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Longitudinal Validity and Minimal Important Change for the Modified Lower Extremity Functional Scale (LEFS) in Orthopedic Foot and Ankle Patients

Open AccessPublished:July 16, 2021DOI:https://doi.org/10.1053/j.jfas.2021.07.004

      ABSTRACT

      The lower extremity functional scale (LEFS) is a patient-reported outcome measure for lower extremity disorders. Aim of this study was to assess the longitudinal validity including responsiveness and test-retest reliability of the revised 15-item version, and to define the minimal important change (MIC) of the modified LEFS in a generic sample of orthopedic foot and ankle patients who underwent surgery. Responsiveness, effect size, and standardized response mean were measured by determining the score change between the baseline and 6 months administration of the LEFS from 156 patients. There was no significant difference between preoperative (median 78, interquartile range [IQR] 64.2-90.3) and postoperative (median 75.0, IQR 61.7-95.0) scores. Both effect size and standardized response mean were low (0.06 and 0.06, respectively). Test-retest reliability of the LEFS was satisfactory. Intraclass correlation coefficient was 0.85 (95% confidence interval 0.81-0.88). MIC value could not be estimated due to the lack of significant score change. The modified LEFS presented with relatively low longitudinal validity in a cohort of generic orthopedic foot and ankle patients. The findings of this study indicate that the modified LEFS might not be the optimal instrument in assessing the clinical change over time for these patients.

