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Orthopaedic Proceedings
Vol. 105-B, Issue SUPP_17 | Pages 31 - 31
24 Nov 2023
Mdingi V Gens L Mys K Zeiter S Marais L Richards G Moriarty F Chitto M
Full Access

Aim

In this study we investigated the effects of non-steroidal anti-inflammatory drugs (NSAIDs) with different cyclooxygenase (COX) selectivity on orthopaedic device-related infections (ODRIs) in a rat model. Specifically, we aimed to measure the impact of NSAID therapy on bone changes, bacterial load, and cytokine levels after treatment with antibiotics. In addition, we compared the effects of long vs short-term celecoxib (a COX-2 inhibitor) treatment on the same outcomes.

Method

Skeletally mature female Wistar rats were implanted with Staphylococcus epidermidis-contaminated polyetheretherketone (PEEK) screws (1.5 × 106 CFU per screw) in the proximal right tibia and monitored for 7 days. All animals received subcutaneous antibiotics (rifampicin plus cefazolin) for two weeks from day 7 to 21. In phase I of the study, rats were randomly assigned to receive 28 days of oral treatment with acetylsalicylic acid, ibuprofen, celecoxib, or vehicle control. In phase II, an additional group received seven days of celecoxib treatment from day 0 to 7. After implantation, bone changes were monitored using in vivo micro-CT and histology. Quantitative bacteriology was performed at euthanasia. Plasma samples were collected to measure cytokine levels at four time points (day 0, 6, 20, and 28).


Orthopaedic Proceedings
Vol. 105-B, Issue SUPP_17 | Pages 16 - 16
24 Nov 2023
Siverino C Gens L Ernst M Buchholz T Windolf M Richards G Zeiter S Moriarty F
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Aim

Debridement, Antibiotics, Irrigation, and implant Retention (DAIR) is a surgical treatment protocol suitable for some patients with fracture related infection (FRI). Clinically relevant pre-clinical models of DAIR are scarce and none have been developed in large animals. Therefore, this project aimed to develop a large animal model for FRI including a DAIR approach and compare outcomes after 2 or 5 weeks of infection.

Method

Swiss Alpine sheep (n=8), (2–6 years, 50–80 kg) were included in this study. This study was approved by cantonal Ethical authorities in Chur, Switzerland. A 2 mm osteotomy was created in the tibia and fixed with a 10-hole 5.5 mm steel plate. Subsequently, 2.5 mL of saline solution containing 106 CFU/mL of Staphylococcus aureus MSSA (ATCC 25923) was added over the plate. Sheep were observed for 2 (n=3) or 5 weeks (n=5) until revision surgery, during which visibly infected or necrotic tissues were removed, and the wound flushed with saline. All samples were collected for bacterial quantification. After revision surgery, the sheep were treated systemically for 2 weeks with flucloxacillin and for 4 weeks with rifampicin and cotrimoxazole. After 2 further weeks off antibiotics, the animals were euthanized. Bacteriological culture was performed at the end of the study. Bone cores were isolated from the osteotomy site and processed for Giemsa & Eosin and Brown and Brenn staining. A radiographical examination was performed every second week.


Orthopaedic Proceedings
Vol. 105-B, Issue SUPP_15 | Pages 30 - 30
7 Nov 2023
Mdingi V Marais L Gens L Mys K Zeiter S Richards G Moriarty F Chittò M
Full Access

We investigated the effects of non-steroidal anti-inflammatory drugs (NSAIDs) with different cyclooxygenase (COX) selectivity on orthopaedic device-related infections (ODRIs) in a rat model. We aimed to measure the impact of NSAID therapy on bone changes, bacterial load, and cytokine levels after treatment with antibiotics. We also compared the effects of long vs short-term celecoxib (a COX-2 inhibitor) treatment on the same outcomes.

Skeletally mature female Wistar rats were implanted with Staphylococcus epidermidis- contaminated polyetheretherketone (PEEK) screws in the proximal right tibia and monitored for 7 days. All animals received subcutaneous antibiotics (rifampicin plus cefazolin) for two weeks from day 7 to 21. In phase I of the study, rats were randomly assigned to receive 28 days of oral treatment with acetylsalicylic acid, ibuprofen, celecoxib, or vehicle control. In phase II, an additional group received seven days of celecoxib treatment from day 0 to 7. Bone changes were monitored using in vivo micro-CT and histology. Quantitative bacteriology was performed at euthanasia. Plasma samples were collected to measure cytokine levels on days 0, 6, 20, and 28.

