Custom Triflanged Devices in the Revision AAcetabulum

 

INDICATIONS

With massive bone loss, these custom devices allow acetabular component placement at the correct anatomic level to restore hip biomechanics and stability. The decision to use a custom triflanged acetabular component (CTAC) must be determined preoperatively.

Periacetabular bone loss that precludes the ability to obtain a stable acetabular reconstruction with a traditional hemispheric cup defect-matching technique

Paprosky 3B (1) (Table 25-1) AAOS III and IV (2) (Table 25-2)

 

 

CONTRAINDICATIONS

Absolute

Persistent infection

Relative

Presence of adequate host bone

Inability to obtain screw fixation secondary to bone deficiency

Massive bone loss associated with pelvic discontinuity without pelvic stabilization (column plating)

 

 

 

 

 

 

 

PREOPERATIVE PREPARATION

History Reason for initial arthroplasty Postoperative complications (wound issues, infection, previous arthroplasty failures)     2
	TABLE 25-1 Paprosky Classification of Acetabular Defects
		Type Description
		1 Columns intact Hemisphere intact   >70% of prosthesis can be in contact with host bone.

	2A Columns intact Defect below superior dome Migration of head center <2 cm No ischial or tear drop lysis Kohler line intact   2B Columns intact Superior lateral migration creating dome defect Migration of head center <2 cm Minimal ischial lysis Kohler's line intact   2C Columns intact Medial wall defect Medial migration with minimal superior migration of head center   3A Columns intact Severe superior lateral migration creating >50% dome defect Migration of head center >2 cm Kohler's line intact   3B Posterior column deficient Severe superior medial migration Severe ischial lysis Kohler's line broken Possible pelvic discontinuity

 

TABLE 25-2 AAOS Classification of Acetabular Defects

Type Description

I

No significant bone loss

II

Columns and rim intact

Contained cavitary loss

III

Columns may be deficient

Uncontained defect involving <50% of acetabulum

IV

Columns deficient

Uncontained defect involving >50% of acetabulum

Pelvic discontinuity may be present.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Physical Examination

Previous incisions Leg lengths

Motor—particularly the function of the abductor musculature and sciatic nerve distribution

 

 

Infection Workup

 

Traditional—ESR, CRP, and hip aspiration (if indicated)

 

Supplemental testing—leukocyte esterase (3), synovial CRP (4,5), and IL-6 (6)

 

 

 

Previous Operative Records Complications or unusual techniques Type, size, and fixation of current implants

 

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Plain Radiographs

 

Anteroposterior (AP) view of the pelvis.

 

 

Judet and inlet/outlet pelvic views may be helpful in classifying bone loss and determining the presence of pelvic discontinuity.

 

AP and lateral views of the hip capturing the entire prosthesis.

 

Full-length orthoroentgenograms may be necessary for preoperative leg length assessment if significant asymmetry is observed.

 

A preoperative anteroposterior radiograph with traction applied to the operative limb may be helpful to assess laxity of the hip and subsequent determination of where the hip center of the CTAC should be placed.

 

Computed Tomography

 

Metal subtraction techniques allow evaluation of osseous defects more precisely (Fig. 25-1A, B).

 

Specific computed tomography (CT) scan protocols are required for the production of CTAC and should be ordered as such to avoid subjecting the patient to multiple CT scans.

 

If severe acetabular component protrusion is present, a CT scan with a concomitant angiogram may be required

(7). This aids in determining whether intrapelvic vessels or visceral structures are in close proximity to the failed acetabular component. In these cases, a preoperative vascular surgery consultation and consideration of a retroperitoneal exposure to free vital intrapelvic structures from the acetabular component may be warranted.

 

 

 

FIGURE 25-1 A: Anteroposterior radiograph of a failed THA with acetabular component loosening and massive periacetabular bone loss. B: Three-dimensional images created from a thin cut CT scan demonstrating severe acetabulae protrusio and a Paprosky 3B acetabular defect. (From Johnson DR, Dennis DA, Kim RH. Acetabular revision: rings/cages/custom implants. In: Berry DJ, Lieberman JR, eds. Surgery of the Hip. Elsevier; 2013.)

