Clinical diagnosis
Case 172
【Progress】
He came back to the local clinic after MRI examination. He probably got medical service there. Then, the information about his prognosis was unclear.
【Discussion】
In the clinical reality, triangular fibrocartilage complex (TFCC) is known to be the bruise of the ulnar dorsal surface of the wrist. Meanwhile, as the bruise of the ulnar palmer surface of the wrist, the injury of pisiform bone and/or hook of hamate bone should be borne in mind. Further, the bruise of the radial palmer surface of the wrist is the injury of the scaphoid bone.
Pisiform bone is a bean-like sesamoid bone and exists in flexor carpi ulnaris muscle which works as flexion of wrist (1, 2). Flexor carpi ulnaris muscle originates from medial epicondyle of humerus and attaches to pisiform bone, hook of hamate bone and 5th metacarpal bone. It indicates that pisiform bone, hamate bone and flexor carpi ulnaris muscle work together in order to abduct and/or bend a little finger.
The ulnar tunnel called Guyon’s canal is approximately 4cm long and composes of pisiform bone in the medial side, hook of hamate bone in the lateral side, transverse carpal ligament in the floor side and palmer carpal ligament in the roof side (3-5). Ulnar artery and ulnar nerve run in this tunnel. Ulnar tunnel syndrome is known to be caused by athletes: cyclists, baseball catchers and karate martial artists. The repetitive compression of this tunnel causes the ulnar nerve palsy.
Pisiform bone and hook of hamate bone are present at the palmer side of the hand. Pisiform bone situates at the more anterior and proximal side than hook of hamate bone. They are susceptible to get load in gripping bat, tennis racket and golf club (1, 2). The repetitive and excessive gripping can cause the traumatic damages to these bones. In case of falling from the height, over-extension of the wrist can also damage these bones together as well as scaphoid bone. Namely, when over-extension of the wrist hits an obstacle to ulnar side, pisiform bone and hook of hamate bone get damaged and when it hits to radial side, scaphoid bone gets damaged.
Our patient is nine-year-old boy. Although we did not get his sequence of the event, we suspect that because he was not imagined to do the excessive repetitive sports, we think he probably got the over-extension of the left wrist damaged.
The wrist MRI showed marked low signal intensity on T1WI rather than slight high signal intensity on fat suppression T2WI. As for T2WI, low signal intensity was obtained which seemed that the signal of edema and the signal of red marrow (fat) counteracts each other on T2WI. It is known that low signal intensity on T2WI implies the existence of connective tissue, smooth muscle fiber and hemorrhage (5). It might be added that water component exists in the fat tissue on T2WI as well as on T1WI. Further, it implies that fat suppression T2WI is not always better than T1WI to detect bone marrow edema. Whether high signal intensity on fat suppression T2WI becomes more marked than low signal intensity on T1WI or not might be dependent on the volume of water component (edema) after traumatic event.
【Summary】
We present a nine-year-old boy with his mother suffering from swollen and painful palmer surface of the left wrist. MRI depict pisiform bone and hook of hamate bone with low signal intensity on T1WI and slight high signal intensity on fat suppression T2WI, indicating bone injury of the pisiform bone and hook of the hamate bone. It is borne in mind that the bruise of the ulnar palmer surface of the wrist implies the injury of pisiform bone and/or hook of hamate bone. Pisiform bone and hook of hamate bone situates in the flexor carpi ulnaris muscle work together which works abduct and/or bend a little finger. Both of pisiform bone and hook of hamate bone compose of ulnar tunnel in which ulnar verve and ulnar artery pass through. Over-extension of the wrist in case of falling from the height and repetitive and excessive gripping baseball bat, golf club and tennis racket can cause pisiform bone and/or hook of hamate bone damage. Whether high signal intensity on fat suppression T2WI becomes more marked than low signal intensity on T1WI or not might be dependent on the volume of water component (edema) after traumatic event. In our case, MRI with T1WI shows marked low signal intensity while MRI with fat suppression T2WI shows slight high signal intensity.
【References】
1.Kjosness, Kelsey M.; Hines, Jasmine E.; Lovejoy, C. Owen; Reno, Philip L. "The pisiform growth plate is lost in humans and supports a role for in growth plate formation". Journal of Anatomy. 2014:225 : 527–538.
2.Young, Richard W. "Evolution of the human hand: the role of throwing and clubbing". Journal of Anatomy. 2003: 202: 165–174.
3.Hoogvliet P, et al, European Hg. How to treat Guyon’s canal syndrome? Results from the European HANDGUIDE study: a multidisciplinary treatment guideline. British Journal of Sports Medicine 2013;47:1063-70.
4.Capitani D, et al. Handlebar palsy–a compression syndrome of the deep terminal (motor) branch of the ulnar nerve in biking. Journal of Neurology 2002;249:1441-5.
5.Pierre-Jerome C, et al. The Guyon’s canal in perspective: 3-T MRI assessment of the normal anatomy, the anatomical variations and the Guyon’s canal syndrome. Surgical and Radiologic Anatomy 2011;33:897-903.
2019.12.4