Effects of General Anesthesia Plus Multimodal Analgesia on Immediate Perioperative Outcomes of Hamstring Tendon Autograft ACL Reconstruction: A Randomized, Double-Blinded, Placebo-Controlled Trial.

Anterior cruciate ligament reconstruction with hamstring tendon autograft (H-ACLR) is a standard ambulatory procedure with the potential for considerable postoperative pain. We hypothesized that general anesthesia combined with a multimodal analgesia regimen would reduce postoperative opioid use associated with H-ACLR. Methods: This study was a single-center, surgeon-stratified, double-blinded, placebo-controlled, randomized clinical trial. The primary end point was the total postoperative opioid use during the immediate postoperative period, and secondary outcomes included postoperative knee pain, adverse events, and ambulatory discharge efficiency. Results: One hundred and twelve subjects, 18 to 52 years of age, were randomized to placebo (57 subjects) or combination multimodal analgesia (MA) (55 subjects). The MA group required fewer opioids postoperatively (mean ± standard deviation, 9.81 ± 7.58 versus 13.88 ± 8.49 morphine milligram equivalents; p = 0.010; effect size = -0.51). Similarly, the MA group required fewer opioids within the first 24 hours postoperatively (mean ± standard deviation, 16.56 ± 10.77 versus 22.13 ± 10.66 morphine milligram equivalents; p = 0.008; effect size = -0.52). The subjects in the MA group reported lower posteromedial knee pain (median [interquartile range, IQR]: 3.0 [0.0 to 5.0] versus 4.0 [2.0 to 5.0]; p = 0.027) at 1 hour postoperatively. Nausea medication was required for 10.5% of the subjects receiving the placebo versus 14.5% of the subjects receiving MA (p = 0.577). Pruritis was reported for 17.5% of subjects receiving the placebo versus 14.5% receiving MA (p = 0.798). The median time to discharge was 177 minutes (IQR, 150.5 to 201.0 minutes) for subjects receiving placebo versus 188 minutes (IQR, 160.0 to 222.0 minutes) for those receiving MA (p = 0.271). Conclusions: A combination of general anesthesia and local, regional, oral, and intravenous multimodal analgesia appears to reduce postoperative opioid requirements after H-ACLR compared with placebo. Adding preoperative patient education and focusing on donor-site analgesia may maximize perioperative outcomes. Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Risk Factors for Athletic Pubalgia in Collegiate Football Student-Athletes: A Retrospective Cohort Study.

BACKGROUND: Athletic pubalgia (AP) is an increasingly recognized injury among young athletes. This study aimed to evaluate the characteristics associated with AP in college football players. HYPOTHESIS: Repetitive explosive movements that require aggressive core muscle activation results in AP in collegiate football players. STUDY DESIGN: Retrospective cohort design. LEVEL OF EVIDENCE: Level 3. METHODS: Football student-athletes at a single Division I collegiate institution from January 2010 to December 2019 were included in the study. The primary outcome measure was surgery for AP. The odds of AP were determined using logistic regression, with the dependent variable being whether or not the student-athlete received AP surgery. Independent variables included Olympic weightlifting (OWL) exposure, primary playing position (skill position vs nonskill position), and body mass index (BMI). RESULTS: A total of 1154 total student-athlete exposures met the inclusion criteria. Of the 576 student-athletes exposed to OWL (OWL occurred throughout entire calendar year), 20 developed AP, whereas 7 student-athletes not exposed to OWL (OWL was not performed at any point during calendar year) developed AP. Student-athletes exposed to OWL had a 2.86 (95% CI, 1.25-7.35; P = 0.02) times higher odds of AP than players not exposed after controlling for primary playing position and BMI. Skill position players had a 9.32 (95% CI, 1.71-63.96; P = 0.01) times higher odds of AP than nonskill position players when controlling for BMI and OWL training. CONCLUSION: Modifiable factors that increase exposure to repetitive explosive activities, such as OWL and playing a skill position, may be important considerations in developing AP. CLINICAL RELEVANCE: The cause of AP is multifactorial and poorly understood. Identifying factors associated with AP informs athletes, athletic trainers, physicians, and coaches.

