The cement mantle in the exeter impaction allografting technique

The Journal of Arthroplasty Vol. 12 No. 7 1997

The C e m e n t Mantle in the Exeter I m p a c t i o n Allografting Technique A Cause for Concern E r i c L. M a s t e r s o n ,

FRCS(Orth),

Bassam

and Clive R Duncan,

A. M a s r i , F R C S ( C ) ,

FRCS(C)

The postoperative radiographs of 35 patients who underwent impaction allografting of the proximal femur were reviewed. Of Gruen zones that could be clearly visualized, 39.9% contained areas where cement was absent. Even when an adequate mantle was present, cement voids were commonly s e e n . These cement mantle deficiencies were confirmed in a series of cadaveric impaction allografting procedures. They appear to be a consequence, at least in part, of an inadequate differential between trial and actual component sizes. Additionally, 4 patients were identified with significant component migration secondary to radiographically visible cement mantle fractures within the first 6 months of surgery. It is concluded that the surgical technique requires modification to ensure a more consistent cement mantle and clinical result. K e y words: revision hip arthroplasty, impaction aIlografting, cement mantle. Abstract:

In 1984, Slooff et al. described a t e c h n i q u e of using particulate b o n e allograft w i t h fine-wire m e s h to reconstruct the deficient a c e t a b u l u m in b o t h p r i m a r y a n d revision total hip arthroplasty (THA) [11. This was followed by reports f r o m Exeter w i t h e n c o u r a g i n g results f r o m the u,~.e of i m p a c t e d morsellized allograft c o m b i n e d wiLh a cemented, polished, t a p e r e d collarless s t e m to reconstruct the deficient p r o x i m a l f e m u r in revision THA [2,3]. M o r e recently, 2 further series using this t e c h n i q u e h a v e b e e n reported [4,5].

It is generally accepted that the longevity of a c e m e n t e d THA is optimized w h e n an adequate c e m e n t m a n t l e is achieved circumferentially, and that a thin c e m e n t m a n t l e carries w i t h it a high risk of fragmentation, particle generation, and osteolysis [6]. Evidence in favor of an a d e q u a t e c e m e n t m a n t l e comes f r o m a variety of sources. These include finite-element analysis studies [7,8], cadaveric retrievals [9], intraoperative observations [10], a n d l o n g - t e r m clinical and radiographic studies [11-13]. We h a v e b e e n using the femoral i m p a c t i o n allograft technique since 1994 a n d h a v e b e e n concerned a b o u t a n u m b e r of cases of early rapid subsidence of the femoral c o m p o n e n t associated with fractures of the c e m e n t mantle. We therefore u n d e r t o o k a detailed analysis of the c e m e n t m a n tle p r o d u c e d by this technique, in our hands, and the m o d e s of failure in those patients w i t h early prosthesis subsidence.

From the Division of Adult Reconstructive Orthopaedics, Department of Orthopaedics, Vancouver Hospital and Health Sciences Centre. Vancouver, British Columbia, Canada. Reprint requests: Clive F. Duncan, FRCS(C), Department of Orthopaedics, Vancouver Hospital and Health Sciences Centre, 3rd Floor, 910 West l 0th Avenue, Vancouver, British Columbia, Canada VSZ 4E3. © 1997 Churchill Livingstone Inc.

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Materials and Methods The technique of impaction bone-grafting with a cemented stem for revision of the femoral component in cases of proximal femoral bone loss was used in 35 revision arthroplasties (35 patients) at our institution between February 1994 and January 1996. Demographic data and other preoperative information, as well as the surgical report and postoperative details, were recorded for each case. In addition, a detailed assessment was made of the preoperative, early postoperative, and 6 - m o n t h followup radiographs. The m e a n age was 62 years (range, 27-80 years). There were I6 m e n and 19 w o m e n . The indications for revision arthroplasty included aseptic loosening of c e m e n t e d hip arthroplasty (21 cases), aseptic loosening of u n c e m e n t e d hip arthroplasty (8 cases), second stage of twostage revision for infection (4 cases), aseptic loosening of a c e m e n t e d h e m i a r t h r o p l a s t y (I case), and revision of a solidly fixed u n c e m e n t e d femoral c o m p o n e n t for intractable thigh pain (I case). In 13 patients, this was the first revision procedure. F o u r t e e n patients had u n d e r g o n e 1 previous revision arthroplasty, 6 had u n d e r g o n e 2 previous revisions, and 2 patients had u n d e r g o n e 3 previous revision procedures. The m e a n time interval from the most recent surgery to the current procedure was 7.7 years (range 3 m o n t h s to 17 years). One patient u n d e r w e n t primary acetabular arthroplasty, and 25 patients u n d e r w e n t revision of the acetabular c o m p o n e n t with an u n c e m e n t e d porous i n g r o w t h socket. In 2 cases, structural acetabular allogralt was also necessary. The a c e t a b u l u m was not revised in 9 cases, although we routinely replaced the p o l y e t h y l e n e liner and r e m o v e d the screws in solidly fixed p o r o u s - i n g r o w t h shells. Our surgical technique of impaction bone-grafting was standard. The proximal f e m u r was debrided of all retained c e m e n t and fibrous m e m branes. Prophylactic cerclage cables were used w h e r e the bone was judged to be too w e a k to withstand the hoop stresses generated by inrpaction of the morsellized allograft (8 cases). Segm e n t a l defects were repaired using cortical strut allografts, w h i c h were coated on their undersurface with morsellized allograft and secured with cerclage cables (9 cases). An occlusive intramedullary plug was t h e n inserted to a point distal to the most distal cortical defect and the femoral canal was filled with impacted morsellized allograft bone prepared from fresh-frozen femoral heads. We used a combination of distal and proximal impactors (X-change Revision I n s t r u m e n t System, Howmedica, Rutherford, N J) to fashion an appro-

