By Thomas K. Fehring, MD, Susan M. Odum, MEd, CCRC, Josh Hughes, BS, Bryan D. Springer, MD, and Walter B. Beaver Jr., MD

Transcription

1 2335 CPYRIGHT Ó 2009 BY THE JURNAL F BNE AND JINT SURGERY, INCRPRATED Differences Between the Sexes in the Anatomy of the Anterior Conyle of the Knee By Thomas K. Fehring, MD, Susan M. um, ME, CCRC, Josh Hughes, BS, Bryan D. Springer, MD, an Walter B. Beaver Jr., MD Investigation performe at the rthocarolina Hip an Knee Center, Charlotte, North Carolina Backgroun: Claims that there are ramatic ifferences in anterior conylar anatomy between the sexes have le to the esign of total knee implants with thinner anterior conyles specifically for use in women. We ha observe, in our patients, ifferences in anterior conylar anatomy that appeare to be highly variable anepenent on the size, height, an ethnicity of the patient as well as his or her sex. Because of this observe variability, we sought to etermine if ifferences in anterior conylar anatomy between the sexes actually exist. Methos: Two hunre an twelve ranomly selecte magnetic resonance images (112 of men an 100 of women) were evaluate. The anterior conyle was efine as the area of bone anterior to the anterior femoral cortex, 10 mm above the joint line. The meial an lateral heights of the anterior conyles were measure in millimeters irectly from magnetic resonance imaging ata obtaine in two planes. The so-calle aspect ratio was calculate to etermine whether patient size ha an effect on the size of the anterior conyles. Results: n the basis of the numbers available, there was no significant ifference (p = 0.16) between the sexes with regar to lateral conylar height. The average ifference was only 0.5 mm. There was a significant ifference (p = 0.001) between men an women with regar to meial conylar height. However, the average ifference was only 1.1 mm. While the ifference between the sexes with regar to anterior conylar height was nominal, the measurements were highly variable regarless of sex. n the basis of the numbers available, there were no significant ifferences between men an women with regar to the conylar aspect ratios. Conclusions: The ifference in anterior conylar anatomy is mentione as one of three reasons for the nee for a socalle gener-specific knee implant. The aspect ratio reporte here, which is a surrogate for patient size, seems to negate any ifference in anterior conylar anatomy base on sex. We have shown that anterior conylar anatomy is highly variable regarless of sex. We believe that implants as well as surgical techniques shoul be esigne with the variability of anterior conylar anatomy taken into account an with an attempt to reprouce such anatomy regarless of sex. Claims that there are ramatic ifferences in anterior conylar anatomy between the sexes has le to the esign of total knee implants with thinner anterior conyles specifically for use in women. Proponents of this moification maintain that using a conventional implant in women may overstuff the patellofemoral joint, leaing to a feeling of tightness an/or limitation of the range of motion 1. While overstuffing of the patellofemoral joint has been escribe as a clinical problem by certain authors 2-4, others have claime that it is not clinically relevant 5,6. ne can theorize that a mismatch between the anteroposterior imension of the host bone an the anteroposterior imension of the prosthetic implant may negatively affect knee kinematics 6. A patient in whom a small anterior conyle has Disclosure: In support of their research for or preparation of this work, one or more of the authors receive, in any one year, outsie funing or grants of less than $10,000 from DePuy rthopaeics. In aition, one or more of the authors or a member of his or her immeiate family receive, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provie such benefits from a commercial entity (DePuy rthopaeics). Also, a commercial entity (DePuy rthopaeics) pai or irecte in any one year, or agree to pay or irect, benefits of less than $10,000 to a research fun, founation, ivision, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immeiate family, is affiliate or associate. A commentary is available with the electronic versions of this article, on our web site ( an on our quarterly CD-RM/DVD (call our subscription epartment, at , to orer the CD-RM or DVD). J Bone Joint Surg Am. 2009;91: oi: /jbjs.h.00834

2 2336 T HE J URNAL F B NE &JINT S URGERY JBJS. RG Fig. 1 The anterior conyle. been replace with an implant with a thicker anterior flange is at risk for anterior knee pain an a iminishe range of motion. A patient in whom a large anterior conyle has been replace with an implant with a thinner anterior flange may have a ecrease quariceps moment arm an a functional isavantage. We ha observe, in our patients, that anterior conylar anatomy appeare to be highly variable anepenent on the Fig. 2-A Figs. 2-A an 2-B Illustrations of the measurements of lanmarks on the magnetic resonance images. Fig. 2-A The anterior cortex of the femur was ientifie on the sagittal miline image. An axial cut was mae at a point 10 mm above the joint line.

