Nov 9, 2018 - Classification and treatment of dis- locations of total hip ... Della Valle CJ, Chang D, Sporer S, Berger RA, Rosenberg AG, Paprosky WG. High.
1845 C OPYRIGHT Ó 2018
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T HE AUTHORS . P UBLISHED
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T HE J OURNAL
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S URGERY, I NCORPORATED
A commentary by Kevin L. Garvin, MD, is linked to the online version of this article at jbjs.org.
Late Dislocation Following Total Hip Arthroplasty Spinopelvic Imbalance as a Causative Factor Downloaded from https://journals.lww.com/jbjsjournal by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD31kf1ZzWr4XuD7hxuesBbhJzBrOWe024vi2d4wQBH7ajnkKOYZBAfmQ== on 11/09/2018
Nathanael Heckmann, MD, Braden McKnight, MD, Michael Stefl, MD, Nicholas A. Trasolini, MD, Hiroyuki Ike, MD, and Lawrence D. Dorr, MD Investigation performed at the Department of Orthopaedic Surgery, Keck Medical Center of the University of Southern California, Los Angeles, California
Background: Late dislocations after total hip arthroplasty (THA) are challenging for the hip surgeon because the cause is often not evident and recurrence is common. Recently, decreased spinopelvic motion has been implicated as a cause of dislocation. The purpose of this study was to assess the mechanical causes of late dislocation, including the influence of spinopelvic motion. Methods: Twenty consecutive patients were studied to identify the cause of their late dislocation. Cup inclination and anteversion were measured on standard pelvic radiographs. Lateral standing and sitting spine-pelvis-hip radiographs were used to measure pelvic motion, femoral mobility, and sagittal cup position by assessing sacral slope, pelvic-femoral angle, and cup ante-inclination. Spinopelvic motion was defined as the difference between the standing and sitting sacral slopes (Dsacral slope). A new measurement, the combined sagittal index, which measures the sagittal acetabular and femoral positions, was used to assess the functional motion of the hip joint and risk of impingement. Results: There were 9 anterior dislocations (45%) and 11 posterior dislocations (55%) at a mean of 8.3 years after a primary THA. Eight of the 9 patients with an anterior dislocation had spinopelvic abnormalities such as fixed posterior pelvic tilt when standing, increased standing femoral extension, and an increased standing combined sagittal index. Ten of the 11 patients with a posterior dislocation had abnormal spinopelvic measurements such as decreased spinopelvic motion (average Dsacral slope [and standard error] = 9.0° ± 2.4°), increased femoral flexion, and a decreased sitting combined sagittal index. For every 1° decrease in spinopelvic motion, there was an associated 0.9° increase in femoral motion and, in some patients, this resulted in osseous impingement and dislocation. Conclusions: Patients with a late dislocation have abnormal spinopelvic motion that precipitates the dislocation, especially when combined with cup malposition or soft-tissue abnormalities. Spinopelvic stiffness is associated with increased age and increased femoral motion, which may lead to impingement and dislocation. Lateral spine-pelvis-hip radiographs may predict the risk and direction of dislocation. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
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ate dislocations following total hip arthroplasty (THA) are a conundrum for the hip surgeon, but little has been published about their treatment1-6. Charnley and Cupic7 described late dislocations as those that occurred >5 years
following THA, prompting Coventry1 and subsequent authors from the Mayo Clinic to adopt a similar time frame2,3. Other authors have used 1 to 2 years after THA to define a late dislocation4-6. At 1 year, the capsule is healed, the bone has
Disclosure: No outside funding was received in support of this study. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work (http://links.lww.com/JBJS/E916). Copyright Ó 2018 The Authors. Published by The Journal of Bone and Joint Surgery, Incorporated. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.
