The Effect of an Open Carpal Tunnel Release on Thumb CMC Biomechanics

Abstract

Purpose. We have observed worsening thumb pain following carpal tunnel release (CTR) in some patients. Our purpose was to determine the effect of open CTR on thumb carpometacarpal (CMC) biomechanics. Methods. Five fresh-frozen cadaver arms with intact soft tissues were used. Each specimen was secured to a jig which fixed the forearm at 45° supination, and the wrist at 20° dorsiflexion, with thumb pointing up. The thumb was axially loaded with a force of 130 N. We measured 3D translation and rotation of the trapezium, radius, and first metacarpal, before and after open CTR. Motion between radius and first metacarpal, radius and trapezium, and first metacarpal and trapezium during loading was calculated using rigid body mechanics. Overall stiffness of each specimen was determined. Results. Total construct stiffness following CTR was reduced in all specimens but not significantly. No significant changes were found in adduction, pronation, or dorsiflexion of the trapezium with respect to radius after open CTR. Motion between radius and first metacarpal, between radius and trapezium, or between first metacarpal and trapezium after open CTR was not decreased significantly. Conclusion. From this data, we cannot determine if releasing the transverse carpal ligament alters kinematics of the CMC joint.

Full text

Hindawi Publishing Corporation
Advances in Orthopedics
Volume 2012, Article ID 151348, 4pages
doi:10.1155/2012/151348
Research Article
The Effect of an Open Carpal Tunnel Release on
Thumb CMC Biomechanics
Marc A. Tanner, Bryan P. Conrad, Paul C. Dell, and Thomas W. Wright
Department of Orthopaedics and Rehabilitation, Orthopaedics and Sports Medicine Institute,
University of Florida, Gainesville, FL 32608, USA
Correspondence should be addressed to Thomas W. Wright, wrightw@ortho.ufl.edu
Received 19 April 2012; Revised 23 October 2012; Accepted 24 October 2012
Academic Editor: Allen L. Carl
Copyright © 2012 Marc A. Tanner et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Purpose. We have observed worsening thumb pain following carpal tunnel release (CTR) in some patients. Our purpose was to
determine the effect of open CTR on thumb carpometacarpal (CMC) biomechanics. Methods. Five fresh-frozen cadaver arms with
intact soft tissues were used. Each specimen was secured to a jig which fixed the forearm at 45◦supination, and the wrist at 20◦
dorsiflexion, with thumb pointing up. The thumb was axially loaded with a force of 130N. We measured 3D translation and rota-
tion of the trapezium, radius, and first metacarpal, before and after open CTR. Motion between radius and first metacarpal, radius
and trapezium, and first metacarpal and trapezium during loading was calculated using rigid body mechanics. Overall stiffness of
each specimen was determined. Results. Total construct stiffness following CTR was reduced in all specimens but not significantly.
No significant changes were found in adduction, pronation, or dorsiflexion of the trapezium with respect to radius after open CTR.
Motion between radius and first metacarpal, between radius and trapezium, or between first metacarpal and trapezium after open
CTR was not decreased significantly. Conclusion. From this data, we cannot determine if releasing the transverse carpal ligament
alters kinematics of the CMC joint.
1. Introduction
Carpal tunnel syndrome and basal joint arthritis often
coexist [1]. A study of 246 patients with basal joint arthritis of
the thumb reported that 39% of the study patients also had
carpal tunnel syndrome [2]. Anecdotally, we have observed
worsening thumb carpometacarpal (CMC) pain in some
patients with previously asymptomatic (or minimally symp-
tomatic) first CMC arthritis after undergoing a carpal tunnel
release. The thumb CMC joint is the most common site for
reconstruction in the upper extremity secondary to osteoar-
thritis [3]. It is a semiconstrained joint composed of two
saddle-shaped articulations with opposing axes perpendic-
ular to each other. Minimal congruence and bony stability
allow for a wide range of motion [4].
The anterior border of the carpal tunnel is formed by
the transverses carpal ligament (TCL) [5]. The transverse
carpal ligament proper inserts into the scaphoid tubercle and
trapezial ridge radially and the hamulus and pisiform ulnarly
[6]. Studies have noted increase in carpal tunnel volume,
increase in the carpal arch width, and an overall decrease
in carpal stiffness after carpal tunnel release (CTR) [6–12].
Rotational changes of the hamate, pisiform, and the trapez-
ium have also been reported, as well as an increase in the
distance between the trapezium and the hook of the hamate
[5]. Previous research suggests a direct relationship between
widening of the transverse carpal arch and loss of grip
strength [13]. Pillar pain is a common complaint after CTR
[14], perhaps as a result of the division of the TCL during
surgery [6].
Pain originates most commonly over the pisotriquetral
joint, possibly secondary to displacement of the pisiform or
alteration of forces over the joint [11,15].Thesametypeof
biomechanical changes could occur with the trapezium and
the CMC joint. The purpose of this study is to determine
the effect of open CTR on the kinematics of the trapezium

