Adjustable suture loops for extracortical fixation of ACL grafts partially fail under cyclic loading and unloading conditions
Author(s):
Glasbrenner J. (Germany)
,
Glasbrenner J. (Germany)
Affiliations:
Willinghöfer T.
,
Willinghöfer T.
Affiliations:
Domnick C.
,
Domnick C.
Affiliations:
Kittl C.
,
Kittl C.
Affiliations:
Michel P.
,
Michel P.
Affiliations:
Wähnert D.
,
Wähnert D.
Affiliations:
Raschke M.
,
Raschke M.
Affiliations:
Herbort M.
Herbort M.
Affiliations:
ESSKA Academy. GLASBRENNER J. 05/09/18; 209260; P02-1218 Topic: Biomechanics
Dr. Johannes GLASBRENNER
Dr. Johannes GLASBRENNER
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Abstract
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Objectives: There is a big market for adjustable button (AB) devices for anterior cruciate ligament (ACL) reconstruction. There are different types of adjustable suture loops, amongst which the "Chinese finger trap technique" is quite common. However clinical and biomechanical studies could not rule out concerns about stability of AB.
The forces acting in the reconstructed ACL remain unknown, although in biomechanical studies the existing AB have never been tested under cyclic loading with complete unloading.
Hypothesis: Adjustable suture loops might loosen even more than actually reported in a testing protocol using cyclic loading and unloading. Furthermore we claim that AB using "Chinese finger trap technique" would show more displacement than other available AB devices.

Methods: ACL reconstruction was performed in a porcine knee model using three different types of extracortical fixation devices: two different AB using the "Chinese finger trap technique" (CFT1 and CFT2), one AB using a locked suture loop (LSL) and two different continuous loops (CL1 and CL2) as a control group (n=40). The specimens were mounted in a material testing machine (Fa. Instron). Cyclic loading and unloading was performed from 0 to 250N while elongation was recorded continuously.
For statistical analysis one-way ANOVA for multiple comparisons was performed in order to determine significant differences between the groups. A p-value lesser than 0,5 was required for a significant difference.

Results: 2500 Cycles of loading and unloading between 0 and respectively 50, 100, 150, 200 and 250 N lead to an elongation of 8,05mm ±1,46 in the CFT1 and 6,13mm ±1,42 in the CFT2 group. CL1 and CL2 showed an elongation of 4,07mm ±0,55 and 4,35mm ±0,32. Lengthening was 4,74mm ±0,98 in LSL.

There was no significant difference between the LSL, CL1 and CL2. However lengthening was significantly higher in CFT 1 and CFT2 compared to LSL, CL1 and CL2 respectively.

Conclusions: Cyclic loading with complete unloading of AB using the "Chinese finger trap technique" leads to significantly more loosening than in the tested CLs. This might destabilize the ACL graft and therefore compromise the outcome of ACL reconstruction. To our knowledge AB have never been tested in a protocol using complete unloading. Furthermore, this is the first laboratory study proofing higher loosening of commercially available AB devices depending on the suture loop technique. Using AB with the "Chinese finger trap technique" might be a possible mode of failure which could compromise graft healing in the bone tunnel.

Keywords:
adjustable button, extracortical fixation, acl reconstruction
Objectives: There is a big market for adjustable button (AB) devices for anterior cruciate ligament (ACL) reconstruction. There are different types of adjustable suture loops, amongst which the "Chinese finger trap technique" is quite common. However clinical and biomechanical studies could not rule out concerns about stability of AB.
The forces acting in the reconstructed ACL remain unknown, although in biomechanical studies the existing AB have never been tested under cyclic loading with complete unloading.
Hypothesis: Adjustable suture loops might loosen even more than actually reported in a testing protocol using cyclic loading and unloading. Furthermore we claim that AB using "Chinese finger trap technique" would show more displacement than other available AB devices.

Methods: ACL reconstruction was performed in a porcine knee model using three different types of extracortical fixation devices: two different AB using the "Chinese finger trap technique" (CFT1 and CFT2), one AB using a locked suture loop (LSL) and two different continuous loops (CL1 and CL2) as a control group (n=40). The specimens were mounted in a material testing machine (Fa. Instron). Cyclic loading and unloading was performed from 0 to 250N while elongation was recorded continuously.
For statistical analysis one-way ANOVA for multiple comparisons was performed in order to determine significant differences between the groups. A p-value lesser than 0,5 was required for a significant difference.

Results: 2500 Cycles of loading and unloading between 0 and respectively 50, 100, 150, 200 and 250 N lead to an elongation of 8,05mm ±1,46 in the CFT1 and 6,13mm ±1,42 in the CFT2 group. CL1 and CL2 showed an elongation of 4,07mm ±0,55 and 4,35mm ±0,32. Lengthening was 4,74mm ±0,98 in LSL.

There was no significant difference between the LSL, CL1 and CL2. However lengthening was significantly higher in CFT 1 and CFT2 compared to LSL, CL1 and CL2 respectively.

Conclusions: Cyclic loading with complete unloading of AB using the "Chinese finger trap technique" leads to significantly more loosening than in the tested CLs. This might destabilize the ACL graft and therefore compromise the outcome of ACL reconstruction. To our knowledge AB have never been tested in a protocol using complete unloading. Furthermore, this is the first laboratory study proofing higher loosening of commercially available AB devices depending on the suture loop technique. Using AB with the "Chinese finger trap technique" might be a possible mode of failure which could compromise graft healing in the bone tunnel.

Keywords:
adjustable button, extracortical fixation, acl reconstruction
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