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Reliability of a New Standardized MeasurementTechnique for Reverse Hill-Sachs Lesions in Posterior

Shoulder DislocationsPhilipp Moroder, M.D., Mark Tauber, M.D., Thomas Hoffelner, M.D.,

Alexander Auffarth, M.D., Gundobert Korn, M.D., Robert Bogner, M.D.,Wolfgang Hitzl, Ph.D., and Herbert Resch, M.D.

Purpose: The purpose of this study was to determine whether standardized measurements are more reliable than mereestimation in determining the extent of the defect in reverse Hill-Sachs lesions.Methods: Twelve patients with 13 reverseHill-Sachs lesions and available computed tomographic scans were included in this study. Based on the computedtomographic scans, estimation and measurement of the defect size in reverse Hill-Sachs lesions using a novel standardizedmethod were carried out twice by 6 observers (3 experts and 3 residents), with an interval of 3 months betweenobservations. To assess and compare the reliability of the estimation of the defect size and the measurement of the defectsize, intraclass correlation coefficients were computed. Results: Estimation of the defect size showed a low interobserverreliability of 0.61 (95% confidence interval [CI], 0.38 to 0.83) and 0.47 (95% CI, 0.24 to 0.74) and a moderate intra-observer reliability of 0.71 (95% CI, 0.51 to 0.89). The estimations of the different observers showed statistically significantdifferences (P < .001). The standardized measurements reached high interobserver reliability (at least �0.81) andexcellent intraobserver reliability (at least �0.88). Residents provided less reliable estimations compared with experts;however, they obtained similarly high reliability when applying the standardized measurements. Conclusions: The mereestimation of the size of reverse Hill-Sachs lesions showed poor reliability, raising the concern for potential overestimationor underestimation in clinical practice. Standardized measurements, which showed good reliability, should be usedwhenever analyzing the size of a reverse Hill-Sachs defect. Level of Evidence: Level IV, diagnostic case series.

osterior shoulder dislocations account for less than

P5% of all episodes of shoulder instability and areassociated with an anterior impression fracture of thehumeral head in approximately 30% of patients.1 Thisdefect of the articular surface is commonly calleda reverse Hill-Sachs lesion in analogy to the Hill-Sachslesions found on the posterior aspect of the humeralhead in anterior dislocations. Surgical treatment iswarranted in the case of a large defect to prevent early

From Department of Traumatology and Sports Injuries (P.M., M.T., T.H.,.A., G.K., R.B., H.R.) and Research Institute for Biostatistics (W.H.), Par-celsus Medical University, Salzburg, Austria; and the Department ofhoulder and Elbow Surgery, Atos Clinic (M.T.), Munich, Germany.The authors report that they have no conflicts of interest in the authorship

nd publication of this article.Received June 7, 2012; accepted October 18, 2012.Address correspondence to Philipp Moroder, M.D., Department of Trauma-logy and Sports Injuries, Paracelsus Medical University, Muellner Haupt-rasse 48, 5020 Salzburg, Austria. E-mail: philipp.moroder@pmu.ac.at� 2013 by the Arthroscopy Association of North America0749-8063/12381/$36.00http://dx.doi.org/10.1016/j.arthro.2012.10.016

78 Arthroscopy: The Journal of Arthroscopic and Related S

osteoarthritis, humeral head necrosis, or engagement ofthe lesion with the posterior glenoid rim, leading torecurrent instability.2-4 According to recent reviews,the size of the defect is the decisive criterion in deter-mining the recommended treatment method.5,6 Cicaket al.5 recommended nonoperative treatment for minorreverse Hill-Sachs lesions affecting less than 25% of thehumeral articular surface; a McLaughlin7 procedure,modified McLaughlin procedure,8 or rotational osteot-omy9 for reverse Hill-Sachs lesions between 25% and50%; and humeral head replacement for defectsaffecting more than 50% of the articulating surface.5

