Anterior cruciate ligament reconstruction
Anterior cruciate ligament reconstruction is a surgical tissue graft replacement of the anterior cruciate ligament, located in the knee, to restore its function after an injury. The torn ligament can either be removed from the knee, or preserved before reconstruction through an arthroscopic procedure.
Background
The Anterior Cruciate Ligament is the ligament that keeps the knee stable. Anterior Cruciate Ligament damage is a very common injury, especially among athletes. Anterior Cruciate Ligament Reconstruction surgery is a common intervention. 1 in every 3,000 American ruptures their ACL and between 100,000 and 300,000 reconstruction surgeries will be performed each year in the United States. Around $500 million health care dollar will come from ACL injuries. ACL injuries can be categorized into groups- contact and non-contact based on the nature of the injury Contact injuries occur when a person or object come into contact with the knee causing the ligament to tear. However, non-contact tears typically occur during the following movements: decelerating, cutting, or landing from a jump. ACL injury is 4-6 times higher in females than in males. ACL injuries account for a quarter of all knee injuries in the high school population. An increased Q angle and hormonal differences are a few causes of the gender disparity in ACL tear rates.Types of grafts
Graft options for ACL reconstruction include:- Autografts.
- Allografts.
- Bridge-enhanced ACL repair.
- Synthetic tissue for ACL reconstruction has also been developed, but little data exists on its strength and reliability.
Autograft
Because the tissue used in an autograft is the patient's own, the risk of rejection is minimal. The retear rate in young, active individuals has been shown to be lower when using autograft as compared to allograft.
No fully ideal autograft site for ACL reconstruction exists. Surgeons have historically regarded patellar tendon grafts as the "gold standard" for knee stability.
Hamstring autografts have failed at a higher rate than bone-tendon-bone autografts, after short- to mid-term followup of primary ACL reconstruction. However, the observed difference in failure rates is small enough that both are still regarded as viable options for primary ACL reconstruction.
Hamstring grafts historically had problems with fixation slippage and stretching out over time. Modern fixation methods avoid graft slippage and produce similarly stable outcomes with easier rehabilitation, less anterior knee pain and less joint stiffness.
The quadriceps tendon, while historically reserved for revision reconstructions, has enjoyed a renewed focus as a versatile and durable graft for primary reconstructions. Use of the quadriceps tendon usually does not result in the same degree of anterior knee pain postoperatively, and quadriceps tendon harvest produces a reliably thick, robust graft. The quadriceps tendon has approximately 20% greater collagen per cross-sectional area than the patellar tendon, and a greater diameter of usable soft tissue is available.
Hamstring tendon
Hamstring autografts are made with the semitendinosus tendon, either alone or accompanied by the gracilis tendon for a stronger graft. The semitendinosus is an accessory hamstring, and the gracilis is not a hamstring, but an accessory adductor. The two tendons are commonly combined and referred to as a four-strand hamstring graft, made by a long piece removed from each tendon. The tendon segments are folded and braided together to form a tendon of quadruple thickness for the graft. The braided segment is threaded through the heads of the tibia and femur, and its ends are fixed with screws on the opposite sides of the two bones.Unlike the patellar ligament, the hamstring tendon's fixation to the bone can be affected by motion after surgery. Therefore, a brace is often used to immobilize the knee for one to two weeks. Evidence suggests that the hamstring tendon graft does as well, or nearly as well, as the patellar ligament graft in the long term. A Cochrane review in 2011 found insufficient evidence to suggest whether a hamstring versus patellar ligament graft was superior. It found that individuals receiving hamstring autografts had reduced flexion range of motion and strength. Common problems during recovery include strengthening of the quadriceps, IT-band, and calf muscles.
