Screw Angulation Research Articles

Computer modeling and validation testing for glenoid component rotation and optimal glenoid screw angles for reverse shoulder arthroplasty in an Asian population.

Good initial fixation of glenoid component for reverse total shoulder arthroplasty (RTSA) relies on component placement and screw purchase in the scapula bone. This is especially difficult in an Asian population with small glenoid geometry. Optimal glenoid component roll angle and screw angulation to achieve the longest screws for best fixation has not been defined in the current literature. Computer 3D modelling of 133 scapulas with RTSA performed were analyzed to determine patient specific optimal glenoid roll angle (GRA) for the longest bi-cortical screws attainable. The cranial-caudal angle (CCA), anterior-posterior angle (APA) and lengths for the superior and inferior screws were measured. Validation testing using calculated average (CA) angles and rounded average (RA) angles to the nearest 5 degree were recomputed for each case to determine the bi-cortical screw lengths achievable. The CA and RA screw lengths were compared against patient specific modelling using paired-sample t-tests. Average GRA was - 1.6°, almost perpendicular to the long axis of the glenoid and achieves an average bi-cortical screw length of 51.3mm and 45.5mm for the superior and inferior screws respectively. The CCA and APA were 9.1° cranial and 6.5° posterior for the superior screw and screw angulation of 11.2° caudal and 0.7° anterior for the inferior screw. Validation testing shows statistically shorter screw lengths in the CA and RA models compared to patient specific modelling (p < 0.01). Validation testing with average angles for GRA, CCA and APA demonstrates strong patient heterogeneity and anatomical variation. Despite this, screw lengths attainable in the RA group were > 38mm with good safety profile. Surgeons may consider the additional use of navigation-assisted, or 3D printed patient specific instrumentation to optimize baseplate and screw configuration for RTSA.

Tibial fracture associated with use of Arthrex self-tapping screws during tibial plateau leveling osteotomy in dogs and development of transcortical tibial fracture.

Medical records for dogs treated with tibial plateau leveling osteotomy (TPLO) using Arthrex 3.5 mm self-tapping screws (STS) were evaluated to determine the incidence rate of transcortical tibial fractures (TCTF) and development of complications. Retrospective case report. A total of 78 dogs. Dogs that underwent a TPLO performed from March 2022 to August 2023 were reviewed. Postoperative TPLO radiographs were examined for evidence of a TCTF with Arthrex 3.5 mm STS. Records were reviewed for complications up to 14 weeks after surgery. Evidence of a TCTF was found in 42% of cases (33 of 78) and 14% (36 of 250) of STS screws distal to the osteotomy. TCTFs were only identified distal to the osteotomy. Three dogs had radiographic evidence of more than one TCTF. Of the dogs with radiographic TCTF, 6% of patients (2 of 33) developed a major complication that required surgical stabilization of a tibial fracture associated with screw angulation relative to the plate. Use of Arthrex 3.5 mm STS for TPLO is associated with risk of TCTF. TCTF can compromise the structural properties of the tibia and cause complete tibial fracture requiring major revision surgery. Development of TCTF after use of STS for TPLO has been recognized, in contrast to use of non-self-tapping screws, and was considered a benign complication. Our findings suggest TCTF associated with Arthrex 3.5 mm STS use in TPLO can contribute to major complications after surgery, including complete tibial fracture, particularly if screws are not placed perpendicular to the plate.

Long-Term Outcome and Complications after Transcondylar Screw Placement for Canine Humeral Intracondylar Fissure.

The aim of this study was to report postoperative complications and long-term outcomes following transcondylar screw placement for humeral intracondylar fissure (HIF). It was a retrospective single-centre case series. Medical records (2018-2022) were reviewed for dogs with HIF treated with transcondylar screw placement. Data collected included signalment, concurrent orthopaedic disease, partial or complete HIF, surgeon, surgical approach, surgical technique and implant type, transcondylar screw angulation, postoperative complications and outcomes. Long-term outcome was assessed with owner questionnaire, orthopaedic examination and follow-up radiography. Statistical analysis was performed to identify risk factors predisposing to a complication or a poor outcome. Forty-seven dogs (57 elbows) met the inclusion criteria; long-term follow-up was available in 41 dogs (50 elbows). Minor and major medical complications were noted in seven and three elbows respectively. The total complication rate was 17.5%. Increasing age was significantly associated with a reduced risk of postoperative complications (p = 0.0051). No other risk factors were identified. A postoperative complication was not associated with a less than full outcome (p = 0.5698). Transcondylar screw placement for HIF is associated with a low complication rate and good outcome.

