Aligned Gelatin Microribbon Scaffolds with Hydroxyapatite Gradient for Engineering the Bone-Tendon Interface.

Injuries of the bone-to-tendon interface, such as rotator cuff and anterior cruciate ligament tears, are prevalent musculoskeletal injuries, yet effective methods for repair remain elusive. Tissue engineering approaches that use cells and biomaterials offer a promising potential solution for engineering the bone-tendon interface, but previous strategies require seeding multiple cell types and use of multiphasic scaffolds to achieve zonal-specific tissue phenotype. Furthermore, mimicking the aligned tissue morphology present in native bone-tendon interface in three-dimensional (3D) remains challenging. To facilitate clinical translation, engineering bone-tendon interface using a single cell source and one continuous scaffold with alignment cues would be more attractive but has not been achieved before. To address these unmet needs, in this study, we develop an aligned gelatin microribbon (µRB) hydrogel scaffold with hydroxyapatite nanoparticle (HA-np) gradient for guiding zonal-specific differentiation of human mesenchymal stem cell (hMSC) to mimic the bone-tendon interface. We demonstrate that aligned µRBs led to cell alignment in 3D, and HA gradient induced zonal-specific differentiation of mesenchymal stem cells that resemble the transition at the bone-tendon interface. Short chondrogenic priming before exposure to osteogenic factors further enhanced the mimicry of bone-cartilage-tendon transition with significantly improved tensile moduli of the resulting tissues. In summary, aligned gelatin µRBs with HA gradient coupled with optimized soluble factors may offer a promising strategy for engineering bone-tendon interface using a single cell source. Impact statement Our 3D macroporous microribbon hydrogel platform with alignment cues zonally integrated with hydroxyapatite nanoparticles enables differentiation across the bone-tendon interface within a continuous scaffold. While most interfacial scaffolds heretofore rely on composites and multilayer approaches, we present a continuous scaffold utilizing a single cell source. The synergy of niche cues with human mesenchymal stem cell (hMSC) culture leads to an over 45-fold enhancement in tensile modulus in culture. We further demonstrate that priming hMSCs towards the chondrogenic lineage can enhance the differential osteogenesis. Relying on a single cell source could enhance zone integration and scaffold integrity, along with practical benefits.

Safety of Releasing the Volar Capsule During Open Treatment of Distal Radius Fractures: An Analysis of the Extrinsic Radiocarpal Ligaments' Contribution to Radiocarpal Stability.

PURPOSE: The contribution of the extrinsic radiocarpal ligaments to carpal stability continues to be studied. Clinically, there is a concern for carpal instability from release of the volar extrinsic ligaments during volar plating of distal radius fractures in which the integrity of the dorsal ligaments may be unknown. The primary hypothesis of this study was that serial sectioning of radiocarpal ligaments would lead to progressive ulnar translation of the carpus. METHODS: We studied the stabilizing roles of the radioscaphocapitate (RSC), short radiolunate (SRL), long radiolunate (LRL), and dorsal radiocarpal (DRC) ligaments. We sequentially sectioned these ligaments in 2 groups of 5 matched pairs and measured the motion of the scaphoid and lunate with the wrist in passive neutral alignment, radial deviation, ulnar deviation, and simulated grip. Displacement of the lunate in the radioulnar plane was used as a surrogate for carpal translation. The groups differed only by the order in which the ligaments were sectioned. RESULTS: In the intact state, the lunate translated ulnarly during simulated grip and radial deviation, whereas radial translation, relative to its position under resting tension, was observed during ulnar deviation. With serial sectioning, the lunate displayed increased ulnar translation in all wrist positions for both groups 1 and 2. The magnitude of ulnar translation exceeded 1 mm after sectioning the LRL plus RSC along with either the DRC or the SRL. CONCLUSIONS: Sectioning of either the DRC or SRL ligaments along with release of the RSC and LRL ligaments leads to notable although minimal (<2 mm) ulnar lunate translation. CLINICAL RELEVANCE: Isolated sectioning of individual radiocarpal ligaments, such as for visualization of the articular surface of the distal radius, leads to minimal ulnar translation. Because prior clinical work found no clinical complications after volar capsule release, it is posited that translation less than 2 mm creates subclinical changes in carpal mechanics.