3 2337 T HE J URNAL F B NE &JINT S URGERY JBJS. RG Fig. 2-B Bone above the anterior cortical line was consiere to represent the anterior conyle (top yellow line). The meial-lateral imension at the epiconylar level (bottom yellow line) was also measure. size, height, an ethnicity of the patient as well as his or her sex. Because of the observe variability in anterior conylar anatomy, we sought to etermine if ifferences in anterior conylar anatomy between the sexes actually exist. The null hypothesis was that there is no ifference between men an women in terms of anterior conylar imensions. Materials an Methos After this stuy was approve by our institutional review boar, 212 magnetic resonance images (112 of men an 100 of women) that ha been ranomly selecte from our orthopaeic hospital s imaging atabase were evaluate. The anterior conyle was efine as the area of bone anterior to the patellofemoral sulcus, 10 mm above the joint line (Fig. 1). In orer to perform the anterior conylar measurements, the anterior cortex of the femur was ientifie on the sagittal miline image (Fig. 2-A). At a point 10 mm above the joint line, an axial cut was mae (Fig. 2-B). This point was selecte to simulate a istal femoral cut in a routine total knee replacement. No attempt was mae to account for the variability in the length of the trochlear groove. All measurements were mae by a single observer (J.H.). Measurements were mae irectly from the igital magnetic resonance images with use of raiographic measuring software (Stentor; Philips Raiology Informatics, San Francisco, California). The meial an lateral heights, in millimeters, of the anterior conyle were then measureirectly from the axial magnetic resonance imaging ata. Bone above the anterior cortical line was consiere to represent the anterior conyle (Fig. 2-B). Aitionally, the meial-lateral imension (with) between the epiconyles was measure at this level (Fig. 2-B). In orer to etermine whether patient size ha an effect on the size of the anterior conyles, a so-calle aspect ratio between these two measurements was calculate by iviing the anterior conylar height by the meial-lateral imension. Statistical Methos Stanarescriptive statistics, incluing the mean an stanar eviation, were calculate. A Kolmogorov-Smirnov test for normality was performe, an the ata were foun to be normally istribute. Differences in conylar imensions were etermine with use of an inepenent t test. To etermine whether ifferences between the sexes in anterior conyle height were affecte by the meial-lateral epiconylar with, an analysis of covariance was performe, with two moels teste. With the first moel, the inepenent variable was sex, the epenent variable was meial conylar height, an meial-lateral with was the covariate. With the secon moel, lateral conylar height was use as the epenent variable, an the other variables remaine the same. The

4 2338 T HE J URNAL F B NE &JINT S URGERY JBJS. RG Fig. 3-A Fig. 3-B Figs. 3-A an 3-B Histograms of the conylar height measurements. Fig. 3-A Meial conylar height. Fig. 3-B Lateral conylar height.

5 2339 T HE J URNAL F B NE &JINT S URGERY JBJS. RG Fig. 4-A Fig. 4-B Figs. 4-A an 4-B Histograms of the conylar aspect ratio measurements. Fig. 4-A Meial conylar aspect ratio. Fig. 4-B Lateral conylar aspect ratio.

