The Effects of the LRU Pillow versus the CPM 
Machine on Active Assistive Knee Range of Motion at 
Hospital Discharge. A Retrospective Summary

Investigators: Scott Johnson, PT , Jennifer Delcamp, MD, and Matthew Lawless, MD 

Background: Pain relief and return of function are the main goals following total knee arthroplasty. One measure of return of function in the acute phase has been range of motion. A continuous passive motion (CPM) machine is a standard postoperative treatment used to regain range of motion following total knee replacement surgery. The efficacy of this piece of equipment has not been supported consistently in the research (1-10). The CPM machine is heavy and cumbersome and requires assistance for proper use. The risk of injury to caregivers exists due to the CPM’s size and weight. Positioning can be difficult, especially in obese and short patients, and if inadequate can cause additional stress to the knee. Extension can be difficult to achieve and the CPM must be used in a bed due to its size. A more portable option may produce better compliance, edema control, and ultimately achieve desired range of motion following a total knee replacement. 

Hypothesis: Edema control is one of the keys to success in regaining range of motion following a total knee replacement. Coupling edema control, through appropriate positioning and elevation, with a standard exercise protocol will yield optimal ROM outcomes. Achieving and maintaining full extension with positioning in the acute postoperative phase will lead to better outcomes for extension. Focusing on elevation will control edema, which will lead to good outcomes for flexion. A specially designed dense foam pillow (LRU 2031) which maintains the knee in an extended position while elevating the lower extremity, will achieve the same results in active assistive ROM as the CPM machine.

Specific Objective: Determine the efficacy of using the LRU pillow following a total knee replacement compared to a CPM machine. Will the use of the LRU pillow, along with a standard exercise protocol, yield better active assistive knee range of motion at hospital discharge compared to the use of a CPM machine with the same standard exercise protocol? 

Significance: The outcomes may reveal a better alternative to the CPM machine following total knee replacements and other knee surgeries. The risk of injury to caregivers may be reduced due to the size and weight of the machine. Alternatives to the CPM machine may reduce healthcare costs to the medical providers, patients, and/or insurance companies.

Methods: This was a retrospective chart review of knee AAROM for patients receiving total knee arthroplasties. All data was obtained from charts of one hospital from January 2011 to October of 2011. The AAROM numbers were obtained from the last acute care physical therapy notes. 111 patients received a CPM machine during their hospital stay while 131 patients received the LRU Pillow. The average length of stay was 3.0 and the average number of physical therapy sessions during the acute hospital stay was 3. Active assistive range of motion of the surgical knee was measured with the use of a long arm goniometer, aligned against anatomical landmarks, by a physical therapist or physical therapist assistant. Active assistive range of motion was defined as an exercise in which an external force assists specific muscles and the knee joint to move through the available excursion. Measurements were taken with patient lying supine. Each patient received the same exercise regime during their acute hospital stay.

Results: The results are listed in Table 1. The percentage of patients achieving full extension (defined as 0-5 degrees) in the CPM group was 87% (97/111) and in the LRU group was 95% (124/131). The percentage of patients achieving at least 85 degrees of flexion was 67% (74/111) in the CPM and 85% (111/131) in the LRU groups, while the percentage of patients achieving at least 90 degrees of flexion was 60% (67/111) and 82% (107/131) for CPM and LRU groups respectively.

LRU vs. CPM: 
Range of Motion Outcomes


The CPM has been used to help regain motion following TKA for many years. The CPM however has several downsides. The size and weight makes care of the extremity cumbersome and sometimes dangerous. The machine has moving parts that may malfunction and also requires an electrical outlet with a cord and potential fall risk. The design of the CPM precludes use in anything but a large firm surface (such as a bed). Positioning of the machine can be difficult and may hold the knee in a flexed position, making achieving full extension difficult. The CPM is an expensive piece of equipment that is only used as a rental for only a small percentage acute post operative period. It was our hypothesis that if we could use a pillow to hold the knee in extension and provide elevation that the motion following total knee arthroplasty would remain the same, without exposure potential downsides to the CPM. Our results (as originally reported in a prospective study) have shown that the use of the LRU provides at least as good postoperative motion, without many of the downsides associated with CPM use.