Changes in abduction and rotation range of motion in response to simulated dorsal and ventral translational mobilization of the glenohumeral joint. (Research Report).

Mobilization techniques such as dorsal, ventral, or inferior glides of the glenohumeral joint are frequently used by physical therapists as an intervention for joints with limited range of motion (ROM) and when impingement syndromes are present. (1-12) Proponents advocate use of gliding movements in what they believe is the direction of limited joint glide in accordance with what is commonly referred to as the "convex-concave rule." (13-15) This rule states that if a convex surface moves on a fixed concave surface, rolling and gliding movements of the joint surfaces occur in opposite directions, and in the same direction if the configuration is reversed. (13) According to this rule, a dorsally directed translational mobilization is selected to manage hypomobility in medial rotation, flexion, and horizontal adduction, and a ventrally directed mobilization is selected to manage hypomobility in lateral rotation, horizontal abduction, and extension. (13-15) Experimental support for this rule, however, is lacking.

In some studies, (16-18) movement predicted by the convex-concave rule did not occur during active or passive movements, especially at the end range. Howell et al (16) reported that in an active motion toward the cocked stage of throwing when the arm is elevated, extended, and maximally rotated laterally, the center of the humeral head was contained within the glenoid cavity throughout the horizontal movement except when the arm was in maximum extension and lateral rotation. At this moment, the center of the humeral head rested approximately 4 mm posterior to the center of the glenoid cavity in what appears to be a violation of the convex-concave rule. (16) Harryman et al (17) and Itoi et al (18) reported that translation occurred in an anterior direction with glenohumeral flexion and horizontal adduction and in a posterior direction with extension and lateral rotation. Anterior translation with flexion could not be prevented by the application of an oppositely directed force. (17) Harryman et al (17) believed these apparent violations of the convex-concave rule to be caused by asymmetrical tightening of the capsule during humeral rotation, resulting in translation of the humeral head in the direction opposite to the tightened capsule (capsular constraint mechanism). (17)

In vitro study of glenohumeral stability and simulation of laxity tests following selective cutting of structures can clarify the roles of the glenohumeral capsular ligaments on joint stability. (17-29) This method appeared to us to have the potential to provide rationales for translational glenohumeral joint mobilization at different joint positions. These studies (17-29) suggest to us that stretching capsular ligaments in a more abducted position will be beneficial in increasing abduction because the inferior glenohumeral ligament complex, we believe, will be resisting further abduction. A few researchers (1, 4-12) have investigated the benefits of glenohumeral joint mobilization in practice. The benefits of specific mobilization movements such as dorsal or ventral glide, however, were not addressed in these studies.

An in vitro simulation of caudally directed mobilization in 20 cadaver glenohumeral joints by using a biaxial material testing system (MTS) led to increases in ROM when the technique was performed at the end range of abduction. (30) Mobilization techniques performed in the resting position (40[degrees] of abduction in the plane of scapula) were not effective against abduction hypomobility. Hsu and colleagues' findings seem to support the usefulness of the convex-concave rule as the guide for choosing mobilization techniques for increasing ROM. (30) Effects on rotation, flexion, and extension ROM, however, were not measured and, therefore, are not known. Use of mobilization at end range to increase ROM was suggested by Edmond, (14) Maitland, (31) and Wadsworth, (32) but they offered no data to suggest that this was more effective than the use of mobilization elsewhere in the ROM. Vermeulen et al, (33) in a multiple-subject case report, described patients as attaining increased ROM in response to end-range mobilization.

In vitro cadaver models when used to study effects of mobilization on joint ROM offer the advantage of allowing invasive procedures and make possible rigid fixation for accurate application of forces/torques and displacements and for measurements of the reactive responses of the joint tissue during simulated maneuvers. This is especially important for the glenohumeral joint because stable fixation of the scapula in viva is extremely difficult, if not impossible, without use of invasive procedures. We believe that any mobilization procedure that could not be proven effective with a properly executed fresh cadaver simulation most likely is not worthwhile to apply clinically. We have no data, however, to support this contention, and we also acknowledge that movement of cadaver limbs is quite different from the movement of limbs that occurs in patients. In addition, there are many changes that occur in the soft tissue of cadaver limbs, which further limits direct application of findings to living tissue. This is further compounded by the freezing of tissue. We conducted this study to evaluate the effect of a set of oppositely directed (dorsal and ventral) translational mobilization techniques (DTM and VTM) of the glenohumeral joint on abduction and rotational ROMs in fresh cadaver shoulder specimens.

Method

Specimens

Fourteen fresh frozen cadaver shoulder specimens from 5 men and 3 women (mean age at the time of death = 77.3 years, SD = 10.1, range = 62-91) were used in our study. Disarticulation at the sternoclavicular, scapulothoracic, and elbow joints was done before the study began. Specimens were stored in a freezer (-20[degrees]C) until the day before testing. A radiograph (anteroposterior [AP] view) of each specimen was taken and inspected so that specimens with gross abnormalities detectable by the radiographs could be eliminated from the study.

Preparation of Specimens

The specimens were thawed overnight at room temperature in preparation for dissection and testing. In an effort to ensure that the glenohumeral joint capsule was not disrupted by the dissection process, only those soft tissues over the scapula, including skin, subcutaneous tissue, and muscles located at least 8 cm medial to the glenohumeral joint, were removed by an instructor with 7 years of anatomy teaching experience (ATH).

