Return to Sports after Lower Extremity Injuries: Assessment of Movement Quality

Numerous high performance athletes experience further damage or recurrent injuries even after successful rehabilitation. This is often caused by an insufficient movement quality, which has been very rarely assessed by test protocols which determine the point of reintegration into high performance sports (Return-to-Play, RTP). In order to assess the movement quality both objective and subjective test protocols exist. Objective methods like 3D-movement analysis are viewed as international gold standard, but are not the most practicable solutions for daily training routine. This study aims at reviewing the available literature on reliability and validity of existing subjective test protocols. Further their use within high-performance sports is evaluated. Up to now subjective methods fail to match sufficient validity. However some practical approaches for assessment of movement quality after injury are known. Based on selected criteria first recommendations for the use of different subjective screening test methods are given. In summary further research focusing on the validity of subjective tests is needed. The subjective testing methods should be used in combination with additional tests (e.g. strength testing) in order to identify other risk factors. Recurrent pre-injury screenings on movement quality should be carried out to enhance injury prevention.

Recent reviews suggest higher rates of recurrence and contralateral injuries after anterior cruciate ligament (ACL) rupture as well as injuries of the hamstring and ankle joint [2] [3]. Besides a high risk of recurrent injury, the risk of suffering from overuse by synovitis and osteoarthritis is increasing after ACL injury. This results in early drop-outs of some athletes or an unsuccessful comeback. The current high rates of reinjured athletes are caused by functional deficits like insufficient neuromuscular control and stability [4] [5] [6]. After rehabilitation of lower extremity injuries primarily the aspects of strength, proprioception, symmetries and neuromuscular control as well as static and dynamic stability are not sufficiently developed. This impacts the kinematics as well as the motor control both distal and proximal of the injury and increases the reinjury-risk [3]. However these aspects are not considered to determine the point of time for a Return-to-Play. Decisions are made by looking at predictive healing periods or single tests like the comparison of the isokinetic force of the injured and non-injured extremity [5] [7]. Barely any objective criteria exist in order to ensure a safe and long-term rehabilitation and re-integration into high performance sport for the injured athlete. One of the most important factors which need to be considered when looking at the time for a RTP is the movement quality. In most patients the movement quality is reduced considerably after injury which leads to an increasing risk of reinjury. Insufficient movement quality comes with deviation in movement axis during dynamic movements, non-functional partial movements, or high impact landings [8] [9]. As a foundation towards specific therapeutic movement training the testing of movement quality should be conducted. Until now almost no standardized test for assessing movement quality is established in order to ensure a safe rehabilitation and re-integration into high performance sports by objective criteria.

Testing Methods
Health keywords athletes, competitive sport, serious sports, sports and performance were used to identify suitable tests for high performance sports. Moreover return to sports, return to play, return criteria, sport criteria, sports participation, reintegration as well as rehabilitation and prevention were used for the aspect of reintegration. To identify articles covering injury-related topics injury and ACL were used. Findings were then compared and analysed in order to identify standardised and feasible assessment methods for movement quality. Because of feasibility only subjective testing methods without any technical or device-related requirements were included. An overview of selected methods is given in Table   1. The judging criteria of the mentioned tests are based on biomechanical risk factors and injury mechanisms of the lower extremity, in particular for ACL-injuries. points. Depending on the sum of the scoring points the test is successfully completed and the athlete is ready for the specified level of rehabilitation. Table 1 shows the specific testing measures of the selected subjective tests for assessing the movement quality. The most known and reviewed screening test is the Functional Movement Screen (FMS). As a further development of the FMS the Athletic Ability Assessment (AAA) aims at high performance sports. The Landing Error Scoring System (LESS) is already used in practice and relatively well known. The Qualitative Analysis of Single Leg Loading (QASLS) is less known and assesses the movement quality during single leg movements only. Another test for assessing the movement quality is the Tuck Jump Assessment (TJA). This simple assessment method is often used in combination with other screening tools. Ultimately the Vail Sport Test (VST) and its specific version for hip injuries, the Vail Hip Sport Test (VHST) is available.