Rotational Stability of Scaphoid Waist Nonunion Bone Graft and Fixation Techniques.

PURPOSE: Rotational instability of scaphoid fracture nonunions can lead to persistent nonunion. We hypothesized that a hybrid Russe technique would provide improved rotational stability compared with an instrumented corticocancellous wedge graft in a cadaver model of scaphoid nonunion. METHODS: A volar wedge osteotomy was created at the scaphoid waist in 16 scaphoids from matched-pair specimens. A wedge was inset at the osteotomy site or a 4 × 16-mm strut was inserted in the scaphoid and a screw was placed along the central axis (model 1). The construct was cyclically loaded in torsion until failure. The screw was removed and the proximal and distal poles were debrided. A matching wedge and packed cancellous bone graft or an 8 × 20-mm strut was shaped and fit inside the proximal and distal pole (model 2). A screw was placed and testing was repeated. RESULTS: In the first model, there was no significant difference in cycles to failure, target torque, or maximal torque between the strut graft and the wedge graft. Cycles to failure positively correlated with estimated bone density for the wedge graft, but not for the strut graft. In the second model, the strut graft had significantly higher cycles to failure, greater target torque, and higher maximal torque compared with the wedge graft. The number of cycles to failure was not correlated with estimated bone density for the wedge or the strut grafts. CONCLUSIONS: The hybrid Russe technique of inlay corticocancellous strut and screw fixation provides improved rotational stability compared with a wedge graft with screw fixation for a cadaver model of scaphoid waist nonunion with cystic change. CLINICAL RELEVANCE: The hybrid Russe technique may provide better rotational stability for scaphoid waist nonunions when the proximal or distal scaphoid pole is compromised, such as when there is extensive cystic change, when considerable debridement is necessary, or with revision nonunion surgery.

Interlocking screw configuration influences distal tibial fracture stability in torsional loading after intramedullary nailing.

PURPOSE: This study evaluated the influence of fracture obliquity and locking screw configuration on interfragmentary motion during torsional loading of distal metaphyseal tibial fractures fixed by intramedullary (IM) nailing. METHODS: The stability of six IM nail locking screw configurations used to fix distal metaphyseal tibial fractures of various obliquities was evaluated. A coronal osteotomy from proximal lateral to distal medial was made in sawbone tibiae at different obliquities from 0° to 60°. After fixation, motion at the fracture was assessed during internal and external rotation tests to 7 Nm under two compressive loading conditions: 20 N and 500 N. RESULTS: With results organized by interlocking configuration, significant differences in interfragmentary rotation between fracture obliquities are observed when the number of interlocking screws is decreased to one distal static and one proximal dynamic during internal rotation. During external rotation testing, significant rotational differences between fracture obliquities are encountered with two distal static screws and one proximal dynamic. No significant differences were seen between different distal interlocking screw orientations (two parallel versus perpendicular distal screws) for all fracture obliquity patterns tested. CONCLUSION: Fracture obliquity influences rotational stability which can be mitigated by interlocking screw configurations when nailing distal tibia fractures. At least two distal and one proximal interlocking screw in a static mode is recommended to resist torsional loading of distal tibia fractures undergoing intramedullary nailing. The addition of more interlocking screws than this did not significantly alter control of torsional displacement with load.

The Effect of Growth Differentiation Factor 8 (Myostatin) on Bone Marrow-Derived Stem Cell-Coated Bioactive Sutures in a Rabbit Tendon Repair Model.

Background: We have reported that bioactive sutures coated with bone marrow-derived mesenchymal stem cells (BMSCs) enhance tendon repair strength in an in vivo rat model. We have additionally shown that growth differentiation factor 8 (GDF-8, also known as myostatin) simulates tenogenesis in BMSCs in vitro. The purpose of this study was to determine the possibility of BMSC-coated bioactive sutures treated with GDF-8 to increase tendon repair strength in an in vivo rabbit tendon repair model. Methods: Rabbit BMSCs were grown and seeded on to 4-0 Ethibond sutures and treated with GDF-8. New Zealand white rabbits' bilateral Achilles tendons were transected and randomized to experimental (BMSC-coated bioactive sutures treated with GDF-8) or plain suture repaired control groups. Tendons were harvested at 4 and 7 days after the surgery and subjected to tensile mechanical testing and quantitative polymerase chain reaction. Results: There were distinguishing differences of collagen and matrix metalloproteinase RNA level between the control and experimental groups in the early repair periods (day 4 and day 7). However, there were no significant differences between the experimental and control groups in force to 1-mm or 2-mm gap formation or stiffness at 4 or 7 days following surgery. Conclusions: BMSC-coated bioactive sutures with GDF-8 do not appear to affect in vivo rabbit tendon healing within the first week following repair despite an increased presence of quantifiable RNA level of collagen. GDF-8's treatment efficacy of the early tendon repair remains to be defined.

