Custom Triflange Implants
Matthew W. Tetreault
Michael J. Taunton
Custom triflange acetabular components provide a unique solution for bridging large acetabular defects that exceed the limits of defect-matching techniques.
These implants possess the strength to provide long-term stability without underlying support, the potential for biologic fixation, and the ability to address specific bony defects and pelvic anatomy.
Collaboration between the surgeon and implant design team is paramount during preoperative planning because intraoperative flexibility is limited.
A minimum of several weeks is required for implant design and fabrication.
Sterile Instruments and Implants
Routine hip retractors
A full set of revision total hip arthroplasty (THA) instruments, including:
Cup explant system
Femoral component explant system
High-speed burrs (short and long pencil-tip burrs, 6.5-mm round burr)
Osteotomes (straight, curved, flexible)
Cement removal set/instruments to clean out intramedullary canal
Drill, drill bits, threaded drill guides, depth gauge
In the event of a trochanteric osteotomy:
Cabling device/wire passers (also for prophylactic use during femoral component revision)
Sterilized models of the hemipelvis and triflange implant
Custom triflange acetabular component and liner
Custom triflange screws
Femoral heads (with trial heads)
Revision femoral components (with trial stems)
Cerclage cables and wires
Allograft bone chips
Lateral decubitus with hip positioners
The operative limb should be draped out and sterilely prepared from the iliac crest to the distal thigh.
The authors typically prefer an extensile posterolateral approach, although an extensile anterolateral or transtrochanteric approach may be used.
A trochanteric osteotomy can facilitate femoral component removal and/or relieve tension when exposure for the iliac flange would risk traction injury to the superior gluteal nerve.
Obtaining the outside operative report and implant stickers is essential.
Assess for infection preoperatively with inflammatory markers and fluoroscopically guided hip aspiration as indicated.
Preoperative imaging is imperative and includes the following:
Anteroposterior (AP) pelvic radiograph
AP hip radiograph
Cross-table lateral hip radiograph
Judet radiographs (obturator and iliac oblique views)
Thin-slice computed tomography (CT) scan with 3-dimensional (3D) reconstruction
The above-mentioned imaging should be used to determine the extent of acetabular bone loss, including the presence and stability of a pelvic discontinuity (separation of the ilium from the ischiopubic segment), as well as the quantity and location of remaining host bone. This imaging also allows for the precise identification of in situ hardware.
If severe protrusion of the acetabular implant is present, CT angiography may be ordered to assess existing implant proximity to intrapelvic vessels. If vascular structures are at risk, preoperative evaluation by a vascular surgeon (who can be on standby at the time of surgery in the event of vascular compromise) is warranted. Very rarely, a retroperitoneal exposure is indicated to free the intrapelvic structures before implant removal.
A custom triflange cup is appropriate for cases of severe acetabular bone loss that exceed the limits of defect-matching techniques whereby the acetabulum can be filled with a larger hemispherical cup or by an augment to achieve stability on host bone (Figure 28.1A-C).
Indications for a custom triflange cup include selected American Academy of Orthopaedic Surgeons (AAOS) type III combined acetabular defects (or Paprosky 3A or 3B defects1) and selected (or in the hands of some surgeon, all) type IV defects (pelvic discontinuities).2
In the setting of a pelvic discontinuity (Figure 28.2A and B), there are 2 simultaneous goals:
Long-term acetabular component stability
Healing across the bony discontinuity or “unitization” of the pelvis through healing of both the superior and inferior pelvis to the cup construct
Contemporary reconstruction options for chronic pelvic discontinuities are detailed in Section II-D, Chapter 6. A custom triflange acetabular component is one solution for bridging a large acetabular defect, as the flanges are strong enough for long-term stability without underlying support and also allow for biologic ingrowth on host iliac and ischial bone (Figure 28.3A and B).
For design and production of a custom triflange component, a CT scan of the pelvis with metal subtraction software is needed. Requisite CT specifications should be discussed in advance with the
implant manufacturer. Three-dimensional (computer and plastic) models of the pelvis and implant are created for review by the surgeon (Figure 28.4A-C). This includes assessment of head center, cup orientation, size and location of the flanges, and trajectory and length of the screws.
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