Mechanistic insights into glenohumeral kinematics derived from positional relationship between the contact path and humeral tuberosity.

Although three-dimensional (3D) glenohumeral (GH) motion has generally been expressed only by rotational elements, its mechanistic details, including GH rotations, remain unknown owing to a lack of geometric investigations. This study aims to investigate the positional relationship between the contact path and humeral tuberosities at the GH joint during arm elevation and to consider the mechanism of GH kinematics. Shoulder kinematics were captured using two-dimensional and 3D single-plane image registration techniques in 15 young healthy subjects during flexion, scaption, and abduction. The glenoid movement relative to the humeral head was calculated to describe the contact path on the humeral head. From the start to 45° of flexion, scaption, and abduction, the glenoid center moved from the anteromedial to the anterior, central, and posterior portions of the humeral head, respectively, as the GH joint rotated externally. From 45° to the maximal elevation for all elevation planes, the glenoid center moved upward to the humeral head and came close to the bicipital groove (BG) at maximal elevation, while the glenoid maintained a constant inclination at 20°-40° relative to the humerus. To investigate this mechanism, the position of humeral tuberosities relative to the glenoid was calculated, and the BG was found to face the supraglenoid tubercle, the attachment site of the long head of biceps (LHB). GH external rotation mainly occurred depending on the elevation planes in the early phase of elevation, and it might be kept constant by the LHB and rotator cuff in the mid- to end range of elevation.

The influence of three-dimensional scapular kinematics on arm elevation angle in healthy subjects.

BACKGROUND: We often clinically observe individual differences in arm elevation angles, but the motion producing these differences remains unclear, partly because of the difficulty of accurately measuring scapular motion. The aim of this study was to determine whether the scapular or glenohumeral (GH) motion has more influence on differences in the arm elevation angles by capturing not only the humerus and scapula but also the trunk using two- (2D) and three-dimensional (3D) shape-matching registration techniques. METHODS: Fifteen healthy subjects (13 male and 2 female; mean age: 27.7 years) were instructed to elevate their arms in the sagittal, scapular, and coronal planes. They were divided into high and low groups based on the average of arm elevation angle measured by a goniometer. The 3D scapular, thoracohumeral, and glenohumeral motions were evaluated using 2D/3D single-plane registration. To compare 3D motions between groups, we performed a two-way repeated measures analysis of variance. RESULTS: Eight subjects were assigned to the high group, while seven subjects were assigned to the low groups based on an average elevation angle of 172°. The low group demonstrated a significant larger scapular protraction during elevation in all planes (P = 0.0002 for flexion; P = 0.0047 for scaption; P = 0.0314 for abduction), and smaller posterior tilting only during flexion (P = 0.0157). No significant differences occurred in scapular upward rotations or the glenohumeral positions and rotations. CONCLUSIONS: This study revealed that insufficient scapular retraction and posterior tilting results in lower arm elevation angles, suggesting that improving the flexibility and activation of muscles surrounding the scapula may be important to achieve complete arm elevation.

The process of bone union after arthroscopic bony Bankart repair in younger athletes with a subcritical glenoid defect: An advantage of remained large bone fragment.

BACKGROUND: The purpose of the present study was to investigate the bone union process after arthroscopic bony Bankart repair (ABBR) in shoulders with a subcritical glenoid defect of 13.5% or larger. METHODS: Bone union process after ABBR performed from 2011 to 2018 were retrospectively investigated in 47 athletes younger than 30 years with a subcritical glenoid defect, who underwent CT at least twice postoperatively. The change of bone union between first CT within 6 months and final CT later than 6 months was investigated, especially noticing bone fragment size (≥7.5% versus <7.5%). RESULTS: The mean period at first CT and at final CT was 4.1 ± 0.6 months (3-6 months) and 16.8 ± 11.6 months (7-71 months), respectively. From the first to final CT, among 15 shoulders with a small bone fragment (<7.5%), complete union increased from 4 shoulders (26.7%) to 8 shoulders (53.3%), while among 32 shoulders with a large bone fragment (≥7.5%), complete union increased from 15 shoulders (46.9%) to 25 shoulders (78.1%). On the other hand, while non-union or disappeared bone fragment was recognized in 8 shoulders (53.3%) with a small fragment and in 2 shoulders (6.3%) with a large fragment at first CT, it was solely recognized in 4 shoulders (26.7%) with a small fragment and in no shoulders with a large fragment at final CT. While postoperative glenoid fracture at the site of bone union was recognized in 7 shoulders, complete union was finally obtained after conservative treatment in 5 shoulders. So, final complete union was obtained in 9 (60%) of 15 shoulders with a small fragment and in 29 (90.6%) of 32 shoulders with a large fragment (p = 0.021). CONCLUSIONS: In shoulders with a subcritical glenoid defect, when a large bone fragment (≥7.5%) was repaired, complete union rate was higher and complete union could be obtained earlier.