 

Component Design

 

The design phase of the CTAC is a critical step. Because the implants are custom made, surgeon input on anticipated further bone removal, hip center, the size and location of the flanged prosthesis, and cup orientation is needed preoperatively. These design decisions have great importance because aside from modular inserts, there are no possible alterations during surgery. The following general steps are utilized to create a custom implant (Fig. 25-2A-G):

 

Plain radiographs

 

Thin cut CT (no greater than 3 mm) with metal subtraction

 

Manufacturer creates three-dimensional (3D) images and a one-to-one computer-aided design (CAD) solid model of the hemipelvis. This model allows for accurate assessment of bone loss and remaining pelvic bone and is utilized to facilitate the design of the CTAC.

 

 

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FIGURE 25-2 Preoperative anteroposterior (A) and lateral (B) radiographs demonstrating a failed THA with acetabular component migration and massive periacetabular bone loss. Three-dimensional anteroposterior (C) and lateral (D) images demonstrating severe acetabulae protrusio and a Paprosky 3B acetabular defect. E: Photographs of a one-to-one CAD model of a hemipelvis demonstrating marked periacetabular bone loss along with the acrylic CTAC model designed for the acetabular reconstruction.

 

 

 

 

 

 

FIGURE 25-2 (Continued) Postoperative anteroposterior (F) and lateral (G) radiographs following reconstruction with a CTAC. (From Johnson DR, Dennis DA, Kim RH. Acetabular revision: rings/cages/custom implants. In: Berry DJ, Lieberman JR, eds. Surgery of the Hip. Elsevier; 2013.)

 

 

The surgeon and the design engineer use the 3D model to create a prototype of the CTAC.

 

The surgeon manipulates the prototype within the 3D hemipelvis and makes recommendations to the design engineer regarding cup orientation, the hip center, and the number and position of the flange fixation screws.

 

These models can be sterilized and used intraoperatively as a trial component to assess position and fit if needed.

 

General Design Considerations

The position of the hip center is determined by many patient-specific considerations, including leg length discrepancy, planned retention or revision of the femoral component, length of the contralateral leg, and the size of the current acetabular component. Serving as an approximate anatomic reference, the superior aspect of the obturator foramen is used to determine the vertical head center location. The remaining bone from the anterior and posterior columns determines the head center in the coronal plane. The sagittal plane head center is from the flange geometry and component face diameter. We have found the contralateral hip center, if not distorted by aberrant anatomy or a previous joint arthroplasty, helpful for determining the true anatomic hip center. In cases where the hip center has been displaced superiorly for an extended period of time with a well-fixed femoral prosthesis, it may be impossible to restore the anatomic hip center without neurovascular compromise. In these cases, we will allow some superior positioning of the vertical hip center.

Instability has been reported as a major concern following placement of CTAC (8,9,10,11,12). As such, it is imperative to critically assess the appropriate cup orientation when designing the prosthesis. The abduction angle is set 35 to 45 degrees from the horizontal plane using the plane of the obturator foramen as a reference. The anteversion angle is set at 25 to 30 degrees with the plane of the iliac wing and the obturator foramen as references. Establishing cup face orientation remains a difficult part of the preoperative planning because many of the reference points are often distorted.

Upon finalization of implant design, the surfaces of the titanium alloy stock are milled. The iliac and ischial flanges contain multiple rows of screw holes for cortical or locking screws. Current designs allow for the inclusion of threaded holes to accommodate locking screws into some or all of the holes. We prefer four to six screw holes in the

ischial flange because it is proven to be the most common site of fixation loss. We critically assess the geometry of the ischial flange because rough edges or overhang may cause irritation to the sciatic nerve. Two rows of three to four screw holes have proven sufficient for fixation of the iliac flange as this bone typically provides the best purchase. The pubic flange is smaller and does not contain screw holes. Dome screw holes may be placed depending on the adequacy of the iliac bone stock to create interlocking screw fixation with the iliac flange screws. The inner acetabular geometry has a modular locking mechanism that can accept any of the manufacturer specific modular liners typically available for standard acetabular components.

