To the Editor:

We appreciate Dr. Ehara’s keen observation that the humeral head lesion could have represented subchondral fracture rather than osteonecrosis. He pointed out that a history of trauma and surgical intervention are possible causes of what could be subchondral fracture. The two studies he cited (1,2) addressed subchondral insufficiency fractures about the knee and of the femoral head in adults. In the study by Vellet et al (1), patients with acute knee trauma and hemarthrosis underwent magnetic resonance imaging evaluation and were found to have subchondral fractures. However, our patient had normal radiographs and magnetic resonance imaging scans after his traumatic dislocations. In the study by Yamamoto and Bullough (2), 10 of 464 presumed cases of femoral head osteonecrosis were identified as subchondral fractures when examined histologically. Although the latter finding is interesting, it does indicate that the overwhelming majority of femoral head lesions with subchondral crescent sign and focal edema are, in fact, osteonecrosis.

We acknowledge Dr. Ehara’s point that trauma certainly can cause a subchondral fracture. However, we believe that our patient most likely had osteonecrosis because the radiographs and magnetic resonance imaging (MRI) scans obtained after the traumatic dislocations and before surgery showed normal bone marrow signal in the humeral head. A fracture secondary to trauma would be expected to result in early bone marrow signal changes in the subchondral humeral head: Extrapolating from studies performed on the hip, MRI has been shown to be 100% sensitive for the detection of occult fracture within the first 24 hours of presentation3. In our patient, the MRI findings at 6 weeks follow-up are characteristic of osteonecrosis (4): a serpentine, low-signal abnormality in the humeral head surrounding a central region of fat on T1-weighted sequences and a peripheral rim of increased signal on T2-weighted sequences. Although such MRI findings may be seen occasionally with subchondral fracture, the initial posttraumatic negative MRI refutes this possibility. Additionally, although surgical intervention could have caused a subchondral fracture of the humeral head, we did not encounter any unusual problems during surgery and are not aware of any such reports.

Sincerely,

Dhruv B. Pateder, MD, Hyung Bin Park, MD, Efstathios Chronopoulos, MD, Laura M. Fayad, MD, and Edward G. McFarland, MD

References

1. Vellet AD, Marks PH, Fowler PJ, Munro TG. Occult posttraumatic osteochondral lesions of the knee: prevalence, classification, and short- term sequelae evaluated with MR imaging. Radiology. 1991;178:271-6.

2. Yamamoto T, Bullough PG. Subchondral insufficiency fracture of the femoral head: a differential diagnosis in acute onset of coxarthrosis in the elderly. Arthritis Rheum. 1999;42:2719-23.

3. Rubin SJ, Marquardt JD, Gottlieb RH, Meyers SP, Totterman SMS, O'Mara RE. Magnetic resonance imaging: a cost-effective alternative to bone scintigraphy in the evaluation of patients with suspected hip fractures. Skeletal Radiol. 1998;27:199-204.

4. Mitchell DG, Rao VM, Dalinka MK, Spritzer CE, Alavi A, Steinberg ME, Fallon M, Kressel HY. Femoral head avascular necrosis: correlation of MR imaging, radiographic staging, radionuclide imaging, and clinical findings. Radiology. 1987;162:709-15.

To the Editor:

In the case report describing a humeral head lesion after anterior shoulder stabilization(1), Dr. Pateder and colleagues concluded the lesion to be osteonecrosis based on subchondral sclerosis on radiography and subchondral signal on MR imaging. The MR abnormality was linear low- signal intensity on T1-weighted image, and edema signal on T2-weighted image. No histological confirmation was available.

Although uncommon in the proximal humerus, such findings, including a subchondral crescent sign, more likely represent occult or stress subchondral fracture, rather than osteonecrosis(2,3). Complete resolution on plain radiography and MR imaging after one year supports a diagnosis of subchondral fracture. In addition, episodes of trauma and surgical intervention in this patient are adequate causes of subchondral fracture.

Based on the published images and the history, I would suggest that subchondral fracture is a more likely diagnosis in this case.

Shigeru Ehara, M.D. Department of Radiology Iwate Medical University School of Medicine Morioka 020-8505 Japan

References 1. Pateder DB, Park HB, Chronopoulus E, Fayad LM, McFarland EG. Humeral head osteonecrosis after anterior shoulder stabilization in an adolescent. J Bone Joint Surg Am 2004;86:2290-2293 2. Vellet AD, Marks PH, Fowler PJ, Munro TG. Occult posttraumatic osteochondral lesions of the knee: Prevalence, classification, and short- term sequalae evaluated with MR imaging. Radiology 1991;178:271-276 3. Yamamoto T, Bullough PG. Subchondral insufficiency fracture of the femoral head: A differential diagnosis in acute onset of coxarthrosis of the elderly. Arthritis Rheum 1999;42:2719-2723