Combination antibiotic therapy resulted in treatment success in 85.71% of cases, while the addition of long-term celecoxib treatment reduced it to 45.45%. Long-term celecoxib treatment significantly reduced bone loss (33.85% mean difference [95% CI 14.12–53.58], p=0.0004 on day 6 bone fraction) and periosteal reaction (0.2760 μm mean difference [95% CI 0.2073–0.3448], p<0.0001 on day 14 periosteal thickness) during early infection compared to the control group. Short- term celecoxib treatment showed similar radiological results without a reduction in treatment success (88.9%). No differences in the inflammatory markers were observed.

Our findings highlight the potential benefits of short-term use of celecoxib in improving bone fraction during the early post-infection period without impairing the efficacy of antibiotic therapy


Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_6 | Pages 117 - 117
1 Jul 2020
Fletcher J Neumann V Wenzel L Richards G Gueorguiev B Gill H Whitehouse M Preatoni E
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Nearly a quarter of screws cause damage during insertion by stripping the bone, reducing pullout strength by over 80%. Studies assessing surgically achieved tightness have predominately shown that variations between individual surgeons can lead to underpowered investigations. Further to the variables that have been previously explored, several basic aspects related to tightening screws have not been evaluated with regards to how they affect screw insertion. This study aims to identify the achieved tightness for several variables, firstly to better understand factors related to achieving optimal intraoperative screw purchase and secondly to establish improved methodologies for future studies.

Two torque screwdrivers were used consecutively by two orthopaedic surgeons to insert 60 cortical, non-locking, stainless-steel screws of 3.5 mm diameter through a 3.5 mm plate, into custom-made 4 mm thick 20 PCF sheets of Sawbone, mounted on a custom-made jig. Screws were inserted to optimal tightness subjectively chosen by each surgeon. The jig was attached to a bench for vertical screw insertion, before a further 60 screws were inserted using the first torque screwdriver with the jig mounted vertically, enabling horizontal screw insertion. Following the decision to use the first screwdriver to insert the remaining screws in the vertical position for the other variables, the following test parameters were assessed with 60 screws inserted per surgeon: without gloves, double surgical gloves, single surgical gloves, non-sterile nitrile gloves and, with and then without augmented feedback (using digitally displayed real-time achieved torque). For all tests, except when augmented feedback was used, the surgeon was blinded to the insertion torque. Once the stopping torque was reached, screws were tightened until the stripping torque was found, this being used to calculate tightness (stopping/stripping torque ratio). Screws were recorded to have stripped the material if the stopping torque was greater than the stripping torque. Following tests of normality, Mann-Whitney-U comparisons were performed between and combining both surgeons for each variable, with Bonferroni corrections for multiple comparisons.

There was no significant (p=0.29) difference in the achieved tightness between different torque screw drivers nor different jig positions (p=0.53). The use of any gloves led to significant (p < 0 .001) increases in achieved tightness compared to not using gloves for one surgeon but made no difference for the other (p=0.38–0.74). Using augmented feedback was found to virtually eliminate stripping. For one surgeon average tightness increased significantly (p < 0 .001) when torque values were displayed from 55 to 75%, whilst for the other, this was associated with significantly decreases (p < 0 .001), 72 to 57%, both surgeons returned to their pre-augmentation tightness when it was removed.

Individual techniques make a considerable difference to the impact from some variables involved when inserting screws. However, the orientation of screws insertion and the type of screwdriver did not affect achieved screw tightness. Using visual feedback reduces rates of stripping and investigating ways to incorporate this into clinical use are recommended. Further work is underway into the effect of other variables such as bone density and cortical thickness.


Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_6 | Pages 118 - 118
1 Jul 2020
Fletcher J Windolf M Gueorguiev B Richards G Varga P
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Proximal humeral fractures occur frequently, with fixed angle locking plates often being used for their treatment. However, the failure rate of this fixation is high, ranging between 10 and 35%. Numerous variables are thought to affect the performance of the fixation used, including the length and configuration of screws used and the plate position. However, there is currently limited quantitative evidence to support concepts for optimal fixation. The variations in surgical techniques and human anatomy make biomechanical testing prohibitive for such investigations. Therefore, a finite element osteosynthesis test kit has been developed and validated - SystemFix. The aim of this study was to quantify the effect of variations in screw length, configuration and plate position on predicted failure risk of PHILOS plate fixation for unstable proximal humerus fractures using the test kit.

