Current Orthopaedics (2005) 19, 255262

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homogeneous transfer of forces to the proximal femur. This is best provided by

Introduction

Arthritis of the hip affects preitself. Early attempts at surgical treatment of hiparthritis were directed at replacing the joint

cies generally led to poor results. However,

swing towards cementless fixation. Long-termsuccess of hip implants is determined by both

pain, and the distal off-loading predisposed tostress shielding with loss of proximal bone stock.4,5

before. They are politically empowered to demandearly surgical intervention to restore quality of life.

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Conservativearthroplasty;Femoral component

Tel.: +44 0 117 928 2658; fax: +44 0 117 929 4217.

Ever younger cohorts are presenting for total hip

0268-0890/$ - see front matter & 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.cuor.2005.04.002

E-mail address: ian.learmonth@bristol.ac.uk.improved materials, better fixation and a greaterunderstanding of the tribological imperatives havegenerated a resurgence of interest in metal-on-metal resurfacing arthroplasty (Fig. 1). Encouragingearly results have been reported.1 The limits of theclinical application are yet to be defined. However,resurfacing arthroplasty does not fall within thescope of this article.

Indeed, when considering the efficacy of porous-coated cementless fixation, Amstutz noted

Theincidence of thigh pain, radiographic stress shield-ing and removal problems must still be solvedy.6

All these issues are addressed by conservativeimplants.Patients today are better informed than eversurfaceseither by interpositional or resurfacingarthroplasty (RA). While there were a few goodlong-term outcomes, material and design deficien-

durability of fixation and articulation. Early ce-mentless implants obtained reproducible fixationdistally. However this was associated with thigh

3retention of the femoral neck.Survivorship of the implant is determined by the durability of fixation and of the

articular interface. Early attempts to achieve a conservative hip replacement werebetrayed by poor materials, inadequate fixation and failure of the articulation. Thispaper explores how these shortcomings were addressed during the evolution of totalhip arthroplasty to produce the contemporary designs of conservative hip implants.& 2005 Elsevier Ltd. All rights reserved.

dominantly the joint

In 1987 Jones and Hungerford2 coined the term

cement disease to describe osteolysis. While thisproved to be a misnomer, it added impetus to theMINI-SYMPOSIUM: HIP REPLACEMENT

(ii) Conservative hip impl

Ian D. Learmonth

University of Bristol, Bristol Royal Infirmary, Bristol

Summary Arthritis offemoral head and the acarticular surfaces. In

KEYWORDSHip arthritis;Surgery;nts

S2 8HW, UK

e hip primarily involves the articulation between thebulum. The primary surgical objective is to replace thesehieving this it is desirable to attempt to obtain a

www.elsevier.com/locate/cuor

arthroplasty.7 The high probability of revision inthese younger more active patients has been one ofthe main factors driving the quest for more bone-sparing conservative options at total hip replace-ment (THR). More bone would then be available in

the proximal femur for any subsequent revisionsurgery. Conservative implants also appeal to thosesurgeons embracing the increasingly popular con-cept of minimally invasive surgery with acceleratedrehabilitation regimens.8

This paper will review the development ofconservative implants over the years.

Conservative implants

There are a variety of short-stemmed prosthesesthat obtain proximal fixation, such as the CFP(Waldemar-Link), Stellcor (Sulzer) and SHO (Bio-mechanica). However this paper will principallyconsider only those implants that are virtuallyconfined to the metaphysis.Huggler and Jacobs designed the thrust plate

prosthesis (TPP), which was first implanted in1978.9 They reviewed their results in 1993.10 Theimplant (Fig. 2a) is designed to load the medialcortex of the femoral neck as physiologically aspossible. The TPP has evolved through threegenerations. The latest version has an oval thrustplate attached to the mandrel. A central boltpasses through the lateral plate just below thegreater trochanter and engages with a screw thread

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Figure 1 Radiograph of a metal-on-metal resurfacingarthroplasty.

ralrity

I.D. Learmonth256Figure 2 (a) Radiograph showing replacement of the femofemoral prosthesis used by Wiles in 1937. Note the similahead using a thrust plate prosthesis. (b) Radiograph of theto the thrust plate.

