Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3263-3
LETTER TO THE EDITOR
A close look at tibiofemoral rotation measurements Daniel Theisen · Caroline Mouton · Romain Seil
Received: 15 July 2014 / Accepted: 22 August 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Dear Editor-in-Chief, The recent paper by Chung et al. [2] published in KSSTA caught our attention. Their study introduces a new laximeter to evaluate static rotational knee laxity termed “Rotatometer” and presents normative data as well as results for its reliability. Overall, it is interesting to see how rotational knee laxity measurements have received increasing interest in the area of orthopaedics, and especially in the field of anterior cruciate ligament (ACL) reconstruction surgery over the past few years [4]. Thus, we would like to congratulate Chung et al. [2] on their efforts to contribute to this emerging and relatively complex field. The complexity of static rotational knee laxity measurements lies with the characteristics of the measurement instrument, the execution of the test and the interpretation of the results. Whatever the instrument used, the execution of a laxity test warrants careful standardisation and strict procedures. The interpretation of the results must be done under consideration of the strengths and weaknesses of the instrument in terms of accuracy, reliability and validity of the measurements, and taking into account the complex anatomy of the knee joint. Unless these conditions are given, it is unlikely that useful conclusions for research and clinical decisions can be reached [4]. Based on the preceding considerations, we wanted to share a few comments on the contribution of Chung et al. [2] that we think are D. Theisen (*) · C. Mouton · R. Seil Sports Medicine Research Laboratory, Public Research Centre for Health, Luxembourg, Luxembourg e-mail: daniel.theisen@crp‑sante.lu R. Seil Department of Orthopaedics, Centre Hospitalier de Luxembourg, Luxembourg, Luxembourg
interesting for clinicians and researchers to bear in mind when reading their article. A first notable aspect is that their new instrument is, in our view, insufficiently described, especially in the absence of a photograph or a schematic representation. The outcome measure is the “degree of rotation” of a footrest located on the top of a “body with a round rotating platform”. The latter is “connected to an electric power source and has a light-emitting diode window in front showing the degree of rotation of the footrest”. The result is not recorded but simply read by the examiner. No information about the measurement characteristics (e.g. accuracy or range) is provided. The test procedure involves the application of a “manual maximal torque from the examiner” via a handlebar. An increasing torque is applied, unfortunately not until a standard torque value is reached, but “until the examinee’s apprehension of end-feel as a displacing force”. In other words, it seems that the Rotatometer allows to measure the examiner’s force or the patient’s apprehension, whichever is reached first, probably with limited accuracy. The authors justify their methodological choice by the desire to avoid introducing a measurement bias that would result from the use of a given torque in patients who might have very different leg sizes or muscle mass. However, the examinee’s apprehension of end-feel might be affected by the presence of a knee injury, may vary from day to day and may even be different between the two legs of an injury-free participant. Thus, in the absence of a standardised applied torque, a standardised measurement is not possible, which makes their results virtually useless. Another feature of the testing procedure is that the knee is positioned at 90° of flexion, an aspect which the authors discuss as a limitation. We do agree on this, especially since the main aim is to evaluate the ACL status. Although this methodological choice seems to have been motivated
13
by the fact that it allows a more convenient positioning of the patient (patient convenience is indeed an important issue), it is a poor one. Indeed, studies suggest that an ACL injury is best detected by side-to-side comparisons of static rotational knee laxity, provided that the knee is tested in a position between 0° and 30°, not more [1, 3, 5, 7]. In other words, the measurements performed at 90° knee flexion provide much less information about the status of the ACL. Another major aim of the study of Chung et al. was to provide a normative rotational profile. They describe the results of 188 knees from 94 healthy volunteers (recruited in two different medical centres), which is an appropriate number of test participants. However, a major flaw in their approach is that the participants were selected based on physical examinations prior to the rotational laxity measurements “to identify and exclude knees with any laxity or hypermobility”. This means that the group on which the normative rotational profile was established is biased and cannot be considered as representative of the general population. The authors then provide “an indirect analysis of accuracy” of the instrument by comparing the results obtained on their participants from the two different centres. Without reiterating the above-described concerns, this approach is inappropriate to assess measurement accuracy, and it merely compares the groups of participants from the 2 centres. By the way, the differences between the two groups (19 % for external rotation and 21 % for internal rotation) were statistically significant. The authors performed additional measurements to evaluate intra- and inter-observer reliability. They provide
13
Knee Surg Sports Traumatol Arthrosc
results for the intra-class correlation coefficient, but fail to define what ICC type was computed. Furthermore, the ICC is a poor choice to determine trial-to-trial consistency, since it depends on the heterogeneity of the sample investigated. Other, more pertinent indicators have been proposed in the literature [6], such as the standard error of measurement or the minimal detectable change.