Other authors already recommend arthroplasty if morethan 40% of the humeral articulating surface isimpacted,10,11 even though allograft reconstruction fordefects slightly greater than 40% has rendered prom-ising results.12,13 Paul et al.6 recommended bonegrafting or a McLaughlin procedure even for smallreverse Hill-Sachs lesions with a defect size of 10% to20%. Recently, some arthroscopic techniques havebeen described to treat defects up to 30%.3,14 Althoughthese and similar articles try to provide an exact

urgery, Vol 29, No 3 (March), 2013: pp 478-484

MEASURING REVERSE HILL-SACHS LESIONS 479

algorithm for the treatment of reverse Hill-Sachs lesionsdepending on the size of the defect, none specifies themeasurement method used to determine that size.To our knowledge, no standardized method for

quantifying the size of reverse Hill-Sachs lesions hasbeen reported in the literature, which is alarmingconsidering that the treatment choice is mainly deter-mined by the defect size. In current practice, the extentof the defect is quantified by estimating the percentageof the impacted humeral articular surface based oncomputed tomographic images, resulting in a poten-tially great risk of misestimation and mistreatment. Inaddition, it is not always clearly defined if thepercentages reported in different studies refer to theaffected articular hemispheric surface or the transversecircumference. The purpose of this study was to intro-duce a standardized method for measuring the size ofreverse Hill-Sachs lesions and to investigate its reli-ability in comparison to the current practice of mereestimation of the defect size. The hypothesis of this

Fig 1. Radial lines are drawn from the midpoint of the best-fitcircle to each superficial edge of the defect to form the alphaangle in the (A) axial and (B) coronal plane.

study was that the standardized measurements wouldprevail over mere estimation of the defect size ofreverse Hill-Sachs lesions in terms of reliability.

MethodsWe retrospectively reviewed the shoulder database at

our institution for patients diagnosed with a posteriorshoulder dislocation and computed tomography (CT)-verified reverse Hill-Sachs lesions between 2006 and2011. All patients with an acute posterior shoulderdislocation and the presence of an impression fracture ofthe anterior humeral head were included. The exclusioncriterion was the presence of a dislocation fracture of thehumeral head and head split fractures. Twelve patientswith 13 reverse Hill-Sachs lesions were identified, andcorresponding CT image sets were retrieved through theinstitution’s digital radiology archives. The image sets all

Fig 2. Radial lines are drawn from the midpoint of the best-fitcircle to the closest superficial edge of the defect and to thebicipital groove in the (A) axial image or the medial border ofthe supraspinatus footprint in the (B) coronal image to formthe beta angle.

Fig 3. To determine the maximum relative depth of thedefect in the (A) axial and (B) coronal images, a line is drawnfrom the midpoint of the best-fit circle to the base of the defect(d). Distance d is then deducted from the radius of the circle(r), and the result is divided by the diameter of the circle(2 times the radius).

Table 1. Means and Standard Deviation of the Six Observers for

Reve

First MeasurementAlpha (axial) 89.2� � 6.0� 53.2� � 5.4� 58.7�

Beta (axial) 37.6� � 1.1� 64.0� � 5.2� 38.4�

Depth (axial) 35.7% � 2.3% 17.7% � 1.9% 30.2%Alpha (coronal) 104.3� � 6.0� 99.9� � 9.6� 100.8�

Beta (coronal) 80.4� � 2.6� 54.1� � 10.0� 47.0�

Depth (coronal) 28.5% � 1.2% 14.6% � 3.2% 31.7%Estimation 39.7% � 12.4% 22.5% � 5.2% 21.2%

Second MeasurementAlpha (axial) 90.9� � 4.0� 53.4� � 3.1� 59.2�

Beta (axial) 37.4� � 1.6� 63.8� � 3.4� 35.5�

Depth (axial) 35.2% � 1.1% 18.2% � 1.8% 29.2%Alpha (coronal) 101.4� � 5.5� 95.3� � 5.2� 98.4�

Beta (coronal) 80.2� � 8.0� 56.0� � 8.1� 48.4�

Depth (coronal) 27.0% � 1.1% 13.1% � 1.3% 32.4%Estimation 38.8% � 16.5% 18.2% � 6.6% 23.8%

480 P. MORODER ET AL.

included axial, sagittal, and coronal planes obtainedusinga 64-slice CT scanner (Siemens SOMATOMSensation64;Siemens, Erlangen, Germany). Three expert shouldersurgeons and 3 orthopaedic residents were blindedregarding patient information, and each received thecomplete CT image sets of every patient included in thestudy. Basedon these images, they individually estimatedthe size of the reverse Hill-Sachs lesion in relation to thesurface area of the articular hemisphere of the humeralhead as they would in clinical practice. They then ob-tained measurements of the reverse Hill-Sachs lesionsusing the method described further on. All results weredocumented and the measurements were repeatedindividually by the same observers 3 months later withthe order of the CT datasets of the different patients beingrandomly switched. Because of the retrospective studydesign without any patient intervention, no local ethicscommittee approval was obtained.

Estimating the Size of the Reverse Hill-Sachs LesionTo determine the defect size, the impacted area on

the humeral articular surface was estimated in relationto the entire surface area of the humeral articularhemisphere.

Localizing the Reverse Hill-Sachs Lesion andQuantifying Its SizeTo quantify the size of the defect, the axial and coronal

images displaying the maximum defect size were chosen,and a “best-fit circle” was drawn over the remainder ofthe borders of the intact articulating surface and the restof the humeral head. A radial line was drawn from thecenter of the circle to each limiting edge of the defect,and the angle resulting from the 2 lines represented thesuperficial extent of the defect in the axial and coronalplanes in terms of alpha degrees (Fig 1).To identify the position of the reverse Hill-Sachs lesion

on the humeral head, a third line was drawn from the

Each Reverse Hill-Sachs Lesion

rse Hill-Sachs Lesions 1-13

� 1.1� 76.1� � 7.8� 110.6� � 2.4� 65.9� � 4.9�

� 3.1� 49.5� � 5.5� 52.0� � 4.1� 37.4� � 1.1�

� 1.7% 22.8% � 2.8% 21.6% � 1.1% 26.5% � 3.1%� 12.9� 117.6� � 9.0� 82.6� � 9.5� 88.4� � 9.0�

� 5.9� 37.9� � 5.8� 89.7� � 4.5� 86.6� � 8.1�

� 1.9% 19.0% � 2.7% 20.1% � 3.0% 31.4% � 1.0%� 6.6% 28.0% � 14.6% 42.5% � 15.7% 28.5% � 9.0%

� 1.9� 71.0� � 5.5� 112.6� � 4.6� 68.2� � 3.8�

� 2.0� 50.0� � 3.2� 52.4� � 4.2� 36.9� � 3.3�

� 1.1% 20.4% � 2.4% 23.0% � 2.3% 26.7% � 1.8%� 4.3� 111.4� � 7.7� 96.7� � 6.3� 91.7� � 7.8�

� 4.8� 44.2� � 4.5� 82.3� � 3.3� 86.6� � 6.0�

� 2.0% 18.3% � 1.5% 20.4% � 2.2% 30.2% � 1.7%� 5.7% 27.0% � 11.5% 43.0% � 14.4% 25.0% � 10.0%

MEASURING REVERSE HILL-SACHS LESIONS 481

center of the circle to the middle of the bicipital groovein the axial image and the most medial aspect of thesupraspinatus tendon footprint in the coronal image,rendering an angle for each plane defining the locali-zation of one edge of the defect (Fig 2).The depth of the defect is determined in the same

axial and coronal images by measuring the shortestdistance of the midpoint of the best-fit circle to the baseof the defect (distance d). Distance d is then deductedfrom the radius of the circle, rendering a value thatresembles the maximum depth of the defect. This valueis subsequently divided by the diameter of the circle toobtain relative values (Fig 3).