Effect of screw angulation and multiple insertions on load-to-failure of polyaxial locking system

Purpose Polyaxial locking plates rely on the alignment between the thread-to-thread connections of the screw head and the plate hole. These implants have provided substantial support for surgeons. In particular, extended screw positioning have proven to be beneficial in the fixation of challenging fractures. This study aimed to investigate the mechanical properties of ChM 5.0 ChLP polyaxial screws inserted in off-axis trajectories, including multiple insertions and to correlate these parameters with the screw head and the plate hole thread-to-thread engagement. Methods Polyaxial locking screws were inserted into the plates at various angles (0°,10°,15°, -15° off-axis). Multiple time inserted screws were placed firstly at 15°, then 0° and finally -15° off-axis in the same plate hole. A microCT scan of the plate-hole and screw-head interface was conducted before destructive tests. Representative screws from each group were also examined by Scanning Electron Microscope. Results The standard insertion at 0° sustained the greatest maximum bending strength without relocation in the screw hole. Screws inserted at 10° and 15° (one time) showed a significant reduction in load-to-failure of up to 36% and 55%, (p = 0.001) (p = 0.001) respectively. Screws inserted at -15° after a maximum of three multiple insertions with angle shift, showed a total reduction in force of up to 70% (p = 0.001). A microCT analysis of thread engagement showed significant correlations. However, the results obtained for multiple insertions were highly variable. Conclusions ChM 5.0 ChLP polyaxial locking system has valuable properties that foster fracture fixation, providing various surgical options. Nevertheless, the freedom of off-axis placement and multiple insertions of the screws comes at the price of reduced force. When possible surgeons should minimize the angles of insertions.

Effect of screw angulation on the bending performance of polyaxial locking interfaces: a micro-CT evaluation

Polyaxial locking plates rely on a specific thread-to-thread interface of the screw head and the plate hole. The objective of this study was to evaluate the mechanical performance of single screw interfaces when inserted off-axis and to establish correlations between those parameters and the engagement of the screw head and the plate hole thread. Three polyaxial locking screw systems were inserted into the corresponding plates at various angles (0°, 5°, 10°, and 15° off-axis). The screws were tested until failure. A micro-CT was performed to examine the interface between the plate hole and the screw head. The standard insertion at 0° sustained the greatest maximum bending strength without relocation in the screw hole. Screws inserted at 15° showed a significant reduction in force of up to 44%, 55% and 57%, respectively. Micro-CT analysis of the interface showed a significant loss of thread engagement for off-axis insertion. Polyaxial plates offer additional advantages for off-axis placement of screws. However, this flexibility is related to a significant decrease in both thread engagement and bending strength compared to monoaxial insertion. Regardless the insertion angle, the loss of stability is comparable when screws are placed off-axis. Surgeons are advised to consider off-axis insertion as a salvage option, providing access to better bone stock.

Cementing a Monoblock Dual-Mobility Implant into a Fully Porous Cup in Revision Total Hip Arthroplasty to Address Hip Instability: Surgical Technique.

Cementing a Monoblock Dual-Mobility Implant into a Fully Porous Cup in Revision Total Hip Arthroplasty to Address Hip Instability: Surgical Technique.

Comparison of infrazygomatic crest bone screw position using a postero-anterior cephalogram versus cone-beam computed tomography: a cross sectional study

Abstract Background The position of infrazygomatic crest bone screws is an important consideration in determining the success of orthodontic treatment. The aim of this study was to compare the position of infrazygomatic crest (IZC) bone screws in relation to skeletal and dental parameters using postero-anterior (PA) cephalograms and cone beam computed tomography (CBCT). Methods A CBCT scan and a PA cephalogram were taken of 19 patients (8 males; 11 females) after IZC bone screw placement. Each CBCT image was reconstructed and oriented using the CS 3D CBCT software (Carestream Dental LLC, Atlanta, USA) and was subsequently analysed. The landmarks were traced on the PA cephalogram. The angulation of the IZC bone screw was measured with respect to three skeletal and two dental landmarks and compared between the two imaging modalities. A paired t-test was applied to compare the means of different variables between the PA cephalogram and CBCT scan. Results The results showed no statistically significant difference between the two imaging modalities with respect to four landmarks, i.e., the inter-jugale plane, the mid sagittal plane, the zygomatic arch and the perpendicular long axis to the 1st molar but a small statistically significant difference was seen with respect to measurements from the facial surface of the 1st molar (P ≤ 0.05). Conclusion The angulation and position of an IZC bone screw are consistent between the two imaging modalities. A PA cephalogram may be used as a substitute for a CBCT scan to reduce the radiation exposure to patients.

