PROM

Illustration showing the normal range of motion of the knee.

What range of motion is needed for ordinary activities?

For ordinary daily activities a person needs -

• <93 degrees of knee flexion for rising from a seated position
• 106 degrees of knee flexion for shoelace tying
• 135 degrees of flexion to properly take a bath

Extension is less forgiving. Only in full extension does the lock-back mechanism work to lock the knee and support the body without any other effort.

The passive range of motion needs a helper to take the knee through the available range of motion without the patient trying to help, so that the muscles are relaxed.

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Using a CPM machine for PROM

A CPM or Continuous Passive Motion machine can be dialled so that the knee is taken through a pre-determined passive range of motion, and that range can be gradually increased during rehabilitation.

• Quote from peer-reviewed paper:

  However "...the ROM the knee experiences in a CPM machine is considerably less than initially anticipated. According to our findings, a CPM motion arc of 0° to 90° may only give rise to 60° to 70° of actual knee motion."

  Citation: Bible JE, Simpson AK, Biswas D, Pelker RR, Grauer JN. Actual knee motion during continuous passive motion protocols is less than expected. Clin Orthop Relat Res. 2009 Oct;467(10):2656-61. doi: 10.1007/s11999-009-0766-1. Epub 2009 Feb 27. PMID: 19247728; PMCID: PMC2745449.

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Forum discussions

• Re: ruptured patellar tendon

  Patient struggling to regain range of motion after patellar tendon rupture.

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