2 Advances in Orthopedics
and first CMC joint. Our hypothesis was that a CTR will
allow rotation of the trapezium altering the biomechanics of
the first CMC joint. These changes could result in the clinical
observation of increased first CMC joint pain in patients with
previous subclinical CMC arthritis.
2. Materials and Methods
Five fresh-frozen cadaver arms with intact soft tissues were
used. There were three male specimens and two female
specimens (donor age was not available). Each specimen was
secured to a custom-made jig with 3.0 threaded Steinman
pins, two at the distal radius and two placed in the second
metacarpal (Figure 1).
Thejigfixedtheforearmat45
◦supination and was
designed to allow free motion at the thumb CMC joint and
radiocarpal joint while the wrist was fixed in 20◦of dorsiflex-
ion. A threaded 2.0 mm K-wire was placed from the tip of
the thumb distal phalanx into the thumb metacarpal, leaving
2 cm of wire out of the skin. The wire out of the skin was
placed into an MTS machine (MTS Systems, Eden Prairie,
MN) and the jig secured to the base of the testing machine.
An electromagnetic tracking system (Liberty, Polhemus
Inc, Colchester, VT) was used to measure the 3D translation
and rotation of the trapezium, radius, and first metacarpal.
Electromagnetic sensors were attached to the radius and
first metacarpal using custom-made fiberglass brackets. A
threaded K-wire was placed into the trapezium, ensuring that
the joint capsule remained intact, and a third electromag-
netic sensor was attached to the K-wire to track the trapez-
ium. The electromagnetic source was positioned within
20 cm of the sensors to minimize the effect of distortion cre-
ated by the testing machine and jig. Internal electronics of the
Polhemus Liberty system are capable of detecting distortions
and, when present, the testing setup was adjusted to elimi-
nate them. After loading at 10 N once to remove any slack,
the thumb was axially loaded with a 130 N force.
The total motion of the first metacarpal relative to the
radius, between the radius and trapezium, and between
the first metacarpal and the trapezium during loading was
calculated using rigid body mechanics. The stiffness of each
specimen was also determined by measuring the slope of the
load-displacement curve during loading. The measurements
werecollectedfromeachspecimenbeforeandafteranopen
CTR. An open CTR was performed in the standard fashion
and verified visually and with palpation. The release was
performed without removing the specimen from the jig. A
paired t-test was used to determine differences in rotation
and translation of the specimen befor and after CTR.
3. Result
Motion and stiffness data is presented in Tab le 1.
All five specimens demonstrated a reduction in the total
construct stiffness following CTR; however, the difference
was not statistically significant (P=0.1). The average adduc-
tion, pronation, and dorsiflexion of the trapezium with
Figure 1: Photograph of a specimen secured in the custom-made
jig. The forearm is at 45-degree supination and the wrist at 20-
degree dorsiflexion, thumb pointing up.
respect to the radius did not change significantly after open
CRT. No significant decrease in range of motion was meas-
ured between the radius and first metacarpal (P=0.12),
between the radius and trapezium (P=0.32), or between
the first metacarpal and trapezium (P=0.55) after an open
CTR.
4. Discussion
The purpose of this study was to determine the effect of
open CTR on the kinematics of the first CMC joint. Our
hypothesis that a CTR would cause rotation of the trapezium
altering the biomechanics of the first CMC joint was not sup-
ported by the data from this study. Less stiffness was seen in
all of the specimens at the radius-metacarpal interface after
CTR; however, the difference was not statistically significant.
The magnitude of change at the trapezium that would cause
symptoms is not known. It may have been that the small
changes in stiffness we observed were not statistically sig-
nificant because the study did not have sufficient power. We
do not know what decrease in stiffness would be enough to
account for a perceived increase in postoperative pain at the
thumb CMC joint in patients with prior subclinical CMC
arthritis. Likewise rotation of the trapezium would likely
affect the scaphotrapezial trapezoid (STT) joint. This could
also cause pain near the base of the thumb. We did not
specifically evaluate the STT joint in this study.
The only previous study which addressed this issue was
presented in 2009 at the American Academy of Orthopaedic
Surgery meeting [16]. Changes in rotation of the trapezium
were noted in their study but were not statistically significant.
Outward rotational changes in the trapezium of 2.25 degrees
(±1.6 degrees) were found after CTR. They also reported
rotational changes in the pisiform and the magnitude of
these changes was greater than those found at the trapezium
(3.83 degrees and 4.5 degrees, resp.).
A weakness of this study is the small sample size and
the inherent variability of cadaveric specimens. Even though
the specimens were preconditioned, it is probable that in the
normal physiologic state some biomechanical changes may

