Uncemented Acetabular Revision with Hemispherical Cup

 

 

INDICATIONS AND CONTRAINDICATIONS

A hemispherical cementless acetabular component can be used for most acetabular revisions that the surgeon will encounter in practice. We prefer to use the Paprosky classification (1) for acetabular defects, and in this classification, a cementless hemispherical acetabular component, with or without some particulate bone grafting, is appropriate for almost all type 1 and 2 defects as well as some type 3A defects.

Type 1 and 2A/2B defects are similar defects that are characterized by less than 3 cm of proximal migration of the failed acetabular component with intact acetabular columns. Type 2C defects are characterized by central protrusion of the component beyond Kohler's line; however, the anterior and posterior columns are typically intact, although there can be damage to the anterior wall of the acetabulum (Fig. 23-1). These defects, while having a dramatic appearance, are easily handled with a hemispherical cup and medial bone grafting. Specifically, the acetabular rim is carefully reamed to accept the shell and the medial defect is filled with particulate, fresh frozen cancellous graft that is tightly reverse reamed into the medial defect. The surgeon should be careful if these types of defects are associated with deep infection or acute loosening as this has been associated with a higher risk of vascular injury upon retrieval of the failed cup (2). Finally, 2C defects may occasionally be associated with a pelvic discontinuity, which is covered below under contraindications.

Type 3A defects are characterized by greater than 3 cm of proximal migration with an “up and out” appearance (Fig. 23-2). In some of these cases, a hemispherical cup can be used alone. Specifically, these defects are typically oblong, and if the surgeon can convert this defect to a hemisphere with the reamer, without damaging or sacrificing the anterior and posterior walls, then a hemispherical cup can be utilized alone. In general, most surgeons will accept up to 1 cm of elevation of the center of rotation before some type of augmentation is utilized superolaterally. If, however, the surgeon cannot fill the defect top to bottom without damaging the acetabular walls and/or columns, then

 

superolateral augmentation is required to restore a reasonable center of rotation and the limits of a hemispherical cup alone have been reached (Figs. 23-3 and 23-4).

 

 

 

FIGURE 23-1 Paprosky 2C acetabular defect with less than 3 cm of proximal migration and protrusion past Kohler's line with intact acetabular columns, although there can be damage to the anterior wall. A hemispherical cementless cup with medial bone grafting can be successfully used to reconstruct this defect.

 

 

 

FIGURE 23-2 Paprosky 3A defect with greater than 3 cm of proximal migration of the acetabular component with an “up and out” pattern.

Paprosky type 3B defects are characterized by greater than 3 cm of proximal migration of the failed component combined with substantial damage to the posterior column, which is usually identified as ischial lysis (Fig. 23-5). In this case, given the damage to the posterior column, which is the main stabilizing structure for a cementless cup, some type of augmentation or alternative reconstructive technique will be required. Similarly, the presence of a pelvic discontinuity is a contraindication to the routine use of a hemispherical cementless cup alone and specialized techniques for reconstruction will be required (3).

Radiographic signs of pelvic discontinuity include a visible fracture line through the posterior column (oftentimes seen most easily on a Judet view of the pelvis), asymmetry of the obturator foramen when compared to the contralateral side, and medial translation of the inferior hemipelvis (Fig. 23-6). Risk factors for the occurrence of pelvic discontinuity include female sex and rheumatoid arthritis (3).

In general, successful osseointegration will occur if the component is mechanically stable and placed in close contact with viable, living bone, and hence, a history of prior irradiation to the pelvis is another

contraindication to the use of a cementless hemispherical cup (4); in this situation, a strong mechanical construct (such as a reconstruction cage) is required. While surgeons often reference specific percentages of host bone contact required for the successful use of a hemispherical

 

 

 

 

cementless cup, this is not only difficult to assess intraoperatively but also not supported by objective data. Hence, as previously described, if the defect encountered can be reamed into a hemisphere and the posterior column is intact to provide long-term support, a cementless acetabular component alone can be used in most cases, so long as the center of rotation is not elevated greater than 1 cm and initial implant stability can be achieved (typically with multiple screws for fixation) so that osseointegration can occur to provide long-term fixation.

