In September 2015, I successfully defended my PhD dissertation, entitled “Postural control in relation to knee and ankle injuries during quasi-static and dynamic tasks” to fulfill the requirements for the degree of Doctor in Rehabilitation Sciences & Physiotherapy. My PhD journey was quite challenging, but I am still very proud on this achievement and thankful to my supervisor Prof. dr. Filip Staes (KU Leuven, Belgium) for giving me the opportunity to start working in the scientific field of sports physiotherapy and guiding me through this process.

PhD popular summary:

Knee and ankle injuries are a major public health concern because of their high prevalence in sports involving running, jumping and cutting activities. Moreover, the consequences of these injuries on the short and long term are often disappointing, as prolonged removal from sport participation, high incidences of residual symptoms and re-injuries, and high socio-economical costs have been reported. The most common and dramatic injuries are acute injuries such as a tear of the anterior cruciate ligament (ACL) and an ankle sprain, or overuse injuries at knee joint, such as patellofemoral pain. In order to minimize injury risk and improve clinical outcomes after injury, it is important to gain more insight in the underlying mechanisms of these injuries.

Although knee and ankle injuries can have multiple risk factors, it can be concluded based on previous literature that the ability to maintain postural control during daily and athletic activities is one of the essential factors to protect the knee and ankle from injury. In short, postural control involves controlling the whole body’s position in space for the dual purposes of postural orientation and stability. Postural orientation is defined as the ability to maintain an appropriate relationship between different body parts, and between the body and the environment. Postural stability, also referred to as balance, is the ability to control the center of mass in relationship to the base of support. As postural control requirements vary according to the task and environment, it is important to evaluate the ability to maintain postural control during both quasi-static and dynamic tasks. An example of a quasi static task is a task whereby a person shifts weight from double-leg stance to single-leg stance, while jumping off a box can be considered as a dynamic task.

The main objective of this doctoral project was to increase our understanding on quasi-static and dynamic postural control aspects in relation to knee and ankle injuries. A combination of methodological, retrospective (measuring injured persons) and prospective studies (measuring non-injured persons, doing a follow-up over time and registering the occurrence of injuries after initial data collection) across quasi-static and dynamic tasks was used.

First, we developed a new standardized methodology to analyze postural stability during a quasi-static test, the transition from double-leg stance to single-leg stance. Using this method, we showed in different studies that subjects with chronic ankle instability (CAI), subjects with an ACL injury, and subjects after an ACL reconstruction showed a decreased ability to maintain postural stability during the single-leg stance phase of this task when eyes were closed, in comparison with non-injured control subjects. Interestingly, no significant differences were found between the injured and non-injured legs of the ACL injured group, or between the operated and non-operated leg of the ACL reconstructed group. However, based on the retrospective design of these studies, it remained unclear whether these findings were the consequence or the cause (or both) of these injuries. To be able to provide a scientific answer to this clinical relevant question, we also performed a prospective study. Postural stability of both legs was measured during the transition from double-leg stance to single-leg stance with our standardized methodology in 50 non-injured female athletes. All tests were performed with eyes closed. During a one-year follow-up, 6 subjects sustained a non-contact ACL injury or ankle sprain. Similar to the retrospective studies, we found a decreased postural stability for both the injured and non-injured leg of the subjects who sustained an injury compared to the subjects who remained injury-free during follow-up. No significant differences were found between the injured and non-injured leg of the injured group.

Next to these postural stability measurements, we also focused on muscle activation patterns during this transition task from double-leg stance to single-leg stance. In contrast with most previous studies, we did not only focus on the muscles surrounding the injured knee joint, but also on hip and ankle muscles of both the injured and non-injured leg. We found that muscle activation onset times were not only delayed around the injured knee joint during the transition from double-leg stance to single-leg stance, but also around other lower extremity joints after ACL injury and ACL reconstruction, while almost no differences between legs within the same groups were found. All tests were performed barefoot in these studies. However, it was not clear whether the results acquired during barefoot conditions during the transition from double-leg stance to single-leg stance are representative for daily life situations where shoes and for some persons foot orthoses were mostly worn. We conducted two studies (one focusing on non-injured subjects, and one focusing on subjects with CAI) to evaluate the effects of shoes and foot orthoses on muscle activation patterns. The results of these studies implicate that shoes and foot orthoses have a neuromuscular “bottom-up” effect, as muscle activation of more distal muscles (more related to the ankle), and to a lesser extent the more proximal muscles (knee-hip), change when using shoes and foot orthoses.

