Pisiform Bone Dislocation in a Pediatric Patient: What is the Best Treatment? Case Report and Review of the Literature

Abstract

Traumatic dislocation of the pisiform bone (PB) is a rare injury of the carpal bones, especially in pediatric patients. A few cases were reported, and there is no consensus about the treatment. Each author supports his own method, such as an open reduction internal fixation (ORIF) approach or a closed reduction. However, failures of both techniques with recurrent dislocation of the PB have been reported in the literature. In this article, a fracture dislocation of the PB was treated with ORIF in an 11-year-old boy with a greenstick radial fracture. In addition, a review of the literature about pisiform fracture dislocation in children has been made.

Introduction

The pisiform bone (PB) is the smallest carpal bone. It is spheroidal in shape, and it works as a sesamoid bone included in the flexor carpi ulnaris (FCU) tendon. It contributes to the stability of the wrist and consequently, the contraction of the FCU pulls the PB proximally and aids in wrist flexion. The pisotriquetral joint has a remarkable mobility. In fact, during wrist extension movements, the PB moves distally and closer to the triquetrum. On the other hand, when the wrist joint is flexed, the PB moves proximally, and the space between PB and triquetrum increases.

PB is the last carpal bone to ossify. The ossification center ossifies from 7 to 10 years of age. At 12 years of age, it is usually fully ossified.

PB dislocation is a rare injury, and if it occurs in a prepubertal patient, it requires a high level of attention and consideration. The literature shows that only adult patients with PB dislocations have been treated with the open reduction internal fixation (ORIF) method. We describe a surgically resolved case of a PB fracture and dislocation in an 11-year-old child.

Case Report

An 11-year-old boy, right hand dominant, was admitted to the emergency department with left wrist pain, edema, and functional impotence, after an accidental fall while walking through a mountain trail.

Physical examination showed painful palpation of the wrist, especially in the distal part of the radius and ulna. It also revealed pain in the wrist during active and passive movements with a full range of motion of all fingers, as well as no neurovascular deficit.

The X-ray evaluation showed a greenstick fracture of the radius with dorsal deviation and fracture of the ulnar styloid with suspicion of pisiform dislocation ( Fig. 1A ). We routinely perform contralateral X-ray control in children with suspected fractures.

Fig. 1.

( A, B ) The first X-ray evaluation ( A ) and CT study ( B ) showed a radial fracture and a pisiform bone fracture and dislocation (yellow arrows) with uncomplete ossification. CT, computed tomography.

The computed tomography (CT) study showed an incomplete ossified PB fracture and dislocation ( Fig. 1B ).

A first, attempt of closed reduction was made with unsatisfactory results, so a hand specialist surgeon was consulted, and we decided to move forward with the surgery, upon informed consent obtained by parents.

First, the surgical procedure consisted of the percutaneous fixation of the radius fracture. Then, a volar approach to the carpus centered on the PB and Guyon's canal was adopted ( Fig. 2 ), and the neurovascular bundle was isolated and protected during the surgery. The dislocated PB was identified, relocated to its position, and fixed using a 1.2-mm Kirschner wire (K-wire), inserted from the volar surface of the PB and fixed on the triquetrum and hamate bones. The last part of the surgery consisted of suturing the pisotriquetrum, pisohamate, and pisometacarpal ligaments with a 3–0 absorbable, synthetic, braided suture of polyglycolic acid. A long-arm cast in a neutral position was applied. The X-ray control showed an anatomical reduction ( Fig. 3 ).

Fig. 2.

The volar approach to the carpus centered on the pisiform bone and Guyon's canal. ( A ) Pisiform bone, ( B ) flexor carpi ulnaris, ( C ) ulnar nerve and artery.

Fig. 3.

The postoperative X-ray control showed an anatomical reduction.

The postoperative period was uneventful. One month after discharge, the splint and the K-wires were removed, and the oblique projection X-ray control showed a positive result ( Fig. 4 ). Indication for active and passive mobilization was given, forbidding any sport and extensive efforts with the treated wrist. After 2 months, the mobilization of the wrist was entirely restored without any pain or discomfort. The patient was considered healed and granted permission to restart with sports activities after 4 months of surgery. The last follow-up was 15 months later and his Mayo wrist score was 95 ( Fig. 5 ).

Fig. 4.

Oblique projection X-ray control at one month follow-up after K-wires removal. K-wire, Kirschner wire.

Fig. 5.

Clinical follow-up at 15 months showed a complete healing (Mayo wrist score: 95; VAS score: zero). VAS, visual analog score.