On-the-Edge Anchor Placement May Be Protective Against Glenoid Rim Erosion After Arthroscopic Bankart Repair Compared to On-the-Face Anchor Placement.

PURPOSE: This retrospective study aimed to compare the effects of 2 different anchoring placements on glenoid rim erosion after arthroscopic Bankart repair (ABR). METHODS: Shoulders that underwent ABR from January 2013 to July 2020 were divided into 2 groups according to anchor placement (on-the-face, group F; on-the-edge, group E). We retrospectively calculated the percent change of glenoid width (Δ) on the first postoperative computed tomography scan (CT; performed within 6 months) and second postoperative CT (performed at 6 to 12 months) relative to the width on the preoperative CT and compared percent changes between the 2 groups. Also, we investigated the influence of preoperative glenoid structures (normal, erosion, bony Bankart) and the postoperative recurrence rate. RESULTS: We examined 225 shoulders in 214 patients (group F, n = 151; group E, n = 74). At first CT, anchoring placement was significantly associated with postoperative decrease of glenoid width (group F, -7.6% ± 7.9%; group E, -0.1% ± 9.7%; P < .0001). The difference between groups F and E was significant in shoulders with a preoperative glenoid defect (bony Bankart, -6.6% ± 8.8% vs 2.5% ± 11.2%, respectively; P < .0001; erosion, -6.6% ± 6.2% vs -2.6% ± 5.3%, respectively; P = .03). In 112 shoulders, CT was performed twice; Δ was -6.9% ± 7.3% in group F (n = 64) and -1.7% ± 10.1% in group E (n = 48; P = .005) at the first CT and -3.2% ± 10.0% and 1.0% ± 10.6% (P = .10), respectively, at the second CT, indicating recovery of glenoid width in both groups. The postoperative recurrence rate in patients with at least 2 years' follow-up was 14.7% in group F and 14.6% in group E. CONCLUSIONS: In the early stage after ABR, on-the-edge glenoid anchor placement was associated with less glenoid rim erosion than on-the-face anchor placement. LEVEL OF EVIDENCE: Level III, retrospective comparative trial.

A Glenoid Defect of 13.5% or Larger Is Not Always Critical in Male Competitive Rugby and American Football Players Undergoing Arthroscopic Bony Bankart Repair: Contribution of Resultant Large Bone Fragment.

PURPOSE: To investigate bone union and postoperative recurrence after arthroscopic bony Bankart repair (ABBR) in male competitive rugby and American football players with a subcritical glenoid defect of ≥13.5% and to compare findings with those in players with a glenoid defect of <13.5%. METHODS: Participants were male competitive rugby or American football players with a glenoid defect and bone fragment who underwent ABBR from July 2011 to December 2018 and were followed for a minimum of 2 years. We investigated the influence of glenoid defect and bone fragment size on bone union and postoperative recurrence after ABBR. RESULTS: We included 45 rugby players and 35 American football players. A total of 38 shoulders were assigned to the small defect group (<13.5%) and 42 to the large defect group (≥13.5%). The complete bone union rate was 47.4% in the small defect group and 71.4% in the large defect group (P = .040), and postoperative recurrence was seen in 13 (34.2%) and 5 shoulders (11.9%), respectively (P = .030). In the small defect group, the bone fragment size was <7.5% in 30 shoulders and ≥7.5% in 8 shoulders; in comparison, the respective numbers were 12 and 30 shoulders in the large defect group, and large fragments (>7.5%) were significantly more common in this group (P < .001). The complete union rate was significantly higher in shoulders with a large fragment (≥7.5%) than in those with a small fragment (<7.5%; 78.9% versus 42.9%, respectively; P = .001). The recurrence rate was 33.3% in shoulders with a small fragment (<7.5%) and 10.5% in shoulders with a large fragment (≥7.5%; P = .017) and was significantly lower in shoulders with a complete union than in those without a complete union (6.3% versus 46.9%, respectively; P < .001). CONCLUSION: The postoperative recurrence rate after ABBR was lower in male competitive rugby and American football players with a large glenoid defect (≥13.5%) than in those with a small glenoid defect (<13.5%) and might be associated with a higher rate of complete bone union of the resultant large bone fragment (≥7.5%). LEVEL OF EVIDENCE: III, case-control study.