StatisticsRepeated measures analysis of variance was used

to compare the means of the defect size estimation,alpha axial, beta axial, depth axial, alpha coronal, betacoronal, and depth coronal measurements among the6 observers. A P value less than 5% (type I error) wasused to indicate a statistically significant difference.Interobserver reliability and intraobserver reliabilitytogether with corresponding 95%CIs were computed bycalculating intraclass correlation coefficients (ICCs) foraverage measurements (2-way random single measures,consistency/absolute agreement, and bootstrap percen-tilemethod).According to Portney et al.,15 an ICC smallerthan 0.75 indicated poor to moderate reliability, an ICCbetween 0.75 and 0.90 indicated good reliability, and anICC greater than 0.9 indicated reasonable reliability forclinical measures. We performed a power calculationfor the alpha coronal variable for a paired Student t testbetween raters 5 and 6 because those differences werelargest. The observed means were 76.3� � 22� and 78.3�

� 24�, and the correlation between both raters was r ¼0.94. With our sample size of n ¼ 13 cases, our studyreached 80% power to detect a difference of 7� betweenboth means. This is mainly attributable to the very highcorrelation between both raters. To analyze this question

able 1. Continued

T

Reverse Hill-Sachs Lesio

72.7� � 2.8� 80.8� � 5.4� 46.1� � 5.0� 45.0� � 1.5�

54.3� � 4.3� 39.5� � 4.8� 56.0� � 4.6� 45.9� � 3.4�

13.6% � 1.2% 21.7% � 1.6% 19.4% � 3.9% 22.9% � 2.7%74.9� � 6.5� 82.0� � 2.1� 65.8� � 3.5� 75.8� � 1.7�

95.5� � 4.7� 85.8� � 7.7� 78.5� � 6.4� 83.9� � 4.3�

7.6% � 1.0% 23.7% � 1.8% 21.7% � 2.0% 21.6% � 2.1%33.3% � 9.8% 24.5% � 9.5% 12.2% � 3.2% 18.5% � 7.6%

74.9� � 2.2� 77.3� � 5.9� 46.3� � 3.6� 46.4� � 1.1�

52.9� � 5.9� 35.5� � 3.0� 59.3� � 2.2� 46.7� � 2.4�

14.2% � 2.0% 21.3% � 1.5% 20.1% � 2.1% 22.7% � 1.3%72.6� � 7.0� 83.7� � 3.8� 68.5� � 3.6� 78.7� � 5.6�

90.1� � 4.2� 84.3� � 3.9� 80.0� � 8.2� 78.9� � 7.0�

8.4% � 0.7% 21.9% � 1.2% 19.7% � 2.0% 21.6% � 2.2%30.4% � 15.9% 27.0% � 8.4% 12.4% � 2.5% 18.0% � 7.6%

for other variables, the same computations were appliedto the alpha axial variable. This analysis revealed thata difference of 4.6� can be detected with 80% power anda sample size of n ¼ 13. For the beta axial variable, theminimal difference is 6.6�. All computations were per-formed with PASW, version 19 (IBM, Armonk, NY) andSTATISTICA, version 10 (StatSoft, Tulsa, OK).

ResultsOf the 12 patients involved in this study, 4werewomen

and 8 were men. The average age of the patients was 56years, with a range from 30 to 88 years. Eleven patientssustained a unilateral posterior shoulder dislocation, andone patient sustained bilateral posterior shoulder dislo-cations with bilateral reverse Hill-Sachs lesions. Sixdislocations were caused by a fall from the standingposition, 3 were caused by a seizure, 2 were caused byamotor vehicle accident, andonebilateral dislocationwascaused by a suicide attempt involving high-voltage elec-trical current.All dislocationswerefirst-timeoccurrences.Statistical analysis showed significant differences in