 

 

 

FIGURE 23-3 Type 3 defect as seen from the surgeon's view. In this case, the surgeon cannot create a hemisphere with the reamer that will fill the defect from top to bottom without damaging or sacrificing the anterior and posterior walls, and hence, some type of augmentation will be required to preserve the center of rotation of the hip.

 

 

 

FIGURE 23-4 Type 3A defect where an augment was utilized to restore the center of rotation.

 

 

 

FIGURE 23-5 Type 3B defect with greater than 3 cm of migration and evidence of severe ischial lysis suggesting damage to the posterior column; note the “up and in” pattern of bone loss. This type of defect is not typically reconstructable with a hemispherical cup alone.

 

FIGURE 23-6 Pelvic discontinuity with a visible transverse fracture line and medial translation of the inferior hemipelvis.

 

 

 

PREOPERATIVE PREPARATION

As with any revision procedure, preoperative planning is crucial to an efficient operative procedure with the lowest risk of complications and optimal outcomes for the patient.

As in all revision procedures, deep infection should routinely be ruled out, as the treatment of infection is fundamentally different than if the reason for failure is aseptic:

 

 

Obtain a serum erythrocyte sedimentation rate and C-reactive protein (CRP).

 

Aspirate the hip if the ESR and CRP are elevated or if clinical suspicion for infection is high (5).

 

The fluid obtained should be sent for a synovial fluid white blood cell count (optimal cutoff value approximately 3,000 WBC/μL), a differential (optimal cutoff value approximately 80% neutrophils), and culture.

Next, it is critical to obtain the prior operative note to determine the manufacturer, model, and size of the implants currently in place. Knowledge of the prior implanted cup size is particularly important if the cup being revised is well fixed, as this will facilitate its removal using curved osteotomes that are specifically sized to the diameter of the implanted cup (Fig. 23-7). Similarly, if screws

 

 

were utilized as part of the original reconstruction, their number should be known to facilitate cup removal; even a loose cup can be difficult to extract if screws are still in place. Along the same lines, special screwdrivers may be required, and finally, trial liners are once again needed to use the curved acetabular osteotomes previously referenced (Fig. 23-7). Specialized instruments from the manufacturer may also facilitate removal of the liner.

The operative note will also yield critical information regarding the make and model of the femoral component so

that appropriate trials and replacement femoral heads are available should the femoral component be retained. If the femoral component is to be removed, knowledge of its geometry and extent of coating will determine the strategies for its removal.

 

 

 

 

FIGURE 23-7 A: Curved acetabular osteotomes were used to remove this well-fixed but poorly positioned acetabular component. Note the original worn liner has been removed and a trial placed to center the osteotome. B: The explanted cup with minimal loss of host bone.

 

SURGICAL TECHNIQUE

The first step in any hip procedure starts with a decision on which surgical approach to utilize, and our preference is the posterior approach as it is technically easy to perform and easily extensile and allows for exposure of the posterior column if required. It is also compatible with an extended trochanteric osteotomy if required and does not damage the abductors. Once the hip capsule has been exposed, the hip is aspirated and an intraoperative synovial fluid white blood cell count is obtained, if one has not been done preoperatively to evaluate for infection (Fig. 23-8). The hip capsule and short external rotators are then released off of the back of the femur as one continuous layer and tagged for later repair (Fig. 23-9). Next, a partial posterior, superior, and inferior capsulectomy is performed and the tissue obtained is sent for histopathologic evaluation for infection as

well as for tissue culture. Debridement of this tissue is required to mobilize the hip and completely visualize the periphery of the acetabulum, to remove the cup that is in place, and to prepare and insert the revision shell.

 

 

 

 

FIGURE 23-8 Intraoperative hip aspiration is performed prior to taking down the posterior capsule, and the fluid obtained is sent for an intraoperative synovial fluid white blood cell count and differential to evaluate for infection.