The Relationship Between the Tensile and the Torsional Properties of the Native Scapholunate Ligament and Carpal Kinematics.

PURPOSE: The purpose of this exploratory study was to examine the relationship between the tensile and the torsional properties of the native scapholunate interosseous ligament (SLIL) and kinematics of the scaphoid and lunate of an intact wrist during passive radioulnar deviation. METHODS: Eight fresh-frozen cadaveric specimens were transected at the elbow joint and loaded into a custom jig. Kinematic data of the scaphoid and lunate were acquired in a simulated resting condition for 3 wrist positions-neutral, 10° radial deviation, and 30° ulnar deviation-using infrared-emitting rigid body trackers. The SLIL bone-ligament-bone complex was then resected and loaded on a materials testing machine. Specimens underwent cyclic torsional and tensile testing and SLIL tensile and torsional laxity were evaluated. Correlations between scaphoid and lunate rotations and SLIL tensile and torsional properties were determined using Pearson correlation coefficients. RESULTS: Ulnar deviation of both the scaphoid and the lunate were found to decrease as the laxity of SLIL in torsion increased. In addition, the ratio of lunate flexion-extension to radial-ulnar deviation was found to increase with increased SLIL torsional rotation. CONCLUSIONS: Our findings support the theory that there is a relationship between scapholunate kinematics and laxity at the level of the interosseous ligaments. CLINICAL RELEVANCE: Laxity and, specifically, the tensile and torsional properties of an individual's native SLIL should guide reconstruction using a graft material that more closely replicates the individual's native SLIL properties.

Influence of fracture obliquity and interlocking nail screw configuration on interfragmentary motion in distal metaphyseal tibia fractures.

The indications for the use of intramedullary (IM) nails have been extended to include extra-articular distal metaphyseal tibia fractures. We hypothesize that interfragmentary motion during physiologic compressive loading of distal tibia fractures is influenced by fracture obliquity and can be modulated by interlocking screw configuration. Sawbone specimens were osteotomized with frontal plane obliquities ranging from 0° to 60° and then fixed by IM nailing with six interlocking screw configurations. Interfragmentary motion was evaluated during loading in axial compression to 1000 N. Comparisons of interfragmentary motions were made (1) between configurations for the various fracture obliquities and (2) between fracture obliquities for the various screw configurations using a mixed-effects regression model. As the degree of fracture obliquity increased, significantly more interfragmentary displacement was shown in configurations with two distal interlocking screws and one proximal screw set in dynamic mode. Fracture obliquity beyond 30° causes demonstrated instability in configurations with less than two distal locking screws and one proximal locking screw. Optimizing the available screw configurations can minimize fracture site motion and shear in distal tibial fractures with larger fracture obliquities.

Biomechanical comparison of bone-screw-fasteners versus traditional locked screws in plating female geriatric bone.

OBJECTIVES: To biomechanically compare plated constructs using nonlocking bone-screw-fasteners with interlocking threads versus locking screws with traditional buttress threads in geriatric female bone. METHODS: Eleven matched pairs of proximal and distal segments of geriatric female cadaveric tibias were used to create a diaphyseal fracture model. Nonlocking bone-screw-fasteners or locking buttress threaded screws were applied to a locking compression plate on the anterolateral aspect of the tibia placed in bridge mode. Specimens were subjected to incrementally increasing cyclic axial load combined with constant cyclic torsion. Total cycles to failure served as a primary outcome measure, with failure defined as 2 mm of displacement or 10 degrees of rotation. Secondary outcome measures included initial stiffness in compression and torsion determined from preconditioning testing and overall rigidity as determined by maximum peak-to-peak axial and rotational motion at 500 cycle intervals during cyclic testing. Group comparisons were made using paired Student's t-tests. Significance was set at p < 0.05. RESULTS: Bone-screw-fastener constructs failed at an average of 40,636 ± 22,151 cycles and locking screw constructs failed at an average of 37,773 ± 8433 cycles, without difference between groups (p = =0.610). Total cycles to failure was higher in the bone-screw-fasteners group for 7 tibiae out of the eleven matched pairs tested. During static and cyclic testing, bone-screw-fastener constructs demonstrated increased initial torsional stiffness (7.6%) and less peak-to-peak displacement and rotation throughout the testing cycle(p < 0.05). CONCLUSIONS: In female geriatric bone, constructs fixed with bone-screw-fasteners incorporate multiplanar interlocking thread geometry and performed similarly to traditional locked plating. These novel devices may combine the benefits of both nonlocking and locking screws when plating geriatric bone.

