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Interobserver reliability of acromial morphology classification: An anatomic study
Interobserver reliability of acromial morphology classification: An anatomic study Joseph D Zuckerman, Michael Greller, MD,
MD, New
Frederick J Kummer, York, N Y.
PhD, Francis
Cuomo,
MD, and
One hundred ten acromial anatomic specimens were classified by three shoulder surgeons with the classification system described by Bigliani et al. to determine the interobserver reliabiliiy. These results demonstrated a fair to poor level of interobserver reliability. Given this relatively low level of agreement, the diagnosis of impingement and rotator cuff tears should be based on clinical findings supplemented, when indicated, by rotatory cuff imaging with less diagnostic reliance placed on the assessment of acromial morphology. (J SHOULDER ELBOWSURG7 997; 6:286-7.)
I
n an attempt to understand the pathomechanics of impingement and rotator cuff tears, considerable emphasis has been placed on the contribution of the anatomic structures of the coracoacromial arch. Within this context the morphology of the acromion has been variously assessed by a number of investigators. 1,2,5-1 ’ Although many different parameters of acromial structure have been studied, the curvature of the acromion is considered to be an important factor associated with rotator cuff tears. Bigliani et at.3 proposed what has now become a widely accepted classification system. They used radiographic analysis to identify three distinctive types of acromion: type I, flat, type II, curved, and type III, hooked. In their study rotator cuff tears were most frequently found in association with type III acromions. However, it is interesting to note that in their study the anterior angularity of the acromion (measured by radiography) was virtually identical for type II and III acromions (26.9” vs 26.7”, respectively). In our previous anatomic studies,12 we noted that the radiographic representation of acromion morphology was dependent partly on the orientation of the x-ray beam and From the Shoulder Service, for Jolnt Diseases
Department
of Orthopaedu,
Reprint requests Joseph D Zuckerman, Department of Orthopaedlcs, Hospital 17th St New York, NY 10003 CopyrIght Board
0 1997 of Trustees
10.58.2746/97/$5
286
by Journal 00+0
MD, Shoulder for Joint Disease,
of Shoulder 32/l/79197
and
Elbow
Ho+ Service, 30 1 E Surgery
that the interpretation of the radiographs resulted in significant interobserver variation. A recent clinical study-by Toivonen et al.9 supports this assessment. Therefore to evaluate the interobserver reliability of the Bigliani classification of acromial shape, we conducted a study with specimens of the acromion.
MATERIAL
AND METHODS
One hundred ten acromial specimens were harvested from 55 formalin-preserved cadavers. Each specimen was resected at the base of the scapular spine and included the entire acromion. The coracoacromial ligament was dissected directly off the anterior acromion. Each specimen was soaked in bleach to remove all remaining soft tissues and was then air-dried. Each specimen was numbered and placed in a plastic bag. Three attending orthopaedic surgeons specializing in shoulder surgery were asked to examine and classify each specimen based on acromial type (I, II, or Ill) with the Bigliani classification. Each observer classified the acromial specimens independently of the other observers. The results were first analyzed for the degree of agreement among the three observers. Kappa values were then determined for pairwise comparisons.4 This method was chosen to correct for the level of agreement that could occur by chance. The level of agreement based on Kappa values was graded as poor (.O to .20), fair (.21 to .40), moderate (.41 to .60), and good (>.60).
Zuckerman
1. Shoulder Elbow Surg. Volume 6, Number 3
RESULTS All three observers agreed on acromial classification in only 22% of the specimens. Two of three observers agreed in 72% of the cases. For 6% of the specimens none of the three observers agreed, with each one choosing a different type. The Kappa values for pairwise comparisons showed an overall level of agreement of 0.42, which represents “fair agreement.” In addition, pairwise comparisons show that agreement was more likely for type II acromions (K = .Ql ) than for type I or type III (K = .27 and .28, respectively).
DISCUSSION Although the classification of acromion morphology developed by Bigliani et al. has received widespread acceptance and use, this study shows that the ability of different observers to agree on an acromial type is quite limited. In our study pairwise comparison showed an average level of agreement of .42, with agreement more likely to occur when type II is chosen. We based our analysis on the examination of gross specimens in which the observer could manipulate and view each specimen in any way desired. We believe that this approach can be expected to provide more information than can be obtained from “supraspinatus outlet” radiographs. Nonetheless the level of agreement with this approach was only “fair.” We recognize that the study by Bigliani et al. was important in enhancing our understanding of the influence of acromial morphology on rotator cuff tears. Rather than emphasize the classification system, we believe the proper emphasis should be on the important finding that increasing acromial concavity and the presence of anterior acromial spurs are correlated with the presence of fullthickness rotator cuff tears6e9, ” These findings are more significant than the ability to classify acromial shape into three distinct types. We believe the evaluation of patients with rotator cuff tears should be based on careful clinical history and physical examination. The analysis of radiographs should include acromial morphology, particularly the
et al.
