Shoulder Kinematics in Subjects With Frozen Shoulder

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1 1473 Shoulder Kinematics in Subjects With Frozen Shoulder Peter J. Rundquist, PT, PhD, Donald D. Anderson, PhD, Carlos A. Guanche, MD, Paula M. Ludewig, PhD, PT From the Program in Physical Therapy, Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, MN (Rundquist, Ludewig); Department of Orthopaedic Surgery, University of Iowa, Iowa City, IA (Anderson); and University of Minnesota, Minneapolis Sports Medicine Center, Minneapolis, MN (Guanche). Preliminary data were presented to the American Physical Therapy Association s Combined Sections Meeting, February 16, 2001, San Antonio, TX. Supported in part by the Minnesota Medical Foundation (equipment grant). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Paula M. Ludewig, PhD, PT, Program in Physical Therapy, MMC 388, University of Minnesota, 420 Delaware St, Minneapolis, MN 55455, ludew001@umn.edu /03/ $30.00/0 doi: /s (03) ABSTRACT. Rundquist PJ, Anderson DD, Guanche CA, Ludewig PM. Shoulder kinematics in subjects with frozen shoulder. Arch Phys Med Rehabil 2003;84: Objectives: To describe 3-dimensional humeral motion in subjects with frozen shoulder and to determine whether a consistent capsular pattern of restriction was present. Design: Descriptive study including repeated measurements of shoulder kinematics. Setting: Motion-analysis laboratory. Participants: Ten (9 women, 1 man) volunteers with a diagnosis of idiopathic adhesive capsulitis and 10 (9 women, 1 man) subjects with asymptomatic shoulders as comparison subjects. Interventions: Not applicable. Main Outcome Measures: Electromagnetic tracking sensors monitored the 3-dimensional position of the trunk, scapula, and humerus throughout active shoulder motions. Peak humeral positions relative to the trunk and scapula were determined for shoulder flexion, abduction, scapular plane abduction, external rotation (ER), and internal rotation (IR). Descriptive statistics (means, standard deviations, percentage of normal) were calculated and capsular patterns described. Results: For humeral position relative to the trunk, subjects mean peak motion was as follows: abduction, 98.4 ; ER at the side, 4.5 ; ER with the arm abducted, 33.5 ; flexion, ; IR at the side, 54.3 ; IR with the arm abducted, 17.8 ; and scapular plane abduction, For humeral position relative to the scapula, subjects mean peak motion was as follows: abduction, 46.4 ; ER at the side, 34.7 ; ER with the arm abducted, 45.3 ; flexion, 70.5 ; IR at the side, 10.3 ; IR with the arm abducted, 6.4 ; and scapular plane abduction, Conclusions: Symptomatic subjects demonstrated substantial kinematic deficits during humeral range of motion. No single capsular pattern emerged. Key Words: Adhesive capsulitis; Biomechanics; Kinematics; Range of motion, articular; Rehabilitation; Shoulder joint by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation THE SIGNS AND SYMPTOMS of frozen shoulder have been recognized since However, to this day, more questions than answers exist regarding this condition. The difficulty in studying frozen shoulder was initially acknowledged by Codman in 1934: This is a class of cases which I find it difficult to define, difficult to treat and difficult to explain.... 2(p216) This observation is still true today. A definition of frozen shoulder was presented by Reeves in 1975, who has called it an idiopathic condition of the shoulder characterized by the spontaneous onset of pain in the shoulder with restriction of movement in every direction. 3(p193) Lundberg 4 proposed dividing frozen shoulder into primary and secondary types. He stated that primary frozen shoulder presents as an idiopathic decreased range of motion (ROM) in which no systemic diagnosis, precipitating shoulder condition, or radiographic explanation can be found. Secondary frozen shoulders are believed to result from a predisposing condition. 4 Primary frozen shoulder was the focus of the present investigation. Reeves 3 was the first author to address the progression of frozen shoulder. He observed 49 cases for up to 10 years. He documented 3 phases: pain for to 9 months, stiffness for 4 to 12 months, and recovery for 12 to 42 months. Phase I was identified by pain and a decrease in capsular volume, phase II by stiffness and discomfort, and phase III by gradual recovery. 3 Several others have proposed theories on frozen shoulder progression. The primary difference presented was in the time frame for each phase. 