ACL reconstructionGraft Selection

Graft Selection• Autograft tissue is used most commonly• but allografts and synthetics also are available

• Autografts • advantages

– low risk of adverse inflammatory reaction– virtually no risk of disease transmission.– As a biological graft, an autograft undergoes revascularization

and recollagenization• but initially a 50% loss of graft strength occurs after implantation• Therefore, it is desirable to begin with a graft stronger than the tissue

to bereplaced

• Virtually every structure around the knee has been used as a substitute

• The most common current graft choices– bone–patellar tendon–bone graft – the quadrupled hamstring tendon graft.

• The bone–patellar tendon–bone graft – an 8- to 11-mm-wide graft– taken from the central third of the patellar tendon– with its adjacent patella and tibial bone blocks– High ultimate tensile load (approximately 2300 N)– its stiffness (approximately 620 N/mm)– the possibility for rigid fixation with its attached bony ends.

the hamstring tendon graft • increased in recent years because of its relatively low donor site morbidity.• single strand of the semitendinosus or gracilis tendon is inadequate

– because the semitendinosus tendon has only 75% and the gracilis tendon only 49% the strength of the anterior cruciate ligament

• A triple- or quadruple-stranded semitendinosus graft • A quadruple-stranded semitendinosus-gracilis tendon graft with both ends

folded in half and combined– an ultimate tensile load reported to be as high as 4108 N.– provides a multiplebundle replacement graft that may better approximate the

function of the two-bundle ACL

• Disadvantages– the concern over tendon healing within the osseous tunnels– the lack of rigid bony fixation.

The quadriceps tendon graft • attracted interest recently.• harvested with a portion of patellar bone or

entirely as a soft tissue graft• the ultimate tensile load of this graft to be as

high as 2352 N. • an alternative replacement graft, especially for

revision ACL surgeries and for knees with multiple ligament injuries.

Comparison of BPTB graft or a quadrupled hamstring graft

• Slight increased laxity on arthrometer testing was reported in the hamstring group

• pain with kneeling was greater for the patellar tendon group • only one of nine studies showed increased anterior knee pain in the

patellar tendon group. • Frequency of additional surgery seemed to be related to the fixation

method and not the graft type. • No study reported a significant difference in graft failure between

patellar tendon and hamstring tendon autografts; – graft failure rates for the combined populations of the nine studies were 3.1%

for patellar tendon grafts and 4.1% for hamstring grafts.• Objective differences (range of motion, isokinetic strength, arthrometer

testing) were not detected between groups in most of the studies,– suggesting that their sensitivity to detect clinical outcomes may be limited.

Comparison of BPTB graft or a quadrupled hamstring graft

• Using ultrasonographic and power Doppler evaluation, Jarvela et al.

studied the morphologic changes in the patellar tendon of 31 patients 10 years after harvest of its central third and closure of the defect.– They found intratendinous calcification in nine patients, hypoechoic lesions in 20

patients, a hyperechoic lesion in one patient, and peritendinous changes in one patient. Only three of the 31 patients had no changes in the harvested patellar tendon.

– In most patients, the harvested patellar tendon was significantly thicker than the contralateral tendon.

• Harvest of the hamstring tendons has raised concerns about potential weakness of knee flexion.– Most studies have reported no significant difference in hamstring muscle torque

between the surgical extremity and the control extremity at 2 years after surgery, possibly because of regeneration of these tendons, as shown in MRI studies by Rispoli et al.

– However, Tashiro et al. reported significant weakness of hamstring muscle strength with both isokinetic and isometric measurements when subjects’ knees were at positions of 70 degrees or more of flexion.

SYNTHETIC MATERIALS FOR LIGAMENT RECONSTRUCTION

• disappointing early clinical results.

• theoretical advantages • no autogenous tissues are sacrificed• the increased morbidity associated with the harvest of autogenous tissues is

avoided• If autogenous tissues have been used in a failed reconstruction• if they are unacceptable, the use of a readily available synthetic device is appealing. • a simpler and easier reconstructive technique (frequently arthroscopic)• allow a more rapid rehabilitation because they do not become weak during tissue

revascularization and reorganization. • Although there has been a rapid development of new materials and surgical

techniques for artificial ligament implantation, the long-term effects of these devices are not yet known.

• Artificial ligaments function in one of three ways: • (1) as a prosthetic ligament, that is, the prosthesis is implanted as a

permanent replacement for the normal ligament• (2) as a stent temporarily protecting or augmenting an autogenous graft• (3) as a scaffold providing support for and stimulating the ingrowth of

collagen tissue.

• No long-term studies of the artificial ligaments currently used support their routine use.