Ankle joint contact loads and displacement in syndesmosis injuries repaired with Tightropes compared to screw fixation in a static model.

BACKGROUND: The effect of syndesmotic fixation on restoration of pressure mechanics in the setting of a syndesmotic injury is largely unknown. The purpose of this study is to examine the contact mechanics of the tibiotalar joint following syndesmosis fixation with screws versus a flexible fixation device for complete syndesmotic injury. METHODS: Six matched pairs of cadaveric below knee specimens were dissected and motion capture trackers were fixed to the tibia, fibula, and talus and a pressure sensor was placed in the tibiotalar joint. Each specimen was first tested intact with axial compressive load followed by external rotation while maintaining axial compression. Next, syndesmotic ligaments were sectioned and randomly assigned to repair with either two TightRopes® or two 3.5 mm cortical screws and the protocol was repeated. Mean contact pressure, peak pressure, reduction in contact area, translation of the center of pressure, and relative talar and fibular motion were calculated. Specimens were then cyclically loaded in external rotation and surviving specimens were loaded in external rotation to failure. RESULTS: No differences in pressure measurements were observed between the intact and instrumented states during axial load. Mean contact presure relative to intact testing was increased in the screw group at 5 Nm and 7.5 Nm torque. Likewise, peak pressure was increased in the TightRope group at 7.5 Nm torque. There was no change in center of pressure in the TightRope group at any threshold; however, at every threshold tested there was significant medial and anterior translation in the screw group relative to the intact state. CONCLUSION: Either screws or TightRope fixation is adequate with AL alone. With lower amounts of torque, the TightRope group appears to have contact and pressure mechanics that more closely match native mechanics.

The Role of Anterior Capsular Laxity in Hip Microinstability: A Novel Biomechanical Model.

BACKGROUND: Hip microinstability is an increasingly recognized source of hip pain and disability. Although the clinical entity has been well described, the pathomechanics of this disease remain poorly understood. PURPOSE/HYPOTHESIS: The purpose of this study was to determine the role of capsular laxity in atraumatic hip microinstability. Our hypothesis was that cyclic stretching of the anterior hip capsule would result in increased hip range of motion and femoral head displacement. STUDY DESIGN: Controlled laboratory study. METHODS: In this study, 7 hip specimens met inclusion criteria (age, 18-46 years). Specimens were stripped of all soft tissue, aligned, cut, and potted by use of a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation while rotating about the mechanical axis of the hip. A motion tracking system was used to record hip rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing was conducted at baseline, after venting, and after capsular stretching. RESULTS: With the hip in anatomic neutral alignment, cyclic stretching of the anterior hip capsule resulted in increased hip rotation ( P < .001). Femoral head displacement significantly increased relative to the vented state in the medial-lateral ( P < .001), anterior-posterior ( P = .013), and superior-inferior ( P = .036) planes after cyclic stretching of the anterior hip capsule. CONCLUSION: The anterior hip capsule plays an important role in controlling hip rotation and femoral head displacement. This study is the first to display significant increases in femoral head displacement through a controlled cyclic stretching protocol of the anterior hip capsule. CLINICAL RELEVANCE: This study is directly applicable to the treatment of atraumatic hip microinstability. The results quantitatively define the relative importance of the hip capsule in controlling femoral head motion. This allows for a better understanding of the pathophysiological process of hip microinstability and serves as a platform to develop effective surgical techniques for treatment of this disease.

Augmentation of chronic rotator cuff healing using adipose-derived stem cell-seeded human tendon-derived hydrogel.

