Trilogy-Constrained Acetabular Component for Recurrent Dislocation

32 patients received a Trilogy- or Trilogy-Longevity-constrained acetabular liner for recurrent dislocations after total hip replacement. The constrained liner was inserted into a well-fixed Trilogy acetabular shell with snap fit. At 1.8-year followup (range 3–63 months), 4 patients had suffered further dislocation(s) (12%), and one patient had revision surgery for a loosened acetabular shell. Radiologic evaluation detected no definitively loose components, but one patient with progressing radiolucent lines around the femoral component and one patient with an acetabular cyst were found, as well as a patient with a loose locking ring (but otherwise no failure). The nineteen patients who were available for the present followup had a mean Harris Hip Score of 81. The constrained liner is an effective method of dealing with recurrent dislocations in well-fixed components.


Introduction
Dislocation remains one of the most common complications aer primary and especially revision hip arthroplasty. e rate of dislocation is in�uenced by many different factors and ranges between 0.3 and 10% in primary arthroplasty [1][2][3][4][5] and between 4 and 28% aer revision arthroplasty [1][2][3][4]. e incidence varies greatly in different studies with a much higher risk for patients with neuromuscular disease or lack of compliance resulting from dementia or substance abuse [1,2]. However, the rate of recurring dislocations has also been associated with surgical approach (including so tissue repair) [6], surgical volume [4], and choice of implant [2].
Many different methods have been used to solve the problem, both nonoperative and surgical methods. Nonoperative in the form of different kinds of immobilizing devices. Surgically by repositioning malpositioned components, inserting jumbo or bipolar heads, or longer necks and last but not least by using a constrained liner [1][2][3].
None of the methods mentioned above have been without complications. e use of different kinds/brands of constrained liners has been reported with mixed results. We report on the use of the Trilogy constrained liner (Trilogy and Trilogy Longevity) in a consecutive series of patients operated on because of recurrent dislocations.

Materials and Methods
We performed a retrospective review of all patients treated with a Trilogy constrained liner in the Hip Clinic Hørsholm Hospital, Denmark, in the period 2005-2009. e cohort comprised 38 patients all treated with a constrained acetabular insert because of recurrent dislocations (average 4.6 dislocations; range (1-10)), one was treated twice. e patients were identi�ed by searching the electronic database for all revision hip arthroplasties. All these patients were reviewed and the ones who were revised using a constrained liner were included in the present study.
Of these patients, a number had to be excluded. Five patients were �tted with another brand of constrained liner and one emigrated and was lost to followup. at le 32 patients all with Bimetric femoral components and the Trilogy acetabular cup. e constrained liners used were either Trilogy (TC) (21 hips) or Trilogy Longevity (TL) (12 hips) (see Figures 1 and 2).  e 32 patients included 24 females and 8 males, 20 right hips (1 hip counts twice), and 13 le hips. e average age at constrained liner insertion was 74 years (range 46-86).
e primary diagnosis in the majority of cases was arthrosis (88%); the rest had avascular necrosis following internal �xation of a femoral neck fracture (12%). (for data on the groups divided by type of liner, see Table 1).
In addition to the hip problems, 3 patients suffered from dementia and 2 had an ongoing problem with alcohol abuse. No patients with neuromuscular disease were registered (5 patients were undetermined regarding the above-mentioned problems).
e patients were all operated through the posterolateral approach by one of the department's 4 senior surgeons. During surgery both stem and cup were tested. In all but one patient, both cup and stem were found to be well �xed. One patient had a loose stem, which was revised during the same procedure. e patients were mobilized using standard precautions (no adduction, no inward rotation, and no �exion past 90 degrees for the �rst 3 months).
At the time of followup, 7 patients had died. ree further patients had had additional surgery and had their constrained liner removed for different reasons (they were included in the study but not seen at followup). e rest of the patients were invited to a clinical examination including radiographs of the relevant hip. e radiographs were evaluated for loosening de�ned as migration of the components or progressive radiolucent lines. e average followup was 26 and 15 months for the Trilogy (range 2-63) and Trilogy longevity (range 4-26), respectively. Of the patients still alive, 3 were not seen for followup due to other health issues and personal obligations. e �rst two patients were interviewed over the phone; the third patient was not available for interviewing.
Twenty-three patients had only one previous surgical procedure (THA), 8 had been operated twice, and a single patient had 3 previous procedures. In addition to the primary THA's, the previous procedures were osteosynthesis of a femoral neck fracture (13%), revisions to treat dislocations (repositioning of cup and lengthening of the neck) (13%), one periprosthetic fracture (3%), one revision because of infection (3%), and one patient had the constrained liner replaced because of failure and another constrained liner inserted (3%) (For data on the groups divided by type of liner see Tables 2 and 3).

Results
Four patients had suffered from one to four further dislocations (12%), three patients with a Trilogy constrained liner, and 1 patient with a Trilogy longevity constrained liner. Two of these were also debrided due to deep infection. One patient had the acetabular shell revised because of loosening (TC), and 2 other patients had debridement with head and liner change because of infection. us a total of 7 (21%) patients had 15 additional procedures including closed reductions.
An additional patient has a loose locking ring but has not had any dislocations.
e time from insertion of the constrained liner to dislocation averaged 24 months.
18 patients were seen for the followup including radiographs and one only for additional radiographs. No migration was seen in any patients; one patient had a slight progression of radiolucent lines at the femoral component. One patient had a small cyst in the lateral part of the acetabulum suggesting osteolysis. e patients who for various reasons were not seen for the present followup had been seen previously 2-15 months postoperatively. Apart from the already noted failures no migration or progression of radiolucent lines was found.  e patients that were seen for followup had an average Harris Hip Score (HHS) of 81.
In the group of patients who suffered further dislocations despite the constrained liner, one suffered from dementia and one had a problem with alcohol abuse.
No difference between the TC liner and the TL in any of parameters investigated could be demonstrated.
In addition to different kinds of liners, the indication for insertion of a constrained liner differs as well. We inserted constrained liners as a measure to prevent further dislocations in patients with repeated dislocations, and the constrained liner has not been used in primary surgery in the present series. Some of the published papers deal with a similar material [13,14,17,22,29], the rest of the published data are on a more diverse group of patients with indications varying from repeated dislocations or intraoperative instability (both primary procedures and revisions) to neurologic impairment and revision procedures on patients with Girdlestone status [9-11, 15, 16, 18-21, 23-25, 27, 28].
Equally important is the rate of "failure" of the constrained liner. is includes not only the dislocations and dissociations, and the breakage of different parts of the liner, but also shells that are pulled out because of increased stress, and revisions because of loosening of the acetabular shell. Failure rates of 5.3%, 5.8%, 14.7%, and 10% have been described [14,17,22,29]. In our material in addition to the dislocations, one locking ring failed (without dislocation), and one acetabular shell was loose. No other failures were registered, probably because the constrained liner only had been used in well-�xed acetabular shells.
e rate of redislocation was 12% and the total failure rate (including loosening of the acetabular shell and loosening of the ring) was 18%.

Conclusion
e constrained liner has in the present material been used only as a salvage procedure in a population of patients with recurrent dislocations, which might explain the rather high rate of failure. Furthermore, patients with conditions predisposing to hip-dislocation also seemed to be at a higher risk for subsequent failure of the constrained liner.
However, 88% of the patients had no further dislocations or loosening of the implant, and no better solution in this group of patients seems available at present.
We continue to use this method as a salvage measure for patients with recurring dislocations and well-positioned and well-�xed components.

Con�ic� of �n�eres�s
e authors have no con�ict of interests.