Fixation of pelvic acetabular fractures using 3D-printed fracture plates: a cadaver study

Open reduction and internal fixation of pelvic acetabular fractures are challenging due to the limited surgical exposure from surrounding abdominal tissue. There have been a number of recent trials using metallic 3D-printed pelvic fracture plates to simplify and improve various elements of these fracture fixation surgeries; however, the amount of time and accuracy involved in the design and implantation of customised plates have not been well characterised. This study recorded the amount of time related to the design, manufacture and implantation of six customised fracture plates for five cadaveric pelvic specimens with acetabular fracture, while manufacturing, and surgical accuracy was calculated from computed tomography imaging. Five of the fracture plates were designed within 9.5 h, while the plate for a pelvis with a pre-existing fracture plate took considerably longer (20.2 h). Manufacturing comprised 3D-printing the plates in Ti6Al4V with a sintered laser melting (SLM) 3D-printer and post-processing (heat treatment, smoothing, tapping threads). The manufacturing times varied from 27.0 to 32.5 h, with longer times related to machining a thread for locking-head screws with a multi-axis computer numerical control (CNC) mill. For the surface of the plate in contact with the bone, the root-mean-square errors of the print varied from 0.10 to 0.49 mm. The upper range of these errors was likely the result of plate designs that were relatively long with thin cross-sections, a combination that gives rise to high thermal stresses when using a SLM 3D-printer. A number of approaches were explored to control the trajectories of locking or non-locking head screws including guides, printed threads or hand-taps; however, the plate with CNC-machined threads was clearly the most accurate with screw angulation errors of 2.77° (range 1.05–6.34°). The implanted position of the plates was determined visually; however, the limited surgical exposure and lack of intra-operative fluoroscopy in the laboratory led to high inaccuracies (translational errors of 1.74–13.00 mm). Plate mal-positioning would lead to increased risk of surgical injury due to misplaced screws; hence, it is recommended that technologies that can control plate positioning such as fluoroscopy or alignment guides need to be implemented into customised plate design and implantation workflow. Due to the plate misalignment and the severe nature of some acetabular fractures comprising numerous small bone fragments, the acetabular reduction exceeded the clinical limit of 2 mm for three pelvises. Although our results indicate that customised plates are unsuitable for acetabular fractures comprising six or more fragments, confirmation of this finding with a greater number of specimens is recommended. The times, accuracy and suggested improvements in the current study may be used to guide future workflows aimed at producing customised pelvic fracture plates for greater numbers of patients.

Risk factors for distal construct failure in posterior spinal instrumented fusion for adolescent idiopathic scoliosis: a retrospective cohort study.

To evaluate risk factors for distal construct failure (DCF) in posterior spinal instrumented fusion (PSIF) in adolescent idiopathic scoliosis (AIS). We hypothesise increased inferior angulation of the pedicle screw in the lowest instrumented vertebra (LIV) predisposes to failure and aim to find the critical angle that predisposes to failure. A retrospective cohort study was performed on all patients who underwent PSIF for AIS at our institution from 2010 to 2020. On lateral radiographs, the angle between the superior endplate of the LIV was measured against its pedicle screw trajectory. Data on demographics, Cobb angle, Lenke classification, instrumentation density, rod protrusion from the most inferior screw, implants and reasons for revision were collected. Of 256 patients, 9 patients had DCF with 3 further failures post-revision, giving 12 cases to analyse. The DCF rate was 4.6%. The mean trajectory angle of DCF patients compared to non-DCF was 13.3° (95% CI 9.2° to 17.4°) vs. 7.6° (7.0° to 8.2°), p = 0.0002. The critical angle is less than 11° (p = 0.0076), OR 5.15. Lenke 5 and C curves, lower preoperative Cobb angle, titanium only rod constructs and one surgeon had higher failure rates. 9.6% of rods protruding less than 3mm from its distal screw disengaged. Increased inferior trajectory of the LIV screw increases the rate of DCF; inferior trajectory greater than 11° predisposes to failure. Rod protrusion less than 3mm from the distal screw increases rate of disengagement. III.