The periosteum was also stripped to expose the medial portion of the scapula. All soft tissues approximately 3 cm distal to the surgical neck of the humerus also were removed. We identified the medial and lateral epicondyles of the humerus, and we used them to define the axis of the elbow joint. A nail 3 mm in diameter and 5 cm in length was aligned parallel to the elbow axis and was driven into the humeral shaft at the level of the deltoid tuberosity to represent the axis of the elbow. The distal portion of the humerus was then sectioned immediately below the deltoid tuberosity. The medial edge of the scapula was fixed in a stainless-steel mold (13 cm in diameter, 7.5 cm in depth) with 2-part polyurethane * mixed at equal percentage by weight. The medial border of the scapula, the tip of the coracoid process, and the lateral angle of the acromion were identified and marked by the investigator (ATH). The plane of the scapula, defined as the plane formed by the medial border of the scapula and the midpoint between the tip of the coracoid process and the lateral angle of the acromion, (34) was oriented perpendicular to the base of the scapular mold, with the medial border of the scapula aligned parallel to the base and with the base evenly divided into halves. The distal end of the humerus was placed at the center of a 10-cm-long and 5-cm-internal-diameter cylindrical mold, with the previously driven nail pointing to the lines bisecting the mold into halves and then fixed with polyurethane.

Instrumentation

The instrumentation used in the study is shown in Figure 1. A biaxial MTS unit (MTS 858 Mini Bionix ([dagger])) equipped with a custom-made X-Y table was used for experimental simulation. This MTS unit is capable of applying torsion (rotation in the horizontal plane) and tensile (upward) or compressive (downward) forces and displacements controlled by either force (torque) or displacement (angle) limit. The X-Y table was used as the stage for the experiment because it allows displacements in the horizontal plane whenever such movements occur as a result of passive constraints during the evaluation and mobilization procedures in order to eliminate undue stress or strain, and it allows relatively normal arthrokinematics in the glenohumeral joint. A torque arm was designed and made by us for holding the humerus through the mobilization and evaluation procedures. Through this torque arm, the piston rod of the MTS actuator was capable of performing downward and upward displacements (dorsal and ventral glide) of the humerus with a predetermined force limit and torsion (abduction and adduction). A third dimension was added by incorporating a servomotor (SINANO CB series AC servomotor, model 7CB30-2DG7F) ([double dagger]) onto the torque arm to perform and record axial (medial and lateral) rotations of the humerus. This servomotor was driven by a digital AC servodriver (SINANO EO series, model E15B-CB301C27F) ([double dagger]) and controlled by Labview 5.1 via an NI PCI-servo 4-axis motor control card (184906B-04). ([section]) A clamp was used to connect the humeral holder to the torque arm to prevent rotation of the humerus during abduction. The clamp was disconnected from the torque arm during the measurement of medial and lateral rotation of the glenohumeral joint. The instrumentation setup diagram is presented in Figure 2.

[FIGURES 1-2 OMITTED]

A 6-camera VICON motion analysis system ([parallel]) was used to test the validity of angle measurement for the servomotor. A 40-cm-long, 5-cm-wide, and 1-cm-thick acrylic plate with 7 retroreflective markers was fixed, at its midpoint, to the shaft of the servomotor. The VICON motion analysis system was used to track the coordinates of each marker and angles of rotation (from-100[degrees] to 100[degrees], with increments of 10[degrees]) performed by the servomotor. Excellent concurrent validity (intraclass correlation coefficient [ICC (2,1)]=.999) was obtained between angle measurements obtained with the servomotor and the VICON system. Excellent test-retest reliability coefficients also were obtained for angle measurements taken with the servomotor (ICC [2,1]=1.000) and with the MTS (ICC [2,1]=1.000).

Experimental Setup

The experimental setup is shown in Figure 3. The scapular block was placed on the top plate of the X-Y table by a special clamp custom made by the authors, with the plane of the scapula horizontal and its anterior aspect facing superiorly. The humerus was oriented in a horizontal plane and was parallel with the medial border of the scapula. We defined the neutral position by pressing the humeral head gently into the glenoid fossa until it sat securely in the glenoid fossa and then adjusting the position of the humeral head and shaft until both the shaft of the humerus and the elbow axis were aligned in the plane of the scapula with the shaft of the humerus remaining parallel to its medial border. (30, 34) While holding the humerus in this position, the scapular block was secured to the top plate of the X-Y table with the scapular block clamp. The piston rod of the actuator on the MTS was positioned over the center of the head of the humerus. The torque arm equipped with the servomotor was clamped to the piston rod of the actuator on one end and to the block with the humerus of the specimen on the other. A stainless steel holder connected to the shaft of the servomotor held the block with the humerus in place.

[FIGURE 3 OMITTED]

Experimental Procedures

Because the number of specimens available for use in this study was limited, a repeated-measurement design was used. The outcome measures ROM in abduction, medial and lateral rotation of the glenohumeral joint, and the magnitudes of dorsal and ventral displacements of the humerus. The abduction ROM was produced and recorded by the MTS unit with the application of a 4-N*m abduction torque to the glenohumeral joint through the torque arm in the plane of the scapula. The medial and lateral rotation ROMs were assessed by applying a 2-N*m torque in the corresponding direction to the glenohumeral joint by the servomotor installed on the torque arm. The MTS unit also registered linear displacements of the head of the humerus in the dorsal and ventral directions with a 100-N force in each corresponding direction.

