Analysis of the kinematical pattern in scaphoid nonunion by 4-dimensional computed tomographic imaging

The main function of the scaphoid is complex; it acts as a lever between the
proximal and distal carpal rows of the wrist and plays an important role in the
carpal stability and wrist mechanics. Nonunion after fracture of the scaphoid
leads to changes in wrist mechanics, bone loss, a humpback deformity, carpal
instability and secondary degenerative changes, known as a scaphoid nonunion
advanced collapse (SNAC) wrist. The changes following scaphoid nonunion are a
significant clinical problem with a large impact on the functionality of the
wrist and the quality of life of the individual patient. Scaphoid fractures are
the most common fractures of the carpals and although union rates vary;
approximately 10% to 15% of all scaphoid fractures progress to nonunion.
There are several ways to diagnose scaphoid nonunion, such as: plain
radiography, CT-scans, MRI scans and currently there are some studies with
3-dimensional imaging with CT- or MRI- scans. But these are all static imaging
procedures and because of the complexity of the movement of the scaphoid, it is
impossible to predict the exact kinematics. Static measurements do not evaluate
any functional effects that might occur during wrist motion with scaphoid
nonunion. Therefore it is important to obtain detailed 4-dimensional
information about the pathological kinematics of the wrist that may lead to
degenerative changes when scaphoid nonunion occurs. Until now, only static 3
dimensional evaluation of the kinematics have taken place, a 4D method would
give us the ability to study the true kinematical pattern of a SNAC wrist.

This will be the first study to investigate dynamic wrist motions patterns, by
a novel 4D-CT method, in patients with scaphoid nonunion and will give us
dynamic information of the carpal bones before and after surgery. We will
specifically test the hypothesis that the fracture location with respect to the
scaphoid apex is related to the kinematical pattern. This is clinically
important for better decision making in treatment planning of scaphoid nonunion
for the individual patient. Because motion patterns of the carpal bones vary
between individuals and anatomic variances are known, this study compares the
fractured wrist with the contralateral *unharmed* side in the same individual.
We expect to detect abnormal motion patterns, which we will quantify in
measurable values: 3 translations and 3 rotations. Delineation of specific
motion patterns of the carpal bones will enable us to set up new definitions
for diagnosing scaphoid nonunion wrist pathologies. We will also investigate
the relation between the kinematical pattern and the patient complaints; and by
rescanning patients with scaphoid nonunion after a reconstructive procedure, we
will investigate the benefit of such interventions.

Observational study.

Study procedure:
Both wrists of the patients will be scanned by our 4D-CT method during
flexion/extension motion (FEM) and radioulnar deviation (RUD). 3 months after a
reconstructive procedure the operated wrist is scanned again with the same
protocol. A MHQ questionnaire will be filled in before and three months after
reconstruction of the scaphoid nonunion. Since not all patients are eligible
for the postoperative 4D-CT scan, due to additional operative procedures, we
need to include additional participant to be able to answer our secondary
research objective. To answer the research question we will need to include 12
participants with a pre-operative DISI stance of the lunate and 12 participants
with a normal stance of the lunate. The patients who are included
pre-operatively and are eligible for post-operative scanning, will still be
scanned post-operatively and included in the analysis of post-operative
research question.

The radiation exposure of 4D-CT scans is estimated to be 0.7 mSv for the
patients. We do not need a healthy control group. The exposure is within the
category IIa (0,1 * 1 mSv) of the International Commission on Radiological
Protection (ICRP), which qualifies as: minor risk. Findings from 4D-CT scans
will be used for a better decision making for the patients involved.
The patients will be scanned twice, one time before surgery and one time 3
months after surgery, this visit will take a few hours. Travel costs are
included.

The postoperative study population: the radiation exposure of 4D-CT scans is
estimated to be 0.5 mSv for the patients. The exposure is within the category
IIa (0,1 * 1 mSv) of the International Commission on Radiological Protection
(ICRP), which qualifies as: minor risk.