Scapular inclination and glenohumeral joint stability: a cadaveric study

Background In shoulders with multidirectional instability, translation of the humeral head on the glenoid is increased in the midrange because of the following three reasons: the increased retroversion, a hypoplastic posteroinferior rim, and decreased scapular abduction during arm elevation. This study aimed to clarify the relationship between glenoid inclination and glenohumeral joint stability. Methods Nine fresh-frozen cadaveric shoulders were tested. With a 50-N compressive load, the translation force was measured in the 3-o’clock, 6-o’clock, 9-o’clock, and 12-o’clock directions by using a tilt of 0°, 5°, 10°, 15°, and 20°. When the glenoid was tilted in one direction, the translation force was measured in the direction of inclination and in the opposite direction. The stability ratio was then calculated. Results The stability ratio in the 3-o’clock direction significantly decreased with a tilt of more than 5° in the 3-o’clock direction. The stability ratio in the 9-o’clock direction significantly decreased with a tilt of more than 15° in the 9-o’clock direction and significantly increased with a tilt of more than 5° in the 3-o’clock direction. The stability ratio in the 6-o’clock direction significantly increased with a tilt of more than 10° in the 6-o’clock direction. Conclusions The posterior and inferior stability increased with an anterior tilt of more than 5° and with a superior tilt of 10°, respectively. The anterior and posterior stability decreased with an anterior tilt of 5° and with a posterior tilt of 15°, respectively.     

The range of glenohumeral joint motion in activities of daily living after rotator cuff repair: a cadaveric biomechanical study

This study was conducted to quantify the restriction of glenohumeral motion and activities of daily living (ADL) after rotator cuff repair. Eight fresh cadaveric shoulders were used. The ranges of passive shoulder motions in models of the intact cuff tendon, and repaired small cuff and large cuff tears were measured using a 6-degree-of-freedom electromagnetic tracking device. The range of motion for reach, perineal care, hair combing, and washing the axilla were also measured as simulated ADL. Elevation, horizontal adduction, and abduction were significantly restricted in the repaired small-tear model, whereas glenohumeral motion in all directions was significantly restricted in the repaired large-tear model. The repair of the small tear significantly restricted perineal care alone, whereas the repair of the large tear significantly restricted all ADL except hair combing. These findings could be helpful in managing restricted shoulder motion and in instructing patients in acceptable ADL after rotator cuff repair.     

Arthroscopic repair of anterior glenohumeral instability and rotator interval lesions

As the techniques and instrumentation for shoulder arthroscopy continue to improve and evolve, its role in the treatment of anterior shoulder instability progresses also. With more surgeons becoming familiar with these advancements and techniques, arthroscopic stabilization results continue to improve and help arthroscopy become the "preferred method" for the treatment of shoulder instability. Adjunct procedures such as closure of the rotator interval also are helping to improve our arthroscopic results and are an important improvement in our understanding of the pathoanatomy of shoulder instability repairs.     

Dynamic glenohumeral stability provided by the rotator cuff muscles in the mid-range and end-range of motion. A study in cadavera

