This study further evaluates the safety profile and efficacy of the Ellipse IM HTO Nail system in subjects with osteoarthritis and varus malalignment of the knee. All subjects will receive treatment with the Ellipse IM HTO Nail System and followed for six months.

The Ellipse IM HTO Nail is intended for open wedge proximal tibial osteotomies. The Ellipse IM HTO Nail is an intramedullary nail that operates on the principles of distraction osteogenesis.

The Ellipse IM HTO Nail is used in valgizing HTO procedures to correct varus malalignment. The Ellipse IM HTO Nail is surgically placed in the intramedullary canal of the tibia. It is lengthened telescopically using the non-invasive external remote control.

Inclusion Criteria:

1. Patient has standing varus malalignment benefitting from high tibial osteotomy correction
2. Patient is diagnosed with current osteoarthritis of the knee
3. Patient is eighteen years of age or greater
4. Patient is a candidate to be implanted with an Ellipse IM HTO System
5. If female of childbearing potential, patient presents with a negative pregnancy test and agrees to employ adequate birth control measures for the duration of the study
6. Patient understands and accepts the obligation to comply with the required follow-up visits and is logistically able to meet all study requirements
7. Patient signs informed consent for the use of their personal private data

Exclusion Criteria:

1. Patient declines to sign informed consent for the use of their personal private data
2. Varus deformity greater than 10°
3. Flexion contracture greater than 15°
4. Knee flexion under 90°
5. Medial/lateral tibial subluxation over 1 cm
6. Medial bone loss of over 3 mm
7. Inflammatory arthritis
8. Arthritis in the lateral compartment
9. Patella baja
10. Weight over 114 kg
11. Severe patellofemoral symptoms
12. Unaddressed ligamentous instability
13. Fixed flexion contracture
14. Known or suspected osteoporosis or osteopenia based on medical history and radiographic images
15. Current use of nicotine products.
16. Requires other surgical procedures at the time of the HTO surgery

Subjects who meet the protocol eligibility criteria including standing varus malalignment in the limb presenting with osteoarthritis of the knee.