ACETABULAR REVISION
The custom triflange cup BUILD IT AND THEY WILL COME
G. P. Goodman, C. A. Engh Jr From Anderson Orthopaedic Research Institute
The custom triflange is a patient-specific implant for the treatment of severe bone loss in revision total hip arthroplasty (THA). Through a process of three-dimensional modelling and prototyping, a hydroxyapatite-coated component is created for acetabular reconstruction. There are seven level IV studies describing the clinical results of triflange components. The most common complications include dislocation and infection, although the rates of implant removal are low. Clinical results are promising given the challenging problem. We describe the design, manufacture and implantation process and review the clinical results, contrasting them to other methods of acetabular reconstruction in revision THA. Cite this article: Bone Joint J 2016;98-B(1 Suppl A):68–72.
G. P. Goodman, DO, Orthopaedic Surgeon C. A. Engh Jr, MD, Orthopaedic Surgeon Anderson Orthopaedic Institute, 2501 Parker’s Lane, Alexandria, Virginia 22306, USA. Correspondence should be sent to Dr C. A. E. Engh; e-mail:
[email protected] ©2016 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.98B1. 36354 $2.00 Bone Joint J 2016;98-B(1 Suppl A):68–72.
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The management of acetabular bone loss is a challenging problem in revision total hip arthroplasty (THA). The treatment of acetabular defects varies widely and depends on the size and amount of bone loss, the quality of remaining bone and ability to obtain fixation and the presence of intact acetabular columns and pelvic continuity. The incidence of Paprosky type 3B acetabular defects, or pelvic discontinuity, has been reported to be between 1% and 5% in patients undergoing revision THA.1-4 The goal of treatment for large acetabular defects or pelvic discontinuity is fixation with a stable acetabular construct, permitting healing of the discontinuity, and ultimately biological fixation of the acetabular component through osseointegration. Revision of the acetabular component in the context of bone loss can be accomplished through a variety of techniques including creating a high hip centre,5 using large hemispherical acetabular components,6 with or without structural allograft bone7-13 or porous metal augments, and cage or cup-cage reconstruction.14-16 Another option is the custom-designed titanium, porous or hydroxyapatite-coated acetabular component with ilial, ischial and pubic flanges, also known as the custom triflange. The custom triflange acetabular component has been advocated for severe acetabular defects (Paprosky 3B) and pelvic discontinuity, cases in which a porous-coated hemisphere will not be expected to result in a successful outcome. The three rigid flanges protruding from the cup provide areas of
contact with the intact bone of the ilium, ischium, and pubis. They also provide areas of screw fixation for initial rigid stability (Fig. 1). The objective of the triflange is to span the acetabular defect and obtain fixation to ilium and ischium with a third arm which rests on the pubis. One advantage to this construct is the ability to provide initial rigid stability until biological fixation is achieved through the implant coating.
Indications Indications for the use of custom triflange components in revision THA include: previous, failed, salvage reconstruction with cage or porous metal construct augments; large contained defects with possible discontinuity; known pelvic discontinuity and complex hips which have previously undergone repeated THA and with insufficient bone stock to reconstruct using other means.4 The design and production process. A critical difference between other acetabular reconstruction techniques and the use of a custom triflange component is the absolute requirement that difficult acetabular reconstructions and possible pelvic discontinuities are recognised before surgery, to facilitate design and production of the component. The authors use Paprosky’s acetabular defect classification and consider CT imaging of patients in whom a type 3 defect is found.1 Manufacturers of custom triflange implants typically have a specific CT protocol for use in these cases. Once imaging and sometimes a model device is available, the decision to proceed rests with CCJR SUPPLEMENT TO THE BONE & JOINT JOURNAL
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Fig. 1a
Fig. 1b
Photographs showing the a) front and b) back views of a custom triflange implant. Three rigid flanges protruding from the cup provide surfaces for contact with the intact bone of the ilium, ischium and pubis. The flanges also feature holes for screws to achieve initial rigid fixation. The backside has porous coating for long-term biologic fixation.
Fig. 2a
Fig. 2b
Fig. 3a
Fig. 3b
A computer generated three-dimensional reconstruction derived from a pre-operative CT scan illustrates the patient’s pelvis with the a) implant in place and b) pelvic defect with the implant removed.
