Elsevier

Clinical Biomechanics

Volume 27, Issue 8, October 2012, Pages 830-836
Clinical Biomechanics

Arthrometric curve-shape variables to assess anterior cruciate ligament deficiency

https://doi.org/10.1016/j.clinbiomech.2012.04.011Get rights and content

Abstract

Background

Instrumented measurement of asymmetry in anterior–posterior knee laxity is commonly used to assess anterior cruciate ligament integrity. Significant advances in arthrometric technology and data visualization have occurred since first generation arthrometers. However, little has changed with regard to diagnostic criteria employed. To our knowledge, no investigations have assessed the shape of laxity curves to diagnose anterior cruciate ligament (ACL) deficiency. We hypothesized that linear stiffness and compliance after positive curve inflection would be more sensitive and specific to anterior cruciate ligament injury than current measures and would require data from the involved limb only.

Methods

Laxity curves were obtained from 130 knees on 65 subjects (Anterior Cruciate Injured n = 15, Controls n = 50) using a CompuKT Knee Ligament Arthrometer. Traditional diagnostic variables and novel descriptive curve-shape variables [(1) inflection point, (2) pre- and post-inflection linear stiffness and (3) a modified compliance index based on the post-inflection linear stiffness] were assessed for sensitivity to anterior cruciate ligament deficiency. Statistical interactions were evaluated using 2-by-2 ANOVA.

Findings

Significant interactions (P < 0.001) were identified for laxity symmetry, stiffness, compliance index and modified compliance index. Modified compliance index predicted anterior cruciate ligament deficiency with the highest sensitivity (93%) and specificity (100%). For a test performed on a single limb, modified compliance index demonstrated 98% sensitivity and 80% specificity.

Interpretation

The modified compliance index is a highly sensitive and specific measure to diagnose anterior cruciate ligament deficiency, and may serve as a simple and accurate diagnostic tool for individuals without a healthy contralateral limb.

Introduction

The anterior cruciate ligament (ACL) is the primary restraint to anterior tibial translation relative to the femur, providing approximately 85% of passive anterior tibial restraint (Butler et al., 1980). Clinical assessment of anterior translation using the Lachman's exam has been identified as the most valid approach to identify ACL deficiency with sensitivity (Sn) of 85% and specificity (Sp) of 94% (Benjaminse et al., 2006). However, instrumented measurement of anterior–posterior (AP) knee laxity (arthrometry) is also a well-established, commonly used diagnostic approach. Some clinicians prefer to use an arthrometer because it provides objective, quantitative, and accurate information that cannot be obtained from a Lachman's exam. These qualities and the fact that the data from an arthrometer is continuously distributed (not discreet as in a Lachman's grade) have also made them an important tool in knee biomechanical research. While a number of devices have been developed, validated and assessed for reliability, the KT arthrometer series (KT-1000, KT-2000, CompuKT, MEDmetric Corp., San Diego, CA) remains the most commonly used and most accurate and reliable device for assessing ACL integrity (Anderson and Lipscomb, 1989, Anderson et al., 1992, Balasch et al., 1999, Pugh et al., 2009, Queale et al., 1994, Riederman et al., 1991, Robnett et al., 1995, Wroble et al., 1990a, Wroble et al., 1990b). Although the KT has been used for over three decades, the fundamental approach to assessment remains unchanged, despite the advances in the technology (Daniel et al., 1985a, Daniel et al., 1985b AJSM, Pugh et al., 2009). Namely, the use of side-to-side differences in AP displacement between knees at set, arbitrary forces, which do not account for inter-patient variability in knee laxity, remains the standard for laxity-based clinical and research assessment of ACL deficiency (Daniel et al., 1985a, Daniel et al., 1985b Highgenboten et al., 1992, Pugh et al., 2009). In this paper, we present a new method for analyzing KT arthrometric data that generates objective, quantifiable laxity data with increased diagnostic accuracy compared to traditional arthrometric protocols. The diagnostic accuracy is also an improvement over the previously reported sensitivity and specificity of the Lachman's exam (Benjaminse et al., 2006).

