A biomechanical investigation of a knotless tension band in medial malleolar fracture models in composite Sawbones®

Mechanical Properties and Corrosion Rate of ZnAg3 as a Novel Bioabsorbable Material for Osteosynthesis

Osteosynthesis in fracture treatment typically uses hardware that remains in the patient's body, which brings a permanent risk of negative side effects such as foreign body reactions or chronic inflammation. Bioabsorbable materials, however, can degrade and slowly be replaced by autologous bone tissue. A suitable material is requested to offer great biocompatibility alongside excellent mechanical properties and a reasonable corrosion rate. Zinc-silver alloys provide these characteristics, which makes them a promising candidate for research. This study investigated the aptitude as a bioabsorbable implant of a novel zinc-silver alloy containing 3.3 wt% silver (ZnAg3). Here, the tensile strength as well as the corrosion rate in PBS solution (phosphate buffered solution) of ZnAg3 were assessed. Furthermore, shear tests, including fatigue and quasi-static testing, were conducted with ZnAg3 and magnesium pins (MAGNEZIX®, Syntellix AG, Hannover, Germany), which are already in clinical use. The detected corrosion rate of 0.10 mm/year for ZnAg3 was within the proposed range for bioabsorbable implants. With a tensile strength of 237.5 ± 2.12 MPa and a shear strength of 144.8 ± 13.2 N, ZnAg3 satisfied the mechanical requirements for bioabsorbable implants. The fatigue testing did not show any significant difference between ZnAg3 and magnesium pins, whereas both materials withstood the cyclic loading. Thus, the results support the assumption that ZnAg3 is qualified for further investigation.

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.

Effects of temperature increase during surgical drilling in acrylic resin

BACKGROUND

Acrylic resin is employed for drilling bone biomodels. Since drilling causes temperature rise, the mechanical properties of thermoplastic acrylic resin can be altered, consequently affecting drilling properties. However, it is currently unclear how this temperature increase impacts drilling.

OBJECTIVE

This study reports the effects of temperature rise on both mechanical and drilling properties through experiments in which acrylic resin is drilled under machining conditions employed in surgical operations.

METHODS

Drilling tests were performed using a surgical drill on medical acrylic resin under dry conditions to observe generated cutting chips and measure drilling properties such as torque, drilling time, and temperature rise. Dynamic mechanical analysis measurements were performed to consider temperature effects.

RESULTS

According to the morphological classification of the cutting chips, the drilling process is divided into three phases corresponding with the generation of cylindrical helix, waved, and rounded nubby chips respectively. During drilling, the temperature of the chips can exceed the glass transition temperature (100∘C) resulting in decreased viscoelasticity, which is associated with decreased torque.

CONCLUSIONS

While drilling acrylic resin under surgical machining conditions, increasing temperature can decrease torque and morphologically change cutting chips due to the decrease in mechanical properties above the glass transition temperature.

Medial malleolus: Operative Or Non-operative (MOON) trial protocol - a prospective randomised controlled trial of operative versus non-operative management of associated medial malleolus fractures in unstable fractures of the ankle

BACKGROUND

There are limited data reporting the outcome of patients with non-operatively managed medial malleolus fractures compared to those treated surgically in the presence of fibular stabilisation for unstable fractures of the ankle. Conservative management could result in fewer complications, reduced surgical time and lower cost. The purpose of this study is to determine if any difference exists in patient reported and surgical outcomes 1 year after surgery between operative and non-operative treatment of medial malleolar fractures in combination with stabilisation of the lateral malleolus.

