Sports injuries to the knee: symptoms, causes, assessment and return to sport

The knee is one of the joints most heavily stressed during sport. Running, jumping, braking, changing direction or pivoting on a planted foot exposes the knee's various structures to considerable forces.

When the load applied exceeds the capacity of the muscles, tendons, ligaments, menisci, or other tissues, an injury can occur. In other cases, symptoms develop gradually, due to an excessive increase in training load, insufficient recovery, or continued repetition of the same movements.

Knee sports injuries can affect professional athletes, amateur practitioners, and people who have recently started exercising. Recognising the symptoms and seeking an adequate assessment allows for the identification of the factors involved, the definition of an individualised clinical strategy, and the reduction of the risk of persistence or recurrence of the problem.

Why is the knee vulnerable during sport?

The knee connects the femur, tibia, and patella. Its stability relies on the coordinated action of various structures:

• Ligaments, which limit excessive movements and contribute to joint stability
• Menisci, which distribute load, absorb some of the impact and participate in knee stability
• Articular cartilage, which facilitates movement between bone surfaces
• Tendons, which transmit the force produced by muscles
• Quadriceps, calf, hip, and trunk muscles, which dynamically control movement

This joint primarily allows for flexion and extension movements, but also has a rotational component. Activities involving running, jumping, physical contact, decelerations, or rapid changes in direction increase the mechanical demands on these structures.

A lesion can occur during a single traumatic movement or develop progressively when repeated exposure to load exceeds the tissues' capacity for adaptation.

Most frequent sports injuries of the knee

Anterior cruciate ligament injury

The anterior cruciate ligament, usually abbreviated as ACL, plays a significant role in controlling knee stability, particularly during rotational movements, deceleration, and changes of direction.

The injury often occurs during a rapid change of direction, deceleration, or landing, frequently without direct contact with another player. The person may feel or hear a pop, followed by pain, rapid swelling of the knee, and a feeling of instability or giving way.

Not all ACL injuries necessarily indicate surgery. The decision depends on factors such as:

• Degree of instability

• Presence of associated lesions

• Demands of the sport

• Functional objectives and needs of the person

• Response to rehabilitation process

In cases where surgery is performed, the return to activities involving changes of direction should be progressive and supported by functional criteria. The time elapsed since the procedure is relevant, but should not be the sole decision-making criterion.

Meniscal injuries

The menisci are two fibrocartilaginous structures located between the femur and the tibia. They contribute to load distribution, shock absorption, and knee stabilisation.

A traumatic meniscal tear can occur when the knee twists while the foot remains planted on the ground. In older people, meniscal changes can develop gradually and be associated with degenerative processes.

Symptoms may include:

• Pain in the inner or outer part of the knee
• Swelling
• Pain when squatting or performing rotational movements
• Joint popping or clicking sensation
• Difficulty fully extending the knee
• Joint lock

The approach can be conservative or surgical. The decision depends on the type and location of the lesion, the presence of joint blockage, the intensity and duration of symptoms, and the person's functional needs.

Following meniscus surgery, the return to sport must simultaneously consider the time required for biological healing and the recovery of mobility, strength, motor control, and load tolerance.

Patellar tendinopathy

Patellar tendinopathy, also known as jumper's knee, is a condition associated with overuse of the tendon that connects the kneecap to the shinbone.

It is more frequent in disciplines with repeated jumps, running, accelerations and decelerations, such as basketball, volleyball and certain athletics disciplines.

The pain is usually located below the kneecap and can increase during activities such as:

• Jump
• Running
• Climb or descend stairs
• Squat
• Sitting for prolonged periods

The approach is mostly conservative and based on load management and a progressive exercise programme.

Currently, the intervention is not limited to eccentric exercise. Load intensity, movement speed, type of muscle contraction and exercise frequency should be adjusted to the phase of the condition, tendon capacity and individual response.

Patellofemoral pain syndrome

Patellofemoral pain syndrome is characterised by pain in the anterior region of the knee or around the kneecap. It is common in runners, cyclists and people who perform repetitive activities with a flexed knee.

Pain may arise or worsen when:

• Running
• Climb or descend stairs
• Squat
• Jump
• To remain seated with knees bent
• Suddenly increase the volume or intensity of training

The approach should consider training load, knee and hip strength, mobility, movement control, and the individual characteristics of the person.

Therapeutic exercise, education, and appropriate load management are central components of clinical intervention.

Sprains and collateral ligament injuries

Sprains result from the stretching or partial or complete tearing of a ligament.

The medial collateral ligament, located on the inner side of the knee, is often affected by impacts that push the knee inwards. Depending on the intensity of the mechanism of injury, localised pain, swelling, difficulty bearing weight on the limb, and a feeling of instability can occur.

