Modelling and Development of a Mechanical Eye for the Evaluation of Robotic Systems for Surgery.

Ophthalmic surgery, which addresses critical eye diseases such as retinal disorders, remains a formidable and arduous surgical pursuit. Nevertheless, with the advent of cutting-edge robotics and automation technology, significant advancement has been made in recent years to enhance the safety and efficacy of these procedures through meticulous research and development efforts. Ensuring the safe and effective execution of micro-surgical procedures requires stringent quality control measures, notably concerning evaluating and testing the devices utilized. During the development phase, these instruments must undergo extensive and continual evaluation by clinical practitioners to guarantee their safety and efficacy. Ideally, the test conditions should be identical to those of an actual operation. When testing robotic systems for ophthalmology, essential variables of the human eye, such as tissue properties and movement mechanisms, should be addressed. To minimize the discrepancy of tests and actual eye surgery conditions, in this paper, we propose a developed mechanical eye model to enable the realistic evaluation of ophthalmic surgical systems. After developing a virtual and physical model, the model was tested by an eye surgeon. The eye surgeon rated the model with four out of five possible points.Clinical relevance- This method ensures minimal discrepancy in verification of ophthalmic surgical devices by allowing the mechanical eye model to behave similar to the human eye, thus providing a realistic surgical procedure.

The benefits of haptic feedback in robot assisted surgery and their moderators: a meta-analysis.

Robot assisted surgery (RAS) provides medical practitioners with valuable tools, decreasing strain during surgery and leading to better patient outcomes. While the loss of haptic sensation is a commonly cited disadvantage of RAS, new systems aim to address this problem by providing artificial haptic feedback. N = 56 papers that compared robotic surgery systems with and without haptic feedback were analyzed to quantify the performance benefits of restoring the haptic modality. Additionally, this study identifies factors moderating the effect of restoring haptic sensation. Overall results showed haptic feedback was effective in reducing average forces (Hedges' g = 0.83) and peak forces (Hedges' g = 0.69) applied during surgery, as well as reducing the completion time (Hedges' g = 0.83). Haptic feedback has also been found to lead to higher accuracy (Hedges' g = 1.50) and success rates (Hedges' g = 0.80) during surgical tasks. Effect sizes on several measures varied between tasks, the type of provided feedback, and the subjects' levels of surgical expertise, with higher levels of expertise generally associated with smaller effect sizes. No significant differences were found between virtual fixtures and rendering contact forces. Implications for future research are discussed.

The development and evaluation of an in-vitro shoulder simulator with active muscle simulation.

The purpose of the present study was to develop a novel active in-vitro shoulder simulator to emulate all forms of planar and non-planar glenohumeral motions with active muscle simulation on cadaver specimens or shoulder models and to critically evaluate its performance. A physiologic shoulder simulator, driven using simulated muscle force, was developed to dynamically realize accurate kinematic control in all three rotational degrees of freedom (DOF) under physiological kinetic boundaries. The control algorithm of the simulator was implemented using three parallel running independent control loops, which regulate the forces of individual muscles in the respect DOF and work asynchronously in disparate sequences adapted to specific motions (abduction, flexion/extension and rotation). Three cadaveric specimens were used to evaluate the kinematic and kinetic performance of the simulator during simulated motions. High kinematic accuracy (maximum mean deviation ≤ 2.35° and RMSE 1.13°) and repeatability (maximum and average SD of ≤ 1.21° and 0.67°) were observed in all three rotational DOF investigated. The reliabilities of all individual muscle forces actuated in the simulator during planar and non-planar motions were generally excellent, with the 95% CIs of ICC estimates of > 0.90 for most instances (30/36). A novel shoulder simulator with active muscle simulation was developed and evaluated. Its capability to reproduce kinematics and kinetics in a physiological range for all DOF was systematically evaluated for multiple kinetic and kinematic outcome variables. The presented simulator is a powerful tool for investigating the biomechanics of physiological and pathological shoulder joints and to evaluate various surgical interventions. Acquisition of reliable data in joint kinetics and translational kinematics during active motions is critical to assess shoulder pathologies and appropriate treatments. We provide a unique muscle activated physiologic shoulder simulator, which allows the comprehensive acquisition of joint kinematic and kinetic data during repeated realistic planar and non-planar motions.