BACKGROUND: Both static and dynamic factors are responsible for glenohumeral joint stability. We hypothesized that dynamic factors could potentially operate throughout the entire range of glenohumeral motion, although capsuloligamentous restraints (a static factor) have been thought to be primarily responsible for stability in the end-range of motion. The purpose of this study was to quantitatively compare the dynamic glenohumeral joint stability in the end-range of motion (the position of anterior instability) with that in the mid-range by investigating the force components generated by the rotator cuff muscles. METHODS: Ten fresh-frozen shoulders from human cadavera were obtained, and all soft tissues except the rotator cuff were removed. The glenohumeral capsule was resected after the rotator cuff muscles had been released from the scapula. A specially designed frame positioned the humerus in 60 degrees of abduction and 45 degrees of extension with respect to the scapula. The compressive and shear components on the glenoid were measured before and after a constant force was applied individually to each muscle with the humerus in five different positions (from neutral to 90 degrees of external rotation). The dynamic stability index, a new biomechanical parameter reflecting these force components and the concavity-compression mechanism, was calculated. The higher the dynamic stability index, the greater the dynamic glenohumeral stability. RESULTS: In the mid-range of motion, the supraspinatus and subscapularis provided higher dynamic stability indices than did the other muscles (p < 0.05). On the other hand, when the position of anterior instability was simulated in the end-range of motion, the subscapularis, infraspinatus, and teres minor provided significantly higher dynamic stability indices than did the supraspinatus (p < 0.005). CONCLUSIONS: The rotator cuff provided substantial anterior dynamic stability to the glenohumeral joint in the end-range of motion as well as in the mid-range. CLINICAL RELEVANCE: A glenohumeral joint with a lax capsule and ligaments might be stabilized dynamically in the end-range of motion if the glenoid concavity is maintained and the function of the external and internal rotators, which are efficient stabilizers in this position, is enhanced.     

Influence of rotator cuff tears on glenohumeral stability during abduction tasks

One of the main goals in reconstructing rotator cuff tears is the restoration of glenohumeral joint stability, which is subsequently of utmost importance in order to prevent degenerative damage such as superior labral anterior posterior (SLAP) lesion, arthrosis, and malfunction. The goal of the current study was to facilitate musculoskeletal models in order to estimate glenohumeral instability introduced by muscle weakness due to cuff lesions. Inverse dynamics simulations were used to compute joint reaction forces for several static abduction tasks with different muscle weakness. Results were compared with the existing literature in order to ensure the model validity. Further arm positions taken from activities of daily living, requiring the rotator cuff muscles were modeled and their contribution to joint kinetics computed. Weakness of the superior rotator cuff muscles (supraspinatus; infraspinatus) leads to a deviation of the joint reaction force to the cranial dorsal rim of the glenoid. Massive rotator cuff defects showed higher potential for glenohumeral instability in contrast to single muscle ruptures. The teres minor muscle seems to substitute lost joint torque during several simulated muscle tears to maintain joint stability. Joint instability increases with cuff tear size. Weakness of the upper part of the rotator cuff leads to a joint reaction force closer to the upper glenoid rim. This indicates the comorbidity of cuff tears with SLAP lesions. The teres minor is crucial for maintaining joint stability in case of massive cuff defects and should be uprated in clinical decision‐making. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1628–1635, 2016.     

Accuracy of intra-articular injection of the glenohumeral joint: a cadaveric study

Intra-articular glenohumeral injections are an important part of orthopedic practices for both therapeutic and diagnostic purposes. Forty human cadaver shoulders were injected, 20 anteriorly and 20 posteriorly, to assess the accuracy of injections placed in the glenohumeral joint. After the needle was placed, 1 cc of gadolinium was injected into the joint to determine accuracy of position. The radiographic presence of intra-articular contrast was judged as an accurate injection. The anterior approach had an 80% accuracy rate and .75 positive predictive value. The posterior approach had a 50% accuracy rate and a .67 positive predictive value. Anterior injections produce a higher rate of accuracy than posterior injections.     

Arthroscopic rotator interval repair in glenohumeral instability: description of an operative technique.

Rotator interval tear is one of the lesions identified in patients with glenohumeral instability. We present our technique for arthroscopic repair that eliminates entry into the subacromial space and allows the surgeon to suture the rotator interval under direct intra-articular vision.     

