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  • Also known as avascular necrosis
  • Epidemiology
    • incidence
      • 20,000 new cases per year in the United States
      • accounts for 10% of total hip arthroplasties performed
    • demographics
      • male > females
      • average age at presentation is 35 to 50
    • location
      • bilateral hips involved 80% of the time
      • multifocal osteonecrosis
        • disease in three or more different joints
        • 3% of patients with osteonecrosis have multifocal involvement
    • risk factors
      • direct causes
        • irradiation
        • trauma
        • hematologic diseases (leukemia, lymphoma)
        • dysbaric disorders (decompression sickness, "the bends") - Caisson disease
        • marrow-replacing diseases (e.g. Gaucher's disease)
        • sickle cell disease 
      • indirect causes
        • alcoholism
        • hypercoagulable states
        • steroids (either endogenous or exogenous)
        • systemic lupus erythematosus (SLE)
        • transplant patient
        • virus (CMV, hepatitis, HIV, rubella, rubeola, varicella)
        • protease inhibitors (type of HIV medication)
        • idiopathic
  • Pathophysiology
    • idiopathic AVN
      • intravascular coagulation is the final common idiopathic pathway
      • pathoanatomic cascade
        • coagulation of the intraosseous microcirculation
        • venous thrombosis
        • retrograde arterial occlusion 
        • intraosseous hypertension 
        • decreased blood flow to femoral head
        • AVN of femoral head 
        • chondral fracture and collapse 
    • AVN associated with trauma
      • due to injury of femoral head blood supply (medial femoral circumflex)
  • Associated conditions
    • AVN rates of specific traumatic injuries
      • femoral head fracture: 75-100%
      • basicervical fracture: 50%
      • cervicotrochanteric fracture: 25%
      • hip dislocation: 2-40% (2-10% if reduced within 6 hours of injury)
      • intertrochanteric fracture: rare
    • higher risk of AVN with greater initial displacement and poor reduction
    • decompression of intracapsular hematoma may reduce risk
    • quicker time to reduction may reduce risk
  • Prognosis
    • risk of femoral head collapse with osteonecrosis is based on the modified Kerboul combined necrotic angle  
      • calculated by adding the arc of the femoral head necrosis on a mid-sagittal and mid-coronal MR image
        • Low-risk group = combined necrotic angle less than 190° 
        • Moderate-risk group = combined necrotic angle between 190° and 240° 
        • High-risk group = combined necrotic angle of more than 240° 

Steinberg Classification (modification of Ficat classification)
0 normal normal MRI and bone scan  
I normal abnormal MRI and/or bone scan  
II cystic or sclerosis changes abnormal MRI and/or bone scan  
III crescent sign (subchondral collapse) abnormal MRI and/or bone scan  
IV flattening of femoral head abnormal MRI and/or bone scan  
V narrowing of joint abnormal MRI and/or bone scan  
VI advanced degenerative changes abnormal MRI and/or bone scan  