Advances in Orthopedics 3
Tab le 1: Summary of mechanical properties for each combination of bones before and after open carpal tunnel release.
Measurement Intact
(mean ±SD)
After release
(mean ±SD) Difference Pvalue
Rad-Met1 Rx(adduction) (deg) 2.2 ±1.3 2.1 ±1.6 6.6% 0.69
Rad-Met1 Ry(pronation) (deg) 0.7 ±0.6 0.7 ±0.4 −7.9% 0.56
Rad-Met1 Rz(dorsiflexion) (deg) 3.5 ±1.4 3.4 ±1.5 3.0% 0.78
Rad-Met1 X(dorsal deviation) (mm) 1.9 ±1.6 2 ±1.7 −3.3% 0.48
Rad-Met1 Y(subluxation) (mm) 1.4 ±0.7 1.5 ±0.7 −9.1% 0.12
Rad-Met1 Z(ulnar deviation) (mm) 1.5 ±0.7 1.5 ±0.6 −5.5% 0.54
Rad-Trap Rx(adduction) (deg) 1.9 ±1.1 2.1 ±1.2 −10.2% 0.17
Rad-Trap Ry(pronation) (deg) 2.9 ±2.2 2.9 ±2.4 −0.9% 0.83
Rad-Trap Rz(dorsiflexion) (deg) 2.0 ±2.7 1.9 ±2.3 4.1% 0.70
Rad-Trap X(dorsal deviation) (mm) 1.3 ±0.9 1.1 ±0.8 11.0% 0.13
Rad-Trap Y(subluxation) (mm) 1.0 ±1.1 1.0 ±1.1 −6.0% 0.32
Rad-Trap Z(ulnar deviation) (mm) 1.2 ±0.5 1.3 ±0.6 −8.6% 0.31
Trap -Met1 Rx(adduction) (deg) 9.0 ±9.8 8.6 ±8.8 5.1% 0.60
Trap -Met1 Ry(pronation) (deg) 2.7 ±1.7 2.6 ±2.0 2.5% 0.83
Trap -Met1 Rz(dorsiflexion) (deg) 12 ±11.2 11.9 ±11.2 1.3% 0.80
Trap -Met1 X(dorsal deviation) (mm) 0.5 ±0.2 0.6 ±0.5 −32.4% 0.36
Trap -Met1 Y(subluxation) (mm) 1.2 ±1.2 1.2 ±1.2 −2.8% 0.55
Trap -Met1 Z(ulnar deviation) (mm) 0.7 ±0.4 0.6 ±0.4 5.3% 0.39
Overall specimen stiffness (N/mm) 48.9 ±23.4 41.4 ±18.4 15.3% 0.11
Rad-Met: radius to 1st metacarpal; Rad-Trap: radius to trapezium; Trap-Met: trapezium to 1st metacarpal.
occur over time as the constraints further stretch out. The
native musculature was not used to dynamically load the
CMC. In a cadaver specimen it is challenging to reproduce
physiological loading and it is possible that the tested
condition does not reproduce normal CMC loading. The
strengths of the study are that the surrounding soft tissues of
the forearm were not disturbed and the carpal tunnel release
was performed without removing the arm from the custom
jig. Many other factors come into play concerning the clinical
onset of 1st CMC joint pain including deconditioning or
increased activity level once the patient has recovered from
carpal tunnel surgery.
Our goal was to explore changes in kinematics at the
trapezium following CTR. These changes could be a result of
the changes in the anatomic relationship due to the release of
the TCL affecting the forces at its insertion onto the trapezial
ridge. Small rotational changes could affect the normal
kinematics of the CMC joint during physiologic loading.
Based on the methodology of this cadaver study, we were
unable to prove our hypothesis that releasing the TCL would
result in kinematic changes of the trapezium with secondary
effects on the 1st CMC joint that could be responsible for
postoperative pain in a previous arthritic but asymptomatic
CMC joint.
Ethical Approval
No human subjects were included in this study; therefore,
IRB approval was not required. At the time this project
began, no approval was needed for cadaver study.
Conflict of Interests
There was no financial or other support received for this
research, and none of the authors have a conflict of interests.
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