Anterior cruciate ligament reconstruction: a look at prosthetics - past, present and possible future

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2322926/

Abstract

• "history of the use of prosthetics"
• "Carbon Fibre, Gore-Tex and Darcon prosthetics... Leeds-Keio Artificial Ligament and the Kennedy Ligament Augmentation Device (LAD)"

Introduction

• "(ACL) is the most
  frequently injured ligament in the knee"
• "poor intrinsic healing ability"
• surgical reconstruction
• "patients who experience ACL injuries
  are significantly younger and more active than those
  who experience many other orthopaedic injuries. The
  need for reconstruction options that exhibit longevity"
• primary repairs- fail
• prosthetic replacements- inadequate
• biological tissue autograft- popular
• "ACL anatomy, tissue
  composition, biomechanics, and the healing processes.
  Unfortunately, to date, no prosthesis has proven itself as
  a viable alternative to the patellar or hamstring tendon
  autografts, currently used in over 90% of ACL
  reconstructions."

Surgical Repair

• "Bone-patellar tendon-bone (BPTB) and
  semitendinosus/gracilis tendon autografts are currently
  the most common grafts"
• "Both techniques
  now offer a high degree of strength and stiffness in the
  reconstructed ligament."
• PROBLEMS W. PATELLA AND HAMSTRING GRAFT- "Nonetheless, with patellar tendon
  autografts, many patients experience impaired function
  and significant morbidity at the donor site including
  secondary anterior knee pain, patellar tendonitis,
  infrapatellar contracture, and patellar fracture.
  Likewise, hamstring weakness and saphenous nerve
  injury can be seen secondary to hamstring harvest in
  semitendinosus/gracilis autograft ACL reconstruction"
• PROBLEMS W. DONOR(CADAVER) ACLS- "the use of
  allografts is not currently considered advantageous due
  to a limited donor tissue supply, delayed biological
  incorporation, risks of disease transmission and tissue
  rejection."

Prosthetics

• history of ACL grafts- 1918 silk sutures fail 3 months
• 1973 PTFE break 1 year
• GRAFTS- "Grafts
  (polyethylene, PTFE), typically fixed at both ends, were
  the initial focus of synthetic ACL replacement and were
  meant to provide stability to the ACL-deficient-knee
  until secondary reconstruction procedures gained
  popularity (11)."
• lig. augmentation- "Similarly, ligament augmentation
  devices (polypropylene, polyester) were intended to
  provide immediate protection for autogenous tissue
  grafts until revascularization was complete and the
  ingrown tissue was capable of withstanding local tensile
  and compressive forces."
• total prosthesis
• no tissue maturation
• long-term -> poor
• scaffold design
• problems- "Problems associated with the biological
  incorporation of scaffolds include variability of tissue
  in-growth, immature degeneration of the implant and
  insufficient maturation of the host tissue resulting in an
  inability of the scaffold to withstand inherent
  mechanical stresses placed on the ACL."

Carbon Fiber

• carbon fibre prostheses
• 1977
• "migration of carbon wear particles into
  the joint space and regional lymph nodes following
  implantation of the prosthesis"
• coat carbon to solve
• "Surgicraft ABC prosthetic ACL"
• "only 11 of 31 knees (41%) had good results
  defined as a Lysholm score greater than 76."
• ADVANTAGE DISADVANTAGE TABLE ON P. 31!!!!

Gore Tex

• "The Gore-Tex ligament prosthesis is composed of a
  single long fiber of expanded polytetrafluoroethylene
  (PTFE) arranged into loops. Extensive mechanical
  testing has shown that the resulting ultimate tensile
  strength is about 3 times that of the human ACL and the
  results from cyclical creep tests and bending fatigue
  testing seem to identify Gore-Tex as the strongest
  synthetic ACL replacement in terms of pure material
  stability"
• deteriorates over time
• decreasing success rate over years
• "90% success rate at 2 years
  versus only a 76% success rate at 3 years or more"
• "The Gore-Tex ACL prosthesis is currently FDA
  approved for use in patients who have had a failed
  autogenous intra-articular graft procedure."