Periostin modulates extracellular matrix behavior in tendons.

Periostin, originally named osteoblast-specific factor 2 (OSF-2) has been identified primarily in collagen rich, biomechanically active tissues where its role has been implicated in mechanisms to maintain the extracellular matrix (ECM), including collagen fibrillogenesis and crosslinking. It is well documented that periostin plays a role in wound healing and scar formation after injury, in part, by promoting cell proliferation, myofibroblast differentiation, and/or collagen fibrillogenesis. Given the significance of periostin in other scar forming models, we hypothesized that periostin will influence Achilles tendon healing by modulating ECM production. Therefore, the objective of this study was to elucidate the effects of periostin during Achilles tendon healing using periostin homozygous (Postn -/-) and heterozygous (Postn +/-) mouse models. A second experiment was included to further examine the influence of periostin on collagen composition and function using intact dorsal tail tendons. Overall, Postn -/- and Postn +/- Achilles tendons exhibited impaired healing as demonstrated by delayed wound closure, increased type III collagen production, decreased cell proliferation, and reduced tensile strength. Periostin ablation also reduced tensile strength and stiffness, and altered collagen fibril distribution in the intact dorsal tail tendons. Achilles tendon outcomes support our hypothesis that periostin influences healing, while tail tendon results indicate that periostin also affects ECM morphology and behavior in mouse tendons.

Pitching Behaviors in Youth Fast-Pitched Softball: High Pitching Volumes With Unequal Pitch Counts Among Pitchers are Common.

BACKGROUND: Softball is a popular sport among youth female athletes. While youth baseball has well-established, evidence-based pitching guidelines, youth softball pitching guidelines lack both evidence and enforcement. Adherence to pitch count limits in youth softball is infrequent and results in pitchers with exceedingly high pitching volumes. METHODS: Pitch counts for youth fast-pitch softball teams competing for 1 consecutive year between January 2018 to December 2019 in age groups 8 and under (8U) to 14 and under (14U) were collected. Pitching volume was assessed based on individual games, single calendar days, and tournaments in which games are played on 2 or more consecutive days. Pitchers on teams were subdivided based on pitch count volumes and compared using a logarithmic transformation and geometric mean. RESULTS: Data was collected for 10 teams from each age division resulting in analysis of 538 pitchers on 70 teams. The average pitcher threw 813 pitches per year and appeared in 20.0% of games while the average highest volume pitcher threw 2500 pitches per year and appeared in 54.5% of games. On average, the highest volume pitcher on each team threw 40% of all team pitches, while the 3 highest volume pitchers combined threw 82% of all team pitches. The average and high-volume pitcher threw pitches in 2 or more games on the same day in 37.5% and 48.6% of possible games while pitching 2 or more consecutive days in 64.0% and 79.6% of possible games, respectively. CONCLUSIONS: Softball pitchers throw high volumes of pitches while also pitching multiple days consecutively. A disparity among pitchers on softball teams exists as 40% of team pitches are thrown by 1 player and over 80% of team pitches are thrown by the top 3 pitchers. These high-volume pitchers may be engaging in unsustainable pitching practices that could predispose to injury. LEVEL OF EVIDENCE: Level IV-cross-sectional.

Quantifying the differential functional behavior between the medial and lateral meniscus after posterior meniscus root tears.

Meniscus tears of the knee are among the most common orthopedic knee injury. Specifically, tears of the posterior root can result in abnormal meniscal extrusion leading to decreased function and progressive osteoarthritis. Despite contemporary surgical treatments of posterior meniscus root tears, there is a low rate of healing and an incidence of residual meniscus extrusion approaching 30%, illustrating an inability to recapitulate native meniscus function. Here, we characterized the differential functional behavior of the medial and lateral meniscus during axial compression load and dynamic knee motion using a cadaveric model. We hypothesized essential differences in extrusion between the medial and lateral meniscus in response to axial compression and knee range of motion. We found no differences in the amount of meniscus extrusion between the medial and lateral meniscus with a competent posterior root (0.338mm vs. 0.235mm; p-value = 0.181). However, posterior root detachment resulted in a consistently increased meniscus extrusion for the medial meniscus compared to the lateral meniscus (2.233mm vs. 0.4705mm; p-value < 0.0001). Moreover, detachment of the posterior root of the medial meniscus resulted in an increase in extrusion at all angles of knee flexion and was most pronounced (4.00mm ± 1.26mm) at 30-degrees of knee flexion. In contrast, the maximum mean extrusion of the lateral meniscus was 1.65mm ± 0.97mm, occurring in full extension. Furthermore, only the medial meniscus extruded during dynamic knee flexion after posterior root detachment. Given the differential functional behaviors between the medial and lateral meniscus, these findings suggest that posterior root repair requires reducing overall meniscus extrusion and recapitulating the native functional responses specific to each meniscus.

