Osteolysis After Unidirectional and Multidirectional Mobile-Bearing Total Knee Arthroplasty in Young Patients

The Journal of Arthroplasty Vol. 24 No. 4 2009

Osteolysis After Unidirectional and MultidirectionalMobile-Bearing Total Knee Arthroplasty

in Young Patients

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

Abstract: We questioned whether a difference exists between multidirectional andunidirectional mobile-bearing total knee arthroplasties in terms of clinical results andthe prevalence of polyethylene wear and periprosthetic osteolysis. We studied 62patients who underwent simultaneous bilateral total knee arthroplasties, with aunidirectional prosthesis implanted in 1 knee and a multidirectional one in the other.Of the patients, 9 were men and 53 were women, with a mean age of 57.6 years (35-60 years). The minimum follow-up was 11 years (mean, 11.8 years; range, 11-13years). Preoperative and postoperative knee and functional scores were not differentbetween the 2 groups. No knee in either group had detectable tibial polyethyleneliner wear or osteolysis on radiographs or on computed tomography scans. Two(3%) knees in each group were revised. Key words: osteolysis, polyethylene wear,uni- and multidirectional TKA.© 2009 Elsevier Inc. All rights reserved.

Greater range of motion is reportedly obtained witha properly inserted posterior cruciate-retaining,anteroposterior glide, low contact stress prosthesiswith a multidirectional polyethylene platform (AP-Glide LCS prosthesis; DePuy, Warsaw, Ind) com-pared with a posterior cruciate-sacrificing, rotatingplatform, low contact stress prosthesis with aunidirectional polyethylene platform (RP-LCS pros-thesis; DePuy) [1]. The AP-Glide LCS prosthesis hasconforming rotating polyethylene tibial insert thatcan translate along a bar on the tibial component inthe sagittal plane. The implant incorporates a highlyconforming proximal articulation between the

From the Joint Replacement Center of Korea, Ewha WomansUniversity School of Medicine, Seoul, South Korea.

Submitted November 6, 2007; accepted February 10, 2008.No benefits or funds were received in support of the study.Reprint requests: Young-Hoo Kim, MD, The Joint Replace-

ment Center of Korea at Ewha Womans University Dong DaeMun Hospital 70, ChongRo 6-Ga, ChongRo-Gu, Seoul 110-783,South Korea.

© 2009 Elsevier Inc. All rights reserved.0883-5403/08/2404-0015$36.00/0doi:10.1016/j.arth.2008.02.007

586

femoral component and the polyethylene tibialinsert, maximizing contact surface area and redu-cing polyethylene stress. The modification of thedistal articulation allow for anteroposterior transla-tion and rotary movement between the flat distalpolyethylene surface and the highly polished prox-imal tray. The design lacks any mechanical stopanteriorly or posteriorly to limit anteroposteriortranslation and relies on soft tissues and the nativeligamentous structures in the knee for stability in thesagittal plane (Fig. 1). The RP-LCS prosthesisfeatures a single plastic bearing that freely rotatesabout its post, which is seated within a hole in thetibial tray. The RP-LCS prosthesis has unlimitedrotation but has a limited range of anteroposteriorand mediolateral translation (Fig. 2).

In an in vitro experimental model, Jones et al [2]suggested mobile-bearing total knee arthroplasties(TKAs) with a multidirectional polyethylene plat-form have wear rates 9 times greater than mobile-bearing TKAs with a unidirectional polyethyleneplatform. Theoretically, increased polyethylenewear will lead to a higher prevalence of osteolysis

http://dx.doi.org/10.1016/j.arth.2008.02.007

Fig. 1. Photograph of the AP-Glide LCS TKA prosthesis.The implant incorporates a highly conforming proximalarticulation between the femoral component and thepolyethylene tibial insert, maximizing contact surface areaand reducing polyethylene stress. The modification of thedistal articulation allows for anteroposterior translationand rotary movement between the flat distal polyethylenesurface and the highly polished proximal tibial tray. Thedesign lacks any mechanical stop anteriorly or posteriorlyto limit anteroposterior translation and relies on softtissues and the native ligamentous structures in the kneefor stability in the sagittal plane.

