Can Hardware Removal be Avoided Using Bioresorbable Mg-Zn-Ca Screws After Medial Malleolar Fracture Fixation? Mid-Term Results of a First-In-Human Study

Is just one screw really enough? Single- versus double-screw in the medial malleolus in supination-external rotation ankle fractures: A comparative biomechanical study using partially threaded cancellous screws

OBJECTIVE

The aim of this study is to investigate stiffness and the maximum load to failure values of single- and double-screw fixation of oblique medial malleolus fractures using partially threaded cancellous screws. Our hypothesis is that single-screw fixation of medial malleolus fractures after SER injuries provides similar stiffness when compared with double-screw fixation.

DESIGN

Biomechanical study.

METHODS

Twelve composite polyurethane synthetic right distal tibiae were used in the experiment. Oblique fractures of the medial malleolus were created with a band saw using a custom-made osteotomy guide to standardize the cuts in all models. Bone models were randomly separated into two groups and fixed with one (n = 6) or two (n = 6) 4.0 mm partially threaded cancellous screws placed perpendicular to the fracture line. These were tested by applying an offset axial tension at 10 mm/minute up to maximum load displacement, defined as subsidence of the medial malleolus fragment. Maximum load to failure was determined for the groups at the point where the curve ceased to be linear and suffered an inflection. Force versus displacement curves were obtained and recorded. The student's t-test for independent samples was used to compare stiffness (N / mm) and maximum load (N) between experimental groups, with a p value of < 0.05.

RESULTS

There were no significant differences in stiffness (p = 0.290) and maximum load (p = 0.191) among the two fixation constructs. Mean stiffness was 62.26 (±SD 21.11) N/mm for double-screw fixation group and 48.24 (±SD 22.40) N/mm for single-screw fixation group. Mean maximum load was 387.83 (±SD 115.78) N for double-screw fixation group and 306.64 (±SD 81.97) N for single-screw fixation group.

CONCLUSION

Fixation with one 4.0 mm partially threaded cancellous screw was not shown to be biomechanically inferior to fixation with two 4.0 mm partially threaded cancellous screws in an oblique fracture of the medial malleolus, supporting previous clinical studies that have shown that one screw is sufficient for fractures of the medial malleolus.

Operative vs Nonoperative Management of Unstable Medial Malleolus Fractures: A Randomized Clinical Trial

Importance

Unstable ankle fractures are routinely managed operatively. However, because of soft tissue and implant-related complications, recent literature has reported on the nonoperative management of well-reduced medial malleolus fractures after fibular stabilization, but with limited evidence supporting the routine application.

Objective

To assess the superiority of internal fixation of well-reduced (displacement ≤2 mm) medial malleolus fractures compared with nonfixation after fibular stabilization.

Design, Setting, and Participants

This superiority, pragmatic, parallel, prospective randomized clinical trial was conducted from October 1, 2017, to August 31, 2021. A total of 154 adult participants (≥16 years) with a closed, unstable bimalleolar or trimalleolar ankle fracture requiring surgery at an academic major trauma center in the UK were assessed. Exclusion criteria included injuries with no medial-sided fracture, open fractures, neurovascular injury, and the inability to comply with follow-up. Data analysis was performed in July 2022 and confirmed in September 2023.

Interventions

Once the lateral (and where appropriate, posterior) malleolus had been fixed and satisfactory intraoperative reduction of the medial malleolus fracture was confirmed by the operating surgeon, participants were randomly allocated to fixation (n = 78) or nonfixation (n = 76) of the medial malleolus.

Main Outcome and Measure

Olerud-Molander Ankle Score (OMAS) 1 year after randomization (range, 0-100 points, with 0 indicating worst possible outcome and 100 indicating best possible outcome).

Results

Among 154 randomized participants (mean [SD] age, 56.5 [16.7] years; 119 [77%] female), 144 (94%) completed the trial. At 1 year, the median OMAS was 80.0 (IQR, 60.0-90.0) in the fixation group compared with 72.5 (IQR, 55.0-90.0) in the nonfixation group (P = .17). Complication rates were comparable. Significantly more patients in the nonfixation group developed a radiographic nonunion (20% vs 0%; P < .001), with 8 of 13 clinically asymptomatic; 1 patient required surgical reintervention for this. Fracture type and reduction quality appeared to influence fracture union and patient outcome.

