The purpose of this study is to evaluate the effect of graft donor age on outcomes of ACL reconstruction with non-irradiated, fresh-frozen allografts. Our hypothesis was that older donor age would not have a significant effect on clinical outcomes for ACL reconstructions.
Discussion
The main finding from this prospective, randomized study is that the data did not show a difference in patient reporting outcomes at the 2-year follow up in patients who underwent ACL reconstruction with tibialis allografts from donors >50 years of age compared with donors <50 years of age. This is a clinically relevant finding because many surgeons may be hesitant to use grafts from older donors, and supply from young donors is at times insufficient to meet demand.
The use of allograft tissue for ACL reconstruction encompassing all age groups is not uncommon, with a survey by the American Academy of Orthopedic Society for Sports Medicine of 833 surgeons reporting allografts use in 27% of primary ACL reconstructions and in one large hospital system registry of 21,304 ACL reconstructions allografts were used in 41% of the cases.
10American Academy of Orthopedic Surgeons
Allografts for ACL reconstruction survey report.
,11- Maletis G.B.
- Chen J.
- Inacio M.C.
- Funahashi T.T.
Age-related risk factors for revision anterior cruciate ligament reconstruction: A cohort study of 21,304 patients from Kaiser Permanente anterior cruciate ligament registry.
Of no surprise, the tissue availability can be inadequate with the concern of donor age by some surgeons being a contributing factor.
ACL reconstruction with allograft tissue is reported to have differing success in the orthopedic literature. It has been well documented that patients age of 25 or younger with high activity levels are at greatest risk for failure.
12MOON Knee Group
Anterior cruciate ligament reconstruction in high school and college-aged athletes. Does autograft choice influence anterior cruciate ligament revision rates?.
,13- Wiggins A.J.
- Grandhi R.K.
- Schneider D.K.
- et al.
Risk of secondary injury in younger athletes after anterior cruciate ligament reconstruction: A systematic review and meta-analysis.
While there is general consensus that allografts should not routinely be used in patients of this category, studies have shown allografts can have comparable results to autografts.
14- Cvetanovich G.L.
- Mascarenhas R.
- Saccomanno M.
- et al.
Hamstring autograft versus soft tissue allograft in anterior cruciate ligament reconstruction: A systematic review and meta-analysis of randomized controlled trials.
, 15- Kaeding C.C.
- Pedroza A.D.
- Reinke E.K.
- et al.
Risk factors and predictors of subsequent ACL injury in either knee after ACL reconstruction: Prospective analysis of 2488 primary ACL reconstruction from the MOON cohort.
, 16- Lambin C.J.
- Waterman B.R.
- Lubowitz J.H.
Anterior cruciate ligament reconstruction with autografts compared with non-irradiated non-chemically treated allografts.
, 17- Barber F.A.
- Cowden III, C.H.
- Sanders E.J.
Revision rates after anterior cruciate ligament reconstruction using bone-patellar tendon-bone allografts or autografts in a population 25 years old and younger.
, 18Allograft ACL reconstruction in patients under 25 years of age.
Other variables need to be taken into consideration before evaluating only the donor age. The graft itself should be from an American Association of Tissue Banks–certified tissue bank to assure proper screening and procurement. The processing method and inherent graft strength can also have a role in outcome beyond the age of the graft.
19American Association of Tissue Banks
Standards for tissue banking.
As none of the key outcomes met statistical significance when comparing across groups, a retrospective sample size and power analysis were performed assuming existing effect sizes and distributions. Both the IKDC subjective and Lysholm outcomes were well short of a
P value of .05, and hence the expected sample size for significance is correspondingly large: 974 for the former and 306 for the latter. Similarly, the IKDC objective assessment showed a needed sample size of 259, whereas the KT-1000, which was closest to significance in the existing data, would have required a sample size of 85, the smallest of the four by a considerable margin.
From another perspective, at the actual sample sizes available, retrospective power for detecting a significant difference between groups was 7% for the IKDC subjective, 10% for Lysholm, 11% for IKDC objective, and 31% for the KT-1000. Available power was therefore low for all outcomes.
Although aseptic technique can limit the risk of infection, tissue banks routinely use sterilization techniques, which can have significant effects on tissue strength. Irradiation is most commonly used, but levels ≥25 Mrads lead to tissue deterioration, which can affect clinical outcomes.
20- Mariscalco M.W.
- Magnussen R.A.
- Mehta D.
- et al.
Autograft versus nonirradiated allograft tissue for anterior cruciate ligament reconstruction. A systematic review.
,21- Rappe M.
