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The Journal of Arthroplasty Vol. 26 No. 6 2011

Comparison of Bone Mineral Density ChangesAround Short, Metaphyseal-Fitting, andConventional Cementless Anatomical

Femoral Components

Young-Hoo Kim, MD, Yoowang Choi, MD, and Jun-Shik Kim, MD

Abstract: We investigated the incidence and degree of stress shielding and clinical andradiographic results in 2 groups of patients. Fifty patients (60 hips) in each group were enrolledfor a randomized study. One group received a short, metaphyseal-fitting femoral component andanother group received a conventional metaphyseal- and diaphyseal-filling femoral component.The mean follow-up was 3.35 years in both groups. Bone mineral density was significantlyincreased in femoral zone 1 but slightly decreased in zone 7 in the short, metaphyseal-fitting stemgroup. In the conventional metaphyseal- and diaphyseal-fitting stem group, bone mineral densitywas markedly decreased in both zones 1 and 7. Clinical and radiographic results were similarbetween the 2 groups. No hip in either group required revision of the component. Keywords:total hip arthroplasty, short stem, metaphyseal stem, stress-shielding, bone mineral density.© 2011 Elsevier Inc. All rights reserved.

Conservation of bone stock by minimizing stress-shielding bone resorption [1,2] is a vitally importantprinciple, especially when considering that cementlessfemoral implants in total hip arthroplasty (THA) aretypically used in younger patients in whom the potentialfor revision during the patient's lifetime is high and theneed to keep reconstructive options open is paramount.To minimize the stress-shielding bone resorption,anatomically designed implants have been developedwith a conical and undersized distal apex or with a distalsplit section [3-7]. The former prevents distal loadtransfer by avoiding contact between the diaphysealfemoral cortex and the implant itself. The latter increasesthe elasticity of the distal portion of the implant to allowit to bend with the diaphyseal bone during loading. Apolished surface that prevents bone ongrowth, and,hence, implant fixation, may further reduce distal loadtransfer. Obviously, the best way to preserve the bonestock and to reduce stress-shielding bone resorption of

e Joint Replacement Center of Korea, Ewha Woman's Universityedicine, Seoul, South Korea.entary material available at www.arthroplastyjournal.org.

ted January 29, 2010; accepted October 1, 2010.efits or funds were received in support of the study.requests: Young-Hoo Kim, MD, The Joint Replacementorea, EwhaWoman's UniversityMokDong Hospital, 911-1,YangChun-Gu, Seoul, South Korea (158-710).Elsevier Inc. All rights reserved.

403/2606-0019$36.00/0016/j.arth.2010.10.001

931

the proximal femur is by suppressing or removing thedistal stem of the femoral component and providingmetaphyseal fixation. The question thus arises whetherit is possible to obtain strong and long-lasting fixation ofthe femoral component without diaphyseal anchoring.We examined 2 hypotheses in this randomized study:

(1) clinical results and the incidence of thigh pain aresimilar between a short anatomical and a conventionalanatomical cementless femoral component; and (2)radiographic results and stress shielding are similarbetween the short anatomical and conventional ana-tomical cementless femoral components.

Materials and MethodsFrom October 2005 to October 2007, the senior author

performed consecutive, primary, cementless THAs on120 hips in 100 patients. Severe osteoporosis of theproximal femur was the only exclusion criterion for ashort stem. No patient was lost to follow-up after theoperation, and no patient died in the interim. Therefore,all patients were available for clinical evaluation at amean of 3.35 years (range, 3-4 years) after the operation.We performed a sample size calculation based ondetecting a difference in the incidence of postoperativethigh pain between the 2 study groups, assuming anoverall α error (2 sided) of 5% with a statistical power of80% (β error = .20). We assumed that the incidence ofthigh pain in the conventional anatomical femoralimplant group would be 15% compared to 5% in the

932 The Journal of Arthroplasty Vol. 26 No. 6 September 2011

short anatomical femoral implant group at 2-yearfollow-up. With these assumptions, approximately 40patients per study group were needed. After agreeing tobe enrolled in this study, patients were randomlyassigned to receive either a conventional anatomicalfemoral implant or a short anatomical femoral implant.Randomization was achieved by means of computer-generated random number tables. The randomizationtables were stored at the coordinating center. At the timeof the preoperative enrollment of the participant, a studynurse added the participant to a randomization table insequential order. There were no differences in thepatient demographic parameters between the groups(Table 1). All patients were examined clinically andradiologically at each follow-up. Bone mineral density(BMD) was evaluated using bone-mineral densitometryat the final follow-up. The study was approved by theinstitutional review board, and all patients providedwritten informed consent. Patients were followed up for3 to 4 years because bone remodeling is prominent overthis period [8-10].In the short, metaphyseal-fitting femoral component

group, a cementless Pinnacle acetabular componentmade of titanium alloy (DePuy, Warsaw, Ind) and aProxima stem (DePuy, Leeds, UK) were used in all hips.Acetabular components were press fitted after theacetabulum had been underreamed by 1 mm. One or2 screws were used for additional fixation in 6 hips(10%); the remainder did not require any additionalscrews. A 28-mm-internal-diameter Biolox forte ceram-ic liner (DePuy) was used in all hips. The Proxima ismanufactured using titanium alloy (9 sizes in each side;lengths, 55.1-102.04 mm) and is entirely porous coatedwith sintered titanium beads having a mean pore size of250 μm, to which a hydroxyapatite is coated (a thicknessof 30 μm), except for the distal tip, and stepped tominimize shear forces. A key feature of the Proximastem design is the medial metaphyseal area, which isproximally longer when compared to a conventionalstem; this feature allows for a higher horizontal femoral

