Supraspinatus and infraspinatus tears (Massive Rotator Cuff Tear- MRCT) cause compensatory activation of the teres minor (TM) and subscapularis (SubS) to maintain humeral head alignment. This study measures force changes in TM and SubS using a dynamic shoulder testing setup. We hypothesize that combining superior capsule reconstruction (SCR) and lower trapezius tendon (LTT) transfer will correct rotator cuff forces. Eight fresh-frozen human shoulder specimens from donors aged 55-75 (mean = 63.75 years), balanced for gender, averaging 219.5 lbs, were used. Rotator cuff and deltoid tendons were connected to force sensors through a pulley system, with the deltoid linked to a servohydraulic motor for dynamic force measurement. The system allowed unrestricted humeral abduction from 0 to 90 degrees.Introduction
Methods
Understanding knee joint biomechanics is crucial, but studying Anterior cruciate ligament (ACL) biomechanics in human adolescents is challenging due to limited availability cadaveric specimens. This study aims to validate the adolescent porcine stifle joint as a model for ACL studies by examining the ACL's behavior under axial and torsion loads and assessing its deformation rate, stiffness, and load-to-failure. Human knee load during high-intensity sports can reach 5-6 times body weight. Based on these benchmarks, the study applied a force equivalent to 5-times body weight of juvenile porcine samples (90 pounds), estimating a force of 520N. Experiments involved 30 fresh porcine stifle joints (Yorkshire breed, Avg 90 lbs, 2-4 months old) stored at -22°C, then thawed and prepared. Joints were divided into three groups: control (load-to-failure test), axially loaded, and 30-degree torsion loaded. Using a servo-hydraulic material testing machine, the tibia's longitudinal axis was aligned with the load sensor, and specimens underwent unidirectional tensile loading at 1 mm/sec until rupture. Data on load and displacement were captured at 100 Hz.Introduction
Methods
Treatment strategies for irreparable Massive Rotator Cuff Tears (MRCTs) are debatable, especially for younger, active patients. Superior Capsular Reconstruction (SCR) acts as a static stabilizer, while Lower Trapezius Transfer (LTT) serves as a dynamic stabilizer. This study compares the biomechanical effectiveness of SCR and LTT, hypothesizing that their combination will enhance shoulder kinematics. Eight human shoulders from donors aged 55-75 (mean = 63.75 years), balanced for gender, averaging 219.5 lbs, were used. Rotator cuff and deltoid tendons were connected to force sensors through a pulley system, with the deltoid linked to a servohydraulic motor for dynamic force measurement.Introduction
Methods
Chondral defects in the knee have cartilage biomechanical differences due to defect size and orientation. This study examines how the tibiofemoral contact pressure is affected by increasing full-thickness chondral defect size on the medial and lateral condyle at full extension. Isolated full-thickness, square chondral defects increasing from 0.09cm2 to 1.0cm2 were created sequentially on the medial and lateral femoral condyles of six human cadaveric knees with intact ligaments and menisci. Chondral defects were created 1.0cm from the femoral notch posteriorly. The knees were fixed to a uniaxial load frame and loaded from 0N to 600N at full extension. Contact pressures between the femoral and tibial condyles were measured using pressure mapping sensors. The peak contact pressure was defined as the highest value in the 2.54mm2 area around the defect. The location of the peak contact pressure was determined relative to the centre of the defect. Peak contact pressure was significantly different between (4.30MPa) 0.09cm2 and (6.91MPa) 1.0cm2 defects (p=0.04) on the medial condyle. On the lateral condyle, post-hoc analysis showed differences in contact pressures between (3.63MPa) 0.09cm2 and (5.81MPa) 1.0cm2 defect sizes (p=0.02). The location of the stress point shifted from being posteromedial (67% of knees) to anterolateral (83%) after reaching a 0.49cm2 defect size (p < 0.01) in the medial condyle. Conversely, the location of the peak contact pressure point moved from being anterolateral (50%) to a posterolateral (67%) location in defect sizes greater than 0.49cm2 (p < 0.01). Changes in contact area redistribution and cartilage stress from 0.49cm2 to 1.0cm2 impact adjacent cartilage integrity. The location of the maximum stress point also varied with larger defects. This study suggests that size cutoffs exist earlier in the natural history of chondral defects, as small as 0.49cm2, than previously studied, suggesting a lower threshold for intervention.
