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