The current KT arthrometer methodology limits its potential applications since assessment of displacement asymmetry at a “manual maximum force” is reported as the most sensitive and specific “force” for the determination of ACL deficiency (Bach et al., 1990, Daniel et al., 1985a, Daniel et al., 1985b AJSM, Highgenboten et al., 1992, Pugh et al., 2009). Bach et al. reported 77% Sn and 90% Sp for this test using a 3 mm side-to-side difference as the diagnostic cutoff point for the manual maximum force test in acute ACL tears (Bach et al., 1990). Similar values have been reported by Highenboten et al. and Daniel et al. for the manual maximum test (Daniel et al., 1994, Highgenboten et al., 1992). The manual maximum force does not currently have a defined value and may be highly variable within and between testers. This may account for the variability in reliability data reported for the KT arthrometers, particularly between raters (ICCs range = 0.38–0.86) (Forster et al., 1989, Hanten and Pace, 1987, Myrer et al., 1996). In addition, the need for side-to-side comparisons poses a limitation for patient populations without an “unaffected” contralateral limb. Currently, no highly sensitive and specific arthrometric diagnostic criteria exist for patients who do not have a healthy contralateral limb. Given that reports of rates of graft failure and/or contralateral ACL tear can be as high as one in four ten years post-reconstruction, or even higher in competitive athletes, this presents a diagnostic conundrum (Paterno et al., 2010, Pinczewski et al., 2007). Development of more sensitive and specific arthrometric protocols that allow for single limb assessment could increase the diagnostic capacity of the KT and still provide the clinician with the insight offered by objective, quantitative data.

The KT-2000 was the initial graphing unit that offered a force–displacement plotter, and was subsequently modified to an electronic plotter in the CompuKT. Despite the significant improvements in data visualization techniques, few studies have analyzed other potential variables to assess ACL integrity (Fleming et al., 1993). Daniel et al. proposed the use of a ‘compliance index’ (CI), defined as the difference in displacements at 67 N and 89 N of anterior force (Daniel et al., 1985a, Daniel et al., 1985b AJSM). Subsequently, this measure has been used as an objective way to quantify asymmetry in the “endpoint” of anterior translation felt during a Lachman exam (Anderson et al., 1992, Bach et al., 1990, Daniel et al., 1985a, Daniel et al., 1985b Myrer et al., 1996, Skinner et al., 1986). Highenboten et al. report a sensitivity of this measure of 79%, but report no value for the specificity of this measure (Highgenboten et al., 1992). However, the assumption of a linear force–displacement relationship in this range of applied forces does not account for the high variability in laxity curve-shape between patients (Liu et al., 2002).

The purpose of the current study was two-fold: to develop an accurate, reliable method for analysis of AP knee laxity curve shapes, and to identify variables that detect ACL deficiency with higher sensitivity and specificity than current diagnostic criteria. The primary hypothesis tested was that the linear stiffness and compliance after a positive curve inflection would discriminate between an ACL-intact knee and an ACL-deficient individual with high sensitivity and specificity, and that the inter-rater reliability of these measures would be high. The secondary hypothesis tested was that stiffness and compliance after positive curve inflection would demonstrate diagnostic utility for arthrometric data from a single limb, which would eliminate the need to assess the contralateral limb. Current diagnostic protocols in arthrometry generally require the patient to have at least one unaffected limb. High rates of graft failure and contralateral limb injury, especially in active populations, preclude the use of current arthrometric techniques for patients who have already suffered a previous injury.