Pitching Behaviors in Youth Baseball: Comparison With the Pitch Smart Guidelines.

BACKGROUND: The Pitch Smart guidelines aim to limit youth baseball pitching behaviors associated with overuse injuries. Despite many youth baseball leagues being compliant with the guidelines, during tournaments, pitch count restrictions or guidelines are often not followed. PURPOSE: To perform a quantitative analysis of pitch counts in youth baseball players and evaluate compliance with regard to the Pitch Smart guidelines in the tournament setting. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Included in the analysis were 100 youth baseball teams that competed in the 8-and-under to 14-and-under age divisions during the 2019 tournament season. Pitching data were compared with the Pitch Smart guidelines. Violations were identified as (1) exceeding maximum daily pitch count, (2) inadequate rest between pitching events, and (3) pitching more than 1 event on the same day. Pitcher and game factors were analyzed for possible relationships to guideline violations using mixed-effects negative binomial regression models, with comparisons of violations using rate ratios (RRs). RESULTS: Analysis included 1046 pitchers and 2439 games. There were 1866 total Pitch Smart guideline violations, with 48.6% of pitchers having at least 1 violation. Inadequate rest was the most common reason for violation, with noncompliance occurring in 43.3% of pitchers. The highest rate of any violation (0.32 per appearance) occurred in the 8-and-under age division. High-volume pitchers had increased violation rates in each category compared with low-volume pitchers (P < .001). Violation rates were increased more than twice the rate when pitchers participated in ≥5 consecutive games without a rest day when compared with a single game (RR, 2.48; P < .001). CONCLUSION: Noncompliance with Pitch Smart guidelines in tournament settings occurred in more than 90% of teams and almost half of all pitchers. Factors associated with noncompliance included younger pitcher age, high-volume pitching, and pitching in multiple consecutive games. Education of tournament directors, coaches, parents, and athletes regarding pitching guidelines is warranted in order to limit the risk of injury.

Running Biomechanics Before Injury and 1 Year After Anterior Cruciate Ligament Reconstruction in Division I Collegiate Athletes.

BACKGROUND: Preinjury running biomechanics are an ideal comparator for quantifying recovery after anterior cruciate ligament (ACL) reconstruction (ACLR), allowing for assessments within the surgical and nonsurgical limbs. However, availability of preinjury running biomechanics is rare and has been reported in case studies only. PURPOSE/HYPOTHESIS: The purpose of this study was to determine if running biomechanics return to preinjury levels within the first year after ACLR among collegiate athletes. We hypothesized that (1) surgical knee biomechanics would be significantly reduced shortly after ACLR and would not return to preinjury levels by 12 months and (2) nonsurgical limb mechanics would change significantly from preinjury. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Thirteen Division I collegiate athletes were identified between 2015 and 2020 (6 female; mean ± SD age, 20.7 ± 1.3 years old) who had whole body kinematics and ground-reaction forces recorded during treadmill running (3.7 ± 0.6 m/s) before sustaining an ACL injury. Running analyses were repeated at 4, 6, 8, and 12 months (4M, 6M, 8M, 12M) after ACLR. Linear mixed effects models were used to assess differences in running biomechanics between post-ACLR time points and preinjury within each limb, reported as Tukey-adjusted P values. RESULTS: When compared with preinjury, the surgical limb displayed significant deficits at all postoperative assessments (P values <.01; values reported as least squares mean difference [SE]): peak knee flexion angle (4M, 13.2° [1.4°]; 6M, 9.9° [1.4°]; 8M, 9.8° [1.4°]; 12M, 9.0° [1.5°]), peak knee extensor moment (N·m/kg; 4M, 1.32 [0.13]; 6M, 1.04 [0.13]; 8M, 1.04 [0.13]; 12M, 0.87 [0.15]; 38%-57% deficit), and rate of knee extensor moment (N·m/kg/s; 4M, 22.7 [2.4]; 6M, 17.9 [2.3]; 8M, 17.5 [2.4]; 12M, 16.1 [2.6]; 33%-46% deficit). No changes for these variables from preinjury (P values >.88) were identified in the nonsurgical limb. CONCLUSION: After ACLR, surgical limb knee running biomechanics were not restored to the preinjury state by 12M, while nonsurgical limb mechanics remained unchanged as compared with preinjury. Collegiate athletes after ACLR demonstrate substantial deficits in running mechanics as compared with preinjury that persist beyond the typical return-to-sport time frame. The nonsurgical knee appears to be a valid reference for recovery of the surgical knee mechanics during running, owing to the lack of change within the nonsurgical limb.