287
presence of significant concavity and anterior acromial spurs. However, the assessment of radiographs should be evaluated in the context of clinical findings. The diagnosis of subacromial impingement should be based primarily on clinical findings, with support provided by radiographic assessment of acromial morphology. The limited interobserver reliability of acromial classification reported in this study emphasizes the importance of clinical findings and the potential to overemphasize acromial morphology as a diagnostic factor. The authors thank Gordon tance
in reviewing
the anatomic
Edelson, MD, specimens.
for
his assis-
REFERENCES 1
Aokr M, lshrr S, USUI M Cllnrcal applrcatron for measurrng the slope of the acromron In Post M, Morrey B, editors Surgery of the shoulder St 10~1s Mosby-Year Book, 1990 200-3
2
Aokr M, Ishrr S, USUI M The slope of the acromron and rotator cuff rmprngement [abstract) Orthop Trans 1986,lO 228
3
Blglranr LU, Morrrson DS, Aprri EW The morphology of the acromron and rts relatlonshrp to rotator cuff tears [abstract) Orthop Trans 1986,lO 228
4
landls)R, Koch GG for categorlal data
5
Morrison DS, Brglranr LU The cllnlcal trons In acromral morphology (abstract) 11 234
6
Nrcholson GP, Goodman DA, Flatow Et, Brglrani LU Acromlon morphology and age-related changes a study of 420 scapulae Paper 168, Transachons of the Srxtreth Meeting of the AAOS, 1993
7
Noblej, Bell RH, Peterson M, Bower R Predictrve value of radrographrc frndlngs In rotator cuff tears Paper 322, Transactions of the Sixtieth Meeting of the AAOS, 1993
8
Ogata S, Uhthoff HK Acromral enthesopathy and rotator cuff tear a radiologrcal hrstologrc postmortem rnvestrgatron of the coracoacromral arch Clan Orthop 1990,254 39-48
9
Torvonen DA, Turte MJ, Olwrn JF Acromral structure and of the rotator cuff j Should Elbow Surg 1995,4 376-83
The measurement of observer Brometncs 1977,33 159-74
agreement
srgnrfrcance of varraOrthop Trans 1987,
JU Type 4 acromron 1995,30(3] 227-9
tears
10
Vanarthos WJ, Monu iron Contemp Ortho
a new classrfrca-
11
Wang JC, lopata 275, Transactions 1995
12
Zuckerman jD, Kummer Fj, Cuomo F, Srmon J, Rosenblum S The Influence of coracoacromial arch anatomy on rotator cuff tears J Shoulder Elbow Surg 1992,l 4-14
SD Etrology of acromral morphology Paper of the Srxti-second Meetrna ” of the AAOS.
MD, New
Frederick J Kummer, York, N Y.
PhD, Francis
Cuomo,
MD, and
One hundred ten acromial anatomic specimens were classified by three shoulder surgeons with the classification system described by Bigliani et al. to determine the interobserver reliabiliiy. These results demonstrated a fair to poor level of interobserver reliability. Given this relatively low level of agreement, the diagnosis of impingement and rotator cuff tears should be based on clinical findings supplemented, when indicated, by rotatory cuff imaging with less diagnostic reliance placed on the assessment of acromial morphology. (J SHOULDER ELBOWSURG7 997; 6:286-7.)
I
n an attempt to understand the pathomechanics of impingement and rotator cuff tears, considerable emphasis has been placed on the contribution of the anatomic structures of the coracoacromial arch. Within this context the morphology of the acromion has been variously assessed by a number of investigators. 1,2,5-1 ’ Although many different parameters of acromial structure have been studied, the curvature of the acromion is considered to be an important factor associated with rotator cuff tears. Bigliani et at.3 proposed what has now become a widely accepted classification system. They used radiographic analysis to identify three distinctive types of acromion: type I, flat, type II, curved, and type III, hooked. In their study rotator cuff tears were most frequently found in association with type III acromions. However, it is interesting to note that in their study the anterior angularity of the acromion (measured by radiography) was virtually identical for type II and III acromions (26.9” vs 26.7”, respectively). In our previous anatomic studies,12 we noted that the radiographic representation of acromion morphology was dependent partly on the orientation of the x-ray beam and From the Shoulder Service, for Jolnt Diseases
Department
of Orthopaedu,
Reprint requests Joseph D Zuckerman, Department of Orthopaedlcs, Hospital 17th St New York, NY 10003 CopyrIght Board
0 1997 of Trustees
10.58.2746/97/$5
286
by Journal 00+0
MD, Shoulder for Joint Disease,
of Shoulder 32/l/79197
and
Elbow
Ho+ Service, 30 1 E Surgery
that the interpretation of the radiographs resulted in significant interobserver variation. A recent clinical study-by Toivonen et al.9 supports this assessment. Therefore to evaluate the interobserver reliability of the Bigliani classification of acromial shape, we conducted a study with specimens of the acromion.
