Analysis of instability patterns in acute scaphoid fractures by 4-dimensional computed tomographic imaging

Scaphoid fractures are the most common fractures of the carpals and account for
50% to 80% of all carpal fractures in young and active patients. The scaphoid
acts as a lever between the proximal and distal carpal rows of the wrist and
therefore plays an important role in carpal stability and wrist mechanics6.
Although union rates vary, approximately 10% to 15% of all scaphoid fractures
progress to nonunion. Because nonunion of the scaphoid leads to changes in the
wrist mechanics, carpal instability and secondary degenerative changes, known
as a scaphoid nonunion advanced collapse (SNAC), it is important to diagnose
those acute fractures that are prone to nonunion.

Scaphoid fractures are considered unstable when they are more than 1 mm
displaced. However, whether displaced fractures truly demonstrate an unstable
motion pattern during wrist motion has never been objectively analyzed. It is
well recorded that the nonunion rates are considerably higher when a fracture
is more than 1mm displaced, with approximately a 55% chance of malunion or
nonunion, in comparison to an 90% overall rate of union in scaphoid fractures.
Other factors associated with the development of a scaphoid nonunion are the
fracture location, vascular supply, concurrent carpal ligament injury (carpal
instability) and time to treatment.

In an attempt to diagnose those fractures that are prone to nonunion, numerous
different scaphoid fracture classification systems are available to improve
treatment selection and prognosis. Current fracture classification is based on
plain radiographs, two-dimensional CT- or three-dimensional CT scans. However,
static imaging procedures do not evaluate any instability that might occur
during normal wrist motion. These imaging techniques only evaluate osseous
damage and have proven to be unreliable to detect ligament damage, whilst
ligament damage is present in approximately 34-63% in acute scaphoid fractures.
If ligament injuries are neglected at time of surgery, this could lead to
symptomatic carpal instabilities and osteoarthrosis of the wrist.

Since prevailing classification systems are based upon static imaging and
fracture instability is considered the most important factor associated with
nonunion, there is still no consensus about the best fracture classification
method. Furthermore, considering the fact that the majority of nondisplaced
fractures are treated conservatively, predicting instability might improve
identification of the subset of scaphoid fractures unlikely to heal in a cast.
Therefore, management of patients with scaphoid fractures could be further
improved with more reliable diagnostic tools to detect interfragmentary motion
and associated ligament damage, and subsequently identify those fractures that
are prone to nonunion. This study protocol is the first to obtain 4-dimensional
and quantitative data regarding the pathological kinematics of the wrist
following scaphoid fracture, using in vivo motion analysis. We compare the
wrist in the same individual, because anatomic variance of carpal ligaments and
osseous geometry are known, possibly resulting in altered kinematics.

Despite the severe clinical consequences of a scaphoid nonunion, the
kinematical mechanisms that influence the healing process of a scaphoid
fracture are still poorly understood. Until now, all in-vivo research is based
on step-wise static imaging procedures. With static imaging one cannot detect
any instability that occur during normal wrist motion. Therefore previous
research about fracture instability is based on assumptions, with only time to
union as their outcome parameter.
This will be the first study to investigate dynamic wrist motion patterns, by a
novel 4-D-CT method. This imaging technique is readily available in the AMC,
providing us the unique opportunity to visualize in vivo carpal kinematics. By
describing fracture instability patterns and ligament damage, we can provide
new insights in the etiology of a scaphoid nonunion and possibly alter
(surgical) treatment strategies.

Research questions:
I . Are there differences of interfragmentary motion patterns between
displaced and non-displaced scaphoid fractures?

II A. Is there a correlation between motion pattern in an acute scaphoid
fracture and the development of a scaphoid nonunion?
II B. Can we detect carpal ligament damage from the motion patterns of carpal
bones in acute scaphoid fractures?

This study is an observational pilot study. Both wrists will be scanned and
analyzed by our 4D-CT method during flexion/extension and radioulnar deviation.
We will include participants from the Academic Medical Center, Amsterdam.
Acquisition of the 4D data will be conducted at the Academic Medical Center,
Amsterdam.

We include patients with a one-sided scaphoid fracture (diagnosis based on a
radiograph or CT-scan), and a contralateral healthy wrist without history of
wrist injury. No control group is necessary, because of the information from
the contralateral wrist of the patient and data available from a former study
group. All patients will undergo a standard CT scan and the 4DCT protocol.

The patient will be categorized into:
- Nondisplaced or minimally displaced fractures
- Displaced fractures; defined as a >1-mm gap or step-off between the bone
segments

Based on a standard CT scan the patients with displaced fractures will receive
surgery with screw fixation (if agreed with the patient). The nondisplaced
patient arm, will receive cast treatment without immobilization of the thumb29.
Follow-up will be conducted with CT scans (Force CT scanner and SOMATOM AS+ CT
scanner). The treatment and follow up are standard care in the AMC.
The patients will be scanned as soon as possible at the emergency department
with the Force CT scanner, following the in detail described scanning protocol
below. When the patient is in pain, pain medication will be provided, as is
standard of care, according to the Pijnprotocol * Acute volwassenen * SEH
(versie 1) at the emergency department. If patients ar in too much pain, they
will be excluded from the study. If the patient is presented to the emergency
department late in the evening or at night and is willing to come to the AMC in
the first week after presentation to participate in the study, travel costs
will be compensated.

We expect that the burden and risk associated with participation is low. The
aim is to include patients during their visit at the emergency department at
the AMC. If the patient is presented to the emergency department late in the
evening or at night and is willing to come to the AMC in the first week after
presentation to participate in the study, travel costs will be compensated.

The radiation exposure of the 4D-CT scans is estimated to be 0,5 mSv for the
patients. We do not need a healthy control group. The exposure is within the
categary IIa (0,1-1 mSv) of the International Commission on Radiological
Protection (ICRP), which qualifies as: minor risk.