Aligned microribbon scaffolds with hydroxyapatite gradient for engineering bone-tendon interface

Injuries of the bone-to-tendon interface, such as rotator cuff and anterior cruciate ligament tears, are prevalent 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 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, here 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 aligned μRBs led to cell alignment in 3D, and HA gradient induced zonal-specific differentiation of MSCs that resembles the transition at the bone-tendon interface. Short chrondrogenic priming prior to 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.

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.

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.

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.

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.

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.

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.

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.

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.

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 β-tricalcium phosphate (β-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-β-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.

A Biomechanical Analysis of 2 Constructs for Metacarpal Spiral Fracture Fixation in a Cadaver Model: 2 Large Screws Versus 3 Small Screws

PURPOSE

Surgeons confronted with a long spiral metacarpal fracture may choose to fix it solely with lagged screws. A biomechanical analysis of a metacarpal spiral fracture model was performed to determine whether 3 1.5-mm screws or 2 2.0-mm screws provided more stability during bending and torsional loading.

METHODS

Second and third metacarpals were harvested from 12 matched pairs of fresh-frozen cadaveric hands and spiral fractures were created. One specimen from each matched pair was fixed with 2 2.0-mm lagged screws whereas the other was fixed with 3 1.5-mm lagged screws. Nine pairs underwent combined cyclic cantilever bending and axial compressive loading followed by loading to failure. Nine additional pairs were subjected to cyclic external rotation while under a constant axial compressive load and were subsequently externally rotated to failure under a constant axial compressive load. Paired t tests were used to compare cyclic creep, stiffness, displacement, rotation, and peak load levels.

RESULTS

Average failure torque for all specimens was 7.2 ± 1.7 Nm. In cyclic torsional testing, the group with 2 screws exhibited significantly less rotational creep than the one with 3 screws. A single specimen in the group with 2 screws failed before cyclic bending tests were completed. No other significant differences were found between test groups during torsional or bending tests.

CONCLUSIONS

Both constructs were biomechanically similar except that the construct with 2 screws displayed significantly less loosening during torsional cyclic loading, although the difference was small and may not be clinically meaningful.

CLINICAL RELEVANCE

Because we found no obvious biomechanical advantage to using 3 1.5-mm lagged screws to fix long spiral metacarpal fractures, the time efficiency and decreased implant costs of using 2-2.0 mm lagged screws may be preferred.

Comparison of mechanical compressive properties of commercial and autologous fibrin glues for tissue engineering applications

BACKGROUND

Fibrin glues are widely used in orthopedic surgery as adhesives and hemostatic agents. We evaluated the compressive properties of selected fibrin glues in order to identify which are appropriate for tissue regeneration applications subject to compression.

METHODS

Uniaxial unconfined compression tests were performed on fibrin gels prepared from commercial and autologous products: (1) Evicel (Ethicon), (2) Tisseel (Baxter), (3) Angel (Arthrex), and (4) ProPlaz (Biorich). Cyclic loads were applied from 0 to 30% strain for 100cycles at 0.5Hz. Following cyclic testing, specimens were subjected to ramp displacement of 1% strain per second to 80% strain.

FINDINGS

Throughout cyclic loading, Evicel and Tisseel deformed (shortened) less than Angel at all but one time point, and deformed less than ProPlaz at cycles 10 and 20. The dynamic moduli, peak stress, and strain energy were significantly greater in Tisseel than all other groups. Evicel displayed significantly greater dynamic moduli, peak stress, and strain energy than Angel and ProPlaz. Following cyclic testing, Tisseel and Evicel were significantly less deformed than Angel. No specimens exhibited gross failure during ramp loading to 80% strain. Ramp loading trends mirrored those of cyclic loading.

INTERPRETATION

The tested commercial glues were significantly more resistant to compression than the autologous products. The compressive properties of Tisseel were approximately twice those of Evicel. All preparations displayed moduli multiple orders of magnitude less than that of native articular cartilage. We conclude that in knee surgeries requiring fibrin glue to undergo compression of daily activity, commercial products are preferable to autologous preparations from platelet-poor plasma, though both will deform significantly.

Gliding Resistance After Epitendinous-First Repair of Flexor Digitorum Profundus in Zone II

PURPOSE

The importance of flexor tendon repair with both core and epitendinous suture placement has been well established. The objective of this study was to determine whether suture placement order affects gliding resistance and bunching in flexor digitorum profundus tendons in a human ex vivo model.