The 4-N*m abduction torque was a whole-number derivation (3.56 [+ or -] 0.43 N*m) of the abduction torque used by 12 physical therapists, with an average of 13.5 years (SD=4.84) of orthopedic experience, while performing passive abduction ROM on a fresh cadaver glenohumeral specimen mounted on a 6-axis load cell. (35) Three ROM measurements were taken to examine the consistency of ROM in response to the same abduction torque. Abduction of the humerus was achieved by a torque applied to the humeral shaft by the torque actuator of the MTS unit through the torque arm at an angular speed of 8[degrees]/s. The applied torque would increase in magnitude when resisted by joint tissues until a maximum moment of 4 N*m was achieved, the angular displacement was stopped and then reversed to the starting position. The simulated DTM or VTM procedure involved a posteriorly or anteriorly directed force applied by the actuator piston of the MTS in the following manner: the force was increased from 0 to 100 N at a controlled displacement rate of 2 mm/s, was held for 20 seconds, and was moved back to the starting position at the same rate. The 100-N force used in this study was based on the findings of McQuade et al, (36) who reported using forces ranging from 101 to 113 N to reach the end point during glenohumeral laxity tests in 21 young subjects with no known pathology.

To date, there are no reports on the differential effects on improving ROM with different durations of force application by therapists during each bout of mobilization in human joints. Research on stretching of hamstring muscles (37-40) and the structures around the hip joint (40) suggests that longer-duration static stretching is more effective than short-duration stretching (39) and that the most effective duration of stretching ranged from 10 to 60 seconds. (37, 38, 40, 41) Therefore, we used a 20-second holding period during each bout of mobilization to maintain the stretch. To decrease the effect of sequence (whether to apply the DTM or VTM procedure first) on the abduction ROM, the 14 specimens were divided randomly into 2 groups. The DTM procedure was conducted first in the AP group (n=7, mean age=79.0 years, SD = 11.1, range = 62-91), and the VTM procedure was conducted first in the posteroanterior (PA) group (n = 7, mean age = 76.3 years, SD = 11.8, range = 62-91). Given the small number of subjects, the use of a repeated-measurement design could not necessarily result in eliminating the effect of multiple tests and the order in which they were administered.

For AP group specimens, the following procedures were executed.

Procedures performed in the resting position. The testing procedures were started by moving the humerus from the neutral position (0[degree]) to 40 degrees of abduction (the resting position). While holding the humerus in this position, measurements of the position (ROM) in medial and lateral rotation and abduction of the glenohumeral joint were taken in the manner described previously. To test the effect of DTM on glenohumeral abduction, 5 repetitions of the dorsal glide maneuver were applied to the head of the humerus through the torque arm. After the fifth maneuver, the measurements were taken again. This was followed by 5 repetitions of VIM, with measurements taken at the end of the procedure.

Procedures performed in the end-range position. The humerus was then moved to the end range of abduction by the MTS unit with 4 N*m of torque. While holding the humerus in this position, the DTM was performed by the MTS and followed by VTM. Outcome measurements were made before and after DTM, and, finally, after VTM. Experimental procedures for the PA group specimens were essentially the same except that the VTM procedure was always done before the DTM procedure in the resting position as well as in the end-range position.

At the end of the experiment, specimens were dissected further to inspect the shoulder joint visually to determine the presence of observable pathology and to exclude data from specimens that had lost the integrity of its joint or joint capsule. No specimens were excluded.

In an effort to eliminate the effect of minor variations on the abduction torque output, the abduction position was interpolated at the moment when 4 N*m was achieved. Likewise, the measure that allowed us to determine displacement of the humeral head was interpolated at 100 N and the medial and lateral rotation at 2 N*m. For tests performed in the resting position, the differences in ROM measurements obtained before and after DTM (improvement of glenohumeral abduction attributed to the DTM procedure [[D.sub.DTMR]) and before and after VTM (improvement of glenohumeral abduction attributed to the VTM procedure [[D.sub.VTMR]]) and their corresponding values in the end-range position ([D.sub.DTME] and [D.sub.VTME) were calculated. These values represent the effects of the mobilization procedure immediately preceding it.

Statistical Analyses

In an effort to determine the effects of mobilization in the different positions, the difference values (before and after) were examined with paired t tests against the value of zero. These values were also used in a two-way analysis of variance (ANOVA) for repeated measures to assess the effect of joint position (resting versus end range) and the effect of direction of glide movements (DTM versus VTM) on the ROM of glenohumeral abduction. The same analyses were performed on changes in the medial and lateral rotation angles due to DTM and VTM procedures and on dorsal and ventral displacement. Grouping (AP and PA groups) was the between-subjects variable. A probability value of less than .05 was considered significant. The Statistical Package for the Social Sciences (version 8.0) (#) was used for all statistical analyses.

Results

Amplitude of Ventral and Dorsal Translation During Mobilization

The peak dorsal and ventral displacements calculated for the VTM and DTM procedures are listed in Table 1. There were main effects of joint position (F=78.52, P=.000) and direction of movement (F=42.98, P=.000) on values of displacements (Tab. 2). No interaction was found. More displacement ([bar]X=11.02 mm [SD=5.59] for DTM, and [bar]X=13.23 mm [SD=6.04] for VTM) was allowed in the resting position than in the end-range position and during VTM ([bar]X= 10.49 mm [SD=6.13] for resting position, and [bar]X=8.27 mm [SD=5.91] for end-range position) than during DTM. The increased displacements between successive bouts of DTM or VTM procedures were inversely related to the order of repetition (Fig. 4).