• At present, it is prudent to use them cautiously and to reserve them for salvage procedures when autogenous grafting and reconstructive procedures have failed

ALLOGRAFT LIGAMENT REPLACEMENT

• The ideal ligament replacement should be readily available;

• It should be of sufficient length and diameter;• it should have biomechanical properties

similar to the ligament it replaces;• it should not disturb normal structures; • it should retain or develop a vascular supply.

ALLOGRAFT LIGAMENT REPLACEMENT

• Although autogenous tissues currently are the most commonly used grafts for reconstruction of the cruciate ligament

• disadvantages of these techniques:1. these transfers sacrifice a normal musculotendinous

structure in an already deficient knee2. adding to the functional disturbance3. Extensive surgical exposure4. long tourniquet times5. prolonged rehabilitation

ALLOGRAFT LIGAMENT REPLACEMENT

• Autografts and allografts both go through four stages after transplantation:

• necrosis, revascularization, cellular proliferation, and remodeling.

• After incorporation, however, neither autograft nor allograft tendons have been demonstrated to return to their original strength 30% to 40% ultimate load strengths.

• most surgeons prefer to use grafts or combinations of grafts that begin with more than 100% of ACL strength, which should result in sufficient strength after incorporation

• Minami et al. studied collagen allografts after various treatment regimens both in vivo and in vitro. They found no evidence of cytotoxicity, no histological signs of rejection, and no activity with antisera from collagen allografts pretreated by freezing and thawing.

• They also showed that the immunoreactivity of the allograft depended solely on the cellular component of the graft;

• they concluded that the freezing and thawing treatment effectively neutralized the immunological antigens by killing the tendon cells.

• Sterilization and preservation techniques have been shown to affect immunological response.– Freeze-drying reduces the response more than fresh freezing does, – Although cryopreservation techniques that preserve cellularity still evoke an

immunological response. – This seems to support the hypothesis that immune response is directed toward the

cellular components within allografts rather than to the antigens of the collagen scaffold.

• elevated antibody titers predominantly in the joint

• This finding raises concern for the potential for graft-versus-host reactions, which may account for the relative delay in the incorporation of allografts compared with autografts.

• The cited advantages of allografts over autografts

• No donor site morbidity• shorter operative times• smaller incisions• greater availability—have been somewhat

• the risk of disease transmission• reports of serious infection associated with allografts heightening these concerns.• transmission of hepatitis or AIDS.• Lochemes et al. demonstrated active viral replication in cells infected with HIV 1

after exposure to 2.5 Mrad of gamma irradiation, the maximal dosage that can be used without destroying the clinical usefulness of the allograft.

• Even though the donor may not demonstrate detectable antibodies to these viruses, a certain “window of vulnerability” exists between the time the patient may have contracted the virus and the production of measurable antibodies, which may be as long as several months.

• Emerging pathogens– West Nile virus, severe acute respiratory syndrome (SARS), coronavirus and prion

disease, also have become a concern in the use of allografts.• The risks of disease transmission are small, however, when the allograft is

obtained with sterile technique and disinfection and secondary sterilization procedures are carried out

• STERILIZATION OF THE GRAFT• ethylene oxide has been questioned

– because of the residual of ethylene glycol remaining in the sterilized tissues, which has been cited as a cause of some sterile effusions in late failures.

• Freeze-drying of the allograft does not appear to significantly alter the mechanical properties compared with deep-freezing, but clinical reports reveal frequent late failures of freeze-dried allograft tissues.

• Gamma irradiation of the allografts with up to 2 Mrad has been shown not to significantly affect the initial mechanical properties of the allograft tissue, but effects are significant after use of 3 Mrad.

• Electron-beam radiation has been used for sterilization of soft tissue grafts because of its lower penetrability compared with gamma irradiation and higher processing speed—seconds, compared with hours for gamma irradiation.

• Currently, the most commonly used method of sterilization probably is a combination of lower doses of irradiation (1 to 3.5 Mrad) and other processing techniques, such as antibiotic soaks

autograft Vs. allograft ?• remains a matter of controversy.• A systematic review of the literature that included 31 studies found that the percentage

of patients receiving a final IKDC score of “A” (normal knee) was statistically higher for allografts (44%) than for autografts (28%);

• however, the graft failure rate was 8.2 per 100 reconstructions for allograft compared with 4.7 for autografts,

• a slightly higher complication rate for allografts. • The authors concluded that, from currently available data, the graft source has a

minimal effect on the outcomes of ACL reconstruction.• Although a number of reports have documented good results with allograft

reconstructions, worse outcomes have been reported with the use of anterior tibial tendon allografts in young, active patients.

• Singhal et al. reported an overall reoperation rate of 38% after primary anterior cruciate ligament reconstruction with anterior tibial tendon allografts in 125 young patients (≤25 years of age); the failure rate in patients younger than 25 years was 55% compared with 24% in those older than 25 years.