Biomechanical tests for type II SLAP lesions of the shoulder joint before and after arthroscopic repair

Superior labral anterior-to-posterior (SLAP) lesions can cause shoulder pain partly by causing glenohumeral instability. The purpose of this study was to examine the effect of a simulated type II SLAP lesion and subsequent repair on glenohumeral translation of the vented shoulder. In eight cadaver joints, a robotic/UFS testing system was used to measure joint translation by applying an anterior, posterior, or inferior load of 50 N to each shoulder. The "apprehension tests" for anterior and posterior instability were simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm or a posterior load of 50 N with an internal rotation torque of 3 Nm. Each loading condition was applied at 30 degrees and 60 degrees of glenohumeral abduction with a constant joint compressive load (44 N) to the intact, simulated SLAP lesion, and repaired shoulder. Repair of the type II SLAP was then performed by placing a Suretac through the labrum both anterior and posterior to the biceps anchor and testing was repeated. ANOVA was used to compare translation of the intact joint, the joint after the type II SLAP lesion had been simulated, and after repair. At 30 degrees of abduction, anterior translation of the intact vented shoulder joint from anterior loading was 18.7+/-8.5 mm and increased to 26.2+/-6.5 mm after simulation of the type II SLAP lesion ( p< or =0.05). The arthroscopic repair did not restore anterior translation (23.9+/-8.6 mm) to the same degree as the intact joint ( p> or =0.05). At 60 degrees of abduction, anterior translation of 16.6+/-9.6mm in the intact joint was not significantly increased at 19.4+/-10.1 after simulation of the type II SLAP lesion ( p=0.0527). AP loading also resulted in inferior translation. At 30 degrees of abduction it was 3.8+/-4.0 mm in the intact joint and increased to 8.5+/-5.4 mm after the type II SLAP lesion ( p< or =0.05. After repair the inferior translation decreased significantly to 6.7+/-5.3 mm ( p< or =0.05). Although inferior translations were less at 60 degrees of abduction, results were similar to those at 30 degrees after repair. There were no significant increases in translation after SI/AP combined external rotation torque or posterior-anterior combined internal rotation torque loading.In this study the repair of a type II SLAP lesion only partially restored translations to the same degree as an intact vented shoulder joint. Therefore, improved repair techniques or an anteroinferior capsulolabral procedure in addition to the type II SLAP lesion repair might be needed to restore normal joint function.     

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.     

The function of passive stabilizers of the glenohumeral joint--a biomechanical study

In a biomechanical study we evaluated the passive stabilizing ligaments of 9 fresh shoulder specimens with mercury bands. While preparing the specimens we found two interesting entities: there are fibers of the coracohumeral ligament running from the humeral head to the coracoacromial ligament and there was an reproducible thickening in the posterior joint capsule. Functional evaluation shows that the coracohumeral ligament limits external rotation independently of the amount of abduction as well as inferior subluxation. The mediale glenohumeral ligament shows the highest tension in external rotation and 30 degrees abduction. The anterior inferior ligament strengthens the joint capsule in abduction and external rotation. The posterior inferior ligament shows the highest tension in abduction and internal rotation. CLINICAL RELEVANCE: Immobilization in internal rotation and adduction may lead to shortening of the coracohumeral ligament, which may result in severe limitation of external rotation and abduction. Resection of the coracoacromial ligament relaxes the coracohumeral ligament leading to an increased cranio-caudal instability. The posterior inferior ligament is complementary to the anterior inferior ligament thus stabilizing the shoulder joint in abduction and internal rotation. Sparing this structure in arthroscopy with dorsal portals and restoring in the case of a rupture seems to be of value for a normal joint function.     