MATERIAL
AND METHODS
One hundred ten acromial specimens were harvested from 55 formalin-preserved cadavers. Each specimen was resected at the base of the scapular spine and included the entire acromion. The coracoacromial ligament was dissected directly off the anterior acromion. Each specimen was soaked in bleach to remove all remaining soft tissues and was then air-dried. Each specimen was numbered and placed in a plastic bag. Three attending orthopaedic surgeons specializing in shoulder surgery were asked to examine and classify each specimen based on acromial type (I, II, or Ill) with the Bigliani classification. Each observer classified the acromial specimens independently of the other observers. The results were first analyzed for the degree of agreement among the three observers. Kappa values were then determined for pairwise comparisons.4 This method was chosen to correct for the level of agreement that could occur by chance. The level of agreement based on Kappa values was graded as poor (.O to .20), fair (.21 to .40), moderate (.41 to .60), and good (>.60).
Zuckerman
1. Shoulder Elbow Surg. Volume 6, Number 3
RESULTS All three observers agreed on acromial classification in only 22% of the specimens. Two of three observers agreed in 72% of the cases. For 6% of the specimens none of the three observers agreed, with each one choosing a different type. The Kappa values for pairwise comparisons showed an overall level of agreement of 0.42, which represents “fair agreement.” In addition, pairwise comparisons show that agreement was more likely for type II acromions (K = .Ql ) than for type I or type III (K = .27 and .28, respectively).
DISCUSSION Although the classification of acromion morphology developed by Bigliani et al. has received widespread acceptance and use, this study shows that the ability of different observers to agree on an acromial type is quite limited. In our study pairwise comparison showed an average level of agreement of .42, with agreement more likely to occur when type II is chosen. We based our analysis on the examination of gross specimens in which the observer could manipulate and view each specimen in any way desired. We believe that this approach can be expected to provide more information than can be obtained from “supraspinatus outlet” radiographs. Nonetheless the level of agreement with this approach was only “fair.” We recognize that the study by Bigliani et al. was important in enhancing our understanding of the influence of acromial morphology on rotator cuff tears. Rather than emphasize the classification system, we believe the proper emphasis should be on the important finding that increasing acromial concavity and the presence of anterior acromial spurs are correlated with the presence of fullthickness rotator cuff tears6e9, ” These findings are more significant than the ability to classify acromial shape into three distinct types. We believe the evaluation of patients with rotator cuff tears should be based on careful clinical history and physical examination. The analysis of radiographs should include acromial morphology, particularly the
et al.
287
presence of significant concavity and anterior acromial spurs. However, the assessment of radiographs should be evaluated in the context of clinical findings. The diagnosis of subacromial impingement should be based primarily on clinical findings, with support provided by radiographic assessment of acromial morphology. The limited interobserver reliability of acromial classification reported in this study emphasizes the importance of clinical findings and the potential to overemphasize acromial morphology as a diagnostic factor. The authors thank Gordon tance
in reviewing
the anatomic
Edelson, MD, specimens.
for
his assis-
REFERENCES 1
Aokr M, lshrr S, USUI M Cllnrcal applrcatron for measurrng the slope of the acromron In Post M, Morrey B, editors Surgery of the shoulder St 10~1s Mosby-Year Book, 1990 200-3
2
Aokr M, Ishrr S, USUI M The slope of the acromron and rotator cuff rmprngement [abstract) Orthop Trans 1986,lO 228
3
Blglranr LU, Morrrson DS, Aprri EW The morphology of the acromron and rts relatlonshrp to rotator cuff tears [abstract) Orthop Trans 1986,lO 228
4
landls)R, Koch GG for categorlal data
5
Morrison DS, Brglranr LU The cllnlcal trons In acromral morphology (abstract) 11 234
6
Nrcholson GP, Goodman DA, Flatow Et, Brglrani LU Acromlon morphology and age-related changes a study of 420 scapulae Paper 168, Transachons of the Srxtreth Meeting of the AAOS, 1993
7
Noblej, Bell RH, Peterson M, Bower R Predictrve value of radrographrc frndlngs In rotator cuff tears Paper 322, Transactions of the Sixtieth Meeting of the AAOS, 1993
8
Ogata S, Uhthoff HK Acromral enthesopathy and rotator cuff tear a radiologrcal hrstologrc postmortem rnvestrgatron of the coracoacromral arch Clan Orthop 1990,254 39-48
9
Torvonen DA, Turte MJ, Olwrn JF Acromral structure and of the rotator cuff j Should Elbow Surg 1995,4 376-83
The measurement of observer Brometncs 1977,33 159-74
agreement
srgnrfrcance of varraOrthop Trans 1987,
JU Type 4 acromron 1995,30(3] 227-9
tears
10
Vanarthos WJ, Monu iron Contemp Ortho
a new classrfrca-
11
Wang JC, lopata 275, Transactions 1995
12
Zuckerman jD, Kummer Fj, Cuomo F, Srmon J, Rosenblum S The Influence of coracoacromial arch anatomy on rotator cuff tears J Shoulder Elbow Surg 1992,l 4-14
SD Etrology of acromral morphology Paper of the Srxti-second Meetrna ” of the AAOS.