Conclusions and Relevance

In this randomized clinical trial comparing internal fixation of well-reduced medial malleolus fractures with nonfixation, after fibular stabilization, fixation was not superior according to the primary outcome. However, 1 in 5 patients developed a radiographic nonunion after nonfixation, and although the reintervention rate to manage this was low, the future implications are unknown. These results support selective nonfixation of anatomically reduced medial malleolar fractures after fibular stabilization.

Trial Registration

ClinicalTrials.gov Identifier: NCT03362229.

Assessing the content validity of the Manchester-Oxford Foot Questionnaire in surgically treated ankle fracture patients: a qualitative study

BACKGROUND

Roughly 10% of fractures in adults are ankle fractures. These injuries are found in both sexes and present with different fracture characteristics. The treatment varies with the patients' biology and fracture type, and the goals are to restore stability, prevent pain and maintain ankle function. Clinicians generally use outcomes like assessment of radiography, pain level, or function. The use of patient-reported outcome measures is increasing, and the Manchester-Oxford Foot Questionnaire (MOXFQ) has been shown to have good measurement properties when validated in patients with foot and ankle disorders. However, the instrument has not been validated for ankle fracture patients. This study aims to assess the content validity of the items in MOXFQ in surgically treated ankle fracture patients.

METHODS

A qualitative deductive design was used to investigate patients' response process of the MOXFQ. Individual interviews were conducted using cognitive interviewing based on the theoretical framework of the 4-step model by Tourangeau. Adult patients that were surgically treated for an ankle fracture between four weeks and 18 months were purposively sampled, and interviews followed a semi-structured interview guide. The predetermined categories were comprehension, retrieval, judgement, and response.

RESULTS

Seventeen respondents (65% females) were interviewed. Respondents' age ranged from 27 to 76 years. Some of the respondents in the early recovery phase were limited by post-operative restrictions and did not find the items in the walking/standing domain relevant. Respondents that were allowed weight-bearing as tolerated (WBAT) were able to recall relevant information for most items. Respondents with time since surgery more than 12 months had less pain and remembered fewer relevant episodes in the recall period. Items in the social interaction domain contained ambiguous questions and were generally considered less important by respondents. The summary index score lacked important concepts in measuring overall quality of life.

CONCLUSIONS

Pain was a central concept in the post-operative recovery of ankle fracture patients. The MOXFQ-subscales for pain and walking/standing had acceptable content validity in patients that were allowed WBAT. The social interaction-subscale and the summary index score had insufficient content validity for this patient population.

In vitro and in vivo degradation behavior of Mg-0.45Zn-0.45Ca (ZX00) screws for orthopedic applications

Magnesium (Mg) alloys have become a potential material for orthopedic implants due to their unnecessary implant removal, biocompatibility, and mechanical integrity until fracture healing. This study examined the in vitro and in vivo degradation of an Mg fixation screw composed of Mg-0.45Zn-0.45Ca (ZX00, in wt.%). With ZX00 human-sized implants, in vitro immersion tests up to 28 days under physiological conditions, along with electrochemical measurements were performed for the first time. In addition, ZX00 screws were implanted in the diaphysis of sheep for 6, 12, and 24 weeks to assess the degradation and biocompatibility of the screws in vivo. Using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), micro-computed tomography (μCT), X-ray photoelectron spectroscopy (XPS), and histology, the surface and cross-sectional morphologies of the corrosion layers formed, as well as the bone-corrosion-layer-implant interfaces, were analyzed. Our findings from in vivo testing demonstrated that ZX00 alloy promotes bone healing and the formation of new bone in direct contact with the corrosion products. In addition, the same elemental composition of corrosion products was observed for in vitro and in vivo experiments; however, their elemental distribution and thicknesses differ depending on the implant location. Our findings suggest that the corrosion resistance was microstructure-dependent. The head zone was the least corrosion-resistant, indicating that the production procedure could impact the corrosion performance of the implant. In spite of this, the formation of new bone and no adverse effects on the surrounding tissues demonstrated that the ZX00 is a suitable Mg-based alloy for temporary bone implants.