Photographs of a three-dimensional hemipelvic model a) of an acetabular defect with areas marked in red indicating bony protuberances that need to be removed before insertion of the final implant and b) with removed bone and trial triflange component.
the surgeon. This decision is multifactorial and includes the acuity of the patient’s problem, individual surgeon experience, and treatment preference for large acetabular defects that are not easily treated with a porous coated acetabular hemisphere. The surgeon has to take into account the waiting time between the decision to proceed with surgery and when the custom implant will be available, which can often be four to eight weeks. The preparation and development of a custom triflange begins with the thin-cut CT scan sent to the manufacturer, where a one-to-one scale computer-generated threedimensional (3D) model of the hemipelvis is created (Fig. 2). Such models are substantially more accurate than plain radiographs for assessing acetabular defects and for surgical planning.17 The surgeon can review either an image file or an actual model of the hemipelvis. If the defect, after
scrutiny, is deemed one which cannot be treated with traditional methods, then a custom triflange component is created. Before the implant can be made, the surgeon must mark on the hemipelvic model areas of overhanging bone that can be removed to make it easier to insert the triflange. This is particularly important for bone that protrudes from the ilium, pubis, or ischium and would prevent the flanges from resting flush on these surfaces (Fig. 3). The surgeon must also mark the preferred size and location of the ilial and ischial flanges for screw fixation. The size of these flanges is a balance between the area required for fixation with multiple screws and the surgical exposure required to implant a device with large flanges. We suggest that those surgeons in doubt over where this balance lies in a specific case should consult the design engineers, who typically have designed and manufactured a number of these for dif-
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Fig. 4 Anteroposterior radiograph (1.7 months post-operatively) showing triflange with screw fixation and trochanteric osteotomy used for exposure.
ferent surgeons and hence can offer authoritative opinion. A prototype of the implant is created, along with a hemipelvic model with the specified areas of bone removed to permit the surgeon to evaluate the position and fit. The implant’s centre of hip rotation, anteversion, and inclination angles are created based on anatomic landmarks including the obturator foramen, iliac wing, and pubic ramus.18 The ischial flange typically has between four and six holes for screw fixation, while the larger ilial flange typically has two rows of three to four screw holes. The smallest flange, for the pubis, typically has no holes. After approval of the initial design, the final implant is created. Reverse engineering techniques are used to create the final component from the clay prototype, milling it from wrought titanium bar stock. Porous or hydroxyapatite coating is used on the medial side of the component to facilitate osteointegration. Surgical technique. A standard revision THA technique is used, paying attention to wide exposure of the ischium, ilium, and pubis in order to obtain an adequate view of the defect and the surfaces required for fixation. Visualisation of the ilium can sometimes be a challenging step of the surgical exposure and a trochanteric osteotomy can be performed to facilitate this. Exposure for placement of the ischial flange can be safely performed by subperiosteal elevation of the posterior aspect of the ischium. During this portion of the exposure, however, care must be taken to avoid injury to the sciatic nerve. A high-speed burr can be used to remove the areas of bone as marked on the pelvic model. The 3D pelvic model is typically used in the operating room and used intra-operatively
