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Introduction Current gold standard for the treatment of symphyseal disruptions includes anterior plating, almost entirely prohibiting symphyseal mobility and resulting in an iatrogenic arthrodesis followed by high rates of implant failure. Minimally invasive tape suture constructs have been found to maintain the micro mobility of ligamentous injuries, yet still providing sufficient biomechanical stability. Recently, this technique has been primarily investigated for symphyseal disruptions on synthetic pelvic models. Therefore, the aim of this study was to examine the feasibility of this novel flexible osteosynthesis on cadaveric pelvic models based on the following hypothesis: tape suture constructs ensure sufficient biomechanical stability without inhibiting micro mobility of the pubic symphysis for the treatment of symphyseal disruptions and maintain stability during long-term loading. Materials and methods 9 cadaveric anterior pelvic rings were used in this study and a symphyseal disruption was created in every specimen. The specimens were then exposed to short- and long-term vertical and horizontal cyclic loading after treatment with a tape suture construct in criss-cross technique. The mean maximum displacement (mm) during cyclic loading and the corresponding stiffness (N/mm) were measured and compared. Results Regarding both displacement (mm) and corresponding stiffness (N/mm), the tape sutures displayed a significant difference between short- and long-term loading for cranial and caudal vertical loading (p p > 0.05). No tape suture suffered from implant failure during long-term loading. Conclusions The tape suture construct displayed sufficient biomechanical stability without exceeding the physiological mobility of 2 mm of the pubic symphysis; however, also maintained the desired micro mobility of the affected joint necessary to prevent an iatrogenic arthrodesis. Further, all tape sutures maintained stability throughout long-term loading.

Purpose Open reduction and internal fixation using anterior plate osteosynthesis currently represents the gold standard for the treatment of symphyseal disruptions. Since postoperative screw loosening with consequent implant failure is frequently observed, this study aims to evaluate if and to what extent augmentation can increase the pull-out force of symphyseal screws to improve the constructs stability. Methods Twelve human cadaveric anterior pelvic rings were separated at the symphyseal joint for bilateral testing, consequently achieving comparable sites. First, one non-augmented screw was drilled into the superior pubic ramus, whereas the contralateral side was primarily augmented. The screws were then withdrawn with a constant speed of 10 mm/min and the fixation strengths determined by the force (N) displacement (mm) curve. Finally, the primary non-augmented site was secondary augmented, representing revision surgery after initial implant failure, and the corresponding fixation strength was measured again. Results Augmentation compared to non-augmented screws displayed significantly higher pull-out forces with an increase in pull-out force by 377% for primary and 353% for secondary augmentation (p p = 0.74). Conclusions Primary and secondary augmentation significantly increases the stability of symphyseal screws and, therefore, potentially decreases rates of implant failure.

Background and objectives The treatment of elderly patients is an increasing challenge and the long-term sequelae often affect activities of daily living and quality of life in those patients. Handgrip strength (HGS) appears as a promising value to predict the outcome after trauma in elderly patients and to assess the overall muscle strength. Besides the possible role of psychological and hormonal factors, vitamin D may have a positive influence. Furthermore, some data suggest that Vitamin D is beneficial regarding muscle strength and possibly prevents further falls and injuries in orthogeriatric patients. The purpose of this study was to identify if Vitamin D is an influencing factor for HGSin elderly trauma patients. Materials and methods 94 elderly patients in a Level I Trauma Center aged 60 years or older were prospectively enrolled and HGS as well as serum 25-OH Vitamin D concentration (VDC) were measured. In addition, the standardized questionnaires Barthel Index (BI), Parker Mobility Score (PMS), Short Physical Performance Battery (SPPB), Strength, Assistance with walking, Rise from a chair, Climb stairs and Falls (SARC-F) and European Quality of Life 5 Dimensions 5 Levels Questionnaire (EQ-5D-5L), were used to record mental health status and demographic data. Results HGS is mainly related to age and sex in elderly trauma patients. HGS was higher in men (meanmale = 27.31 kg (± 8.11), meanfemale = 15.62 kg (± 5.63), p age = − 0.58, p VDC = − 0.27, pVDC VDC VDC anxiety+depression = − 0.26, panxiety+depression Conclusions These results do not support the hypothesis that Vitamin D has a positive influence on muscle strength measured by HGS. Nevertheless, this study could confirm the usefulness of HGS as a tool to detect the risk for frequent falls or stumbling. Furthermore, HGS seems to be associated with dizziness and age at onset of menopause. A significant decrease of HGS could also be shown in patients with anxiety and depression. This underlines the importance of interdisciplinary treatment of elderly trauma patients and needs to be taken into account for further studies, as especially the psychological motivation seems to have a significant influence and is sometimes not considered enough in elderly musculo-skeletal patients.