Mild and moderate sprains are often managed without the need for surgery. More extensive injuries, or those associated with damage to other structures, require medical assessment and a specific rehabilitation plan.

Main causes and factors associated with knee injuries

Knee sports injuries do not have a single cause. They usually result from the interaction between the demands of the activity, the person's physical capacity, load exposure, and the context in which the movement occurs.

Rapid changes in direction

Rotational movements, braking, and changes of direction can expose ligaments and menisci to high forces, particularly when the foot remains fixed to the ground.

The risk also depends on the speed of movement, the position of the trunk and lower limb, the level of fatigue, and the ability to produce and absorb force.

Excessive increase in training load

A rapid increase in distance, intensity, frequency, duration of sessions, or number of competitions may not allow tissues to adapt adequately.

This pattern may contribute to the development of conditions associated with overload, such as patellar tendinopathy and patellofemoral pain.

The load must be analysed individually, considering training history, current physical capacity, sleep, recovery and other activities performed throughout the week.

Deficits in strength and motor control

The strength of the quadriceps, hamstrings, calves, and hip muscles contributes to knee control during running, jumping, landing, and changing direction.

Deficits in these areas do not necessarily mean an injury will occur. However, they can be relevant when associated with other factors such as fatigue, sudden increases in load, changes in mobility, or frequent exposure to demanding movements.

Fatigue and insufficient recovery

With increasing fatigue, the quality and precision of movement can decrease. The person may lose the ability to control the landing, deceleration, or alignment of the lower limb.

Sleep, recovery periods and the distribution of load throughout the week are important components of physical preparation and reducing the risk of injury.

Sports technique

The manner in which a person runs, lands, brakes, or changes direction must be analysed within the context of the sport, the speed of the movement, and their individual characteristics.

There is no single, universally ideal movement pattern. However, certain strategies can increase the load on specific structures and justify technical adaptations or targeted preparation programmes.

Symptoms of a sports knee injury

The symptoms depend on the affected structure, the mechanism of injury, and its severity. The most frequent include:

• Localized or diffuse pain
• Swelling
• Stiffness
• Loss of mobility
• Difficulty supporting body weight
• Feeling of instability or giving way
• Clicking accompanied by pain
• Knee lock
• Loss of strength
• Difficulty running, jumping, stopping or changing direction

An isolated click, without pain, swelling or loss of function, does not always indicate the presence of an injury. Conversely, a click associated with severe pain, rapid swelling or instability should be clinically assessed.

When to seek urgent medical assessment?

You should seek urgent medical assessment when there is:

• Visible deformity after a fall or impact
• Inability to bear weight on the foot
• Rapid and significant swelling
• Blockage preventing knee extension
• Severe pain after trauma
• Loss of sensation in the lower limb
• Changes in temperature, colour or circulation of the foot
• Very hot, red knee accompanied by a fever

Even without signs of urgency, it is advisable to seek a healthcare professional when symptoms persist, worsen, or prevent normal participation in training, competition, or daily activities.

Como é realizada a avaliação clínica?

The assessment begins with the collection of the medical history and the analysis of the injury mechanism. It is important to understand:

• How did the episode occur
• If there was contact, rotation, fall or impact
• When did the swelling appear
• Where is the pain located
• Which movements worsen the symptoms
• If there is instability or blockage
• What is the sport played
• What is the usual training load
• If there are previous injuries to the knee or lower limb

The assessment of mobility, strength, stability, motor control, functional capacity, and load tolerance follows.

Specific clinical tests can be performed for ligaments, menisci, tendons and other structures. These tests help to guide the diagnosis, but must be interpreted in conjunction with the clinical history and other collected data.

When necessary, further tests may be requested:

• X-ray, especially when a fracture or bone abnormality is suspected
• MRI scan, to assess menisci, ligaments, cartilage, and other internal structures
• Ultrasound, particularly useful in the assessment of tendons and superficial structures

Not all knee pain requires imaging. In many situations, a clinical assessment allows for a safe and appropriate approach to be initiated.

The changes identified in the tests should be related to the person's symptoms and function, as some structural changes may be present without causing pain or limitation.

Clinical approach to sports injuries of the knee

The clinical strategy depends on the affected structure, the severity of the injury, age, personal goals, and the demands of the sporting modality.

Conservative approach

Many injuries can be managed conservatively, including:

• Some ligament sprains
• Tendinopathies
• Patellofemoral pain
• Certain meniscal lesions
• Some cases of ACL injury

A conservative approach does not just involve rest. It typically includes education, load management, mobility recovery, therapeutic exercise, progressive strengthening, and a gradual reintroduction of activities.

Prolonged, complete rest is rarely necessary and can contribute to loss of strength, physical capacity, and confidence in movement.