[FIGURE 4 OMITTED]

Effect of Dorsal and Ventral Glide on Glenohumeral Abduction

The means, standard deviations, and ranges for glenohumeral abduction ROM before DTM (the initial abduction angle [[A.sub.INR]]), after DTM ([A.sub.DGR]), and after VTM ([A.sub.VGR]) in the resting position and the corresponding variables of the end-range position ([A.sub.INE], [A.sub.DGE], and [A.sub.VGE]) are listed in Table 3. No group effects were observed. Changes in abduction ROM attributable to DTM ([D.sub.DGR]) and VTM ([D.sub.VGR]) in the resting position ([bar]X=0.17[degrees] [SD=0.48[degrees]] and [bar]X=0.03[degrees] [SD=0.79[degrees]], respectively) and at the end range of abduction ([D.sub.DGE] [[bar]X=2.10[degrees], SD=1.76[degrees]] and [D.sub.VGE] [[bar]X=2.06[degrees], SD=1.96[degrees]]) are presented in Table 4. There was an effect of joint position (F=33.710, P=.000) on the changes in abduction ROM. No effect of direction of gliding movement or interaction between position and direction were noted (Tab. 5).

Effect of Dorsal and Ventral Glide on Glenohumeral Rotation ROM

The ranges of medial rotation measured during various procedures are listed in Table 6, and those of the lateral rotation are listed in Table 7. Two procedures produced small increases in ROM: lateral rotation ROM after the VTM procedure in the resting position ([bar]X=0.90[degrees], SD=0.92[degrees], t=3.65, P=.003) and medial rotation ROM after the DTM procedure in the end-range position ([bar]X=0.97[degrees], SD=1.45[degrees], t=2.51, P=.026). Medial rotation ROM was affected by joint position (F=61.421, P=.000) and glide direction (F=4.342, P=.024, Tab. 6). No interaction was found between position and direction. No main effects of joint position or direction of mobilization were found in values of lateral rotation.

Discussion

Effects of Dorsal and Ventral Translational Mobilization on Glenohumeral Abduction

In response to DTM and VTM, there was an effect due to of joint position and direction of movement on the amount of translation of the humeral head. More displacement (11.02 mm more for DTM and 13.23 mm more for VTM) occurred in the resting position than in the end-range position. Such a finding could be attributable to the cradling of the inferior glenohumeral ligament around the humeral head at the end range of abduction. (27) More displacement occurred during anterior glide (10.49 mm more for the resting position and 8.27 mm more for the end-range position) than during dorsal glide. Comparison of our findings with those from other studies is difficult because different experimental setups, (18, 23, 24, 29, 42-49) different angles of abduction and rotation, (18,24,29,42-49) and different magnitudes and directions of translation forces (18, 24, 29, 42-49) were used in various studies. The results of our study (Tab. 1) are very similar to those of Black et al, (48) who reported mean anterior displacements of 27.6 mm (SD=7.5) and 16.9 mm (SD=7.7) in 9 cadaver glenohumeral joints at 45 and 90 degrees of abduction, respectively, in response to a smaller (50-N) anterior force. With the humerus in a neutral position relative to rotation, Debski and colleagues (23, 24) found that anterior displacement of the humeral head was about 5 mm more than that of the posterior displacement in response to an 89 N force in 10 fresh cadaver glenohumeral joints. Pagnani et al, (29) Harryman et al, (46) and Speer et al, (47) however, reported that anterior and posterior translations were almost the same in magnitude.

In our study, both dorsal and ventral glide (DTM and VTM) procedures when applied at the end-range position were equally effective in increasing glenohumeral abduction. The sequence of testing (regardless of whether DTM or VTM was performed first), in our view, did not affect the outcome. Many factors affect the stability of the head of the humerus: joint surface congruity, joint capsule, labrum, rotator cuff, and negative intra-articular pressure. (19-27) As was noted by Debski et al (23) and Terry et al, (50) the role of different parts of the glenohumeral joint capsule, due to its continuous nature, leads to a complex distribution of force throughout the capsule in response to displacement of the head of the humerus. Effects of joint position on tensile stress in different portions of the capsule have been studied using simulated laxity tests and selective cutting methods in vitro. (18, 19, 23, 24, 43, 45-47) Anterior humeral head translation was primarily restricted by the coracohumeral and anterior superior glenohumeral ligaments in the neutral position and by the anterior middle and inferior glenohumeral ligaments in the abducted position. (23, 43, 45) Like our study, however, these studies were conducted on cadaver specimens; therefore, application to living tissue must be done cautiously. The middle posterior capsule restricted motion for posterior translation of the head in the neutral position, whereas both the middle and inferior capsules were involved in limiting the posterior glide of the head in the abducted position. (23, 43, 45) Lateral rotation in the abducted position stretches the anterior middle and inferior glenohumeral ligaments. (43, 46, 47)

Our results are consistent with the findings that laxity tests in the posterior direction primarily stretch the posterior band of the inferior glenohumeral ligament and that anterior translation stretches the anterior band of the inferior glenohumeral ligament when the arm is held near the end range of abduction. (23, 43, 45) The anterior and posterior bands and the axillary pouch of the inferior glenohumeral ligament are the primary restraints to the abduction of the glenohumeral joint. Stretching of the these capsular ligaments, in our opinion, can lead to improvement in abduction ROM.