Zusammenfassung3-D-Druck wird in der Unfallchirurgie und Orthopädie zunehmend für die Herstellung patientenspezifischer Implantate verwendet. Ziel dieses strukturierten Reviews ist es, aktuelle Merkmale und Fähigkeiten zu ermitteln und hieraus Anforderungen an das Implantatdesign und den -druck abzuleiten. Hierzu wurden 98 Veröffentlichungen der letzten 5 Jahre analysiert.Neben Kunststoffen und Metallen können auch biologisches Material und Medikamentensuspensionen zum Druck verwendet werden. Der 3-D-Druck bietet den Vorteil, dass die Implantate individuell an die Anatomie und Pathologie des Patienten angepasst werden können, also auch bewusst Einfluss auf biomechanischen und -mimetischen Eigenschaften genommen werden kann. Beispielsweise kann die Oberfläche der Implantate gezielt so optimiert werden, dass eine Osteoinduktivität bewirkt wird. Angewandt wird das Verfahren zum Gelenk- und Knochenersatz sowie für Knorpel- und Weichteilrekonstruktionen.Somit ergeben sich diverse Anforderungen an das Design und die Herstellung. Da es sich um ein sehr zeit- und kostenintensives Verfahren handelt, sollte eine klare Überlegenheit zu herkömmlichen Behandlungsmethoden bestehen. Aufgrund der Komplexität des Prozesses ist eine Qualitätssicherung unabdingbar, um die Sicherheit des Patienten zu gewährleisten.Bei komplexen oder von der Norm abweichenden Fällen wird der 3-D-Druck sich zunehmend durchsetzen. Um Qualität zu gewährleisten und effiziente Prozesse zu etablieren, ist eine engere Verzahnung zwischen Behandlern und Herstellern unabdingbar.

Purpose The incidence of atlanto-axial injuries is continuously increasing and often requires surgical treatment. Recently, Harati developed a new procedure combining polyaxial transarticular screws with polyaxial atlas massae lateralis screws via a rod system with promising clinical results, yet biomechanical data is lacking. This biomechanical study consequently aims to evaluate the properties of the Harati technique. Methods Two groups, each consisting of 7 cervical vertebral segments (C1/2), were formed and provided with a dens axis type 2 fracture according to Alonzo. One group was treated with the Harms and the other with the Harati technique. The specimen was loaded via a lever arm to simulate extension, flexion, lateral flexion and rotation. For statistical analysis, dislocation (°) was measured and compared. Results For extension and flexion, the Harati technique displayed a mean dislocation of 4.12° ± 2.36° and the Harms technique of 8.48° ± 1.49° (p p p Conclusion This study found a significant increase in biomechanical stability of the Harati technique when compared to the technique by Harms et al. Consequently, this novel technique can be regarded as a promising alternative for the treatment of atlanto-axial instabilities.

