Anterior cruciate ligament (ACL) injuries are one of the most well-known orthopaedic injuries and... more Anterior cruciate ligament (ACL) injuries are one of the most well-known orthopaedic injuries and are treated with one of the most common orthopaedic procedures performed in the United States. This surgical procedure, ACL reconstruction, is successful at restoring the gross stability of the knee. However, the outcomes of ACL reconstruction can be limited by short and long term complications, including muscle weakness, graft rupture and premature osteoarthritis. Thus, new methods of treating this injury are being explored. This review details the pathway of how a tissue engineering strategy can be used to improve the healing of the ACL in preclinical studies and then translated to patients in an FDA-approved clinical study. This review paper will outline the clinical importance of ACL injuries, history of primary repair, the pathology behind failure of the ACL to heal, pre-clinical studies, the FDA approval process for a high risk medical device, and the preliminary results from a first-inhuman study.
The last few years have witnessed significant advancements in arthroplasty. The procedure is main... more The last few years have witnessed significant advancements in arthroplasty. The procedure is mainly used to treat osteoarthritis of the hip and knee joint. Other joints such as the shoulder or ankle are also being successfully replaced by arthroplasty. The success of the operation depends on the implantation technique as well as the choice of material and fixation technique. Excellent results have been achieved especially in hip arthroplasty, with long-term survival rates of 90 %. However, the potential complications and sequelae are also worthy of mention, although they concern just a fraction of the treated patients. Careful preoperative planning, informing the patient accurately about the chances of success, and discussing the patient's expectations are essential aspects of the treatment.
The relationship between cartilage and synovium is a rapidly growing area of osteoarthritis resea... more The relationship between cartilage and synovium is a rapidly growing area of osteoarthritis research. However, to the best of our knowledge, the relationships in gene expression between these two tissues have not been explored in mid-stage disease development. The current study compared the transcriptomes of these two tissues in a large animal model one year following posttraumatic osteoarthritis induction and multiple surgical treatment modalities. Thirty-six Yucatan minipigs underwent transection of the anterior cruciate ligament. Subjects were randomized to no further intervention, ligament reconstruction, or ligament repair augmented with an extracellular matrix (ECM) scaffold, followed by RNA sequencing of the articular cartilage and synovium at 52 weeks after harvest. Twelve intact contralateral knees served as controls. Across all treatment modalities, the primary difference in the transcriptomes was that the articular cartilage had greater upregulation of genes related to im...
Non-invasive methods to document healing anterior cruciate ligament (ACL) structural properties c... more Non-invasive methods to document healing anterior cruciate ligament (ACL) structural properties could potentially identify patients at risk for revision surgery. The objective was to evaluate machine learning models to predict ACL failure load from magnetic resonance images (MRI) and to determine if those predictions were related to revision surgery incidence. It was hypothesized that the optimal model would demonstrate a lower mean absolute error (MAE) than the benchmark linear regression model, and that patients with a lower estimated failure load would have higher revision incidence 2 years post-surgery. Support vector machine, random forest, AdaBoost, XGBoost, and linear regression models were trained using MRI T2* relaxometry and ACL tensile testing data from minipigs (n = 65). The lowest MAE model was used to estimate ACL failure load for surgical patients at 9 months post-surgery (n = 46) and dichotomized into low and high score groups via Youden’s J statistic to compare revi...
Background: Quantitative magnetic resonance imaging (qMRI) methods were developed to establish th... more Background: Quantitative magnetic resonance imaging (qMRI) methods were developed to establish the integrity of healing anterior cruciate ligaments (ACLs) and grafts. Whether qMRI variables predict risk of reinjury is unknown. Purpose: To determine if qMRI measures at 6 to 9 months after bridge-enhanced ACL restoration (BEAR) can predict the risk of revision surgery within 2 years of the index procedure. Study Design: Cohort study; Level of evidence, 2. Methods: Originally, 124 patients underwent ACL restoration as part of the BEAR I, BEAR II, and BEAR III prospective trials and had consented to undergo an MRI of the surgical knee 6 to 9 months after surgery. Only 1 participant was lost to follow-up, and 4 did not undergo MRI, leaving a total of 119 patients for this study. qMRI techniques were used to determine the mean cross-sectional area; normalized signal intensity; and a qMRI-based predicted failure load, which was calculated using a prespecified equation based on cross-sectio...