Osteolysis After Mobile-Bearing TKA � Kim et al 587

with resultant synovitis and component loosening[3]. However, Kim and Kim [4] observed similarresults after AP-Glide LCS (multidirectional) andRP-LCS (unidirectional) TKAs in elderly patients.One commonly stated reason for using a mobile-

bearing TKA was that it allows younger patients tobe more active and to reduce the wear of tibialpolyethylene bearing. Callaghan et al [5] stated thatthis is a theoretical argument because there are nodata in the literature that support this concept. Weconducted a prospective and randomized study inyoung patients (b60 years of age) to evaluate thehypothesis that the clinical and radiographic resultsof the AP-Glide LCS TKAs are better than those inthe RP-LCS TKAs in the same patients who under-went bilateral simultaneous TKAs. We furtherevaluated the hypothesis that the prevalence ofosteolysis would be higher in the AP-Glide LCSTKAs than that in the RP-LCS TKAs.

Fig. 2. Photograph of the RP-LCS TKA prosthesis. Theimplant has unlimited rotation but has a limited range ofanteroposterior and mediolateral translation.

Materials and Methods

Between January 1994 and February 1996,primary bilateral simultaneous TKAs were per-formed in 65 consecutive patients under the sameanesthetic in 1 institute by the senior author , with 1side treated immediately after the other. Patientswho were older than 60 years and patients withrheumatoid arthritis were excluded. We routinely

perform bilateral simultaneous TKAs unless patientshave serious medical problems preoperatively.Three patients were lost to follow-up, leaving 62patients (124 knees) available for review. Theaverage age of the patients at the time of the indexoperation was 57.6 years (range, 35-60 years).There were 9 men and 53 women. The meanweight of the patients was 54.2 kg (range, 43-88 kg),and their mean height was 152.2 cm (range, 141-178 cm). The mean body mass index was 26.4 kg/m2 (range, 22-38 kg/m2). The diagnosis wasosteoarthritis in 56 patients and traumatic arthritisin 6 patients. There were 48 (77%) patients whohad no previous knee operation and 14 patients(23%) who had arthroscopic debridement of one orboth knees. The minimum follow-up was 11 years(mean, 11.8 years; range, 11-13 years). The studywas approved by our institutional review board, andall patients provided informed consent.

All procedures were performed through a midlineskin incisionmeasuring 10 to 12 cm in length, with asubvastus approach into the joint. The anteriorcruciate ligament was excised in all patients. Theposterior cruciate ligament was relatively wellpreserved in all knees because none of the patientshad inflammatory arthritis. In all knees that weretreated with the AP-Glide LCS prosthesis, theposterior cruciate ligament was preserved. In allknees that were treated with the RP-LCS prosthesis,the posterior cruciate ligament was excided.

Ligamentous balancing was done, and an attemptwas made to resect 10 mm of tibial bone distallyfrom what was considered to be the intact articularsurface to achieve a surface that was perpendicularto the shaft of the tibia in the coronal plane with a7° posterior slope in the sagittal plane. The distal

588 The Journal of Arthroplasty Vol. 24 No. 4 June 2009

and posterior femoral condylar resection was donewith an attempt being made to remove a thicknessof bone that was equal to the thickness of thefemoral component to be inserted. The patellarthickness was measured before the resection, andan attempt was made to remove a segment of bonethat was equal or slightly thicker than the compo-nent to be inserted. All implants were inserted withcement after pulsed lavage, drying, and pressuriza-tion of the cement.A splint was applied with the knee in 15° of

flexion and was worn for the first 24 hours afterthe operation. The knee then was placed in acontinuous passive-motion machine. All patientsbegan walking with crutches or walker and startedactive and passive range-of-motion exercise onthe second day after the operation. The patientsused crutches or walker, with full weight-bearing,for 6 weeks and then used a cane since then, ifthey need it.An AP-Glide LCS prosthesis was implanted in 62