The second part of this doctoral project focused on postural control aspects during more dynamic tasks. The main goal of these dynamic postural control measurements was to develop new clinical oriented methodologies to measure movement patterns using two-dimensional video analysis. Previous studies using similar methodologies mainly focused on movements of the knee. However, the positioning of the trunk can also be important in relation to knee injuries. In this study, we evaluated movements of the knee and trunk with a standard digital camera placed in front of the athletes. The main findings of this study were that lateral trunk motion can be measured with excellent intra- and intertester reliability using two-dimensional video analysis. In addition, we showed that the combination of knee valgus (the inward movement of the knee in relation to the hip and foot) and lateral trunk motion (KVLTM) in the direction of the stance limb during a single-leg drop vertical jump task was significantly correlated with increased knee loading.

A similar two-dimensional video analysis approach was used in another study, where we focused on hip, knee and ankle angles measured from a side view during double-leg and single-leg drop vertical jumps in 50 non-injured female athletes. The most consistent finding in this study was that the two-dimensional measured hip flexion during the deepest landing phase was significantly related to knee loading outcome parameters, while the knee flexion and ankle dorsiflexion angles were not.

In our last study, we prospectively investigated whether the two-dimensional measured angles in the frontal and side view could be used to assess non-contact knee injury risk. Fifty non-injured female athletes participated in the study. Seven subjects sustained a time-loss non-contact knee injury during a one-year follow-up. The KVLTM angles during the single-leg drop vertical jump were significantly smaller in the injured and non-injured leg of those subjects who sustained a non-contact knee injury during follow-up, compared to the respective matched legs of those subjects who remained injury-free. This indicates that landing with a combination of increased lateral trunk motion in the direction of the stance limb and knee valgisation during the single-leg drop vertical jump may increase non-contact knee injury risk. No significant results were found for the hip flexion angle.

In conclusion, the results of this doctoral project contributed to a better understanding of the relationship between quasi-static and dynamic postural control and knee and ankle injuries. The current findings imply that focusing only on the injured joint after injury, or on one particular joint of interest before injury may be too simplistic. Lower extremity joints dynamically interact with each other during functional tasks. Proximal (hip-trunk) neuromuscular and biomechanical factors play an essential role. Using the non-injured leg as a normal reference may lead to underestimations of postural control deficits, as bilateral dysfunctions can be present. Based on the results of the prospective and retrospective studies in this doctoral project, we can conclude that postural control deficits after injury represent at least partially pre-existing dysfunctions that may have increased the risk to sustain the injury. However, caution is warranted when extrapolating the group-based results of our retrospective and prospective studies towards an individual. The evaluation of (re-)injury risk can only be interpreted within a multifactorial framework.

The exact mechanisms underlying the current results cannot directly be deduced from the measurements in this doctoral project. However, it can be concluded that the postural control alterations before and after injury cannot simply and exclusively be related to mechanical dysfunctions within a single joint. Complex processes within the central nervous system may play an essential role. Future studies should further elaborate on the role of the central nervous system during postural control tasks in relation to knee and ankle injuries. The development of methodologies and the results in this doctoral project may allow future exploration of the relation between postural control and knee and ankle injuries on a larger scale. Future intervention studies should focus on motor learning principles targeting the underlying central mechanisms to successfully improve postural control related outcomes before and after knee and ankle injuries, and to optimize the effectiveness of injury prevention and rehabilitation programs.

All studies (11) within this doctoral project have been published and can be found here.