Joint assessment through manual physical examination is a fundamental skill that must be acquired by orthopaedic surgeons. These joint assessments allow surgeons to identify soft tissue injuries (e.g. ligament tears) which are critical in identifying appropriate treatment options.

The difficulty in communicating the feeling of different joint conditions and the limited opportunities for practice can make these skills challenging to learn, resulting in reduced treatment effectiveness and increased costs. This research seeks to improve the training of joint assessment with the creation of a haptic joint simulator that can train surgeons with increased effectiveness.

A first of its kind haptic simulator is presented, which incorporates: a newly defined kinetic knee simulation, a haptic device for user interaction, and a haptic control algorithm. The knee model has been specifically created for this application and allows six degree-of-freedom manipulation of the tibia while considering the effects of ten knee ligament bundles. The model has been mathematically formulated to allow for the high update rates necessary for smooth and stable haptic simulation.

Two quantitative assessments were made of the model to confirm its clinical validity. The first was against the widely used OpenSim biomechanical simulation software. Simulations of the model's performance for both anterior-posterior draw tests and varus-valgus rotation tests showed less than 0.7%RMSE for force and 5.5%RMSE for moments. Crucially, the proposed model could generate updated forces in less than 1ms, compared to 188ms for OpenSim. The second validation of the model was against a cadaveric knee that was tested using a validated robotic testing platform. This comparison showed that the model could generate similar force- motion pathways to the cadaveric knee after the model's parameters were scaled to match.

Having demonstrated that it is possible to create a computational knee model that has good conformance to gold-standard knee simulations and cadaveric recordings, while updating at less than 1ms, this research has overcome a major hurdle. The next stage of this research will be to incorporate the knee model into a full haptic simulator and perform skill acquisition trials. Given the effectiveness of past haptic training systems in aiding clinical skills acquisition, this research offers a promising way to improve surgeon training, and therefore also patient diagnosis and treatment.

Patient Specific Instruments (PSIs) are becoming an increasingly common method to provide surgeons with assistance in accurately performing procedures; however, to our knowledge, these new instruments have only been applied to traditional, highly invasive surgical approaches. However, PSIs have the potential to decreased surgical invasiveness by reducing the surgeon's need to clearly visualise anatomical landmarks. Therefore, we designed and evaluated a novel PSI for minimally invasive shoulder arthroplasty.

The proposed minimally invasive approach prevents en face access to the articular surfaces and thus the PSI was designed to guide the accurate placement of a trans-humeral bone tunnel which would permit surgical steps to be conducted. To accurately create this tunnel and place a guide pin in the glenoid, the PSI was designed as a two sided guide that incorporates unique anatomical features from both bones, which would lock the two bones in a predefined pose relative to one another. Proper registration of the PSI is aided by the joint's passive compression force, which is not disrupted due to the soft tissue sparing approach. Once the bones are locked together, a guide pin could be passed through the humeral head – creating a bone tunnel to guide later humeral bone preparation – and into the glenoid to guide reaming and drilling. By designing the guide in this way, it is possible to avoid the need to perform surgical steps with a clear en face view.

The PSI was created by loading 3D reconstructed CT models of the humerus and scapula into a CAD package, aligning the desired humeral and scapular guide axes such that the bones' relative pose is fully defined, and finally constructing the guide itself between and around the articular surfaces, such that sufficient anatomical features are incorporated to provide complete physical registration with the bones. This PSI was subsequently customised, based on a cadaveric specimen and fabricated using a 3D printer. The PSI's usability and accuracy in achieving the pre-operative plan were then assessed using optical tracking and surface based registration procedure.

Results of the evaluation demonstrated that the designed PSI is capable of accurately registering the two bones to within 5mm and 14° of the intended pre-operative plan, while also effectively reducing the invasiveness of the surgical procedure. Therefore, this novel PSI may represent a new avenue to improve the clinical impact of CAOS systems, by achieving good surgical accuracy, but with a greatly reduced invasiveness.

Purpose

Glenoid component loosening is a common reason for failed total shoulder arthroplasty. Multiple factors have been suggested as causes for component loosening that may be related to cement technique. The purpose of the study was to compare the load transfer across a polyethylene glenoid bone construct with two different cementing techniques.

