Retractor Placement Research Articles

Anterior acetabular retractors and the femoral neurovascular bundle in anterior total hip arthroplasty: a cadaveric study.

The direct anterior approach for primary total hip arthroplasty (THA) has become increasingly popular in recent years. Nerve compression or traction with a retractor is a common cause of nerve injury in this approach. The purpose of this cadaveric study was to evaluate the anatomic relationship of the femoral neurovascular bundle to the anterior acetabular retractor during direct anterior approach THA. Eleven fresh-frozen cadavers underwent a standard direct anterior THA, with placement of an anterior acetabular retractor in the usual fashion between the iliopsoas and acetabulum for visualization during acetabular preparation. Careful dissection of the femoral triangle was performed, and the distances from the anterior retractor tip to the femoral nerve, artery, and vein were recorded and analyzed as mean distance ± standard deviation. In all 11 cadavers, the retractor tip was medial to the femoral nerve. The mean distance from retractor tip to femoral artery and vein was 5.9mm (SD = 5.5, range 0-20) and 12.6mm (SD 0.7, range 0-35), respectively. Surgeons should be aware of the proximity of the neurovascular structures in relation to the anterior acetabular retractor in the direct anterior approach, taking care to avoid perforating the iliopsoas muscle during retractor insertion and limit excessive traction to prevent nerve injury.

Safe Zone for Anterior Retractor Placement in Total Hip Arthroplasty: A Cadaveric Study

Aim: Femoral nerve entrapment during placement of anterior retractors for total hip replacement results in considerable morbidity, although it is uncommon. The aim of this study is to describe a safe zone for placement of anterior retractors during total hip arthroplasty by studying anatomy in cadavers. Materials and Methods: Ten hips from 6 cadavers were dissected and studied. The clock face anatomy of the acetabulum was used as pins were placed at various clock positions before proceeding with the sectioning of the surrounding muscles. For the left hip 6, 5, 3, 1, and 12’o clock positions and for the right hip 6, 7, 9, 11, and 12’o clock positions were pinned along the anterior acetabular wall. The limbs were dissected axially, beginning from the inferior aspect of the acetabulum and proceeding in a proximal sequence with an interval of 1 cm. The plane of the first section passed through the distal end of the acetabulum and was named plane A. The subsequent proximal planes were named planes B, C, and D, respectively. The distance between the femoral nerve and the anterior acetabular wall was measured. Results: The distance from the anterior acetabular rim to the femoral nerve was closest at plane C, measuring 10.76±2.58 mm (which coincides with the 3’o clock position in the left hip and the 9’o clock position in the right hip). The anteroposterior diameter of Iliacus muscle was maximum at plane A, measuring 17.56±3.90 mm (which coincides with the 6’o clock position in both the right and left hips), and mediolateral diameter of iliopsoas was maximum at plane D, measuring 28.50±3.74 mm (which coincides with the 11’o clock position in the right hip and the 1’o clock position in the left hip). Conclusions: The femoral nerve is closest to the anterior acetabular rim at plane C (9’o clock position of the right hip/3’o clock position of the left hip). Hence, the Hohmann retractor should not be placed on this plane. Anterior retractors can be safely placed adjacent the acetabular rim at planes A, B, and D.

Anatomical Implications Regarding Femoral Nerve Palsy During a Direct Anterior Approach to Total Hip Arthroplasty: A Cadaveric Study.

Femoral nerve palsy is a serious neurological complication following total hip arthroplasty (THA) via a direct anterior approach. One hypothesis is that the nerve injury is caused by malpositioning of retractors over the anterior wall of the acetabulum. The purpose of this cadaveric study was to clarify the anatomical features of the femoral nerve around the anterior acetabular rim and the potential risk of nerve injury during a direct anterior approach to THA. We dissected 84 cadaveric hips from 44 formalin-embalmed cadavers. When the cadavers were supine, the iliopsoas muscle and the femoral nerve were exposed and the anterior joint capsule and labrum were resected. The measurement points were determined along the acetabular rim every 30°, and a reference line was drawn from the anterior superior iliac spine to the center of the acetabulum, with the intersection of the rim at 0°. The minimum distance to the femoral nerve margin was measured from 0° to 150° (6 points). Other anatomical structures were measured to determine their association with the distance of the shortest measurement points. The mean minimum distances to the femoral nerve were 33.2 mm at 0°, 24.4 mm at 30°, 18.4 mm at 60°, 16.6 mm at 90°, 17.9 mm at 120°, and 23.2 mm at 150°, showing that the distance at 90° was the shortest (p < 0.001). The thickness of the iliopsoas muscle and the femoral length were positively associated with the distance to the femoral nerve at 90°. In this cadaveric study, the femoral nerve was within 16.6 to 33.2 mm of the acetabular rim at points from 0° to 150° of a line drawn from the anterior superior iliac spine. The nerve was closest to the rim at 90°, indicating that this is an area of high risk during retractor placement. Retractor placement at 90° to the anterior acetabular rim should be avoided to reduce the risk of femoral nerve injury.