Postoperative knee stability is critical in determining the success after reconstruction; however, only posterior and anterior stability is assessed. Therefore, this study investigates medial and lateral rotational knee laxity changes after partial and complete PCL tear and after PCL allograft reconstruction. The extending Lachman test assessed knee instability in six fresh-frozen human cadaveric knees. Tibia rotation was measured for the native knee, after partial PCLT (pPCLT), after full PCLT (fPCLT), and then after PCLR tensioned at 30° and 90°. In addition, tests were performed for the medial and lateral sides. The tibia was pulled with 130N using a digital force gauge. A compression load of 50N was applied to the joint on the universal testing machine (MTS Systems) to induce contact. Three-dimensional tibial rotation was measured using a motion capture system (Optotrak). On average, the tibia rotation increased by 33%-42% after partial PCL tear, and by 62%-75% after full PCL tear when compared to the intact case. After PCL reconstruction, the medial tibia rotation decreased by 33% and 37% compared to the fPCL tear in the case that the allograft was tensioned at 30° and 90° of flexion, respectively. Similarly, lateral tibial rotation decreased by 15% and 2% for allograft tensioned at 30° and 90° of flexion respectively, compared to the full tear. Rotational decreases were statistically significant (p<0.005) at the lateral pulling after tensioning the allograft at 90°. PCLR with the graft tensioned at 30° and 90° both reduced medial knee laxity after PCLT. These results suggest that while both tensioning angles restored medial knee stability, tensioning the Achilles graft at 30° of knee flexion was more effective in restoring lateral knee stability throughout the range of motion from full extension to 90° flexion, offering a closer biomechanical resemblance to native knee function.
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.
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. Three-dimensional elbow models were obtained through manual segmentation and reconstruction from 142±40 slices of CT scans per elbow in 15 cadeveric specimens. Epicondylar axis was defined to be the axis through the 2 epicondyles manually identified on the elbow models. F-E axis was defined to be the normal of a circle fitted on 20 points identified on the trochlear groove. The long axis of the elbow was identified through a line fit through the center of the distal humerus on several slices along the elbow CT. Angle between the long axis and epicondylar axis was measured. Angular deviation of the epicondylar axis and the F-E axis was calculated in reference to the long axis. All axes were projected onto the orthogonal planes on the elbow CTs and all measurements were repeated. Angular differences in the axial, saggital and coronal planes are described in internal/external rotation, flexion/extension and valgus/varus respectively. Offset in the axial and coronal planes are described in the following directions respectively: proximal/distal and anterior/posterior respectively. Comparisons between angles were performed using student's t-test.Introduction
Methods
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. Total elbow arthroplasty (TEA) is an established treatment for varying pathologies of the elbow with very good functional outcomes. Optimal fit of ulna components in TEA is predicated on a detailed appreciation of the 3-dimensional anatomy of the proximal ulna intra-medullary cavity, but literature remains scarce. Three-dimensional (3D) models of the proximal ulna have been constructed using computed tomography (CT) programs, accurately defining the angular relations with the cross-sectional extra-medullary dimensions. However, current CT-based thresholding techniques lack accuracy in differentiating cortical from cancellous bone in the metaphyseal region, and thus cannot properly define the intra-medullary region of uncored proximal ulnae. We investigate the geometric dimensions of the proximal ulna intra-medullary cavity using CT studies of cored cadaveric ulnae.Summary Statement
Introduction
