Thursday, November 30, 2023
The anterior cruciate ligament (ACL) tear is one of the most common injuries seen by orthopaedic surgeons. Over 100,000 ACL reconstructions are performed annually in the United States.[1] The autologous bone-patellar tendon-bone autograft has long been the graft of choice for reconstruction of the ligament. It has higher tensile load and stiffness (2977 N and 620 N/mm, respectively) compared with the native ACL (2160 N and 242 N/mm, respectively).[2] This graft has enjoyed a 30-year track record for stabilizing an ACL-deficient knee. It has some limitations in regard to donor-site morbidity, including patella fracture, postoperative patella baja, and persistent anterior knee pain or kneeling pain. Hamstring tendon grafts have recently gained increasing popularity, due to reduced harvest morbidity and improved soft tissue fixation techniques. Several recent studies in the literature report equal results to bone-patellar tendon-bone ACL reconstruction with respect to functional outcome and patient satisfaction.[3] However, many studies also report a higher degree of instrumented laxity (KT-1000) for hamstring reconstruction. There seems to be no correlation between the objectively measured laxity tests with the subjectively assessed outcomes and ability to return to high levels of competitive sports.
The use of allografts for primary ACL reconstruction has increased steadily over the past decade, and the demand is expected to increase. Allografts eliminate the disadvantages associated with autografts, including the perioperative pain and graft-site morbidity associated with harvesting a graft. During the 1990s, allograft use decreased in popularity. This was due mostly to reports of graft failure from re-tears and "stretching out" of the graft, which was attributed to poor fixation techniques and also to the high-dose gamma radiation required to sterilize allografts. The high-dose radiation leads to weakening of the graft as a result of denaturing the structural properties of the graft. In addition, the demand for allograft tissue far exceeded the supply. Most surgeons used bone-patellar tendon-bone allograft, which was very limited in supply. Recently, there has been a resurgence of allograft use due to improved fixation techniques, better sterilization processes, and new graft sources (tibialis anterior, Achilles tendon) leading to increased availability. In addition, use of allograft tissue decreases surgical time and can be prepared by the surgeon prior to the patient's arrival into the operating room.
The drawback to using allografts is the potential risk for disease transmission and cost. A minimum of 3.5 Mrad (35 kGy) of gammairradiation is needed to completely destroy the DNA of HIV.[4] Initially, allografts were being irradiated by 5 Mrad (50 kGy) ("high dose radiation") which led to high failure rates. Currently,the average dose of irradiation used in the United States rangesfrom 1 to 2.5 Mrad (10-25 kGy) ("low-dose radiation").[4] Some tissue banks do not use radiation at all but process grafts aseptically or via other proprietary chemical solutions. When comparing research studies, it is important to pay close attention to how the allografts were processed and sterilized.
The cost of allograft tissue has been a concern in the past. A recent article by Cole and colleagues[5] compared the costs associated with ACL reconstruction using either autograft or allograft. Patients underwent reconstruction using either bone-patellar tendon-bone autograft or freeze-dried Achilles tendon allograft. The hospital charge for ACL reconstruction was $4622 for allograft and $5694 for autograft (P < .0001). Allograft reconstruction of the ACL was significantly less expensive than autograft bone-patellar tendon-bone reconstruction. The difference in the cost was due to increased operating room time and a greater likelihood for overnight hospitalization in patients undergoing autograft ACL reconstruction.
At the Annual American Orthopaedic Sports Society for Sports Medicine (AOSSM) Meeting, July 14-17, 2005, Keystone, Colorado, several key investigators presented their findings detailing the use of allograft tissue in primary ACL reconstruction. Kurt Spindler, MD,[3] Vanderbilt University Medical Center, Nashville, Tennessee, was the moderator for the session. Dr. Spindler published an article in 2004 that compared autograft bone-patellar tendon-bone vs hamstring tendons. This was an evidence-based medicine systematic reviewof randomized controlled trials in the literature. In one of the sections of his paper, Dr. Spindler evaluated the graft failure rates of autograft tissue. Twenty-four failures of 664 patients at short-term follow-upproduced an overall incidence of 3.6% graft failure rate (95% confidenceinterval [CI], 2.3%-5.3%). He stated that the graft failure rate for allograft ACL reconstructions should try to achieve this standard of low graft failure rate.[3]
Jeffrey A. Rihn, MD,[6] University of Pittsburgh, Pittsburgh, Pennsylvania, highlighted a study from his group, entitled "Does Irradiation Affect the Clinical Outcome of Patellar Tendon Allograft Anterior Cruciate Ligament Reconstruction?" The goal of this study was to compare the clinical outcome of irradiated allograft vs autograft bone-patellar tendon-bone. Between 1995 and 2001, 102 patients met the study's inclusion criteria. Of those, 39 had allograft and 63 had autograft. The allograft tissues were obtained from a single tissue bank and received a dose of 2.5 Mrad (25 kGy) of irradiation for sterilization. The patients were evaluated at an average of 4 years. The patients in the allograft group were significantly older and had a longer time from injury to surgery. The authors found no significant differences in IKDC scores or in range of motion between the 2 groups. There were no significant differences in KT-1000 side-to-side measurements when adjusted for age, and no difference in patellofemoral crepitus and pain. The authors concluded that patients treated with bone-patellar tendon-bone allografts treated with low-dose irradiation for sterilization had similar clinical outcomes as those with autograft bone-patellar tendon-bone.