Mg-Zn-Ca Alloy (ZX00) Screws Are Resorbed at a Mean of 2.5 Years After Medial Malleolar Fracture Fixation: Follow-up of a First-in-humans Application and Insights From a Sheep Model

BACKGROUND

In the ongoing development of bioresorbable implants, there has been a particular focus on magnesium (Mg)-based alloys. Several Mg alloys have shown promising properties, including a lean, bioresorbable magnesium-zinc-calcium (Mg-Zn-Ca) alloy designated as ZX00. To our knowledge, this is the first clinically tested Mg-based alloy free from rare-earth elements or other elements. Its use in medial malleolar fractures has allowed for bone healing without requiring surgical removal. It is thus of interest to assess the resorption behavior of this novel bioresorbable implant.

QUESTIONS/PURPOSES

(1) What is the behavior of implanted Mg-alloy (ZX00) screws in terms of resorption (implant volume, implant surface, and gas volume) and bone response (histologic evaluation) in a sheep model after 13 months and 25 months? (2) What are the radiographic changes and clinical outcomes, including patient-reported outcome measures, at a mean of 2.5 years after Mg-alloy (ZX00) screw fixation in patients with medial malleolar fractures?

METHODS

A sheep model was used to assess 18 Mg-alloy (ZX00) different-length screws (29 mm, 24 mm, and 16 mm) implanted in the tibiae and compared with six titanium-alloy screws. Micro-CT was performed at 13 and 25 months to quantify the implant volume, implant surface, and gas volume at the implant sites, as well as histology at both timepoints. Between July 2018 and October 2019, we treated 20 patients with ZX00 screws for medial malleolar fractures in a first-in-humans study. We considered isolated, bimalleolar, or trimalleolar fractures potentially eligible. Thus, 20 patients were eligible for follow-up. However, 5% (one patient) of patients were excluded from the analysis because of an unplanned surgery for a pre-existing osteochondral lesion of the talus performed 17 months after ZX00 implantation. Additionally, another 5% (one patient) of patients were lost before reaching the minimum study follow-up period. Our required minimum follow-up period was 18 months to ensure sufficient time to observe the outcomes of interest. At this timepoint, 10% (two patients) of patients were either missing or lost to follow-up. The follow-up time was a mean of 2.5 ± 0.6 years and a median of 2.4 years (range 18 to 43 months).

RESULTS

In this sheep model, after 13 months, the 29-mm screws (initial volume: 198 ± 1 mm3) degraded by 41% (116 ± 6 mm3, mean difference 82 [95% CI 71 to 92]; p < 0.001), and after 25 months by 65% (69 ± 7 mm3, mean difference 130 [95% CI 117 to 142]; p < 0.001). After 13 months, the 24-mm screws (initial volume: 174 ± 0.2 mm3) degraded by 51% (86 ± 21 mm3, mean difference 88 [95% CI 52 to 123]; p = 0.004), and after 25 months by 72% (49 ± 25 mm3, mean difference 125 [95% CI 83 to 167]; p = 0.003). After 13 months, the 16-mm screws (initial volume: 112 ± 5 mm3) degraded by 57% (49 ± 8 mm3, mean difference 63 [95% CI 50 to 76]; p < 0.001), and after 25 months by 61% (45 ± 10 mm3, mean difference 67 [95% CI 52 to 82]; p < 0.001). Histologic evaluation qualitatively showed ongoing resorption with new bone formation closely connected to the resorbing screw without an inflammatory reaction. In patients treated with Mg-alloy screws after a mean of 2.5 years, the implants were radiographically not visible in 17 of 18 patients and the bone had homogenous texture in 15 of 18 patients. No clinical or patient-reported complications were observed.

CONCLUSION

In this sheep model, Mg-alloy (ZX00) screws showed a resorption to one-third of the original volume after 25 months, without eliciting adverse immunologic reactions, supporting biocompatibility during this period. Mg-alloy (ZX00) implants were not detectable on radiographs after a mean of 2.5 years, suggesting full resorption, but further studies are needed to assess environmental changes regarding bone quality at the implantation site after implant resorption.

