A Systematic Review of Return to Sport Physical Performance Tests of the Foot and Ankle

Michael Jeanfavre^1*, Amy Humphrey² & Matthew Klein³

¹Department of Physical Therapy, Azusa Pacific University, USA, OP Ortho & Sports Medicine Rehab, Stanford Health Care, USA
²Department of Physical Therapy, Azusa Pacific University, USA, Doctor of Physical Therapy Program, Messiah University, USA
³Department of Physical Therapy, Azusa Pacific University, USA, Physical Therapy Assistant Program, Stanbridge University, USA

*Correspondence to: Dr. Michael Jeanfavre, Department of Physical Therapy, Azusa Pacific University, USA, OP Ortho & Sports Medicine Rehab, Stanford Health Care, USA.

Copyright © 2021 Dr. Michael Jeanfavre, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abbreviations
ANT = anterior AOFAS = American Orthopedic Foot and Ankle Society Ankle-Hindfoot Score BAPS = biomechanical ankle platform system BESS = Balance Error Scoring System Test CAI = chronic ankle instability CAIT = Cumberland Ankle Instability Tool CKC = closed kinetic chain CLARITY = Clinical Advances Through Research and Information Translation COSMIN = Consensus-based Standards for the selection of health Measurement Instruments F = females FAAM = Foot and Ankle Ability Measure FAI = functional ankle instability FAOS = Foot and Ankle Outcome Score FTB = Functional test battery HHD = hand-held dynamometer Hx = history IAC = International Ankle Consortium ICCs = intraclass correlations IdFAI = Identification of Functional Ankle Instability questionnaire IKDC = international knee documentation committee subjective evaluation form JPS = joint positional sense KT = kinesio-tape LAS = lateral ankle sprain LE-YBT = Lower Extremity Y-Balance Test LSI = limb symmetry index M = males MDC = minimal detectable change MIC = miniml important difference MMT = manual muscle testing mo. = month OKC = open kinetic chain PICOT = Population, Intervention, Comparison, Outcome, Time PL = posterior lateral PM = posterior-medial PPT = Physical Performance Test RCT = randomized control trial RoB = risk of bias assessment RTS = Return to sport SEBT = star excursion balance test SEM = standard error of measure SLB = single leg balance sec = seconds SL = single limb TCJ = talocrural joint Wk = week(s) YBT = lower quarter y-balance test y/a = years of age Yr = year(s)

Introduction
Research shows that a high prevalence of foot and ankle injuries exist in sports activity, particularly ankle sprains, chronic ankle instability, and Achilles tendinitis/osis [1]. Occurrence rate estimates are around 10- 30%, and in certain sports, particularly football, indoor volleyball, netball, and field events in track and field, this percentage is even higher [1,2]. Acute and chronic injury to the foot or ankle often limits an athlete’s ability to run, jump, kick, or change direction, which can ultimately hamper participation in sports activity [3]. Given the physical limitations that can occur from the above injuries, adequate physical performance metrics should be utilized to assess for and make decisions on return to sport (RTS) readiness.

Physical performance tests (PPTs) are tools that qualify and quantify function and assist in the clinical RTS decision-making process [4,5]. Often these tests are used by healthcare professionals to determine when an athlete can safely return to sport following surgery or injury. Extensive literature on PPTs for knee and hip rehabilitation and RTS has been published. A majority have focused on RTS criteria for anterior cruciate ligament (ACL) injuries, with the hop tests being the most utilized measures [6]. Specifically, these tests include the single-leg hop for distance, medial hop, triple hop, 6m timed hop, crossover hop, single-leg vertical hop[4,5]. Current evidence has begun to emphasize using a battery of tests along with functional testing algorithms for determining RTS readiness [7]. However, further work is still needed to validate whether these tests accurately determine RTS readiness [8]. While the tests performed for the hip and knee all involve the ankle, no literature has specifically addressed whether the tests are also valid for return to sport assessments in those with ankle injuries. Systematic reviews on RTS PPT have been done for the hip, specific foot and ankle conditions, and the entire lower extremity, but conclusions have remained the same that further research continues to be needed to establish appropriate reliability and validity for PPTs [4,5,9-12].