Bipolar Bone Defects in Shoulders With Primary Instability: Dislocation Versus Subluxation.

BACKGROUND: In shoulders with traumatic anterior instability, a bipolar bone defect has been recognized as an important indicator of the prognosis. PURPOSE: To investigate bipolar bone defects at primary instability and compare the difference between dislocation and subluxation. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: There were 156 shoulders (156 patients) including 91 shoulders with dislocation and 65 shoulders with subluxation. Glenoid defects and Hill-Sachs lesions were classified into 5 size categories on 3-dimensional computed tomography (CT) scans and were allocated scores ranging from 0 (no defect) to 4 points (very large defect). To assess the combined size of the glenoid defect and Hill-Sachs lesion, the scores for both lesions were summed (range, 0-8 points). Patients in the dislocation and subluxation groups were compared regarding the prevalence of a glenoid defect, a bone fragment of bony Bankart lesion, a Hill-Sachs lesion, a bipolar bone defect, and an off-track Hill-Sachs lesion. Then, the combined size of the bipolar bone defects was compared between the dislocation and subluxation groups and among patients stratified by age at the time of CT scanning (<20, 20-29, and ≥30 years). RESULTS: Hill-Sachs lesions were observed more frequently in the dislocation group (75.8%) compared with the subluxation group (27.7%; P < .001), whereas the prevalence of glenoid defects was not significantly different between groups (36.3% vs 29.2%, respectively; P = .393). The combined defect size was significantly larger in the dislocation versus subluxation group (mean ± SD combined defect score, 2.1 ± 1.6 vs 0.8 ± 0.9 points, respectively; P < .001) due to a larger Hill-Sachs lesion at dislocation than subluxation (glenoid defect score, 0.5 ± 0.9 vs 0.3 ± 0.6 points [P = .112]; Hill-Sachs lesion score, 1.6 ± 1.2 vs 0.4 ± 0.7 points [P < .001]). Combined defect size was larger in older patients than younger patients in the setting of dislocation (combined defect score, <20 years, 1.6 ± 1.2 points; 20-29 years, 1.9 ± 1.5 points; ≥30 years, 3.4 ± 1.6 points; P < .001) but was not different in the setting of subluxation (0.8 ± 1.0, 0.7 ± 0.9, and 0.8 ± 0.8 points, respectively; P = .885). An off-track Hill-Sachs lesion was observed in 2 older patients with dislocation but was not observed in shoulders with subluxation. CONCLUSION: The bipolar bone defect was significantly more frequent, and the combined size was greater in shoulders with primary dislocation and in older patients (≥30 years).

Three-dimensional kinematic features in large and massive rotator cuff tears with pseudoparesis.

