- See:
Total Hip Replacement Menu:
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acetabular components
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acetabular component position:
- Discussion:
- occurs in 1-4% of primary THA and upto 16% in revision cases;
- about 74% of THR dislocations are posterior, 16% anterior, and 8% lateral; (from T.K. Cobb et al, 1996);
- most commonly caused by looseness of hip (improper neck length), and component malposition (see
acetabular component position);
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revision arthroplasty:
- dislocation is much more common in revision THA;
- careful testing w/ trial components w/ correction of neck lengths w/ correction of neck length, impingement, &
repair of trochanter may avoid this complication;
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acetabular liner:
- as noted by Cobb et al 1996, the presence of a high wall liner can reduce the incidence of dislocation in
primary THR from about 3.8% to 2.2%
- the beneficial effect is probably higher w/ revision surgery;
- paradoxically, the high wall liner may actually increase the incidence of anterior dislocation (due to impingement between
femoral neck and the elevated lip of the liner);
- liners may also contribute to increased
polyethylene wear;
- Differential Dx:
- patient risk factors:
- excessive alcohol intake (dislocation of upto 20 %);
- in patients w/ DDH, risk of dislocation may be as high as 8%;
- positional dislocations:
- components are positioned correctly & soft tissues are balanced;
- patient puts the hip into a position that is beyond the range possible w/ prosthetic components;
- soft tisse laxity:
- shortening in either verticle or horizontal direction causes soft tissue imbalance, possibly resulting in dislocation;
- radiographs should be evaluated for limb length inequaility;
- late dislocation may be related to gradual stretching of pseudocapsule;
- laxity of soft tissue is most frequent cause of instability of THR when radiographs reveal good position of components;
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trochanteric non union is another risk factor for dislocation because of soft tissue tension;
- component malposition: (
acetabular component position)
- safe position: 35 +/- 10 deg anteversion 40 +/- 10 deg abduction
- acetabular abduction angle
- horizontal cup placement (less than 40 deg) may lead to early impingement in flexion;
- in this case there is impingement between neck and poly liner;
- result can cause osteolysis, liner dislodgement, and component loosening;
- version of acetabulum (true lateral view)
- anteversion is determination directly by measuring angle between line drawn thru axis of metal shell
or wire marker & verticle on cross table lateral view of acetabulum;
- unnoticed forward rotation of pelvis when surgical procedure is done in lateral postion is one cause
of malalignment of component that can result in an unnoticed retroversion position of cup;
- version of femoral component;
- references:
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Factors predisposing to dislocation after primary total hip arthroplasty.
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The Effect of the Orientation of the Acetabular and Femoral Components on the Range of Motion of the Hip at Different Head-Neck Ratios.
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Joint motion and surface contact area related to component position in total hip arthroplasty.
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Computed tomographic evaluation of component position on dislocation after total hip arthroplasty.
- componenet impingement:
- posterior dislocation may be caused by anterior osteophytes which protrude beyond the edge of the acetabular cup;
- anterior dislocation may be partially due to the presence of a high wall liner placed posteriorly;
- overmedialization of the cup:
- more common in
protrusio
- overmedialization causes impingement of the femoral neck on the pelvis
- management of this situation may involve use of a lateralized liner (high wall liner will not help this);
- horizontal cup placement (less than 40 deg) may lead to early impingement in flexion;
- in this case there is impingement between neck and poly liner;
- result can cause osteolysis, liner dislodgement, and component loosening;
- acetabular occupancy:
- cause of dislocation in RR, & once hip is rereduced, hip is stable;
- femoral head size:
- smaller diameter head (22 mm) allow less stress/torque but may result in increased central acetabular wear and dislocation;
- larger head sizes (upto 32 mm) allow increased ROM and reduced dislocation, but have less net wall thickness for long term wear;
- 26-28 mm heads appear to be ideal compromise & are most commonly used;
- references:
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Independent contribution of elevated-rim acetabular liner and femoral head size to the stability of total hip implants.
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Relationship of femoral head and acetabular size to the prevalence of dislocation.
- component subsidence:
- limb length shortening is a known cause of dislocation;
- lateral / medial offset:
- lateralized femoral stem may be used to restore stability, but this may increase component micromotion;
- ref:
Micromotion measurements with hip center and modular neck length alterations.
