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Assessment of Lower Limb Alignment: Supine Fluoroscopy Compared with a Standing Full-Length Radiograph
Sanjeev Sabharwal, MD1; Caixia Zhao, MD1
1 Department of Orthopedics, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Doctor's Office Center, 90 Bergen Street, Suite 7300, Newark, NJ 07103. E-mail address for S. Sabharwal: sabharsa@umdnj.edu
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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.
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Investigation performed at University of Medicine and Dentistry of New Jersey—New Jersey Medical School, Newark, New Jersey

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Jan 01;90(1):43-51. doi: 10.2106/JBJS.F.01514
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Abstract

Background: While a full-length standing anteroposterior radiograph of the lower extremity provides the best radiographic method for assessing limb alignment, other methods must be used intraoperatively. We have employed intraoperative fluoroscopy with use of an electrocautery cord to assess limb alignment in the supine patient.

Methods: We retrospectively compared the measurements of lower limb alignment that were obtained with use of supine intraoperative fluoroscopy with those that were obtained with use of a full-length standing anteroposterior radiograph of the lower extremity. A single examiner compared 102 sets of supine fluoroscopy images and full-length standing anteroposterior radiographs of the lower extremity to assess mechanical axis deviation and the joint line convergence angle. For the intraoperative fluoroscopic examination, an electrocautery cord was positioned overlying the center of the femoral head and the tibial plafond and an anteroposterior radiograph of the knee was made. The effect of age, gender, diagnosis, body mass index, pelvic height difference, joint line convergence angle, and the magnitude and direction of malalignment (varus or valgus) on the discrepancy in the observed mechanical axis deviation with use of the two methods was assessed.

Results: The mean absolute difference between the two techniques was 13.4 mm for the measurement of mechanical axis deviation (p < 0.0001) and 2.8° for the joint line convergence angle (p < 0.0001). The correlation coefficient (r) for the measurement of mechanical axis deviation with use of the two radiographic methods was 0.88. An increase in body mass index was associated with a greater magnitude of discrepancy in the measurement of mechanical axis deviation between the two techniques (p = 0.0014). Age, gender, pelvic height difference, and the direction of malalignment had no effect on the discrepancy in the measurement of mechanical axis deviation. Limbs with >2 cm of mechanical axis deviation and those with a joint line convergence angle of >3° on the standing radiograph were significantly more likely to have >10 mm of discrepancy in the measurement of mechanical axis deviation with use of the two imaging techniques (p < 0.005).

Conclusions: Intraoperative fluoroscopy with use of the electrocautery cord method is a useful tool for assessing lower limb alignment in patients with a normal body mass index and =2 cm of mechanical axis deviation and =3° of joint line convergence angle on the standing anteroposterior radiograph. However, the results obtained with fluoroscopy should be interpreted with caution in patients who are obese or who have substantial residual mechanical axis deviation or pathologic laxity of the knee joint.

Level of Evidence: Diagnostic Level II. See Instructions to Authors for a complete description of levels of evidence.

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    References

    Accreditation Statement
    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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    Sanjeev Sabharwal, MD
    Posted on September 27, 2008
    Dr. Sabharwal responds to Drs. Hankemeier and Krettek
    UMDNJ- New Jersey Medical School

    We appreciate the comments of Dr. S. Hankmeier and are pleased that he too has found the intraoperative use of electrocautery cord for determining lower limb mechanical axis useful. As was correctly pointed out by the author, and mentioned quite clearly in our manuscript, the patella should face anteriorly when the fluoroscopic image of the knee is taken. While it can be debated whether or not the radiograph of the knee of a 10 year old child is acceptable, based on the minimal and similar amount of overlap of the proximal fibula to the tibial metaphysis on the standing radiograph (Figure 1) and the fluoroscopic image (Figure 2C), we feel that the two images are quite comparable, especially given the skeletal immaturity of the patient and the retrospective nature of our study.

