Keywords
Fenton syndrome - scaphocapitate - trans-scapholunate - carpus - fracture - dislocation
Introduction
Perilunate fractures-dislocations at the wrist represent a broad spectrum of complex
carpal injuries. They are relatively rare, accounting for approximately 7% of all
carpal injuries.[1] Most of these injuries result from high-energy trauma, including motor vehicle accidents,
bicycle falls, falls from height, or contact sports. A particular pattern of these
injuries associates a scaphoid fracture to a capitate bone fracture, and it is known
as Fenton syndrome, trans-scaphocapitate fracture-dislocation, or scaphocapitate syndrome.
This rare, complex wrist injury (accounting for 1–2% of carpal fractures) was first
described in 1937 by Perves et al,[2] but it was named Fenton syndrome after the author who described 2 cases in 1956.[3] This injury is important not only because of its difficult diagnosis but also for
its treatment, since it is essential to regain range of motion and minimize pain to
avoid devastating future complications trans-scaphocapitate fracture-dislocation.
The classic method for Fenton syndrome diagnosis includes posteroanterior, lateral
and oblique radiographs, potentially complemented with a computed tomography (CT)
scan. Even so, the diagnosis can still be difficult due to several causes, such as
poor radiological technique, carpal anatomy, and multiple bone fractures, displacement
or comminution, which result in uncertainty, insecurity and discordant opinions on
the treatment to be carried out. Therefore, new technologies are critical for allowing
us to establish the fracture type and to print of a full-scale three-dimensional (3D)
model, which is the simplest method to understand the mechanism of injury, diagnose
with certainty, and plan surgical procedures with a very high degree of anatomical
correlation, since the current therapeutic trend is open reduction with internal fixation.
Here, we report an unusual case of trans-scaphocapitate fracture-dislocation, with
displacement and multiple fragments, and also show a novel diagnostic technique for
meticulous presurgical planning, a 3D-printed model which helped us to understand
and treat this injury in a safe and successful manner.
Clinical Case
A 17-year-old male went to the emergency room after falling from a bicycle and sustaining
direct trauma to the left wrist, with hyperextension and axial compression as a potential
lesion mechanism. A physical examination revealed dorsal swelling, pain, and functional
disability but no distal neurovascular findings. The posteroanterior and lateral wrist
radiographs ([Figure 1A]) showed a scaphoid fracture and a complex capitate fracture with two dorsal bone
fragments. Due to difficulties in image interpretation, an emergency computed tomography
(CT) scan ([Figure 1B]) was requested. The CT scan reported “a multiple line fracture at the proximal pole of the scaphoid bone with preserved
joint congruence with the trapezius, trapezoid and capitate bones. The distal segment
presents a volar angulation. Two bone fragments are observed dorsal to the scaphoid
and lunate bones, and they appear to depend on the proximal articular surface of the
capitate bone. The capitate bone lost part of its articular congruence with the lunate
bone due to a slight volar angulation of its proximal segment.”
Fig. 1 (A and B) (A
) Initial posteroanterior and lateral radiographs. Note the dorsal dislocation of the
capitate bone fragments on the lateral image. (B) Axial computed tomography scan showing scaphoid fracture and dorsal bone fragments.
The process begins with the analysis of a Digital Imaging and Communications in Medicine
(DICOM) study from a multi-slice helical CT scan performed after the evaluation of
a plain radiograph. The study was imported into the OsiriX radiological software (Pixmeo
Sàrl, Bernex, Switzerland) using a domestic equipment. Next, segmentation was applied
to individualize carpal bones and fragments and 3D surface rendering. The 3D object
was then exported in stereolithography (.stl) format. Using the UltimakerCura software
(Ultimaker, Ultrecht, Netherlands), the setting details on the impression tray were
finalized. The printing was performed using a “fine” setup and acrylonitrile-butadiene-styrene
(ABS) thermoplastic material with 1.75 mm in diameter. The printing lasted 9 hours,
15 minutes.
The 3D customized model was evaluated, and each bone was individualized to better
understand the injury mechanism. This was a scaphoid fracture and dorsal capitate
fracture-luxation with three fragments. Two of these fragments presented a 180° rotation
and originated from the proximal pole of the capitate bone. The fracture was classified
as Fenton syndrome involving three capitate bone fragments ([Figure 2]).
Fig. 2
Full-scale three-dimensional models. (A) Presurgical reconstruction, dorsal view, showing dislocated, dorsally rotated fragments
(arrows). (B) Presurgical reconstruction, volar view. (C) Two anatomically reduced capitate bone fragments (arrows) (D) Capitate bone fragments assembled as a puzzle, volar view. (E) Reconstruction image, dorsal view.
