Mark W. Rodosky

The Role of the Long Head of the Biceps Muscle and Superior Glenoid Labrum in Anterior Stability of the Shoulder

The authors conducted a study to determine if the long head of the biceps muscle and its attachment at the superior glenoid labrum play a role in stability of the shoulder in an overhead position. Their study used a dynamic cadaveric shoulder model that simulated the forces of the rotator cuff and long head of biceps muscles as the glenohumeral joint was abducted and externally rotated. Their data suggest that the long head of the biceps muscle contributes to anterior stability of the glenohumeral joint by increasing the shoulders re sistance to torsional forces in the vulnerable abducted and externally rotated position. The biceps muscle also helps to diminish the stress placed on the inferior gle nohumeral ligament. Detachment of the superior gle noid labrum is detrimental to anterior shoulder stability as it decreases the shoulders resistance to torsion and places a greater magnitude of strain on the inferior gle nohumeral ligament.

Biomechanical Rationale for Development of Anatomical Reconstructions of Coracoclavicular Ligaments After Complete Acromioclavicular Joint Dislocations

Background Surgical treatments of complete acromioclavicular joint dislocations replace or reconstruct the coracoclavicular ligaments with a single structure and do not account for the anatomical variance of each ligament in the design. Purpose To evaluate the cyclic behavior and structural properties of an anatomic tendon reconstruction of the coracoclavicular ligament complex after a simulated acromioclavicular joint dislocation. Study Design Controlled laboratory study. Methods Cyclic loading followed by a load-to-failure protocol (simulated dislocation) of the normal coracoclavicular ligament complex was performed and repeated after an anatomic reconstruction on the same specimen (n = 9). The anatomical reconstruction consisted of a semitendinosus tendon that replicated the direction and orientation of both the trapezoid and conoid ligaments. Results The coracoclavicular ligament and anatomical reconstruction complexes had clinically insignificant (<3 mm) permanent elongation after cyclic loading. The stiffness and ultimate load of the coracoclavicular ligament complex (60.8 ± 12.2 N/mm and 560 ± 206 N) were significantly greater than for the anatomical reconstruction complex (23.4 ± 5.2 N/mm and 406 ± 60 N), respectively (P < .05). Further analysis of the complexes revealed a 40% decrease in the bending stiffness of the clavicle after the simulated dislocation and failure of the normal coracoclavicular ligament complex (P < .05), which contributed to the diminished properties of the anatomic reconstruction. Conclusions The low level of permanent elongation after cyclic loading suggests that the anatomic reconstruction complex could withstand early rehabilitation; however, the decrease in the structural properties and stiffness of the clavicle should be considered in optimizing the anatomic reconstruction technique. Clinical Relevance Despite the differences compared to the normal coracoclavicular ligament complex, the anatomical reconstruction complex more closely approximates the stiffness of the coracoclavicular ligament complex than current surgical constructs, and the incorporation of biological tissue could improve the overall structural properties with healing.

Reflexive Muscle Activation Alterations in Shoulders With Anterior Glenohumeral Instability

Background Patients with glenohumeral instability have proprioceptive deficits that are suggested to contribute to muscle activation alterations. Hypothesis Muscle activation alterations will be present in shoulders with anterior glenohumeral instability. Study Design Posttest-only control group design. Methods Eleven patients diagnosed with anterior glenohumeral instability were matched with 11 control subjects. Each subject received an external humeral rotation apprehension perturbation while reflexive muscle activation characteristics were measured with indwelling electromyography and surface electromyography. Results Patients with instability demonstrated suppressed pectoralis major and biceps brachii mean activation; increased peak activation of the subscapularis, supraspinatus, and infraspinatus; and a significantly slower biceps brachii reflex latency. Supraspinatus-subscapularis coactivation was significantly suppressed in the patients with instability as well. Conclusions and Clinical Relevance In addition to the capsuloligamentous deficiency and proprioceptive deficits present in anterior glenohumeral instability, muscle activation alterations are also present. The suppressed rotator cuff coactivation, slower biceps brachii activation, and decreased pectoralis major and biceps brachii mean activation may contribute to the recurrent instability episodes seen in this patient group. Clinicians can implement therapeutic exercises that address the suppressed muscles in patients opting for conservative management or rehabilitation before and after capsulorraphy procedures.

