ObjectiveThe main object of this study was to use a geometric morphometric
approach to quantify the left-right symmetry of talus bones. MethodsAnalysis was carried out using CT scan images of 11 pairs of
intact tali. Two important geometric parameters, volume and surface
area, were quantified for left and right talus bones. The geometric
shape variations between the right and left talus bones were also
measured using deviation analysis. Furthermore, location of asymmetry
in the geometric shapes were identified. ResultsNumerical results showed that talus bones are bilaterally symmetrical
in nature, and the difference between the surface area of the left
and right talus bones was less than 7.5%. Similarly, the difference
in the volume of both bones was less than 7.5%. Results of the three-dimensional
(3D) deviation analyses demonstrated the mean deviation between
left and right talus bones were in the range of -0.74 mm to 0.62
mm. It was observed that in eight of 11 subjects, the deviation
in symmetry occurred in regions that are clinically less important
during talus surgery. ConclusionsWe conclude that left and right talus bones of intact human ankle
joints show a strong degree of symmetry. The results of this study
may have significance with respect to talus surgery, and in investigating
traumatic talus injury where the geometric shape of the contralateral
talus can be used as control.Cite this article: Bone Joint Res 2014;3:139–45.
Proper understanding of the complex geometric shape of the talus bone is important for the design of generic talar body prosthetics and restoration of the proper ankle joint function after surgery. To date, all talus implants have been patient-specific with the limitation that complex computer modeling is required to produce a mirrored image from the unaffected opposite side followed by machining a patient-specific prosthesis. To develop an "off-the-shelf" non-custom talar prosthesis, it is important to perform a thorough investigation of the geometric shape of the talus bone. This article addresses the applicability of a scaling approach for investigating the geometric shape and similarity of talus bones. This study used computed tomography scan images of the ankle joints of 27 different subjects to perform the analysis. Results of the deviation analyses showed that the deviation in the articulating surfaces of the talus bones was not excessive in terms of talus size. These results suggest that a proposed range of five implant sizes is possible. Finally, it is concluded that the talus bones of the ankle joints are geometrically similar, and a proposed range of five implant sizes will fit a wide range of subjects. This information may help to develop generic talus implants that might be applicable to patients with a severe talus injury.
The biomechanics of the patellofemoral (PF) joint is complex in nature, and the aetiology of such manifestations of PF instability as patellofemoral pain syndrome (PFPS) is still unclear. At this point, the particular factors affecting PFPS have not yet been determined. This study has two objectives: (1) The first is to develop an alternative geometric method using a three-dimensional (3D) registration technique and linear mapping to investigate the PF joint contact stress using an indirect measure: the depth of virtual penetration (PD) of the patellar cartilage surface into the femoral cartilage surface. (2) The second is to develop 3D PF joint models using the finite element analysis (FEA) to quantify in vivo cartilage contact stress and to compare the peak contact stress location obtained from the FE models with the location of the maximum PD. Magnetic resonance images of healthy and PFPS subjects at knee flexion angles of 15°, 30° and 45° during isometric loading have been used to develop the geometric models. The results obtained from both approaches demonstrated that the subjects with PFPS show higher PD and contact stresses than the normal subjects. Maximum stress and PD increase with flexion angle, and occur on the lateral side in healthy and on the medial side in PFPS subjects. It has been concluded that the alternative geometric method is reliable in addition to being computationally efficient compared with FEA, and has the potential to assess the mechanics of PFPS with an accuracy similar to the FEA.
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