METHODS/DESIGN

This is a single-centre, prospective, randomised controlled trial that aims to randomise 154 participants with an unstable ankle fracture to 'non-fixation' (n = 77) or 'fixation' (n = 77) of an associated well-reduced medial malleolus fracture following fibular stabilisation. The study will include patients ≥ 16 years of age with a closed bimalleolar or trimalleolar ankle fracture who are able to consent, complete questionnaires in the English language, and complete follow-up over a 1-year period. Randomisation will occur intra-operatively when the medial malleolus fracture is deemed 'well-reduced', with 2 mm or less of fluoroscopic displacement. The technique for fixation of both the medial and lateral malleoli is at the discretion of the operating surgeon. Patient-reported, observer-rated, and radiographic assessments will be collected at baseline and then at the following post-operative assessment points: 2 weeks, 6 weeks and 1 year. Postal questionnaire outcome data will be collected at 3 and 6 months. The primary outcome measure will be the Olerud Molander Ankle Score (OMAS) at 1 year following surgery. Secondary outcome measures will include the Manchester-Oxford Foot Questionnaire (MOXFQ), EuroQol-5D (EQ-5D), pain, treatment satisfaction, time to return to activity, operative tourniquet time, and complications.

DISCUSSION

There is only one previous randomised trial comparing non-fixation with fixation of associated medial malleolus fractures but that was limited by the lack of baseline patient-reported outcome data and an inferior sample size. This current prospective trial aims to provide high-quality evidence regarding the requirement for medial malleolar fixation in unstable ankle fractures.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03362229 . Registered retrospectively on 5 December 2017.

Medial malleolar fractures: current treatment concepts

The medial malleolus, once believed to be the primary stabilizer of the ankle, has been the topic of conflicting clinical and biomechanical data for many decades. Despite the relevant surgical anatomy being understood for almost 40 years, the optimal treatment of medial malleolar fractures remains unclear, whether the injury occurs in isolation or as part of an unstable bi- or trimalleolar fracture configuration. Traditional teaching recommends open reduction and fixation of medial malleolar fractures that are part of an unstable injury. However, there is recent evidence to suggest that nonoperative management of well-reduced fractures may result in equivalent outcomes, but without the morbidity associated with surgery. This review gives an update on the relevant anatomy and classification systems for medial malleolar fractures and an overview of the current literature regarding their management, including surgical approaches and the choice of implants. Cite this article: Bone Joint J 2019;101-B:512-521.

Medial malleolus fractures: A biomechanical comparison of tension band wiring fixation methods

BACKGROUND

This study compared the biomechanical properties of three different fixation methods of tension band wirings, used in the treatment of medial malleolus fractures. The first method used an innovative "handmade bent pin" for cerclage fixation. The second method used a U-shaped K-wire to attach the cerclage to the medial tibial cortex. These two novel fixation techniques were compared with the traditional tension band wiring technique which is fixated to the bone by a screw.

HYPOTHESIS

Novel fixation techniques of tension band wiring provide stable fixation.

MATERIAL AND METHODS

In this study 27 artificial bone models, which medial malleolus fractures were simulated on, were used. Using an electromechanical test device, the force required to pull out each implant was assessed and compared.

RESULTS

This study found that; while handmade bent pinning resulted averagely 840.25N (range: 647-1066±118.72) and U-shaped K-wire fixation was 381.71N (range: 176-651±150.2) pull out strength, traditional tension band wiring indicated 871.33N (range: 549-1008±137.74) pull out strength.

DISCUSSION

Handmade bent pinning method provide similar results with traditional tension band wiring. Therefore, in suitable cases, it may be an acceptable alternative to traditional tension band wiring techniques when treating malleolar fractures. Although the outcomes of U-shaped K-wire fixation indicated lower than other two groups, the outcomes were comparable with the literature. So while performing tension band wiring, both handmade fixation systems may be used in certain cases. For Orthopaedic surgeons, it is better to know and think about these alternative handmade pinning systems created from simple K-wires during the surgery if needed.

LEVEL OF EVIDENCE

IV, Biomechanical trial.