Introduction Open book fractures are challenging injuries oftentimes requiring surgical treatment. The current treatment of choice is symphyseal plating, which requires extensive surgery and entirely limits physiological movement of the symphyseal joint, frequently resulting in implant failure. Therefore, we investigated the biomechanical properties of a semi-rigid implant (modified SpeedBridge™) as a minimally invasive tape suture construct for the treatment of open book fractures and evaluated the superiority of two techniques of implementation: criss-cross vs. triangle technique. Materials and methods Nine synthetic symphyseal joints were dissected creating an open book fracture. The different osteosynthesis methods (plating, modified SpeedBridge™ in criss-cross/triangle technique) were then applied. All constructs underwent horizontal and vertical loading, simulating biomechanical forces while sitting, standing and walking. For statistical analysis, dislocation (mm) and stiffness (N/mm) were calculated. Results Symphyseal plating for the treatment of open book fractures proved to be a rigid osteosynthesis significantly limiting the physiological mobility of the symphyseal joint (dislocation: 0.08 ± 0.01 mm) compared to the tape sutures (dislocation: triangle technique 0.27 ± 0.07 mm, criss-cross technique 0.23 ± 0.05 mm) regarding horizontal tension (p ™ techniques showed sufficient biomechanical stability without one being superior to the other (p > 0.05 in all directions). Considering vertical loading, no statistical difference was found between all osteosynthesis methods (caudal: p = 0.41; cranial: p = 0.61). Conclusions Symphyseal plating proved to be the osteosynthesis method with the highest rigidity. The modified SpeedBridge™ as a semi-rigid suture construct provided statistically sufficient biomechanical stability while maintaining a minimum of symphyseal movement, consequently allowing ligamental healing of the injured joint without iatrogenic arthrodesis. Furthermore, both the criss-cross and the triangle technique displayed significant biomechanical stability without one method being superior.

Purpose Three-dimensional (3D) printed patient-specific instruments (PSI) have been introduced to increase precision and simplify surgical procedures. Initial results in femoral and tibial osteotomies are promising, but validation studies on 3D planning, manufacturing of patient-specific cutting blocks and 3D evaluation of the attained results are lacking. Methods In this study, patient-specific cutting blocks and spacers were designed, fabricated, and used to perform a high tibial osteotomy (HTO). After segmentation of CT data sets from 13 human tibiae, 3D digital planning of the HTO was performed with a medial opening of 8 mm. These 3D models were used to fabricate patient-specific cutting blocks and spacers. After the surgical procedure, accuracy was evaluated measuring 3D joint angles and surface deviations. Results The lowest mean deviation was found to be 0.57° (SD ± 0.27) for the MPTA. Medial and lateral tibial slope deviated from the 3D planning by an average of 0.98° (SD ± 0.53) and 1.26° (SD ± 0.79), respectively, while tibial torsion deviated by an average of 5.74° (SD ± 3.24). Color analysis of surface deviations showed excellent and good agreement in 7 tibiae. Conclusion With 3D cutting blocks and spacers, the 3D planning of the HTO can be translated into reality with small deviations of the resulting joint angles. Within this study, the results of the individual steps are examined for errors and thus a critical evaluation of this new and promising method for performing patient-specific HTOs is presented.

Purpose Osteoporotic bone tissue appears to be an important risk factor for implant loosening, compromising the stability of surgical implants. However, it is unclear whether lumbar measured bone mineral density (BMD) is of any predictive value for stability of surgical implants at the pubic symphysis. This study examines the fixation strength of cortical screws in human cadaver specimens with different BMDs. Methods The lumbar BMD of ten human specimens was measured using quantitative computed tomography (qCT). A cut-off BMD was set at 120 mg Ca-Ha/mL, dividing the specimens into two groups. One cortical screw was drilled into each superior pubic ramus. The screw was withdrawn in an axial direction with a steady speed and considered failed when a force decrease was detected. Required force (N) and pull-out distance (mm) were constantly tracked. Results The median peak force of group 1 was 231.88 N and 228.08 N in group 2. While BMD values differed significantly (p p = 0.481). Conclusion Higher lumbar BMD did not result in significantly higher pull-out forces at the symphysis. The high proportion of cortical bone near the symphyseal joint allows an increased contact of pubic screws and could explain sufficient fixation. This condition is not reflected by a compromised lumbar BMD in a qCT scan. Therefore, site-specific BMD measurement could improve individual fracture management.