BACKGROUND: Although massive rotator cuff tears occasionally lead to severe impairment of shoulder function, the criteria for losing the ability to elevate the arm are unclear. This study aimed to analyze the features of both tear size and 3-dimensional (3D) shoulder kinematics that correspond to the loss of the ability to elevate the arm in patients with large and massive rotator cuff tears. METHODS: We prospectively enrolled patients with rotator cuff tears, including the supraspinatus and more than half of the subscapularis or more than two-thirds of the infraspinatus, without severe pain. A total of 13 patients (15 shoulders) were divided into 2 groups: 9 shoulders in the pseudoparesis (P) group and 6 shoulders in the non-pseudoparesis (NP) group. Fluoroscopic images were collected during active scapular-plane elevation, and 3D shoulder kinematics was analyzed using 2-dimensional-3D registration techniques. The radiographic findings and 3D kinematic results were compared between the groups. The correlation between tear size and 3D kinematics was also investigated. RESULTS: The most superior position of the humeral head center was significantly higher in the P group (6.7 ± 3.0 mm in P group vs. 3.6 ± 1.3 mm in NP group, P = .0321). Superior migration, which was defined as the most superior position > 5 mm, was significantly more frequent in the P group (7 shoulders and 1 shoulder in the P and NP groups, respectively; P = .0201). Thoracohumeral external rotation was significantly smaller in the P group (16° ± 31° in P group vs. 91° ± 21° in NP group, P < .0001). The total tear size and the tear sizes of the anterior and posterior rotator cuffs were significantly correlated with the superior (r = 0.68, P = .0056), anterior (r = 0.68, P = .0058), and posterior (r = -0.80, P = .0004) positions of the humeral head center. The tear size of the posterior rotator cuff also tended to be correlated with glenohumeral external rotation (r = -0.48, P = .0719). CONCLUSION: Anterior and posterior rotator cuff tears cause significant superior and anteroposterior translations of the humeral head, and posterior cuff tears may lead to loss of glenohumeral external rotation. With these abnormal kinematics, superior migration and loss of thoracohumeral external rotation were identified as features of pseudoparesis.

Insufficient integrity of partial articular surface tendon avulsion lesions after arthroscopic trans-tendon repair: Comparison with integrity after arthroscopic repair after conversion to a full thickness tear.

BACKGROUND: For the surgical treatment of severe partial articular surface tendon avulsion (PASTA) lesions, 2 repair techniques, i.e., arthroscopic trans-tendon repair and arthroscopic repair after conversion to a full thickness tear, are widely used, and a satisfactory clinical outcome with both has been reported. The purpose of this study was to investigate integrity of the repaired rotator cuff based on second-look arthroscopy and to compare the above two repair techniques. METHODS: Thirty-seven shoulders underwent PASTA lesion repair arthroscopically, with 20 shoulders receiving second-look arthroscopy. According to the repair technique, the shoulders were divided into 2 groups, which were 10 shoulders with trans-tendon repair (group P) and 10 shoulders with repair after conversion to a full thickness tear (group C). Second-look arthroscopy was done at a minimum of 3 months after initial surgery, with the mean interval until second-look arthroscopy being 5.6 months (3-13) in group P and 5.1 months (3-9) in group C. The reasons for second-look arthroscopy were pain with contracture in 15 patients, as well as pain in 4 patients and muscle weakness at abduction in one patient. RESULTS: In group P, there was complete rotator cuff continuity in 3 shoulders, partial continuity in 4, and failure in 3, while group C had complete continuity in 8 shoulders, partial continuity in 1, and failure in 1. Adhesions of the subacromial bursa were seen in all shoulders, while contracture of the posterior capsule was noted in 5 shoulders from group P and 9 shoulders from group C, and contracture of the rotator interval was identified in 7 shoulders from group P and 9 shoulders from group C. CONCLUSIONS: Second-look arthroscopy revealed that the integrity of the rotator cuff after trans-tendon repair of severe PASTA lesions was often unsatisfactory in patients with symptomatic shoulder. On the other hand, complete continuity was seen in most shoulders underwent repair after conversion to a full thickness tear.

The glenohumeral micromotion and influence of the glenohumeral ligaments during axial rotation in varying abduction angle.

BACKGROUND: The patients with shoulder instability or disorders in overhead athletes have been considered to have an abnormal micromotion at the glenohumeral joint. However, the normal range of the micromotion has not been available during axial rotation with various abduction angles, especially above 90° abduction. This study aimed to investigate the glenohumeral translation and influence of the glenohumeral ligaments during axial rotation with up to maximum abduction. METHODS: Fourteen healthy volunteers performed active axial rotations at 0°, 90°, 135°, and maximal abduction angles. The positions of the humeral head center relative to the glenoid at maximally external, neutral, and maximally internal rotations (ER, NR, IR, respectively) for each abduction angle were evaluated using two- (2D) and three-dimensional (3D) shape matching registration techniques. The shortest pathway and its length between the origin and insertion of the superior, middle, and inferior glenohumeral ligaments (SGHL, MGHL, and IGHL, respectively) were calculated for each position. RESULTS: The glenohumeral joint showed 3.1 mm of superoinferior translation during axial rotation at 0° abduction (P < 0.0001), and 2.6 mm and 4.5 mm anteroposterior translation at 135° and maximal abduction (P < 0.0001), respectively. The SGHL and MGHL reached a maximum length at ER with 0° abduction, and the anterior and posterior bands of the IGHL reached a maximum at ER with 90° abduction and IR with 0° abduction. CONCLUSIONS: These findings indicated that the SGHL played a role as an inferior suppressor at 0° abduction, while the anterior band of IGHL played a role as an anterior stabilizer at 90° abduction. Every glenohumeral ligament did not get taut and the anteroposterior translation became greater with increasing abduction angle, above 90°. These results could be used as a reference when comparing with the pathological shoulders in the future study.