priate n e o m e d u l l a r y canal for the p r e d e t e r m i n e d prosthesis size. As r e c o m m e n d e d , we always impacted the trial stem a further 5 m m to create space for the centralizer and c e m e n t mantle. We used grading systems of b o t h the EndoKlinik [14] and the A m e r i c a n A c a d e m y of Orthopaedic Surgeons (AAOS) Committee on the Hip [15] to assess the preoperative femoral bone stock. Using the Endo-Klinik grading system, we found 6 with grade 2, 22 with grade 3 and 7 with grade 4 bone loss. Under the AAOS system, we found I6 cavitary defects, 10 combined cavitary and segmental defects, and 9 cases of femoral ectasia. After surgery, we routinely obtained an anteroposterior (AP) radiograph of the l e m u r to rule out any u n d e t e c t e d perioperative problems. Because the quality and magnification of this were variable, we obtained repeat radiographs on postoperative day 5. These included an AP view of the pelvis, including the proximal third of b o t h femurs, a lateral view of the hip, and full AP and lateral radiographs of the entire f e m u r . Radiographs were repeated at 6, 12, and 26 weeks. On each set of radiographs, we d o c u m e n t e d the distance from the tip of the greater trochanter to the tip of prosthesis, the distance from the tip of the prosthesis to the intramedullary plug, and the a m o u n t of migration of the stem tip into the polym e t h y l methacrylate distal centralizer. By measuring the length of the prosthesis on the radiograph, we were able, in each set of radiographs, to eliminate any bias created by variable magnification factors. These m e a s u r e m e n t s permitted accurate determination of early subsidence. We routinely m e a s u r e d the varus/valgus position of the prosthesis on the AP radiograph and w h e t h e r the prosthesis angled anteriorly or posteriorly o n the lateral radiograph. We also routinely assessed the degree of prosthesis anteversion on the lateral radiograph. The postoperative c e m e n t mantle was e x a m i n e d for each of G r u e n zones 1-14 [16]. We d e t e r m i n e d the m i n i m u m thickness of the c e m e n t mantle in each zone w h e r e the mantle could be clearly distinguished from the impacted allograft. W h e r e this distinction could not be m a d e with confidence, we m a r k e d the result as unclear. In addition, for each zone w h e r e a c e m e n t mantle could be identified, we n o t e d the presence or absence of voids within the mantle. The follow-up radiographs were carefully evaluated for the presence of radiolucencies and the prosthesis-cement and cement-allograft interfaces. Any evidence of fractures in the c e m e n t mantle was recorded.

Cement Mantle in Impaction AIIografting

Finally, to p e r m i t m o r e detailed assessment of the c e m e n t mantle, w e p e r f o r m e d 4 i m p a c t i o n allografting p r o c e d u r e s w i t h the X-change system on 4 cadaveric femurs. In each case, the femoral h e a d a n d condyles w e r e r e m o v e d a n d morseEized and the p r o x i m a l f e m u r was r e a m e d m a x i m a l l y using a c o m b i n a t i o n of flexible, straight, a n d conical r e a m e r s to create a cavitary defect. An i m p a c t i o n allografting was t h e n p e r f o r m e d in the standard m a n n e r . Pre- and postoperative radiographs w e r e taken, after w h i c h the f e m u r was transected t h r o u g h the centers of G r u e n zones 1 a n d 7, 2 a n d 6, and 3 a n d 5, respectively, to allow visual inspection of the c e m e n t m a n t l e at each level. More detailed radiographic assessment was m a d e by p e r f o r m i n g contact radiographs of 0.5-cm disks of f e m u r at each of the 3 levels.