J Bone Joint Surg Am. 2018;100:1845-53
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http://dx.doi.org/10.2106/JBJS.18.00078
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matured, and gait has returned to normal8-10. Studies from the Mayo Clinic have identified increased hip motion, weak abductors, acetabular cup malposition, polyethylene wear, implant loosening, and neurological disease as risk factors for late dislocation1-3. However, many patients who have a late dislocation have normal component position on standard anteroposterior pelvic radiographs without any identifiable risk factors11-13. Spinopelvic imbalance changes the functional position of the acetabulum, creating a potential for dislocation11,12. The functional position of the acetabulum is determined by the coordinated motion of the spine, pelvis, and hip. When an individual is standing, the pelvis is tilted anteriorly and the lumbar spine has a lordotic curve, with the acetabulum relatively closed over the femoral head (Fig. 1). When a person is sitting, the lumbar spine straightens, the pelvis tilts posteriorly an average of 15° to 20°, and the acetabulum opens approximately 15° to 20° to accommodate the femur, which flexes 55° to 70°13-15. As patients age, the spine may undergo degenerative changes causing lumbar stiffness and decreased pelvic motion during postural changes14. The lumbosacral junction acts as a posterior hinge of the spine-pelvis-hip unit, and the hip joint functions as an anterior hinge (Fig. 2). If the posterior hinge becomes stiff (as a result of surgical fusion or degenerative changes), flexion of the anterior hinge must increase for a person to sit and anterior impingement may occur, a concept
supported by the increased THA dislocation rates reported following surgical fusion of the spine16-21. If the anterior hinge (the hip) becomes stiff from arthritic changes, the motion of the lumbosacral junction must increase for the person to sit, which may explain why back pain often decreases following THA22-24. Three abnormal patterns of pelvic motion have been described15,25,26: (1) the pelvis remains in fixed posterior tilt when the person is standing (Fig. 3), (2) the pelvis is fixed in anterior tilt when the person is sitting (Fig. 4), and (3) the spinopelvic motion is severely decreased, with 1 year following a primary THA. In our cohort, the mean time from surgery to dislocation was 8.3 years (range, 1.2 to 17.9 years). We included subluxations because Charnley and Cupic did so in their initial description of late hip instability7. Prior to data collection, an institutional review board approved the study design and all patients consented to allow analysis of their data.
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Radiographic Measurements Anteversion and inclination of the acetabular cup, as well as the length and offset of the operatively treated and contralateral hips, were measured on a standard postoperative supine anteroposterior pelvic radiograph using previously described methods28 (Fig. 5). Acetabular cup angles were considered abnormal if the inclination was >50° or 1 factor was used to
determine the direction of the dislocation. Hips dislocated anteriorly while the patient was walking or standing with the hip extended, while hips dislocated posteriorly while the patient was sitting, bending at the waist, or hyperflexing the hip. Additional mechanical risk factors for dislocation included acetabular cup angles and hip length and offset on anteroposterior radiographs as well as abductor weakness
Fig. 4
Figs. 4-A and 4-B Standing and sitting lateral spine-pelvis-hip radiographs of a patient with a posterior dislocation (Case 12; Table II). Fig. 4-A Standing lateral radiograph showing a surgical fusion in lordosis indicated by a sacral slope (SS) of 38°. Fig. 4-B Sitting lateral radiograph showing a fused spine with a sacral slope of 39°, which means that the pelvis is fixed in anterior tilt; an acetabular cup that does not open, with a cup ante-inclination (AI) of 32° in both positions; and a femur in relative hyperflexion, indicated by a pelvic-femoral angle (PFA) of 102°, to compensate for a pelvis that does not tilt posteriorly during sitting. The sitting combined sagittal index (CSI) is low (134°: 32° 1 102°), which is predictive of anterior impingement.
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Fig. 5
Low anteroposterior pelvic radiograph illustrating how inclination, anteversion, and hip offset and length were measured. Inclination is angle ABC, formed by the interteardrop line and the long axis of the acetabular cup. Anteversion is assessed by measuring angle ABD and adding an additional 4°, as prior studies 29
have shown that an anteroposterior pelvic radiograph underestimates anteversion compared with an anteroposterior hip radiograph . Hip offset (line EF) is measured from the teardrop to a line drawn down the center of the femoral diaphysis. Hip length (line GH) is measured from the lesser trochanter to line EF.
