NextLens-The Next Generation of Surgical Navigation: Proof of Concept of an Augmented Reality System for Surgical Navigation.

Objective The aim of this work was the development of an augmented reality system including the functionality of conventional surgical navigation systems. Methods An application software for the Augmented Reality System HoloLens 2 from Microsoft was developed. It detects the position of the patient as well as position of surgical instruments in real time and displays it within the two-dimensional (2D) magnetic resonance imaging or computed tomography (CT) images. The surgical pointer instrument, including a pattern that is recognized by the HoloLens 2 sensors, was created with three-dimensional (3D) printing. The technical concept was demonstrated at a cadaver skull to identify anatomical landmarks. Results With the help of the HoloLens 2 and its sensors, the real-time position of the surgical pointer instrument could be shown. The position of the 3D-printed pointer with colored pattern could be recognized within 2D-CT images when stationary and in motion at a cadaver skull. Feasibility could be demonstrated for the clinical application of transsphenoidal pituitary surgery. Conclusion The HoloLens 2 has a high potential for use as a surgical navigation system. With subsequent studies, a further accuracy evaluation will be performed receiving valid data for comparison with conventional surgical navigation systems. In addition to transsphenoidal pituitary surgery, it could be also applied for other surgical disciplines.

Analysis of the Technical Accuracy of a Patient-Specific Stereotaxy Platform for Brain Biopsy.

The use of stereotactic frames is a common practice in neurosurgical interventions such as brain biopsy and deep brain stimulation. However, conventional stereotactic frames have been shown to require modification and adaptation regarding patient and surgeon comfort as well as the increasing demand for individualized medical treatment. To meet these requirements for carrying out state-of-the-art neurosurgery, a 3D print-based, patient-specific stereotactic system was developed and examined for technical accuracy. Sixteen patient-specific frames, each with two target points, were additively manufactured from PA12 using the Multi Jet Fusion process. The 32 target points aim to maximize the variability of biopsy targets and depths for tissue sample retrieval in the brain. Following manufacturing, the frames were measured three-dimensionally using an optical scanner. The frames underwent an autoclave sterilization process prior to rescanning. The scan-generated models were compared with the planned CAD models and the deviation of the planned target points in the XY-plane, Z-direction and in the resulting direction were determined. Significantly lower (p < 0.01) deviations were observed when comparing CAD vs. print and print vs. sterile in the Z-direction (0.17 mm and 0.06 mm, respectively) than in the XY-plane (0.46 mm and 0.16 mm, respectively). The resulting target point deviation (0.51 mm) and the XY-plane (0.46 mm) are significantly higher (p < 0.01) in the CAD vs. print comparison than in the print vs. sterile comparison (0.18 mm and 0.16 mm, respectively). On average, the results from the 32 target positions examined exceeded the clinically required accuracy for a brain biopsy (2 mm) by more than four times. The patient-specific stereotaxic frames meet the requirements of modern neurosurgical navigation and make no compromises when it comes to accuracy. In addition, the material is suitable for autoclave sterilization due to resistance to distortion.

Application accuracy of a frameless optical neuronavigation system as a guide for craniotomies in dogs.

BACKGROUND: Optical neuronavigation systems using infrared light to create a virtual reality image of the brain allow the surgeon to track instruments in real time. Due to the high vulnerability of the brain, neurosurgical interventions must be performed with a high precision. The aim of the experimental cadaveric study was to determine the application accuracy of a frameless optical neuronavigation system as guide for craniotomies by determining the target point deviation of predefined target points at the skull surface in the area of access to the cerebrum, cerebellum and the pituitary fossa. On each of the five canine cadaver heads ten target points were marked in a preoperative computed tomography (CT) scan. These target points were found on the cadaver skulls using the optical neuronavigation system. Then a small drill hole (1.5 mm) was drilled at these points. Subsequently, another CT scan was made. Both CT data sets were fused into the neuronavigation software, and the actual target point coordinates were identified. The target point deviation was determined as the difference between the planned and drilled target point coordinates. The calculated deviation was compared between two observers. RESULTS: The analysis of the target point accuracies of all dogs in both observers taken together showed a median target point deviation of 1.57 mm (range: 0.42 to 5.14 mm). No significant differences were found between the observers or the different areas of target regions. CONCLUSION: The application accuracy of the described system is similar to the accuracy of other optical neuronavigation systems previously described in veterinary medicine, in which mean values of 1.79 to 4.3 mm and median target point deviations of 0.79 to 3.53 mm were determined.