contained within the mandrel thrust plate unit. It isof interest how closely this implant resembles theimplant designed by Philip Wiles first inserted in1938 (Fig. 2b).In seeking a

conservative uncemented implantwith proximal fixation, surgeons at the Mayo Clinicrecognised that a wedge-shaped device whichtapered in both the sagittal and coronal planesshould give stability when inserted into an irregu-larly shaped cavity by providing multiple pointcontact. In 1982 these features were incorporatedinto a short double-tapered titanium alloy proximalfemoral replacementthe Mayo Conservative Hip(Fig. 3). The distal end of the implant was curvedinferiorly to provide a flat surface to contact thelateral cortex. The rigidity of mechanical fixation inall planes was found to be similar to that of aconventional cementless implant.The ESKA femoral neck endoprosthesis (CUT) is a

mini-prosthesis which is anchored in the metaphysisand provides proximal physiological stress trans-

mission, thus avoiding stress shielding (Fig. 4). Itlends itself to minimal access surgery and is itselfminimally invasive as only the femoral head isremoved. It has been recommended for youngarthritic patients with good bone quality.11

The IPS (DePuy) femoral stem (Fig. 5a) wasdeveloped approximately 10 years ago. This ana-tomic stem was designed to provide pure proximalloading, thus optimising load transfer in themetaphyseal region and reducing stress shielding.The stem was used principally for alignment andwas designed to have no contact in the diaphysis,thus avoiding distal off-loading. In 1999 Walker etal.12 noted that a lateral flare which loaded thelower region of the greater trochanter would assistin transmitting loads to the proximal femur. Theyalso suggested that stems with a lateral flare couldbe made shorter than designs not incorporating alateral flare.In 1995 Santori designed a customised short-

stemmed implant with the team at StanmoreCustoms. This stem provided an anatomic fit in

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Figure 4 The ESKA femoral neck endoprosthesis.

Conservative hip implants 257Figure 3 The Mayo conservative femoral prosthesis(illustration kindly provided by Dr. B Morrey).

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I.D. Learmonth258the metaphysis with longitudinal slots for rotationalstability, a pronounced lateral flare and no distalstem. The design and manufacture of this implantwas taken over by DePuy International in 2002(Fig. 5b).The similarity of the design of the metaphyseal

region between the IPS and the Santori stem wasrecognised and the Proxima stem was evolved as aresult of the combination of these philosophies.

Figure 5 (a) The proximally fixed IPS. Note that the stem makmetaphysis. (b) Radiograph of the Santori customised femoralthe Santori stemthe Proxima, a conservative metaphysealThe Proxima is a stemless, proximally fixed ana-tomic implant (Fig. 5c). Appropriate sizing andthe anatomic shape provide rotational and axialstability.DePuy have also developed a wedge-shaped

cylindrical implantthe Silent Hipwhich has atextured surface and is impacted into the neck toprovide initial stability (Fig. 6). Long-term stabilityis provided by bone ingrowth. This is a very

es no contact with the diaphyseal cortex, thus loading theimplant. (c) Combining the design features of the IPS andimplant.

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Conservative hip implants 259conservative implant and is not dissimilar to theESKA

cigar prosthesis.

Results

Buergi et al.13 reported on the radiological andclinical outcome of 102 consecutive THRs in whichthe third generation of thrust plate was used.12 Themean follow-up was 58 months (range 26100).

Figure 6 (a, b) The Silent fEighty per cent of patients were younger than 60years of age. Four implants were revisedtwo forinfection and two for aseptic loosening. They notedthat in 85% of cases load transmission occurredthrough the most proximal part of the medialcortex. Huggler et al. reviewed their

long-termresults in 1993 and noted that the basic feature ofthe thrust plate is direct load transfer to the medialcortical bone of the femoral neck. They reportedthat histological examination of an implant re-moved at 8 years confirmed that newly formed

emoral neck prosthesis.

tioIm

in

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relate to conservation of bone stockalthough this

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I.D. Learmonth260bone is in direct contact with the thrust plate withno interposed fibrous tissue.Ishaqui et al.14 reviewed 170 thrust plate

prostheses clinically and radiologically at a meanfollow-up of 58 years. KaplanMeier survivorshipat 8 years was 90.5%. However they noted thatgood to excellent clinical results were achievedafter revising the thrust plate.Morrey et al.15 reported on 162 total hip

replacements in which the Mayo conservativeuncemented femoral component was used. Themean age of the patients was 50.8 years and themean follow-up 6.2 years (range 213). Survivalwithout mechanical loosening was 98.2% at both 5and 10 years, while survival without osteolysis was99% at 5 and 91% at 10 years. While recognising theproblem of osteolysis associated with wear debris,the authors note that its reliable mechanicalstability makes this implant an attractive design,particularly for use in younger patients. They alsoobserved a statistically significant reduction in theamount of blood loss compared with a control groupof uncemented implants and ascribe this to theabsence of reaming of the femoral canal. Inaddition they frequently saw increased bonedensity in zones 3 and 6.Kim16 prospectively followed up a consecutive

