Return to sports: Restoring function and performance in sport after injury

Summary
After a sporting injury, alongside the diagnostic and resulting therapeutic aspects, the return and timing of the return to sport have an important role to play for patients. Generally speaking, a time-based recommendation in relation to the return to sport is made according to clinical and radiological investigations and the patient's own estimates. These factors, however, are not sufficient for judging an individual's capacity for sport. The nature of the injury and its treatment determine the healing processes. These normally occur in different phases. The neuromuscular function required comes from the requirements profile of the type and level of sport in question. It is achieved as a function of the quality and quantity of the rehabilitation measures. Extrinsic and intrinsic factors influence this course, as do psychological processes. To safeguard rehabilitation goals and to control the rehab process, return to sports tests, when used in a manner that is appropriate to the phase of the patient's recovery, can be useful.

Key words: return to sports, sporting injury, rehabilitation

Introduction
In our active society, sport plays a key role. Injuries, on the other hand, are seen as undesirable side effects. The risk of injury, the location and the type of injury depend among other things on the type of sport and the level at which it is being played. Convalescence and the return to training and possibly competitions are very important to the patient.

A targeted diagnostic process forms the basis for differentiated treatment concepts to ensure adequate healing and the recovery of the ability to take part in sports and competitions. In addition to the history and clinical examination, imaging methods and possibly biomechanical measurements are used. With the data obtained, the nature of the injury is determined and possibly classified into various types or degrees of severity. Known anatomical and biomechanical risk factors that influence the injury can also be determined. This means that conservative or surgical treatment options can be applied to best effect for the various pathologies involved. Despite these prerequisites, the return to sporting stresses after injury is significantly limited. Only around 40-80% of patients with various sporting injuries return to their original performance level in their type of sport. 1,27,37

Clinical tests, radiological examinations and subjective patient self-assessments following rehabilitation are unable to adequately explain this fact. 4

Even the very different information regarding the timing of the return to sport is unsatisfactory and is based mostly on the criteria outlined above.

The recommendations for a return to sport vary, for example following an ACL repair, from 3 to 9 months. 2,21,30.34

Another reason to tackle this issue - return to sports - is the secondary risk of injury which in some cases is of a not inconsiderable order. Re-rupture rates of 2.5 - 13% following ACL reconstruction are described, reluxation rates of up to 40% following the treatment of patellar luxations, and high rates of recurrence of up to 80% following supination trauma of the upper ankle with capsular ligament injuries.6,11,23,33,36

The timing of the repeat injury is also interesting. Following an ACL repair, the re-rupture rate upon the resumption of competitive stress < 7 months following surgical treatment (15.3%) is significantly higher than after 7 months post-operatively (5.2%), regardless of the surgical technique used.22 A large proportion of new inversion injuries to the ankle occur in the first 12 months following the primary injury.6 Clearly, the factors applied in everyday clinical situations to assess the capacity for sport in relation to the timing and risk of secondary injury following injury are inadequate. It would be ideal to be able to assess load capacity using defined criteria. However this would require more work with a multi-layered analysis.

Around 30 years ago, various specialist disciplines were looking at the issue of returning to sports following injury. Even then, it was clear that rehabilitation must relate to the demands of the type and level of sport involved, the therapy content must be built up gradually and the content must relate to the various demands and functions of the musculoskeletal tissues involved.15,26

Stages of activity level
Various stages are worked through during the return to sport. These are described below. <strong/>

Return to Activity
The term "Return to Activity" represents the first level of rehabilitation to be achieved. This is taken to mean the resumption of basic motor functions or activation of fundamental movement patterns. <strong/>

Return to Sports
The next step is  "Return to Sports", which is characterised by the resumption of sport-specific training with selected content, such as dribbling in football, and the avoidance of risky stresses. <strong/>

Return to Play
The "Return to Play" is characterised by the resumption of training content that closely approximates actual competitive performance, simulated under training conditions. 

This status corresponds to almost complete sporting capacity. The athlete has only slight or no injury-related limitations. The neuromuscular and metabolic capacity becomes appropriate for the requirements profile of the sport in question. Negative movement strategies that can favour injury are no longer present in the training situations carried out.

Return to Competition
The "Return to Competition" then represents the full recovery where the requirements in the particular type and level of sport chosen can be met without limitations and if possible without any increased risk of further injury (Fig. 1).18,19,20.

Influencing factors
Various criteria should be used to assess load capacity following injury. Structural, functional and psychological factors can be classified (Fig. 2). <strong/>

Structural factors
The structural factors relate on the one hand to the injury itself, and on the other to anatomical influencing factors. The location, type and severity of the injury, as well as the treatment, determine the healing processes that, together, form a highly complex biological process. A distinction can be made between the different phases of wound healing. After actual damage to the musculoskeletal tissues following the injury with haemostasis and exudation, the inflammation phase begins followed by the proliferation phase. The repair or generation phase comes next.14

For optimum healing, these phases and their biological functions should take place in the best possible chronological sequence, and with an optimum intensity.13 Defined healing processes apply following surgical interventions too. An anterior crucial ligament transplant, for example, undergoes a remodelling process following the primary healing phase in the drill channels.10,16 The chronological component required for this cannot be easily accelerated up until the final conversion of the tendon transplant into a new ligament structure.

