
repaired tendon and replace this with a tendon graft.

43. Tendon Grafting

44. History
• Tendon transplantation was reported as early as 1904 in the
California State Journal of Medicine, in which Hunkin
reported the transplantation of the semitendinosus part of the
biceps to restore a boy’s leg function.
• In 1905 and 1910, Lange and Kurtz respectively reported
tendon graft transplantation.
• In the 1920s, Tuner, Simmonds, and Evans also reported cases
of tendon transplantations.
• Tendon graft may primarily be used in hand surgery to repair
flexor profundus injury, extensor pollicis longus tendon
rupture.
• when there is an unsuitable bed for tendon grafting, a two-
stage tendon grafting procedure is necessary. This technique
was first described by Carroll and Bassett and Hunter.

45. INDICATIONS
• Single-staged tendon grafts should be used if tendon ends
cannot be approximated.
.
Single-staged tendon grafts

46. REQUIREMENTS FOR TENDON
GRAFTING
• Before tendon grafting, there must
be complete wound healing, with
adequate soft tissue coverage.
• There must be an absence of
edema and induration.
• The skeletal alignment must be
satisfactory and stable, and
optimally, there should be full
range of passive motion of the
joint.
Contraindications for grafting
• An bsence of any of these
elements,
• Adherent extensor tendons,
• Planned capsulotomy for stiff
joints,
• Need for pulley reconstruction

47. To achieve success in tendon grafting, Pulvertaft
listed the following requirements:
• Mobile digit with minimal scarring and at least one digital
nerve intact;
• Meticulous surgical technique;
• Cooperative patient;
• Careful, graduated mobilization.

48. TWO-STAGED TENDON GRAFTING
• Severely scarred wound beds, as in digits with bone exposure.
• Simultaneous fracture fixation and when flexor and extensor
tendons must be repaired.
• An injured tendon bed that might provide poor nutrition to a
tendon graft
• Joint stiffness, when capsulotomy is planned,
• where local finger flaps are needed to provide soft tissue
coverage in severe crushing injuries.
• Two-staged tendon grafts may be indicated in failed zone II
flexor tendon repairs.
Indications

49. Timing Considerations for Two-Staged Tendon
Graft
• The initial stage consists of removal of scarred tissue; reconstruction
of key pulleys; repair of digital nerve; and then placement of a
pliable tendon rod, composed of a woven Dacron spacer that is
encased in silicone, within the tendon pulleys.
• After a minimum period of 3 months, a pseudosheath will have
formed around the silicone rod as a foreign body reaction, providing
a surface for the future autologous tendon graft to glide on.
• As the temporary rod is removed, the ultimate goal in two-staged
tendon grafting is survival of the tendon graft within the
pseudosheath before vascular adhesions are formed.
• Tendon grafts are not mobilized until 3 weeks postoperatively, after
the transplanted tendon has obtained sufficient vascularity from its
bed.

50. DONOR SITES FOR TENDON GRAFTS
• Potential tendon donors should have adequate length, be in a
superficial location for ease of harvest, have little or no functional
loss, and be thin enough to become revascularized yet strong enough
to move the digit.
• In order of preference,potential tendon donors are the following:
Palmaris longus
Plantaris
Extensor digitorum longus
Extensor indicis proprius
Flexor digitorum superficialis
Spare parts Tendon graft harvested from an
irreparably injured structure.

51. • Palmaris longus
Advantage: easy access, no functional
loss, and good caliber for digital flexors.
Disadvantage: may be absent in 10% and
may be too short for fingertip to wrist
grafts.

52. • Plantaris
Advantage: long tendon, with no
functional loss; easily braided if a
thicker graft is required.
Disadvantage: requires a second
operative site, and there is no test
to determine its presence
beforehand. It may be missing in
20% of cases, and if it is not
present on one side, only one in
three will have a plantaris tendon
on the other side .

53. • Extensor digitorum longus
Advantage: reliable source of graft from the second, third, and
fourth toes and may provide a long, many-tailed graft without
injury to epitenon.
Disadvantage: possible flexion deformity of the toes.

54. • Extensor indicis proprius
Advantage: within the same
operative field.
Disadvantage: short length; may
lead to a small extensor lag.

55. • Flexor digitorum superficialis Not
really recommended; harvest may
cause proximal interphalangeal
joint hyperextension and may
decrease flexion power.
• Spare parts Tendon graft
harvested from an irreparably
injured structure.

56. RESULTS OF TENDON GRAFT
• Kraemer et al, in a review of 220 consecutive grafts, reported
an incidence of 1.1% tendon graft disruption for one-staged
tendon grafts compared with an incidence of 7.6% graft
disruption in two staged tendon grafts.
• One incredible report described the complication of
transplantation of the median nerve as a tendon graft in four
cases. This serves as a somber reminder of the importance of
careful identification of nerve during dissection and clinical
determination of the presence or absence of the palmaris
longus tendon preoperatively.

57. Tendon substitute and
engineered tendon

58. • None of the available autologous tendon grafts is able to meet
all the requirements of an ideal tendon graft.It is almost not
possible completely to avoid functional disturbance to the
donor area where a tendon graft is harvested
• This becomes a major concern when large quantities of
autologous tendon grafts are needed to repair severe tendon
injury and defect. Therefore it has been a challenge in plastic
surgery for long time. To address this concern, several
strategies have been proposed and developed.