  • Symptoms
    • insidious onset of pain
    • pain with stairs, inclines, and impact
    • pain common in anterior hip
  • Physical exam
    • mostly normal initially
    • advanced stages similar to hip OA (limited motion, particularly internal rotation)
  • Radiographs
    • recommended views
      • AP hip
      • frog-lateral of hip
      • AP and lateral of contralateral hip 
    • classification systems based largely on radiographic findings (see below)
  • MRI
    • highest sensitivity (99%) and specificity (99%)
    • double density appearance
      • T1: dark (low intensity band)
      • T2: focal brightness (marrow edema)
    • order when radiographs negative and osteonecrosis still suspected
    • presence of bone marrow edema on MRI is predicitve of worsening pain and future progression of disease 
  • Bone scan
  • Nonoperative
    • bisphosphonates
      • indicated for precollapse AVN (Ficat stages 0-II)
      • trials have shown that alendronate prevents femoral head collapse in osteonecrosis with subchondral lucency 
        • However, other studies have also shown no benefit of preventing collapse with bisphosphonates
  • Operative
    • core decompression with or without bone grafting
      • indications
        •  for early AVN, before subchondral collapse occurs
        • reversible etiology
      • technique
        • traditional method
          • drill an 8-10  mm hole through the subchdonral necrosis
        • alternative method
          • pass a 3.2 mm pin into the lesion two to three times for decompression
        • relieves intraosseous hypertension equals less pain
        • stimulates a healing response via angiogenesis
    • rotational osteotomy
      • indications
        • only for small lesions (<15%) in which the lesion can be rotated away from a weight bearing surface 
      • technique
        • typically performed through intertrochanteric region
        • for medial disease
          • perform varus rotational osteotomy
        • for anterolateral disease
          • perform valgus flexion osteotomy
      • outcomes
        • reported success rate of 60% to 90%, mainly in Japan
        • distorts the femoral head making THA more difficult
    • curettage and bone grafting through Mont trapdoor technique or Merle D'Aubigne lightbulb technique
      • indications
        • preferably pre-collapse
      • technique
        • lightbulb - through the cortex of the femoral neck-head junction to access the necrotic area of the femoral head and place bone graft
        • trapdoor - through articular surface
    • vascularized free-fibula transfer
      • indications
        •  for both pre-collapse and collapsed AVN in young patient
        • reversible etiology preferred
      • technique
        • remove the necrotic area with large core hole
        • fibular strut is placed under subchondral bone to help prevent collapse or tamp up small areas of collapse
      • outcomes
        • some centers demonstrating 80% success at 5 to 10-year follow-up
        • less predictable in patients >40
      • complications
        •  related to donor site morbidity
          • sensory deficit
          • motor weakness
          • FHL contracture
          • tibial stress fracture from side graft is taken
    • total hip replacement  
      • indications
        • younger patient with crescent sign or more advanced femoral head collapse, +/- acetabular DJD
        • irreversible etiology (chronic steroid use)
        • patients >40 with large lesions
      • techniques
        • cementless cup and stem
        • care must be taken while preparing the femur as there are high rates of femoral canal perforation  
      • outcomes
        • in young patients with osteonecrosis, there is a higher rate of linear wear of the polyethylene liner and a higher rate of osteolysis than compared to older patients who have THA for osteoarthritis 
        • provides good pain relief and function
    • total hip resurfacing
      • indications
        • in advanced DJD with small, isolated focus of AVN
        • requires adequate bone to support resurfacing component
        • contraindicated in underlying disease process or chronic steroid use causing AVN (poor bone quality) and renal disease (metal ions from metal-on-metal implant)
      • outcomes
        • medium-term follow-up showing problems with acetabular erosion and pain
    • hip arthrodesis
      • indications
        • only consider in the very young patient in a labor intensive occupation

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Questions (7)

(OBQ13.50) Which of the following is the most common intraoperative complication in a patient with sickle cell disease undergoing a total hip arthroplasty? Review Topic


Periprosthetic fracture distal to the implant




Iatrogenic fracture causing pelvic discontinuity




Perforation of the femoral canal




Cardiac arrest from fat embolization to lungs




Injury to the sciatic nerve



Select Answer to see Preferred Response


Perforation of the femoral canal during preparation of the femur is not an uncommon complication, with rates ranging from 4.9-18.2%.

While total hip arthroplasty is extremely effective for pain relief in patients with osteonecrosis of the hip secondary to sickle cell disease, the procedure carries a higher rate of complications compared with non-sickle cell disease patients. Particular attention should be given to the preparation of the femur as femoral medullary widening from chronic marrow hyperplasia adjacent to patchy areas of dense sclerosis can make preparation of the canal difficult. Some surgeons prefer to ream over a guide-wire to avoid perforation.

Jeong et al. reviewed total hip arthroplasty in patients with sickle cell disease. Amongst other things, they discuss the difficulties associated with preparation of the femoral canal, quoting a perforation rate between 4.9-18.2%. They also state there are no prospective studies comparing cementless to cemented THA, but retrospective data has shown promising results with cementless components.

Hernigou et al. retrospectively reviewed 244 patients with sickle cell disease that underwent cemented total hip arthroplasty. They had a 3% infection rate, a relatively low rate of revision for aseptic loosening, and a 27% rate of medical complications. Overall, they viewed their results as favorable.

Illustration A shows a patient with bilateral AVN secondary to sickle cell disease. Note the areas of patchy dense sclerosis in the metaphyseal region of the proximal femur.

