Investigating carpal kinematics after pisiformectomy by new developed 4-dimensional Rotational X-ray imaging - A pilot study

Wrist problems are responsible for a significant social-economic problem for
the employers and the community as they are responsible for the longest absence
period from work with substantial financial consequences due to workers'
compensation, medical expenses, and productivity losses. Malfunctioning of the
wrist often leads to reduced quality of life and has profound consequences for
the patients involved. Due to the complex anatomy, diagnosis of wrist injuries
is hampered by the various levels of trauma severity and the large number of
possible trauma locations. Therefore it is of great importance for the patient
and the medical doctor to recognize and properly diagnose problems in the wrist
at an early stage.

The year-prevalence of wrist complaints among Dutch adults in 1998 was
estimated by the Dutch Institute for public health and environment (RIVM) at
approximately 17.5%. Injuries to hand and wrist account for 28.6% of all
attendances at the accident and emergency department.

The wrist is the most complex joint in the human body. It consists of 8 wrist
bones, 26 ligaments and numerous articular surfaces. The complex movements of
these bones during wrist motion are still poorly understood. Diagnosis is
sometimes difficult owing to poor understanding of carpal kinematics;
inconsistencies in the physical examination and limited value of imaging
methods. Treatment outcomes are variable by lack of quantitative data.

Wrist stability can be described as the ability of the wrist to maintain a
normal balance between the articulating bones under physiologic loads and
movements without overloading or loss of motion control. The pisiform is a
small bone in the proximal row of the wrist which only articulates by a smooth
oval concave facet with the slightly convex triquatrum forming the
pisotriquatral joint. This joint is enclosed by a loose but though capsule,
formed by various soft-tissue structures from different directions. Together
they provide the pisiform to be a stability factor of the wrist. These
soft-tissue structers are: the tendon of the flexor carpi ulnaris(FCU), the
abductor digiti quinti muscle, the pisometacarpal ligament, the pisohamate
ligament, the extensor retinaculum, the flexor retinaculum, the anterior carpal
ligament, the pisotriquatral joint capsule and a superficial fibrous band
extending from the pisiform to the hook of the hamate.
Diseases of the pisiform are not infrequent and mainly consist of degenerative
changes as pisotriquatral-arthrose and enthesopathy [9-11]. The major symptom
of dysfunction at the pisotriquatral joint is pain in the hypothenar eminence
[8]. When patients do not respond to non-operative treatment with local steroid
injections, pisiformectomy is the first choice of treatment.

Due to a lack of biomechanical studies it was assumed that the pisiform bone
does not play any role in the stability of the wrist joint and therefor
dispensable in situations when the pisiform was affected. Concomitant to these
assumptions many authors have described good short-time results in most
patients after an excision of the pisiform.

Contrary to the previous findings Beckers and Koebke demonstrated that the
pisiform mechanically contributes to the stability of wrist by preventing
triquatral subluxation and also acts as a fulcrum for the powerful forces that
are transmitted from the forearm to the hand. Despite the fact that their
experiments were performed on cadaver wrists they showed that the extirpation
of the pisiform alters wrist*s kinematic behavior. Although findings from the
cadaver experiments might be foreboding there are no studies where kinematic
effects of pisiformectomy have been studied in living patients. Therefore the
aim of this study is to improve our understanding of the role of the pisiform
and the pisotriquetral joint in stability of the wrist in patients undergoing
an pisiformectomy operation.

We hypothesize that the abnormal carpal kinematics will be detectible in
patients undergoing pisiformectomy. By quantitative analysis of the operated
and the not operated patient wrists we hope to investigate the kinematic
changes of such interventions afterwards.

For in vivo quantitative analysis of the wrists kinematics we developed a new
method for the acquisition of dynamic 3D images of a moving joint.In our method
a 3D-rotational x-ray system is used to image a cyclic moving joint during a
period of time. This results in multiple sets of projection images, which are
reconstructed to a series of time resolved 3D images i.e. 4D-rotational X-ray.
In this way we are able to investigate dynamic wrist behavior in a non-invasive
way (figure 3). The resulting data are processed whereby movements can be
quantified, and studied. By using these quantitative data we will be able to
differentiate between normal and abnormal wrist kinematics which occur after
ligament disruption.
In vivo motion pattern measurement with 4D-RX imaging and processing is
accurate and non-invasive. The accuracy of the method is 0.028±0.018 mm for
translation and 0.13±0.07 degrees for rotation. This is the situation in which
the system will be tested clinically. The reproducibility of two scans with a
time delay is 0.19±0.04 mm for translation and 0.5±0.1 degrees for rotation.


Relevance for science, technology or society
In a professional setting wrist problems often lead to a strongly reduced
capability of an employee to perform job related manual tasks. Apart from
discomfort and pain for the patient, reduced manual performance is associated
with economic damage to the employer. Since the functionality of the hand is
essential in almost any professional environment improvement of wrist
functionality will have a direct impact on economic value as well as social
functioning of the patient involved.
This research will contribute to a better understanding of wrist*s principal
biomechanics and dyskinematics after ligamentous injury which will give an
onset for further investigation of mechanisms of various instability patterns.
Better understanding of basic dynamic properties of the wrist results into
further development a new technology for the acquisition of dynamic 3D images
of a moving joint. This is crucial for functional assessment of the joint*s
characteristics including degree joint function or malfunction. In this order
better understanding of the wrists characteristics will improve therapy
methods, the quality of life for the patients involved and will reduce the lost
working time that will reduce the society*s expenses due to workers'
compensation, medical expenses, and productivity losses.

The aim is to gain basic dynamic information of both healthy and operated
wrists to eveluate the outcome of pisiformectomy. By comparing the healthy
wrist of the patient with the operated wrist we expect to detect abnormal
motion patterns which we will quantify in measurable values.

This experiment is a Pilot study. The aim is to gain information of the outcome
of pisiformectomy on the wrist movements and stability.
Both wrists of all patients will be scanned by our 4D-RX method during
flexion/extension, radioulnar deviation. The scans of the healthy and operated
wrists will be compared to eveluate and study the effects of pisiformectomy.

A group of patients with unilateral pisiformectomy in the history who*s healthy
and affected wrist will be scanned. First a regular dose CT scan will be
obtained to acquire volume reconstructions of carpal bones. Hereafter both
wrists will be scanned by our 4D-RX method during flexion/extension motion
(FEM) and radioulnar deviation (RUD). The total radiation exposure of the
experiments is about 0.25 mSv which is comparable to 5 weeks natural background
exposure in the Netherlands.