Keywords bone screws - shoulder dislocation/surgery - shoulder joint/surgery - computed tomography
x-ray
Introduction
Recurrent shoulder dislocation results from lesions of the stabilizing joint structures,
active or passive, resulting from traumatic events or not. It is more frequent in
young male adults, in whom the possibility of recurrent instability reaches up to
90%.[1 ]
[2 ] Treatment is preferably surgical, with Latarjet and its modifications being some
of the used techniques.[2 ] These are based on the use of bone blocks with good safety and excellent results
mainly in cases with erosion of the anterior edge of the glenoid.[3 ]
[4 ]
[5 ]
In Latarjet surgery, the positioning of the graft and screws is essential for the
success of the procedure.[2 ]
[6 ]
[7 ]
[8 ]
[9 ]
[10 ] The lateralized graft favors the appearance of early osteoarthritis and limits the
range of motion. When mediated, it predisposes to degenerative changes and varying
degrees of instability. Therefore, the understanding of each step of this procedure
minimizes the risks of poor positioning of the screws used for graft fixation. Even
with appropriate technique, other complications such as non-consolidation or resorption
of the graft may occur.[7 ]
[8 ]
[11 ]
[12 ]
The evaluation of graft and screws positioning in the postoperative period by computed
tomography (CT) images can help in understanding complications. However, there is
a lack of consistent data from a reproducible evaluation of the position of the screws
and their inter-relationships with the postsurgical results.
The aim of this study was to evaluate whether the parallelism of the screws with the
glenoid in modified Latarjet surgery interferes with the positioning of the graft
and, at the same time, to verify the reproducibility of a method for evaluating the
position of the screws in relation to the glenoid.
Methodology
This is a retrospective, multicenter study with recruitment of patients from two centers
specialized in shoulder and elbow surgery. The procedure was performed by surgeons
with more than 5 years of training in shoulder and elbow surgery.
Approved by the ethics and research committee with CAAE number: 89698818.5.0000.5505.
Study Population
Patients diagnosed with recurrent anterior shoulder instability submitted to surgical
treatment using the modified Latarjet technique and who underwent outpatient clinical
and radiographic postop follow-up with a minimum follow-up time of 1 year were included.
The indication of the Latarjet procedure was based on clinical data such as physical/sports
activity, presence of bone defects of the glenoid or humeral, and, in cases of recurrence
after Bankart repair, by arthroscopic technique.
Patients submitted to treatment of shoulder instability by other techniques, surgeries
for the treatment of other shoulder disorders, such as rotator cuff repair, with previous
diagnosis of arthrosis, or who did not undergo CT 1 year postoperatively were excluded.
Surgical Technique
The patients were in beach chair position, under general anesthesia and brachial plexus
block. Access was made in the deltopectoral interval with anterior skin incision of
5 to 8 centimeters (cm). Dissection, exposure, and osteotomy of the coracoid process
were performed, preserving the joint tendon after the release of the pectoralis minor
and the coracoacromial ligament. The subscapularis muscle was longitudinally opened
between the upper and lower two thirds. The joint capsule was opened vertically near
the glenoid. After preparation of the anterior rim of the glenoid, the bone graft
was fixed vertically, with 2 screws of 3.5 to 4 mm in diameter. The position of the
graft and screw was verified with fluoroscopy after fixation. As described in the
modified Latarjet technique, no coracoacromial ligament repair was made in the joint
capsule.[13 ]
[14 ]
Postsurgical Tomographic Evaluation
Postsurgical Tomographic Evaluation
Two radiologists, one with 7 years (named observer 1) and the other with 1 year (named
observer 2) of experience in musculoskeletal radiology, performed 2 evaluations, independently,
with an interval of 2 weeks of tomographic images for analysis of screws positioning
and radiographic complications after surgery. Horos for Mac software (Nimble Co, Annapolis,
MD USA.) was used for image analysis. The tomograph used was the 64-channel Philips
Brilliance (Philips Health, Best, Netherlands), and the patients were positioned in
horizontal supine position.
Evaluation of Screws Parallelism and Alpha Angle
Evaluation of Screws Parallelism and Alpha Angle
The evaluation of the positioning of each of the bone graft fixation screws was performed
by measuring the angle formed between the largest longitudinal axis of the screw and
the articular surface of the adjacent glenoid, called alpha angle. For this, we chose
the tomographic cut in which the screw was visualized in its entire longitudinal length
in the true sagittal plane of the glenoid ([Figs. 1 ] and [2 ]). Thus, the image of the entire length of the screw located in the oblique axial
plane was defined, because the graft fixation screws present anterior craniocaudal
inclination due to the surgical technique that positions the bone graft in the margin
of the anteroinferior glenoid ([Fig. 3 ]). The top screw is screw 1, and the bottom one is screw 2.