59. OPTIONS
• Tendon allograft
• Artificial tendon
• Tissue engineering

60. Tendon allograft
• Liu reported the use of refrigerated flexor tendon graft for
second-stage tendon graft and the results showed 63% had
good flexion, 21% fair, and 16% poor; and 8% had good total
active motion, 71% fair, and 21% poor.
• It was concluded that allograft could be applied for tendon
repair but was inferior to autograft.

61. Artificial tendon
• Nondegraded materials to substitute tendon tissue.
• The difficulty in healing between host tissue and artificial
tendon, fibrotic tissue formation, and the fatigue of implanted
materials remain the challenges to functional repair.

62. Tissue engineering
• It is able to generate autologous graft without causing donor
site morbidity.The two key factors in tendon engineering are
scaffold materials and seed cells.
• Regarding seed cells, tenocytes,dermal fibroblasts, and bone
marrow stem cells (BMSC) have become the candidates for
tendon engineering.

63. Tissue Engineering Strategies for
Tendon and Ligament Regeneration
 Tissue Engineering and Regeneration
 Cell-Based Strategies for Tendon and
Ligament Tissues
 Design and Fabrication of 3D Sophisticated
Scaffolds
 Electrospinning
Electrochemical Alignment Technique

64. Tissue Engineering and Regeneration
• Tissue engineering and regenerative medicine proposes
alternative approaches combining living agents, the cells, with
3D structures to mimic the biophysical and chemical cues of
native extracellular matrix, and/or bioactive molecules to
biochemically stimulate cells and the tissue milieu, to meet the
demanding requirements of tissue regeneration.

65. Cell-Based Strategies for Tendon and Ligament Tissues
• Tendon and ligament resident cells are an obvious choice since these
cells are harvested from the target tissue and an eventual level of
epigenetic memory could match the desired cell response to meet
regeneration in damaged tendons or ligaments.
• In 2007 Bi and co-workers discovered a tendon stem/progenitor cell
population with functionally attractive features including universal
stem cell characteristics such as clonogenicity, multipotency and self-
renewal capacity, and with the capability to generate a tendon-like
tissue after in vitro expansion and in vivo transplantation .

66. • Pluripotent embryonic stem cells (ESCs) are an alternative
source to tendon cells, whose potential for the treatment of
tendon injuries has been demonstrated in a patellar defect of a
rat model , resulting in improved mechanical and structural
properties without teratoma formation
• Induced pluripotent stem cells (iPSCs) technology also
presents value for tendon and ligament regeneration, as iPSCs
can be reprogrammed into a wide range of cell.

67. Design and Fabrication of 3D Sophisticated
Scaffolds
• A key challenge in tendon and ligament TE is exactly
the recreation of 3D scaffolding biomaterials that can
mimic this unique architecture and support tissue
regeneration while remaining mechanically competent
• 3D structures that would recreate tendon
microenvironment with specific topographical and
biophysical cues such as the substrate geometry and
topography of fiber based scaffolds.
• The incorporation of growth factors (GFs) and other
bioactive molecules within a 3D scaffold can also
improve the biofunctionality of the system.

68. Ideal tendon scaffold :
1. Biodegradability with adjustable degradation rate
2. Biocompatibility before, during, and after degradation
3. Superior mechanical properties and maintenance of
mechanical strength during the tissue regeneration process
4. Biofunctionality: the ability to support cell proliferation and
differentiation, extracellular matrix secretion, and tissue
formation
5. Processability: the ability to be processed to form desired
constructs of complicated structures and shapes, such as
woven or knitted scaffolds.

69. • Major categories of scaffold materials for tendon engineering
include:
- poly (α-hydroxy acids),
- collagen derivatives,
- acellular tendon,
- xenogenic acellular extracelluar matrix,
- silk derivatives, and
- polysaccharides.

71. Electrospinning
• Electrospinning produces long continuous fibers with
controlled diameter from nanometers to microns.
• The advantage of electrospinning is it produce fibrilar systems
better mimic the nanoscale morphological structure of tendon
and ligament ECM, in order to provide the topographical cues
and promote cells contact guidance, increasing the potential
for regeneration
• This technique also enables the production of fibers from
different polymers including those from natural origin, such as
collagen, chitosan, hyaluronic acid and silk fibroin; or
synthetic, for example poly(e-caprolactone) (PCL),
poly(glycolide) (PLGA), poly(L-lactide) (PLA).

73. Electrochemical Alignment Technique
• Producing anisotropically aligned collagen bundles through a
process based on the pH gradient created between two parallel
electrodes .
• This strategy was firstly proposed for TE of connective tissues
by Akkus group , that have been developing this technique,
culminating in a recent proposed system for the production of
continuous electrochemically aligned collagen (ELAC) threads

74. A Schematic of the rotating electrode electrochemical alignment device

75. Future
• Functional repair of massive tendon tissue defect remains a challenge in
plastic surgery not because of surgical technique, but rather due to the lack
of autologous tendon graft.
• As reported in the literature, current experiments demonstrate the
possibility of generating autologous tendon graft via a tissue-engineering
approach.
• One future direction is to employ a proper bioreactor system with dynamic
mechanical loading to generate engineered autologous tendon graft and
therefore to enhance matrix production and maturation of in vitro-
engineered tendon tissues.
• In addition, design of a proper scaffold material with enhanced mechanical
strength would also help to provide an engineered tendon graft that is
strong enough for functional requirements after in vivo implantation.
• The other potential direction is to employ acellular allogenic/xenogenic
tendon tissue to reconstitute tendon graft given that new methods can be
applied to facilitate cell penetration

76. T H A N K YOU