Smart knee prosthesis kinematics estimation and validation in a robotic knee simulator

In this work we present the smart knee prosthesis designed for in-vivo kinematics measurement and its validation in two knee simulators, i.e. a robotic knee simulator to provide realistic condition, and a manual simulator with more degrees of freedom. The sensor configuration including three magnetic sensors was designed, and the machine learning techniques were used to translate the magnetic measurements to knee rotations. First the concurrent flexion-extension and internal-external rotations were estimated via linear and nonlinear estimators, and technically validated in a manual knee simulator against motion capture system. Then the flexion-extension estimation was validated in a robotic knee simulator providing the realistic sagittal kinematics of treadmill and over-ground walking. The obtained results showed the high accuracy and precision of the estimates

Accurate angle estimation in smart knee prostheses via magnetic implantable and skin-mounted sensors

In this work we investigated how to measure concurrently flexion-extension and internal-external rotations in a smart knee prosthesis. A configuration of magnetic sensors and magnets were designed and embedded in knee prostheses in which each sensor measures a mixture of information related to both rotations. Using correlation analyses, angle estimators were designed to separate the flexion-extension and internal-external rotations information. The estimators were validated in a mechanical knee simulator towards a reference system. The effect of imposed abduction-adduction was also analyzed on the estimations performances. To reduce the power consumption of the internal system, we reduced the sampling rate and duty cycled the sensors and compensated the lack of information with skin-mounted sensors on four subjects. The fusion between implantable and skin-mounted sensors drastically improved the flexion-extension angle estimation, but not the internal-external estimation

Design and integration of an instrumented knee prosthesis

Total knee arthroplasty is nowadays one of the most important orthopedic surgery. It consists of a procedure in which parts of the knee are replaced by a prosthesis. The largest indication for total knee arthroplasty is osteoarthritis, a knee disease that can cause the cartilage of the femur and tibia to wear away, so that the bones rub together with use. The major risk factors for osteoarthritis are aging and obesity. Both the life expectancy and the obesity rate are increasing in the developed countries, thus the number of estimated total knee arthroplasties is growing over the years. Although over one million of prosthetic joints are implanted every year in the developed countries, none of them contains sensors to help the orthopedic surgeons in improving the precision of the replacement surgery. The goal of this study is to design an electronic system to be embedded inside a total knee prosthesis, in order to measure the force applied to it and its kinematics. Providing the orthopedic surgeons with quantitative data on the biomechanics of the prosthetic knee can help them in improving the implant precision and, as a consequence, could reduce the risk of an early revision surgery. In the frame of this thesis, we worked with the F.I.R.S.T. prosthesis by Symbios Orthopedie SA, that was instrumented with sensors and electronics to measure, process and transmit force and kinematics data to an external reader. The constraints in the design have been established by the medical doctors and the prosthesis manufacturer and the technical solutions adopted are presented. In order to simplify a future approval for human tests, we decided to keep the shape of the knee artificial joint. To achieve that, we put all the sensors and the electronics inside the middle part of the prosthesis, constituted of a polyethylene insert located between the metallic parts of the artificial joint and whose function is to reduce the rubbing. An original encapsulation was designed to guarantee the bio-compatibility of the instrumented prosthesis and to avoid a potentially dangerous contact between the electronics and the human body. This should be ensured even in case of extreme wearing of the polyethylene insert, that can occur some years after the prosthesis implant and is one of the main indications for a revision surgery. The sensors were tested by using mechanical simulators of the knee joint and validated by means of reference sensors. Different demonstrators have been designed, from the first, with only the sensors located inside the prosthesis and all the electronics fabricated in a large-scale outside of it, to the last miniaturized versions, that can be entirely embedded inside the prosthesis. Moreover, an autonomous sensor for balancing the ligaments tension during the knee replacement surgery was designed, fabricated and tested. Such a device could be an important help for the medical doctors during the surgery to improve the precision of the implant and, being not-implantable, could easily obtain an approval for human clinical trials

Studies on Spinal Fusion from Computational Modelling to ‘Smart’ Implants

Low back pain, the worldwide leading cause of disability, is commonly treated with lumbar interbody fusion surgery to address degeneration, instability, deformity, and trauma of the spine. Following fusion surgery, nearly 20% experience complications requiring reoperation while 1 in 3 do not experience a meaningful improvement in pain. Implant subsidence and pseudarthrosis in particular present a multifaceted challenge in the management of a patient’s painful symptoms. Given the diversity of fusion approaches, materials, and instrumentation, further inputs are required across the treatment spectrum to prevent and manage complications. This thesis comprises biomechanical studies on lumbar spinal fusion that provide new insights into spinal fusion surgery from preoperative planning to postoperative monitoring. A computational model, using the finite element method, is developed to quantify the biomechanical impact of temporal ossification on the spine, examining how the fusion mass stiffness affects loads on the implant and subsequent subsidence risk, while bony growth into the endplates affects load-distribution among the surrounding spinal structures. The computational modelling approach is extended to provide biomechanical inputs to surgical decisions regarding posterior fixation. Where a patient is not clinically pre-disposed to subsidence or pseudarthrosis, the results suggest unilateral fixation is a more economical choice than bilateral fixation to stabilise the joint. While finite element modelling can inform pre-surgical planning, effective postoperative monitoring currently remains a clinical challenge. Periodic radiological follow-up to assess bony fusion is subjective and unreliable. This thesis describes the development of a ‘smart’ interbody cage capable of taking direct measurements from the implant for monitoring fusion progression and complication risk. Biomechanical testing of the ‘smart’ implant demonstrated its ability to distinguish between graft and endplate stiffness states. The device is prepared for wireless actualisation by investigating sensor optimisation and telemetry. The results show that near-field communication is a feasible approach for wireless power and data transfer in this setting, notwithstanding further architectural optimisation required, while a combination of strain and pressure sensors will be more mechanically and clinically informative. Further work in computational modelling of the spine and ‘smart’ implants will enable personalised healthcare for low back pain, and the results presented in this thesis are a step in this direction