CLINICAL RELEVANCE

The study demonstrated successful healing of medial malleolar fractures using bioresorbable Mg-alloy screws without clinical complications or revision surgery, resulting in pain-free ankle function after 2.5 years. Future prospective studies with larger samples and extended follow-up periods are necessary to comprehensively assess the long-term effectiveness and safety of ZX00 screws, including an exploration of limitations when there is altered bone integrity, such as in those with osteoporosis. Additional use of advanced imaging techniques, such as high-resolution CT, can enhance evaluation accuracy.

Long-term in vivo degradation of Mg-Zn-Ca elastic stable intramedullary nails and their influence on the physis of juvenile sheep

The use of bioresorbable magnesium (Mg)-based elastic stable intramedullary nails (ESIN) is highly promising for the treatment of pediatric long-bone fractures. Being fully resorbable, a removal surgery is not required, preventing repeated physical and psychological stress for the child. Further, the osteoconductive properties of the material support fracture healing. Nowadays, ESIN are exclusively implanted in a non-transphyseal manner to prevent growth discrepancies, although transphyseal implantation would often be required to guarantee optimized fracture stabilization. Here, we investigated the influence of trans-epiphyseally implanted Mg-Zinc (Zn)-Calcium (Ca) ESIN on the proximal tibial physis of juvenile sheep over a period of three years, until skeletal maturity was reached. We used the two alloying systems ZX10 (Mg-1Zn-0.3Ca, in wt%) and ZX00 (Mg-0.3Zn-0.4Ca, in wt%) for this study. To elaborate potential growth disturbances such as leg-length differences and axis deviations we used a combination of in vivo clinical computed tomography (cCT) and ex vivo micro CT (μCT), and also performed histology studies on the extracted bones to obtain information on the related tissue. Because there is a lack of long-term data regarding the degradation performance of magnesium-based implants, we used cCT and μCT data to evaluate the implant volume, gas volume and degradation rate of both alloying systems over a period of 148 weeks. We show that transepiphyseal implantation of Mg-Zn-Ca ESIN has no negative influence on the longitudinal bone growth in juvenile sheep, and that there is no axis deviation observed in all cases. We also illustrate that 95 % of the ESIN degraded over nearly three years, converging the time point of full resorption. We thus conclude that both, ZX10 and ZX00, constitute promising implant materials for the ESIN technique.

Attaining High Functional Performance in Biodegradable Mg-Alloys: An Overview of Challenges and Prospects for the Mg-Zn-Ca System

This article presents a concise overview of modern achievements and existing knowledge gaps in the area of biodegradable magnesium alloys. Hundreds of Mg-based alloys have been proposed as candidates for temporary implants, and this number tends to increase day by day. Therefore, while reviewing common aspects of research in this field, we confine ourselves primarily to the popular Mg-Zn-Ca system, taken as a representative example. Over the last decades, research activities in this area have grown enormously and have produced many exciting results. Aiming at highlighting the areas where research efforts are still scarce, we review the state-of-the-art processing techniques and summarize the functional properties attained via a wide variety of processing routes devised towards achieving a desired properties profile, including the mechanical response in terms of strength, ductility, and fatigue resistance paired with biocompatibility and bio-corrosion resistance or controlled degradability. We pay keen attention to a summary of corrosion properties and mechano-chemical interactions between an aggressive environment and loaded Mg-based structures, resulting in stress corrosion cracking and premature corrosion fatigue failures. The polemic issues and challenges practitioners face in their laboratory research are identified and discussed.

Degradation behavior and osseointegration of Mg-Zn-Ca screws in different bone regions of growing sheep: a pilot study

