Murine Flexor Tendon Injury and Repair Surgery

Summary

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.

Abstract

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. 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.

Introduction

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 r....

Protocol

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)

1. Autoclave surgical instruments to sterilize, wear sterile gloves throughout, and maintain a sterile operating field.
2. Anesthetize the mouse via intraperitoneal injection (i.p.) with a volume of ketamine (80 mg/kg) and xylazine (10 mg/kg) corresponding to body weight. Confirm depth of sedation via absence of toe-pinch reflex.
3. Administer pre-emptive analgesia (buprenorphine, 0.05-0.1 mg/kg) via sub....

Results

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.......

Discussion

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.......

Materials

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