Table 1. Details of the 100 Patients

Parameters

Type

Proxima

No. of patients (hips) 50 (60)Sex (M/F) 22:28Mean age in years (range, SD) 54.3 (26-77, 12.97DiagnosisOsteoarthritis 24 (48%)Osteonecrosis 18 (36%)Traumatic arthritis 5 (10%)Femoral neck fracture 3 (6%)Mean height (range, SD) 160.9 cm (142-179, 8.7Mean weight (range, SD) 66.5 (51-93, 9.51)Mean body mass index (range, SD) 25.6 (20.5-33.3, 2.Mean duration of follow-up in years (range) 3.3 (3-4)

neck cut (at head-neck juncture), thus preserving themedial portion of the neck, which is usually sacrificedduring femoral neck osteotomy with conventionalfemoral stems. The second key feature of this implantis the highly pronounced lateral flare, which allows theimplant to laterally rest where the arciform fibers end onthe greater trochanter. The rationale of this design is toobtain full load transfer onto the proximal femur. A 28-mm-diameter Biolox forte ceramic femoral head(DePuy) was used in all hips (Fig. 1).In the conventional metaphyseal- and diaphyseal-

fitting femoral component group, a cementless Pinnacleacetabular component made of titanium alloy and aProfile femoral component (DePuy) were used in allhips. Acetabular components were press fitted after theacetabulum had been underreamed by 1 mm. One or 2screws were used for additional fixation in 8 hips (13%);the remainder did not require any additional screws. A28-mm-internal-diameter Biolox forte ceramic liner wasused in all hips. The cementless Profile femoralcomponent is made of titanium alloy and is ananatomical metaphyseal- and diaphyseal-fitting stem.The proximal, metaphyseal portion of the stem (ap-proximately one third of the stem) is porous coated withsintered beads. The pore size was 250 μm. A femoralneck cut in the Profile group was performed at 2 cmabove the lesser trochanter. A 28-mm-diameter Bioloxforte ceramic femoral head (DePuy) was used in all hips(Fig. 2). All operations were performed using aposterolateral approach.Clinical and radiologic follow-up was performed at 3

months, 1 year, and yearly thereafter in both groups.The Harris hip score [11] was determined before surgeryand at each follow-up. Patients scored thigh pain on a10-point visual analog scale [12] (zero = no pain, 10 =severe pain) at each follow-up. The level of activity ofthe patients after THA was assessed using the activityscore of Tegner and Lysholm [13]. This grading scale,which grades work and sports activities numerically, wasused as a complement to the functional score. The

of Component

PProfile

50 (60) –

24:26 .423 (χ2 test)) 51.8 (21-74, 12.3) .326 (Student t test)

24 (48%) .448 (Mantel-Haenszel χ2 test)22 (44%)3 (6%)1 (2%)

2) 161.9 cm (141-181, 10.3) .634 (Student t test)64.8 (46.88, 10.6) .433 (Student t test)

82) 24.7 (16.9-34.2, 3.6) .193 (Student t test)3.4 (3-4) .609 (Student t test)

Fig. 1. Proxima stem. Manufactured using titanium alloy and entirely porous coated with sintered titanium beads with a meanpore size of 250 μm to which a hydroxyapatite coat is applied (a thickness of 30 μm), except for the distal tip. The features of theprosthetic design are the longer proximomedial portion of the stem, highly pronounced lateral flare, and preservation of thefemoral neck.

Fig. 2. Profile stem. Manufactured of titanium alloy and having an anatomical metaphyseal- and diaphyseal-fitting stems. Theproximal, metaphyseal portion of the stem (approximately one third of the stem) is porous coated with sintered titanium beadshaving a mean pore size of 250 μm.

BMD Changes Around Stemless and Conventional Cementless Anatomical Stem � Kim et al 933

934 The Journal of Arthroplasty Vol. 26 No. 6 September 2011

patients were given a score according to the activities inwhich they engaged in daily life, ranging from 0 pointsfor a hip-related disability to 10 points for participationin competitive sports at a national level.The emanation of any clicking or squeaking sound

from the ceramic-on-ceramic bearing was recorded inboth groups.A supine anteroposterior radiograph of the pelvis with

both hips in 15° internal rotation and 0° of abductionwas taken for every patient. Consistent positioning ofthe patient was ensured with the use of a frame whichwas placed at the end of a standard x-ray table. Thepatient's feet were secured to polypropylene orthosesattached to the frame, which could be adjusted toaccommodate patients of different height. Supine ante-roposterior radiograph of the involved hip and cross-table lateral radiograph of each hip were taken.The femoral morphology was determined in preoper-