Magnesium (Mg)-based implants are highly attractive for the orthopedic field and may replace titanium (Ti) as support for fracture healing. To determine the implant-bone interaction in different bony regions, we implanted Mg-based alloy ZX00 (Mg < 0.5 Zn < 0.5 Ca, in wt%) and Ti-screws into the distal epiphysis and distal metaphysis of sheep tibiae. The implant degradation and osseointegration were assessed in vivo and ex vivo after 4, 6 and 12 weeks, using a combination of clinical computed tomography, medium-resolution micro computed tomography (µCT) and high-resolution synchrotron radiation µCT (SRµCT). Implant volume loss, gas formation and bone growth were evaluated for both implantation sites and each bone region independently. Additionally, histological analysis of bone growth was performed on embedded hard-tissue samples. We demonstrate that in all cases, the degradation rate of ZX00-implants ranges between 0.23 and 0.75 mm/year. The highest degradation rates were found in the epiphysis. Bone-to-implant contact varied between the time points and bone types for both materials. Mostly, bone-volume-to-total-volume was higher around Ti-implants. However, we found an increased cortical thickness around the ZX00-screws when compared with the Ti-screws. Our results showed the suitability of ZX00-screws for implantation into the distal meta- and epiphysis.

Osteotomy after medial malleolus fracture fixed with magnesium screws ZX00 - A case report

Magnesium alloys have recently become the focus of research, as these implants exhibit suitable biocompatibility and appropriate mechanical properties (Grün et al., 2018 [1]). Through intensive preclinical and clinical investigation, many questions regarding stability, biocompatibility and degradation behavior have been answered (Holweg et al., 2020 [2]). This case report aims to describe handling of these implants in a revision situation, especially when located in situ. To describe available options and relevant considerations, including planning and implementation, a revision surgery of a healed medial malleolus fracture is presented. A medial malleolus fracture was primarily treated by a trauma surgeon with two magnesium screws. Due to an osteochondral lesion of the talus, a revision surgery with osteotomy of the medial malleolus was necessary after 17 months. In this revision, conventional screw removal was not possible due to the degradation of the implant. Taking the degradation and the yield strength of the implant into account, we have chosen on the one hand to over-drill and on the other to leave and perforate the screw. To the best of our knowledge, this is the first case study focusing on the clinical intraoperative site of human bone stabilized with magnesium screws. Despite the hydrogen gas production that occurs during degradation, a solid bone-to-implant interface was evident. With this report, we want to encourage the surgical user to get more involved with resorbable magnesium implants.

Radiolucent zones of biodegradable magnesium-based screws in children and adolescents-a radiographic analysis

INTRODUCTION

Albeit the implantation of magnesium-based biodegradable implants can avoid a second surgery for implant removal, the postoperative occurrence of radiolucent zones around these implants based on corrosion processes has not been previously investigated in children and adolescents. We sought to characterize the distinct temporal and spatial dynamics for magnesium-based implants based on standard clinical routine radiographs.

MATERIALS AND METHODS

We retrospectively analyzed 29 patients, treated with magnesium-based compression screws (MAGNEZIX^® CS 2.7 mm, CS 3.2 mm, CS^C 4.8 mm; Syntellix AG) for fracture fixation, osteotomy, or osteochondral refixation. During a follow-up examination, the clinical and functional status was evaluated. Based on digital radiographs, the ratio of the area of the radiolucent zone and that of the screw was evaluated to assess implant degradation at two follow-up visits (i.e., after 6-8 weeks and 12-24 weeks).

RESULTS

In 29 patients (16/29 females, 14.03 ± 2.13 years), a total of 57 implants were evaluated that were used for osteotomy (n = 13, screws n = 26), fracture fixation (n = 9, screws n = 18), or osteochondral refixation (n = 7, screws n = 13). All patients healed without complications and regained full function. Radiolucent zones were observed in 27/29 patients at the first follow-up, with significantly decreased ratios at the second follow-up (2.10 ± 0.55 vs 1.64 ± 0.60, p = 0.0006). Regression analyses were performed to assess the temporal dynamics of radiolucent zones and revealed significant logarithmic developments for the 2.7 mm and 3.2 mm screws, marked by a strong ratio decrease during the first weeks and an almost complete disappearance after approximately 100 days and 200 days, respectively. In contrast, the ceramic-coated 4.8 mm screws presented a significant linear and slower decrease of radiolucent zones.

CONCLUSION

Radiolucent zones are a common phenomenon in the course of implant degradation. However, they represent a self-limiting phenomenon. Remarkably, neither implant failure nor affected implant function is noted in this context. Yet, the microstructural changes accompanying the presence of radiolucent zones remain to be analyzed by three-dimensional high-resolution imaging.