5-7 The clinical diagnosis of frozen shoulder is based on patients subjective history and clinicians objective findings. Most authors 1,8-22 cite a decrease in motion of at least 3 months in duration as 1 diagnostic criterion. Quantifying the ROM diagnostic of frozen shoulder has not been consistent. Maximal abduction and maximal external rotation (ER) reported vary considerably. 1,4,6,8-10,12,15,16,18-23 Rotation values have also been described as percentages of normal, with maximal ER ranging from 50% to 60%. 8-10,13,17,20 Reported maximal internal rotation (IR) percentages range from 45% to 50%. 10,17,19,20 The pathogenesis of primary frozen shoulder is unknown. In 1945, Neviaser 24 was the first to attempt to implicate shoulder capsule adhesions as the etiology of frozen shoulder. Since then, several others 4,17,18,25 have agreed with his proposal. More recently, arthrography and arthroscopy have been used to investigate the involved tissue(s). Adhesive capsulitis, 7 loss of dependent fold, 7,20 decreased capsular volume, 13,23,24,26 and capsular contractions 13,27 have been demonstrated. Additionally, contracture of the coracohumeral ligament, 16,27 adhesion of the subacromial bursa, rotator interval thickening and fibrosis, and capsular and intraarticular subscapularis tendon thickening have all been reported. 28 Cyriax 29 initially proposed that tightness in a joint capsule would result in a pattern of proportional motion restriction. He used the concept of a capsular pattern to differentiate in diagnosis between loss of motion secondary to bony and/or muscle or joint changes and that caused by the capsule. He believed that an irritated capsule would restrict motion in a predictable pattern. For the shoulder, he proposed that ER would be more limited than abduction, which would be more limited than IR. Alternatively, different areas of capsular adhesions (superior, anterior, inferior) 16,27,28 may result in no consistent capsular pattern across subjects. The techniques used to determine the ROMs cited in subjects with frozen shoulder have not been consistent. The majority of

2 1474 SHOULDER KINEMATICS IN FROZEN SHOULDER, Rundquist authors 8,10,11,13,15-21,30 did not identify the measurement technique they used. One documented by using visual estimation. 1 Two studies 20,31 measured IR by the level of the lumbar spine reached. Three other investigators measured goniometrically. 9,14,20 Only Shaffer 20 documented the reliability of the technique he used. There have been 2 previous studies 32,33 with a primary objective to define the ROM of frozen-shoulder subjects. Both used 2-dimensional analyses. Projection errors from evaluating a 3-dimensional movement with a 2-dimensional technique are possible. Further, neither study discussed the validity of the measurements. Recent technical advances permit accurate and reliable 3-dimensional analysis for the evaluation of shoulder ROM Although 3-dimensional techniques can better capture the true movement of the shoulder and separate glenohumeral and scapulothoracic motion, no quantitative 3-dimensional ROM data for frozen-shoulder subjects are currently available in the literature. The 2 purposes of the present investigation were to provide a 3-dimensional kinematic description of the motion of the humerus relative to the trunk and scapula for subjects with frozen shoulder and to determine whether a capsular pattern of restriction was consistently present. METHODS Participants The population of interest was people with a diagnosis of idiopathic frozen shoulder. Symptomatic volunteers were recruited through a local orthopedic surgeon and physical therapy clinics. The asymptomatic shoulders from volunteers with full motion and no shoulder symptoms were used for comparison purposes. All subjects were at least 18 years old. Symptomatic shoulders demonstrated active (AROM) and passive range of motion (PROM) losses of 25% or greater compared with the noninvolved shoulder in at least 2 of the following shoulder motions relative to the trunk: abduction, ER, or IR. Current symptoms were used to identify symptomatic subjects. Subjects were included if they were in the Reeves 3 phase II (stiffness) or phase III (recovery) of frozen shoulder. Subjects were excluded if their pain and/or stiffness had increased in the past month. This approach was taken to avoid subjects who were in Reeves 3 phase I (pain) of frozen shoulder. Asymptomatic control subjects were similar in age range and gender distribution to the