The Relationship Between Grading and Instrumented Measurements of Anterior Knee Joint Laxity

Transcription

1 Journal of Sport Rehabilitation, 2008, 17, Human Kinetics, Inc. The Relationship Between Grading and Instrumented Measurements of Anterior Knee Joint Laxity Wendy L. Hurley, Craig Denegar, and William E. Buckley Context: The relationship between clinical judgments of anterior knee laxity and instrumented measurement of anterior tibial translation is unclear. Objective: To examine the relationship between certified athletic trainers grading of anterior knee laxity and instrumented measurements of anterior tibial translation. Design: Randomized, blinded, clinical assessment. Setting: Laboratory. Participants: Model patients receiving evaluation of anterior knee laxity. Intervention: Twelve model patients were evaluated using a MEDmetric KT1000 knee ligament Arthrometer to establish instrumented measurements of anterior translation values at the tibio-femoral joint. Twenty-two certified athletic trainers were provided with operational definitions of potential laxity grades and examined the model patients to make judgments of anterior knee laxity. Main Outcome Measures: Correlation between clinical judgments and instrumented measurements of anterior tibial translation. Results: Clinical judgments and instrumented measurements were mutually independent. Conclusions: Anterior tibial translation grading by certified athletic trainers should be interpreted with caution during clinical decision-making. Keywords: Lachman test, KT1000, clinical judgments The relationship between clinical judgments of anterior knee laxity and instrumented measurement of anterior translation at the tibio-femoral joint has not been elucidated. Recently, progressive approaches to athletic training research have explored the influence of clinician technique on various aspects of the Lachman test. 1-3 Findings indicate that variations in clinician technique may influence the kinematics of the skill execution 3 and the kinetics of the stress test. 2 The mounting body of scientific evidence suggests deviation from true Lachman test procedure 4 may mask ligamentous instability, thus altering diagnostic accuracy which could inadvertently hinder injury evaluation. 1-3 The purpose of the present study was to perform a detailed follow-up analysis on existing data. 1 The goal was to investigate the relationship between clinical judgments of anterior knee laxity and instrumented measurements of anterior translation at the tibio-femoral joint. Wendy Hurley is with the Kinesiology Department at SUNY Cortland. hurleyw@em.cortland. edu. Craig Denegar is with the Department of Orthopedics and W.E. Buckley is with the Department of Kinesiology, both at Penn State University in State College, PA. 60

2 Anterior Knee Joint Laxity 61 Methods The current report uses data that were collected, analyzed, and updated in order to further investigate manual clinical evaluation procedures using the Lachman test. 4 Detailed description of the methods and procedures used to collect these data can be found in an earlier study that explored the influence of clinician technique on diagnostic efficacy of manual examination procedures. 1 This report is intended as an extension and continuance of earlier research and for comparison and compilation with foregoing results. Participants All participants in the study provided written informed consent. All procedures were approved by the Institutional Review Board for Human Subject Research. Clinicians. Twenty-two certified athletic trainers (8 female, 14 male; age 33.9 ± 7.3 years) volunteered as clinicians. Clinicians were trained professionals with distinctive educational and experiential backgrounds. Three participant clinicians were entry level at a bachelor degree, 14 held a master degree, and 5 had completed a doctorate degree. All clinicians were credentialed by the National Athletic Trainers Association Board of Certification (NATABOC) from 2 to 26 years (9.79 ± 6.53 years certified). Eleven clinicians served as Approved Clinical Instructors (ACIs) in a CAAHEP accredited Athletic Training Education Program. While all 22 clinicians were active certified athletic trainers, the extent and frequency of their clinical experience on a day-to-day basis were not recorded. Model Patients. Twelve undergraduate students (7 female, 5 male; age 21 ± 4.5 years) served as model patients. Three of the model patients were known to the researchers to have an ACL deficient and/or compromised left knee. Model patients were medically cleared for participation by one orthopedic surgeon. All model patients were asymptomatic by self-report, regardless of history with respect to knee injury. Asymptomatic was operationally defined as having no physical complaints (such as pain, swelling, buckling, giving way, shifting, etc.) for a minimum of 3 months prior to participation in the study. Reference Standard MEDmetric KT1000 Knee Ligament Arthrometer. One orthopedic surgeon, trained and experienced with the use of knee ligament arthrometers, obtained instrumented values of anterior tibial translation for each of the model patients. Objective measurements of sagittal plane motions of the tibia relative to the femur were established using the MEDmetric KT1000 Knee Ligament Arthrometer (MEDmetric Corporation, San Diego, CA). Measurements of anterior tibial translation were conducted bilaterally according to the sequence of detailed instructions specific for the MEDmetric KT1000 protocol for anterior cruciate ligament (ACL) tests. 5 This method of testing uses each knee as its own control. 6 The KT1000 has been shown to be valid 7-9 and reliable The MEDmetric Knee Ligament Arthrometer model KT1000 is a selfcontained anterior/posterior tibio-femoral displacement measuring instrument (Figure 1). The KT1000 is designed to quantitatively record objective clinical