 

 

 

 

 

FIGURE 23-9 The posterior capsule is tagged for later repair.

 

 

 

The hip is then dislocated posteriorly, and if the femur is to be retained, the modular femoral head is removed with a special tool that avoids damage to the taper (Fig. 23-10). Next, a partial anterior capsulectomy is performed to both enhance exposure and create a pocket for the femoral component if it is to be retained. If a modular liner is present, it can now be removed and the periphery of the acetabulum exposed in its entirety to facilitate removal of the implanted shell (Fig. 23-11). Next, any screws present are removed and the acetabular component is carefully removed to minimize loss of host bone; as previously described, curved acetabular osteotomes are helpful in this regard (Fig. 23-7). The acetabular defect can now be assessed along with the integrity of the acetabular columns and walls to determine if they are supportive for the revision component.

Next, soft tissue debris present in the acetabulum is removed with a Cobb elevator to expose the underlying bone (Fig. 23-12). Oftentimes, it is possible to visualize anatomic structures such as the transverse acetabular ligament that can help guide both acetabular component insertion and judge the “height” of the acetabulum or where the center of rotation will be (Fig. 23-13). Specifically, the face of the cup should in general lie parallel to

the transverse acetabular ligament, and the inferior aspect of the component should lie within its vicinity suggesting that the center of rotation has not been raised.

Next, the acetabulum is sequentially reamed until circumferential contact is achieved with the reamer (Fig 23-14). As described earlier, the limits of a hemispherical cup alone are reached when the defect cannot be filled “top to bottom” without sacrificing or reaming away the anterior and posterior walls or columns (Fig. 23-3). An acetabular trial is then placed to determine if the proposed component will have inherent stability and to give the surgeon a picture in his or her mind about how the final component should look once implanted with regard to anteversion and abduction, which is oftentimes more easily judged with the trial in place and is easily adjusted to optimize position

 

 

 

(Fig. 23-15). While a tight press fit of the trial is not mandatory (as screws will be used for adjunctive fixation), the component should have some inherent stability when a posterosuperior force is exerted on the trial; if not, this suggests posterior column deficiency, which is a contraindication to the use of a hemispheric cup alone. The final reamer used will depend on the specifics of the manufacturer labeling; some components are oversized compared to their labeled size and hence, a “line-to-line” ream is suggested while others are “true-to-size” and hence, some degree of underreaming is suggested. Keep in mind that in larger component sizes, a greater amount of underreaming may be tolerated; that is to say that 2 mm of underreaming of a 70-mm component is more easily accommodated than the same amount of underreaming in a 50-mm cup, which may lead to a fracture of the acetabulum (6).

 

 

 

 

FIGURE 23-10 The modular femoral head is removed with a special tool that will not damage the taper.

 

 

 

 

FIGURE 23-11 The femoral component has been retracted anteriorly and the modular liner removed to allow for complete visualization of the periphery of the acetabulum.

 

 

 

 

 

FIGURE 23-12 Removal of soft tissue debris from the acetabulum with a Cobb elevator.

 

 

 

 

 

FIGURE 23-13 The transverse acetabular ligament is identified (tip of the forceps), which can assist with determining anteversion of the revision component as well as restoration of an appropriate center of rotation.

 

 

 

FIGURE 23-14 The acetabulum is sequentially reamed with hemispherical reamers until circumferential contact has been obtained.

 

At this point, with the trial in place, the surgeon can also determine if bone grafting is desired for contained defects. Our preference is fresh frozen cancellous graft, which is placed into the socket and then firmly reverse reamed into place, initially with a reamer that is 1 mm smaller than the last reamer used and finally with the

same-size reamer that was last used (Fig. 23-16). It is important that the graft be firmly reverse reamed to ensure that a slurry of dead bone is not interposed between the native acetabulum and the implanted component.

