Review Question - QID 219981

The patient has spontaneous osteonecrosis of the knee (SONK) with crescentic subchondral collapse along the medial femoral condyle and loss of cartilage that is best treated with arthroplasty when symptomatic treatment fails.

Spontaneous osteonecrosis of the knee (SONK) is an idiopathic condition that leads to the development of a crescent-shaped osteonecrosis lesion, most commonly in the epiphysis of the medial femoral condyle. It occurs most commonly in middle-aged and elderly females (>55yo), and though the exact pathophysiology is not known, it may occur secondary to subchondral insufficiency fractures or associated meniscal root tears that alter the joint biomechanics. It is important to differentiate SONK from osteochondritis dissecans, transient osteoporosis, and bone bruises or occult fractures, which are more common in adolescent males, young to middle-aged men, and post-traumatic patients, respectively. Treatment for SONK typically starts with conservative management using nonsteroidal anti-inflammatory drugs, physical therapy, and unloader braces. When these options fail, either medial-UKA or TKA are indicated to treat the patient's pain and deformity.

Akhavan et al. provide a review of the clinical significance and treatment options for patients with symptomatic bone marrow edema (BME). The authors note that regardless of the cause, physiologic remodeling of the subchondral bone in the setting of BME can be limited because of ongoing joint forces, increased focalization of stress, and reduced healing capacity of the subchondral bone, with perpetual BME being a known prognostic factor associated with pain, dysfunction, and progressive cartilage damage. They conclude that surgical management of BME is reserved for those who fail non-operative management, and can range from core-decompression and biologically augmented bone graft injections to arthroplasty.

Flores-Robles et al. reviewed the use of zoledronic acid for the treatment of primary bone marrow edema syndrome (BMES). The authors reviewed 633 patients and identified 17 patients with BMES. They found that the most frequently affected joint was the ankle followed by the hip, with sixteen patients presenting with moderate to severe pain initially. Of those patients, 13 had no pain after 12 months of zoledronic acid use. They concluded that zoledronic acid is an option in the management of BMES, given that 75% of patients treated with it presented with a complete response.

Cohen et al. reviewed the use of subchondroplasty for treating bone marrow lesions. The authors note that the prognosis of osteoarthritis (OA) is worsened by persistent subchondral defects known as bone marrow lesions (BMLs), which herald severe joint degeneration and the need for joint replacement. Subchondroplasty is a procedure developed to treat BMLs by injecting a calcium phosphate bone substitute into compromised subchondral bone, under fluoroscopic guidance. The authors reviewed 66 patients undergoing this procedure and found significant improvements in both pain and function following subchondroplasty with arthroscopic debridement, as measured by the visual analog scale (VAS) and the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, through 2 years postoperative follow-up. They concluded that subchondroplasty may be a promising approach for the treatment of OA with BMLs.

Figures A-C are sequential coronal and sagittal PD fat-saturated MRI cuts showing a subchondral hypo-intense crescent line at the medial femoral condyle with cortical surface irregularity and moderate surrounding marrow edema reflecting spontaneous osteonecrosis of the knee.

Incorrect Answers:
Answer 2: Though newer techniques exist on the market for the treatment of persistent bone marrow edema that involve a combination of core decompression and subchondral injection of combined bone matrix or substitute and PRP, full-thickness lesions with collapse cannot be successfully treated with this technique.
Answer 3: Isolated high tibial osteotomy (HTO) would be indicated if this patient were younger with an angular deformity or to protect and offload an osteochondral allograft-type procedure.
Answer 4: Isolated medial meniscus root repair would not address this patient's cartilage loss.
Answer 5: Stem cell injections are neither indicated for full-thickness cartilage lesions nor FDA-approved for regular use in the United States.