45 research outputs found
The measurement of wear in hip arthroplasties
Metal-on-metal (MOM) total hip replacement (THR) and resurfacing implants were designed to form a low friction bearing that would improve implant longevity, in response to the ever-aging population. However, the unanticipated release of cobalt chromium wear debris had a detrimental impact on periprosthetic tissue, resulting in many being revised and some designs being recalled. The aim of this thesis was to identify the surgeon, implant and patient factors that contributed to the increased wear of MOM hip arthroplasties and ultimately their failure. A developed software solution was found to provide improved accuracy during the quantification of volumetric wear from the bearing surface of retrieved hip implants, overcoming the limitations of current methods. Through its application, neither diametrical clearance nor manufacture dates were found to influence the wear performance of MOM Pinnacle hips, contrary to previous speculation. A high proportion of Pinnacle and ASR hips had a diametrical clearance below their specifications. Its detrimental impact on ASR bearing wear, further implicated its acetabular design in the increased prevalence of edge loading. The comparably high wear rates and whole blood metal ion levels of the ASR could explain their high revision rates. Nevertheless, the greater toxicity of taper junction debris was identified as the primary contributor to the disproportionately greater revision rates of the ASR XL, compared to its resurfacing form. Bearing wear was successfully located in vivo for the first time and predominantly isolated to the anterosuperior portion of the acetabular component, analogous to cartilage damage mapped in native hips. A potential relationship was also identified between component positioning and the location of this wear. These findings will help inform the management of a million patients worldwide that remain with implanted MOM hips, while influencing future design, quality control and the regulation of all orthopaedic implants
Интегральный анализ параметров вертлужной впадины в патоморфологической оценке диспластического коксартроза
Background. Despite the successes in the hip arthroplasty the incidence of complications in cases of dysplas- tic hip arthritis remains higher then after other forms of hip arthritis. Objective. To pick up the anthropometric criteria of dysplastic acetabulum that determine the correct implantation of the hip implant’s cup. Methods. X-ray anthropometric analysis was carried out for 194 dysplastic acetabula, which were divided into 4 groups according to classification by Eftek- har N.S. The same parameters of 70 normal acetabula are studied. Results. Petal diagrams with 4 axes were constructed to visualize the changes in the shape of the dysplastic acetabulum. On each axis of the diagram one of next parameters was de- posited: the acetabular width and depth, the thickness of acetabular bottom and the index of the acetabulum, which is calcu- lated as the ratio of depth to width. The indices of the normal acetabular parameters were taken as 1, and the dysplastic indi- ces were expressed as fractions of 1. Variations in the shape of the acetabulum according to Eftekkar’s classification are de- scribed. An algorithm of action for the implantation of the endoprosthetic cup is proposed for each type of deformation. Also the sketches of preoperative planning for each type of the deformation are presented. Discussion. The ratio of the depth of the acetabulum and the thickness of its bottom is the most significant for the correct implantation of the cup. This indicator en- ables to surgeon to make the decision about resection of the acetabular bottom during the preparing of the implant’s bed. The acetabular width becomes the determining criterion for the dicision onrequarment for bone grafting of acetabular roof only for types C and D by Eftekhar. Conclusion. The proposed technique allows to visualize the acetabular deformation from the position of hip replacement in cases of dysplastic hip arthritis. Also this one is suitable for other nosological forms of hip arthritis. Довготривала стабільність штучного суглоба – головне завдання ендопротезування, особливо якщо операція виконується у молодих активних пацієнтів. Проте, при диспластичному коксар- трозі виживання імплантатів нижче, ніж при рутинному ендопротезуванні. Диспластична аномалія куль- шового суглоба не є статичною і прогресує не тільки в міру формування скелета людини, а й зазнає змін у ході дегенеративно-дистрофічного процесу, незмінно вражаючи біомеханічно неповноцінний суглоб. Сукупність змін кульшової западини і проксимального відділу стегнової кістки при диспластичному кок- сартрозі, супутні компенсаторні зміни навколишніх м'яких тканин і всіх ланок біомеханічної ланки ске- лета вимагають від хірурга ретельного виконання передопераційного планування ендопротезування кульшового суглоба при диспластичному коксартрозі. Очевидно, що облік критеріїв аномалії будови кульшової западини при передопераційному плануванні