Changes of Bipolar Bone Defect Size After Arthroscopic Bankart Repair for Traumatic Anterior Shoulder Instability: Evaluation Using a Scoring System and Influence on Postoperative Recurrence.

BACKGROUND: The combination of a glenoid defect and a Hill-Sachs lesion in shoulders with traumatic anterior instability has been termed bipolar bone loss, and the preoperative size of these lesions has been reported to influence postoperative recurrence of instability after arthroscopic Bankart repair. PURPOSE: To investigate the influence of postoperative bipolar bone defect size on postoperative recurrence of instability. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A total of 64 male collision/contact athletes (69 shoulders) were evaluated for a minimum of 2 years after surgery, and the pre- and postoperative sizes of both lesions (glenoid defect and Hill-Sachs) were evaluated retrospectively with 3-dimensional computed tomography. The sports played by the athletes included rugby (n = 28 shoulders), American football (n = 24 shoulders), and other collision/contact sports (n = 17 shoulders). Glenoid defects and Hill-Sachs lesions were classified into 5 size categories and assigned scores from 0 (no defect) to 4 (very large defect). Patients were then classified according to the total score (sum of the scores for both lesions). The influence of pre- and postoperative bipolar bone defect sizes on recurrence of instability was investigated by using the total scores for bipolar bone defects. The influence of postoperative glenoid morphology (normal preoperative glenoid, preoperative glenoid erosion, bone union after arthroscopic bony Bankart repair [ABBR], or nonunion after ABBR) was also investigated, as well as changes in shoulders with a preoperative off-track Hill-Sachs lesion. RESULTS: Of 69 shoulders, 15 (21.7%) developed recurrent instability after surgery. The postoperative recurrence rate was 0% in shoulders with a total score ≤1, while the recurrence rate was consistently higher in shoulders with a total score ≥2 at both pre- and postoperative evaluation (mean, 28.8% and 32.6%, respectively). Postoperative recurrence was uncommon when there was a normal preoperative glenoid or bone union after ABBR, while it was frequent in shoulders with preoperative glenoid erosion or shoulders with nonunion after ABBR and a total score ≥2. An off-track lesion was recognized in 9 shoulders preoperatively. It was transformed to on-track lesions in 4 of the 5 shoulders showing bone union after ABBR, and there was no recurrence in the 5 shoulders with bone union. In contrast, postoperative recurrence of instability occurred in 3 of the 4 shoulders without bone union. CONCLUSION: Postoperative recurrence was influenced by the pre- and postoperative size of bipolar bone defects. Recurrence was uncommon if bone union was achieved after ABBR, even if there had been an off-track lesion preoperatively.

Three-Dimensional Corrective Osteotomy for Malunited Fractures of the Upper Extremity Using Patient-Matched Instruments: A Prospective, Multicenter, Open-Label, Single-Arm Trial.