Case Report: Clinical Use of a Patient-Individual Magnetic Resonance Imaging-Based Stereotactic Navigation Device for Brain Biopsies in Three Dogs.

Three-dimensional (3D) printing techniques for patient-individual medicine has found its way into veterinary neurosurgery. Because of the high accuracy of 3D printed specific neurosurgical navigation devices, it seems to be a safe and reliable option to use patient-individual constructions for sampling brain tissue. Due to the complexity and vulnerability of the brain a particularly precise and safe procedure is required. In a recent cadaver study a better accuracy for the 3D printed MRI-based patient individual stereotactic brain biopsy device for dogs is determined compared to the accuracies of other biopsy systems which are currently used in veterinary medicine. This case report describes the clinical use of this 3D printed MRI-based patient individual brain biopsy device for brain sampling in three dogs. The system was characterized by a simple handling. Furthermore, it was an effective and reliable tool to gain diagnostic brain biopsy samples in dogs with no significant side effects.

Significance of nutritional status in the development of periprosthetic infections : A retrospective analysis of 194 patients.

BACKGROUND: Malnutrition caused by protein and vitamin deficiencies is a significant negative prognostic factor in surgical wound healing disorders and infections. Particularly in elective surgery, preoperative compensation of deficiencies is advisable to avoid negative postoperative consequences. This study examined the nutritional and protein balance of patients with periprosthetic hip and knee joint infections. MATERIAL AND METHODS: Patients with periprosthetic hip or knee joint infections constituted the study group (SG). Control group I (CG I) included patients with primary implants and CG II included patients who required revision surgery because of aseptic loosening. Relevant nutritional and protein parameters were determined via analysis of peripheral venous blood samples. In addition, a questionnaire was used to evaluate the nutritional and eating patterns of all patients. The nutritional risk screening (NRS) 2002 score and body mass index (BMI) were also calculated for all participants. RESULTS: Differences were found in the albumin level (SG: 36.23 ± 7.34, CG I: 44.37 ± 3.32, p < 0.001, CG II: 44.06 ± 4.24, p < 0.001) and total protein in serum (SG: 65.42 ± 8.66, CG I: 70.80 ± 5.33, p = 0.004, CG II: 71.22 ± 5.21, p = 0.004). The number of patients with lowered albumin levels (SG 19/61, CG I 1/78, CG II 2/55) and total protein in serum (SG: 12/61, CG I 5/78, CG II 2/55) also showed considerable variation. The number of patients with a NRS 2002 score ≥3 differed significantly between SG and both CGs (SG: 5/61, CG I 1/78, CG II 0/55); however, these differences could not be confirmed using BMI. CONCLUSION: As expected, lowered albumin and total protein levels were observed in PJI due to the acute phase reaction. The NRS can be performed to exclude nutritional deficiency, which cannot be excluded based on BMI. In cases of periprosthetic joint infection it is reasonable to compensate the nutritional deficiency with dietary supplements.

The impact of polyethylene abrasion on the occurrence of periprosthetic proximal femoral fractures in patients with total hip arthroplasty.