 

 

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The bone interface of the CTAC, including the flanges, has a porous ingrowth surface for osteointegration. This may be enhanced with the addition of a hydroxyapatite coating. Current CTAC designs allow for easier insertion and provide space behind the implant for additional bone graft at the time of operation. A critical design characteristic is creating a central dome that has intimate contact with the remaining ilium superiorly to reduce shear stresses on the three fixation flange interfaces with bone. In a hip with massive acetabular bone loss or even pelvic discontinuity, this iliac shelf may be the only structurally sound bone available for the construct to rely upon.

Throughout the development process of the CTAC, multiple iterations of the prototype are often required with extensive communication between the surgeon and design engineer. With this careful planning and custom design process, the patient and surgeon should understand that the preoperative wait period may be 2 to 3 months.

TECHNIQUE (TABLE 25-3)

Exposure and Implant Removal

The authors' preferred approach is an extensile posterolateral approach with the liberal use of either a trochanteric slide (13) or traditional greater trochanteric osteotomy. The addition of a trochanteric osteotomy facilitates exposure and hip dislocation, particularly in cases with severe acetabulae

 

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protrusio (Fig. 25-3A, B). Additionally, this technique may prevent injury to the superior gluteal nerve, which is typically placed under tension during exposure of the ilium, which is required for implantation of CTAC.

 

 

TABLE 25-3 Surgical Technique

 

Extensile anterolateral, transtrochanteric, or posterolateral approach (authors' preferred) Identify the sciatic nerve

If surgical planes are confusing, the nerve should be identified distally and traced proximally Neurolysis may be necessary in the case of significant scarring

Maintain hip extension and knee flexion while clearing the tissue from the ischium to the level of the hamstring origin

Assess femoral component fixation

If femoral component maintained—anterior capsular release to allow mobilization of the femur and exposure of the pubis

Occasionally, release of the iliopsoas and gluteus maximus tendons and an extensive anterior capsulotomy are necessary to allow for mobilization of the femoral component to allow acetabular exposure

Ilium exposure

Typically 3-5 cm to allow placement of the CTAC

A trochanteric osteotomy or slide may be used if there is excessive tension on the superior gluteal neurovascular pedicle

Ischium exposure

 

 

Elevate soft tissue as a sleeve

Acetabular exposure and implant removal (if present)

Trimming of excessive bone if needed (refer to sterile pelvis model) Trial CTAC—determine the need for further exposure and assess fit CTAC implantation

Iliac flange first-facilitated by translating the leg proximally with hip flexion and abduction to relax the abductor musculature. Slide under the abductor musculature.

The knee is flexed and hip extended in order to relax the posterior soft tissues. This allows rotation of the pubic and ischial flanges into position. Critically assess ischial overhang to avoid irritation to the sciatic nerve.

Compare CTAC to trail CTAC on the pelvic model.

Assess stability—there should be little to no toggle if positioned appropriately.

CTAC fixation

One to two locking screws into weakened ischial bone followed by 1-2 locking screws into the ilium for provisional fixation.

Trial liner, hip reduction, intraoperative radiograph to confirm implant position.

If appropriate position confirmed, place ischial screws followed by iliac screws to avoid superior migration of the implant.

In cases with pelvic discontinuity, we use a posterior column plate after placement of the CTAC.

 

 

 

 

FIGURE 25-3 A: Preoperative AP pelvis radiograph of a failed THA with severe periacetabular bone loss and acetabulae protrusio. B: Postoperative AP pelvis radiograph following revision THA with a CTAC performed with use of a standard trochanteric osteotomy. (From Johnson DR, Dennis DA, Kim RH. Acetabular revision: rings/cages/custom implants. In: Berry DJ, Lieberman JR, eds. Surgery of the Hip. Elsevier; 2013.)

The femoral component should be carefully scrutinized both preoperatively on radiographs and intraoperatively in order to assess its degree of fixation. Although removal of a well-fixed femur is not encouraged, removal of a marginally fixed stem will improve the acetabular exposure.