Fig. 1 Tomographic reconstruction in the true sagittal plane of the glenoid with visualization
of screws 1 (upper) and 2 (inferior) graft fixation.
Fig. 2 Sagittal section of orientation for reconstruction of the best axial cut of screw
1 (upper) on the largest longitudinal axis.
Fig. 3 Axial cut of the upper screw.
The positioning of the bone graft in relation to the articular surface of the glenoid
was classified according to the distance between the anterior surface of the graft
and the glenoid joint surface's plan, being classified as:
Medial: when the distance was greater than 5.0 mm medially to the joint surface ([Fig. 4 ]).
Lateral: when the distance was greater than 1.0 mm laterally to the joint surface
([Fig. 5 ]).
Neutral: when the distance was between 5.0 mm medial to 1.0 mm lateral in relation
to the joint surface ([Fig. 6 ]).
Fig. 4 Medial position screw (7 mm medial to joint surface).
Fig. 5 Lateral position screw (5 mm lateral to joint surface).
Fig. 6 Neutral position screw (at joint surface level).
From the axial cut of the CT, visualizing the upper screw, two reference lines were
drawn: the largest longitudinal axis of the screw and another of the joint surface
of the glenoid, forming the alpha angle, measured in degrees ([Fig. 7 ]).
Fig. 7 Alpha angle formation measured in degrees.
Radiographic Complications
Radiographic Complications
The analysis of postsurgical complications on CT images used the following definitions:
Pseudoarthrosis: cases in which there were no signs of bone graft consolidation near
the glenoid. We consider as signs of consolidation on CT images the presence of bone
bridges, fusion of bone corticals close between fragments and bone callus formation
([Fig. 8 ]) in any tomographic section with a minimum of 6 months
Osteolysis: cases in which hypoattenuating (radiolucent) foci were evidenced in the
cortical and bone marrow of the graft; or when the graft showed a reduction in its
dimensions, signs of resorption, when the graft was not visualized, leaving only the
screw head near the joint surface ([Fig. 9 ]).
Fig. 8 Computed tomography cut showing pseudoarthrosis.
Fig. 9 Computed tomography cut showing osteolysis.
Statistical analysis
Statistical inference analysis used the IBM SPSS Statistics for Windows, Version 20.0
(IBM Corp. Armonk, NY, USA), Minitab 16 (Minitab Inc, State College, PA, USA), and
Microsoft Excel Office 2010 (Microsoft Corp. Redmond, WA, USA) software. A significance
level of 0.05 (5%) was defined, with a 95% confidence interval. The quantitative variables
of main outcome were tested for normality using the Kolmogorov-Smirnov test; the alpha
angle was evaluated using the paired Student t-test. Kappa coefficient was used to
evaluate the intra and interobserver agreement of the alpha angle values, bone graft
positioning and presence/absence of postsurgical radiographic complications. Landis
and Kock[15 ] proposed the following correlation between kappa coefficient values: < 0.00 = very
bad, 0.00–0.20 = bad, 0.21–0.40= reasonable, 0.41–0.60 = good, 0.61–0.80 = very good
and above 0.81 = excellent.
Then, results obtained by observer 1 were submitted to statistical analysis to evaluate
the following relationships between variables and their associations through the Chi-squared
and analysis of variance (ANOVA) tests:
Alpha angle and positioning of the bone graft.
Alpha angle and presence/absence of postsurgical complications.
Positioning of the bone graft and presence/absence of postsurgical complications.
Cut-off value of the alpha angle for the presence of postsurgical complications.
For the analysis of these relationships involving the alpha angle, there was grouping
of the values of the measurements into 2 ranges, one from 0 to 15 degrees and another
equal to or greater than 16 degrees. These ranges of values were defined from the
conclusion of two studies by Hovelius et al., according to which the angulation of
the screw should be less than 15 degrees for adequate position of the coracoid and
stable fixation.[11 ]
[16 ]
Results
Thirty-four patients were included, one with bilateral involvement, totaling 35 shoulders,
22 right and 13 left. Four were women and 30 men, aged between 21 and 60 years old.
The general results obtained in the evaluation of bone graft positioning in relation
to the glenoid and complications are illustrated in [Table 1 ].