Intraoperative Conversion to Five-Strand Hamstring Autograft Configuration Significantly Increases Anterior Cruciate Ligament Graft Diameter Independent of Patient Characteristics.

Intraoperative conversion of a four-strand hamstring autograft to a five-strand configuration during an anterior cruciate ligament (ACL) reconstruction has been reported. However, the expected change in graft size and the dependence on patient characteristics are currently not well described. The purpose of this study was to determine the effective change in hamstring graft diameter and reliance on patient characteristics when intraoperatively converting a four-strand hamstring autograft into a five-strand configuration during an ACL reconstruction. A prospective, paired cohort study design was used to measure individual hamstring autograft diameter intraoperatively using traditional four-strand configuration followed by a five-strand configuration. All hamstring tendons included were long enough to consider a five-strand configuration. Five-strand hamstring autograft increased graft diameter in all patients. Hamstring tendon graft diameter increased by an average of 0.99 mm (95% confidence interval [CI]: 0.84-1.11) in the five-strand configuration compared with the traditional four-strand configuration (mean: 7.8 mm). There was no significant difference in the average increase in graft diameter between males (1.04 mm) and females (0.92 mm) (p = 0.323). Eighty-three percent (95% CI: 57.8-95.6) of average graft diameters ≤ 8 mm in the four-strand configuration achieved an average graft diameter of >8 mm in the five-strand configuration, and 70% (95% CI: 35.4- 91.9) of four-strand configuration average diameters < 8 mm achieved an average graft diameter > 8.0 mm in the five-strand configuration. Five-strand hamstring autograft reliably increased intraoperative hamstring tendon autograft diameter, with an average of 1 mm, compared with traditional four-strand configuration. This increase in diameter is independent of sex and remained significant when controlling for age, laterality, body mass index, and semitendinosus length.

Anterior Cruciate Ligament Graft Tunnel Placement and Graft Angle Are Primary Determinants of Internal Knee Mechanics After Reconstructive Surgery.

