This work was partially supported by the American Society for Surgery of the Hand Pilot Award and NIH/NIAMS 1K01AR068386-01&#160;(to AEL) and NIAMS/NIH P30AR061307.

The University Committee on Animal Research at the University of Rochester approved all animal experiments. Ten-12 week old female C57BL/6J mice were used.
1. Preparation of Animals for Flexor Tendon Surgery (~15 min)
<ol>
	<li>Autoclave surgical instruments to sterilize, wear sterile gloves throughout, and maintain a sterile operating field.</li>
	<li>Anesthetize the mouse via intraperitoneal injection (i.p.) with a volume of ketamine (80 mg/kg) and xylazine (10 mg/kg) corresponding to body...

<ol>
	<li>Lin, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomechanics+of+tendon+inury+and+repair.">Biomechanics of tendon inury and repair.</a> J Biomech. 37, 865-877 (2004).</li><li>Strickland, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+flexor+tendon+surgery:+twenty-five+years+of+progress.">Development of flexor tendon surgery: twenty-five years of progress.</a> J Hand Surg [Am]. 25, 214-235 (2000).</li><li>Bunnell, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repair+of+tendons+in+the+fingers+and+description+of+two+new+instruments.">Repair of tendons in the fingers and description of two new instruments.</a> Surg Gynecol Obstet. 26, 103-110 (1918).</li><li>Aydin, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-stage+flexor+tendoplasty+in+the+treatment+of+flexor+tendon+injuries.">Single-stage flexor tendoplasty in the treatment of flexor tendon injuries.</a> Acta Orthop Traumatol Turc. 38, 54-59 (2004).</li><li>Gelberman, R. H., Steinberg, D., Amiel, D., Akeson, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fibroblast+chemotaxis+after+tendon+repair.">Fibroblast chemotaxis after tendon repair.</a> J Hand Surg Am. 16, 686-693 (1991).</li><li>Lundborg, G., Rank, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+intrinsic+healing+of+flexor+tendons+based+upon+synovial+fluid+nutrition.">Experimental intrinsic healing of flexor tendons based upon synovial fluid nutrition.</a> J Hand Surg Am. 3, 21-31 (1978).</li><li>Aoki, M., Kubota, H., Pruitt, D. L., Manske, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomechanical+and+histologic+characteristics+of+canine+flexor+tendon+repair+using+early+postoperative+mobilization.">Biomechanical and histologic characteristics of canine flexor tendon repair using early postoperative mobilization.</a> J Hand Surg Am. 22, 107-114 (1997).</li><li>Kim, H. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Technical+and+biological+modifications+for+enhanced+flexor+tendon+repair.">Technical and biological modifications for enhanced flexor tendon repair.</a> J Hand Surg Am. 35, 1031-1037 (2010).</li><li>Aoki, M., Manske, P. R., Pruitt, D. L., Kubota, H., Larson, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Work+of+flexion+after+flexor+tendon+repair+according+to+the+placement+of+sutures.">Work of flexion after flexor tendon repair according to the placement of sutures.</a> Clin Orthop Relat Res. , 205-210 (1995).</li><li>Zhao, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Award+for+Outstanding+Orthopaedic+Research:+Engineering+flexor+tendon+repair+with+lubricant,+cells,+and+cytokines+in+a+canine+model.">Award for Outstanding Orthopaedic Research: Engineering flexor tendon repair with lubricant, cells, and cytokines in a canine model.</a> Clin Orthop Relat Res. 472, 2569-2578 (2014).</li><li>Wong, J., Bennett, W., Ferguson, M. W., McGrouther, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscopic+and+histological+examination+of+the+mouse+hindpaw+digit+and+flexor+tendon+arrangement+with+3D+reconstruction.">Microscopic and histological examination of the mouse hindpaw digit and flexor tendon arrangement with 3D reconstruction.</a> J Anat. 209, 533-545 (2006).</li><li>Katzel, E. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+Smad3+loss+of+function+on+scarring+and+adhesion+formation+during+tendon+healing.">Impact of Smad3 loss of function on scarring and adhesion formation during tendon healing.</a> J. Orthop. Res. 29, 684-693 (2011).</li><li>Loiselle, A. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bone+marrow-derived+matrix+metalloproteinase-9+is+associated+with+fibrous+adhesion+formation+after+murine+flexor+tendon+injury.">Bone marrow-derived matrix metalloproteinase-9 is associated with fibrous adhesion formation after murine flexor tendon injury.</a> PloS one. 7, e40602 (2012).</li><li>Lee, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parathyroid+hormone+1-34+enhances+extracellular+matrix+deposition+and+organization+during+flexor+tendon+repair.">Parathyroid hormone 1-34 enhances extracellular matrix deposition and organization during flexor tendon repair.</a> J Orthop Res. 33, 17-24 (2015).</li><li>Geary, M. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systemic+EP4+Inhibition+Increases+Adhesion+Formation+in+a+Murine+Model+of+Flexor+Tendon+Repair.">Systemic EP4 Inhibition Increases Adhesion Formation in a Murine Model of Flexor Tendon Repair.</a> PloS one. 10, e0136351 (2015).</li><li>Loiselle, A. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+antisense+oligonucleotide+(ASO)+technology+against+Tgf-beta+signaling+to+prevent+scarring+during+flexor+tendon+repair.">Development of antisense oligonucleotide (ASO) technology against Tgf-beta signaling to prevent scarring during flexor tendon repair.</a> J Orthop Res. 33, 859-866 (2015).</li><li>Orner, C. A., Geary, M. B., Hammert, W. C., O'Keefe, R. J., Loiselle, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-dose+and+short-duration+Matrix+Metalloproteinase+9+Inhibition+does+not+affect+adhesion+formation+during+murine+flexor+tendon+healing.">Low-dose and short-duration Matrix Metalloproteinase 9 Inhibition does not affect adhesion formation during murine flexor tendon healing.</a> Plast Reconstr Surg. , (2016).</li><li>Loiselle, A. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remodeling+of+murine+intrasynovial+tendon+adhesions+following+injury:+MMP+and+neotendon+gene+expression.">Remodeling of murine intrasynovial tendon adhesions following injury: MMP and neotendon gene expression.</a> J Orthop Res. 27, 833-840 (2009).</li><li>Tsubone, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+TGF-beta+inducible+early+gene+deficiency+on+flexor+tendon+healing.">Effect of TGF-beta inducible early gene deficiency on flexor tendon healing.</a> J Orthop Res. 24, 569-575 (2006).</li><li>Beason, D. P., Kuntz, A. F., Hsu, J. E., Miller, K. S., Soslowsky, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+evaluation+of+multiple+tendon+injury+models+in+the+mouse.">Development and evaluation of multiple tendon injury models in the mouse.</a> J Biomech. 45, 1550-1553 (2012).</li><li>David, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tendon+repair+is+compromised+in+a+high+fat+diet-induced+mouse+model+of+obesity+and+type+2+diabetes.">Tendon repair is compromised in a high fat diet-induced mouse model of obesity and type 2 diabetes.</a> PloS one. 9, e91234 (2014).</li><li>Wong, J. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cellular+biology+of+flexor+tendon+adhesion+formation:+an+old+problem+in+a+new+paradigm.">The cellular biology of flexor tendon adhesion formation: an old problem in a new paradigm.</a> Am J Pathol. 175, 1938-1951 (2009).</li></ol>