METHODS

The flexor digitorum profundus tendons of the index, middle, ring, and little fingers of paired cadaver forearms were tested intact for excursion and mean gliding resistance in flexion and extension across the A2 pulley. Tendons were subsequently transected and repaired with either an epitendinous-first (n = 12) or a control (n = 12) repair. Gliding resistance of pair-matched tendons were analyzed at cycle 1 and during the steady state of tendon motion. The tendon repair breaking strength was also measured.

RESULTS

The mean steady state gliding resistance was less for the epitendinous-first repair than for the control repair in flexion (0.61 N vs 0.72 N) and significantly less in extension (0.68 N vs 0.85 N). Similar results were seen for cycle 1. None of the repairs demonstrated gap formation; however, control repairs exhibited increased bunching. Load to failure was similar for both groups.

CONCLUSIONS

The order of suture placement for flexor tendon repair is important. Epitendinous-first repair significantly decreased mean gliding resistance, allowed for easier placement of core sutures, and resulted in decreased bunching.

CLINICAL RELEVANCE

Epitendinous-first flexor tendon repairs may contribute to improved clinical outcomes compared with control repairs by decreasing gliding resistance and bunching.

Cyclic and Load to Failure Properties of All-Suture Anchors in Synthetic Acetabular and Glenoid Cancellous Bone

PURPOSE

To evaluate the cyclic displacement, maximum load to failure, and failure mode of multiple all-suture anchors (ASAs) in 2 different densities of sawbones cancellous bone substitute.

METHODS

Anchors tested included the Suturefix Ultra 1.7 mm, JuggerKnot 1.45 mm (No. 1 and No. 2 MaxBraid) and 2.9 mm, Y-Knot Flex 1.3 mm and 1.8 mm, Iconix 1, 2, 25, and 3, Q-Fix 1.8 mm, and Bioraptor 2.3 PK. The Bioraptor served as a non-all-suture-based control. Seven to eleven anchors were tested in both 20 and 30 pounds per cubic foot (pcf) test blocks that were chosen to simulate glenoid and acetabular cancellous bone, respectively. After a 40 N deployment force, anchors were cyclically loaded at 0.5 Hz from 10 to 50 N and then 10 to 100 N for 200 cycles each. Surviving specimens were pulled to failure at 10 mm/s. Displacement, stiffness, maximum load, and failure mode were recorded. Welch t-tests and Welch analysis of variance with Games-Howell post hoc tests were used for statistical analysis.

RESULTS

In higher density blocks, 11 of 12 anchors had significantly (P < .05) higher maximum loads to failure, and 8 anchors showed significantly lower post-cyclic displacement. The Q-Fix 1.8 displayed the lowest post-cyclic displacement in both densities (0.1 ± 0.2 mm, mean ± standard deviation, in both densities). All other groups exhibited at least 2.8 mm and 0.6 mm post-cyclic displacement in 20 and 30 pcf, respectively. The Bioraptor did not survive cyclic testing in 20 pcf and had 0.6 ± 0.3 mm post-cyclic displacement in 30 pcf.

CONCLUSIONS

ASAs show better fixation in higher density synthetic bone. The cyclic displacement and maximum load of ASAs vary widely depending on anchor design and bone density. Most anchors fail by suture anchor pullout. In general, the Bioraptor 2.3 PK outperformed ASAs in higher density test blocks with mixed results in lower density test blocks.

CLINICAL RELEVANCE

ASAs show mixed results compared with a traditional suture anchor. They perform better in higher density bone substitute.

Cancellous Screws Are Biomechanically Superior to Cortical Screws in Metaphyseal Bone

Cancellous screws are designed to optimize fixation in metaphyseal bone environments; however, certain clinical situations may require the substitution of cortical screws for use in cancellous bone, such as anatomic constraints, fragment size, or available instrumentation. This study compares the biomechanical properties of commercially available cortical and cancellous screw designs in a synthetic model representing various bone densities. Commercially available, fully threaded, 4.0-mm outer-diameter cortical and cancellous screws were tested in terms of pullout strength and maximum insertion torque in standard-density and osteoporotic cancellous bone models. Pullout strength and maximum insertion torque were both found to be greater for cancellous screws than cortical screws in all synthetic densities tested. The magnitude of difference in pullout strength between cortical and cancellous screws increased with decreasing synthetic bone density. Screw displacement prior to failure and total energy absorbed during pullout strength testing were also significantly greater for cancellous screws in osteoporotic models. Stiffness was greater for cancellous screws in standard and osteoporotic models. Cancellous screws have biomechanical advantages over cortical screws when used in metaphyseal bone, implying the ability to both achieve greater compression and resist displacement at the screw-plate interface. Surgeons should preferentially use cancellous over cortical screws in metaphyseal environments where cortical bone is insufficient for fixation. [Orthopedics.2016; 39(5):e828-e832.].