ендопротезування кульшового суглоба повинен забезпечити кращі результати імплантації. Мета роботи – на основі антропометричних змін форми куль- шової западини виділити критерії, які впливають на коректну імплантацію чашки ендопротезу кульшо- вого суглоба. Проведений аналіз 194 диспластичних кульшових западин, які були розподілені на 4 групи за классифікацією Eftekhar N.S. Також досліджені 70 нормальних кульшових суглобів. Для візуалізації змін форми кульшової западини побудовані пелюсткові діаграми, на 4 вісях яких позначалися досліджу- вані параметри. При цьому нормальні показники виражені як 1, а диспластичні – у вигляді часток від 1. Найбільш значущим для коректної імплантації чашки ендопротезу виявилося співвідношення глибини кульшової западини й товщині її дна. Ширина западини стає визначним критерієм щодо вирішення пи- тання про необхідність кісткової пластики криши западини тільки при типах С і D. Запропонована мето- дика оцінки кульшової западини з позиції ендопротезування кульшового суглоба підходить також для інших нозологічних форм коксартрозу
Personalized Hip and Knee Joint Replacement
This open access book describes and illustrates the surgical techniques, implants, and technologies used for the purpose of personalized implantation of hip and knee components. This new and flourishing treatment philosophy offers important benefits over conventional systematic techniques, including component positioning appropriate to individual anatomy, improved surgical reproducibility and prosthetic performance, and a reduction in complications. The techniques described in the book aim to reproduce patients’ native anatomy and physiological joint laxity, thereby improving the prosthetic hip/knee kinematics and functional outcomes in the quest of the forgotten joint. They include kinematically aligned total knee/total hip arthroplasty, partial knee replacement, and hip resurfacing. The relevance of available and emerging technological tools for these personalized approaches is also explained, with coverage of, for example, robotics, computer-assisted surgery, and augmented reality. Contributions from surgeons who are considered world leaders in diverse fields of this novel surgical philosophy make this open access book will invaluable to a wide readership, from trainees at all levels to consultants practicing lower limb surger
The Design of a Novel Hip Resurfacing Prosthesis
PhDTotal hip replacement (THR) is one of the most successful and most frequently
performed operations. For most implants the published rate of revision at 10 years is
less than 10%. However the revision rates are higher for younger and more active
patients who are likely to outlive their implants.
The most frequent cause of THR failure is aseptic loosening, commonly accompanied
by bone loss at the implant site. THR revisions give worse functional results and fail
sooner than primary THR and are complicated by this loss of bone stock.
A resurfacing hip prosthesis replaces the diseased surface layer of bone and cartilage
and retains the majority of the femoral head. The stress distribution in the proximal
femur is closer to that in an intact hip. A conservative resurfacing prosthesis will
present the surgeon with no greater problems at revision than encountered at primary
conventional 11-JR.
Early designs of resurfacing prosthesis conserved femoral bone stock at the expense
of acetabular bone. Revision rates were high and while some failures were caused by
avascular necrosis and femoral neck fracture the predominant cause was acetabular
loosening.
The design of a bone conserving prosthesis requires knowledge of the shape of the
bony surfaces of the hip joint. A survey of the morphology of the acetabulum showed
a wide variation in shape. While early resurfacing designs had hemispherical
acetabular cups the bony surface is less than hemispherical. The morphology and
desired range of hip motion constrain prosthesis thickness and shape.
A novel resurfacing design using a polyacetal femoral component and an UHMWPE
acetabular component is proposed. This bearing combination has a lower volumetric
wear rate than an equivalent Co-Cr on UHWMPE bearing. Computer modelling of the
resurfacing concept showed that lower moduli materials reduced stress shielding and
distributed implant-bone interface stresses more evenly. Mechanical testing of
polyacetal following immersion in Ringer's solution showed substantial decreases in
Young's modulus while strength was unaffected.EPSRC core programme grant of the IRC in Biomedical Materials
EPSRC Research studentshi
Hip simulator wear testing of the taper-trunnion junction and bearing surfaces of modular hip prostheses
PhD ThesisAdverse reaction to metal debris (ARMD) released from the taper-trunnion junction of modular total hip replacements (THRs) is an issue of contemporary concern, not only in metal-on-metal (MoM) but in ceramic-on-ceramic (CoC) and metal-on-cross linked polyethylene (MoP) THRs. Moreover, there is no consensus in the literature regarding the mechanisms behind material loss at the taper-trunnion junction.