Background: Anterior cruciate ligament (ACL) revision surgery is challenging for both patients an... more Background: Anterior cruciate ligament (ACL) revision surgery is challenging for both patients and surgeons. Understanding the risk factors for failure after bridge-enhanced ACL restoration (BEAR) may help with patient selection for ACL restoration versus ACL reconstruction. Purpose: To identify the preoperative risk factors for ACL revision surgery within the first 2 years after BEAR. Study Design: Case-control study; Level of evidence, 3. Methods: Data from the prospective BEAR I, II, and III trials were used to determine the preoperative risk factors for ACL revision surgery. All patients with a complete ACL tear (aged 13-47 years, depending on the trial), who met all other inclusion/exclusion criteria and underwent a primary BEAR procedure within 30 to 50 days from the injury (dependent on the trial), were included. Demographic data (age, sex, body mass index), baseline patient-reported outcomes (International Knee Documentation Committee [IKDC] subjective score, Marx activity s...
Background: The cross-sectional area (CSA) of the anterior cruciate ligament (ACL) and reconstruc... more Background: The cross-sectional area (CSA) of the anterior cruciate ligament (ACL) and reconstructed graft has direct implications on its strength and knee function. Little is known regarding how the CSA changes along the ligament length and how those changes vary between treated and native ligaments over time. Hypothesis: It was hypothesized that (1) the CSA of reconstructed ACLs and restored ACLs via bridge-enhanced ACL restoration (BEAR) is heterogeneous along the length. (2) Differences in CSA between treated and native ACLs decrease over time. (3) CSA of the surgically treated ACLs is correlated significantly with body size (ie, height, weight, body mass index) and knee size (ie, bicondylar and notch width). Study Design: Cohort study; Level of evidence, 2. Methods: Magnetic resonance imaging scans of treated and contralateral knees of 98 patients (n = 33 ACL reconstruction, 65 BEAR) at 6, 12, and 24 months post-operation were used to measure the ligament CSA at 1% increments a...
The primary source of synovial fluid inflammatory mediators is currently unknown and may include ... more The primary source of synovial fluid inflammatory mediators is currently unknown and may include different tissues comprising the joint, including the synovium and articular cartilage. Prior work in a porcine model has demonstrated that anterior cruciate ligament (ACL) surgery leads to significant changes in early gene expression in the synovium and articular cartilage, which are the same whether concomitant ligament restoration is performed or not. In this study, 36 Yucatan minipigs underwent ACL surgery, and a custom multiplex assay was used to measure synovial fluid protein levels of MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-12, MMP-13, IL-1α, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18, GM-CSF, and TNFα in 18 animals at 1 and 4 weeks after surgery. Linear regressions were used to evaluate the relationships between synovial fluid protein levels and the previously reported gene expression levels in the articular cartilage and synovium from the same animal cohort. Synovial fluid levels of MMP-13 and IL-6 were significantly correlated with synovial gene expression (P=.003 and P<.001 respectively), while IL-1α levels were significantly correlated with articular cartilage gene expression (P=.037). The synovium may be an important source of MMP-13 and IL-6, and the articular cartilage may be an important source of IL-1α in post-surgical inflammation. In developing treatments for post-surgical inflammation, the synovium may therefore be a promising target for modulating inflammatory mediators such as MMP-13 and IL-6 in the synovial fluid.
The inflammatory response to joint injury has been thought to play a key role in the development ... more The inflammatory response to joint injury has been thought to play a key role in the development of osteoarthritis. In this preclinical study, we hypothesized that synovial fluid presence of inflammatory cytokines, as well as altered loading on the injured leg, would be associated with greater development of macroscopic cartilage damage after an ACL injury. Thirty-six Yucatan minipigs underwent ACL transection and were randomized to: 1) no further treatment, 2) ACL reconstruction, or 3) scaffold-enhanced ACL restoration. Synovial fluid samples and gait data were obtained pre-operatively and at multiple time points post-operatively. Cytokine levels were measured using a multiplex assay. Macroscopic cartilage assessments were performed following euthanasia at 52 weeks. General estimating equation modeling found the presence of IL-1α, IL-1RA, IL-2, IL-4, IL-6, and IL-10 and MMP-2, MMP-3, MMP-12, and MMP-13 in the synovial fluid was associated with better cartilage outcomes. Higher peak...
