Maxwell C. Park

Tendon-to-Bone Pressure Distributions at a Repaired Rotator Cuff Footprint Using Transosseous Suture and Suture Anchor Fixation Techniques

Background Interface contact pressure between the tendon and bone has been shown to influence healing. This study evaluates the interface pressure of the rotator cuff tendon to the greater tuberosity for different rotator cuff repair techniques. Hypothesis The transosseous tunnel rotator cuff repair technique provides larger pressure distributions over a defined insertion footprint than do suture anchor techniques. Study Design Controlled laboratory study. Methods Simulated rotator cuff tears over a 1 × 2-cm infraspinatus insertion footprint were created in 25 bovine shoulders. A transosseous tunnel simple suture technique (n = 8), suture anchor simple technique (n = 9), and suture anchor mattress technique (n = 8) were used for repair. Pressurized contact areas and mean pressures of the repaired tendon against the tuberosity were determined using pressure-sensitive film placed between the tendon and the tuberosity. Results The mean contact area between the tendon and tuberosity insertion footprint was significantly greater for the transosseous technique (67.7 ± 5.8 mm2) compared with the suture anchor simple (34.1 ± 9.4 mm2) and suture anchor mattress (26.0 ±5.3 mm2) techniques (P < .05). The mean interface pressure exerted over the footprint by the tendon was also greater for the transosseous technique (0.32 ± 0.05 MPa) compared with the suture anchor simple (0.26 ± 0.04 MPa) and suture anchor mattress (0.24 ± 0.02 MPa) techniques (P < .05). Conclusion The transosseous tunnel rotator cuff repair technique creates significantly more contact and greater overall pressure distribution over a defined footprint when compared with suture anchor techniques. Clinical Relevance Stronger and faster rotator cuff healing may be expected when beneficial pressure distributions exist between the repaired rotator cuff and its insertion footprint. Tendon-to-tuberosity pressure and contact characteristics should be considered in the development of improved open and arthroscopic rotator cuff repair techniques.

Dynamic Contributions of the Flexor-pronator Mass to Elbow Valgus Stability

BACKGROUND Previous studies have indicated that the demands placed on the medial ulnar collateral ligament of the elbow when it is subjected to valgus torque during throwing exceed its failure strength, which suggests the necessary dynamic contribution of muscle forces. We hypothesized that the flexor-pronator mass assists the medial ulnar collateral ligament in stabilizing the elbow against valgus torque. METHODS Six cadaveric elbows were tested at 30 degrees and 90 degrees of flexion with no other constraints to motion. A full medial ulnar collateral ligament tear was simulated in each elbow. Muscle forces were simulated on the basis of the centroids and physiological cross-sectional areas of individual muscles. The biceps, brachialis, and triceps were simulated during flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum superficialis and flexor carpi ulnaris, and pronator teres-loading conditions. Kinematic data were obtained at each flexion angle with use of a three-dimensional digitizer. RESULTS Release of the medial ulnar collateral ligament caused a significant increase in valgus instability of 5.9 degrees +/- 2.4 degrees at 30 degrees of elbow flexion and of 4.8 degrees +/- 2.0 degrees at 90 degrees of elbow flexion (p < 0.05). The differences in valgus angulation between each muscle-simulation condition and the medial ulnar collateral ligament-intact condition were significantly different from each other (p < 0.05), except for the difference between the flexor carpi ulnaris contraction condition and the flexor digitorum superficialis-flexor carpi ulnaris co-contraction condition. This co-contraction provided the most correction of the valgus angle in comparison with the intact condition at both 30 degrees and 90 degrees of elbow flexion (1.1 degrees +/- 1.8 degrees and 0.38 degrees +/- 2.3 degrees , respectively). Simulation of the flexor carpi ulnaris alone provided the greatest reduction of the valgus angle among all individual flexor-pronator mass muscles tested (p < 0.05), whereas simulation of the pronator teres alone provided the least reduction of the valgus angle (p < 0.05). CONCLUSIONS The flexor-pronator mass dynamically stabilizes the elbow against valgus torque. The flexor carpi ulnaris is the primary stabilizer, and the flexor digitorum superficialis is a secondary stabilizer. The pronator teres provides the least dynamic stability.

Two-part and three-part fractures of the proximal humerus treated with suture fixation.