Our findings also suggest that DTM and VTM procedures, when performed in the resting position, may not be effective for increasing abduction ROM. Similar results were reported for simulated dorsal and caudal translational mobilization of the glenohumeral joint in fresh cadaver models. (30, 49) In the resting position, the coracohumeral, superior glenohumeral, and middle glenohumeral ligaments are stressed during the anterior laxity test, and the coracohumeral ligament is stretched during the posterior laxity test. (23, 45) Again, we urge caution in using the data because we used cadaver specimens and, in addition, they were from elderly subjects who were over 70 years of age. The influence of translational mobilization performed in the resting position, in our opinion, is minimal on the inferior glenohumeral ligament and, thus, does not have a meaningful effect on the glenohumeral abduction ROM.

Effect of Dorsal and Ventral Glide on the Glenohumeral Rotation ROM

The anterior or posterior translation of the head of the humerus can be affected by the length and tension of the posterior capsule in medial rotation and by the length and tension of the anterior capsule in lateral rotation. (42) Without load, the humeral head can translate anteriorly with medial rotation of the arm and posteriorly with lateral rotation of the arm. (17,18) Asymmetric tightening of the capsule during humeral rotation, in our view, results in translation of the humeral head in the opposite to the direction of capsular tightening. (17) When the arm is medially rotated, the posterior capsule becomes tight and pushes the humeral head anteriorly, which may result in anterior translation through the capsular constraint mechanism. (17) Because of the capsular constraint mechanism, in our view, it appears that a longer anterior capsule will lead to a greater ROM in lateral rotation and that a longer posterior capsule will lead to a greater ROM in medial rotation. Thus, we believe that the VTM or DTM procedure would stretch the anterior or posterior capsule and could increase the lateral or medial rotation ROM. Our findings, however, were not conclusive on this issue, and data are still lacking for this hypothesis.

The 2 procedures that produced small increases in rotation ROM were lateral rotation after the VTM procedure in the resting position (0.90[degrees]) and medial rotation after the DTM procedure at end range (0.97[degrees]). This suggests to us support for the convex-concave rule, with dorsal glide improving medial rotation and ventral glide improving lateral rotation. (13) The other 2 procedures that were supposed to improve rotational ROM--lateral rotation after the VTM procedure at end range and medial rotation after the DTM procedure in the resting position--led to large variability in changes in ROM. Our findings also showed that at the end range of abduction, both medial and lateral rotation ROMs were less than what could be achieved in the resting position, indicating a strong influence by the inferior glenohumeral ligament on restricting mobility of the glenohumeral joint in this position.

In our study, the magnitude of the torque we used to assess the rotational ROM was limited mainly by the capability of the servomotor we used. How this factor might have affected the variability of the rotational ROM measurements is uncertain and may depend on where 2 N*m falls in the torque-angle relationship of the tissues tested. If the 2-N*m torque falls at the linear elastic region of the torque-angle relation, we believe less variability should be expected. However, if it falls within the toe region of the torque-angle relationship, greater variability would be expected in angle measurements. Judging from data reported by Novotny et al, (51) 2 N*m appears to fall at the upper end of the toe region.

Clinical Implications

Our findings provide some evidence for the use of both DTM and VTM techniques performed close to the end range of abduction to increase abduction ROM. According to the literature, (23,24,29,42-48) the AP and PA translation of the head of the humerus in the abducted position stretch primarily the posterior and anterior bands of the inferior glenohumeral ligaments and thus can contribute to an increase in abduction. Our findings also point to the need to assess the mobility of a hypomobile glenohumeral joint at a fixed location closer to the end range of abduction rather than in just the resting position as was suggested by several authors. (14,49) In the resting position, capsular structures responsible for the abduction restrictions appear to have not been stressed, because we found no improvement in abduction ROM after the translational mobilization in this study.

Although statistically significant, gains in ROM following the VTM and DTM procedures were quite small in magnitude. We believe that these differences, however, are within the differences detectable by the MTS and the servomotor. Data to support this belief are lacking. For angle measurements, both units are, according to the manufacturer's specification, capable of resolutions up to 0.045 degree (360[degrees]/8,000). Exceptional test-retest reliability in angle measurements for the MTS unit and the servomotor (with intraclass correlation coefficient [2,1] values of 1.000 and 1.000, respectively) were obtained in a pilot study. In our study, only VTM and DTM procedures were applied to the specimens. We contend that such procedures may represent only a portion of a single treatment session and that there is very low risk of injury involved with these procedures. We argue that the minimum worthwhile effect can be much smaller than what would be expected of a single session or weekly treatment. We lack data, however, to support this view. Furthermore, in the clinical setting, other techniques such as caudal glide procedures, are also applied. The caudal glide procedure was shown to be more effective in improving abduction ROM (4.38[degrees] in response to caudal glide mobilization at the end range of abduction (30)) than the VTM procedure (2.06[degrees]) or the DTM procedure (2.10[degrees]) in our present study. We argue that the cumulative effect of such treatment sessions could be meaningful, but again this is our opinion and we lack supporting data.