3 62 Hurley, Denegar, and Buckley Figure 1 MEDMetric KT1000 (reprinted with permission). assessment of sagittal plane motions of the tibia relative to the femur. By pulling the force-sensing handle (in the direction away from the arthrometer), electronic audible force levels are indicated at anteriorly directed forces of 67 N, 89 N, and 133 N. Relative movement of the tibio-femoral joint is displayed on a dial and measured in millimeters as the relative motion between the patellar and tibial sensor pads. Intratester and intertester reliability for the MEDmetric KT1000 has been reported to be high, 9,15 particularly when the examiner has prior training and clinical experience with the KT ,11-14,16-17 The orthopedic surgeon followed the instructions as specified in the MEDmetric KT1000 protocol for anterior cruciate ligament (ACL) tests. 5 Data were collected bilaterally for all model patients. For the purposes of this study, it was decided a priori that the left knee would be considered the test knee or potentially injured knee for all clinical evaluations. Test Methods A copy of the conventional orthopedic laxity rating scale used by the orthopedic surgeon for determination of anterior laxity grades and side-to-side differences in measurements of anterior translation of the tibia relative to the femur during the KT1000 protocol was provided for all clinicians prior to presentation of the first model patient. The laxity rating scale is illustrated in Table 1. The pathologic laxity criteria were available to all clinician participants for reference throughout testing sessions. Model patients were assigned a random testing order for each clinician. For the purposes of standardizing the test environment across clinicians, model patients were instructed by the researcher to lie supine on the examination table at the start of each testing session. Model patients removed their shoes and socks prior to testing and wore shorts in order to permit clinicians to access their mid-thigh region, as necessary. During physical examination, neither the tibia nor the femur of the model patient s limb was in a fixed position allowing clinicians to perform natural, rather than constrained, movement patterns in their evaluation. Clinicians were partially blinded to model patient history of knee injury. While it was implicit that visible scars would provide indication of patient history, clinicians were not permitted to ask model patients any questions. Participant clinicians

4 Anterior Knee Joint Laxity 63 Table 1 Categorized Degree of Anterior Translation/Grade of Laxity Grade Translation Amount a Judgment Description 0 Grade 2 mm Tight with firm end-feel Grade I 3-5 mm Nominal increase in laxity compared to contralateral knee Grade II 6-9 mm Slight increase in anterior translation compared to contralateral knee Grade III 10 mm Excessive anterior translation compared to contralateral knee a Side-to-side differences in anterior displacement of tibio-femoral joint (eg, anterior translation of tibia relative to femur). were instructed by the researcher to estimate anterior knee laxity for the left knee for each of the model patients by using only the Lachman test. 4 Clinicians were instructed that they would not be permitted to perform any additional manual stress test in their examination of anterior tibial translation (ATT). Clinicians performed the test in a manner consistent with their clinical practice, and without intervention of instructional feedback. Clinicians were asked to announce their interpretation of ATT (grade of laxity) 4, for the left knee of all model patients. As laxity categorization is traditionally based upon side-to-side comparison, clinicians were allowed to perform bilateral examination and to repeat side-to-side comparison to their satisfaction before announcing their results. The number of trials was not standardized to allow clinicians to perform the Lachman test in a manner reflective of their usual clinical technique. Clinicians performed the test and announced the results of his or her evaluation before being presented with another model patient. Clinicians were tested individually in an athletic training laboratory classroom. Participant clinicians were not permitted to observe each other conduct their examination. Each clinician was tested for one session. Statistical Methods KT1000 measurements of anterior tibial translation were calculated and interpreted in accordance with the MEDmetric Knee Ligaments Arthrometer Model KT1000 support materials for data interpretation and protocol for ACL tests. 5 Anterior tibial translation (ATT) was expressed in millimeters (mm) and calculated as the mean test value for three trials. For the purposes of the current study, sideto-side differences in ATT were calculated by subtracting right knee ATT from left knee ATT, regardless of medical history with respect to knee injury. Positive values are indicative of increased excursion on the left knee when comparing sideto-side (right/left) differences in ATT. A side-to-side difference was considered as a measurement indicating pathologic laxity. 4-5,18-20 Grades and levels of excursion used to categorize knee joint laxity in the conventional orthopedic laxity rating scale can be found in Table 1. Following the MEDmetric KT1000 protocol for anterior cruciate ligament (ACL) tests, 5 the non-injured knee is used as the control knee for calculating