Purpose

The management of moderate to large engaging Hill-Sachs lesions is controversial and surgical options include remplissage, allograft reconstruction, and partial resurfacing arthroplasty. Few in-vitro studies have quantified their biomechanical characteristics and none have made direct comparisons. The purpose of this study was to compare joint stability and range of motion (ROM) among these procedures using an in-vitro shoulder simulator. It was hypothesized that all procedures would prevent defect engagement, but allograft and partial resurfacing would most accurately restore intact biomechanics; while remplissage would provide the greatest stabilization, possibly at the expense of motion.

Purpose

The remplissage procedure may be performed as an adjunct to Bankart repair to address an engaging Hill-Sachs defect. Clinically, it has been reported that the remplissage procedure improves joint stability but that it may also restrict shoulder range of motion. The purpose of this biomechanical study was to examine the effects of the remplissage procedure on shoulder motion and stability. We hypothesized that the remplissage procedure would improve stability and prevent engagement but may have a deleterious effect on motion.

Purpose

The remplissage technique of insetting the infraspinatus tendon and posterior joint capsule into an engaging Hill-Sachs lesion has gained in popularity. However, a standardized technique for suture anchor and suture placement has not been defined for this novel procedure. The purpose of this biomechanical study was to compare three remplissage techniques by evaluating their effects on joint stiffness and motion.

Purpose

Coracoid transfer is an effective reconstructive procedure for complex glenohumeral joint instability. Recently, the congruent-arc Latarjet procedure has been described which orients the coracoid graft undersurface flush to the glenoid articular margin. The purported advantage of this modification is that the radii of curvature of the coracoid undersurface and the anterior glenoid rim are believed to be similar, and therefore, congruent. The purpose of this study was to determine the dimensions of the coracoid and to compare the radius of curvature (ROC) of the coracoid undersurface to the ROC of the intact glenoid and various glenoid bone-loss scenarios.

Purpose: Glenoid component loosening is a common reason for failed total shoulder arthroplasty. Multiple factors have been suggested as causes for component loosening including asymmetric loading of the glenoid prosthesis by the humeral head (rocking horse phenomenon). A novel technique was employed to measure in-vitro strain in the subchondral bone adjacent to a cemented all polyethylene pegged glenoid prosthesis. The purpose of the study was to develop and validate a testing protocol to investigate load transfer in the polyethylene glenoid implant and bone construct.

Method: Eight polyethylene components were implanted using standard cementing techniques in eight cadaveric specimens. Loading was performed with a pneumatic actuator capable of applying loads at various angles. A dynamic 10 N/s force was applied for a total of 15 seconds producing a maximum force of 150N at angles of 0, 10, 20, 30, 40 and 50o. Strain gauges were placed around the implant 1mm proximal to the bone-cement interface at the four quadrants. The humeral head was simulated with a custom steel ball with a non-conforming diameter in relation to the prosthesis that is typical in total shoulder arthroplasty.

Results: During pure compressive loading, tension was observed in the superior and inferior quadrants of the glenoid. Superior and inferior loading caused increasing same side (ipsilateral) tension, occurring from 0 to 30o and 0 to 20o, respectively. Compression was recorded superiorly when loading was applied at 40o and 50o in the superior direction while contralateral tension was recorded in the inferior gauges. Strain measurements were less consistent in the anterior and posterior glenoid quadrants and varied between tension and compression.

Conclusion: Tension measurements in the ipsilateral direction at lower angles were unexpected. This observation differs from the previous assumption that applied loads at relatively perpendicular angles to the implant should dissipate as compression. Tension at the bone cement interface is unfavorable. The identification of tension in some quadrants of the implant in this study, therefore, may have revealed a mechanism of implant loosening. Our data support the previously described rocking horse phenomena and also illustrate a new umbrella type effect of polyethylene flexure, which causes the periphery of the glenoid implant to flex upwards superiorly and inferiorly. These findings have the potential to influence future designs of total shoulder arthroplasty perhaps leading to increased implant survival.

Purpose: Blocking screws placed adjacent to intramedullary nails supplement fixation in long bone fractures with a short proximal or distal segment. Clinically, blocking screws are placed using fluoroscopy, resulting in variability in screw placement. The clinical significance of the accuracy of screw placement is unknown. Recently, a targeted blocking screw device was developed, enabling precise placement of screws adjacent to the nail. The purpose of this study was to evaluate the mechanical effects of locking screws (LS) and targeted (TBS) and non-targeted blocking screws (NBS) in distal femur fractures.

Method: Sawbone^® femurs were used to create a fracture model. Femoral sawbone specimens were osteotomized eight cm proximal to the knee joint and a two cm gap was created. Intramedullary nails were used for stabilization, including one proximal locking screw and varying the distal screw configuration for study purposes. Targeted blocking screws were inserted directly adjacent to the intramedullary device using the commercially-available targeting device. Non-targeted screws were inserted one screw diameter medial or lateral to the “ideal” position. Four study groups were created; group one consisted of TBS and two distal LS. Group two had TBS and one LS. Group three had NBS and two LS, and group four consisted of NBS and one LS. Specimens were subjected to a cyclic compression protocol along the mechanical axis of the femur. Applied load varied from 100 to 700 N in 100 N incremental staircase loading protocol. Load-displacement curves recorded construct stiffness. Fracture gap motion was measured with electronic calipers.

Results: Targeted constructs were stiffer at all load levels, and 10% stiffer overall. Differences were statistically significant at moderate load levels (Group one vs three, 400N and 500N, p< 0.05).

Conclusion: Targeted constructs were stiffer at all load levels despite Sawbones^® undergoing significant deformation at the proximal femur, masking the relatively smaller differences in motion at the fracture site. A difference in sagittal motion was found between groups with one and two LS, independent of the position of blocking screws. In conclusion, targeted blocking screw constructs were stiffer at all load levels compared to non-targeted constructs. The number of LS was a factor in sagittal plane stability. This study suggests that using targeted blocking screws in distal femur fractures may reduce fracture motion and decrease post operative malalignment.

Purpose: Loosening of glenoid components in total shoulder arthroplasty is a common clinical problem which can necessitate revision surgery. The mechanism of loosening is poorly understood and may relate to implant design, component fixation techniques, and interfacial tensile stresses. We are unaware of any studies that have examined the fundamental aspects of load transfer to bone for various joint loading configurations. Hence, the objective of this study was to investigate the effect of joint loading on bone strain adjacent to a poly-ethylene glenoid implant.

Method: Five specimens (4 males; avg age: 59.5 yrs) implanted with a cemented, all polyethylene component (Anatomical Shoulder; Zimmer) were tested using an apparatus capable of producing loading vectors with various angles, magnitudes and directions. Each specimen was tested using a ramp load of 0–150 N (at 10N/sec) in two directions (superior and inferior) and with six angles of load application. A uniaxial strain gauge was placed in each of the four quadrants of the glenoid, approximately 1 mm medial to the glenoid rim. The primary axis of each strain gauge was oriented medio-laterally to record bone strains. The humeral head was simulated by a custom steel ball with a radius of curvature consistent with a nonconforming humeral prosthesis.

Results: The relationship between strain and applied force was not linear (superior quadrant at 40o: linear fit R2=0.96; quadratic fit R2=0.999; p< 0.0005), and was dependent on the loading angle. During pure compressive loading, tension was observed in the superior and inferior quadrants of the glenoid; while less consistent results in the anterior and posterior quadrants revealed variable tension and compression. Superior and inferior loading each caused increasing ipsilateral tension, occurring from 0–30o and 0–20o, respectively.

Conclusion: The current study is thought to be the first to directly measure load transfer at the implant-bone interface. We demonstrated load transfer nonlinearities between a surgically implanted glenoid component and the underlying bone in all locations and for a wide range of loading conditions. This has important implications towards the modeling of these constructs using finite element analyses. The results also illustrate tensile loading during compressive and small eccentricity loading cases. These results suggest a polyethylene flexure, causing the periphery of the glenoid implant to flex upwards placing the cement mantle and underlying bone in tension. Tensile loads that are linked to cement mantle fracture and implant loosening are produced under loading conditions associated with activities of daily living. This study has provided insight into the mechanisms of load transfer between a cemented polyethylene glenoid implant and the underlying bone. Reduction or elimination of these interfacial tensile stresses around the glenoid periphery should be considered when developing novel methods for component fixation.