The aim of this research work to investigate the material loss, if any, at the taper-trunnion junction of modular CoC and MoP THRs under physiological walking cycles. Following ISO-14242, material loss from the bearing surfaces was also quantified alongside surface topographical and microscopic analysis.
After 5 million cycles, the mean material loss from the ceramic bearing surfaces was 0.25mm3, and from the metallic trunnions, it was 0.29mm3 in the CoC hip simulator test. The three-dimensional surface roughness (Sa) of the trunnions on the unworn and worn areas showed a statistically significant decrease from 0.558 ± 0.060 to 0.312 ± 0.028μm respectively (p < 0.001). In the MoP hip simulator test, the mean material loss from the polymeric liners, metallic tapers and trunnions were 14.28, 0.22 and 0.24mm3 respectively. The Sa of the femoral tapers on the unworn and worn areas showed a statistically significant increase from 0.510 ± 0.068 to 0.867 ± 0.233μm respectively (p < 0.001).
Until this research, no long-term hip simulator tests had quantified material loss from the taper-trunnion junction of commercially available modular CoC and MoP THRs. Metallic material loss from the taper-trunnion junctions of CoC and MoP THRs may explain the ARMD reported in the literature for these THRs. Material loss at the taper-trunnion junction needs to be measured in preclinical testing using the hip simulator to avoid ARMD and further increase the longevity of modular THRs. Based on the results, the mechanisms responsible for the material loss at the metallic taper still a multivariable process
The use of 3D-CT Planning and Patient Specific Instrumentation in Total Hip Arthroplasty: Pre-, Intra- and Post-Operative Evaluation
Optimal implant placement in Primary Total Hip Arthroplasty (THA) aims to restore physiological hip function. Three-Dimensional Computed-Tomography (3D-CT) and Patient-Specific Instrumentation (PSI) can guide implant positioning in THA. Despite growing evidence of preferable results compared to conventional templating, these tools remain underused in clinical practice. This thesis aimed to assess the role of 3D-CT planning and PSI in terms of femoral stem implantation through pre- and post-operative 3D-CT image analysis in primary THA. 3D-CT planning accurately predicted the femoral stem size (96% within one size) and femoral offsets in uncemented THA. Predicting Prosthetic Femoral Version (PFV) proved to be the unmet need given the limited surgical control of uncemented femoral stems to avoid an insufficient or retroverted PFV associated with THA instability. An insufficient PFV (<5°) was reported in 20% of the femoral stems. The malleable nature of cement in cemented fixation offers increased control and can avoid delivering an insufficient PFV. All cases in a cemented THA group were anteverted more than 5°. However, both uncemented and cemented THA reported high PFV variability, indicating the need to develop PSI to guide PFV. First, the accuracy of a PSI osteotomy guide was evaluated by aligning pre- and postoperative 3D-CT reconstructed osteotomy levels to quantify their relative discrepancy, proving that planned neck osteotomy was delivered within the clinically accepted 5mm in 96% of cases. Finally, a pilot study was conducted to evaluate whether a PSI guide, engineered to indicate the angle at which the stem was positioned intra-operatively, can achieve the target range of PFV. Post-operative CT measurements suggested its efficacy in achieving a lower variability of PFV, when compared to the non-guided THA. These findings will inform that planning software cannot predict PFV in uncemented THA and highlight the potential of PSI in delivering the intended PFV in cemented THA
Biomechanics of Contemporary Implants and Prosthesis: Modeling, Experiments, and Clinical Application
Modern medicine is now more oriented towards patient-based treatments. Taking into account individual biological features allows for increasing the quality of the healing process. Opportunities for modern hardware and software allow not only the complex behavior of implants and prostheses to be simulated, but also take into account any peculiarities of the patient. Moreover, the development of additive manufacturing expands the opportunities for materials. Technical limits for composite materials, biomaterials, and metamaterials are decreasing. On the other hand, there is a need for more detailed analyses of biomechanics research. A deeper understanding of the technological processes of implants, and the mechanobiological interactions of implants and organisms will potentially allow us to raise the level of medical treatment. Modern trends of the biomechanics of contemporary implants and prostheses, including experimental and mathematical modeling and clinical application, are discussed in this book