the estimation of defect size among the 6 observers in thefirst (P < .001) and second (P < .001) measurements(Table 1). The interobserver reliability for estimation ofdefect size was 0.61 (95% CI, 0.38 to 0.83) for the firstmeasurement and 0.47 (95% CI, 0.24 to 0.74) for thesecond measurement (Table 2). When comparing theconsistency in estimation for all observers between thefirst and second measurements, the average intra-observer reliability was 0.71 (Table 3). Expert shouldersurgeons reached higher interobserver reliability (0.74;95% CI, 0.47 to 0.90 and 0.64; 95% CI, 0.33 to 0.86)than did the orthopaedic residents (0.54; 95%CI, 0.21 to0.81 and 0.47; 95% CI, 0.13 to 0.77) (Table 4).In the different standardized measurements for deter-

mining the size of the reverse Hill-Sachs defect, the 6observers showed no statistically significant differences(Table 1). The interobserver reliability was highest for the

ns 1-13 P Value

33.3� � 3.8� 40.5� � 3.0� 40.8� � 1.3� .9159.8� � 3.4� 43.0� � 6.6� 54.2� � 2.0� .297.7% � 1.6% 14.3% � 2.2% 15.2% � 1.6% .2924.9� � 3.6� 77.9� � 9.9� 44.5� � 3.8� .051

144.8� � 11.4� 42.1� � 2.8� 109.7� � 5.3� .5710.2% � 0.8% 16.5% � 3.6% 10.6% � 2.8% .587.5% � 2.7% 10.8% � 5.8% 20.5% � 9.1% <.001

33.6� � 2.0� 41.1� � 2.4� 40.3� � 1.3� .3759.8� � 3.2� 48.6� � 6.3� 53.1� � 2.5� .247.4% � 1.2% 14.5% � 1.0% 14.0% � 1.6% .2924.7� � 3.2� 80.9� � 11.8� 44.8� � 2.8� .056

140.6� � 10.5� 42.8� � 4.7� 100.8� � 9.4� .349.8% � 1.3% 15.4% � 2.0% 10.7% � 2.4% .318.2% � 2.5% 12.0% � 7.6% 15.4% � 6.4% <.001

Table 2. Interobserver Reliability Displayed in Terms ofIntraclass Correlation Coefficients (ICCs)

First MeasurementICC (95% CI)

Second MeasurementICC (95% CI)

Alpha (axial) 0.96 (0.92-0.99) 0.98 (0.95-0.99)Beta (axial) 0.82 (0.67-0.93) 0.83 (0.69-0.94)Depth (axial) 0.92 (0.83-0.97) 0.91 (0.83-0.97)Alpha (coronal) 0.92 (0.84-0.97) 0.81 (0.65-0.93)Beta (coronal) 0.95 (0.90-0.98) 0.94 (0.87-0.98)Depth (coronal) 0.92 (0.83-0.97) 0.94 (0.87-0.98)Defect size estimation 0.61 (0.38-0.83) 0.47 (0.24-0.74)

CI, confidence interval.

482 P. MORODER ET AL.

alpha axial measurements (0.96; 95%CI, 0.92 to 0.99 and0.98; 95% CI, 0.95 to 0.99) and lowest for the alphacoronal measurements (0.81; 95% CI, 0.65 to 0.93) andbeta axial measurements (0.82; 95% CI, 0.67 to 0.93 and0.83; 95% CI, 0.69 to 0.94). All measurements exceptthose of the beta axial and the second alpha coronalmeasurements achievedan ICChigher than0.90 (Table 2).Similarly, alpha axial measurements showed the highestaverage intraobserver reliability (0.97) and beta axialmeasurements showed the lowest (0.88) (Table 3). Nosignificant differences in the interobserver reliability ofthe standardized measurements were found for expertshoulder surgeons and orthopaedic residents (Table 4).

