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The Reproducibility and Repeatability of Varus Stress Radiographs in the Assessment of Isolated Fibular Collateral Ligament and Grade-III Posterolateral Knee InjuriesAn in Vitro Biomechanical Study
Robert F. LaPrade, MD, PhDa; Christie Heikes, MDa; Adam J. Bakker, MSa; Rune B. Jakobsen, MDb
a Sports Medicine and Shoulder Divisions, Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue, R-200, Minneapolis, MN 55454. E-mail address for R.F. LaPrade: lapra001@umn.edu
b Department of Orthopaedic Surgery, Ullevaal University Hospital, University of Oslo, N-0407 Oslo, Norway
View Disclosures and Other Information
Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the University of Minnesota Biomechanics Laboratory, Minneapolis, Minnesota

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Oct 01;90(10):2069-2076. doi: 10.2106/JBJS.G.00979
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Abstract

Background: Objective measures to quantitate the amount of lateral compartment opening for patients with lateral and posterolateral knee injuries have not been well documented. The purpose of the present study was to measure lateral compartment opening secondary to applied varus stresses following posterolateral corner structure sectioning and to develop radiographic guidelines to quantify the amount of lateral compartment gapping seen with these injuries.

Methods: Ten nonpaired fresh-frozen cadaver lower extremities were used. Two varus loads, a 12-Nm moment and a clinician-applied varus stress, were applied to the intact knees and after sequential sectioning of the fibular collateral ligament, popliteus tendon, popliteofibular ligament, and anterior and posterior cruciate ligaments to simulate degrees of posterolateral knee and associated combined cruciate ligament injuries. The shortest distance between the most distal subchondral bone surface of the lateral femoral condyle and the corresponding lateral tibial plateau was measured to quantify lateral compartment opening and was analyzed on digital radiographs. Three observers were used to determine interobserver reproducibility and intraobserver repeatability.

Results: In the intact knee, the mean lateral compartment gapping due to a 12-Nm moment and a clinician-applied varus stress was 8.9 and 9.7 mm, respectively. Lateral gapping significantly increased by 2.1 and 2.7 mm in association with sectioning of the fibular collateral ligament and by 3.4 and 4.0 mm in knees with a simulated posterolateral corner injury for each respective load-application technique (p < 0.0001 for all comparisons). Intraobserver repeatability was high, with all observers independently obtaining an intraclass correlation coefficient of 0.99, whereas the analysis of interobserver reproducibility demonstrated an intraclass correlation coefficient of 0.97.

Conclusions: Measurements with use of current clinical digital imaging systems can be used to quantify the amount of lateral compartment knee opening. Clinicians should suspect an isolated fibular collateral ligament injury if opening on clinician-applied varus stress radiographs increases by approximately 2.7 mm and a grade-III posterolateral corner injury if values increase by approximately 4.0 mm.

Clinical Relevance: Varus stress radiographs appear to provide an objective and reproducible measure of lateral compartment gapping that should prove useful for the diagnosis, management, and postoperative follow-up of patients with fibular collateral ligament and posterolateral knee injuries.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Robert F. LaPrade, MD, PhD
    Posted on October 23, 2008
    Dr. LaPrade responds to Drs. Clarke and Nunn
    University of Minnesota

    We thank Drs. Clarke and Nunn for their kind comments on our goals of providing more objective clinical assessment of these injuries(1). We have rather extensive clinical use with these techniques, and their excellent questions will help to disseminate our quantitative findings to assist clinicians with improving their diagnostic skills with these very difficult injuries.

    In terms of their questions about the use of cadaveric knees, it can be said with certainty that almost all biomechanical testing is performed on older specimens. However, we have been performing this technique in our clinic for over ten years, with thousands of varus stress x-rays generated. We can state that the amount of gapping seen in the intact state in the cadaver knees in our study is effectively what we see clinically in the contralateral normal knee in patients. In addition, it has been validated in other cadaver studies, most recently for posterior knee stress radiographic techniques, that the results of stress radiography in cadavers(2) are similar to what is seen in the human clinical situation(3).

