Noyes and colleagues set out to measure how strong the common knee ligament grafts are compared with the native ACL.
Cadaver study loading 9 graft tissues from young adult donors to failure at a high strain rate, compared with ACLs from similar donors.
Methods
Model
Autopsy tissue from 18 young adult donors, compared with young‑donor ACLs
Constructs
9 grafts
Bone–patellar tendon–bone (central and medial thirds)
Semitendinosus
Gracilis
Fascia lata
Iliotibial tract
Retinacular strips
Loading
Uniaxial tension to failure at 100% of specimen length per second
Outcome measures
Maximum load
Stiffness
Maximum stress
Energy to failure
Local surface strain
Key Findings
The 14 to 15 mm bone‑patellar tendon‑bone graft was the strongest, at 159% to 168% of native ACL strength.
In grip‑to‑grip testing, bone‑patellar tendon‑bone units were 3 to 4 times stiffer than the ACL.
The widest distal iliotibial tract graft usually available (about 25 mm) would reach only about 62% of ACL strength, by the authors' width‑adjusted calculation.
Extra graft width adds strength only when the added fibers run the full length between insertions and bear load.
The authors estimate ACL ultimate strength at about 1730 N but hypothesize that most activities load it to only about 454 N.
Citing primate work, the authors note that patellar tendon grafts fall to 15% of their preimplantation strength by 6 weeks after surgery.
Board pearl
A single gracilis tendon reached only 49% of native ACL strength and a single semitendinosus 70%, though the semitendinosus difference was not significant.
Authors' conclusion
The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces.
Noyes and colleagues set out to measure how strong the common knee ligament grafts are compared with the native ACL.
Cadaver study loading 9 graft tissues from young adult donors to failure at a high strain rate, compared with ACLs from similar donors.
Methods
Model
Autopsy tissue from 18 young adult donors, compared with young‑donor ACLs
Constructs
9 grafts
Bone–patellar tendon–bone (central and medial thirds)
Semitendinosus
Gracilis
Fascia lata
Iliotibial tract
Retinacular strips
Loading
Uniaxial tension to failure at 100% of specimen length per second
Outcome measures
Maximum load
Stiffness
Maximum stress
Energy to failure
Local surface strain
Key Findings
The 14 to 15 mm bone‑patellar tendon‑bone graft was the strongest, at 159% to 168% of native ACL strength.
In grip‑to‑grip testing, bone‑patellar tendon‑bone units were 3 to 4 times stiffer than the ACL.
The widest distal iliotibial tract graft usually available (about 25 mm) would reach only about 62% of ACL strength, by the authors' width‑adjusted calculation.
Extra graft width adds strength only when the added fibers run the full length between insertions and bear load.
The authors estimate ACL ultimate strength at about 1730 N but hypothesize that most activities load it to only about 454 N.
Citing primate work, the authors note that patellar tendon grafts fall to 15% of their preimplantation strength by 6 weeks after surgery.
Board pearl
A single gracilis tendon reached only 49% of native ACL strength and a single semitendinosus 70%, though the semitendinosus difference was not significant.
Authors' conclusion
The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces.