To quantify bone-nail fit in response to varying nail placements by entry point translation in straight antegrade humeral nailing using three-dimensional (3D) computational analysis

CT scans of ten cadaveric humeri were processed in 3D Slicer to obtain 3D models of the cortical and cancellous bone. The bone was divided into individual slices each consisting of 2% humeral length (L) with the centroid of each slice determined. To represent straight antegrade humeral nail, a rod consisting of two cylinders with diameters of 9.5mm and 8.5mm and length of 0.22L mm and 0.44L mm respectively joined at one end was modelled. The humeral head apex (surgical entry point) was translated by 1mm in both anterior-posterior and medio-lateral directions to generate eight entry points. Total nail protrusion surface area, maximum nail protrusion distance into cortical shell and top, middle, bottom deviation between nail and intramedullary cavity centre were investigated. Statistical analysis between the apex and translated entry points was conducted using paired t-test.

A posterior-lateral translation was considered as the optimal entry point with minimum protrusion in comparison to the anterior-medial translation experiencing twice the level of protrusion. Statistically significant differences in cortical protrusion were found in anterior-medial and posterior-lateral directions producing increased and decreased level of protrusion respectively compared to the apex. The bottom anterior-posterior deviation distance appeared to be a key predictor of cortical breach with the distal nail being more susceptible. Furthermore, nails with anterior translation generated higher anterior-posterior deviation (>4mm) compared to posterior translation (<3mm).

Aside from slight posterolateral translation of the entry point from the apex, inclusion of a distal posterior-lateral bend into current straight nail design could improve nail fitting within the curved humeral bone, potentially improving distal working length within the flat and narrow medullary canal of the distal humeral shaft.

To analyse bone stresses in humerus-megaprosthesis construct in response to axial loading under varying implant lengths in proximal humeral replacement following tumour excision.

CT scans of 10 cadaveric humeri were processed in 3D Slicer to obtain three-dimensional (3D) models of the cortical and cancellous bone. Megaprostheses of varying body lengths (L) were modelled in FreeCAD to obtain the 3D geometry. Four FE models: group A consisting of intact bone; groups B (L=40mm), C (L=100mm) and D (L=120mm) comprising of humerus-megaprosthesis constructs were created. Isotropic linear elastic behaviour was assigned for all materials. A tensile load of 200N was applied to the elbow joint surface with the glenohumeral joint fixed with fully bonded contact interfaces. Static analysis was performed in Abaqus. The bone was divided at every 5% bone length beginning distally. Statistical analysis was performed on maximum von Mises stresses in cortical and cancellous bone across each slice using one-way ANOVA (0-45% bone length) and paired t-tests (45-70% bone length). To quantify extent of stress shielding, average percentage change in stress from intact bone was also computed.

Maximum stress was seen to occur distally and anteriorly above the coronoid fossa. Results indicated statistically significant differences between intact state and shorter megaprostheses relative to longer megaprostheses and proximally between intact and implanted bones. Varying levels of stress shielding were recorded across multiple slices for all megaprosthesis lengths. The degree of stress shielding increased with implant lengthening being 2-4 times in C and D compared to B.

Axial loading of the humerus can occur with direct loading on outstretched upper limbs or indirectly through the elbow. Resultant stress shielding effect predicted in longer megaprosthesis models may become clinically relevant in repetitive axial loading during activities of daily living. It is recommended to use shorter megaprosthesis to prevent failure.

This study aims to compare the biomechanical properties of the “Double Lasso-Loop” suture anchor (DLSA) technique with the commonly performed interference screw (IS) technique in an ex vivo ovine model.

Fourteen fresh sheep shoulder specimens were used in this study. Dissection was performed leaving only the biceps muscle attached to the humerus and proximal radius before sharply incised to simulate long head of biceps tendon (LHBT) tear. Repair of the LHBT tear was performed on all specimens using either DSLA or IS technique. Cyclical loading of 500 cycles followed by load to failure was performed on all specimens. Tendon displacement due to the cyclical loading at every 100 cycles as well as the maximum load at failure were recorded and analysed. Stiffness was also calculated from the load displacement graph during load to failure testing.

No statistically significant difference in tendon displacement was observed from 200 to 500 cycles. Statistically significant higher stiffness was observed in IS when compared with DSLA (P = .005). Similarly, IS demonstrated significantly higher ultimate failure load as compared with DSLA (P = .001). Modes of failure observed for DSLA was mostly due to suture failure (7/8) and anchor pull-out (1/8) while IS resulted in mostly LHBT (4/6) or biceps (2/6) tears. DSLA failure load were compared with previous studies and similar results were noted.

After cyclical loading, tendon displacement in DLSA technique was not significantly different from IS technique. Despite the higher failure loads associated with IS techniques in the present study, absolute peak load characteristics of DLSA were similar to previous studies. Hence, DLSA technique can be considered as a suitable alternative to IS fixation for biceps tenodesis.

This study aims to investigate the mechanical properties of a rotator cuff tear repaired with a polypropylene interposition graft in an ovine infraspinatus ex-vivo model.

Twenty fresh shoulders from skeletally mature sheep were used in this study. A tear size of 20 mm from the tendon joint was created in the infraspinatus tendon to simulate a large tear in fifteen specimens. This was repaired with a polypropylene mesh used as an interposition graft between the ends of the tendon. Eight specimens were secured with mattress stitches while seven were secured to the remnant tendon on the greater tuberosity side by continuous stitching. Remaining five specimens with an intact tendon served as a control group. All specimens underwent cyclic loading with a universal testing machine to determine the ultimate failure load and gap distance.

Gap distance increased with progressive cyclic loading through 3000 cycles for all repaired specimens. Mean gap distance after 3000 cycles for both continuous and mattress groups are 1.7 mm and 4.2 mm respectively (P = .001). Significantly higher mean ultimate failure load was also observed with 549.2 N in the continuous group, 426.6 N in the mattress group and 370 N in the intact group.

The use of a polypropylene mesh as an interposition graft for large irreparable rotator cuff tears is biomechanically suitable and results in a robust repair that is comparable to an intact rotator cuff tendon. When paired with a continuous suturing technique, it demonstrates significantly resultant superior biomechanical properties that may potentially reduce re-tear rates after repairing large or massive rotator cuff tears.

Introduction and Objective

Curative resection of proximal humerus tumours is now possible in this era of limb salvage with endoprosthetic replacement considered as the preferred reconstructive option. However, it has also been linked with mechanical and non-mechanical failures such as stem fracture and aseptic loosening. One of the challenges is to ensure that implants will endure the mechanical strain under physiological loading conditions, especially crucial in long surviving patients. The objective is to investigate the effect of varying prosthesis length on the bone and implant stresses in a reconstructed humerus-prosthesis assembly after tumour resection using finite element (FE) modelling.

The function of the shoulder joint has traditionally been evaluated based on range of motion (ROM) in predefined anatomical planes and also by using functional scores, which assessed shoulder function based on the ability to conduct certain activities of daily living (ADLs). However, measuring ROM only in terms of flexion-extension, abduction-adduction and internal-external rotation may under-account for the 3-dimensional mobility of the shoulder joint. Furthermore, functional scores, such as the Oxford shoulder score or American shoulder and elbow surgeons (ASES) score, are subjective measures and are not an accurate assessment of shoulder joint function. In this study, we proposed the use of the globe model of the shoulder joint which can be used to provide an objective measure of the global ROM and also function of the shoulder joint – termed the Global and Functional arc of motion (GAM and FAM).

Thirty-three young, healthy male patients (23.7 ± 1.5 years) were recruited and tasked to perform eight ADLs and a full humeral circumduction movement which represented their active global ROM. Reflective markers were placed in accordance to the International Society of Biomechanics (ISB) and optical-based motion capture cameras were used to track relative motion of the dominant humerus with respect to the thorax (i.e. thoracohumeral motion). The GAM and FAM were generated by plotting the thoracohumeral on a spherical coordinate system during global ROM and the eight ADLs respectively. Shoulder joint global ROM and function were quantified by calculating the area enclosed by the closed loop of GAM and FAM respectively.

The spherical coordinate system, or more commonly referred to as the globe model, describes thoracohumeral movement using plane of elevation (POE), angle of elevation (AOE) and rotation. In our model, POE and AOE represents longitude and latitude of the globe respectively, and rotation is depicted using a red-green-blue (RGB) colour scale. Overall, subject's GAM of the shoulder joint covered an area of 4.64 ± 0.48 units2 compared to only 1.12 ± 0.26 units2 for the FAM. Subjects only required 24.4 ± 5.7 % of their global shoulder ROM for basic daily functioning.

Studies that reduced shoulder joint movement into planar movements (i.e. sagittal, coronal and rotation) do not account for the 3-dimensional nature of the joint and doing so may overestimate the requirement of the shoulder joint for ADLs relative to its ROM in each plane. While others have attempted to use the globe model, such studies tend to reduce the globe into its descriptive angles (i.e. POE, AOE and rotation), reducing its intuitiveness. In contrast, by keeping an intact globe, the proposed globe model was more intuitive and yet capable of quantifying both shoulder joint global ROM and function. Doing so, we found that young healthy subjects only required approximately a quarter of their global ROM of the shoulder joint to complete the most common daily tasks, which was significantly less than what was previously reported.

Introduction

The epicondylar axis of the elbow is a surface anatomical approximation of the true flexion-extension (F-E) axis used in the application of an external fixator/elbow arthroplasty. We hypothesise that the epicondylar axis coincides with the true F-E axis in terms of both angular displacement and position (ie. offset). This suggests that it can serve as a good landmark in total dynamic external fixator application and elbow arthroplasty.

Objective

Patient-specific instrumentation (PSI) is a novel technique in total knee arthroplasty (TKA) which potentially permits more accurate alignment of the components; however, there is no consensus in literature regarding the accuracy and reliability of PSI as many studies have shown controversial and inconsistent results of various PSI systems. A 24-month follow-up study was carried out to compare perioperative clinical outcomes, radiological limb alignment and component positioning, as well as functional outcomes following TKA between PSI and conventional instrumentation (CI).

Introduction

Failures in total knee arthroplasty (TKA) have been associated with overall lower limb malalignment and component malposition. Although traditional computer navigation systems improve component placement, they require fixation of the femoral and tibial reference arrays for software recognition using anchoring pins. This increases the risk of bony fracture, pin sites infection and osteomyelitis.

Introduction

Total hip replacement is an established surgical procedure done to alleviate hip pain due to joint diseases. However, this procedure is avoided in yonger patients with higher functional demands due to the potential for early failure. An ideal prosthesis will have have a high endurance against impact loading, with minimal micromotion at the bone cement interface, and a reduced risk of fatigue failure, with a favourable stress distribution pattern in the femur. We study the effect of varying the material properties and design element in a standard cemented total hip using Finite Element Analysis.

Summary Statement

This 3-dimensional CT study on cadaveric proximal ulna provides further insight into the size and geometry of the proximal ulna intramedullary cavity with potential applications to design and sizing of proximal ulna components.

Introduction

Total knee arthroplasty (TKA) has proven to be cost-effective and efficative in the treatment of osteoarthritic knees. Although traditional computer navigation systems improve implant placement, they require fixation of the femoral and tibial reference arrays for software recognition using anchoring pins. This increases the risk of bony fracture, pin sites infection and osteomyelitis. Our study aims to investigate the accuracy of a new inless navigation system (Brainlab VectorVision Knee 2.5 Navigation System) that would avoid these complications.