Objective To evaluate the radiographic and clinical outcomes of patients with displaced proximal humerus fractures (two-part and three-part) treated with nonabsorbable rotator cuff–incorporating sutures. Design Retrospective. Setting University hospital. Patients There were 27 patients (28 shoulders) with displaced proximal humerus fractures. There were 13 greater tuberosity (GT) and 9 surgical neck (SN) two-part fractures and 6 GT/SN three-part fractures. The average age was 64 years (range 38 to 84 years). The average follow-up was 4.4 years (range 1.0 to 11.5 years). Intervention All patients were surgically treated solely with heavy polyester nonabsorbable sutures. Main Outcome Measurements Functional assessment was obtained using the American Shoulder and Elbow Surgeons (ASES) score and Neers criteria, which grade outcomes as excellent, satisfactory, or unsatisfactory. Results Overall, there were 22 (78%) excellent, 3 (11%) satisfactory, and 3 (11%) unsatisfactory results, and the average ASES score was 87.1 (range 35.0 to 100.0). All shoulders healed radiographically without evidence of avascular necrosis of the humeral head. Twenty-four shoulders (86%) had anatomic alignment on postoperative radiographs. Of four shoulders with nonanatomic alignment, three had ASES scores of ≥90, with excellent Neer scores. When comparing patients with isolated two-part GT fractures (n = 13) with patients having two-part SN or three-part SN/GT fractures (n = 15), there were no statistically significant differences with respect to range of motion (P > 0.05) and outcome measures (P > 0.05). All patients who had unsatisfactory outcomes were noncompliant with physical therapy, with ASES scores averaging 39.4 (range 35.0 to 43.3). Conclusion Two-part and three-part GT and SN fractures can be treated satisfactorily with heavy nonabsorbable rotator cuff–incorporating sutures, particularly in elderly patients. Hardware-associated complications are obviated. Patients with SN fractures treated with sutures can have outcomes similar to patients with two-part GT fractures. Although the goal is to reconstruct a “one-part” fracture pattern, some residual deformity does not preclude an excellent outcome. A compliant patient is crucial for a successful result.

The Effect of Dynamic External Rotation Comparing 2 Footprint-Restoring Rotator Cuff Repair Techniques

Background Allowing for humeral external rotation while loading rotator cuff repairs has been shown to affect tendon biomechanics when compared with testing with the humerus fixed. Adding dynamic external rotation to a tendon-loading model using footprint-restoring repairs may improve our understanding of rotator cuff repair response to a common postoperative motion. Hypothesis A tendon suture-bridging repair will demonstrate better load sharing compared to a double-row repair, and there will be a differential gap formation between the anterior and posterior tendon regions. Study Design Controlled laboratory study. Methods In 6 fresh-frozen human cadaveric shoulders, a tendon suture-bridging rotator cuff repair was performed; a suture limb from each of 2 medial anchors was bridged over the tendon and fixed laterally with an interference screw. In 6 contralateral match-paired specimens, a double-row repair was performed. For all specimens, a custom jig was employed that allowed dynamic external rotation (0° to 30°) with loading. A materials testing machine was used to cyclically load each repair from 0 N to 90 N for 30 cycles; each repair was then loaded to failure. A deformation rate of 1 mm/s was employed for all tests. Gap formation between tendon edge and insertion was measured using video digitizing software. Results The yield load for the suture-bridging technique (161.88 ± 35.09 N) was significantly larger than the double-row technique (135.17 ± 24.03 N) (P = .026). The yield gap between tendon and lateral footprint was significantly greater anteriorly than posteriorly (1.62 ± 0.82 mm and 0.68 ± 0.47 mm, respectively) for the suture-bridging technique (P = .024) but not for the double-row technique (1.35 ± 0.52 mm and 1.05 ± 0.50 mm, respectively) (P = .34). There were no differences for gap formation, stiffness, ultimate load to failure, and energy absorbed to failure between the 2 repairs (P > .05). The anterior regions of the repair were the first to fail in all constructs. The suture-bridging repair remained interconnected for 5 of 6 repairs. Conclusions The tendon suture-bridging rotator cuff repair has a yield load that is higher than the double-row repair when allowing for external rotation during load testing. External rotation can accentuate gap formation anteriorly at a repaired rotator cuff footprint. Clinical Relevance Based on the tension of repair, there may be a role for reinforcing the repair anteriorly and limiting external rotation postoperatively.

Elbow Medial Ulnar Collateral Ligament Insufficiency Alters Posteromedial Olecranon Contact

Background The effect of elbow medial ulnar collateral ligament injury on posteromedial compartment contact is unknown. Hypothesis Medial ulnar collateral ligament injury causes altered contact area and pressure in the posteromedial compartment of the elbow. Study Design Controlled laboratory study. Methods Seven elbow cadaveric specimens were tested in an apparatus that positioned the elbow at 30° and 90° of flexion. Partial and full tears were simulated by releasing the medial ulnar collateral ligament. Pressure-sensitive film was placed in the posteromedial compartment for each condition. Valgus torques of 1.25 and 2.0 N.m were applied for each ligament condition, and kinematic data were obtained at each flexion angle using a 3-dimensional digitizer. Results Both ligament condition and valgus load had significant effects on contact area and pressure (P < .05). For a given load and flexion angle, the contact area decreased and the pressure increased with increasing medial ulnar collateral ligament insufficiency. Within these trends, statistical significance was found at 30° of elbow flexion for both area and pressure (P < .05); at 90° of elbow flexion, increasing medial ulnar collateral ligament insufficiency did not significantly affect contact area or pressure (P > .05). Discussion Medial ulnar collateral ligament insufficiency alters contact area and pressure between the posteromedial trochlea and olecranon and helps explain the development of posteromedial osteophytes.

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.