References 1. Andersen HN, Dyhre-Poulsen P (1997) The anterior cruciate ligament does play a role in controlling axial rotation in the knee. Knee Surg Sports Traumatol Arthrosc 5:145–149 2. Chung JH, Ryu KJ, Lee DH, Yoon KH, Park YW, Kim HJ et al (2014) An analysis of normative data on the knee rotatory profile and the usefulness of the Rotatometer, a new instrument for measuring tibiofemoral rotation: the reliability of the knee Rotatometer. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/ s00167-014-3039-9 3. McQuade KJ, Crutcher JP, Sidles JA, Larson RV (1989) Tibial rotation in anterior cruciate deficient knees: an in vitro study. J Orthop Sports Phys Ther 11:146–149 4. Mouton C, Theisen D, Pape D, Nuhrenborger C, Seil R (2012) Static rotational knee laxity in anterior cruciate ligament injuries. Knee Surg Sports Traumatol Arthrosc 20:652–662 5. Nielsen S, Ovesen J, Rasmussen O (1984) The anterior cruciate ligament of the knee: an experimental study of its importance in rotatory knee instability. Arch Orthop Trauma Surg 103:170–174 6. Weir JP (2005) Quantifying test-retest reliability using the intraclass correlation coefficient and the SEM. J Strength Cond Res 19:231–240 7. Zarins B, Rowe CR, Harris BA, Watkins MP (1983) Rotational motion of the knee. Am J Sports Med 11:152–156
LETTER TO THE EDITOR
A close look at tibiofemoral rotation measurements Daniel Theisen · Caroline Mouton · Romain Seil
Received: 15 July 2014 / Accepted: 22 August 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Dear Editor-in-Chief, The recent paper by Chung et al. [2] published in KSSTA caught our attention. Their study introduces a new laximeter to evaluate static rotational knee laxity termed “Rotatometer” and presents normative data as well as results for its reliability. Overall, it is interesting to see how rotational knee laxity measurements have received increasing interest in the area of orthopaedics, and especially in the field of anterior cruciate ligament (ACL) reconstruction surgery over the past few years [4]. Thus, we would like to congratulate Chung et al. [2] on their efforts to contribute to this emerging and relatively complex field. The complexity of static rotational knee laxity measurements lies with the characteristics of the measurement instrument, the execution of the test and the interpretation of the results. Whatever the instrument used, the execution of a laxity test warrants careful standardisation and strict procedures. The interpretation of the results must be done under consideration of the strengths and weaknesses of the instrument in terms of accuracy, reliability and validity of the measurements, and taking into account the complex anatomy of the knee joint. Unless these conditions are given, it is unlikely that useful conclusions for research and clinical decisions can be reached [4]. Based on the preceding considerations, we wanted to share a few comments on the contribution of Chung et al. [2] that we think are D. Theisen (*) · C. Mouton · R. Seil Sports Medicine Research Laboratory, Public Research Centre for Health, Luxembourg, Luxembourg e-mail: daniel.theisen@crp‑sante.lu R. Seil Department of Orthopaedics, Centre Hospitalier de Luxembourg, Luxembourg, Luxembourg
interesting for clinicians and researchers to bear in mind when reading their article. A first notable aspect is that their new instrument is, in our view, insufficiently described, especially in the absence of a photograph or a schematic representation. The outcome measure is the “degree of rotation” of a footrest located on the top of a “body with a round rotating platform”. The latter is “connected to an electric power source and has a light-emitting diode window in front showing the degree of rotation of the footrest”. The result is not recorded but simply read by the examiner. No information about the measurement characteristics (e.g. accuracy or range) is provided. The test procedure involves the application of a “manual maximal torque from the examiner” via a handlebar. An increasing torque is applied, unfortunately not until a standard torque value is reached, but “until the examinee’s apprehension of end-feel as a displacing force”. In other words, it seems that the Rotatometer allows to measure the examiner’s force or the patient’s apprehension, whichever is reached first, probably