Limitations of the Study

Several limitations are common to studies such as ours. Specimens, in general, are from fresh cadavers of an elderly population with unknown medical history (except the cause of death) and are frozen. Whether the shoulder specimens studied had decreased ROM in life is not known. Accordingly, discretion should be used in generalizing the results to living patient populations. No active (voluntary or reflexive) tension from muscles crossing the glenohumeral joint were involved during the experimental simulation. During the experiment, the room temperature was kept constant at 25[degrees]C. This temperature, however, was lower than the core temperature within the shoulder joint of a living person. This inevitably would have affected the material properties of the capsule and the results of the study. In addition, living tissue differs from cadaver tissue. In our study, the joint capsule was not vented. Thus, the effect of intraarticular negative pressure could have affected our results.

The mechanical responses of intrinsically viscoelastic joint tissue depends, in part, on the magnitude, number of repetitions, rate of loading of the force applied, and mechanical constraints that were inherent to this study. The loading used in our study and the mechanical responses obtained might differ from those used in clinical practice, depending on factors such as pain, inflammation, muscle activity, co-contractions, and pathology of the glenohumeral joint.

We did not assess the effect of the number of repetitions of the mobilization procedures applied on the glenohumeral ROM. During the simulated mobilization procedures, progressive increases in the magnitude of dorsal and ventral displacements were measured. The increase in displacements was related inversely to the order of repetition (Fig. 4). How the increases in magnitude of dorsal and ventral displacements translated to changes in abduction and rotational ROMs was uncertain.

Riddle (52) contended that there are 3 primary sources of error in the practice of manual therapy: error attributable to the examiner, error inherent in the variable being assessed, and error attributable to the examination procedure. We believe that the source of error attributable to the examiner was greatly reduced with the use of MTS unit to simulate the movement of the therapist in our study. Error inherent in the variable being assessed was lessened to certain degree by the use of cadaver specimens. However, by eliminating these sources of variability, we made our study less like what occurs in clinical practice.

Conclusion

Our findings suggest that both DTM and VTM of the glenohumeral joint are effective in improving glenohumeral abduction ROM if they are applied at the end range of glenohumeral abduction. The same techniques performed in the resting position, however, do not appear to be effective in increasing glenohumeral mobility Conclusions, however, are based on the use of a cadaver model, with specimens coming from elderly subjects.

Table 1.
Peak Dorsal and Ventral Displacement Values (in Millimeters) of
the 5 Consecutive Repetitions of the Simulated Glenohumeral Joint
Mobilization Executed and Recorded by the Material Testing
System with 100 N of Dorsally and Ventrally Directed Forces in
the Resting and End-Range Positions

                             REP 1 (c)

Position (a)  Direction (b)  [bar]X  SD    Range

Resting       Dorsal          15.25  5.46  6.85-26.27
              Ventral         25.23  7.30  6.43-35.36

End range     Dorsal           4.04  1.70  0.76-6.88
              Ventral         11.65  4.87  4.87-23.45

                             REP2

Position (a)  Direction (b)  [bar]X  SD    Range

Resting       Dorsal          15.81  5.32  7.33-26.61
              Ventral         25.99  7.35  6.88-36.19

End range     Dorsal           4.67  1.75  1.06-7.65
              Ventral         12.58  4.97  5.36-24.22

                             REP3

Position (a)  Direction (b)  [bar]X  SD    Range

Resting       Dorsal          16.04  5.27  7.40-26.65
              Ventral         26.37  7.37  7.11-36.72

End range     Dorsal           4.96  1.79  1.21-8.04
              Ventral         13.02  5.01  5.51-24.53

                             REP4

Position (a)  Direction (b)  [bar]X  SD    Range

Resting       Dorsal          16.22  5.24  7.55-26.83
              Ventral         26.64  7.39  7.32-37.06

End range     Dorsal           5.20  1.84  1.32-8.32
              Ventral         13.35  5.07  5.65-24.97

                             REP5

Position (a)  Direction (b)  [bar]X  SD    Range

Resting       Dorsal          16.35  5.21  7.59-26.82
              Ventral         26.84  7.42  7.45-37.32

End range     Dorsal           5.34  1.86  1.40-8.49
              Ventral         13.61  5.11  5.70-25.18

(a) Position: resting=in resting position of abduction, end
range=in end-range position of abduction.

(b) Direction: dorsal=dorsal translation, ventral=ventral translation.

(c) REP1-REP5=displacement values of the first to fifth repetitions
of mobilization.
Table 2.
Summary Results of the Two-Way Analysis of Variance for Repeated
Measures on the Effects of Joint Position (Resting Versus End Range)
and Direction (Dorsal Versus Ventral) of Displacements (a)

Source                        df  SS        MS        F       P

Position                       1  2058.372  2058.372  78.525  .000
Error (position)              13   340.767    26.213
Direction                      1  1231.443  1231.433  42.976  .000
Error (direction)             13   372.504    28.654
Position x direction           1    17.214    17.214   2.252  .157
Error (position x direction)  13    99.363     7.643

(a) Values of displacement were measured in millimeters.
Displacement values of the 5th repetitions in
Table 1 were used for analyses.
Table 3.
Means, Standard Deviations and Ranges (in Degrees) for Glenohumeral
Abduction Range of Motion (ROM) (a) Measured During the Procedure
Performed in the Study