The surgical procedure for a murine model of complete transection and repair of the flexor digitorum longus tendon is presented in this study. In addition a novel application of concentrating small cell populations with cytology centrifuge is demonstrated, allowing for quantitative immunocytochemical analysis of the cellular environment during flexor tendon healing. This model of flexor tendon repair demonstrates a reproducible healing response, which can be used to assess changes in the healing process using knockout mo...

Flexor tendons in the hand work in concert with the flexor muscles of the forearm and digital sheaths to enable flexion of the digits and grasping function of the hand. Flexor tendons run along the palmar aspect of the hand; this relatively superficial location often results in injuries to the flexor tendons during trauma to the hand. Tendons heal through a scar tissue response rather than regeneration of normal tendon tissue 1. While this scar tissue provides continuity to the tendon, function is dramatically decreased relative to healthy tendon. Tendon-scar tissue composites are characterized by impaired mechanical properties 1, rendering the repaired tendons more likely to rupture. In addition, scar tissue lacks the organization of the native tendon collagen fiber structure, resulting in an increase in tendon size and bulk. Given the anatomic constraints of the tendon-sheath unit, even a modest increase in tendon size can drastically reduce the gliding function of the tendon, and therefore digit range of motion and hand function.
Prior to the 1960&#39;s injuries to the flexor tendons, particularly those in Zone II of the hand, were not routinely repaired due to the severe complications in healing that arose with these repairs 2. This area of the hand was referred to as &#39;no man&#39;s land&#39; 3. However, improvements in surgical techniques, suture patterns and physical therapy rehabilitation protocols have dramatically improved outcomes of flexor tendon repairs 2. Despite these advances, up to 40% of repairs result in sufficient adhesion formation to impede hand function 4. Therefore, a biological approach is required to improve healing. Unfortunately, very little is known about the tendon healing process at the cellular and molecular level. Thus, the goal was to develop a murine model that could be used to improve the fundamental understanding of the cellular and molecular components of flexor tendon healing and the scar formation response, as a means to identify novel therapeutic targets to improve healing.
Larger animal models have been instrumental in furthering understanding of the flexor tendon healing process. Canine and rabbit studies have demonstrated both the intrinsic and extrinsic healing ability of flexor tendons 5,6, the importance of early controlled passive motion in minimizing adhesion formation relative to immobilization 7, as well as the effects of different suture patterns on the healing process 8,9. In addition, the canine model has been useful in testing translational tissue-engineering approaches to improve healing 10. However, there are several important advantages in using a murine model relative to a large animal model, including the relative cost, availability of murine specific reagents, and the ease of generating global knock-outs or tissue-specific deletion/overexpression constructs. Moreover, the functional similarities between human and mice with respect to flexor tendons 11 indicate the potential utility in developing a murine model.
Development of a murine model of flexor tendon transection and repair mimics many aspects of clinical healing, including the formation of abundant scar tissue and impaired mechanical properties. The model described here is not a true recapitulation of clinical practice due to transection of the FDL at the myotendinous junction in order to protect the repair site. Furthermore, this model does not account for the contribution of synovial sheath cells to the healing response, as there is no synovial sheath covering the mid-portion of the tendon where the repair occurs. Despite these limitations, this model has the advantage of generating range of motion-limiting adhesions, which has yet to be demonstrated in murine models that more closely approximate the clinical scenario. This model has been used to assess knock-out mouse models 12,13, and to test different pharmacological approaches to improve healing 14-17. Histological analyses of this model, using immunohistochemistry and in situ hybridization, can provide important insights in to the localization of key genes and proteins during healing. However, histology provides only a cross-sectional spatial analysis and does not permit quantification throughout the entire tissue. Flow cytometry represents a more quantitative approach, but only a very limited number of cells can be isolated from the healing tendon tissue in the mouse model, and this number is further decreased during fixation, permeabilization, and washing steps. Taking this in to account, flow