Biomechanical Comparison of Two Fixation Techniques for Lateral Ulnar Collateral Ligament Repair With Ligament Bracing.

PURPOSE: Ligament bracing is a technique of suture reinforcement that can be used to augment lateral ulnar collateral ligament repair in the treatment of posterolateral rotatory instability of the elbow, thereby improving early stability of the repair. However, multiple failures of the ulnar anchor during implantation have been documented. We hypothesized that the use of a cortical button for ulnar fixation of the ligament brace would be biomechanically comparable to a suture anchor construct. METHODS: Sixteen elbows were tested with a materials testing machine. The intact, dissected, and repaired lateral collateral ligament complex was tested with a cyclic varus rotational torque of 0.5-3.5 Nm in 120°, 90°, 60°, and 30° elbow flexion. For the repair, the specimens were randomized into 2 groups: ulnar fixation of the ligament bracing using a suture anchor and ulnar fixation of the ligament bracing using a cortical button. The number of implant failures was documented. A load-to-failure protocol was conducted in 90° elbow flexion. RESULTS: Load to failure was comparable and was found to be 20.7 Nm in the suture anchor group and 21.8 Nm in the cortical button group. Laxity after ligament bracing did not differ significantly between suture anchor and cortical button fixation. Compared with the native ligament, the laxity was significantly reduced after ligament bracing. The failure mode was slippage of the suture tape through the humeral anchor in all cases. Additionally, the capitellum was damaged in 9 of 16 cases. CONCLUSIONS: A cortical button for ulnar fixation of the ligament bracing was comparable with a suture anchor fixation with regard to biomechanical properties such as laxity and load to failure. CLINICAL RELEVANCE: A cortical button fixation is less prone to failure of insertion. This would improve the implantation technique, while clinical results are expected to be comparable.

The novel arthroscopic subscapular quadriceps tendon-bone sling procedure provides increased stability in shoulder cadavers with severe glenoid bone loss.

PURPOSE: Treatment of anterior glenoid bone loss in patients with recurrent anterior shoulder instability is a challenge. The subscapular sling method with quadriceps tendon bone (QTB) graft is a modification of the subscapular sling with a semitendinosus (ST) graft. The aim of the study was to test the biomechanical stability of the QTB sling procedure in human shoulder cadavers with severe anterior glenoid bone loss. METHODS: Fourteen cadaveric shoulders were tested with a force-moment-guided robot in three conditions: physiologically intact, anterior glenoid bone resection, and the subscapular sling procedure with a QTB graft. Joint stability was measured in anterior, anterior inferior and inferior directions in four glenohumeral joint positions: 0° and 60° of glenohumeral abduction, with each at 0° and 60° of external rotation. Maximum external rotation was measured at 0° and 60° glenohumeral abduction. Computer tomography scans were obtained preoperatively to plan the glenoid bone resection, as well as postoperatively to calculate the proportion of the glenoid bone actually resected. RESULTS: Significantly decreased translations were observed in the shoulders with the QTB sling compared to the intact joint and the glenoid bone loss model. No significant differences in maximum external rotation were observed between the three different conditions. CONCLUSION: This biomechanical study revealed a significant stabilizing effect of the arthroscopic subscapular QTB graft sling procedure in human shoulder cadavers without compromising external rotation. Clinical trials may reveal the usefulness of this experimental method.

Suture tape augmentation of the lateral ulnar collateral ligament increases load to failure in simulated posterolateral rotatory instability.

