The Retrograde Tibial Nail: Presentation and biomechanical evaluation of a new concept in the treatment of distal tibia fractures

Abstract

Displaced distal tibia fractures require stable fixation while minimizing secondary damage to the soft tissues by the surgical approach and implants. Antegrade intramedullary nailing has become an alternative to plate osteosynthesis for the treatment of distal metaphyseal fractures over the past two decades. While retrograde intramedullary nailing is a standard procedure in other long bone fractures, only few attempts have been made on retrograde nailing of tibial fractures. The main reasons are difficulties of finding an ideal entry portal and the lack of an ideal implant for retrograde insertion.

The Retrograde Tibial Nail (RTN) is a prototype intramedullary implant developed by our group. The implant offers double proximal and triple distal interlocking with an end cap leading to an angle-stable screw-nail construct of the most distal interlocking screw. Its design meets the requirements of a minimally invasive surgical approach, with a stable fracture fixation by multiple locking options. The 8 mm diameter curved nail, with a length of 120 mm, is introduced through an entry portal at the medial malleolus. We see possible indications for the RTN in far distal tibial shaft fractures, distal extraarticular metaphyseal tibial fractures and in distal tibia fractures with simple extension into the ankle joint when the nail is combined lag screw fixation.

A biomechanical comparison of the current RTN prototype against antegrade nailing (Expert Tibial Nail, Synthes^®, ETN) was performed. Both implants were fixed with double proximal and triple distal interlocking. Seven biomechanical composite tibiae were treated with either osteosynthesis techniques. A 10 mm defect osteotomy 40 mm proximal to the joint line served as an AO 43-A3 type distal tibial fracture model. The stiffness of the implant-bone constructs was measured under low and high extra-axial compression (350 and 600 N) and under torsional load (8 Nm). Results show a comparable stability during axial loading for the two implant types with slightly higher stability in the RTN group. Rotational stability was superior for the RTN. Statistical analysis proved a significant difference (p < 0.05) between the ETN and RTN for rotational stability. This study suggests that retrograde tibia nailing with the RTN is a promising new concept for the treatment of distal tibia fractures.

Introduction

Fractures to the distal tibial metaphysis and pilon are often high-energy injuries combined with extensive soft-tissue damage. Treatment may be complicated by soft tissue and bone infection, delayed-union and non-union, all pointing to secondary or revision surgeries. Displaced fractures need stable fixation while minimizing secondary damage to the soft tissues by the surgical approach and implants. The optimal method of fixation remains debatable. Intramedullary nailing is an alternative to plate osteosynthesis [1], [2], [3].

Open reduction and internal fixation has the drawbacks of devascularizing fracture fragments and damaging the soft tissue mantle. Minimal invasive percutaneous plate osteosynthesis (MIPPO) reduces these risks. Nevertheless, precontoured and angular stable plates may be prominent under the skin of the medial malleolus and may cause secondary skin necrosis. This is especially dangerous in older patients with a compromised and very thin soft tissue mantle [4], [5].

Intramedullary nailing offers stable fixation while preserving the vascularity of the fracture site and the integrity of the surrounding soft-tissue [6], [7], [8], [9]. However, antegrade intramedullary nailing is a technically challenging procedure, comprising the specific risk of primary and secondary malalignment. Additionally, anterior knee pain is a common complaint after antegrade tibial nailing, with variable incidence rates from 10 to 86% reported [10], [11], [12], [13], [14].

The latest generation tibial intramedullary implants with multiple locking options near the ends of the nail have extended the spectrum of fractures amenable to intramedullary nailing [15], [16], [17], [18]. Favourable clinical results support the extending indications for intramedullary nailing in distal tibial fractures. These nails allow the placement of up to 4 distal interlocking screws in three different planes within 40 mm of the nail end [17]. This design makes the implants suitable for distal metaphyseal fractures and specific intraarticular Pilon fractures. Following the AO classification, multiple locking tibial nails can be used as a sole implant in 43-A1/A2/A3 fractures and in case of simple extension of these fracture types into the joint (43-C1/C2) in combination with primary lag screw fixation [19]. Intramedullary nails are regularly used in secondary procedures or revision surgery such as non-unions and mal-unions of the distal tibia.

While retrograde intramedullary nailing is a standard procedure in other long bone fractures, only few attempts have been made on retrograde nailing of tibia fractures. A few case series of retrograde tibia nailing were published addressing proximal tibial pathologies ranging from proximal tibial fractures to allogenic vascularized knee transplantations and callus distraction [20], [21]. But retrograde nailing did not find application in common practice. With the IP-XS-Nail^® system (Smith & Nephew^®), Gehr and Friedl performed nail osteosynthesis of distal tibia, pilon and medial malleolus as well as olecranon and patella fractures. Locking is achieved by threaded K-wires, which are shortened after insertion. The outcome showed mixed results in a limited patient collective [22], [23].

The Retrograde Tibial Nail (RTN) is a prototype intramedullary implant that has been under design by our group since 2008. We developed the new implant through multiple prototype stages and conducted anatomical insertion studies and preliminary biomechanical testing. The concept of minimal invasive percutaneous plate osteosynthesis is transferred to a minimal invasive local intramedullary osteosynthesis. Its goal is to offer stable fracture fixation with minimal additional soft-tissue injury distally and without additional damage of the structures around the knee joint. In this paper we present the prototype implant and the results of the biomechanical testing comparing the Retrograde Tibial Nail (RTN) against a standard antegrade intramedullary nail (ETN^®, Synthes).