Hallux valgus (HV) is a common foot deformity that may cause pain, disability, difficulty in shoe wear, and gait disturbance. Initially, a period of conservative care can be tried but if the symptoms are not relieved and the deformity has progressed, surgical correction is usually necessitated. More than 300 surgical procedures have been described over the years for the correction of HV deformity [
The technique for a distal chevron osteotomy was initially described by Austin and Leventen without performing an osseous fixation [
Metallic screw fixation is now the most frequently used fixation method for modified chevron osteotomies [
Recently, alternative bioabsorbable screws made of magnesium (Mg) alloys have been introduced in HV surgery, particularly in the fixation of distal chevron osteotomy. Magnesium screws are produced from an alloy (MgYREZr) that contains more than 90% pure magnesium, which is naturally found in human body. When implanted in the human body, a degradation or corrosion process takes place within a certain period of time and the implant is completely absorbed and/or replaced by the native bone [
However, there are four clinical studies that have evaluated the efficacy of magnesium bioabsorbable screws in HV surgery [
A retrospective review was made of patients who underwent modified distal chevron osteotomy for HV deformity between August 2014 and December 2017 in our hospital. Institutional review board approved the study protocol and this study was carried out in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments (IRB approval number: 2017-134/11.07). Demographic information, clinical findings, and imaging findings were extracted from the hospital database, patient charts, medical records, operation notes, notes taken during follow-up visits, and radiological images which were stored in the picture archiving and communication system (PACS).
During the study period, a total of 45 patients were identified who underwent isolated modified chevron osteotomy with no other surgical procedures. Of these, 31 patients completed a follow-up of at least 12 months and were included in the analysis. The remaining 14 patients were either lost in follow-up (8 patients) or denied participation (6 patients) and were excluded from the study. Bioabsorbable headless Mg compression screw fixation was applied to 16 patients (17 feet) and headless titanium (Ti) compression screw to 15 patients (17 feet). Thus, the patients were separated into two groups as the Mg group and the Ti group, according to the type of screw.
All patients were operated on under spinal anesthesia and tourniquet control in the supine position. A medial 4-6 cm incision was made over the MTP joint, and dissection was continued down to the capsule with careful protection of the dorsal and plantar medial cutaneous nerves. A V-shaped capsular flap was created to expose the bunion and MTP joint. The medial eminence was removed at the lateral edge of the sagittal sulcus with an oscillating saw. A 90° chevron osteotomy was created, in which the plantar cut was proximal to the synovial fold, again with the oscillating saw. The capital fragment was displaced laterally (usually 2-5 mm) until sufficient correction of first ray alignment was achieved. The osteotomy was stabilized with single or double cannulated headless compression screws from the dorsum of the distal metatarsal head to the plantar shaft. The direction of screw fixation was performed in two different ways, either from the proximal fragment towards the distal fragment or from the distal fragment towards the proximal fragment according to the preference of the surgeon. A capsular flap was used to shift the proximal phalanx and was anchored to the proximal fragment with nonabsorbable sutures through a dorsal metaphyseal drill hole. The skin and subcutaneous tissues were closed in the routine manner.
Bioabsorbable Mg screws (MAGNEZIX® CS, Syntellix AG, Hanover, Germany) were used for the fixation of the osteotomy in the Mg group. It is a variable pitch cannulated headless screw (2.7 mm Ø), which provides interfragmentary compression, similar to a Herbert screw. Titanium (Alloy: Ti 6Al 4V) screws (Tasarımmed, Istanbul, Turkey) were also variable pitch cannulated headless compression screws (2.5 mm Ø), but the pitch varied continuously along the length (Figure
The appearance of (a) magnesium and (b) titanium screws used in the study.
A short-leg plaster cast with the toe in anatomic alignment was applied to all the patients for two weeks. At the end of the second week, the cast was opened and the sutures were removed. Weight-bearing as tolerated was encouraged on the heel and lateral side of the foot with the patient wearing with stiff-soled shoes. MTP joint active movements were started. At the end of the sixth week, full weight-bearing with normal shoes was allowed.
Functional outcomes were assessed with the American Orthopaedic Foot and Ankle Society hallux metatarsophalangeal-interphalangeal (AOFAS-MTP-IP) scale and pain was assessed using the visual analogue scale (VAS). MTP joint range of motion (ROM, flexion plus extension) was evaluated using a goniometer and rated as normal (>75°), moderate (30°-74°), or severe (<30°) restriction. Any complications including infection, wound problems, recurrence, and revision surgery during the follow-up period were recorded.