BACKGROUND: Medical image processing has facilitated simulation of 3-dimensional (3-D) corrective osteotomy, and 3-D rapid prototyping technology has further enabled the manufacturing of patient-matched surgical guides and implants (patient-matched instruments, or PMIs). However, 3-D corrective osteotomy using these technologies has not been the standard procedure. We aimed to prospectively verify the efficacy and safety of PMIs in corrective osteotomy for deformities of the upper extremity. METHODS: We enrolled 16 patients with a total of 17 bone deformities in the upper extremity. Eight patients had distal radial malunion; 5, distal humeral malunion; and 3, forearm diaphyseal malunion. All cases underwent 3-D corrective osteotomy with PMIs. The primary end point was the residual maximum deformity angle (MDA), which was calculated from 2 deformity angles-1 on the anteroposterior and 1 on the lateral postoperative radiograph. Secondary end points included the deformity angle on radiographs, 3-D error between the preoperative planning model and the postoperative result, range of motion, grip strength, pain measured with a visual analog scale (VAS), patient satisfaction, and Disabilities of the Arm, Shoulder and Hand (DASH) score. RESULTS: The average MDA significantly improved from 25.5° preoperatively to 3.3° at the final follow-up (p < 0.001). The angular deformity was within 5° in all cases, except for 1 with distal radial malunion who had a higher angle on the anteroposterior radiograph. The error between the correction seen on the postoperative 3-D bone model and the planned correction was <1° and <1 mm. Flexion and extension of the wrist and pronation of the forearm of the patients treated for distal radial malunion improved significantly, and pronation improved for those treated for forearm diaphyseal malunion. The average VAS score, grip strength, and DASH score significantly improved as well. Of the 16 patients, 15 were very satisfied or satisfied with the outcomes. CONCLUSIONS: Corrective osteotomy using PMIs achieved accurate correction and good functional recovery in the upper extremity. Although our study was limited to cases without any deformity on the contralateral side, 3-D corrective osteotomy using PMIs resolved treatment challenges for complex deformities in upper extremities. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Influence of humeral abduction angle on axial rotation and contact area at the glenohumeral joint.

BACKGROUND: Although the elevation angle of the arm affects the range of rotation, it has not been evaluated up to the maximal abduction angle. In this study we conducted an evaluation up to maximal abduction and determined the contact patterns at the glenohumeral (GH) joint. METHODS: Fourteen healthy volunteers (12 men and 2 women; mean age, 26.9 years) with normal shoulders (14 right and 8 left) were instructed to rotate their shoulders at 0°, 90°, 135°, and maximal abduction for each shoulder at a time. Using 2-dimensional and 3-dimensional single-plane image registration, the internal rotation (IR), external rotation (ER), and range of motion (ROM; ie, axial rotations) at the thoracohumeral (TH) and GH joints, and the contribution ratio (%ROM = GH-ROM/TH-ROM) were calculated for each abduction. The glenoid position with respect to the humeral head was also analyzed. RESULTS: The TH-IR and TH-ER shifted toward an ER with increasing abduction angle, whereas the TH-ROM significantly decreased except at abduction between 0° and 90° (P < .001). The GH-IR and GH-ROM significantly decreased except at abduction between 0° and 90° (P < .001), but the GH-ER remained constant regardless of the abduction. The contribution ratio exceeded 80% for every abduction angle. The glenoid moved on the central and posterior areas of the humeral head at 0° and 90° abduction, respectively, and on the posterosuperior and anterosuperior areas at 135° and maximal abduction, respectively. CONCLUSION: Our results provide new knowledge about wide axial rotation up to maximal abduction and constant GH-ER at any abduction.

Directional bias of soft-tissue artifacts on the acromion during recording of 3D scapular kinematics.

Scapular kinematics during sports performances can be recorded using skin-mounted trackers attached to the skin overlying the acromion for continuous data collection without restricting natural motions of the subject relative to medical imaging analyses limiting its use for wide-range or high-speed motions. This study aimed to describe the existence of a directional bias in the translational and rotational errors of skin-mounted trackers using a 3D magnetic resonance imaging (3D-MRI) protocol. 3D-MRI scans of the healthy right shoulders of 19 males were acquired in 12 arm positions. The relative transformation of the scapular configuration determined to be the measurement error, as recorded by the configuration of the small cuboid imitating a skin-mounted tracker relative to the actual scapular configuration measured by the voxel-based registration. These measurement errors were expressed with either positive or negative values to describe the bias. Overall translational errors in the lateral, anterior, and superior directions were 3.7 ±â€¯8.4 mm, 9.5 ±â€¯6.4 mm, and 6.2 ±â€¯4.6 mm, respectively. Overall rotational errors in protraction, upward rotation, and posterior tilt were 7.8 ±â€¯8.4°, 0.2 ±â€¯7.4°, and - 4.0 ±â€¯7.5°, respectively. The skin-mounted tracker displayed a high probability of displacement in antero-superior (93% and 91%) directions and rotates in a protracting manner (82%) relative to the position of the underlying bone with the gradual nature of its change. The existence of the directional bias with its gradual change suggests a statistical predictability in measurement errors, which can be used to predict accurate scapular translation and rotation.

Influence of posterior capsular tightness on throwing shoulder injury.

PURPOSE: The role of posterior capsular tightness in throwing shoulder injury has not yet been clarified. Accordingly, the influence of posterior capsular tightness on the occurrence of throwing shoulder injury was investigated. METHODS: Sixty-one shoulders with throwing injury were retrospectively reviewed, including 50 tight shoulders and 11 non-tight shoulders. Occurrence of long head of biceps (LHB) lesions, superior glenohumeral ligament (SGHL) and middle glenohumeral ligament (MGHL) injuries, type 2 SLAP lesions, and supraspinatus and subscapularis tendon injuries was compared between the tight and non-tight groups. RESULTS: There were LHB lesions in 8 tight shoulders and 6 non-tight shoulders, SGHL injury in 14 and 8 shoulders, and subscapularis tendon injury in 6 and 5 shoulders, respectively, showing significant differences between tight and non-tight shoulders. In contrast, MGHL injury, type 2 SLAP lesions, and supraspinatus tendon injury showed no significant differences. The SLAP lesion was located anteriorly in 6 tight shoulders, posteriorly in 5, and combined in 4 versus 0, 3, and 0 for the non-tight shoulders, respectively, so anterior SLAP lesions only occurred in tight shoulders. Similarly, anterior supraspinatus tendon injuries had a higher incidence in tight shoulders than in non-tight shoulders (19 vs 3). CONCLUSIONS: Rotator interval lesions were frequent in non-tight shoulders, while anterior SLAP lesions and anterior supraspinatus tendon injuries were predominant in tight shoulders. The significance of posterior capsular tightness should be reconsidered. LEVEL OF EVIDENCE: Retrospective, Level IV.

In vivo three-dimensional evaluation of the functional length of glenohumeral ligaments.

BACKGROUND: Glenohumeral ligaments play an important role in stabilizing the shoulder. However, it is impossible to know how they function in vivo during shoulder motion. To help elucidate this stabilizing role, we studied the in vivo three-dimensional kinematics of the normal shoulder joint using a markerless bone-registration technique. METHODS: Our technique utilized image registration to determine corresponding relations between several image volumes represented at different coordinates. Magnetic resonance images of 14 shoulder joints of seven healthy volunteers were acquired for seven isometric abduction orientations between 0 degrees and 180 degrees . We then calculated three-dimensional shortest path between the origin and insertion of each ligament based on anatomical study in each abduction orientation. FINDINGS: At 0 degrees of abduction, the posterior band of the coracohumeral ligament displayed the maximum length. At 30 degrees of abduction, the superior glenohumeral ligament displayed the maximum length. At 60 degrees of abduction, the anterior band of the coracohumeral ligament and the middle glenohumeral ligament displayed the maximum length. At 120 degrees of abduction, the anterior band of the inferior glenohumeral ligament displayed the maximum length. INTERPRETATION: Based on progressive abduction of the arm, each ligament had different pattern in change of length. At different arm orientation of abduction, each ligament displayed the maximum length. We think that each ligament might play an important role in stabilizing the shoulder at different arm orientation.

The mode of destruction in shoulders with rheumatoid arthritis based on radiographic findings.

The objective of the present study was to elucidate the mode of rheumatoid arthritis shoulder destruction. The study included 402 shoulders from 201 patients with rheumatoid arthritis. Plain radiographic findings were used to assess and statistically analyze the severity of the glenohumeral joint destruction (GHD) and greater tuberosity destruction (GTD). For both GHD and GTD scores, a statistically significant correlation was found between the left and right sides and also between the GHD and GTD scores within the same shoulder. However, 97 shoulders of 67 patients showed a heterogeneous pattern. An interesting finding was that no patients showed a combination of the GHD type plus the GTD type. Shoulders with rheumatoid arthritis showed statistically significant symmetry and uniform destruction. Even if they showed heterogeneous destruction, there were no cases of a different pattern of heterogeneity on the opposite side. The mode of destruction was not always definite, however.