series of 60 hips (50 patients) for a minimum of 6years in which a

close proximal fit and shorttapered distal stem prosthesis (IPS) was used. Themean age was 46.6 years with a mean follow-up of6.3 years. Transitory thigh pain was present in 2% ofcases. No component had been revised and therewas no radiological evidence of aseptic loosening.However, a metal-on-polyethylene couple was usedin all hips and a higher rate of polyethylene wearwas noted in these younger patients.We have reviewed 81 consecutive IPS stems

followed up for a mean of 3 years 9 months (range26 years). One hip was revised for deep infection.There have been no other revisions and there wasno radiological evidence of aseptic loosening.Indeed good buttressing of the bone was routinelyencountered in the metaphyseal region. No patientcomplained of thigh pain. This review is due to bepresented at the 7th EFORT Congress in Lisbon inJune 2005.The author reviewed 106 Santori customised

femoral stems. The mean age of the patients was55 years. There were no revisions at a mean follow-up of 2 years (range 19 years). Good condensationof bone was noted circumferentially around thoseimplants that were confined to the metaphysis withno stem. There was no evidence of bone resorptionin any zone in these implants. Early results areencouraging.is seldom the practice of surgeons carrying out thissurgical technique. A concept relating to both thesoft tissue and the bone is to be applauded, butshould be embraced with caution. Few mid-termand long-term results are available for the con-servative implants. In addition the mini-incisionmay be associated with an increased risk ofcomplications. Woolson et al.17 compared THRsperformed with a standard or a mini-incision andfound that the mini-incision group had a signifi-cantly higher risk of wound complications, acet-abular component malposition and poor fit and fillof cementless femoral components.litith reduced soft tissue damage, shorter hospita-ation and an accelerated programme of rehabi-ation and recovery. Minimally invasive should alsowve to last longer, they will also be exposed to ancreased level of activity.Minimally invasive surgery should be associatedhanal activities such as golf, tennis, skiing, etc.plants inserted in these patients will not onlyDiscussion

There has been a recent tremendous resurgence ofinterest in resurfacing arthroplasty. This is the onlysurgical treatment for arthritis of the hip whichpreserves the femoral head. However, RA does notlend itself to minimal access surgery and clinicalconcerns remain regarding the vascularity of thefemoral head and the incidence of femoral neckfractureboth in the short and the longer term. Inaddition there are well-identified contra-indica-tions for RA. These can be broadly defined asfollows:

Anatomical: excessive anteversion, severe slip ofthe femoral epiphysis, etc.

Biomechanical: inability to restore offsetand limb length (valgus neck, coxa breva, coxaplana, etc.).

Pathological: poor supporting bone (osteonecro-sis, multiple large cysts, etc.).

There is therefore a need for alternative con-servative prostheses. There are two major con-temporary issues that are driving the developmentof conservative implants. Firstly the increasingpopularity of minimally invasive surgery and sec-ondly the desire to optimise the loading of theproximal femur and to preserve bone stock.Ever younger cohorts of patients are presenting

for total hip replacement. These patients demandrestoration of their quality of life, which isreflected by their ability to pursue their recrea-

Long-term clinical and radiological results of the Lord totalhip prosthesis. A prospective study. J Bone Joint Surg Br

survey. Ann R Coll Surg Engl 2000;82:338.

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Conservative hip implants 261Wroblewski et al.18 noted that the successfullong-term clinical results with the Charnley lowfriction torque arthroplasty identified proximalfemoral shielding as a long-term problem. Theyascribed this problem to distal load transfer in astiffer stem that no longer fractured. Wroblewskiintroduced the triple taper polished cementedstem to address this problem.18

Proximal stress protection is encountered earlierwith cementless stems, particularly those whichgain fixation in the diaphysis.Many surgeons have therefore sought a more

bone preserving, bone conserving option foryounger more active patients. It has beenshown that forces developed on weightbearingare more evenly distributed to the proximo-medialfemur if the femoral neck is preserved. Thisalso allows for anatomical reconstruction ofthe proximal femur and provides enhancedrotational stability. However a disadvantageof these femoral neck implants is that theycannot adjust for or accommodate anatomicabnormalities of the proximal femur (e.g. excessiveanteversion, etc.).Achieving initial stability may also present

a problem and this initial stability is essentialfor osseointegration and subsequent durablefixation. This led Santori19 to develop the

