Understanding in shoe rockers

In 2011 we designed what I believe is one of the first in shoe rocker orthoses. It was used to treat a patient who had stepped on a bomb whilst serving in Afghanistan. At the same time, we developed a rocker brace which was also used for the same patient. Fig.1 & 2. Since then, the rocker has been used successfully in the management of over 500 patients. Some of these patients had arthritic ankles some had tibialis posterior dysfunction but by far the greatest number were patients who had been through some type of surgical procedure or in many cases multiple procedures usually after traumatic injury. Approximately 25-30 of these patients were considering below knee amputation had the rocker been unsuccessful. 

Fig 1. and 2. Rocker orthotic and rocker brace

So, what changes have we made to the rocker and perhaps more importantly what lessons have been learned in the intervening years? 

The overriding lessons from a manufacture standpoint are.

  1. That the correct positioning of the rocker fulcrum is essential in order to optimize the function of the device. This seems obvious but the critical nature of this was highlighted by a patient who came into the clinic wearing a rocker shoe and who was suffering from extreme knee pain (due to hyper extension). When we calculated the position of the rocker fulcrum of the shoe, we realised that it was a full 30mm forward of where we calculated it should be. The reason for this wasn’t that the manufacturer had calculated wrongly but rather they were basing their calculation of the length of the shoe and not the length of the patient’s foot from the posterior surface of the calcanium to the 1st MPJ. Fig 3. With the fulcrum so far forward the rocker was blocking the patients forward progression rather than facilitating it.
Fig 3. Rocker shoe, the black mark shows the fulcrum of the shoe while the red mark shows the fulcrum of the foot
  1. The materials we use for the rocker are now much more flexible than previously. This means that we can adjust the springing aspect of the device by means of raising or lowering the sidewalls. For any rocker to work successfully it essential to have exactly the right balance between rigidity and what we call recoil spring.

The lessons learned clinically are generally concerned with the type of conditions we have been able to treat successfully using the rocker and its worth highlighting a few of these.

  1. Patients wearing fixed ankle braces – The conditions for the use of these braces are many and varied. They can be extremely beneficial; however, they have one functional limitation. They work well during heel strike and mid-stance but as the patient tries to move through into the propulsive phase the brace acts against them by preventing dorsiflexion. In cases such as this we now take a cast of the patient’s foot whilst wearing the brace and then fit a rocker to under surface of the brace. Fig4 This allows the patients centre of gravity to move forward easily into the propulsive phase which facilitates a longer stride length and reduces the need for hip flexion and or hyper extension of the knee joint. As well as a longer stride length, patients often report a reduction in general fatigue with their modified brace. 
Fig 4. Brace with rocker attached.
  1. Talepes Equino Varus- The residual effects of TEV can be quite difficult to deal with and although treatments for TEV have improved over the years, many patients still struggle to get past the residual lack of functional ankle joint dorsiflexion. We have successfully used the rocker in a number of cases allowing patients to transition forward more easily. In one case the patient was able to take up jogging which had hither to been impossible without considerable pain.
  2. Gross subtalar joint pronation – In most cases this is caused by rupture or total disfunction of the tibialis posterior and this results in a complete collapse of the foots normal architectural integrity. 

A great many of these patients end up having some type of surgical intervention. However, there are quite a few who are unwilling or for various reasons unable to have surgery. Correction of these feet can be challenging. Many years ago, we moved away from the calcaneal wedging paradigm taught in podiatry schools as a means of correcting pronated feet. Switching to a more orthopaedic paradigm of stabilizing the calcaneum and applying supinatory force to the talonavicular joint. In this way we are controlling both sides of the subtalar joint rather than one side as when wedging the calcaneum. It also prevents the setting up of a detrimental torque within the lower limb caused by the calcaneus being wedged into inversion while the talus slips medially and downwards. With this in mind we design many of our braces with an expansive medial surface area to spread the corrective load along the whole medial border of the foot. This allows us to create very high levels of corrective force. However, this high level of correction can potentially cause intolerance issues. The collapse of the foot causes a bowstringing and shortening of the tendo Achilles which then acts as a pronatory muscle, this means that we have a situation where on one hand we have high levels of corrective force and on the other a foot which has an increased pronatory impulse force. The foot can literally be like a ship dashing against rocks. Fig 5 & 6. By simply integrating a rocker into the brace we open up an alternative movement pathway (AMP) which reduces the pronatory force and therefore substantially reduces the potential for intolerance. In many cases these patients do well and can eventually move into a high flanged rocker orthotic.

Fig 5. & 6. A grossly pronated foot and a brace with a larger medial surface area and rocker.

Surgical fusion – By far the greatest number of patients receiving rockers are those who have had some form of surgical intervention normally a fusion of some kind. Many of these patients will have suffered severe trauma and may have required multiple procedures. The clinical picture is almost always one of limited and in most cases a complete absence of ankle dorsiflexion. The standard post operative care for patients who are still symptomatic is the use of a heel raise in order to tip the bodies centre of gravity forward and therefore reduce the dorsiflexory resistance on the foot. In situations where the rearfoot or ankle is fused the midfoot is often the area of compensatory breakdown, although in a few cases the breakdown is more proximal and may take the form of repeated tibial stress fractures. As podiatrists we were trained to assess dorsiflexion as one of the more important biomechanical parameters. However, the treatment of these patients opens up a completely new set of biomechanical parameters. When the foot and ankle are fused there is inevitably a concomitant reduction of plantarflexion (a measurement which is often ignored in biomechanical assessments). A heel raise used in a healthy unrestricted ankle causes rapid plantarflexion at heel strike, however in the case of the fused ankle this plantarflexion is not available. The only way that the lower limb can adapt to the increased plantarflexory force in a way that allows the foot to become plantargrade is to rapidly flex the knee joint. This creates a lurching gait with concomitant stress on the knee, hip joint and lower back. Patients who have used a heel raise for extended periods often describe lower back pain and exhibit severe gluteal wastage on the affected side. The rocker however does not produce a plantarflexory force and therefore does not flex the knee joint. The foot and ankle are not moving in relationship to each other but rather the rocker is creating its own movement by mimicking the ankles movement. Fig 1.

Fig 7. Midfoot breakdown after ankle fusion
Fig 8. A patient who had requested below knee amputation after multiple surgical procedures and who is successfully using a rocker brace

One surgeon who regularly sends patients for the rocker described where he sees the rocker clinically. 

“The rocker can prevent or delay the need for surgical fusion and in cases where the patient ultimately has a fusion, the rocker becomes even more important for preventing post-surgical compensatory complications”

Rocker case studies

If the reader would like to see the successful rocker case studies just head to our testimonials page for patient stories and video footage.