Anteroposterior centering of the humeral head on the glenoid in vivo

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.

Multidirectional instability of the shoulder: biomechanics, clinical presentation, and treatment strategies

Multidirectional instability (MDI) of the shoulder is a condition where the dislocation occurs in more than one direction with minimal or no causative trauma. Its pathoanatomy is complex and characterized by a redundant capsule, resulting in increased glenohumeral joint volume. The fact that several further factors may contribute to symptom onset complicates the diagnosis and hampers the identification of a therapeutic approach suitable for all cases. There is general agreement that the initial treatment should be conservative and that surgery should be reserved for patients who have not responded to an ad hoc rehabilitation program. We review the biomechanics, clinical presentation, and treatment strategies of shoulder MDI.

Glenohumeral relationships at different angles of abduction

PURPOSE

The objective of this study was to clarify the relationships among anatomical landmarks of the glenohumeral joint at different angles of abduction.

METHODS

Fifteen volunteers (ten men, five women; mean age 29 years) were enrolled in this study. Images of externally and internally rotated positions at 45°, 90°, and 135° of abduction in the plane 30° anterior to the trunk were taken using an open magnetic resonance imaging system. Landmarks including the glenoidal long axis with its center, bicipital groove, center of the head, and humeral shaft axis were determined. Using a line set on the surface of the head in the plane parallel to the humeral axis (including the head center and bicipital groove with its parallel and perpendicular lines), the glenoid location and rotational relationships were investigated in each position.

RESULTS

The average angles of axial rotation were 48° ± 27° at 45º of abduction, 71° ± 20° at 90° of abduction, and 40° ± 27° at 135° of abduction. The trajectories of the glenoid center primarily extended over the anterior portion of the humeral head at 45° of abduction and over the posterior portion at 90° of abduction, while those at 135° of abduction were localized on a small upper portion of the head.

CONCLUSIONS

The glenohumeral relationships demonstrated that arm abduction might influence shoulder function through its effects on the portion of the humeral surface in contact with the glenoid during rotation and the resultant changes in the glenohumeral relationships.

Determination of a reference system for the three-dimensional study of the glenohumeral relationship

OBJECTIVE

Knowledge of the normal and pathological three-dimensional glenohumeral relationship is imperative when planning and performing a total shoulder arthroplasty. There is, however, no consensus on which references should be used when studying this relationship. The purpose of the present study was to define the most suitable glenoid plane with normally distributed parameters, narrowest variability, and best reproducibility.

MATERIALS AND METHODS

Three-dimensional reconstruction CT scans were performed on 152 healthy shoulders. Four glenoid planes, each determined by three surgically accessible bony reference points, were determined. Two planes were triangular, with the same base defined by the most anterior and posterior point of the glenoid. The most inferior and the most superior point of the glenoid, respectively, define the top of Saller's inferior plane and the Saller's superior plane. The two other planes are formed by best-fitting circles. The circular max plane is defined by the superior tubercle, and two points at the distal third of the glenoid. The circular inferior plane is defined by three points at the rim of the inferior quadrants of the glenoid.

RESULTS

The parameters of all four planes behave normally. The humeral center of rotation is identically positioned for both the circular max and circular inferior plane (X = 91.71°/X = 91.66° p = 0.907 and Y = 90.83°/Y = 91.7° p = 0.054, respectively) and different for the Saller's inferior and Saller's superior plane (p ≤ 0.001). The circular inferior plane has the lowest variability to the coronal scapular plane (p < 0.001).

CONCLUSIONS

This study provides arguments to use the circular inferior glenoid plane as preferred reference plane of the glenoid.

Change in labrum height after arthroscopic Bankart repair: correlation with preoperative tissue quality and clinical outcome

HYPOTHESIS

Arthroscopic factors, such as labral and capsular tissue quality or anterior labral periosteal sleeve avulsion (ALPSA) lesion, affect postoperative labral height stability. Labral height stability has a correlation with clinical outcome.

METHODS

The study included 40 patients who underwent arthroscopic surgery for a Bankart lesion between August 2005 and May 2009. The mean follow-up and patient age were 29.1 ± 10.9 months (range, 15-60 months) and 24.7 ± 8.4 years (range, 12-55 years), respectively. Labral and capsular tissue quality, ALPSA lesions, Hill-Sachs lesions, glenoid erosion, and superior labrum anterior-posterior tears were identified by arthroscopic examination. Stepwise postoperative computed tomography arthrography to estimate the labral height was performed at 3 months and 1 year.

