The rotator cuff. Commentary

Articular Cartilage Defects of the Glenohumeral Joint: A Systematic Review of Treatment Options and Outcomes

OBJECTIVE

To report radiographic and magnetic resonance imaging findings, patient-reported outcomes, and complications and/or reoperations following nonarthroplasty surgical intervention for focal glenohumeral cartilage defects.

DESIGN

A literature search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Patients were included if they possessed a chondral defect of the humeral head, glenoid, or both, which had been treated with a joint preserving nonarthroplasty procedure. Risk of bias assessment was performed using the Methodological Index for Non-Randomized Studies scoring system. Study demographics, surgical technique, imaging findings, patient-reported outcomes, complications, failures, and reoperations were collected.

RESULTS

Fourteen studies with 98 patients (100 shoulders) met the inclusion criteria. Patient ages ranged from 7 to 74 years. The nonarthroplasty surgical techniques utilized included microfracture (67 shoulders), osteochondral transplantation (28 shoulders), chondrocyte transplantation (4 shoulders), and internal fixation (1 shoulder). The rates of radiographic union and progression of osteoarthritis ranged between 90% to 100% and 57% to 100%, respectively. Visual analog scores ranged from 0 to 1.9 at final follow-up. Mean postoperative ASES (American Shoulder and Elbow Surgeons) shoulder scores ranged from 75.8-100. Mean postoperative CSS (Constant Shoulder Score) scores ranged from 83.3-94. Mean postoperative SSV (Subjective Shoulder Value) ranged from 70% to 99%. Failure and reoperation rates ranged between 0% to 35% and 0% to 30%, respectively, with the most common reoperation being conversion to prosthetic arthroplasty.

CONCLUSIONS

In this systematic review, nonarthroplasty surgical techniques demonstrated acceptable rates of radiographic healing, improved patient reported outcomes, minimal complications, and low rates of failure or reoperation. Joint preserving techniques are likely viable options to prolong function of the native shoulder and provide short- to midterm pain relief in young and highly active patients.

LEVEL OF EVIDENCE

Level IV.

Evaluation of global load sharing and shear-lag models to describe mechanical behavior in partially lacerated tendons

The mechanical effect of a partial thickness tear or laceration of a tendon is analytically modeled under various assumptions and results are compared with previous experimental data from porcine flexor tendons. Among several fibril-level models considered, a shear-lag model that incorporates fibril-matrix interaction and a fibril-fibril interaction defined by the contact area of the interposed matrix best matched published data for tendons with shallow cuts (less than 50% of the cross-sectional area). Application of this model to the case of many disrupted fibrils is based on linear superposition and is most successful when more fibrils are incorporated into the model. An equally distributed load sharing model for the fraction of remaining intact fibrils was inadequate in that it overestimates the strength for a cut less than half of the tendon's cross-sectional area. In a broader sense, results imply that shear-lag contributes significantly to the general mechanical behavior of tendons when axial loads are nonuniformly distributed over a cross section, although the predominant hierarchical level and microstructural mediators for this behavior require further inquiry.

The influence of partial and full thickness tears on infraspinatus tendon strain patterns

Tears on the bursal and articular sides of the rotator cuff tendons are known to behave differently and strain is thought to play a role in this difference. This study investigates the effect of tear location on the changes in three strain measurements (grip-to-grip, insertion, and mid-substance tissue) in a sheep infraspinatus tendon model during axial loading. We introduced a 14 mm wide defect near the insertion from either the articular or bursal side of the tendon to three depths (3 mm, 7 mm & full) progressively. For each condition, tendons were sinusoidally stretched (4% at 0.5 Hz) while insertion and mid-substance strains were tracked with surface markers. For a fixed load, grip-to-grip strain increased significantly compared to intact for both cuts. Insertion strain increased significantly for the bursal-side defect immediately but not for the articular-side until the 66% cut. Mid-substance tissue strain showed no significant change for partial thickness articular-side defects and a significant decrease for bursal-side defects after the 66% cut. All full thickness cuts exhibited negligible mid-substance tissue strain change. Our results suggest that the tendon strain patterns are more sensitive to defects on the bursal side, and that partial thickness tears tend to induce localized strain concentrations in regions adjacent to the damaged tissue.

Influence of tendon tears on ultrasound echo intensity in response to loading

Acoustoelastic (AE) ultrasound image analysis is a promising non-invasive approach that uses load-dependent echo intensity changes to characterize stiffness of tendinous tissue. The purpose of this study was to investigate whether AE can detect localized changes in tendon stiffness due to partial and full-thickness tendon tears. Ovine infraspinatus tendons with different levels of damage (Intact, 33%, 66% and full thickness cuts initiated on the articular and bursal sides) were cyclically loaded in a mechanical testing system while cine ultrasound images were recorded. The load-induced changes in echo intensity on the bursal and articular side of the tendon were determined. Consistent with AE theory, the undamaged tendons exhibited an increase in echo intensity with tendon loading, reflecting the strain-stiffening behavior of the tissue. In the intact condition, the articular region demonstrated a significantly greater increase in echo intensity during loading than the bursal region. Cuts initiated on the bursal side resulted in a progressive decrease in echo intensity of the adjacent tissue, likely reflecting the reduced load transmission through that region. However, image intensity information was less sensitive for identifying load transmission changes that result from partial thickness cuts initiated on the articular side. We conclude that AE approaches may be useful to quantitatively assess load-dependent changes in tendon stiffness, and that disruption of AE behavior may be indicative of substantial tendon damage.