The use of three-dimensional (3D) printing for surgical applications is steadily increasing. Errors in the printed models can lead to complications, especially when the model is used for surgery planning or diagnostics. In patient care, the validation of printed models should therefore be performed routinely. However, there currently is no standard method to determine whether the printed model meets the necessary quality requirements. In this work, we present a method that not only finds surface deviations of a printed model, but also shows high accuracy zones of a potentially corrupted model, that are safe to be used for surgery planning. Our method was tested on printed patient bone models with acetabular fractures and was compared to two common methods in orthopedics, simple landmark registration as well as landmark plus subsequent iterative closest point registration. In order to find suitable parameters and to evaluate the performance of our method, 15 digital acetabular bone models were artificially deformed, imitating four typical 3D printing errors. A sensitivity of over 95% and a specificity of over 99% was observed in finding these surface deformations. Then, the method was applied to 32 printed models that had been re-digitized using a computed tomography scanner. It was found that only 25% of these printed models were free of significant deformations. However, focussing on two common implant locations, our method revealed that 72% of the models were within the acceptable error tolerance. In comparison, simple landmark registration resulted in a 9% acceptance rate and landmark registration followed by iterative closest point registration resulted in a 41% acceptance rate. This outcome shows that our method, named Similarity Subgroups Registration, allows clinicians to safely use partially corrupted 3D printed models for surgery planning. This improves efficiency and reduces time to treatment by avoiding reprints. The similarity subgroups registration is applicable in further clinical domains as well as non-medical applications that share the requirement of local high accuracy zones on the surface of a 3D model.

Introduction: Operative treatments of T-type acetabular fractures are challenging surgical procedures. Open reduction and internal fixation is the standard method for the operative management of these fractures, however this is associated with high blood loss, long hospital stay and longer rehabilitation. Anterior subcutaneous pelvic fixation (internal fixation = INFIX) and retrograde pubic screw fixation have shown promising results in minimally invasive treatment of pelvic ring fractures. For T-type acetabular fractures, however, minimally invasive treatment concepts are still rare. Therefore we performed a mechanical in vitro study to: - investigate the potential favorability of minimally invasive treatment options over the already established open anterior locking plate osteosynthesis of acetabular T-fractures regarding biomechanical stability and post-surgical stiffness;- explore the biomechanical feasibility of the INFIX;- assess its potential ability to reduce the anterior acetabular column. Hypothesis: A minimally invasive treatment of acetabular T-type fractures is biomechanically equivalent to an open anterior plate osteosynthesis. Methods: Twenty-four synthetic hemipelvis specimens with a T-type acetabular fracture were divided in four groups. A posterior column screw was placed in every pelvis of every group. The anterior column was fixed with: - anterior column screw;- anterior column screw incl. INFIX;- INFIX alone;- 14-hole angular stable locking plate (standard fixation method). Displacement of the anterior column was reduced in group 2 +3 using the INFIX. All specimens were cyclically loaded with 200 N until a maximum of 600 N. Movement/displacement of the fracture fragments were detected with a 3D-ultrasound measuring system. Displacement (mm) and Stiffness (N/mm) of the construction were analyzed. Results: Statistical assessment showed no significant differences between the four fixation types (p > 0.05). The 14-whole locking plate (group 4) displayed the overall highest stability with a displacement of 1.3 +/- 0.04 mm and stiffness of 76.3 +/- 2.4 N/mm. Anterior screw fixation (group 1) proved to be the minimally invasive fixation method with the least displacement and highest stiffness (1.5 +/- 0.2 mm, 68.3 +/- 6.8 N/mm). The combination of an INFIX and an anterior column screw (group 2), showed a mean stiffness of 62.1 +/- 6.0 N/mm and a mean displacement of 1.7 +/- 0.2 mm. INFIX only (group 3) presented a displacement of 1.6 +/- 0.1 mm and a stiffness of 64.5 +/- 4.5 N/mm. Discussion: Minimally invasive fixation techniques for T-type acetabular fractures show promising biomechanical stability in non- or slightly displaced fractures. Furthermore, INFIX could be a feasible tool for the reduction of the anterior acetabular column.