- Horodyski M.
- Meister K.
- Indelicato P.A.
Nonirradiated versus irradiated Achilles allograft: In vivo failure comparison.
Even doses as low as 1.2 Mrads can decrease graft stiffness by 20%.
22- Yanke A.B.
- Bell R.
- Lee A.
- et al.
The biomechanical effects of 1.0 to 1.2 Mrad of gamma irradiation on human bone-patellar tendon-bone allografts.
Chemical processing can be performed, but many such as ethylene oxide have been discontinued.
23- Jackson D.W.
- Windler G.E.
- Simon T.M.
Intra-articular reaction associated with the use of freeze-dried, ethylene oxide-sterilized bone–patella tendon–bone allografts in the reconstruction of the anterior cruciate ligament.
BioCleanse is one chemical-processing method that has been reported to have no detrimental effects on preimplantation biomechanical properties strength and used in this study.
24- Chan D.B.
- Temple H.T.
- Latta L.L.
- et al.
A biomechanical comparison of fan-folded, single-looped fascia lata with other graft tissues as a suitable substitute for anterior cruciate ligament reconstruction.
,25- Roberson T.A.
- Abildgaard J.T.
- Wyland D.J.
- et al.
“Proprietary processed” allografts. Clinical outcomes and biomechanical properties in anterior cruciate ligament reconstruction.
The tibialis tendon allografts procured by an AATB-certified tissue bank and processed in a single method. While one cannot state that tibialis tendons are clinically better simply based on biomechanical testing, their ultimate load to failure is as high or higher than other grafts before implantation. In a systematic review by Lansdown et al.
26- Lansdown D.A.
- Riff A.J.
- Meadows M.
- Yanke A.B.
- Bach B.R.
What factors influence the biomechanical properties of allograft tissue for ACL reconstruction? A systematic review.
examining common ACL grafts, the native ACL is reported to have a load to failure of 1,730 to 2,160 N, whereas a double looped tibialis tendon was greatest at 3,012 to 4,112 N.
Several basic science studies have looked at the mechanical properties relating to graft donor age, but results vary because different grafts, processing, and testing methods were used. However, the general consensus on critical analysis of the studies with stringent parameters is that grafts from donor age ≤65 years (upper limit of most tissue bank suppliers) have limited differences in biomechanical properties.
Greaves et al.
27- Greaves L.L.
- Hecker A.T.
- Brown Jr., C.H.
The effect of donor age and low-dose gamma irradiation on the initial biomechanical properties of human tibialis tendon allografts.
tested 126 tibialis tendon allografts divided into 3 age groups: <45 years, 46-55 years, and 56-65 years. They found that donor age up to 65 years did not significantly affect the initial failure load, stiffness, or displacement of failure. Jones et al.
28- Jones D.B.
- Huddleston P.M.
- Zobitz M.E.
- Stuart M.J.
Mechanical properties of patellar tendon allografts subjected to chemical sterilization.
tested BioCleanse versus untreated bone–patellar tendon–bone (BPTB) grafts. Although they found no difference in biomechanical properties between the processed and unprocessed grafts, they also found no significant differences between donor grafts 29-40 years old compared with 41-65 years of age. However, the grafts in the 65-90 years age group did have significantly less maximum strength. Blevins et al.
29- Blevins F.T.
- Hecker A.T.
- Bigler G.T.
- Boland A.
- Hayes W.
The effects of donor age and strain rate on the biomechanical properties of bone–patellar tendon–bone allografts.
tested 82 BPTB procured from donors aged 17-54 years of age and found no significant correlation between tensile strength and donor age.
In the largest number of allografts tested Swank et al.
30- Swank K.R.
- Behn A.W.
- Dragoo J.L.
The effect of donor age on structural and mechanical properties of allograft tendons.
reported their results of 550 tibialis posterior tendons. The specimens were divided into 6 donor age groups: 15-29, 30-39, 40-49, 50-59, 60-69, and 70-79 years and underwent numerous tests including stiffness, ultimate tensile force, strength and displacement. They found that ultimate tensile strength increased slightly with age up to 40-49 years and decreased with further increase in age. However, the magnitude of difference between age groups was <15% for all outcome parameters. Their conclusion was that age explained at most 6% of the variation in structural and mechanical properties of tibialis posterior allograft tendons, and most likely not clinically relevant.
Although well-controlled basic science studies indicate that the donor age should not have a significant effect on graft failure rate, a concern of its clinical application exists because of lack of clinical data. Only a few studies have specifically evaluated outcomes as it relates to donor age.
Hampton et al.
31- Hampton D.M.