If the femoral component is retained, an anterior capsular release is necessary to create a pocket anteriorly, which allows mobilization of the femur and exposure of the pubis. Release of soft tissue and scar from the anterior and medial femur proximal to the lesser trochanter is often necessary to allow mobilization. Occasionally, release of the iliopsoas and gluteus maximus tendons and an extensive anterior capsulotomy to mobilize the femur for acetabular

exposure are warranted. Approximately 3 to 5 cm of the ilium must be exposed with use of a CTAC. Care must be taken with surgical dissection and mobilization of the gluteus minimus and medius muscles from the iliac wing to avoid damage to the superior gluteal neurovascular pedicle. We have found the utilization of a trochanteric slide or standard trochanteric osteotomy to be invaluable in cases where excess tension is encountered.

It is imperative to identify the sciatic nerve prior to beginning posterior dissection. Most patients with massive periacetabular bone loss have significant distortion from normal anatomy. We find the nerve at the greater sciatic notch and palpate this to below the ischium. If significant scarring of the sciatic nerve is present, meticulous neurolysis is necessary to allow safe mobilization of the nerve posteriorly from the ischium. The sciatic nerve may be further protected by maintaining hip extension and knee flexion while clearing the tissue from the ischium to the level of the hamstring origin. This relaxes the tension on the nerve and allows it to fall away from the ischium. The assistant holding the leg should also alert the surgeon of foot twitches during the exposure of the ischium to create awareness regarding the proximity of the sciatic nerve.

The acetabular component, cement, and pseudomembrane (if present) may be removed after obtaining adequate exposure to the acetabulum and to allow for placement of the CTAC. Care is taken to avoid further damage to the remaining acetabular bone.

CTAC Implantation

We use the hemipelvis model created during design of the CTAC during the operative procedure to assure appropriate implant placement. This is sterilized to allow use on the operative field. Typically, a thin rim of bone surrounding portions of the remaining acetabulum needs to be removed to allow

 

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placement of the custom prosthesis. This is part of the preoperative plan and is marked on the hemipelvis to assist with this process intraoperatively. Care is taken to remove only the thin rim needed for the placement of the CTAC as this avoids further destabilization of the pelvis. Cancellous particulate bone graft is then packed into remaining cavitary bone defects as needed.

Insertion of the acrylic trial initially is wise to assess the best final method of insertion, overall fit, and the need for additional trimming of bone to maximize fit and position. Initial implantation of the CTAC may be via the iliac or ischial flange. We attempt to insert the iliac flange first because it places less tension on the superior gluteal neurovascular pedicle. This initial insertion can be facilitated by translating the leg proximally with hip flexion and abduction to relax the abductor musculature. We then slide the iliac flange under the hip abductor musculature onto the iliac wing. As previously discussed, care should be taken to avoid undue traction on the superior gluteal neurovascular bundle via excessive retraction of the gluteus medius and minimus. After implantation of the iliac flange, the knee is flexed and hip extended to relax the posterior soft tissues. This allows rotation of the pubic and ischial flanges into position.

Care must be taken to avoid entrapment of the sciatic nerve underneath the ischial flange during CTAC insertion. We use the pelvic model after implantation as a reference to assure that implant position is similar to that of the preoperative plan. Typically, very little or no toggle of the implant is present if the CTAC is in the appropriate position. One should critically reassess the CTAC placement if significant motion is encountered.

CTAC Fixation

In the setting of pelvic discontinuity, the surgeon should be aware that the pelvic model may not accurately replicate the relative in vivo position of the ilium to the ischium, and reduction of the discontinuity may be required in order to accurately place the CTAC. We begin our fixation with the ischial screws where bone is typically the poorest and severe osteolysis is common. We favor placement of four to six locking screws into the weakened ischial bone.

Occasionally, cement augmentation of the osteolytic ischium allows for better fixation. Two ischial screws typically are placed prior to placing one or two iliac screws for provisional fixation. Care is taken to assure there is no overhang of the ischial component to avoid irritation of the sciatic nerve. A trial liner is then placed, the hip is reduced, and intraoperative radiographs to confirm implant position are performed. Judet views may be performed to

ensure accurate component position as well as to assess screw lengths. The remaining screws are then placed if appropriate position is confirmed. We complete placement of the ischial screws prior to placing the iliac screws to avoid vertical migration of the component. Newer CTAC designs allow for the placement of dome screws. These may be of use in the case of severe osteolysis to improve iliac fixation via an interlocking screw construct.