Anterior-inferior capsular shift of the shoulder: a biomechanical comparison of glenoid-based versus humeral-based shift strategies

This study compared the biomechanical effects of an anterior-inferior capsular shift based at the humeral side with one on the glenoid side of the joint on resultant multidirectional glenohumeral translation and rotation. Nine matched pairs of fresh cadaveric shoulders were placed in a testing apparatus that constrained 3 rotations but allowed simultaneous free translation of the humeral head with respect to the glenoid. The right and left shoulders of each of the matched pairs were randomized to undergo either a glenoid-based or humeral-based anterior capsular shift. The shoulders were tested vented and following the capsular shift procedure. Translational testing was performed at 0 degrees, 45 degrees, and 90 degrees of glenohumeral elevation with the humerus in neutral rotation, 30 degrees internal rotation, and 30 degrees external rotation. Sequential loads of 30 N in anterior, posterior, and inferior directions were applied while maintaining a 22-N joint compressive load. The maximum arc of internal and external rotation after application of a 1-newton-meter moment was determined for the vented specimens and then after the capsular shift procedure. Both shift strategies resulted in significant limitation of anterior, posterior, and inferior translation in all of the tested positions. No significant differences were noted between the 2 shift strategies with respect to restriction of translation in the anterior or inferior directions. The glenoid-based shift caused a significantly greater decrease in posterior translation at 45 degrees and 90 degrees of abduction. With respect to rotation, the glenoid-based shift exerted significantly greater restriction on external rotation than the humeral-based shift. This study supports the use of either a humeral-based or glenoid-based shift to control multidirectional glenohumeral instability. Greater reduction in external rotation was demonstrated after the glenoid-based shift. Specific differences demonstrated in translation control for humeral-based versus glenoid-based capsular shift procedures may be useful in tailoring a procedure for specific instability patterns.     

Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavity-compression : an in vitro study.

BACKGROUND: Although the glenohumeral joint is the most mobile articulation of the human body, it is known to exhibit ball-and-socket kinematics. Compression into the glenoid labral concavity keeps the humeral head centered. The purpose of the present study was to determine the effects of joint position on glenohumeral stability through concavity-compression. METHODS: Ten cadaveric shoulders were tested. The glenoid was mounted horizontally onto a six-component load-cell while the humerus was clamped to a vertically unconstrained slide. An x-y stage translated the load-cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of 20, 40, and 60 N were applied. The tests were repeated in 0 degrees, 30 degrees, 60 degrees, and 90 degrees of glenohumeral abduction with and without the labrum. Relative translations between the glenoid and the humeral head and the forces resisting translation were recorded. Then the stability ratio, defined as the peak translational force divided by the applied compressive force, was calculated. RESULTS: The average stability ratio was higher in the hanging-arm position than it was in glenohumeral abduction. The highest stability ratio was detected in the inferior direction (59.8% 7.7%) when the labrum was intact and in the superior direction (53.3% 7.9%) when the labrum had been resected. Under both conditions, the anterior direction was associated with the lowest stability ratio (32.0% 4.4% with the labrum and 30.4% 4.1% without the labrum). Resection of the glenoid labrum resulted in an average decrease in the stability ratio of 9.6% 1.7%. With increasing compressive load, the average stability ratio slightly decreased. CONCLUSIONS: Glenohumeral stability through concavity-compression was greater in the hanging-arm position than it was in glenohumeral abduction. The average contribution of the labrum to glenohumeral stability through concavity-compression was approximately 10%, about one-half of the value previously reported. With the labrum intact, the glenohumeral joint was most stable in the inferior direction. Without the labrum, it was most stable in the superior direction. Under both conditions, it was least stable in the anterior direction. Glenohumeral joint stability through concavity-compression decreases with higher compressive loads.     

In situ force distribution in the glenohumeral joint capsule during anterior-posterior loading.