Percutaneous sacroiliac (SI) screw fixation is the standard operative treatment of traumatic disruptions to the posterior pelvic ring. The technique offers good outcomes and early postoperative mobilization, which is vital in elderly patients with fragility fractures of the pelvis. While a double-screw technique has been shown to provide optimal biomechanical stability compared to a single-screw construct, anatomic variations and patient-specific characteristics may prevent the safe insertion of two SI screws. We aimed to determine whether cement augmentation of a single SI screw would provide biomechanical stability comparable to that of the double-screw technique.Three sacroiliac screw osteosynthesis configurations were tested on 10 human cadaveric pelvis specimens: a single cannulated screw; two cannulated screws; and a single, cement-augmented cannulated screw. Displacement and stiffness of the anterior and posterior pelvic ring after fixation with each technique were measured under axial load. Results where compared using linear regression and paired t-tests.A single uncemented screw offered significantly worse stability in the anterior pelvis compared to a double-screw technique (P 0.05) and to a single cement-augmented screw technique (P 0.05). There was no significant difference in anterior pelvic ring stability between the single cement-augmented screw technique and the double-screw technique (P 0.05). There was no significant difference in the stability of the posterior pelvic ring between the three techniques (P 0.05).A single cement-augmented cannulated sacroiliac screw provides biomechanical stability similar to that of a non-augmented double-screw technique in the treatment of posterior pelvic ring fractures.

Background Elderly patients suffering from hip fractures are usually not able to fulfil postoperative weight-bearing restrictions. Therefore, the operative fixation construct has to be as stable as possible. Aim of the present study was to determine (1) whether a therapeutic advantage could be achieved when using hip arthroplasty to treat acetabular fractures in geriatric patients; (2) whether an acetabular revision cup would be suitable for achieving fast postoperative mobilization and full weight-bearing; and (3) when a treatment with an uncemented hip revision cup for the primary fixation of osteoporotic acetabular fractures in geriatric patients is indicated. Materials and methods The functional outcome of THA using a reconstruction cup for an acetabular fracture was evaluated in ten patients using standardized scoring instruments. In addition, an analysis of the preexisting literature referring to total hip replacement in geriatric acetabular fractures was conducted and an algorithm for standardizing the treatment approach for geriatric patients with acetabular fractures was developed. Results The mean EQ-5D-3L quality of life score 0.7. The mean VAS Score was 58.2. The average Barthel Index was 80.0 points [range: 0–100]. The mean HHS was 72.0 points, while the MHH Score yielded an average of 63.4 points. The average AP Score was 7.5. The literature analysis showed that total hip arthroplasty could be a feasible option for geriatric acetabular fractures. Conclusion Primary hip arthroplasty using uncemented revision cup fixed with angular stable screws showed good results and is a feasible treatment option of acetabular fractures in geriatric patients. The approach is especially beneficial in patients with poor bone stock and allows postoperative full weight-bearing. The presented treatment algorithm could be a useful tool for identifying the most appropriate treatment option. Level of evidence IIb.

Background The definite treatment of pelvic C fractures presents a widely discussed issue and undergoes continuous evolution. While the stabilization of the posterior ring has been studied extensively, the fixation of the anterior pelvic ring continuous to be rarely investigated. The importance of the simultaneous stabilization however lays in the earlier mobilization and prevention of long-term damage to the pelvis. Therefore we investigated four combinations of minimally invasive fixation techniques for unstable type C1-3 pelvic injuries and aimed to answer the following research questions: (1) what combination of fixation methods yields the highest stiffness and the least displacement? (2) Is the combination of a single sacroiliac screw (SI-screw) with a transiliac internal fixator (TIFI) a reasonable alternative to two SI-screws? (3) Is a modified unilateral anterior fixation comparable to a retrograde transpubic screw? Hypothesis Minimally invasive fixation techniques provide sufficient biomechanical stability for type C pelvic fractures. Methods Thirty synthetic full pelvises were divided into 5 groups, of which 4 groups were assigned a different osteosynthesis method and one was an intact pelvis used as reference (group 1: internal fixator + 2 sacroiliac screws, group 2: internal fixator + transiliac internal fixator + 1 sacroiliac screw, group 3: retrograde transpubic screw + 2 sacroiliac screws, group 4: retrograde transpubic screw + transiliac internal fixator + 1 sacroiliac screw). The pelvises underwent a protocol of cyclic loading between 100 N and 200 N, during which they were subjected to compression loads while the position of the fracture fragments was measured every 30 milliseconds. Displacement and stiffness were calculated for statistical analysis. Results The minimally invasive fixation methods investigated in this study all provide sufficient biomechanical stability without one method being superior to the others (p [anterior displacement] = 0.61 and p [posterior displacement] = 0.88). Group 3 was allowed the least displacement (1.8 ± 0.2 mm for anterior and posterior fracture) for the treatment of a C1.3 fracture. The other fixation methods displayed the following dislocations (mm) of the anterior pelvic ring: group 1: 1.9 ± 0.3, group 2: 2.1 ± 0.4, group 4: 2.0 ± 0.5. Posteriorly, the displacements (mm) were the following: group 1: 1.8 ± 0.6, group 2: 1.9 ± 0.2, group 4: 2.0 ± 0.5. Discussion The minimally invasive fixation methods investigated in this study all provide sufficient biomechanical stability without one method being superior to the others since differences were not significant regarding anterior and posterior displacements. Even if not significantly, we could reveal that out of all the methods tested the combination of 2 SI-screws with a retrograde transpubic screw (group 3) displayed the least displacement and highest stiffness. These techniques could therefore potentially improve patient's clinical outcome by reducing the surgical invasiveness and procedure time while providing sufficient biomechanical stability. Level of evidence III, comparative in vitro study.

