Imaging diagnosis
Case 127
【Progress】He was forbidden to play baseball. He was scheduled to take a long-term rest, at least eight week-rest, without running or playing baseball .
【Discussion】
Stress fracture for baseball pitcher is reported to occur in ulnar olecranon, ulnar shaft, radial shaft, ribs and vertebrae (1, 2). It is well-known that for an adolescent (little league) pitcher, epicondylar apophysis is susceptible to be damaged, while for a major league pitcher, ulnar collateral ligament is susceptible to be damaged (1, 2). Meanwhile, stress fracture of ischial tuberosity occurs in running, soccer and jumping but rare in baseball pitching. In our case of an adolescent pitcher aged 15, stress fracture occurred in ischial tuberosity. To our best of our knowledge, there is no case of stress fracture of ischial tuberosity in a pitcher except one case that is reported to be apophysitis of the ischial tuberosity mimicking a neoplasm (3).
Ischial bone composes of ischial body, ischial tuberosity and ischial ramus. Ischial tuberosity is known as “sitting bone” and serves the origin of hamstring which includes femoral biceps, semitendinosus and semimembranosus (4 - 6). The distal portion of femoral biceps attaches to fibula and the semitendinosus and semimembranosus attaches to tibia. Namely, hamstring is the biarticular muscle which functions knee flexion and hip extension. Hamstring plays an important role in walking, running and jumping. It is sometimes difficult to differentiate hamstring strain from stress fracture of ischial tuberosity because of their similar symptoms (7, 8). In our case, his pain increased when he was in a pitching form with a right hander, that occurred in his left knee bending and his left hip extension, implying left hamstring strain and left ischial tuberosity burden. The repetitive body weight shift burden when throwing to ischial tuberosity in a little league pitcher is considered to damage contralateral ischial tuberosity rather than hamstring because of the growing process of ischial tuberosity.
Bone turn over indicates that osteoclasts activate the absorption of bone and osteoblasts activate production of bone. The athletic stimulation accelerates bone turn over. The initial response to repeated stress first induces the activation of osteoclasts and then, does the activation of osteoblasts. The problem is that the osteoclastic bone absorption is greater than the osteoblastic bone production. The mechanism of stress fracture is that the repeated athletic stimulation makes the gap between bone absorption and its embedding bone production much greater (9). Then, it can be possible that radiograph and CT of stress fracture shows fracture line in the diffuse osteosclerosis, while MRI of stress microfractures shows bone marrow edema irrespective of presence or absence of fracture line (9). In our case, pelvic MRI showed the lesion in the ischial tuberosity with diffuse high signal intensity on fat-suppression T2WI and low signal intensity on T1WI (Figs.1-3), indicative of bone marrow edema. Further, the lesion included bone necrosis with marked high signal intensity on fat-suppression T2WI (Fig.2A).
【Summary】
We present a fifteen-year-old boy suffering from a pain of left sacroiliac joint and left hip joint especially when in a pitching form with a right hander. MRI showed bone marrow edema with bone necrosis, indicative of stress fracture in his left ischial tuberosity. It is least yet to be known that stress fracture of ischial tuberosity occurs in a little league pitcher. Further, interestingly, left ischial tuberosity is damaged to stress fracture after repeated hard pitching training with a right hander. We should keep in mind that ischial bone, “sitting bone” serves the origin of hamstring which includes femoral biceps, semitendinosus and semimembranosus. Hamstring is the biarticular muscle which functions knee flexion and hip extension. It is sometimes difficult to differentiate hamstring strain from stress fracture of ischial tuberosity because of their similar symptoms. MRI can contribute to differentiate them, showing bone marrow edema, fracture line and bone necrosis. The mechanism of stress fracture is that the repeated athletic stimulation makes the gap between bone absorption and its embedding bone production much greater, causing occurrence of stress fracture with edema in diffuse osteo-sclerotic bone.
【References】
1.Rettig AC, et al. Nonunion of olecranon stress fractures in adolescent baseball pitchers: a case series of 5 athletes. Am J Sports Med. 2006 Apr;34(4):653-6.
2.Gerrie BJ, et al. Lower thoracic rib stress fractures in baseball pitchers. Phys Sportsmed. 2016;44(1):93-6. doi: 10.1080/00913847.2015.1116363. Epub 2015 Nov 26.
3.Yamamoto T et al. Apophysitis of the ischial tuberosity mimicking a neoplasm on magnetic resonance imaging. Skeletal Radiol. 2004;12:737-40. Epub 2004 Jun 15.
4.Yang BK, et al. Ischial Tuberosity Avulsion Stress Fracture after Short Period of Repetitive Training. Hip Pelvis. 2016; 28(3): 187–190.
5.Behrens SB, Deren ME, Matson A, Fadale PD, Monchik KO. Stress fractures of the pelvis and legs in athletes: a review. Sports Health. 2013;5:165–174.
6.Gidwani S, Jagiello J, Bircher M. Avulsion fracture of the ischial tuberosity in adolescents--an easily missed diagnosis. BMJ. 2004;329:99–100.
7.Lenhart R, Thelen D, Heiderscheit B. Hip muscle loads during running at various step rates. J Orthop Sports Phys Ther. 2014;44:766–774.
8.Schache AG, Dorn TW, Blanch PD, Brown NA, Pandy MG. Mechanics of the human hamstring muscles during sprinting. Med Sci Sports Exerc. 2012;44:647–658.
9.Liong, SY, et al. Lower extremity and pelvic stress fractures in athletes. Br J Radiol. 2012 Aug; 85(1016): 1148–1156.
2018.10.31