Synthesis and characterization of polycaprolactone urethane hollow fiber membranes as small diameter vascular grafts

The design of bioresorbable synthetic small diameter (<6mm) vascular grafts (SDVGs) capable of sustaining long-term patency and endothelialization is a daunting challenge in vascular tissue engineering. Here, we synthesized a family of biocompatible and biodegradable polycaprolactone (PCL) urethane macromers to fabricate hollow fiber membranes (HFMs) as SDVG candidates, and characterized their mechanical properties, degradability, hemocompatibility, and endothelial development. The HFMs had smooth surfaces and porous internal structures. Their tensile stiffness ranged from 0.09 to 0.11N/mm and their maximum tensile force from 0.86 to 1.03N, with minimum failure strains of approximately 130%. Permeability varied from 1 to 14×10(-6)cm/s, burst pressures from 1158 to 1468mmHg, and compliance from 0.52 to 1.48%/100mmHg. The suture retention forces ranged from 0.55 to 0.81N. HFMs had slow degradation profiles, with 15 to 30% degradation after 8weeks. Human endothelial cells proliferated well on the HFMs, creating stable cell layer coverage. Hemocompatibility studies demonstrated low hemolysis (<2%), platelet activation, and protein adsorption. There were no significant differences in the hemocompatibility of HFMs in the absence and presence of endothelial layers. These encouraging results suggest great promise of our newly developed materials and biodegradable elastomeric HFMs as SDVG candidates.

Posterior glenoid wear in total shoulder arthroplasty: eccentric anterior reaming is superior to posterior augment

BACKGROUND

Uncorrected glenoid retroversion during total shoulder arthroplasty may lead to an increased likelihood of glenoid prosthetic loosening. Augmented glenoid components seek to correct retroversion to address posterior glenoid bone loss, but few biomechanical studies have evaluated their performance.

QUESTIONS/PURPOSES

We compared the use of augmented glenoid components with eccentric reaming with standard glenoid components in a posterior glenoid wear model. The primary outcome for biomechanical stability in this model was assessed by (1) implant edge displacement in superior and inferior edge loading at intervals up to 100,000 cycles, with secondary outcomes including (2) implant edge load during superior and inferior translation at intervals up to 100,000 cycles, and (3) incidence of glenoid fracture during implant preparation and after cyclic loading.

METHODS

A 12°-posterior glenoid defect was created in 12 composite scapulae, and the specimens were divided in two equal groups. In the posterior augment group, glenoid version was corrected to 8° and an 8°-augmented polyethylene glenoid component was placed. In the eccentric reaming group, anterior glenoid reaming was performed to neutral version and a standard polyethylene glenoid component was placed. Specimens were cyclically loaded in the superoinferior direction to 100,000 cycles. Superior and inferior glenoid edge displacements were recorded.

RESULTS

Surviving specimens in the posterior augment group showed greater displacement than the eccentric reaming group of superior (1.01 ± 0.02 [95% CI, 0.89-1.13] versus 0.83 ± 0.10 [95% CI, 0.72-0.94 mm]; mean difference, 0.18 mm; p = 0.025) and inferior markers (1.36 ± 0.05 [95% CI, 1.24-1.48] versus 1.20 ± 0.09 [95% CI, 1.09-1.32 mm]; mean difference, 0.16 mm; p = 0.038) during superior edge loading and greater displacement of the superior marker during inferior edge loading (1.44 ± 0.06 [95% CI, 1.28-1.59] versus 1.16 ± 0.11 [95% CI, 1.02-1.30 mm]; mean difference, 0.28 mm; p = 0.009) at 100,000 cycles. No difference was seen with the inferior marker during inferior edge loading (0.93 ± 0.15 [95% CI, 0.56-1.29] versus 0.78 ± 0.06 [95% CI, 0.70-0.85 mm]; mean difference, 0.15 mm; p = 0.079). No differences in implant edge load were seen during superior and inferior loading. There were no instances of glenoid vault fracture in either group during implant preparation; however, a greater number of specimens in the eccentric reaming group were able to achieve the final 100,000 time without catastrophic fracture than those in the posterior augment group.