      Level of Clinical Evidence

      Keywords

      In recent years, use of patient-reported outcome measures (PROMs) has become more frequent in orthopedic surgery (
      • Zwiers R
      • Weel H
      • Mallee WH
      • Kerkhoffs GMMJ
      • van Dijk CN
      Ankle Platform Study Collaborative – Science of Variation Group
      Large variation in use of patient-reported outcome measures: a survey of 188 foot and ankle surgeons.
      ). PROMs are clinical assessment tools used for evaluating patients’ direct subjective health outcomes such as function or health-related quality of life (HRQL) (
      • Hunt KJ
      • Hurwit D.
      Use of patient-reported outcome measures in foot and ankle research.
      ). PROMs should be chosen for use according to the validity, reliability, and repeatability of the instrument (
      US Department of Health and Human Services FDA Center for Drug Evaluation and Research laurie[email protected], US Department of Health and Human Services FDA Center for Biologics Evaluation and Research toni. [email protected] fda. hhs. gov, US Department of Health and Human Services FDA Center for Devices and Radiological Health [email protected] cdrh. fda. gov
      Guidance for industry: patient-reported outcome measures: use in medical product development to support labeling claims: draft guidance.
      ,
      • Frost MH
      • Reeve BB
      • Liepa AM
      • Stauffer JW
      • Hays RD
      Mayo/FDA Patient-Reported Outcomes Consensus Meeting Group
      What is sufficient evidence for the reliability and validity of patient-reported outcome measures?.
      ,
      • Mokkink LB
      • Terwee CB
      • Patrick DL
      • Alonso J
      • Stratford PW
      • Knol DL
      • Bouter LM
      • de Vet HC
      The COSMIN checklist for assessing the methodological quality of studies on measurement properties of health status measurement instruments: an international Delphi study.
      . There are at least 139 different instruments used in the literature for foot and ankle patient (
      • Hunt KJ
      • Hurwit D.
      Use of patient-reported outcome measures in foot and ankle research.
      ). While the majority of foot and ankle specialists utilize PROMs in their clinical work, there is a significant variation in the use of PROMs (
      • Hunt KJ
      • Hurwit D.
      Use of patient-reported outcome measures in foot and ankle research.
      ). Without a clear consensus on the preferable instrument, further research on measurement properties of foot and ankle PROMs is needed (
      • Button G
      • Pinney S.
      A meta-analysis of outcome rating scales in foot and ankle surgery: is there a valid, reliable, and responsive system?.
      ).
      Lower extremity functional scale (LEFS) was developed by Binkley et al in 1999 for assessing lower extremity function including foot and ankle (
      • Binkley JM
      • Stratford PW
      • Lott SA
      • Riddle DL
      North American Orthopaedic Rehabilitation Research Network
      The Lower Extremity Functional Scale (LEFS): scale development, measurement properties, and clinical application.
      ). It originally consisted of 20 items on a 0 to 4 scale, with a maximum score of 80 indicating no functional limitations. Prior studies have reported high reliability and internal consistency for the LEFS (
      • Repo JP
      • Tukiainen EJ
      • Roine RP
      • Ilves O
      • Järvenpää S
      • Häkkinen A.
      Reliability and validity of the Finnish version of the Lower Extremity Functional Scale (LEFS).
      ,
      • Naal FD
      • Impellizzeri FM
      • Torka S
      • Wellauer V
      • Leunig M
      • von Eisenhart-Rothe R
      The German Lower Extremity Functional Scale (LEFS) is reliable, valid and responsive in patients undergoing hip or knee replacement.
      ,
      • Mehta SP
      • Fulton A
      • Quach C
      • Thistle M
      • Toledo C
      • Evans NA.
      Measurement properties of the lower extremity functional scale: a systematic review.
      ). Furthermore, test-retest reliability of the LEFS instrument has been reported as high (
      • Mehta SP
      • Fulton A
      • Quach C
      • Thistle M
      • Toledo C
      • Evans NA.
      Measurement properties of the lower extremity functional scale: a systematic review.
      ,
      • Hoogeboom TJ
      • de Bie RA
      • den Broeder AA
      • van den Ende
      • Cornelia HM.
      The Dutch Lower Extremity Functional Scale was highly reliable, valid and responsive in individuals with hip/knee osteoarthritis: a validation study.
      ). However, its convergent validity and distribution of scores in different patient groups have been criticized (
      • Uimonen MM
      • Ponkilainen VT
      • Toom A
      • Miettinen M
      • Häkkinen AH
      • Sandelin H
      • Latvala AO
      • Sirola T
      • Sampo M
      • Roine RP
      • Lindahl J
      • Ilves O
      • Sandbacka A
      • Repo JP
      Validity of five foot and ankle specific electronic patient-reported outcome (ePRO) instruments in patients undergoing elective orthopedic foot or ankle surgery.
      ). Factor analyses have presented LEFS with loading on 2 or more factors (
      • Repo JP
      • Tukiainen EJ
      • Roine RP
      • Ilves O
      • Järvenpää S
      • Häkkinen A.
      Reliability and validity of the Finnish version of the Lower Extremity Functional Scale (LEFS).
      ,
      • Naal FD
      • Impellizzeri FM
      • Torka S
      • Wellauer V
      • Leunig M
      • von Eisenhart-Rothe R
      The German Lower Extremity Functional Scale (LEFS) is reliable, valid and responsive in patients undergoing hip or knee replacement.
      ,
      • Negahban H
      • Hessam M
      • Tabatabaei S
      • Salehi R
      • Sohani SM
      • Mehravar M.
      Reliability and validity of the Persian lower extremity functional scale (LEFS) in a heterogeneous sample of outpatients with lower limb musculoskeletal disorders.
      ,
      • Garratt AM
      • Naumann MG
      • Sigurdsen U
      • Utvåg SE
      • Stavem K.
      Evaluation of three patient reported outcome measures following operative fixation of closed ankle fractures.
      ). Several prior studies presented multidimensionality in Rasch analysis on the original 20-item LEFS (
      • Garratt AM
      • Naumann MG
      • Sigurdsen U
      • Utvåg SE
      • Stavem K.
      Evaluation of three patient reported outcome measures following operative fixation of closed ankle fractures.
      ,
      • Repo JP
      • Tukiainen EJ
      • Roine RP
      • Sampo M
      • Sandelin H
      • Häkkinen AH.
      Rasch analysis of the lower extremity functional scale for foot and ankle patients.
      ,
      • Bravini E
      • Giordano A
      • Sartorio F
      • Ferriero G
      • Vercelli S.
      Rasch analysis of the Italian Lower Extremity Functional Scale: insights on dimensionality and suggestions for an improved 15-item version.
      ,
      • Alnahdi AH.
      Rasch validation of the Arabic version of the lower extremity functional scale.
      ). In a Rasch Model analysis, the Finnish version of the LEFS was modified to achieve unidimensionality by removing 5 items and reducing the response categories into 4 (
      • Repo JP
      • Tukiainen EJ
      • Roine RP
      • Sampo M
      • Sandelin H
      • Häkkinen AH.
      Rasch analysis of the lower extremity functional scale for foot and ankle patients.
      ). The modified 15-item version of the LEFS showed improved structural validity. Nonetheless, the modified version of the LEFS lacks investigation on its longitudinal validity and minimal important change (MIC) for foot and ankle patients.
      Longitudinal validation refers to testing the ability of an instrument to detect change over time (
      • Roach KE.
      Measurement of health outcomes: reliability, validity and responsiveness.
      ). It can be assessed with responsiveness to change and estimating measurement error. Responsiveness of the PROM stands for ability to detect real change in measurements (
      • Beaton DE
      • Bombardier C
      • Katz JN
      • Wright JG.
      A taxonomy for responsiveness.
      ). Two measurements of HRQL conducted over a short time with no real change in the clinical status should produce similar outcome scores for the score to be reproducible. This is also referred to as test-retest reliability (
      • Roach KE.
      Measurement of health outcomes: reliability, validity and responsiveness.
      ).
      MIC value is used for interpreting clinically significant change in the PROM scores (
      • de Vet HC
      • Terwee CB
      • Ostelo RW
      • Beckerman H
      • Knol DL
      • Bouter LM.
      Minimal changes in health status questionnaires: distinction between minimally detectable change and minimally important change.
      ). Change in clinical status over time can be used both in clinical and scientific work in assessing the effect of a treatment on patients or as an endpoint in scientific studies. PROM score changes larger than the MIC is considered as clinically significant change.
      The current study aimed to assess the longitudinal validity of responsiveness and repeatability, and to define the MIC for the modified Finnish version of LEFS in orthopedic foot and ankle patients who undergo surgery.

