Evaluation of the Radial Procurvatum Using the Center of Rotation of Angulation Methodology in Chondrodystrophic Dogs

The radial joint orientation angles were calculated using the center of rotation of angulation (CORA) methodology within the frontal and sagittal planes in chondrodystrophic dog breeds, including Welsh Corgi, Dachshund, Pekinese, Poodle, Beagle and Maltese, and it was compared whether there is a statistically significant difference between the breeds. Radial joint orientation angles were obtained in eighty-eight dogs, including 23 Welsh Corgis, 16 Dachshunds, 14 Pekinese, 13 Maltese, 12 Poodles and 10 Beagles. Using the CORA methodology, the cranial proximal radial angle (CrPRA) and caudal distal radial angle (CdDRA) in the sagittal plane and medial proximal radial angle (MPRA) and lateral distal radial angle (LDRA) in the frontal plane were measured for the six breeds studied. The mean values of joint angles for each breed were compared statistically were observed. The CrPRA, CdDRA, and LDRA mean values of Dachshund and Welsh Corgi breeds were significantly smaller than other breeds, and in MPRA, Pekingese showed significantly smaller values than other breeds. This study confirms that the mean values of radial joint orientation angles can be significantly different among chondrodystrophic breeds. To accurately evaluate the degree of angular deformity of the radius, it may be helpful to refer to the average value for each breed with chondrodystrophy.

Medialized versus Lateralized Center of Rotation in Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-Analysis

One of the original biomechanical principles of reverse total shoulder arthroplasty (RTSA) is medialization of the center of rotation (COR) relative to the native level of the glenoid. Several authors have proposed the lateralized center of rotation, which is characterized by a lateralized (L) glenoid and medialized (M) humeral component. The aim of this review is to compare the clinical and functional outcomes of COR in medialized (M-RTSA) and lateralized (L-RTSA) RTSA in patients with uniform indications and treatment through a meta-analysis. A PRISMA-guided literature search of PubMed, Medline, Embase, Scopus, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and Cochrane Clinical Answers was conducted from April to May 2021. Twenty-four studies were included in the qualitative synthesis, and 19 studies were included in the meta-analysis. Treatment with RTSA resulted in positive post-operative outcomes and low complication rates for both groups. Statistically relevant differences between L-RTSA group and M-RTSA group were found in post-operative improvement in external rotation with arm-at-side (20.4° and 8.3°, respectively), scapular notching rates (6.6% and 47.7%) and post-operative infection rates (1% and 7.7%). Both lateralized and medialized designs were shown to improve the postoperative outcomes. Nevertheless, a lateralized COR resulted in greater post-operative external rotation.

Analysis of the Risk of Wear on Cemented and Uncemented Polyethylene Liners According to Different Variables in Hip Arthroplasty

Wear debris in total hip arthroplasty is one of the main causes of loosening and failure, and the optimal acetabular fixation for primary total hip arthroplasty is still controversial because there is no significant difference between cemented and uncemented types for long-term clinical and functional outcome. To assess and predict, from a theoretical viewpoint, the risk of wear with two types of polyethylene liners, cemented and uncemented, a simulation using the finite element (FE) method was carried out. The risk of wear was analyzed according to different variables: the polyethylene acetabular component’s position with respect to the center of rotation of the hip; the thickness of the polyethylene insert; the material of the femoral head; and the relationship of the cervical–diaphyseal morphology of the proximal end of the femur to the restoration of the femoral offset. In all 72 simulations studied, a difference was observed in favour of a cemented solution with respect to the risk of wear. With regard to the other variables, the acetabular fixation, the thickness of the polyethylene, and the acetabular component positioning were statistically significant. The highest values for the risk of wear corresponded to a smaller thickness (5.3 mm), and super-lateral positioning at 25 mm reached the highest value of the von Mises stress. According to our results, for the reconstruction of the acetabular side, a cemented insert with a thickness of at least 5 mm should be used at the center of rotation.

The Reconstruction Accuracy of the Hip Center of Rotation After Cementless Total Hip Arthroplasty for Failed Treatment of Acetabular Fractures. Does It Matter?

Background To assess the impaction of reconstruction accuracy of hip center of rotation (COR) on midterm clinical and radiographic results of cementless reconstruction of total hip arthroplasties (THAs) for patients after failed treatment of acetabular fractures. Methods One hundred and four patients (107 hips) who underwent THAs after failed treatment of acetabular fractures were retrospectively evaluated and cementless cups and stems were implanted in all hips. Clinical outcomes were assessed using the Harris hip score (HHS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC) scoring system. Radiographic results were analyzed by serial perioperative x-rays. Results At the latest follow-up examination, the median HHS increased from 52 (42-65) before surgery to 93 (90-97) (p < 0.001) and the median WOMAC decreased from 52 (36-65) before surgery to 5.8 (1.5-8) (p < 0.001). Compared with normal contralateral hip, 79 cups migrated superiorly (0.2-33.6mm) and 22 cups migrated inferiorly (0.2-16.1mm). The distance of superior migration of reconstructed COR was correlated with positive Trendelenburg sign at the latest follow-up examination (r=0.504; p < 0.001). The percentage of postoperative Trendelenburg sign was significantly higher in superior migration subgroup than that in subgroup with anatomical restoration of COR (P=0.015). Conclusions Cementless THAs in patients after failed treatment for acetabular fractures achieved predictable clinical and radiographic outcomes. A superiorly migrated hip COR appeared to exert a negative effect on abductor muscle function.

Defect free optimization of a polycentric prosthetic knee design using imperialist competition-inspired optimization method

The disability of lower limbs is one of the major problems facing human lives. In order to restore the missing functionality and aesthetic feature of the amputee's locomotion, finding the optimal design of the human lower limb knee prosthesis is crucial. This paper focuses the design optimization of a four bar knee mechanism capable to reproduce the complex flexion/extension knee joint motion in the sagittal plane with variable instantaneous center of rotation positions. Thus an optimization approach with appropriate constraints is formulated in order to consider the degree of compatibility between the instantaneous center of rotation trajectories of the human reference knee joint and the four bar knee mechanism. To solve this high nonlinear optimization problem, an algorithm based on multi-objective modified imperialist competitive method is proposed where all the constraints are managed with the penalty method. The results obtained by the multi-objective modified imperialist competitive method showed the capability to reach a small tracking error. The obtained results prove the effectiveness of the proposed optimization approach for the optimal synthesis of the four bar knee mechanism, compared with other literature techniques.

A multi-patient analysis of the center of rotation trajectories using finite element models of the human mandible

Studying different types of tooth movements can help us to better understand the force systems used for tooth position correction in orthodontic treatments. This study considers a more realistic force system in tooth movement modeling across different patients and investigates the effect of the couple force direction on the position of the center of rotation (CRot). The finite-element (FE) models of human mandibles from three patients are used to investigate the position of the CRots for different patients’ teeth in 3D space. The CRot is considered a single point in a 3D coordinate system and is obtained by choosing the closest point on the axis of rotation to the center of resistance (CRes). A force system, consisting of a constant load and a couple (pair of forces), is applied to each tooth, and the corresponding CRot trajectories are examined across different patients. To perform a consistent inter-patient analysis, different patients’ teeth are registered to the corresponding reference teeth using an affine transformation. The selected directions and applied points of force on the reference teeth are then transformed into the registered teeth domains. The effect of the direction of the couple on the location of the CRot is also studied by rotating the couples about the three principal axes of a patient’s premolar. Our results indicate that similar patterns can be obtained for the CRot positions of different patients and teeth if the same load conditions are used. Moreover, equally rotating the direction of the couple about the three principal axes results in different patterns for the CRot positions, especially in labiolingual direction. The CRot trajectories follow similar patterns in the corresponding teeth, but any changes in the direction of the force and couple cause misalignment of the CRot trajectories, seen as rotations about the long axis of the tooth.

Biomechanical Gain in Joint Excursion from the Curvature of the Achilles Tendon: Role of the Geometrical Arrangement of Inflection Point, Center of Rotation, and Calcaneus

The dorsal movement of the Achilles tendon during ankle rotation is restricted by anatomical obstructions. Previously, we demonstrated that the anatomical obstruction provides a gain (gainAT) in the proximal displacement of the calcaneus compared to the change in the Achilles tendon length. Here, we empirically validate and extend our previous modeling study by investigating the effects of a broad range of obstruction locations on gainAT. The largest gainAT could be achieved when the obstruction was located on the most ventral and distal sides within the physiological range of the Achilles tendon, irrespective of the ankle position.

The Influence of Acetabular Morphologic Variations on the Cup Position in Total Hip Arthroplasty for Crowe type III Dysplastic Hip

Background: We aimed to (1) evaluate the acetabular morphologic variations of Crowe III hips; (2) study the influence of different morphologies on the cup position in total hip arthroplasty.Methods: From November 2008 to February 2019, we retrospectively evaluated 101 patients (110 hips) with Crowe III developmental dysplasia of the hip. We classified Crowe III hips into two subtypes, the IIIA when the acetabular roof was extensively deficient and the junction between the false and the true acetabulum was indistinct, and the IIIB when there is a significant crest between the false and the true acetabulum. Based on the radiographs, we measured the morphological characteristic of the acetabulum and the postoperative cup position.Results: The false acetabulum of IIIB hips had larger Tonnis angle and smaller center-edge angle than the IIIA hips. The width of true acetabular roof in the IIIB hips was thicker than the IIIA group. Fifty-one (100%) IIIA hips and 48 (81.4%) IIIB hips were reconstructed using high hip center while 11 (18.6%) IIIB hips were reconstructed anatomically. The mean vertical distance of center of rotation in the IIIA group was 33.5±4.5 mm while it was 31.2±6.3 mm in the IIIB group (p=0.040). The vertical distance of the hip center was positively correlated with the height of dislocation in the IIIA group (r=0.493, p<0.001). According to the four-zone system, in the IIIA group, 5 hips were located in the inferomedial zone, 23 hips in the superomedial zone, 22 hips in the superolateral zone and 1 hip in the inferolateral zone. In the IIIB group, the corresponding numbers were respectively 15, 17, 1 and 5. Compared with the IIIA group, there were more IIIB hips located in the inferomedial zone (p=0.008) and less in the superolateral zone (p=0.033).Conclusions: There are distinct morphologic subtypes based on the relationship between the false and the true acetabulum. More bone stock located in the superior wall of the true acetabulum can bring more possibilities for anatomical reconstruction, and lower the height of center of rotation when using high hip center.