Bong Jae Jun

The Biomechanical Effects of Dynamic External Rotation on Rotator Cuff Repair Compared to Testing With the Humerus Fixed

Background Biomechanical testing without humeral motion is a standard method for evaluating rotator cuff repair constructs. This cannot elucidate the effects of dynamic external rotation on the repair, which is a common postoperative motion. Hypothesis Biomechanical properties and gap formation of rotator cuff repairs will be different when dynamic external rotation is allowed to occur during loading. Study Design Controlled laboratory study. Methods In 6 matched pairs of human cadaveric shoulders, a commonly used single-row rotator cuff repair was performed. In 6 shoulders, a materials testing machine and a custom testing apparatus that permits cyclic rotation (0°-30°) were employed (group 1). In contralateral shoulders, the apparatus was fixed to prevent humeral rotation (group 2). All repairs were cyclically loaded from 0 to 60 N at a displacement rate of 1 mm/s for 30 cycles. The constructs were then loaded to failure. Repair strength, gap formation, and strain were compared between groups. Results Cyclic loading revealed no difference in linear stiffness between testing conditions. Hysteresis was significantly greater when dynamic external rotation was allowed to occur. With load to failure, there were no differences in yield or ultimate load. Anterior tendon gap formation was greater at end rotation (30° of humeral external rotation) and at yield load, and strain on the posterior tendon was less with dynamic external rotation. With dynamic external rotation, gap formation and tendon strain were significantly greater in the anterior region of the supraspinatus tendon compared with the posterior region. Discussion External rotation using postoperative physiologic loads affects gap formation and tendon strain between anterior and posterior supraspinatus tendon regions. Previous testing models without humeral rotation may underestimate gap formation and anterior tendon strain and overestimate posterior tendon strain. Clinical Relevance Understanding regional differences with respect to these variables, depending on quality of repair, may provide the surgeon a framework from which to prescribe guidelines for postoperative rehabilitation.

Does a Critical Rotator Cuff Tear Stage Exist?: A Biomechanical Study of Rotator Cuff Tear Progression in Human Cadaver Shoulders

BACKGROUND It is unknown at which stage of rotator cuff tear the biomechanical environment is altered. The purpose of this study was to determine if a critical rotator cuff tear stage exists that alters glenohumeral joint biomechanics throughout the rotational range of shoulder motion, and to evaluate the biomechanical effect of parascapular muscle-loading. METHODS Eight cadaver shoulders were used with a custom testing system. Four progressive rotator cuff tear stages were investigated on the basis of footprint anatomy. Three muscle-loading conditions were examined: rotator cuff only; rotator cuff with deltoid muscle; and rotator cuff, deltoid, pectoralis major, and latissimus dorsi muscles. Testing was performed in the scapular plane with 0°, 30°, and 60° of shoulder abduction. The maximum internal and external rotations were measured with 3.4 Nm of torque. The position of the humeral head apex with respect to the glenoid was calculated with use of a MicroScribe 3DLX digitizing system throughout the rotational range of motion. The abduction capability was determined as the abduction angle achieved with increasing deltoid load. RESULTS Tear of the entire supraspinatus tendon significantly increased maximum external rotation and significantly decreased abduction capability with higher deltoid loads (p < 0.05). Tear of the entire supraspinatus tendon and half of the infraspinatus tendon significantly shifted the humeral head apex posteriorly at the midrange of rotation and superiorly at maximum internal rotation (p < 0.05). Loading the pectoralis major and latissimus dorsi muscles decreased the amount of humeral head elevation due to deltoid loading. CONCLUSIONS Tear of the entire supraspinatus tendon was the critical stage for increasing rotational range of shoulder motion and for decreased abduction capability. Further tear progression to the infraspinatus muscle was the critical stage for significant changes in humeral head kinematics. The pectoralis major and latissimus dorsi muscles played an important role in stabilizing the humeral head as the rotator cuff tear progressed.

