Interlocking Nails - Designs and Outcomes

Introduction

As a result of biological and mechanical advantages, interlocking nails (ILNs) are considered the standard of care for the treatment of most diaphyseal fractures in people and have become an increasingly accepted method of fixation for femoral, tibial and to some extent humeral as well as some ulnar fractures in veterinary orthopedics.

Historically, the ILN concept in the treatment of long bone fractures evolved from the original “detensor” nail designed by Kuntscher (Germany) in the 1940’s and late 60’s. The first true interlocking nail was developed in the 70’s by Huckstep (Australia) to treat femoral fractures in humans. Following the successful experimental and clinical use of modified Huckstep nails in animals by Johnson and Muir, several veterinary systems were independently designed in the early 90’s by Duhautois (France), Durall (Spain) and Dueland (USA).

Implants and Instrumentation

Regardless of design, ILNs have common characteristics. They are solid intramedullary rods featuring transverse nail holes (cannulations) at both extremities and sometimes along the whole length of the nail (Durall system). The nail is locked in place via bone screws or solid bolts that engage both cortices and the nail. The proximal end of the nail features keying flanges which permit rigid linkage of the nail and aiming jig via extension rods. The distal end of the nail presents a dull or trocar point to facilitate insertion.

To accommodate the large range of bone sizes, nail dimensions vary widely in term of diameter (3 to 10 mm) and lengths (68 to 230 mm). Similarly, locking screws or bolts vary in size depending on the nail diameter. While the position and number of locking screws varies between systems, all ILNs allow placement of at least one locking device proximally and one distally. The use of an ILN requires dedicated instrumentation comprised of 1) an alignment guide, 2) extension rods that connects nail and alignment guide and 3) drilling sleeves. [...]