BACKGROUND: Graft placement is a modifiable and often discussed surgical factor in anterior cruciate ligament (ACL) reconstruction (ACLR). However, the sensitivity of functional knee mechanics to variability in graft placement is not well understood. PURPOSE: To (1) investigate the relationship of ACL graft tunnel location and graft angle with tibiofemoral kinematics in patients with ACLR, (2) compare experimentally measured relationships with those observed with a computational model to assess the predictive capabilities of the model, and (3) use the computational model to determine the effect of varying ACL graft tunnel placement on tibiofemoral joint mechanics during walking. STUDY DESIGN: Controlled laboratory study. METHODS: Eighteen participants who had undergone ACLR were tested. Bilateral ACL footprint location and graft angle were assessed using magnetic resonance imaging (MRI). Bilateral knee laxity was assessed at the completion of rehabilitation. Dynamic MRI was used to measure tibiofemoral kinematics and cartilage contact during active knee flexion-extension. Additionally, a total of 500 virtual ACLR models were created from a nominal computational knee model by varying ACL footprint locations, graft stiffness, and initial tension. Laxity tests, active knee extension, and walking were simulated with each virtual ACLR model. Linear regressions were performed between internal knee mechanics and ACL graft tunnel locations and angles for the patients with ACLR and the virtual ACLR models. RESULTS: Static and dynamic MRI revealed that a more vertical graft in the sagittal plane was significantly related (P < .05) to a greater laxity compliance index (R2 = 0.40) and greater anterior tibial translation and internal tibial rotation during active knee extension (R2 = 0.22 and 0.23, respectively). Similarly, knee extension simulations with the virtual ACLR models revealed that a more vertical graft led to greater laxity compliance index, anterior translation, and internal rotation (R2 = 0.56, 0.26, and 0.13). These effects extended to simulations of walking, with a more vertical ACL graft inducing greater anterior tibial translation, ACL loading, and posterior migration of contact on the tibial plateaus. CONCLUSION: This study provides clinical evidence from patients who underwent ACLR and from complementary modeling that functional postoperative knee mechanics are sensitive to graft tunnel locations and graft angle. Of the factors studied, the sagittal angle of the ACL was particularly influential on knee mechanics. CLINICAL RELEVANCE: Early-onset osteoarthritis from altered cartilage loading after ACLR is common. This study shows that postoperative cartilage loading is sensitive to graft angle. Therefore, variability in graft tunnel placement resulting in small deviations from the anatomic ACL angle might contribute to the elevated risk of osteoarthritis after ACLR.

Extracellular Vesicle-Educated Macrophages Promote Early Achilles Tendon Healing.

Tendon healing follows a complex series of coordinated events, which ultimately produces a mechanically inferior tissue more scar-like than native tendon. More regenerative healing occurs when anti-inflammatory M2 macrophages play a more dominant role. Mesenchymal stromal/stem cells (MSCs) are able to polarize macrophages to an M2 immunophenotype via paracrine mechanisms. We previously reported that coculture of CD14+ macrophages (MQs) with MSCs resulted in a unique M2-like macrophage. More recently, we generated M2-like macrophages using only extracellular vesicles (EVs) isolated from MSCs creating "EV-educated macrophages" (also called exosome-educated macrophages [EEMs]), thereby foregoing direct use of MSCs. For the current study, we hypothesized that cell therapy with EEMs would improve in vivo tendon healing by modulating tissue inflammation and endogenous macrophage immunophenotypes. We evaluated effects of EEMs using a mouse Achilles tendon rupture model and compared results to normal tendon healing (without any biologic intervention), MSCs, MQs, or EVs. We found that exogenous administration of EEMs directly into the wound promoted a healing response that was significantly more functional and more regenerative. Injured tendons treated with exogenous EEMs exhibited (a) improved mechanical properties, (b) reduced inflammation, and (c) earlier angiogenesis. Treatment with MSC-derived EVs alone were less effective functionally but stimulated a biological response as evidenced by an increased number of endothelial cells and decreased M1/M2 ratio. Because of their regenerative and immunomodulatory effects, EEM treament could provide a novel strategy to promote wound healing in this and various other musculoskeletal injuries or pathologies where inflammation and inadequate healing is problematic. Stem Cells 2019;37:652-662.

American Society of Biomechanics Clinical Biomechanics Award 2017: Non-anatomic graft geometry is linked with asymmetric tibiofemoral kinematics and cartilage contact following anterior cruciate ligament reconstruction.

