Natalie L. Leong

Current tissue engineering strategies in anterior cruciate ligament reconstruction

Rupture of the anterior cruciate ligament (ACL) is one of the most common ligamentous injuries of the knee. Limitations of allografts and autografts in ACL reconstruction as well as recent advancements in biology and materials science have spurred interest in developing tissue-engineered ACL replacements that have the potential to mimic the native ACL in terms of both biological and mechanical properties. This article reviews the current literature regarding contemporary tissue engineering strategies. The four basic components of tissue engineering, biomaterial scaffolds, cell sources, growth factors, and mechanical stimuli, as applied to the development of tissue-engineered ACL replacement grafts, will be systematically addressed. In addition, animal models that have been used to test these tissue-engineered ACL replacements will also be reviewed. To date, there is no tissue-engineered ACL construct that has been successfully implanted in humans. We expect that continued progress in designing a viable tissue-engineered ACL replacement will accompany rapidly advancing techniques in materials science and biology.

In vitro and in vivo evaluation of heparin mediated growth factor release from tissue-engineered constructs for anterior cruciate ligament reconstruction.

Anterior cruciate ligament (ACL) rupture is a common injury often necessitating surgical treatment with graft reconstruction. Due to limitations associated with current graft options, there is interest in a tissue‐engineered substitute for use in ACL regeneration. While they represent an important step in translation to clinical practice, relatively few in vivo studies have been performed to evaluate tissue‐engineered ACL grafts. In the present study, we immobilized heparin onto electrospun polycaprolactone scaffolds as a means of incorporating basic fibroblast growth factor (bFGF) onto the scaffold. In vitro, we demonstrated that human foreskin fibroblasts (HFFs) cultured on bFGF‐coated scaffolds had significantly greater cell proliferation. In vivo, we implanted electrospun polycaprolactone grafts with and without bFGF into athymic rat knees. We analyzed the regenerated ACL using histological methods up to 16 weeks post‐implantation. Hematoxylin and eosin staining demonstrated infiltration of the grafts with cells, and picrosirius red staining demonstrated aligned collagen fibers. At 16 weeks postop, mechanical testing of the grafts demonstrated that the grafts had approximately 30% the maximum load to failure of the native ACL. However, there were no significant differences observed between the graft groups with or without heparin‐immobilized bFGF. While this study demonstrates the potential of a regenerative medicine approach to treatment of ACL rupture, it also demonstrates that in vitro results do not always predict what will occur in vivo.

Demographic Trends and Complication Rates in Arthroscopic Elbow Surgery

PURPOSE To investigate demographic trends in elbow arthroscopy over time, as well as to query complication rates requiring reoperation associated with these procedures. METHODS The Current Procedural Terminology (CPT) billing codes of patients undergoing elbow arthroscopy were searched using a national insurance database. From the years 2007 to 2011, over 20 million orthopaedic patient records were present in the database with an orthopaedic International Classification of Diseases, Ninth Revision diagnosis code or CPT code. Our search for procedures and the corresponding CPT codes for the elbow included diagnostic arthroscopy, loose body removal, synovectomy, and debridement. The type of procedure, date, gender, and region of the country were identified for each patient. In addition, the incidence of reoperation for infection, stiffness, and nerve injury was examined. RESULTS There was a significant increase in arthroscopic elbow procedures over the study period. Male patients accounted for 71% of patients undergoing these procedures. Of the elbow arthroscopy patients, 22% were aged younger than 20 years, 25% were aged 20 to 39 years, 47% were aged 40 to 59 years, and 6% were aged 60 years or older. Other than synovectomy, there were regional variations in the incidence of each procedure type. The overall rate of reoperation was 2.2%, with specific rates of 0.26% for infection, 0.63% for stiffness, and 1.26% for nerve injury. It should be noted that because only the complications requiring reoperation are recorded in the database, these numbers are lower than the overall complication rate. CONCLUSIONS Overall, the incidence of elbow arthroscopy in this patient population is relatively low and appears to be increasing slightly over time. In the database used in this study, elbow arthroscopy procedures were most commonly performed in male patients and in patients aged 40 to 59 years, with regional variation in the incidence of the different procedures. Furthermore, the rate of complications requiring reoperation was low, with a nerve operation being the most common reoperation performed. LEVEL OF EVIDENCE Level IV, therapeutic case series.