Incorrect Answers:
Answer 1: Periprosthetic fracture usually occurs at the area of perforation, not distal to the implant.
Answer 2: Acetabular fractures are more common in this patient population as well, but the rate of iatrogenic pelvic discontinuity is lower than that of femoral perforation.
Answer 4: The rate of cardiac arrest from fat embolization to the lungs is quite low.
Answer 5: While injury to the sciatic nerve is possibly, it has not been shown to be more common in this patient population. The rate of post-operative hematoma causing sciatic nerve dysfunction may be higher in this patient population.


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(OBQ12.254) A 45-year-old with a history of sickle cell anemia reports hip pain for the past 6 months. A radiograph of the affected hip is shown in Figure A. Which of the following interventions has been shown to have the best outcomes in this patient population? Review Topic














Uncemented metal on polyethylene total hip arthroplasty




Cemented metal on polyethylene total hip arthroplasty



Select Answer to see Preferred Response


Based on the radiographs and current literature, the best intervention is an uncemented metal on polyethylene total hip arthroplasty.

Avascular necrosis of the hip may be idiopathic in nature or associated with alcoholism, steroid use, or as in this case, sickle cell anemia. The Ficat staging system is used to classify avascular necrosis of the hip. Changes in treatment are driven by development of symptoms as well as the development of subchondral bone collapse (Ficat Stage 3). In those with with femoral head flattening (Ficat Stage 4) and acetabular degenerative changes (Ficat Stage 5), total hip replacement has good to excellent outcomes.

Mont et al. review surgical options for avascular necrosis of the hip. Head preserving procedures are generally reserved for those patients where the femoral head has not collapsed. Collapse and associated arthritis warrant utilization of arthroplasty procedures.

Mont et al. conducted a systematic review to better delineate the symptomatic progression of asymptomatic avascular necrosis of the hip. They found that patients with sickle cell disease have the highest rate of progression to collapse. Medium sized, laterally located lesions were associated with a higher frequency of collapse and joint preserving procedures are recommended for these.

Figure A shows radiograph of a patient with avascular necrosis; note the femoral head flattening, narrowing of the joint space and acetabular sclerosis.

Incorrect Answers:
Answer 1: Conservative measures in this patient would not improve this patient’s outcome give the degree of the femoral head collapse and presence of acetabular degeneration.
Answer 2: Bisphosphonates can be used in patients with avascular necrosis of the hip prior to collapse. Current data is conflicting as to whether they prevent collapse or not.
Answer 3: Outcomes for patients undergoing hemiarthroplasty for avascular necrosis of the hip in the young patient are poor; and as a result, this has been largely abandoned.
Answer 5: Higher failure rates have been seen in patients undergoing cemented total hip arthroplasty in treatment of avascular necrosis of the hip.

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(OBQ12.270) A 65-year-old patient was treated with an open reduction/internal fixation for a left femoral neck fracture sustained 25 years ago. Five years ago he developed hip pain and was converted to a left hip hemiarthroplasty. He presents with complaints of groin pain for the past 6 weeks. A recent radiograph is shown in Figure A. The patient’s physical exam is limited secondary to pain. Serum laboratory values are WBC-8.0, ESR-20, CRP-0.5. A synovial fluid aspirate of the hip demonstrates < 500 cells (60% PMN). What is the most likely cause of this patient's symptoms? Review Topic


Acetabular protrusio




Infected hip hemiarthroplasty




Lumbar radiculopathy




Impingement of the hip hemiarthroplasty




Iliopsoas tendinitis



Select Answer to see Preferred Response


Based on the history, radiographs, and laboratory values, the patient has developed failure of his hip hemiarthroplasty. At this point in time he warrants a conversion to a total hip arthroplasty.

Avascular necrosis (AVN) of the femoral head after traumatic injury to the femoral neck occurs at an incidence of 10-45%. Although the risk increases with failure to anatomically reduce the fractue, it can still occur in non displaced settings. Treatment of avascular necrosis in older patients includes hip hemiarthroplasty or a total hip replacement. With the former, development of acetabular protrusio can contribute to groin symptoms. Functional outcomes have been reported to be higher in those receiving total hip replacement for AVN of the femoral head.