Discussion

The international literature shows that PB fracture dislocation is a rare event, especially in pediatric patients, whose few cases have been reported. According to a review by Hurni et al, 1 only six papers (reporting seven case reports), describing children younger than 16 years, were published. 2 3 4 5 6 7 Three of them described concomitant fracture luxation of the PB associated with distal radius fracture, but contrary to our performance, they have been managed with conservative treatment.

A systematic research using PubMed and Google Scholar databases was performed. The keyword “pisiform” was used in combination with “luxation,” “dislocation,” “displacement,” and “fracture.” Since the review by Hurni et al, 1 only one of seven published reports 8 9 10 11 12 13 14 described the PB fracture dislocation in pediatric population. 14

PB dislocations are generally due to two mechanisms. First, a direct trauma on the hypothenar eminence that frequently leads to PB fracture instead of dislocation. Second, an indirect trauma due to hyperextension of the wrist leading to durable traction of the FCU tendon. 1

The FCU tendon is the most powerful muscle of the wrist, and the PB enhances the mechanic action of this tendon acting as a sesamoid bone. A significant traction force can lead to the rupture of the pisotriquetral capsule joint and tear the pisometacarpal, pisotriquetral, and pisohamate ligaments, displacing the PB proximally.

In this case report, a combination of the two mechanisms occurred: the pull of this robust muscle, as well as the forced wrist hyperextension, associated with a fall onto the outstretched hand, caused significant traction to displace the pisiform proximally.

Furthermore, in some cases, PB dislocations can be caused by ligamentous laxity of the patient or capsular tissue relaxation secondarily of distal radius fractures.

From the standard radiographs, it is easy to miss the diagnosis of PB dislocation. It should be presumed from the injury mechanism and the clinical presentation of swelling and pain on the ulnar side of the wrist. When suspected, an oblique view with the wrist in neutral position and the forearm in semisupine position (supinated 10–30 degrees from the straight lateral position) is necessary. A comparison of the contralateral wrist might be useful.

According to Vasilas et al, 15 PB subluxation in adult patients, can be diagnosed when at the oblique X-ray examination of the wrist one or more of the following findings are observed: the pisotriquetral joint is wider than 4 mm, loss of parallelism of the joint greater than 20 degrees, and proximal or distal overriding of the pisiform amounting to more than 15% of the width of the joint surfaces.

Some authors even recommend the systematic use of CT for the confirmation of the diagnosis and magnetic resonance imaging to investigate ligamentous or soft tissue injuries. 16

According to the current literature, different choices of treatment are described, but still there is no agreement on the best method. Each author supports his approach; however, it seems that the best option is the closed manipulative reduction. When it is not possible to obtain a satisfactory closed reduction or the diagnosis is delayed, open reduction and internal fixation is advised.

Emergency reduction of the PB is necessary if there are any signs of neurological injury to ulnar nerve. 17

In the case of pisiform luxation associated with distal radial fractures, the treatment of the latter is often sufficient to restore the pisotriquetral joint to normal. 11 17

Some authors also described the excision of the pisiform as either primary or secondary. 17 Even after treatment, recurrent dislocations of the PB are possible, and the consequences are the same as leaving the PB luxation untreated, such as pain due to the development of pisotriquetral arthritis. In this case, favorable outcomes were achieved with arthrodesis or excision. PB excision does not impair wrist functionality, but it leaves the ulnar nerve and artery exposed to trauma. 17

Both good outcomes and recurrent dislocations of the PB after closed or open reduction have been reported in the scientific papers included in our review. In this specific case, a persistent instability of the PB inhibited the attempted closed reduction and an ORIF was necessary. This decision was made also considering the coexisting radial fracture that needed surgery anyway.

Furthermore, there is not a protocol after PB dislocation that standardizes time and position of immobilization. Each author describes his method of achieving good outcomes. To allow full relaxation of the FCU, the wrist should be in palmar flexion and pronation. Nevertheless, in this instance, we opted for a 4-week immobilization in a neutral position due to the K-wire fixation, full FCU relaxation was not necessary.

Conclusion

PB fracture or dislocation is an extremely rare event that can occur in wrist traumas. As it is easily overlooked, an oblique radiograph may be helpful in addition to standard radiographs, when ulnar swelling and tenderness is suspect for such an injury. Since other essential lesions of the wrist could present similar clinic manifestations, PB fracture/dislocation should be viewed as a differential diagnosis.

The described case achieved excellent functional and radiological results. Although no papers are describing the surgical technique of pisiform luxation in children, our experience showed that if conservative treatment does not lead to immediate results, open reduction with a K-wire fixation may be needed to avoid pisiform malalignment, arthritis of the pisotriquetral joint, and a future excision of the PB.