Our objective was to examine the function of the glenohumeral capsule and ligaments during application of an anterior-posterior load by directly measuring the in situ force distribution in these structures as well as the compliance of the joint. We hypothesized that interaction between different regions of the capsule due to its continuous nature results in a complex force distribution throughout the glenohumeral joint capsule. A robotic/universal force-moment sensor testing system was utilized to determine the force distribution in the glenohumeral capsule and ligaments of intact shoulder specimens and the joint kinematics resulting from the application of external loads at four abduction angles. Our results suggest that the glenohumeral capsule carries no force when the humeral head is centered in the glenoid with the humerus in anatomic rotation. However, once an anterior-posterior load is applied to the joint, the glenohumeral ligaments carry force (during anterior loading, the superior glenohumeral-coracohumeral ligaments carried 26+/-16 N at 0 degrees and the anterior band of the inferior glenohumeral ligament carried 30+/-21 N at 90 degrees). Therefore, the patient's ability to use the arm with the humerus in anatomic rotation should not be limited following repair procedures for shoulder instability because the repaired capsuloligamentous structures should not carry force during this motion. Separation of the capsule into its components revealed that forces are being transmitted between each region and that the glenohumeral ligaments do not act as traditional ligaments that carry a pure tensile force along their length. The interrelationship of the glenohumeral ligaments forms the biomechanical basis for the capsular shift procedure. The compliance of the joint under our loading conditions indicates that the passive properties of the capsule provide little resistance to motion of the humerus during 10 mm of anterior or posterior translation with anatomic humeral rotation. Finally, this knowledge also enhances the understanding of arm positioning relative to the portion of the glenohumeral capsule that limits translation during examination under anesthesia.     

The effect of radiofrequency thermal capsulorrhaphy on glenohumeral translation, rotation, and volume

The purpose of this study is to evaluate the effects of radiofrequency (RF) thermal capsulorrhaphy on the kinematic properties of the glenohumeral joint as determined by changes in resistance to multidirectional translational forces, alteration in the range of internal and external rotation, and changes in glenohumeral joint volume. Nonablative RF thermal energy was used to contract the glenohumeral joint capsule in 6 cadaveric shoulders. Measurements of translation were made after application of a 30-N load in anterior, posterior, and inferior directions. The maximum arc of internal and external rotation after application of a 1-N-m moment was also determined for vented specimens before and after thermal capsulorrhaphy. The percent reduction in glenohumeral capsular volume was measured by use of a saline solution injection-aspiration technique. Capsular shrinkage resulted in reductions in anterior, posterior, and inferior translation. The largest percent reductions in anterior translation were seen in external rotation at 45 degrees (48%, P <.05) and 90 degrees (41%, P <.05) abduction. For inferior translation, the largest percent reductions were seen in internal rotation at 45 degrees (40%, P <.05) and 90 degrees (45%, P <.05) abduction. Reductions in posterior translation were noted in internal rotation at 45 degrees (27%, P <.05) and 90 degrees (26%, P <.05) abduction. Other changes in translation were observed but were not statistically significant. The maximum arc of humeral rotation was reduced by a mean of 14 degrees at 45 degrees abduction and 9 degrees at 90 degrees abduction. The mean percent reduction in capsular volume for all shoulders was 37% (range, 8%-50%). This could not be correlated with percent reductions in translation and rotation. This study demonstrated the significant effect of RF thermal capsulorrhaphy in reducing glenohumeral multidirectional translation and volume with only a small loss of rotation in cadaveric shoulders.     

The influence of arthroscopic subscapularis tendon and anterior capsular release on glenohumeral translation: a biomechanical model

The effect of an arthroscopic release of the intraarticular portion of the subscapularis tendon and the anterior capsule on glenohumeral translation was investigated in a cadaveric model. Ten human cadaveric shoulders with a mean age of 63.5 years (range, 52-79 years) were tested in a robot-assisted shoulder simulator. Joint translation was measured before and after an arthroscopic release of the intraarticular portion of the subscapularis tendon and a subsequent release of the anterior capsule at 0 degrees , 30 degrees , 60 degrees , and 90 degrees of glenohumeral elevation. Translation was measured in the anterior, anterior-inferior, and inferior directions under 20 N of applied load. Testing of the specimen revealed that the release of the intraarticular portion of the subscapularis tendon and the anterior capsule increased translation in all directions. Significant increases in translation were observed after release of the intraarticular portion of the subscapularis tendon in the midrange of motion. The influence of the arthroscopic capsular release, in conjunction with the release of the subscapularis tendon, was very high above 60 degrees of elevation. The study indicates that the intraarticular component of the subscapularis tendon functions as a restraint to anterior-inferior translation primarily in the midrange of glenohumeral motion, whereas the anterior capsule adds anterior-inferior stability to the glenohumeral joint mainly above 60 degrees of elevation.     

