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The Journal of Arthroplasty Vol. 27 No. 1 2012

A Prospective Short-Term Outcome Studyof a Short Metaphyseal Fitting Total

Hip Arthroplasty

Young-Hoo Kim, MD, Jun-Shik Kim, MD, Jong-Hwan Joo, MD,and Jang-Won Park, MD

Abstract: The purpose of this study was to determine whether the short, metaphyseal fittingfemoral stem would achieve stable fixation without diaphyseal fixation. A total of 126 patients(144 hips) were included in the study, and their mean age was 53.9 years (26-65 years). The meanduration of follow-up was 4.5 years (4-5 years). The predominant diagnosis was osteonecrosis offemoral head (88 of 144 hips, or 61%). The mean preoperative Harris hip score was 45 points,which improved to 96 points by the final follow-up. Western Ontario and McMaster UniversitiesOsteoarthritis score and patient's activity score were improved substantially at the final follow-up.This short, metaphyseal fitting cementless femoral component achieved stable fixation withoutdiaphyseal fixation, and there was minimal stress-shielding bone resorption in the calcar region.Keywords: primary total hip arthroplasty, short stemless, metaphyseal fitting, cementlessanatomical femoral component.© 2012 Elsevier Inc. All rights reserved.

Although excellent long-term results have been reportedwith cementless femoral stems in total hip arthroplasty(THA) [1-4], proximal stress shielding and thigh pain arethe main concerns after THA [1-4]. An optimal fit of thecementless stem in themetaphysis of the proximal femuris known to be important to achieve physiologicproximal load transfer [5]. To reproduce natural loadtransfer while obtaining optimal stability, a short stemwas developed [6]. A short stem is bone conserving,violating less bone stock and providing more favorableconditions should revision be required. Several types ofshort stems have been introduced, with promising short-term results [7-11]. However, Albanese et al [12] foundthat most of these short stems had substantial stressshielding in the proximal femur as indicated by bonemineral density examinations.

e Joint Replacement Center of Korea, Ewha Womans Universityedicine, Seoul, South Korea.ted July 19, 2010; accepted February 7, 2011.nflict of Interest statement associated with this article can beoi:10.1016/j.arth.2011.02.008.ic exhibit presentation at the annual meeting of theAcademy of Orthopaedic Surgeons, February 25 to 28,Vegas, NV.requests: Young-Hoo Kim, MD, The Joint ReplacementKorea at Ewha, Womans University, MokDong Hospital,kDong, YangCheon-Gu, Seoul 158-710, Korea.Elsevier Inc. All rights reserved.

403/2701-0015$36.00/0016/j.arth.2011.02.008

88

To attempt reduction of stress shielding and thigh painas well as to improve survivorship, a new short, meta-physeal fitting cementless anatomical femoral stem(Proxima; DePuy, Leeds, UK) was developed (Fig. 1).This new short stem provided vertical stability by thewedge shape of the stemwith the addition of a lateral flareand preservation of the femoral neck. Preservation offemoral neck provides greater trosional stability andreduces distal migration of the femoral stem [13]. Theabsence of the distal stem fixation is allowed because ofthe effective stability given by the lateral flare andpreservation of the femoral neck. The absence of thediaphyseal anchorage attempts proximal load transfer toreduce stress shielding and thigh pain. It also attemptspreservation of the femoral canal and femoral elasticityand ease of revision [6].We conducted a prospective, nonrandomized study to

evaluate the short-term clinical and radiographic resultsof the short, metaphyseal fitting femoral stem. Boneremodeling of the proximal femur was also examinedusing dual-energy x-ray absorptiometry (DEXA).

Materials and MethodsBetween May 2005 and April 2006, the senior author

(YHK) performed consecutive primary cementless THAsusing a Proxima stem (DePuy, Leeds, UK) on 144 hips in126 patients at a single university hospital. The seniorauthor used only this prosthesis during this period. Nopatient was lost to follow-up examination, and no

Fig. 1. A Proxima femoral stem is designed with a longerproximomedial portion and a highly pronounced lateral flareand allows for preservation of the femoral and neck.

Short Metaphyseal Loading Femoral Stem � Kim et al 89

patient died. Therefore, all patients were available forclinical evaluation at a mean period of 4.5 years (range,4-5 years) after surgery. All patients were examinedclinically and radiographically at each follow-up. Thestudy was approved by our institutional review board,and all patients provided informed consent.