ative radiographs using Dorr classification [14]. Theposition of the Proxima and Profile stems in the antero-posterior and lateral planes was determined. In bothgroups, we analyzed the radiographs at the final follow-up for identifying the presence of radiolucent lines andosteolytic lesions around the acetabular component (inzones 1, 2, and 3, according to the system of DeLee andCharnley [15]) and the femoral component (in zones 1and 7, according to the system of Gruen et al [16]).Because the Proxima femoral component had no distalstem, the region from the lower border of the lessertrochanter to the tip of the greater trochanter was definedas zone 1 in both groups and the region from the lowerborder of the lesser trochanter to the femoral neck-cutlevel was defined as zone 7. In addition, the center ofrotation, limb length, femoral neck length, femoral offset,and abductor-moment arm were measured in all hips.Loosening of the femoral component in both groups

was defined as when there was a progressive axialsubsidence of more than 2 mm, or varus or valgus shiftof more than 2° [17]. Stem subsidence was evaluated bymeasuring 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 and theupper border of the lesser trochanter. These measuredvalues in the anteropostrior radiographs taken 1 weekafter the operation were compared with those in theanteroposterior radiographs taken at the final follow-upexamination to define the amount of subsidence.Radiographs were analyzed by a research associate(SML) with no knowledge of the patient's name. Theintraobserver error in all the radiographic measure-ments was determined by the intraclass correlationcoefficient after repeated measurements for 3 times at 3-day intervals. This was 0.97 (0.95-1.00), indicatingexcellent reproducibility. A femoral component wasconsidered to be possibly loose when there was a

complete radiolucent line surrounding the entire po-rous-coated surface on both the anteroposterior and thelateral radiograph [17]. Bone ingrowth into the femoralcomponents was considered to have occurred whenthere was a direct extension of the trabecular striationbetween the femur and 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 wider than 2mm on both the anteroposterior and lateral radiographs[17]. Bone ingrowth into the acetabular component wasconsidered to have occurred when there was directcontact of the trabecular striation between the acetab-ulum and the component.Proximal femoral bone resorption was graded radio-

logically [1], 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 cortical wallto the level of the lesser trochanter; and grade 4, loss ofdensity in the entire medial cortical wall distal to thelevel of the lesser trochanter. Measurement of the linearwear of the Biolox forte ceramic liner was attempted butwas found to be below the level of detection.All patients underwent dual-energy x-ray absorptio-

metry (DEXA) scanning of the pelvis and proximalfemur using the Hologic QDR 4500A densitometer(Hologic Inc, Waltham, Mass) in the metal-removalhip-scanning mode. Acquisition of the pelvic scancommenced 2 cm below the lower border of the inferiorpubic ramus using a field width of 15 cm. The scans wereorientated so that the acetabular component lay in thecenter of the field. Acquisition was continued proximallyto 2 cm above the lower limit of the ipsilateral sacroiliacjoint. Acquisition of the femoral scan was startedapproximately 2.5 cm distal to the tip of the femoralcomponent, with the longitudinal axis of the shaft of theprosthesis in the vertical position and occupying thecenter of the scan field. The scan was continued proxi-mally to 4 cm above the tip of the greater trochanter. Thefirst DEXA scan was taken 1 week after surgery andserved as a baseline for BMD in the subsequent scans.Further scans were obtained at the final follow-up. Bonemineral density in both groups was measured from thelower border of the lesser trochanter to the tip of thegreater trochanter in zone 1 and from the lower borderof the lesser trochanter to the femoral neck-cut level inzone 7. Bone mineral density was calculated by oneobserver (SML) in 2 regions of interest surrounding thefemoral component (Fig. 3). The intraobserver error forBMD measurement was determined by the interclasscorrelation coefficient after repeated measurements for3 times at 3-day intervals. This was 0.94 (0.91-0.97),indicating excellent reproducibility.

Fig. 3. The BMD is calculated in 2 regions of interest surrounding the femoral component in both groups.

BMD Changes Around Stemless and Conventional Cementless Anatomical Stem � Kim et al 935

Heterotopic ossification, if present, was graded accord-ing to the classification of Brooker et al [18].

Statistical AnalysisWe calculated the descriptive statistics (mean, SD, and

proportions) for the continuous study variables. TheHarris hip score was the primary outcome variable. Thisvariable was analyzed with a Student independent t test.Radiographic and BMD data were compared betweenthe 2 groups using Student independent t test. Compli-cation rates were compared between the 2 groups withthe χ2 test. All statistical analyses were performed withthe Statistical Package for the Social Sciences (version14.0, SPSS, Inc, Chicago, Ill), with 2-tailed t test. Valueswere considered significant at P b .05.