for comparison with the patient’s pelvis and to ensure proper alignment of the component. Fixation of the pubic flange requires subperiosteal elevation with meticulous avoidance of the anterior neurovascular structures. Fixation begins at the ischial flange and between nine and 15 screws are generally used to secure the implant. (Fig. 4). After fixation, trial polyethylene liners are then used to perform a trial reduction. The modularity of liners varies between companies and it is therefore important to know the available options pre-operatively. Lateralised, elevated, and constrained options are typically available to aid in achieving appropriate hip length, soft-tissue tensioning, and stability. Published results. Seven papers providing level IV evidence are presently available, which comprise retrospective case series of 19 to 78 patients. They range in follow-up from a mean of 31 months to 123 months (24 to 215). To our knowledge, there are no prospective trials comparing custom triflange revision to other forms of acetabular reconstruction for the treatment of Paprosky 3A/3B or AAOS Type-III or IV defects. The results of published series are summarised in Table I.19-23 The rates of complications in the studies varied. Instability was the most common complication, with an incidence ranging from 0% to 30%. Rates of infection were reported to range from 0% to 8%. Injury to the superior gluteal and sciatic nerves was also described. Taunton et al18 compared the cost of custom triflange implants with a trabecular metal cup-cage construct equivalent and found implant costs to be similar at $12 500 and $11 250, respectively. CCJR SUPPLEMENT TO THE BONE & JOINT JOURNAL
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Table I. Review of case series of custom triflanges Reference
Number of hips Type of defect
Mean follow-up (mths) Clinical results
Dislocations (n, %)
Triflange removal Aseptic loosening (n, %) (n, %)
4 18 23 19
24 57 78 26
57 76 53 54
Post-op HHS score 65 Post-op HHS score 74.8 Post-op HHS score 82.1 Post-op HHS score 78
0 (0) 12 (21) 12 (15.6) 2 (7)
2 infections 3 (5.3) 0 (0) 0 (0)
0 (0) 1 (1.8) 0 (0) 3 (11.5)
20 21
20 27
123 58
0 (0) 1 (3.7)
0 (0) 0 (0)
22
19
Post-op HHS score 80 6 (30) Modified Merle d’Aubigne 1 (3.7) and Postel 5.3 Post-op HHS score 63 5 (26)
2 (11)
1 (5.5)
Paprosky Type 3B Pelvic Discontinuity AAOS Types III/IV Paprosky Type 3B and AAOS Types III/IV Pelvic Discontinuity AAOS Type III Paprosky Types 3A/3B and AAOS Types III/IV
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Post-op, post-operative; HHS, Harris hip score; AAOS, American Academy of Orthopaedic Surgeons
Table II. Comparison with other techniques of revision total hip arthroplasty Reference No. hips Type of defect
Mean follow-up (mths) Clinical results
Implant removal Dislocations (n, %) (n, %)
Aseptic loosening (n, %)
26 27
38 33
Winter et al 2003 AAOS III and IV
88 6.2
1 (2.6) 3 (9)
0 (0) 4 (12)
2 (5.2) 3 (10)
28 14
18 42
Pelvic discontinuity AAOS III
13.5 5
2 (11) 1 (2.4)
3 (16.7) 12 (28.5)
2 (11) 5 (12)
3 24
26 28
Pelvic discontinuity Paprosky IIIa
44 37
2 (7.6) 1 (3.5)
0 (0)
3 (11.5) 0 (0)
25
97
Paprosky IIIa & IIIb
45
HHS 82.6 post-op Merle d’Aubigne and Postel improved by 9.3 HHS 31.9 to 77.0 Merle d’Aubigne and Postel improved HHS 46.6 to 76.6 Merle d’Aubigne and Postel improved from 6.8 to 10.6 HHS improved from 55 to 76
7 (7.2)
8 (8.2) all for infection
0 (0)
HHS, Harris hip score; AAOS, American Academy of Orthopaedic Surgeons
The results of the custom triflange are compared with other reconstructive options in Table II; these techniques include porous metal augments,24,25 cage reconstruction26-28,14 and cup-cage constructs.3
Discussion The primary disadvantages of this technique are the complexity of the pre-operative planning process and the time required to manufacture the device. This disadvantage is, however, overcome by the relatively uncomplicated surgical technique without the need to shape, fit, or fix allograft or to bend and fix cages, cups, or augments.23 Such a solution does, however, require perfect design prior to surgery, as the implant cannot be modified intra-operatively. The triflange cup provides a viable solution for difficult acetabular reconstructions involving severe bone loss or pelvic discontinuity. By achieving stable and rigid initial implant fixation on host bone, through its ability to re-distribute load anatomically, its restoration of the native hip centre, and its ability to support osseointegration, the triflange cup accomplishes the major goals of reconstruction.23 VOL. 98-B, No. 1, JANUARY 2016
Author contributions: G. P. Goodman: Writing the paper. C. A. Engh Jr: Writing the paper. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. This article was primary edited by P. Page. This paper is based on a study which was presented at the 31st Annual Winter 2014 Current Concepts in Joint Replacement® meeting held in Orlando, Florida, 10th-13th December.
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