12.4 Return-to-Sport Decision Making and Functional Testing

Return-to-Sport Decision Making and Functional Testing

Returning to sport after a musculoskeletal injury is a progression from protected participation to the demands of competition. After anterior cruciate ligament (ACL) reconstruction, elapsed time informs the assessment of healing. Clinical findings, physical performance, the athlete's confidence and the demands of their sport also guide when to advance. Concussion follows its own clinical and graduated recovery criteria, covered in Acute Athletic Injury Assessment and On-Field Management.

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The Return-to-Sport (RTS) Continuum

The 2016 Bern consensus describes three stages in the return-to-sport (RTS) continuum.

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The Multi-Domain Objective RTS Testing Battery

Select the tests and progression criteria for the injury, procedure and sport. For ACL rehabilitation, a multidomain assessment combines knee status, objective strength and function, movement quality, sport-specific exposure and psychological readiness.

Domain 1: Clinical examination and knee status

Check pain, effusion, motion and stability. An athlete with persistent swelling, loss of extension or episodes of giving way during training needs reassessment before advancing to higher loads. Use goniometry for motion and an appropriate examination of ligament stability where indicated. These findings guide progression alongside expected tissue healing and any procedure-specific restrictions.

Domain 2: Quantitative strength

Use standardized dynamometry when available and document the test position, device, muscle group and velocity or contraction type. Isokinetic peak torque can be reported in newton-metres per kilogram of body mass. Record absolute scores for both sides and compare them with the athlete's own prior performance or an applicable reference measured with a comparable protocol.

For tests where a higher value indicates better performance, such as quadriceps torque and hop distance:

$$\text{LSI} = \frac{\text{Involved limb score}}{\text{Uninvolved limb score}} \times 100\%$$

Limb symmetry index (LSI) reports a relative result. If quadriceps torque is 1.65 N·m/kg on the involved side and 1.75 N·m/kg on the uninvolved side, the LSI is about 94%. If the athlete previously produced 2.4 N·m/kg on each side with the same test, the current values also show bilateral loss. A weakened comparison limb can make the symmetry result look reassuring. Compare both absolute values before progressing.

Some ACL protocols use approximately 90% symmetry in a wider test battery. For professional athletes leaving clinical rehabilitation to begin club training for high-demand pivoting sports, the Aspetar guideline proposes 100% isokinetic quadriceps and hamstring peak-torque symmetry at 60 degrees per second, along with restoring absolute values and meeting other criteria. The appropriate target depends on the protocol and the stage of return.

Domain 3: Functional hop tests

When the knee tolerates impact and the athlete is ready for functional testing, compare three distance tests (single hop, triple hop and crossover hop) and the 6-metre timed hop. Observe how the athlete takes off, lands and decelerates as well as the distance or time. An athlete can cover a similar distance while changing how load is distributed through the knee, hip and trunk.

For the 6-metre timed hop, faster is better, so divide the uninvolved time by the involved time. If the uninvolved limb takes 2.0 seconds and the involved limb takes 2.5 seconds, the LSI is 80%. Reversing the ratio would report 125% and make the slower limb look better. Apply any symmetry criterion to each test as specified by the protocol.

Domain 4: Dynamic balance and control

The Lower Quarter Y-Balance Test uses single-leg stance and anterior, posteromedial and posterolateral reaches. Compare reach direction and movement quality between sides. Calculate a composite score for each stance limb from its three maximal valid reaches using the same units as limb length:

$$\text{Composite reach} = \frac{\text{Anterior} + \text{Posteromedial} + \text{Posterolateral}}{3 \times \text{Limb length}} \times 100\%$$

In one study of high-school basketball players using the Star Excursion Balance Test, an anterior reach difference greater than 4 cm was associated with injury. The association for a composite below 94% was reported in the female players. These findings were specific to that test and population. Use the Y-Balance findings to identify limitations and monitor progress. Individual reinjury risk or clearance cannot be assigned from those cutoffs.

Domain 5: Agility and reactive change of direction

A planned shuttle measures performance on a known route. Reactive drills add a decision, such as changing direction after a visual cue. Progress both the movement demand and the unpredictability to resemble the athlete's sport. Record how the athlete controls deceleration and responds to repeated efforts, alongside timing and tolerance.

Domain 6: Psychological readiness

The ACL–Return to Sport after Injury scale (ACL-RSI) measures emotions, confidence and appraisal of risk after ACL injury. The original form has 12 items and reports a score from 0 to 100. Use the result with the interview to understand concerns and track change. A low score can help identify a need for support. It does not quantify an individual's risk of another tear.

If the athlete is reluctant to cut under pressure despite good performance on planned drills, start with the situations that feel manageable and progress toward unpredictable drills and team play. Involve the athlete in choosing the progression and consider additional psychological support when needed.

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The StARRT Framework and Shared Decision-Making

The Strategic Assessment of Risk and Risk Tolerance (StARRT) framework organizes a shared decision by asking three questions.

1. Tissue health. What load can the healing tissue and athlete currently tolerate? Consider healing, symptoms, stability, strength, performance and psychological readiness.
2. Tissue stresses. What load will the proposed activity impose? Compare the position and competition level, the training volume, the surface, and the frequency of actions such as high-speed cutting or contact.
3. Risk tolerance modifiers. What contextual factors affect how the athlete and team weigh the risk? Discuss the athlete's goals, timing in the season and practical pressures. These factors inform the decision without substituting for clinical readiness.

The athlete and treating team can agree on a graded plan with specific exposures and reassessment points, such as completing a team session and checking swelling and confidence before adding competition minutes. Follow the applicable team, clinical and competition requirements for clearance.