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Passive Stretching and Continuous Passive Motion (CPM)

CPMs should never be used to forcefully increase bend

Care must be taken not to force the joint beyond its ability to stretch – CPMs should never be used to forcefully increase bend. CPM can be useful for increasing range of motion (ROM)[1] and reducing inflammation[2]. CPM has been controversial with studies citing little evidence of efficacy [3]. However, these studies were not about treating arthrofibrosis, they were conducted on the general surgical population undergoing their first joint replacement without complications [3]. The great majority of people who have surgery do not develop arthrofibrosis. Therefore, any positive response to CPM from the small number of people who would have developed post-surgical arthrofibrosis was diluted in the pooled result [4]. More research is needed into the efficacy of CPM for treating people with arthrofibrosis [3,4].


Care must be taken not to force the joint beyond its ability to stretch. The joint should only be bent or straightened to the point at which it is mildly uncomfortable – think of the discomfit of pushing your finger backwards and stretching it. Pushing further than discomfit risks tearing tissue, and that is a major setback.

Tissue contraction

During periods of little to no movement the collagen fibres in the connective tissue in muscles, tendons and ligaments contracts and the structure of the fibres changes, making them less flexible. This even occurs overnight [5], and it occurs in all people to some extent. This is the reason that stretching first thing in the morning feels pleasurable. When tissues are inflamed the contraction process is greatly increased due to the presence of the special cells that make scar tissue, called myofibroblasts. This contraction can create a severe lack of ROM, particularly in the morning and after periods of immobilisation. For more information on tissue contraction, see [5,6]. Passive stretching is therefore likely to be most beneficial early in the morning. It gently stretches collagen fibres out, permitting greater ROM and thereby avoiding tearing during daily use. Mobilisation and stretching also flushes out toxins (inflammatory cytokines, dead cells etc) and rehydrates connective tissue and membranes so that they slide against each other properly and do not form adhesions.

How to be used by Arthrofibrosis patients

Each session should begin in the safe zone. When the joint is comfortable moving through the range of motion the limits of bend and extension are increased 1 degree. This process is repeated until the maximum safe limits for that session are reached. ROM settings should only ever be increased by 1 degree at a time, never more than that. In our opinion, legs should not be strapped in. It is our view that CPMs should be used often, at least twice a day in the early stages of arthrofibrosis. Some people sleep with the affected limb in a CPM, and this may be necessary in the early healing stages if there is aggressive arthrofibrosis. The amount of inflammation and aggressive healing influences the treatment time needed for each session, and this varies between individuals.

Knee CPM device ,Rehabilitation after knee surgery.jpg

Computer controlled CPM

Computer controlled CPMs have an emergency button to quickly lower the amount of bend, and for safety the person being treated should always hold the controller and know how to operate it. The joint should be flexed through the comfortable range of motion and held the maximum position for 2 to 10 seconds to permit stretching of tissues. Optiflex describes their program for knee CPMs “When the carriage reaches the Programmed (maximum) Flexion Angle, it will oscillate between the Programmed Flexion Angle and 10° less than the flexion angle, three times. On the third oscillation cycle, the carriage will hold at the flexion angle for the Programmed Extension/Flexion Delay Time”.

In the US there are several hand-operated stretching devices available for the treatment of knees, but in our opinion motorised, computer controlled CPMs do a better job since they have precise 1o incremental control of ROM and there is less likelihood of accidental tears. In addition, a CPM used correctly takes a joint through the full range of motion many times during a session, so there are greater benefits from mobilisation. Good reconditioned second-hand CPMs can sometimes be purchased on Ebay (ex-hospital) and these can be a good option. Always look for computer controlled CPMs.


  1. Aspinall, S. K. et al. Medical stretching devices are effective in the treatment of knee arthrofibrosis: A systematic review. J Orthop Translat27, 119-131, doi:10.1016/ (2021).

  2. Ferretti, M. et al. Anti-inflammatory effects of continuous passive motion on meniscal fibrocartilage. J. Orthop. Res. 23, 1165–1171 (2005).

  3. Chaudhry, H. & Bhandari, M. Cochrane in CORR ((R)): Continuous passive motion following total knee arthroplasty in people with arthritis (Review). Clin Orthop Relat Res 473, 3348-3354, doi:10.1007/s11999-015-4528-y (2015).

  4. Usher, K.M, S. Zhu, G. Mavropalias, J.A. Carrino, J. Zhao, and J. Xu (2019) Pathological mechanisms and therapeutic outlooks for arthrofibrosis. Bone Research 7:9

  5. Corcoran, P. Use it or lose it –the hazards of bed rest and inactivity- adding life to years. Western J. Med. 154, 536-538 (1991).



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The materials presented in this site are provided voluntarily as a public service. It is of a general nature, based on the scientific literature. The information and advice provided is made available in good faith but is provided solely on the basis that readers will be responsible for managing their own assessment of the matters discussed herein and that they should verify all relevant representations, statements and information. Please consult your doctor.

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