Effect of Clavicle Shortening on In Vivo Rotations of the Shoulder Complex During Abduction
+1Giphart, J E; 1Hvidston, J A; Torry, M R; 1,2Hackett, T R
+1Steadman Philippon Research Institute, Vail, CO; 2Steadman Clinic, Vail, CO
[email protected]
RESULTS:
In general, the SC joint was positioned in a retracted, elevated and
posterior tilted position which all increased significantly with elevation
angle (p < 0.001). The malunited shoulder was 3.8 0 less posteriorly
tilted compared to the healthy shoulder (p = 0.001).
In general, the AC joint was positioned in a protracted, laterally
rotated and posterially tilted position of which lateral rotation and
posterior tilt increased with elevation angle (p < 0.001). The malunited
shoulder was significantly more protracted (5.7 0), laterally tilted (7.4 0),
and posteriorly tilted (4.7 0) (p < 0.001).
DISCUSSION:
Our results indicate that during scaption a clavicular malunion creates
an offset in at least one of the rotations of each of the joints in the
shoulder complex. The protraction offset in the ST joint is primarily
determined by the protraction offset in the AC joint (Table 1). There was
no significant posterior tilting in the ST joint of the malunited shoulder,
and, thus the increased posterior tilt in the AC joint is compensated for
by the decreased posterior tilt in the SC joint (Figure 1). In addition, the
GH joint was less internally rotated in the malunited shoulder to keep
the thumb pointing upward. Lastly, the increased ST lateral rotation is
primarily determined by the increased AC lateral rotation. These data
show the complicated effects of clavicle malunion on the 4 joints of the
shoulder complex in vivo.
Table 1. Mean difference in degrees between the shoulder with the
malunited clavicle and the healthy shoulders for the three rotations of the
SC, AC, GH and ST joint (* indicates p < 0.05)
Protraction
SC
1.3
AC
5.7 *
GH
0.0
ST
7.8 *
Elevation
-0.1
7.4 *
0.3
2.8 *
Post. tilt
-3.9 *
4.7 *
11.5 *
0.5
ST Post tilt (deg)
Malunion
Healthy
SC Post tilt (deg)
METHODS:
A biplane fluoroscopy system was used to measure the 3D position
and orientation of the clavicle, scapula, humerus and thorax (rib cage) of
both shoulders of 5 male subjects (age: 33±10 yrs, height: 1.82±0.05 m,
weight: 78±4 kg) with isolated, unilateral clavicle malunions. Each
subject performed continuous and smooth abduction in the scapular
plane over 2s.
The biplane fluoroscopy system consisted of two commercially
available BV Pulsera C-arms with 30 cm image intensifiers (Philips
Medical Systems, Best, The Netherlands). The image intensifiers were
removed from the C-arm configuration and mounted on a custom gantry
for maximum movement freedom. Images were recorded with two highspeed, high-resolution (1024 X1024) digital cameras (Phantom V5.1,
Vision Research, Wayne, NJ) which were interfaced with the image
intensifiers. Biplane fluoroscopy data were originally collected at 100
Hz, but were tracked at 12.5 Hz, because the motions were sufficiently
slow. A bilateral high-resolution CT scan was also obtained. This
protocol was approved by the governing IRB and informed consent was
obtained prior to participation.
The 3D geometries of the clavicle, scapula, humerus and thorax were
extracted from the CT data using commercially available software
(Mimics, Materialize, Ann Harbor, MI). For each frame the 3D bone
positions and orientations were estimated using a contour matching
algorithm (Model-Based RSA, Medis Specials BV, Leiden, the
Netherlands). Coordinate systems and angular measures were
determined according to ISB standards3. The ST, SC, AC and GH
orientation data were filtered at 2 Hz and normalized to arm elevation
angle at 10 0 increments from 20 0 to 150 0 of arm elevation and
averaged across all participants. A 2-way repeated-measures ANOVA
was performed for each rotation to determine the effect of elevation
angle and malunion on the rotation.
The GH joint was elevated slightly anterior to the pure scapular plane
(2.9 0) and in internal rotation both of which which did not significantly
vary with elevation. The malunited shoulder was 11.5 0 less internally
rotated compared to the healthy shoulder (p = 0.002).
Finally, the ST joint was generally positioned in a protracted, laterally
rotated and posteriorly tilted position all of which varied significantly
with elevation angle (p < 0.001). The malunited shoulder was positioned
significantly more protracted (7.8 0) and laterally rotated (2.8 0) (p <
0.001)
10
0
-10
20
40
60
80
100
120
140
20
40
60
80
100
120
140
20
40
60
80
100
Arm elevation (deg)
120
140
40
20
0
40
AC Post (deg)
INTRODUCTION:
The clavicle acts as a dynamic strut connecting the upper extremity to
the axial skeleton (chest). Clavicle fractures account for roughly 2.6% to
4% of fractures1,2. Middle-third fractures account for up to 80% of the
presenting fractures and approximately 50% are displaced.1,2. When
treated non-operatively, displaced clavicle fractures will heal with some
degree of deformity, most commonly shortening with superior
displacement of the medial fragment. A malunion is not well defined in
the literature, but most authors consider more than 15 mm of clavicle
shortening a malunion.
Controversy exists regarding the operative indications for displaced
middle-third clavicle fractures. Clinically, patients with clavicle
malunions may not show deficiencies in strength and range of motion
(ROM). However, studies have also reported that 25%-50% of patients
were dissatisfied3,4 with their shoulder function and this was positively
correlated with the amount of clavicular shortening4. Patients with
malunions may experience pain, weakness, fatigability, neurologic
symptoms and cosmetic deformity.
The purpose of this study was to determine the 3D acromioclavicular
(AC), glenohumereal (GH), scapulothoracic (ST), and sternoclavicular
(SC) rotations in shoulders with clavicular malunions compared with the
intact opposite shoulder during abduction in the scapular plane. It was
hypothesized that clavicular malunion causes abnormal joint kinematics
compared to the contralateral shoulder.
20
0
-20
Figure 1. Posterior tilting as a function of arm elevation angle for the
malunited and healthy shoulders.
REFERENCES:
1. Nordqvist & Petersson, (1994) CORR, 300:127-132.; 2.Postacchini
et al., (2002) JSES 11:452-456.; 3. Can Orthop Trauma Soc, (2007)
JBJS-Am, 89: 1-10.; 4. Lazarides et al. (2006) JSES, 15: 191-194.; 5.
Bourne et al., (2007) JSES, 16:150-162. 6. Ludewig et al., (2009) JBJS,
91:378-89.
Paper No. 0289 • ORS 2012 Annual Meeting