cytometry becomes an unfeasible approach due to the number of animals that would be required. An alternative method is necessary to preserve the majority of this small cell population in order to further characterize the healing milieu. The method used to accomplish this, shown here, involves concentration of the isolated cells via cytology centrifugation onto a glass slide, followed by immunocytochemistry. In the present study EdU (5-ethynyl-2&#39;deoxyuridine, a thymidine analog) incorporation and subsequent labeling was used to determine the relative proliferative state of cells at the healing site. This approach can be applied to test the efficacy of pharmacological treatments on cell proliferation, gene knock-out or overexpression, or to identify and quantify different cell populations.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;">Surgical preparation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">C57BL/6J mice&#160;</td>
			<td>Jackson Laboratories</td>
			<td>000664</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ketamine</td>
			<td>Hospira</td>
			<td>NDC# 0409-2051-05</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Xylazine</td>
			<td>Lloyd Inc.</td>
			<td>NDC# 61311-482-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Buprenorphine</td>
			<td>Par Pharmaceutical Inc.</td>
			<td>NDC# 42023-179-10</td>
			<td></td>
		</tr>
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			<td height="21" style="height:21px;">0.9% sodium chloride irrigation</td>
			<td>Hospira</td>
			<td>NDC# 0409-6138-03</td>
			<td>For preparation of ketamine/xylazine and buprenorphine solutions</td>
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			<td height="21" style="height:21px;">1ml syringe</td>
			<td>BD</td>
			<td>309659</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">30G needle</td>
			<td>BD</td>
			<td>305106</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Povidone-Iodine solution</td>
			<td>Aplicare</td>
			<td>82-226</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">70% ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Puralube vet opthalmic ointment</td>
			<td>Dechra Veterinary Products</td>
			<td>NDC# 17033-211-38</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Surgical tools</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Portable balance 200g</td>
			<td>Ohaus</td>
			<td>SP202</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">Spring scissors</td>
			<td>Fine Science Tools</td>
			<td>15124-12</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">Dumont #5 forceps</td>
			<td>Fine Science Tools</td>
			<td>11251-30</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">Needle holders</td>
			<td>Fine Science Tools</td>
			<td>91201-13</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micro spring scissors</td>
			<td>Fine Science Tools</td>
			<td>15003-08</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micro needle holders</td>
			<td>Fine Science Tools</td>
			<td>12061-02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">5-0 nylon sutures</td>
			<td>Ethicon</td>
			<td>668G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">8-0 microsurgery nylon sutures</td>
			<td>Ethicon</td>
			<td>2808G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lab-Line histology slide warmer</td>
			<td>Barnstead International</td>
			<td>26025</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cytospin method</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Collagenase Type I, lyophilized</td>
			<td>Life Technologies&#160;</td>
			<td>1700-017</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">Bovine Serum Albumin</td>
			<td>Cell Signaling Technologies</td>
			<td>9998S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1X PBS</td>
			<td>Thermo Fisher</td>
			<td>10010-023</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cytology funnels</td>
			<td>Fisher HealthCare</td>
			<td>10-354</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HistoBond+ microscope slides</td>
			<td>VWR</td>
			<td>16005-110</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cytospin 2 centrifuge</td>
			<td>Shandon</td>
			<td>SH-CYTO2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immunocytochemistry</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Slide staining tray with black lid</td>
			<td>IHC World</td>
			<td>M920-2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Click-iT Plus EdU Imaging Kit</td>
			<td>Life Technologies&#160;</td>
			<td>C10639</td>
			<td>Includes EdU and&#160; Hoeschst 33342</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immedge hydrophobic barrier pen</td>
			<td>Vector Laboratories</td>
			<td>H-4000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ProLong Diamond mounting medium</td>
			<td>Thermo Fisher</td>
			<td>P36970</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glass coverslips 24x50mm #1.5</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Clear nail polish</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

