CPM Machine

Changing the realm of continuous passive motion towards accessible and affordable rehabilitation.


CPM also called Continuous Passive Motion, is a device that is used to gently flex and extend the knee joint. The CPM machine can be used after surgery to allow the knee joint to slowly bend. CPM machines are seen as a significant medical advancement that can help prevent postoperative complications from knee surgery. By getting the knee joint bending immediately following surgery, the goal is to improve restoration of mobility, and ultimately to speed up recovery.

The Problem Statement

The cost of the CPM machines can be restrictively expensive. At face-value there seemed to exist an opportunity to develop a lower cost version of a CPM with the additional benefit of being portable.

Product Development Process


At the time of the project, the cost of buying a knee CPM device could range from R60 000 to R80 000 ($3000-$4000). These high prices result in hospitals or medical practices being able to only afford one or two devices. The number of patients who need treatment outweighs the availability of the devices which result in patients only receiving one 30 minute session a day. This has a negative knock-on effect on the patient and the medical practitioner and is not a sustainable operating model. Additionally, the cost of operation is influenced by the complexity of CPM devices as they require the help of a technician or medical practitioner.

As part of the Skeg Discovery process, we scrutinise assumptions which could influence any value delivery of a new product idea. Our research showed that frequency of use is a key metric to achieve positive and timely results when using a CPM for knee rehabilitation. In fact, during rehabilitation a patient should have up to 8 hours of daily machine interaction with sessions lasting approximately 30 minutes (depending on the patient’s limitations) for 6 weeks.

The Decisive Competitive Edge

The Decisive Competitive Edge (DCE) was revealed when looking beyond only cost, to accessibility and correct treatment.

Experimental Prototyping

This user journey outlined a direction of solution which needed to be practically supported by technology. Our Experimental Prototyping phase addresses prioritised experiments to confirm the solution’s feasibility. The experiments include:

  • Investigating suitable technology options.
  • Experimenting to calculate key procedural parameters such as angle measurements.

Alpha and Beta Prototyping

The CPM was designed to be a mobile connected device to allow for consultative patient management over the course of rehabilitation.
As such, the detailed development of the product integrated multiple capabilities, from material expertise, industrial design, mechanical design, electronics, and back-end software.

Project Status

The client is currently demonstrating the product to potential investors with the aim to realise a technology exit.

Key Learnings

Even though several product’s development journey find their origin in the objective to make a “better, cheaper” device, this is seldom the DCE to ensure market success. Instead, an in-depth understanding of the current reality reveals coping mechanisms which implies opportunities for change and innovation.