Is it time we better understood the tests we are using for return to sport decision making following ACL reconstruction? A critical review of the hop tests

Key points

1. 01The four standard hop tests (single, triple, crossover, and 6-metre timed) show adequate reliability but poor-to-moderate sensitivity for detecting deficits, with values ranging from 44 to 58% at an 85% limb symmetry index threshold
2. 02Using more than two hop tests provides no greater ability to detect abnormality due to high collinearity; the single hop for distance alone showed equivalent sensitivity to any two-test combination
3. 03Hop distance symmetry can appear normal (mean LSI 92%) while the involved knee still shows reduced peak flexion and altered loading, meaning performance scores overestimate true recovery
4. 04Testing the uninjured limb before surgery as a pre-operative benchmark is strongly recommended; one study found only 29% of patients met 90% LSI criteria when pre-operative distance was the reference, versus 57% when post-operative uninvolved limb performance was used
5. 05Vertical and side-hop tests show higher sensitivity (72-86%) for detecting deficits compared to horizontal hops, but specificity concerns limit their routine use at standard LSI cut-offs

How it was conducted

Design

Critical narrative review

Focus

Four standard single-leg hop tests used in ACL reconstruction return-to-sport protocols: single hop for distance, triple hop for distance, crossover hop for distance, and 6-metre timed hop

Constructs examined

Reliability, measurement error, relationships with strength and subjective function, temporal change over time, sensitivity and specificity, collinearity, and movement quality

Literature scope

Studies from early 1980s to 2019 covering ACL reconstruction populations and healthy controls

What they found

• Reliability of the three hop-for-distance tests was excellent with ICC values reported at 0.92, and similar for single, triple, and crossover hop for distance; the 6-metre timed hop consistently showed lower ICC values
• The single hop for distance displayed the lowest percentage change required to detect meaningful change beyond typical error (8.09%), while the 6-metre timed hop required the largest change (12.96%)
• Individual hop test sensitivity for detecting deficits using an LSI threshold of 85% ranged from 44 to 58%; the 6-metre timed hop showed sensitivity as low as 26% in one study
• Using 2 hop tests increased sensitivity to 50% versus 2% for a single test, but using all 4 tests provided no greater sensitivity than using any 2 tests
• The SHD and THD showed strong correlation (r > 0.8); SHD and T6H showed similar strong correlation (r = 0.89); only SHD and CHD showed relatively lower correlation (r = 0.56), suggesting they may measure different constructs
• When pre-operative uninvolved limb distance was used as the reference, only 29% of patients met 90% LSI hop criteria at return to sport, compared to 57% when post-operative uninvolved limb performance was used
• At 52 weeks post-surgery LSI values were within the acceptable range (>90%), yet the data indicated recovery was still on an upward trajectory at that time point
• Unilateral repeated vertical hop test sensitivity at 54 weeks post-surgery was 72% versus 28% and 16% for SHD and THD respectively, with matched specificity of 96%
• Side hop test sensitivity was 77% but specificity dropped to 87% at 90% LSI, meaning 13% of healthy subjects would appear abnormal
• Patients achieving 90% LSI on single hop for distance still showed reductions in peak knee flexion on the involved limb, indicating compensatory strategies

Limitations

• This is a narrative critical review, not a systematic review or meta-analysis, so selection and interpretation of studies may be subject to author bias
• The underlying primary studies reviewed have substantial clinical and methodological heterogeneity, making direct comparisons and pooled conclusions difficult
• The standard hop tests were not originally designed with biomechanical assessment in mind, and most clinical settings lack the equipment to measure movement quality routinely
• The contralateral limb used as a reference benchmark is itself affected by deconditioning and fear after ACL injury, potentially inflating apparent symmetry scores

Why it matters

For patients

Passing the standard hop tests does not guarantee your knee is truly ready for a full return to sport, because these tests can miss ongoing movement quality problems and re-injury risk that your physiotherapist should also assess.

For clinicians

The current 4-test hop battery is likely redundant; 2 tests (particularly single hop for distance plus one other measuring a different construct) appear sufficient for detecting deficits, freeing time to assess movement quality and use pre-operative contralateral limb values as the benchmark.

For readers

This review challenges the routine use of all four hop tests and the sole reliance on hop distance symmetry as return-to-sport criteria after ACL reconstruction, pointing toward more individualized, multi-construct assessment strategies.