Despite the amount of literature on lower extremity PPTs, there is a dearth of information on each measure’s standards for RTS with a foot and ankle musculoskeletal injury. Though the foot and ankle complex’s physical demand requirements may vary from one sport to the next, foundational lower leg physical performance competencies and capacities are required across many sports [13]. Thus, similar PPT performance may be used as criteria for safe RTS activity regardless of the type of injury in similar weight-bearing sports. Though information on standardized predictive assessments and RTS is available for specific pathologies, such as lateral ankle sprains (LAS) and mid-portion Achilles tendinopathy, there remains a lack of consensus on RTS criteria [9,11,14]. Lack of agreement is especially concerning given the well-known high rates of reinjury, reduced percentage of individuals that return to their prior level of competition, and effects on long-term health and quality of life [7,15]. Due to the high rate of reinjury, which can be as high as 61% in some athletic populations for acute lateral ankle sprains, additional information is needed to guide clinicians on the appropriate use of PPTs to determine readiness for RTS post foot and ankle musculoskeletal injury [15-17].

The the current systematic review’s primary purpose was to answer the following question: ‘What are the current clinically applicable RTS PPTs to determine readiness in competitive athletes, ages 12 to 65, following musculoskeletal foot and ankle pathology?’ The study question was framed using the PICOT format. The PICOT question variables, study elements, respective inclusion and exclusion criteria are shown in Table 1. The secondary purpose was to ensure ease of clinical application of the results by proposing a RTS functional test battery (FTB).

Note: N/A, indicates information not applicable; PPT, physical performance tests; RCTs, randomized control trial; y/a, years of age.

Methods
A comprehensive systematic review of RTS PPTs for the hip and ankle was previously published [5]. The current investigation is not solely an update nor builds solely upon the previous work by Hegedus et al. (2015b) [5] as it focuses solely on the foot and ankle. Additional articles were also identified during the article search utilizing the strategy below that were not included in the prior work. The current investigation sought to identify RTS PPTs for the foot and ankle that have been published since 2015. An update to Hegedus’s (2015b) [5] prior results was indicated due to: sufficient time elapsed, new evidence becoming available, and based on need or priority [18-20].

Eligibility Criteria
The inclusion and exclusion criteria for each of the PICOT question components are outlined in Table 1. The operational definition of PPT utilized by this review is defined as “a single test that attempts to measure constructs related to sports (strength, postural control, power, and agility)”[5]. The operational definition utilized by this review of the foot and ankle is defined as any anatomical structure at the level of and distal to the syndesmosis of the tibiofibular joint. The author’s definition of RTS was defined as a Tegner Level 5 or above (i.e., recreational level of sport or higher) [21]. The justification for the selected age ranges from 12 to 65 years of age was (1) to capture studies that investigated or used PPT in high school populations and (2) the upper bound of age 65 was selected to be sure to capture senior athletes. A broad age range was selected to be as comprehensive as possible and capture PPT that would be pertinent across the life span. However, the limit at 65 was placed secondary to the age of 65 being defined as elderly (Tanaka, 2012).

Search Strategy
Relevant articles were identified by searching PubMed, CINHAL, and SportsDiscuss databases. The strategy’s derivation was based on previous reviews [4,5]. Furthermore, it was audited by a senior author to ensure the appropriate use of Boolean modifiers, accurate translation of the search strategy across databases, and appropriateness of the search based upon the study’s stated purpose. The intended search strategy for PubMed with the respective results is shown in Figure 1. The keywords used were variations and derivatives of: “return to sport,” “musculoskeletal injuries,” and “foot and ankle.” Keywords of PPTs were not included in the search strategy due to artificially limiting the number of articles identified in preliminary database searches. The search strategies used for CINHAL and SPORTDiscus are shown in Appendix A.

Study Selection
Search results of the different databases were combined, duplicates deleted and filtered independently according to the specified inclusion and exclusion criteria by two research team members (AH, MJ) using a citation manager (Calarvate Analytics, EndNote, X9.2, Zotero). Discrepancies in filtering the search results were discussed by the two independent reviewers (AH, MJ). Discrepancies of the included article(s) that could not be resolved through discussion of the two reviewers were addressed by a priori identified third member of the research team (MK). Figure 2 outlines the study selection process in a PRISMA flow diagram.