symptomatic subjects. Additional inclusion criteria for asymptomatic subjects were full pain-free shoulder motion and no history or current symptoms of shoulder pathology. Additional specific exclusion criteria for both groups included a history of (1) stroke with residual upper-extremity involvement, (2) rheumatoid arthritis, (3) documented rotator cuff tear, (4) surgical stabilization of the shoulder, (5) nonhealed fracture of the shoulder complex, (6) osteoporosis, or (7) severe skin allergies, sensitivities, or other dermatologic problems in the examination area. Also, subjects whose symptoms were exacerbated during a cervical screening examination were excluded. All subjects reviewed and signed institutional review board approved consent forms for human subjects before participating. Instrumentation The 3-dimensional position and orientation of each subject s humerus, scapula, and thorax were tracked (40-Hz sampling rate) by the Polhemus FASTRAK a electromagnetic motioncapture system. An additional sensor attached to a stylus manually digitized anatomic coordinates. Within a source-to-sensor separation of 76cm, a root mean square (RMS) accuracy of.15 for orientation and 0.3 to 0.8mm for position has been reported by the manufacturer. 37 Experimental Procedure Three FASTRAK sensors were used. With adhesive tape, we attached 1 sensor to the sternum and another to the skin overlying the flat superior bony surface of the scapular acromion process. The third was attached to a thermoplastic cuff secured to the distal humerus with Velcro straps. The scapular sensor was placed to minimize the movement error caused by deltoid contraction. This method closely tracks underlying scapular movement. 34 For humeral motion, previous validity data compared with an external humeral fixator found less than a4 RMS error for all motions except for long-axis rotation. IR and ER resulted in an RMS error of 7.5, with the greatest error at the end ROM. Range of worst case errors were from less than 1 to 15.6 (for long-axis rotation), with smaller errors in the middle of the range and larger errors at the end of the range. 38 Subjects were in a standing position throughout testing. Digitization of bony landmarks on the humerus, scapula, and thorax enabled transformation of sensor data to local anatomically based coordinate systems (fig 1). 35 Kinematic data were then collected for each subjects full AROM into flexion, abduction, scapular plane abduction, ER, and IR. The scapular plane was defined as 40 anterior to the coronal plane. 35 ER and IR were collected both with the arm at the side (ER1, IR1) and with the arm at as close as possible to 90 of coronal plane abduction (ER2, IR2). The starting position for abduction, flexion, and scapular plane abduction was with the arm at the side. The starting position for IR1 and ER1 was with the arm adducted to the side and the elbow flexed to 90. The starting position for ER2 and IR2 was with the arm abducted to as close to 90 as possible with the elbow flexed to 90 and the forearm parallel to the floor. Subjects were instructed to move their arm as far as possible for each motion at a self-selected slow, steady speed. Five repetitions of each motion were collected. Subjects were allowed to rest, if necessary, between each set of motion repetitions. Data Reduction and Analysis Digitized anatomic points were used to define clinically relevant local anatomic coordinate systems for each segment based on previously described methods for the shoulder (fig 1). 35 Matrix transformations were performed to describe the position and orientation of the humerus in relation to the thorax and scapula. 35,39 Humeral orientation relative to the thorax for flexion, abduction, and scapular plane abduction was described as rotation about z h (orients the humerus in a plane of elevation), rotation about y h (elevation angle), and rotation about z h (axial rotation) (z, y, z Euler angles; see fig 1). Humeral orientation relative to the thorax for IR and ER was described as rotation about y h (adduction, abduction), rotation about x h (flexion, extension), and rotation about z h (IR, ER) (y, x, z Cardan angles; see fig 1). The alternate sequence for ER and IR was used to avoid singular or gimbal lock positions. With a Euler rotation sequence where the second rotation equals or approaches 0, as would occur with the arm adducted at the side, the other 2 rotations are undefined, and such a position is referred to as a singular position. 39 Also, when interested in clinically interpretable