The revision component is impacted into place in the same anteversion and abduction as the trial (Fig. 23-17). It is important to optimize component position that will lead to hip joint stability and not necessarily maximize host bone contact; maximizing host bone contact may often lead to a vertical and retroverted position that can increase the risk of dislocation. Next, screws are placed for

 

 

adjunctive fixation, and while this must be done carefully to avoid neurovascular injury, our preference is to place multiple bicortical screws, including screws inferiorly into the ischium and pubis when possible (Fig. 23-18) (7).

This will maximize the initial implant stability that is required for osseointegration of the revision component to occur.

 

 

 

 

FIGURE 23-15 An acetabular trial is placed to determine if the proposed component will have inherent stability.

 

 

 

FIGURE 23-16 A: Fresh frozen cancellous allograft is used to fill contained defects. B: The graft has been reversed reamed to tightly impact it into the defects taking care not to leave a slurry of dead bone that will cover the remaining acetabular bed.

 

The final and among the most important steps is trialing (Fig. 23-19). A trial liner is placed into the acetabulum and hip trial reduction is performed to optimize leg length, offset, and stability. Given the

 

 

high risk of instability associated with revision total hip arthroplasty (THA) (8), we routinely use 36 mm and

greater head sizes for revision THA based on level 1 data that show they reduce the risk of this key complication

(9). If stability is inadequate, the anteversion of the femur and acetabulum should be carefully assessed to ensure they are appropriate, and in some cases, an intraoperative radiograph may be helpful to identify component malposition or inadequate restoration of length and/or offset.

 

 

 

 

FIGURE 23-17 The final component is inserted in anteversion and abduction that will optimize stability; note the substantial overhang or “uncoverage” of the component superolateral, which is common in the revision scenario.

 

 

 

FIGURE 23-18 Multiple screws are placed for adjunctive fixation.

 

 

 

 

 

FIGURE 23-19 Trial reduction is performed to ensure adequate stability. In this case, the hip is stable to approximately 70 degrees with the hip flexed 60 degrees and in some adduction.

 

The surgeon should have a full complement of offset and elevated rim or face-changing liners available to maximize stability. If an elevated rim or face-changing liner is used, the surgeon should ensure that instability does not occur in the opposite direction secondary to impingement on the elevated rim of the liner. In cases of abductor deficiency, revisions specifically for instability, cases where only smaller heads (less than 36 mm) are available for a retained stem, or cases where intraoperative stability is inadequate, a dual-mobility articulation or a constrained liner is strongly considered (Fig. 23-20). After the final head and liner are placed and the hip is reduced, the posterior capsule, which was tagged earlier in the case, is repaired back to the posterior border of the gluteus medius tendon (Fig. 23-21). We generally place three sutures into the capsule, with the most distal capsular tag stitch repaired as closely as possible to the tip of the greater trochanter in the tendon of the gluteus medius and with the final two sutures placed more proximally.

 

 

 

FIGURE 23-20 Postoperative radiograph of a case where a dual-mobility articulation was utilized as a head size of 36 mm or greater could not be obtained given the vintage of the retained stem. Note the inferior screws in the ischium and pubis for adjunctive fixation.

 

 

 

 

 

FIGURE 23-21 The sutures that were tagged earlier in the case are repaired back to the posterior aspect of the gluteus medius.

 

 

 

PEARLS AND PITFALLS

Pearls

 

The key to any complex surgical procedure is adequate exposure. If full circumferential exposure of the

acetabulum is obtained, both removal of the failed cup and preparation of the acetabulum for the revision component will be facilitated.

 

If exposure is not adequate, consideration should be given to an extensile exposure such as a standard

trochanteric osteotomy, trochanteric slide, or extended trochanteric osteotomy.

 

Component stability in the bony bed is critical for osseointegration to occur, and hence, the surgeon should use as many screws as possible for adjunctive fixation of the cup.

 

The importance of preoperative planning cannot be overemphasized to ensure that the surgeon knows what components are presently in place so that appropriate trials and replacement parts are available. Similarly, the operative plan should be clear, as should a backup plan in case the defect encountered is more severe than anticipated or if an intraoperative complication occurs.

