Embodiments of the knee brace disclosed herein provide a combination of external ligament support and/or relief from pain caused by osteoarthritis with patellofemoral support. The brace includes a rigid frame and a flexible strap configured to extend across the wearer's patella to provide anterior loading thereto. The strap is operatively secured at either end to components of the rigid frame, thereby providing maximum leverage for applying force to the wearer's patella. In some embodiments, the strap includes a removable and adjustable buttress for directly contacting the wearer's patella. The patellar strap provides dynamic loading to the patella through the wearer's range of motion for relief of patellofemoral dysfunction, such as patellar shift, subluxation and dislocation, and malalignments such as patella alta, patella baja, tilt and glide. In some embodiments, a conversion kit is provided for converting a rigid brace frame into a knee brace capable of providing patellofemoral support to a wearer's knee. The kit includes at least a patellar strap and at least one tab for securing the strap to the rigid frame.