We discussed several of the movements we see in the core/hips specifically with single leg testing. Most of us that have assessed movement for a while see this and the impact this has on the center of mass (COM) displacement during single limb testing. We are now starting to see this investigated in the research.
Before we get into the study, we first need to understand what does knee robustness mean. Knee robustness is the ability to tolerate perturbation during functional activities and still maintain joint configuration.
Testing procedures included:
- Patient reported outcome measures – IKDC, KOOS and Lysholm scale
- KT 1000 arthrometer
- 3 hop tests
- One leg hop for distance
- One leg vertical hop
- One leg rebound side hop – standing on one leg, athlete hops lateral over a distance 25% of body height and immediately back medially.
- Isometric knee extension and flexion strength
Discussion: Keeping in mind this study was done in Sweden, there is a difference when comparing ACLR and rehab done in Sweden versus the US. Couple of things to keep in mind is that in a socialized medicine environment, surgery is very different. There is often a long delay in getting an MRI and having surgery. This can sometimes be as long as 6 months. In addition, the therapy that is done is also very different. Neither is wrong but it is different than what happens in the US. So this is important when comparing outcomes from studies that are done abroad. That said, one of the things you will see is that the subjects were average 22-14 years of age and all of them had a hamstrings graft. Most surgeons in the US would do more bone patellar bone grafts than hamstring. In addition, the ACLR subjects, 85% were back in sports and were all 16 months post op.
One (of the many) things I liked about this study was the hop testing. The one leg rebound test is very similar to the hop plant test that we use. One of the things we find is that the landing on the medial hop is one of the most telling motions. If you break down the moment where they are hopping back (rebounding) medially, the subject moves their COM medial, explosively pushes off with the leg, attempts to stick the landing and has to stop the COM from continuing medially and control their knee from collapsing into a dynamic valgus. This is extremely hard to do. We actually find this to be one of the most telling motions. Those with larger displacement of their COM and higher speeds of dynamic valgus in this movement, we see are at higher risk of lower kinetic chain non-contact injuries.
One of the challenges with the way they looked at this motion was they had the subject hold a rope behind their back with both hands. The challenge with this is that this dramatically changes the mechanics of the motion. If we think about it, doing this causes the subject to extend their arms back, elevate the chest. The resulting posture brings the thoracic spine and lumbar spine into an increased amount of extension. Doing this alters the mechanics of the jump. You will have less side flexion and sidebending with the lateral and medial hop in addition to some increase in bony stability (due to the extension) of the core. This is not how hopping occurs and I think you will miss a lot of natural or pathological motion that occurs in the core/hips with this positioning.
The natural motion is to have the arms forward and the arms behind results in a more upright posture. That aside this was done with both groups (ACLR and control) and there was notable differences. That said, I would love to see more studies actually looking at COM displacement during these motions and looking at speeds of dynamic valgus on the medial hop. There is a correlation there but of course, we can't say that until they prove that in the research.
Next week, we will look a little more at the concept of knee robustness and what happens when there is a disruption to the COM prior to the landing (shoulder contact with another player when going for a header). Some interesting things we are seeing in this realm as well. Stay tuned as I am super excited to share with you. If you enjoy this blog, please share with your colleagues, athletes and training partners and please be sure to follow us on instagrm @ bjjpt_acl_guy and twitter @acl_prevention. Train hard and stay well. #ViPerformAMI #ACLPlayItSafe