[Single-compartment knee arthroplasty prosthesis and idiopathic necrosis of the medial tibia surface]

Idiopathic necrosis of the medial articular surface of the tibia is exceptional. Diagnosis is quite difficult and often made late. Among the different treatments proposed, we preferred single-compartment arthroplasty.

We report 8 cases in women with a mean age of 71.1 years. Diagnosis was suspected due to drug-resistant knee pain, particularly frequent at night, initially with radiographically normal knees. The first radiographic signs, seen 3 months after the onset of pain, were pathognomonic for osteonecrosis evidencing subchondral defects of the tibial surface with a dense peripheral rim and apparently "sequestered" in a notch. Bone scintigraphy evidenced intense uptake in the medial compartment. MRI confirmed the diagnosis evidencing a band of low intensity signals completely surrounding a sequestered zone reaching the cortical. This band was stable and irreversible. In 5 cases CT scan and in 3 cases tomography identified the width and height of the necrotic area that was limited to the medial compartment in all cases. All patients were treated with a single compartment implant. The diagnosis of necrosis was confirmed at pathology.

At 4,6 years of mean follow up all patients had an excellent outcome, "forgetting" their knee. No lucent lines developed along the femoral or tibial implants.

Necrosis of the medial articular surface of the tibia is exceptional and often diagnosed late by bone scintigraphy or MRI. Surgical treatment is usually based on tibial osteotomy for valgisation or a single or three-compartment prosthesis. In our 8 cases, the necrosis was limited to the medial compartment, warranting our therapeutic option.