Fig. 2. The round-the-corner technique for femoral broaching andof damaging the greater trochanter and the abductor muscles if a cused. Accordingly, the short stem permits preparation of the femtrochanter. The broach is inserted into the divided femoral neck athen, steadily tilted in the correct alignment while advancing intothe-corner.

The mean age of the patients at the time of THA was53.9 years (range, 26-65 years). There were 70 men and56 women. The diagnosis necessitating THA was osteo-necrosis of femoral head in 88 hips (61%), osteoarthritisin 28 hips (19%), developmental dysplastic hip in 23hips (16%), and traumatic arthritis in 5 hips (4%). Thepresumed cause of the osteonecrosis was ethanol abuse in53 patients (60%), unknown in 31 (35%), and steroiduse in 4 (5%). Patients' mean weight was 66.3 kg (range,46-94.8 kg), mean height was 161 cm (range, 142-180 cm), and mean body mass index was 25.6 kg/m2

(range, 17.4-33.3 kg/m2).A cementless pinnacle acetabular component (DePuy,

Warsaw, IN) was used in all hips. These componentswere press fitted after the acetabulum had been under-reamed by 1 mm. The cup sizes used ranged from 52 to58 mm, and 36-mm Biolox delta liner (DePuy, Leeds,UK) was used in all hips. All patients received a Proximafemoral component with a 36-mm Biolox delta ceramichead (DePuy). All operations were performed using aposterolateral approach by the senior author. Thefemoral neck was cut horizontally at a head-neckjuncture. A “round-the-corner” technique was used forfemoral broaching and implant insertion (Fig. 2). Thetechnique for femoral broaching and insertion of the

implant insertion. The presence of lateral flare produces a riskonventional technique of femoral preparation and insertion isur with a curved movement of the broach distal to the greaternd driven distally in a varus direction by hammer blows and,the femoral metaphysis. We refer to this technique as round-

90 The Journal of Arthroplasty Vol. 27 No. 1 January 2012

implant is specific to it as the presence of lateral flareproduces a risk of damaging the greater trochanter andthe abductor muscles if a conventional technique offemoral preparation and insertion is used. Accordingly,the short stem permits the preparation of the femurwith a curved movement of the broach distal to thegreater trochanter. The broach is inserted into thedivided femoral neck and driven distally in a varusdirection by hammer blows and then steadily tilted inthe correct alignment while advancing into the femoralmetaphysis. We refer to this technique as round-the-corner. The size of the femoral component selectedmatched the size of the largest broach used. The dimen-sion of the coated component was 0.5 mm larger thanthat of the prepared metaphysis.Patients were allowed to stand on the second post-

operative day, and they progressed to full weight-bearing with crutches as tolerated. They were advisedto use a pair of crutches for 6 weeks and to use a canethereafter if required.Clinical follow-up was conducted at 3 months, 1 year,

and yearly thereafter. Radiographs were taken at 1 weekafter surgery and at each follow-up. Harris hip scores[14] and Western Ontario and McMaster UniversitiesOsteoarthritis (WOMAC) score [15] were determined

Fig. 3. Postoperative assessment of implant position. (A) The stcomparison of the angle of the anteroposterior prosthetic neck-fe(130°). Neutral position, a equals b or within 3° of each other; var(B) The stem position in the lateral plane was determined by cofemoral shaft (c) with the angle of the lateral prosthetic neck shaftanterverted, c less than d.

before surgery and at each follow-up. Patients scoredany thigh pain on a 10-point visual analog scale [16] (0,no pain; 10, severe pain). Patients' activity level afterTHA was assessed using the scoring system of Tegnerand Lysholm [17]. This scale, in which work and sportsactivities are graded numerically (0 points, hip-relateddisability; 10 points, participation in competitive sportsat the national level), was used as a complement to thefunctional score.Radiographs were analyzed by a research associate

