Expert Speaker Series: Ben Serpell on ACL Injuries in High Performance Sport
Updated: Aug 23, 2021
Ben is currently the Athletic Performance Coach at the Brumbies, acting as the link between the medical and performance teams. He also has experience working in rehabilitation at Port Adelaide FC (AFL) and Gloucester Rugby. His current research focus is on improving the prevention of ACL injuries, seeing as though rates have not decreased despite improved Sport Science and Medicine provision. Specifically, Ben is researching the role of pretension and preactivation, and the potential relationship between stiffness and injury risk. Much of this presentation included research and discussion that has been presented in Ben’s 2012 review of ACL injuries:
Common Mechanisms & Risk Factors
According to the literature about 70% of ACL injuries are non-contact in nature and although the contact injuries remain out of our control we often see the same kinematics as during non-contact injuries. These mechanisms are discussed at length in his very insightful literature review article (Serpell et al, 2012) and include a low knee flexion angle, knee valgus, anterior translation of the tibia and knee joint rotation. Likewise the risk factors are also covered in depth during that review but some of them include gender, skill level, ground friction and tibial plateau slope.
Ben described two key mechanisms for non-contact injuries; the Power Cut and the Speed Cut and showed some videos of ACL injuries occurring in professional soccer, AFL and rugby via these mechanisms.
The Power Cut involves a change of direction in a contralateral direction to the stance leg, for example a left change of direction off the right foot with the outside foot planted wide of the sternum (and vice versa).
The Speed Cut involves an ipsilateral change of direction, for example a left change of direction off the left foot (and vice versa).
One of Ben’s key take home messages was focussing on trying to prevent non-contact ACL injuries and given the consistent rate of injury in recent times plus the consequences on athlete availability, perhaps we need to do more to implement some of these prevention strategies in the High Performance environment. After all the ACL injury is the second most severe injury in sport behind hamstring injuries, from the combined perspective of duration, frequency and the resources associated with requiring surgery.
Ben’s research is looking at pretension to reduce joint laxity, which can be achieved through various methods including plyometric training and sand running. Ben also talked about other prevention strategies that originate from Frans Bosch’s movement philosophies. Change of direction should be viewed as a cork screw in that if you lead with your shoulders, the body will follow. This synchronisation through the shoulders and hips reduces rotational forces through the planted leg.
In the applied world, if you can teach good running mechanics in a straight line, with good posterior chain function, then good change of direction mechanics should follow. There was also a lot of emphasis placed on hip control and the link throughout the core, glute and hamstring chain. Hip control seems to be an important area for prevention as rotational and sagittal strength at the hip will control a stable and synchronised foot plant during landing and cutting.
Motor control strategies are all about trying to make the patterns unconscious; players, especially at the elite level, do not have the time during match play to think about how they are moving. But we do also need to consider the practical side, what does this actually look like in the High Performance programme? Where does this training fit in? Can we incorporate it into our prevention and warm ups? Perhaps we can also observe how the players move in situ during training and competition and identify those most at risk.
Two key points stood out to me during Ben’s discussion about his rehabilitation philosophy; firstly that no two injuries are the same so you have to treat each one individually and secondly that we need to consider the specific playing demands for the sport and the individual position when designing rehabilitation.
Despite this need for individuality Ben did mention some key milestones that he looks for within his ACL rehabilitation philosophy. These include 6-10 weeks during which the graft is most vulnerable, full extension by 12 weeks, 12 weeks of running progressions through pool running and on the gymnastics floor into 4 weeks of straight line running outside and change of direction in the gym before transferring change of direction work to outside. Once again the hip, hamstring, core relationship was mentioned with the strength and function of this chain a constant theme throughout rehabilitation. There are also implications depending on the type of graft, particularly in terms of secondary injuries.
A side note to this section was the influence of diet and Ben mentioned some very interesting work being carried out by the AIS and Keith Baar regarding how the diet can help create stiffness during the religamentisation process. I wonder how often diet is adapted in the High Performance environment in response to an injury. Perhaps portion sizes are reduced in response to the reduced energy expenditure but the influence of diet to this detail seems a very exciting area.
Finally some of the focuses on returning to sport are VMO work to maintain bulk, ITB lengthening to reduce fat pad irritation, avoid asymmetry and ultimately Ben believes you should function better post rehabilitation than beforehand!