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Research Papers

Endoscopic Functional Imaging of Partial Tendon Tears—Proof of Concept and Intraoperative Feasibility

[+] Author and Article Information
Yufei Li

Department of Orthopaedics,
University of Zürich,
Balgrist University Hospital,
Zürich 8008, Switzerland;
Institute for Biomechanics,
ETH Zürich,
Zürich 8093, Switzerland

Christian Gerber

Department of Orthopaedics,
University of Zürich,
Balgrist University Hospital,
Zürich 8008, Switzerland

Jess G. Snedeker

Department of Orthopaedics,
University of Zürich,
Balgrist University Hospital,
Zürich 8008, Switzerland;
Institute for Biomechanics,
ETH Zürich,
Zürich 8093, Switzerland
e-mail: jess.snedeker@balgrist.ch

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received October 1, 2012; final manuscript received January 29, 2013; accepted manuscript posted February 22, 2013; published online April 2, 2013. Assoc. Editor: Tammy Haut Donahue.

J Biomech Eng 135(4), 041007 (Apr 02, 2013) (6 pages) Paper No: BIO-12-1448; doi: 10.1115/1.4023702 History: Received October 01, 2012; Revised January 29, 2013; Accepted February 22, 2013

The ability to quantify the biomechanical integrity of tendons could provide useful information for both clinical diagnostics and for clinical follow-up in tracking functional recovery of the injured tissue. This study develops and characterizes a functional endoscopy approach for intraoperative quantification of tendon tear severity using both ex vivo and in vivo experimental models. We first verified the accuracy of endoscopic strain (i.e., tissue stretch) imaging in an ex vivo tear model by comparing endoscopic measurements against gold standard measurements with research grade optics. We then tested in vivo feasibility by endoscopically quantifying altered tissue strain distributions in a rat supraspinatus model of partial tendon tear. The endoscopic method was able to achieve diagnostically relevant levels of accuracy compared to research grade optics (mean error = 26.2 ± 19.1%), and tissue strain analysis could sensitively discern torn tendon subregions. Applying this approach to free-hand in vivo endoscopic strain measurements, we were similarly able to discern functional changes in partially torn tendons (average maximum principal strains surrounding the lesion: 5.1 ± 2.9% versus intact controls: 1.9 ± 1.4%; p = 0.023). These findings indicate that the functional endoscopic assessment of tendon mechanical integrity is not only possible but could potentially offer intraoperative arthroscopic guidance for management of tendon tears in man.

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Figures

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Fig. 1

(a) Ex vivo experimental setup with an intact SDFT sample. (b) Endoscopic image of an SDFT sample injured with a 1 mm diameter biopsy punch. The surface has been covered with graphite powder to provide contrast to facilitate tracking. (c) Endoscopic image of an SDFT sample injured with a 2 mm diameter biopsy punch.

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Fig. 2

(a) Passive tendon stretching device with the rat humeral head centered on a turning axis, with the scapula and upper limb constrained in a fixed orientation. (b) Simultaneous loading of the shoulder and endoscopic imaging. (c) Representative in vivo endoscopic image of an injured tendon with the calculated displacement field; injury is located at bottom right of the image, and the surface has been covered with graphite powder to provide contrast to facilitate tracking. (d) Corresponding strain map with injured region showing high strain concentration.

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Fig. 3

Bland-Altman plot of telecentric and endoscopic measurements. Solid line shows the mean difference (bias) between the two methods and the dotted lines show the 95% confidence interval limits of agreement.

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Fig. 4

Representative strain maps from the in vitro endoscopic measurements for (a) intact sample, (b) sample injured with 1 mm biopsy punch, and (c) sample injured with 2 mm biopsy punch

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Fig. 5

Results of endoscopic strain measurement using average values over the strain field comparing measurements of injured and noninjured tendons

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