Arthroscopic rotator interval repair and anterior portal closure: An alternative technique

The rotator interval capsule has been implicated as an important restraint to shoulder subluxation, and plays an important role in shoulder stability. Anterior portal placement during arthroscopic shoulder instability repair violates the interval capsule and compromises the biomechanical integrity of the rotator interval. The following is a technique for interval capsule repair. Using an 18-gauge needle via the anterior portal, a monofilament suture is passed through the capsule just above the subscapularis. A Penetrator suture retriever (Arthrex, Naples, FL) is passed high into the capsule just anterior to the biceps. The intra-articular end of the suture is then removed from the superior aspect of the interval capsule. The suture limbs are then tied into the portal onto the anterior capsule. The technique is advantageous because it may be repeated as needed until appropriate interval plication has been achieved. Furthermore, it does not require an interval portal through which to pass the suture. It appears to be a safe, effective, and reproducible technique for arthroscopic rotator interval closure.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 4 (April), 2002: pp 436–439     

The role of the rotator interval capsule in passive motion and stability of the shoulder.

The purpose of this study was to characterize the role of the capsule in the interval between the supraspinatus and subscapularis tendons with respect to glenohumeral motion, translation, and stability. We used a six-degrees-of-freedom position-sensor and a six-degrees-of-freedom force and torque-transducer to determine the glenohumoral rotations and translations that resulted from applied loads in eight cadaver shoulders. The range of motion of each specimen was measured with the capsule in the rotator interval in a normal state, after the capsule had been sectioned, and after it had been imbricated. Operative alteration of this capsular interval was found to affect flexion, extension, external rotation, and adduction of the humerus with respect to the scapula. Modification of this portion of the capsule also affected obligate anterior translation of the humeral head on the glenoid during flexion. Limitation of motion and obligate translation were increased by operative imbrication and diminished by sectioning of the rotator interval capsule. Passive stability of the glenohumeral joint was evaluated with the use of anterior, posterior, and inferior stress tests. Instability and occasional frank dislocation of the glenohumeral joint occurred inferiorly and posteriorly after section of the rotator interval capsule. Imbrication of this part of the capsule increased the resistance to inferior and posterior translation.     

Tendon-Defect and muscle-unloaded models for relating a rotator cuff tear to glenohumeral stability.

Rotator cuff tear and glenohumeral instability are closely related. Any tear may disturb muscle force generation due to pain inhibition. In addition, a full-thickness tear may foster instability by removing a structural element constraining the joint. It was hypothesized that the loss of both dynamic force and static constraint with a rotator cuff tear will affect glenohumeral stability. In a tendon-defect model, dynamic and static elements of the joint were sacrificed. In a muscle-unloaded model, only the dynamic element was removed. The location and size of the defect were also investigated. The effect on instability of a small tendon defect was less than that of muscle unloading, implying that a patient with a small tear would have less instability than a patient with weak or nonfunctioning supraspinatus and infraspinatus muscles. On the other hand, with a larger tear the defect had a greater effect than muscle-unloading because sectioning of the glenohumeral and coracohumeral ligaments was included in the model. Clinically, such a defect in the front is critical for anterior stability because it might insult the important anterior capsule ligamentous complex. Orthopaedic surgeons should pay attention, therefore, to the effect of possible associated lesions of static constraints based on the size and location of the tear in addition to the dynamic stabilizer.     

Latissimus dorsi tendon transfer for massive rotator cuff tears: a cadaveric study

Certain massive defects of the rotator cuff tendinous insertion cannot be repaired primarily to the greater tuberosity. If restoration of strength is an important treatment goal to the patient, then a tendon transfer may be considered. Ten cadaver shoulders were dissected to define the anatomy of the latissimus dorsi tendon (LDT) and its distance relationship to the axillary and radial nerves with the arm in various positions. The axillary nerve lies superior to the LDT insertion, and the radial nerve passes medial and inferior to the LDT insertion. With the arm internally rotated and the shoulder flexed, the distances from the axillary and radial nerves to the LDT insertion were 2.3 cm and 2.8 cm, respectively. With the arm internally rotated and the shoulder abducted, the distances from the axillary and radial nerves to the LDT insertion were 1.8 cm and 2.0 cm, respectively. Understanding specific anatomic relationships is one of the factors contributing to the safety of the LDT transfer procedure with respect to nerve injury.