Twenty-six low-density humerus models were selected and osteotomized to create a malreduced unstable three-part fracture AO/OTA 11-B3.2 with medial comminution which was virtually fixed with the PHILOS plate. In turn, four different screw lengths, twelve different screw configurations and five plate positions were simulated. Each time, three physiological loading cases were modelled, with an established finite element analysis methodology utilized to evaluate average peri-screw bone strain, this measure has been previously demonstrated to predict experimental fatigue fixation failure.

All three core variables lead to significant differences in peri-screw strain magnitudes, i.e. predicted failure risk. With screw length, shortening of 4 mm in all screw lengths (the distance of the screw tips to the joint surface increasing from 4 mm to 8 mm) significantly (p < 0 .001) increased the risk of failure. In the lowest density bone, every additional screw reduced failure risk compared to the four-screw construct, whereas in more dense bone, once the sixth screw was inserted, no further significant benefit was seen (p=0.40). Screw configurations not including calcar screws, also demonstrated significant (p < 0 .001) increased risk of failure. Finally, more proximal plate positioning, compared to the suggested operative technique, was associated with reduced the predicted failure risk, especially in constructs using calcar screws, and distal positioning increased failure risk.

Optimal fixation constructs were found when placing screws 4 mm from the joint surface, in configurations including calcar screws, in plates located more proximally, as these factors were associated with the greatest reduction in predicted fixation failure in 3-part unstable proximal humeral fractures. These results may help to provide practical recommendations on the implant usage for improved primary implant stability and may lead to better healing outcomes for osteoporotic proximal fracture patients. Whilst prospective clinical confirmation is required, using this validated computational tool kit enables the discovery of findings otherwise hidden by the variation and prohibitive costs of appropriately powered biomechanical studies using human samples.


Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_6 | Pages 93 - 93
1 Jul 2020
Gueorguiev B Hadzhinikolova M Zderic I Ciric D Enchev D Baltov A Rusimov L Richards G Rashkov M
Full Access

Distal radius fractures have an incidence rate of 17.5% among all fractures. Their treatment in case of comminution, commonly managed by volar locking plates, is still challenging. Variable-angle screw technology could counteract these challenges. Additionally, combined volar and dorsal plate fixation is valuable for treatment of complex fractures at the distal radius. Currently, biomechanical investigation of the competency of supplemental dorsal plating is scant. The aim of this study was to investigate the biomechanical competency of double-plated distal radius fractures in comparison to volar locking plate fixation.

Complex intra-articular distal radius fractures AO/OTA 23-C 2.1 and C 3.1 were created by means of osteotomies, simulating dorsal defect with comminution of the lunate facet in 30 artificial radii, assigned to 3 study groups with 10 specimens in each. The styloid process of each radius was separated from the shaft and the other articular fragments. In group 1, the lunate facet was divided to 3 equally-sized fragments. In contrast, the lunate in group 2 was split in a smaller dorsal and a larger volar fragment, whereas in group 3 was divided in 2 equal fragments. Following fracture reduction, each specimen was first instrumented with a volar locking plate and non-destructive quasi-static biomechanical testing under axial loading was performed in specimen's inclination of 40° flexion, 40° extension and 0° neutral position. Mediolateral radiographs were taken under 100 N loads in flexion and extension, as well as under 150 N loads in neutral position. Subsequently, all biomechanical tests were repeated after supplemental dorsal locking plate fixation of all specimens. Based on machine and radiographic data, stiffness and angular displacement between the shaft and lunate facet were determined.

Stiffness in neutral position (N/mm) without/with dorsal plating was on average 164.3/166, 158.5/222.5 and 181.5/207.6 in groups 1–3. It increased significantly after supplementary dorsal plating in groups 2 and 3.

Predominantly, from biomechanical perspective supplemental dorsal locked plating increases fixation stability of unstable distal radius fractures after volar locked plating. However, its effect depends on the fracture pattern at the distal radius.