knees (31 components in the right side and 31 inthe left). An RP-LCS prosthesis was implanted in62 knees (31 components in the right side and 31in the left). Randomization determined which kneewas done first using a sequential pool on the basisof the table of randomized numbers. The order ofinsertion of the AP-Glide LCS and the RP-LCScomponents was assigned alternately to each side.All patellae were resurfaced, and all-polyethylenepatellar prostheses were used in all knees. Allfemoral and tibial components had a polishedcobalt-chromium articular surface (average rough-ness, b0.1 μm).The minimum thickness of the polyethylene

insert averaged 12 ± 2 mm in both groups. Thetype of resin of all polyethylene inserts was 4150resin, and all inserts were machined to their finalshape from a ram-extruded bar. All polyethyleneinserts were sterilized with gamma irradiation invacuum. Themean shelf age of the insert, that is, thenumber of years that had elapsed between steriliza-tion and implantation, was 0.9 ± 1.0 year in the AP-Glide LCS multidirectional group and 0.7 ± 1.1 yearin the RP-LCS unidirectional group.Knee scores were determined preoperatively and

postoperatively with The Hospital for Special Sur-gery system [6]. The Knee Society system [7] wasused to determine knee and functional scorespreoperatively and postoperatively. The patients'preference as to the functional performance of eachprosthesis was assessed in a blinded fashion.Radiographs were analyzed by 2 of the authors

who had no knowledge of the identities of thepatients, and the findings were recorded by a

research assistant who knew the identities of thepatients. The κ statistics were used to assess inter-and intraobserver reliability for the radiographicmeasurements. For angular measurements (includ-ing alignment of the limb, component position, andpatellar angle), the mean interobserver differencewas 1.9°(±1.3°), and the mean intraobserver differ-ence was 1.5° (±1.2°). For metric measurements(including radiolucent line, osteolysis, joint line, andposterior femoral condylar offset), the mean inter-observer difference was 1.8 ± 1.6 mm, andintraobserver difference was 1.6 ± 1.2 mm.

Radiographs obtained before and after surgery,which included anteroposterior radiographsobtained with the patient standing and supine,lateral radiographs, and a skyline patellar radio-graph, were assessed for alignment of the limb, theposition of the component, and the presence andlocation of all radiolucent lines at the bone-cementinterface according to the recommendations of theKnee Society [7]. All radiographs were taken underthe control of fluoroscopic radiographic examina-tions at each follow-up to critically determine theinterfaces. Magnification of the radiographs wascontrolled as much as possible by maintaining thedistance between the x-ray tube and x-ray filmconstantly same while the x-rays are taken at eachfollow-up examinations The joint lines weredetermined in anteroposterior radiographsobtained before and after surgery with the patientsupine by measuring the distance between the tipof the fibular head and the distal margin of thelateral femoral component postoperatively. Theskyline patellar radiographs were examined forpatellar tilt, subluxation, or dislocation.

Postoperative computed tomography (CT) scansusing a multislice scanner (General Electric LightPlus; General Electric Co, Waukesha, Wis) wereperformed at final follow-up to determine theosteolysis in all knees. A scan sequence wasperformed from 10 cm above the superior pole ofthe patella to 10 cm below the tibial tuberosity using2.5-mm contiguous slices. Osteolysis was defined asany nonlinear region of periprosthetic cancellousbone loss with delineable margins in both conven-tional radiographs and CT scans. The prevalence ofosteolysis on anteroposterior, lateral, and skylineviews of radiographs was compared with theprevalence of osteolysis on CT scans.

To detect an effect size of 0.5, corresponding to ananticipated difference of 4 points and a standarddeviation of 8 points, with a power of 85% and asignificant level of 5%, we calculated that 55patients were required. In anticipation of a smalldropout rate 62 patients were required.