ResultsComparison of the preoperative and postoperative

Harris hip scores revealed no significant differencebetween the 2 groups (Student independent t test, P =.124 and P = .790, respectively) (Table 2). The mean

Table 2. Preoperative and Postoperative Data for Patients in Bot

Parameter

Harris Hip Sc

Proxima

Preoperative Postoperative Pr

Harris hip score (points) * 44.6 (0-61) 97 (79-100) 48Pain score (points) * 11.6 (0-30) 43.4 (40-44) 11Function score (points) * 26.2 (0-40) 43.7 (30-50) 29

* Values are expressed as mean, with range in parentheses.

preoperative Harris hip score was 44.6 points in theProxima group and 48.4 points in the Profile group. Themean postoperative hip score was 97 points in theProxima group and 96 points in the Profile group. Fivepatients (10%) with a Profile stem had mild ormoderate thigh pain (5- or 6-point visual analog scale)at the final follow-up, but no patient with a Proximastem had thigh pain at any follow-up period. Allpatients in both groups had an activity score of 5 or 6points at the final follow-up. No clicking or squeakingsound emanated from any patient.We found no radiographic difference between the 2

groups in the following parameters: bone type,alignment of the stem, cup and stem position andprevalence of radiolucent lines, the center of rotation,limb length, femoral neck length, and femoral offset(Table 3; available online at www.arthroplastyjournal.org). All hips had bone ingrowth into the femoralcomponents, and no hip in either group requiredrevision of any component for any reason. No hip witha Proxima stem had pedestal formation, distal cortical

h Groups

ore

P (Student t test)Profile

eoperative Postoperative Preoperative Postoperative

.4 (0-65) 96 (75-100) .124 .790

.9 (10-30) 42.9 (40-44) .725 .130

.8 (5-40) 44.5 (26-47) .110 .999

936 The Journal of Arthroplasty Vol. 26 No. 6 September 2011

hypertrophy, or cortical thinning. Thirty-seven (62%)of 60 hips with a Profile femoral stem had pedestalformation, and 51 (85%) of 60 hips with a Profile stemhad developed distal cortical hypertrophy. Stressshielding–related bone resorption was markedly lessin the femurs with a Proxima than with a Profile stem.No hip with a Proxima stem had any stress-shieldingbone loss except at the rounding off of the calcarfemorale on the most recent follow-up (Fig. 4). All hipswith a Profile stem had grade 3 (15 hips) or 4 (45 hips)bone loss (Fig. 5).We found that BMD findings were significantly

different (P b .00001) between the 2 groups. In theProxima group, around the femoral component, theBMD at 3 years after surgery was significantly increasedin zone 1 (from 3.154 to 3.484 [9%]; P = .001) butslightly decreased in zone 7 (from 3.283 to 2.961 [10%];P = .177). In the Profile group, the BMD at 3 years aftersurgery was significantly decreased in zones 1 (from3.189 to 2.223 [30.3%]; P = .00001) and 7 (from 3.321to 2.232 [32.8%]; P = .00001) (Table 4).No patient had a grade 3 or 4 heterotopic ossification in

either group.

DiscussionIn this randomized study, we examined 2 hypotheses.

First, clinical results and the incidence of thigh pain aresimilar between a short anatomical and a conventionalanatomical cementless femoral component. Second,radiographic results and stress shielding are similarbetween the short anatomical and conventional ana-tomical cementless femoral components.For most femoral implants, clinical and radiographic

data are available to allow an analysis of the influence ofdesign principles on load transfer and periprostheticbone change. Midterm [19] and long-term [20,21]follow-up of the Zweymueller stem (Allopro SL;Zimmer, Warsaw, Ind) found excellent survival rateswith few cases of aseptic loosening after 10 to 15 years.However, in most studies, a high degree of proximalbone atrophy was observed, usually in association withdistal cortical hypertrophy, indicating distal load transferand fixation. Long-term observations of the SpotornoCement-Less-Stem (CLS Stem; Zimmer) showed asurvival rate of approximately 95% for aseptic looseningafter 10 years [22,23]. However, between 30% and 50%of the stable implants had a high degree of proximalbone atrophy in association with distal cortical hyper-trophy, indicating distal load transfer and fixation.Anatomical or anatomically adapted stems are designedto accommodate the natural geometry of the proximalfemur. The Profile design (DePuy) aims to reestablishanatomical load transfer by following the naturalcontours of the femur in all 3 dimensions. Kim et al[24] found in a prospective evaluation of 118 Profilestems after a minimum of 8 years that all stems were

radiographically stable. However, in 45% of the casespedestal formation was seen and 25% had developeddistal cortical hypertrophy. All of the femora exhibitedcortical thinning and proximal bone atrophy. Despite anexcellent clinical performance and survival rate for thisstem, radiographic analysis confirmed stress transfer tothe diaphyseal region [19,20].In our series, all femoral stems in both groups had

radiographically stable fixation, and these radiographicresults are comparable with the results reported byothers [7,25-29]. The Proxima stem appears to satisfythe prerequisite for reconstruction of the proximalloading lines. All patients with a Proxima stem wereshown radiographically to have the formation of newbone trabecular lines connecting the surface of theimplant to the metaphyseal endosteum of the proximalfemur. No hip with a Proxima stem had pedestalformation, distal cortical hypertrophy, or cortical thin-ning. All hips with a Proxima stem had mild boneatrophy limited to the calcar region (Gruen zone 7).These radiographic findings clearly confirmed that stressis transferred to the metaphyseal region. All Profilestems were also radiographically stable. However, 62%(37/60 hips) of the hips had pedestal formation and 85%(51/60 hips) had developed distal cortical hypertrophy.All femora with a Profile stem exhibited cortical thinningand bone atrophy in Gruen zones 1, 2, 6, and 7. Despitean excellent clinical performance and survival rate forthis stem, radiographic analysis confirmed stress transferto the diaphyseal region. The type and extent of boneresorption in the Profile femoral stem would alter theirultimate clinical performance and ultimate failure in thelong run. We believe that revision surgery of the Profilestem to contend with bone defects would be moredifficult than the Proxima stem.The correct transmission of loads in the metaphyseal