Lee et al. prospectively compared the use of bipolar hip hemiarthroplasty versus total hip arthroplasty for advanced stages of AVN of the femoral head (Ficat Stage 3). Total hip scores were most improved in the total hip arthroplasty group. Migration of the outer head in the hemiarthroplasty group was seen in 23% of patients. They recommend use of a total hip arthroplasty in patients with Ficat Stage 3 AVN of the femoral head

Ito et al. evaluated the outcomes of patients who underwent bipolar hemiarthroplasties for femoral head avascular necrosis. They found that proximal migration and acetabular degeneration were risk factors for groin symptoms. They also found that outcomes were inferior to patients who had undergone total hip arthroplasty for AVN of the femoral head. They recommend use of total hip arthroplasty in advanced osteonecrosis of the femoral head

Diwanji et al. evaluated outcomes of patients who underwent a conversion from a bipolar hip arthroplasty to total hip arthroplasty in 25 patients. Thirteen (52%) patients were revised to THA because of acetabular erosions. Follow up was completed for an average of 7.2 years. At final follow-up, they found improvement of the Harris Hip Scores and improvement of the pain portion of the WOMAC index. They recommend use of total hip replacement as an option to salvage failed bipolar hip hemiarthroplasty

Figure A shows the radiograph of a hip hemiarthroplasty where acetabular protrusion has developed.

Incorrect Answers
Answer 2: There is no evidence of infection based on laboratory results.
Answer 3: There is no evidence of lumbar based pathology in this patient.
Answer 4: While impingement could be a cause of pain, it is not as likely given the history, clinical findings and radiographs seen here.
Answer 5: While irritation of the iliopsoas could occur, it is not as likely given the radiograph seen here.

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(OBQ11.196) A 47-year-old man presents with 1 week of left leg pain. 6 months prior he underwent a vascularized free-fibula bone graft from his left leg to his right hip for avascular necrosis. The pain is located at the level of his donor site and is worse with weight-bearing and relieved by rest. Physical exam shows focal tenderness over his tibia. A lateral radiograph from the day of presentation is shown in Figure A. WBC, ESR, and CRP are all within normal limits. What is the next best step in management to confirm the diagnosis? Review Topic


Compartment pressure measurements




CT scan




MRI scan




Ultrasound to rule out deep abscess




Bone biopsy



Select Answer to see Preferred Response


The clinical presentation is suspicious for a stress fracture of the tibia following free-fibula bone grafting. If plain radiographs are negative, more sensitive imaging such as a MRI or bone scan should be performed.

Tibial stress fractures are a known complication following free-fibula bone grafting. Radiographs may be normal (as is the case in figure A), or might show the "dreaded black line" and/or new periosteal bone formation. If a stress fracture is confirmed with imaging, appropriate management would then consist of protective weight bearing until symptoms subside.

Pacifico et al detail a case report of tibial stress fractures after vascularised free-fibula graft to the mandible. They report non-traumatic stress fracture to the tibia following a vascularised free-fibula graft is an uncommon but important complication.

Ivey et al detail a case report of a tibial stress fracture after vascularised free-fibula graft for repair of non-union of the humerus.

Emery et al report a case-series of 5 patients who sustained tibial stress fractures after a graft had been obtained from the ipsilateral fibula for use in anterior reconstruction of the spine. They theorize that the increased load the tibia bears as a result of the missing fibular graft may result in stress fractures.

Illustration A shows new periosteal bone formation on the lateral cortex of the tibia consistent with a stress fracture.

Incorrect Answer Choices:
1: While compartment syndrome is on the differential diagnosis, his signs and symptoms are not most consistent with that diagnosis.
2: While CT scan may show evidence of a stress fracture, MRI/bone scans have been shown to be superior methods for detection.
4: As infectious laboratories are normal, an ultrasound to rule out a deep abscess would likely be negative.
5: Bone biopsy is not appropriate without evidence of a lesion or concern for osteomyelitis.


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(OBQ09.8) In patients with sickle cell disease and asymptomatic osteonecrosis of the femoral head identified with magnetic resonance imaging, what percentage will eventually go on to femoral head collapse? Review Topic


< 10%




11% to 25%




26 to 50%




51 to 75%




> 75%



Select Answer to see Preferred Response


Untreated asymptomatic osteonecrosis of the femoral head in patients with sickle cell disease has a > 75% likelihood of progression to pain and collapse.