 

Pitfalls

 

The difficulties encountered with acetabular component positioning are magnified in the revision scenario, as the anatomic landmarks may be altered. Care should be taken to optimize both abduction and anteversion, and if there is any question regarding component position, an intraoperative radiograph should be obtained.

 

Along these same lines, it is critical to optimize component position to avoid instability and not to place the cup in a more vertical or retroverted position to optimize host bone contact.

 

The most common complication after revision THA is dislocation, and we routinely use the largest femoral head size available. Constrained liners and dual-mobility articulations should be strongly considered in cases in which a femoral head size of 36 mm or greater is not available, if the abductors are deficient, or if the revision is being specifically performed for instability.

 

As emphasized in the surgical technique section of this chapter, if cancellous allograft is used to fill contained defects, it must be tightly reverse reamed into the defects to ensure that a slurry of dead bone is not interposed between the ingrowth surface and the underlying native bony bed.

 

All patients should have a preoperative evaluation for deep infection, even when a mechanical cause of failure is the primary indication for revision (such as recurrent instability) because infection can coexist with other modes of failure.

 

POSTOPERATIVE MANAGEMENT

Patients typically are allowed touchdown weight bearing for 6 weeks using two crutches or a walker and advanced to weight bearing as tolerated with a cane after that time; the assistive device can be discarded once the patient has been judged to be safe by a physical therapist. Abductor strengthening is an integral part of postoperative physical therapy to both enhance gait and lower the risk of instability. Given the high risk of dislocation postoperatively, patients are asked to follow posterior hip precautions for 3 months.

 

COMPLICATIONS

The most common complication following any revision hip procedure is dislocation (8). Hence, we focus on this aspect of the procedure intently, including not only optimizing component position intraoperatively but also ensuring that adequate options are available for femoral heads and liners to lower the risk. As previously discussed, dual-mobility articulations and constrained liners are used judiciously in cases where the risk of dislocation is felt to be highest, including those cases associated with abductor deficiency, when larger femoral head sizes are not available, or when the revision is being performed specifically for recurrent instability.

Periprosthetic joint infection remains among the most common complications of revision THA. In addition to performing the surgery expeditiously, preoperative patient optimization may decrease the risk of this complication. Specifically, data from our center suggest that malnutrition is associated with a higher risk of

 

postoperative infection (10) and surgeons may consider delaying operative intervention if malnutrition is

identified. Similarly, perioperative glucose control may be important, particularly in patients with diabetes. Finally, we do not routinely withhold antibiotics in revision cases to obtain operative cultures as one single dose of preincisional antibiotics does not appear to affect operative culture results (11).

Neurovascular injury is also more common in revision procedures and patients should be educated regarding this risk. Care with placement of fixation screws is paramount and the sciatic nerve,

 

which is most commonly injured, should be palpated and protected throughout the case. Finally, patients undergoing revision procedures should be educated that leg length discrepancy is also more common after revision procedures than primary arthroplasty and understand that given the high risk of dislocation after a revision, leg lengthening may be necessary to optimize stability.

 

 

RESULTS

Long-term results from our center suggest that at a minimum of 20 years, the durability of cementless fixation for acetabular revisions is outstanding, with 95% survivorship at 20 years when revision for loosening or radiographic evidence of loosening was considered as an endpoint (12). The most common causes of failure were infection and recurrent instability. At longer term follow-up, revisions for polyethylene wear and osteolysis were seen more commonly; however, this included the use of polyethylene that was not highly cross-linked. Series from other centers suggest similar durability and survivorship (13,14,15,16).

Although the use of highly porous metal cups has become commonplace in contemporary practice, there is only one study that suggests superiority over traditional porous-coated shells (17). However, these shells do offer higher coefficients of friction, which may augment implant stability and encourage osseointegration

(18). Further, the ability to easily drill through fully porous-coated versions is an advantage for augmenting screw fixation in more complex cases, as is the use of porous augments, which are covered in another chapter.