Contact pressure and glenohumeral translation following subacromial decompression: how much is enough?

Subacromial decompression is a common surgical procedure that has historically included coracoacromial ligament resection. However, recent reports have advocated preserving the coracoacromial ligament to avoid the potential complication of anterosuperior escape. The optimal subacromial decompression would achieve a smooth coracoacromial arch and decreased rotator cuff contact pressures while preserving the function of the arch in glenohumeral stability. We hypothesized that a subacromial decompression with a limited acromioplasty with preservation of the coracoacromial ligament can decrease extrinsic pressure on the rotator cuff similar to a coracoacromial ligament resection, without altering glenohumeral translation. Three different subacromial decompressions, including a "smooth and move," a limited acromioplasty with coracoacromial ligament preservation, and a coracoacromial ligament resection, were performed on 6 cadaveric specimens with intact rotator cuffs. Glenohumeral translation and peak rotator cuff pressure during abduction were recorded. No change in translation was observed after a smooth and move or a limited acromioplasty. Compared to baseline specimens, anterosuperior translation was increased at 30° of abduction following coracoacromial ligament resection (P<.05). Baseline rotator cuff pressure was greatest during abduction with the arm in 30° of internal rotation. Peak rotator cuff pressure decreased up to 32% following a smooth and move, up to 64% following a limited acromioplasty, and up to 72% following a coracoacromial ligament resection. Based on the present study, a limited acromioplasty with coracoacromial ligament preservation may best provide decompression of the rotator cuff while avoiding potential anterosuperior glenohumeral translation.     

Glenohumeral translation after arthroscopic thermal capsuloplasty with a radiofrequency probe

The purpose of this study was to determine whether there are changes in anterior and posterior glenohumeral translation after arthroscopic thermal capsuloplasty with a radiofrequency probe. Anteriorly directed loads of 15 N and 20 N were sequentially applied to the humerus of each of 5 cadaveric glenohumeral joints, and anterior translation on the glenoid was measured through use of a customized translation apparatus and an electromagnetic tracking device. The tests were then repeated with posteriorly directed forces, and posterior translation was measured. During testing, the glenoid was rigidly fixed and the glenohumeral joint was positioned to simulate 90 degrees of shoulder abduction and 90 degrees of external rotation. By means of the radiofrequency probe, thermal energy was then applied to the anteroinferior capsuloligamentous structures; anterior and posterior translation measurements were repeated. The results showed a significant reduction in anterior and posterior translations after thermal capsuloplasty (P < .05). Anterior translation decreased from 6.8 to 4.0 mm (a 41% decrease) with the 15-N load and from 8.6 to 4.9 mm (a 42% decrease) with the 20-N load. Posterior translation decreased from 9.3 to 5.8 mm (a 36% decrease) with the 15-N load and from 10.4 to 6.5 mm (a 35% decrease) with the 20-N load. The results of this study indicate that the radiofrequency probe can be used to decrease both anterior and posterior glenohumeral translation in vitro. The biological effect on heat-treated tissues over time needs to be studied to prove that this is a satisfactory treatment for glenohumeral instability.     

Glenohumeral motion after complete capsular release.