Effect of Scapular Orientation on Shoulder Internal Impingement in a Cadaveric Model of the Cocking Phase of Throwing

BACKGROUND Although deviations in scapular orientation are thought to predispose to shoulder injuries in throwing athletes, the biomechanical mechanism underlying shoulder injuries in throwing athletes with an altered scapular orientation remains unclear. METHODS Seven fresh-frozen cadaveric shoulders were evaluated at 90° of abduction, with the humerus externally rotated from 90° to the maximum angle, to simulate the late cocking phase of the throwing motion. Loads were applied to the deltoid, pectoralis major, latissimus dorsi, teres major, and all rotator cuff muscles. Contact pressure in the glenohumeral joint was measured with use of a pressure sensor. The area of internal impingement was calculated on the basis of three-dimensional position data. Glenohumeral contact pressure and the area of impingement were compared between 20°, 30°, and 40° of internal scapular rotation; between 20°, 30°, and 40° of upward scapular rotation; and between 0° and 10° of anterior scapular tilt. Data were analyzed with use of repeated-measures analysis of variance with the Tukey post hoc test. RESULTS Contact pressure was at its maximum in the posterior aspect of the glenohumeral joint. The glenohumeral contact pressure and internal impingement area increased with increasing internal scapular rotation. The glenohumeral contact pressure at 40° of internal scapular rotation was significantly (43.4%) greater than that at 20° of internal scapular rotation (p < 0.01), and the impingement area at 40° of internal scapular rotation was significantly (43.1%) greater than that at 20° of internal scapular rotation (p < 0.05). Decreasing upward scapular rotation resulted in an increase in internal impingement area. The internal impingement area at 40° of upward motion was 38.1% less than that at 20° of upward rotation (p < 0.001) and 28.9% less than that at 30° of upward rotation (p < 0.01). CONCLUSIONS Increasing internal scapular rotation and decreasing upward scapular rotation significantly increase glenohumeral contact pressure and the area of impingement of the rotator cuff tendon between the greater tuberosity and glenoid during simulated throwing motion.

Three-Dimensional Imaging and Templating Improve Glenoid Implant Positioning

BACKGROUND Preoperative quantitative assessment of glenoid bone loss, selection of the glenoid component, and definition of its desired location can be challenging. Placement of the glenoid component in the desired location at the time of surgery is difficult, especially with severe glenoid pathological conditions. METHODS Forty-six patients were randomly assigned to three-dimensional computed tomographic preoperative templating with either standard instrumentation or with patient-specific instrumentation and were compared with a nonrandomized group of seventeen patients with two-dimensional imaging and standard instrumentation used as historical controls. All patients had postoperative three-dimensional computed tomographic metal artifact reduction imaging to measure and to compare implant position with the preoperative plan. RESULTS Using three-dimensional imaging and templating with or without patient-specific instrumentation, there was a significant improvement achieving the desired implant position within 5° of inclination or 10° of version when compared with two-dimensional imaging and standard instrumentation. CONCLUSION Three-dimensional assessment of glenoid anatomy and implant templating and the use of these images at the time of surgery improve the surgeons ability to place the glenoid implant in the desired location.

Subscapularis Tendon Tear Classification Based on 3-Dimensional Anatomic Footprint: A Cadaveric and Prospective Clinical Observational Study