      Materials and Methods

      Ethics Committee approval was granted from the Hospital District of Helsinki and Uusimaa. Patients were recruited at hospital visits on the day of surgery or mail before surgery from 4 hospitals providing surgical treatment for different orthopedic foot and ankle complaints. Patients completed the validated Finnish 15-item version of the LEFS (
      • Repo JP
      • Tukiainen EJ
      • Roine RP
      • Ilves O
      • Järvenpää S
      • Häkkinen A.
      Reliability and validity of the Finnish version of the Lower Extremity Functional Scale (LEFS).
      ). Written informed consent was obtained from the patients. Inclusion criteria were age at least 18 years, fluent in Finnish and planned foot and ankle surgery. Final analysis included patients that completed the LEFS on 3 different occasions: preoperatively, 6 months after the surgery, and at 6.5 months’ follow-up.

      Statistical Methods

      The data are presented as means with standard deviations (SD) or as medians and interquartile ranges (IQR). Total scores for the LEFS in each administration were calculated by summing the scores of all items and dividing the result by the number of valid completed items. Lastly, the resulted score was multiplied by 100 to obtain the total score on a scale of 0 to 100. The patients that had more than 4 missing values were regarded as invalid and, thus, were excluded from the analysis.

      Responsiveness

      Responsiveness was measured by determining the score change between the baseline and at 6 months administrations of the LEFS as well as effect size (ES) and standardized response mean (SRM). Furthermore, differences in the pre- and postoperative scores were examined using Mann-Whitney U test for paired samples. ES was calculated as follows: ([mean postoperative score – mean preoperative score] / preoperative score SD) (
      • Kazis LE
      • Anderson JJ
      • Meenan RF.
      Effect sizes for interpreting changes in health status.
      ). The formula used in SRM calculation was: (mean score change / score change SD) (
      • Liang MH
      • Fossel AH
      • Larson MG.
      Comparisons of five health status instruments for orthopedic evaluation.
      ). ES and SRM were interpreted according to criteria defined by Cohen with less than 0.2 meaning no change, 0.2 to 0.5 for small change, 0.5 to 0.8 for moderate change, and over 0.8 for large change (
      • Cohen J.
      Statistical Power Analysis for the Behavioral Sciences.
      ).