PURPOSE: Simple elbow dislocations are accompanied with lateral ulnar collateral ligament ruptures. For persisting instability, surgery is indicated to prevent chronic posterolateral rotatory instability. After lateral collateral ligament (LCL) complex repair the repair is protected by temporary immobilization, limited range of motion and hinged bracing. Internal bracing is an operative alternative augmenting the LCL repair using non-absorbable suture tapes. However, the stability of LCL repair with and without additional augmentation remains unclear. The hypothesis was that LCL repair with additional suture tape augmentation would improve load to failure. Secondary goal of this study was to evaluate different humeral fixation techniques. A humeral fixation using separate anchors for the LCL repair and the augmentation was not expected to provide superior stability compared to using only one single anchor. METHODS: Twenty-one elbows were tested. A cyclic varus rotational torque of 0.5-3.5 Nm was applied in 90°, 60°, 30°, and 120° elbow flexion to the intact, torn, and repaired LCLs. The specimens were randomized into three groups: repair alone (group I), repair with additional internal bracing using two anchors (group II), repair using one humeral anchor (group III). A load-to-failure protocol was conducted. RESULTS: Load to failure was significantly higher in groups II (26.6 Nm; P = 0.017) and III (23.18 Nm; P = 0.038) than in group I (12.13 Nm). No significant difference was observed between group II and III. All specimens lost reduction after LCL dissection by a mean of 4.48° ± 4.99° (range 0.66-15.82). The mean reduction gain after repair was 7.21° ± 4.97° (2.70-21.23; mean over reduction, 2.73°). The laxity was comparable between the intact and repaired LCLs (n.s.), except for varus movements at 30° in group II (P = 0.035) and 30° (P = 0.001) and 120° in group III (P = 0.008) with significantly less laxity. Inserting the ulnar suture anchor showed failure in the thread in 10 cases. CONCLUSION: LCL repair with additional internal bracing yielded higher load to failure than repair alone. Repair with additional internal bracing for the humeral side using one anchor was sufficient. A higher primary stability would facilitate postoperative management and allow immediate functional treatment. Reducing the number of humeral anchors would save costs.

Anatomic factors influencing the anterior stability of reverse total shoulder arthroplasty.

BACKGROUND: Several factors affect the stability of the reverse shoulder arthroplasty. The influence of bony anatomy on anterior stability remains unclear. This study aimed to identify the correlations between bony anatomy and anterior dislocation forces. METHODS: The differences in anterior dislocation force in reverse total shoulder arthroplasty reported in a previous biomechanical study were used to analyze the anatomic factors influencing anterior stability. The critical shoulder angle, glenocoracoid distance in 2 planes, and glenoid inclination were measured in the tested specimens using 3-dimensional computed tomographic scans and radiographs. Anatomic parameters were then correlated with the anterior dislocation forces. RESULTS: The critical shoulder angle had no correlation with anterior stability. The glenocoracoid distance in anteroposterior direction showed a negative correlation with the stability of a reverse shoulder arthroplasty with a 9-mm lateralized glenosphere and 155° humeral inclination in 30° and 60° glenohumeral abduction with the arm in 30° external rotation (r = -0.662, P = .004; r = -0.794, P = .011) and 30° glenohumeral abduction with neutral rotation (r = -0.614, P = .009). Using the same hardware configuration, the anterior stability had a negative correlation with the glenocoracoid distance in the mediolateral direction in 30° of glenohumeral abduction with the arm in 0° and 30° of external rotation (r = -0.542, P = .025; r = -0.497, P = .042). CONCLUSION: The distance between the coracoid tip and glenoid in 2 planes had a significant negative correlation with the anterior stability of the reverse shoulder arthroplasty with a lateralized glenosphere and 155° humeral inclination. The findings suggest that only glenoid lateralization is influenced by the bony anatomy.

The Laxity of the Native Knee: A Meta-Analysis of in Vitro Studies.