It is very difficult to assess such fractures using imaging techniques because the
spatial assessment of the size, location, and orientation of each carpal bone and
fragment is challenging. Surgery was planned on the 3D printed model, reconstructing
the three capitate fragments as a puzzle, and measuring the length of the scaphoid
and capitate bone to synthesize both of them with screws. The size of the two dislocated
capitate fragments was also determined as 11 mm and 12 mm on its long axis; this measurement
was performed due to the possibility of synthesis with screws. The approach route
was evaluated with these data at hand, and we decided for a dorsal approach.
Surgical treatment was carried out four days after the production of the model. Using
a dorsal approach, the scaphoid fracture was synthesized with a 2.5-mm AutoFix (Stryker
Corportation, Kalamazoo, MI, US) headless compression cannulated screw, as we would
do in any trans-scapholunate fracture-dislocation, because scaphoid stabilization,
integrating two rows of carpal bones, facilitates capitate bone reduction. Next, the
dislocation of the capitate fragments was reduced and synthesized with a 2.0-mm AutoFix
(Stryker) cannulated screw ([Figure 3]). The patient was immobilized with a splint for 6 weeks, which was then replaced
by a semi-rigid wrist brace with palmar-dorsal-thumb support to begin assisted rehabilitation.
Fig. 3 (A) Comparison between the two capitate bone fragments: the real and the three-dimensional
printed bones (intraoperative image). (B) Postsurgical posteroanterior and lateral radiographs.
Results
Follow-up lasted for 12 months, with rehabilitation and physical therapy starting
at the 6th week. The patient had no pain, and he was able to perform his usual activities.
In addition, he had a non-painful dorsal scar, in addition to 85° of dorsal flexion,
50° of palmar flexion, 25° of radial deviation, 30° of ulnar deviation, and complete
pronation-supination ([Figure 4]). Wrist, claw, and grip functions are normal. Overall muscle balance was 4 +/5 (according
to the modified muscle strength scale from the Medical Research Council), with no
sensitive disturbances. Radiological fracture consolidation was observed with no signs
of pseudoarthrosis or necrosis of the scaphoid and capitate bones ([Figure 5]). As final functional outcomes, the scores on the Disabilities of the Arm, Shoulder,
and Hand (DASH) and the Mayo Wrist Score questionnaires were of 25 and 65 (satisfactory),
respectively.
Fig. 4 Final functional outcomes at 12 months.
Fig. 5 Posteroanterior and lateral radiographs at 12 months.
Discussion
Fenton syndrome is a rare, severe condition, mostly reported as single cases. Some
authors believed scaphocapitate syndrome was a variety of transscaphoid-transcapitate
perilunar fracture-dislocation, since it is spontaneously reduced by inversion of
the proximal capitate fragment.
There are two common presentations; one is characterized by transverse scaphoid fracture
and capitate fracture with no dislocation, whereas the other features a lunate dorsal
dislocation.
The most frequently mentioned fracture pattern is indicated by Vance et al.,[4] who classified scaphoid and capitate fractures into six different patterns, depending
on fragment geometry and displacement ([Figure 6]).
Fig. 6
Scaphocapitate syndrome fracture patterns. Type I, transverse scaphoid and capitate fracture with no dislocation. Type II, the
inverted proximal fragment of the capitate remains at the joint with the lunate bone.
Type III, lunate dorsal dislocation. Type IV, carpal and proximal capitate fragment
volar perilunate dislocation. Type V, Isolated volar dislocation of the proximal capitate
fragment. Type VI, isolated dorsal dislocation of the proximal capitate fragment.
Designed by JL Muñoz based on Vance et al.[6]
Lesion Mechanism
The lesion mechanism is a controversial matter; most authors agree that it would be
trauma with the hand in forced hyperextension associated with axial compression. According
to Jones,[5] the absence of lunate dislocation at the radiographic evaluation is due to the instantaneous,
spontaneous reduction occurring in all cases. For Stein et al.,[6] the injury would go through three stages during trauma ([Figure 7]). Fenton suggests that hyperextension and radial deviation of the wrist results
in the radial styloid crashing the scaphoid and capitate bones. Stein and Siegel[6] suggest that direct compression of the radial styloid over the capitate bone during
wrist hyperextension with no radial deviation results in a capitate fracture and a
90° rotation of the proximal fragment due to the forced extension; next, when the
hand resumes its neutral position, the capitate fragment completes a 180° rotation.