PURPOSE The purpose of this study was to define the subscapularis tendon footprint anatomy in 3-dimensional (3D) perspective, report the incidence of tears, and classify the tear patterns prospectively during shoulder arthroscopic surgery. METHODS The cadaveric study consisted of a pilot study that revealed 4 different bony facets by simple observation at the subscapularis attachment. The 3D footprint anatomy was digitally evaluated in 39 cadavers. The clinical study was conducted from 2011 to 2013 and was based on 3D footprint anatomy. All consecutive arthroscopic shoulder operations were prospectively evaluated for subscapularis tendon integrity. A new classification system was developed with 5 categories: (1) type I-fraying or longitudinal split of the subscapularis tendon leading edge; (2) type IIA-less than 50% subscapularis tendon detachment of the first facet; (3) type IIB-greater than 50% detachment without complete disruption of the lateral hood, which is approximately a one-quarter to one-third tear of the entire subscapularis tendons superior-inferior length; (5) type III-entire first facet with complete-thickness tear (lateral hood tear), (5) type IV-first and second facets are exposed with much medial retraction of the tendon (approximately a two-thirds tear of the entire footprint; entire tendinous portion), and (6) type V-complete subscapularis tendon involving the muscular portion (rare). RESULTS The medial-lateral and superior-inferior dimensions of the first facet dimensions were 13.8 × 13.5 mm, respectively; its surface area was 34% of the entire footprint. From superior to inferior, the facets medial-lateral dimensions and surface area decreased. The fourth facet was 77 mm(2) from medial to lateral and encompassed 15% of the footprint. Clinically, among 821 shoulder arthroscopies performed over a 29-month-period, the incidence of subscapularis tears was 415 (50.5%). The most common tear was type IIB (29.4%) or a one-quarter to one-third tear of the entire subscapularis footprint length. However, the incidence between types I, IIA, and IIB did not show a statistically significant difference, indicating an equal distribution. The mean ages of the torn group versus the intact subscapularis group showed a difference. CONCLUSIONS The first facet of the subscapularis tendon footprint consists of approximately one third of the entire footprint, and the first 2 facets consist of 60% of the entire footprint. The probability of finding any extension of the subscapularis tendon tear occurs in approximately 50% of the patients who undergo shoulder arthroscopy for all forms of shoulder disease. Among those subscapularis tendon tears, less than or equal to 80% are first facet tears. LEVEL OF EVIDENCE Level II, diagnostic study.

Effect of Shoulder Abduction Angle on Biomechanical Properties of the Repaired Rotator Cuff Tendons With 3 Types of Double-Row Technique:

Background: After rotator cuff repair, the shoulder is immobilized in various abduction positions. However, there is no consensus on the proper abduction angle. Purpose: To assess the effect of shoulder abduction angle on the biomechanical properties of the repaired rotator cuff tendons among 3 types of double-row techniques. Study Design: Controlled laboratory study. Methods: Thirty-two fresh-frozen porcine shoulders were used. A simulated rotator cuff tear was repaired by 1 of 3 double-row techniques: conventional double-row repair, transosseous-equivalent repair, and a combination of conventional double-row and bridging sutures (compression double-row repair). Each specimen underwent cyclic testing followed by tensile testing to failure at a simulated shoulder abduction angle of 0° or 40° on a material testing machine. Gap formation and failure loads were measured. Results: Gap formation in conventional double-row repair at 0° (1.2 ± 0.5 mm) was significantly greater than that at 40° (0.5 ± 0.3mm, P = .01). The yield and ultimate failure loads for conventional double-row repair at 40° were significantly larger than those at 0° (P < .01), whereas those for transosseous-equivalent repair (P < .01) and compression double-row repair (P < .0001) at 0° were significantly larger than those at 40°. The failure load for compression double-row repair was the greatest among the 3 double-row techniques at both 0° and 40° of abduction. Conclusion: Bridging sutures have a greater effect on the biomechanical properties of the repaired rotator cuff tendon at a low abduction angle, and the conventional double-row technique has a greater effect at a high abduction angle. Clinical Relevance: Proper abduction position after rotator cuff repair differs between conventional double-row repair and transosseous-equivalent repair. The authors recommend the use of the combined technique of conventional double-row and bridging sutures to obtain better biomechanical properties at both low and high abduction angles.

Restoration of Shoulder Biomechanics According to Degree of Repair Completion in a Cadaveric Model of Massive Rotator Cuff Tear Importance of Margin Convergence and Posterior Cuff Fixation