- Lamb J.
- Kimkiewicz J.J.
Effect of donor age on patellar tendon allograft ACL reconstruction.
reported in a retrospective study on the outcome of 75 patients at a mean 2-year follow-up after BPTB allograft. Donor age ranged from 14-65 years and the average patient age was 37 years (range 18-60 years). The finding was that the donor age had no effect on the degree of postoperative improvement using Lysholm or Tegner scores. However, information was gathered only via phone calls and chart review with no objection assessment performed.
In a retrospective cohort study of 5968 primary ACLR with allograft tissue, Tejwani et al.
32- Tejwani S.G.
- Chen J.
- Funahashi T.T.
- Love R.
- Maletis G.B.
Revision risk after allograft anterior cruciate ligament reconstruction. Association with graft processing techniques, patient characteristics, and graft type.
reported on the revision rates looking at several variables. The donor age was separated into 4 age groups: <20, 20-40, 41-59, and >60 years with the number of cases in each group being 276, 1,301, 3,497, and 892, respectively with 2 not reported. The revision rate was low for all groups with the percent being 2.17, 2.84, 2.49, and 2.91 in chronologic order of young to old. They concluded that the donor age did not significantly affect revision risk.
The data collected were extensive, and the revision rate across all donor age categories was similar. Numerous other variables were included at the same time as looking at donor age. The grafts ranged from BPTB (17.2%), Achilles tendon (19.9%), to all soft tissue (62.9%). Four different sterilization methods were used, including 1,146 (19.2%) had irradiation of >1.8 Mrads. as negative effects on the graft strengths as cited previously. In addition, the age of the patients varied widely with 1,747 (29.3%) being in the high-risk age group of ≤25 years.
Shumborski et al.
5- Shumborski S.
- Salmon L.J.
- Monk C.
- et al.
Allograft donor characteristics significantly influence graft rupture after anterior cruciate ligament reconstruction in a young active population.
reported differing results when it came to the age of the allografts and outcomes. They reported that tendons from female donors >50 years had significantly greater rates of graft failure compared to male donors aged <50 years. However, they used multiple tissues for grafts including patellar tendon, Achilles tendon, and tibialis. When they analyzed the outcome based solely on graft type, they found the failure rate was 11% for tibialis, which we studied, and combined failure of 29.9% for patellar tendon and Achilles tendon. The most critical factor in comparing their study to this one is the patient’s age which is known to have an increased failure rate. Patients in their cohort were younger than the age of 25 years with a range of 13 to 25 years.
In this study, it demonstrated that donor age was not associated with tibialis tendon allograft failure. Although the donor age groups were separated into younger than older than 50 years of age, the groups were noticeably more divided in age. The younger group donor average was 33.8 years, with the oldest being 46 years. The older group average was 60.7 years, with the youngest being 53 years. The number of patients was small, but it had the benefit of being prospective and randomized with a single surgical technique and all other graft variables controlled to allow specific evaluation of donor age. In addition, both subjective and extensive objective evaluations were performed.
As none of the key outcomes met statistical significance when comparing across groups, a retrospective sample size and power analysis were performed assuming existing effect sizes and distributions. Both the IKDC subjective and Lysholm outcomes were well short of a P-value of .05, and hence the expected sample size for significance is correspondingly large: 974 for the former and 306 for the latter. Similarly, the IKDC objective assessment showed a needed sample size of 259, whereas the KT-1000, which was closest to significance in the existing data, would have required a sample size of 85, the smallest of the four by a considerable margin.
From another perspective, at the actual sample sizes available, retrospective power for detecting a significant difference between groups was 7% for the IKDC subjective, 10% for Lysholm, 11% for IKDC objective, and 31% for the KT-1000. Available power was therefore low for all outcomes. Longer follow-up will be needed to see if the results of this study will be upheld.
Limitations
This study is not without limitations. The main limitation of this study was the small patient population, which was not large enough to show statistical significance. In standard practice, patients rarely ask the age of the donor. However, the number of patients to agree to participate in a prospective, randomized study using an allograft of a wide donor age group was limited and thus accounted for the study size. The protocol was to enroll 50 patients, but we were only able to enroll 40 patients over a 6-year time period. The age of the graft donors affected enrollment as potential patients were apprehensive to receive an older donor tendon which led to enrollment being stopped prior to the initial goal of 50 patients.
An additional limitation was the predominant sex in both groups was female. Further, Group A had a greater proportion of females to males (82.4%) compared with Group B (60%). The composition of the groups was solely on the randomized order of presentation and thus could not be controlled in our study design.