The range of glenohumeral motion is primarily limited by the joint capsule. If the capsule is contracted, greater restriction in glenohumeral motion is exhibited. Release of a tight capsule has been an effective means of managing refractory stiffness of the glenohumeral joint. The effect of a complete capsular release on glenohumeral kinematics has not been previously studied in a cadaver model. Elevation, rotation, and translation of eight cadaveric glenohumeral preparations were studied before and after complete capsular release. As the intact joint was positioned near the limits of motion, glenohumeral torque rose rapidly with relatively small concomitant increases in elevation and rotational angles. Notable torque, due to tension in the capsule or cuff, ensued only after glenohumeral elevation reached approximately 80% of maximal range. After complete capsular release, maximal elevation increased on average 15%, yet retained definitive endpoints due to residual tension in the rotator cuff. Axial humeral rotation with an intact capsule decreased as maximum elevation approached, especially at elevation angles greater than 60 degrees. Maximum internal rotation was less than external, for all planes except +90 degrees. After complete capsular release, the greatest net gains for external rotation tended to be in the posterior scapular planes, whereas gains for internal rotation tended to be in the anterior scapular planes. Maximal translation in an intact vented capsule was 21 mm, 14 mm, and 15 mm in the anterior, posterior, and inferior directions, respectively. After complete capsular release, translation increased in all positions with maximal anterior, posterior, and inferior translations of 28 mm, 25 mm, and 28 mm, respectively. In general, relative gains in translation were greater in planes posterior to the scapula and at extremes of the range of motion. Although large glenohumeral translations were measured, no preparation could be dislocated before or after complete capsular release. Complete capsular release significantly increased glenohumeral range of motion and translation. The intact rotator cuff myotendinous units serves to limit the range of motion and translation after all capsuloligamentous attachments are rendered incompetent by complete capsular release.     

Effect of joint compression on inferior stability of the glenohumeral joint

To determine the relative importance of negative intraarticular pressure, capsular tension, and joint compression on inferior stability of the glenohumeral joint we studied 17 fresh, normal adult cadaver shoulders using a "3 degrees of freedom" shoulder test apparatus. Translations were measured in intact and vented shoulders while a 50-N superior and inferior directed force was applied to the shoulder. Three different joint compressive loads (22 N, 111 N, 222 N) were applied externally. Tests were performed in 3 positions of humeral abduction in the scapular plane (0 degree, 45 degrees, 90 degrees) and in 3 positions of rotation (neutral, maximal internal, and maximal external). After tests of the intact and vented shoulder, the glenohumeral ligaments were sectioned and tests were repeated. With minimal joint compression of 22 N, negative intraarticular pressure and capsular tension limited translation of the humeral head on the glenoid. Increasing the joint compressive load to 111 N resulted in a reduction of mean inferior translation from 11.0 mm to 2.0 mm at 0 degree abduction, from 21.5 mm to 1.4 mm at 45 degrees abduction, and from 4.5 mm to 1.2 mm at 90 degrees abduction. With a compressive load of 111 N, venting the capsule or sectioning of glenohumeral ligaments had no effect on inferior stability. Clinical relevance: Glenohumeral joint compression through muscle contraction provides stability against inferior translation of the humeral head, and this effect is more important than negative intraarticular pressure or ligament tension.     

The effect of articular malposition after total shoulder arthroplasty on glenohumeral translations, range of motion, and subacromial impingement