Safe Zones for Anterior Acetabular Retractor Placement in Direct Anterior Total Hip Arthroplasty: A Cadaveric Study.

There is paucity of literature evaluating anterior acetabular retractor proximity to the femoral nerve and external iliac vessels during total hip arthroplasty through the direct anterior approach. In this cadaveric study, we evaluated three retractor locations to identify optimal positioning of anterior retractors. A direct anterior approach was performed in 22 hips of 15 cadavers. Anterior acetabular retractors were placed over the anterior acetabular wall in-line with the femoral neck (12-o'clock or middle position). The anterior neurovascular structures were identified through the ilioinguinal approach. Retractors were reinserted at 10-o'clock (right hip; superior) and 2-o'clock (right hip; inferior) locations marked using K-wires. Horizontal and vertical distances from retractor tip positions to neurovascular structures were measured with a digital caliper. Retractor tips moved significantly from lateral to the femoral nerve when placed in the superior position (mean, 2.8 mm) to medial to the femoral nerve in the middle (mean, -2.3 mm) and inferior (mean, -4.8 mm) locations. Retractor tips moved significantly medial toward the external iliac artery when retractors were moved from superior (mean, 15.3 mm) to inferior (mean, 6.6 mm) positions placing the retractor tip closer to the vessels. As retractor placements moved inferior, retractor tips moved medial to neurovascular structures. Inferior retractor positioning placed the femoral nerve and external iliac artery at the risk of injury during the initial retractor placement or adjustment. Retractors should be placed in a relative safe zone superior to the 12-o'clock position to avoid damage to neurovascular structures. IV.

Periprosthetic Humeral Fractures in Shoulder Arthroplasty.

» The reported combined rates of intraoperative and postoperative periprosthetic humeral fractures range widely, from 1.2% to 19.4%.» The risk factors for an intraoperative humeral fracture and literature-reported strength of association include a press-fit humeral component (relative risk [RR], 2.9), revision arthroplasty (RR, 2.8), history of instability (odds ratio [OR], 2.65), female sex (OR, 4.19), and posttraumatic arthritis (RR, 1.9). The risk factors for a postoperative humeral fracture include osteonecrosis and increased medical comorbidity index (OR, 1.27).» Intraoperative fractures, in order of decreasing frequency, most often occur during implant removal in cases of revision arthroplasty (up to 81%), during reaming or broaching of the humerus (up to 31%), during trial or implant insertion (up to 18% to 19%), or because of excessive humeral torque or forceful retractor placement during exposure or reduction (up to 13% to 15%). Postoperative fractures typically occur from a fall onto the outstretched extremity or through an area of osteolysis.» The treatment of intraoperative or postoperative fractures is based on fracture location, prosthesis type and stability, rotator cuff status, and available bone stock.» Nonoperative treatment for periprosthetic humeral fractures appears to have high failure rates. When treating a periprosthetic humeral fracture operatively, surgical techniques for tuberosity fractures include suture repair, cerclage wiring, or revision to reverse components. For humeral shaft fractures, techniques include revision to a long-stem component, cerclage wiring, plate-and-screw fixation, and use of a strut allograft. For extensive humeral bone loss, techniques include component-allograft composites or humeral endoprostheses. All techniques have the goals of permitting early range of motion and preserving function.

