A novel technique for the removal of well-fixed cementless, large-diameter metal-on-metal acetabular components

Removing well-fixed cementless acetabular components can be a challenge for every orthopedic surgeon involved in revision hip arthroplasty. Forceful removal of such components often leads to acetabular bone loss and compromises reimplantation of a new socket. Instruments like the Explant Acetabular Cup Removal System (Zimmer, Warsaw, Ind) are developed to avoid such issues. We report a novel technique, cementing a polyethylene liner inside the uncemented metal-on-metal shell and using systems such as the Explant to safely extract it without the need for matching large-diameter heads. We successfully used this technique on 3 occasions and recommend its use.     

Removal of well-fixed femoral and acetabular components

One of the more difficult procedures in revision total hip arthroplasty is removal of a well-fixed femoral stem or acetabulum. Techniques to remove well-fixed, fully coated implants (cemented or uncemented) are discussed here. Results of these techniques show that operative time can be decreased and femoral and pelvic bone loss can be minimized, making a complicated revision more straightforward.     

Revision of well-fixed cementless acetabular components for polyethylene failure

The results of revision of well-fixed Porous Coated Anatomic cementless acetabular components for polyethylene failure or periacetabular osteolysis in 18 hips (14 patients) are reported. Revisions were done with larger diameter cementless acetabular components replacing one-piece Porous Coated Anatomic devices for which no replacement liner was available. The objective was to determine the increase in size of the revision acetabular component and to assess clinical and radiographic outcomes. The Porous Coated Anatomic components were in place for an average of 7.8 years. At an average followup of 68 months, all revision components remain in place. Preoperatively, 12 hips in 10 patients had radiographic osteolysis, and 25 osteolytic lesions in 17 patients were grafted at revision. All grafted lesions showed partial or complete evidence of bone graft consolidation. The average revision component size increased 8.5 mm in diameter (range, 3-14 mm) compared with the primary component size. This corresponded to an average 6.5-mm increase in the acetabular cavitary diameter. When locking mechanism failure in a well-fixed cementless acetabular component prevents polyethylene liner replacement, acetabular component revision can provide good clinical and radiographic results with acceptable bone loss and improved access to osteolytic areas for debridement and grafting.     

In vitro initial fixation of porous-coated acetabular total hip components. A biomechanical comparative study

Two-phase in vitro testing was performed to determine the initial mechanical stability of uncemented but fixed porous coated acetabular components. Six each of three-screw fixation, two-peg fixation, and three-spike fixation porous acetabular components were implanted into fresh and embalmed human cadaver acetabula. Measurement of prosthesis-bone displacement at a load of 100 kg did not show a significant difference among the three methods of fixation. However, torque testing showed that three-screw fixation failed at significantly higher loads (46 N-m) than two-peg fixation (32 N-m) or three-spike fixation (32 N-m).     

Removal of well-fixed, cementless, acetabular components in revision hip arthroplasty

Removal of well-fixed, cementless, acetabular components during revision arthroplasty remains a challenging problem. Further damage to host bone may limit options for reconstruction and compromise the long-term result of the revision operation. We report the results of 31 hips with well-fixed, cementless sockets which were removed using a new cup extraction system. In all hips the socket was removed without difficulty and with minimal further bone loss.     

Tissue growth into porous-coated acetabular components in 42 patients. Effects of adjunct fixation.

Histologic examination was performed on 42 uncemented, porous-coated acetabular components removed for reasons not related to fixation. Included were 20 devices that had fixed pegs or spikes to aid in initial fixation and 22 devices that used screws through the component. The diagnoses and patient ages at insertion, times in situ, and reasons for removal were comparable for the two groups. Bone ingrowth was observed in 28 of the 42 acetabular components (67%). Of the 20 components with pegs or spikes, nine had no bone ingrowth, six had minimal bone ingrowth, four had moderate ingrowth, and one had extensive bone ingrowth. Of the 22 components with screws, five had no bone ingrowth, six had minimal bone ingrowth, six had moderate bone ingrowth, and five had extensive bone ingrowth. Two of the devices with screws also had external threads on the metallic shell; neither had any bone ingrowth, and the two accounted for two of the five devices having no bone ingrowth in this group. Bone ingrowth occurred more frequently, in greater amounts and was more evenly distributed anatomically in cups using screws for initial adjunct fixation. Roentgenographic and clinical findings were unreliable in predicting ingrowth of bone.     

The removal of well-fixed porous ingrown femoral components

It is now evident that some biologically well-fixed hip prostheses may require removal and/or revision much earlier than originally anticipated. The relatively atraumatic removal of porous ingrown but clinically unacceptable femoral components, while difficult, has become increasingly feasible because of accumulated clinical experience and advances in biomedical technology. Preoperative planning, adequate instrument armamentarium, and intraoperative patience are important keys to the successful removal of these implants.     