region should theoretically prevent proximal boneresorption. Unfortunately, the phenomenon becomesradiographically apparent only after a reduction inbone mass of at least 30% [30]. Dual-energy x-rayabsorptiometry is considered the most effective andreliable method for detecting postoperative stressremodeling of BMD around cementless implants[30-32]. Bidimensional assessment by DEXA achievesgreater reproducibility of measurement, with a preci-sion error of 5% or less, by means of positioningdevices that limit limb rotation [8,33-36]. A 3.35-yearfollow-up period after the placement of the implant isconsidered sufficient to evaluate the presence of stressshielding as it has been shown that bone loss beginsimmediately after surgery and is most prominentwithin the first year [37-40].It has been suggested that stress shielding may be

minimized by a low-modulus, intimately fit, proximallyfixed device that does not bypass the proximal medialregions with distal fixation [9,41]. Short-stem prostheses

Fig. 4. Postoperative radiographs of a 48-year-old woman with a Proxima stem. (A) An anteroposterior view of the Proxima stemtaken 1 week after surgery reveals that the Proxima stem is embedded in a satisfactory position. (B) An anteroposterior view ofProxima stem taken 3 years after surgery reveals that the Proxima stem is solidly fixed in a satisfactory position. No discernible siteof bone resorption is observable.

Fig. 5. Postoperative radiographs of a 58-year-old woman with Profile stem. (A) An anteroposterior view of the Profile stemtaken 1 month after surgery reveals that the Profile stem is embedded in a satisfactory position. (B) An anteroposterior view ofthe Profile stem taken 4 years after surgery reveals that the Profile stem is rigidly fixed in a satisfactory position. Grade 4 boneresorption is evident.

BMD Changes Around Stemless and Conventional Cementless Anatomical Stem � Kim et al 937

Table 4. Bone Mineral Density Around Proxima and Profile Systems

Period

Locations

Proxima Stem Profile Stem

Zone 1 Zone 7 Zone 1 Zone 7

1 wk after surgery Mean (SD) 3.154 g/cm2 (0.271) 3.283 g/cm2 (0.447) 3.189 g/cm2 (0.111) 3.321 g/cm2 (0.219)3 y after surgery Mean (SD) 3.484 g/cm2 (0.391) 2.961 g/cm2 (0.312) 2.223 g/cm2 2.232 g/cm2 (0.227)Difference (%) 0.33 g/cm2 (9) −0.322 g/cm2 (–10) 0.966 g/cm2 (–30.3) 1.089 g/cm2 (–32.8)P (Student paired t test) .001 .177 .00001 .00001

938 The Journal of Arthroplasty Vol. 26 No. 6 September 2011

were introduced to obtain a nearly physiologic proximalload transfer combined with limited bone resection.Theoretically, there should be minimal changes in loadtransfer and therefore little change in the periprostheticbone is expected. The midterm results of the Mayo stems(Zimmer) showed a survival rate of 98.2% after 10 years[42]. However, a high degree of proximal bone atrophywas observed in 20% of the hips in association withincreased bone density in Gruen zones 3 and 6. Theincrease in bone density confirms that the area of higherstress patterns is in these Gruen zones 3 and 6, leading toa certain amount of bone atrophy in the more proximalzones. Huggler et al [43] showed good long-term resultsof Thrust Plate Prosthesis (Zimmer). Another group [44],however, reported that in the early years after implan-tation, a high degree of bone atrophy under the thrustplate or aseptic loosening occurred. They suggested thatthe radiographic signs of stress shielding and looseningmight indicate nonphysiologic proximal load transfer. Itremains unclear whether these short-stem designs withthese load transfer patterns are useful in young patientswith respect to outcome and revision surgery. Theperiprosthetic bone changes after implantation of aProxima stem indicated predominantly proximal loadtransfer. Therefore, we hypothesized that a Proximastem would prove useful, particularly in youngerpatients. This hope was validated by the Proximaprosthesis used in this study. The slight decrease of theBMD in zone 7 in the Proxima group appears to berelated to the stiffness of the proximal stem with respectto the metaphysis of the proximal femur (a mismatch inthe modulus of elasticity between the bulky proximalstem and the metaphysis of the proximal femur).A high prevalence of thigh pain has been reported

after cementless THA [45-47], which has been attributedto micromovement of the stem in the presence of atightly fitted, distally rigid stem. The absence or lowprevalence of thigh pain in the Proxima group in ourstudy may be attributed to the rigid axial and torsionalstability of the stems in the proximal femur and anabsence of contact between the distal stem and thefemoral cortex.There are certain limitations of this study. First, the