Factors for Prolonged Pain and Restriction of Movement Following Hemiepiphysiodesis Plating for the Correction of Lower Limb Malalignment in the Frontal Plane: An Explorative Analysis.

The correction of valgus leg malalignment in children using implant-mediated growth guidance is widely used and effective. Despite the minimal invasive character of the procedure, a relevant number of patients sustain prolonged pain and limited mobility after temporary hemiepiphysiodesis. Our aim was to investigate implant-associated risk factors (such as implant position and screw angulation), surgical- or anesthesia-related risk factors (such as type of anesthesia, use, and duration), and pressure of tourniquet or duration of surgery for these complications. Thirty-four skeletally immature patients with idiopathic valgus deformities undergoing hemiepiphysiodesis plating from October 2018-July 2022 were enrolled in this retrospective study. Participants were divided into groups with and without prolonged complications (persistent pain, limited mobility of the operated knee between five weeks and six months) after surgery. Twenty-two patients (65%) had no notable complications, while twelve patients (35%) had prolonged complications. Both groups differed significantly in plate position relative to physis (p = 0.049). In addition, both groups showed significant differences in the distribution of implant location (p = 0.016). Group 1 had a shorter duration of surgery than group 2 (32 min vs. 38 min, p = 0.032) and a lower tourniquet pressure (250 mmHg vs. 270 mmHg, p = 0.019). In conclusion, simultaneous plate implantation at the femur and tibia and metaphyseal plate positioning resulted in prolonged pain and a delay of function. In addition, the amplitude of tourniquet pressure or duration of surgery could play a factor.

The relationship of the posterior iliac interval and the S1 screw trajectory

IntroductionSurgical fixation is widely practised in the management of spinal deformity. S1 screws are commonly incorporated in lumbosacral fusions and can be performed in both open and percutaneous techniques. However, their entry point is determined by the position of the pedicle as well as the posterior iliac interval (PII), as it creates an impedance for screw angulation. A wider angle screw has the potential to achieve a greater length and thus strength versus a narrow screw angle insertion due to risk of anterior breach. MethodsA retrospective analysis of 50 consecutive patients between July 2018 andDecember 2021 undergoing lumbo-sacral fusion with include S1 screw insertion from a single institution and surgeon. The age, screw angles, and the posterior iliac intervals were measured. ResultsThe patients ranged from age 27 to 83 years old (mean 64.7) with a posterior iliac interval (PII) ranging from 7.76 to 12.62 cm (mean 10.24) and the average S1 screw angle on the right was 76.01 degrees (range 59.37 to 88.48) and on the left 74.37 degrees (range 59.75 to 87.47 degrees). Applying the Pearson Correlation co-efficient, a wider PII correlated with a more angulated screw entry (P < 0.05). ConclusionAs expected, a wider PPI is significantly associated with a more angulated S1 screw trajectory and may have implication on patient biomechanics in lumbo-sacral fusion constructs.

Does preoperative glenoid bony defect determine final coracoid graft positioning in arthroscopic Latarjet?

It has been demonstrated that the accurate positioning of the graft is key to restoring shoulder stability and preventing future arthrosis development. Preoperative anteroinferior glenoid bone loss is frequently encountered when performing a Latarjet, and it has not been determined yet if the amount of bony defect can influence graft positioning. The aim of the study was to determine if a preoperative glenoid bony defect has an influence on the final coracoid graft position in the arthroscopic Latarjet procedure. Fifty-five patients who underwent the arthroscopic Latarjet procedure were included, with a minimum follow-up of 2 years. There were 51 men (92.7%). Mean age was 29.1 (SD 7.63). Western Ontario Shoulder Instability Index, Rowe, and Single Assessment Numeric Evaluation scores were fulfilled. All measurements were performed by a musculoskeletal radiologist based on a multiplanar bidimensional CT scan. Dimensions of the glenoid, glenoid defect, and glenoid track were calculated. Position of the graft was evaluated in the axial (distance to glenoid surface, angulation of the graft and screws) and sagittal planes (percentage of the coracoid graft below the equator) as described by Kany etal and Barth etal respectively. There was a glenoid defect in 41 patients (74.5 %). Mean width of the defect was 4.32 mm (SD 3.08) which represented 15.3% of the native glenoid surface (SD 10.8). 78.2% of the patients were offtrack preoperatively, and 11.9% remained offtrack postoperatively. The final glenoid diameter with the graft was 32.1 mm (SD 4.34). Mean distance from the graft to the glenoid at 50% height was 1.1 mm (SD 2.19 mm) and at 25% height was 1.31 mm (SD 2.05). Mean angulation of the superior and inferior screws were 26.9° (SD 8.2°) and 27.1° (SD 7.35°), respectively. In 81.8% of the cases, the graft was deemed to be flush with the glenoid. The percentage of the coracoid graft under the equator of the glenoid was 71.2 % (SD 21.8). There was not a statistically significant difference in screw angulation or graft positioning in the axial plane when comparing patients who had a glenoid defect with those who did not, or depending on the size (P>.05). Percentage of graft below the equator was, however, lower in patients without bony defect (P=.04). This study showed that accurate position of the coracoid graft is achieved in the presence of a glenoid bony defect. In the cases of intact glenoid, the height of the graft should be carefully evaluated.