Quality Criteria
An overview of studies on reliability, validity and objectivity of the selected tests is shown in Table 2. It shows clearly that none of the selected tests is explicitly validated yet. This is due to an insufficient number of studies on quality criteria of the mentioned testing methods. Due to the nature of subjective testing on the basis of movement observations it is challenging to fulfill quality criteria in an optimal way. Assessment criteria were developed in order to be able to give -predictive validity partially given [12] -predictive validity given [13] -internal and external criterion validity not given [13] -acceptable [12] [14] -good [15] -excellent [13] -acceptable [12] [14] -excellent [13] AAA n.a.
-excellent [27] -excellent [27] FMS The test design must reflect the complexity of requirements in high performance sports though. Therefore the type of functional testing within the tests is assessed. The test should include different unilateral, bi-lateral and high intensity functional tests in order to create comparable physical demands like the specific sport.
At the same time the series of tests should integrate well observable movement tasks for improving reliability and objectivity.
The used criteria for assessing movement quality are also relevant to ensure a safe rehabilitation/reintegration into high performance sport. If possible these criteria should be based on risk factors and mechanisms of sports injuries (e.g. valgus degree of deformity during landing [28] [29]). Table 3 gives an overview on the fulfillment of selected criteria of the different testing methods.

Recommendations for Use of Testing Methods
No explicit recommendation can be given for any of the subjective testing methods for assessing the movement quality. This is due to a small amount of scientific research on some tests and contradictory results on the validity of others. Based on the mentioned quality criteria advices for the use of subjective tests and first possibilities for the assessment of movement quality within the scope of rehabilitation shall be given.
Although recent studies verified the FMS' reliability and objectivity [12] [13] [14] [15] it cannot be recommended for the assessment of high performance athletes because of the insufficient physical demands of the functional tests included in the FMS. In order to use the FMS in high performance sports a combination with further and physically demanding tests like the TJA can be considered. The current design of the FMS is suitable for non-elite athletes as well as health and fitness athletes performing sports with submaximal load.
The AAA is a result of further development of the FMS [16]. It contains different functional tests which are comparatively physically demanding but still good for monitoring. The addition of maximal plyometric jumps, for example tuck jumps (the athlete jumps for 10 seconds with the knees at hip height each time) should be considered. Disadvantage of the AAA is the complex evaluation sheet due to the versatile functional tests included. Since the AAA is a newly developed tool, further research can redevelop simplified versions. The AAA is recommended conditionally with only one study analyzing the AAA, however showing good reliability and objectivity [16].  [27]. Based on these aspects, the LESS and AAA can be recommended conditionally. A refined depiction of selected tests and associated compliance with listed criteria is given in Table 3.

Objectification and Supplementation of Testing Methods
The Another possibility is the use of straight lines and angles within snapshots (e.g. Valgus angle) by using video technology, which can increase reliability and objectivity [34] and is partially viewed as an objective measure. Although it has to be noted that no rotation can be seen when conducting 2D measures [27]. Investigators who conduct presented screening tests without any technological aid should be experienced in monitoring movements in general and receive specific training within the selected testing method. This enhances inter-rater reliability as well as intra-rater reliability [12] [34] [35]. In order to increase quality criteria and the accuracy of measurement the inspection of the athlete should be carried out by using different points of view-ideally in frontal and sagittal plane as different deviations in movement quality can be viewed from different angles [20].

Outlook
Further studies on the validation of quality criteria under the use of objective and technical measures are essentially needed in order to apply subjective measures reliably.
In general subjective measures within the assessment of movement quality should be used in combination with further tests like strength-, flexibility-and agility testing as well as EMG-measurements. All of these methods are of particular importance for matching the abilities of the injured athlete with the requirements in high performance sports and to eliminate risk factors which could lead to further injuries. The tests should be incorporated in all different stages of rehabilitation to ensure a safe RTP. Only a few basic approaches on an ideal integration of these measures exist up to now [36] [37]. Further studies are necessary. Especially the assessment of movement quality as a measurement of injury risk should not only be done after injury. Regular pre-injury screenings assessing the movement quality should be carried out to prevent injuries.