Background: Complete repair in massive rotator cuff tear may not be possible, allowing for only partial repair. However, the effect of partial repair on glenohumeral biomechanics has not been evaluated. Therefore, the purpose of this study was to compare the rotational range of motion (ROM), glenohumeral kinematics, and gap formation at the repaired tendon edge following massive cuff tear and repair according to the degree of repair completion. Hypothesis: Posterior fixation will restore the altered biomechanics of massive rotator cuff tear. Study Design: Controlled laboratory study. Methods: Eight cadaveric shoulders were tested at 0°, 30°, and 60° of abduction in the scapular plane. Muscle loading was applied based on physiological muscle cross-sectional area ratios. Maximum internal (MaxIR) and external rotations (MaxER) were measured. Humeral head apex (HHA) position and gap formation at the repaired tendon edge were measured using a MicroScribe from MaxIR to MaxER in 30° increments. Testing was performed for intact, massive cuff tear, complete repair, and 4 types of partial repair. A repeated-measures analysis of variance was used to determine significant differences. Results: Massive tear significantly increased ROM and shifted HHA superiorly in MaxIR at all abduction angles (P < .05). The complete repair restored ROM to intact (P < .05), while all partial repairs did not. Abnormal HHA elevation due to massive tear was restored by all repairs (P < .05). Release of the anterior single row alone and release of the marginal convergence significantly increased gap formation at the anterior tendon edge (P < .05). Conclusion: This study emphasizes the importance of anterior fixation in massive cuff tear to restore rotational range of motion and decrease gap formation at the repaired tendon edge and of posterior fixation to restore abnormal glenohumeral kinematics due to massive cuff tear. Clinical Relevance: If complete repair of massive cuff tear is not possible, posterior cuff (infraspinatus) repair is necessary to restore abnormal glenohumeral kinematics, and margin convergence anteriorly is recommended to decrease gap formation of the repaired tendon edge, which may provide a better biomechanical environment for healing.

Is Supplementary Fixation Necessary in Anterior Cruciate Ligament Reconstructions

Background: There has been concern regarding the fixation of anterior cruciate ligament reconstruction, with soft tissue grafts being strong and stiff enough to allow for early accelerated postoperative rehabilitation. Therefore, some have recommended supplementary fixation for soft tissue tibia interference screw fixation with a staple, to improve the strength and stiffness of the fixation. Unfortunately, with staple supplementation, there is a risk for symptomatic hardware, which may require a second surgery to remove the staple. Hypothesis: Supplementary fixation with a bioabsorbable knotless suture anchor will improve the structural properties of soft tissue tibia bioabsorbable interference screw (BIS) fixation and be comparable with supplementary fixation with a staple. Study Design: Controlled laboratory study. Method: Fifteen porcine tibias and flexor profundus tendons were randomized into 3 fixation study groups: group 1, BIS; group 2, BIS + staple; and group 3, BIS + push-lock screw. The structural properties of the 3 fixation groups were tested under displacement-controlled cyclic loading and load to failure. Results: No significant difference in mean stiffness (N/mm ± SEM) under cyclic loading was found for BIS (335.31 ± 15.43), BIS + staple (344.81 ± 44.97), and BIS + push-lock (353.28 ± 38.93). Under load-to-failure testing, there were no differences found in stiffness, yield load, displacement at yield load, displacement at ultimate load, and energy absorbed among the 3 fixation methods. BIS + push-lock fixation had a significantly higher ultimate load than BIS alone and BIS + staple (917.85 ± 58.30 N vs 479.83 ± 66.04 N, P = .0003 vs 618.89 ± 8.94 N, P = .004). Conclusion: Supplementary fixation with staple or push-lock screw did not significantly increase the structural strength and stiffness of the BIS soft tissue graft fixation under cyclic loading, but it did show improvement under load-to-failure testing for ultimate tensile load. Clinical Relevance: The indication for supplementary fixation for tibial BIS soft tissue graft fixation depends on the fixation that the BIS achieves at the time of the surgery because the tensile load is transferred to the secondary fixation if and only when there is slippage of graft at the primary fixation. The supplementary fixation may be of value in those cases with poor bone quality, such as revision surgery with tunnel widening and/or graft-tunnel mismatch, or possibly in cases with older patients or patients with disorders affecting bone mineral density.