follow-up period was short and it would thus beinappropriate to make generalization about the partic-

ular implants used in this study or even to make generalconclusions regarding all cementless femoral prosthe-ses. However, the overall changes documented in thisstudy reflect general trends that have been documentedin the literature by other studies with short follow-upperiods [8,48-50]. Second, evaluating longitudinalchanges in the BMD with DEXA in the differentprosthetic designs can be problematic. Bone mineraldensity, as measured by this method, is defined as thebone mineral content divided by the area in theradiographic frontal plane of the targeted bone. Minorchanges in femoral rotation or patient position can leadto a 5% precision error possibly by altering the area ofthe medial femoral cortex [33]. Third, we performed nointerobserver variability studies on the measurement ofthe radiographs and on the BMD measurements. Oneobserver can systematically bias the observationsleading to error (either underestimation or overestima-tion). However, we did determine intraobserver agree-ment of radiographic and BMD measurements.Intraobserver agreement for radiographic measure-ments was 0.97 (0.95-1.00), and for BMD measure-ments it was 0.94 (0.91-0.97), indicating excellentreproducibility. Finally, without serial measurements,it is not possible to determine when these changesoccurred and whether they would have been found tohave stabilized on the longer term follow-up.In conclusion, the Proxima femoral component

achieved a level of fixation in the proximal femur thatwas as adequate as that of the Profile femoral compo-nent, but it provided substantially less stress-shieldingbone resorption than the Profile femoral stem.

References1. Engh CA, Bobyn JD, Glassman AH. Porous coated hip

replacement. The factors governing bone ingrowth, stressshielding, and clinical results. J Bone Joint Surg Br 1987;69:45.

2. Engh CA, McGovern TF, Bobyn JD, et al. A quantitativeevaluation of periprosthetic bone-remodeling aftercementless total hip arthroplasty. J Bone Joint Surg Am1992;74:1009.

3. Bourne RB, Rorabeck CH, Patterson JJ, et al. Taperedtitaniumcementless total hip replacements: a 10- to 13-yearfollow-up study. Clin Orthop Relat Res 2001;393:112.

BMD Changes Around Stemless and Conventional Cementless Anatomical Stem � Kim et al 939

4. Mallory TH, HeadWC, Lombardi Jr AV. Tapered design forthe cementless total hip arthroplasty femoral component.Clin Orthop Relat Res 1997;344:172.

5. Schmidt R, Mueller L, Nowak TE, et al. Clinical outcomeand periprosthetic bone remodeling of an uncementedfemoral component with taper design. Int Orthop 2003;27:204.

6. Kim YH. Titanium and cobalt-chrome cementless femoralstems of identical shape produce equal results. Clin OrthopRelat Res 2004;427:148.

7. Kim YH. The results of a proximally-coated cementlessfemoral component in total hip replacement. A five to 12-year follow-up. J Bone Joint Surg Br 2008;90:299.

8. Nishii T, Sugano N, Masuhara K, et al. Longitudinalevaluation of time related bone remodeling after cement-less total hip arthroplasty. Clin Orthop Relat Res 1997;339:121.

9. Aldinger PR, Sabo D, Pritsch M, et al. Pattern ofperiprosthetic bone remodeling around stable uncemen-ted tapered hip stems: a prospective 84-month follow-upstudy and a median 156-month cross-section study withDXA. Calcif Tissue Int 2003;73:115.

10. Galli M, Leone A, Tamburrelli FC, et al. Periprostheticmineralization changes around femoral stems: a prospec-tive 12-month study with DEXA. Skeletal Radiol 2008;37:723.

11. Harris WH. Traumatic arthritis of the hip after dislocationand acetabular fractures: treatment by mold arthroplasty.An end-result study using a new method of resultevaluation. J Bone Joint Surg Am 1969;51:737.

12. Kim YH, Kim VE. Uncemented porous-coated anatomictotal hip replacement. Results at six years in a consecutiveseries. J Bone Joint Surg Br 1993;75:6.

13. Tegner Y, Lysholm J. Rating systems in the evaluation ofknee ligament injuries. Clin Orthop Relat Res 1985;198:43.

14. Dorr LD. Total hip replacement using the APR system.Tech Orthop 1986;1:22.

15. DeLee JG, Charnley J. Radiological demarcation ofcemented sockets in total hip replacement. Clin OrthopRelat Res 1976;121:20.

16. Gruen TA, McNeice GM, Amstutz HC. “Modes of failure”of cemented stem-type femoral components: a radio-graphic analysis of loosening. Clin Orthop Relat Res 1979;141:17.

17. Kim YH, Kim JS, Oh SH, et al. Comparison of porous-coated titanium femoral stems with and withouthydroxy-apatite coating. J Bone Joint Surgy Am 2003;85:1682.

18. Brooker AF, Bowerman JW, Robinson RA, et al. Ectopicossification following total hip replacement. Incidence anda method of classification. J Bone Joint Surgy Am 1973;55:1629.

19. Grubl A, Chiari C, Gruber M, et al. Cementless total hiparthroplasty with a tapered, rectangular titanium stem anda threaded cup: a minimum ten-year follow-up. J BoneJoint Surg Am 2002;84:425.

