Age / Sex : 30 / F

Chief complaint : Dull forearm pain

Clinical Hx: 30 -year old women with right breast cancer was performed bone scan for evaluation of bone metastasis. She complaint dull forearm pain during Pole dance which was her hobby for several months.      

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Yeo Ju Kim, Inha University Hospital

Discussion

Answer: 

Stress fracture (Fatigue fracture) at ulnar shaft

Findings:

Bone scan shows a mild increased MDP uptake at mid portion of ulnar shaft, left in bone scan.

In the SPECT -CT, there is a focal radiolucency at volar side of mid ulnar shaft with increased uptake.

MRI shows mild cortical thickening at volar side of the mid ulnar shaft. Mild T2- high and T1- intermediate signal intensity is seen at the cortical thickening with mild periosteal high signal intensity Differential Diagnosis:

Most likely, stress fracture (Fatigue fracture)

DDX less likely, osteoid osteoma, intracortical abscess, intracortical metastasis

Diagnosis: 

Stress fracture (Fatigue fracture)

Discussion:

Stress fracture of the ulna has been noted in athletes who exert substantial stress on the ulna during sports by repetitive excessive pronation, excessive external rotation, excessive weight lifting or by repeated flexor profundus muscle contraction. Imaging findings of stress fracture of ulna are the same as the stress fracture in other site. The shape and cross-sectional area of the ulna affects the location where stress fractures typically occur. According to literatures, the stress fracture of ulna was developed in middle one third of shaft, most commonly, followed by distal one third and proximal one third. The cross sectional area of the middle third of the total length of the ulna was smaller in area, thinner in cortex, and triangular in shape compared with the other parts of the bone. This implies that stress fractures may develop in the middle third of the ulna when the ulna shaft sustains excessive torsional stress.

Reference

1. Tanabe S, Nakahira J Bando E, et al: Fatigue fracture of the ulna occurring in pitchers of fast-pitch softball. Am J Sports Med 1991; 19: 317–21.


2. Wu JL, Huang GS, Wu CC, Lee CH, Wu SS. Stress fracture of the ulna occurring in military recruits after rifle drill training. Mil Med. 2004 Oct;169(10):839-41.