PM R XXX (2015) 1-8
www.pmrjournal.org
Original Research
Optimal Elbow Angle for Sonographic Visualization of the Ulnar Collateral Ligament Daniel R. Lueders, MD, Adam M. Pourcho, DO, Jacob L. Sellon, MD, Diane L. Dahm, MD, Jay Smith, MD
Abstract Objective: To formally examine the sonographic appearance of the elbow ulnar collateral ligament (UCL) at 30 versus 70 of elbow flexion in asymptomatic baseball pitchers. Design: A prospective, cross-sectional design. Setting: Sports medicine clinic in a tertiary academic medical center. Participants: Thirty asymptomatic adolescent baseball pitchers 13-18 years of age (mean 15.8 years), with at least 3 years of continuous pitching experience and no significant history of elbow pain or injury. Methods: Static sonographic images of the bilateral UCLs were obtained at 30 and 70 of elbow flexion by a single experienced examiner. Images were anonymized and randomized into a slide set. Three clinicians with different levels of ultrasound experience reviewed the static 30 and 70 images for each elbow and chose their preferred image based on UCL conspicuity. The clinicians reviewed a re-randomized slide set 1 week later. A different study co-investigator measured UCL cross-sectional area (CSA) on all images using ultrasound machine electronic calipers. Main Outcome Measures: Preference for the sonographic conspicuity of the UCL at 30 versus 70 of elbow flexion, and UCL CSA at 30 versus 70 of flexion. Results: Each clinician demonstrated a significant preference for UCL images obtained at 70 of flexion when compared to those obtained at 30 (80.3% overall preference for 70 , P < .001). There was no statistically significant effect of clinician experience or arm dominance on image preference. The sonographically determined CSA of the UCLs were on average 1.4 mm2 greater at 70 than at 30 of flexion (P < .001) when combining dominant and nondominant arms. Conclusions: Static sonographic evaluation of the UCL at 70 of elbow flexion should be integrated into UCL imaging protocols. Furthermore, when performing sonographically guided procedures targeting the UCL, clinicians should consider positioning the elbow at >30 of flexion to optimize UCL conspicuity and CSA.
Introduction The elbow ulnar collateral ligament (UCL) is the primary restraint to valgus stress at the medial elbow during overhead throwing activities and is therefore susceptible to acute or, more commonly, cumulative attritional injury [1-4]. In the evaluation of a suspected UCL injury, advanced soft tissue imaging with magnetic resonance imaging (MRI; with or without arthrography) or sonography can be performed to identify and characterize the extent of any UCL injury [5-12]. One advantage of ultrasound (US) is the ability to evaluate the UCL both statically and dynamically [8,9,11-16].
Previous publications describing the sonographic evaluation of the UCL have positioned the elbow at various angles ranging from full extension to 90 of flexion [6,8,9,11,15-20]. Although most authors have reported examining the UCL at 30 of flexion, sonographic evaluation of the UCL at higher degrees of elbow flexion (eg, 90 ) has been reported previously [9,12,14-16,19-21]. It is noteworthy that justification for the use of specific elbow positions for the static evaluation of the UCL is generally lacking from previous publications, and, to our knowledge, the effect of different elbow positions on the static sonographic appearance of the UCL has not been formally evaluated.