20. Pieringer H, Auersperg V, Griessler W, et al. Long-termresults with the cementless Alloclassic brand hip arthro-plasty system. J Arthroplasty 2003;18:321.

21. Garcia-Cimbrelo E, Cruz-Pardos A, Madero R, et al. Totalhip arthroplasty with use of the cementless Zweymüller

Alloclassic system. A ten to thirteen-year follow-up study.J Bone Joint Surg Am 2003;85:296.

22. Aldinger PR, Thomsen M, Mau H, et al. CementlessSpotorno tapered titanium stems: excellent 10-15-yearsurvival in 141 young patients. Acta Orthop Scand 2003;74:253.

23. Schramm M, Keck F, Hohmann D, et al. Total hiparthroplasty using an uncemented femoral componentwith taper design: outcome at 10-year follow-up. ArchOrthop Trauma Surg 2000;120:407.

24. Kim YH, Oh SH, Kim JS. Primary total hip arthroplastywith a second-generation cementless total hip prosthesisin patients younger than fifty years of age. J Bone JointSurg Am 2003;85:109.

25. Westphal FM, Bishop N, Püschel K, et al. Biomechanics ofa new short-stemmed uncemented hip prosthesis: an in-vitro study in human bone. Hip Int 2006;16(Suppl 3):S22.

26. Westphal FM, Bishop N, Honl M, et al. Migration andcyclic motion of a new short-stemmed hip prosthesis—abiomechanical in vitro study. Clin Biomech (Bristol, Avon)2006;8:834.

27. Santori FS, Manili M, Fredella N, et al. Ultra-shortstems with proximal load transfer: clinical and radio-graphic results at five-year follow-up. Hip Int 2006;16(Suppl 3):S31.

28. Whiteside LA, White SE, McCarthy DS. Effect of neckresection on torsional stability of cementless total hipreplacement. Am J Orthop 1995;24:766.

29. Kulkarni M, Wylde V, Aspros D, et al. Early clinicalexperience with a metaphyseal loading implant: why havea stem? Hip Int 2006;16(Suppl 3):S3.

30. Cohen B, Rushton N. Accuracy of DEXA measurement ofbone mineral density after total hip arthroplasty. J BoneJoint Surg Br 1995;77:479.

31. Zerahn B, Storgaard M, Johansen T, et al. Changes in bonemineral density adjacent to two biomechanically differenttypes of cementless femoral stems in total hip arthroplasty.Int Orthop 1998;22:225.

32. Hughes SS, Furia JP, Smith P, et al. Atrophy of theproximal part of the femur after total hip arthroplastywithout cement. A quantitative comparison of cobalt-chromium and titanium femoral stems with use of dual x-ray absorptiometry. J Bone Joint Surg Am 1995;77:231.

33. Mortimer ES, Rosenthall L, Paterson I, et al. Effect ofrotation on periprosthetic bone mineral measurements ina hip phantom. Clin Orthop Relat Res 1996;324:269.

34. Sabo D, Reiter A, Simank HG, et al. Periprostheticmineralization around cementless total hip endoprosth-esis: longitudinal study and cross-sectional study ontitanium threaded acetabular cup and cementless Spot-orno stem with DEXA. Calcif Tissue Int 1998;62:177.

35. Venesmaa PK, Kröger HP, Miettinen HJ, et al. Monitoringof periprosthetic BMD after uncemented total hip arthro-plasty with dual-energy x-ray absorptiometry—a 3-yearfollow-up study. J Bone Miner Res 2001;16:1056.

36. Goh JC, Low SL, Bose K. Effect of femoral rotation on bonemineral density measurements with dual energy x-rayabsorptiometry. Calcif Tissue Int 1995;57:340.

37. Bobyn JD, Pilliar RM, Binnington AG, et al. The effect ofproximally and fully porous-coated canine hip stem designon bone modeling. J Orthop Res 1987;5:393.

940 The Journal of Arthroplasty Vol. 26 No. 6 September 2011

38. Jacobs JJ, Sumner DR, Galante JO. Mechanisms of boneloss associated with total hip replacement. Orthop ClinNorth Am 1993;24:583.

39. Paz Jimenez J, Hernandez Vaquero D, Murcia Mazon A,et al. The value of a densitometric follow-up in theevaluation of a total hip prosthesis. Rev ESP Cir Osteoart1994;173:253.

40. Hernandez Vaquero D, Paz Jimenez J, Murcia Mazon A, etal. Behavior of the femoral stem in the Bihapro hipprosthesis. Orthopedics 1999;22:1049.

41. Panisello JJ, Herrero L, Herrera A, et al. Bone remodel-ling after total hip arthroplasty using an uncementedanatomic femoral stem: a three-year prospective studyusing bone densitometry. J Orthop Surg (Hong Kong)2006;14:32.

42. Morrey BF, Adams RA, Kessler M. A conservative femoralreplacement for total hip arthroplasty. A prospective study.J Bone Joint Surg Br 2000;82:952.

43. Huggler AH, Jacob HA, Bereiter H, et al. Long-term resultswith the uncemented thrust plate prosthesis (TPP). ActaOrthop Belg 1993;59(Suppl 1):215.