Vance et al.[4] suggest two mechanisms of injury: extreme dorsiflexion and volar wrist flexion ([Figure 8]); a greater force would result in rotation of the proximal part of the capitate
fragment.
Fig. 7
Injury mechanism on Fenton syndrome. (A) Scaphoid (blue), capitate (red) and pisiform bones (purple). (B) Stage 1: capitate fracture after impact with the dorsal edge of the radius. (C) Stage 2: scaphoid fracture and 90° rotation of the proximal capitate fragments (note
two fragments, as in our case report). (D) Stage 3: Initial position of the hand with both proximal capitate fragments at an
180° rotation at the dorsal area of the wrist. Designed by JL Muñoz based on Vance
et al.[6]
Fig. 8
Injury mechanism on Fenton syndrome. (A) Capitate fracture in extreme dorsiflexion; the dorsal distal part of the radius
crashes the capitate bone. (B) Volar hyperflexion injury mechanism; the volar part of the radius causes capitate
fracture. Designed by JL Muñoz based on Vance et al.[6]
Diagnosis
Diagnosis is based on a high index of suspicion on physical examination and conventional
radiographs. Even so, diagnosis is difficult, and we believe that CT scans have a
critical role in assessing concomitant injuries and the degree of capitate bone rotation.
Here, we used a 3D-printed model as an essential tool to plan a safe and successful
surgery. However, 3D model building requires computer knowledge, and it is associated
with printing costs and a variable time delay. Although sometimes not acceptable,
this time delay is often enough for surgery planning and performance during the acute
period. Our experience shows that 3D models change surgical planning and help solving
cases.
Treatment
Historically, closed reduction and immobilization are the gold standard for perilunate
lesion treatment. Conservative treatment can be considered in fractures with no displacement.
Today, there is a consensus that carpal anatomical restoration is difficult to achieve
and maintain using a conservative approach; numerous studies have shown poor outcomes
when stabilizing such complex intercarpal relationships. Several studies have shown
better functional outcomes and an earlier return to work in patients with perilunate
lesions submitted to open surgery compared to conservative treatment; inadequate carpal
bones alignment has been associated with chronic carpal instability, posttraumatic
arthritis with persistent pain, scapholunate collapse, and loss of range of motion.[7] Open reduction allows a direct visualization of the injury for carpal anatomy repair,
so it is currently the treatment of choice in all acute perilunate fractures-dislocations,
with no significant differences compared to fixation with screws or Kirschner wires.
However, recent publications showed that arthroscopy-assisted treatment provides outcomes
comparable to open surgery, with stable carpal restoration, alignment, and fixation,
in addition to satisfactory radiological and clinical results.[8]
Kumar et al.[9] reported pseudoarthrosis and avascular necrosis of the scaphoid-lunate bones and
carpal collapse with osteoarthritis when performing open reduction and fixation with
a Hebert screw; therefore, they recommended the addition of a bone graft in primary
surgeries. Most authors agree that non-anatomical reduction of the scaphoid and capitate
bones results in higher rates of avascular necrosis and nonunion; therefore, some
suggested the excision of the proximal fragment of the capitate bone when synthesis
is not an option due to the potential development of avascular necrosis; this recommendation
does not apply to the head of the capitate bone, in which revascularization is more
likely.[3]
[6]
Prognosis
Prognosis is contingent on the type of injury and whether reduction has been optimal
and stable. It is probable, however, that most patients will not present a full range
of motion or excellent grip strength, but their wrists will be functional and with
minimal pain. Sequela, including capitate bone necrosis or delayed union, radiocarpal
and midcarpal osteoarthritis, scaphoid pseudoarthrosis, carpal instability, loss of
strength, limitation of mobility or residual pain, must be reported.
In advanced cases, in which early treatment has not been carried out, carpal reconstructive
surgery is complicated by scaphoid pseudoarthrosis, capitate degeneration, and arthritis
of other carpal bones, including the distal lunate surface. In these cases, the surgical
treatment options are total wrist arthrodesis; scaphoid resection with lunate-capitate
bone arthrodesis, or “four corner” arthrodesis; proximal row carpectomy; or capitate
head replacement with a silastic prosthesis (resurfacing capitate pyrocarbon implant,
RCPI).[10]
Conclusions
Fenton syndrome is a rare condition with challenging diagnosis and treatment. Three-dimensional
models facilitate the understanding, in full-scale, of anatomical relationships, concomitant
fractures, comminution degrees, and fragment rotation. In addition, these models make
preoperative planning simpler and more intuitive, providing the surgeon with clarity
and security to face the procedure.