1934-1482/$ - see front matter ª 2015 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j.pmrj.2015.03.015
2
Sonography Angle for Ulnar Collateral Ligament
During elbow US examinations, the senior author has observed that the UCL often appears more distinct and larger when imaged at higher degrees of elbow flexion (w70 ) when compared to the traditionally recommended position of 30 of elbow flexion. Consequently, the primary purpose of this investigation was to formally examine the appearance of the UCL at 30 versus 70 of elbow flexion in a group of asymptomatic baseball pitchers. We hypothesized that clinicians with different levels of US experience who were blinded to elbow flexion position would subjectively prefer the static sonographic appearance of the UCL obtained at 70 of elbow flexion compared to 30 of elbow flexion. Furthermore, we hypothesized that the cross-sectional area (CSA) of the UCL in the long axis obtained at 70 of elbow flexion would be significantly greater than that obtained at 30 . Clinically, the results of this investigation would have significant implications for the sonographic evaluation of the UCL, as well as the position of the elbow when performing sonographically guided procedures with respect to the UCL. Methods Subjects This study was approved by the Mayo Clinic Institutional Review Board. Thirty asymptomatic adolescent baseball pitchers from local high schools were recruited from a sample of convenience by word of mouth and by flier posting at local high schools. Inclusion criteria were 13-18 years of age and at least 3 years of continuous pitching experience. We elected to study throwers 13-18 years of aged based on the increasing number of young throwers presenting to our sports medicine center
with medial elbow pain in recent years. Subjects were excluded if they had any current elbow pain that limited their ability to throw, had pitched more than 100 pitches in the last 72 hours, had a history of elbow symptoms requiring modification of activity or medical evaluation, or had a history of previous elbow surgery. Written informed consent or assent (in the case of minors) was obtained for each participant. A total of 60 elbows in 30 subjects were sonographically examined by the same experienced clinician (with 3 years’ experience in diagnostic musculoskeletal [MSK] ultrasound) using an 18-5eMHz linear array transducer (Phillips Epiq, Phillips Ultrasound Systems, Bothell, WA). Computerized randomization was used to assign coded identifiers and to determine the order of scanning (throwing versus nonthrowing arm and 30 versus 70 of flexion). Imaging Protocol Sonographic evaluation of the anterior bundle of the UCL was performed with the subject in a lateral recumbent position, the side being evaluated in the dependent position, and the shoulder in 90 of forward flexion in the sagittal plane. For measurement of elbow flexion, a goniometer was placed with its axis over the medial humeral epicondyle, with the stationary arm parallel to the longitudinal axis of the humerus directed toward the acromion and the moving arm parallel to the longitudinal axis of the ulna directed toward the ulnar styloid process (Figures 1A and 2A). Once the desired angle of elbow flexion was confirmed, a high-frequency 18-5eMHz linear array transducer was placed over the medial elbow and manipulated to obtain the best long-axis image of the anterior bundle of
Figure 1. Positioning for sonography of the ulnar collateral ligament (UCL) at 30 of elbow flexion with corresponding sonographic image. (A) Patient position for sonographic evaluation of the UCL with the elbow at 30 of flexion as measured by goniometer. (B) Transducer positioning for optimal viewing of the anterior bundle of the UCL. The proximal aspect of the transducer overlies the medial epicondyle, whereas the distal end is angled slightly dorsal to provide a long-axis view of the UCL. (C) Corresponding sonographic image of the UCL at 30 of flexion. The borders of the fibrillar-appearing UCL (arrowheads) can be visualized deep to the flexor/pronator muscles (F) as the UCL courses from its anteroinferior medial epicondyle (ME) origin and over the ulnohumeral joint (*) to its distal insertion at the sublime tubercle and proximal ulna (U). Note the curvature of the UCL, likely reflecting a low-tension state in this position. This relatively relaxed position may account for the hypoechoic appearance of the ligament despite its orientation parallel to the transducer face. Orientation for US image: Top ¼ superficial/medial, Bottom ¼ deep/lateral, Left ¼ distal, Right ¼ proximal.
D.R. Lueders et al. / PM R XXX (2015) 1-8
3
Figure 2. Positioning for sonography of the ulnar collateral ligament (UCL) at 70 of elbow flexion with corresponding sonographic image. (A) Patient position for sonographic evaluation of the UCL with the elbow at 70 of flexion as measured by goniometer. (B) Transducer positioning for optimal viewing of the anterior bundle of the UCL. Similar to Figure 1, the transducer is oriented parallel to the long axis of the UCL. (C) Corresponding sonographic image of the UCL at 70 of flexion. Compared to Figure 1C, the UCL appears to be larger and more taut, and exhibits more defined margins, greater echogenicity, and a more prominent internal fibrillar echotexture. Abbreviations and orientation as in Figure 1.