The articular surface of the normal humeral head has a variable posterior and medial offset with respect to the central axis of the humeral shaft. Recreation of the normal humeral head shaft offset is postulated to be an important consideration during shoulder arthroplasty. However, the effect of humeral head malposition is unknown. The purpose of this study was to determine the effect of articular malposition after total shoulder arthroplasty on glenohumeral translation, range of motion, and subacromial impingement. Twenty-one human cadavers were dissected and tested with the use of an active or passive shoulder model. Range of motion and translation were recorded by means of an electromagnetic tracking device. The experiment was performed in 2 phases. For kinematics study, 11 cadaver shoulders were positioned both passively and actively from maximum internal rotation to maximum external rotation at 90 degrees of total elevation in the scapular plane. Three rotator cuff and 3 deltoid muscle lines of action were simulated for active joint positioning. Passive joint positioning was accomplished with the use of a torque wrench and a nominal centering force. The testing protocol was used for the natural joint as well as for 9 prosthetic head locations: centered and 2- and 4-mm offsets in the anterior, posterior, inferior, and superior directions. Repeated-measures analysis of variance was used to test for significant differences in the range of motion and translation between active and passive positioning of the natural joint as well as all prosthetic head positions. (2) For impingement study, 10 cadaver shoulders were used in a passive model, loading the tendons of the rotator cuff with a 30-N centering force. The humerus was passively rotated from maximum internal rotation (1500 Nmm) to maximum external rotation (1500 Nmm) by means of a continuous-recording digital torque wrench. Trials were performed with the use of centered, 4-, 6-, and 8-mm offset heads in the anterior, posterior, superior, and inferior positions before and after removal of the acromion and coracoacromial ligament. The relation between change in mean peak torque (with and without acromion), passive range of motion, and humeral head offset was analyzed by means of repeated-measures analysis of variance. In the kinematics study, total range of motion and all humeral translations were greater with passive joint positioning than with active positioning (P =.01) except for total superior-inferior translation and superior-inferior translation in external rotation. Anterior to posterior humeral head offset was associated with statistically significant changes in total range of motion (P =.02), range of internal rotation (P =.02), range of external rotation (P =.0001), and total anterior-posterior translation (P =.01). Superior to inferior humeral head offset resulted in statistically significant changes in total range of motion (P =.02), range of internal rotation (P =.0001), anterior-posterior translation during external rotation (P =.01), and total superior-inferior translation (P =.03). In the impingement study, there was a significant increase in torque from centered to 4-mm inferior offset (P =.006), 6-mm inferior offset (P <.001), and 8-mm inferior offset (P <.001). There was no significant increase in torque with superior, anterior, and posterior offsets. Glenohumeral motion significantly decreased from 129 degrees for centered head to 119 degrees for 8-mm superior (P =.002), 119 degrees for 8-mm anterior (P =.014), 118 degrees for 8-mm inferior (P <.001), and 114 degrees for 8-mm posterior (P =.001). Humeral articular malposition of 4 mm or less during prosthetic arthroplasty of the glenohumeral joint may lead to small alterations in humeral translations and range of motion. Inferior malposition of greater than 4 mm can lead to increased subacromial contact; offset of 8 mm in any direction results in significant decreases in passive range of motion. Therefore if subacromial contact is to be minimized and glenohumeral motion maximized after shoulder replacement, anatomic reconstruction of the humeral head-humeral shaft offset to within 4 mm is desirable.     

Glenohumeral translations are increased after a type II superior labrum anterior-posterior lesion: a cadaveric study of severity of passive stabilizer injury

The effects of simulated type II superior labrum anterior-posterior (SLAP) lesions were studied to determine whether the severity of the lesion affected glenohumeral joint translations. A robotic/universal force-moment sensor testing system was used to simulate load-and-shift tests by applying an anterior or posterior load of 50 N to each shoulder. The apprehension test for anterior instability was simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm at 30 degrees and 60 degrees of abduction. This loading protocol was repeated after creating two type II SLAP lesions of different severity. In the first the superior labrum and the biceps anchor were elevated subperiosteally from the glenoid bone (SLAP-II-1), and in the second the biceps anchor was completely detached (SLAP-II-2). Statistical analysis was performed with a 2-factor repeated-measures analysis of variance followed by multiple contrasts, and the significance level was set at P <.05. At 30 degrees of abduction, anterior translation of the vented joint from anterior loading was 18.5 +/- 8.5 mm. It was significantly increased (26.2 +/- 6.5 mm, P =.03), after the SLAP-II-2 lesion and compared with the SLAP-II-1 lesion (25.0 +/- 6.8 mm, P =.03). Increases in anterior translations at 60 degrees of abduction were not significantly differ in comparison to the two SLAP lesions. Inferior translation also resulted from anterior loading. At 30 degrees of abduction in the vented joint, it was 3.8 +/- 4.0 mm and was significantly increased (8.5 +/- 5.4 mm, P =.05) after the SLAP-II-2 lesion, no different than that after the SLAP-II-1 lesion (7.8 +/- 4.9 mm). No significant increases in anterior translation occurred in response to the combined loading condition between the two SLAP lesions. Glenohumeral translation was increased, regardless of severity, after simulation of type II SLAP lesions. During stabilizing surgical interventions, passive stabilizers that are injured in the type II SLAP lesion should be considered as well as dynamic activity in the tendon of the long head of the biceps brachii.     