RESULTS

Correlation of postoperative 1 year Rowe scores with labral height maintenance was statistically significant (P < .01). Correlation of Rowe scores at 1 year postoperatively with labral height at 1 year postoperatively was also statistically significant (P < .01). The mean postoperative labral height at 3 months and at 1 year was 5.13 ± 1.56 mm (range, 2.9-8.8 mm) and 4.69 ± 1.75 mm (range, 1.6-8.5 mm), respectively (P < .01). The decrease in labral height at 1 year after surgery was significant in those patients with ALPSA lesions, Hill-Sachs lesions, and a poor labrum along with a poor capsule (P < .01).

CONCLUSIONS

The patients with less labral height decrease between 3 months and 1 year or higher labral height at 1 year postoperatively showed higher Rowe scores at 1 year postoperatively. Shoulders with ALPSA lesions, Hill-Sachs lesions, and a poor labrum with poor capsular tissue quality correlated more strongly with postoperative labral height decrease.

In-vivo glenohumeral translation and ligament elongation during abduction and abduction with internal and external rotation

Study Design

Basic Science. To investigate humeral head translations and glenohumeral ligament elongation with a dual fluoroscopic imaging system.

Background

The glenohumeral ligaments are partially responsible for restraining the humeral head during the extremes of shoulder motion. However, in-vivo glenohumeral ligaments elongation patterns have yet to be determined. Therefore, the objectives of this study were to 1) quantify the in-vivo humeral head translations and glenohumeral ligament elongations during functional shoulder positions, 2) compare the inferred glenohumeral ligament functions with previous literature and 3) create a baseline data of healthy adult shoulder glenohumeral ligament lengths as controls for future studies.

Methods

Five healthy adult shoulders were studied with a validated dual fluoroscopic imaging system (DFIS) and MR imaging technique. Humeral head translations and the superior, middle and inferior glenohumeral ligaments (SGHL, MGHL, IGHL) elongations were determined.

Results

The humeral head center on average translated in a range of 6.0mm in the anterior-posterior direction and 2.5mm in the superior-inferior direction. The MGHL showed greater elongation over a broader range of shoulder motion than the SGHL. The anterior-band (AB)-IGHL showed maximum elongation at 90° abduction with maximum external rotation. The posterior-band (PB)-IGHL showed maximum elongation at 90° abduction with maximum internal rotation.

Discussion

The results demonstrated that the humeral head translated statistically more in the anterior-posterior direction than the superior-inferior direction (p = 0.01), which supports the concept that glenohumeral kinematics are not ball-in-socket mechanics. The AB-IGHL elongation pattern makes it an important static structure to restrain anterior subluxation of the humeral head during the externally rotated cocking phase of throwing motion. These data suggest that in healthy adult shoulders the ligamentous structures of the glenohumeral joint are not fully elongated in many shoulder positions, but function as restraints at the extremes of glenohumeral motion. Clinically, these results may be helpful in restoring ligament anatomy during the treatment of anterior instability of the shoulder.

Acromioclavicular joint pain in patients with adhesive capsulitis: a prospective outcome study

Diagnosis of adhesive capsulitis is a clinical diagnosis based on history and physical examination. Afflicted patients exhibit active and passive loss of motion in all planes and a positive capsular stretch sign. The effect of adhesive capsulitis on acromioclavicular biomechanics leading to tenderness has not been documented in the literature. This study reports on the incidence of acromioclavicular tenderness in the presence of adhesive capsulitis. Furthermore, we note the natural history of such acromioclavicular joint pain in relation to that of adhesive capsulitis. Over a 2-year period (2005-2007), 84 patients undergoing initial evaluation for adhesive capsulitis were prospectively examined with the use of validated outcome measures and physical examination. Acromioclavicular joint tenderness results were compared and analyzed on initial evaluation and final follow-up of at least 1 year. Forty-eight patients (57%) with adhesive capsulitis had acromioclavicular joint pain on examination. At final follow-up, as range of motion improved, a significant increase in American Shoulder and Elbow Surgeons/Penn shoulder score and decrease in number of patients with acromioclavicular pain was noted with only 6 patients with residual pain (P<.05). In the presence of adhesive capsulitis, there is not only compensatory scapulothoracic motion but also acromioclavicular motion. This often results in transient symptoms at the acromioclavicular joint, which abate as the frozen shoulder resolves and glenohumeral motion improves. This is important to recognize to avoid unnecessary invasive treatment of the acromioclavicular joint when the patient presents with adhesive capsulitis.

