Validation of Noncontact Anterior Cruciate Ligament Tears Produced by a Mechanical Impact Simulator Against the Clinical Presentation of Injury

The American Journal of Sports Medicine, June 4th, 2018

Bates Et. Al   

Mayo Clinic, Rochester, Minnesota, USA

Imagine if there was a tool that could consistently produce realistic ACL tears ( in vitro, of course – researchers aren’t that evil) and what kind of future breakthroughs that could provide for prevention and intervention? Look no further, some pretty smart individuals at the Mayo Clinic might just be on to something.

ACL tear mechanical impact simulators have been around before, one of which was able to produce tears at an 88% rate. Unfortunately, this device consistently produced the tear at the tibial eminence. We know from other research that most ACL tears actually occur more towards the femoral origin or mid-substance of the ligament. If future intervention studies are going to be based on a simulator then we better make sure that it accurately creates the environment and location of ACL ruptures that we see in vivo.

Bates and his team performed a validation study on a new mechanical impact simulator that they felt could accurately represent non-contact ACL tears at a high proficiency.  In addition to guiding future interventions, it could aid in understanding joint mechanics, loads, and stresses on the intra-articular structures that we aren’t capable of seeing outside the cadaver lab.

What Happened To the Cadaveric Knees During the Study

The study had a final count of 39 cadaveric specimens from 25 donors (19 male and 20 female) with an average age of 41 years old.

The mechanical simulator created externally generated loads to have the knee undergo anterior tibial shear (ATS), knee abduction moment (KAB) and internal tibial rotation (ITR) at a knee flexion angle of 25 degrees, the typical knee angle seen during jump-landings. The forces applied to ATS, KAM and ATR from the simulator were calculated based on previously recorded drop landing tests from 67 young healthy adults.

And The Results…?

• The simulator was able to perform an ACL tear 87% of the time with MCL tears also occurring 31% of the time.
• ACL tears were 85% complete and 15% partial.
• Significant changes in Lachman, anterior drawer, MCL integrity, and LCL integrity were seen upon clinical examination by an orthopedic surgeon on the specimens that aligned with the laboratory findings.
• Most of the ACL ruptures occurred near the femoral insertion (71%) followed by the mid-substance of the ACL (21%) and least at the tibial aspect (9%).
• Peak ligament strain before failure: ACL (15.3%) and MCL (5.1%)
• No significant differences were seen between sexes with regards for peak ACL and MCL strain, though the change in strain was greater for ACL than MCL in female specimens.

Further Insights

Overall, the mechanical impact simulator was very successful in reproducing ACL injuries for the specimens and in a manner that aligns with what we see clinically in terms of where the injury occurs along the ACL and in concomitant MCL injury incidence.

The peak strain to failure was 3 times larger for the ACL than the MCL, which makes sense as the ACL has to support larger forces during gait and athletic tasks. There was a difference in change of strain between females in males with regards to ACL to MCL. Perhaps this plays a role in the increased incidence of ACL tears in females, but the authors indicate that certainly more research is needed here.

To me, the idea of having a device that simulates ACL tear in cadaveric specimens is really exciting with regard to what direction it can have towards future research. I definitely encourage everyone to click the link at the top of the page to the article itself to see what the device looks like and how it works in more detail.

I look forward to hearing everyone’s thoughts on how this could shake up the research world and where this can be applicable!

Tyler Cope

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