Use of a CTAC with Pelvic Discontinuity

Pelvic discontinuity increases the complexity of this already difficult procedure. The only failures of CTAC in the authors' hands have been in patients with a preoperative pelvic discontinuity. We now use supplemental posterior column plating in this situation. Two options are available in cases with discontinuity with placement of a CTAC. The first allows for placement “in situ” or with planned reduction of the discontinuity.

When using the “in situ” method, the design and implantation of the CTAC is the same as previously described. When planning a reduction, the CTAC must be designed to allow for placement of the cup in the “reduced” position. An intraoperative assessment must be made to ensure that the relative position of the ischium and ilium will reduce to an anatomic position. Then, after placing the CTAC, the iliac screws should be placed first, prior to reduction.

This will drive the component into intimate contact with the host bone causing the inferior hemipelvis to rotate against the component, thus reducing the discontinuity.

The addition of a posterior column plate requires further ischial and iliac exposure as well as precise planning during the CTAC design to ensure there is room for the plate after the CTAC is placed. The CTAC should be secured with screw fixation prior to placement of the posterior column plate. We maintain the hip in extension with the knee flexed during plating, aiming to place three or more screws each above and below the nonunion.

 

 

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PEARLS AND PITFALLS

 

Preoperative assessment of the CTAC is critical as intraoperative changes are not possible.

 

The ischial flange must be assessed for sharp edges or overhang to avoid irritation to the sciatic nerve.

 

 

Liberal use of a standard or extended trochanteric osteotomy allows for improved visualization and protection of the superior gluteal nerve.

 

Maintain knee flexion and hip extension during dissection and ischial flange placement to minimize the risk of sciatic nerve injury.

 

If motion of the CTAC is noted at the time of implantation, failure is imminent.

 

We recommend posterior plating and bone graft in all cases of pelvic discontinuity despite some reports of successful management with implantation of a CTAC alone (14).

 

To minimize the risk of dislocation, use of high-wall, face-changing, or constrained modular polyethylene liners may be necessary.

 

POSTOPERATIVE MANAGEMENT

Weight Bearing

 

 

Toe-touch weight bearing typically for 1 to 2 months postoperatively. Partial weight bearing with walking aids for another 1 to 2 months.

 

We typically restrict weight bearing longer in the setting of pelvic discontinuity.

 

Anticoagulation

 

We risk stratify our patients and carefully monitor to avoid hematoma or wound complications.

Hip Precautions

 

 

 

 

Hip abduction orthosis for 6 to 12 weeks

 

No active abduction for 6 weeks if a trochanteric osteotomy is performed

COMPLICATIONS

Instability (8,9,10,11,12)—the most common complication encountered may be multifactorial. If instability is noted intraoperatively, we have a low threshold to use a high-wall, face-changing, or constrained polyethylene liner. Notable reasons for instability include:

Component malposition

Abductor insufficiency or weakness—from multiple surgeries or superior gluteal nerve injury Trochanteric nonunion

Sciatic nerve injury (9,11)—usually a traction injury rather than direct nerve injury Mechanical failure (10,12)

Infection

 

 

RESULTS A paucity of evidence is available for review given the rare need to use these custom implants (Table 25-4) (8,9,10,11,12). The short- and midterm results have been promising with clinical success reported between 70% and 100%. In addition, radiographic healing of pelvic discontinuities has been reported in 81% to 97% of cases. Mechanical failures were evident in only four of the reported patients, culminating in an aseptic loosening rate of 2%. Of these patients, three had a pelvic discontinuity, none of which had received a supplementary posterior column plate. The pattern of failure was early loosening of the ischial screws and subsequent disengagement of the ischial flange. The most common reason for revision surgery was recurrent instability requiring conversion to a more constrained liner.   P.330
	TABLE 25-4 Selected Results with Use of a CTAC
		Author	Year	Number of Hips	Mean Age (Years)	Mean Follow-up (Years) (Range)	Results
		Taunton 2012 57 61 5 1.8% et al. (2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17) mechanical (12) failures 21% dislocation rate 17.4% revision for instability