Note: ANT, anterior; AOFAS, American Orthopedic Foot and Ankle Society Ankle-Hindfoot Score; BAPS, biomechanical ankle platform system; BESS, Balance Error Scoring System Test; CAI, chronic ankle instability; CAIT, Cumberland Ankle Instability Tool; F, females; FAAM, Foot and Ankle Ability Measure; FAI, functional ankle instability; FAOS, Foot and Ankle Outcome Score; Hx, history; IAC, International Ankle Consortium; IdFAI, Identification of Functional Ankle Instability questionnaire JPS, joint positional sense; KT, kinesiotape; LAS, lateral ankle sprain, M, males; mo., month; PL, posterior lateral; PM, posterior-medial; SEBT, star excursion balance test; SLB, single leg balance; wk; week(s); TCJ, talocrural joint; YBT, lower quarter y-balance test; yr, year(s); y/a, years of age.

Data Extraction
Data elements of identified full-text articles were prospectively determined based upon the PICOT question, the primary and secondary purposes of the current study, and examination of reviews previously published related to this topic [4,5]. These included: author, year, study design, sample size, subject demographic data, medical diagnosis(es), type and level of sport of subjects, clinically feasible PPT, information necessary for conducting quality and risk of bias assessments, and psychometric properties of PPT (reliability, agreement, hypothesis testing, responsiveness, criterion validity, etc.). The specific data elements were extracted by a member of the research team (MK), and all elements were double-checked by two other members (MJ and AH). A pre-piloted data collection sheet was used to collect the extracted study elements. Corresponding authors of primary studies were contacted in the case of missing data.

Summary Measures and Synthesis of Results
PPTs were categorized after data extraction as either a muscle performance, postural control, or functional test to clarify constructs measured and for ease of application by clinicians and healthcare providers. Additionally, the PPTs identified were summarized into a clinically recommended testing battery, consistent with proposed RTS decision-making models previously described for other body regions [7,44,45].

Risk of Bias Assessment
Consistent with the Cochrane Handbook [46], the risk of bias and quality appraisal of the included RCTs and non-RCTs were assessed. The risk of bias assessment (RoB) of included studies was performed using the respective RoB tools for RCTs and cohort studies developed by the CLARITY (Clinical Advances Through Research and Information Translation) from the McMaster University of Health Sciences [47,48]. The CLARITY RoB tool differs from the COSMIN (Consensus-based Standards for the selection of health Measurement Instruments) checklist, which is the quality appraisal tool used in previous reviews [4,5]. The justification for changing tools was due to the prior authors’ acknowledging in their limitations that the COSMIN’s measurement properties are not well understood [4,5,49]. The RoB assessments for RCTs and non-RCTs were performed by two independent research members (MJ and AH, respectively), and the assessment outcomes were audited by a third member of the research team (MK). Any discrepancies identified by the secondary review were clarified by a priori identified third member of the research team.

Results

Study Selection and Characteristics
Of the 119 articles read in total, 25 articles were deemed appropriate for final analysis. Nine were RCTs, five were case-control studies, ten were case series studies, and one study was a cross-sectional study. The following PPTs were identified: Star Excursion Balance Test, Modified Rhomberg Test, Side Hop Test, Foot Lift Test, Single Limb Hop for Distance Test, Balance Error Scoring System Test, Single Limb Heel Raise Test, 6 Meter Crossover Hop Test, Figure 8 Hop Test, Triple Crossover Hop Test, and the Lateral Hop Test. Additionally, through a review of identified articles references, an additional test, the Square Hop Test, was included in our selection [4,50]. For reasons unknown, the Square Hop Test was not included in Hegedus’s previous review (2015a) [4]. Due to the Square Hop Test’s ability to discriminate between healthy and injured limbs and meet the operational definition of a PPT, this test was also included within the current results. A summary of the test characteristics is provided in Appendix B. Study characteristics included authors, names and alternate names given to the test, the methodology by which the test was performed and scored, the measurement property, and the quality of the measurement property. The description of each of the included studies is provided in Table 2. provided in Appendix B. Study characteristics included authors, name and alternate names given to the test, the methodology by which the test was performed and scored, the measurement property, and the quality of the measurement property. The description of each of the included studies is provided in Table 2.