two-step solution in which a titanium femoralneck prosthesis was initially inserted through thelateral cortex. At 3 months, having achieved securebony fixation, the femoral head is removed, theacetabulum is replaced and a prosthetic femoralhead is applied. While this highlights the potentialproblem of achieving adequate initial stabilityin those cigar-shaped prostheses that rely onimpaction into the femoral neck for fixation,I doubt if this two-stage solution would find wideacceptance.Significant cortical bone mass has been demon-

strated at the proximo-lateral flare of the femur.20

Experiments have shown that if a femoral stem hasa medial and lateral flare proximally, the loads aretransferred to the proximal femur and stressprotection in this area is avoided. This is particu-larly true if there is no stem contact distally, whichcould promote distal off-loading. Indeed, theresults suggest that a stem below the lessertrochanter is unnecessary.12

Another important benefit of a bone-sparing andpreserving proximal femoral implant is the relativeease with which this can be converted to a

conservative revision prosthesis, which needonly invade the proximal diaphysis. This providesone extra step in the revision programme of ayounger patient.8. Irving JF. Direct two-incision total hip replacement withoutfluoroscopy. Orthop Clin North Am 2004;35:17381.

9. Huggler AH, Jacob HA. A new approach towards hipprosthesis design. Arch Orthop Trauma Surg 1980;97:1414.

10. Huggler AH, Jacob HA, Bereiter H, Haferkom M, Ryf C,Schenk R. Long-term results with the uncemented thrustplate prosthesis (TTP). Acta Orthop Belg 1993;59(Supp 1):21523.

11. Thomas W, Lucente L, Mantegna N, Grundei H. ESKA (CUT)endoprosthesis. Orthopaedics 2004;33:12438.

12. Walker PS, Culligan SG, Hua J, Muirhead-Allwood SK, BentleyG. The effect of a lateral flare feature on uncemented hipstems. Hip Int 1999;9:7180.

13. Buergi ML, Stoffel KK, Jacob HA, Bereiter HH. Radiologicalfindings and clinical results of 102 thrust plate femoral hip1996;78-B:88491.6. Amstutz HC, Namba R. Cementless femoral fixation using

porous ingrowth fixation. In: Amstutz HC, editor. Hiparthroplasty. New York: Churchill Livingstone; 1991.p. 285293.

7. Tennent TD, Goddard NJ. Current attitudes to total hipreplacement in the younger patient: results of a nationalConclusion

There is an old surgical aphorism

the ability toperform an operation is not an indication to do it.Similarly the mere ability to manufacture and toinsert a conservative femoral implant is notnecessarily an indication to use it. If the surgeonis confident that the implant that he routinely useswill outlast the patientthen he should use it.Otherwise he should think about the next operationand consider a bone-sparing option. Conservativeproximal femoral implants offer such an option.

Acknowledgements

I would like to thank Alison Foxwell and Martha vander Lem for their assistance in the preparation ofthis manuscript.

References

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2. Jones LC, Hungerford DS. Cement disease. Clin Orthop1987;225(Dec):192206.

3. Callaghan JJ, Dysart SH, Savory CG. The uncementedporous-coated anatomic total hip prosthesis. Two-yearresults of a prospective consecutive series. J Bone JointSurg Am 1988;70-A:33746.

4. Engh CA, Bobyn JD, Glassman AH. Porous coated hipreplacement. The factors governing bone ingrowth, stressshielding and clinical results. J Bone Joint Surg Br 1987;69-B:4455.

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15. Morrey BF, Adams RA, Kessler M. A conservativefemoral replacement for total hip arthroplasty.A prospective study. J Bone Joint Surg Br 2000;82-B:9528.

16. Kim YH. Cementless total hip arthroplasty with a closeproximal fit and short tapered distal stem (third-generation)prosthesis. J Arthroplasty 2002;17:84150.

17. Woolson ST, Mow CS, Syquia JF, Lannin JV, Schurman DJ.Comparison of primary hip replacements performed with astandard incision or a mini-incision. J Bone Joint Surg Am2004;86-A:13538.

18. Wroblewski BM, Siney PD, Fleming PA. Triple taper polishedstem in total hip arthroplasty: rationale for the design,surgical technique and seven years of clinical experience.J Arthroplasty 2001;16(Supp 1):3741.

19. Santori F. Personal communication; 2004.20. Fetto JF, Bettinger P, Austin K. Reexamination of hip

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(ii) Conservative hip implantsIntroductionConservative implantsResultsDiscussionConclusionAcknowledgementsReferences