the UCL (Figures 1B, 1C and 2B, 2C). A static sonographic image was obtained at the location at which the clinician observed the most distinct ligamentous margins and the most discrete internal fibrillar architecture. This process was repeated according to the computerrandomized order to obtain images at 30 and 70 of elbow flexion bilaterally in all subjects. Outcome Measures Best Image Selection All images were anonymized and randomized into a slide set to blind reviewers to subject, side, arm dominance, and elbow flexion angle at which the sonographic images were obtained. A slide was produced for each arm (throwing and nonthrowing) of each subject. Each slide contained 2 static images, labeled A and B, which represented the ultrasound images of the UCL obtained at 30 and 70 of elbow flexion from a single elbow (throwing or nonthrowing) of a single subject. The order of appearance of the images on the slide were randomized in terms of which image (30 versus 70 of elbow flexion) appeared on the left of the slide and was labeled as “A” and which image appeared on the right of the slide and was labeled as “B.” The slides were then reviewed by 3 blinded clinicians of different levels of diagnostic US experience (a sports medicine physiatrist with 11 years of experience in MSK ultrasound, a sports medicine physiatrist with 3 years of experience in MSK ultrasound, and an orthopedic surgeon with less than 1 year of experience in MSK ultrasound). In the absence of validated criteria to identify the “best” UCL image, we used clinicians of varied experience to allow our results to be more generalizable. Consequently, our statistical analysis aimed to verify that no significant differences were present among our reviewers. For each slide, all clinicians independently reviewed both images and selected the image (A or B) that they
subjectively determined provided the better overall UCL conspicuity. Reviewers did not receive objective criteria on which to determine the “optimal” image but were instructed to consider all elements of each image to choose the image that they would prefer to interpret for diagnostic purposes. All original images were then randomized into a second slide set, again implementing the randomized ordering process described above. One week after evaluating the first slide set, the same clinicians assessed the second slide set and again selected the image (A or B) that they subjectively determined provided the better overall UCL conspicuity. UCL Cross-Sectional Area Subsequent to image acquisition, the senior author completed CSA measurements on the saved images of the bilateral UCLs of the study subjects using the electronic calipers and the continuous trace function on the US machine. Measurements were completed on the images obtained at both 30 and 70 of elbow flexion. CSA measurements were obtained by tracing the perimeter of the UCL, being careful to accurately identify the deep (i.e., lateral) margin of the UCL, adjacent to the medial recess of the ulnohumeral articulation (Figure 3A-3B). When measuring CSA, the distal perimeter of the UCL was considered to be the sublime tubercle. Although the long ulnar attachment of the UCL was visualized in all cases, as recently described, this portion of the UCL was excluded from CSA measurements because of its long, thin structure and unclear clinical significance [2,22]. Statistical Analysis Power analysis identified that a sample size of at least 25 subjects would provide greater than 80% power to detect a statistically significant k coefficient
4
Sonography Angle for Ulnar Collateral Ligament
Figure 3. Ulnar collateral ligament (UCL) cross-sectional area (CSA) at 30 and 70 of elbow flexion. Sonographic images obtained from the dominant elbow of a single subject using positioning demonstrated in Figures 1 and 2. The left image represents 30 and the right image 70 of elbow flexion. The perimeter of the UCL has been traced using the machine’s electronic calipers and the continuous trace function to calculate UCL CSA. As discussed in the text, the distal UCL margin was considered to be the proximal aspect of the ulna for the purposes of this investigation. Changes in the appearance of the UCL are similar to those demonstrated in Figures 1 and 2. Note the greater CSA of the UCL at 70 of elbow flexion, which reached statistical significance in the study population. Abbreviations and orientation as in Figures 1 and 2.
of 0.60 or greater (a ¼ 0.05) on the agreement of our dichotomous rating [23]. Preference was determined at each reading by tallying the number of choices for the 30 and 70 angles on each slide. The distributions of the totals for each angle were compared using the Friedman test for nonparametric, repeated-measures analysis of variance. Logistic regression was used to test for a difference in preference between dominant versus nondominant elbows, and between those with open versus closed growth plates. The McNemar test and Cohen k were used to compare individual rater preferences between readings. CSA measurements between angles were compared using paired t-tests. Results All 3 clinicians demonstrated a statistically significant preference for the UCL images obtained at 70 of elbow flexion when compared to those obtained at 30 of flexion (P < .001; Table 1). When the selections of all clinicians from both weeks were evaluated together, UCL images at 70 were preferred 80.3% of the time. There was a statistically significant preference difference in slide set 2 (ie, the second week) between the intermediate and novice clinicians, with the intermediate clinician preferring 70 in 88.3% of selections compared to 73.3% for the novice clinician (P ¼ .02; Table 1). However, there was no significant difference in the overall image preferences among clinicians of different levels of experience. In addition, there was no statistical significance of image preference based on arm dominance. The sonographically determined CSAs of the UCLs were on average 1.43 mm2 greater at 70 than at 30 of elbow flexion (P < .001), when combining all dominant and nondominant arms (Table 2). Furthermore, UCL CSA was greater at 70 versus 30 by an average of 1.63 mm2 (P < .001) in the dominant arms and by an average of 1.22 mm2 (P < .001) in the nondominant arms. Arm dominance did not affect UCL CSA at either 30 or 70 of flexion (P ¼ .16).