Background Elderly patients suffering from hip fractures are usually not able to fulfill postoperative weight-bearing restrictions. Therefore, the operative fixation construct has to be as stable as possible. Aim of the present study was to determine: (1) whether a therapeutic advantage could be achieved when using hip arthroplasty to treat acetabular fractures in geriatric patients; (2) whether an acetabular revision cup would be suitable for achieving fast postoperative mobilization and full weight-bearing; and (3) when a treatment with an uncemented hip revision cup for the primary fixation of osteoporotic acetabular fractures in geriatric patients is indicated. Materials and methods The functional outcome of THA using a reconstruction cup for an acetabular fracture was evaluated in ten patients using standardized scoring instruments. In addition, an analysis of the preexisting literature referring to total hip replacement in geriatric acetabular fractures was conducted and an algorithm for standardizing the treatment approach for geriatric patients with acetabular fractures was developed. Results The mean EQ-5D-3L quality of life score 0.7. The mean VAS score was 58.2. The average Barthel Index was 80.0 points [range: 0–100]. The mean HHS was 72.0 points, while the MHH Score yielded an average of 63.4 points. The average AP Score was 7.5. The literature analysis showed that total hip arthroplasty could be a feasible option for geriatric acetabular fractures. Conclusion Primary hip arthroplasty using uncemented revision cup fixed with angular stable screws showed good results and is a feasible treatment option of acetabular fractures in geriatric patients. The approach is especially beneficial in patients with poor bone stock and allows postoperative full weight-bearing. The presented treatment algorithm could be a useful tool for identifying the most appropriate treatment option. Level of evidence IIb.