      MIC

      Anchor question was used to define the patients whose foot had and had not improved after the surgery. The anchor question used was “Assess the current condition of your foot/ankle compared to the condition before the surgery.” The response categories were on a 5-step Likert scale varying from “a lot better” to “a lot worse” with neutral midpoint. The patients that declared their foot/ankle was “a lot better” or “better” were counted as Improved and other patients were counted as Not improved.
      Predictive MIC estimation method was applied in calculation of the MIC between the baseline LEFS score and the LEFS score of 6 months after the operation (
      • Terluin B
      • Eekhout I
      • Terwee CB
      • de Vet HC.
      Minimal important change (MIC) based on a predictive modeling approach was more precise than MIC based on ROC analysis.
      ). Pretest probability of improvement was calculated by dividing the proportion of improved patients with the whole sample. The MIC value with 95% confidence intervals (CI) were calculated using logistic regression modeling with anchor question based reported change as a dependent variable and LEFS score change as an independent variable. Moreover, MIC values adjusted to the proportion of improved patients were calculated (
      • Terluin B
      • Eekhout I
      • Terwee CB.
      The anchor-based minimal important change, based on receiver operating characteristic analysis or predictive modeling, may need to be adjusted for the proportion of improved patients.
      ). In addition, to assess the capability of the LEFS to discriminate improved and not improved patients, receiver operating characteristic curves were drawn and area under curve was calculated.

      Test-Retest-Reliability

      Test-retest-reliability is a degree of which scores of two independent questionnaire administrations of the same patient correspond with each other. Test-retest-reliability was examined by calculating intraclass correlation coefficient between 6 and 6.5 months LEFS administration scores. In addition, dependent samples t test was performed to examine the difference in the LEFS total scores between the administrations. Lastly, standard error of the measurement (SEM) was estimated by calculating the square root of the ANOVA error variance of the two postoperative administrations.