Hallux valgus angle (HVA) and the first and second intermetatarsal angle (IMA) were measured on preoperative, early postoperative (within the first month), and final follow-up radiographs. Measurements were taken according to the recommendations of the ad hoc committee of the American Orthopaedic Foot and Ankle Society [
Continuous variables were stated as mean ± standard deviation (SD) and categorical variables as number (n) and percentage (%). The Shapiro-Wilk test was used to assess the normality of the data, and either parametric or nonparametric tests were selected according to the distribution of each variable. The comparison of independent continuous variables was performed using Student’s
A total of 34 feet (17 in Mg group and 17 in Ti group) were analyzed. The baseline demographic and clinical characteristics of both groups were similar in respect of age, gender, side, preop HVA, preop IMA, preop VAS, preop AOFAS-MTP-IP scale, preop ROM, and follow-up duration (Table
Demographic characteristics of the patients (F: female, M: male, R: right, L: left, HVA: hallux valgus angle, IMA: intermetatarsal angle, VAS: visual analogue scale, AOFAS-MTP-IP: American Orthopaedic Foot and Ankle Society hallux metatarsophalangeal-interphalangeal scale, ROM: range of motion).
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| 49.9 ± 15.1 | 48.5 ± 14.6 | 0.796 |
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| 2 M /14 F | 2 M / 13 F | 0.675 |
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| 7 R /10 L | 10 R / 7 L | 0.247 |
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| 31.0 ± 5.9 | 30.1 ± 6.2 | 0.675 |
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| 12.7 ± 1.8 | 12.1 ± 2.3 | 0.424 |
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| 4.7 ± 2.1 | 5.1 ± 1.9 | 0.620 |
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| 71.2 ± 8.3 | 69.2 ± 9.4 | 0.505 |
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| 0.360 | ||
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| 10 | 12 | |
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| 7 | 5 | |
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| 0 | 0 | |
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| 19.0 ± 6.8 | 16.2 ± 6.19 | 0.234 |
MTP joint ROM (dorsiflexion plus plantar flexion),
Clinically significant improvements were obtained in both groups in both the AOFAS-MTP-IP scale and VAS. In the Ti group, one patient had complaints of pain during daily activities and further examination revealed irritation of the extensor tendon by prominent screw heads. The patient’s discomfort was relieved after removal of the screw at six months postoperatively (Figure
Summary of radiographic results (vs.: versus).
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| 31.0 ± 5.9 | 18.7 ± 6.3 | 19.6 ± 5.8 | Pre vs. early vs. final: 0.000 |
Early vs. final: 0.321 | ||||
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| 30.1 ± 6.2 | 17.3 ± 4.3 | 17.4 ± 4.2 | Pre vs. early vs. final: 0.000 |
Early vs. final: 0.605 | ||||
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| 0.675 | 0.454 | 0.226 | |
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| 12.7 ± 1.8 | 7.8 ± 2.2 | 8.2 ± 2.3 | Pre vs. early vs. final: 0.000 |
Early vs. final: 0.067 | ||||
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| 12.1 ± 2.3 | 8.5 ± 1.9 | 8.0 ± 1.8 | Pre vs. early vs. final: 0.000 |
Early vs. final: 0.058 | ||||
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| 0.424 | 0.337 | 0.712 |
(a) Protrusion of titanium screw (
Radiological parameters (HV and IMA) were significantly improved in all patients. The correction obtained remained stable until union in both groups. No patient in either group showed significant loss of correction between the early postoperative and final follow-up radiographs. At the final follow-up, all radiographic measurements were similar in both groups (Table
Summary of functional results.
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| 4.7 ± 2.1 | 1.9 ± 1.9 | .000 |
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| 5.1 ± 1.9 | 2.0 ± 0.5 | .000 |
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| 0.620 | 0.535 | |
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| 71.2 ± 8.3 | 84.1 ± 9.6 | .000 |
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| 69.2 ± 9.4 | 83.0 ± 11.7 | .000 |
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| 0.505 | 0.764 | |
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| 10 7 0 | 4 10 3 | .0290 |
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| 12 5 0 | 2 12 3 | .0100 |
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| 0.360 | 0.654 |
MTP joint ROM (dorsiflexion plus plantar flexion),
In almost all patients in the Mg group (13 of 17 feet), there was a variable amount of gas accumulation within the soft tissue around the hallux during the first 2 months. After 3 months postoperatively, no gas shadows were observed within the soft tissues (Figure
(a) Postoperative first month radiographs showing gas along the first metatarsal bone. (b) The amount of gas decreased and was limited to the metatarsal head. (b) Total absorption of gas at the third month’s follow-up.
Gradual disappearance of the radiolucent zone around the screw on the 3-month (a) and 8-month (b) follow-up radiographs. (c) Complete disintegration of the Mg screws at 27 months.
