Keywords
anatomy - pisiform bone - trauma - dislocation
Introduction
The pisiform bone, from the Latin pisum (pea) and formis (form), is the fourth proximal carpal bone, and it is considered by some authors
as a sesamoid bone due to its location in the tendon of the flexor carpi ulnaris muscle.[1]
[2]
[3]
[4]
[5] It is the only carpal bone that has a tendon insertion of a forearm muscle.[6] Fleege et al indicate that the pisiform ossification center usually appears between
7.5 and 10 years of age and is fully developed up to the age of 12 years old, being
the last carpal bone to ossify[5] ([Fig. 1]).
Fig. 1 (A-B) Anatomical arrangement of the carpal bones. Right hand, palmar view. Proximal
row: scaphoid (1), lunate (2), triquetrum (3) and pisiform (4). Distal row: trapezium
(5), trapezoid (6), capitate (7) and hamate (8). (C) Development of the carpal bones
and ossification centers. Based and adapted from Werner Platzer.[7]
The pisiform bone acts as an important point of fixation of soft tissues ([Fig. 2]). Pevny et al demonstrated the existence of 10 soft tissue structures related to
the pisiform bone, described as the flexor carpi ulnaris tendon, the extensor retinaculum,
the abductor digiti minimi muscle, the flexor retinaculum, the ulnar collateral ligament
of the wrist joint, the articular disc of the distal radioulnar joint, the pisohamate
ligament, the pisometacarpal ligament, and the pisiform joint capsule, plus a superficial
fibrous bundle between the pisiform bone and the hook of hamate.[3]
[8]
[9]
Fig. 2 Main structures attached to the pisiform bone. Right hand, palmar view. Pisiform
(P); abductor digiti minimi muscle (ADM), pisometacarpal ligament (PML), pisohamate
ligament (PHL), flexor carpi ulnaris muscle (FCU), flexor retinaculum (“transverse
carpal ligament”) (FR), extensor retinaculum (ER), ulnar collateral ligament of wrist
joint (UCL). Based and adapted from Moojen et al.[9]
The biomechanics of this region contribute to the kinematics of the wrist and of the
hand in an indirect and not very relevant way, being the pisiform bone restricted
to a fixation point for the aforementioned soft tissues and participating in the joint
with the pyramidal bone.[6]
[10]
[11] The pisiform bone, like the patella, also acts as a lever and provides increased
flexion strength of the wrist and extra stability when the wrist is flexed.[3]
[6]
[9]
Historically, the isolated pisiform fracture was identified and described by Guibout
in 1847 during a necropsy, along with other carpal fractures.[1]
[12]
[13] Although traumatic luxation of the pisiform is a condition reported as rare in the
scientific literature, it usually is a result of a trauma in dorsal flexion of the
wrist, in which the impact occurs immediately on the hypothenar eminence with the
wrist in hyperextension, the forearm in pronation, and the upper limb in adduction.[13]
[14]
There are also other mechanisms for the pisiform fracture, commonly observed in sports,
especially in volleyball players, in which repetitive trauma causes vascular injuries
and leads to microfractures and, later, to the evolution to a complete fracture.[1]
[12]
[14]
Fractures of the carpal and metacarpal bones represent ∼ 6% of all fractures. Isolated
fracture of the pisiform is a rare condition, since it is constantly associated with
other injuries of the carpus or of the distal end of the radius. In the fracture with
concomitant rotation of the pisiform and/or ligament rupture, the treatment can be
conservative or surgical, ending up or not with the removal of the pisiform bone.[2]
[14]
[15]
The objective of the present study is to report a case of a 9-year-old child who suffered
a pisiform dislocation, emphasizing the importance of previous knowledge of the anatomy
in the clinical practice, aiming at the correlation of the clinical findings for the
correct diagnosis.
Case Report
A 9-year-old male child, led by his parents, presented to the emergency room of the
Vitória Apart Hospital reporting pain in the wrist and in the left hand after falling
from his own height playing soccer.
During the anamnesis, it was observed that the fall occurred with the wrist in hyperextension
and, on the physical examination, there was a slight limitation of the range of motion
due to pain. Anteroposterior (AP) and lateral X-ray examinations were performed, showing
an anterior deviation of the pisiform bone ([Figs. 3] and [4]). The child was referred for a computed tomography (CT) scan of the wrist with suspected
fracture and/or carpal dislocation.
Fig. 3 Lateral radiography view of the left wrist showing the anterior dislocation of the
pisiform bone (arrow).
Fig. 4 Lateral radiography view of the right wrist showing a normal anatomical position
of the pisiform and carpal bones.
The results of the CT scan showed an anterior dislocation of the pisiform bone; bone
irregularity in the pisiform bone with a small adjacent bone fragment measuring 0.2
cm suggestive of microfissure; avulsion or a small ossification nucleus; small joint
effusion; slight obliteration of the myotendinous planes; and adipose tissue of the
wrist of post-traumatic origin, with preservation of the other bone structures ([Figs. 5] and [6]).
Fig. 5 Axial computed tomography view of the left wrist showing the anterior dislocation
of the pisiform bone (*) and a small adjacent bone fragment (arrow).
Fig. 6 Sagittal computed tomography view of the left wrist showing the anterior dislocation
of the pisiform bone (*) and a small adjacent bone fragment (arrow).
A conservative treatment with plaster immobilization for analgesia was performed for
1 week. As there were no signs of trauma consistent with the images, such as edema
and local ecchymosis, in addition to the early complete disappearance of pain, the
responsible team proposed the hypothesis of chronic asymptomatic dislocation of the
pisiform bone.
Discussion
The early diagnosis of pisiform fracture is important, since late treatment may result
in nonconsolidation and may manifest with chronic pain and limitation of movement.[14] In the present report, the treatment consisted of plaster immobilization for a short
period of time that resulted in a good clinical response.
Moojen et al pointed to the fact that traumas of the pisiform bone and of the pisopyramidal
joint are not rare. A correct diagnosis, however, is often difficult, in part due
to the lack of attention to anatomical structures during the inspection of the wrist
and to the lack of knowledge of the kinematics of the region.[9]
An adequate clinical evaluation and a thorough examination of imaging exams in orthopedic
traumatology are essential for an accurate diagnosis. Deep knowledge of the anatomy
is essential to correlate the findings of these exams with the anamnesis and to understand
the possible existence of silent, asymptomatic, and pre-existent conditions in the
clinical practice.