(SML) who had no knowledge of the patients' names. Asupine anteroposterior radiograph of the pelvis withboth hips in 15° internal rotation and no abduction andcross-table lateral radiograph of each hip were obtainedfor every patient. The femoral morphology was deter-mined in preoperative radiographs using Dorr's classifi-cation system [18]. The position of the stems inanteroposterior and lateral planes was determined (Fig.3). We analyzed radiographs at final follow-up for thepresence of radiolucent lines and osteolytic lesionsaround the acetabular component (in zones I, II, andIII according to the classification system of DeLee andCharnley [19]) and the femoral component (Gruenzones 1 and 7) [20]. Given the lack of distal stem in theshort femoral components, region from the lower border

em position in the anteroposterior plane was determined bymoral shaft (a) with the angle of the prosthetic neck stem (b)us position, a less than b; and valgus position, a greater than b.mparison of the angle of the anteroposterior prosthetic neck-(d) (5°). Anatomical, c equals d or within 3° of each other, and

Short Metaphyseal Loading Femoral Stem � Kim et al 91

of the lesser trochanter to the tip of the greatertrochanter was defined as zone 1, and the region fromthe lower border of the lesser trochanter to femoral neckcut level was defined as zone 7.Loosening of the femoral component was defined

when there was a progressive axial subsidence ofgreater than 2 mm or a varus or valgus shift of greaterthan 2° [21]. Stem subsidence was evaluated by mea-suring the distance between the tip of the greatertrochanter and the lateral flare of the stem as well as bymeasuring the distance between the most proximome-dial part of the porous-coated surface of the stem andthe upper border of the lesser trochanter. These values,obtained from anteroposterior radiographs taken 1week after surgery, were compared with those obtainedfrom the anteroposterior radiographs taken at the finalfollow-up to define the amount of the subsidence. Theintraobserver error for this measurement was deter-mined by the intraclass correlation coefficient aftermeasurements were obtained 3 times at 3-day intervals.Bone ingrowth into the femoral components was con-sidered to have occurred when there was a direct ex-tension of the trabecular striation between the femurand the component.Definite loosening of the acetabular component was

diagnosed when there was a change in the position ofthe component (N2 mm vertically and/or medially orlaterally) or a continuous radiolucent line greater than2 mm in width on both anteroposterior and lateralradiographs [21]. Vertical change in the position of theacetabular component was measured between its in-ferior margin and the inferior margin of the ipsilateralanatomical teardrop, and a horizontal change was mea-sured between the Köhler line and the center of theouter shell of the acetabular component [22]. Boneingrowth into the acetabular component was consideredto have occurred when there was a direct contact of thetrabecular striation between the acetabulum and thecomponent. The sites of any osteolysis in the acetabulumwere recorded according to the classification system ofDeLee and Charnley [19], and the Gruen zones 1 and7 in the femur [20] were recorded.Proximal femoral bone resorption was graded radio-

logically [3], with grade 1 indicating atrophy or round-ing off of the calcar; grade 2, loss of density in the calcarregion with preservation of the medial cortical wall tothe level of the lesser trochanter; grade 3, loss of densityin the calcar region with loss of the medial corticalwall to the level of the lesser trochanter; and grade 4,loss of bone density in the entire medial cortical walldistal to the level of the lesser torchanter. Measurementof linear wear of the Biolox delta ceramic liner was notreadily feasible.All patients underwent DEXA scanning of the pelvis

and proximal femur (zones 1 and 7) using the HologicQDR 4500A densitometer (Hologic Inc, Waltham, MA)

and the metal-removal hip-scanning mode. The firstDEXA scan was taken 1 week after surgery and servedas a baseline of bone mineral density (BMD) for thesubsequent scans. Further scan was obtained at finalfollow-up. Bone mineral density was calculated in 2regions of interest surrounding the femoral component.Heterotopic ossification, if present, was graded accord-

ing to the classification system of Brooker et al [23]. Wedetermined potential complications, such as dislocationand periprosthetic fracture.Intraobserver reliability was almost perfect for both

the measurements of radiographic and BMD findings(P b .01 in each case) [24]. The value of κ (intraobserverreliability) was 0.97 for the measurement of radiograph-ic findings and 0.95 for the measurement of BMDfinding. Changes in Harris hip scores and BMD findingswere evaluated with the 2-tailed t test. The χ2 test withYates correction was used to analyze radiographic data.All statistical analyses were performed using the statis-tical software package for social sciences, version 14(SPSS Inc, Chicago, IL). Statistical significance was setat P b .05.