Risk of Bias Assessment
The RoB assessment results for RCTs are summarized in Table 3 and graphical representation of the results are shown in Figure 3. The RoB assessment results for each individual study, RCTs and non-RCTs, are provided in Appendix C. The highest risk of bias was in the blinding of participants, personnel, and outcome assessments. The lack of blinding in rehabilitation and physical therapy literature is well documented and the RoB assessment results in this review further corroborate this limitation [51]. However, a majority of RCTs were deemed to have a low level of selection, reporting and other biases (see Figure 3).

Figure 3: Graphical Summary of Risk of Bias Assessment for Randomized Control Trials

The RoB assessment results for non-RCTs are summarized in Table 4 and graphical representation of the results are shown in Figure 4. The highest RoB for non-RCTs is in the selection process as well as in the assessment of prognostic factors and outcomes. Overall, RoB appeared to be unclear in the majority of these studies. Selection of the cohort, being able to control for con-founding factors, and the inability to follow-up over time are documented limitations that contribute to RoB in cohort studies [52].

Table 4: Summary of Risk of Bias Assessment for Non-randomized Control Trials

Figure 4: Graphical Summary of Risk of Bias Assessment for Non-randomized Control Trials

Summary Measures and Synthesis of Results
The included studies that described each PPT and the respective reported measurement properties are synthesized in Appendix B. Summary statements that can be made regarding the PPT results are:

 Results suggest the 20 Times Single-Leg Heel Raise Test is a valid, reliable, and responsive test to assess readiness for return to sport post-Achilles tendon repair.
 There is moderate evidence the Side Hop Test and Square Hop Tests are reliable, valid, and responsive in assessing those with foot and ankle pathology.
 There is strong evidence that the Figure 8 Hop Test, Triple Crossover Hop Test, Lateral Hop for Distance are not capable of differentiating between healthy feet/ankles and those with chronic pathology.
 There is moderate evidence the SEBT is valid, responsive and reliable in assessing those with foot/ ankle pathologies. This may further suggest that balance and proprioception are essential to assess in this population.

Quality of Statistical Properties of Identified Tests
The summary of statistical properties can be found in Table 5. Reporting and ratings of these properties varied somewhat, with gaps present among all the PPTs.

Table 5: Summary of Measurement Properties by Test

Note: *Cited by Hegedus, ICC, intraclass correlation coefficient; MDC, minimal detectable change; SEM, standard error of measure.

Reliability
Reliability was rated positive for 10 of the 12 PPTs. None of the included studies reported intraclass correlations (ICCs) for the BESS Test or the Single Leg Hop for Distance Test. All included studies that reported on reliability suggested good to excellent reliability for all 10 tests for which the ICCs were reported.

Agreement/Measurement
Of the 25 studies included in this review, only two reported on measurement error (SEM) or minimal detectable change (MDC). SEMs were reported for five PPTs, with the SEBT at 1.6cm, the Side Hop Test at 0.06 seconds to 0.37 seconds, the 6 Meter Cross-Over Hop Test at 0.37 seconds, the Figure-of-Eight Hop Test at 1.66 seconds and the Square Hop Test at 1.4 seconds [35,50]. MDCs were reported for four hopping PPTs, with the Side Hop Test at 5.82 seconds, 6 Meter Hop Test at 1.03 seconds, the Figure-of- Eight Hop Test at 4.59 seconds and the Square Hop Test at 3.88 seconds [50]. However, as the MIC was not calculated for the above PPTs, a grade could not be determined.

Construct Validity
Construct validity is the ability of a PPT to be able to discriminate between healthy (i,e., athletes that are ready for RTS) and those that are unhealthy athletes (i.e., those not physically ready to RTS) based upon the PPT performance. Only six of the PPTs had any form of quality rating for construct validity. Of the six, only the SEBT and the Side Hop Test demonstrated positive quality ratings for construct validity. The SEBT had all six studies report positive quality ratings, while the Side Hop Test had one study address and report positive quality ratings for construct validity [30,35,38,40,41,60]. The 6 Meter Cross-Over Hop Test, Figure-of-Eight Hop Test, Triple Cross-Over Hop Test and Lateral Hop Test for Distance all received a negative rating on construct validity from the single study that assessed this [36]. None of the four tests with negative ratings were able to detect differences between limbs with histories of chronic lateral ankle sprains and healthy controls. No other PPTs had any study address construct validity ratings.