murine flexor tendon injury and repair surgery

Tendon connects skeletal muscle and bone, facilitating movement of nearly the entire body. In the hand, flexor tendons (FTs) enable flexion of the fingers and general hand function. Injuries to the FTs are common, and satisfactory healing is often impaired due to excess scar tissue and adhesions between the tendon and surrounding tissue. However, little is known about the molecular and cellular components of FT repair. To that end, a murine model of FT repair that recapitulates many aspects of healing in humans, including impaired range of motion and decreased mechanical properties, has been developed and previously described. Here an in-depth demonstration of this surgical procedure is provided, involving transection and subsequent repair of the flexor digitorum longus (FDL) tendon in the murine hind paw.&#160;This technique can be used to conduct lineage analysis of different cell types, assess the effects of gene gain or loss-of-function, and to test the efficacy of pharmacological interventions in the healing process. However, there are two primary limitations to this model: i) the FDL tendon in the mid-portion of the murine hind paw, where the transection and repair occur, is not surrounded by a synovial sheath. Therefore this model does not account for the potential contribution of the sheath to the scar formation process. ii) To protect the integrity of the repair site, the FT is released at the myotendinous junction, decreasing the mechanical forces of the tendon, likely contributing to increased scar formation. Isolation of sufficient cells from the granulation tissue of the FT during the healing process for flow cytometric analysis has proved challenging; cytology centrifugation to concentrate these cells is an alternate method used, and allows for generation of cell preparations on which immunofluorescent labeling can be performed. With this method, quantification of cells or proteins of interest during FT healing becomes possible.

The flexor digitorum longus (FDL) muscle, located in the calf, acts to flex the digits of the mouse hind paw via the flexor tendon (outlined in blue in Figure 1A, and shown histologically in Figure 2A), which runs proximally from the myotendinous junction and terminates in the distal phalanges. In this model of flexor tendon healing, the FDL tendon is transected and repaired at the mid-foot, proximal to the bifurcation in to the digits of the hind paw (re...

Watch this Scientific Journal Video about Murine Flexor Tendon Injury and Repair Surgery at JoVE.com

Murine Flexor Tendon Injury and Repair Surgery

Flexor tendons in the hand are commonly injured, leading to impaired hand function. However, the scar-tissue healing response is not well characterized. A murine model of flexor tendon healing is demonstrated here. This model can enhance overall understanding of the healing process and assess therapeutic approaches to improve healing.

Tendon connects skeletal muscle and bone, facilitating movement of nearly the entire body. In the hand, flexor tendons (FTs) enable flexion of the fingers ...

