Knee and Joint Protractor - goniometer

by tc_fea, published

Knee and Joint Protractor - goniometer by tc_fea Jan 29, 2013

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This is an amateur version of a medical device called a goniometer, which can be used to measure range of motion in joints.

My daughter broke both bones in her lower leg (tibia and fibula) and wanted to measure the progress she was making in physical therapy with the range of motion (flexing) in her knee. It was difficult to measure the angle of the knee joint with a standard protractor. The midpoint of the circle on the goniometer is placed in the middle of the knee joint on the outside of the leg, and the arms are pointed toward the ankle and the hip.

A "good range of motion" in a normal patient is around a 120-130 degree angle, according to the physical therapist. Print yours and measure away!


You will need the following hardware:

  • three 3 mm x 15 mm long bolts

  • one 3 mm elastomeric stop nut

  • two 3 mm regular nuts

  • print one of each of the three.stl files

  • align the stationary.stl with two outer holes in the protractor and glue together with acetone. temporarily bolt together to maintain alignment while the acetone is drying..

  • attach the pointer to the center hole with bolt and stop nut. the nut should be snug but permit motion of the pointer


Align the device on the side of the knee or joint with the center bolt at the pivot point of the joint.

hold the stationary piece and the pointer to opposite sides of the joint.

the angle of movement can be read from the device.

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Jun 22, 2015 - Modified Jun 22, 2015

And an unintended use is woodworking. I'm building a staircase in our basement and this will be very useful for determining the cut angles. Thanks!

glad to hear it. clever

Nice adaptation Zorgglub

I recently had a total right knee replacement, and have been receiving physical therapy for the last couple months. I use this at home, it matches the results the PT was getting with her professional goniometer. Great idea. Thanks!

you are welcome.

This is really really cool

Printable medical equipment! Medical protractors can cost anywhere from $50 - $500!

Maybe the Solidoodle just paid for itself! thanx for the info