In this retrospective study, bioabsorbable magnesium and metallic titanium headless compression screws were compared for fixation of the modified chevron osteotomy used in the treatment of HV. Similar clinical and radiological outcomes were obtained in both groups. Furthermore, the rate of complications was not significantly different between the groups. None of the patients in the Mg group and one in the Ti group (statistically insignificant) required implant removal. Magnesium bioabsorbable screws may be used as an alternative fixation method in modified chevron osteotomy, as they provide a potential advantage of a decreased rate of implant removal.
To the best of our knowledge, four previous clinical studies have reported the outcome of magnesium bioabsorbable screw fixation in HV surgery (Table
List of previously reported clinical studies on the use of magnesium screws in modified chevron osteotomy (RCT: randomized clinical trial, SF-36: Short Form-36, VAS: visual analogue scale, NRS: numeric rating scale, FAAM: foot and ankle ability measurement).
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| 2013 | RCT (Mg. vs. Ti.) | 26 | AOFAS-MTP-IP | 6 months | 1 in Ti. group | None |
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| 2016 | Prospective case-series | 45 | AOFAS-MTP-IP | n: 39, 6 weeks | None | 1 relapse |
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| 2017 | RCT (Mg. vs. Ti.) | 26 | AOFAS-MTP-IP | 3 years | 1 in Ti. group | None |
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| 2018 | Retrospective comparison | 200 | Clinical findings | Mg. group: 12.2 weeks | None | Soft tissue irritation: 1 vs. 0 |
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| 2018 | Retrospective comparison | 31 | AOFAS-MTP-IP | 17.6 months | 1 in Ti. group | Prolonged swelling: 1 vs. 0 |
In addition to previous studies, this study further reports the detailed radiographic findings of the corrosion process as the patients had sequential follow-up radiographs. However, because this was a retrospective study, there were no scheduled radiographs within the same time intervals. Some unique changes were detected in the radiological follow-up that was seen in almost all patients. First, gas evolution starts immediately after implantation of magnesium screws, so, during the first two months, variable amounts of gas can be observed in soft tissues. This finding may be interpreted as a gas-producing infection similar to gas gangrene, and surgeons may be anxious about this appearance. However, this gas is quickly absorbed and is not observed later than the third month. Although Windhagen et al. did not mention this phenomenon, gas within the soft tissues has been observed by other previous authors [
When the metallic magnesium is exposed to body fluids, particularly the water, magnesium atoms can transfer two electrons each to water molecules. As a result of this chemical reaction, gaseous hydrogen, divalent magnesium cations, and two hydroxide ions are produced and released to the surrounding tissues. Because the hydrogen is poorly soluble in biological liquids, the gas readily diffuses away [
In this study, no superficial or deep infection developed in any patient of either group. Previous studies have only reported 2 cases of deep infection in patients with magnesium screw fixation. It has been shown that corrosion products of the magnesium increase the pH of the surrounding media, and this alkalization inhibits bacterial growth in vitro [
The need to remove metal implants is not uncommon in foot surgery due to weak soft tissue support around the foot bones, close anatomic proximity of overlying tendons, and external pressure from shoes. Prominent screw heads or plates may irritate the skin and cause pain and discomfort when wearing shoes. In literature, implant removal rates in chevron osteotomy operations vary between 2.3% and 23.6% [
One of the major advantages of magnesium screws is the elimination of the need for implant removal. None of the patients in the Mg group required implant removal even if the screw head had been left protruding. It can be considered that although the screw removal rate is very low for Ti screws, the initial higher cost of magnesium screws cannot be justified. However, even decreasing this low implant removal rate saves a significant amount of money lost in removal operations (both direct and indirect costs). Klauser performed an economic analysis of magnesium-based implants in HV surgery in Germany with the assumption that 8% of implants would require removal in 2015. According to this analysis, the money spent during the removal of the implants (direct costs) plus loss of working days (indirect costs) was calculated to be approximately 9 million Euros [
There are some strengths and limitations of this study. The inclusion of a small number of patients and retrospective study design are two important limitations. However, both groups were similar in terms of several preoperative demographic and clinical characteristics. All patients were followed up for at least one year, up to 32 months, with both radiographic and clinical assessment. The follow-up duration was deemed to be sufficient for the emergence of several implant-related complications.
In conclusion, bioabsorbable Mg screw fixation is an appropriate fixation technique for distal metatarsal modified chevron osteotomy in HV surgery, as the therapeutic efficacy and complication rates were seen to be comparable with titanium screw fixation. Moreover, implant removal operations were avoided. Unlike other bioabsorbable biomaterials, Mg screws create distinct radiological findings during degradation or the corrosion process. Both surgeons and radiologists should be familiar with these images for proper interpretation, since it can neither be called “loosening” nor infection nor does it affect bone healing.
The data used in this study is stored and is available in our institutions’ clinical data base and picture archiving and communications (PACS).
The authors have no conflicts of interest to declare.