This research has investigated the influence of gait cycle, malalignment and overweight on total knee replacements using a finite element method. Dynamic and finite element models of fixed- and mobile-bearing implants have been created and solved; the fixed- and mobile-bearing implants demonstrated different performance on movement and contact pressure distribution in the tibio-femoral contact surfaces. More contact areas were found in the mobilebearing implant than in the fixed-bearing implant, but the maximum contact pressures were almost the same in both. The thickness of the tibial bearing component influenced the fixed- and mobile-bearing implants differently. A dynamic model of an implanted knee joint has been developed using MSC/ADAMS and MSC/MARC software. Stress shielding was found in the distal femur in the implanted knee joint. The stresses and strains in the distal femur were found to increase with body weight, especially during the stance phase. Serious stress shielding and more bone loss appear in condition of overweight. The increase of bone loss rate and stress in the distal femur with increase of body weight will result in a higher risk of migration of femoral component after total knee replacement. The peg size effect has been studied using this dynamic model; a longer peg with smaller diameter was found to be the best. Varus/valgus malalignment redistributed the tibio-femoral contact force and stress/strain distribution in the distal femur. The difference between contact forces on the medial and lateral condyle decreased in the valgus malalignment condition. Contact pressure increased in the varus/valgus malalignment condition in the dynamic models of both the fixed- and mobile-bearing implant. However, the mobile-bearing implant performed better in conditions of malalignment, especially malrotation. Body weight had less influence on the maximum contact pressure in the mobile-bearing implant.

Background: Cryotherapy is commonly used during physiotherapeutic rehabilitation of patients following total knee replacement (TKR). Evidence for treatment effectiveness within the current literature is contradictory and there are no clinical guidelines to inform cryotherapy treatment within this particular patient group. This study surveys current cryotherapy treatment efficacy in the acute post-operative management of TKR patients. Methods: In total 263 senior physiotherapists completed and returned a postal questionnaire, which, using open and closed questions investigated the use of cryotherapy following TKR. Survey results were used to inform a pragmatic randomized clinical trial (RCT) involving 133 consecutive TKR patients. The RCT investigated cryotherapy treatment efficacy in the acute post-operative management of TKR patients. Patients were randomized into three groups; no cryotherapy (NC), delayed cryotherapy (DC) and immediate cryotherapy (IC). The primary outcome measure was post-operative pain with knee swelling, active range of motion (AROM), function and levels of physiotherapy input assessed as secondary outcome measures. Observations were taken pre-operatively and at 3, 7 and 42 days post-operatively. Results: The survey reported that 33% of respondents used some form of cryotherapy routinely following TKR surgery. The two main methods of cryotherapy application were Cryocuff (59%) and crushed ice (30%). Treatments were most frequently applied between 24 hrs and 48 hrs post-surgery for 20 minutes, twice a day. Chi square analysis indicated significant differences (p<0.01) in between NHS and private sites relating to a lack of cryotherapy resources and treatment time for cryotherapy in the NHS. A lack of proven efficacy was the most cited reason for not applying cryotherapy treatment, and swelling the most common treatment indicator. There was particular uncertainty regarding the cleaning and sterilization of the Cryocuff device. The RCT indicated that patients in IC group had significantly less post-operative pain than the NC and DC groups at 3 days. Mean difference (p <0.05, 95% CI) in post-operative analogue scores (VAS, scale 0-10) was -1.6 (p <0.01, CI -2.49- to -0.707) for IC and NC; and -0.922 (p= 0.044, CI -0.183 to -0.009) for IC and DC groups. At 7 and 42 days there were significant reductions in VAS scores for both cryotherapy groups compared to the NC group. There was significant improvement in knee swelling, AROM, ability to transfer and need for additional physiotherapy in both cryotherapy treatment groups although no significant reduction in opiate requirement was found. Conclusions: In current clinical practice there was little consensus regarding treatment indicators, method of application and management of cryotherapy following TKR. However, in a RCT the use of cryotherapy combined with compression, as compared to a no cryotherapy control, led to significant reductions in patient reported pain, less post-operative swelling, greater recovery of AROM, faster return of function and less reliance on OPD physiotherapy treatment. It is concluded that cryotherapy combined with compression has an important role to play in the acute rehabilitation of TKR and should be considered as part of routine management.

Low trauma hip fractures, due to bone fragility, are a major healthcare burden with serious consequences for individuals in terms of long-term morbidity and mortality; and also for society due to the high medical and care costs associated with these injuries. Because of the association with low bone mass, these fractures are particularly prevalent in elderly populations and are likely to become more common as longevity increases globally. Avoidance of these fractures is therefore an extremely important goal. Low bone mass, manifested in the conditions of osteopenia and osteoporosis, is the primary cause of bone fragility, and reductions in bone mass are the inevitable corollary of aging and menopause. Bone loss may be exacerbated by immobilisation and reduced weight-bearing activity, giving rise to the condition of disuse osteopenia. Immobilisation may itself be the result of low trauma leg fragility fractures that potentially causes further bone density loss. If this loss occurs at the hip, there is an increased risk for hip fracture as a sequela to the original injury. Osteoarthritis is also a condition strongly associated with aging that may necessitate knee arthroplasty as a last stage treatment, potentially causing a period of reduced mobility and weight-bearing activity following surgery. Leg fracture and knee replacement both present additional risk factors for hip fracture due to changes in muscle mass, gait and postural stability that may increase the risk of falls. This study aims primarily to investigate the effects of immobilisation on leg fracture and knee replacement patients, immediately following injury or surgery, in order to quantify bone and muscle loss and to monitor recovery over a one year period. A postmenopausal population were studied as they are already losing bone density systemically and may be at greater risk of further bone loss following immobilisation. Factors of activity, function, weight-bearing, pain, treatments, therapies, health perceptions and mental wellbeing, that potentially contribute to bone loss and recovery, were also investigated. Results from the study may provide information relating to increased future hip fracture risk and lead to treatment options to alleviate bone loss in these groups.