Mechanical compromise of partially lacerated flexor tendons

Tendons function to transmit loads from muscle to move and stabilize joints and absorb impacts. Functionality of lacerated tendons is diminished, however clinical practice often considers surgical repair only after 50% or more of the tendon is lacerated, the "50% rule." Few studies provide mechanical insight into the 50% rule. In this study cyclic and static stress relaxation tests were performed on porcine flexor tendons before and after a 0.5, 1.0, 2.0, or 2.75 mm deep transverse, midsubstance laceration. Elastic and viscoelastic properties, such as maximum stress, change in stress throughout each test, and stiffness, were measured and compared pre- and post-laceration. Nominal stress and stiffness parameters decreased, albeit disproportionately in magnitude, with increasing percent loss of cross-sectional area. Conversely, mean stress at the residual area (determined using remaining intact area at the laceration cross section) exhibited a marked increase in stress concentration beginning at 47.2% laceration using both specified load and constant strain analyses. The marked increase in stress concentration beginning near 50% laceration provides mechanical insight into the 50% rule. Additionally, a drastic decrease in viscoelastic stress parameters after only an 8.2% laceration suggests that time-dependent mechanisms protecting tissues during impact loadings are highly compromised regardless of laceration size.

Effect of anterior supraspinatus tendon partial-thickness tears on infraspinatus tendon strain through a range of joint rotation angles

BACKGROUND

Rotator cuff tears are common shoulder problems whose propagation is difficult to predict because of the structural and mechanical inhomogeneity of the supraspinatus tendon. We have previously shown that the supraspinatus and infraspinatus tendons interact mechanically when the supraspinatus tendon is intact or exhibits a full-thickness tear, so that an increase in supraspinatus tendon strain is paralleled by an increase in infraspinatus tendon strain. Such interaction is critical and suggests that an increase in infraspinatus tendon strain that accompanies an increase in supraspinatus tendon strain may shield the supraspinatus tendon from further injury, but increase the risk of injury to the infraspinatus tendon. In this study, the mechanical interactions between the supraspinatus and infraspinatus tendons were evaluated for the commonly occurring supraspinatus tendon partial-thickness tears through a range of rotation angles.

METHODS

For each joint rotation and supraspinatus tendon tear size evaluated, the supraspinatus tendon was loaded, and images corresponding to 5 N, 30 N, 60 N, and 90 N of supraspinatus tendon load were isolated for the speckle painted supraspinatus and infraspinatus tendons. A region of interest outlining the insertion site was isolated and displacements between the 5 N loaded image and each of the others were measured, from which normalized average principal strains were quantified in both tendons.

RESULTS

The observed effect on infraspinatus tendon strain paralleled that observed on strain in the supraspinatus tendon. Introducing a supraspinatus tendon partial-thickness tear and increasing load caused an increase in normalized average maximum and a decrease in normalized average minimum principal strain in the infraspinatus tendon. Increasing rotation angle from internal to external rotation caused a general decrease in normalized average maximum and increase in normalized average minimum principal strain in both tendons.

CONCLUSION

The supraspinatus and infraspinatus tendons mechanically interact for the intact and partially torn supraspinatus tendons for neutral and rotated glenohumeral joint.

Interaction between the supraspinatus and infraspinatus tendons: effect of anterior supraspinatus tendon full-thickness tears on infraspinatus tendon strain

BACKGROUND

Rotator cuff tears are common and not well-understood shoulder problems. Structural and mechanical inhomogeneity of the supraspinatus tendon complicates accurate prediction of risk of tear propagation and may affect appropriate clinical treatment.

HYPOTHESIS

We propose that interactions between the supraspinatus and infraspinatus tendons are critical to load bearing at the glenohumeral joint and warrant investigation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Principal strains in the infraspinatus tendon of cadaveric human shoulders were evaluated with increasing anterior full-thickness supraspinatus tendon tear sizes and loading to evaluate whether a mechanical interaction between the supraspinatus and infraspinatus tendons exists. A constant nominal load was attached to the infraspinatus throughout all experimental conditions.

RESULTS

Increasing supraspinatus tendon tear width from intact and 33% to 66% and increasing supraspinatus tendon load caused an increase in maximum and a decrease in minimum principal strain in the infraspinatus tendon. Increasing the supraspinatus tendon tear size from intact to 33% of the width had no significant effect on infraspinatus tendon strain.

CONCLUSION

Supraspinatus and infraspinatus tendons mechanically interact. The observed significant increase in maximum and decrease in minimum principal strain was concurrent in both the infraspinatus and supraspinatus tendons.