44. Taylor WR, Ploeg H, Hertig D, et al. Bone remodelling of aproximal femur with the thrust plate prosthesis: an in

vitro case. Comput Methods Biomech Biomed Engin2004;7:131.

45. Engh Jr CA, Culpepper II WJ, Engh CA. Long-termresults of use of the anatomic medullary lockingprosthesis in total hip arthroplasty. J Bone Joint SurgAm 1997;79:177.

46. 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;70:337.

47. Bourne RB, Rorabeck CH, Ghazal ME, et al. Pain in thethigh following total hip replacement with a porous-coated anatomic prosthesis for osteoarthrosis: a five-yearfollow-up study. J Bone Joint Surg Am 1994;76:1464.

48. Boden HS, Sköldenberg OG, Salemyr MO, et al. Contin-uous bone loss around a tapered uncemented femoralstem: a long-term evaluation with DEXA. Acta Orthop2006;77:877.

49. Hananouchi T, Sugano N, Nishii T, et al. Effect of roboticmilling on periprosthetic bone remodeling. J Orthop Res2007;25:1062.

50. Dan D, Germann D, Burki H, et al. Bone loss after total hiparthroplasty. Rheumatol Int 2006;26:792.

Table 3. Radiographic Results for Patients in Both Groups

Parameters Proxima Profile P

Dorr bone type [14]A 58 hips (96.7%) 55 hips (92%) .605B 2 hips (3.3%) 5 hips (8%) .616

Femoral component positionCoronal planeNeutral position 57 hips (94%) 54 hips (90%) .915Varus position 3 hips (6%) 6 hips (10%) .779Sagittal planeAnteverted 60 hips (100%) 60 hips (100%) 1.000

Center of rotationHorizontal (mm) 38.1 (34-42) 37.9 (32-41) .175Vertical (mm) 16.3 (13-21) 15.9 (8-23) .162

Femoral offset (mm) 40.3 (32-48) 38.9 (28-47) .812Abductor moment arm (mm) 44.9 (39-53) 43.1 (37-51) .912Femoral neck length (mm) 34.9 (30-43) 35 (31-37) .789Limb-length discrepancy (cm) * 0.8 ± 0.6 (–1.1 to 2.1) 0.9 ± 0.9 (–1.3 to 2.8) .715Radiolucent line around porous-coated stem (N1 mm) 0 hip (0%) 0 hip (0%) –

Migration of femoral component (N2 mm) 0 hip (0%) 0 hip (0%) –

•Femoral component position:- Neutral position of Proxima stem: Angles of Proxima neck with femoral shaft and Proxima neck with Proxima stem are equal or ±3°.- Varus of Proxima stem: Angle of Proxima neck with femoral shaft is smaller than the angle of Proxima neck with Proxima stem.- Valgus of Proxima stem: Angle of Proxima neck with femoral shaft is larger than the angle of Proxima neck with Proxima stem.-Anteverted Proxima stem: Angle of Proxima neck with femoral shaft is smaller than the angle of Proxima neck with Proxima stem in cross-tablelateral x-ray.

- Neutral position of Profile stem: Angle of longitudinal axes of Profile femoral stem and femoral shaft is less than ±3°.- Varus of Profile stem: Angle of longitudinal axes of Profile femoral stem and femoral shaft is N3° medially.- Valgus of Profile stem: Angle of longitudinal axes of Profile femoral stem and femoral shaft is N3° laterally.

•Center of rotation: a horizontal line is constructed to connect the inferior margin of both teardrops on the anteroposterior pelvic radiograph.Vertical lines are constructed to bisect the teardrops and extend superiorly. The centers of femoral heads are located, and the horizontal andvertical distance from the teardrops to the center of the femoral head is determined. The horizontal and vertical coordinates provide a recording ofthe center of rotation of the hip.•Femoral offset: The perpendicular distance from the neutral long axis of the femur and the center of the femoral head.•Abductormoment arm: This is estimated by drawing a line between the anterior-superior and posterior-superior iliac spine. A line is drawn from apoint one third of the distance from the posterior-superior to the anterior-superior spine to the tip of the greater trochanter. This approximates theline of the pull of the gluteus medius. A perpendicular line is then constructed from the center of rotation of the head to this line, and its lengthrepresents the abductor moment arm.•Femoral neck length: The distance between the center of the femoral head and the cutting level of the femoral neck.•Limb length discrepancy: The difference in limb length between the operated and the nonoperated side. This is estimated by drawing a horizontalline along the inferior margin of both ischial tuberosities (interischial line). The vertical distance from this line to the top of the lesser trochanter ofeach hip is measured and is recorded as the limb length. Positive value represents longer and negative value represents shorter limb length.•Migration of stem: Any change in the distance from the upper border of the lesser trochanter to the medial neck-shaft junction and in the ratio ofthe length of the prosthesis to the distance from the tip of the stem to the proximal tip of the greater trochanter.* Values are expressed as mean ± SD (range).

BMD Changes Around Stemless and Conventional Cementless Anatomical Stem � Kim et al 940.e1