The over all goal of this surgical procedure is to enhance the understanding of the cellular and molecular processes of scar and adhesion formation during flexor tendon healing. This method can help answer key questions about the flexor tendon healing process, such as which cell types contribute to scar formation and repair. The main advantage of this technique is that transgenic and knock out mice can be used to better understand the healing process.This technique may identify potential biological targets for improving the outcomes of flexor tendon healing as it facilitates the investigation of these poorly designed cell populations that contribute to scarring. After confirming a lack of response to toe pinch, apply a ophthalmic ointment to the animals eyes, and clip the fur from the entire hind limb. Sterilize the surgical site with sequential povedone iodine and 70%ethanol scrubs, and locate the flexor digitorum longus, or FDL tendon within the medial aspect of the calf.Next, make a 0.5 to once centimeter incision in the skin to expose the tendon. Use the forceps to separate the FDL tendon from the surrounding tissue and trace the tendon up to the miotendinous junction. Using spring scissors, release the tendon at the junction, taking care to avoid the posterior tibial artery.Then close the skin with 5-0 nylon sutures. Now transfer the mouse under a stereo microscope and use spring micro scissors to make a three millimeter incision over the posterolateral aspect of the hind paw. Use the forceps to gently retract the surrounding soft tissue and muscle, taking care to minimize the tissue damage, and identify the FDL tendon.Then gently raise the tendon and use micro scissors to completely transect the tissue. Using 8.0 sutures in a modified Kessler pattern, ligate the ends of the FDL tendon. Periodically hydrating the tendon with saline throughout the procedure if necessary.When the ends have been sutures, return the soft tissue and muscle over the tendon and use 5.0 nylon sutures to close the incision. Then place the mouse on a 37 degrees Celsius slide warmer with monitoring until fully recovered. 24 hours before the experimental end point, inject the mice with 100 micro liters of EDU.The next day, locate the repaired tendon as just demonstrated, and harvest the transected tissue. Isolating the granulated tissue surrounding the healing tendon is a critical step for allowing the eventual aminocytochemical analysis. And care must be taken to minimize the inclusion of peripheral tissues.Place the tendon in a petri dish containing one milliliter of collagenase. Then, mince the tissues with the scalpel followed by trituration of the fragments with several passes through an 18 gauge needle. Transfer the slurry into 1.5 milliliter centrifuge tubes and digest the tendon pieces for one hour and 37 degrees Celsius with shaking.At the end of the digestion, centrifuge the tissue suspensions and resuspend the pellets in 500 micro liters of three percent BSA in PBS. Next, filter the cells through a 70 micron strainer to remove the debris and large pieces of undigested tendon. And place the cells in a 37 degrees Celsius incubator.Transfer the undigested tendon pieces to new, 1.5 milliliter micro centrifuge tubes containing one milliliter of fresh collagenase, and mix the pieces by pipe heading. After another hour of digestion with shaking, spin down the tissue pieces again, and resuspend the pellets in 500 microliters of BSA supplemented PBS. Then filter the suspension through a new 70 micron cell strainer into the tube of cells collected after the first digestion.Count the cells and spin them down by centrifugation. Then resuspend the pellet at a three to six times 10 to the fourth cells per 100 microliters of PBS supplemented with BSA concentration. To detect EDU incorporation by immunocytochemistry, first use a hydrophobic barrier pen to circle the cells on the slides and immediately fix the samples with 150 microliters of three percent paraformaldehyde and PBS at room temperature.After 15 minutes, rinse the cells with two five minute washes in 150 microliters of BSA supplemented PBS. Then permeableize the samples with 0.5%triton X 100 in PBS for 20m minutes. After washing as just demonstrated, add 150 microliters of freshly prepared EDU reaction cocktail to the cells for a 30 minute incubation at room temperature.Then wash the cells again and counter stain the samples with 150 microliters of Hoechst. After 30 minutes at room temperature, add one to two drops of antifade mounting medium to the cells, and carefully cover each sample with the cover slip, taking care to avoid bubbles. Cure the mounting medium over night in the dark at room temperature.Then seal the cover slips with clear nail polish. Finally, image the slides on a fluorescent microscope using 40X magnification. In a successful repair, the granulation tissue displays a greatly increased cellularity compared to the uninjured tendon.In this image, a histological example of a ruptured flexor tendon repair is shown. EDU labeling highlights only those cells that actively proliferate during the 24 hours following the EDU pulse in life mice. Facilitating a quantitative assessment of the proliferation within the granulation tissue of the healing tendon.After watching this video you should have a good understanding of how to perform the flexor tendon injury and repair surgery in mice, to better understand the cell populations that contribute to scar formation in the flexor tendon during healing.

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Research

JoVE Journal

Medicine

12.9K Views.  University of Rochester Medical Center. The over all goal of this surgical procedure is to enhance the understanding of the cellular and molecular processes of scar and adhesion formation during flexor tendon healing. This method can help answer key questions about the flexor tendon healing process, such as which cell types contribute to scar formation and repair. The main advantage of this technique is that transgenic and knock out mice can be used to better understand the healing process.This technique may identify potenti...