Dislocation after Total Hip Replacement
Etiology and management
Pekka YlinenORTON/ Invalid Foundation
Dislocation
leaves a patient apprehensive tarnishes a surgeons reputation cause extra cost to health care system
Dislocation
incidence risk factors (patient, surgical, implant) diagnosis principles of treatment case presentations
Dislocation after THR
overall incidence 2-3% (0,4-11%) in elderly (even 4% if older than 80 y) females ( f:m ~ 2:1) in revision 10-20%
Dislocation after THR
Patient factors age female gender prior surgery DDH, prior fracture neuromuscular disorders dementia low grade infection alcohol abuse
Dislocation after THR
Surgical factors component malpositioning offset not restored failure to preserve abductor mechanism
leg length not restored posterior approach
Risk factors
bilaterality weight leg length difference
suspected:
Dislocation after THR
Implant factors neck design
- neck cross section- offset- Morse taper length
small head skirted head std. acetabular design vs. elevated cup wall
skirt
poor head-neckratio
greatest risk within the first few weeks after op. - 60%-80% occur in three months- component malorientation
late instability- 23% after one year, 14 % after 5 years- loss of soft tissue integrity
Dislocation after THR
Dislocation rate vs. head size and surgical approach
Position 22 mm 28 mm 32 mm
Anterior 2,6% 1,3% 2,1%
Posterior 6,8% 6,0% 3,5%
Woo, Morrey JBJS (Am) 64:1295, 1982
Dislocation after THR
Rates according to surgeon volume
1-5/year 4,2 % 6-10/year 3,4 % 11-25/year 2,6 % 26-50/year 2,4 % > 50/year 1,5 %
JBJS (Am) 83:1622, 2001
Surgical approach and THR dislocation
controversial according to literature - quality of orthopaedic literature recarding
THR dislocation is limited
- no prospective studies of sufficient power exist
14 articles fulfilling 5 to 8 inclusion criteria:
- 3,23% for the posterior approach- 0,55% for the direct lateral approach
Clin Orthop 405, 2002
Treatment
modular component exchange trochanteric advancement bipolar rearthroplasty jumbo femoral heads constrained acetabular components
For patients who do not have malpositioning of the components or abductor dysfunction increasing neck lenth increasing femoral head size using more lipped and/or reoriented liners
Modular component exchange
be aware about - malposition- impingement
?
Effectiveness of Modular component exchange*
Author N Follow-up
(years)
Success (%)
Toomey et al. JBJS 2001
13 5,8 77
McGann and WelchJ Arthroplasty 2001
26 3,6 96
Earll et al.J Arthroplasty 2002
29 4,6 69
* without implant malpositioning
Trochanteric advancement
in monobloc implants without option to increase neck length proximal migration of fractured or ununited trochanter
Bipolar rearthoplasty
good in gaining stability (~ 80%) bad in functional outcome due to articulation with exposed acetabular bone
JBJS (Am) 82:1132,2001
Jumbo femoral heads
maximal head to neck ratio minimizes implant impingement 32 mm
- acetabular component size - thickness of the polyethylene
36-38 mm ? tripolar arthroplasty
Constrained acetabular components
restricted range of motion and impingement thin polyethylene outcome maybe implant dependent? - Osteonics: loosening 2%
dislocations 4% J JBJS (Am) 80:502, 1998
- S-Rom: loosening 4% dislocations 9-29% J Arthroplasty 9:17,325, 1994
Treatment strategy
Unstable THR
Implant malposition Implant in good position
Revise Impingement Abductor dysfunction
Modular exhangeLipped polyAnterverted polyLateralized poly
laxity non-union incompetent
Longer neckTrochantericadvancement
Refixation Constrained cup
Large head
Treatment strategy
Pathology Surgical plan
Acetabular malposition
Revision
Rim augmentation
Femoral malposition Revision
Loss of tissue integrity
Trochanteric advancement
Constrained implant
Not defined
Constrained
implant
First dislocation: treatment strategy
identify the direction of instability determine the cup orientation with C-arc cup orientation acceptable, one-half hip brace for 6 to 8 weeks anterior dislocation: cup in 20° - 30° anteversion, one half hip brace for 6-8 weeks posterior dislocation: cup in retroversion, cup revision
Cup orientation
direct ap-view:if anterior and posterior rims are coincident the orientation is about 6° in anteversion
Cup orientation
Cup orientation
45°
Cup orientation
the position of C-arcwhen the anterior and posterior rims are coincident shows the cup orientation
female 60 years, mild right hemiparesis
C-arc fluoroscope
x-rays (C-arc) vertical X-rays (C-arc) 13° to 15° anteverted
male, 58 years
trochanteric advancement
Constrained liner
Prevention on hip dislocation
identify patient at risk restore femoral head offset larger femoral head restore leg length proper postoperative care