Orthopaedic Proceedings
Vol. 101-B, Issue SUPP_14 | Pages 75 - 75
1 Dec 2019
Boot W Foster A Schmid T D'este M Zeiter S Eglin D Richards G Moriarty F
Full Access

Aim

Implant-associated osteomyelitis is a devastating complication with poor outcomes following treatment, especially when caused by antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). A large animal model of a two-stage revision to treat MRSA implant-associated osteomyelitis has been developed to assess novel treatments. A bioresorbable, thermo-responsive hyaluronan hydrogel (THH) loaded with antibiotics has been developed and our aim was to investigate it´s in vivo efficacy as a local antibiotic carrier compared to the current standard of care i.e. antibiotic-loaded polymethylmethacrylate (PMMA) bone cement.

Method

12 female, 2 to 4 year old, Swiss Alpine Sheep were inoculated with MRSA at the time of intramedullary nail insertion in the tibia to develop chronic osteomyelitis. After 8 weeks sheep received a 2-stage revision protocol, with local and systemic antibiotics. Group 1 received the gold standard clinical treatment: systemic vancomycin (2 weeks) followed by rifampicin plus trimethoprim/sulfamethoxazole (4 weeks), and local gentamicin/vancomycin via PMMA. Group 2 received local gentamicin/vancomycin delivered via THH at both revision surgeries and identical systemic therapy to group 1. Sheep were euthanized 2 weeks following completion of antibiotic therapy. At euthanasia, soft tissue, bone, and sonicate fluid from the hardware was collected for quantitative bacteriology.


Orthopaedic Proceedings
Vol. 101-B, Issue SUPP_14 | Pages 87 - 87
1 Dec 2019
Burch MA Thompson K Eberli U Arens D Milstrey A Stadelmann V Richards G Moriarty F
Full Access

Aim

Non-steroidal anti-inflammatory drugs (NSAIDs) are a cornerstone of perioperative pain management in orthopedic trauma surgery, although concerns persist regarding the potential impact of these drugs on fracture healing. Furthermore, NSAIDs may also exert an influence on host immune defenses, which may also be important in the context of infection treatment. However, this has been very much under-investigated in the clinical and scientific literature. The aim of this study was to determine the impact of NSAIDs on the course of an orthopedic device-related infection (ODRI) and its response to antibiotic therapy in a rat model.

Method

A polyetheretherketone (PEEK) screw was inserted in the proximal tibia of 48 skeletally mature female Wistar rats: 12 control animals received a sterile screw, of which 6 also received NSAID therapy (carprofen, 5 mg/kg s.c. once daily); 36 rats received a Staphylococcus epidermidis-inoculated screw, of which 18 received NSAID therapy. Antibiotic therapy was administered from day 7–21 in 9 animals from all groups receiving S. epidermidis-inoculated screws (cefazolin: 30 mg/kg; s.c., b.i.d. plus rifampin: 25 mg/kg; s.c., b.i.d.). Bone histomorphometric changes were monitored using longitudinal microCT scanning, performed postoperatively, and at 3, 6, 9, 14, 20 and 28 days (euthanasia). Quantitative bacteriology of the implant, bone and overlying soft tissue was performed to assess infection status of individual animals.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_22 | Pages 63 - 63
1 Dec 2017
Pützler J Arens D Metsemakers W Zeiter S Richard K Richards G Raschke M Moriarty F
Full Access

Aim

Open fractures still have a high risk for fracture-related Infection (FRI). The optimal duration of perioperative antibiotic prophylaxis (PAP) for open fractures remains controversial due to heterogeneous guidelines and highly variable prophylactic regimens in clinical practice. In order to provide further evidence with which to support the selection of antibiotic duration for open fracture care, we performed a preclinical evaluation in a contaminated rabbit fracture model.

Method

A complete humeral osteotomy in 18 rabbits was fixed with a 7-hole-LCP and inoculated with Staphylococcus aureus (2×106 colony forming units, CFU per inoculum). This inoculum was previously shown to result in a 100% infection rate in the absence of any antibiotic prophylaxis. Cefuroxime was administered intravenously in a weight adjusted dosage equivalent to human medicine (18.75 mg/kg) as a single shot only, for 24 hours (every 8 hours) and for 72 hours (every 8 hours) in separate groups of rabbits (n=6 per group). Infection rate per group was assessed after two weeks by quantitative bacteriological evaluation of soft tissue, bone and implants. Blood samples were taken from rabbits preoperatively and on days 3, 7 and 14 after surgery to measure white blood cell count (WBC) and C-reactive protein (CRP) levels.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_22 | Pages 102 - 102
1 Dec 2017
Pützler J Zeiter S Vallejo A Gehweiler D Raschke M Richards G Moriarty F
Full Access