Use of Virtual Reality Platforms in the Preoperative Planning and Intraoperative Navigation of Deep-Seated Cavernomas

Abstract INTRODUCTION Cavernous malformations in deep-seated eloquent cortex pose significant management challenges. Surgical resection, when indicated, carries a high risk of postoperative neurologic deficit. Obtaining safe surgical access is highly dependent upon location and the patient's clinical status. Three-dimensional (3D) virtual reality platforms, neuronavigation, and advanced neuroimaging can be used as adjuncts to determine and perform the safest surgical approach. METHODS Five patients who underwent surgical resection of deep seated cavernomas in eloquent cortex were included. 3D images were created from Diffusion Tensor MR Imaging (DTI) using a 360 Virtual Reality planning software (Surgical Theater SRP, Version7.4.0, Cleveland, Ohio). The Surgical Theater system was integrated with the neuronavigation system (Brainlab AG Version 3.0.5, Feldkirchen, Germany) to allow for real time evaluation of the 3D tractography. The 360°VR model was used to assess the location of the cavernoma and relevant anatomy, map multiple trajectories, and compare the advantages and disadvantages of each. SRP and Brainlab projections were used to determine the limits of the cavernoma, guide the placement of the tubular retractor, and confirm the approach vector intraoperatively. RESULTS Locations of the cavernomas included left caudate head, right superior colliculus, right posteroinferior thalamus, right insula, and left medulla. All patients underwent craniotomy and microsurgical resection. Two patients who presented with a neurologic deficit partially improved after prolonged rehabilitation. Three patients who were neurologically intact on presentation remained so post-op. Gross-total resection was obtained in all patients. CONCLUSION Virtual segmentation allows for better understanding of complex anatomic relationships between the lesion and surrounding critical structures. Advanced planning familiarizes surgeons to the patient in the context of the surgical field, increasing spatial and positional orientation. 3D virtual reality planning platforms in conjunction with neuronavigation and DTI can assist in choosing the optimal surgical corridor to achieve gross-total resection of deep-seated cavernomas while minimizing neurologic risk.

The cheek expander enables tonsillectomy with a wide view and working space

ObjectiveTonsillectomy is the most commonly performed otolaryngological surgeries.Although a surgical method had been established, obtaining a clear surgical field still remains problematic, and injury to the corners of the mouth may occur. For safer tonsillectomy, we use a cheek expander coupled with a Davis mouth gag. The devise retract both corners of the mouth to a wide lateral position. We report here our investigation in the application of a cheek retractor for tonsillectomy and also report the advantages of this device. MethodsA series of 13 tonsillectomies (7 adults and 6 children) using the cheek retractor from November 2017 to March 2018 were enrolled for this study. The cheek retractor was applied after the Davis mouth-opening device was in place. We measured the oral angle diameter before and after placement of the cheek retractor. ResultsThis devise increases the width of the visual field 1.6 times and provides a good surgical field. In addition, this device covers the mouth fully and safely, so no lip injury develops ConclusionThe cheek retractor is useful for improving the narrow working space in tonsillectomy.

Multi-modal Framework for Image-guided Trans-oral Surgery with Intraoperative Imaging and Deformation Modeling.

Treatment of throat cancers have improved due to minimally-invasive trans-oral approaches. Surgeons rely on preoperative imaging to guide their resection; however, large tissue deformations occur during trans-oral procedures due to placement of necessary retractors and laryngoscopes which hinders the surgeon's ability to accurately assess tumor extent and location of critical structures. We propose an image-guided framework utilizing intraoperative imaging and deformation modeling to improve surgeon accuracy and confidence. A CT-compatible laryngoscopy system previously developed was evaluated in this framework. Intraoperative images were acquired during laryngoscopy; force-sensing capabilities were enabled in the laryngoscope; and tracking of the scope and anatomic features was trialed. Tissue deformation and displacement were quantified and determined to be extensive, with values <; 4.6 cm in the tongue, <; 1.8 cm in bony structures, and <; 108.9 cm3 in airway volume change. Surgical navigation using intraoperative imaging and tracking was evaluated. Preliminary assessment of deformation modeling showed potential to supplement intraoperative imaging. Future work will involve streamlined integration of the components of this framework.

