Skip to Main Content

Minimally Invasive Avascular Necrosis Treatment Is Developed at Yale, Combining 3D Modeling With Computer Navigation

March 11, 2024
by John Ready

In a paper published in the journal Arthroplasty Today, Daniel Wiznia, MD, assistant professor of orthopaedics & rehabilitation and co-director of Yale Medicine’s Avascular Necrosis Program, presents a new surgical technique designed to prevent or delay hip collapse in patients with femoral head avascular necrosis (AVN). Thanks to 3D innovations and novel applications of intraoperative navigation technology developed at Yale, Wiznia is leading a multidisciplinary approach to optimizing clinical outcomes.

Femoral AVN, otherwise known as osteonecrosis, is a debilitating condition associated with compromised blood supply to the portion of the thighbone closest to the hip. It particularly impacts the head of the bone. When the small vessels there are injured, the bone can no longer repair itself. Upwards of 20,000 new cases of femoral AVN are diagnosed each year in the United States, and those with the condition face a range of potential complications, such as collapse of the femoral head.

AVN is commonly diagnosed in people between the ages of 30 and 65. For some patients, there are no symptoms, which results in the condition being discovered incidentally. Up to 67 percent of patients with femoral AVN progress to symptomatic disease. A total hip arthroplasty (THA), otherwise known as a total hip replacement, is the current best treatment when the femoral head ultimately collapses. However, THA in younger patients has an increased risk of mechanical failure due to a higher level of physical activity and the length of time that the hip implant will be utilized. Therefore, there is a need for therapeutic strategies that effectively delay and prevent hip collapse, reducing the likelihood of requiring a THA.

Avascular necrosis: current treatments

According to Wiznia, treatment of AVN using core decompression and concentrated bone marrow with stem cells has been shown to reduce pain and hip collapse in early stages of disease, but current surgical techniques lack the ability to consistently direct treatment to the primary necrotic region where the bone is dying. These techniques can adversely lead to decompression and adjuvant treatment of an incorrect region of the femoral head, as well as multiple attempts to correct the surgical instrument trajectory, thereby compromising the healing process and further increasing the risk of fracture.

Additionally, multiple entry and re-orientation attempts, including the heat and forces experienced during excessive drilling, can significantly reduce the potential for bone regeneration, weaken already-compromised bone structure, and increase the risk of iatrogenic fracture, which is when a new fracture occurs during surgery.

A novel approach

“In this paper, we demonstrate a minimally invasive, real-time 3D image-guided approach for delivering personalized treatment to the optimal location in the femoral head,” Wiznia said.

“For 31 patients, autologous [taken from the patient's own body] bone marrow aspirate was obtained from the iliac crest and concentrated using a bone marrow processing system,” he continued. “An intraoperative CT scan was used to create a 3D model of the hip and identify the necrotic region. Next, computer navigation was used to orient instruments and decompress the region with necrotic bone and deliver the bone marrow aspirate concentrate with stem cells to the central location of the necrotic region. Using this method, we successfully reached the necrotic region without instrument re-orientation in 20 of 21 patients during an estimated operative time of one hour.”

Maximizing outcomes with unparalleled precision

Previous techniques to treat AVN did not incorporate minimally invasive instruments. As such, patients were usually unable to weight bear for up to four months following surgery. By using this new surgical technique, more than 95 percent of patients were able to weight bear immediately following surgery without even requiring the assistance of crutches.

The novel image-guided technique was developed here at Yale using computed tomography. This combines a series of scans taken from different angles around the patient’s body and uses computer processing to create cross-sections or slices of bones, blood vessels, and soft tissues. The 3D model, used in conjunction with computer navigation, allows for highly precise surgical intervention in the afflicted area of the femoral head.

“There is no guessing where the lesion is located,” Wiznia said. “We know in three dimensions both where it is as well as its exact shape. We also know how best to access the lesion as minimally invasively as possible.”

The enhanced accuracy reduces the total number of drill passes needed to effectively conduct a core decompression to one single pass, which is critical since each drill pass carries the risk of fracture. More accuracy also means that more of the lesion can be cut out and the patient’s own stem cells, which are used as part of this procedure, can be directed to the most precise location.

“Through this technique, we are aiming to improve clinical outcomes for patients with early-onset femoral head AVN by precisely targeting necrotic regions and allowing for better comparison between therapies by standardizing treatment protocols,” Wiznia said. “Although it currently requires technology and equipment unique to our surgical center at Yale, my hope is that this technique will become more accessible to patients with AVN so fewer total hip replacements are required.”

Submitted by John Ready on March 11, 2024