Several other hopping tests may also provide adequate discriminative ability yet have only been reported by 1 or 2 studies. The single-limb hurdle test, 6-m crossover hop test, square hop test, and up-down hop test also demonstrated moderate-large individual effect sizes. Each of these tests are similar to the timed-hop tests, as they each require the participants to perform a task or course as fast as they can on a single limb. The greatest differences exist regarding the amount of vertical, lateral, or forward movement across tasks. However, the relative effectiveness of these tasks, although less studied than the single-limb side-hop or figure-of-8, suggests that tests that require components of speed, power, and agility in a combination of planes will serve to differentiate patients with CAI. These findings are consistent with several theories behind CAI that suggests a multifaceted problem affecting multiple functional abilities.61,62 Thus, including a timed-hop test such as the side-hop or figure-of-8 test during evaluation of individuals with CAI is valid and appropriate.
Interestingly, based on the results of the meta-analysis, the single-hop jump for distance does not differentiate those with CAI from healthy controls. The single-hop jump is much different than the timed-hop and side-hop jump testing because of the fact that it assesses and requires greater muscular strength and power rather than speed and agility. Although interesting, this negative result is rather unsurprising because of the evidence that the role of ankle strength in CAI is widely disputed and equivocal.63–68 Furthermore, this test stresses the joint primarily in the sagittal plane, rather than the frontal and transverse planes that would be more difficult for patients with CAI. Similarly, another primarily uniplanar test that was studied by only 1 group, the triple-crossover hop test demonstrated a small effect size. The triple-crossover hop test such as the single-limb hop for distance requires participants to jump as far as possible, but in this test it is the maximum distance after 3 jumps across a 15-cm line. Although the incorporation of a crossover adds a lateral component, the test outcome is primarily the distance advanced in the forward direction. Therefore, using FPTs in those with CAI that require muscular power within the sagittal plane seems to be ineffective compared with agility-based hopping tests.
A third class of hopping tests observed in this review were those requiring individuals to hop across a pattern, scoring individuals on “errors” rather than a measure of time or distance. The multiple-hop test across 3 studies demonstrated a large pooled effect with the rest demonstrating conflicting results according to effect size calculations. Although similarly requiring the functional ability of muscle strength, power, and agility to perform hops, an additional component of postural stability is added by scoring individuals on their ability to “stick” a landing. Although intriguing, this does require a degree of subjectivity for the assessor that may serve to bias results. Similar measures exist throughout the CAI literature using instrumented measures derived from force plates. Moderate evidence exists establishing diminished postural control during hopping as quantified through the dynamic Postural Stability Index.69–72 However, this measure relies on precise force calculations with differences between uninjured and injured individuals often not grossly visual to an assessor. As conflicting results exist using noninstrumented measures, additional studies are necessary to determine the ability of FPTs using error systems during hop landing to discriminate between healthy and CAI individuals.
The SEBT, depending on the direction, also provides adequate discriminative ability between those with without CAI. The anteromedial, medial, and posteromedial directions each demonstrated moderate mean-effect sizes; however, the anterior and posterolateral directions were small and considered unimportant. Based on these results, those with shorter anteromedial, medial, and posteromedial reach distances are more likely to have CAI. This could potentially be explained by considering the shifts in the center of gravity occurring through reaches in medial direction, causing tensile forces to be applied on the lateral ankle. A previous systematic review has also been completed on the SEBT73; however, the authors chose not only CAI, but other pathologies such as ACL injuries. In addition, studies were included that assessed the injured compared with uninjured limbs as well as CAI compared with controls. Although the authors similarly concluded that the SEBT was an effective FPT in those with CAI, their study did not resynthesize data to determine mean effects, nor was their main purpose to identify the differences in the SEBT across CAI populations. Based on the current results, not all directions of the SEBT have similar prognostic ability as the anteromedial, medial, and posteromedial directions provided the best clinical utility. Although this is not a particularly new finding, some previous studies have attempted to address this by simplifying the SEBT to the Y Balance Test, which includes only the anterior, posteromedial, and posterolateral directions.74,75 However, it seems that the anterior direction may not be as sensitive enough to differentiate between controls, and CAI and clinicians should consider the anteromedial, medial, and posteromedial directions specifically for individuals with CAI.
Balance and postural control deficits are often described in those with CAI, which could potentially contribute to functional performance deficits observed during the SEBT.50,70,72,76,77 Although the SEBT is considered a dynamic postural control task, requiring movement of the body over a stationary base of support, additional clinical tests are used to assess static postural control. The foot-lift test (counting the number of times a part of the foot lifts off the ground) seems to be an adequate discriminating test, whereas the time-in balance36 also demonstrated large effects in a single study. The BESS—an error system identifying gross instability during 3 to 6 stance conditions—was reported in 2 studies36,59 and demonstrated a moderate-large effect size between CAI and control participants. These findings suggest that FPTs requiring an individual to maintain static postural control are able to yield similar results as seen in studies using advanced equipment such as force plates.