Use of ultra-high molecular weight polycaprolactone scaffolds for ACL reconstruction

Previously, we reported on the implantation of electrospun polycaprolactone (PCL) grafts for use in ACL tissue engineering in a small animal model. In the present study, we hypothesized that grafts fabricated from ultra‐high molecular weight polycaprolactone (UHMWPCL) would have similarly favorable biologic properties but superior mechanical properties as compared to grafts fabricated from PCL. Two forms of polycaprolactone were obtained (UHMWPCL, MW = 500 kD, and PCL, MW = 80 kD) and electrospun into scaffolds that were used to perform ACL reconstruction in 7–8 week old male Lewis rats. The following groups were examined: UHMWPCL, PCL, flexor digitorum longus (FDL) allograft, native ACL, as well as sham surgery in which the ACL was transsected. At 16 weeks post‐operatively, biomechanical testing, histology, and immunohistochemistry (IHC) were performed. Analysis of cellularity indicated that there was no significant difference among the UHMWPCL, PCL, and FDL allograft groups. Quantification of birefringence from picrosirius red staining demonstrated significantly more aligned collagen fibers in the allograft than the PCL group, but no difference between the UHMWPCL and allograft groups. The peak load to failure of the UHMWPCL grafts was significantly higher than PCL, and not significantly different from FDL allograft. This in vivo study establishes the superiority of the higher molecular weight version of polycaprolactone over PCL as a scaffold material for ACL reconstruction. By 16 weeks after implantation, the UHMWPCL grafts were not significantly different from the FDL allografts in terms of cellularity, peak load to failure, stiffness, and collagen fiber alignment.

Hypoxic culture conditions induce increased metabolic rate and collagen gene expression in ACL-derived cells.

There has been substantial effort directed toward the application of bone marrow and adipose‐derived mesenchymal stromal cells (MSCs) in the regeneration of musculoskeletal tissue. Recently, resident tissue‐specific stem cells have been described in a variety of mesenchymal structures including ligament, tendon, muscle, cartilage, and bone. In the current study, we systematically characterize three novel anterior cruciate ligament (ACL)‐derived cell populations with the potential for ligament regeneration: ligament‐forming fibroblasts (LFF: CD146neg, CD34negCD44pos, CD31neg, CD45neg), ligament perivascular cells (LPC: CD146posCD34negCD44pos, CD31neg, CD45neg) and ligament interstitial cells (LIC: CD34posCD146neg, CD44pos, CD31neg, CD45neg)—and describe their proliferative and differentiation potential, collagen gene expression and metabolism in both normoxic and hypoxic environments, and their trophic potential in vitro. All three groups of cells (LIC, LPC, and LFF) isolated from adult human ACL exhibited progenitor cell characteristics with regard to proliferation and differentiation potential in vitro. Culture in low oxygen tension enhanced the collagen I and III gene expression in LICs (by 2.8‐ and 3.3‐fold, respectively) and LFFs (by 3‐ and 3.5‐fold, respectively) and increased oxygen consumption rate and extracellular acidification rate in LICs (by 4‐ and 3.5‐fold, respectively), LFFs (by 5.5‐ and 3‐fold, respectively), LPCs (by 10‐ and 4.5‐fold, respectively) as compared to normal oxygen concentration. In summary, this study demonstrates for the first time the presence of three novel progenitor cell populations in the adult ACL that demonstrate robust proliferative and matrix synthetic capacity; these cells may play a role in local ligament regeneration, and consequently represent a potential cell source for ligament engineering applications.

Outpatient Total Knee Arthroplasty Is Associated with Higher Risk of Perioperative Complications

Background: As concerns regarding health-care expenditure in the U.S. remain at the national forefront, outpatient arthroplasty is an appealing option for carefully selected patient populations. The purpose of this study was to determine the nationwide trends and complication rates associated with outpatient total knee arthroplasty (TKA) in comparison with standard inpatient TKA. Methods: We performed a retrospective review of the Humana subset of the PearlDiver Patient Record Database to identify patients who had undergone TKA (Current Procedural Terminology [CPT] code 27447) as either outpatients or inpatients from 2007 to 2015. The incidence of perioperative medical and surgical complications was determined by querying for relevant International Classification of Diseases, Ninth Revision (ICD-9) and CPT codes. Multivariate logistic regression analysis adjusted for age, sex, and Charlson Comorbidity Index (CCI) was used to calculate odds ratios (ORs) of complications among outpatients relative to inpatients treated with TKA. Results: Cohorts of 4,391 patients who underwent outpatient TKA and 128,951 patients who underwent inpatient TKA were identified. The median age was in the 70 to 74-year age group in both cohorts. The incidence of outpatient TKA increased across the study period (R2 = 0.60, p = 0.015). After adjustment for age, sex, and CCI, outpatient TKAs were found to more likely be followed by tibial and/or femoral component revision due to a noninfectious cause (OR = 1.22, 95% confidence interval [CI] = 1.01 to 1.47; p = 0.039), explantation of the prosthesis (OR = 1.35, CI = 1.07 to 1.72; p = 0.013), irrigation and debridement (OR = 1.50, CI = 1.28 to 1.77; p < 0.001), and stiffness requiring manipulation under anesthesia (OR = 1.28, CI = 1.17 to 1.40; p < 0.001) within 1 year. Outpatient TKA was also more frequently associated with postoperative deep vein thrombosis (OR = 1.42, CI = 1.25 to 1.63; p < 0.001) and acute renal failure (OR = 1.13, CI = 1.01 to 1.25; p = 0.026). Conclusions: With the potential to minimize arthroplasty costs among healthy patients, outpatient TKA is an increasingly popular option. Nationwide data from a private insurance database demonstrated a higher risk of perioperative surgical and medical complications including component failure, surgical site infection, knee stiffness, and deep vein thrombosis. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Graft Selection in Posterior Cruciate Ligament Surgery