Results Complications Intraoperative complications included 4 longitudinal cracks in the proximal f e m u r during impaction, which were treated with cerclage wires, and 1 case of severe hypoxia and h y p o t e n s i o n following ~raft impaction, w h i c h resolved uneventfully. Early postoperative complications included a partial foot drop in 1 case, w h i c h resolved fully within 2 weeks, a n d 1 case of unstable angina requiring e m e r g e n c y balloon angioplasty. There w e r e 2 postoperative f e m o r a l shaft ~!ractures occurring at 6 and 8 weeks. Both w e r e treated w i t h cortical o n l a y allograft and b o t h healed uneventfully. Postoperative dislocations occurred in 2 cases, at 3 a n d 6 m o n t h s . Both w e r e in patients with m o r e t h a n 10 m m of prosthesis subsidence ( l l a n d 20 ram). One was treated w i t h closed reduction. The patient w i t h 20 m m of shortening was treated with revision to an u n c e m e n t e d prosthesis, a n d this a c c o u n t e d for the only revision in the series.

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cortical defect. In the r e m a i n i n g 7 cases, there was generalized diaphyseal cortical thinning w i t h o u t a discrete cortical deficit.

Cement Mantle The postoperative AP and lateral radiographs w e r e carefully assessed for all 35 patients, with the exception of 2 unavailable lateral radiographs. This yielded 476 G r u e n zones for analysis. In 90 zones, the radiodensity of the c e m e n t was not sufficiently different f r o m that of the i m p a c t e d allograft to permit confident m e a s u r e m e n t of the c e m e n t mantle, a n d these w e r e excluded. Of the r e m a i n i n g 386 zones, I 5 4 (39.9%) h a d areas w h e r e the c e m e n t m a n t l e was absent (Fig. I), a n d a further 23 (6.0%) h a d areas with a c e m e n t m a n t l e less t h a n 2 mrn wide. Of the 208 zones with a c e m e n t m a n t l e of 2 m m or wider, 152 s h o w e d evidence of voids within the cement. The distribution of the c e m e n t m a n t l e for the different G r u e n zones is displayed in Figure 2. It can be seen that c e m e n t was m o s t consistently f o u n d in zones 6, 7, 8, a n d 14 and was m o s t consistently deficient in zones 3 a n d 5. Of particular note is that 71.4% of patients had areas of no c e m e n t in zone 5.

Subsidence and Cement Fracture The a m o u n t of subsidence of the femoral c o m p o n e n t into the f e m u r was m e a s u r e d on available fol-

Component Positioning The position of the femoral stem on the postoperative AP radiograph ranged f r o m neutral to 4 ° of varus. No c o m p o n e n t was placed in a valgus position. On the lateral radiograph, stem position ranged f r o m 6 ° of anterior angulation to 3 ° of posterior angulation. The distal i n t r a m e d u l l a r y plug was inserted to a m e a n of 46.7 m m distal to the m o s t distal cortical defect in 26 cases (range, 1 2 - I 3 0 m m ) . In 2 cases, the plug did not e x t e n d distal to the m o s t distal

Fig. I. Radiograph of the femur of a 74-year-old woman following impaction allografting with supplementary lateral cortical strut allograft. Note the paucity of cement in Gruen zones 3 and 5.

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72"4%

S2.2%

33 "3%

Fig. 2. Percentage of cases with a cement mantle of more than 2 mm for each Gruen zone. Unclear cases have been excluded.

Fig. 3. Radiograph of the femur of a 76-year-old man 12 weeks following impaction allografting. There has been catastrophic subsidence associated with fragmentation of the cement mantle.

l o w - u p radiographs. We identified a group of 7 patients in w h o m the c o m p o n e n t migrated distally m o r e t h a n I0 m m in the first 6 m o n t h s after surgery (range, 11-34 m m ) . We assessed this group separately. Four were p e r f o r m e d for aseptic loosening and 3 as second-stage procedures in two-stage revisions for infection. None s h o w e d clinical or laboratory evidence of ongoing sepsis. Four of these patients had obvious fracture and fragmentation of the c e m e n t mantle on plain radiographs (Fig. 3). In 2 further cases, the c o m p o n e n t appeared to be migrating t h r o u g h the c e m e n t mantle w i t h o u t radiographic evidence of c e m e n t fracture. In a final case, the prosthesis with its c e m e n t mantle appeared to be migrating distally as a composite within the allograft. In 5 cases, the lateral radiograph d e m o n s t r a t e d a reduction in anteversion or a swing into retroversion of the femoral c o m p o n e n t as it migrated distally. This corresponded to the clinical impression of increasing external rotation of the limb. Only I patient d e m o n s t r a t e d a change in alignment on the AP radiograph with an increase in c o m p o n e n t varus from 2 ° to 6 ° (Fig. 4).