BACKGROUND: Abnormal knee mechanics may contribute to early cartilage degeneration following anterior cruciate ligament reconstruction. Anterior cruciate ligament graft geometry has previously been linked to abnormal tibiofemoral kinematics, suggesting this parameter may be important in restoring normative cartilage loading. However, the relationship between graft geometry and cartilage contact is unknown. METHODS: Static MR images were collected and segmented for eighteen subjects to obtain bone, cartilage, and anterior cruciate ligament geometries for their reconstructed and contralateral knees. The footprint locations and orientation of the anterior cruciate ligament were calculated. Volumetric, dynamic MR imaging was also performed to measure tibiofemoral kinematics, cartilage contact location, and contact sliding velocity while subjects performed loaded knee flexion-extension. Multiple linear regression was used to determine the relationship between non-anatomic graft geometry and asymmetric knee mechanics. FINDINGS: Non-anatomic graft geometry was related to asymmetric knee mechanics, with the sagittal plane graft angle being the best predictor of asymmetry. A more vertical sagittal graft angle was associated with greater anterior tibial translation (ß = 0.11mmdeg, P = 0.049, R2 = 0.22), internal tibial rotation (ß = 0.27degdeg, P = 0.042, R2 = 0.23), and adduction angle (ß = 0.15degdeg, P = 0.013, R2 = 0.44) at peak knee flexion. A non-anatomic sagittal graft orientation was also linked to asymmetries in tibial contact location and sliding velocity on the medial (ß = -4.2mmsdeg, P = 0.002, R2 = 0.58) and lateral tibial plateaus (ß = 5.7mmsdeg, P = 0.006, R2 = 0.54). INTERPRETATION: This study provides evidence that non-anatomic graft geometry is linked to asymmetric knee mechanics, suggesting that restoring native anterior cruciate ligament geometry may be important to mitigate the risk of early cartilage degeneration in these patients.

Osteochondral Graft Size Is Significantly Associated With Increased Force and Decreased Chondrocyte Viability.

BACKGROUND: Insertion force has been shown to significantly reduce chondrocyte viability during osteochondral allograft transplantation. How graft size influences the required insertion force and chondrocyte viability has yet to be determined. Hypothesis/Purpose: The purpose was to characterize how graft size influences insertion force requirements and chondrocyte viability during osteochondral transplantation. The hypothesis was that larger grafts would require greater force and reduce chondrocyte viability. STUDY DESIGN: Controlled laboratory study. METHODS: Four graft sizes-15 × 5 mm, 15 × 10 mm, 25 × 5 mm, and 25 × 10 mm (diameter × depth)-were harvested from 13 thawed fresh-frozen human cadaveric distal femurs. Average, maximum, and cumulative force and number of impacts were recorded for 44 grafts by a surgical mallet embedded with a calibrated force sensor. In a separate experiment, fresh osteochondral tissues were subjected to mechanical loading. To capture a range of clinically important forces, categories were selected to correspond to impaction force data. Chondrocyte viability was assessed with confocal laser microscopy and live/dead staining. RESULTS: Total force for all grafts averaged 4576 N. Median number of impacts for all grafts was 20 (range, 7-116). The mean number of impacts for 5-mm-deep grafts was 14.2 (95% CI, 10.8-18.6), as compared with 26.3 (95% CI, 19.9-34.4) for 10-mm-deep grafts ( P < .001). The mean cumulative force for 5-mm-deep grafts was 2128 N (95% CI, 1467-3087), as opposed to 4689 N (95% CI, 3232-6803) for 10-mm-deep grafts ( P = .001). For every 1 mm in graft depth, an average of 13.1% (95% CI, 6.2%-20.3%) more impacts are required when controlling for diameter and density ( P < .001). For every 1 mm in graft depth, the force required increases on average by 17.1% (95% CI, 7.7%-27.4%) when controlling for diameter and density ( P = .001). There was a significant reduction in chondrocyte viability for the forces required for graft thickness values >10 mm. Only forces associated with graft thickness <10 mm had chondrocyte viabilities consistently >70%. CONCLUSION: Insertion force increases significantly with increasing graft depth. Controlling for diameter and bone density, a 1-mm increase in graft depth is associated with 13.1% more impacts and 17.1% more force. Chondrocyte viability was significantly reduced to <70% at average forces associated with grafts thicker than 10 mm. CLINICAL RELEVANCE: Based on the current data, graft depth is an important consideration for surgeons when sizing osteochondral allograft transplant for chondral lesions of the knee.

Level-specific amputations and resulting regenerative outcomes in the mouse distal phalanx.