Rotator cuff (RTC) repair outcomes are unsatisfactory due to the poor healing capacity of the tendon bone interface (TBI). In our preceding study, tendon hydrogel (tHG), which is a type I collagen rich gel derived from human tendons, improved biomechanical properties of the TBI in a rat chronic RTC injury model. Here we investigated whether adipose-derived stem cell (ASC)-seeded tHG injection at the repair site would further improve RTC healing. Rats underwent bilateral supraspinatus tendon detachment. Eight weeks later injured supraspinatus tendons were repaired with one of four treatments. In the control group, standard transosseous suture repair was performed. In the ASC, tHG, tHGASC groups, ASC in media, tHG, and ASC-seeded tHG were injected at repair site after transosseous suture repair, respectively. Eight weeks after repair, the TBI was evaluated biomechanically, histologically, and via micro CT. Implanted ASCs were detected in ASC and tHGASC groups 7 weeks after implantation. ACS implantation improved bone morphometry at the supraspinatus insertion on the humerus. Injection of tHG improved biomechanical properties of the repaired TBI. RTC healing in tHGASC group was significantly better than control but statistically equivalent to the tHG group based on biomechanical properties, fibrocartilage area at the TBI, and bone morphometry at the supraspinatus insertion. In a rat RTC chronic injury model, no biomechanical advantage was gained with ASC augmentation of tHG. Clinical Significance: Tendon hydrogel augmentation with adipose derived stem cells does not significantly improve TBI healing over tHG alone in a chronic rotator cuff injury model. © 2019 Orthopaedic Research Society. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Human Tendon-Derived Collagen Hydrogel Significantly Improves Biomechanical Properties of the Tendon-Bone Interface in a Chronic Rotator Cuff Injury Model.

PURPOSE: Poor healing of the tendon-bone interface (TBI) after rotator cuff (RTC) tears leads to high rates of recurrent tear following repair. Previously, we demonstrated that an injectable, thermoresponsive, type I collagen-rich, decellularized human tendon-derived hydrogel (tHG) improved healing in an acute rat Achilles tendon injury model. The purpose of this study was to investigate whether tHG enhances the biomechanical properties of the regenerated TBI in a rat model of chronic RTC injury and repair. METHODS: Tendon hydrogel was prepared from chemically decellularized human cadaveric flexor tendons. Eight weeks after bilateral resection of supraspinatus tendons, repair of both shoulders was performed. One shoulder was treated with a transosseous suture (control group) and the other was treated with a transosseous suture plus tHG injection at the repair site (tHG group). Eight weeks after repair, the TBIs were evaluated biomechanically, histologically, and via micro-computed tomography (CT). RESULTS: Biomechanical testing revealed a larger load to failure, higher stiffness, higher energy to failure, larger strain at failure, and higher toughness in the tHG group versus control. The area of new cartilage formation was significantly larger in the tHG group. Micro-CT revealed no significant difference between groups in bone morphometry at the supraspinatus tendon insertion, although the tHG group was superior to the control. CONCLUSIONS: Injection of tHG at the RTC repair site enhanced biomechanical properties and increased fibrocartilage formation at the TBI in a chronic injury model. CLINICAL RELEVANCE: Treatment of chronic RTC injuries with tHG at the time of surgical treatment may improve outcomes after surgical repair.

Contributions of the Capsule and Labrum to Hip Mechanics in the Context of Hip Microinstability.

