A Matsushita

A Terrier

AK Nilsdotter

BJ McGrory

CH Rorabeck

DP Sakalkale

Filip Bjørdal

I Asayama

JM Matta

Kristian Bjørgul

M Klassbo

M Maruyama

NJ Little

P Paillard

P Soderman

PA Devane

RB Bourne

RL Barrack

SL Delp

T Karachalios

WB Kurtz

Journal of Orthopaedics and Traumatology

Crossref

ORIGINAL ARTICLEThe role of femoral offset and abductor lever arm in total hiparthroplastyFilip Bjørdal1 • Kristian Bjørgul2Received: 13 November 2014 / Accepted: 22 May 2015 / Published online: 12 June 2015 The Author(s) 2015. This article is published with open access at Springerlink.comAbstractBackground In order to create a well-functioning totalhip arthroplasty (THA), it is important to restore femoraloff-set and thus the abductor lever arm. The aim of thisstudy was to investigate the clinical effect of increasing theabductor lever arm to and beyond the anatomical nativelever arm in minimally invasive total hip arthro-plasty performed through a direct anterior approach.Materials and methods We compared the lever arm of theoperated hip to the lever arm of the contralateral native hip onradiographs in 148 patients following THA. The patients weredivided in two groups based on whether they kept theiranatomical lever arm or had an increased lever arm. Theclinical outcomewas assessed using hip osteoarthritis outcomescore (HOOS), Harris hip score and UCLA activity score.Results Patients who kept their anatomical lever arm didnot experience a significantly better clinical outcome thanthe patients with an increased abductor lever arm. Wefound no significant difference in clinical scores at any ofthe follow-ups during the first year after THA.Conclusion The results of this study suggest that anincrease in the abductor lever arm does not have majoreffects on the clinical outcome after THA. To avoid thepotential negative effects of decreasing the lever arm, thesurgeon should aim for an equal or slightly increased leverarm.Level of evidence Level 3, prospective cohort study.Keywords Hip arthroplasty  Minimally invasive hiparthroplasty  Femoral off-set  Uncemented  HOOS Harris Hip ScoreIntroductionTotal hip arthroplasty (THA) is a well-established treat-ment in patients suffering from arthritic disease of the hip,reducing pain and improving function [1]. By replacing thedegenerative joint with a prosthetic stem and cup, oneseeks to restore the normal anatomy of the joint, but severalcontroversies remain regarding the optimal placement ofthe components [2–4].In order to restore the optimal biomechanical forces ofthe joint, the acetabulum may be medialized, thusreducing the distance between the center of rotation andthe body axis [5], which provides better mechanicalconditions for the abductor muscles of the hip [6]. Bymedializing the cup there is a risk of reducing the globaloffset. It is therefore considered important to compensatewith an equivalent increase in the femoral offset to ensurethe biomechanical benefits [6–8]. However, whenincreasing the femoral offset, there is an inherent risk ofexaggerated compensation, which may lead to increasedtension on the abductor muscles and possibly pain andreduced function. We have not been able to find any lit-erature investigating the clinical consequences of anovercorrection of the femoral offset.The aim of this study was to investigate any correlationbetween a change in lever arm of the abductor muscles andclinical outcome, including the possible consequences ofan exaggerated offset. To clarify this aspect we& Kristian Bjørgulkrisbjorgul@gmail.comFilip Bjørdalfilipbjordal@hotmail.com1 University of Oslo, Hollandveien 26, 1555 Son, Norway2 Østfold Hospital Trust, Aleris Health Oslo, Chr. Svendsensgate 6, 1771 Halden, Norway123J Orthopaed Traumatol (2015) 16:325–330DOI 10.1007/s10195-015-0358-7investigated whether there were any differences in clinicaloutcome between patients who had an increase in lever armcompared to patients who kept their anatomical lever arm.Materials and methodsDuring 2010 we performed THA in 166 patients using thedirect anterior approach to the hip through the Smith-Peter-sen interval. Of these, 148 were included in our study group;15 of the 166 patients were excluded due to previous con-tralateral hip arthroplasty, and 3 were excluded due to adecrease in the abductor lever arm (ALA) beyond 5 mm. Allpatients were followed and assessed with Harris hip score,UCLA activity score and hip disability and osteoarthritisoutcome score (HOOS) with the added dimensions walkingability and recreational ability. Evaluations were made after6 weeks, 4 months and 1 year postoperatively.HOOS is a patient-administered questionnaire thatconsists of five subscales (pain, symptoms, activity of dailyliving, sport and recreation, function, and hip-relatedquality-of-life). Each question was answered using a Likertscale from 0 to 4 points and a score was calculated for eachsubscale, where 100 indicate no symptoms and 0 representsextreme symptoms [9].The UCLA activity score is a scale ranging from 1 to 10,where 1 indicates inactivity and 10 the highest level of activity.The THA was performed through the anterior approachon a fracture table. The method has been described thor-oughly