Biomechanical Evaluation of 2 Arthroscopic Biceps Tenodeses: Double-Anchor Versus Percutaneous Intra-Articular Transtendon (PITT) Techniques

Background Recently, there is increasing interest in different arthroscopic biceps tenodesis techniques. However, little data have been published about the biomechanical properties of soft tissue tenodesis. Purpose This study was undertaken to evaluate the biomechanical properties of 2 different arthroscopic biceps tenodeses: the percutaneous intra-articular transtendon (PITT) technique and the suture-anchor technique. Study Design Controlled laboratory study. Methods Fifteen fresh-frozen cadaveric specimens were randomly allocated to the 2 different biceps tenodesis techniques. The humerus with biceps tenodesis was mounted on a materials testing machine to perform a load to failure test. The structural properties including ultimate load (N) and stiffness (N/mm) were derived from the load-displacement curve. The mode of failure was also recorded. Ultimate load and stiffness were compared with the parametric Student t test. Results Both repairs showed typical load-displacement curves followed by a constant increase in load and displacement until failure occurred. Suture-anchor and PITT techniques had ultimate loads of 175.4 ± 40.4 N and 142.7 ± 30.9 N (P = .10) and stiffness of 15.9 ± 8.4 N/mm and 13.3 ± 3 N/mm (P = .36), respectively, with no significant differences between them. All of the surgical constructs failed in the tendon site by pulling out with the sutures through the substance of the tendon. Conclusion The suture-anchor and PITT techniques exhibited satisfactory initial strength with no statistical difference between the 2 groups. These findings, along with the consistent pullout of the suture through the tendon during failure, suggest that the most important factor for initial strength is not the attachment site but the quality of the biceps tendon. Clinical Relevance The quality of the tendon should be taken into account when deciding the surgical technique and the rehabilitation program. The PITT technique has the benefit of avoiding hardware complications and cost.

Joint compression alters the kinematics and loading patterns of the intact and capsule‐transected AC joint

High compressive loads are transmitted through the shoulder across the acromioclavicular (AC) joint to the axial skeleton during activities of daily living and can lead to early joint degeneration or instability. The objective of this study was to quantify the effect of joint compression on the biomechanics of the intact and capsule‐transected AC joint during application of three loading conditions. A robotic/universal force‐moment sensor testing system was utilized to apply an anterior, posterior or superior load of 70 N in combination with 10 or 70 N of joint compression to fresh‐frozen cadaveric shoulders (n = 12). The application of joint compression to the intact AC joint decreased the posterior translation in response to a posterior load (−6.6 ± 2.5 vs −3.7 ± 1.0 mm, p<0.05). Joint compression also decreased the in situ force in the superior AC capsule by 10 N while increasing the joint contact force by 20 N for all loading conditions (p<0.05). The application of joint compression to the capsule‐transected AC joint significantly decreased the amount of posterior and superior translation during posterior (−12.7 ± 6.1 vs −5.5 ± 3.2 mm, p < 0.05) and superior (5.3 ± 2.9 vs 4.2 ± 2.3 mm, p < 0.05) loading, respectively, while significantly increasing the coupled translations (anterior–posterior, superior–inferior or proximal–distal) in all loading conditions (p < 0.05). The joint contact force also significantly increased by 20 N for all loading conditions (p < 0.05). This quantitative data suggests: (1) common surgical techniques such as distal clavicle resection, which initially reduce painful joint contact, may cause unusually high loads to be supported by the soft tissue structures at the AC joint; and (2) compressive loads transmitted across a capsule‐transected AC joint could be concentrated over a smaller area due to the increased coupled motion and joint contact force.

Arthroscopic Biceps Tenodesis Using the Percutaneous, Intra-articular Trans-tendon Technique: Preliminary Results

The percutaneous intra-articular trans-tendon procedure relieved pain, increased or maintained strength and function, and did not cause a cosmetic deformity in this small consecutive series of patients.

Symptomatic os acromiale.

Abstract Os acromiale, the joining of the acromion to the scapular spine by fibrocartilaginous tissue rather than bone, is an anatomic variant that has been reported in approximately 8% of the population worldwide. It is more common in blacks and males than in whites and females. Although it is often an incidental finding, os acromiale has been identified as a contributor to shoulder impingement symptoms and rotator cuff tears. When nonsurgical management of a symptomatic os acromiale fails to relieve symptoms, surgical intervention is considered. Options include os acromiale excision, open reduction and internal fixation, and arthroscopic decompression. Excision usually is reserved for small to midsized fragments (preacromion) or after failed open reduction and internal fixation. Persistent deltoid dysfunction may result from excision of a large os acromiale. Open reduction and internal fixation preserves large fragments while maintaining deltoid function. Cannulated screw fixation has been shown to result in good union rates. Arthroscopic techniques have shown mixed results when used for treating impingement secondary to an unstable os acromiale. Associated rotator cuff tears may be addressed arthroscopically or through an open transacromial approach, followed by open reduction and internal fixation of the os acromiale.