3 SHOULDER KINEMATICS IN FROZEN SHOULDER, Rundquist dimensional positions are defined when the humeral axes are parallel with the axes of the proximal reference frame (either the cardinal axes of the trunk or the scapular axes). For example, for ER and IR relative to the trunk, the humeral axis parallel with a line through the medial and lateral epicondyles would be aligned with the frontal plane of the trunk in a neutral position. From the 3 trials of each motion, an individual subject s overall peak position value (single trial) was identified. Position values were described relative to the 0, 0, 0 position (90, 0, 0 for IR2 and ER2), rather than an ROM from an individual s self-selected position with the arm at the side. Descriptive statistics (mean, standard deviation [SD], percentage of maximum) were calculated across subjects for each motion. Dependent variables included peak elevation of the humerus in relation to the trunk and scapula in flexion, scapular plane abduction, and abduction and peak long-axis humeral IR and ER. Symptomatic shoulder rotation values that did not reach neutral were recorded as negative values. The normative values used for the calculations of the percentage of maximum were the mean peak values from the asymptomatic shoulder group data. Each symptomatic subject s peak values were expressed as a percentage of the asymptomatic group data. Average percentages were then calculated across subjects. Negative ROM values resulted in negative percentage values. Patterns of motion loss were determined from the percentage reduction numbers. Fig 1. Local coordinate systems for the thorax, scapula, and humerus. NOTE. Trunk coordinate systems are aligned with the coronal planes. Abbreviations: AC, acromioclavicular joint; AD/AB, adduction/abduction; C7, spinous process of the C7 vertebrae; DR/UR, downward/upward rotation; Flex/Ext, flexion/extension; IA, inferior angle of the scapula; LE, lateral epicondyle; ME, medial epicondyle; PT/AT, posterior/anterior tipping; RS, root of the spine of the scapula; SN, suprasternal notch; T8, spinous process of the T8 vertebrae; XP, xiphoid process. Reprinted with adaptations from Ludewig and Cook 35 with permission of the American Physical Therapy Association. values of long-axis rotation, the use of a y, x, z sequence is not complicated by the 2 long-axis rotations inherent to a z, y, z description. A y, x, and z Cardan angle sequence was used to describe all humeral orientations relative to the scapula (see fig 1). These rotation sequences (z, y, z equivalent 34,35,40,41 and y, x, z 35 ) permit clinically relevant descriptions of humeral motion and are consistent with those previously published. For all motions using these axis descriptions, the neutral or 0, 0, 0 RESULTS Subject demographics are in table 1. Nine of the 10 subjects in both groups were women. The right shoulder was the involved shoulder for 4 subjects. Means, SDs, and ranges across all subjects with frozen shoulder for the 6 motions and total long-axis rotation relative to the trunk and scapula are in table 2. In general, for elevation of the arm, the maximum ROM progressively decreased for subjects from flexion to scapular plane abduction to coronal plane abduction. For ER, greater range was generally available with the arm abducted than with the arm at the side. For IR, however, the available ROM decreased when the arm was abducted. The variability between subjects was substantial, as noted by the range and SD values. Additionally, IR1 was limited by contact with the trunk for all asymptomatic and most symptomatic subjects. Mean peak asymptomatic values and average percentages of motion relative to asymptomatic controls are in table 3 for the humerus relative to the trunk and scapula. The pattern of humerus relative to trunk ROM restriction was dependent on the test position for IR and ER (fig 2). With the humerus adducted to the subjects sides, 7 of 10 subjects demonstrated the Cyriax 29 pattern of proposed capsular restriction (fig 2). One subject showed IR most limited, followed by ER, followed by abduction. One showed ER most limited, followed by IR, followed by abduction. One showed abduction most limited, followed by ER, followed by IR. With the humerus abducted as close to 90 as possible, the predicted Cyriax 29 capsular pattern Table 1: Subject Demographics Group Weight (kg) Height (m) Age (y) Duration of Symptoms (mo) Symptomatic Asymptomatic NA NOTE. Values are mean SD. Abbreviation: NA, not applicable.