Mouse digit tip regeneration involves an intricate coordinated regrowth of the terminal phalanx, nail, dermis and epidermis. During this time, regenerating digits undergo wound healing, blastema formation, and differentiation. However, the regenerative response of the digit is dependent on the level of the amputation. Amputation of <30% of the distal phalanx (P3), with part of the base nail remaining, results in extensive digit regeneration. In contrast, >60% P3 removal results in no regeneration. This level-dependent regenerative ability of the mouse digit provides a comparative model between regeneration and non-regeneration that may enable identification of specific factors critical to regeneration. Although the ability to create regenerating and non-regenerating conditions has been well established, the regenerative response between these regions ("intermediate" zone) has received less scrutiny, and may add insight to the regenerative processes, including the degree of histolysis, and the level of blastema formation. The objective of this study is then to compare the regeneration capacity between amputation levels within the regenerating (<30%), intermediate (40-59%), and non-regenerating (>60%) regions. Results indicated that regenerative and intermediate amputations led to significant histolysis and blastema formation of the distal phalanx 14 days post-amputation. Unlike the regenerating digits, intermediate amputations led to incomplete regeneration whereby regrowth of the digits were not to the levels of the intact or regenerating digits. Non-regenerating amputations did not exhibit significant histolysis or blastema formation. Remarkably, the histolytic process resulted in day 14 P3 lengths that were similar regardless of the initial amputation over 19%. The differences in histolysis, blastema formation and injury outcomes were also marked by changes in the number of proliferating cells and osteoclasts. Altogether, these results indicate that although intermediate amputations result in histolysis and blastema formation similar to regenerating digits, the resulting cellular composition of the blastema differs, contributing to incomplete regeneration.

Intratendinous injections of platelet-rich plasma: feasibility and effect on tendon morphology and mechanics.

BACKGROUND: Intratendinous injections may have important effects on the properties of collagen microarchitecture, morphology, and subsequent mechanical properties of the injected tendon. The purpose of this study was to examine the effects of intratendinous PRP injections; the injectant retention within tendons, the distribution of intratendinous injectant, and whether intratendinous injection or needle fenestration alters tendon morphology or mechanics. DESIGN: Controlled Laboratory Study. INTERVENTIONS: In the first part of the study, 18 lamb extensor tendons were selected to receive methylene blue-containing PRP injection (PRP/MB), methylene blue only injection (MB), or needle fenestration. The volume of retained injectant was measured and injectant distribution and tendon morphology were examined microscopically. In the second portion of the study, 18 porcine flexor tendons were divided into control, needle fenestration, or saline injection groups. Young's Modulus was then determined for each tendon under 0-4% strain. MAIN OUTCOME MEASURES: 1) Injectant volume retained; 2) Injectant distribution; 3) Post-injection/fenestration alterations in morphology, biomechanics. RESULTS: Intratendinous injectant is retained within the tendon. The difference between PRP and PRP/MB groups was not significant (p = 0.78). Intratendinous spread of the injectant solution within the tendon occurs primarily in the proximodistal direction, with very little cross-sectional penetration. Intratendinous injections resulted in microscopic morphology disruption (e.g., separation and disorganization of both the collagen bundles and cellular distribution). There were significant differences in Young's Modulus between control (Ectrl = 2415.48) and injected tendons (Einj = 1753.45) at 4% strain (p = 0.01). There were no differences in Young's Modulus between fenestrated and control tendons. CONCLUSIONS: Intratendinous PRP injections are retained within the tendon, and primarily distributes longitudinally with minimal cross-sectional spread. Intratendinous injections may alter tendon morphology and mechanics.

Effects of BMP-12-releasing sutures on Achilles tendon healing.