Group (b)  [A.sub.INR] (c)  [A.sub.DGR]   [A.sub.VGR]

AP
 [bar]X    83.99            84.17         84.34
 SD        19.51            19.26         19.49
 Range     58.79-116.30     59.22-115.84  59.09-116.27

PA
 [bar]X    84.55            84.61         84.44
 SD        12.61            12.51 d       12.60
 Range     56.99-95.88      57.65-96.01   57.22-95.88

Total
 [bar]X    84.27            84.39         84.39
 SD        15.78            15.60         15.77
 Range     56.99-116.30     57.65-115.84  57.22-116.27

Group (b)  [A.sub.INE]   [A.sub.DGE]   [A.sub.VGE]

AP
 [bar]X    86.60         88.53         89.64
 SD        20.16         20.42         20.41
 Range     59.80-117.51  61.17-117.72  62.16-118.26

PA
 [bar]X    86.60         91.88         89.60
 SD        12.74         13.23 (d)     13.21
 Range     59.35-97.51   65.77-107.82  61.99-101.83

Total
 [bar]X    86.60         90.20         89.62
 SD        16.20         16.62         16.51
 Range     59.35-117.51  61.17-117.72  61.99-119.26

(a) The abduction ROM was achieved by a 4-N*m abduction torque
applied to the glenohumeral joint and recorded by the material
testing system unit.

(b) Group AP contains specimens with the dorsal glide procedure
performed first. Group PA contains specimens with the ventral
glide procedure performed first.

(c) Values represent the initial abduction ROM measured in the
resting position ([A.sub.INR]), after the dorsal glide procedure
in the resting position ([A.sub.DGR]), and after the ventral glide
procedure in the resting position ([A.sub.VGR]) and ROM measured
after the joint was moved to the end-range position ([A.sub.INE]),
after the dorsal glide procedure in the end-range position
([A.sub.DGE]), and after the ventral glide procedure in the
end-range position ([A.sub.VGE]).

(d) The testing sequence was reversed in relation to the variable
to its right.
Table 4.
Descriptive Statistics for Changes in Glenohumeral Abduction Range
of Motion (ROM) (in Degrees) Due to the Effects of Dorsal Glide
and Ventral Glide in the Resting and End-Range Positions

Group (a)  [D.sub.DGR] (b)   [D.sub.VGR]   [D.sub.DGE]    [D.sub.VGE]

AP (n=7)
 [bar]X    0.18             0.17          1.92           1.11
 SD        0.61             0.62          1.57           1.03
 Range    -0.46 to 1.28    -0.98 to 0.82  0.21 to 4.50  -0.04 to 3.19

PA (n=7)
 [bar]X    0. 17           -0.11          2.27          3.00
 SD        0.34             0.96          2.04          2.28
 Range    -0.31 to 0.71    -1.86 to 1.33  0.22 to 5.99  0.42 to 7.37

Total
(N = 14)
 [bar]X    0.17             0.03          2.10           2.06
 SD        0.48             0.79          1.76           1.96
 Range    -0.46 to 1.28    -1.86 to 1.33  0.21 to 5.99  -0.04 to 7.37

(a) Group AP contains specimens with the dorsal glide procedure
performed first. Group PA contains specimens with the ventral
glide performed first.

(b) Values represent changes in the abduction ROM due to dorsal
glide in resting position ([D.sub.DGR]), ventral glide in resting
position ([D.sub.VGR]), dorsal glide in end-range position
([D.sub.DGE]), and ventral glide in end-range position ([D.sub.VGE]).
Table 5.
Summary Results of the Two-Way Analysis of Variance for Repeated
Measures on Changes in Glenohumeral Abduction Range of Motion
Due to Two Within-Subject Factors (Joint Position and Direction of
Mobilization) and One Between-Subjects Factor (Group (a))

Source                         df   SS       MS       F        P

Position                        1   54.777   54.777   33.710   .000
Position x group                1    5.590    5.590    3.440   .088
Error (position)               12   19.500    1.625
Direction                       1    0.123    0.123    0.317   .584
Direction x group               1    1.411    1.411    3.628   .081
Error (direction)              12    4.666    0.389
Position x direction            1    0.004    0.004    0.041   .843
Position x glide x group        1    2.894    2.894    3.096   .104
Error (position x direction)   12   11.217    0.935

(a) Specimens were divided randomly into 2 groups. In group AP, the
dorsal glide mobilization procedure was performed first. In group PA,
the ventral glide mobilization procedure was performed first.
Table 6.
Medial Rotation Range of Motion (ROM) (a) (in Degrees) Before and
After Dorsal and Ventral Glide Procedures in the Resting and End-Range
of Abduction Positions

Group (b)  [MR.sub.INR] (c)  [MR.sub.DGR]    [MR.sub.VGR]

AP
 [bar]X    39.19             39.77           39.71
 SD        14.35             12.42           14.71
 Range     16.56 to 62.11    18.85 to 57.17  16.77 to 62.79

PA
 [bar]X    40.45             41.07           40.63
 SD        22.15             22.48 (d)       22.76
 Range      8.35 to 69.44     8.99 to 70.22   7.93 to 69.64

Group (b)  [MR.sub.INE]    [MR.sub.DGE]    [MR.sub.VGE]

AP
 [bar]X    3.96            5.59            5.14
 SD        2.50            2.71            3.50
 Range     0.58 to 7.63    1.08 to 8.57    0.45 to 11.41

PA
 [bar]X    3.01            4.17            3.85
 SD        3.23            3.55 (d)        3.83
 Range     -0.54 to 8.40   0.63 to 11.05   -0.32 to 10.23

(a) Medial rotation was achieved by a 2-N*m torque applied by
the servomotor, and the rotation angle was monitored by the computer.

