Introduction
Injuries to the knee joint, like surgical therapies, lead to a significant restriction of motor joint functions. Early functional passive and active movement therapy is recommended to restore motor skills. In addition to passive manual movement therapy, power-assisted therapeutic movement splints have also been used for various indications for years. Basic scientific research into CPM therapy (continuous passive motion) began in the 1970s. Since the 1980s, CPM therapy has been used, initially in the inpatient area for immediate post-operative follow-up treatment with various purposes. In the early 1990s, the use of joint motion splints was introduced into outpatient care. Since then, such motor-driven movement splints have been prescribed as an aid, so that patients can also complete passive movement therapy at home on these CPM splints for several hours a day. Ensuring early functional mobilization has been a key focus after surgical interventions on joints since the 1990s and contributes significantly to the success of the therapy. Although the use of CPM is recognized in the medical literature, there are currently no guidelines from a German specialist society for defined CPM therapy in the knee joint.
The scientific basis of this CPM therapy is based on the 1994 by Dr. Salter published studies «The Physiologic Basis of Continuous Passive Motion for Articular Cartilage Healing and Regeneration. In it he presents his experiences after 23 years of basic research and 15 years of clinical practice.
The goal of Dr. Salter was to regenerate the cartilage. He performed the basic experimental work on a rabbit animal model. It was shown that the CPM therapy was well tolerated and significant, stimulating effects on the articular cartilage and extra-articular structures were detectable, adhesions and joint stiffening could be prevented and the regeneration of articular cartilage through neochondrogenesis was stimulated. Clinical applications then also showed that the hospital stay and the rehabilitation time could be reduced by CPM treatment.This led to a paradigm shift in the 1980s and 1990s with the development of early functional rehabilitation treatment. The CPM treatment became an integral part of the postoperative treatment of the newly developed cartilage regenerative surgical techniques (Brittberg et al. 1994, Steadman et al. 2002, Hangody et al.2008, Kon E et al. 2011, Knutsen et al. 2016, Saris et al 2018). In the majority of published RCTs related to cartilage regeneration, CPM treatment was performed during rehabilitation.
Results:
In experimental studies, the negative aspects of joint immobilization after trauma and surgical therapies on cartilage metabolism and joint homeostasis could also be proven. (Sakamoto J et al. 2009) In addition, recent studies also show the positive effect of CPM therapy on the chondrogenic biosynthesis of PRG4 (Nugent-Derfus GE et al. 2007) and anti-inflammatory effects on the joint (Ferretti M et al. 2005). Despite a large number of positive effects of CPM therapy, Fazalare J and co-authors were unable to prove any valid clinical evidence (only 4 studies) in their systematic review in their final conclusions regarding the benefit of CPM therapy postoperatively in knee cartilage surgery due to the great heterogeneity of the studies.Unfortunately, despite an overwhelming body of fundamental scientific work and the current clinical practice of implementing continuous passive movement postoperatively in knee cartilage repair procedures, a corresponding number of methodological high-quality studies are lacking (Fazalare J et al. 2010). In the review by Goosmann et al. 2019, seven clinical studies (ØRCTs) and 3 reviews on the use of CPM after cartilage repair surgery were included in the literature analysis. The current study situation is characterized by great heterogeneity. The available studies show that the use of CPM after cartilage repair surgery resulted in good defect filling, good results in the questionnaires on knee stability, activity, quality of life and functionality, and a reduction in pain and swelling could be proven. Although CPM therapy has a major benefit according to the majority of experts, the level of evidence must be classified as low due to inhomogeneous studies.
In the systematic literature review by Rogan S et al. 2013, a review and ten original papers were included for further evaluation. The included studies showed methodological weaknesses. Heterogeneity in outcome measures and the fact that 6 of 9 studies with a one-group pre-post design measured the combined effect of surgical treatment and CPM precluded a meta-analysis. The authors were only able to document significant improvements in subjective outcomes such as pain, swelling, Quality Life Survey, Knee Society Score, WOMAC Score or Rating Cincinnati in only three studies as a result of surgical treatment and the use of CPM therapy postoperatively. Six (case) studies indicated improved cartilage quality in patients after CPM. The authors recommend more high-quality randomized controlled trials to provide high-level evidence.
Conclusion:
The CPM therapy is an important part of postoperative treatment after cartilage regenerative therapy. Experimentally, an improved metabolism and vitality of the cartilage cells, a reduction in inflammatory metabolites, improved regeneration filling and differentiation as well as a reduction in pain and swelling can be demonstrated in experimental and clinical studies. Due to the study heterogeneity and the low methodological study quality, there is a low level of evidence for CPM therapy and a need for RCT´s.
The use of CPM therapy is indicated according to the current health care standard (G-BA) if a range of motion of the affected joint that is relevant to everyday life is only possible through the additional use, despite regular physical therapy measures (especially physiotherapy) and the patient’s learned exercises of these rails can be reached. Furthermore, the therapy can be used if the postoperative follow-up treatment requires a longer restriction of mobility with joint relief to achieve the therapy goal. (cartilage repair)
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