Criterion Validity
Only one of the 12 PPTs and one study of the 25 included in this review had any rating on criterion validity. The Single Limb Heel Raise Test was found to a positive rating on determining readiness for return to sport post Achilles tendon repair [42]. No other studies or PPTs had any reports or mentions of criterion validity.

Responsiveness
Six of the 12 PPTs had positive ratings for responsiveness. The SEBT, Modified Rhomberg, Side Hop Test, Foot Lift Test, BESS Test and Single Limb Heel Raise Test all demonstrated the ability to detect changes in function in relation to various interventions. The Figure-of-Eight Hop Test was found to not be responsive to the use of kinesio-tape on dynamic balance, muscle strength and functional performance in those with FAI [30].

Discussion
The current systematic review aimed to determine the clinically applicable PPT to assess RTS readiness in competitive athletes, ages 12 to 65, following musculoskeletal foot and ankle pathology. Across the 25 articles that were included, 12 PPTs were identified. One test assessed muscle performance, four tests measured postural control, and the remaining 7 PPT involved hopping in one or multiple directions for either distance or time. The results expand on existing knowledge by updating previous reviews, identifying additional PPTs, and recording each PPT’s measurement properties. However, we found a lack of evidence on RTS standards among the currently available PPTs. Most included studies focused on CAI and LAS rather than specific RTS testing for musculoskeletal foot and ankle pathologies in general.

A prior systematic review by Hegedus et al. (2015b) [5] included 31 studies, identifying 14 lower extremity PPTs. The current systematic review included 25 studies and identifiedadditional PPTs (i.e., Foot Lift Test, BESS Test, Modified Rhomberg Test, Side Hop Test, Single Limb Heel Raise Test, Square Hop Test, and the Figure-of-Eight Hop Test) while omitting six of the 14 PPTs identified by Hegedus et al., (2015b) [5] (the 40-yard Sprint, Shuttle Run Test, Vertical Leap, T-Agility Test, and the Beep Test) (see Table 6). Reasons for the discrepancies between the current results and that of Hegedus et al. (2015b) [5] were due to one (or more) of the following reasons: (1) new available research that has been published since 2015; (2) Hegedus et al., (2015b) [5] investigated PPTs for the hip and the knee, as well as the ankle, and (3) the current review only included studies that applied the PPTs to injured athletes. For example, the vertical jump and the multistage fitness test or “beep” test were excluded as the reported injuries were not specific to the foot and ankle [62].

Table 6: Comparison of Identified Physical Performance Tests

Note: Red text indicates the physical performance test was not included in the other systematic review; green text indicates the physical performance test was identified in both systematic reviews. SEBT, Star Excursion Balance Test
^aExcluded due to looking at knee injuries [62,63], excluded due to not specific to foot and ankle injuries [64], excluded due to healthy population [65-67]; ^bPPT described by Sekir et al. (2008; 2007) [68,69] and included from Hegedus et al., (2015a)[4]; ^cExcluded due to looking at hip injuries [70]; ^dHand selected test from Caffrey et al., (2009) [50] as it was able to discriminate between functional ankle instability (FAI) limb from uninvolved limb, for reasons unknown, the test was not included by Hegedus et al., (2015a) [4]; ^eExcluded due to healthy population [71]; ^fExcluded due to healthy population [66,67,71]; ^gExcluded due to healthy population [65]; ^hExcluded due to looking at knee injuries [62,63]

More recent reviews related to RTS decision-making following foot and ankle injuries have been published [9,11,12]. Habets et al. (2018) [9] performed a systematic review to investigate RTS criteria for individuals with Achilles tendinopathy. Likewise, both Wikstrom et al. (2020) [12] and Tassignon et al. (2019) [11] reviewed prospective studies that used a criterion-based RTS decision-making process for patients with LAS. Each of these reviews was challenged to identify PPTs that helped to determine RTS readiness in their perspective injured populations [9,11,12]. Habets et al. (2018) [9] found that criteria for RTS as related to Achilles tendinopathy were determined by factoring the following criteria: level of pain, level of functional recovery, muscular strength, range of motion, endurance, medical advice, psychosocial factors, and anatomical/physiological properties of the Achilles tendon. Furthermore, there is evidence in sports literature suggesting that combining results of multiple functional performance tests has excellent clinical utility compared to a single stand-alone test [72]. These findings, combined with the current results, demonstrate the need to produce and study a criterion-based RTS test battery that can be used for individuals recovering from a foot or ankle injury.