4 1476 SHOULDER KINEMATICS IN FROZEN SHOULDER, Rundquist Motion Table 2: Humeral ROM (deg) Relative to Trunk Relative to Scapula Mean SD Range Mean SD Range Flexion Abduction Scapular plane abduction ER1* to ER IR1* to 29 IR to 20 Total rotation Total rotation NOTE. Values are mean SD. *ER1 and IR1 performed with the humerus adducted at the side. Negative values indicate that a neutral position was not attained. ER2 and IR2 performed with the humerus abducted to as close to 90 as possible. Negative values indicate that a neutral position was not attained. was present in 4 subjects. Four showed IR most limited, followed by ER, followed by abduction. Two showed IR most limited, followed by abduction, followed by ER (see fig 2). The mean actual coronal plane abduction for the symptomatic shoulders was 86.2 for peak ER2 and 66.7 for peak IR2. For the asymptomatic shoulders, subjects showed the same tendency to reduce the abduction position for IR2. The average abduction position was 97.4 for peak ER2 and 70 for peak IR2. DISCUSSION The results of this investigation showed substantial ROM deficits in subjects with frozen shoulder compared with the comparison group data. Frozen-shoulder subjects showed decreased humeral motion as a percentage of normal relative to the trunk in all planes of motion investigated, except for 3 subjects for IR1, 1 for IR2, and 1 for flexion. Excluding these values, restricted motions in relation to the trunk ranged between 76% and 99% of the normative values. Comparison of the percentage-of-normal value relative to the scapula was more variable. The descriptive humerus abduction data relative to the scapula and the trunk closely followed the 2-dimensional fluoroscopic results previously published by Eto, 33 who studied 17 symptomatic subjects with a diagnosis of periarthritis scapulo- Table 3: Motion Relative to the Trunk and Scapula as a Percentage of Normal humeralis. Inclusion criteria for that study required subjects to have a maximum elevation angle relative to the trunk of less than 120. In relation to the trunk, Eto 33 documented maximum elevation ranging from 65 to 117 across subjects, with an average of In the present study, the peak abduction values ranged from 57 to 134, with an average of In relation to the scapula, Eto 33 documented maximum elevation ranging from 21 to 67, with an average of In the present study, the peak abduction values ranged from 27 to 89, with an average of Comparison with the hydrogoniometer data from Clarke et al 32 for 30 symptomatic frozen-shoulder subjects was less similar. A hydrogoniometer is a fluid-filled goniometer that uses gravity as a reference point. Our ER values were less than those reported by Clarke 32 (men averaged 23 ; women, 28 ), and our abduction values were generally greater (men averaged 42 ; women, 51 ). Eto s methods 33 (standing AROM) were more similar to those of the present study. Clarke 32 investigated PROM and did not provide subject position information. A difficulty in comparing the results of the present study with those from previous investigations of frozen-shoulder ROM is the lack of humeral data described relative to the scapula. Only Eto 33 provides glenohumeral motion data for subjects with ROM deficits. The technology used for this investigation does allow for differentiation of glenohumeral motion. In general for our results during arm elevation, the average humerus to scapula percentages of normal are some- Motion Mean Peak Asymptomatic Values (deg) Mean % of Symptomatic to Asymptomatic Subjects Trunk Scapula Trunk Scapula Flexion Abduction Scapular plane abduction ER1* ER IR1* IR *ER1 and IR1 performed with the humerus adducted at the side. ER2 and IR2 performed with the humerus abducted to as close to 90 as possible. Negative values indicate that a neutral position was not attained. Fig 2. Distribution of motion patterns across subjects and arm positions. Abbreviation: ABD, abduction.

