Osteonecrosis of the Knee

Michael B. Boyd, Simon Görtz and William D. Bugbee

• Osteonecrosis (ON) of the knee is a challenging condition; its cause is unclear. ON of the knee can be broken down into two categories: primary or spontaneous ON and secondary ON. Nonsurgical treatment can be pursued for lower-grade lesions. Surgical treatment of ON of the knee includes arthroscopy, core decompression, osteochondral grafting, realignment procedures, and prosthetic arthroplasty. This chapter focuses on the presentations of and treatment options for ON of the knee.

Important Points

• Degenerative subchondral bone cysts (usually large, isolated defects about the medial femoral condyle) are commonly misdiagnosed as ON but are rather a variant presentation of early osteoarthritis.

• Defining the stage and lesion size (volume and surface area) are keys to sound application of our treatment algorithm.

• Subchondral fracture or collapse drastically alters prognosis and limits treatment options.

Clinical and Surgical Pearls

• For deep posterior femoral condyle lesions to be accessed, the meniscus may need to be detached and reflected, leaving a cuff of tissue for later repair.

• If mobilization of the patella is necessary, the fat pad can be released while the anterior horn of the opposite meniscus is protected.

Clinical and Surgical Pitfalls

• Concomitant distal femoral osteotomy and juxtaposed femoral condyle osteochondral allografting are not recommended; procedures should be staged to avoid nonunion of the allograft.

• Uncemented total knee arthroplasty (TKA) is not recommended in the treatment of ON.

• When performing TKA for multifocal ON, have stems available.

Osteonecrosis (ON) of the knee is a difficult clinical entity. Although the exact causes of ON are not well understood, there are several theories. However, the diagnosis of ON of the knee can be arduous, and its management remains challenging and controversial. In general, ON of the knee can be classified as (1) primary or spontaneous ON (also known as Ahlbäck disease) or (2) secondary ON, commonly associated with known risk factors. Spontaneous ON of the knee is usually unilateral and typically affects just a single femoral condyle. Secondary ON is often multifocal, bilateral, and/or polyarticular. This chapter focuses on the unique presentations of and various treatment options for ON of the knee.

Secondary ON can result from vascular insufficiency or occlusion, direct cell damage, or elevated intraosseous pressures. Radiofrequency or laser use can lead to postarthroscopic ON. In addition, the use of mechanical instruments can alter cartilaginous biomechanics, leading to postarthroscopic ON.

Preoperative Considerations

History

A thorough history may simplify the diagnosis of ON and help delineate an effective treatment algorithm. For spontaneous ON, antecedent (often minor) trauma should be elucidated. Likewise, the use of arthroscopic instrumentation, including radiofrequency wands, has been implicated in a separate entity recognized as postarthroscopic ON. Risk factors for secondary ON should be sought, the most common being corticosteroid use, alcohol abuse, and systemic lupus erythematosus, with multiple risk factors potentiating the odds for the development of the disease.

A common error is to misdiagnose degenerative subchondral bone cysts commonly seen in osteoarthritis as spontaneous ON of the knee, which typically affects obese female patients over the age of 55 years. Postarthroscopic ON most often involves the femoral condyles and rarely affects the plateaus and patella. In secondary ON, screening additional joints might be of benefit, even in the absence of current symptoms.

• Notch (Fig. 66-1C) or Rosenberg view of knee

Optional:

• Merchant view of patellofemoral joint

• Long-leg AP mechanical axis view to evaluate for axial malalignment

Other Modalities

• Magnetic resonance imaging (MRI) can help to confirm the diagnosis and the extent of lesion(s) (Fig. 66-2).

Figure 66-2 A, Magnetic resonance imaging (MRI) scan of a knee exhibiting spontaneous osteonecrosis. B, MRI scan of a knee demonstrating secondary osteonecrosis.

• Technetium-99m bone scanning is generally unreliable but may assist in diagnosis when radiographs are negative. Bipolar uptake is more indicative of osteoarthritis, except in the late stages of ON. Conversely, simultaneous atraumatic ON of the ipsilateral tibial plateau and femoral condyle is certainly possible during any stage and usually causes more intense uptake than osteoarthritis.

Staging

The Aglietti classification for spontaneous ON of the knee (modified Koshino) and the Mont and Hungerford classification for secondary ON of the knee (modified Ficat and Arlet) are described in Boxes 66-1 and 66-2.

Box 66-1 Aglietti Classification for Spontaneous Osteonecrosis of the Knee (Modified Koshino Classification)

Stage I: Normal radiographs, magnetic resonance imaging scans

Stage II: Some flattening of the weight-bearing portion of the condyle

Stage III: Subchondral radiolucency with surrounding sclerosis without sequestration

Stage IV: Increased sclerosis with subchondral collapse and sequestration; visible as a calcium plate

Stage V: Secondary degenerative changes (narrowing of joint space, osteophyte formation, subchondral sclerosis) associated with some erosions

Box 66-2 Mont and Hungerford Classification for Secondary Osteonecrosis of the Knee (Modified Ficat and Arlet Classification)

Stage I: Normal radiographs, magnetic resonance imaging scans

Stage II: Cysts and sclerosis present

Stage III: Subchondral collapse is crescent sign

Stage IV: Secondary degenerative changes (narrowing of joint space, osteophyte formation) on both sides of joint

Treatment

Nonoperative Treatment (Only in Low-Grade, Low-Symptom, Precollapse Lesions)

• Nonsteroidal antiinflammatory drugs (NSAIDs), if tolerated

• Analgesics

• Pharmacologic treatment based on underlying disease process

• Activity modifications and protective weight bearing

• Closed-chain quadriceps exercises

• Unloader knee brace

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Sep 11, 2016 | Posted by admin in SPORT MEDICINE | Comments Off

Musculoskeletal Key

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Osteonecrosis of the Knee

Osteonecrosis of the Knee

Preoperative Considerations

Signs and Symptoms

Secondary Osteonecrosis

Physical Examination

Spontaneous Osteonecrosis

Secondary Osteonecrosis

Imaging

Other Modalities

Staging

Treatment

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