BACKGROUND: Hip microinstability and labral pathology are commonly treated conditions with increasing research emphasis. To date, there is limited understanding of the biomechanical effects of the hip capsule and labrum on controlling femoral head motion. PURPOSE/HYPOTHESIS: The purpose of this study was to determine the relative role of anterior capsular laxity and labral insufficiency in atraumatic hip microinstability. Our hypotheses were that (1) labral tears in a capsular intact state will have a minimal effect on femoral head motion and (2) the capsule and labrum work synergistically in controlling hip stability. STUDY DESIGN: Controlled laboratory study. METHODS: Twelve paired hip specimens from 6 cadaveric pelvises (age, 18-41 years) met the inclusion criteria. Specimens were stripped of all soft tissue except the hip capsule and labrum, then aligned, cut, and potted using a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation, while rotating about the mechanical axis of the hip. Labral insufficiency was created with a combined radial and chondrolabral tear under direct visualization. A motion tracking system was used to record hip internal-external rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing variables included baseline, postventing, postcapsular stretching, and postlabral insufficiency. RESULTS: When comparing the vented state with each experimental pathologic state, increases in femoral head motion were noted in both the capsular laxity state and the labral insufficiency state. The combined labral insufficiency and capsular laxity state produced statistically significant increases (P < .001) in femoral head translation compared with the vented state in all planes of motion. CONCLUSION: Both the anterior capsule and labrum play a role in hip stability. In this study, the anterior hip capsule was the primary stabilizer to femoral head translation, but labral tears in the setting of capsular laxity produced the most significant increases in femoral head translation. CLINICAL RELEVANCE: This study provides a physiologic biomechanical assessment of the hip constraints in the setting of hip microinstability. It also sheds light on the importance of the hip capsule in the management of labral tears. Our study demonstrates that labral tears in isolation provide minimal changes in femoral head translation, but in the setting of a deficient capsule, significant increases in femoral head translation are seen, which may result in joint-related symptoms.

Bennett Fractures: A Biomechanical Model and Relevant Ligamentous Anatomy.

PURPOSE: This study examined a palmar beak fracture model to determine which thumb carpometacarpal (CMC) joint ligament is the primary ligament relevant to the pattern of injury. METHODS: Six fresh-frozen cadaveric wrists were used. The radius, ulna, and first metacarpal were secured and tested with a materials testing system, holding the wrist in 20° extension, 20° ulnar deviation, and 30° palmar abduction of the first metacarpal. Testing consisted of preconditioning cycles followed by compressive loading at 100 mm/s. We confirmed fractures with fluoroscopy and dissected the specimens to examine the CMC joint ligaments. The metacarpal was stressed through a range of motion to determine which maneuvers reduced or displaced the fractures. RESULTS: Our model successfully created palmar beak fractures in all cadaveric specimens. All fractures were displaced and intra-articular. The anterior oblique ligament (AOL) was thin and partially attached to the palmar beak fracture fragment. The ulnar collateral ligament was attached in its entirety to the fracture fragment and represented a thicker, more robust ligament compared with the AOL. Radial abduction and pronation of the metacarpal reduced fracture displacement. Extension of the CMC joint or tensioning the AOL did not decrease fracture displacement. CONCLUSIONS: This model successfully created a reproducible and clinically relevant palmar beak fracture in a biomechanical setting. The primary ligament attached to the palmar beak fracture fragment was the ulnar collateral ligament, and not the AOL as previously described. These findings suggest that the AOL may not be a substantial contributor to palmar beak fracture morphology. CLINICAL RELEVANCE: A refined description of the ligamentous anatomy of the palmar break fracture enhances opportunities for improved reduction and treatment of this common hand injury.

Knotless Anchors in Acetabular Labral Repair: A Biomechanical Comparison.

PURPOSE: To analyze the failure mechanism, stiffness, and pullout strength of acetabular knotless suture anchors. METHODS: Seven suture anchors were tested in high-density (0.48 g/cc) synthetic blocks. The anchors were implanted perpendicular to the bone block. The anchor's suture(s) were tied around a loop of 8 high-strength nonabsorbable sutures and pulled in line with the anchor at a rate of 1 mm/s until failure. The following knotless anchors were tested: Stryker Knotilus 3.5, Arthrex Pushlock 2.9, Linvatec PopLok 2.8, Linvatec PopLok 3.3, ArthroCare SpeedLock HIP (3.4-mm), and Smith & Nephew Bioraptor Knotless 2.9. The standard knot tying Smith & Nephew Bioraptor 2.9 mm served as a baseline for comparison. RESULTS: Stiffness was highest in the Pushlock, the SpeedLock HIP, and Knotilus. At 1 mm displacement, the SpeedLock HIP exhibited significantly higher load than all other anchors, excluding the Pushlock and PopLok 3.3 (P ≤ .012 for all comparisons). Excluding the SpeedLock HIP and Knotilus, the Pushlock displayed significantly higher load than all other anchors at 2-mm displacement (P ≤ .015 for all comparisons). Maximum load was the highest for the Knotilus and Bioraptor knotted anchor (P < .001 compared with all other anchors). CONCLUSIONS: All knotless suture anchors used in hip arthroscopy, except for the Knotilus 3.5, failed by suture pullout from the anchor. The 2 anchors with the highest maximum load, the Knotilus 3.5 and knotted Bioraptor 2.9, failed by suture failure; however, these anchors displayed the lowest stiffness and load at 1 mm displacement among all anchors tested. Stiffness and loads at clinically relevant displacements, not maximum load alone, may be most important in predicting anchor clinical performance during the early phases of labral healing. CLINICAL RELEVANCE: Knotless suture anchors tend to fail by suture pullout from the anchor, yet the stiffness of these constructs suggests that minimal displacement of the repair will occur under physiologic loads.