Isolated revision acetabuloplasty using a porous-coated cementless acetabular component without removal of a well-fixed femoral component: A 3- to 9-year follow-up study

The results of isolated acetabular revision performed in 31 patients (32 hips) were monitored for between 3 and 9 years. All femoral components were well fixed and not removed or revised at the time of index surgery. There were 4 hips with little or no acetabular bony defect, 2 hips with pure segmental defects (type I), 10 hips with cavitary defects (type II), 15 with combined segmental cavitary defects (type III), and 1 with pelvic discontinuity (type IV). All revision acetabular implants were cementless, using a porous-coated hemispheric cup with or without bone-graft. There were four grade I reconstructions, 16 grade II reconstructions, and 12 grade III reconstructions. At final follow-up evaluation 94% of the cups were judged to be stable. Two hips required a second revision acetabuloplasty because of loss of fixation of the cup. The 2 repeat revisions were also done without removal of the femoral component. One acetabular component had evidence of rotational migration, which stabilized and remained nonprogressive. There were no cases of femoral component radiographic or clinical failure. The mean pre and postoperative hip scores were 44 and 83, respectively. The pre- and postoperative pain scores were 12 and 42, respectively. The findings of this study suggest that isolated acetabular revision, using a cementless porous-coated hemispheric cup, can be successfully performed without removing or revising a well-fixed femoral stem and not compromise the final outcome.     

A technique for removing a well-fixed cemented acetabular component in revision total hip arthroplasty

We describe a relatively safe technique for the removal of a cemented acetabular cup using multiple drill holes in the polyethylene cup. This technique helps to keep the integrity of the acetabular ring such that only the cup with the cement is removed. This technique has been shown to be relatively safe where a significant medial acetabular wall defect exists. We have been using this technique for several years with excellent results.     

A simple technique to remove well-fixed, all-polyethylene cemented acetabular component in revision hip arthroplasty

Well-fixed, all-polyethylene acetabular components may have to be removed in cases of recurrent dislocations, infection, or fracture of ceramic femoral heads. We describe a simple technique using acetabular reamers that allow cup thinning. Through this technique, the polyethylene rigidity is diminished considerably, allowing its easy removal without any risk of fracture, particularly of the acetabulum walls.     

Analysis of migration of press-fit porous-coated acetabular components with medial lucencies using Ein-Bild-Roentegen-Analyse

A total of 136 patients who underwent total hip arthroplasty (154 hips) with press-fit acetabular components were evaluated for the presence of medial radiographic lucencies. Thirty patients (22.1%) demonstrated radiolucencies greater than 1 mm in zone 2 on initial postoperative films. Ein-Bild-Roentegen-Analyse (EBRA) was used to evaluate component migration over a 5-year follow-up period. Migration, measured by EBRA, was not observed during the first 6 months when the radiolucencies were noted to disappear. After 2 years, the mean total migration was 0.8 mm, and at 5 years, it was 1.6 mm. Our results indicate that disappearance of a medial radiolucency seen on early postoperative radiographs is not associated with component migration, which supports the concept that the medial radiolucency fills in with bone or represents bony remodeling around a stable implant.     

Removal of the well-fixed hip resurfacing acetabular component: a simple, bone preserving technique

Removal of the acetabular component of a hip resurfacing prosthesis is occasionally necessary for infection, malposition, metal sensitivity, wear, or as a necessary part of a femoral revision. Extraction of a well-fixed acetabular component can be technically demanding as it is often extremely well integrated into host bone and can result in catastrophic bone loss or fracture. We present an undescribed, simple technique that enables use of the Explant system (Zimmer, Warsaw, Ind) to remove the component with minimal bone loss and reduce fracture risk. Bone stock is therefore preserved for subsequent cup reimplantation.     

Mechanical stability of porous-coated acetabular components in total hip arthroplasty.

Five different porous-coated acetabular prosthetic configurations underwent in vitro testing to assess mechanical stability in embalmed cadaver hemipelves: Harris Galante II cup with three cancellous screws, Biomet Universal cup, Whiteside cup with peripheral pegs, Whiteside cup with two cancellous screws, and plain Whiteside cup. Following implantation in a neutral frame, cyclic load testing was done using 33 specimens at 100-kg load for 100,000 cycles using an MTS machine (MTS Systems Corp., Minneapolis, MN). Subsequently, static load-to-failure testing was done in all specimens. Subsidence and micromovement were determined for each specimen using linear variable differential transformers. With cyclic testing, overall cup subsidence revealed a significant increase, from 500 to 100,000 cycles. Overall cup micromovement revealed a significant decrease, and all cup groups demonstrated less than 125 microns (.125 mm) of average mean micromotion at the completion of cyclic testing. The best cup configuration was a 1-mm, oversized, press-fit cup using two 6.5 cancellous screws for additional fixation, which revealed an average mean of 60 microns (.06 mm) of micromovement. Static load testing revealed unacceptable micromovement over 150 microns (.150 mm) in most cups with 300-kg loads.     

