Development of a novel indentation device suitable for arthroscopic evaluation of articular cartilage

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2011
Thesis identifier
  • T12861
Qualification Level
Qualification Name
Department, School or Faculty
  • Background: The size of lesions on articular cartilage are difficult to estimate using conventional preoperative imaging techniques, which may prevent the use of conservative procedures in the restoration of joint function following osteoarthritis (OA). Arthroscopic probes have been designed to be used intraopertively which can assess the mechanical integrity of the cartilage surface. These devices may not have the sensitivity to detect early OA. Therefore, there exists the need for a low load indentation system which can determine both static and time-dependent properties of the tissue and thereby improve the likelihood of early OA detection. Such a probe also has the potential for mounting on a robotic arm for precise excision of tissue. In order to determine the early signs of OA, it is important to characterise the repeatability, variation and mechanical response of the articular cartilage surface to being indented with respect to different experimental parameters. Objective: To design, build and evaluate a bench top indentation system to assess the viscoelastic properties of articular cartilage, which has the potential to be converted to a device that could be used arthroscopically and intraopertively. In particular, it was the aim to: - investigate the difference between a spherically headed indenter and a flat headed indenter in assessing the cartilage mechanical properties in vitro; - evaluate articular cartilage's preconditioning properties by cyclic indentation testing; - and to evaluate the recovery of articular cartilage subsequent to the preconditioning. Methods: A bench top materials testing device was designed and built using a high resolution linear actuator and a spring-loaded Linear Variable Differential Transducer (LVDT). The actuator drove the tip of the LVDT, with either a flat or spherical tip, into the cartilage surface and the spring of the LVDT provided a known force and displacement. The surface deformation of the cartilage could then be determined from such a device. Healthy osteochondral plugs were harvested from the bovine tibial plateau articulating surface using an osteochondral coring tool. Plugs were mounted in plaster of paris with the cartilage surface normal to the indenter. All test procedures were identical: an actuator displacement of 5mm, a ramp speed of 5mm/second and a holding time of 30 seconds. An initial experiment was performed on a metal plug to ensure that any recorded deformation was that of the cartilage surface and not of the underlying environment. Subsequently the indentation mechanics of two indenter tips was evaluated: a spherical head indenter of diameter 4.8 mm and a flat ended indenter with a diameter of 5.1 mm. Then the cartilage preconditioning properties were evaluated using the flat-ended indenter. Each plug was tested 10 times in exactly the same place on the cartilage surface with a time interval of 20 seconds between each test. Finally, to test how long the cartilage takes to recover from its preconditioned state, each plug was indented 5 times in exactly the same place on the cartilage surface with a time interval of 20 seconds between each test and a further 6th indentation was also done in the same place on the cartilage surface but after either 1, 5, 10, 20 or 30 minutes interval. This 6th result was compared to the initial indentation. If the properties determined from the 6th indentation were the same as those of the first indentation, one could say that the sample had recovered. Results: Indenting the metal plug did not result in any measurable deformation indicating that subsequent measures are that of the cartilage surface and not of any underlying structures. When indenting with the spherical head indenter the deformation was deeper and quicker than using the flat-ended indenter due to the small contact region on the cartilage surface which means that there was higher stress on the surface compared with the flat-ended indenter. The preconditioning experiment indicated that the indentation depth decreased with each cycle of loading until approximately the 5th cycle after which the cartilage may be assumed to be preconditioned, since successive indentations exhibited similar mechanical behaviour. The time constant describing the surface deformation with time did not undergo any preconditioning which means that only the stiffness is affected by preconditioning, not permeability. Thirty minutes of recovery was sufficient for the surface to fully recover to its original state. Conclusions: A bench top device has been designed and manufactured that can assess the mechanical characteristics of articular cartilage. Furthermore, this device has demonstrated mechanical differences in the surface response between indenter geometries and the preconditioning and recovery characteristics of cartilage. Suggestions and comments have been made regarding the next phase of this research into the development an arthroscopic indentation device.
Resource Type
Date Created
  • 2011
Former identifier
  • 831730