 

	DeBoer et al. (9)	2007	20	56	10 (7,8,9,10,11,12,13)	0 mechanical
						failures
						30%
						dislocation
						rate
						25%
						revision for
						instability
						5% revision
						for sciatica
						and loose
						ischial
						screws
	Holt and Dennis (10)	2004	26	68	4.5 (2,3,4,5,6,7)	3% mechanical failures
						6%
						radiographic
						loosening
						without
						revision
						7.8%
						dislocation
						rate
	Joshi et al. (11)	2002	27	68	5 (4,5,6)	0 mechanical
						failures
						3% revision
						for
						instability
						3% revision
						for sciatic
						nerve palsy
	Christie et al. (8)	2001	67	59	4.5 (2,3,4,5,6,7,8,9)	0 mechanical
						failures
						15%
						dislocation
						rate
						8% revision
						for
						instability

 

 

 

 

 

 

 

 

 

 

 

 

 

REFERENCES

1. Paprosky WG, Perona PG, Lawrence JM: Acetabular defect classification and surgical reconstruction in revision arthroplasty. A 6-year follow-up evaluation. J Arthroplasty 9(1): 33-44, 1994.

    

    

2. D'Antonio JA, Capello WN, Borden LS, et al.: Classification and management of acetabular abnormalities in total hip arthroplasty. Clin Orthop Relat Res (243): 126-137, 1989.

    

    

3. Parvizi J, Jacovides C, Antoci V, et al.: Diagnosis of periprosthetic joint infection: the utility of a simple yet unappreciated enzyme. J Bone Joint Surg Am 93(24): 2242-2248, 2011.

    

    

4. Parvizi J, Jacovides C, Adeli B, et al.: Mark B. Coventry Award: synovial C-reactive protein: a prospective evaluation of a molecular marker for periprosthetic knee joint infection. Clin Orthop Relat Res 470(1): 54-60, 2012.

    

    

5. Parvizi J, McKenzie JC, Cashman JP: Diagnosis of periprosthetic joint infection using synovial C-reactive protein. J Arthroplasty 27(8 Suppl): 12-16, 2012.

    

    

6. Deirmengian C, Hallab N, Tarabishy A, et al.: Synovial fluid biomarkers for periprosthetic infection. Clin Orthop Relat Res 468(8): 2017-2023, 2010.

    

    

7. Fehring TK, Guilford WB, Baron J: Assessment of intrapelvic cement and screws in revision total hip arthroplasty. J Arthroplasty 7(4): 509-518, 1992.

    

    

8. Christie MJ, Barrington SA, Brinson MF, et al.: Bridging massive acetabular defects with the triflange cup: 2-to 9-year results. Clin Orthop Relat Res (393): 216-227, 2001.

    

    

9. DeBoer DK, Christie MJ, Brinson MF, et al.: Revision total hip arthroplasty for pelvic discontinuity. J Bone Joint Surg Am 89(4): 835-840, 2007.

    

    

10. Holt GE, Dennis DA: Use of custom triflanged acetabular components in revision total hip arthroplasty. Clin Orthop Relat Res (429): 209-214, 2004.

     

     

11. Joshi AB, Lee J, Christensen C: Results for a custom acetabular component for acetabular deficiency. J Arthroplasty 17(5): 643-648, 2002.

     

     

12. Taunton MJ, Fehring TK, Edwards P, et al.: Pelvic discontinuity treated with custom triflange component: a reliable option. Clin Orthop Relat Res 470(2): 428-434, 2012.

     

     

13. Glassman AH, Engh CA, Bobyn JD: A technique of extensile exposure for total hip arthroplasty. J Arthroplasty 2(1): 11-21, 1987.

     

     

14. Dennis DA: Management of massive acetabular defects in revision total hip arthroplasty. J Arthroplasty 18(3 Suppl 1): 121-125, 2003.