      Results

      One-hundred and fifty-six patients provided sufficiently completed preoperative and postoperative LEFS questionnaires (Fig. 1). Seventy-eight percent of the patients were female. Mean age of the patients was 55 years (range 18-80 years). Patient characteristics are presented in more detail in Table 1 and Table 2. Forty-two percent of the patients had received prior operative treatment on foot or ankle. The top 3 indications for primary surgery were hallux valgus (16%), hallux rigidus (9%), and digiti malleiformis (6.4%).
      Table 1Clinical and sociodemographic characteristics
      Female, n (%)120 (77)
      Age (years), mean (SD, range)55 (15, 18-80)
      BMI, mean (SD, range)27 (6.5, 18-77)
      Education level, n (%)
       Comprehensive school57 (37)
       Upper secondary school, not graduated4 (2.6)
       Upper secondary school, graduated16 (10)
       Undergraduate degree, not graduated3 (1.9)
       Undergraduate degree, graduated50 (32)
       Graduate degree, not graduated1 (0.6)
       Graduate degree, graduated16 (10)
      Marital status, n (%)
      In a relationship21 (13)
      Married81 (52)
      Never been married24 (15)
      Divorced15 (9.6)
      Widow13 (8.3)
      8 (10, 0-49)
      Duration of symptoms (years), mean (SD, range)
      Patient-reported health state, n (%)
       Excellent4 (2.6)
       Very good30 (19)
       Good85 (54)
       Moderate32 (21)
       Poor2 (1.3)
      Previous operations, n (%)66 (42)
      Number of previous operations, mean (SD, range)0.80 (1.3, 0-6)
      Patient-reported comorbidities, n (%)
      Hypertension38 (24)
      Cardiovascular disease26 (17)
      Respiratory disease22 (14)
      Rheumatic disease18 (12)
      Diabetes12 (7.7)
      Cancer11 (7.1)
      Table 2Diagnoses and procedures
      Diagnosisn (%)
      Hallux valgus25 (16)
      Hallux rigidus14 (9.0)
      Digiti malleiformis10 (6.4)
      Other fractures of lower leg6 (3.8)
      Pseudarthrosis after fusion or arthrodesis4 (2.6)
      Metatarsalgia4 (2.6)
      Primary osteoarthritis of other joints4 (2.6)
      Pain in joint3 (1.9)
      Procedure
      Fusion of first tarsometatarsal joint28 (18)
      Internal fixation of fracture of ankle using wire, rod, cerclage or pin8 (5.1)
      Osteotomy or rotation osteotomy of first metatarsal or tarsal bone8 (5.1)
      Other operation on fascia, ganglion, synovial sheath or bursa of ankle or foot7 (4.5)
      Osteotomy or rotation osteotomy of II-V metatarsal or tarsal bone7 (4.5)
      Fusion of talocrural joint4 (2.6)
      Fusion between bones of ankle or ankle and foot3 (1.9)
      Tenodesis, shortening or lengthening of tendon of foot3 (1.9)
      Examination of the difference between the preoperative and postoperative scores revealed no significant difference (p = .61) as the preoperative score median was 78.3 (IQR 64.2-90.3) and postoperative median 75.0 (IQR 61.7-95.0). In accordance, both the ES and the SRM were low, 0.06 and 0.06, respectively, indicating no actual change in the scores when interpreted by means of Cohen criteria.
      The classification of the patients into improved and not improved resulted in 127 improved patients giving the pretest probability of improvement of 0.81. The distributions of the score change in the improved and not-improved patients groups followed a similar pattern with mean score change of +1.6 (SD 19.0) in the improved subgroup and –1.0 (SD 22.4) in not-improved subgroups (Fig. 2). There was no significant difference between the subgroups (p = .56). Further, the absence of the difference in the score change between the subgroups complicated calculations of MIC. Logistic regression model of improvement probability by the LEFS score change is presented in Fig. 2. The estimated MIC value for the LEFS was +0.25 (95% CI -69.0 to 152.8) points at the pretest probability of improvement of 0.81. Adjusted MIC estimate was -2.4 points (Fig. 3). Although the scores did not differ between the improved and not-improved patients, when inspecting the LEFS score change distributions in each of the original 5-step anchor question subgroups, there was a slight pattern towards higher score change in the patients that reported better outcome with their foot or ankle (Fig. 4). However, the number of the patients that reported impairment of their foot was rather small. The receiver operating characteristic curve and the area under curve value of 0.55 indicated poor discriminative properties of the LEFS (Fig. 5).
      Fig. 2
      Fig. 2Proportion of patients and their scores in groups where the foot and ankle situation improved (light gray) and did not improve (dark gray).
      Fig. 3
      Fig. 3Estimation of the minimal important change for the modified LEFS. The estimate is at the point where the lines cross (0.25). The gray area shows the 95% CI.
      Fig. 4
      Fig. 4The change in LEFS scores according to improvement or impairment of the foot or ankle situation after surgery.
      Fig. 5
      Fig. 5The receiver operating characteristic curve and the area under curve value of 0.55 indicate poor discriminative properties of the LEFS.
      A total of 127 patients, that provided sufficient data on the LEFS at 6 months and 6.5 months administrations, were included into test-retest reliability analysis. There was no significant difference between the mean scores of the administrations (6 months 77.1 vs 6.5 months 76.9; p = .92). The ICC of the LEFS was 0.85 (95% CI 0.81-0.88, p < .001; Fig. 6). The SEM estimate for the LEFS was 7.9 (95% CI 6.7-9.1) indicating low variation in repeated measures scores.
      Fig. 6
      Fig. 6Linearity of scores for the modified LEFS in the time points of 6 and 6.5 months after surgery.