Use of stance control knee-ankle-foot orthoses : a review of the literature

The use of stance control orthotic knee joints are becoming increasingly popular as unlike locked knee-ankle-foot orthoses, these joints allow the limb to swing freely in swing phase while providing stance phase stability, thus aiming to promote a more physiological and energy efficient gait. It is of paramount importance that all aspects of this technology is monitored and evaluated as the demand for evidence based practice and cost effective rehabilitation increases. A robust and thorough literature review was conducted to retrieve all articles which evaluated the use of stance control orthotic knee joints. All relevant databases were searched, including The Knowledge Network, ProQuest, Web of Knowledge, RECAL Legacy, PubMed and Engineering Village. Papers were selected for review if they addressed the use and effectiveness of commercially available stance control orthotic knee joints and included participant(s) trialling the SCKAFO. A total of 11 publications were reviewed and the following questions were developed and answered according to the best available evidence: 1. The effect SCKAFO (stance control knee-ankle-foot orthoses) systems have on kinetic and kinematic gait parameters 2. The effect SCKAFO systems have on the temporal and spatial parameters of gait 3. The effect SCKAFO systems have on the cardiopulmonary and metabolic cost of walking. 4. The effect SCKAFO systems have on muscle power/generation 5. Patient’s perceptions/ compliance of SCKAFO systems Although current research is limited and lacks in methodological quality the evidence available does, on a whole, indicate a positive benefit in the use of SCKAFOs. This is with respect to increased knee flexion during swing phase resulting in sufficient ground clearance, decreased compensatory movements to facilitate swing phase clearance and improved temporal and spatial gait parameters. With the right methodological approach, the benefits of using a SCKAFO system can be evidenced and the research more effectively converted into clinical practice

The effect of prefabricated wrist-hand orthoses on performing activities of daily living

Wrist-hand orthoses (WHOs) are commonly prescribed to manage the functional deficit associated with the wrist as a result of rheumatoid changes. The common presentation of the wrist is one of flexion and radial deviation with ulnar deviation of the fingers. This wrist position Results in altered biomechanics compromising hand function during activities of daily living (ADL). A paucity of evidence exists which suggests that improvements in ADL with WHO use are very task specific. Using normal subjects, and thus in the absence of pain as a limiting factor, the impact of ten WHOs on performing five ADLs tasks was investigated. The tasks were selected to represent common grip patterns and tests were performed with and without WHOs by right-handed, females, aged 20-50 years over a ten week period. The time taken to complete each task was recorded and a wrist goniometer, elbow goniometer and a forearm torsiometer were used to measure joint motion. Results show that, although orthoses may restrict the motion required to perform a task, participants do not use the full range of motion which the orthoses permit. The altered wrist position measured may be attributable to a modified method of performing the task or to a necessary change in grip pattern, resulting in an increased time in task performance. The effect of WHO use on ADL is task specific and may initially impede function. This could have an effect on WHO compliance if there appears to be no immediate benefits. This orthotic effect may be related to restriction of wrist motion or an inability to achieve the necessary grip patterns due to the designs of the orthoses

The effect of prefabricated wrist-hand orthoses on grip strength

Prefabricated wrist-hand orthoses (WHOs) are commonly prescribed to manage the functional deficit and compromised grip strength as a result of rheumatoid changes. It is thought that an orthosis which improves wrist extension, reduces synovitis and increases the mechanical advantage of the flexor muscles will improve hand function. Previous studies report an initial reduction in grip strength with WHO use which may increase following prolonged use. Using normal subjects, and thus in the absence of pain as a limiting factor, the impact of ten WHOs on grip strength was measured using a Jamar dynamometer. Tests were performed with and without WHOs by right-handed, female subjects, aged 20-50 years over a ten week period. During each test, a wrist goniometer and a forearm torsiometer were used to measure wrist joint position when maximum grip strength was achieved. The majority of participants achieved maximum grip strength with no orthosis at 30° extension. All the orthoses reduced initial grip strength but surprisingly the restriction of wrist extension did not appear to contribute in a significant way to this. Reduction in grip must therefore also be attributable to WHO design characteristics or the quality of fit. The authors recognize the need for research into the long term effect of WHOs on grip strength. However if grip is initially adversely affected, patients may be unlikely to persevere with treatment thereby negating all therapeutic benefits. In studies investigating patient opinions on WHO use, it was a stable wrist rather than a stronger grip reported to have facilitated task performance. This may explain why orthoses that interfere with maximum grip strength can improve functional task performance. Therefore while it is important to measure grip strength, it is only one factor to be considered when evaluating the efficacy of WHOs