Adjustable Crank Arm and Seat

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[toggle title=”Adjustable pedal and seat permit quantitative, systematic, and progressive early mobilization therapy” open=”no”]

Discrete pedal crank lengths from 2” to 6” at 1-inch intervals plus seat positioning by 1-inch intervals allow the therapist to move the patient’s joint incrementally, systematically through increasing flexion and extension therapy.

Quantitative considerations.

The two basic facts are

 1) length of the pedal crank determines hip arc of motion
2) position of the seat with respect to the pedals determines flexion and extension angles.

labelThe figure shows the top rail label on the OrthoBike. It reminds the therapist and patient that

    1) the range of motion is specified for each pedal crank position when the seat position puts the knee in full extension
2) the ROM increases by about 10° from 0°-60° to 0°-100° for every one-inch increase in pedal crank

The seat-crank system is calibrated for any leg length by setting the seat position so the knee is in full extension at pedal position 1 when the pedal is at about 4 o’clock (maximum extension). The range of motion will be about 0°-60°.

For every inch the pedal crank length is increased, the seat must be moved one inch closer to the bike to maintain full extension. For example, a patient whose knee is in full extension at pedal position 1 and seat position 15 will still be in full extension at pedal position 2 by moving the seat to position 14. Then the range of motion will increase to about 0°-70°. And so forth to pedal position 5 and 0°-100°.

The top rail label also reminds the therapist and patient that

Flexion increases by ~4° with every inch the seat is moved forward.

Moving the seat forward without changing the pedal position increases the maximum knee flexion by about 4° for every inch.

The fixed length of the pedal crank arm determines the diameter of the pedal rotation circle. Hip flexion and maximum knee flexion are directly proportional to the diameter of the circle the pedal/foot traverses. The maximum knee flexion and ROM can be altered by moving the seat but the total hip flexion angle is determined solely by the length of the pedal crank arm.

The adjustable seat-pedal crank system allows a patient to incrementally increase knee flexion from the comfort zone into the stretch zone in one session while accumulating cycling reps, “by the numbers”

Further, the patient can assume responsibility because the seat and pedal settings show him/her the knee flexion status. The adjustable seat and pedal also transform the OrthoBike into a patient-friendly measurement and diagnostic device because an accurate estimate of flexion can be made independently by the patient.

In addition to transferring the responsibility for progress from the therapist to the patient, giving the patient control over the treatment and pain, the OrthoBike builds the patient’s confidence.


Therapist strategies.

After the initial evaluation of a new patient, the therapist knows how to configure the OB1, according to the patient’s extension, maximum flexion, and range of motion.

Patients who can start rehab close to full extension but have ≤ 60° of flexion start at pedal position 1 (2” radius) with the seat adjusted to produce the desired extension (placing the ball of the foot on the pedal).

“This was instrumental in helping me do a rotation where I could not do a full rotation with the regular bike. It was causing too much pain. With yours I could do it without causing the extreme pain and discomfort…. It was 4 weeks into it last time before I could get full rotation. But this time with your OrthoBike I could get full rotation the first week.” David (Second TKA, shortly after surgery)

Patients exhibiting a greater degree of flexion can start with a longer crank.

There is no minimum knee flexion or range of motion required before a patient can use the OrthoBike OB1.

The Flexion Rock N Roll techniques are used to stretch the knee when the pedal crank is lengthened (or the seat is moved closer at the same crank length).

“That [bike with pedals at position 1] was the first time that I could see my knees continuously move, rather than feeling that soreness and stiffness. It was pretty exciting to see a continuous movement of my legs rather than just up and bend and extend….Since I am a mountain biker myself it was really nice to see that I could pedal at that particular time.” Glenn S. (Bilateral knee replacement, clinic and home use)

Every patient systematically continues from the starting pedal position to the next, some faster than others.

When they reach pedal position 5, they have developed sufficient flexion (100°) and range of motion to ride the exercise bikes and ergometers. They are also accustomed to the circular motion after several weeks of riding and thousands of reps. It becomes an incremental step to the 7-inch pedal crank, not a major move fraught with pain.

“When I first got on it the pedal was on the number one hole, and I was so elated that day that I could make the pedals go around. Now I am out to the furthest pedal hole, which is 5, and am pretty much at the full range of motion.” Glenn S.

This systematic and consistent rehab therapy using OrthoBike’s adjustable pedal and seat helps fast and slow patients to make their milestones and recognize progress.

“I needed more range of motion for my flexibility. I felt that the stretching and pulling on the strap on the board wasn’t sufficient to carry through after therapy. If I would get on a regular bicycle, I would not have the full range of motion to pedal it. This one has the adjustable pedals, so I could always start at a smaller radius and range of motion and work up. It has done excellent for my knees… I was back bicycling probably 3-4 weeks after the use of this bike. I would recommend this for anybody who has knee surgery to get the range of motion back for them.” Glenn S. 


[toggle title=”Advanced technique: Repetitive short arc quad exercise” open=”no”]

When their TKA and ACL reconstruction patients are ready, PTs add the short arc quad exercises in primarily the backward pedaling direction, at pedal position 1 or 2 and substantially increased resistance. This is a short-crank and high resistance exercise that has been shown to activate the quads and remodel the soft tissues in fibrotic knees over time.


“In the beginning the short pedal setting was difficult with the tension turned up, but as I did it I went from 25 RPM to 50 RPM, I was able to double it. It gives you the confident feeling that you are getting stronger, that it is getting easier to do. I feel the short arc was really helpful as well as the other ROM exercises you could get with the bike.” Don A.


[toggle title=”No minimum knee flexion requirement” open=”no”]

There is no minimum knee flexion or range of motion before a patient can use the OrthoBike OB1.

If the patient’s maximum knee flexion does not permit a full pedal revolution at the shortest crank length without compensation, the patient uses the lever arms to assist stretching at maximum tolerable flexion, incrementally increasing it until the minimum of 55°-60° of flexion is achieved.


[toggle title=”Important patient perception” open=”no”]

Seeing their knee go around at pedal position 1 and becoming comfortable pedaling at 50 RPM means a lot to the TKA patients. It gives them more comfort and hope that they will one day be able to use their knee again than being told their knee flexion has reached 60°, because they do not see with the same experienced eyes as their therapists.

We have heard it spontaneously sung so many times that we call it the OrthoBike Anthem. In one of its popular variations: “I love this bike. Look at my knee going around! I just could not imagine I would be doing this so soon. This bike is the best!”

“I love seeing my knees going around. I haven’t ridden a bike in 30 years, and I have ridden one mile already!” Lois H. (Bilateral knee replacement)