A reproducible and practical method for documenting the position of the humeral head center relative to the scapula on standardized plain radiographs

BACKGROUND

Recent articles in this journal showed the clinical importance of the position of the humeral head center in relation to the glenoid. However, the precision, reproducibility, and sensitivity of this and other methods of documenting the head center position have not been evaluated in detail.

MATERIALS AND METHODS

We used templates to fit a coordinate system to the scapular anatomy visible on standardized radiographs. Two observers then used these templates to measure the position of the head center relative to this coordinate system on 25 normal shoulder radiographs and on 25 radiographs of shoulders with cuff tear arthropathy (CTA).

RESULTS

Head center measurements had excellent precision. Normal shoulder radiographs showed a consistent head center position (0.7 ± 1.7 mm medial and 0.6 ± 1.3 mm inferior to the coordinate origin on the anteroposterior view and 0.1 ± 1.3 mm medial and 0.0 ± 1.3 mm anterior to the coordinate origin on the axillary view). The head center of CTA shoulder radiographs was 10.18 ± 5.16 mm above the coordinate origin on the anteroposterior view, significantly different from that for the normal shoulder radiographs (P < .001).

DISCUSSION

The relative position of the humeral head center to the scapula determines the resting length and the moment arms of the scapulohumeral muscles. Correlation of shoulder function with the head center position may provide insights into both shoulder pathomechanics and the optimization of shoulder arthroplasty.

CONCLUSION

This practical technique showed a high degree of precision and reproducibility for normal and CTA shoulder radiographs as well as a high level of discrimination between these two groups.

Hill-Sachs defects and repair using osteoarticular allograft transplantation: biomechanical analysis using a joint compression model

BACKGROUND

Humeral head defects have been associated with failed anterior shoulder instability repairs. Quantitative data are required to determine (1) the critical defect size for consideration of surgical repair and (2) the ability of proposed repair techniques to restore normal joint function.

HYPOTHESES

Increasing defect size will decrease stability and anterior translation before dislocation. Stability will decrease in shoulder positions where the defect is oriented in line with the anterior glenoid. Osteoarticular repair will restore joint stability to intact shoulder level.

STUDY DESIGN

Controlled laboratory study. Methods A robotic/universal force-moment sensor testing system was used to apply joint compression (22 N) and an anterior load (40 N) to cadaveric shoulders (n = 9) with all soft tissues removed (intact) at joint orientations with 60 degrees of glenohumeral abduction and 0 degrees and 60 degrees of external rotation. Four posterolateral osteoarticular defects were created (12.5%, 25.0%, 37.5%, and 50.0% defect) followed by an osteoarticular allograft transplantation (repair). The loading protocol was repeated in each shoulder state for both joint orientations. The anterior translation and stability ratio (anterior load/compressive load) were recorded before dislocation.

RESULTS

All shoulders dislocated at 60 degrees of external rotation with all sizes of defects. At 0 degrees of external rotation, shoulders with the 12.5% to 37.5% defects did not dislocate, and only 2 shoulders with the 50.0% defect dislocated. At 60 degrees of external rotation, the 25.0% defect and 37.5% defect had significantly less anterior translation before dislocation, as compared with the intact (P < .05), both of which became similar to the intact after repair (P > .05). The stability ratio at 60 degrees of external rotation significantly decreased in the 25.0% and 37.5% defects, as compared with the intact (P < .05), representing a 25% and 40% decrease in stability ratio. The stability ratio became similar to intact after repair (P > .05).

CONCLUSION

The size and orientation of the defect has important contributions to glenohumeral joint function. Increasing defect size required less anterior translation before dislocation and decreased the stability ratio, thereby increasing the risk of recurrent instability.

CLINICAL RELEVANCE

Defects as small as 12.5% of the humeral head have biomechanical consequences that may affect joint stability. In addition, shoulders with large osteoarticular defects (37.5% or 50.0%) may benefit from osteoarticular allograft transplantation to restore shoulder stability.

