Can grafts used for knee ligament reconstructions mimic the original native ligament? An analysis of mechanical properties of knee ligaments and tendons.
Author(s):
Smeets K. (Belgium)
Smeets K. (Belgium)
Affiliations:
ESSKA Academy. Smeets K. 05/09/18; 209805; P17-141
Kristof Smeets
Kristof Smeets
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Abstract
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Objectives: The use of tendon autografts for knee ligament reconstructions is extremely common. Too stiff grafts have the potential to overconstrain a certain part of the joint, more elastic grafts can cause residual joint laxity.
The primary purpose of this study was to provide information about the mechanical properties of typical grafts currently
used for knee ligament reconstructions. The secondary purpose was to compare those results with the mechanical
properties of native knee ligaments. The hypothesis was that the mechanical properties of knee ligaments are distinct
from the tendon grafts used to reconstruct them.

Methods: Eleven cadaveric knees were dissected for the semitendinosus, gracilis, iliotibial band (ITB), quadriceps and patellar
tendon. Another twelve knees were dissected for the medial collateral ligament (MCL), lateral collateral ligament (LCL),
anterolateral ligament (ALL) and medial patellofemoral ligament (MPFL). Uniaxial testing to failure was performed using a
standardized method and mechanical properties (elastic modulus - ultimate stress - ultimate strain - strain energy density) were determined.

Results: The elastic modulus of the gracilis tendon (1458±476 MPa) (P<0.001) and the semitendinosus tendon (1036±312 MPa) (P<0.05) was significantly higher than the ITB (610±171 MPa), quadriceps tendon (568±194 MPa) and patellar tendon (417±107 MPa). Also the ultimate stress of the hamstring tendons was significant higher (P<0.05), relative to the ITB, quadriceps tendon and patellar tendon. A significant higher difference (P<0.05) could be noticed between the ultimate strain of the patellar tendon relative to the hamstrings. No significant difference in strain energy density between the grafts was observed.
The MCL had the highest elastic modulus (441.8±117.2 MPa). The ultimate stress was significant higher (P<0.05) for the LCL and MCL, relative to the MPFL and ALL. The ultimate strain of the LCL and ALL were significantly higher (P<0.05) compared to the MCL and MPFL. The strain energy density of the LCL was significantly greater (P<0.05) than all other ligaments.

Conclusions: The primary purpose of this study was to provide information about the mechanical properties of grafts used for knee ligament reconstructions. Our data showed that different grafts possess distinct mechanical properties. The hamstring tendons have an elastic modulus and ultimate stress that is significantly higher than the patellar and quadriceps tendon. No significant difference in mechanical properties was seen between the quadriceps and patellar tendon. The elastic modulus and ultimate stress of the gracilis was higher than the semitendinosus.
The target of the ideal graft is to mimic the properties of the original ligament. Therefore, the secondary purpose of our study was to compare our results with data from the native knee ligaments. Hereby our hypothesis was confirmed and mechanical properties of the investigated grafts possess different characteristics as those of the native knee ligaments.

Keywords:
knee, grafts, ligaments, material properties, mechanical testing
Objectives: The use of tendon autografts for knee ligament reconstructions is extremely common. Too stiff grafts have the potential to overconstrain a certain part of the joint, more elastic grafts can cause residual joint laxity.
The primary purpose of this study was to provide information about the mechanical properties of typical grafts currently
used for knee ligament reconstructions. The secondary purpose was to compare those results with the mechanical
properties of native knee ligaments. The hypothesis was that the mechanical properties of knee ligaments are distinct
from the tendon grafts used to reconstruct them.

Methods: Eleven cadaveric knees were dissected for the semitendinosus, gracilis, iliotibial band (ITB), quadriceps and patellar
tendon. Another twelve knees were dissected for the medial collateral ligament (MCL), lateral collateral ligament (LCL),
anterolateral ligament (ALL) and medial patellofemoral ligament (MPFL). Uniaxial testing to failure was performed using a
standardized method and mechanical properties (elastic modulus - ultimate stress - ultimate strain - strain energy density) were determined.

Results: The elastic modulus of the gracilis tendon (1458±476 MPa) (P<0.001) and the semitendinosus tendon (1036±312 MPa) (P<0.05) was significantly higher than the ITB (610±171 MPa), quadriceps tendon (568±194 MPa) and patellar tendon (417±107 MPa). Also the ultimate stress of the hamstring tendons was significant higher (P<0.05), relative to the ITB, quadriceps tendon and patellar tendon. A significant higher difference (P<0.05) could be noticed between the ultimate strain of the patellar tendon relative to the hamstrings. No significant difference in strain energy density between the grafts was observed.
The MCL had the highest elastic modulus (441.8±117.2 MPa). The ultimate stress was significant higher (P<0.05) for the LCL and MCL, relative to the MPFL and ALL. The ultimate strain of the LCL and ALL were significantly higher (P<0.05) compared to the MCL and MPFL. The strain energy density of the LCL was significantly greater (P<0.05) than all other ligaments.

Conclusions: The primary purpose of this study was to provide information about the mechanical properties of grafts used for knee ligament reconstructions. Our data showed that different grafts possess distinct mechanical properties. The hamstring tendons have an elastic modulus and ultimate stress that is significantly higher than the patellar and quadriceps tendon. No significant difference in mechanical properties was seen between the quadriceps and patellar tendon. The elastic modulus and ultimate stress of the gracilis was higher than the semitendinosus.
The target of the ideal graft is to mimic the properties of the original ligament. Therefore, the secondary purpose of our study was to compare our results with data from the native knee ligaments. Hereby our hypothesis was confirmed and mechanical properties of the investigated grafts possess different characteristics as those of the native knee ligaments.

Keywords:
knee, grafts, ligaments, material properties, mechanical testing
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