CONCLUSIONS

When addressing posterior glenoid wear in surrogate scapula models, use of angle-backed augmented glenoid components results in accelerated implant loosening compared with neutral-version glenoid after eccentric reaming, as shown by increased implant edge displacement at analogous times.

CLINICAL RELEVANCE

Angle-backed components may introduce shear stress and potentially compromise stability. Additional in vitro and comparative long-term clinical followup studies are needed to further evaluate this component design.

Anterolateral Versus Medial Plating of Distal Extra-articular Tibia Fractures: A Biomechanical Model

Both medial and anterolateral plate applications have been described for the treatment of distal tibia fractures, each with distinct advantages and disadvantages. The objective of this study was to compare the biomechanical properties of medial and anterolateral plating constructs used to stabilize simulated varus and valgus fracture patterns of the distal tibia. In 16 synthetic tibia models, a 45° oblique cut was made to model an Orthopedic Trauma Association type 43-A1.2 distal tibia fracture in either a varus or valgus injury pattern. Each fracture was then reduced and plated with a precontoured medial or anterolateral distal tibia plate. The specimens were biomechanically tested in axial and torsional loading, cyclic axial loading, and load to failure. For the varus fracture pattern, medial plating showed less fracture site displacement and rotation and was stiffer in both axial and torsional loading (P<.05). For the valgus fracture pattern, there was no statistically significant difference between medial and anterolateral plating. There were no significant differences between the 2 constructs for either fracture pattern with respect to ultimate load, displacement, or energy absorption in load to failure testing. When used to stabilize varus fracture patterns, medial plates showed superior biomechanical performance compared with anterolateral plates. In this application, the medial plates functioned in anti-glide mode. For valgus fracture patterns, no biomechanical differences between anterolateral and medial plating were observed. In clinical practice, surgeons should take this biomechanical evidence into account when devising a treatment strategy for fixation of distal tibia fractures.

Ankle Joint Contact Loads and Displacement With Progressive Syndesmotic Injury

BACKGROUND

Ligamentous injuries to the distal tibiofibular syndesmosis are predictive of long-term ankle dysfunction. Mild and moderate syndesmotic injuries are difficult to stratify, and the impact of syndesmosis injury on the magnitude and distribution of forces within the ankle joint during athletic activities is unknown.

METHODS

Eight below-knee cadaveric specimens were tested in the intact state and after sequential sectioning of the following ligaments: anterior-inferior tibiofibular, anterior deltoid (1 cm), interosseous/transverse (IOL/TL), posterior-inferior tibiofibular, and whole deltoid. In each condition, specimens were loaded in axial compression to 700 N and then externally rotated to 20 N·m torque.

RESULTS

During axial loading and external rotation, both the fibula and the talus rotated significantly after each ligament sectioning as compared to the intact condition. After IOL/TL release, a significant increase in posterior translation of the fibula was observed, although no syndesmotic widening was observed. Mean tibiotalar contact pressure increased significantly after IOL/TL release, and the center of pressure shifted posterolaterally, relative to more stable conditions, after IOL/TL release. There were significant increases in mean contact pressure and peak pressure along with a reduction in contact area with axial loading and external rotation as compared to axial loading alone for all 5 conditions.

CONCLUSION

Significant increases in tibiotalar contact pressures occur when external rotation stresses are added to axial loading. Moderate and severe injuries are associated with a significant increase in mean contact pressure combined with a shift in the center of pressure and rotation of the fibula and talus.

CLINICAL RELEVANCE

Considerable changes in ankle joint kinematics and contact mechanics may explain why moderate syndesmosis injuries take longer to heal and are more likely to develop long-term dysfunction and, potentially, ankle arthritis.

The effect of donor age on structural and mechanical properties of allograft tendons

BACKGROUND

Allograft tendons are commonly used in surgical ligament reconstruction. While it is commonly accepted that donor age will affect mechanical properties of graft tissue, the apparent age threshold is unknown.

HYPOTHESIS

Donor age will significantly influence the structural and mechanical properties of tibialis posterior allograft tendons.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 550 allograft posterior tibialis tendons were examined. Linear stiffness, ultimate tensile force, ultimate displacement, tensile modulus, ultimate tensile strength, and ultimate tensile strain were calculated for specimens from donors in each of 6 age groups: 15-29, 30-39, 40-49, 50-59, 60-69, and 70-79 years. Both first- and second-order polynomial regressions were performed to determine the correlation between structural and mechanical properties and age. Welch analyses of variance with Games-Howell post hoc tests were performed to facilitate comparisons among age groups.