The Modified Anterolateral Approach to the Humerus

The Modified Anterolateral Approach to the Humerus

Innervation of the subscapularis: an anatomic study

BackgroundSuccessful healing of the subscapularis during anatomic total shoulder arthroplasty surgery is critical to optimize functional outcomes and avoid complications. The purpose of this study was to examine the upper and lower subscapularis nerve insertion in relation to the musculotendinous junction to estimate the risk of nerve injury. Our hypothesis was that arm position changes the risks to these nerves when exposing the anterior glenoid.MethodsTwenty cadaveric shoulders were dissected, and the subscapular nerves were identified from the posterior cord of the brachial plexus to the muscle insertion. The nerve length from the origin to the muscle insertion and the distance to the myotendinous junction were measured in various shoulder positions including neutral, external, and internal rotation.ResultsThe mean length of the upper subscapular nerve was 51.4 ± 12.8 mm; that of the lower subscapular nerve was 50.5 ± 14 mm. The mean distance from the insertion of the upper subscapular nerve to the myotendinous junction 53.0 ± 14.7 mm with external rotation, 38.5 ± 9.7 mm with neutral rotation, and 30.0 ± 9.2 mm with internal rotation. The mean distance from the lower subscapular nerve to the myotendinous junction was 44.5 ± 13.8 mm with external rotation, 31.9 ± 9.3 mm with neutral rotation, and 25.4 ± 8.8 mm with internal rotation. The internally rotated position placed these nerves closest to the glenohumeral joint.ConclusionThe upper and lower subscapular nerves insert in the muscle belly close to the myotendinous junction, putting them at risk of iatrogenic injury. Care must be taken to avoid damage with retractor placement in the anterior glenoid neck as these nerves are at risk of compression or torsional injury.

Avoiding the Esophageal Branches of the Recurrent Laryngeal Nerve During Retractor Placement: Precluding Postoperative Dysphagia During Anterior Approaches to the Cervical Spine.

Study Design:Anatomical cadaver study.Objectives:Postoperative dysphagia is a significant complication following anterior approaches to the cervical spine and the etiology of this complication is poorly understood. Herein, we studied the esophageal branches of the recurrent laryngeal nerves to improve understanding of their anatomy and potential involvement in dysphagia.Methods:Ten fresh frozen cadaveric human specimens were dissected (20 sides). All specimens were adults with no evidence of prior surgery of the anterior neck. The recurrent laryngeal nerves were identified under a surgical microscope and observations and measurements of their esophageal branches made.Results:For each recurrent laryngeal nerve, 5-7 (mean 6.2) esophageal branches were identified. These branches ranged from 0.8 to 2.1 cm (mean 1.5 cm) in length and 0.5 to 2 mm (mean 1 mm) in diameter. They arose from the recurrent laryngeal nerves between vertebral levels T1 and C6. They all traveled to the anterior aspect of the esophagus. No statistical differences were seen between left and right sides or between sexes.Conclusion:The esophageal branches of the recurrent laryngeal nerve have been poorly described and could contribute to complications such as swallowing dysfunction following anterior cervical discectomy and fusion procedures. Therefore, a better understanding of their anatomy is important for spine surgeons. Our study revealed that these branches are always present on both sides and the anterior surface of the esophagus should be avoided while retracting it in order to minimize the risk of postoperative dysphagia.

Surgical technique for the protection of the cervical sympathetic trunk in anterolateral oblique corpectomy: A new cadaveric demonstration

The cervical oblique corpectomy (OC) approach has the advantages of no grafting or instrumentation necessities and theoretically maintains natural neck motions. However, the risk of cervical sympathetic trunk (CST) injury and Horner’s syndrome is one of the main difficulties of this demanding surgical approach. The upper necks of 3 adult human cadavers (6 sides) were dissected under a Zeiss surgical microscope. OC was performed in a stepwise manner to simulate the surgical procedure. We specifically studied the technique of the protection of the CST during the cervical OC approach. The superior ganglion of the cervical sympathetic chain is located under the prevertebral fascia over the longus capitis muscle at the level of C3 transverse process, while the CST is situated under the prevertebral fascia over the longus colli muscle. The CST courses obliquely from superolateral to inferomedial. The ganglia and CST are carefully dissected; the fascia of the longus colli muscle is cut medially, preferably in the midline over the vertebrae, and the fascia lifted up. Then, the aponeurotic flap is gently retracted laterally to cover the sympathetic chain safely and secured with a 3/0 suture laterally. Preservation of the CST while performing cervical OC is essential to avoid postoperative Horner’s syndrome. The placement of self-retaining retractors, particularly inferiorly, where the sympathetic chain is located more medially, is probably the main cause of its injury. Further studies are needed documenting the incidence of Horner’s syndrome in the application of this technique to live patients.

