been made with unusual variant wheels, like the omniwheel or the mecanum wheel. These allow for a broader spectrum of movement, but have made no mass-market penetration. The electric wheelchair shown on the right is fitted with mecanum wheels (sometimes known as Ilon wheels) which give it complete freedom of movement. It can be driven forwards, backward, sideways, and diagonally, and also turned around on the spot or turned around while moving, all operated from a simple joystick. Other variants Foot propulsion of a manual wheelchair by the occupant is possible for users who have limited hand movement capabilities or simply do not wish to use their hands for propulsion. Foot propulsion also allows patients to exercise their legs to increase blood flow and limit further disability. Users who do this commonly may elect to have a lower seat height and no footplate to better suit the wheelchair to their needs. Wheelbase chairs are powered or manual wheelchairs with especially molded seating systems interfaced with them for users with a more complicated posture. A molded seating system involves taking a cast of a person's best achievable seated position and then either carving the shape from memory foam or forming a plastic mesh around it. This seat is then covered, framed, and attached to a wheelbase. A bariatric wheelchair is one designed to support larger weights; most standard chairs are designed to support no more than 250 lb (113 kg) on average. Pediatric wheelchairs are another available subset of wheelchairs. These can address needs such as being able to play on the floor with other children, or cater for children in large hip-spica casts due to problems such as hip dysplasia. Hemi wheelchairs have lower seats which are designed for easy foot propulsion. The decreased seat height also allows them to be used by children and shorter individuals. A knee scooter is a related device with some features of a wheelchair and some walking aids. Unlike wheelchairs they are only suitable for below knee injuries to a single leg. The user rests the injured leg on the scooter, grasps the handlebars, and pushes with the uninjured leg. Some walkers can be used as a wheelchair. These walkers have seat and foot plates, so an attendant can push while the patient is sitting on the walker. This is useful for a person who gets tired while walking with a walker, or has