by several authors [10, 11]. All patients weremobilized on the day of surgery. We recommended partialweight bearing as needed and did not impose any restric-tions on activities or range of motion. The implants usedwere an SL-PLUS MIA stem and a REFLECTION press fitcup (Smith and Nephew, Memphis, TN, US). The SL-PLUS MIA stem was available in a high offset version aswell as in a normal offset version. In this study, we usedexclusively the high offset stem, which has a CCD angle of123. The standard stem has an angle of 131, and thedifference in femoral offset between the stems is 8 mmwhen a size 6 stem is used with a neutral head.Radiological assessmentA standardized anteroposterior pelvic and hip radiographwas performed in all patients following THA. The ALAwas defined as the distance from the center of the hip jointto the line of action of the abductor muscles (Fig. 1) [12].The lever arm and the line of action of the abductor shouldform a 90 angle. The lever arm was then measured in thecontralateral hip and compared to the operated side. Thepatients were divided into two groups based on the dif-ference in ALA between the operated hip and thecontralateral native hip. Group 1 consisted of patients witha lever arm restored to within 5 mm of the native leverarm, while group 2 comprised patients with a lever arm thatwas increased to greater than 5 mm of the native lever arm.The two groups were compared in regards to all parametersof Harris hip score and HOOS.Statistical analysisStatistical analysis was performed using Microsoft Excel.Data were expressed as mean ± standard deviation (SD).Comparisons were made using the unpaired Student’s t test.A P value of less than 0.05 was considered to be significant.ResultsThe study population consisted of 51 men and 97 womenwith a mean age of 67.7 ± 10.9 years. Mean body massindex was 27.0 ± 4.3 (Table 1). An analysis of Harris HipScore and HOOS preoperatively did not show any statis-tically significant differences between the two groups.Radiological resultIn our sample we found a native ALA of 58.0 ± 6.6 mm,whereas the mean lever arm of the operated side was65.4 ± 5.9 mm.Group 1 consisted of 56 patients with a mean nativeALA of 61.6 ± 6.1 mm. The mean lever arm of theoperated side was 63.0 ± 5.4 mm; 17 of the patients in thisgroup experienced a shortening of the lever arm, whereas34 had an increase. Five patients did not experience aFig. 1 Radiograph demonstrating the abductor lever arm (ALA),defined as the distance from the center of rotation to the line of actionof the abductor muscles326 J Orthopaed Traumatol (2015) 16:325–330123difference in lever arm between the two hips (Fig. 2a). Themean difference in lever arm between the contralateralnative hip and the operated hip was 1.4 ± 3.12 mm.Group 2 comprised 95 patients with a mean native leverarm of 55.8 ± 5.9 mm. The mean lever arm of the oper-ated side was 66.9 ± 5.8 mm. These patients had a meanincrease in the lever arm of 11.2 ± 4.3 mm (range6–28 mm) (Fig. 2b).Clinical outcomePatients whose lever arm was restored to within 5 mm ofthe contralateral native hip did not experience a signifi-cantly better clinical outcome than the patients with agreater postoperative increase in lever arm (Fig. 3). After1 year of follow-up there were still no statistically signif-icant differences in any parameters of HOOS or Harris hipscore between the two groups (Table 2).DiscussionOur data showed no significant difference in clinical out-come between the two groups at any of the follow-upsduring the 1st year after operation. This suggests that achange in ALA does not have a large impact on the clinicaloutcome as measured by HOOS or Harris hip score duringthe 1st year after THA.There is evidence that offset plays an important rolewhen it comes to the clinical result following THA. Severalstudies have documented that an increase in offset resultsin increased range of motion, better mechanical advantageof the abductors and increased stability due to increasedsoft tissue tension [6, 12, 13]. Failure to restore offset hasbeen associated with increased joint reactive force andhence an increase in polyethylene wear [14–16]. However,Little et al. [17] suggested that an increase beyond 5 mm ofthe contralateral hip might also result in increased poly-ethylene wear.Although the importance of femoral offset in THA hasbeen emphasized in several studies, there is limited researchdirectly investigating the role of the abductor lever arm andits effect on clinical outcome. Studies have reported acorrelation between the ALA and abductor muscle strength.McGrory et al. [12] reported that ALA length was amongthe most important factors influencing abductor musclestrength. Using a 3-dimensional biomechanical model, Delpet al. [8] demonstrated that lateral displacement of the hipcenter adversely affected the function of the abductormuscles by decreasing the lever arm, thereby decreasing thecapacity to generate hip abduction moments. Recently,Terrier et al. [18] found that the benefits of cup medial-ization varies according to individual patient anatomy andstated that medialization should be balanced against possi-ble disadvantages such as increased bone loss.Our study