No studies provided a direct comparison between abilities of hopping tests and balancing tests in discriminating CAI. As previously stated, these assess different components of ankle function with the former addressing muscular strength, power, and agility and the latter assessing proprioception and neuromuscular control. Given these different components, it may be recommended that both hopping- and balance-based measures be included in the assessment of patients with CAI. Although these would combine yield very high effect sizes and a strong ability to predict functional instability in these patients, there are additional components that should be considered. Dorsiflexion deficits are consistently observed in those with CAI.78–80 To some extent, this may be assessed through the anterior reach of the SEBT, as a recent study found that dorsiflexion range of motion, eversion strength, and time-to-boundary contributed most to SEBT reach distances.77 However, further studies assessing dorsiflexion range-of-motion through simple tests such as the weight-bearing lunge should be considered.79
The included studies in the systematic review were case–control and cross-sectional studies, described as level IV and III evidence, respectively, indicating limited methodological quality. In addition, the average STROBE score indicates relative consistency in the methodological quality of the evidence. With a maximum of 22, the average score as a percentage was 78.6% ± 7.3%. The 2 most common faults were no indication of addressing sources of bias, including blinding procedures as well as providing a sample size justification. Other notable sources of demerits included providing information related to distributive statistics, funding sources, and indications of study design early in the manuscript. Improving methodological quality and study design stands to greatly improve FPT evidence. Because of these differences in reporting only pooled effect sizes were able to be calculated as opposed to cutoff scores for individual tests. Future studies may want to better identify and address systematic ways to improve the quality of manuscripts to elevate the literature.
Across the studies, there was also inconsistent reporting of inclusion and exclusion criteria making comparisons difficult. In 2013, recommendations put forth by the International Ankle Consortium established guidelines for reporting populations of individuals with CAI; however, many of these studies predated these recommendations and therefore did not provide information necessary to understand these populations. One notable point of caution that should be added is that most of the studies included in the analysis were conducted on relatively physically active individuals. This is because most of the research on CAI is conducted by sports medicine specialists. Whether these results apply to more sedentary populations is unknown. Thus, additional CAI research may want to focus on nonphysically active populations. It remains possible that different measures may better apply to different populations.
Other limitations include the sample size of both the included studies and the total number of studies included in this meta-analysis. The sample sizes of the studies themselves limit their statistical power and generalizability of the effects found. Larger samples would provide superior evidence for the use of FPTs in those with CAI. The total number of studies also limits the effects of this meta-analysis. As reported, many of the FPTs have only been assessed in 1 or 2 limiting the ability to perform a meta-analysis on those individual tests. In addition, pertaining to the SEBT anteromedial and posteromedial directions, the estimates for the fail-safe N calculations indicate that publication bias may be present with 4 additional publications necessary to negate the present results.81 Although this is concerning for the SEBT, the fail-safe N calculations for the timed-hop and side-hop calculations are very high, indicating strong, stable effect sizes. This provides evidence that more studies with larger samples need to be conducted to properly evaluate the alterations in muscle activation strategies during jump landing activities in those with CAI.
Level B evidence exists suggesting that the side-hop, timed-hopping, multiple-hop tests, and foot-lift test are able to discriminate between those with CAI and healthy individuals. Level B evidence also exists suggesting that the medial, anteromedial, and posteromedial components of the SEBT are similarly able to differentiate. Although a multitude of additional tests exist presenting a wide range of effect sizes, it seems that those tests that include timed measures of lateral hopping and those quantifying balance may have clinical utility. Recent evidence suggests that combining the results of multiple FPTs has greater clinical utility than singular tests.40 Specifically, a combination of a version of the side-hop test and SEBT displayed the greatest clinical utility. However, limited research is available to corroborate additional tests, and a more comprehensive assessment of FPTs may be necessary to determine the best combination of FPTs to assess CAI.
These tests present an advantage to clinicians aiming to address functional deficits in patients with CAI as they are cheap, effective alternatives compared with instrumented measures. However, further research is necessary to aid in the full implementation of these tests clinically. Greater sample sizes and study volume would improve on evaluation methods and decrease publication bias to more appropriately determine clinical measures to assess those with CAI. Furthermore, consistency in test implementation must be encouraged to calculate precise protocols and cutoff scores that may improve clinical utility. Last, it remains largely unknown in which ways the current treatment methods may serve to modify these values, affecting the implementation of these measures through patient rehabilitation.
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