(i.e., side-lying abduction strength)2,30,31. Several additional factors were assessed at the time of surgery, including interstitial capsular integrity, direction of instability, and presence of osseous impingement. Statistical Analysis Stata software (version 13.0; StataCorp) was used for all statistical analyses. A Student t test was used for continuous variables, and a Fisher exact test was used for categorical variables. A standard Pearson correlation coefficient was used to describe the relationship between the Dpelvic-femoral angle and Dsacral slope. A p value of 0.05 was used as a cutoff to determine significance, and the variance is standard error. Results Patient Cohort ine (45%) of the 20 patients had a late anterior dislocation (Table II); their mean age was 74.4 years (range, 65 to 82 years), and their mean BMI was 26.7 kg/m2 (range, 20.7 to 30.0 kg/m2). Eleven patients (55%) had a late posterior dislocation; their mean age was 67.8 years (range, 56 to 94 years), and their mean BMI was 26.2 kg/m2 (range, 20.3 to 32.4 kg/m2). The mean time after the primary surgery was 10.4 years (range, 2.2 to 17.9 years) for the anterior dislo-
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cations and 6.6 years (range, 1.2 to 13.0 years) for the posterior dislocations. All surgical revisions were performed through a posterior approach. Mechanical Factors Eighteen (90%) of the 20 patients with a late dislocation had spinopelvic abnormalities that contributed to the instability (Table II). One patient with an anterior dislocation (Case 9)
TABLE I Normal Spinopelvic Measurements* Range (deg)
Standing Sacral slope
Sitting
Difference Between Sitting and Standing
30-50
11-29
11-29
Pelvic-femoral angle
165-195
110-140
51-69
Cup ante-inclination
25-45
41-63
—
203-233
162-198
—
Combined sagittal index
*Established from 160 consecutive hips which underwent a 14 primary THA without evidence of subsequent hip instability .
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TABLE II Measurements from Anteroposterior Pelvic and Lateral Sitting and Standing Spine-Pelvis-Hip Radiographs of Patients Who Had a Late Dislocation >1 Year Following Primary THA Cup AnteInclination (deg)
Sacral Slope (deg) Case
Direction of Dislocation
Stand
Sit
Δ
Stand
Sit
Pelvic-Femoral Angle (deg) Stand
Sit
Δ
1
Anterior
32
32
0†
44
49
191
117
74†
2
Anterior
19†
17
2†
36
40†
201†
109†
92†
3
Anterior
28†
25
3†
47†
45
211†
125
86†
4
Anterior
14†
141
74†
5
Anterior
6
Anterior
7 8 9
3†
11
34
47
215†
17†
0†
17
54†
71†
202†
146†
56
15†
22†
17
34
55
188
126
62
Anterior
19†
24†
23
41
69†
197†
140
57
Anterior
28†
5†
23
36
56
202†
158†
44
Anterior
31
13
18
43
64†
198†
135
63
10
Posterior
34
36†
22†
45
47
197†
112
85†
11
Posterior
46
37†
9†
31
37†
187
111
76†
12
Posterior
38
39†
21†
32
32†
184
102†
82†
13
Posterior
28†
29
21†
40
45
194
124
70†
14
Posterior
30
21
9†
19†
30†
179†
111
68
15
Posterior
25†
15
10†
16†
28†
177†
114
63
16
Posterior
37
27
10†
29
36†
195
104†
91†
17
Posterior
24†
13
11
35
48
205†
148†
57
18
Posterior
32
17
15
35
50
202†
129
73†
19
Posterior
28†
12
16
36
51
197†
118
79†
20
Posterior
33
10†
23
38
54
189
112
77†
27.9
17.3
10.7
36.3
47.7
195.6
124.1
71.5
Standard deviation
8.2
13.2
8.3
8.8
12.0
9.8
15.9
12.8
Standard error
1.8
3.0
1.9
2.0
2.7
2.2
3.6
2.9
Average
*1 = loss of capsular integrity due to excessive polyethylene wear, 2 = abductor weakness, 3 = decreased hip length and offset, and 4 = prior lumbar fusion surgery. †Abnormal values.
and 1 with posterior dislocation (Case 18) had no evidence of spinopelvic imbalance. In addition to spinopelvic causes, cup anteversion of
