Intellectual Properties

  • Know-how Statistical Shape Model
  • Know-how Surgical Navigation
  • PCT Patent Phone handle
  • Patent Italian patent

Total knee replacement

Total knee replacement (TKR) to replace joints with osteoarthritis is a highly effective procedure to treat this type of knee pain, resulting in a dramatic reduction in pain, restoration of function, and improved quality of life. In 2019 (pre-COVID), around 100,000 and 1,000,000 surgeries were performed in the UK and the US, respectively. This number is predicted to continue to rapidly increase due to demographic and lifestyle changes, particularly an ageing population, and increasing levels of obesity. Although TKR is a very successful operation overall, inaccuracies in implant positioning and ligament tension of up to 30% have been reported using conventional techniques. This is associated with pain and instability, and is a significant determinant of need for further (revision) surgery (~ 7% of TKRs are revised every year).

A primary total knee replacement costs approximately £6,500 and $10,000 in the UK and US, respectively. More than 80% of these procedures are done using conventional instrumentation which has been the gold standard for more than 20 years. This approach has been found to deliver inaccurate implant positioning in up to 30% of cases, independent of the surgeon’s experience. Indeed, approximately 7% of TKRs are revised every year, a procedure which is technically challenging, and has a high failure rate, with further revision surgery necessary in 22% of these cases within 5 years. Malpositioned knee replacements resulting in post-operative pain and reduced joint function significantly impact patients’ quality of life, as well as impacting their families and carers. There is also a significant impact on society given that these patients are unlikely to return to work. Revision surgery is also expensive, costing £10k on average, and is estimated to cost the NHS £67m annually when wider healthcare costs are considered. These issues are set to become more prevalent as the number of patients requiring knee replacement surgery is predicted to rise significantly in the coming years.


The navigation device we are developing is easy to use and with no investment required from healthcare providers such as the NHS. The device will help surgeons place implants in the best possible position, ensuring optimum ligament balancing. This is expected to improve patient satisfaction and long-term outcomes. The current M.A.R.I.O system is designed for knee joint replacement but the technology is easily transferable to other joint replacement and orthopaedic procedures. The system consists of a pre-operative surgical planner and navigation software which are provided free of charge. We are confident this will contribute to the surgical training of the next generation of orthopaedic surgeons, improve surgical outcomes and in doing so, reduce the financial burden on the NHS.

M.A.R.I.O Features

M.A.R.I.O. device offers a comprehensive and affordable solution with several key advantages:

  • Intra-operative Flexibility
  • Affordability and Accessibility: It offers an affordable alternative to expensive robotic systems and patient-specific instrumentation, increasing global accessibility.
  • Universal Compatibility: M.A.R.I.O. utilises standard smartphones, ensuring widespread accessibility and integration into existing healthcare systems.
  • Real-time Ligament Balancing: M.A.R.I.O. incorporates real-time ligament balancing, a feature currently lacking in low-cost navigation technology.
  • Enhanced Surgical Outcomes: By providing accurate alignment and ligament balancing, M.A.R.I.O is expected to improve surgical outcomes, reducing complications and the need for expensive revision surgery.

M.A.R.I.O Animation

Key Publications

  • Nolte, D., Xie, S. and Bull, A.M., 2023. 3D shape reconstruction of the femur from planar X-ray images using statistical shape and appearance models. BioMedical Engineering OnLine, 22(1), pp.1-14.
  • Nolte, D., Ko, S.T., Bull, A.M. and Kedgley, A.E., 2020. Reconstruction of the lower limb bones from digitised anatomical landmarks using statistical shape modelling. Gait & posture, 77, pp.269-275.
  • Nolte, D. and Bull, A.M., 2019. Femur finite element model instantiation from partial anatomies using statistical shape and appearance models. Medical Engineering & Physics, 67, pp.55-65.
  • Zhang, K.Y., Kedgley, A.E., Donoghue, C.R., Rueckert, D. and Bull, A.M., 2014. The relationship between lateral meniscus shape and joint contact parameters in the knee: a study using data from the Osteoarthritis Initiative. Arthritis research & therapy, 16, pp.1-9.
  • Yang, Y.M., Rueckert, D. and Bull, A.M., 2008. Predicting the shapes of bones at a joint: application to the shoulder. Computer Methods in Biomechanics and Biomedical Engineering, 11(1), pp.19-30.
  • Yang, Y., Bull, A., Rueckert, D. and Hill, A., 2006. 3D statistical shape modeling of long bones. In Biomedical Image Registration: Third International Workshop, WBIR 2006, Utrecht, The Netherlands, July 9-11, 2006. Proceedings 3 (pp. 306-314). Springer Berlin Heidelberg.

Experimental work

We have implemented a robust testing protocol and conducted usability assessments involving surgeons using device design #1. Participants provided valuable feedback through questionnaires, as outlined in our testing methodology. Both average location and angular errors exceeded clinically acceptable thresholds, set at 3 mm for location and 3° for angular error. This real-world usage and feedback collection process unveiled key insights.

During these usability assessments, it became evident that the pilot holes designed for the installation of referential pins in design #1 were too loose, causing difficulties for the participants during the surgery. In response to this feedback, we made substantial improvements in our design approach, leading to the development of design #2.
The results obtained with design #2 demonstrated remarkable improvements in performance compared to design #1. Errors in location and angular measurements consistently fell below the clinically acceptable thresholds, with significantly reduced variations between data points. Notably, location errors consistently remained below the 3 mm threshold, aligning with clinically accepted standards. While the sagittal plane exhibited slightly larger errors compared to the transverse plane, the overall average error remained within acceptable clinical limits.

Our rigorous laboratory validation process conclusively affirms the efficacy of the M.A.R.I.O device. Its capacity to achieve implant alignment with remarkable accuracy has the potential to revolutionise total knee arthroplasty procedures, offering the prospect of reduced complications and improved patient well-being. This technology stands as a game-changer in the field, enhancing surgical outcomes and marking a significant advancement in orthopaedic care.