Proposed Functional Performance Testing
Though several individual PPT and the respective measurement properties have been established in the athletes with ankle and foot musculoskeletal injuries, the clinical application of the results may remain ambiguous for several reasons:

1.The current results, nor previous reviews, have demonstrated high-quality evidence and consensus on RTS PPT criteria for the musculoskeletal injuries of the foot and ankle complex [5,11,12].
2.There are several qualitative and quantitative factors to consider in the RTS decision-making beyond the constructs that PPT can capture [11,13,73,74].
3.Further studies have sought to establish the predictive, or criterion, the validity of PPT by testing uninjured athletes, tracked the athletes over time, and correlate PPT performance to subsequent foot and ankle injury incidences [46,75-78]. Though studies that investigated the predictive ability of PPT performance of future foot and ankle injuries in healthy athletes were not included in the current review, the additional PPT that demonstrate injury prediction validity may still provide value in considering RTS decisions for injured athletes.

To summarize the current results, provide clinical application recommendations, and illustrate a framework for future research in the implementation, reliability, and validation of comprehensive RTS criteria, a functional testing battery is proposed (See Table 7). Previously published RTS functional testing algorithms for the upper and lower extremity, related systematic reviews, the synthesized results of the included studies, and relevant identified articles were used to compose the proposed functional testing battery using low cost (<$1000) equipment (See Table 7) [7,45,79-83].

Table 7: Foot and Ankle Functional Testing Battery

Note. IKDC, international knee documentation committee subjective evaluation form; MMT, manualmuscle testing; HHD, hand-held dynamometer, CKC, closed kinetic chain; OKC, open kinetic chain; LSI, limb symmetry index = involved limb/non-involved limb; sec, seconds; SL, single limb; LEYBT, Lower Extremity Y-Balance Test.

^aSee Axe & Snyder-Mackler, (2005) [84] for proposed tissue healing timelines for specific pathoanatomical structures; ^bWikstrom et al., (2020) [12]; ^cDelahunt et al., (2018) [55]; ^dShultz et al., (2013) [86], ^eMartin & Irrgang, (2007) [87], ^fTassignon et al., (2019) [11], ^gHabets, (2018) [9], ^hPowden et al., (2019) [44]; ⁱCook, (2010) [88]; ^jOzinga et al., (2018) [89]; ^kSpringer et al., (2007) [90]; ^lFunctional Movement Systems, (2015) [24]; ^mWitchalls et al., (2013) [75]; ⁿPowers et al., (2017) [78], ^oMonahan, (2018) [92]; ^pSekir et al., (2008) [68]. ^qCaffery et al., (2009) [50]; ^rSekir et al., (2007) [69], ^sGreisberg et al., (2019) [93], Gokeler et al., (2017) [94], Logerstedt et al., (2012) [95], Greenberg et al. (2020a) [96], Brumitt et al. (2013) [44]; ^tDavies & Zillmer (2000) [97]; ^uWitchalls et al., (2013) [3]. ^vYalfani et al., (2017) [98]; ^wMadsen et al., (2020) [99]; ^xOnate et al. (2018) [100]; ^yGreenberg et al. (2020b) [101]; ^zBrumitt et al., (2013) [44], Brumitt et al., (2018) [102], Haitz et al., (2014) [103]; ^aaHardesty et al., (2017) [104]

Strengths and Limitations
A strength of the current review is that it contributes the following points to the existing body of knowledge of lower extremity PPTs to assess return to function following musculoskeletal foot and ankle injuries:

 A synthesis of PPT and clinical recommendations of how these might supplement a more comprehensive RTS test battery.
 There exists a lack of consensus on the appropriate standards and criteria for RTS following ankle and foot injuries in the athletic population.
 Several measurement properties of the identified PPTs have yet to be established. Nearly all the PPT lack predictive and criterion validity (i.e., the ability to predict a successful return to sport), agreement, and/ or reliability measures on injured populations. The lack of these values is concerning. Future research is needed to establish the specified measurement properties to support these tests for rehab and return to sport decision-making.