      Discussion

      As patients completed the modified LEFS preoperatively and after surgery, change in the scores would have been expected. However, the difference in preoperative and postoperative LEFS scores did not reach statistical significance. The effect size and the standardized response mean values indicated no actual change in the LEFS scores in the preoperative and 6 months postoperative scores. The finding suggests that the modified LEFS was unable to detect change in the clinical status after operative treatment of foot and ankle pathologies. In addition, comparison of patients that reported improvement of the foot condition with those reporting no improvement showed no significant difference in the score distributions between the groups. These findings complicated the assessment of responsiveness and estimation of the MIC. In previous studies, MIC has been successfully determined after operative treatment for other outcome measures in similar patient samples (
      • Dawson J
      • Boller I
      • Doll H
      • Lavis GJ
      • Sharp R
      • Cooke P
      • et al.
      Minimally important change was estimated for the Manchester–Oxford foot questionnaire after foot/ankle surgery.
      ,
      • Chan HY
      • Chen JY
      • Zainul-Abidin S
      • Ying H
      • Koo K
      • Rikhraj IS.
      Minimal clinically important differences for American Orthopaedic Foot & Ankle Society score in hallux valgus surgery.
      ,
      • Coe MP
      • Sutherland JM
      • Penner MJ
      • Younger A
      • Wing KJ.
      Minimal clinically important difference and the effect of clinical variables on the ankle osteoarthritis scale in surgically treated end-stage ankle arthritis.
      ,
      • Saarinen AJ
      • Uimonen MM
      • Sandelin H
      • Toom A
      • Richter M
      • Repo JP.
      Minimal important change for the visual analogue scale foot and ankle (VAS-FA).
      ,
      • Tapaninaho K
      • Uimonen MM
      • Saarinen A J
      • Repo J P
      Minimal important change for Foot and Ankle Outcome Score (FAOS).
      ). On the other hand, test-retest reliability was acceptable as the analysis presented no significant change in the score distributions of repeated measures and high ICC (0.85). SEM value indicated low variance caused by measurement error in the repeated measures.
      Measurement properties and validity of a PROM may vary between differing patient samples, ie, diagnoses and type of treatment received. Few prior studies have analyzed LEFS on only foot and ankle patients (
      • Mehta SP
      • Fulton A
      • Quach C
      • Thistle M
      • Toledo C
      • Evans NA.
      Measurement properties of the lower extremity functional scale: a systematic review.
      ,
      • Garratt AM
      • Naumann MG
      • Sigurdsen U
      • Utvåg SE
      • Stavem K.
      Evaluation of three patient reported outcome measures following operative fixation of closed ankle fractures.
      ,
      • Alcock G.
      Validation of the Lower Extremity Functional Scale on athletic subjects with ankle sprains.
      ,
      • Lin CC
      • Moseley AM
      • Refshauge KM
      • Bundy AC.
      The lower extremity functional scale has good clinimetric properties in people with ankle fracture.
      ,
      • Pinsker E
      • Inrig T
      • Daniels TR
      • Warmington K
      • Beaton DE.
      Reliability and validity of 6 measures of pain, function, and disability for ankle arthroplasty and arthrodesis.
      ). Alcock et al reported good responsiveness of the LEFS in athletes after ankle sprain (
      • Alcock G.
      Validation of the Lower Extremity Functional Scale on athletic subjects with ankle sprains.
      ) whereas Lin et al got parallel results in patients with ankle fractures in a short reassessment (
      • Lin CC
      • Moseley AM
      • Refshauge KM
      • Bundy AC.
      The lower extremity functional scale has good clinimetric properties in people with ankle fracture.
      ). In addition, the LEFS has been reported to be responsive in patients with general musculoskeletal conditions, total replacement of knee or hip and patients with osteoarthritis (
      • Mehta SP
      • Fulton A
      • Quach C
      • Thistle M
      • Toledo C
      • Evans NA.
      Measurement properties of the lower extremity functional scale: a systematic review.
      ). However, in the current study, the patient sample consisted of patients that received operative treatment for a wide range of foot and ankle pathologies, which may explain the differences in the results of the current study and previous literature. Satisfactory function of a PROM in one patient group, for example, patients with total hip replacement, does not guarantee comparative results in other groups. This may partly be explained with different levels of disability due to the disease: osteoarthritis of the hip limits life significantly more than osteoarthritis of the first metatarsal. The similarity of the scores between the assessments in the current study suggests suboptimal responsiveness for the modified LEFS in generic orthopedic foot and ankle patients.
      The Finnish validation study of the LEFS instrument revealed maximum scores in 17% in a sample of mostly injury-related foot and ankle patients (
      • Repo JP
      • Tukiainen EJ
      • Roine RP
      • Ilves O
      • Järvenpää S
      • Häkkinen A.
      Reliability and validity of the Finnish version of the Lower Extremity Functional Scale (LEFS).
      ). A study by Garrat et al found 80% of patients with full scores on 7 of the items of LEFS when compared to only one item in both OMAS and SEFAS in a sample of foot and ankle patients in a long-term follow-up (
      • Garratt AM
      • Naumann MG
      • Sigurdsen U
      • Utvåg SE
      • Stavem K.
      Evaluation of three patient reported outcome measures following operative fixation of closed ankle fractures.
      ). These are similar to the findings of the current study.
      A study by Pinsker et al comparing 6 lower extremity PROMs including the LEFS in patients with ankle arthroplasty and arthrodesis found no significant differences between the measurement properties of the instruments and thus reported no superior instrument (
      • Pinsker E
      • Inrig T
      • Daniels TR
      • Warmington K
      • Beaton DE.
      Reliability and validity of 6 measures of pain, function, and disability for ankle arthroplasty and arthrodesis.
      ). According to their study, LEFS had satisfactory test-retest reliability and internal consistency. They reported relatively high minimum detectable changes for all the instruments (17.8 for LEFS, translating to almost 20% of the maximum score). This may indicate problems when evaluating the change over time. A study by Uimonen et al presented the modified LEFS with unsatisfactory convergent validity compared to 4 other foot and ankle PROMs (FAAM, FAOS, MOXFQ, VAS-FA) and to a general HRQL assessment using the EQ-5D (
      • Uimonen MM
      • Ponkilainen VT
      • Toom A
      • Miettinen M
      • Häkkinen AH
      • Sandelin H
      • Latvala AO
      • Sirola T
      • Sampo M
      • Roine RP
      • Lindahl J
      • Ilves O
      • Sandbacka A
      • Repo JP
      Validity of five foot and ankle specific electronic patient-reported outcome (ePRO) instruments in patients undergoing elective orthopedic foot or ankle surgery.
      ). The authors hypothesized that the lack of general quality of life items in the LEFS leads to more function focused assessment. Foot and ankle pathologies requiring operative treatment may be too minor to lead to meaningful change in physical function and consequently LEFS assessment. The LEFS could potentially be used in the acute phase when assessing only lower extremity patient's momentary status or rehabilitation process. According to the findings of the current study, the modified LEFS might not be an ideal PROM for assessing long-term quality of life in foot and ankle patients. Based on general understanding, it is important to test the psychometric properties of PROMs in different patient groups to get an understanding of how the instrument functions in a specific pathology or anatomical region.