Anterior occipital condyle screw placement through the endonasal corridor: proof of concept study with cadaveric analysis.

Odontoidectomy for ventral compressive pathology may result in O-C1 and/or C1-2 instability. Same-stage endonasal C1-2 spinal fusion has been advocated to eliminate risks associated with separate-stage posterior approaches. While endonasal methods for C1 instrumentationand C1-2 trans-articularstabilization exist, no hypothetical construct for endonasal occipital instrumentation has been validated. We provide an anatomic description of anterior occipital condyle (AOC) screw endonasal placement as proof-of-concept for endonasal craniocervical stabilization. Eight adult, injected cadaveric heads were studied for placing 16 AOC screws endonasally. Thin-cut CT was used for registration. After turning a standard inferior U-shaped nasopharyngeal flap endonasally, 4 mm × 22 mm AOC screws were placed with a 0° driver using neuronavigation. Post-placement CT scans were obtained to determine: site-of-entry, measured from the endonasal projection of the medial O-C1 joint; screw angulation in sagittal and axial planes, proximity to critical structures. Average site-of-entry was 6.88mm lateral and 9.74mm rostral to the medial O-C1 joint. Average angulation in the sagittal plane was 0.16° inferior to the palatal line. Average angulation in the axial plane was 23.97° lateral to midline. Average minimum screw distances from the jugular bulb and hypoglossal canal were 4.80mm and 1.55mm. Endonasal placement of AOC screws is feasible using a 0° driver. Our measurements provide useful parameters to guide optimal placement. Given proximity of hypoglossal canal and jugular bulb, neuronavigation is recommended. Biomechanical studies will ultimately be necessary to evaluate the strength of AOC screws with plate-screw constructs utilizing endonasal C1 lateral mass or C1-2 trans-articular screws as inferior fixation points.

Freehand Juxtapedicular Screws Placed in the Apical Concavity of Adult Idiopathic Scoliosis Patients: Technique, Computed Tomography Confirmation, and Radiographic Results.

The purpose of this study is to highlight our technique for freehand placement of juxtapedicular screws along with intraoperative computed tomography (CT) and radiographic results. Consecutive patients with adult idiopathic scoliosis undergoing primary surgery by the senior author were identified. All type D (absent/slit like channel) pedicles were identified on preoperative CT. Three-dimensional visualization software was used to measure screw angulation and purchase. Radiographs were measured by a fellowship trained spine surgeon. The freehand technique was used to place all screws in a juxtapedicular fashion without any fluoroscopic, radiographic, navigational or robotic assistance. Seventy-three juxtapedicular screws were analyzed. The most common level was T7 (9 screws) on the left and T5 (12 screws) on the right. The average medial angulation was 20.7° (range, 7.1°-36.3°), lateral vertebral body purchase was 13.4 mm (range, 0-28.9 mm), and medial vertebral body purchase was 21.1 mm (range, 8.9-31.8 mm). More than half (53.4%) of the screws had bicortical purchase. Two screws were lateral on CT scan, defined by the screw axis lateral to the lateral vertebral body cortex. No screws were medial. There was a difference in medial angulation between screws with (n = 58) and without (n = 15) lateral body purchase (22.0 ± 4.9 vs. 15.5 ± 4.5, p < 0.001). Three of 73 screws were repositioned after intraoperative CT. There were no neurovascular complications. The mean coronal cobb corrections for main thoracic and lumbar curves were 83.0% and 80.5%, respectively, at an average of 17.5 months postoperative. Freehand juxtapedicular screw placement is a safe technique for type D pedicles in adult idiopathic scoliosis patients.