DiscussionThe treatment of a reverse Hill-Sachs lesion is deter-

mined by its size.5,6 Curiously, up to now, no standard-ized method of measurement has been described in theliterature, and surgeons have had to rely on estimation ofthe defect size based on computed tomographic imagesto determine the accurate treatment. This approach isheavily prone to mistakes in estimating the defect sizeand subsequent choice of treatment methods, as shownby the low interobserver and intraobserver reliabilityreported in this study. The reliability of a standardizedmethod of measurement for reverse Hill-Sachs lesionsbased on a best-fit circle technique and using simpleangle and distance measurements in the axial andcoronal CT scanning planes was investigated in thisstudy.

Table 3. Average Intraobserver Reliability Displayed in Termsof Intraclass Correlation Coefficients (ICCs)

ICC (95% CI)

Alpha (axial) 0.97 (0.97-0.99)Beta (axial) 0.88 (0.85-0.91)Depth (axial) 0.92 (0.90-0.94)Alpha (coronal) 0.93 (0.90-0.96)Beta (coronal) 0.95 (0.94-0.96)Depth (coronal) 0.94 (0.90-0.97)Defect size estimation 0.71 (0.51-0.89)

CI, confidence interval.

According to our data, the standardized measurementmethod prevailed over the current practice, which reliesmerely on estimation. The defect size and its localizationwere identified with excellent reliability when usingstandardized measurements. Almost all measurementsachieved an interobserver reliability higher than 0.9,which, according to Portney et al.,15 suggests reasonablereliability for clinical measures. In contrast to standard-izedmeasurements, the estimation of the size of a reverseHill-Sachs defect by 6 different observers showed signif-icant differences in both attempts and poor to moderateinterobserver reliability. Similarly, the intraobserverreliabilitywas considerably lowerwhenestimating ratherthan measuring the defect. These results indicate thatunderestimation or overestimation of the reverse Hill-Sachs defect size can easily occur in clinical practice,highlighting the potential risk for mistreatment. Forexample, in one patient the estimation of defect sizediffered by 45% (absolute value) from one observer toanother.The less experienced orthopaedic residents especially

had difficulty providing reliable estimations of the defectsize. However, the expert shoulder surgeons also ach-ieved only moderate levels of reliability when merelyestimating the defect size. In contrast, when using thestandardized measurement method, both residents andexperts provided highly reliable measurements. Thisindicates that the standardization of reverse Hill-Sachsmeasurements could help improve diagnostic accuracyand subsequent treatment planning when a patient isevaluated not only by an orthopaedic resident but also byan experienced shoulder surgeon. When comparing theICCs for the different variables, no learning effect isapparent between thefirst and the secondmeasurements.Posterior dislocations account for less than 5% of

instability episodes in the shoulder, and most studiesreported in the literature describing the differentmethods of treatment of reverse Hill-Sachs lesionsinclude only a very small number of patients.1 There-fore it seems reasonable to question whether an errorin estimation of the defect size might have led todistorted conclusions in some of the reported studies.A re-evaluation of the appropriate choice of treatmentbased on a standardized measurement method couldhelp provide more reliable treatment guidelines.The decision to characterize the reverse Hill-Sachs

defect size in terms of degrees rather than mere edge-to-edge distance offers 2 advantages. First, usingdegrees the arch resembling the impacted humeralsurface is described rather than a defect width. Second,degrees represent a relative value rather than anabsolute measurement, thus allowing comparison orpooling of the data of patients even when a largedifference in the humeral head size exists. For the samereason, degrees were also chosen to define the positionof the defect in relation to clear anatomic landmarks.

Table 4. Interobserver Reliability Based on Level of Experience Displayed in Terms of Intraclass Correlation Coefficients (ICCs)

First Measurement ICC (95% CI) Second Measurement ICC (95% CI)