Internal and external rotation of the shoulder: effects of plane, end-range determination, and scapular motion

The purpose of this study was to determine whether plane, end-range determination, or scapular motion affects shoulder range-of-motion measurements. In 16 healthy subjects, instrumentation with a magnetic tracking device was used to measure shoulder internal and external range of motion. The arm was supported while it was rotated either actively or passively with a measured torque. There was a significant main effect of plane for internal rotation (P < .001) but not for external rotation (P = .584). Passive humerothoracic motion was significantly greater than active humerothoracic motion for internal rotation (P < .006) and external rotation (P < .01). Active and passive humerothoracic motion was significantly greater than active and passive glenohumeral motion in 6 of the 7 active conditions and all 7 passive conditions (P < .002). Our results suggest that significant amounts of scapulothoracic motion may impact measurements of isolated glenohumeral joint motion.

Multidirectional kinematics of the glenohumeral joint during simulated simple translation tests: impact on clinical diagnoses

At the end ranges of motion, the glenohumeral capsule limits translation of the humeral head in multiple directions. Since the 6-degree of freedom kinematics of clinical tests are commonly utilized to diagnose shoulder injuries, the objective of this study was to determine the magnitude and repeatability of glenohumeral joint kinematics during a simulated simple anteroposterior translation test in the anterior and posterior directions. A magnetic tracking system was used to determine the kinematics of the humerus with respect to the scapula in eight cadaveric shoulders. At 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension, a clinician applied anterior and posterior loads to the humerus at 0 degrees, 30 degrees, and 60 degrees of external rotation until a manual maximum (simulating a simple translation test) was achieved. Prior to each test, the reference position of the humerus shifted posteriorly 1.8+/-2.0 and 4.1+/-3.8 mm at 30 degrees and 60 degrees of external rotation, respectively. Anterior translation decreased significantly (p < 0.05) from 18.2+/-5.3 mm at 0 degrees of external rotation to 15.5+/-5.1 and 9.9+/-5.5 mm at 30 degrees and 60 degrees, respectively. However, no significant differences were detected between the posterior translations of 13.4+/-6.4, 17.1+/-5.0, and 15.8+/-6.0 mm at 0 degrees, 30 degrees, and 60 degrees of external rotation, respectively. Coupled translations (perpendicular to the direction of loading) at 0 degrees (6.1+/-4.0 and 3.8+/-2.9 mm), 30 degrees (4.7+/-2.7 and 5.9+/-3.1 mm), and 60 degrees (2.3+/-2.3 and 5.0+/-3.5 mm) of external rotation were in the inferior direction in both the anterior and posterior directions, respectively. Based on the data obtained, performing a simulated simple translation test should result in coupled inferior translations and anterior translations that are a function of external rotation. The low standard deviations demonstrate that the observed translations should be repeatable. Furthermore, capsular stretching or injury to the anterior-inferior region of the capsule should be detectable during clinical examination if excessive coupled translations exist or no posterior shift of the reference position with external rotation is noted.

Excessive humeral external rotation results in increased shoulder laxity

BACKGROUND

The quantitative relationship between increased anterior shoulder laxity and increased humeral external rotation observed in throwers remains unclear.

HYPOTHESIS

An elongated anterior capsule, especially the anterior band of the inferior glenohumeral ligament, produced by excessive humeral external rotation will result in increased anterior shoulder laxity and increased humeral external rotation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven cadaveric shoulders were tested to measure the humeral rotational range of motion, glenohumeral translations, and length of the anterior band of the inferior glenohumeral ligament. Data were collected for the intact shoulders and after nondestructive stretching of 10%, 20%, and 30% beyond maximum humeral external rotation.

RESULTS

Nondestructive excessive external rotational stretching resulted in a significant increase in superior (30%, 3.3 mm) and inferior (30%, 2.3 mm) length of the anterior band of the inferior glenohumeral ligament, external rotation (30%, 35 degrees), and anterior (30%, 2.4 mm), inferior (30%, 2.2 mm), and anterior-posterior (30%, 5.1 mm) translations. There were significant positive linear correlations between the length of the anterior band of the inferior glenohumeral ligament, external rotation, and anterior translation.

CONCLUSIONS

Excessive humeral external rotation results in an elongation of the anterior band of the inferior glenohumeral ligament and an increase in anterior and inferior glenohumeral translations and humeral external rotation.

CLINICAL RELEVANCE

Repetitive excessive humeral external rotation observed in throwers may be one of the biomechanical causes for increased shoulder laxity and increased humeral external rotation.