Dacron

• "The implant is a
  composite of four tightly woven polyester strips
  wrapped in a sheath of loosely woven velour, designed
  to minimize abrasion of the graft and act as a scaffold
  for fibrous tissue ingrowth."
• failure rate- 31.7% in 50 months
• failure rate- 47.5% in 4 years
• deterioration
• NOT VIABLE

Leeds-Keio Artificial Ligament

• "a polyester meshlike
  structure anchored to the femur and tibia with bone
  plugs (24)"
• "The implant was considered
  sufficiently flexible to be effective with a maximal
  tensile strength of approximately 2100 Newtons (N),
  which significantly exceeds that of the average young
  adults’ natural ACL (about 1730 N)"
• ingrowth of unaligned fibrous tissue
• long-term show deterioration
• NOT VIABLE

Kennedy Ligament Augmentation

• "The graft,
  composed of a band-like braid of polypropylene, was
  originally developed to reinforce the area of pre-patellar
  tissue considered to be a weak area of autogenous
  patellar tendon grafts."
• "Comparisons of the patellar tendon and
  semitendinosus/gracilis LAD composite grafts revealed
  that the LAD will accept approximately 28% and 45%
  of the applied load, respectively (31)."
• attached to bone at one end only
• collagen fibers
• "Furthermore, as an intra-articular foreign body, the
  LAD has been reported to induce an inflammatory
  response characterized by foreign body giant cells and
  macrophages in the surrounding tissue."
• LACK OF WIDESPREAD USE- NOT GOOD

LARS artificial ligament

• "The Ligament Advanced Reinforcement System
  (LARS) (Arc-sur-Tille, France) artificial ligament
  consists of fibres made of polyethylene terephthalate
  (PET)."
• knitted structure
• fibers twisted at right angles (90 degrees)
• mimic natural lig. structure
• encourage tissue ingrowth b/c of porosity
• "Thirty-eight
  of forty-seven patients suffered from chronic
  ruptures of the ACL, while nine others presented with
  acute or subacute ruptures at a mean follow-up of 21.9
  months. Six patients had previously had an
  unsuccessful ACL reconstruction."
• Scales to test knees- Tenger activity scale, telos radioactive stress system
• "no patients returned to pre-injury activity levels"
• chronic instability
• Lysholm score
• RISK OF RUPTURE

Tissue Eng.

• "Permanent synthetic prostheses are capable of
  duplicating the mechanical and structural properties of
  the ACL. However, they generally tend to lose strength
  with time. Tissue-based or tissue-aided implants offer
  the additional possibility of the restoration of normal
  joint kinematics while the mechanical behaviour of
  these implants is expected to improve over time as tissues are remodelled within the knee"
• "must also degrade at a rate similar to that
  of tissue ingrowth. Accordingly, the ACL scaffold
  should lose its mechanical integrity while allowing the
  remodelled tissues to gain strength and accept an
  increasing amount of the mechanical demands placed
  on the ACL. Current research into this novel tissueengineering
  approach has focused on seeding either
  collagen-based scaffolds or synthetic biodegradable
  polymers with a variety of different cell types."
• "rabbit fibroblasts on skin and ACL scaffolds"
• "As an alternative to the scaffolds made of nondegradable
  polymers, investigators have begun to
  examine biodegradable materials that would provide
  immediate stabilization to the repaired ligament but
  would also act as a scaffold for the ingrowth and/or
  replacement by host cells. Cao et al. described the
  generation of neo-tendons in a nude mice model by
  implanting polyglycolic acid (PGA) scaffolds seeded
  with bovine tendon fibroblasts in the subcutaneous
  space of athymic mice"
• PGA scaffolds
• bone marrow stomal cells
• "The future of tissue engineering may also require a
  significant contribution from cell-specific growth
  factors influencing the maturation and homeostasis of
  the healing response of ligament tissue."
• "the optimal activity of each growth factor"

Computer-Assisted ACL Reconst.

• "computer-assisted surgery in an attempt
  to reduce the incidence of graft failure"
• "the use of computer-assisted
  ACL reconstruction may lead to similarly dramatic
  improvements in technical and functional outcomes"

CONCLUSION

• past 30 years
• "Most of the grafts that have been
  developed to date have failed due to unsatisfactory
  long-term physiologic and functional performance.
  Most permanent ACL prostheses are prone to creep,
  fatigue, and mechanical failure within several years
  after implantation (40). Tissue ingrowth scaffolds and
  ligament augmentation devices require further
  refinement to provide effective mechanical support
  while avoiding stress-shielding of the host tissue. In
  view of these factors, prosthetics are not widely used
  today in ACL reconstruction, and autogenous tissue
  grafts remain the gold standard used by the majority of
  surgeons."
• FUTURE- "Advances in
  tissue engineering combined with developments in
  molecular biology and gene therapy may couple with
  the rapid gains in computer-assisted surgery to provide
  improved options for the ACL-deficient knee, with a
  greater potential to restore its pre-injury state."