Onen Procedure

What is the Onen Procedure?

The Onen Procedure is a surgical technique introduced to the literature in 2014 by my late mentor Dr. Ahmet Önen and his team, of which I was one of the co-authors. The method was named after Dr. Önen to honor his memory, and it has been particularly effective in treating pectus arcuatum and mixed-type deformities.

How Does It Differ from Ravitch?

The Onen Procedure is based on wedge osteotomy, similar to Ravitch. However, its unique feature is the following:

• After wedge osteotomy, if the bone edges do not perfectly meet end-to-end,
• An additional Nuss bar is inserted beneath the sternum to lift the lower part.
• This way, the chest wall is corrected using a combination of wedge osteotomy and Nuss bar elevation.

In other words, the Onen Procedure is essentially a hybrid technique – Ravitch + Nuss.

• Wedge osteotomy for primary correction
• Screw/plate fixation for stabilization : We now use biocompatible titanium plates and screws instead of mesh. Two straight plates are placed on either side of the sternum, leaving the middle part free. This not only provides strong stabilization and proper healing but also ensures that a future median sternotomy (e.g., for heart surgery) can be performed safely if needed.
• Optional Nuss bar support to elevate the lower sternum
• Ideal for mixed-type deformities (Pectus Arcuatum)

Our Innovation: 3D Surgical Guide

Thanks to the Pectus Arcuatum guide designed in 3D and custom made, we now guarantee error-free and trouble-free surgery.

Since 2014, wedge osteotomy has remained at the core of the Onen Procedure. However, the risks have always been the same:

• Miscalculation of the cutting angle → undercorrection or overcorrection

We determine the cutting angle of the bone accurately by calculating it with special formulas in the 3D architectural program based on the patient’s computed tomography image and take this angle as a basis when designing the 3D Guide. Thus, we offer the guarantee of providing the optimum angle in wedge resection

• Posterior table fracture → the sternum fails to heal properly, leading to a lifelong “clicking” and unstable chest bone, or life-threatening injuries to the heart and great vessels

This X-ray comparison shows the sternum with a posterior table fracture after wedge osteotomy performed without a 3D surgical guide (left), versus a safely corrected and solidly healed sternum using a patient-specific 3D surgical guide (right). In Ravitch and Onen procedures, this innovative patient-specific 3D surgical guide allows wedge osteotomy to be performed safely with permanent and reliable results”

To solve these issues, we developed the world’s first patient-specific 3D surgical guide

Patient-specific 3D surgical guide: innovative surgical technology that accurately calculates the wedge osteotomy angle, protects the posterior tabula and provides clear vision.

Patient-specific 3D surgical guide: innovative surgical technology that accurately calculates the wedge osteotomy angle, protects the posterior tabula and provides clear vision.

• Guaranteed correct angle: The saw only follows the pre-planned wedge angle

• Depth control: Cuts only the anterior two-thirds of the sternum, never reaching the posterior table

• Clear view: Built-in channels allow aspiration of bone dust and fluids

• Standardized safety: Wedge osteotomy becomes reproducible and predictable

Today, when performing the Onen Procedure, we integrate this unique guide to make surgery safer and more precise than ever.

An operative image of a wedge osteotomy using a 3D Pectus Arcuatum guide

Scientific Background

• 2014: Onen Procedure published → Ravitch + Nuss hybrid technique

• 2017–2021: International CAD-based surgical guide studies (Carfagni, Servi, Leng)

• 2025: Development of our generative design-based 3D guide

• 2025: First clinical case successfully performed, presented as an oral presentation at CWIG 2025 in Japan

The Legacy of Dr. Ahmet Önen

Dr. Ahmet Önen was one of the pioneers of chest wall surgery in Turkey. Naming this procedure after him represents both a scientific contribution and a personal tribute.

A photo of Dr. Ersöz with his mentor, Dr. Ahmet Önen, taken during his residency in thoracic surgery

Summary:The Onen Procedure is a hybrid technique that combines Ravitch wedge osteotomy with Nuss bar support when needed, making it particularly effective for pectus arcuatum and mixed deformities. Today, with our 3D surgical guide, wedge osteotomy is safer, more precise, and more predictable than ever before.