Case:

A 28-year-old male presents to the Emergency Department with acute-on-chronic hip pain.  His past medical history includes sickle cell disease and poorly controlled asthma for which he takes daily prednisone. He has been ambulating with a cane for one year due to his hip pain. He immigrated one week ago from Puerto Rico and reports worsening hip pain since arriving.  He denies fevers, chills, weakness, or numbness.  No tobacco, alcohol, or drug use.  His radiographs are shown below.  Can you make the diagnosis? Click the answer box below. 

This patient’s AVN is more advanced on the right hip compared to the left, with demonstrated right-sided cortical collapse, subchondral cyst formation, and remodeling of the femoral head and acetabulum. The left hip displays increased density and sclerosis. 

Definition and Epidemiology:

Avascular necrosis (AVN) of the femoral head refers to a decrease in blood flow to the femoral head that ultimately leads to cell death, fracture, and collapse of the articular surface.  The demographics of the disease vary based on the underlying cause of AVN. Across all causes, the average age at presentation ranges from 35-45 years, and males are affected up to three times more commonly than females (Kaushik, Das, & Cui, 2012) .  

Pathophysiology and Risk Factors:

The exact underlying pathophysiology of AVN is controversial, but numerous traumatic and atraumatic causes have been identified that lead to interruption of the vascular supply to the femoral head and/or direct death of osteophytes and bone marrow. Risk factors for 75-90% of cases include hip trauma (injury to medial femoral circumflex artery), chronic steroid use, and alcoholism  (Mont & Hungerford, 1995) . Other risk factors include gout, sickle cell disease, Legg-Calve-Perthes disease, Caisson disease (aka “the bends”), myeloproliferative disorders, hypercoagulable states, hyperlipidemia, pregnancy, and smoking  (Moya-Angeler, Gianakos, Villa, Ni, & Lane, 2015) .   

Making the Diagnosis:

Typically, patients present with insidious onset of pain, pain with climbing stairs, and anterior hip pain. On physical exam, presentation may range from painless range of motion to severe hip pain with internal rotation. Plain radiographs are the first-line imaging modality of choice. MRI should be obtained when radiographs are negative but clinical suspicion for AVN remains high (Table 1). Multiple staging systems have been created to characterize the breadth of this disease. The modified Ficat Classification system is the most widely utilized, but it was invented prior to the advent of MRI and relies solely on x-ray imaging (Table 2) (Mont, et al., 2006) . 

Why early diagnosis matters!

AVN ultimately leads to collapse of the femoral head and severe osteoarthritis requiring total hip arthroplasty. Early diagnosis allows for surgical procedures (core decompression, bone grafting) that preserve the femoral head and may delay the need for total arthroplasty. This is especially important for the young adults most affected by this disease who are likely to outlive their joint prosthesis and require revision at a later age. AVN is often multifocal, and clinical signs and symptoms are quite subtle in the early stages. Therefore, diagnosis of atraumatic AVN at one site should prompt evaluation of other high-risk sites, or a search underlying risk factors. In particular, greater than 80% of non-traumatic AVN in the femoral head is bilateral, so imaging of the full pelvis and contralateral hip should be obtained  (Hauzeur, Pasteels, & Orloff, 1987) . 

Treatment:

For Ficat stages 0-II, bisphosphonates are used to prevent femoral head collapse. Alendronate has been shown to reduce pain, improve articular function, and slow collapse progression in adults with AVN in some trials, but other studies have shown no benefit  (Luo, Lin, Zhong, Yan, & Wang, 2014) . In these early stages, operative interventions such as core decompression and/or bone grafting are available to stimulate angiogenesis and promote healing.  For post-collapse stages (Ficat III-IV), operative interventions are required and include total hip replacement, hip resurfacing, or arthrodesis.

Case Resolution:

This patient was diagnosed with bilateral AVN at Ficat stage IV in his right hip and Ficat stage II in his left hip. His sickle cell disease and use of chronic oral steroids increased his risk for this condition. Ultimately, his hip pain did not require acute intervention or hospital admission, so he was referred to the orthopedic outpatient clinic for follow up and will require operative intervention.

Pearls:

• Consider AVN in the differential diagnosis when patients present with insidious onset of pain, pain with climbing stairs, and/or anterior hip pain
• Plain films are first-line imaging, but MRI (not CT) is gold standard for diagnosis
• Early diagnosis may allow for surgical interventions that delay the need for total hip arthroplasty
  
  Faculty Reviewer: Dr. Jeff Feden
   

References:

Ficat, R. (1985). Idiopathic Bone Necrosis of the Femoral Head. Early Diagnosis and Treatment. J Bone Joint Surg Br, 3-9.

Hauzeur, J., Pasteels, J., & Orloff, S. (1987). Bilateral non-traumatic aseptic osteonecrosis in the femoral head. An experimental study of incidence. J Bone Joint Surg Am, 1221-5.

Kaushik, A., Das, A., & Cui, Q. (2012). Osteonecrosis of the femoral head: An update in year 2012. World J Orthop, 49-57.

Luo, R.-b., Lin, T., Zhong, H.-M., Yan, S.-G., & Wang, J.-A. (2014). Evidence for Using Alendronate to Treat Adult Avascular Necrosis of the Femoral Head: A Systematic Review. Med Sci Monit, 2439-2447.

Mont, M., & Hungerford, D. (1995). Non-traumatic avascular necrosis of the femoral head. J Bone Joint Surg Am, 459.

Mont, M., Marulanda, G., Jones, L., Saleh, K., Gordon, N., Hungerford, D., & Steinberg, M. (2006). Systematic analysis of classification systems for osteonecrosis of the femoral head. J Bone Joint Surg Am, 16-26.

Moya-Angeler, J., Gianakos, A., Villa, J., Ni, A., & Lane, J. (2015). Current concepts on osteonecrosis of the femoral head. World J Orthop, 590-601.