The Effect of Abduction and Rotation on Footprint Contact for Single-Row, Double-Row, and Modified Double-Row Rotator Cuff Repair Techniques

Background An abduction pillow and abduction and rotation exercises are commonly used after rotator cuff repair. The effect of glenohumeral abduction and rotation on footprint contact has not been elucidated. Hypothesis Abduction will decrease tendon-to-bone contact for all repairs. A modified double-row repair will maintain footprint contact more effectively at each position of humeral abduction and rotation than double- or single-row repairs. Study Design Controlled laboratory study. Methods In 6 fresh-frozen human shoulders, a modified double-row supraspinatus tendon repair was performed; a suture limb from each of 2 medial anchors was bridged over the tendon and fixed laterally. Double- and single-row repairs were performed sequentially; a total of 3 repairs were tested. For all repairs, a Tekscan pressure sensor was fixed at the tendon-footprint interface. The tendon was loaded with 30 N. The shoulders were tested at 0°, 30°, and 60° of abduction with 0° of rotation. For both dual-row repairs, 5 rotation positions were tested. Results The greatest contact areas at neutral rotation were achieved at 0° of abduction for the modified double-row, double-row, and single-row repairs (151.3 ± 10.7 mm2, 80.7 ± 30.0 mm2, and 61.3 ± 26.1 mm2, respectively), with values decreasing as abduction increased. Each repair was significantly different from one another at each abduction angle (P <. 05), except between single-and double-row repairs at 0° of abduction. Mean interface pressure exerted over the footprint was greater for the modified double-row technique than for the other techniques at each abduction angle (P <. 05). With respect to rotation, the modified double-row repair had significantly more footprint contact than did the double-row repair at each position tested (P <. 05). Conclusion For a given repair, increasing abduction at neutral rotation reduced footprint contact. Internal rotation to 60° provided among the highest contact measurements. The modified double-row technique provided the most contact. Clinical Relevance Results are consistent with the practice of immobilizing the shoulder with 30° or less of abduction and up to 60° of internal rotation to optimize footprint contact. A dual-row repair may maximize contact when initiating rehabilitation that involves abduction and rotation.

Influence of distinct anatomic subregions of the supraspinatus on humeral rotation

The supraspinatus, having distinct anterior and posterior subregions, is most commonly considered an abductor of the humerus, but it has also been shown to induce humeral rotation. The objective of this study was to quantify the magnitude and direction of humeral rotation that results from loading the distinct anterior and posterior subregions of the supraspinatus. Fourteen cadaver specimens were tested under four loading conditions based on physiological cross section area of the supraspinatus: (1) anterior only; (2) posterior only; (3) physiologic (each subregion loaded simultaneously); and (4) nonphysiologic (the tendon loaded as a whole). Each specimen was tested at 0, 15, 30, 45, and 60° of glenohumeral abduction in the scapular plane and from 60° of internal to 45° of external rotation in 15° increments. The humeral rotation that occurred with loading from the initial starting rotation position was measured using a rotary variable inductance transducer. In the scapular plane, the anterior subregion of the supraspinatus acts as both an internal and external rotator depending on the initial position of the humerus. The posterior subregion either acted as an external rotator or did not induce rotation. This study demonstrated a distinct functional difference between the anatomic subregions of the supraspinatus. This understanding will help to improve testing methods and the development of repair strategies of the supraspinatus.

Revision Ulnar Collateral Ligament Reconstruction Using a Suspension Button Fixation Technique

Background Revision ulnar collateral ligament reconstruction remains a challenging problem. The objective of this study was to biomechanically evaluate an ulnar collateral ligament reconstruction technique using a suspension button fixation technique that can be used even in the case of ulnar cortical bone loss. Hypothesis An ulnar suspension fixation technique for ulnar collateral ligament reconstruction can restore elbow kinematics and demonstrate failure strength comparable to that of currently available techniques. Study Design Controlled laboratory study. Methods Nine pairs of cadaveric elbows were dissected free of soft tissue and potted. After simulating ulnar cortical bone loss, ulnar collateral ligament reconstruction was performed in 1 elbow of each pair using palmaris longus autograft and a 30-mm RetroButton suspended from the far (lateralmost) ulnar cortex. A docking technique was used for humeral fixation of the graft. Elbow valgus angle was quantified using a Microscribe 3DLX digitizer at multiple elbow flexion angles. Valgus angle was measured with the ulnar collateral ligament intact, transected, and reconstructed. In addition, load-to-failure testing was performed in 1 elbow of each pair. Results Release of the ulnar collateral ligament caused a significant increase in valgus angle at each flexion angle tested (P < .002). Reconstructed elbows demonstrated no significant differences in valgus angle from the intact elbow at all flexion angles tested. Load-to-failure tests showed that reconstructed elbows had an ultimate torque (10.3 ± 5.7 N·m) significantly less than intact elbows (26.4 ± 10.6 N·m) (P = .001). Conclusion Ulnar collateral ligament reconstruction using a suspension button fixation technique reliably restored elbow kinematics to the intact state. Load-to-failure testing demonstrated comparable fixation strength to several historic controls of primary reconstruction techniques despite the simulated ulnar cortical bone loss. Clinical Relevance Ulnar collateral ligament reconstruction using a suspension button fixation technique can be considered in the case of ulnar cortical bone loss in a primary or revision setting.

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.