provides clinical data that enables us toinvestigate how a change in lever arm affects the outcomeafter THA in a clinical setting where the surgery wasperformed by two surgeons using the direct anteriorapproach through the Smith-Petersen interval in every case.The same types of implants were used in all patients.The radiological assessments were made using digitalimages from our database, enabling the radiologist to usemeasurement tools with high degree of precision.Table 1 Patient demographicsStudy population Group 1 Group 2 P valueALA increase/decrease B5 mm ALA increase[5 mmNumber of patients 148 56 92Gender (male/female) 51/97 27/29 24/68Age (years)a 67.7 ± 10.9 66.2 ± 13.0 68.6 ± 9.3 0.23Body mass index (kg/m2)a 27.0 ± 4.3 27.2 ± 4.5 26.8 ± 4.3 0.57Preoperative clinical scoringHarris Hip Score 47.4 ± 18.1 46.4 ± 16.7 48.7 ± 18.6 0.45HOOS––pain 35.7 ± 16.9 33.2 ± 16.0 37.3 ± 18.0 0.18HOOS––symptom 40.6 ± 17.9 38.0 ± 18.1 42.2 ± 18.3 0.2HOOS––ADL 36.7 ± 16.8 34.9 ± 17.3 38.2 ± 17.2 0.29HOOS––sport/recreation 20.2 ± 18.9 17.9 ± 16.7 21.5 ± 20.6 0.28HOOS––quality of life 27.8 ± 13.6 25.1 ± 11.9 29.1 ± 14.8 0.09HOOS––activity 1a 2.7 ± 1.2 2.6 ± 1.0 2.7 ± 1.3 0.81HOOS––activity 1b 2.6 ± 1.2 2.8 ± 1.2 2.6 ± 1.2 0.21HOOS––activity 2 3.7 ± 2.0 3.5 ± 1.9 3.9 ± 2.0 0.19ALA abductor lever arm, HOOS Hip disability and osteoarthritis outcome scorea Values are expressed as mean ± SDJ Orthopaed Traumatol (2015) 16:325–330 327123Furthermore, all measurements were performed by thesame investigator (J.B.), which eliminated interobservervariability. Intraobserver variability was not assessed.There are some limitations to our study. The patientswere only followed for 1 year postoperatively. It is possi-ble that more time is required to demonstrate a differencein clinical outcome. Another limitation may be that we didnot perform an intra-observer validation study.It is also possible that the instruments used to score theclinical outcome in our study lack sufficient sensitivity todemonstrate a significant difference between the groups.Although both HOOS and Harris hip score have shown ahigh degree of validity, it is possible that these instrumentsare not sensitive enough to demonstrate an underlyingdifference in clinical outcome between the groups [19, 20].In our study population only 17 out of 148 patientsexperienced a shortening of the ALA. Several studies havereported that a shortening of the lever arm may result inweakness of the abductor muscles and reduced stability [6,8, 12, 21]. It is possible that a higher frequency of patientswith a decreased lever arm would have had a larger impacton the clinical scores.Fig. 2 a, b Change in offset inpatient groups 1 (a) and 2 (b).Each patient is represented byone bar328 J Orthopaed Traumatol (2015) 16:325–330123The results of this study suggest that patients who pre-serve their anatomical ALA do not experience a signifi-cantly better clinical outcome than patients that have theirlever arm increased. When considering the potential dis-advantages of decreasing the lever arm, the surgeon shouldaim for an equal or slightly increased lever arm duringTHA.Conflict of interest None.Ethical standards Patients gave the informed consent prior tobeing included in the study. The study was authorized by the localethics committee and was performed in accordance with the Ethicalstandards of the 1964 Declaration of Helsinki as revised in 2000.Open Access This article is distributed under the terms of theCreative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricteduse, distribution, and reproduction in any medium, provided you giveappropriate credit to the original author(s) and the source, provide alink to the Creative Commons license, and indicate if changes weremade.References1. Rorabeck CH, Bourne RB, Laupacis A et al (1994) A double-blind study of 250 cases comparing cemented with cementlesstotal hip arthroplasty. Cost-effectiveness and its impact on health-related quality of life. Clin Orthop Relat Res 298:156–164Fig. 3 Error bars showing95 % confidence intervals forthe mean of hip disability andosteoarthritis outcome score(HOOS) subgroups and Harriship score among group 1(circles) and group 2(diamonds). The two groupsdisplay overlap in all clinicalparametersTable 2 Clinical outcome1 year after total hiparthroplasty (THA)Group 1 Group 2 P valueALA increase/decreaseB5 mmaALA increase[5 mmaMean ± SD Mean ± SDHOOS––pain 86.0 ± 19.0 91.3 ± 12.6 0.16HOOS––symptom 86.7 ± 18.9 90.0 ± 13.0 0.37HOOS––ADL 85.1 ± 20.1 87.8 ± 16.0 0.5HOOS––sport/recreation 74.5 ± 27.5 73.4 ± 22.7 0.85HOOS––quality of life 78.1 ± 25.0 79.4 ± 21.9 0.81HOOS––activity 1a 3.7 ± 1.8 3.9 ± 1.5 0.69HOOS––activity 1b 4.5 ± 1.5 4.2 ± 1.4 0.48HOOS––activity 2 5.9 ± 2.4 5.8 ± 2.3 0.84Harris hip score 94.1 ± 9.7 94.4 ± 10.6 0.86a Values are expressed as mean ± standard deviationJ Orthopaed Traumatol (2015) 16:325–330 3291232. 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The role of femoral offset and abductor lever arm in total hip arthroplasty

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The role of femoral offset and abductor lever arm in total hip arthroplasty

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