Static stabilizers of the shoulder joint

Anatomic dissection of 220 cadaver shoulders was performed to find out more about the static stabilizers of the shoulder joint. The static stabilizers, i.e. the glenohumeral ligaments, were always found to be present and strong in healthy shoulders. It was revealed that in anatomic preparations with all the organs removal except the synovial capsule, the capsule ligaments completely stabilized the joint. Anterior dislocation at 45 degrees of abduction was prevented by the superior and medial glenohumeral ligaments, while at 90 degrees of abduction the inferior glenohumeral ligament prevented dislocation. When anterior dislocation has occurred even the coracohumeral ligament must be ruptured. A new finding recorded is that the glenoid labrum is the origin of the inferior glenohumeral ligament and not a triangular static organ enlarging the socket and having a similar function to the menisci in the knee. This ligament is the most important ventral stabilizer of the humeral joint. With the conventional arthrotomy technique the medial and inferior ligaments are immediately cut through and therefore cannot be seen. The inferior glenohumeral ligament must be reconstructed in cases of anterior recurrent dislocation.     

Reconstruction of the antero-superior shoulder capsule with the subscapularis tendon: A case report

A 14-year-old boy presented with recurrent, anteroinferior, and multidirectional instability of his dominant shoulder. Examination with the patient under anesthesia demonstrated marked anterior and inferior translation when drawer testing was performed in adduction; however, abduction of the shoulder reduced the magnitude of humeral head translation in both these directions. Arthroscopy and open surgical dissection revealed the absence of any capsuloligamentous structures above the anterior band of the inferior glenohumeral ligament complex. This superior capsular defect could not be closed by a capsular shift procedure; therefore it was reconstructed with a portion of the subscapularis tendon. This case provides a clinical correlation of capsular anatomy with laxity on drawer testing. The glenohumeral laxity documented on examination with the patient under anesthesia supports experimental ligament-cutting studies that suggest the inferior glenohumeral ligament complex is the important stabilizer in abduction, whereas the superior and middle glenohumeral ligaments are more important in adduction.     

In vivo quantification of capsular end-point in the nonimpaired glenohumeral joint using an instrumented measurement system

STUDY DESIGN: Single-group factorial. OBJECTIVES: Quantify glenohumeral joint translations as a function of force using an instrumented measurement system. Our first specific aim was to compare the magnitude of force (N) required to reach capsular end-point between the anterior, posterior, and inferior directions. Our second specific aim was to compare the magnitude of translation (mm) at capsular end-point between the anterior, posterior, and inferior directions. BACKGROUND: Manual force-displacement techniques are subjective in nature, and the clinician must rely on "feel" to determine capsular end-point. Several investigators have attempted to utilize more objective measures at the glenohumeral joint, however none have quantified the force or displacements necessary to achieve a true capsular end-point. METHODS AND MEASURES: An arthrometric technique was used to measure anterior, posterior, and inferior glenohumeral translations in 20 nonimpaired shoulders (11 women and 9 men with a mean age of 20.9 +/- 3.6 years). RESULTS: The magnitude of applied force required to reach capsular end-point was significantly different between directions of translations. Anterior-directed translations required a significantly greater magnitude of applied force to reach capsular end-point than inferior-directed translations. The magnitude of translation was not significantly different between directions at capsular end-point. CONCLUSIONS: Applied forces in the range of 181 to 203 N are necessary to reach capsular end-point in subjects with nonimpaired shoulders. Anterior translation required significantly higher forces (203.1 +/- 13.1 N) to reach capsular end-point than inferior translation (181.4 +/- 31.9 N).     