5 SHOULDER KINEMATICS IN FROZEN SHOULDER, Rundquist 1477 what less than the average humerus to trunk percentages, suggesting scapular substitution of increased motion to obtain maximum elevation ROM (table 3). These results are supported by Vermeulen et al, 42 who demonstrated an increased scapular contribution to the scapulohumeral rhythm in subjects with frozen shoulder. However, an approximation of the contribution of glenohumeral and scapulothoracic components of elevation motion can be made by review of the average data in table 2. During abduction, the asymptomatic group s humerus to thorax motion was 151, and the humerus to scapular motion was 100. For the symptomatic group, humerus to thorax abduction was 98, and humerus to scapular motion was 46. Therefore, on average, 53 of abduction was lost overall, whereas 54 was lost at the glenohumeral joint, indicating only minimal, if any, scapular substitution. By using this same approximation during flexion, on average, 31 of overall motion was lost, and 26 of this loss occurred at the glenohumeral joint, suggesting no positive scapular substitution. During scapular plane abduction, on average, 38 of motion was lost, and the glenohumeral motion loss was nearly equivalent, at 37. Therefore, this approximation method does not support the theory of any consistent substantive scapular substitution to maximize endrange elevation motion. It should be noted, however, that because this method is essentially a 2-dimensional approximation of a 3-dimensional motion, it must have some inherent error. This method also is based on average rather than on individual results and considers only end ROM. Scapular substitution earlier in the ROM would not be detected with this method and may occur in some subjects. Further investigation of this issue is warranted in future studies. It is interesting to note the changes in ER and IR ROM with the arm abducted as compared with the arm adducted (table 2). Greater ROM for ER was obtained when the arm was abducted. The IR ROM, however, decreased when the arm was abducted. This same pattern was apparent for healthy shoulders (table 3) and is consistent with an abducted position resulting in differential capsular tightness as compared with a humeral adducted position. 43,44 However, the percentages of normal motion are greater for ER2 than for ER1 and for IR1 than for IR2. The pattern of loss for ER supports a premise of coracohumeral ligament restrictions. 16,27 The coracohumeral ligament is believed to limit ER ROM in an adducted arm position to a greater degree than when the arm is in an abducted position. 43,44 Other potential factors limiting ER are the rotator interval and the superior glenohumeral ligament, which have greater resistance to ER as the arm is abducted. The rotator interval resists ER at 60, 44 and the superior glenohumeral ligament resists ER at The pattern of loss for IR is consistent with capsular tightness in the posterior band of the inferior glenohumeral ligament complex, which restricts IR in abducted but not adducted humeral positions. 44 Tightness in any or all of these structures may lead to the development of frozen shoulder and has been implicated by various authors. 27,45,46 These positional influences on the available rotation ROM contributed to a lack of consistent support for a single capsular pattern. If the shoulder capsular pattern proposed by Cyriax 29 exists, ER should be most limited, followed by abduction, followed by IR. This pattern was not consistently supported by these results. With the humerus adducted to the side, the capsular pattern proposed by Cyriax 29 was present for 7 of the 10 subjects. However, this finding decreased to 4 of 10 subjects when the arm was abducted. In the abducted position, IR was limited more than ER, and both were limited more than abduction for 4 subjects. The IR was limited more than abduction, and both were limited more than ER for 2 subjects. Cyriax 29 did not specify the position of the arm when he described the capsular pattern. Considering these inconsistent capsular pattern results, we have 2 possibilities to consider. First, different areas of the capsule may tighten in different subgroups of frozen-shoulder patients. If so, the ROM changes would be different across the different groups. This would support different treatment intervention emphasis in terms of joint mobilization and stretching for each distinct group. For example, interventions with the arm adducted to the side might focus on regaining abduction and ER. With the arm abducted, the focus might be on regaining ER and IR. For subjects with the greatest restriction for IR with the arm abducted, greater emphasis on mobilizing the posterior capsule might be used, whereas for subjects with the greatest restriction for ER with the arm at the side, emphasis might be placed on mobilizing the anterior capsule. Currently, very limited research data on the effectiveness of stretching or mobilization for frozen shoulder are available in the peerreviewed literature. 