Respiratory mechanics with volume-controlled auto-flow ventilation mode in cardiac surgery.

Aim:We aimed to investigate the changes in respiratory mechanics in adult patients undergoing open heart surgery (OHS) while using volume-controlled auto-flow (VCAF) ventilation mode.Materials and Methods:After obtaining ethics committee's approval and informed consent, 30 patients (17 males and 13 females; mean age: 57.3 ± 17.0 years; mean weight; 74.9 ± 13.6 kg) scheduled for OHS were enrolled. Mechanical ventilation was carried out using VCAF mode (VT: 5–8 mL/kg, I/E: 1/2, 10 ± 2 fr/min). Values of dynamic compliance (Cdyn) and resistance (R) were obtained at six time points (TPs). Normally distributed variables were analyzed with repeated measure of analysis of variance and Bonferroni tests. For abnormally distributed variables, Friedman variance analysis and Wilcoxon signed-rank tests were used. Values were expressed as mean ± standard deviation. P value <0.05 was considered significant.Results:Cdyn (mL/mbar) and R (mbar/L/s) values were as follows – (1) before sternotomy (S): 49.9 ± 17.1 and 7.8 ± 3.6; (2) after S: 56.7 ± 18.3 and 7.1 ± 3.7; (3) after S and after sternal retractor placement: 48.7 ± 16.1 and 8.3 ± 4.4; (4) after weaning from cardiopulmonary bypass and following decannulation while retractor was in place: 49.6 ± 16.5 and 8.1 ± 4.0; (5) after retractor removal: 56.5 ± 19.6 and 7.4 ± 3.7; and (6) after sternal closure: 43.1 ± 14.2 and 9.6 ± 9.1, respectively. Significant differences were observed in Cdyn and R between; first and second TPs, second and third TPs, fourth and fifth TPs, and fifth and sixth TPs. Also, significant difference in Cdyn was found between first and sixth TPs, but it was not found in R.Conclusion:Cdyn decreases, but R remains the same in cardiac surgical patients when mechanical ventilation is performed with VCAF ventilation mode. Additionally, Cdyn is negatively affected by the presence of sternal retractor and the sternal closure in OHS.

Magnetic-assisted robotic surgery: initial case series of reduced-port robotic prostatectomy

Minimally invasive radical prostatectomy has rapidly been adopted as the primary means of surgical intervention for prostate cancer. Intraoperative tissue retraction relies on either gravity (via positioning) or use of additional ports and instrumentation. We report the use of a novel trocar-less magnetic retractor system to aid with tissue retraction. Three patients underwent robotic-assisted radical prostatectomy in the treatment of prostatic adenocarcinoma at a single tertiary care institution. All surgeries utilized the Levita™ Magnetic Surgical System (San Mateo, CA) without the use of a fourth robotic arm. The magnetic grasper was used to manipulate the bowel, peritoneum, seminal vesicles, and prostatic capsule. Demographic, pre-operative, and perioperative information were collected. No cases required placement of any additional ports. No intraoperative or immediate post-operative complications occurred. No tissue tearing or subjective tissue damage was noted by placement or removal of the magnetic retractor. Mean operative time was 216 ± 17min and mean blood loss was 333 ± 57mL. All patients were discharged to home on post-operative day 1. Robotic prostatectomy utilizing a magnetically anchored tissue grasper appears to be safe and effective while reducing the number of ports (fourth robotic arm) needed. Further investigation is warranted.

Maintaining endotracheal tube cuff pressure at 20mmHg during anterior cervical spine surgery to prevent dysphagia: a double-blind randomized controlled trial.