Residents Experts Residents Experts

Alpha (axial) 0.96 (0.91-0.99) 0.96 (0.91-0.99) 0.98 (0.95-0.99) 0.98 (0.95-0.99)Beta (axial) 0.86 (0.69-0.95) 0.80 (0.58-0.93) 0.85 (0.67-0.95) 0.86 (0.69-0.95)Depth (axial) 0.91 (0.78-0.97) 0.93 (0.82-0.97) 0.92 (0.81-0.97) 0.96 (0.90-0.99)Alpha (coronal) 0.95 (0.87-0.98) 0.89 (0.74-0.96) 0.95 (0.87-0.98) 0.94 (0.87-0.98)Beta (coronal) 0.95 (0.88-0.98) 0.96 (0.90-0.99) 0.95 (0.88-0.98) 0.91 (0.77-0.97)Depth (coronal) 0.86 (0.70-0.95) 0.82 (0.62-0.94) 0.87 (0.71-0.96) 0.94 (0.86-0.98)Defect size estimation 0.54 (0.21-0.81) 0.74 (0.47-0.90) 0.47 (0.13-0.77) 0.64 (0.33-0.86)

MEASURING REVERSE HILL-SACHS LESIONS 483

The defect depth is expressed as a relative measurementas well and is based on measuring the shortest distancebetween the circle center and the defect. This approachinvolves more steps than the method described bydifferent authors for Hill-Sachs lesions, who simplymeasure the distance between the bottom of the defectand the corresponding arch.16-18 However, consideringthe often irregular shape of reverse Hill-Sachs lesions,we believe that using the method described in thisstudy is helpful for the observer to reliably identify theactual maximum depth of the defect, as reflected by ourresults. In general, the importance of measuring thedepth of reverse Hill-Sachs lesions has yet to be eval-uated because until now only the amount of impactedsurface was deemed decisive in choosing the appro-priate treatment.In developing the new measurement method, close

attention was paid to using only techniques available inclinical routine, such as CT in axial and coronal planes,digital line and circle drawing on computed tomo-graphic images, angle measurement, and distancemeasurement. This should facilitate replicating thismethod in clinical practice whenever CT is available.Regarding the imaging planes for humeral head

defects, Kodali et al.17 noticed that the axial and sagittalplanes offer the most accurate measurements of Hill-Sachs lesions because both are perpendicular to themain plane of the defect on the posterior aspect ofthe humerus, making it easier for the observer to pickthe right image for the depth and width measurements.Accordingly, the typical localization and orientation ofthe reverse Hill-Sachs lesion on the humeral headsuggests the use of the axial and coronal planes for thestandardized measurements rather than the sagittalplane. Obviously, in the case of a defect localized moretoward the anterior aspect of the humeral head, coronalviews are less suited for the measurement of thesuperoinferior extent of the reverse Hill-Sachs lesion.Similarly, apically located defects would limit theusefulness of axial images. Therefore, when performingCT on a reverse Hill-Sachs lesion, attention should bepaid to obtaining imaging planes perpendicular to themain plane of the defect to facilitate the subjectivechoice of the image slice showing the biggest extent ofthe defect for measurement purposes.

LimitationsA limitation of the standardized measurement tech-

nique proposed in this study is that it is difficult to placea best-fit circle in the case of a very large defect involvingmore than half the articulating surface. Similarly, in thecase of concomitant humeral head fractures, e.g., headsplit fractures, the best-fit circle technique becomesimpracticable. Another limitation might be the occur-rence of blunt defect edges in case of chronic or lockedposterior shoulder dislocations possibly complicating clearline drawing. No chronic or locked cases were includedin this study. Finally, the new measurement methodwas designed for 2-dimensional computed tomographicscans and is not easily applicable to 3-dimensionalcomputed tomographic scans. However, 3-dimensionalcomputed tomographic scans might facilitate the estima-tion of defect sizes and improve its reliability. A limitationof this study itself is the small number of assessed reverseHill-Sachs lesions; however, according to our data eventhis limited number of analyzed defects sufficed to detecta significantdifferencebetween thedefect size estimationsof the different observers.

ConclusionsThe mere estimation of the size of reverse Hill-Sachs

lesions showed poor reliability, raising the concern forpotential overestimation or underestimation in clinicalpractice. Standardized measurements, which showedgood reliability, should be used whenever analyzing thesize of a reverse Hill-Sachs defect.

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