Knee scooters, also known as knee walkers, have been a welcome alternative to crutch-assisted ambulation when a patient with an injured lower extremity must be non-weightbearing. However, like all new breakthrough treatments, knee scooters have shown certain challenges and risks that are now posted on the internet.¹ Among these problems are knee pain, discomfort with immobilizing devices and hazards of falling off the scooter.

This month, I encountered a new possible complication of prolonged use of a knee scooter: a deep vein thrombosis (DVT). Here is the brief clinical history. 

A healthy active 65-year-old gentleman got a referral to my practice from the local urgent care clinic, having suffered a plantarflexion twisting injury of the left foot and ankle 24 hours prior to the visit. He had a diagnosis of a fifth metatarsal fracture and wore a posterior splint. The urgent care clinic gave him crutches and told him to keep his injured left foot non-weightbearing. Examination of the radiographs confirmed a non-displaced fracture at the metaphyseal-diaphyseal junction of the base of the fifth metatarsal. My conservative treatment consisted of immobilizing the patient in a pneumatic walking boot and mandating non-weightbearing of the left lower extremity for six weeks. We referred the patient to our local medical supply shop to rent a knee scooter, which the patient found far more practical and useful than crutches.

A follow-up visit at four weeks post-fracture revealed some increased swelling and pain in the injured foot, but no other findings or cause for concern. Four days after that office visit, the patient paged the office on a Sunday night complaining of severe pain and swelling of the entire left leg from the foot to the hip. We immediately directed the patient to the emergency room where a Doppler ultrasound study detected three clots in the thigh: two in the deep femoral vein and one in the popliteal vein.

The emergency room suggested that a knee scooter had caused the three clots in his thigh, an allegation that I quickly dismissed. However, upon further reflection and study, I must now consider this possible cause-effect relationship.

Knee scooters require prolonged, 90-degree flexion of the knee. This is a position in which we previously never placed patients for any extended period of time, particularly when requiring full body weight on the flexed knee. While patients have complained about pain in their knees, hips and back with this prolonged posturing, I have never considered other potential negative effects.

Blood flow through the deep venous system of the legs depends greatly upon the pumping action of the calf musculature.² This peripheral pumping action helps push venous blood flow through the more proximal thigh veins. When the knee flexes significantly and for a prolonged period of time, as when ambulating on a knee scooter, we would presume that this blood flow could be compromised.

My patient had no risk factors for a DVT but he did report that two days before symptoms started, he was on his knee scooter for over eight hours while helping his family set up for a party. Yes, he was also immobile in a walking boot but did the unique environment posed by the knee scooter play the major role in the formation of three distinct clots in the thigh veins?

My brief research on the Internet found no postings or warnings about the risk of DVT and long-term use of a knee scooter. I am curious whether any of my colleagues have had any similar experiences or observations.

References

1. Knee walker caution. Patient. Available at https://patient.info/forums/discuss/knee-walker-caution-504610 .

2. Recek C. Conception of the venous hemodynamics in the lower extremity. Angiology. 2006;57(5):556-63.