Anterior cervical spine surgery is associated with postoperative dysphagia, sore throat and dysphonia. It is unclear, whether this is caused by increased endotracheal tube (ETT) cuff pressure after retractor placement. This study aims to assess the effect of ETT cuff pressure adjustment on postoperative dysphagia, sore throat and dysphonia. In this, single-centre, observer and patient-blinded randomized controlled trial patients treated with anterior cervical spine surgery were randomized to adjustment of the ETT cuff pressure to 20mmHg after placement of the retractor versus no adjustment. Primary outcome was the incidence and severity of postoperative dysphagia. Secondary outcomes were sore throat and dysphonia. Outcomes were evaluated on day one and 2months after the operation. Of 177 enrolled patients, 162 patients (92.5%) could be evaluated. The incidence of dysphagia was 75.9% on day one and 34.6% 2months after surgery. Dysphagia in the intervention and control group was present in 77.8% versus 74.1% of patients on day one (odds ratio (OR) 1.2, 95% confidence interval (CI) (0.6-2.5)) and 28.4% versus 40.7% of patients after 2months (OR 0.6, 95% CI 0.3-1.1), respectively. Severity of dysphagia, sore throat and dysphonia was similar in both groups. Anterior cervical spine surgery is accompanied by a high incidence of postoperative dysphagia, lasting until at least 2months after surgery in over a third of our patients. Adjusting ETT cuff pressure to 20mmHg after retractor placement, as compared to controls, did not lower the risk for both short- and long-term dysphagia. Netherlands National Trial Registry Number: NTR 3542. These slides can be retrieved under electronic supplementary material.

Beneficios inmediatos de la utilización de un separador pulmonar flexible durante la disección esqueletizada de la arteria mamaria interna

ObjectiveTo determine the trans-operative benefits of a malleable lung retractor placement during skeletonised internal mammary artery harvesting in coronary artery bypass graft surgery. MethodsA descriptive cross-sectional study was conducted by analysing the trans-operative variables of 62 patients who required a lung retractor placement during left internal mammary artery harvesting. ResultsThe separator was used in 57 patients. The duration of mammary dissection was significantly longer when the retractor was not used (55.5±4.5 vs. 50.4±4.67min). There was also more bleeding during the procedure in that group (69±20.74 vs. 57.2±12.17ml). Pleural cavity integrity was preserved in 87.7% of the patients in whom the retractor was used. ConclusionsClear benefits of the use of lung retractor were demonstrated in terms of decreased mammary artery dissection time, and preservation of pleural cavity, as well as mammary vein integrity.

Motor-Evoked Potential Analysis of Femoral Nerve Status During the Direct Anterior Approach for Total Hip Arthroplasty.

During the direct anterior approach for total hip arthroplasty, a retractor is placed on the anterior wall of the acetabulum to retract the iliopsoas muscle. This step with the retractor has been reported to put the patient at risk for femoral nerve damage. The present study aimed to clarify the effects of the anterior acetabular retractor on the status of the femoral nerve during the direct anterior approach on the basis of transcranial motor-evoked potential (MEP) analysis. Between July 2016 and February 2017, 22 patients underwent primary total hip arthroplasty via the direct anterior approach with MEP analysis. The integrity of the femoral nerve was tested at 3 time points: preoperatively, as a control (first period); just after retractor placement on the anterior wall of the acetabulum (second period); and after the procedure (third period). The association between operative time and femoral nerve status was examined. Postoperative femoral nerve damage was determined by the presence of causalgia and the results of a manual muscle test (MMT) for strength of knee extension. The mean amplitude of the femoral nerve was significantly reduced, from 100% in the first period to 54% (range, 5% to 100%) in the second period (p < 0.01), but then significantly improved to 77% (range, 20% to 100%) in the third period (p < 0.01). In 17 (77%) of the 22 patients, the amplitude of the femoral nerve in the second period was reduced, while only 5 patients (23%) showed no reduction. The mean operative time was 83 minutes (range, 63 to 104 minutes), and no significant correlation was observed between operative time and improvement of femoral nerve status between the second and third periods (p = 0.83 and r = -0.05). All 22 patients had a postoperative MMT grade of 5 for knee extension without causalgia of the femoral nerve. On the basis of the MEP analysis, 17 (77%) of the 22 patients showed a significant reduction of the femoral nerve amplitude despite careful placement of the retractor on the anterior wall of the acetabulum. Although this reduction appears reversible, placement of an anterior retractor should be performed with careful attention to the femoral nerve. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Quantifying Anatomic Deformations During Laryngoscopy.