INTRODUCTION: In addition to abrasion-induced osteolysis and ensuing instabilities, the polyethylene (PE) abrasion of total hip arthroplasty (THA) inlays can also cause gait instability due to the decentralization of the hip joint. The current literature yields, as yet, insufficient findings whether these two factors are linked directly or indirectly to a higher risk for periprosthetic proximal femoral fractures (PPFF). The aim of our retrospective evaluation is to analyse the impact of PE abrasion on the pathology of PPFF in patients with THA. MATERIAL AND METHODS: The retrospective evaluation comprises all PPFF in patients with THA in the period from 01/2010 up to 12/2016. The study group (SG) included 66 cases (n = 66). The control group (CG) was comprised of patients with asymptomatic THA (n = 66), who were treated by our outpatient department including routine check-ups and X-ray examinations. We used the matched-pair methodology to scale the period of postsurgical care of the CG to the lifetime of the implant up to PPFF in the SG. We included epidemiologic data, radiological femoral head decentralization, osteolysis (Gruen classification), instabilities, acetabular cup position, and implant properties in our analysis. For the SG, we also included intra-operative signs of abrasion. FINDINGS: The SG showed significantly higher numbers of decentralized THA as signs of inlay erosion with 73% compared to only 41% in the CG (p > 0.001). The SG showed 1 ± 0.68 mm hip joint decentralization as to 0.5 ± 0.59 mm in the CG (p = 0.004). We found significantly more cases of osteolysis in the SG (n = 25) than in the CG (n = 13) (p = 0.003). We found no notable differences in acetabular cup inclination or anteversion as well as cup size. However, differences were significant in femoral head size (SG 32 ± 2.3 mm, CG 36 ± 2.4 mm; p = 0.042) and head material. We found more widespread use of metal femoral heads in the SG than in the CG (SG 1:1, CG 1:21; p = 0.001). CONCLUSION: PPFF patients showed significantly higher rates of inlay erosion, resulting in femoral head decentralization and osteolysis. The higher rate of fracture is likely caused by the increasing instability of the implant fixation due to abrasion-induced osteolysis and the associated degradation of bone quality. It is conceivable that the abrasion and decentralization of the THA can also lead to gait instability, and thus, a higher proneness to falls. Gait instability can also be aggravated by increased granulation tissue and effusion due to the inlay abrasion. Although this cannot be substantiated by the investigation. In patients with decentralization of the THA and osteolysis, a radiological follow-up should be performed, and in case of gait instability (femoral head and) inlay replacements should be considered.

Knee arthrodesis as last resort for persistent knee joint infections : Comparison of extramedullary and intramedullary treatment.

BACKGROUND: Knee joint arthrodesis is an established treatment for periprosthetic infections (PPI) providing stability and pain relief. In this study the outcome after arthrodesis of the knee joint for persistent infections was compared and evaluated depending on the surgical procedure (intramedullary vs. extramedullary). MATERIAL AND METHODS: In a retrospective case analysis, all patients who underwent knee joint arthrodesis between 1 January 2010 and 31 December 2016 were identified and divided into two groups: IMA and EMA. All patients were examined clinically and radiologically and the patient files were evaluated. In addition, the FIM score, the LEFS, the WHOQOL-BREF and NRS were evaluated. RESULTS: The median LEFS score for the IMA group was 26 points and in the EMA group 2 points (p = 0.03). The IMA patients showed a median pain scale at rest of 0 and during exercise of 2. The EMA group recorded a pain scale of 3 at rest and 5 during exercise (p = 0.28 at rest; p = 0.43 during exercise). In the IMA group the median postsurgical leg length difference was -2.0 cm and -2.5 cm in the EMA group (p = 0.31). At the end of the follow-up examinations, the FIM score of patients in the IMA group was 74.5 points and 22 points in the EMA group (p = 0.07). CONCLUSION: The study showed that no arthrodesis procedure is obviously superior with respect to the postoperative outcome. The IMA combines advantages especially in the early phase after surgery in terms of function as well as patient comfort and is therefore currently the procedure of choice. The attending physician should be familiar with the advantages and disadvantages of the various procedures in order to be able to make an individual decision and thus maximize the chance of treatment success.

Results after surgical treatment of periprosthetic proximal femoral fractures. Osteosynthesis with prosthesis preservation vs. prosthesis change.