Surgical approach

Surgery may be considered when there is disabling functional instability, persistent joint locking, certain structural tears, or a lack of satisfactory clinical progress with an adequately managed conservative approach.

The decision must be individualised, weighing up potential benefits, limitations, risks, the person's objectives and sporting demands.

Even when surgery is indicated, physiotherapy can play an important role before and after the procedure.

The role of physiotherapy in recovery

Physiotherapy intervention should be adapted to the injury, the stage of recovery, the physical capacity of the person and the demands of the sport practised.

Initial symptom control

In the early days, goals may include protecting the injured structure, managing oedema, preserving possible movement and reducing activities that significantly aggravate symptoms.

The PEACE & LOVE model proposes an approach that combines protection and education in the early stages with progressive loading, exercise, cardiovascular conditioning, and restoration of movement confidence throughout rehabilitation.

The application of this model should be adjusted to the type of lesion and the individual clinical response.

Mobility recovery

Stiffness and swelling can limit knee flexion or extension. Progressive range of motion recovery is relevant for walking, climbing stairs, squatting, and returning to running.

Full knee extension deserves particular attention in several injuries, as its limitation can alter gait and hinder adequate quadriceps activation.

Progressive strengthening

The exercise programme may involve:

• Quadriceps
• Hamstrings
• Gemini
• Hip muscles
• Trunk musculature
• Global lower limb exercises

The load should evolve according to the individual's capacity, symptoms, and response in the hours and days following exercise.

Strengthening can involve different types of muscle contraction, ranges of motion, speeds, and resistance levels.

Neuromuscular balance and control

Balance, proprioception, landing, deceleration, and change of direction training can contribute to regaining knee control in specific sports situations.

These exercises should progress from predictable, controlled tasks to situations that are faster, more complex, and closer to the actual demands of the sport.

Sport-specific training

In the final phase of rehabilitation, movements progressively closer to the demands of training and competition are introduced, such as:

• Race
• Acceleration
• Deceleration
• Jumps
• Landings
• Changes of direction
• Physical contact, when applicable
• Tasks performed while fatigued

Progression should consider not only the isolated execution of movements but also the ability to repeat them with quality and adequate tolerance.

When is it safe to return to sport?

The absence of pain does not necessarily mean recovery is complete.

The return to sport should consider different criteria:

• Absence or adequate control of oedema
• Full or sufficient mobility for the modality
• Strength compatible with sporting demands
• Ability to run, jump, stop, and change direction
• Quality and movement control
• Tolerance to training volume and intensity
• Confidence in the knee
• No significant fear of movement
• Capacity to perform specific tasks for the modality

The comparison between the two limbs can be useful, but should not be used in isolation. Seemingly adequate symmetry may hide loss of capacity in both limbs or differences in the way force is produced and absorbed.

The return should be progressive. Typically, the person starts with individual and controlled activities, progresses to conditioning training, then participates in full training, and only then returns to competition.

The return to participation, the return to sport, and the return to performance correspond to distinct phases. Presence in training or competition does not necessarily mean that the athlete has recovered their pre-injury performance level.

How to reduce the risk of knee injuries?

Not all injuries can be avoided. However, some strategies can help reduce the risk and improve preparation for the demands of sport:

• Increase the training load progressively
• Maintain a regular strength program
• Training jumps, landings, braking, and changes of direction
• Carry out a structured warm-up
• Respecting adequate periods of rest and recovery
• Monitor pain, fatigue and performance changes
• Assess relevant limitations in strength, mobility, or motor control
• Adapt training to the sport, age and experience level
• Maintain preventive work after returning to sport

Prevention should be specific to the person, the sport practised, and their clinical and sporting history.

Structured programmes that integrate strength, balance, neuromuscular control, running, jumping, and changes of direction can help reduce the incidence of some injuries, particularly when carried out regularly and with appropriate progression.

Understanding knee recovery from an integrative perspective

A sports injury should not be addressed solely with the aim of reducing pain. It is necessary to understand the mechanism of the injury, identify the factors that may have contributed to the problem, restore physical capacity, and prepare the body again for the real demands of training and competition.

An integrated perspective may consider:

• Damaged structure and its biological process
• Mobility, strength and the ability to produce and absorb load
• Motor control and technical requirements of the sport
• Volume, intensity and distribution of training
• Sleep and recovery
• Injury history
• Trust and perception of safety during movement
• Personal and sporting goals

Individualised assessment allows these factors to be framed and a progression compatible with the clinical condition and the person's requirements to be defined.

Sports physiotherapy can integrate therapeutic exercise, manual therapy, functional training, education, and prevention strategies. The selection of these interventions should be based on clinical assessment, functional progression, and individual response.

The presence of persistent knee pain, swelling, instability, locking, or limitation warrants assessment by a qualified healthcare professional.