The main surgical wound is over the upper proximal tibia, which prevents the typical pain experienced when kneeling after surgery. The wound is typically smaller than that of a patellar ligament graft, and so causes less post-operative pain. Another option first described by Kodkani et al in 2004, a minimally invasive technique for harvesting from the back of the knee, is faster, produces a significantly smaller wound, avoids the complications of graft harvesting from the anterior incision, and decreases the risk of nerve injury. Saphenous Nerve Injury prevention during Hamstring tendon harvesting is achieved primarily through careful incision planning and meticulous surgical technique. Oblique or modified oblique skin incisions are preferred over vertical or transverse incisions to minimize the risk of injuring the infrapatellar branch of the saphenous nerve. Limited soft-tissue dissection and delicate handling of the subcutaneous layer are essential to preserve small sensory branches. Direct visualization and protection of the nerve may be performed when its course is identifiable. The use of posterior or popliteal incisions, as well as minimally invasive or endoscopic harvesting techniques, has been shown to further decrease the incidence of iatrogenic nerve damage.
There is some controversy as to how well a hamstring tendon regenerates after the harvesting. Most studies suggest that the tendon can be regenerated at least partially, though it will still be weaker than the original tendon.
Advantages of hamstring grafts include their high "load to failure" strength, the stiffness of the graft, and the low postoperative morbidity. The natural ACL can withstand a load of up to 2,160 newtons. With a hamstring graft, this number doubles, decreasing the risk of re-injury. The stiffness of a hamstring graft—quadruple that of the natural ACL —also reduces the risk of re-injury.
Patellar tendon
The patellar tendon connects the patella to the tibia. The graft is normally taken from the injured knee, but in some circumstances, such as a second operation, the other knee may be used. The middle third of the tendon is used, with bone fragments removed on each end. The graft is then threaded through holes drilled in the tibia and femur, and screwed into place. It is slightly larger than a hamstring graft.A 2011 Cochrane review, found no significant difference in long term outcome between patellar and hamstring autografts. Those receiving patellar autografts had improved static stability but a loss of extension range of motion and strength.
Disadvantages compared with a hamstring graft include:
- Increased wound pain
- Increased scar formation
- Risk of fracturing the patella during harvesting of the graft
- Increased risk of tendinitis.
- Increased pain levels, even years after surgery, with activities that require kneeling.
The rehabilitation after the surgery is different for each knee. The beginning rehab for the ACL graft knee is focused on reducing swelling, gaining full range of motion, and stimulating the leg muscles. The goal for the graft donor need is to immediately start high repetition strength training exercises.
Allograft
The patellar ligament, tibialis anterior tendon, or Achilles tendon may be recovered from a cadaver and used in ACL reconstruction. The Achilles tendon, because of its large size, must be shaved to fit within the joint cavity.Although there is less experience with the use of tibialis anterior grafts, preliminary data has shown no difference in short-term subjective outcomes between tibialis anterior allografts and patellar tendon allografts.
Bridge Enhanced ACL Restoration (BEAR Implant)
A new approach to treating ACL tears was developed at Boston Children's Hospital and is currently in clinical trials. The Bridge Enhanced ACL Restoration implant is a bio-engineered bridging implant made from cow extracellular matrix scaffold. It is injected with a small amount of patient's own blood, which turns the scaffold into a flexible material. The combination of blood and collagen is able to stimulate healing and reconnection of the ACL.To install the scaffold, tunnels are drilled into the tibia and femur. The scaffold is placed at the femur end of the ligament. A few nonadsorbable sutures go through the femoral tunnel and then the scaffold to end up anchored the tibial tunnel. A few adsorbable sutures goes through the same femoral tunnel and then the scaffold to become attached to the tibial stump of the broken ACL. Blood is then added to the scaffold to make it flexible. The adsorbable wires are then pulled up, so that the stump comes into tight contact with the scaffold. This will allow the stump to regrow into a full ACL.
Results from the first-in-human study published in March 2019 in the Orthopedic Journal of Sports Medicine showed the 10 patients who received the BEAR implant had similar clinical, functional and patient-reported outcomes as the 10 patients undergoing autograft ACL reconstruction. Additional clinical studies are underway. In a study by the American Journal of Sports Medicine, they looked at a young and active population two years post surgery using the BEAR technique. The results showed that the BEAR technique was non-inferior to the autograft ACLR, and that it can also show an improvement in hamstring muscle strength at a two year follow up.