Background: Periprosthetic fractures (PPF) of the femur close to the hip joint have serious consequences for most geriatric affected patients. In principle, apart from the highly uncommon conservative therapy, there are two therapeutic options. On the one hand, the prosthesis-preserving treatment by means of osteosynthesis using plates and/or cerclages in general is available. On the other hand, a (partial) change of the prosthesis with optionally additive osteosynthesis or a proximal femoral replacement can be performed because of prosthesis loosening or non-reconstructable comminuted fractures as well as most cemented stem variations. The aim of this retrospective study is the analysis of periprosthetic proximal femoral fractures in the presence of a total hip arthroplasty (THA). The outcome of the operated patients is to be investigated depending on the type of care (osteosynthesis with prosthesis preservation vs. prosthesis change). Material and methods: In a retrospective case analysis, 80 patients with THA and PPF were included. They were divided into two groups. Group I represents the osteosynthetic treatment to preserve the implanted THA (n=42). Group II (n=38) includes those patients who were treated by a change of their endoprosthesis with or without additional osteosynthesis. Specifics of all patients, like gender, age at fracture, interval between fracture and implantation, length of in-patient stay, body mass index, osteoporosis, corticomedullary index and complications such as infections, re-fracture, loosening, material failure or other complications, were recorded and compared. Furthermore, the patients were re-examined by a questionnaire and the score according to Merle d'Aubigné and Postel. Results: In group I the mean follow-up time was 48.5±23 months (4 years) whereas group II amounted 32.5±24.5 months (2.7 years) (p=0.029). Besides, there were significant differences in age (81± 11 years vs. 76±10 years, p=0.047) and length of in-patient stay (14.5±8.6 days vs. 18.0±16.7 days, p=0.014). According to the score of Merle d'Aubigné and Postel, there were significantly better values for the pain in group II with comparable values for mobility and walking ability. Conclusion: The treatment of periprosthetic proximal fractures of the femur is dependent on the classification (Vancouver and Johannsen) and in particular on the prosthetic anchoring as well as the extent of the comminution zone. Older patients and patients with osteoporosis are more frequently treated with an endoprosthesis revision. Patients, who have been treated with an osteosynthesis for preserving their endoprosthesis, showed a shorter length of in-patient stay and fewer complications than people with replacement surgery. In contrast to that, patients with prosthesis revision had better outcomes concerning the score of Merle d'Aubigné and Postel.

Accuracy of a magnetic resonance imaging-based 3D printed stereotactic brain biopsy device in dogs.

BACKGROUND: Brain biopsy of intracranial lesions is often necessary to determine specific therapy. The cost of the currently used stereotactic rigid frame and optical tracking systems for brain biopsy in dogs is often prohibitive or accuracy is not sufficient for all types of lesion. OBJECTIVES: To evaluate the application accuracy of an inexpensive magnetic resonance imaging-based personalized, 3D printed brain biopsy device. ANIMALS: Twenty-two dog heads from cadavers were separated into 2 groups according to body weight (<15 kg, >20 kg). METHODS: Experimental study. Two target points in each cadaver head were used (target point 1: caudate nucleus, target point 2: piriform lobe). Comparison between groups was performed using the independent Student's t test or the nonparametric Mann-Whitney U Test. RESULTS: The total median target point deviation was 0.83 mm (range 0.09-2.76 mm). The separate median target point deviations for target points 1 and 2 in all dogs were 0.57 mm (range: 0.09-1.25 mm) and 0.85 mm (range: 0.14-2.76 mm), respectively. CONCLUSION AND CLINICAL IMPORTANCE: This magnetic resonance imaging-based 3D printed stereotactic brain biopsy device achieved an application accuracy that was better than the accuracy of most brain biopsy systems that are currently used in veterinary medicine. The device can be applied to every size and shape of skull and allows precise positioning of brain biopsy needles in dogs.

A concept for a 3D-printed patient-specific stereotaxy platform for brain biopsy -a canine cadaver study.

The treatment of intracranial lesions requires a precise diagnosis with subsequent identification of an adequate therapeutic approach. Stereotactic tumor biopsy may be considered the safest neurosurgical procedure in terms of anticipated results and potential surgical complications. The aim of the present paper was to demonstrate a new method of stereotactic biopsy, based on a patient-specific 3D printed platform in dogs. The system was tested on two canine cadavers, a small (Shih Tzu) and a large (Labrador) breed. Imaginary biopsy targets were defined in a superficial (caudate nucleus) and a deep (piriform lobe) position. Based on 3 Tesla MRI, individualized stereotactic platforms were designed using a semi-automatic approach, and manufactured additively using ABS M30. A pre- and intra-operative CT was performed to compare the planned vs. the realized needle position for precision analyses of the procedure. The target points varied with a precision between 0.09 mm and 0.48 mm. Manufacturing time required 480 to 700 min per platform. The presented patient-specific stereotactic system seems a suitable instrument for application in small animal neurosurgery. In particular, the implementation of relevant stereotactic data may help performing the procedure in rapid sequence and with higher precision than currently-used systems. Required adjustments and adaptions to the respective anatomical conditions are omitted and make the procedure reliable and safe.