Of the 60 elbows examined, 18 (9 subjects) were skeletally immature, with open growth plates (Figure 4A, 4B). Among the 9 skeletally immature subjects, the 3 clinicians demonstrated a preference for the UCL image obtained at 70 of elbow flexion 74.1% of the time, whereas in the 21 skeletally mature subjects, clinicians preferred the image obtained at 70 of flexion 83.0% of the time. The clinicians volunteered that evaluation of the UCL was more challenging in the skeletally immature subjects. Although growth plates seemed to play a role in elbow flexion image preference, there was no statistically significant difference in image preference between skeletally immature and skeletally mature elbows in the current study (P ¼ .11 for the first reading, P ¼.56 for the second reading). Discussion The elbow UCL is the primary restraint to valgus loads in overhead athletes, and UCL injury is a welldocumented cause of medial elbow pain among Table 1 Reviewer preferences for sonographic ulnar collateral ligament (UCL) images taken at 70 and 30 of elbow flexion Preferred Elbow Flexion Position Reviewer*
Evaluation No.
30
1
1 2 1 2 1 2 1 2 Overall
12 11 9 7 16 16 37 34 71
2 3 Total
†
70 (20%) (18.3%) (15%) (11.7%) (26.7%) (26.7%) (20.6%) (18.9%) (19.7%)
48 49 51 53 44 44 143 146 289
P (80%) (81.7%) (85%) (88.3%) (73.3%) (73.3%) (79.4%) (81.1%) (80.3%)
www.pmrjournal.org
Original Research
Optimal Elbow Angle for Sonographic Visualization of the Ulnar Collateral Ligament Daniel R. Lueders, MD, Adam M. Pourcho, DO, Jacob L. Sellon, MD, Diane L. Dahm, MD, Jay Smith, MD
Abstract Objective: To formally examine the sonographic appearance of the elbow ulnar collateral ligament (UCL) at 30 versus 70 of elbow flexion in asymptomatic baseball pitchers. Design: A prospective, cross-sectional design. Setting: Sports medicine clinic in a tertiary academic medical center. Participants: Thirty asymptomatic adolescent baseball pitchers 13-18 years of age (mean 15.8 years), with at least 3 years of continuous pitching experience and no significant history of elbow pain or injury. Methods: Static sonographic images of the bilateral UCLs were obtained at 30 and 70 of elbow flexion by a single experienced examiner. Images were anonymized and randomized into a slide set. Three clinicians with different levels of ultrasound experience reviewed the static 30 and 70 images for each elbow and chose their preferred image based on UCL conspicuity. The clinicians reviewed a re-randomized slide set 1 week later. A different study co-investigator measured UCL cross-sectional area (CSA) on all images using ultrasound machine electronic calipers. Main Outcome Measures: Preference for the sonographic conspicuity of the UCL at 30 versus 70 of elbow flexion, and UCL CSA at 30 versus 70 of flexion. Results: Each clinician demonstrated a significant preference for UCL images obtained at 70 of flexion when compared to those obtained at 30 (80.3% overall preference for 70 , P < .001). There was no statistically significant effect of clinician experience or arm dominance on image preference. The sonographically determined CSA of the UCLs were on average 1.4 mm2 greater at 70 than at 30 of flexion (P < .001) when combining dominant and nondominant arms. Conclusions: Static sonographic evaluation of the UCL at 70 of elbow flexion should be integrated into UCL imaging protocols. Furthermore, when performing sonographically guided procedures targeting the UCL, clinicians should consider positioning the elbow at >30 of flexion to optimize UCL conspicuity and CSA.