Table 1
Bone graft positioning
Graft
Observer 1
Observer 2
Interobserver agreement (Kappa)
Medial
12
13
0.86
Neutral
20
19
Articular
3
3
Intraobserver agreement (Kappa)
0.92
0.88
Complications
Graft
Observer 1
Observer 2
Interobserver agreement (Kappa)
No complications
21
27
0.77
With complications
14
8
Intraobserver agreement (Kappa)
0.9
0.88
The positioning of the bone graft in relation to the glenoid joint surface was classified
as:
Medial: when the distance was greater than 5.0 mm medially to the joint surface.
Articular: when the distance was greater than 1.0 mm laterally to the joint surface.
Neutral: when the distance was between 5.0 mm medial to 1.0 mm lateral in relation
to the joint surface.
The alpha angles obtained are described in [Table 2 ]. There was no statistically significant difference between the two observers, so
the observers similarly evaluated the deviations.
Table 2
Observer 1
0–15
> 16
Average (+-SD)
Min; Max
N
P -value
Screw 1
18
17
16.7(±9.6)
0; 44
35
0.069
Screw 2
18
17
19.4 (±12.1)
2; 46
35
0.107
Observer 2
0–15
> 16
Average
Min; Max
N
P
-value
Screw 1
19
16
18.2 (±11.4)
2; 55
35
0.069
Screw 2
15
20
20.9 (±14)
1; 61
35
0.107
Regarding the evaluation of the relationship between the position of the bone graft
and the alpha angle ranges for screw 1 (p = 0.341), it was observed that of the 18 patients with alpha angle between 0 and
15 degrees, 6 of the grafts (33.3%) were in a medial position, 11 (61.1%) in neutral
position, 1 of the grafts (5.6%) in joint position. Of the 17 patients with an alpha
angle greater than 16 degrees, 5 of the grafts (29.4%) were obtained in a medial position,
10 of the grafts (58.8%) in a neutral position, and 2 (11.8%) in joint position. For
screw 2 (p = 0.242), of the 18 patients with an alpha angle between 0 and 15 degrees, the positions
of the grafts were: 7 of the grafts (38.8%) in the medial position; 11 (61.2%) in
neutral position, and none of the grafts in joint position. Of the 17 patients with
values greater than 16 degrees, 4 of the grafts (23.5%) were in a medial position,
10 (58.8%) in neutral position, and 3 of the grafts (17.7%) in joint position. [Table 3 ] illustrates the relationship between graft position and screw angle but using the
mean value of the measurements.
Table 3
Position
Average
Median
Standard deviation
Min
Max
N
P -value
Screw 1
Articular
26.3
28
8.6
17
34
3
0.112
Medial
11.8
11
2.5
10
16
5
Neutral
16.5
14.5
9.9
0
44
28
Screw 2
Articular
35.3
39
7.2
27
40
3
0.052
Medial
17.8
14
14.2
3
41
5
Neutral
17.9
18
11.1
2
46
27
In both evaluations, there was no statistical significance between the angle and the
positioning of the graft. However, in screw 2, it tended to be significant when the
angle was evaluated by mean angle values, highlighting the three cases of lateral
grafts with higher mean value of alpha angle. The relationship between angle values
and the presence of postsurgical complications is illustrated in [Table 4 ].
Table 4
Complication
No
Yes
Total
P -value
N
%
N
%
N
%
Screw 1
0–15
11
61.2
7
38.8
18
51.4
0.084
> 16
9
52.9
8
47.1
17
48.6
Screw 2
From 0–15
11
61.2
7
38.8
18
51.4
0.079
> 16
10
58.8
7
41.2
17
48.6
There was no statistical significance between the angle and the presence of complications.
However, there is a tendency to ratio the angle of screws 1 and 2 to the presence
or not of complications, noting that the lower the alpha angle, the lower the number
of complications. [Table 5 ] illustrates the evaluation between the presence of complications and screw angle.
Table 5
Complication
Average
Median
Standard deviation
Min
Max
N
P -value
Screw 1
No
13.6
12
7.9
0
27
19
0.043
Yes
20.1
17
10.4
8
44
17
Screw 2
No
14.2
13
9.1
2
34
19
0.004
Yes
25.6
19
12.5
8
46
16
In both screws, we observed that the mean value of the angles measured is higher in
cases in which complications were evidenced, with statistical significance. The relationship
between complications and graft positioning is illustrated in [Table 6 ].