High placement of porous-coated acetabular components in complex total hip arthroplasty

The authors retrospectively evaluated the results of 56 hips in 51 patients with an acetabular deficiency who had a total hip arthroplasty with a porous-coated, cementless acetabular component implanted at a high hip center. Forty-nine cases were revisions and seven were primary operations. The mean height of the hip center was 43 mm above the interteardrop line compared to 14 mm for the anatomic center, threefold higher than normal. In contrast, the mean horizontal locus was reduced compared to normal (33 vs 37 mm for the anatomic center). Sixteen acetabular components were small (46–48 mm o.d.) and eight were miniature (40–44 mm o.d.). Despite superior placement of the acetabular component, 32 limbs were lengthened by the procedure. The mean preoperative Harris hip score was 51 (range, 28–93). At a mean follow-up period of 40 months (range, 24–64 months), the mean Harris hip score was 86 (range, 36–100). In 23 hips no radiolucent lines were present at the interface of the bone to the porous mesh, and 33 hips had a thin (0.5 mm), nonprogressive radiolucent line in one or more zones. No acetabular component had migrated and no problems occurred with the screws. Four hips (3 revisions and 1 primary operation) had a complete radiolucent line on one oblique view of the acetabulum. No acetabular component has been revised for loosening. These short-term data suggest that under circumstances in which the acetabulum cannot be reconstructed at the anatomic level without a major structural bone-graft, superior placement of the porous-coated acetabular component against viable host-bone at a higher level than normal may be an acceptable alternative.     

Analysis of retrieved uncemented porous-coated acetabular components in patients with and without pelvic osteolysis

Retrieved polyethylene liners and femoral heads from a consecutive series of revision components of one design were examined. All patients had Long-Term Stable Fixation (OsteoTechnology International, Timonium, Md) total hip arthroplasties (THAs) implanted between 1987 and 1992. The retrieved femoral heads and liners from patients with osteolysis were compared to those without osteolysis. Patients with osteolysis had significantly thinner polyethylene (5.1 mm versus 7.4 mm, P<.01 ) and a higher linear wear rate (0.5 mm/y versus 0.3 mm/y, P=.05). The average femoral head surface roughness also was significantly greater in patients with osteolysis (67 nm versus 35 nm, P<.05). Patients with osteolysis had more total volumetric wear, total linear wear, and volumetric wear rate compared to patients without osteolysis. Age, obesity index, time in situ, and cup inclination were not different between the two groups. Excessive polyethylene wear, probably accelerated by surface roughness of the femoral heads, was associated with pelvic osteolysis in these patients.     

Intrapelvic migration of a well-fixed femoral stem after removal of an acetabular cup

Failure of total hip arthroplasty with central migration of prosthetic components is uncommon. Various pelvis and visceral complications have been reported from intrapelvic migration of the acetabular cup or the cement or from the heat generated by methylmethacrylate polymerization. To our knowledge, we are the first to report intrapelvic migration of a femoral stem causing ipsilateral lower-extremity swelling, pressure sores, and severe bowel symptoms after the removal of the acetabular component.     

Ingrowth of bone in failed fixation of porous-coated femoral components

In five straight-stemmed, proximally porous-coated femoral components that were retrieved at revision arthroplasty from patients who had radiographic and clinical evidence of loosening, there was growth of bone into the porous coating. The components had been inserted during a primary arthroplasty in one woman and four men. The patients ranged in age from thirty-seven to sixty-seven years. Three patients were heavy, and all five were active. All patients had had an excellent early result from the initial arthroplasty; at the one-year follow-up, the mean Harris hip score had been 91 points. Pain in the hip developed in all of the patients, between one and three years after the index procedure. Initial radiographs had revealed excellent position and fixation of the prosthetic components, but the components then subsided between one and three and one-half years after the index procedure. All of the femoral components were found to be grossly loose at the revision operation. Nevertheless, all of the prosthetic components demonstrated growth of bone into 4 to 44 per cent (mean, 24 per cent) of the pore spaces available for ingrowth. Woven bone and fracture callus were found in the curettings from the proximal part of the femur. The findings in these five patients suggest that late failure of uncemented porous-surfaced femoral components can occur despite the presence of extensive ingrowth of bone. These failures may be the result of fatigue fractures of the trabeculae of the osseous ingrowth into the porous surfaces. Caution is warranted in the liberal use of these prosthetic components in heavy, active patients.     

A novel anatomical self-locking plate fixation for both-column acetabular fractures

PurposeTo compare the stability of the posterior anatomic self-locking plate (PASP) with two types of popular reconstruction plate fixation, i.e. double reconstruction plate (DRP) and cross reconstruction plate (CRP), and to explore the influence of sitting and turning right/left on implants.MethodsPASP, DRP and CRP were assembled on a finite element model of both-column fractures of the left acetabulum. A load of 600 N and a torque of 8 N·m were loaded on the S1 vertebral body to detect the change of stress and displacement when sitting and turning right/left.ResultsThe peak stress and displacement of the three kinds of fixation methods under all loading conditions were CRP > DRP > PASP. The peak stress and displacement of PASP are 313.5 MPa and 1.15 mm respectively when turning right; and the minimal was 234.0 Mpa and 0.619 mm when turning left.ConclusionPASP can provide higher stability than DRP and CRP for both-column acetabular fractures. The rational movement after posterior DRP and PASP fixation for acetabular fracture is to turn to the ipsilateral side, which can avoid implant failure.