CLINICAL RELEVANCE

Changes in infraspinatus tendon strain associated with increases in supraspinatus tendon tear size and loading may shield a torn supraspinatus tendon from further injury or may have an effect on the load-bearing capacity of the infraspinatus tendon. Results also imply that the effect of a small tear that does not compromise the confluent region between the supraspinatus and infraspinatus tendon may be localized, eliminating its effect on infraspinatus tendon strain.

Predictive factors of subtle residual shoulder symptoms after transtendinous arthroscopic cuff repair: a clinical study

BACKGROUND

Transtendinous repair is a well-known technique for the arthroscopic management of partial rotator cuff tear. However, there are not a lot of clinical follow-up studies in the literature reporting data on this approach, and, moreover, potential factors responsible to influence the outcomes have not been investigated.

PURPOSE

To evaluate clinical outcomes after arthroscopic transtendinous repair and to identify predictive factors of residual shoulder symptoms.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Fifty-four patients with a mean age of 56.7 +/- 8.8 years (range, 31-71 years) who had undergone an arthroscopic transtendon repair for a painful articular-sided rotator cuff tear with a minimum of 2 years of follow-up were contacted. Clinical outcomes using a patient-based questionnaire, the Constant score, University of California at Los Angeles score, Simple Shoulder Test, and visual analog scale were evaluated. The influence of patient age, presence or absence of a trauma responsible for the cuff tear, presence of associated shoulder lesions, millimeters of exposed footprint, and millimeters of torn tendon retraction on the outcomes were assessed.

RESULTS

The mean cuff tear exposure footprint was 5.2 mm, and the mean retraction of the torn part of the tendon was 8 mm. Only one patient reported dissatisfaction with surgery because of persistence of pain during overhead activities. After arthroscopic repair, University of California at Los Angeles, Constant, and Simple Shoulder Test scores were significantly improved from 14.1, 45.3, and 9.8 to 32.9, 90.6, and 0.8, respectively (P < .001). Twenty-two patients (41%) reported occasional shoulder discomfort at the extremes of range of motion (particularly at extremes of abduction and internal rotation) occurring during some daily living and sports activities. The best multivariate model showed that residual shoulder discomfort is strongly linked with a partial thickness supraspinatus tendon avulsion-type articular-sided rotator cuff lesion consisting of a large tendon retraction and/or a relatively small exposure footprint area in an older patient in the absence of a specific trauma (P < .001).

CONCLUSION

Arthroscopic transtendon partial articular supraspinatus tendon avulsion-type rotator cuff repair was a reliable procedure that resulted in a good outcome in terms of pain relief and shoulder scores in 98% of the 54 patients. Better results could be expected in patients with less tendon retraction, a larger footprint exposure, of younger age, and with a clinical history of trauma.

Rotator cuff tendon strain correlates with tear propagation

Rotator cuff tears are a common tendon injury often requiring surgical treatment. Understanding the relationships between tear size, tendon loading, and tendon strain adjacent to a rotator cuff tear can provide important insights into predicting the likelihood of propagation to larger tears which would influence clinical treatment. Previous studies assume that an increase in strain correlates with an increase in risk of tear propagation. However, these studies did not explicitly investigate these important relationships. Therefore, the objective of this study was to quantify two-dimensional strain fields adjacent to a rotator cuff tendon tear under loading to failure and to assess the relationship between tendon strain and tear size. Sheep infraspinatus tendons were used to evaluate the effect of tear size on principal strains in the region adjacent to the tear. The relationship between strain, tear propagation, and the direction of tear propagation was quantified. Results showed that principal strains linearly correlated with tear propagation and that tear propagation began at strains as low as 1.7%. In addition, tears propagated in the direction of highest maximum and lowest minimum principal strain. Finally, maximum and minimum principal strains were higher and lower, respectively, adjacent to larger tears compared to smaller tears. Findings from this study validate the use of local strain adjacent to a rotator cuff tear as an indicator of the risk and direction of tear propagation.

Intratendinous strain fields of the supraspinatus tendon: effect of a surgically created articular-surface rotator cuff tear

Articular-surface partial-thickness rotator cuff tears play a significant role in shoulder pathology, but the role of the articular-surface tissue is poorly understood. This investigation assessed the effect of an articular-surface partial-thickness rotator cuff tear on intratendinous strain fields. A magnetic resonance imaging-based technique quantified intratendinous strains in healthy cadaveric shoulders at 15 degrees, 30 degrees, 45 degrees, and 60 degrees of glenohumeral abduction. A second set of magnetic resonance images was acquired after an articular-surface partial-thickness tear was created arthroscopically. Measures of strain were grouped into 3 tendon regions. A 3-factor analysis of variance assessed the effects of joint position, tendon region, and tendon tear. Intratendinous strains were influenced significantly by joint position, but few differences existed between tendon regions. The articular-surface partial-thickness tear increased intratendinous strain for all joint positions except 15 degrees. The results lend insight into the mechanical behavior of the normal and pathologic rotator cuff.