ResultsHarris hip score, WOMAC score, thigh pain, and pa-

tients' activity level improved significantly (P ≤ .001)after THA. The mean Harris hip score was 45 points(range, 15-58 points) before surgery and 96 points(range, 85-100 points) at the final follow-up. The meanpreoperative WOMAC score was 63 ± 13.24 points(range, 43-95 points). The mean postoperative WOMACscore was 11 ± 5.3 points (range, 5-20 points) at the finalfollow-up. No patient had thigh pain at any follow-upperiod. Many patients were active despite postoperativeadvice to avoid activities involving high impact. Allpatients had a Tegner and Lysholm [17] activity scoreof 5 or 6 points at review, indicating participation instrenuous farm work (5 points) or playing recreationalsports such as tennis (6 points). No clicking or squeakingsound was heard in any hip.The morphology of the proximal femur was Dorr

type A in 138 (96%) of 144 hips and type B in 6 hips(4%). In the anteroposterior plane, 136 femoral com-ponents (94%) were in a neutral position, and 8 (6%)were in varus. In the lateral plane, all femoral compo-nents were in an anatomical position. No hip had migra-tion of the femoral component in excess of 1 mm (mean,0.3 mm; range, 0.0-0.8 mm). No hip had a radiolucentline around the porous-coated surface of the femoralcomponent on either anteroposterior or lateral radio-graphs. All acetabular components were deemed to havebone ingrowth at the latest follow-up (Fig. 4). No hiprequired revision of any component for aseptic loosen-ing. No hip had a dislocation or periprosthetic fracture.At the latest evaluation, all hips had no discernible sites

of resorption or only slight rounding off of osteomized

Fig. 4. Radiographs of a 43-year-old man with osteonecrosisof both femoral heads. (A) Preoperative radiograph of bothhips revealed collapse of both femoral heads (Ficat stage IV).(B) Postoperative radiograph of both hips obtained 2 yearsafter surgery reveals that the Proxima stem is solidly fixed in asatisfactory position in both hips.

92 The Journal of Arthroplasty Vol. 27 No. 1 January 2012

neck. No acetabular or femoral osteolysis was identified.Around the acetabular component, the mean BMD wasdecreased in all acetabular zones by the final follow-up.Around the femoral component, the BMD was slightlydecreased in Gruen zone 7, but it was increased slightlyin zone 1 (Table 1).No patient had heterotopic ossification (grade III or IV).

DiscussionWe obtained rigid fixation of this short, metaphyseal

fitting Proxima stem without diaphyseal fixation in all

hips; these results were similar to those reported forconventional tapered cementless stems [1-4] and othershort stems [7-11,25,26]. We found that bone resorptionrelated to stress shielding was minimal, as indicatedradiographically and by DEXA.All patients in our series had marked improvement in

hip pain and hip function after the THA with this shortstem. The improvement of Harris hip score in ourpatients with this short stem was better than other shortstems reported by others [7-11,25,26]. The absence ofthigh pain in our study may be attributable to the rigidaxial and torsional stability of this stem in the proximalfemur and an absence of contact between the distal stemand the femoral cortex.One major concern with the short stem was whether

stable fixation of the short stem can be obtained withoutdiaphyseal fixation. Walker et al [27] suggested that thefemoral stem below the lesser trochanter would beunnecessary for a cementless anatomical stem with alateral flare and that a short stem would suffice.Accordingly, Leali and Fetto [28] concluded that aproximally fixed cementless femoral component with aproximal lateral flare provides significant initial stability,which has been shown to be vital to obtain long-termstability through early bone ingrowth. Biomechanicaltests performed in vitro by Westphal et al [29] with theproximal-fitting short metaphyseal stem showed thatadequate stem stability was achieved when bone qualitywas good. Santori et al [30] reported solid fixation oftheir custom-made short femoral stem similar to theproximal-fitting short metaphyseal stem. Their findingsvalidated the assumption that torsional loads can becontrolled without diaphyseal fixation by femoral-neckpreservation and lateral flare of the stem. In our study,early rigid fixation of this short stem was attributable togood bone quality in these young patients, preservationof the femoral neck, and loading for the lateral flare ofthe short stems. Therefore, the short stem can be used inall patients including patients with a deformed femur oran obliterated femoral canal, which would makeconventional THA difficult.The predominant diagnosis in our series was osteone-

crosis of the femoral head. In a histomorphometricevaluation of iliac bone biopsies, Arlot et al [31] andCalder et al [32] proposed that osteonecrosis in theGruen zones [20] 1, 2, 6, and 7 of femur may reduce theremodeling capacity of bone at the implant-bone orimplant-cement interface and thus impair osseointegra-tion and adequate prosthesis fixation. In contrast, Kimand Kim [33] found that most patients who hadidiopathic or osteonecrosis secondary to alcohol abusehad normal or nearly normal bone in the acetabulumand in the areas of the proximal part of the femur thatare crucial for fixation of the implant. In their series,osteonecrosis was predominantly confined to the fem-oral heads. In our series, the rigid fixation of the stem