Introduction The elbow ulnar collateral ligament (UCL) is the primary restraint to valgus stress at the medial elbow during overhead throwing activities and is therefore susceptible to acute or, more commonly, cumulative attritional injury [1-4]. In the evaluation of a suspected UCL injury, advanced soft tissue imaging with magnetic resonance imaging (MRI; with or without arthrography) or sonography can be performed to identify and characterize the extent of any UCL injury [5-12]. One advantage of ultrasound (US) is the ability to evaluate the UCL both statically and dynamically [8,9,11-16].
Previous publications describing the sonographic evaluation of the UCL have positioned the elbow at various angles ranging from full extension to 90 of flexion [6,8,9,11,15-20]. Although most authors have reported examining the UCL at 30 of flexion, sonographic evaluation of the UCL at higher degrees of elbow flexion (eg, 90 ) has been reported previously [9,12,14-16,19-21]. It is noteworthy that justification for the use of specific elbow positions for the static evaluation of the UCL is generally lacking from previous publications, and, to our knowledge, the effect of different elbow positions on the static sonographic appearance of the UCL has not been formally evaluated.
1934-1482/$ - see front matter ª 2015 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j.pmrj.2015.03.015
2
Sonography Angle for Ulnar Collateral Ligament
During elbow US examinations, the senior author has observed that the UCL often appears more distinct and larger when imaged at higher degrees of elbow flexion (w70 ) when compared to the traditionally recommended position of 30 of elbow flexion. Consequently, the primary purpose of this investigation was to formally examine the appearance of the UCL at 30 versus 70 of elbow flexion in a group of asymptomatic baseball pitchers. We hypothesized that clinicians with different levels of US experience who were blinded to elbow flexion position would subjectively prefer the static sonographic appearance of the UCL obtained at 70 of elbow flexion compared to 30 of elbow flexion. Furthermore, we hypothesized that the cross-sectional area (CSA) of the UCL in the long axis obtained at 70 of elbow flexion would be significantly greater than that obtained at 30 . Clinically, the results of this investigation would have significant implications for the sonographic evaluation of the UCL, as well as the position of the elbow when performing sonographically guided procedures with respect to the UCL. Methods Subjects This study was approved by the Mayo Clinic Institutional Review Board. Thirty asymptomatic adolescent baseball pitchers from local high schools were recruited from a sample of convenience by word of mouth and by flier posting at local high schools. Inclusion criteria were 13-18 years of age and at least 3 years of continuous pitching experience. We elected to study throwers 13-18 years of aged based on the increasing number of young throwers presenting to our sports medicine center
with medial elbow pain in recent years. Subjects were excluded if they had any current elbow pain that limited their ability to throw, had pitched more than 100 pitches in the last 72 hours, had a history of elbow symptoms requiring modification of activity or medical evaluation, or had a history of previous elbow surgery. Written informed consent or assent (in the case of minors) was obtained for each participant. A total of 60 elbows in 30 subjects were sonographically examined by the same experienced clinician (with 3 years’ experience in diagnostic musculoskeletal [MSK] ultrasound) using an 18-5eMHz linear array transducer (Phillips Epiq, Phillips Ultrasound Systems, Bothell, WA). Computerized randomization was used to assign coded identifiers and to determine the order of scanning (throwing versus nonthrowing arm and 30 versus 70 of flexion). Imaging Protocol Sonographic evaluation of the anterior bundle of the UCL was performed with the subject in a lateral recumbent position, the side being evaluated in the dependent position, and the shoulder in 90 of forward flexion in the sagittal plane. For measurement of elbow flexion, a goniometer was placed with its axis over the medial humeral epicondyle, with the stationary arm parallel to the longitudinal axis of the humerus directed toward the acromion and the moving arm parallel to the longitudinal axis of the ulna directed toward the ulnar styloid process (Figures 1A and 2A). Once the desired angle of elbow flexion was confirmed, a high-frequency 18-5eMHz linear array transducer was placed over the medial elbow and manipulated to obtain the best long-axis image of the anterior bundle of
Figure 1. Positioning for sonography of the ulnar collateral ligament (UCL) at 30 of elbow flexion with corresponding sonographic image. (A) Patient position for sonographic evaluation of the UCL with the elbow at 30 of flexion as measured by goniometer. (B) Transducer positioning for optimal viewing of the anterior bundle of the UCL. The proximal aspect of the transducer overlies the medial epicondyle, whereas the distal end is angled slightly dorsal to provide a long-axis view of the UCL. (C) Corresponding sonographic image of the UCL at 30 of flexion. The borders of the fibrillar-appearing UCL (arrowheads) can be visualized deep to the flexor/pronator muscles (F) as the UCL courses from its anteroinferior medial epicondyle (ME) origin and over the ulnohumeral joint (*) to its distal insertion at the sublime tubercle and proximal ulna (U). Note the curvature of the UCL, likely reflecting a low-tension state in this position. This relatively relaxed position may account for the hypoechoic appearance of the ligament despite its orientation parallel to the transducer face. Orientation for US image: Top ¼ superficial/medial, Bottom ¼ deep/lateral, Left ¼ distal, Right ¼ proximal.