6 2340 T HE J URNAL F B NE &JINT S URGERY JBJS. RG significance level for all statistical tests was establishe a priori to be A post hoc power analysis was performe with use of the anterior an meial conyle ratio variables. Source of Funing DePuy rthopaeics (Warsaw, Iniana) provie partial financial support to rthocarolina Research Institute for research staff. Results Conylar Height n the basis of the numbers available, there was no significant ifference between the sexes with regar to lateral conylar height. The average ifference was only 0.5 mm. The average lateral conylar height (an stanareviation) was 7.3 ± 3.0 mm (95% confience interval = 0.58) for men compare with 6.8 ± 3.1 mm (95% confience interval = 0.59) for women (p = 0.16, 1 2 b = 0.63). There was a significant ifference between the sexes with regar to meial conylar height. However, the average ifference was only 1.1 mm. The average meial conylar height was 5.7 ± 2.4 mm (95% confience interval = 0.48) for men compare with 4.6 mm ± 2.6 (95% confience interval = 0.49) for women (p = 0.001, 1 2 b = 0.92). While the ifference in the anterior conylar height between the sexes was nominal, the measurements were highly variable regarless of sex. The range for both meial conylar height an lateral conylar height was from 0 to 18 mm (Figs. 3-A an 3-B). Epiconylar Dimension There was a significant ifference in the meial-lateral epiconylar imension between the sexes. The variability of this measurement was greater for women. The average meial-lateral imension between the epiconyles was 86.6 ± 4.9 mm (95% confience interval = 0.92) for men compare with 76.6 ± 6.5 mm (95% confience interval = 1.29) for women (p < , 1 2 b = 0.99). Intheanalysisofcovariancemoels,therewerenosignificant ifferences, on the basis of the numbers, between the sexes with regar to meial conylar height (F[1,209] = 0.14, p = 0.71]) or lateral conylar height (F[1,209] = 3.45, p = ]) after we ajuste for the meial-lateral epiconylar with. Aspect Ratio (Anterior Conylar Height/Meial-Lateral With) n the basis of the numbers, there was no significant ifference between men an women with regar to the conylar aspect ratio. The average meial conylar aspect ratio was 0.07 ± 0.03 mm (95% confience interval = 0.005) for men compare with 0.06 ± 0.03 mm (95% confience interval = 0.006) for women (p = 0.13, 1 2 b = 0.67). The average lateral conylar aspect ratio was 0.08 ± 0.03 mm (95% confience interval = 0.006) for men compare with 0.09 ± 0.04 mm (95% confience interval = 0.007) for women (p = 0.50, 1 2 b = 0.44). A graphical illustration of the aspect ratios resulte in two nearly ientical bellshape curves for each sex (Figs. 4-A an 4-B). Discussion There appear to be ifferences between men an women with regar to musculoskeletal isease. Women are at higher risk for the evelopment of osteoarthritis an have higher rates of isability attributable to osteoarthritis 7. A number of authors have note that the results of total knee arthroplasty in women are equal or superior to those in men Despite these favorable results, the necessity for a so-calle gener-specific total knee replacement has been markete to patients an surgeons alike. The ifference in anterior conylar anatomy is cite as one of three reasons for a gener-specific knee implant 1. However, ifferences in anterior conylar anatomy between the sexes were negligible both in the series reporte here an in previously publishe reviews of the subject. Like us, Poilvache et al. 12 foun that the anterior extent of the conyles was highly variable. They reporte an average ifference between men an women of 1.48 mm anterolaterally an 1.67 mm anteromeially. Conley et al. 1 note that the ifference between the sexes with regar to conylar anatomy average only 1.3 mm anteromeially an 0.8 mm anterolaterally. The above values were strikingly similar to those note in the current series, in which there was a 0.5 mm ifference in the lateral height of the anterior conyle an a 1.1 mm ifference in the meial height. While there are no firm ata to substantiate whether this small a ifference woul be clinically relevant, we oubt that it is. Aitionally, neither of the two previously publishe reports 1,12 inclue an aspect ratio to ajust for patient size, as we i in this stuy. We believe that correcting for the meial-lateral imension is a surrogate for correcting for patient size regarless of sex an is an important factor to take into account when analyzing this type of ata. The aspect ratios reporte in our stuy (0.07 for men compare with 0.06 for women) seem to negate any ifference base on sex. This fining corroborates the finings of Grelsamer et al. 13, who contraicte another claim that there is a significant ifference in the Q angle between the sexes 1. It has been suggeste that overstuffing of the patellofemoral joint is a major clinical problem. Star et al. 14 note increase patellofemoral compressive forces with increase patellar bone an implant thickness. In a review article, Bong an DiCesare 2 state that stiffness an tightness of the extensor mechanism were a result of inaequate resection of the patella or anterior placement of the femoral component. Shoji et al. 4 foun that an increase in patellar thickness of 20% le to iminishe flexion. In contrast, Daluga et al. 3 faile to fin a correlation between a change in the anteroposterior measurement an the postoperative knee range of motion. They foun that at least a 12% increase in the anteroposterior imension was necessary before the nee for manipulation was increase. Mihalko et al. 6 foun that, when a cut was mae flush with the anterior femoral cortex, the lateral conylar height of a conventional implant increase the lateral height of the anterior conyles by only 1.1 ± 2.6 mm an the meial anterior conylar height was increase by only 0.5 ± 2.2 mm. This negligible increase with use of conventional implants of three ifferent manufacturers is noteworthy. Pierson et al. 5 state that overstuffing of the