C1 Lateral Mass Screw Placement Through Endonasal Corridor for Purpose of O-C1 Fusion: Morphometric Analysis in Cadaveric Specimens

Odontoidectomy may pose some risks for O-C1 and/or C1-C2 instability, with previous authors reporting techniques for endonasal C1-C2 fusion. However, no technique for endonasal O-C1 fusion currently exists. We sought to describe the feasibility of endonasal anterior C1 (AC1) screw placement for endonasal O-C1 fusion. Seven adult cadaveric heads were studied for endonasal placement of 14 C1 screws. Using thin-cut computed tomography (CT)-based "snapshot" neuronavigation assistance, 4 mm x 22 mm screws were placed in the C1 lateral mass using a 0° driver. Post-placement CT scans were obtained to determine site-of-entry measured from C1 anterior tubercle, screw angulation in axial and sagittal planes, and screw proximity to the central canal and foramen transversarium. Average site-of-entry was 16.57 mm lateral, 2.23 mm rostral, and 5.53 mm deep to the anterior-most portion of the C1 ring. Average axial angulation was 19.49° lateral to midline, measured at the C1 level. Average sagittal angulation was 13.22° inferior to the palatal line, measured from the hard palate to the opisthion. Bicortical purchase was achieved in 11 screws (78.6%). Partial breach of the foramen transversarium was observed in 2 screws (14.3%), violation of the O-C1 joint space in 1 (7.1%), and violation of the central canal in 0 (0%). Average minimum screw distances from the unviolated foramen transversaria and central canal were 1.97 mm and 4.04 mm. Navigation-assisted endonasal placement of AC1 screws is feasible. Additional studies should investigate the biomechanical stability of anterior C1 screw-plating systems, with anterior condylar screws as superior fixation point, compared to traditional posterior O-C1 fusion.

Optimization of Locking Plate Screw Angle Used to Treat Two-Part Proximal Humerus Fractures to Maintain Fracture Stability

Proximal humerus fractures increase with the aging of the population. Due to the high failure rates of surgical treatments such as open reduction and internal fixation (ORIF), biomechanical studies seek to optimize the treatments and intervening factors to improve the quality of life of people undergoing these treatments. The aim of the present study was to determine the optimal insertion angle configuration of screws used in a two-part proximal humerus fracture-locking plate osteosynthesis treatment based on finite element analysis (FEA). A series of 3D models of PHILOS locking plates with different screw insertion angle configurations were designed using a matrix system for screw angulation. The locking plate models were evaluated in a two-part proximal humerus fracture with surgical neck fracture under bending and compressive loading conditions using FEA and statistically analyzed using a design of experiments (DOE). The optimal screw insertion angle setting showed an improvement in relation to the interfragmentary strain value of the fracture. Moreover, calcar screws were the most significant feature in fracture stability throughout the tests, followed by the divergence of the most proximal screws and the proximal–distal alignment of the locking plate.

Computed Tomographic Evaluation of the Accuracy of Minimally Invasive Sacroiliac Screw Fixation in Cats.

The aim of this study was to report the use of computed tomography (CT) for postoperative evaluation of the accuracy of sacroiliac reduction and minimally invasive screw fixation in a series of five cats. Medical records between January 2016 and March 2017 of cats presenting to the author's institution were reviewed. Included were cats that had undergone minimally invasive sacroiliac screw fixation with a complete medical record and pre- and postoperative radiographs. Screw size was obtained from the medical records. CT images were acquired prospectively and evaluated to assess joint reduction, relative screw size and screw positioning. Six sacroiliac luxations and 6 screws were available. Fixation was achieved with either a 2.4 (n = 1) or 2.7 mm (n = 5), 316L stainless steel, cortical bone screw. Mean screw size as a proportion of sacral diameter was 47.7%. Sacroiliac reduction >90% in the craniocaudal plane and sacral screw purchase >60% of the sacral width were achieved in 3/5 cases. Mean dorsoventral screw angulation was 1.6 degrees (range: -9.7 to 11.7 degrees) and craniocaudal angulation was -4.5 degrees (range: -16.6 to 6.6 degrees). Complications included screw loosening in the one case of bilateral repair and penetration of the neural canal in one case which was not detected with postoperative radiographic evaluation. CT evaluation provides a useful method for the assessment of sacroiliac reduction and the accuracy of screw placement.