The effects of a functionally-graded scaffold and bone marrow-derived mononuclear cells on steroid-induced femoral head osteonecrosis.

Osteonecrosis of the femoral head (ONFH) is a debilitating disease that may progress to femoral head collapse and subsequently, degenerative arthritis. Although injection of bone marrow-derived mononuclear cells (BMMCs) is often performed with core decompression (CD) in the early stage of ONFH, these treatments are not always effective in prevention of disease progression and femoral head collapse. We previously described a novel 3D printed, customized functionally-graded scaffold (FGS) that improved bone growth in the femoral head after CD in a normal healthy rabbit, by providing structural and mechanical guidance. The present study demonstrates similar results of the FGS in a rabbit steroid-induced osteonecrosis model. Furthermore, the injection of BMMCs into the CD decreased the osteonecrotic area in the femoral head. Thus, the combination of FGS and BMMC provides a new therapy modality that may improve the outcome of CD for early stage of ONFH by providing both enhanced biological and biomechanical cues to promote bone regeneration in the osteonecrotic area.

Functionally Graded, Bone- and Tendon-Like Polyurethane for Rotator Cuff Repair.

Critical considerations in engineering biomaterials for rotator cuff repair include bone-tendon-like mechanical properties to support physiological loading and biophysicochemical attributes that stabilize the repair site over the long-term. In this study, UV-crosslinkable polyurethane based on quadrol (Q), hexamethylene diisocyante (H), and methacrylic anhydride (M; QHM polymers), which are free of solvent, catalyst, and photoinitiator, is developed. Mechanical characterization studies demonstrate that QHM polymers possesses phototunable bone- and tendon-like tensile and compressive properties (12-74 MPa tensile strength, 0.6-2.7 GPa tensile modulus, 58-121 MPa compressive strength, and 1.5-3.0 GPa compressive modulus), including the capability to withstand 10 000 cycles of physiological tensile loading and reduce stress concentrations via stiffness gradients. Biophysicochemical studies demonstrate that QHM polymers have clinically favorable attributes vital to rotator cuff repair stability, including slow degradation profiles (5-30% mass loss after 8 weeks) with little-to-no cytotoxicity in vitro, exceptional suture retention ex vivo (2.79-3.56-fold less suture migration relative to a clinically available graft), and competent tensile properties (similar ultimate load but higher normalized tensile stiffness relative to a clinically available graft) as well as good biocompatibility for augmenting rat supraspinatus tendon repair in vivo. This work demonstrates functionally graded, bone-tendon-like biomaterials for interfacial tissue engineering.

Headless compression screw for horizontal medial malleolus fractures.

BACKGROUND: Horizontal medial malleolus fractures are caused by the application of rotational force through the ankle joint in several orientations. Multiple techniques are available for the fixation of medial malleolar fractures. METHODS: Horizontal medial malleolus osteotomies were performed in eighteen synthetic distal tibiae and randomized into two fixation groups: 1) two parallel unicortical cancellous screws or 2) two Acutrak 2 headless compression screws. Specimens were subjected to offset axial tension loading. Frontal plane interfragmentary motion was monitored. FINDINGS: The headless compression group (1699 (SD 947) N/mm) had significantly greater proximal-distal stiffness than the unicortical group (668 (SD 298) N/mm), (P = 0.012). Similarly, the headless compression group (604 (SD 148) N/mm) had significantly greater medial-lateral stiffness than the unicortical group (281 (SD 152) N/mm), (P < 0.001). The force at 2 mm of lateral displacement was significantly greater in the headless compression group (955 (SD 79) N) compared to the unicortical group (679 (SD 198) N), (P = 0.003). At 2 mm of distal displacement, the mean force was higher in the headless compression group (1037 (SD 122) N) compared to the unicortical group (729 (SD 229) N), but the difference was not significant (P = 0.131). INTERPRETATION: A headless compression screw construct was significantly stiffer in both the proximal-distal and medial-lateral directions, indicating greater resistance to both axial and shear loading. Additionally, they had significantly greater load at clinical failure based on lateral displacement. The low-profile design of the headless compression screw minimizes soft tissue irritation and reduces need for implant removal.

