An Intramedullary Locking Nail for Standardized Fixation of Femur Osteotomies to Analyze Normal and Defective Bone Healing in Mice

Summary

This protocol describes an osteosynthesis technique using an intramedullary locking nail for standardized fixation of femur osteotomies, which can be used to analyze normal and defective bone healing in mice.

Abstract

Bone healing models are essential to the development of new therapeutic strategies for clinical fracture treatment. Furthermore, mouse models are becoming more commonly used in trauma research. They offer a large number of mutant strains and antibodies for the analysis of the molecular mechanisms behind the highly differentiated process of bone healing. To control the biomechanical environment, standardized and well-characterized osteosynthesis techniques are mandatory in mice. Here, we report on the design and use of an intramedullary nail to stabilize open femur osteotomies in mice. The nail, made of medical-grade stainless steel, provides high axial and rotational stiffness. The implant further allows the creation of defined, constant osteotomy gap sizes from 0.00 mm to 2.00 mm. Intramedullary locking nail stabilization of femur osteotomies with gap sizes of 0.00 mm and 0.25 mm result in adequate bone healing through endochondral and intramembranous ossification. Stabilization of femur osteotomies with a gap size of 2.00 mm results in atrophic non-union. Thus, the intramedullary locking nail can be used in healing and non-healing models. A further advantage of the use of the nail compared to other open bone healing models is the possibility to adequately fix bone substitutes and scaffolds in order to study the process of osseous integration. A disadvantage of the use of the intramedullary nail is the more invasive surgical procedure, inherent to all open procedures compared to closed models. A further disadvantage may be the induction of some damage to the intramedullary cavity, inherent to all intramedullary stabilization techniques compared to extramedullary stabilization procedures.

Introduction

The biology of bone healing may be studied in vitro using cell and spheroid cultures, but it also requires in vivo approaches using animal studies. While large-animal experiments still play an important role in preclinical testing, early stage testing of products or hypotheses has changed during the last 10 years and is nowadays often conducted in small animal models¹. This switch was performed for several reasons. Production and maintenance of mice and rats are cheaper compared to pigs and sheep. In addition, small animals have shorter reproduction times and shorter normal healing periods, both of which facilitate the performance of large....

Protocol

All procedures were IACUC-approved and followed institutional guidelines (Landesamt für Verbraucherschutz, Zentralstelle Amtstierärztlicher Dienst, Saarbrücken, Germany). Analgesia and infection prevention should be in agreement with the respective guidelines of the country and institution where the experiments are to be performed.

1. Preparation of Implants and Surgical Instruments

1. Select a scalpel blade (size 15), small preparation scissors, fine forceps, dressing forceps, small pincers, 24 gauge (G) and 27 G needles, a non-resorbable 5-0 suture, and a needle holder from the microsurgical instrument box.
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Results

The overall time for the surgical procedure was about 30 min from skin incision to wound closure. Using the surgical implants provided, surgery can be performed without a stereo-microscope. Postoperatively, the animals were monitored daily. Post-operative analgesia was terminated after 3 days because none of the animals showed evidence of pain (vocalization, restlessness, lack of mobility, failure to groom, abnormal posture, or lack of normal interest in surroundings) after this time peri.......

Discussion

The most critical steps of the surgical technique are the correct positioning of the nail, the aiming device, and the pins. The nail has to be inserted completely to the marked indent at the distal end of the nail, because a protrusion of the nail into the knee joint at the level of the condyles can restrict the movement of the knee (Figure 3 A). Therefore, the size of the femur and, accordingly, the body weight of the animals, must be considered. The surgeon should also pay special attention to the fina.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
MouseNail	RISystem AG	221,122
MouseNail aiming device	RISystem AG	221,201
MouseNail interlocking pin	RISystem AG	221,121
Centering bit	RISystem AG	592,205
Drill bit	RISystem AG	590,200
Gigli wire saw	RISystem AG	590,100
Suture (5-0 Prolene)	Ethicon	8614H
Forceps	Braun Aesculap AG &CoKG	BD520R
Dressing forceps	Braun Aesculap AG &CoKG	BJ009R
Scissors	Braun Aesculap AG &CoKG	BC100R
Needle holder	Braun Aesculap AG &CoKG	BM024R
24 G needle	BD Mircolance 3	304100
27 G needle	Braun Melsungen AG	9186182
Scalpel blade size 15	Braun Aesculap AG &CoKG	16600525
Pincers	Knipex	7932125
Heat radiator	Sanitas	605.25
Depilatory cream	Asid bonz GmbH	NDXZ10
Eye lubricant	Bayer Vital GmbH	2182442
Xylazine	Bayer Vital GmbH	1320422
Ketamine	Serumwerke Bernburg	7005294
Tramadol	Grünenthal GmbH	2256241
Disinfection solution (SoftaseptN)	Braun Melsungen AG	8505018
CD-1 mice	Charles River	22