Table 1. Preoperative and Postoperative Knee and Functional Scores in the Multidirectional and Unidirectional Groups

Group *

The Hospital for SpecialSurgery [7] (Points) The Knee Society [6] (Points) Range of Motion (°)

PreoperativeKnee Score

PostoperativeKnee Score


PreoperativeFunctionalScore


PostoperativeFunctionalScore



Multidirectional 27.9 (28-63) 87.8 (48-100) 26 (19-45) 32 (15-50) 91 (45-100) 82 (35-100) 129 (85-150) 126 (80-150)Unidirectional 26.8 (17-65) 89.1 (45-100) 26 (19-45) 30 (11-50) 90 (52-100) 81 (46-100) 131 (95-150) 128 (88-150)

(P = .906) y (P = .558) y (P = .733) y (P = .526) y (P = .851) y (P = .701) y (P = .679) y (P = .812) y

Values are expressed as means, with ranges in parentheses.*Multidirectional group—knees implanted with AP-Glide LCS prostheses; unidirectional group—knees implanted with RP-LCS

prostheses.yComparison between the multidirectional and unidirectional groups using Student t test.


Statistical comparisons of the clinical and radio-graphic results associated with the 2 groups wereperformed with analysis of variance, χ2 analysis,and Student 2-tailed t test. All statistical analysesof the data were performed with version 13.0SPSS software (Chicago, Ill) by an independentbiostatistician who was not directly involved inthe study. Probability values of .05 or less wereconsidered to indicate significance. Survivorshipanalysis was performed to determine the cumula-tive rate of survival of the implant during theperiod of the study [8,9]. The end point for theanalysis was revision surgery for any reason or arecommendation for revision surgery by thesenior author.

Table 2. Radiogra

Parameters Multidirectional Grou

AlignmentPreoperative, no. of knees (%)Varus1°-10° 33 (53)11°-20° 20 (32)

Valgus1°-10° 9 (15)

PostoperativeValgus 4.8° (−3.8° to 9°)

Femoral component position(femoral angle)*Anteroposterior 96.3° ± 2.8° (88° to 103Sagittal 6.5° ± 4° (−7.7° to 16.2Tibial component position(tibial angle)*Anteroposterior 88.5° ± 2.6° (83.2° to 97Sagittal 84.2° ± 2.6° (77.4° to 89Radiolucent lines(number of knees)Absence 55 (89%)Presence (tibial side) 7 (11%)Osteolysis 0 (0%)

*Values are expressed as mean ± standard deviation, with range in

Results

The preoperative and postoperative Knee Societyknee scores, functional scores, the Hospital forSpecial Surgery knee scores, and range of motionof knees were similar between the 2 groups (Table1). Fifty-one patients had no preference of eitherprosthesis. There were 6 patients who preferred AP-Glide LCS prosthesis, and the remaining 5 patientspreferred the RP-LCS prosthesis.

The postoperative radiographic results were simi-lar between the 2 groups (Table 2). No knee in eithergroup had detectable osteolysis on radiographs or onCT scans. It was unexpected that CT scans did notdiscern any osteolysis at this length of follow-up.

phic Results

p Unidirectional Group P

31 (50)25 (40) .501

6 (10)

4.9° (−5° to 8°) .834

°) 96.3° ± 2.6° (84° to 103°) .923°) 6.1° ± 4.4° (7° to 14.7°) .615

.3°) 87.8° ± 2.7° (81.1° to 95.4°) .183

.3°) 84.4° ± 2.7° (78° to 94.7°) .591

54 (87%) .4478 (13%)0 (0%)

parentheses.


A total of 55 (89%) knees in the AP-Glide LCS TKAgroup and 54 (87%) knees in the RP-LCS TKAgroup had no radiolucent lines around any compo-nents. Therefore, the prevalence of radiolucent linesaround the components was similar in the 2 groups(7 knees or 11% in the AP-Glide LCS TKA groupand 8 knees or 13% in the RP-LCS TKA group).Two (3%) knees in each group had aseptic

loosening of the tibial component. All of these 4knees that failed had 3° to 5° more varus alignmentfrom the mean alignments, but body mass indexwas not different from the mean body mass index.These 4 knees were revised. No knee had patellardislocation. Kaplan-Meier analysis [8] with revisionor aseptic loosening as the end point revealed a 12-year survival rate of 97% (95% confidence inter-val, 0.94-1.0) in both groups. In the worst-casescenario (if all 3 patients who were lost to follow-up have revision or aseptic loosening), 12-yearsurvival rate is 92% (95% confidence interval,0.91-1.0) in both groups.