- Assessment:
- need to review operative note for specific details about hip stability;
- flouroscopy to determine range of hip stability and to determine whether any of the components
are loose (femoral component, acetabular cup, and acetabular liner);
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exam: neurovascular exam before and after the reduction;
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posterior dislocation
- caused by flexion, adduction, and internal rotation;
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anterior dislocation
- caused by extension, adduction, and external rotation;
- in the example below, the patient sustained an anterior dislocation in the RR;
- it was felt that the dislocation occurred as a result of performing a partial anterior capsulotomy in addition
to the lingering effects of the spinal anesthetic;
- he was placed in a bledsoe brace, which held the hip in 30 deg flexion;
- Reduction Maneuver: (Havard Technique)
- typically the patient will be placed on a flouro bed (if one is available);
- an assistant stands near the patients head, and provides downward traction on the pelvis;
- the surgeon should step up onto the bed, standing over the patient;
- grasp the patient's leg between the surgeon's arm and armpit, leaving both hands free to grasps the knee;
- the surgeon uses his/her legs to effect an appropriate amount of traction, while the surgeon uses his hands to internally and externally rotate
the hip (as directed by the flouroscopic picture) inorder to guide the hip into a reduced position;
- Treatment Options:
- treatment depends on the etiology of the dislocation;
- if alcoholism was related to the dislocation then education and bracing are necessary;
- if component mal-positioning or gluteus medius laxity are present, then these may need to be managed operatively;
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simple closed reduction:
- in general, if more than 2 dislocations have occurred, revision surgery should be considered;
- if a dislocation occurs late after surgery, then consider surgery as recurrent dislocations can be expected;
- ref:
Late Dislocation After Total Hip Arthroplasty.
- in the report by
E. Li MD et al 2000, the authors followed a total of 1,036 consecutive total hip replacements between 1989 and 1992;
- 40 (3.9%) were known to have dislocated posteriorly (24 of these dislocations occurred after primary replacements, and 16 occurred after revision);
- 85 % of the dislocations occurred within 2 months and were reduced closed;
- 23 of the 40 dislocated hips (57.5%) redislocated
- 16 of the 40 hips (40%) required reoperation for recurrent dislocation;
- ref:
The Natural History of a Posteriorly Dislocated Total Hip Replacement
Emile Li, MD, John B. Meding, MD, Merrill A. Ritter, MD, E. Michael Keating, MD, and Philip M. Faris, MD
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modular revision:
- ref:
Modular revision for recurrent dislocation of primary or revision total hip arthroplasty.
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trochanteric advancement:
- may be indicated if options for increased neck length are not present;
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revision total hip replacement:
- femoral component revision: increased lateral offset can be achieved by increasing neck length;
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acetabular component revision
- increased anteversion (if posterior dislocation is present);
- increased lateral offset (using lateralized liner);
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constrained acetabular liner component:
- is especially indicated when other treament methods are not effective;
- specific indications include significant extremity shortening, significant extremity shortening, multidirectional instability, recurrent instability
following revision, neurologic disorder;
- osteonics constrained acetabular component:
- consists of a polyethylene socket w/ an inner diameter of 22 or 28 mm and a bipolar type locking ring;
- socket is covered by a metal shell, which in turn is covered by an outer polyethylene socket;
- the component can be snapped into an osteonics acetabular component (if 52 mm or more) or can be cemented into an acetabular shell made by another manufacturer;
- complications:
- fatigue fracture of the constraining ring (due to chronic impingement of the constraining ring against the neck of the femoral component;
- dislocation following the insertion of a constrained liner will require open reduction;
- references:
- Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular liner. A retrospective analysis of 56 cases. DD Goetz et al.
JBJS Vol 80-A. No 4. Apr 1988. p 502.
- Failure of a constrained acetabular prosthesis of a total hip arthroplasty.
A report of four cases. BP Kaper and PM Bernini.
JBJS Vol 80-A. No 4. Apr 1988. p 561.
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Bipolar Hip Arthroplasty as a Salvage Treatment for Instability of the Hip
- in the report by J. Parvizi and BF Morrey (J Bone Joint Surg [Am] 82-A: 1132-9, 2000), reviewed the records
of 27 patients who had undergone bipolar hip arthroplasty as a salvage procedure for the treatment of recurrent instability
of the hip after total hip replacement;
- all patients had undergone at least two, and a mean of three, stabilizing operative procedures
on the hip prior to the bipolar arthroplasty.
- the mean duration of follow-up was five years (range, two to twelve years), with no patient lost to follow-up;
- bipolar arthroplasty prevented redislocation in twenty-two hips (81 %);
- 25 patients (93 %) had a stable hip at the time of last followup;
- complications: revision because of disassembly of the cup in one hip, revision bipolar arthroplasty because of continuing
instability in two, resection arthroplasty because of deep infection in two, revision arthroplasty because of recalcitrant
groin pain in one, and revision arthroplasty because of deep infection and superior migration of the implant in one;
- 12 patients in our study had hip pain, and two had severe groin pain;
1990 Proceedings of The Hip Society--Symposium: Dislocation After Total Hip Arthroplasty: Causes and Prevention.
Late dislocations in patients with Charnley total hip arthroplasty.
Position, orientation and component interaction in dislocation of the total hip prosthesis.
Bipolar hip arthroplasty for recurrent dislocation after total hip arthroplasty. A report of three cases.
Dislocations after total hip arthroplasty.
The Elevated Rim Acetabular Liner in Total Hip Arthroplasty. Relationship to Postoperative Dislocation.
T.K Cobb, B.F. Morrey, and D.M. Ilstrup
JBJS Vol 78-A No 1 Jan 1996.
Dislocation After Revision Total Hip Arthroplasty An Analysis of Risk Factors and Treatment Options;
Hospital Cost of Dislocation After Primary Total Hip Arthroplasty.