    With regard to the experimental setup of the knee, we appreciate Drs. Clarke's and Nunn's concerns and believe we have addressed them successfully in our clinical practice. In the article in Investigative Radiology that they are referring to(4), the authors were describing the difficulties with measuring the jointline space and long leg alignment on standing AP radiographs. We do concur with them that obtaining stress radiographs in full extension has been problematic due to rotational issues and overlap. However, we have found that obtaining reproduceable stress radiographs at 20° of knee flexion (like we performed in our biomechanical study,(1))can be achieved by placing a simple polyurethane foam block under the patient's knee.

    The only clinical issues that I have found to be relevant are to make sure that patients are lying down so that they are relaxed, and that their shoewear is removed so that the shoe does not catch on the examining bed when the varus stress is applied by the clinician. Thus, we believe that we have answered the question of whether this technique can be performed in the clinical setting; we do believe that the examination is very accurate when the patient can relax.

    We even have found that with acute injuries, if we discuss our plans with the patient and obtain their agreement to relax one time while the stress is being applied,they can often relax sufficiently to reveal a diagnosis of a grade III injury. Timing this applied stress with the x-ray technician to obtain the x-ray at the same time the stress is applied allows for a very reproducible and accurate assessment.

    In terms of the last questions posed, we do believe that our research in this area has led us to increased utilization of stress x- rays to discern the clinical diagnosis of these injuries. In fact, our extensive clinical experience has led us to believe that stress radiographs are the most accurate means to evaluate lateral compartment gapping in these patients and that the clinical examination may not be able to quantitatively assess for initial or postoperative gapping, especially between visits. This same technology and evolution is how assessment of ACL tears with the arthrometer devices and PCL tears with stress radiographs has evolved.

    In terms of the comparison to MRI scans(5), as our experience with these injuries has grown, we believe that MRI scans can be very accurate in determining an injury pattern, but it may not always quantitate the amount of laxity and whether increased signal in acute injuries in the fibular collateral ligament and other structures is consistent with a partial or complete tear. While one may not always be able to get the patient to relax sufficiently to determine significant differences in gapping which documents a complete tear as we have noted in our laboratory study(1), a quantitative measurement of increased gapping will confirm that the ligament is in effect completely torn. If the stress radiographs are inconclusive, all we can say in the acute situation is that they may be inconclusive at that point in time due to the potential for patient guarding and that a repeat evaluation in 2-3 weeks may be indicated. Finally, due to the large patient referral practice that we have for this injury pattern, we have found that stress radiographs for chronic posterolateral knee injuries are more accurate than “non-stress” MRI scans. This is because the fibular collateral ligament, similar to the posterior cruciate ligament, can still be intact but be functionally lax in a chronic injury. However, it also can be difficult to determine if the fibular collateral ligament is intact but nonfunctional in some chronic posterolateral corner knee injuries on MRI examinations. In addition, it may be difficult using MRI to interpret the laxity of a fibular collateral ligament in these injuries because its course may be affected by a concurrent anterior cruciate or posterior cruciate ligament injury and the resultant translation of the joint which can affect the appearance of the fibular collateral ligament and other posterolateral corner structures.

    We thank Drs. Clarke and Nunn for their observant questions. In our practice, varus stress radiographs have become the standard of care for the initial assessment of these injuries and the postoperative evaluation of surgical repairs and reconstructions. We encourage other physicians to utilize this technique to improve patient diagnostic techniques and to ultimately strive for improved patient surgical outcomes.

    REFERENCES

    1. LaPrade RF, Heikes C, Bakker AJ, Jakobsen RB. The Reproducibility and Repeatability of Varus Stress Radiographs in the Assessment of Isolated Fibular Collateral Ligament and Grade III Posterolateral Knee Injuries. J Bone Joint Surg Am. 2008;90:2069-76.