5 64 Hurley, Denegar, and Buckley side-to-side (left knee compared to right knee) differences in anterior tibial translation. For the purposes of this study, the right knee was used as the control knee to calculate side-to-side differences for all model patients, regardless of their history with respect to knee injury (because the left knee was decided a priori to be the test knee for all clinical evaluations). In other words, the mean test value of anterior tibial translation for the right knee was subtracted from the mean test value of anterior tibial translation for the left knee. The relationship between clinician judgments of anterior knee laxity, and MEDmetric KT1000 knee ligament Arthrometer measurements of anterior translation values at the tibio-femoral joint was explored through Spearman rank order correlation coefficients (r 3 ) calculated for each clinician. Results Instrumented Measurements of Anterior Tibial Translation KT000 measurements of model patients anterior tibial translation (ATT) at 89 N force displacements and the corresponding grades used to categorize knee joint laxity are reported in Table 2. Positive values in side-to-side differences were found for all model patients, regardless of their history with respect to knee injury. Laxity, when it did not grade 0, was found across model patients to be greater on the left Table 2 KT1000 Measurements and Grades of Anterior Knee Laxity a for Model Patients Model Patient Left Knee b KT1000 Anterior Laxity Grade a 89N force Side-to-Side Difference c Left Knee 1* Grade I Grade Grade Grade I Grade Grade I Grade II Grade I 9* Grade II 10* Grade I Grade Grade II a Anterior laxity grade for tibio-femoral joint reported for left knee of all model patients regardless of knee injury history. b ATT expressed in mm, calculated as mean test value for three trials. c Side-to-side difference calculated by subtracting right knee ATT from left knee ATT. Note. Model patients 1, 9, & 10 had surgically confirmed failed ACL reconstructions of their left knee.

6 side. Specifically, 8 of the model patients had left-side laxity. While this finding was unexpected, it was nevertheless noted as a coincidental characteristic among these model patients. Four model patients were categorized as having a Zero Grade ( 2 mm) of left knee anterior laxity, 5 were categorized as having a Grade I (3-5 mm) of left knee anterior laxity, and 3 were categorized as having a Grade II (6-9 mm) of left knee anterior laxity. Correlation Between Instrumented Measurement and Clinical Judgments The Spearman rank correlation coefficient (r 3 ) values indicate that in the sample population, certified athletic trainers estimates of anterior knee laxity and instrumented measurements of anterior translation values are mutually independent for 82% (N = 18) of the participant clinicians. Spearman s rho values were found to be significant for only 18% (N = 4) of the clinicians. These results are reported in Table 3. Table 3 Correlation Between Clinical Judgments and KT1000 Measurements Clinicians Clinical-technique category 1 Spearman s rho values Significant values (2-tailed) 1 A B B B B A.723** B B B A.849** B B B B B B A.705* B.696* B B B B ** indicates significance at the.01 level (2-tailed) * indicates significance at the.05 level (2-tailed) Note: The data in column 2 are adapted 1 and based on the following: Clinician technique categorized according to tibia hand preference. Categories of clinician technique were operationally defined as condition A (Lachman test, as described by Torg et al 4 ) and condition B (generalized anterior tibial translation test) (p. 215). 1 65

7 66 Hurley, Denegar, and Buckley Comments In view of the finding that the Spearman rank order correlation coefficient values did not reach statistical significance at the.05 level for 82% (N = 18) of the participant clinicians, it is reasoned that no overall relationship was found between clinical judgments and the instrumented measurements of anterior knee joint laxity. The current study represents exploratory research. The specified hypothesis leads to a two-sided test because it was the desire of the investigators to detect any departure from independence among the dependent variables. If a more liberal alpha level of.10 is considered, a significant relationship between instrumented and manually assessed values was identified for 3 additional clinicians. 7,12,20 The magnitude of these relationships grouped around Spearman s rho =.50. The.50 magnitude is moderate therefore it is possible that other factors not collected in this study may account for different variance. Based on the results of the current study, if no overall relationship between these clinical judgments and the KT1000 instrumented measurement exists, then we are left to speculate on what this means in terms of the ability of clinicians to quantify laxity through physical examination. If we assume the validity and reliability of the instrumented laxity measures, then we are left with the two plausible explanations for these results. The first is that the assessments test different qualities. The Lachman test was primarily developed to identify patients with a torn anterior cruciate ligament in a dichotomous manner rather than grade laxity. 4 The KT1000 knee ligament Arthrometer was developed to quantify differences in laxity with the potential to create diagnostic dichotomy. One difference in these procedures is that the Lachman test permits qualification of endfeel while instrumented measures of laxity do not. The second possibility is that most of the participant clinicians in this study were unable to estimate differences in knee laxity. That presents questions about how the clinical anterior knee joint laxity skill was learned and practiced. While we asked participants about the length of their athletic training experience, we did not inquire as to how frequently they performed the Lachman test in routine professional activities. It is certainly possible that frequent examination of anterior cruciate (ACL) deficient knees is needed to develop the ability to accurately estimate laxity. This issue of clinical experience is the focus of a study currently in progress by one of the authors. Perhaps more importantly, it may be that deviation from the exact technique of a specialized clinical test compromises the accuracy of the assessment. In a previously reported study, 1 only 4 of the 22 participant clinicians demonstrated a Lachman technique as originally described by Torg. 4 Three of these 4 same clinician participants are now being reported to have grading values that correlated significantly with the instrumented measurements, while only 1 of the clinicians who did not demonstrate proper technique achieved similar results. While the portion of the participants demonstrating proper technique was too small to draw conclusions as to the importance of technique, these results raise issues regarding the teaching/learning processes for psychomotor competencies.

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