Viscoelastic behavior and structural properties of the coracoclavicular ligaments

During contact sports such as football, hockey or rugby, the coracoclavicular ligaments are commonly ruptured. Currently, the limited biomechanical data on the properties and function of these ligaments have led to debate on the “gold standard” treatment for these injuries. Therefore, the objective of this study was to characterize the geometry, viscoelastic behavior and structural properties of the coracoclavicular ligaments (n=11). The trapezoid and conoid were found to have similar length (9.6±4.4 vs. 11.2±4.1 mm) and cross‐sectional area (103±43 vs. 69±51 mm2), respectively (P>0.05). Static and cyclic stress relaxation tests were then performed, followed by uniaxial tensile testing with the insertions of each ligament aligned to ensure a uniform distribution of load across the fibers. No significant differences were observed for the trapezoid and conoid during the static (36±8% vs. 31±7%) and cyclic (23±12% vs. 16±6%) stress relaxation tests, respectively (P>0.05). Similarly, no statistically significant differences were found between the trapezoid and conoid for linear stiffness (83±40 vs. 70±23 N mm−1), ultimate load (312±133 vs. 266± 108 N), energy absorbed at failure (820±576 vs. 752± 410 N mm), percent elongation (74±47% vs. 62±22%) and elongation at failure (5.8±2.2 vs. 6.1±1.6 mm), respectively (P>0.05). A comparison of our data to previous studies suggests that the complex fiber orientation of these ligaments has a significant role in determining the maximum load that can be transferred between the clavicle and scapula by each bone–ligament–bone complex. Our findings also further confirm the functional role of the coracoclavicular ligaments in supporting the upper extremity, and provide data for reconstruction and rehabilitation protocols as well as computational models.

A Biomechanical Analysis of the Native Coracoclavicular Ligaments and Their Influence on a New Reconstruction Using a Coracoid Tunnel and Free Tendon Graft

PURPOSE To understand and characterize the kinematic properties of the 2 coracoclavicular ligaments and to evaluate the biomechanical performance of a new 3-tunnel reconstruction of the coracoclavicular ligaments by use of a free tendon graft. METHODS Ten fresh-frozen cadaveric shoulders were tested. The kinematics and in situ forces of the coracoclavicular ligaments were tested with a robotic testing system. Kinematics of the shoulder in the intact state, in the sectioned state, and finally, after a coracoclavicular reconstruction and a coracoclavicular sling reconstruction were evaluated. RESULTS The conoid had higher in situ forces during anterior and superior loading of the clavicle when compared with the trapezoid ligament, whereas the trapezoid ligament had higher in situ forces during posterior loading. Sectioning the trapezoid ligament significantly increased translation of the clavicle in the posterior direction, whereas sectioning the conoid ligament significantly increased superior translation. When we compared the 2 reconstruction techniques, the coracoid tunnel reconstruction was superior in controlling anterior translation whereas the coracoclavicular sling reconstruction was inferior because of anterior displacement of the graft. There was no significant difference in posterior or superior translation between either reconstruction technique. CONCLUSIONS The trapezoid and conoid ligaments have unique functions in normal shoulder kinematics because of their anatomic attachments. By more faithfully restoring these insertion sites on the clavicle and controlling motion of the graft on the coracoid, the 3-tunnel reconstruction technique more closely restores native shoulder kinematics than the coracoclavicular sling technique. CLINICAL RELEVANCE Understanding the unique roles of the conoid and trapezoid bundles of the coracoclavicular ligament may improve surgical techniques in the management of acromioclavicular joint injuries. The reconstructive technique presented more faithfully restores normal kinematics and forces across the acromioclavicular joint than the coracoclavicular sling technique.

Shoulder injuries in the athlete

Shoulder injuries are common in the athletic population. Injuries can be a result of repetitive overhead use or from direct trauma. Common injury sites include the rotator cuff, glenohumeral joint, acromioclavicular joint, biceps tendon, scapulothoracic articulation, and sternoclavicular joint. The identification, physical exam, and treatment options of these conditions will be discussed.