Background: Threshold to detect passive motion (TTDPM) tests of the knee joint are commonly implemented among individuals with anterior cruciate ligament (ACL) injury to assess proprioceptive acuity. Their psychometric properties (PMPs), i.e. reliability, validity and responsiveness, are however unclear. This systematic review aimed to establish the PMPs of existing knee joint TTDPM tests among individuals with ACL injury.

Methods: The databases PubMed, AMED, CINAHL, SPORTDiscus, Web of Science, Scopus, CENTRAL and ProQuest were searched to identify studies that assessed the properties of knee joint TTDPM tests in individuals with ACL injury. The risk of bias for each included study was assessed at the outcome level for each test. Overall quality and levels of evidence for each property were rated according to established criteria. Meta-analyses with mean differences were conducted using random-effects models when adequate data were available.

Results: Fifty-one studies covering 108 TTDPM tests and 1632 individuals with unilateral ACL injury were included. A moderate-to-strong level of evidence indicated insufficient quality for all of the following: convergent validity, known-groups validity, discriminative validity, responsiveness between subgroups, and responsiveness to intervention. Subgroup meta-analyses for known-groups validity did however find that a starting angle of 15° resulted in significantly worse TTDPM for knees with ACL injury compared to those of asymptomatic persons (mean difference 0.28°; 95% CI 0.03 to 0.53; P = 0.03), albeit based on only three studies. Due to the lack of evidence, it was not possible to estimate the quality of reliability, measurement error, and criterion validity, nor responsiveness from a criterion and construct approach.

Conclusions: Among persons with ACL injury, existing tests of knee joint TTDPM lack either sufficient quality or evidence for their reliability, validity and responsiveness. Significantly worse thresholds for ACL-injured knees compared to those of asymptomatic controls from a 15° starting angle and trends towards significance for some validity measures nevertheless encourage the development of standardised tests. Further research investigating the influence of modifiable test components (e.g. starting angle and motion direction) on the PMPs of knee joint TTDPM tests following ACL injury is warranted.