    The other issue raised was regarding the less than perfect positioning of the electrocautery cord in identifying the centers of the hip and ankle joints. This has been acknowledged by us as one of the pitfalls of this technique in the discussion section of the manuscript. Interestingly, Dr Hankmeier has provided three images of his own to illustrate his point. However, he fails to demonstrate the position of the electrocautery cord in the images of the hip and ankle joints which, in itself, is another source of measurement error, since the position of the instrument overlying the hip or ankle may not correspond exactly to the position of the electrocautery cord. Therefore, as demonstrated in Figures 2A and 2B, we rely on the fluoroscopic images with the electrocautery cord overlying our best estimate of the center of the hip and ankle joints.

    In summary, while intraoperative assessment of lower limb alignment using the electrocautery cord is a useful technique, several potential sources of error still persist. We noted that patient factors such as magnitude of deformity, body habitus and knee joint laxity can affect the accuracy of this technique. Nevertheless, proper attention to intraoperative positioning of the limb and reliable methods to identify the centers of the hip and ankle joint will hopefully minimize the errors in assessing lower limb alignment using the bovie cord in the supine patient. Perhaps a prospective multicenter study would further enhance our understanding and test the validity of this technique.

    S. Hankemeier, MD
    Posted on September 17, 2008
    Technique of "Cable method" for intraopeartive evaluation of mechanical lower limb axis
    Trauma Department, Hanover Medical School (MHH), Germany

    To the Editor:

    We read with great interest the article by Sabharwal et al.(1)and we agree that intraoperative determination of the mechanical axis with the use of an electrocautery cord (“cable technique” or “electrocautery cord technique”) is a very useful tool(2). However, we feel that the technique used by Sabharwal et al. to determine the mechanical axis of the lower extremity during surgery was incorrect(2,3). To exclude several sources of error when using this method, the patella must be oriented directly anterior. The hip and ankle centers must be in the center of the image, and the knee joint must be fully extended(2,3).

    In Fig. 1 and Fig. 2C of the article by Sabharwal et al.(1), the patella is not directed anteriorly, but is rotated internally, which can influence the measurement of the mechanical axis(4). Their Figures. 2A and 2B present another source of error-- Fig. 2A shows that the electrocautery cord runs medial to the centre of the hip joint, and in Fig 2B, the cord runs medial to the ankle center. Several small errors can be cumulative and can cause discrepancies between the cable technique and the gold standard long standing AP radiographs.

    We offer our own examples of the proper technique of intraoperative evaluation of the mechanical axis with the use of an electrocautery cord in the accompanying figures (Figs 1 A-C). The knee is extended with the patella directed anteriorly. Using an image intensifier in the anterior-posterior position, the centers of the hip and ankle joint are identified. The electrocautery cord is spanned between these two points and the mechanical axis is determined.


    Figs. 1A-C. Intraoperative evaluation of the mechanical axis with the use of an electrocautery cord. The knee is extended with the patella directed anteriorly. Figs. 1A and 1B: Using an image intensifier in the anterior-posterior position, the centre of the hip and ankle joint are identified. Fig. 1C: The electrocautery cord is spanned between these two points and alignment determined using the projection of the cable.

    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. Sabharwal S, Zhao C. Assessment of lower limb alignment: supine fluoroscopy compared with a standing full-length radiograph. J Bone Joint Surg [Am] 2008 ;90-A:43-51

    2. Krettek C, Miclau T, Grün O, Schandelmaier P, Tscherne H. Intraoperative control of axes, rotation and length in femoral and tibial fractures. Technical note. Injury. 1998;29 Suppl 3:C29-39

    3. Hankemeier S, Hufner T, Wang G, Kendoff D, Zheng G, Richter M, Gosling T, Nolte L, Krettek C. Navigated intraoperative analysis of lower limb alignment. Arch Orthop Trauma Surg. 2005 Oct;125(8):531-5

    4. Paley D. Principles of deformity correction. Chapter 3: Radiographic assessment of lower limb deformities. New York: Springer; 2002,

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