“High Nitrogen, Low Stress, Maximum Flex”

Technical Skills

✅ Engineering Sketching

✅ Computer-Aided 3D Design and Modelling

✅ 3D Printing

✅ Literature Research

Interpersonal Skills

✅ Communication

✅ Collaboration

✅ Task Management

✅ Presenting

Overview

Design Project 2 centered around designing a custom hip implant that serves as a suitable, non-commercially available alternative for a patient suffering from osteoarthritis resulting from undiagnosed childhood Perthes Disease. Through this project, I gained an understanding of how to diagnose a condition through radiographs and medical history, as well as how to justify the properties of our chosen materials in relation to the needs of our patient. I also learned how to model the complex geometry of a hip implant using CAD software.

Patient Profile and Diagnosis

At the onset of the project, we were given a full medical profile of the patient, including a recount of their life, personal information such as name and age, medical information such as height and weight, as well as a series of X-ray scans of the hip. Using this information, my team and I were tasked to diagnose the patient with a specific condition requiring a hip implant. In retrospect, this activity immediately built up a sense of community within our team.

<aside> 🏥 After some time spent researching, I proposed that the patient had Perthes Disease, whereas another member discovered that this disease is very frequently followed by the development of osteoarthritis.

We therefore correctly diagnosed the patient with osteoarthritis due to untreated Perthes Disease in childhood.

</aside>

<aside> 🏥 My team and I made this diagnosis using signs and symptoms such as:

• limited mobility and hip pain
• radiographs showing bone spurs and excess bone mass in the
  left femoral head.
• leg length discrepancy (right leg is 3 cm taller).

</aside>

A radiograph of the left femur-acetabulum joint from a frontal view. Bone spurs are apparent and the interface is uneven.

Design Process

Knowing the patient’s specific condition and personal situation (e.g. having one shorter leg than the other), we were able to generate a set of objectives, constraints, and functions catered particularly to him.

Objectives

• The implant should be durable
• The implant should be affordable
• The implant should be lightweight
• The implant should balance weight on each leg
• The implant should readjust hips to equalize leg length

Constraints

• The design must be implanted
• The implant must be sterile
• The implant must be biocompatible with the femur
• The implant must accommodate patient height and weight specifications
• The implant must conform to medical standards

Functions

• Relieves pain
• Improves hip mobility
• Provides greater range of motion
• Allows walking

Sketching and Concept Planning

Before embarking on any 3D modeling, our team came up with several concept sketches of a possible hip implant design that would meet our design criteria. After considerable debate and discussion, we decided we wanted to have a cemented hip implant due to the patient’s old age and concerns surrounding his body’s osteogenesis capabilities.

Preliminary Sketch

My preliminary sketch was relatively simple, focusing more explicitly on materials than on any geometric considerations and therefore resembling a usual hip implant. The same was true of most of my teammates.

However, one teammate discovered a specific geometry that was unique, composed of different components in the femoral head that rotate in different axes. Our whole team agreed that this geometry was favourable after reading a research article that the teammate provided on a similar proposed design [source].

Aim:

• better interlocking of the head into the acetabulum
• reduced contact surface for rotation to minimize friction and increase mobility

Chosen sketch, made by a teammate, as a preliminary design concept.

Final Design Before CAD

After reading further through the research article and discussing, we decided we likewise wanted to create four different head components: the abductor, rotator, flexor, and cup.

The abductor, rotator, and flexor rotate in different axes while the cup rotates in all directions.

Adjustments:

• polyethylene liner replaced with two components rotating on different axes to reduce cross-shear stress and wear.
• changed to cemented fixation due to the patient’s old age and possibly poor osteogenesis capabilities.

A very rough schematic representation I drew of the 3D model.

• Benefits of this geometry

Final Design Solution

3D Modelling (Inventor) and Prints

I and my modeling subteam partner designed these components in AutoDesk Inventor. I was responsible for modeling the femoral stem and the abductor, whereas my partner modeled the flexor, abductor, and uni-directional cup.

We then created an unconstrained assembly of the parts to visualize the components.

Final Assembly

The abductor, rotator, and flexor are responsible for abduction, medial/lateral rotation, and flexion motion, respectively.

Physical Assembly

After confirming my partner’s satisfaction with the design and ensuring that the dimensions of his parts allowed them to fit comfortably into my parts, we went to 3D print the design. This marked my first time using a 3D printer, and I learned how to configure a print using PrusaSlicer.

Assembled prototype consisting of the various 3D printed parts.

Ordered left to right: uni-directional cup, flexor, rotator, abductor (inbuilt with femoral stem).

The components rotated within each other as expected. However, in order to keep print times low, we had to scale down our design by 70% and remove the grooves and holes along the stem. Nonetheless, the parts were anatomically accurate to accommodate the patient in Inventor.