D.R. Lueders et al. / PM R XXX (2015) 1-8
3
Figure 2. Positioning for sonography of the ulnar collateral ligament (UCL) at 70 of elbow flexion with corresponding sonographic image. (A) Patient position for sonographic evaluation of the UCL with the elbow at 70 of flexion as measured by goniometer. (B) Transducer positioning for optimal viewing of the anterior bundle of the UCL. Similar to Figure 1, the transducer is oriented parallel to the long axis of the UCL. (C) Corresponding sonographic image of the UCL at 70 of flexion. Compared to Figure 1C, the UCL appears to be larger and more taut, and exhibits more defined margins, greater echogenicity, and a more prominent internal fibrillar echotexture. Abbreviations and orientation as in Figure 1.
the UCL (Figures 1B, 1C and 2B, 2C). A static sonographic image was obtained at the location at which the clinician observed the most distinct ligamentous margins and the most discrete internal fibrillar architecture. This process was repeated according to the computerrandomized order to obtain images at 30 and 70 of elbow flexion bilaterally in all subjects. Outcome Measures Best Image Selection All images were anonymized and randomized into a slide set to blind reviewers to subject, side, arm dominance, and elbow flexion angle at which the sonographic images were obtained. A slide was produced for each arm (throwing and nonthrowing) of each subject. Each slide contained 2 static images, labeled A and B, which represented the ultrasound images of the UCL obtained at 30 and 70 of elbow flexion from a single elbow (throwing or nonthrowing) of a single subject. The order of appearance of the images on the slide were randomized in terms of which image (30 versus 70 of elbow flexion) appeared on the left of the slide and was labeled as “A” and which image appeared on the right of the slide and was labeled as “B.” The slides were then reviewed by 3 blinded clinicians of different levels of diagnostic US experience (a sports medicine physiatrist with 11 years of experience in MSK ultrasound, a sports medicine physiatrist with 3 years of experience in MSK ultrasound, and an orthopedic surgeon with less than 1 year of experience in MSK ultrasound). In the absence of validated criteria to identify the “best” UCL image, we used clinicians of varied experience to allow our results to be more generalizable. Consequently, our statistical analysis aimed to verify that no significant differences were present among our reviewers. For each slide, all clinicians independently reviewed both images and selected the image (A or B) that they
subjectively determined provided the better overall UCL conspicuity. Reviewers did not receive objective criteria on which to determine the “optimal” image but were instructed to consider all elements of each image to choose the image that they would prefer to interpret for diagnostic purposes. All original images were then randomized into a second slide set, again implementing the randomized ordering process described above. One week after evaluating the first slide set, the same clinicians assessed the second slide set and again selected the image (A or B) that they subjectively determined provided the better overall UCL conspicuity. UCL Cross-Sectional Area Subsequent to image acquisition, the senior author completed CSA measurements on the saved images of the bilateral UCLs of the study subjects using the electronic calipers and the continuous trace function on the US machine. Measurements were completed on the images obtained at both 30 and 70 of elbow flexion. CSA measurements were obtained by tracing the perimeter of the UCL, being careful to accurately identify the deep (i.e., lateral) margin of the UCL, adjacent to the medial recess of the ulnohumeral articulation (Figure 3A-3B). When measuring CSA, the distal perimeter of the UCL was considered to be the sublime tubercle. Although the long ulnar attachment of the UCL was visualized in all cases, as recently described, this portion of the UCL was excluded from CSA measurements because of its long, thin structure and unclear clinical significance [2,22]. Statistical Analysis Power analysis identified that a sample size of at least 25 subjects would provide greater than 80% power to detect a statistically significant k coefficient
4
Sonography Angle for Ulnar Collateral Ligament
Figure 3. Ulnar collateral ligament (UCL) cross-sectional area (CSA) at 30 and 70 of elbow flexion. Sonographic images obtained from the dominant elbow of a single subject using positioning demonstrated in Figures 1 and 2. The left image represents 30 and the right image 70 of elbow flexion. The perimeter of the UCL has been traced using the machine’s electronic calipers and the continuous trace function to calculate UCL CSA. As discussed in the text, the distal UCL margin was considered to be the proximal aspect of the ulna for the purposes of this investigation. Changes in the appearance of the UCL are similar to those demonstrated in Figures 1 and 2. Note the greater CSA of the UCL at 70 of elbow flexion, which reached statistical significance in the study population. Abbreviations and orientation as in Figures 1 and 2.