Background The definite treatment of pelvic C-fractures presents a widely discussed issue and undergoes continuous evolution. While the stabilization of the posterior ring has been studied extensively, the fixation of the anterior pelvic ring continuous to be rarely investigated. The importance of the simultaneous stabilization however lays in the earlier mobilization and prevention of long-term damage to the pelvis. Therefore we investigated four combinations of minimally invasive fixation techniques for unstable type C1-3 pelvic injuries and aimed to answer the following research questions: (1) what combination of fixation methods yields the highest stiffness and the least displacement? (2) Is the combination of a single sacroiliac screw (SI-screw) with a transiliac internal fixator (TIFI) a reasonable alternative to two SI-screws? (3) Is a modified unilateral anterior fixation comparable to a retrograde transpubic screw? Hypothesis Minimally invasive fixation techniques provide sufficient biomechanical stability for type C pelvic fractures. Methods Thirty synthetic full pelvises were divided into 5 groups, of which 4 groups were assigned a different osteosynthesis method and one was an intact pelvis used as reference (group 1: internal fixator + 2 sacroiliac screws, group 2: internal fixator + transiliac internal fixator + 1 sacroiliac screw, group 3: retrograde transpubic screw + 2 sacroiliac screws, group 4: retrograde transpubic screw + transiliac internal fixator + 1 sacroiliac screw). The pelvises underwent a protocol of cyclic loading between 100 N and 200 N, during which they were subjected to compression loads while the position of the fracture fragments was measured every 30 milliseconds. Displacement and stiffness were calculated for statistical analysis. Results The minimally invasive fixation methods investigated in this study all provide sufficient biomechanical stability without one method being superior to the others (p [anterior displacement] = 0.61 and p [posterior displacement] = 0.88). Group 3 was allowed the least displacement (1.8 ± 0.2 mm for anterior and posterior fracture) for the treatment of a C1.3 fracture. The other fixation methods displayed the following dislocations (mm) of the anterior pelvic ring: group 1: 1.9 ± 0.3, group 2: 2.1 ± 0.4, group 4: 2.0 ± 0.5. Posteriorly, the displacements (mm) were the following: group 1: 1.8 ± 0.6, group 2: 1.9 ± 0.2, group 4: 2.0 ± 0.5. Discussion The minimally invasive fixation methods investigated in this study all provide sufficient biomechanical stability without one method being superior to the others since differences were not significant regarding anterior and posterior displacements. Even if not significantly, we could reveal that out of all the methods tested the combination of 2 SI-screws with a retrograde transpubic screw (group 3) displayed the least displacement and highest stiffness. These techniques could therefore potentially improve patient's clinical outcome by reducing the surgical invasiveness and procedure time while providing sufficient biomechanical stability. Level of evidence III, comparative in vitro study.

Introduction Operative treatments of T-type acetabular fractures are challenging surgical procedures. Open reduction and internal fixation is the standard method for the operative management of these fractures, however this is associated with high blood loss, long hospital stay and longer rehabilitation. Anterior subcutaneous pelvic fixation (internal fixation = INFIX) and retrograde pubic screw fixation have shown promising results in minimally invasive treatment of pelvic ring fractures. For T-type acetabular fractures, however, minimally invasive treatment concepts are still rare. Therefore we performed a mechanical in vitro study to: (1) investigate the potential favorability of minimally invasive treatment options over the already established open anterior locking plate osteosynthesis of acetabular T-fractures regarding biomechanical stability and post-surgical stiffness, (2) explore the biomechanical feasibility of the INFIX, (3) assess its potential ability to reduce the anterior acetabular column. Hypothesis A minimally invasive treatment of acetabular T- type fractures is biomechanically equivalent to an open anterior plate osteosynthesis. Methods Twenty-four synthetic hemipelvis specimens with a T-type acetabular fracture were divided in four groups. A posterior column screw was placed in every pelvis of every group. The anterior column was fixed with (1) anterior column screw, (2) anterior column screw including INFIX, (3) INFIX alone, (4) 14-hole angular stable locking plate (standard fixation method). Displacement of the anterior column was reduced in group 2 + 3 using the INFIX. All specimens were cyclically loaded with 200 N until a maximum of 600 N. Movement/displacement of the fracture fragments were detected with a 3D-ultrasound measuring system. Displacement (mm) and stiffness (N/mm) of the construction were analyzed. Results Statistical assessment showed no significant differences between the four fixation types (p > 0.05). The 14-whole locking plate (group 4) displayed the overall highest stability with a displacement of 1.3 ± 0.04 mm and stiffness of 76.3 ± 2.4 N/mm. Anterior screw fixation (group 1) proved to be the minimally invasive fixation method with the least displacement and highest stiffness (1.5 ± 0.2 mm, 68.3 ± 6.8 N/mm). The combination of an INFIX and an anterior column screw (group 2), showed a mean stiffness of 62.1 ± 6.0 N/mm and a mean displacement of 1.7 ± 0.2 mm. INFIX only (group 3) presented a displacement of 1.6 ± 0.1 mm and a stiffness of 64.5 ± 4.5 N/mm. Discussion Minimally invasive fixation techniques for T-type acetabular fractures show promising biomechanical stability in non- or slightly displaced fractures. Furthermore, INFIX could be a feasible tool for the reduction of the anterior acetabular column. Level of evidence Level III case control prospective experimental study.