The impact of capsular repair on the risk for dislocation after revision total hip arthroplasty - a retrospective cohort-study of 259 cases.

BACKGROUND: Dislocation following total hip arthroplasty has to date not been resolved satisfactorily. Previous work has shown that using a less-invasive adaption of Bauer's lateral transgluteal approach with capsular repair significantly reduces dislocation rates in primary total hip arthroplasty. The aim of this retrospective cohort study was to assess whether this approach also helps to reduce the dislocation rate in revision total hip arthroplasty. METHODS: We analyzed revision total hip arthroplasty cases performed between 10/2005 and 12/2013 in our department, classifying capsular repair cases as study group and capsular resection cases as control group. The WOMAC score, the dislocations and the revisions were observed. RESULTS: A total of 259 cases were included, 100 in the study group and 159 in the control group. In the 12-month follow-up, dislocation rates were significantly lower in the study group (3%, n = 3) compared to the control group (21.4%, n = 34; p = 0.001). Overall follow-up periods were 49 and 79 months, revision frequencies were 10 and 29%, pain improvements were 5.5 compared to 4.4 and the WOMAC global scores averaged 2.0 ± 2.1 and 2.9 ± 2.6 for the study group and the control group, respectively. CONCLUSION: The modified, less-invasive, lateral transgluteal approach with capsular repair was accompanied by an 86% reduction in dislocation rates when compared to the conventional technique with capsular resection via the anterolateral Watson-Jones-approach. Capsular repair is possible in about 60% of the revision total hip arthroplasty cases, may be considered as beneficial to avoid dislocation and can therefore be recommended.

The significance of the vitamin D metabolism in the development of periprosthetic infections after THA and TKA: a prospective matched-pair analysis of 240 patients.

BACKGROUND: The importance of the vitamin D homeostasis in infections is already known. However, its significance in periprosthetic infections (PPIs) after total hip arthroplasty and total knee arthroplasty is largely unexplored. The aim of the study is to precisely analyze the vitamin D balance in patients with PPIs after total hip arthroplasty and total knee arthroplasty. Here, cases with primary endoprosthesis implants and aseptic loosening are used as comparison groups. MATERIALS AND METHODS: In this prospective matched-pair analysis, patients with PPI at the hip and knee joints were included in the study group (SG). The control groups (CGs) consisted of patients with primary implants (CG I) and who underwent replacement surgery due to aseptic loosening (CG II). In addition to 25 OH vitamin D3 and calcium, bone mineral and protein parameters were determined. An osteoporosis-specific questionnaire was collected. RESULTS: There are no significant differences in the 25 OH-vitamin D levels between the SG (17.9±8.9) and both CGs (CG I: 16.8±6.90; CG II: 19.7±7.90). However, compared with the SG, significantly higher levels of calcium (Ca) and bone-specific alkaline phosphatase were found in both CGs in comparison with the SG. Significantly lower values concerning the protein balance in PPI were conspicuous. Acute PPI showed a significant reduction in 25 OH vitamin D3 compared with chronic infections (8.3±5.98 vs 21.6±8.40, P=0.002). Calcium and protein balance were also significantly reduced in acute PPIs. CONCLUSION: Acute PPIs of the hip and knee joints show a significantly reduced calcium and 25 OH vitamin D3 levels as well as lowered proteins (albumin and total protein) compared with chronic infections as well as primary endoprostheses and aseptic replacement operations. Substitution of vitamin D3 and calcium with simultaneous adaptation of the protein balance is recommended in all PPIs, especially in the acute PPI.

Novel concept of a modular hip implant could contribute to less implant failure in THA: a hypothesis.

