Magnesium-Based Alloys Used in Orthopedic Surgery

Abstract

Magnesium (Mg)-based alloys have become an important category of materials that is attracting more and more attention due to their high potential use as orthopedic temporary implants. These alloys are a viable alternative to nondegradable metals implants in orthopedics. In this paper, a detailed overview covering alloy development and manufacturing techniques is described. Further, important attributes for Mg-based alloys involved in orthopedic implants fabrication, physiological and toxicological effects of each alloying element, mechanical properties, osteogenesis, and angiogenesis of Mg are presented. A section detailing the main biocompatible Mg-based alloys, with examples of mechanical properties, degradation behavior, and cytotoxicity tests related to in vitro experiments, is also provided. Special attention is given to animal testing, and the clinical translation is also reviewed, focusing on the main clinical cases that were conducted under human use approval.

Keywords: Mg-based alloys; biocompatibility; biomaterials; clinical translation; mechanical properties; orthopedy.

Figure 1

The main six Mg-based binary alloys for orthopedical applications.

Figure 2

Methods used for the evaluation of the biodegradable Mg alloys for temporary orthopedic implants.

Figure 3

Absorption phenomenon and excretion equilibrium of Mg in the human body system.

Figure 4

Degradation behavior of Mg-based temporary implants in bone fracture healing process, in ideal conditions (adapted after [50]).

Figure 5

Schematic illustration of the corrosion behavior of Mg in the commonly used media [75].

Figure 6

Schematic illustration of the mechanisms to control the degradation rate of Mg-based alloys.

Figure 7

Optical microscopy images of some magnesium alloys for biomedical application.

Figure 8

Small and large animal models and associated tested geometries.

Figure 9

Examples of bone fixation devices made from Mg and Mg-based alloys: (a) pins from MAGNEZIX^® [152] (courtesy of Synthellix AG, Hannover, Germany); (b) compression screw from MAGNEZIX^® [156] (courtesy of Synthellix AG, Hannover, Germany); (c) magnesium plate and screw for fracture fixture [43], (d) intramedullary nail made from magnesium [43], (e) screw and wire from RESOMET^® [154], (f) pin [129], and (g) scaffold [127].

Figure 10

Mg-based screws used for bone flap fixation (shaft diameter = 4 mm and length = 40 mm). X-ray images of the femoral head in which Mg screws were implanted at 1 (A), 3 (B), 6 (C), and 12 (D) months after surgery. (a–d) Details of surgical zones taken for screw diameter measurement (scale bar is 10 mm) [63].

Figure 11

(a) The titanium screw from Koenigsee Implantate GmbH. (b) MAGNEZIX^® Compression screw from Syntellix AG. (c) Preoperative and postoperative X-rays images of a hallux valgus deformity. Correction was performed using a Chevron osteotomy [139].

Figure 12

Patient radiographs (a) anteroposterior- and (b) lateral- elbow X-ray images taken after the operation. Yellow arrows marked the places, where Mg screws are used [21].

Figure 13

Clinical observation of complete screw degradation and bone healing. (A) 1 year follow up; (B) radiographs, (i) distal radius fracture, (ii) implantation site immediately after surgery, (iii) 6 months after surgery, and (iv) 1 year follow up situation; and (C) schematic diagram of the case [159].

Figure 14

Hybrid system used for mandible fracture fixation. The system is composed of a Ti plate (2 mm × 50 mm), a Mg screw covered with PLA coating, and a Ti screw (the scale bar is 10 mm) [166].