Aim

Treatment regimens for fracture-related infection (FRI) often refer to the classification of Willenegger and Roth, which stratifies FRIs based on time of onset of symptoms. The classification includes early (<2 weeks), delayed (2–10 weeks) and late (>10 weeks) infections. Early infections are generally treated with debridement and systemic antibiotics but may not require implant removal. Delayed and late infections, in contrast, are believed to have a mature biofilm on the implant, and therefore, treatment often involves implant removal. This distinction between early and delayed infections has never been established in a controlled clinical or preclinical study. This study tested the hypothesis that early and delayed FRIs respond differently to treatment comprising implant retention.

Method

A complete humeral osteotomy in 16 rabbits was fixed with a 7-hole-LCP and inoculated with Staphylococcus aureus. The inoculum size (2×106 colony forming units per inoculum) was previously tested without antibiotic intervention to result in infection of all animals persisting for at least 12 weeks.4 The infection was allowed to develop for either 1 (early group) or 4 (delayed group) weeks (n= 8 per group) after bacterial inoculation. At these time points, treatment involved debridement and irrigation of the wound (no implant removal) and quantitative bacteriological evaluation of the removed materials. Systemic antibiotics were administered according to a common clinical regimen (2 weeks: rifampin + nafcillin, followed by 4 weeks: rifampin + levofloxacin). After an additional one-week antibiotic washout period, animals were euthanized and a quantitative bacteriology of soft tissue, implant (after sonication) and bone was performed.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_22 | Pages 7 - 7
1 Dec 2017
Vallejo A Morgenstern M Puetzler J Arens D Moriarty T Richards G
Full Access

Aim

Antibiotic prophylaxis is critical for the prevention of fracture related infection (FRI) in trauma patients, particularly those with open wounds. Administration of prophylactic antibiotics prior to arrival at the hospital (e.g. by paramedics) may reduce intraoperative bacterial load and has been recommended; however scientific evidence for pre-hospital administration is scarce.

Methods

The contaminated rabbit humeral osteotomy model of Arens was modified to resemble the sequence of events in open fractures. In an initial surgery representing the “accident”, a 2mm mid-diaphyseal hole was created in the humerus and the wound was contaminated with a clinical Staphylococcus aureus strain (mean 1.6×106 Colony Forming Units, CFU). The animals were allowed recover for 4 hours mimicking the period from trauma to debridement. At this time, a second procedure was performed in order to debride and irrigate the wound, and to fix a complete osteotomy that was made through the initial defect. Three test groups were included (n=8 rabbits per group): 1) no antibiotic therapy; 2) standard “in-hospital” antibiotic prophylaxis (24 hours therapy starting 30 minutes before surgery); 3) “pre-hospital” antibiotics (single dose 15 minutes after the “accident”). The antibiotic used was cefuroxime and was administered in a weight-adjusted dosage.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_22 | Pages 65 - 65
1 Dec 2017
Post V Morgenstern M Harris L Mageiros L Hitchings MD Méric G Pascoe B Sheppard SK Richards G Moriarty F
Full Access

Aim

Staphylococcus epidermidis has emerged as an important opportunistic pathogen causing orthopedic device-related infections (ODRIs). In this prospective clinical and laboratory study, we have investigated the association of genome variation and phenotypic features of the infecting S. epidermidis isolate with the clinical outcome of the infected patient.

Method

One hundred and four invasive S. epidermidis isolates were prospectively collected from patients with ODRI. Upon patient entry into the study, surgical parameters such as type of implant; open or closed fracture were documented. Personal characteristics were also documented and included: gender; age; body mass index (BMI); smoker/non-smoker; overall medical condition (Charlson comorbidity index); and chronic immunosuppressive conditions. Any revision surgeries involving the site of interest and all isolated pathogens were recorded throughout the course of treatment and follow-up. The clinical outcome after treatment was measured with a mean follow-up period (FUP) of 26 months, and each patient was then considered to have been “cured” or “not cured”. The isolates were tested for their antibiotic susceptibility and ability to form biofilm. Whole genome sequencing was performed on all isolates and genomic variation was related to features associated with “cured” and “not cured”.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_23 | Pages 31 - 31
1 Dec 2016
Metsemakers W Schmid T Zeiter S Ernst M Keller I Cosmelli N Arens D Moriarty F Richards G
Full Access

Aim

The aim of this study was to define the role of implant material and surface topography on infection susceptibility in a preclinical in vivo model incorporating appropriate fracture biomechanics and bone healing.