A model to evaluate Pauwels type III femoral neck fractures

While many femoral neck fractures can be reliably treated with surgical intervention, Pauwels III femoral neck fractures in the young adult population continue to be a challenging injury, and there is no consensus on optimal treatment. As such, there are past and ongoing biomechanical studies to evaluate the fixation provided by different constructs for this inherently unstable fracture. While many investigations rely on cadavers to evaluate the biomechanical performance of a construct, significant inter-subject variability can confound the analysis. Biomechanical femur analogs are being used more frequently due to more consistent mechanical properties; however, they have not been stringently evaluated for morphology or suitability for instrumentation. This study sought to determine the variability among composite femoral analogs as well as consistently create a Pauwels III injury and instrument the analogs without the need for fluoroscopic guidance. In total, 24 fourth-generation composite femoral analogs were evaluated for femoral height, neck-shaft angle, anteversion, and cortical thickness. A method was developed to simulate a Pauwels III fracture and to prepare three different constructs: an inverted triangle of cannulated screws, a sliding hip screw, and a hybrid inverted triangle with cannulated screws and a sliding hip screw. Radiographs were utilized to evaluate the variation in implant position. All but one of the morphological parameters varied by <1%. The tip-to-apex distance for all sliding hip screw hardware was 18.8 ± 3.3 mm, and all relevant cannulated screw distances were within 5 mm of the adjacent cortex. All screws were parallel, on average, within 1.5° on anterior-posterior and lateral films. Fourth-generation composite femora were found to be morphologically consistent, and it is possible to consistently instrument the analogs without the use of fluoroscopy. This analog and hardware implantation model could serve as a screening model for new fracture repair constructs without the need for cadaveric tissues or radiologic technology.

Comparing the Knotless Tension Band and the Traditional Stainless Steel Wire Tension Band Fixation for Medial Malleolus Fractures: A Retrospective Clinical Study

The traditional stainless steel wire tension band (WTB) has been popularized for small avulsion fractures at the medial malleolus. Despite the tension band principle creating a stable construct, complications continue to arise utilizing the traditional stainless steel WTB with patients experiencing hardware irritation at the tension band site and subsequent hardware removal. Coupled with hardware irritation is fatigue failure with the wire. The goal of this investigation was to retrospectively compare this traditional wire technique to an innovative knotless tension band (KTB) technique in order to decrease costly complications. A total of 107 patients were reviewed with a minimum follow-up of 1 year. Outcome measures include descriptive data, fracture classification, results through economic costs, and fixation results (including hardware status, healing status, pain status, and time to healing). The KTB group had a 13% lower true cost as compared to the WTB group while the fixation results were equivocal for the measured outcomes. Our results demonstrate that the innovative KTB is comparable to the traditional WTB while offering a lower true cost, an irritation free reduction all without the frustration of returning to the operating room for additional hardware removal, which averages approximately to $8,288.

Comparison of surgical techniques of 111 medial malleolar fractures classified by fracture geometry

BACKGROUND

Evaluation of operative techniques used for medial malleolar fractures by classifying fracture geometry has not been well documented.

METHODS

One hundred eleven patients with medial malleolar fractures (transverse n = 63, oblique n = 29, vertical n = 7, comminuted n = 12) were included in this study. Seventy-two patients had complicating comorbidities. All patients were treated with buttress plate, lag screw, tension band, or K-wire fixation. Treatment outcomes were evaluated on the basis of radiological outcome (union, malunion, delayed union, or nonunion), need for operative revision, presence of postoperative complications, and AOFAS Ankle-Hindfoot score.

RESULTS

For transverse fractures, tension band fixation showed the highest rate of union (79%), highest average AOFAS score (86), lowest revision rate (5%), and lowest complication rate (16%). For oblique fractures, lag screws showed the highest rate of union (71%), highest average AOFAS score (80), lowest revision rate (19%), and lowest complication rate (33%) of the commonly used fixation techniques. For vertical fractures, buttress plating was used in every case but 1, achieving union (whether normal or delayed) in all cases with an average AOFAS score of 84, no revisions, and a 17% complication rate. Comminuted fractures had relatively poor outcomes regardless of fixation method.

CONCLUSIONS

The results of this study suggest that both tension bands and lag screws result in similar rates of union for transverse fractures of the medial malleolus, but that tension band constructs are associated with less need for revision surgery and fewer complications. In addition, our data demonstrate that oblique fractures were most effectively treated with lag screws and that vertical fractures attained superior outcomes with buttress plating.

LEVEL OF EVIDENCE

Level III, retrospective comparative series.