The current results are derived from a majority (n = 15) of non-RCTs with varying levels of IV (prospective observational studies) and III evidence (cross-sectional studies). In combination with the consistent lack of blinding in the RCTs (see Figure 3) and lack of transparency of the non-RCTs in defining the assessment of outcomes, confounding factors in the outcomes, and the cohort selection (see Figure 4) the level and quality of existing evidence is a limitation of the current study. Clinicians need to consider these limitations when interpreting and implementing these results. Future RCTs that blind participants, personnel, and assessors, when feasible, are recommended to improve the quality and level of evidence that exists regarding PPT for the foot and ankle complex.

Limitations due to the methodology of the current systematic review include: (1) although a prospective protocol was written for the present review, it was not formally registered on the PROSPERO website, (2) the final search strategy and its translation across searched databases was not audited by a medical school or academic institution librarian, and (3) the inability to perform two independent data extractions, RoB, and quality assessments, as recommended in the Cochrane Handbook for Systematic Reviews of interventions secondary to the time allotted to conduct the review and the size of the research team [105]. Finally, to make the result of the current study most clinically applicable across a broad spectrum of clinical settings, studies including outcomes requiring one or more expensive (>$1000) “laboratory” equipment (i.e., isokinetic dynamometers, Biodex balance system, force plates, motion capture systems, and surface electromyography) were excluded from this review. When budgets allow, or such pieces of equipment are readily available, it is recommended that clinicians supplement the proposed RTS testing battery with isokinetic strength and power tests, ground reaction forces during hoping tasks, and/or center of pressure evaluations during dynamic and static lower extremity tasks [106].

Conclusion
Overall, there is a lack of consensus among RTS standards and criteria following foot and ankle injuries in the athletic population. Among the 12 PPT identified, several measurement properties have yet to be established for these tests. However, the SEBT, Side Hop Test, and Square Hop Test were the most responsive and reliable in assessing foot and ankle pathologies. Furthermore, only the SEBT and Side Hop tests have established psychometric analysis supporting their validity. The 20 Times Single-Leg Heel Raise test was also a valid, reliable, and responsive test to assess RTS readiness, but it was specific to patients who are post- Achilles tendon repair.

Using the current review results and encompassing other tests identified before 2015, a comprehensive RTS test battery for individuals with foot and ankle injuries is proposed. Further research is needed to establish validity and reliability for the proposed test battery and each test within the test battery.

Supplemental Materials

Appendix A
CINAHL Search Strategy

SPORT Discus Search Strategy

Appendix B
Physical Performance Tests and Descriptions

Appendix C

Tool to Assess Risk of Bias (RoB) Assessment of Randomized Control Trials

Alves et al., (2018) [22]

Note. *May omit this item

Anguish & Sandrey, (2018) [23]

Bagherian et al., (2019) [25]

Best et al., (2015) [26]

Cain et al., (2017) [27]

Cruz-Diaz et al., (2014) [29]

Hall et al., (2018a) [32]

Kamali et al., (2017) [34]

Sierra-Guzmán et al., (2018) [40]

Tool to Assess Risk of Bias (RoB) in Cohort Studies

Bagherian et al. (2018) [24]

Cho et al., (2019) [28]

Coetzee et al., (2018) [53]

Fereydounnia et al., (2019) [30]

Golditz et al., (2016) [31]

Harriss et al., (2019) [33]

Ko et al., (2018) [35]

Madsen et al., (2018) [36]

McCann et al., (2018) [60]

Powden et al., (2019) [37]

Ryu et al. (2019) [38]

Sierra-Guzman et al., (2018) [40]

Someeh et al., (2015) [41]

Toyooka et al., (2017) [42]

Toyooka et al., (2018) [43]

Acknowledgements
There were no sources of funding or grants that supported the current systematic review or the investigators. The authors would like to acknowledge the guidance, consultation and support of Dr. Abebaw Yohannes, Ph.D. throughout the duration of this initiative.

Conflict of Interest
The authors declare no conflict of interest in this work.

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