Discussion

The kinematics of the AP-Glide LCS TKA and RP-LCS TKA have been evaluated [10,11]. The AP-Glide LCS prosthesis showed femoral tibial contactposterior to the midsagittal plane of the tibia invirtually all positions. Again, there was a fairlypredictable posterior femoral rollback with earlyflexion up to 30°, which could be attributed to thehigh conformity of the design in this position. After60° flexion, there was anterior translation of thecondyles that persisted with flexion up to 90°.Again, this results from the decreased conformityof the design in higher degrees of flexion with thesmaller radii curvature of the posterior femoralcondyles and from the freedom of excursion in thetracks. The RP-LCS prosthesis demonstrated midlinesagittal plane proximal tibia position throughout thedeep knee bend and gait cycle, which is optimal forcongruency and weight bearing. The minor earlyposterior femoral rollback could be attributed to thehigh conformity of this design up to 30° of flexion,whereas the anterior translation seen from 60° to90° related to the freedom due to the smaller radii ofcurvature of the posterior femoral condyles. Themost desirable features were the midline positionrelated to the design conformity and the lack ofmajor anterior posterior translation over the prox-imal tibia, which could be detrimental both for tibialbase plate fixation and polyethylene wear [10,11].This study was performed to evaluate the hypoth-

esis that clinical and radiographic results of the AP-

Glide LCS TKAs are better than those in the RP-LCSTKAs in the same young patients who underwentbilateral TKAs. We further evaluated the hypothesisthat the prevalence of osteolysis would be higher inthe AP-Glide LCS TKAs than that in the RP-LCSTKAs. We were not able to support the hypothesisthat clinical and radiographic results of AP-GlideLCS TKAs were better than those in the RP-LCSTKAs. Furthermore, we were not able to support thehypothesis that the prevalence of osteolysis washigher in the AP-Glide LCS TKAs than that in theRP-LCS TKAs. We found no differences in post-operative clinical and radiographic results betweenthe 2 groups. In addition, we found no knee ineither group had gross tibial polyethylene liner wearor periprosthetic osteolysis.

This study has some limitations. Firstly, thepatients in this study, who were mostly female,had relatively light weight and may not haveprovided sufficient stress to the implant surfacesand interfaces to demonstrate a difference betweenthe 2 designs despite the long follow-up. Secondly,differentiation of the knee scores between theknees of one individual posed some difficulties.The components of pain, support, and range ofmovement were easily differentiated, but thecomponents of distance walked and stair climbingability were more difficult to differentiate. In thesedomains, however, if the patients had difficulties,they could always identify the knee that mostlimited their activities. Thirdly, there are noaccurate methodologies to measure wear of thepolyethylene bearing. Fourthly, there is very littlepatient-perceived outcome.

The strengths of our study are as follows: wedescribed 1 surgeon's experience with a consecutivegroup of patients in whom simultaneous bilateralTKAs were performed, and this minimizes con-founding factors; and there was no bias involved inthe selection of our patients.

It has been claimed that the most significantdifference between the AP-Glide LCS and RP-LCSdesigns is the ability of AP-Glide LCS bearings tomove in multiple directions as compared with themore constrained rotational motion of the RP-LCSdesign. The damage resulting from this principaldifference was best observed on the superior surfaceof the tibial tray. In the case of the RP-LCS design, thescratches were concentric and aligned with theprincipal direction of bearing movement. In contrast,multidirectional scratches were observed on theAP-Glide LCS tray and will probably result in higherwear rates due to scratch cross-sectional geometrybeing potentially orthogonal to the tibial bearingmotion. Furthermore, multidirectional polyethylene


platforms in the mobile-bearing TKA would producemore volumetric wear than the unidirectional poly-ethylene platforms. Jones et al [2] demonstrated thatmultidirectional polyethylene platforms have wearrates 9 times greater than unidirectional platforms.Theoretically, more volumetric polyethylene wearparticles will lead to a higher prevalence of osteolysisin the former group than in the latter group.However, Kop and Swarts [12] reported that thelinear penetration and volumetric wear measured forthe AP-Glide LCS and RP-LCS designs were similarand compare more than favorably to reported valuesfor fixed-bearing designs. They wondered whetherthe AP-Glide LCS design may predispose the bearingto increased inferior articulation wear due to multi-directional movement [13]. From our study, wefound that no knee in either group had gross tibialpolyethylene liner wear or periprosthetic osteolysis.In the clinical series of mobile-bearing TKAs, low

