Chapter 15: Continuous Passive Motion

Introduction

Continuous passive motion units are motorized devices that move one or more joints through a preset range of motion at a controlled speed. The joint movement is theorized to improve healing of soft tissue and certain articular pathologies and may prevent joint contractures and delay atrophy. Although these devices were originally designed for use on the knee, models have been developed for most joints.

• Continuous passive motion (CPM) is the antithesis of immobilization, a common postsurgical management technique. To deter the unwanted effects of immobilization, CPM devices deliver gentle stresses to the healing tissues. Still predominantly used for knee injuries, CPM units have been designed for the hand, wrist, hip, shoulder, elbow, and ankle (Fig. 15-1). Although passive motion can be applied through a dedicated CPM unit, it can be delivered manually by the clinician, but for a much shorter time.

Robert Salter,²⁰ a Canadian physician, originally proposed the use of CPM to assist in the healing of synovial joints. On the basis of his clinical observations, Salter hypothesized that the application of CPM would be beneficial in three ways:

• Enhancing the nutrition and metabolic activity of articular cartilage

• Stimulating tissue remodeling and regrowth of articular cartilage

• Accelerating the healing of articular cartilage, tendons, and ligaments

CPM devices are categorized into three types of design: free linkage, anatomical, and nonanatomical.^21,22 The free linkage design is similar to manually moving the patient's limb through the range of motion (ROM) by grasping it proximal and distal to the joint. Because the joint itself is not supported, free linkage units are not suitable for unstable joints.²² CPM devices that incorporate an anatomical design attempt to mimic the natural motion of the involved joint and the proximal joints. Anatomical CPMs are the most suitable for the knee.

Nonanatomically designed CPM units make no attempt to replicate the natural joint motion, with compensatory movement occurring between the patient's extremity and the CPM's carriage. Table 15-1 summarizes the advantages and disadvantages of each of these styles of CPM units. Regardless of the type of CPM unit used, avoid placing unwanted stress on the joint's structures.