The healing processes must therefore often be protected through limitations of movement and a reduction of the forces impacting on the injured structure until it heals.

Orthoses that meet the protection requirements can be used in a targeted manner for this. This can be achieved through carefully calculated functional elements combined with comfortable constructions and makes exacting demands of the developer and product manufacturer.

The forces impacting on an anatomical structure depends on the everyday stresses, the rehabilitation content and the sporting challenges. This is an area that can be specifically determined, managed and controlled. It is only possible to a certain degree to specifically define the best possible stimulus for each phase of healing. As the healing processes advance, the function is increasingly improved with suitable rehabilitation and becomes the focus of the treatment content.

There are also other factors involved in relation to possible follow-on injury or negative healing processes. These can be classified into extrinsic and intrinsic factors. Intrinsic factors can be taken to include, among others, conditional and coordinative performance, the psychological status and anatomical and anthropometric data.39 Anatomical risk factors for ACL injuries include the notch width, the tibial slope, the geometry of the medial tibial plateau and the different condylar radii.28,40,41 Extrinsic factors relate, for example, to the type of sport and its rules, the floor characteristics, the equipment used, the weather conditions and the support team.39

If there is an apparently equivalent injury but a different constellation of extrinsic and intrinsic risk factors and demands, the treatment recommendation as well as the process up until "return to competition" can be assessed differently, and goals, content and the speed of rehabilitation can be defined in a different way.

Functional factors <strong/>

Requirements profile
A defined goal is essential for determining the performance required. Each type of sport has a specific sports motor requirements profile. The level of sport and the goals determining the importance of each individual skill required for each type of sport.

The patient's starting point before the injury is often only known in performance sports through regular performance diagnostic and biomechanical investigations as well as the current stage of development in training and the competition. In amateur sports, information on the type of sport being carried out, the level and the training history with its content, extent and intensity, however, provide a good summary of the current situation.

Phase-adapted rehabilitation
A phase-adapted rehabilitation programme must firstly be adapted to one of the four healing phases and secondly to the four phases of activity, allowing the healing of the injured structure and restoration of desired function to be brought together in the various areas.

The healing of the injured structure can often only be accelerated to a small degree. Unfavourable disruptive factors such as swelling, adhesions, pain, long periods of immobility and excessive inflammation must be checked regularly and avoided as much as possible through suitable therapeutic measures.

Functional performance
The range of functional performance behaves reciprocally with healing. While the emphasis at the beginning is on the healing process and this influences the chronological sequence considerably, it becomes increasingly less relevant as the healing process progresses. Neuromuscular and metabolic performance increases in importance for the assessment of load capacity.

Following the comparison between the current and determined target status, first general and then specialist and sport-specific treatment content is defined. This must be adapted to the limits of the healing processes of the injured structure. The treatment is implemented in accordance with physiotherapy expertise and sports science, training methods-related and biomechanical principles.

The development of neuromuscular function and metabolic performance depends greatly on the quantity as well as quality of rehabilitation and training content. The rehabilitation plan should be customised to the starting situation, the potential or realistic amount of time involved and the defined goals. Step-by-step training uses relevant stimulus for accommodation, however it also protects against over-taxing and under-achieving and minimises the risk of further injury.

The training time required to achieve the goals depends partly on the difference between the current and target status, and partly on the customisation of the training.

Optimised movement sequences and muscular support around a joint reduce the resulting forces and therefore the stress on various joint structures, however these often cannot be measured directly. However it is useful to systematically train stopping and starting movements, as these occur in many types of sport. Methodical series can be used to practice stability for the leg and pelvic axes or ability to balance first generally and then later on a more specific basis (Fig. 3,4,5,6). Determining the causes of the injury is also an important element. This includes the analysis of the mechanism of injury and can lead to the development of treatment and training content that are suitable for minimising negative movement patterns. This creates favourable conditions for the anticipated stresses and strains. One training option is the simulation of risk situations under controlled and manageable conditions. This firstly familiarises the athlete with the problem situation, and secondly he can develop solution strategies without fearing injury to be able to manage these risk situations successfully.

Safety / tests
Circumference measurement and a visual assessment of the muscles alone have only a slight correlation with neuromuscular performance. So increasingly, return to sport tests are being used in everyday clinical situations even though there is no significant evidence for these tests based on strict scientific criteria.5

Sports biomechanical and metabolic-physiological measurements can be carried out in the domains of conditioning, technique, suitability and load. The results of these analyses are used as the basis for managing the design of the load, the conditioning and technique training, the performance prognosis and safety in the individual phases of the rehabilitation process.