Method

The implants included in this experimental study were composed of: standard Electro polished Stainless Steel (EPSS), standard titanium (Ti-S), roughened stainless steel (RSS) and surface polished titanium (Ti-P). In an in vivo study, a rabbit humeral fracture model was used. Each rabbit received one of three Staphylococcus aureus inocula, aimed at determining the infection rate at a low, medium and high dose of bacteria. Outcome measures were quantification of bacteria on the implant and in the surrounding tissues, and determination of the infectious dose 50 (ID50).


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_23 | Pages 66 - 66
1 Dec 2016
Samara E Moriarty F Decosterd LA Richards G Gautier E Wahl P
Full Access

Aim

Thermal stability is a key property determining the suitability of an antibiotic agent for local application. Long-term data describing thermal stability without interference from carrier materials are scarce.

Method

In this study, a total of 38 common antibiotic agents have been maintained at 37 °C in saline solution, and degradation and antibacterial activity assessed over 6 weeks. The impact of an initial supplementary heat exposure mimicking exothermically-curing bone cement has also been tested. Antibiotic degradation was assessed by chromatography coupled to mass spectrometry or immunoassays, as appropriate. Antibacterial activity was determined by Kirby-Bauer disk diffusion assay.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_23 | Pages 84 - 84
1 Dec 2016
Wahl P Post V Richards G Moriarty F
Full Access

Aim

Determine the time concentration profile required to achieve vancomycin-mediated eradication of Staphylococcus aureus biofilm. This is critical for the identification of performance targets for local antibiotic delivery, yet has not been described.

Method

Mature S. aureus UAMS-1 biofilms were grown on titanium-aluminum-niobium discs in Mueller Hinton broth (MHB). After 7 days, the discs were incubated in MHB containing vancomycin at 100, 200, 500, 1′000 and 2′000 mg/L. Both static and shaking conditions were tested. Samples were retrieved at intervals for up to 28 days for quantification of residual biofilm by sonication and serial dilution plating. One additional disc was processed per time point for scanning electron microscopy.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XLIV | Pages 78 - 78
1 Oct 2012
Schroeder J Fliri L Liebergall M Richards G Windolf M
Full Access

The common practice for insertion of distal locking screws of intramedullary (IM) nails is a freehand technique under fluoroscopic control. The process is technically demanding, time-consuming and afflicted to considerable radiation exposure to patient and surgical personnel. A new technique is introduced which guides the surgeon by landmarks on the X-ray projection.

18 fresh frozen human below-knee specimens (incl. soft tissue) were used. Each specimen was instrumented with an Expert Tibial Nail (Synthes GmbH, Switzerland) and was mounted on an OR-table. Two distal interlocking techniques were performed in random order using a Siemens ARCADIS C-arm system (Siemens AG, Munich, Germany). The newly developed guided technique, guides the surgeon by visible landmarks projected onto the fluoroscopy image. A computer program plans the drilling trajectory by 2D-3D conversion and provides said guiding landmarks for drilling in real-time. No additional tracking or navigation equipment is needed.

All four distal screws (2 mediolateral, 2 anteroposterior) were placed in each procedure. Operating time, number of taken X-rays and radiation time were recorded per procedure and for each single screw.

8 procedures were performed with the freehand technique and 10 with the guided technique. A 58% reduction in number of fluoroscopy shots per screw was found for the guided technique (7.4±3.4 vs. 17.6±10.3; p < 0.001). Total radiation time was 55% lower for the guided technique (17.1 ± 3.7s vs. 37.9 ± 9.1s) (p = 0.001). Operating time was shorter by 22% in the guided technique (3.2±1.2 min vs. 4.1±2.1 min p = 0.018).

In an experimental setting, the newly developed guided freehand technique has proven to markedly reduce radiation exposure when compared to the conventional freehand technique. The method enhances established clinical workflows and does not require cost intensive add-on devices or extensive training.

A newly developed simple navigated technique has proven to markedly reduce radiation exposure and time for distal locking of intramedullary nails.