All operations have some risk. Those specific include (but are not limited to):
Incomplete bone healing
In a small percentage (less than 5%) of patients the bone may not fully heal, or may change position whilst healing. This is monitored by the progress Xray, and in the rare case where it is necessary a second surgery may be required to promote complete healing.
Deep venous thrombosis can occur after any surgery, and is more common after Orthopaedic procedures including osteotomy. All precautions are taken to avoid their occurrence including stockings, calf pumps, and medications. If a blood clot does occur it can generally be treated by medications.
Nerve and blood vessel injury
The major nerves and blood vessels supplying the leg are in the vicinity of the surgery and can rarely be injured. All care is taken to avoid these structures.
Infection can occur after any surgical procedure. It is uncommon after osteotomy, though possible, and antibiotics are given during the procedure to decrease it risk.