A lean bioabsorbable magnesium-zinc-calcium alloy ZX00 used for operative treatment of medial malleolus fractures

Abstract

Aims This study is a prospective, non-randomized trial for the treatment of fractures of the medial malleolus using lean, bioabsorbable, rare-earth element (REE)-free, magnesium (Mg)-based biodegradable screws in the adult skeleton. Methods A total of 20 patients with isolated, bimalleolar, or trimalleolar ankle fractures were recruited between July 2018 and October 2019. Fracture reduction was achieved through bioabsorbable Mg-based screws composed of pure Mg alloyed with zinc (Zn) and calcium (Ca) ( Mg-Zn0.45-Ca0.45, in wt.%; ZX00). Visual analogue scale (VAS) and the presence of complications (adverse events) during follow-up (12 weeks) were used to evaluate the clinical outcomes. The functional outcomes were analyzed through the range of motion (ROM) of the ankle joint and the American Orthopaedic Foot and Ankle Society (AOFAS) score. Fracture reduction and gas formation were assessed using several plane radiographs. Results The follow-up was performed after at least 12 weeks. The mean difference in ROM of the talocrural joint between the treated and the non-treated sites decreased from 39° (SD 12°) after two weeks to 8° (SD 11°) after 12 weeks (p ≤ 0.05). After 12 weeks, the mean AOFAS score was 92.5 points (SD 4.1). Blood analysis revealed that Mg and Ca were within a physiologically normal range. All ankle fractures were reduced and stabilized sufficiently by two Mg screws. A complete consolidation of all fractures was achieved. No loosening or breakage of screws was observed. Conclusion This first prospective clinical investigation of fracture reduction and fixation using lean, bioabsorbable, REE-free ZX00 screws showed excellent clinical and functional outcomes. Cite this article: Bone Joint Res 2020;9(8):477–483.

Early osteoimmunomodulatory effects of magnesium–calcium–zinc alloys

“… 84 The corrosion products (mainly Mg 2+ ions) interact with chloride ions in the body fluid or are digested by macrophages. 49 However, during the early stages of Mg implantation, it corrodes quicker, causing an implant mechanical instability. This occurs owing to the lack of MgO + Mg(OH) 2 protective layer on the fresh surface.…”

“… 46 , 47 Biodegradable alloys made of Mg, zinc (Zn), and calcium (Ca), known as Mg-Zn-Ca ternary or ZX alloys, are among the most recent developed Mg-based alloys that have gained attention in the field. 7 , 48 – 51 Theoretically, due to the presence of all three elements in the body, the organism could metabolize the implanted alloy safely. 52 Cipriano et al 53 studied the influence of degradation products over time on bone cell functions and reported that the ZX alloys can increase the cell functions toward new bone formation.…”

Bioresorbable Magnesium-Based Alloys as Novel Biomaterials in Oral Bone Regeneration: General Review and Clinical Perspectives

“…Despite the fast in vivo degradation, some trials investigated the use of pure Mg in the femoral head [ 86 , 89 , 106 ] and in the metatarsus [ 101 ]. ZX00, a lean Mg-Ca-Zn was also evaluated in a prospective pilot study for medial malleolar fractures [ 108 ]. Another alloy made with Mg-Ca-Zn, was studied as bioresorbable Mg alloy screws for hand fractures requiring internal fixation [ 87 ].…”

“…Upon resorption, Mg and its alloy release Mg 2+ ions, which are either stored in bone or released into the circulation, thereby potentially resulting in the manifestation of hypermagnesemia. However, Holweg et al demonstrated the normal range of Mg concentration in the blood up to 12 weeks after Mg-based screw fixation in 20 patients [ 108 ]. This Mg blood level assessment was confirmed by two other trials [ 85 , 89 ].…”

“…( f ) CT scan at 52 weeks, decrease of radiolucent zones, increased endosteal bone mass, and periosteal bone ingrowth at the screw head (white arrow). Reproduced from [ 108 ].…”