rates of failure resulting from polyethylene wear orosteolysis have been reported (Table 3). Sorrells [14]reported the results with a partially congruentrotating platform at a follow-up interval of 1 to 11years. The failure rate resulting from wear was 0.2%;the single failure in that study was ascribed to poor-quality polyethylene. He reported no aseptic loosen-ing. Buechel et al [15] reported 3 (1.8%) of 169cementless RP-LCS knees failed from osteolysis at10.2 years follow-up. Callaghan et al [5] reported noperiprosthetic loosening or failure from wear at 9 to12 years with 119 mobile-bearing knee prostheses ofthe same design. At intermediate follow-up of fullycongruent multidirectional platforms used in 172knees, Kaper et al [16] reported only 2 (1.2%) of 172TKAs required revision as a result of wear. Kim andKim [4] reported no detectable polyethylene wear orperiprosthetic osteolysis at 5 to 7 years with RP-LCSand AP-Glide LCS TKAs. In our current series ofpatients, we detected no periprosthetic osteolysis ineither group. This finding confirmed the previousreports that the failure rate resulting from osteolysis isvery low.

Table 3. Reported Failure Rate of Mobile-bearing TKA

Study Types of Prosthesis

Buechel et al [15] RP-LCS (cementless)Callaghan et al [5] RP-LCS (cemented)Kaper et al [16] Self-aligning I TKA

(cemented)Kim and Kim [4] RP-LCS and AP-Glide

LCS (cemented)Sorrells [14] RP-LCS (cemented)Current series RP-LCS and AP-Glide

LCS (cemented)

Collier et al [17] analyzed risk factors forosteolysis after TKA. Men were 3.6 times morelikely to have osteolysis than women. Knees inwhich the baseplate had a grit-blasted proximalsurface were 2.6 times more likely to be affected byosteolysis than knees treated with a polished-surfacebaseplate. Knees with an insert that had beengamma-irradiated in air were 4.0 times more likelyto have osteolysis than knees with an insert that hadbeen gamma-irradiated in nitrogen. The risk ofosteolysis increased by a factor at 1.5 with any 1-year increase in the shelf age of the insert. Inaddition, the intercomponent hyperextension anglewas associated with osteolysis.

The low prevalence of osteolysis in both RP-LCSand AP-Glide LCS TKAs in our current series ofpatients may be related to a number of factors:preponderance of female patients; use of a cobalt-chromium tibial baseplate (a stiff cobalt-chromiumplate maintains even load distribution for thepolyethylene); the polished proximal surface of thetibial baseplate; polyethylene sterilized with gammairradiation in vacuum; improved quality of poly-ethylene of the insert; the short shelf age of theinsert; reduction of access channels for wear debris;no intercomponent hyperextension; solid fixation ofthese prostheses with a good cementing technique,which limits the so-called effective joint space [18];and diminutive patients in this series. In addition, itis possible that the rate of osteolysis was low becausethe follow-up was not long enough.

Buechel et al [19] and Goodfellow and O'Connor[20] postulated the mobile-bearing TKA wouldminimize bone-prosthesis stress at the tibial surface.Kim et al [21] reported the overall prevalence ofradiolucent lines was 34% in the fixed-bearing TKAand 25% in the mobile-bearing TKA. Our lowprevalence of radiolucent lines in fewer than 2zones around the tibial component is consistentwith this notion.