BACKGROUND: Although soft-tissue balancing plays an important role in knee arthroplasty, we are aware of no objective target parameters describing the soft-tissue tension of the native knee. In the present study, we aimed to meta-analyze data from studies investigating native knee laxity to create a guide for creating a naturally balanced knee joint. METHODS: PubMed and Web of Science were searched for studies with laxity data published from 1996 through 2016. Graphs were digitally segmented in cases in which numerical data were not available in text or table form. Three-level random-effects meta-analyses were conducted. RESULTS: Seventy-six studies evaluating knee laxity at various flexion angles (0° to 90°) were included. Knee laxity was significantly different between 0° and 90° of flexion (p < 0.001) in all 6 testing directions, with mean differences of 0.94 mm and -0.35 mm for anterior and posterior translation, 1.61° and 4.25° for varus and valgus rotation, and 1.62° and 6.42° for internal and external rotation, respectively. CONCLUSIONS: Knee laxity was dependent on the flexion angle of the knee joint in all degrees of freedom investigated. Furthermore, asymmetry between anterior-posterior, varus-valgus, and internal-external rotation was substantial and depended on the joint flexion angle. CLINICAL RELEVANCE: If the goal of knee arthroplasty is to restore the kinematics of the knee as well as possible, pooled laxity data of the intact soft tissue envelope could be useful as a general guide for soft-tissue balancing in total knee arthroplasty.

Cement augmentation as revision strategy for loosened thick-diameter non-fenestrated iliac screws - A biomechanical analysis.

BACKGROUND: Loosened/pulled-out iliac screws can be a challenging complication, as revision opportunities are limited because more distal anchorage is impossible. Insertion of thick-diameter screws is an option in cases with loosened thin-diameter screws. However, this is occasionally infeasible in patients with loosened thick-diameter screws. Therefore, this study aimed to biomechanically analyze whether loosened/pulled-out thick iliac screws regain strong anchorage following cement augmentation. METHODS: Six human pelvis specimens were dissected to isolate 12 hemipelves, and 9 × 80 mm iliac screws were implanted. The pullout maneuver was performed followed by cement augmentation of the same screw within the same screw hole. After cement hardening, pullout was performed again. Forces needed for pullout and the insertion torque were measured for the 12 iliac screws. FINDINGS: Cement augmentation significantly increased stability, with the pullout forces required being as high as 953.23 N (standard deviation [SD] 1070.46 N; median 306.30 N) for the uncemented screws and 2897.53 N (SD 585.83 N; median 2907.81 N) after cement augmentation (p < 0.001). No correlation was found between insertion torques and pullout forces. INTERPRETATION: While revision of loosened iliac screws can often be achieved using higher diameters, this method is limited by the thickness of the screws already in place. We demonstrated that cement augmentation significantly increases stability even in thick-diameter screws, achieving more pullout stability than before the initial pullout. This method may be a cost-effective and rapid option for revision, even with significant defects and with no thicker-diameter iliac screw being available.

Effect of the humeral neck-shaft angle and glenosphere lateralization on stability of reverse shoulder arthroplasty: a cadaveric study.

BACKGROUND: Lateralizing the glenosphere and decreasing the humeral neck-shaft angles are implant design parameters that reduce the risk of scapular impingement. The effects of these parameters on joint stability remain unclear. This study evaluated the effect of glenosphere lateralization and humeral neck-shaft angle on joint stability by quantifying the anterior dislocation force in different arm positions. METHODS: Reverse shoulder arthroplasty was performed on 19 human shoulder specimens. Anterior dislocation force and maximum external rotation were evaluated using a robot-based shoulder simulator. By varying the neck-shaft angle and magnitudes of glenosphere lateralization, 12 configurations were analyzed with the glenohumeral joint in 30° and 60° of abduction, in neutral, and in 30° of external rotation. RESULTS: At 30° of abduction, measurements showed significantly higher dislocation forces for the 9-mm and 6-mm lateralized glenosphere than for the 0-mm (P < .0001, P = .007) nonlateralized glenosphere. At 60° of abduction, measurements showed significantly higher dislocation forces for the 9-mm and 6-mm lateralized glenosphere than for the 0-mm (P < .0001, P = .0007) and 3-mm (P = .0003, P = .04) glenosphere. Configurations with a neck-shaft angle of 135° showed significantly higher dislocation forces than configurations with a neck-shaft angle of 145° (P = .02) or 155° (P = .02) at 30° of abduction in 30° of external rotation. Neck-shaft angle and glenosphere lateralization had no influence on maximum external rotation capability. CONCLUSION: Glenosphere lateralization significantly increased anterior stability of the glenohumeral joint without influencing the range of passive external rotation. The humeral neck-shaft angle only had a minor effect on anterior stability.