Section snippets

Patient population

KT knee arthrometer data of 65 subjects, which included 15 ACL-deficient (ACLD) subjects and 50 healthy controls (CTRL) without history of knee ligament injury, were used for analysis. The ACLD subjects consisted of patients with a complete tear of the ACL confirmed by MRI and/or arthroscopy. No ACLD subjects reported contralateral limb ACL or PCL injury. Descriptive statistics of the patient groups are shown in Table 1. Informed consent and assent were obtained from all control subjects and

Results

Group-by-side effects were observed for a number of variables. Main effects of group and side were also observed, however post-hoc testing revealed that these effects were driven by the affected limb in ACL-deficient subjects for all variables. The predictive strength for four between-limb and two single limb variables for comparison of ACLD and normal knees is presented in Table 3. Eight variables demonstrated statistically significant group-by-side interactions between all healthy (n = 115)

Discussion

This study outlines an accurate, reliable method to assess ACL integrity using arthrometric data from a single limb. The primary hypothesis tested was that linear stiffness and compliance after a positive curve inflection would discriminate between a healthy and ACL-deficient individual with higher sensitivity and specificity than currently used measures. The results demonstrated increased diagnostic accuracy in ACL injury for the modified compliance index compared to traditionally defined

Conclusion

This study introduces a new method for assessment of AP knee translation curves and demonstrates the value of the MCI as a diagnostic indicator of ACL injury. The MCI is both a highly sensitive and specific predictor of ACL deficiency. This measure may serve as an accurate, objective, and quantitative diagnostic tool to assess ACL integrity and provide a method to assess AP knee laxity in a single limb in an individual without a healthy contralateral limb.

Acknowledgments

The work presented in this manuscript was funded in part by NIH/NIAMS Grants R01-AR049735, R01-AR055563 and R01-AR056259 and The NFL Charities. The authors would also like to thank Dr. Marepalli B. Rao for his assistance with the statistical methodology. None of the authors of this manuscript have any relationship, professional or otherwise, that presents a potential conflict of interest with regard to the work presented. Finally, the authors would like to acknowledge the assistance and support

References (28)

  • B.C. Fleming et al.

    An in vivo comparison of anterior tibial translation and strain in the anteromedial band of the anterior cruciate ligament

    J. Biomech.

    (1993)
  • A.F. Anderson et al.

    Preoperative instrumented testing of anterior and posterior knee laxity

    Am. J. Sports Med.

    (1989)
  • A.F. Anderson et al.

    Instrumented evaluation of knee laxity: a comparison of five arthrometers

    Am. J. Sports Med.

    (1992)
  • B.R. Bach et al.

    Arthrometric evaluation of knees that have a torn anterior cruciate ligament

    J. Bone Joint Surg. Am.

    (1990)
  • H. Balasch et al.

    Evaluation of anterior knee joint instability with the rolimeter: a test in comparison with manual assessment and measuring with the KT-1000 arthrometer

    Knee Surg. Sports Traumatol. Arthrosc.

    (1999)
  • B.T. Ballantyne et al.

    Influence of examiner experience and gender on interrater reliability of KT-1000 arthrometer measurements

    Phys. Ther.

    (1995)
  • A. Benjaminse et al.

    Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis

    J. Orthop. Sports Phys. Ther.

    (2006)
  • J. Berry et al.

    Error estimates in novice and expert raters for the KT-1000 arthrometer

    J. Orthop. Sports Phys. Ther.

    (1999)
  • D.L. Butler et al.

    Ligamentous restraints to anterior-posterior drawer in the human knee. A biomechanical study

    J. Bone Joint Surg. Am.

    (1980)
  • W.D. Cannon

    Use of arthrometers to assess knee laxity and outcomes

    Sports Med. Arthrosc. Rev.

    (2002)
  • D.M. Daniel et al.

    Instrumented measurement of anterior laxity of the knee

    J. Bone Joint Surg. Am.

    (1985)
  • D.M. Daniel et al.

    Instrumented measurement of anterior knee laxity in patients with acute anterior cruciate ligament disruption

    Am. J. Sports Med.

    (1985)
  • D.M. Daniel et al.

    Fate of the ACL-injured patient. A prospective outcome study

    Am. J. Sports Med.

    (1994)
  • I.W. Forster et al.

    Is the KT 1000 knee ligament arthrometer reliable?

    J. Bone Joint Surg. Br.

    (1989)
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