Anterior soft tissue impingement has been notedanecdotally after the use of AP-Glide LCS TKA. This

Resulting From Polyethylene Wear and Osteolysis

Follow-Up (y)

Failure Rate(No. of Failed Knees/Total No. of Knees)

10.2 3/169 (1.8%)9-12 0/119 (0%)5-8 2/172 (1.2%)

5-7 0/172 (0%)

1-11 1/500 (0.2%)11-13 0/124 (0%)


problem was resolved after an alteration of the tibialinsert. The AP-Glide LCS prosthesis is totallyunconstrained in the sagittal plane, and the kine-matic study has shown the potential for anteriortranslation in the non–weight bearing condition.Flexion space balancing must be accurate and nottoo tight to allow adequate flexion, but if too loosemay allow for abnormal anterior translation andpotential fat-pad impingement. Another problemhas been potential instability that may result fromposterior cruciate ligament disruption. We havepreserved a bone block at the insertion of theposterior cruciate ligament to prevent late ligamentfailure. From our study, we had neither abnormallyincreased flexion gap nor late posterior cruciateligament failure that led to abnormal anterior-posterior motion requiring revision.Several studies suggested that there was a greater

mean range of motion in association with AP-Glidemobile bearings. In a 10-year follow-up study, thereported mean range of motion was 107° for RP-LCSprostheses and 117° for AP-Glide bearings [15]. Themean preoperative range of motion in that study ofprimary TKAs, however, was greater for the AP-GlideLCS (106° compared with 93°). In a multicenteranalysis, the mean range of motion was 120° for AP-Glide LCS TKAs and 108° for RP-LCS TKAs (P b .001),but the preoperative range of motion had beensignificantly greater in the AP-Glide LCS TKAs [22].Aigner at al [23], however, reported that the use of anAP-Glide LCS prosthesis did not improve range ofmotion after TKA compared with the findings seen inassociation with use of a RP-LCS prosthesis. Theythought that the behavior of the AP-Glide LCS TKA intheir study was in accordance with the findings ofprevious kinematic studies, which have rarely shownphysiologic femoral rollback in association with thisdesign [24-26]. In our study, the pre- and post-operative range of motion in the 2 groups were notstatistically different (126° vs 128°) (Table 1). The lackof correlation between translation and knee flexionsuggests that AP-Glide LCS bearings probably do notimprove the range of motion [27].There have been a few prospective, randomized

clinical trials that have compared fixed and mobile-bearing TKAs [20]. In addition, there have been afew prospective, randomized clinical trials that havecompared different types of mobile bearing TKAs[4,23]. In this study, the interventions were iden-tical except for the allocated bearing and themandatory resection of the posterior cruciate liga-ment in the RP-LCS TKA. A tight posterior cruciateligament would narrow the flexion gap and conse-quently would reduce knee flexion. Because therewas no difference in total flexion between the 2

groups, it is unlikely that the posterior cruciateligament influenced the result.

In conclusions, we were not able to support thehypothesis that clinical and radiographic results ofAP-Glide LCS TKAs (multidirectional) were betterthan those in the RP-LCS TKAs (unidirectional).Furthermore, we were not able to support thehypothesis that the prevalence of osteolysis washigher in the AP-Glide LCS TKAs than that in theRP-LCS TKAs. Based on these results, we feel thatthere is no reason to continue the use of an AP-GlideLCS mobile-bearing TKA.

References

1. Oakeshott RD, Komistek RD, Stiel JB. The A/P-glideknee prosthesis—rationales, kinematics and results.In: Hamelynck KJ, Stiehl JB, editors. LCS Mobilebearing knee arthroplasty: a 25 year worldwidereview. Berlin, Germany: Springer; 2002. p. P313.

2. Jones VC, Barton DC, Fitzpatrick DP, et al. Anexperimental model of tibial counter face polyethy-lene wear in mobile bearing knees: the influence ofdesign and kinematics. Biomed Mater Eng 1999;9:189.

3. Engh GA, Ammeen DJ. Periprosthetic osteolysis withtotal knee arthroplasty. Instr Course Lec 2001;50:391.

4. Kim YH, Kim JS. Comparison of anterior-posterior–glide and rotating-platform low contact stress mobile-bearing total knee arthroplasties. J Bone Joint SurgAm 2004;86:1239.

5. Callaghan JJ, Squire MW, Goetz DD, et al. Cementedrotating-platform total knee replacement: a nine totwelve-year follow-up study. J Bone Joint Surg Am2000;82:705.

6. Insall JN, Ranawat CS, Aglietti P, et al. A comparisonof four models of total knee-replacement prostheses.J Bone Joint Surg Am 1976;58:754.