47 Alternatively, consistent capsular patterns may not exist at all, necessitating individualized intervention strategies for each subject. The measurement method used in the present study has both advantages and limitations as compared with standard clinical goniometric methods. Besides providing the advantage of 3-dimensional measurement, a trunk sensor also enables better separation of humeral motion from trunk movement. Further, the moving axis is embedded in the humerus, providing a more direct measure of humeral long-axis rotation, rather than being aligned with the forearm, as in clinical goniometry. However, both IR and ER in all subjects may be underrepresented by using the surface thermoplastic cuff around the humerus. The cuff may not fully track humeral motion at the end ROM. 38 Validation of this surface cuff technique demonstrated a 7.5 average error in long-axis rotation measurements, with the largest discrepancies occurring at end range, whereas a 3 average error was described for all other planes of humeral motion. 38 Additionally, IR1 was limited by contact with the trunk for all asymptomatic and most symptomatic subjects, thus possibly underrepresenting full motion. In future studies, collection of IR beginning with the forearm in the small of the back and moving away from the body might clarify the end range available. All of these factors, plus the average age of the subjects, contribute to lower IR and ER values than often reported in the literature for healthy subjects. Two different rotation sequences were used in the present study to describe humeral motions. Optimally, to avoid any possible confounding of mathematical sequence effects influencing the interpretation of humerus to scapula versus humerus to thorax motion, a single sequence would be desired. However, as identified in the Methods section, the alternate sequence for ER and IR was used to avoid singular or gimbal lock positions for IR1 and ER1. 39 In addition, when interested in clinically interpretable values of long-axis rotation, the use of a y, x, z sequence is not complicated by the 2 long-axis rotations inherent in a z, y, z description. Alternatively, using only a y, x, z sequence is not possible because of singular positions with humeral flexion relative to the trunk. Despite the use of these 2 sequences across motions, all comparisons across subjects and groups are made without confounding. The same rotation sequences are used across subjects. A further limitation of the present study is the sample size and proportion of female subjects. The study sample may not fully represent the spectrum of patients with a frozen-shoulder diagnosis. This factor may be particularly true if subgroups of patients exist. Also, 9 of 10 symptomatic subjects were women.

6 1478 SHOULDER KINEMATICS IN FROZEN SHOULDER, Rundquist The incidence of frozen shoulder is higher in women than men. 42 Thus, our data may not be fully generalizable to men with frozen shoulders. Despite these study limitations, this study provides the first 3-dimensional description of shoulder ROM deficits for this subject population. There are several avenues to pursue in future investigations. Further studies focusing on humeral motion relative to the scapula could more directly measure the influence of a tight capsule on glenohumeral motion. Correlation of ROM deficits to surgically identified capsular adhesions would be optimal; however, surgical treatment approaches are not common with these patients. Additional avenues of investigation might include treatment efficacy studies, patient classification studies, and longitudinal investigations of motion loss and recovery. Longitudinal studies would provide greater insight into how frozen shoulder develops and resolves clinically. CONCLUSION Humeral ROM deficits relative to the trunk and scapula were present in subjects with a diagnosis of idiopathic frozen shoulder. The pattern of motion loss for IR and ER was dependent on arm position and was not consistent across all subjects. The results raise questions about the validity of a theorized single capsular pattern of motion in these subjects. References 1. Duplay S. Dela periarthrite scapulohumerale. Med Week 1896;4: Codman EA. The shoulder. Rupture of the supraspinatus tendon and other lesions in or about the subacromial bursa. Boston: Thomas Todd; Reeves B. The natural history of the frozen shoulder syndrome. Scand J Rheumatol 1975;4: Lundberg BJ. The frozen shoulder: clinical and radiographical observations. The effect of manipulation under general anesthesia. Structure and glycosaminoglycan content of the joint capsule. Local bone metabolism. 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