with limited accuracy. The authors justify their methodological choice by the desire to avoid introducing a measurement bias that would result from the use of a given torque in patients who might have very different leg sizes or muscle mass. However, the examinee’s apprehension of end-feel might be affected by the presence of a knee injury, may vary from day to day and may even be different between the two legs of an injury-free participant. Thus, in the absence of a standardised applied torque, a standardised measurement is not possible, which makes their results virtually useless. Another feature of the testing procedure is that the knee is positioned at 90° of flexion, an aspect which the authors discuss as a limitation. We do agree on this, especially since the main aim is to evaluate the ACL status. Although this methodological choice seems to have been motivated
13
by the fact that it allows a more convenient positioning of the patient (patient convenience is indeed an important issue), it is a poor one. Indeed, studies suggest that an ACL injury is best detected by side-to-side comparisons of static rotational knee laxity, provided that the knee is tested in a position between 0° and 30°, not more [1, 3, 5, 7]. In other words, the measurements performed at 90° knee flexion provide much less information about the status of the ACL. Another major aim of the study of Chung et al. was to provide a normative rotational profile. They describe the results of 188 knees from 94 healthy volunteers (recruited in two different medical centres), which is an appropriate number of test participants. However, a major flaw in their approach is that the participants were selected based on physical examinations prior to the rotational laxity measurements “to identify and exclude knees with any laxity or hypermobility”. This means that the group on which the normative rotational profile was established is biased and cannot be considered as representative of the general population. The authors then provide “an indirect analysis of accuracy” of the instrument by comparing the results obtained on their participants from the two different centres. Without reiterating the above-described concerns, this approach is inappropriate to assess measurement accuracy, and it merely compares the groups of participants from the 2 centres. By the way, the differences between the two groups (19 % for external rotation and 21 % for internal rotation) were statistically significant. The authors performed additional measurements to evaluate intra- and inter-observer reliability. They provide
13
Knee Surg Sports Traumatol Arthrosc
results for the intra-class correlation coefficient, but fail to define what ICC type was computed. Furthermore, the ICC is a poor choice to determine trial-to-trial consistency, since it depends on the heterogeneity of the sample investigated. Other, more pertinent indicators have been proposed in the literature [6], such as the standard error of measurement or the minimal detectable change.
References 1. Andersen HN, Dyhre-Poulsen P (1997) The anterior cruciate ligament does play a role in controlling axial rotation in the knee. Knee Surg Sports Traumatol Arthrosc 5:145–149 2. Chung JH, Ryu KJ, Lee DH, Yoon KH, Park YW, Kim HJ et al (2014) An analysis of normative data on the knee rotatory profile and the usefulness of the Rotatometer, a new instrument for measuring tibiofemoral rotation: the reliability of the knee Rotatometer. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/ s00167-014-3039-9 3. McQuade KJ, Crutcher JP, Sidles JA, Larson RV (1989) Tibial rotation in anterior cruciate deficient knees: an in vitro study. J Orthop Sports Phys Ther 11:146–149 4. Mouton C, Theisen D, Pape D, Nuhrenborger C, Seil R (2012) Static rotational knee laxity in anterior cruciate ligament injuries. Knee Surg Sports Traumatol Arthrosc 20:652–662 5. Nielsen S, Ovesen J, Rasmussen O (1984) The anterior cruciate ligament of the knee: an experimental study of its importance in rotatory knee instability. Arch Orthop Trauma Surg 103:170–174 6. Weir JP (2005) Quantifying test-retest reliability using the intraclass correlation coefficient and the SEM. J Strength Cond Res 19:231–240 7. Zarins B, Rowe CR, Harris BA, Watkins MP (1983) Rotational motion of the knee. Am J Sports Med 11:152–156