 

 

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. Wera GD, Ting NT, Della Valle CJ, et al.: External iliac artery injury complicating prosthetic hip resection for infection. J Arthroplasty 25(4): 660.e1-4, 2010.

    

    

3. Berry DJ, Lewallen DG, Hanssen AD, et al.: Pelvic discontinuity in revision total hip arthroplasty. J Bone Joint Surg Am 81(12): 1692-1702, 1999.

    

    

4. Jacobs JJ, Kull LR, Frey GA, et al.: Early failure of acetabular components inserted without cement after previous pelvic irradiation. J Bone Joint Surg Am 77(12): 1829-1835, 1995.

    

    

5. Della Valle C, Parvizi J, Bauer T, et al.: Diagnosis of periprosthetic joint infections of the hip and knee: AAOS clinical practice guideline summary. J Am Acad Orthop Surg 18: 760-770, 2010.

    

    

6. Ries MD, Harbaugh M: Acetabular strains produced by oversized press fit cups. Clin Orthop Relat Res 334: 276-281, 1997.

    

    

7. Meneghini RM, Stultz AD, Watson JS, et al.: Does ischial screw fixation improve mechanical stability in revision total hip arthroplasty? J Arthroplasty 25(7): 1157-1161, 2010.

    

    

8. Murray TG, Wetters NG, Kancherla V, et al.: Risk factors for dislocation following revision total hip arthroplasty. Clin Orthop Relat Res 471: 410-416, 2013.

    

    

9. Garbuz DS, Masri BA, Duncan CP, et al.: Prevention of dislocation in revision total hip arthroplasty: a randomized clinical trial of 36/40 and 32mm femoral heads. The Frank Stinchfield Award. Clin Orthop Relat Res 470: 351-356, 2012.

    

    

10. Yi PH, Frank RM, Vann E, et al.: Is potential malnutrition associated with septic failure and acute infection after revision total joint arthroplasty? Clin Orthop Relat Res 473(1):175-182, 2015. doi: 10.1007/s11999-014-3685-8.

     

     

11. Tetreault MW, Wetters NG, Aggarwal V, et al.: The Chitranjan Ranawat Award: should prophylactic antibiotics be withheld prior to revision surgery to obtain appropriate cultures? Clin Orthop Relat Res 472: 52-56, 2014.

     

     

12. Park DK, Della Valle CJ, Quigley L, et al.: Revision of the acetabular component without cement. A concise follow-up, at twenty to twenty-four years, of a previous report. J Bone Joint Surg Am 91(2): 350-355, 2009.

     

     

13. Lachiewicz PF, Soileau ES: Fixation, survival, and dislocation of jumbo acetabular components in revision hip arthroplasty. J Bone Joint Surg Am 95(6): 543-548, 2013.

     

     

14. Wysocki RW, Della Valle CJ, Shott S, et al.: Revision of the acetabulum with a contemporary cementless component. J Arthroplasty 24(6 Suppl): 58-63, 2009.

     

     

15. Whaley AL, Berry DJ, Harmsen WS: Extra-large uncemented hemispherical acetabular components for revision total hip arthroplasty. J Bone Joint Surg Am 83-A(9): 1352-1357, 2001.

     

     

16. Templeton JE, Callaghan JJ, Goetz DD, et al.: Revision of a cemented acetabular component to a cementless acetabular component. A ten to fourteen-year follow-up study. J Bone Joint Surg Am 83(11): 1706-1711, 2001.

     

     

17. Kremers HM, Howard JL, Loechler Y, et al.: Comparative long-term survivorship of uncemented acetabular components in revision total hip arthroplasty. J Bone Joint Surg Am 94(12): e82, 2012.

     

     

18. Meneghini RM, Meyer C, Buckley CA, et al.: Mechanical stability of novel highly porous metal acetabular components in revision total hip arthroplasty. J Arthroplasty 25(3): 337-341, 2010.