HTO involves cutting a wedge out the tibia to correct the alignment of that bone with the knee joint, to redistribute load from the affected medial part to lateral part. To keep the tibia in the new position, a medical nail device is attached to keep it in place and allow new bone to regenerate within the wedge. Currently, the market leader for HTO is the TomoFix (by DePuySynthes company) plate and nail device. As the name suggests, TomoFix is fixed at surgery and therefore the change in bone angle cannot be changed afterwards. It does mean that patients can be weight-bearing on the affected leg soon after the HTO procedure. A new CE-marked device is being tested in an interventional trial; it is produced by Ellipse Technologies. This device is an extendable nail and inserted intramedullary; following surgery the nail is tend slowly extended over a period of time until the bone correction is satisfactory.