For a variety of head and neck cancers, specifically those of the oropharynx, larynx, and hypopharynx, minimally invasive trans-oral approaches have been developed to reduce perioperative and long-term morbidity. However, in trans-oral surgical approaches anatomical deformation due to instrumentation, specifically placement of laryngoscopes and retractors, present a significant challenge for surgeons relying on preoperative imaging to resect tumors to negative margins. Quantifying the deformation due to instrumentation is needed in order to develop predictive models of operative deformation. In order to study this deformation, we used a CT/MR-compatible laryngoscopy system in concert with intraoperative CT imaging. 3D models of preoperative and intraoperative anatomy were generated. Mandible and hyoid displacements as well as tongue deformations were quantified for eight patients undergoing diagnostic laryngoscopy. Across patients, we found on average 1.3cm of displacement for these anatomic structures due to laryngoscope insertion. On average, the maximum displacement for certain tongue regions exceeded 4cm. The anatomical deformations quantified here can serve as a reference for describing how the upper aerodigestive tract anatomy changes during instrumentation and may be helpful in developing predictive models of intraoperative upper aerodigestive tract deformation.

Preferential peroneal nerve injury after acetabular fracture and reconstruction

Background: Sciatic nerve dysfunction typically involving the peroneal division infamously plagues acetabular reconstruction through a posterior exposure. Competing explanations include mechanical compression from retractor placement at the hip versus overstretch. In an effort to improve the current care paradigm, we asked what underlying mechanisms of injury lead to preferential injury to the peroneal division of the sciatic nerve. Methods: A cadaver model was established to measure both sciatic nerve strain and intraneural pressure generated during simulated retraction performed during acetabular reconstruction. The tibial and peroneal divisions were studied independently using a micro differential variable reluctance transducer (DVRT) to quantify strain and an angiocatheter to measure intraneural pressure. Measurements were recorded at both the hip and knee. Results: Both divisions of the sciatic nerve experienced significantly more pressure at the hip than at the knee. Knee flexion reduced intraneural pressure of the peroneal division at the hip by approximately 30%. Intraneural pressure at the knee was significantly greater in the peroneal versus tibial nerve during knee extension, yet was reduced with knee flexion. Conclusions: Our results suggest that direct compression of the peroneal nerve during hip retraction has the most potential to cause iatrogenic sciatic nerve injury. Knee flexion was beneficial for decreasing nerve stretch and pressure. The peroneal division, however, is vulnerable to dysfunction because of the higher intraneural pressures experienced by the tethering effect of the fibular tunnel at the knee.

Preventing brachial plexus injury during shoulder surgery: a real-time cadaveric study

Brachial plexopathy is not uncommon after shoulder surgery. Although thought to be due to stretch neuropathy, its etiology is poorly understood. This study aimed to identify arm positions and maneuvers that may risk causing brachial plexopathy during shoulder arthroplasty. Tensions in the cords of the brachial plexuses of 6 human cadaveric upper limbs were measured using load cells while each limb was placed in different arm positions and while they underwent shoulder hemiarthroplasty and revision reverse arthroplasty. Arthroplasty procedures in 4 specimens were performed with standard limb positioning (unsupported), and 2 specimens were supported from under the elbow (supported). Each cord then underwent biomechanical testing to identify tension corresponding to 10% strain (the stretch neuropathy threshold in animal models). Tensions exceeding 15 N, 11 N, and 9 N in the lateral, medial, and posterior cords, respectively, produced 10% strain. Shoulder abduction >70° and combined external rotation >60° with extension >50° increased medial cord tension above the 10% strain threshold. Medial cord tensions (mean ± standard error of the mean) in unsupported specimens increased over baseline during hemiarthroplasty (sounder insertion [4.7 ± 0.6 N, P = .04], prosthesis impaction [6.1 ± 0.8 N, P = .04], and arthroplasty reduction [5.0 ± 0.7 N, P = .04]) and revision reverse arthroplasty (retractor positioning [7.2 ± 0.8 N, P = .02]). Supported specimens experienced lower tensions than unsupported specimens. Shoulder abduction >70°, combined external rotation >60° with extension >50°, and downward forces on the humeral shaft may risk causing brachial plexopathy. Retractor placement, sounder insertion, humeral prosthesis impaction, and arthroplasty reduction increase medial cord tensions during shoulder arthroplasty. Supporting the arm from under the elbow protected the brachial plexus in this cadaveric model.