Background: Previous clinical studies have shown that psychological factors have significant effe... more Background: Previous clinical studies have shown that psychological factors have significant effects on an athlete’s readiness to return to sport after anterior cruciate ligament (ACL) reconstruction (ACLR). Hypothesis: We hypothesized that patients who underwent bridge-enhanced ACL restoration (BEAR) would have higher levels of psychological readiness to return to sport compared with patients who underwent ACLR. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 100 patients (median age, 17 years; median preoperative Marx activity score, 16) with complete midsubstance ACL injuries were randomized to either the BEAR procedure (n = 65) or autograft ACLR (n = 35 [33 hamstring and 2 bone--patellar tendon—bone]) and underwent surgery within 45 days of injury. Objective, functional, and patient-reported outcomes, including the ACL--Return to Sport after Injury (ACL-RSI) scale, were assessed at 6, 12, and 24 months postoperatively. Results: Patients who u...
Research article Hypertrophy is induced during the in vitro chondrogenic differentiation of human... more Research article Hypertrophy is induced during the in vitro chondrogenic differentiation of human mesenchymal stem cells by bone morphogenetic protein-2 and bone morphogenetic protein-4 gene transfer
Background: Little is known about sex-based differences in anterior cruciate ligament (ACL) tissu... more Background: Little is known about sex-based differences in anterior cruciate ligament (ACL) tissue quality in vivo or the association of ACL size (ie, volume) and tissue quality (ie, normalized signal intensity on magnetic resonance imaging [MRI]) with knee anatomy. Hypothesis: We hypothesized that (1) women have smaller ACLs and greater ACL normalized signal intensity compared with men, and (2) ACL size and normalized signal intensity are associated with age, activity levels, body mass index (BMI), bicondylar width, intercondylar notch width, and posterior slope of the lateral tibial plateau. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Knee MRI scans of 108 unique ACL-intact knees (19.7 ± 5.5 years, 62 women) were used to quantify the ACL signal intensity (normalized to cortical bone), ligament volume, mean cross-sectional area, and length. Independent t tests were used to compare the MRI-based ACL parameters between sexes. Univariate and multivariate linear...
The roles that cytokines and matrix metalloproteinases play in the onset and progression of postt... more The roles that cytokines and matrix metalloproteinases play in the onset and progression of posttraumatic osteoarthritis (PTOA) remain a topic of debate. The study objective was to evaluate the concentrations of these inflammatory mediators during the development of mild to moderate PTOA in the porcine anterior cruciate ligament (ACL) surgical model. We hypothesized that there would be more animals with detectable mediators in the pigs that develop moderate PTOA (those receiving ACL reconstruction or untreated ACL transection) compared to those that develop mild PTOA (those receiving scaffold-enhanced ACL repair). 36 Yucatan minipigs underwent ACL transection and were randomized to: 1) no further treatment, 2) ACL reconstruction, or 3) scaffold-enhanced ACL repair. Synovial fluid samples were obtained pre-operatively, and at 1, 4, 12, 26 and 52 weeks post-operatively. The concentrations of inflammatory mediator in the synovial fluid samples were evaluated via multiplex assay. Macros...