Matt Rappé, MD,[7] from Gainesville, Florida, presented a paper entitled "Non-Irradiated Versus Irradiated Achilles Allograft In Vivo Failure Comparison." The authors of this study retrospectively reviewed the records for 90 patients who had received an Achilles tendon allograft for a primary unilateral ACL reconstruction. Half of the patients received nonirradiated allografts, whereas the other half received allografts irradiated with 2-2.5 Mrad of gamma irradiation. The reconstructions were performed by 2 senior authors using the same surgical technique. All patients underwent the same rehabilitation protocol, were seen at regular intervals, and had failures documented. There was a significant difference in failure rates between the 2 groups with regard to catastrophic failures. Twelve patients who underwent reconstruction with an irradiated allograft had a catastrophic failure as opposed to only 1 patient who received a nonirradiated graft.
J.R. Gardiner, MD,[8] from Louisville, Kentucky, summarized a study entitled "Failure of Primary Anterior Tibialis Allograft Anterior Cruciate Ligament Surgery." Between 1999 and 2001, 125 patients underwent an arthroscopically assisted ACL reconstruction, consecutively, using an anterior tibialis tendon allograft (cryopreserved and nonirradiated) and interference screw fixation on both the tibial and femoral side, the latter of which was supplemented with an EndoPearl (Linvatec; Largo, Florida). All patients underwent an accelerated rehabilitation program. At an average follow-up of 55 months, 69 of 125 patients (55.2%) were available for evaluation. The average age was 33.7 years. The average Lysholm knee score was 85.6 out of 100 and the average Tegner activity score was 4.36 out of a maximum of 9. Of the 69 patients available for follow-up, 86.2% rated their knee normal or nearly normal. The overall failure rate, which was defined as requiring revision ACL reconstruction, was 23.1% (16 of 69). This occurred at an average of 22 months after initial surgery. Twenty-six of 69 patients (38%) required additional surgical intervention, including revision ACL reconstruction (16), meniscal procedures (9), and a total knee arthroplasty (1). There was a significant difference in the age of the patients who had a failure (22.8 years) compared with those who did not (38.3 years). In patients who younger than 25 years of age, the revision rate was 35.4% (11 of 31), and of those who were older than 25 years, the revision rate was 13% (5 of 38). This difference was statistically significant. The study authors concluded that the use of tibialis anterior allograft for primary ACL reconstruction had an unacceptably high failure rate, especially in patients younger than 25 years. A couple of factors in this study may have influenced the results. First, nearly half of the patients were not available for follow-up, which may have introduced a selection bias. This is an unusually high attrition for a follow-up study. However, if we assumed that all of the patients who did not return for follow-up did not have graft failure, the overall failure rate would be 12.8% (16 of 125), which is still quite high. In addition, there was no control group to compare the results to. Also, the high subjective satisfaction of patients (86.2% normal or nearly normal) did not match the high revision rate. Further studies need to validate the findings of this study.
Warren King, MD,[9] Palo Alto Medical Clinic, Palo Alto, California, outlined a study from his group, entitled "Anterior Cruciate Ligament Reconstruction With Sterilized Achilles Tendon Allograft: Report of a New Graft Preparation Technique and Early Clinical Follow-up." Dr. King used Achilles tendon allografts that had been processed by the Clearant Process (Clearant; Los Angeles, California). The process utilizes a proprietary solution to protect the grafts during high-dose irradiation with 5.0 Mrad (50 kGy). This process neutralizes the free radicals formed by high-dose radiation which denature proteins and lead to mechanical strength reduction and harm the graft. Sixty-eight patients underwent ACL reconstruction with Achilles tendon allograft. There were 33 men and 35 women, and their mean age was 32 years (14-49 years). The mean follow-up was 14 months (12-24 months). There were no side-to-side differences in range of motion postoperatively. Eight patients developed a mild effusion. The IKDC was 83 ±13 (38-100). Nine patients had a 1+ Lachman, but none had a 2+ or 3+ Lachman. There were 6 (8.6%) traumatic failures at 7-9 months postoperatively. These were caused by trauma during basketball and skiing events. Theses patients were noted to have persistent swelling after the index operation. On review, they were noted to have received tissue from donors over the age of 45 years.
The study author concluded that with the Clearant Process, the grafts were effectively sterilized, which leads to good early clinical results.