    2. Garavaglia G, Lubbeke A, Dubois-Ferriere V, Suva D, Fritschy D, Menetrey J. Accuracy of Stress Radiography Techniques in Creating Isolated and Combined Posterior Knee Injuries. A Cadaveric Study. Am J Sports Med. 2007;35(12):2051-2056. 3. Jackman T, LaPrade RF, Pontinen T, Lender PA. Intraobserver and Interobserver Reliability of the Kneeling Technique of Stress Radiography for the Evaluation of Posterior Knee Laxity. Am J Sports Med. 2008; 36(8):1571-1576. 4. Suid-Cooke TD, Broekhoven LD, Lam M, Fisher B, Saunders G, Challis TW. A Standardized Technique for Lower Limb Radiography. Practice, Applications, and Error Analysis. Invest Radiol. 1991; 26(1):71-77.

    5. LaPrade RF, Gilbert TJ, Bollom TS, Wentorf F, Chaljub G. The Magnetic Resonance Imaging Appearance of Individual Structures of the Posterolateral Knee. A Prospective Study of Normal Knees and Knees with Surgically Verified Grade III Injuries. Am J Sports Med. 2000;28:191- 199.

    Jon V Clarke
    Posted on October 13, 2008
    Is an In Vitro Study of Posterolateral Knee Injuries Using Stress Radiographs Clinically Applicable?
    Western Infirmary, Glasgow, UK

    To the Editor:

    We read with interest the recent paper by LaPrade et al [1] which aimed to address the lack of quantitative data on the diagnosis of posterolateral knee ligament injuries. We commend the authors for attempting to provide a more objective clinical assessment of these injuries. We question however whether the conclusions drawn from the study are supported by the evidence presented.

    The authors conclude that their study establises a "feasible, cost-effective objective measurement tool" that can be used on patients in a clinical setting. However, this in vitro study used cadaveric knees from a predominantly elderly age group (average 71.6 years) This may not represent the knee ligament behaviour of younger patients in whom this type of injury is more prevalent [2].

    The experimental set up of the knee also raises some questions. Firstly, was there any rotational control of the knee when measuring the lateral compartment gap? Lack of rotational control can introduce potential error [3]. Second, are the authors suggesting that this model be adapted for clinical use? If so, then it would be extremely difficult to control the amount of knee flexion during clinical examination which again could lead to radiographic errors [3].

    In view of these concerns, we question whether these in-vitro results can realistically be applied to the clinical setting and particularly to the degree of accuracy suggested. It is difficult to be convinced that a difference of 1-2mm can differentiate between an isolated fibular collateral ligament and a grade III posterolateral injury, especially given the range of measurements for clinician-applied varus stress.

    LaPrade and co-workers have published extensively in this field including a magnetic resonance imaging evaluation [4]. Do the authors feel that the proposed method of using stress radiographs is a realistic alternative to clinical examination and MRI scanning? It would certainly be an interesting clinical comparison that could potentially validate their in- vitro measurements.

    The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

    References

    1. LaPrade RF, Heikes C, Bakker AJ, Jakobsen RB. The reproducibility and repeatability of varus stress radiographs in the assessment of isolated fibular collateral ligament and grade-III posterolateral knee injuries. J Bone Joint Surg Am. 2008;90:2069-76.

    2. Majewski M, Susanne H, Klaus S. Epidemiology of athletic knee injuries: A 10-year study. Knee. 2006;13(3):184-88.

    3. Sui D, Cooke TD, Broekhoven LD, Lam M, Fisher B, Saunders G, Challis TW. A standardised technique for lower limb radiography. Practice, applications and error analysis. Invest. Radiol. 1991;26(1):71-7.

    4. LaPrade RF, Gilbert TJ, Bollom TS, Wentorf F, Chalijub G. The magnetic resonance imaging appearance of individual structures of the posterolateral knee. A prospective study of normal knees and knees with surgically verified grade III injuries. Am J Sports Med. 2000;28:191-9.

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