A distinction can be made between tests that measure one component of performance in isolation and functional tests. The advantage of isolated testing methods such as strength measurement is that the measuring parameter can be very accurately attributed to an individual ability, in this case strength (Fig. 7). The results of the measurements are indexed either according to known reference values, compared with the target values of the requirements profile or the limb symmetry index (LSI) is used to determine any deficits compared to the uninjured side of the body. With the LSI, for a safe return to sporting stress at the original level, values are required that are equivalent to > 90% of the healthy extremity. The primary objective here is to ensure that the injured extremity achieves an acceptable status in order to minimise overloading.36 The disadvantage of an isolated measuring parameter is that conclusions regarding a safe return to everyday or sporting activities are very difficult to draw. Since it is rare that only one performance component determines the requirements profile, it makes sense to carry out multiple tests in order to cover the bandwidth of relevant factors and to increase the results' informative value.

Functional tests to  determine performance simulate the influencing forces during sport-specific stress under controlled clinical conditions. Test criteria can be derived based on biomechanical knowledge and requirements profiles of loads. The tests should determine the various performance-relevant factors and take account of the timing of the rehabilitation process. In other words, do not exceed the anticipated load capacity and require realistic performance. To put it another way, the difficulty of the tests should always be commensurate with the current status of the joint function and the neuromuscular status. It is also essential to satisfy the quality criteria of measurements as much as possible, i.e. they should be reliable, reproducible, valid and objectifiable.7 Usually both quantitative and qualitative criteria are used to evaluate the tests.

Relatively simple tests are various hop tests. In a single hop test, for example, the hop width is measured and in the side hop test (Fig. 8) the number of hops in a defined time are measured to determined the jumping strength stamina. The values can also be compared here with reference values or the LSI can be calculated. The functional movement patterns are evaluated in qualitative terms based on suitable factors. An example of this is the landing error score system (LESS). In this case, a defined drop jump from a height of 30 cm is completed and then various joint and body positions are systematically evaluated via a points system and a total value determined that measures the quality of a landing.29

The various tests should demonstrate good informative merit with regard to load capacity and safety during stress. This means that the control of the rehabilitation process can be optimised. In addition, training and therapy content can be derived in the case of deficits. These are now used in prevention programmes such as the "FIFA 11+" programme to avoid knee injuries in football. Validated training programmes have now also been described for other types of sport.

Psychological factors
Not least, psychological factors must also be included in rehabilitation and decision-making regarding the exposure to training and competition stress.

Injuries generally primarily lead to a somewhat negative psychological reaction such as tension, a diminished sense of self-worth, anxiety and depression.35 The social environment around an athlete with their family, trainer, group of friends, doctor, physiotherapist and other people can provide help but can also trigger negative psychological reactions through unrealistic expectations. Extrinsic motivation is more associated with a negative perception of and attitude to the "return to sports" process than intrinsic motivation, which usually generates a positive attitude.32

The athlete's ability to handle stress also influences the rehabilitation measures.24 The current data indicates that positive psychological behaviour is associated with a higher likelihood of returning to sport at the original level following injury.3

Key factors for healthy psychological development during the rehabilitation process were determined to be independence, especially with intrinsic motivation and the feeling of self-worth.12 In terms of cognitive emotional abilities, the learning of a modified willingness to take risks, the resolution of anxieties and an increase in self-confidence, as well as satisfaction with a positive mood are crucial.31 Athletes can be made aware of all of these factors even before injury and trained in a positive manner. However during the rehabilitation process, these points can also be influenced by realistic rehabilitation goals and appropriate expectations by the individual's surroundings and help towards achieving a positive attitude to the healing process.17 The fear of re-injuring oneself or not being able to return to sport is lost during an optimised rehabilitation process and then increases significantly prior to returning to competitive sport.8,9 Fear of further injury is also the main reason for giving up the sport or practising the sport at a lower level4 The phase-like progress of treatment with the development of the required performance in accordance with the sport-specific requirements and the batteries of tests between the stages of therapy create confidence around the challenges in the sport. Special psychological screening tools, such as the patient-orientated, disease-specific ACL RSI (return to sport after injury) questionnaire (German version), can objectivise the psychological factors.25

Conclusion
Since sporting injuries can lead to limited sporting ability and produce a secondary risk of injury, various principles should be borne in mind in relation to treatment. A phase-adapted rehabilitation process should take account of structural, functional and psychological factors and be coordinated with the sport-specific requirements profile.  To begin with, the healing process is the priority and its chronology can be influenced little, however targeted therapeutic and protective measures are needed. Further on, the functional component gains in importance, which can be trained at first generally and later specifically in order to improve and assess the load-bearing capacity. This means that the various stages of activity can be achieved reliably and with low risk.

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