c e m e n t were f o u n d in 22 of 48 Gruen zones examined, and a further 17 h a d areas w h e r e the mantle was less t h a n 2 m m . Only 9 zones h a d a u n i f o r m

In vitro Studies Transection of the cadaveric femurs t h r o u g h the relevant Gruen zones confirmed the i n a d e q u a c y of the c e m e n t mantle in each case. Areas of absent

Fig. 4. Radiograph of the femur of a 70-year-old woman 6 months following impaction allografting. The component has subsided and drifted into varus. There is an obvious cement mantle fracture (solid arrow).

Cement Mantle in Impaction AIIografting

m a n t l e of at least 2 m m . C e m e n t was m o s t consistently f o u n d a r o u n d the middle of the stem a n d was almost always absent a r o u n d the distal stem.

Discussion This study d e m o n s t r a t e s that the c e m e n t m a n t l e p r o d u c e d b y the Exeter i m p a c t i o n allograft technique is c o m m o n l y i n c o m p l e t e a n d frequently associated w i t h the presence of voids within the c e m e n t mantle. A l t h o u g h not i n t e n d e d as a clinical follow-up report, we h a v e also identified 4 patients w i t h radiographic evidence of c e m e n t m a n t l e fracture w i t h i n 6 m o n t h s of surgery, a n d we are concerned a b o u t the longevity of a n y c e m e n t e d f e m o r a l c o m p o n e n t w i t h a c e m e n t m a n t l e fracture rate in excess of 10% at 6 m o n t h s . It has b e e n suggested that the design ot the Exeter prosthesis i m p r o v e s torsional stability a n d increases c o m p r e s s i o n at the b o n e - c e m e n t interface, a n d that this occurs by subsidence ol the prosthesis b o t h w i t h i n the graft a n d within the c e m e n t [3]. The latter p h e n o m e n o n has Seen attributed to cold flow of c e m e n t u n d e r compression [17] F r a n z e n et al., h o w e v e r , in an analysis of m i g r a t i o n of the f e m o r a l c o m p o n e n t following i m p a c t i o n allografting using a different prosthesis, d e m o n s t r a t e d a t e n d e n c y for prosthesis subsidence a n d r e t r o v e r s i o n that t h e y believed was m o r e than could be explained b y creep of the c e m e n t [18]. They suggested t h a t insufficient i m p a c t i o n of b o n e - g r a f t , revascularization of the graft, or fracture of the c e m e n t - g r a f t c o m p l e x m i g h t cause early migration. We h a v e s h o w n that radiologically evident fractures of the c e m e n t m a n t l e w e r e present in 4 of 7 of o u r patients w h o h a d m a r k e d early m i g r a t i o n of the prosthesis. There are several possible explanations for the i n a d e q u a c y of the c e m e n t mantle. First, we beEeve that the p r o x i m a l impactors and trial prostheses should be designed to allow for a circumferential c e m e n t m a n t l e of at least 2 m m a r o u n d the definitive prosthesis. M e a s u r e m e n t s of the trial c o m p o n e n t relative to the actual prosthesis d e m o n s t r a t e that w h e r e a s the differential does allow a d e q u a t e r o o m for c e m e n t proximally, there is almost no space for c e m e n t distally. This takes into consideration the r e c o m m e n d a t i o n that the trial s t e m be i m p a c t e d a f u r t h e r 5 m m to allow r o o m for cement. In addition, the actual s t e m is longer t h a n the trial s t e m a n d so the only cavity that is created to a c c o m m o d a t e the distal s t e m a n d c e m e n t m a n fie is that created by the guidewire. Second, it is possible that s o m e e x p a n s i o n ot the i m p a c t e d allograft occurs as blood is absorbed prior