(b) Group AP contained specimens with the dorsal glide procedure
performed first. Group PA contained specimens with the ventral glide
procedure perform first.

(c) Value represent initial medial rotation ROM in the resting
position ([MR.sub.INR]), after dorsal glide procedure in resting
position ([MR.sub.DGR]), after ventral glide procedure in resting
position ([MR.sub.VGR]), in end-range position ([MR.sub.INE]), alter
dorsal glide procedure in end-range position ([MR.sub.DGE]), and
after ventral glide procedure in end-range position ([MR.sub.VGE]).

(d) The testing sequence was reversed with the variable to its right.
Table 7.
Lateral Rotation Range of Motion (ROM) (a) (in Degrees) Before and After
Dorsal and Ventral Glide Procedures in the Resting and End-Range of
Positions

Group (b)  [LR.sub.INR] (c)  [LR.sub.DGR]    [LR.sub.VGR]

AP
 [bar]X    71.55             71.29           72.42
 SD        25.78             25.76           24.58
 Range     22.75-94.40       22.62-94.23     25.52-93.73

PA
 [bar]X    57.50             58.24           58.17
 SD        28.53             28.85 (d)       28.45
 Range      7.16-93.41        7.50-95.68      7.93-94.40

Group (b)  [LR.sub.INE]    [LR.sub.DGE]    [LR.sub.VGE]

AP
 [bar]X    65.53           63.23           62.89
 SD        26.66           27.80           28.40
 Range     13.42-96.72     12.49-96.82     14.76-96.62

PA
 [bar]X    49.32           46.19           48.19
 SD        29.67           29.46 (d)       28.71
 Range      4.59-94.40      3.39-89.83      5.00-91.35

(a) Lateral rotation was achieved by a 2-N*m torque applied by
the servomotor, and the rotation angle was monitored by the computer.

(b) Group AP contained specimens with the dorsal glide procedure
performed first. Group PA contained specimens with the ventral
glide procedure perform first.

(c) Value represent initial lateral rotation ROM in the resting
position ([LR.sub.INR]), after dorsal glide procedure in resting
position ([[LR.sub.DGR]), after ventral glide procedure in
resting position ([LR.sub.VGR), in end-range position ([LR.sub.INE]),
after dorsal glide procedure in end-range position ([LR.sub.DGE]),
and after ventral glide procedure in end-range position ([LR.sub.VGE).

(d) The testing sequence was reversed with the variable to its right.

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* BJB Enterprises Inc, 14791 Franklin Ave, Tustin, CA 92780.

([dagger]) MTS System Corp, 1400 Technology Dr, Eden Prairie, MN 55344.

([double dagger]) Sinano Electric Co Ltd, 23-11 Sengoku 1-Chome, Bonky-Ku, Tokyo, 112, Japan.

([section]) National Instruments Corp, 11500 N Mopac Expressway, Austin, TX 78759-3504.

([parallel]) Vicon Motion System Inc, 14 Minns Business Park, West Way, Oxford, OX2 0JB, United Kingdom.

(#) SPSS Inc, 233 S wacker Dr, Chicago, IL 60606.

AT Hsu, PT, PhD, is Professor, Department of Physical Therapy, College of Medicine, National Cheng Kung University, 1 University Rd, Tainan 701, Taiwan ([e-mail]). Address all correspondence to Dr Hsu.

T Hedman, PhD, is Assistant Professor, Orthopedic Research Laboratory, Department of Orthopedics, University of Southern California, Los Angeles, Calif.

JH Chang, MS, is PhD Student, Institute of Biomedical Engineering, College of Engineering, National Cheng Kung University.

C Vo, BS, C[M.sub.fg]E, is Chief Engineer, Orthopedic Research Laboratory, Department of Orthopedics, University of Southern California.

L Ho, PT, DPT, OCS, is Adjunct Assistant Professor, Department of Biokinesiology and Physical Therapy, University of Southern California.

S Ho, PT, DPT, is Adjunct Assistant Professor, Department of Biokinesiology and Physical Therapy, University of Southern California.

GL Chang, PhD, is Professor, Institute of Biomedical Engineering, College of Engineering, National Cheng Kung University.

Dr Hsu provided concept/research design and writing. Dr Hsu, Dr Hedman, Mr JH Chang, Mr C Vo, Dr L Ho, Dr S Ho, and Mr Chiang An-Chi provided data collection. Dr Hsu and Mr Chang provided data analysis. Dr Hsu and Dr GL Chang provided fund procurement. Dr Hsu, Dr Hedman, and Dr Chang provided facilities/equipment. Dr Hedman, Mr C Vo, and Dr Chang provided consultation (including review of manuscript before submission).

This research was funded by a grant (NSC89-2320-B-006-080-M08) from the National Science Council, Taiwan.

This article was submitted January 19, 2001, and was accepted November 28, 2001.

APTA is a sponsor of the Decade, an international, multidisciplinary initiative to improve health-related quality of life for people with musculoskeletal disorders.