Tensile and Torsional Structural Properties of the Native Scapholunate Ligament.

PURPOSE: The ideal material for reconstruction of the scapholunate interosseous ligament (SLIL) should replicate the mechanical properties of the native SLIL to recreate normal kinematics and prevent posttraumatic arthritis. The purpose of our study was to evaluate the cyclic torsional and tensile properties of the native SLIL and load to failure tensile properties of the dorsal SLIL. METHODS: The SLIL bone complex was resected from 10 fresh-frozen cadavers. The scaphoid and lunate were secured in polymethylmethacrylate and mounted on a test machine that incorporated an x-y stage and universal joint, which permitted translations perpendicular to the rotation/pull axis as well as nonaxial angulations. After a 1 N preload, specimens underwent cyclic torsional testing (±0.45 N m flexion/extension at 0.5 Hz) and tensile testing (1-50 N at 1 Hz) for 500 cycles. Lastly, the dorsal 10 mm of the SLIL was isolated and displaced at 10 mm/min until failure. RESULTS: During intact SLIL cyclic torsional testing, the neutral zone was 29.7° ± 6.6° and the range of rotation 46.6° ± 7.1°. Stiffness in flexion and extension were 0.11 ± 0.02 and 0.12 ± 0.02 N m/deg, respectively. During cyclic tensile testing, the engagement length was 0.2 ± 0.1 mm, the mean stiffness was 276 ± 67 N/mm, and the range of displacement was 0.4 ± 0.1 mm. The dorsal SLIL displayed a 0.3 ± 0.2 mm engagement length, 240 ± 65 N/mm stiffness, peak load of 270 ± 91 N, and displacement at peak load of 1.8 ± 0.3 mm. CONCLUSIONS: We report the torsional properties of the SLIL. Our novel test setup allows for free rotation and translation, which reduces out-of-plane force application. This may explain our observation of greater dorsal SLIL load to failure than previous reports. CLINICAL RELEVANCE: By matching the natural ligament with respect to its tensile and torsional properties, we believe that reconstructions will better restore the natural kinematics of the wrist and lead to improved outcomes. Future clinical studies should aim to investigate this further.

Customized, degradable, functionally graded scaffold for potential treatment of early stage osteonecrosis of the femoral head.

Osteonecrosis of the femoral head (ONFH) is a debilitating disease that results in progressive collapse of the femoral head and subsequent degenerative arthritis. Few treatments provide both sufficient mechanical support and biological cues for regeneration of bone and vascularity when the femoral head is still round and therefore salvageable. We designed and 3D printed a functionally graded scaffold (FGS) made of polycaprolactone (PCL) and ß-tricalcium phosphate (ß-TCP) with spatially controlled porosity, degradation, and mechanical strength properties to reconstruct necrotic bone tissue in the femoral head. The FGS was designed to have low porosity segments (15% in proximal and distal segments) and a high porosity segment (60% in middle segment) according to the desired mechanical and osteoconductive properties at each specific site after implantation into the femoral head. The FGS was inserted into a bone tunnel drilled in rabbit femoral neck and head, and at 8 weeks after implantation, the tissue formation as well as scaffold degradation was analyzed. Micro-CT analysis demonstrated that the FGS-filled group had a significantly higher bone ingrowth ratio compared to the empty-tunnel group, and the difference was higher at the distal low porosity segments. The in vivo degradation rate of the scaffold was higher in the proximal and distal segments than in the middle segment. Histological analysis of both non-decalcified and calcified samples clearly indicated new bone ingrowth and bone marrow-containing bone formation across the FGS. A 3D printed PCL-ß-TCP FGS appears to be a promising customized resorbable load-bearing implant for treatment of early stage ONFH. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1002-1011, 2018.