      Strengths and Limitations

      The current study was conducted on a patient sample with a wide range of foot and ankle diagnosis. Assessing longitudinal validity and MIC for a specific condition could have provided further insight of the measurement properties of the modified LEFS. However, the subgroup analysis was not possible due to small subgroups. The study investigated the modified LEFS for foot and ankle patients. The results of the current study cannot be generalized for general lower extremity patients or the original LEFS instrument.
      In conclusion, the modified version of the LEFS instrument presented with suboptimal longitudinal validity on orthopedic foot and ankle patients who underwent operative treatment. Similarity between the preoperative and postoperative scores complicated the definition of the MIC. Further research on measurement properties is still needed for choosing the preferably foot and ankle PROM. Due to the findings of the current study, the modified LEFS seems not to be optimal as an assessment instrument of functionality for orthopedic foot and ankle patients.

      Data Availability Statement

      The data that support the findings in this study are available from the corresponding author, JR, upon reasonable request.

      Declaration of Patient Consent

      Informed consent was collected from the patients.

      Author Contributions

      AJS: data analysis, drafting of the manuscript, ASB: data analysis, drafting of the manuscript, JPR: original study idea, revision of the manuscript, HS: original study idea, revision of the manuscript, MMU: statistical analysis, drafting of the manuscript. All authors discussed the results and contributed to the final manuscript

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