Three-dimensional clavicular and acromioclavicular rotations during arm abduction using vertically open MRI.

There have been several reports about the clavicular and acromioclavicular motion, but a precise motion has been unknown. The purpose of this study was to analyze the 3D kinematics of the clavicle and acromioclavicular joint during arm abduction, using 3D MR images obtained by a vertically open MRI. Seven subjects participated in this investigation, which included 14 shoulders. From a seated position, we obtained MR images of their shoulder in seven abducted positions of the arm in the coronal plane. We evaluated the 3D movements of each bone in the shoulder using the volume-based registration technique, and analyzed the clavicular positions relative to the lung and the scapular positions relative to the clavicle. During arm abduction, the clavicular motion relative to the lung showed 30.6 degrees retraction, 7.3 degrees elevation, and 33.2 degrees posterior axial rotation. During arm abduction, the scapular motion relative to the clavicle showed 15.6 degrees protraction, 21.5 degrees upward rotation, and 22.2 degrees posterior tilting. This study succeeded in describing the 3D clavicular and acromioclavicular motion including the axial rotation of the clavicle, and it revealed that both motions had large degrees of rotations.

The three-dimensional motions of glenohumeral joint under semi-loaded condition during arm abduction using vertically open MRI.

BACKGROUND: Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bones. It also provides 3D coordinate values. The purpose of the present study was to visualize and quantify the 3D positions of the glenohumeral joint during isometric abduction of the arm using vertically open magnetic resonance imaging. METHODS: We examined 14 shoulders of seven healthy volunteers. Magnetic resonance images were obtained in a seated position and in seven static positions of the arm from 0 degrees to maximum abduction using vertically open magnetic resonance imaging. 3D surface models were created and 3D movements of each bone in the glenohumeral joint were calculated using a computer algorithm. We analyzed the translation and contact pattern of the glenohumeral joint. FINDINGS: In supero-inferior direction, the humeral head translated slight inferiorly from +1.9 (SD 1.0) mm at 0 degrees to +0.8 (SD 1.8) mm at the maximum abduction. In antero-posterior direction, the humeral head translated anteriorly from 0 degrees to 90 degrees (mean +2.4, SD 2.6 mm) and posteriorly from 90 degrees to 150 degrees of abduction (mean -1.4, SD 2.7 mm). Furthermore, the humeral head had a unique contact patterns with the glenoid; the contact part of the humeral head with the glenoid changed from the central part to the posterior in the midrange of abduction. INTERPRETATION: The humeral head showed a small translation in the antero-posterior direction between 90 degrees and 150 degrees of abduction. In addition, the posterior part of the humeral head contacted the glenoid in this range of abduction. These findings of motion patterns in asymptomatic subjects will be necessary when comparing the kinematics with pathologic condition such as the glenohumeral instability and rotator cuff tear.

3D kinematic analysis of the acromioclavicular joint during arm abduction using vertically open MRI.

Many researchers have evaluated the motions of the shoulder girdle, especially scapular and humeral motion. However, few reports exist that describe motions of the acromioclavicular joint. The purpose of the present study was to analyze the 3D kinematics of the acromioclavicular joint during arm abduction using 3D MR images obtained by a vertically open MRI. Fourteen shoulders of seven volunteers were examined in seven static positions from 0 degrees to the maximum abduction in a seated position. 3D surface models of the clavicle and scapula were created, and the movements of the acromioclavicular joint from 0 degrees to each position were calculated using the volume-based registration technique. From these calculations, the translations were evaluated and the rotational motions were analyzed using the concept of the screw axis. In the anteroposterior direction, the clavicle translated most posteriorly (-1.9 +/- 1.3 mm) at 90 degrees of abduction and most anteriorly (1.6 +/- 2.7 mm) at maximum abduction. In the superoinferior direction, the clavicle translated slightly superiorly (0.9 +/- 1.9 mm). When analyzing relative motion of the scapula with respect to the clavicle, the scapula generally rotated about a specific screw axis passing through the insertions of both the acromioclavicular and the coracoclavicular ligaments on the coracoid process. The average rotation was 34.9 +/- 8.4 degrees.