Generalized joint laxity (GJL), a condition in which most joints of the body move beyond the accepted normal range of motion, is present in many ballet and modern dancers. It has been associated with an increased risk of injury, decreased muscle strength, and greater landing forces. Increased joint laxity results in joint instability and may precede the development of osteoarthritis, which is associated with a reduction in cartilage thickness. We hypothesized that dancers with GJL would have decreased hip cartilage thickness, as well as greater hip adduction angles and greater ground reaction force on landings. Twenty female ballet and modern dancers (mean age: 21.0 ± 1.79 years; mean weight: 57.0 ± 5.71 kg; mean years of dance experience: 14.6 ± 3.53 years; mean hours of training per week: 19.2 ± 7.24 hours) were recruited from college and local dance programs and screened for GJL. Each dancer performed three forward drop landings onto a force plate and received an MRI on their dominant hip. There was a significant difference in hip cartilage thickness, as viewed in the frontal plane (GJL group average: 2.66 ± 0.33 mm; control group average: 3.14 ± 0.48 mm; p = 0.0160), between the groups. There were no significant differences in peak hip adduction angle on landing (GJL group average: 80.9 ± 5.04 degrees; control group average: 77.9 ± 5.78 degrees; p = 0.2269) or peak landing ground reaction force (GJL group average: 5.56 ± 1.28 body weights; control group average: 5.17 ± 0.82 body weights; p = 0.4274) between the generalized joint laxity group and the control group. Dancers with GJL have thinner cartilage at the hip. These results suggest that dancers with GJL may be at a greater risk for injury. Therefore, these dancers may benefit from strength training programs, rather than flexibility training, to help counteract the joint instability that can lead to injury.

Elbow joint laxity is a problem that normally comes with age; it increases up to critical levels due to rupture or damage to the ligaments of the elbow and affects the stability and capacities of the joint, interfering even with daily activities. This work investigates the kinematics of the elbow through in-vivo experimental measurement. To this end, a platform based on Stewart Platform mechanism was built and used at the bioengineering labs of Brunel University in West London, the UK, to measure the six degrees of freedom of the joint. This thesis aims to develop a method to simulate such motion which could be used for elbow implant design and manufacture. This work contributes to both the basic science of joint movement measurement and to the clinical applications of diagnosing elbow illness. In addition this research presents the preliminary results for a design for elbow implants. Tracking system developed in house was used to measure the degrees of freedom in healthy elbow motion. A pilot study was performed to assess the joint motion and its repeatability. A group of volunteers with normal elbow movement was used to carry out this study. A Stewart Platform mechanism based on the tracking system was used in this study as a non-invasive tool to capture elbow joint motion and track the trajectory and pattern of the motion in three-dimensional space. This thesis aimed to develop a method to simulate the elbow joint motion that could potentially be used for the elbow implants design and there manufacture. The goal of this study was achieved by in vivo measurement of the elbow movement. It was found that the results vary from person to person, but a healthy pattern of motion can be distinguished from an abnormal pattern. To ensure the result, the motion of the right and left hand of each person was compared,allowing the behaviour of the elbow motion to be judged and the results can help surgeons to analyze the motion of the elbow joint and follow up suspicions of abnormal behaviour in the joint or trace any possible joint laxity. Furthermore, the errors involved with the mechanism were calculated and appropriate factors were applied to correct them. As part of this study the manufacturing of medical implants was reviewed and discussed.

Gymnastics is noted for involving highly specialized strength, power, agility and flexibility. Flexibility is perhaps the single greatest discriminator of gymnastics from other sports. The extreme ranges of motion achieved by gymnasts require long periods of training, often occupying more than a decade. Gymnasts also start training at an early age (particularly female gymnasts), and the effect of gymnastics training on these young athletes is poorly understood. One of the concerns of many gymnastics professionals is the training of the spine in hyperextension—the ubiquitous ‘arch’ seen in many gymnastics positions and movements. Training in spine hyperextension usually begins in early childhood through performance of a skill known as a back-bend. Does practising a back-bend and other hyperextension exercises harm young gymnasts? Current information on spine stretching among gymnasts indicates that, within reason, spine stretching does not appear to be an unusual threat to gymnasts’ health. However, the paucity of information demands that further study be undertaken.

Objectives: To explore if joint mobility, as a measure of connective tissue quality, could be a predictor for pregnancy-related low back pain after pregnancy and to evaluate local corticosteroid injection treatment in women with persistent pelvic girdle pain long after childbirth. Material and methods: To investigate joint mobility in relation to pain, 200 women were examined repeatedly from early pregnancy until three months after delivery. Their mobility in left fourth finger abduction in early pregnancy was compared with clinically assessed low back and pelvic pain 3 months after delivery. To evaluate local corticosteroid injection treatment, 36 women with persistent PGP were included in a randomised controlled trial (RCT) and randomised to either corticosteroid injection or saline injection on one occasion at the ischial spine bilaterally, with a follow-up after four weeks. In both studies, the women were asked about obstetric history, to complete a pain drawing, estimate their level of pain on a visual analogue scale (0-100) and estimate how they manage their everyday activities on a questionnaire, Disability Rating Index (DRI). In the RCT, the 36 women also completed Short Form 36 (SF-36), a quality of life questionnaire, six-minute walk test (6MWT), and isometric trunk flexion and extension were examined. Results: Women with low back and pelvic pain three months after pregnancy had increased finger laxity in early pregnancy. The larger the finger angle and the more pregnancies, the greater the risk of low back and pelvic pain after pregnancy. In the RCT, at follow-up, the women who received corticosteroid injection treatment improved in walking ability, estimated physical ability and isometric trunk extension more than those who received saline injections. Conclusions: Increased joint mobility, as measured by finger joint mobility, together with the number of previous pregnancies, may be an indicator of low back and pelvic pain postpartum. One single corticosteroid injection treatment to intra-pelvic structures improved function in women with persistent PGP which may indicate a source of pain.

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