Tendon healing is a complex coordinated event orchestrated by numerous biologically active proteins. Unfortunately, tendons have limited regenerative potential and as a result, repair may be protracted months to years. Current treatment strategies do not offer localized delivery of biologically active proteins, which may result in reduced therapeutic efficacy. Surgical sutures coated with nanostructured minerals may provide a potentially universal tool to efficiently incorporate and deliver biologically active proteins directly to the wound. Additionally, previous reports indicated that treatment with bone morphogenetic protein-12 (BMP-12) improved tendon healing. Based on this information, we hypothesized that mineral-coated surgical sutures may be an effective platform for localized BMP-12 delivery to an injured tendon. The objective of this study was, therefore, to elucidate the healing effects of mineral-coated sutures releasing BMP-12 using a rat Achilles healing model. The effects of BMP-12-releasing sutures were also compared with standard BMP-12 delivery methods, including delivery of BMP-12 through collagen sponge or direct injection. Rat Achilles tendons were unilaterally transected and repaired using BMP-12-releasing suture (0, 0.15, 1.5, or 3.0 µg), collagen sponge (0 or 1.5 µg BMP-12), or direct injection (0 or 1.5 µg). By 14 days postinjury, repair with BMP-12-releasing sutures reduced the appearance of adhesions to the tendon and decreased total cell numbers. BMP-12 released from sutures and collagen sponge also tended to improve collagen organization when compared with BMP-12 delivered through injection. Based on these results, the release of a protein from sutures was able to elicit a biological response. Furthermore, BMP-12-releasing sutures modulated tendon healing, and the delivery method dictated the response of the healing tissue to BMP-12.

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

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

Interleukin-1 receptor antagonist modulates inflammation and scarring after ligament injury.

Ligaments have limited regenerative potential and as a consequence, repair is protracted and results in a mechanically inferior tissue more scar-like than native ligament. We previously reported that a single injection of interleukin-1 receptor antagonist (IL-1Ra) delivered at the time of injury, decreased the number of M2 macrophage-associated inflammatory cytokines. Based on these results, we hypothesized that IL-1Ra administered after injury and closer to peak inflammation (as would occur clinically), would more effectively decrease inflammation and thereby improve healing. Since IL-1Ra has a short half-life, we also investigated the effect of multiple injections. The objective of this study was to elucidate healing of a medial collateral ligament (MCL) with either a single IL-1Ra injection delivered one day after injury or with multiple injections of IL-1Ra on days 1, 2, 3, and 4. One day after MCL injury, rats received either single or multiple injections of IL-1Ra or PBS. Tissue was then collected at days 5 and 11. Both single and multiple IL-1Ra injections reduced inflammatory cytokines, but did not change mechanical behavior. A single injection of IL-1Ra also reduced the number of myofibroblasts and increased type I procollagen. Multiple IL-1Ra doses provided no additive response and, in fact, reduced the M2 macrophages. Based on these results, a single dose of IL-1Ra was better at reducing the MCL-derived inflammatory cytokines compared to multiple injections. The changes in type I procollagen and myofibroblasts further suggest a single injection of IL-1Ra enhanced repair of the ligament but not sufficiently to improve functional behavior.

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

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

Interleukin expression after injury and the effects of interleukin-1 receptor antagonist.

Ligament healing follows a series of complex coordinated events involving various cell types, cytokines, as well as other factors, producing a mechanically inferior tissue more scar-like than native tissue. Macrophages provide an ongoing source of cytokines to modulate inflammatory cell adhesion and migration as well as fibroblast proliferation. Studying interleukins inherent to ligament healing during peak macrophage activation and angiogenesis may elucidate inflammatory mediators involved in subsequent scar formation. Herein, we used a rat healing model assayed after surgical transection of their medial collateral ligaments (MCLs). On days 3 and 7 post-injury, ligaments were collected and used for microarray analysis. Of the 12 significantly modified interleukins, components of the interleukin-1 family were significantly up-regulated. We therefore examined the influence of interleukin-1 receptor antagonist (IL-1Ra) on MCL healing. Transected rat MCLs received PBS or IL-1Ra at the time of surgery. Inhibition of IL-1 activation decreased pro-inflammatory cytokines (IL-1α, IL-1ß, IL-12, IL-2, and IFN-γ), myofibroblasts, and proliferating cells, as well as increased anti-inflammatory cytokines (IL-10), endothelial cells/blood vessel lumen, M2 macrophages, and granulation tissue size without compromising the mechanical properties. These results support the concept that IL-1Ra modulates MCL-localized granulation tissue components and cytokine production to create a transient environment that is less inflammatory. Overall, IL-1Ra may have therapeutic potential early in the healing cascade by stimulating the M2 macrophages and altering the granulation tissue components. However, the single dose of IL-1Ra used in this study was insufficient to maintain the more regenerative early response. Due to the transient influence on most of the healing components tested, IL-1Ra may have greater therapeutic potential with sustained delivery.