RESULTS

All parameters displayed a weak correlation with age, with the highest R (2) term being 0.063 for ultimate tensile strength. Linear stiffness, ultimate tensile force, and tensile modulus displayed almost no correlation with age. Ultimate tensile strength increased slightly with age up to 40-49 years and then decreased with further increases in age. Slight decreases in ultimate displacement and ultimate tensile strain were observed with increasing age. Numerous statistically significant differences were observed between age groups for each outcome parameter; however, the magnitudes of the differences between age groups are relatively small (<15%) for all outcome parameters.

CONCLUSION

Age explained at most 6% of the variation in structural and mechanical properties of tibialis posterior allograft tendons.

CLINICAL RELEVANCE

Posterior tibialis tendons from all age groups displayed structural properties superior to the native anterior cruciate ligament, with higher stiffness and ultimate force, and less displacement to failure. Although statistically significant differences in structural and mechanical properties were observed between age groups, the magnitudes of the differences are small and most likely not clinically relevant. The age of the donor will not likely affect the suitability of a graft for use in surgical reconstruction.

Comparative potential of juvenile and adult human articular chondrocytes for cartilage tissue formation in three-dimensional biomimetic hydrogels

Regeneration of human articular cartilage is inherently limited and extensive efforts have focused on engineering the cartilage tissue. Various cellular sources have been studied for cartilage tissue engineering including adult chondrocytes, and embryonic or adult stem cells. Juvenile chondrocytes (from donors below 13 years of age) have recently been reported to be a promising cell source for cartilage regeneration. Previous studies have compared the potential of adult and juvenile chondrocytes or adult and osteoarthritic (OA) chondrocytes. To comprehensively characterize the comparative potential of young, old, and diseased chondrocytes, here we examined cartilage formation by juvenile, adult, and OA chondrocytes in three-dimensional (3D) biomimetic hydrogels composed of poly(ethylene glycol) and chondroitin sulfate. All three human articular chondrocytes were encapsulated in the 3D biomimetic hydrogels and cultured for 3 or 6 weeks to allow maturation and extracellular matrix formation. Outcomes were analyzed using quantitative gene expression, immunofluorescence staining, biochemical assays, and mechanical testing. After 3 and 6 weeks, juvenile chondrocytes showed a greater upregulation of chondrogenic gene expression than adult chondrocytes, while OA chondrocytes showed a downregulation. Aggrecan and type II collagen deposition and glycosaminoglycan accumulation were high for juvenile and adult chondrocytes but not for OA chondrocytes. Similar trend was observed in the compressive moduli of the cartilage constructs generated by the three different chondrocytes. In conclusion, the juvenile, adult and OA chondrocytes showed differential responses in the 3D biomimetic hydrogels. The 3D culture model described here may also provide a useful tool to further study the molecular differences among chondrocytes from different stages, which can help elucidate the mechanisms for age-related decline in the intrinsic capacity for cartilage repair.

Plating of metacarpal fractures with locked or nonlocked screws, a biomechanical study: how many cortices are really necessary?

BACKGROUND

Dorsal plate and screw fixation is a popular choice for metacarpal stabilization. The balance between construct stability and soft tissue dissection remains a surgical dilemma. Historically, six cortices of bone fixation on either side of a fracture were deemed necessary. This study aims to elucidate whether four cortices of locked fixation on either side of the fracture is equivalent to the current gold standard of six cortices of nonlocked fixation on either side of the fracture. If so, less dissection to insert shorter plates with fewer screws could be used to stably fix these fractures.

METHODS

With biomechanical testing-grade composite Sawbones, a comminuted metacarpal fracture model was used to test two fixation constructs consisting of a standard dorsal plate and either six bicortical nonlocking screws (three screws per segment) or four bicortical locking screws (two screws per segment). Thirty specimens were tested to failure in cantilever bending and torsion.

RESULTS

There was statistical equivalence between the locking and nonlocking constructs in cantilever bending stiffness, torsional stiffness, maximum bending load, and maximum torque.

CONCLUSION

The tested metacarpal fracture model had equivalent biomechanical properties when fixed with a standard dorsal plate and either six bicortical nonlocking screws or four bicortical locking screws. By utilizing fewer cortices of fixation, there will be less dissection and less soft tissue stripping during fixation of metacarpal fractures. This will also be of benefit in very proximal or distal fractures as multiple cortices of fixation are often difficult to obtain during stabilization of these challenging fractures.