Glenohumeral movement patterns after puncture of the joint capsule: An experimental study

In on experimental series comprising 22 shoulder specimens obtained at autopsy, we investigated the influence of an intact capsule on glenohumeral stability. Puncture of the capsule resulted in significant glenohumeral translation in unloaded and loaded specimens during shoulder abduction. A maximum of 16.6 mm of distal translation was observed at 20° of abduction. Concomitant with this translation the humerus spontaneously rotated externally, with a maximum rotation of 15.8° at 50° of abduction. After venting the capsule, anterior and posterior translation and external rotation were increased significantly. Maximum total increase in anteroposterior translation was 14 mm at 30° of abduction. The external rotation was increased up to 7.1° at 40° of abduction. These findings indicate that studies evaluating glenohumeral instability are compromised unless the translations resulting from capsular venting ore corrected. Evaluation of shoulder stability should be performed before violation of the intraarticular pressure mechanisms.     

The effect of capsular tightening on humeral head translations.

Idiopathic or surgical tightening of the glenohumeral joint capsule may cause displacement of the humeral head relative to the glenoid fossa and favor the development of instability and/or osteoarthritis. In the present investigation the relative position of the humerus to the glenoid fossa was determined at the end of the ranges of eight different passive movements before and after selective capsular plication in eight cadaveric shoulders to study the effects of selective capsular plications on the kinematics of the shoulder. While the capsule was in its unaltered state, translation of the humeral head was 3.8 mm superiorly in abduction, 7.3 mm antero-superiorly in flexion. In internal rotation in 0 degrees, 45 degrees and 90 degrees of abduction the head moved 6.1, 8.0 and 12.0 mm antero-inferiorly. In external rotation at 0 degrees of abduction the translation was 0.9 mm antero-inferiorly, at 45 degrees and 90 degrees of abduction it was 4.3 and 5.6 mm postero-inferiorly, respectively. Plications of the anterior part of the capsule reproducibly and significantly either increased or decreased translations during flexion (up to 5.9 mm anteriorly and up to 3.8 mm inferiorly), external rotation (up to 2.9 mm posteriorly and 1 mm inferiorly) and internal rotation (from 5.5 mm posteriorly to 2 mm anteriorly and up to 2.2 mm superiorly). Posterior plications had only little effect on translations (mainly a decrease of anterior translation during flexion of 2.8 mm). CLINICAL RELEVANCE: The 'obligate' glenohumeral translations which occur towards the end of passive shoulder movements are altered in a reproducible fashion by tightening specific parts of the glenohumeral joint capsule, as often carried out in treatment of shoulder instability. These alterations of the kinematics of the glenohumeral joint may be relevant for the development of static subluxation and osteoarthitis as seen after too tight plication in the treatment of instability [Int. Orthop. (SICOT) 67-B (1985) 709; J. Bone Joint Surg. Am. 72 (1990) 1193; J. Bone Joint Surg. Am. 66-A (1984) 169; J. Bone Joint Surg. Am. 65 (1983) 456].     

Anatomy and function of the glenohumeral ligaments in anterior shoulder instability

The anatomy of the glenohumeral ligaments has been shown to be complex and variable and their function is highly dependent on the position of the humerus with respect to the glenoid. The superior glenohumeral ligament with the coracohumeral ligament was shown to be an important stabilizer in the inferior direction, even though the coracohumeral ligament is much more robust than the superior glenohumeral ligament. The middle glenohumeral ligament provides anterior stability at 45 degrees and 60 degrees abduction whereas the inferior glenohumeral ligament complex is the most important stabilizer against anteroinferior shoulder dislocation. Therefore, this component of the capsule is the most frequently injured structure. An appropriate surgical procedure to repair the inferior glenohumeral ligament complex after shoulder dislocation must be considered. In addition, a detached labrum can lead to recurrent anterior instability and a compromised inferior glenohumeral ligament complex. However, additional capsular injury usually is necessary to allow anterior dislocation.