In contrast to asymptomatic osteonecrosis in patients without sickle cell disease, patients with sickle cell disease have a high incidence of progression to collapse and functional impairment secondary to pain (33% compared to 75%, respectively). In patients with sickle cell disease who present with a symptomatic hip, the contralateral (presumably asymptomatic) hip should be screened carefully and periodically for signs of disease. Given the high rate of progression, some argue for operative treatment of the asymptomatic hip at the same time the symptomatic hip is being treated.

Hernigou et al. studied patients with sickle cell disease who had symptomatic avascular necrosis (AVN) in one hip and asymptomatic AVN in the contralateral hip. Their goal was to understand the natural history of the asymptomatic side. Ninety-one percent eventually developed pain and 77% developed collapse. Collapse was preceded by symptoms of pain in all patients.

Aguilar et al. report bone and joint disorders are the most common cause of chronic pain in patients who have sickle cell disease, and that the femoral head is the most common area of bone destruction in sickle cell patients.

Incorrect Answers:
Answers 1-4: Patients with sickle cell disease and osteonecrosis of the femoral head have a high rate of progression to painful collapse.

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(OBQ08.239) A 40-year-old man complains of increasing groin pain. Radiographs show femoral head avascular necrosis with subchondral lucency but without femoral head collapse. Which of the following medical treatments have been shown to decrease the risk of subsequent femoral head collapse? Review Topic


Cyclic parathyroid hormone therapy




Bisphosphonate therapy




RANK ligand therapy




RANK therapy




Selective estrogen receptor modulator therapy



Select Answer to see Preferred Response


Bisphosphonate therapy is a proven method of preventing femoral head collapse in patients with avascular necrosis and subchondral lucency.

Lai et al evaluated the effect of alendronate on patients with Steinberg stage-II or III osteonecrosis of the femoral head. They found that alendronate prevented early collapse of the femoral head at twenty-four months.

Agarwala et al evaluated the effect of bisphosphonate therapy on patient reported and radiographic outcomes in femoral head avascular necrosis. They found alendronate reduces pain, improves function and may prevent disease progression at 5 year followup.

Nishii et al evaluated the effect of alendronate on 20 hips with osteonecrosis of the femoral head without collapse. They found a lower frequency of collapse and less patient reported pain in patients treated with bisphosphonate therapy compared to controls at 12 month follow up.

Thanks to Dr. Chris Rice at UW Madison:
"Recent level 1 evidence seems to cast doubt on the efficacy of bisphosphonate treatment in precolapse AVN with medium to large lesions. There is also some thought that the supposed success seen in smaller lesions is due to the natural history of these lesions which often do not progress to collapse even in the absence of any treatment. "
Lee YK, Ha YC, Cho YJ, Suh KT, Kim SY, Won YY, Min BW, Yoon TR, Kim HJ, Koo KH Does Zoledronate Prevent Femoral Head Collapse from Osteonecrosis? A Prospective, Randomized, Open-Label, Multicenter Study. J Bone Joint Surg Am. 2015 Jul 15.

Incorrect Answers:
Answer 1: Cyclic parathyroid hormone therapy is used in osteoporosis treatment, and not in the treatment of femoral head avascular necrosis.
Answer 3 & 4: Neither RANK nor RANK ligand are being used in therapeutic forms currently. Denosumab, an anti-RANK ligand antibody, has shown early success in the treatment of bone lysis in oncologic applications.
Answer 5: Selective estrogen receptor modulator therapy is used in osteoporosis, and not in the treatment of femoral head avascular necrosis.

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(OBQ04.220) A 41-year-old male has steroid-induced avascular necrosis of the hip and decides to undergo metal on polyethylene total hip arthroplasty. His 80-year-old, sedentary father had a total hip replacement 5 years ago. With comparison to his father, the patient should be informed of the following risk? Review Topic


Increased risk of sciatic nerve palsy




Increased longevity of prothesis




Increased risk for polyethylene wear and osteolysis




Reduced range of motion




Lower likelihood of revision surgery



Select Answer to see Preferred Response


A younger, active patient will sustain more polyethylene wear and osteolysis due to greater activity levels and more years of use.

Kim et al prospectively studied 98 consecutive patients with osteonecrosis of the femoral head with an average follow-up was 9.3 years. Although there was no aseptic loosening of the components, they reported a high rate of linear wear of the polyethylene liner and a high rate of osteolysis in these high-risk young patients (16% in cemented femoral stems, 24% in uncemented stems).

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