Table 1. Mean Bone Mineral Density (g/cm2) of the Proximal Femur

Zone

Duration of Follow-Up Monitoring

% Change P Value (2-Tailed t Test)1 wk (Range) 4.5 y (Range)

Femur1 0.824 (0.65-0.88; SD, 0.08) 0.849 (0.56-0.87; SD, 0.07) +3 .0057 1.234 (0.67-1.31; SD, 0.23) 1.141 (0.34-1.35; SD, 0.22) −8 .072

Short Metaphyseal Loading Femoral Stem � Kim et al 93

in the patients with osteonecrosis of the femoral headsupports the findings of Kim and Kim [33].Santori et al [30] reported that their custom-made

femoral stem similar to our short stem had no asepticloosening at the 5-year follow-up point. They observedmild stress shielding (calcar rounding off) in 60% ofcases (78 of 131 femurs), and it was generally non-progressive after 6months after surgery. In our study, nofemoral stem had aseptic loosening. There was onlycalcar rounding off in all hips, and it was nonprogressiveafter 1 year after surgery. We believe that absence of thedistal stemminimizes stress shielding related to proximalfemoral bone resorption.Leali and Fetto [28] performed a BMD study of stems

with a lateral flare, which demonstrated that the bonecontent was preserved at the baseline level or abovethroughout the follow-up period of 1 year. This wasparticularly evident in the proximal prosthesis supportzones (Gruen zones 1, 2, 6, and 7). Likewise, BMDaround the custom short stem of Santori et al [30] wassignificantly higher in zones 1 and 7 when comparedwith other short- or conventional-tapered cementlessimplants 3 years after implantation [12]. In our study,compared with baseline values, BMD decreased in allacetabular zones, suggesting that the stiff metallic ace-tabular shell with Biolox delta ceramic liner led to stressshielding of the cancellous bone of acetabulum. TheBMD changes in all femoral zoneswere very slight (Table1), suggesting a lower level of bending stiffness andallowing a physiologic load transfer in the short stem.The absence of detectable acetabular or femoral

osteolysis appeared to be attributable to the short-termfollow-up and the use of an Biolox delta ceramic bearingwith negligible wear particles and solid fixation of thecomponent in the acetabulum and in the proximalfemur, limiting the so-called effective joint space [34].The absence of osteolysis in our series echoes the similarfindings for other ceramic-on-ceramic THA [35,36].Our study has some limitations. First, we prospec-

tively collected all data, but the study was not ran-domized, and we had no control group for which weused a different component or different surgicaltechnique to compare and contrast outcomes. Second,our migration analysis of the stem did not use the moreprecise methods of radiostereophotogrammetric analy-sis [37]. Third, the duration of follow-up was shortand was insufficient to allow us to draw significantconclusions because any type of prosthesis shows good

results at less than 5 years. However, there is strongevidence that early (b2 years) stability of cementlessfemoral stem produces good late clinical results [38,39].Kim and Kim [38] reported that early migration (lessthan 1 year) of uncemented porous-coated anatomicalfemoral component was related to the aseptic loosen-ing of the component. Engh and Massin [39] concludedthat a component was loose if there was evidence ofmigration of cementless femoral component at 1 yearafter the operation. The finding from these 2 studiesclearly indicates that the stable femoral stem at 4.5 yearsafter the operation can maintain the long-term stablefixation of the femoral component. Finally, 1 potenialargument is that although the stem is short and doesnot violate much of the medually cancal, it is quitethick proximally and extends a good distance laterallyinto the grater trochanter. Thus, it might lead to moredifficulties at the time of revision than more conven-tional proximally coated cementless components, whichare thinner proximally.The short, metaphyseal fitting stem provides stable

fixation without diaphyseal fixation. We believe thatfemoral-neck preservation and the lateral flare of thestem provide an axial and a torsional stability and seemto provide more natural loading of the proximal femur.

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