Biomechanical Analysis of a Knotless Transtendon Interimplant Mattress Repair for Partial-Thickness Articular-Sided Rotator Cuff Tears

Background A transtendon interimplant mattress repair along the medial row for partial-thickness rotator cuff repairs has been described with clinical success. However, the biomechanical characteristics for such a repair have not been elucidated. Hypothesis A knotless interimplant mattress repair may show improved or equivalent load and strain characteristics, compared with a repair using isolated mattress repairs over each of 2 anchors. Study Design Controlled laboratory study. Methods Seven matched pairs of human cadaveric shoulders were dissected. Articular-sided tears were created involving 50% of the supraspinatus footprint. In 7 shoulders, repairs were performed with mattress configurations isolated over each of 2 anchor sites (control group). In 7 contralateral shoulders, a knotless interimplant mattress suture configuration was employed creating bridging sutures between implants. For all specimens, a materials-testing machine was used to cyclically load each repair from 10 to 180 N for 30 cycles; each repair was then loaded to failure. A deformation rate of 1 mm per second was employed for all tests. A video-digitizing system was employed to quantitatively measure the gap formation and strain on the footprint area of the repair. For detecting gap formation, 7 matched pairs were necessary for achieving a power of at least 90%. Results During cyclic loading, gap formation at the anterior tendon was significantly lower in the control group (P < .05) but did not exceed 0.5 mm. There were no significant differences for linear stiffness, hysteresis, and strain between the 2 constructs. During tensile load-to-failure testing, there were no significant differences at yield load between the control and knotless techniques (293.90 ± 132.72 N and 320.38 ± 237.01 N, respectively; P > .05). There were no differences for stiffness, ultimate load, and energy absorbed to failure between the 2 repairs (P > .05). Gap formation in 3 regions was not significantly different between groups at yield and ultimate loads (P > .05). The anterior regions of the repair were the first to fail in all constructs. Conclusion A transtendon interimplant mattress rotator cuff repair for partial articular-sided tendon tears involving 50% of the footprint has biomechanical characteristics similar to those of a repair employing 2 isolated mattress configurations. An interim-plant mattress repair can protect tendon strain; it also exhibits yield loads that exceed those typically experienced in the early postoperative period. Clinical Relevance A medial-row interimplant mattress repair configuration that is knotless may facilitate repair without compromising biomechanical characteristics.

Margin Convergence Anchorage to Bone for Reconstruction of the Anterior Attachment of the Rotator Cable

PURPOSE The purpose of this study was to compare the biomechanical characteristics of a massive L-shaped retracted rotator cuff tear repaired with either soft-tissue side-to-side sutures or margin convergence anchorage to bone. METHODS Eight matched pairs of cadaveric shoulders were used. The supraspinatus and infraspinatus were secured in a clamp at 30° of glenohumeral abduction. The subscapularis was secured in a separate clamp, and a constant load was applied. A massive L-shaped rotator cuff tear of the supraspinatus and infraspinatus tendon was created. In all specimens the posterior aspect of the tear was repaired by a transosseous-equivalent technique. In 1 group we placed 2 margin convergence sutures between the supraspinatus and the rotator interval. In the comparison group, a suture anchor was inserted at the anterior attachment of the rotator cable. Margin convergence anchorage to bone was then performed between the supraspinatus and the rotator interval. Each specimen was tested with an Instron machine (Instron, Canton, MA) and a video digitizing system. A paired t test was used for statistical analysis. RESULTS Margin convergence anchorage to bone decreased gap formation at cycle 1, cycle 30, and yield load across the entire footprint (P < .05). In both constructs the anterior gap was greater than the posterior gap at cycle 1, cycle 30, and yield load (P < .05). Margin convergence anchorage to bone decreased hysteresis and increased stiffness during the first cycle and increased yield load (P < .05). CONCLUSIONS Using margin convergence anchorage to bone to restore the anterior attachment of the rotator cable decreased gap formation across the entire footprint and improved biomechanical properties for cycle 1 and yield load compared with soft-tissue margin convergence for massive rotator cuff repairs. CLINICAL RELEVANCE Repairing the anterior rotator cuff with margin convergence anchorage to bone may improve clinical outcomes of an L-shaped massive tear repair.