The Intersection Between Lateral Mass and Inferomedial Edge of the C1 Posterior Arch: A Reference Point for C1 Lateral Mass Screw Insertion

ObjectiveTo determine the ideal Atlas (C1) lateral mass screw placement and trajectory using the intersection between the lateral mass and inferomedial edge of the posterior arch as an easily identifiable and reproducible medial reference point. Selection of an ideal entry point and trajectory of C1 lateral mass screw insertion can help to minimize neurovascular injuries. While various techniques for screw insertion have been proposed in the past, they all require extensive dissection of the C1 lateral mass, which can cause profuse bleeding. MethodsNinety-three 3-dimensional computed tomography reconstructed images of C1 lateral masses in adult patients were utilized to simulate the placement of C1 lateral mass screws via 4 entry points and 2 trajectory angles referencing off of a medial reference point using Vero’s VISI 17 software. The safety during screw insertion simulation, as well as the screw length, were evaluated. ResultsWe found that C1 lateral mass screws could be safely placed bilaterally at 3 mm lateral to the reference point in both 0° and 15° medial screw angulation without violation of the cortex. The 15° medial angulation allowed for longer (18 mm) screws than the 0° angulation. ConclusionWe recommend starting C1 lateral mass screws 3 mm lateral to the intersection between the lateral mass and inferomedial edge of the posterior arch at a 15° medial angulation.

Tomographic mapping of buccal shelf area for optimum placement of bone screws: A three-dimensional cone-beam computed tomography evaluation

Introduction: Buccal shelf bone screws have become increasingly popular as a preferred method of skeletal anchorage in the mandibular arch. Anatomic variations and clinical experience suggest that width and slope of the bone at buccal shelf vary in different population groups, with some individual variations. Aims and Objectives: The objective of this study was to evaluate angulation of the bone screw of mandibular buccal shelf area, total bone width, thickness of the cortical bone, and proximity to neurovascular structures. Materials and Methods: Cone-beam computed tomography scans were used to obtain measurements of the buccal shelf region of 35 patients (18 females, 17 males; mean age, 23.6 years). Measurements were taken at three locations (L1, L2, and L3) and total bone width was measured at two levels from the cementoenamel junction (CEJ, H1 and H2). Bone screws were virtually placed and their proximity evaluated from digitally traced inferior alveolar neurovascular bundle. Results: Permissible angulation for placement of buccal shelf bone screw considering the safety distance from the root and avoiding excessive buccal projection to minimize cheek irritation was found to be 74.48 (SD ± 4.26). Total bone width was maximum at the distobuccal cusp of mandibular second molar (L3H2; 6.40 ± 1.35) when measured at the level of 8 mm from the CEJ. Bone screws were well within the safety range from causing any iatrogenic damage to the inferior alveolar neurovascular bundle at all the three aforementioned locations. Conclusion: Thus, area buccal to the mandibular second molar region seems to be the most favorable site for placement of buccal shelf bone screws in Indian patients.

Accuracy of three-dimensional printed patient-specific drill guides for treatment of canine humeral intracondylar fissure.

To determine the accuracy of three-dimensional printed patient-specific drill guides (3D-PDG) as treatment of humeral intracondylar fissures (HIF) in dogs. Retrospective consecutive case series. Client-owned dogs with HIF treated with a 5-mm transcondylar screw (TCS) placed from medial to lateral with a 3D-PDG. The proposed TCS entry point and trajectory were planned using computed tomography (CT) data and computer-aided design software (CAD), and a 3D-PDG was produced. During surgery the 3D-PDG was used to drill the pilot hole from medial to lateral; the guide was then removed, the pilot hole was overdrilled, and a 5-mm TCS was placed. Postoperative CT data were imported into CAD software, and the entry points, exit points, and trajectories were compared between the planned and actual screw locations. Sixteen elbows from 11 dogs were included. Mean (SD) entry point translation was 1.3 mm (0.64), with all screws entering cranial to the proposed location. Mean maximum screw angulation was 5.2° (2.10°), with most screws directed caudodistal to the desired trajectory. Mean (SD) exit point translation was 1.8 mm (0.89) from the planned location. There was no intra-articular screw placement. Use of a 3D-PDG permitted accurate placement of a mediolateral 5-mm locking TCS within the humeral condyle. Three-dimensional printed patient-specific drill guides should be considered as accurate and consistent for placing TCS for treatment of HIF in dogs.