BACKGROUND: The modularity in total hip arthroplasty (THA) allows orthopaedic surgeons for an exact reconstruction of hip biomechanical parameters especially in revision and tumor arthroplasty. Modular structured femoral stems using taper junctions showed increased implant breakage in the recent past. PRESENTATION OF THE HYPOTHESIS: We hypothesize that a novel modular stem-neck-interface leads to less implant breakage compared to conventional femoral stems. TESTING OF THE HYPOTHESIS: For this purpose, a novel modular femoral stem for THA was to design and manufacture. Therefore, three different variants of interface mechanisms were developed that enable a simple connection between the stem and the neck modules and allow for intra-operatively adjustment. Three prototypes A, B and C were manufactured and subsequently dynamic fatigue (ISO 7206-6) and body donor tested. IMPLICATION OF THE HYPOTHESIS: Modularity in THA is mainly applied in THA as well as in revision and tumor arthroplasty. Modular implants are barely used because of the high risk of breakage. Another risks in this context are taper fretting, corrosion and disconnection. With the novel design, it should be possible to detach the stem and neck module intra-operatively to adapt the anatomical situation. The novel coupling mechanism of the rotating interface seems to be the most suitable for a secure stem-neck connection and is characterized by good intraoperative handling.

Subthalamic nucleus volumes are highly consistent but decrease age-dependently-a combined magnetic resonance imaging and stereology approach in humans.

The subthalamic nucleus (STN) is a main target structure of deep brain stimulation (DBS) in idiopathic Parkinson's disease. Nevertheless, there is an ongoing discussion regarding human STN volumes and neuron count, which could potentially have an impact on STN-DBS. Moreover, a suspected functional subdivision forms the basis of the tripartite hypothesis, which has not yet been morphologically substantiated. In this study, it was aimed to investigate the human STN by means of combined magnetic resonance imaging (MRI) and stereology. STN volumes were obtained from 14 individuals (ranging from 65 to 96 years, 25 hemispheres) in 3 T MRI and in luxol-stained histology slices. Neuron number and cell densities were investigated stereologically over the entire STN and in pre-defined subregions in anti-human neuronal protein HuC/D-stained slices. STN volumes measured with MRI were smaller than in stereology but appeared to be highly consistent, measuring on average 99 ± 6 mm3 (MRI) and 132 ± 20 mm3 (stereology). The neuron count was 431,088 ± 72,172. Both STN volumes and cell count decreased age-dependently. Neuron density was different for the dorsal, medial and ventral subregion with significantly higher values ventrally than dorsally. Small variations in STN volumes in both MRI and stereology contradict previous findings of large variations in STN size. Age-dependent decreases in STN volumes and neuron numbers might influence the efficacy of STN-DBS in a geriatric population. Though the study is limited in sample size, site-dependent differences for the STN subregions form a morphological basis for the tripartite theory. Hum Brain Mapp 38:909-922, 2017. © 2016 Wiley Periodicals, Inc.

Load and failure behavior of human muscle samples in the context of proximal femur replacement.

BACKGROUND: To ensure adequate function after orthopedic tumor reconstruction, it is important to reattach the remaining soft tissue to the implant. This study aimed at obtaining mechanical properties of textile muscle-implant and muscle-bone connections in a preliminary test. METHODS: Two groups of soft-tissue attachment were mechanically tested and compared: Native bone-muscle samples obtained from human femora and muscles attached to a prosthetic implant by means of Trevira® attachment tubes. Additionally, muscle samples were tested with muscle fibers aligned parallel and perpendicular to the tension load. A uniaxial load was exerted upon all samples. RESULTS: Failure loads of 26.7 ± 8.8 N were observed for the native bone-muscle group and of 18.1 ± 9.9 N for the Trevira® group. Elongations of 94.8 ± 36.2 % were observed for the native bone-muscle group and 79.3 ± 51.8 % for the Trevira® group. The location of failure was mainly observed in the central area of the muscle fibers. Muscle fibers with parallel fiber orientation (47.6 ± 11.5 N) yielded higher tensile strength than those with perpendicular fiber orientation (14.8 ± 4.1 N). CONCLUSIONS: Our experiments showed that higher forces were transmitted in the origin and insertion areas than in areas of flat soft tissue reconstruction using attachment tubes. The data indicate that the tested material allows reattaching muscles, but without reinforcing the insertion site. Therefore, attachment tubes with region-dependent and potentially anisotropic material behavior might be advantageous to optimize muscle-bone load transmission after surgery, which may allow lower complication rates and shorter physical recovery.