of 0.60 or greater (a ¼ 0.05) on the agreement of our dichotomous rating [23]. Preference was determined at each reading by tallying the number of choices for the 30 and 70 angles on each slide. The distributions of the totals for each angle were compared using the Friedman test for nonparametric, repeated-measures analysis of variance. Logistic regression was used to test for a difference in preference between dominant versus nondominant elbows, and between those with open versus closed growth plates. The McNemar test and Cohen k were used to compare individual rater preferences between readings. CSA measurements between angles were compared using paired t-tests. Results All 3 clinicians demonstrated a statistically significant preference for the UCL images obtained at 70 of elbow flexion when compared to those obtained at 30 of flexion (P < .001; Table 1). When the selections of all clinicians from both weeks were evaluated together, UCL images at 70 were preferred 80.3% of the time. There was a statistically significant preference difference in slide set 2 (ie, the second week) between the intermediate and novice clinicians, with the intermediate clinician preferring 70 in 88.3% of selections compared to 73.3% for the novice clinician (P ¼ .02; Table 1). However, there was no significant difference in the overall image preferences among clinicians of different levels of experience. In addition, there was no statistical significance of image preference based on arm dominance. The sonographically determined CSAs of the UCLs were on average 1.43 mm2 greater at 70 than at 30 of elbow flexion (P < .001), when combining all dominant and nondominant arms (Table 2). Furthermore, UCL CSA was greater at 70 versus 30 by an average of 1.63 mm2 (P < .001) in the dominant arms and by an average of 1.22 mm2 (P < .001) in the nondominant arms. Arm dominance did not affect UCL CSA at either 30 or 70 of flexion (P ¼ .16).
Of the 60 elbows examined, 18 (9 subjects) were skeletally immature, with open growth plates (Figure 4A, 4B). Among the 9 skeletally immature subjects, the 3 clinicians demonstrated a preference for the UCL image obtained at 70 of elbow flexion 74.1% of the time, whereas in the 21 skeletally mature subjects, clinicians preferred the image obtained at 70 of flexion 83.0% of the time. The clinicians volunteered that evaluation of the UCL was more challenging in the skeletally immature subjects. Although growth plates seemed to play a role in elbow flexion image preference, there was no statistically significant difference in image preference between skeletally immature and skeletally mature elbows in the current study (P ¼ .11 for the first reading, P ¼.56 for the second reading). Discussion The elbow UCL is the primary restraint to valgus loads in overhead athletes, and UCL injury is a welldocumented cause of medial elbow pain among Table 1 Reviewer preferences for sonographic ulnar collateral ligament (UCL) images taken at 70 and 30 of elbow flexion Preferred Elbow Flexion Position Reviewer*
Evaluation No.
30
1
1 2 1 2 1 2 1 2 Overall
12 11 9 7 16 16 37 34 71
2 3 Total
†
70 (20%) (18.3%) (15%) (11.7%) (26.7%) (26.7%) (20.6%) (18.9%) (19.7%)
48 49 51 53 44 44 143 146 289
P (80%) (81.7%) (85%) (88.3%) (73.3%) (73.3%) (79.4%) (81.1%) (80.3%)
