The term athlete conjures thoughts of elite sportsmen or women but encompasses our active population whether development to international athlete, weekend warrior, social netball player or runner trying to keep fit and healthy. Injuries can not only result in a significant period of time off sport and training but also come with the added complication of a tertiary injury on return to sport or a recurrence of the injury that has just been rehabilitated. For sports physiotherapists one of our roles is to minimise the risk of injury recurrence and subsequent injury on an athletes return. There are a variety of factors that must be addressed to achieve this including:
· A progressive rehabilitation programme that is sports and individual specific
· The use of additional aids such as strapping and bracing where appropriate
· The alteration of technique as required.
· Graduated exposure to training and competition
· Ensuring appropriate criteria are achieved throughout the rehabilitation journey.
· Appropriate timing of their return related to both their physical and mental readiness.
One of the greatest challenges, particularly after significant injuries such as ACL ruptures is how as therapists we can objectively determine if an athlete is ready to return to sport. In recent years the use of horizontal plyometric tests such as the triple hop, cross over hop, and hop for distance have been utilized as the “gold standard” of return to play testing post ACL reconstruction. These were utilized in the absence of other options, but recent research has thrown doubt at their ability to provide valuable information for the return to play process, particularly for knee injuries.
Force plates have historically been expensive, complicated to easy and not easy to access and therefore not an option for private practice health care in New Zealand but with increasing competitiveness in this market and increasing research worldwide supporting the benefits of the use of these in the “everyday” and elite population these will become “commonplace” in the near future in physiotherapy practices worldwide.
When utilising ACL ruptures as our example we know the majority of these injuries are non-contact in nature, involving single leg deceleration, change of direction, landing and pivoting. Typically, a return to sport post ACL reconstruction (or conservative management of an ACL rupture) involves a battery of tests including strength assessment and a combination of horizontal hop tests to assess limb symmetry in addition to sport specific assessments. Unfortunately, what we see anecdotally and in the research is despite passing this battery of tests reduced performance on return and high reinjury rates are common. The question must be asked “what are these tests really telling us and is it valuable information with regards to their return to sport?”. It has been shown (Abrams et al, Nagai et al) that horizontal hop performance returns to “normal” from a limb symmetry perspective prior to quadricep strength symmetry returning. This may result in us overestimating their readiness to return to sport.
Kotsafaki et al, 2021 assessed a group of male athletes using vertical hop testing who had been cleared to return to sport with greater than 90% limb symmetry quadricep strength and horizontal hop distance. They identified that despite passing horizontal hop return to play measures only 83% and 77% passed limb symmetry expectations from a vertical hop height perspective during single leg jump and single leg drop jump respectively. In the control group 98% and 100% limb symmetry was achieved.
In reasoning the above findings, it has been surmised that vertical and horizontal hops measure different aspects of lower limb function. Kotsafaki et al, 2021 identified that the knee joint contributes approximately a third to vertical hop height but only an eighth to horizontal hop distance.
Jump height is mostly related to the concentric phase of a vertical jump task and assesses the ability to take off with powerful extension of the hip, knee and ankle (Linthorne N). Kotsafaki et al, 2021 concluded that the greater knee work contribution during vertical hops likely explains the performance deficits that are more apparent than they are during horizontal hop testing.
When considering more than the concentric propulsive phase the eccentric braking phase and reactive strength should play an important role in the return to sport assessment of athletes post ACL reconstruction. This requires the use of force plate technology to effectively measure and is unable to be assessed during standard horizontal hop tests.
Force plates allow us the ability to assess a multitude of metrics including (but not limited to) many that are relevant in this population:
· Ground contact time
· Eccentric impulse
· Concentric impulse
· Reactive strength
· Jump height
· Landing force
· Eccentric utilization ratio
A variety of tests including the counter movement jump, squat jump, drop jump and 10/5 can be completed both bilaterally and unilaterally. Bilateral assessments give us an indication into the strategy utilized to complete the jump while unilateral assessments give us a greater insight into the capacity available.
There are many essential elements to ensuring a thorough return to play assessment is completed including unilateral movement competency, change of direction and jump landing competency, strength of the lower limb, proprioception, plyometric ability and successful graduated return to training demands in addition to mental readiness to return. Force plates allow us to ensure that we are assessing throughout the mid to late stage rehab to identify remaining deficits. At the very least this allows us to ensure that deficits are reduced to an appropriate level and an athlete is returned as safely to their chosen sport as possible and at a “gold standard” level allows us to assess these components throughout the rehabilitation programme ensuring that deficits are minimized and programmes are specifically targeted to the individuals impairments reducing unnecessary rehabilitation and an increase in time to return to sport safely.
Research utilising forceplates has grown substantially over the past few years and continues to evolve. This growth allows for ongoing benchmarking in specific populations allowing for expectations to be set that are not only derived from limb symmetry. The use of force plates is not limited to ACL injuries but has the ability to provide beneficial data throughout the rehabilitation and return to sport process of athletes with both upper and lower limb injuries.
References
Kotsifaki A, Korakakis V, Graham-Smith P, Sideris V, Whiteley R. Vertical and Horizontal Hop Performance: Contributions of the Hip, Knee, and Ankle. Sports Health. 2021;13(2):128-135. doi:10.1177/1941738120976363
Kotsifaki A, Van Rossom S, Whiteley R, Korakakis V, Bahr R, Sideris V, Jonkers I. Single leg verical jump performance identifies knee function deficits at return to sport after ACL reconstruction in male athletes. British Journal of Sports Medicine 2022;0:1-10.
Abrams GD, Harris JD, Gupta AK, et al. Functional performance testing after anterior cruciate ligament reconstruction: a systematic review. Orthop J Sports Med 2014;2:232596711351830.
Nagai T, Schilaty ND, Laskowski ER, et al. Hop tests can result in higher limb symmetry index values than isokinetic strength and leg press tests in patients following ACL reconstruction. Knee Surg Sports Traumatol Arthrosc 2020;28:816–22
Linthorne NP. Analysis of standing vertical jumps using a force platform. Am J Phys 2001;69:1198–204
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