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to c e m e n t i n g a n d this reduces the space available for cement. Finally, the c e m e n t technique has b e e n transferred f r o m that developed for use in p r i m a r y hip arthroplasty with the Exeter prosthesis ( H o w m e d ica, Rutherford, N J). It m a y be that the p r o x i m a l femoral seal, w h i c h is used to pressurize the cement, actually produces implosion and collapse of the columns of i m p a c t e d allograft and that this further reduces the available space for cement. A review of the o t h e r reports on the use of impaction allografting in the p r o x i m a l f e m u r did not reveal adequate i n f o r m a t i o n on the c e m e n t mantles being produced. Gie et al. classified their c e m e n t filling as excellent, good, fair, poor, or defective but gave no indication as to the criteria e m p l o y e d for assigning these categories [3]. Neither Elting et al. [4] n o r Meding et al. [5] comm e n t e d on the a d e q u a c y of their initial c e m e n t mantles. In principle, we are attracted by the potential of i m p a c t i o n allografting to recreate a viable p r o x i m a l femur, but w e believe that modifications of the surgical technique are necessary to i m p r o v e the consistency of the c e m e n t m a n t l e a n d optimize the clinical result.

References 1. Slooff TJJH, Huiskes R, van Horn J, Lemmens AJ: Bone grafting in total hip replacement for acetabular protrusion. Acta Orthop Scand 5:593, 1984 2. Simon JE Fowler JL, Gie GA et al: Impaction cancellous grafting of the femur in cemented total hip revision arthroplasty. J Bone Joint Surgery 73B (suppt 73):1991 3. Gie GA, Linder L, Ling RSM et al: Impacted cancellous allografts and cement for revision total hip arthroplasty. J Bone Joint Surg 75B:14, 1993 4. Elting J J, Mikhail WEM, Zicat BA et al: Preliminary report of impaction grafting for exchange femoral arthroplasty. Clin Orthop 319:159, 1995 5. Meding JB, Ritter MA, Keating EM, Faris PM: Impaction bone grafting with cemented stem in revision total hip arthroplasty: minimum two-year follow-up. Presented at the 63rd annual meeting of the American Academy of Orthopaedic Surgeons, Atlanta, Georgia, February 1996 6. Noble PC, Tullos HS, Landon GC: The optimum cement mantle for total hip replacement: theory and practice, p. 145. In Instructional course lectures, the American Academy of Orthopaedic Surgeons, vol. 40. American Academy of Orthopaedic Surgeons, Park Ridge, IL, 1991 7. Huiskes R: Some fundamental aspects of human joint replacement: analyses of stresses and heat conduction in bone-prosthesis structures. Acta Orthop Scand Suppl 185:1980

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8. Kwak BM, Lim OK, Kim YY, Rim K: An investigation of the effect of cement thickness on an implant by finite element stress analysis. Int Orthop 2:315, 1979 9. Jasty M: W h y cemented femoral components become loose, p. 151 In: Instructional course lectures, the American Academy of Orthopaedic Surgeons, vol. 40. American Academy of Orthopaedic Surgeons, Park Ridge, IL, 1991 10. A n t h o n y PP, Gie GA, Howie CR, Ling RSM: Localized endosteal bone lysis in relation to the femoral components of cemented total hip arthroplasties. J Bone Joint Surg 72B:971, 1990 l l. Ebramzadeh E, Sarmiento A, McKellop HA et al: The cement mantle in total hip arthroplasty: analysis of long-term radiographic results. J Bone Joint Surg 76A:77, 1994 12. Mulroy WF, Estok DM, Harris WH: Total hip arthroplasty with use of so-called second-generation cementing techniques. J Bone Joint Surg 77A: 1845, 1995 13. Sarmiento A, Grnen TA: Radiographic analysis of a low-modulus titanium-alloy femoral total hip com-

14.

15.

i6.

17.

18.

portent: two to six-year follow-up. J Bone Joint Surg 67A:48, 1985 Engelbrecht E, Heinert I¢: Klassifikation und Behandlungsrichtlinien yon Knochensubstanzverlusten bei Revisionsoperationen am Huftgelenkmittelfristige Ergebnisse: Primare und Revisionsalloarthroplastik hrsg-Endo-Klinik, p. 189. SpringerVerlag, Hamburg/Berlin, 1987 D'Antonio J, McCarthy JC, Bargar WL, et al: Classification of femoral abnormalities in total hip arthroplasty. Clin Orthop 296:133, 1993 Gruen TA, McNeice GM, Amstutz HC: "Modes of failure" of cemented stem-type femoral components. Clin Orthop 141:17, I979 Lee AJC, Perkins RD, Ling RSM: Time-dependent properties of polymethylmethacrylate bone cement. p. 85. In: Older J (ed): Implant bone interface. Springer-Verlag, London, 1990 Franzen H, Toksvig-Larsen S, Lidgren L, Onnerfalt R: Early migration of femoral components revised with impacted cancellous allografts and cement: a preliminary report of five patients. J Bone Joint Surg 77B: 862, 1995