Why is the Knee Mobilizer worth it?

Current Research shows minimal benefits of conventional CPM machines.

  • Knee PROM increased 4.7 degrees at 17 days
  • AROM increased 2 degrees (78 to 80 degrees) after 3 months
  • Manipulation under anesthesia decreased from 7.2% to 1.6%

Currently most insurance companies are unwilling to pay for CPM machines, because the vast majority of TKA do extremely well without extra intervention.  However there are 20% of patients who are very restricted. Insurances will likely be willing to pay for the very restricted patients at a 2 week follow-up.  The Knee Mobilizer is designed for the Arthrofibrotic patient.  The Knee Moblilizer will become the leader in Continuous Passive Motion technology.

Specifications

Joint Distraction – 93 Newtons (N) with air compressor set at 120 PSI.  The MCL and LCL require 63 and 59 N for 1 mm of lengthening and will rupture at 799 +/- 209 N (for the MCL) 392 +/- 104 (for the LCL).   The force of Distraction, will take of the slack of the ligaments and the posterior joint capsule (prevent shortening) but are well within the tissues tensile tolerance.

Joint Translation – 170 N at most (force declines due to rapid oscillation of pressure) with air compressor set at 120 PSI.  While the ACL and PCL are usually removed during arthroplasty the force to elongate the ACL is 242 +/- 28 N/mm with failure at 10 mm of elongation or 2160 +/- 157 N. Tensile strength of the ACL of the elderly population before failure is 658 ± 129 N for failure of elderly (60-97).

Which means, a force of 170 N will at least take up the slack of the ligament and maybe provide elongation of a ligament (if spared) 1 mm. 

Posterior Cruciate Ligament Tensile Strength – In an average of people 53-98 the average tensile strength of the anterior fibers of the PCL is 1,600 N. The posterior fibers are less taut in flexion.  170 N are well within the PCL tolerance, but will provide elongation.

 

Contraindications

Excessive joint laxity

Rheumatoid Arthritis

Altered Mental Status

Compromised Ligamentous Structure (ACL, PCL, MCL, LCL) if retained.

Excessive Edema in Foot