Table 6
Complication
No
Yes
Total
P -value
N
%
N
%
N
%
Position
Articular
0
0.0
3
21.5
3
8.5
0.030
Medial
7
33.3
5
35.7
12
34.4
Neutral
14
66.7
6
42.8
20
57.1
There was statistical significance in the relationship between graft positioning and
the presence of complications, with p < 0.03. Using the receiver operating characteristic (ROC) curve to obtain some cutoff
value of the screw angle related to the complication, there was only statistical significance
for screw 2, and the value obtained was of 11 degrees, with a sensitivity of 93.8%
and specificity of 47.4% to predict a patient with postsurgical complications.
Discussion
When describing his surgical technique, Latarjet recommended that the bone graft fixation
screw should be parallel to the joint surface to improve bone containment, avoiding
complications and treatment failures.[17 ]
[18 ] Despite these recommendations in relation to the surgical technique, the literature
is scarce regarding precise recommendations for screw parallelism or if there is any
degree of acceptable angulation to obtain favorable results in the surgical treatment
of recurrent shoulder dislocation.
The proposal of a method for evaluating the position of the graft and the alpha angle
by means of tomography was initially validated by Kraus et al.[10 ] In 2016, these authors conducted a study with 27 patients who evaluated, over 2
years, the reproducibility to classify the position of the graft after the Latarjet
procedure, as lateral, neutral, or medial, by CT. This study showed positive results
regarding the reproducibility of the method, showing that the CT evaluation accurately
described the positioning of the graft.[10 ]
In our study, the intra and interobserver agreement for the analysis of graft positioning
and for the measurement of the inclination of the fixation screw with the glenoid
joint surface was statistically positive. The measurement of the alpha angle by the
two observers showed no statistical difference, corroborating the reproducibility
of the method in this evaluation. Some degree of difficulty may occur in obtaining
the best tomographic cut by tilting the scapula, as Barth et al.[19 ] concluded in their study in 2017.
The surgical procedure of bone block is the treatment of choice in cases of recurrent
dislocation of the shoulder in which there is bone loss.[4 ]
[10 ]
[20 ]
[21 ] The procedure aims to restore the stability of the shoulder joint, and its success
depends on several technical factors.[2 ]
[6 ]
[9 ]
[17 ] Among the main ones, the position of the coracoid graft ideally below the glenoid
equator and parallel to the glenoid joint surface, avoiding the minimum medial deviation
of the graft and the inclination of the fixation screws in relation to the joint line,
stand out.[18 ]
[22 ]
In addition to the classical Latarjet technique or its modifications, there is the
possibility of performing arthroscopic surgery.[7 ]
[16 ]
[17 ]
[23 ] Both forms present good results in functional and postoperative pain scores.[24 ] In a systematic review, Horner directly compared the open Latarjet technique with
the arthroscopic approach and concluded that three out of five studies did not find
significant differences in relation to graft positioning[20 ]
[25 ]
[26 ]
[27 ]; and two out of three studies found no statistical difference in the angle of the
screws.[25 ]
[27 ]
[28 ] Still, there are studies that demonstrate that graft positioning in arthroscopic
surgery can be challenging, as well as the proper angle of the screws.[29 ]
[30 ]
Our results demonstrate a relationship between the alpha angle and the presence of
radiographic complications. In both screws, we observed that the mean value of the
angles measured is higher in cases in which complications were evidenced, with statistical
significance. These results are in line with previous studies that recommend a maximum
inclination of 15 degrees of the fixation screws in relation to the glenoid joint
line.[9 ]
[11 ]
[16 ]
[22 ]
Limitations
Osteoarthritis was not included in the analysis of complications due to the time for
the onset of this alteration. Another limitation of the study was that, because it
was a strictly radiological study, there was no collection of clinical and epidemiological
data, and occurrence of postoperative recurrence. Furthermore, this study did not
analyze the dimensions of the bone defect secondary to instability, since this study
used CT scans performed postoperatively, which may be a bias to evaluate the bone
resorption of the grafts.
Conclusion
The technique described to measure the parallelism of the screws in the Latarjet surgery
presented a very good and excellent intra and interobserver agreement, respectively.
We found that screw parallelism with glenoid is recommended; however, it is not a
mandatory and unique condition to avoid radiological complications.
There is a tendency of the relationship between the position of the graft and the
inclination of the lower screw when measured by the mean of the values obtained from
the alpha angle. Lateral grafts presented higher mean value compared to neutral and
mediated grafts. We observed that the mean value of the inclination angle of screws
1 and 2 is higher in cases that presented radiological complications. There is also
a significant relationship between graft position and the presence of radiological
complications.