7. Insall JN, Dorr LD, Scott RD, et al. Rationale of theKnee Society clinical rating system. Clin Orthop1989;248:13.

8. Kaplan EL, Meier R. Nonparametric estimation fromincomplete observations. J Am Stat Assoc 1958;53:457.

9. Rand JA, Ilstrup DM. Survivorship analysis of totalknee arthroplasty: cumulative rates of survival of9200 total knee arthroplasties. J Bone Joint Surg Am1991;73:397.

10. Stiehl JB, Dennis DA, Komistek RK, et al. Kinematicanalysis of a mobile bearing total knee arthroplasty.Clin Orthop 1997;345:60.

11. Stiehl JB, Komistek RD, Dennis DA. In vivo kinematiccomparison of posterior cruciate retention or sacrificewith a mobile bearing total knee arthroplasty. Am JKnee Surg 2000;13:13.

12. Kop AM, Swarts E. Quantification of polyethylenedegradation in mobile bearing knees: a retrievalanalysis of the anterior-posterior–glide (APG) and


rotating platform (RP) low contact stress (LCS) knee.Acta Orthop 2007;78:364.

13. Wasielewski RC, Parks N,Williams I, et al. Tibial insertsurface as a contributing source of polyethylene wearin mobile-bearing knees: the influence of design andkinematics. Biomed Mater Eng 1999;9:189.

14. Sorrells RB. The rotating platform mobile bearingTKA. Orthopedics 1996;19:793.

15. Buechel Sr FF. Long-term followup aftermobile-bearingtotal knee replacement. Clin Orthop 2002;404:40.

16. Kaper BP, Smith PN, Bourne RB, et al. Medium termresults of a mobile bearing total knee replacement.Clin Orthop 1999;367:201.

17. Collier MB, Engh Jr CA, McAuley JP, et al. Osteolysisafter total knee arthroplasty: influence of tibialbaseplate surface finish and sterilization of polyethy-lene inert. Findings at five to ten years postopera-tively. J Bone Joint Surg Am 2005;87:2702.

18. Schmalzried TP, Jasty M, Harris WH. Periprostheticbone loss in total hip arthroplasty: polyethylenewear debris and the concept of the effective jointspace. J Bone Joint Surg Am 1992;74:849.

19. Buechel Sr FF, Buechel Jr FF, Pappas MJ, et al.Twenty-year evaluation of meniscal bearing androtating platform knee replacements. Clin Orthop2001;388:41.

20. Goodfellow JW, O'Connor J. Clinical results of theOxford knee: surface arthroplasty of the tibiofemoral

joint with a meniscal bearing prosthesis. Clin Orthop1986;205:21.

21. Kim YH, Kook HK, Kim JS. Comparison of fixed-bearing and mobile-bearing total knee arthroplasties.Clin Orthop 2001;392:101.

22. Stiehl JB, Voorhorst PE, Keblish P, et al. Comparisonof range of motion after posterior cruciate ligamentretention or sacrifice with a mobile-bearing total kneearthroplasty. Am J Knee Surg 1997;10:216.

23. Aigner C, Windhager R, Pechmann M, et al. Theinfluence of an anterior-posterior gliding mobile-bearing on range of motion after total knee arthro-plasty. J Bone Joint Surg Am 2004;86:2257.

24. Komistek RD, Scott RD, Dennis DA, et al. In vivocomparison of femorotibial contact positions forpress-fit posterior stabilized and posterior cruciate-retaining total knee arthroplasties. J Arthroplasty2002;17:209.

25. Dennis DA, Komistek RD, Hoff WA, et al. In vivo kneekinematics derived using an inverse perspectivetechnique. Clin Orthop 1996;331:107.

26. Dennis DA, Komistek RD, Stiehl JB, et al. Range ofmotion after total knee arthroplasty: the effect ofimplant design and weight-bearing conditions. JArthroplasty 1998;13:748.

27. Banks S, Bellemans J, Nojaki H, et al. Knee motionsduring maximum flexion in fixed and mobile-bearingarthroplasties. Clin Orthop 2003;410:131.

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