7 2341 T HE J URNAL F B NE &JINT S URGERY JBJS. RG patellofemoral joint ha no effect on clinical symptoms. They foun that increasing the height of the patellofemoral joint i not change the range of motion an conclue that overstuffing oes not iminish the clinical outcome. Shortcomings of our ata analysis are that it is base solely on magnetic resonance images of patients for whom we ha no clinical history. Because these magnetic resonance images were ranomly selecte, we o not know the stature or ethnicity of these patients. Regarless, our ata were nearly ientical to those in previous stuies 1,12. Aitionally, we i not measure the absolute length of the trochlear groove in each case, which may have affecte our results. We chose to measure at the level of a routine istal femoral resection, which more closely replicates the clinical situation. n the basis of our ata, we cannot comment on the other aspects of a so-calle generspecific knee implant that is, whether there is a nee for a narrower femoral component or an increase Q angle 1.However, the necessity of a thinner anterior conyle for women is not substantiate by the ata presente in our stuy or our review of the literature. We conclue that anterior conylar anatomy is highly variable with a bell-shapeistribution regarless of sex. While narrowing the prosthetic anterior conyle may iminish anterior knee pain or improve the range of motion, the clinical avantage of oing so has not been stuie, to our knowlege. Placing a thinner anterior conyle in someone who use to have a large anterior conyle may have a negative effect on quariceps function as the quariceps lever arm woul be iminishe. We believe that implants as well as surgical techniques shoul be esigne with the variability of anterior conylar anatomy taken into account an an attempt to reprouce such anatomy regarless of the sex of the patient. n Thomas K. Fehring, MD Josh Hughes, BS Bryan D. Springer, MD Walter B. Beaver Jr., MD rthocarolina Hip an Knee Center, 1915 Ranolph Roa, Charlotte, NC aress for T.K. Fehring: Thomas.Fehring@orthocarolina.com Susan M. um, ME, CCRC rthocarolina Research Institute, 4601 Park Roa, Suite 250, Charlotte, NC References 1. Conley S, Rosenberg A, Crowninshiel R. The female knee: anatomic variations. J Am Aca rthop Surg. 2007;15 Suppl 1:S Bong MR, DiCesare PE. Stiffness after total knee arthroplasty. J Am Aca rthop Surg. 2004;12: Daluga D, Lombari AV Jr, Mallory TH, Vaughn BK. Knee manipulation following total knee arthroplasty. Analysis of prognostic variables. J Arthroplasty. 1991; 6: Shoji H, Solomonow M, Yoshino S, D Ambrosia R, Dabezies E. Factors affecting postoperative flexion in total knee arthroplasty. rthopeics. 1990;13: Pierson JL, Ritter MA, Keating EM, Faris PM, Meing JB, Beren ME, Davis KE. The effect of stuffing the patellofemoral compartment on the outcome of total knee arthroplasty. J Bone Joint Surg Am. 2007;89: Mihalko W, Fishkin Z, Krakow K. Patellofemoral overstuff an its relationship to flexion after total knee arthroplasty. Clin rthop Relat Res. 2006;449: Petterson SC, Raisis L, Boenstab A, Snyer-Mackler L. Disease-specific gener ifferences among total knee arthroplasty caniates. J Bone Joint Surg Am. 2007;89: Lingar EA, Katz JN, Wright EA, Slege CB; Kinemax utcomes Group. Preicting the outcome of total knee arthroplasty. J Bone Joint Surg Am. 2004; 86: McDonal SJ, Charron KD, McCalen RW, Bourne RB, Rorabeck CH. Gener specific total knee replacement outcomes: an analysis using prospectively collecte clinical patient ata. Poster presentation at the Seventeenth Annual Meeting of the American Association of Hip an Knee Surgeons; 2007 Nov 2-4; Dallas, TX. Poster no Dalury DF, Aams MJ. Little ifferences in outcomes between geners using a contemporary total knee system. Poster presentation at the Seventeenth Annual Meeting of the American Association of Hip an Knee Surgeons; 2007 Nov 2-4; Dallas, TX. Poster no Ritter MA, Meing JB, Beren ME, Wing J, Davis K. The effect of gener on outcome of TKR. Rea at the Seventeenth Annual Meeting of the American Association of Hip an Knee Surgeons; 2007 Nov 2-4; Dallas, TX. 12. Poilvache PL, Insall JN, Scueri GR, Font-Roriguez DE. Rotational lanmarks an sizing of the istal femur in total knee arthroplasty. Clin rthop Relat Res. 1996;331: Grelsamer RP, Dubey A, Weinstein CH. Men an women have similar Q angles: a clinical an trigonometric evaluation. J Bone Joint Surg Br. 2005; 87: Star MJ, Kaufman KR, Irby SE, Colwell CW Jr. The effects of patellar thickness on patellofemoral forces after resurfacing. Clin rthop Relat Res. 1996;322: