Inter-subject variability is inherently present in patient anatomy and is apparent in differences in shape, size and relative alignment of the bony structures. Understanding the variability in patient anatomy is useful for distinguishing between pathologies and to assist in surgical planning. With the aim of supporting the development of stratified orthopaedic interventions, this work introduces an Articulated Statistical Shape Model (ASSM) of the lower limb. The model captures inter-subject variability and allows reconstructing ‘virtual’ knee joints of the lower limb shape while considering pose.

A training dataset consisting of 173 lower limbs from CT scans of 110 subjects (77 male, 33 female) was used to construct the ASSM of the lower limb. Each bone of the lower limb was segmented using ScanIP (Simpleware Ltd., UK), reconstructed into 3D surface meshes, and a SSM of each bone was created. A series of sizing and positioning procedures were carried out to ensure all the lower limbs were in full extension, had the same femoral length and that the femora were aligned with a coincident centre. All articulated lower limbs were represented as: (femur scale factor) × (full extension articulated lower limb + relative transformation of tibia, fibula and patella to femur). Articulated lower limbs were in full extension were used to construct a statistical shape model, representing the variance of lower limb morphology. Relative transformations of the tibia, fibula and patella versus the femur were used to form a statistical pose model. Principal component analysis (PCA) was used to extract the modes of changes in the model.

The first 30 modes of the shape model covered 90% of the variance in shape and the first 10 modes of the pose model covered 90% of the pose variance. The first mode captures changes of the femoral CCD angle and the varus/valgus alignment of the knee. The second mode represents the changes in the ratio of femur to tibia length. The third mode reflects change of femoral shaft diameter and patella size. The first mode characterising pose captures the medial/lateral translation between femur and tibia. The second mode represents variation in knee flexion. The third mode reflects variation in tibio-femoral joint space.

An articulated statistical modelling approach was developed to characterize inter-subject variability in lower limb morphology for a set of training specimens. This model can generate large sets of lower limbs to systematically study the effect of anatomical variability on joint replacement performance. Moreover, if a series of images of the lower limb during a dynamic activity are used as training data, this method can be applied to analyse variance of lower limb motion across a population.

The aim of this study was to perform a comprehensive evaluation of the changes in function from pre- to post-surgery in total and unilateral knee arthroplasty (UKA/TKA) patients. Twenty healthy (age 62.4 ±5.9, 11 male), 14 UKA (age 60.9 ±10.1, 8 male) and 17 TKA (age 67.2 ±8.1, 9 male) patients were studied. KA patients were assessed four weeks pre- and six months post-operation. Measures of perceived pain and function were collected using Oxford Knee Score (OKS) questionnaire. Tests of objective function included joint range of motion (RoM), ultrasound imaging, and 3-D motion analysis/inverse modelling from gait and sit-stand. An optimal set of variables was used to classify KA function using the Cardiff DST method. Pre-KA and healthy individuals were accurately classified (96%). Post-operation questionnaire measures of function improved for both UKA and TKA groups. However, observed measures of RoM, muscle atrophy and gait had only limited gains. This resulted in 57% of UKA and only 27% of TKA patients being classified as healthy post-operation. The results of this study show that 6 months post-surgery UKA patients had higher function than TKA. Using statistical approaches to combine functional assessments has provided an accurate platform to classify function and estimate changes from pre- to post-surgery. The clinical application of this tool requires further investigation and comparison to commonly used clinical techniques.

Introduction

Both the RANK/RANKL system and the endocannabinoid system have roles in bone remodelling. Activation of CB1 receptors on sympathetic nerve terminals in trabecular bone modulates bone remodelling by attenuating adrenergic inhibition over bone formation. CB2 receptors are involved in the local control of bone cell differentiation and function. Osteoblastic CB2 receptor activation negatively regulates RANKL mRNA expression indicating an interaction between the two systems and that efficient bone remodelling requires a balance between these two systems. The aim of the study was to establish the presence of the different components of the endocannabinoid system and the RANK/RANKL signalling pathway in human bone and osteoclast culture.