Graft selection for posterior cruciate ligament (PCL ) injuries is controversial and remains an active area of orthopedic research. The type of ligament graft selected by a surgeon for PCL reconstruction is an important determinant in the clinical management and outcome of these patients. The need to appropriately select a graft while managing the individual concerns of well-informed patients necessitates a broad understanding of the variety of graft options available for PCL reconstruction. In this chapter, the medically relevant differences among the many graft options currently utilized in PCL reconstruction will be reviewed. Common autografts, along with their benefits, drawbacks, and harvesting techniques will be reviewed. In addition, various commercially available tissue allografts will be reviewed with regard to their origin, mechanical properties, and processing. Other important aspects that pertain to allografts including information concerning the commercial procurement, regulatory parameters, and clinical safety will also be addressed, with the goal of providing physicians with a fund of knowledge that will allow them to critically assess which PCL graft is best suited for the expectations of their patient.

Athymic rat model for evaluation of engineered anterior cruciate ligament grafts.

Anterior cruciate ligament (ACL) rupture is a common ligamentous injury that often requires surgery because the ACL does not heal well without intervention. Current treatment strategies include ligament reconstruction with either autograft or allograft, which each have their associated limitations. Thus, there is interest in designing a tissue-engineered graft for use in ACL reconstruction. We describe the fabrication of an electrospun polymer graft for use in ACL tissue engineering. This polycaprolactone graft is biocompatible, biodegradable, porous, and is comprised of aligned fibers. Because an animal model is necessary to evaluate such a graft, this paper describes an intra-articular athymic rat model of ACL reconstruction that can be used to evaluate engineered grafts, including those seeded with xenogeneic cells. Representative histology and biomechanical testing results at 16 weeks postoperatively are presented, with grafts tested immediately post-implantation and contralateral native ACLs serving as controls. The present study provides a reproducible animal model with which to evaluate tissue engineered ACL grafts, and demonstrates the potential of a regenerative medicine approach to treatment of ACL rupture.

142 – Outlook for Tissue Engineering Strategies for Anterior Cruciate Ligament Reconstruction

Looking towards the future, there is great interest in developing tissue engineered ACL replacements that have the potential to mimic the native ACL in terms of both biological and mechanical properties while minimizing the disadvantages of allografts and autografts. This chapter reviews the current status regarding contemporary tissue engineering strategies. The four basic components of tissue engineering: biomaterial scaffolds, cell sources, growth factors, and mechanical stimuli, as applied to the development of tissue engineered ACL replacement grafts, will be addressed. In addition, animal models that have been developed to test these tissue engineered ACL replacements will also be reviewed. We expect that continued progress in designing a viable tissue-engineered ACL replacement will accompany rapidly advancing techniques in materials science and biology.

Relative Complications and Trends of Outpatient Total Shoulder Arthroplasty

Outpatient arthroplasty is an appealing option among select patient populations as a mechanism for reducing health care expenditure. The purpose of this study was to determine the nationwide trends and complication profile of outpatient total shoulder arthroplasty (TSA). The authors reviewed a national administrative claims database to identify patients undergoing TSA as outpatients and inpatients from 2007 to 2016. The incidence of perioperative surgical and medical complications was determined by querying for relevant International Classification of Diseases, Ninth Revision, and Current Procedural Terminology codes. Multivariate logistic regression adjusted for age, sex, and Charlson Comorbidity Index was used to calculate odds ratios of complications among outpatients relative to inpatients undergoing TSA. The query identified 1555 patients who underwent outpatient TSA and 15,987 patients who underwent inpatient TSA. The median age was in the 70 to 74 years age group in both the outpatient and the inpatient cohorts, and the age distribution was comparable between the 2 cohorts (P=.287). The incidence of both outpatient (P<.001) and inpatient (P<.001) TSA increased during the study period. On adjustment for age, sex, and comorbidities, patients undergoing outpatient TSA had significantly lower rates of stiffness requiring manipulation under anesthesia (outpatient, 1.09%; inpatient, 2.35%; odds ratio, 0.52; 95% confidence interval, 0.38-0.71; P<.001) and higher rates of postoperative surgical site infections requiring reoperation (outpatient, 0.90%; inpatient, 0.65%; odds ratio, 1.65; 95% confidence interval, 1.15-2.35; P<.001) at 1 year. Rates of all other postoperative complications were comparable. Ambulatory TSA is increasing in incidence nationwide and is associated with an overall favorable postoperative complication profile. [Orthopedics. 2018; 41(3):e400-e409.].