Anterior cruciate ligament (ACL) reconstruction has been long considered as the gold standard in ... more Anterior cruciate ligament (ACL) reconstruction has been long considered as the gold standard in treatment of ACL injuries. The primary goal of ACL reconstruction is to re-approximate normal joint biomechanics as much as possible. However, patients who have suffered ACL injury are at high risk of developing knee osteoarthritis (OA) within 10-15 years post-injury, even with ACL reconstruction [1]. No study has yet demonstrated that a better graft or surgical technique can result in decreased risk of post-traumatic OA in the human population. Recent validation of a porcine large animal model [2,3] allows for novel testing of hypotheses around the causative relationship between outcomes of ACL repair/reconstruction and potential risk of OA. Previous investigators have hypothesized that the development of OA in a large animal model would be dependent on how well a surgical procedure (repair OR reconstruction) restored normal joint biomechanics. In this study, we hypothesized specifically that the graft (or repaired ACL) yield load and cross sectional area, as well as joint laxity, would be strong predictors of post-traumatic OA risk after an ACL injury. Methods: Following IACUC approval, 18 adolescent Yucatan mini-pigs (4 months of age) underwent ACL transection. The pigs were randomized into one of three groups: 1) no further treatment (ACL-T), 2) conventional ACL reconstruction (ACL-R) using bone-patellar tendon-bone allograft, or 3) bio-enhanced ACL repair (REPAIR) [3]. Animals were euthanized after 12 months, and both the surgical and contralateral limbs were tested for knee A-P laxity and ACL/graft mechanical properties. Biomechanical testing was performed using a universal testing machine (MTS, Eden Prairie, MN). The A-P knee laxity was measured at 30º of knee flexion through 12 cycles of ±40 N A-P shear force. The capsule and other ligaments were then dissected and ACL/graft size was measured using calipers [3]. Tissue mechanical properties were determined at 30º of knee flexion under a ramping tensile load to failure. Finally, macroscopic cartilage damage was assessed by measuring the area of all visible lesions across the tibiofemoral cartilage using India Ink and calipers [3]. Measurements were conducted by two independent examiners, blind to the treatment, and averaged values were used. Tissue structural properties and joint laxity were normalized to the contralateral intact leg (Surgical-Intact). A general linear model, an ANOVA with post-hoc Bonferroni, and multiple linear regression models were used for statistical analyses. Correlations were classified as poor (<0.4), good (0.4 to 0.74) and strong (≥0.75) based on determined Pearson's correlation coefficient (r) [4]. Results: The linear regression model (Figure 1) demonstrated strong correlations between total cartilage lesion area and normalized ACL/graft yield strength in all groups (ACL-R [r=-0.99, p<0.0005], REPAIR [r=-0.94, p=0.004], and ACL-T [r=-0.84, p=0.037]). Strong linear correlations were observed between total cartilage lesion area and normalized A-P knee laxity for the reconstructed and repaired groups but not the transected group (ACL-R [r=0.78, p=0.045], REPAIR [r=0.71, p=0.115], and ACL-T [r=0.24, p=0.647]). Finally, good to strong correlations were observed between normalized ACL/graft cross-sectional area and total cartilage area for all groups (ACL-R [r=-0.75, p=0.141], REPAIR [r=-0.7, p=0.122], and ACL-T [r=-0.61, p=0.211]). In all cases, the closer that treated knees were to the intact knee in terms of ACL/graft yield load, A-P knee laxity and ACL/graft crosssectional area, the less cartilage damage was observed. The general linear model showed that treatment type is a significant factor in overall cartilage lesion area (p=0.022). Both ACL-R (74.5±77.6 mm 2) and REPAIR (20.9±13.0 mm 2) specimens demonstrated less cartilage lesion area compared to the specimens with no treatment (125.9±61.6 mm 2). REPAIR resulted in minimum cartilage damage which was statistically significant compared to no treatment (p=0.020). As previously reported [3], both ACL-R (-546.8±269.3 N) and REPAIR (-743.5±411.7 N) resulted in significantly smaller normalized (less variation from intact) ACL yield strength compared to no treatment option (-1310±182.9 N, p<0.035). REPAIR and ACL-R resulted in similar normalized ACL yield loads (p=0.982). Similarly, both ACL-R (0.5±1.3 mm) and REPAIR (1.9±1.9 mm) resulted in smaller normalized A-P knee laxity compared to the specimens with no treatment (3.7±1.8 mm). These changes were only statistically significant between ACL-R and ACL-T groups (p=0.017). While both ACL-R (21.8±27.2 mm 2) and REPAIR (1.4±53.4 mm 2) resulted in greater ACL/graft cross-sectional area compared to the contralateral intact ACL, the specimens with no treatment (-12.0±32.0 mm 2) demonstrated smaller ACL cross-sectional compared to intact. None of these differences were statistically significant. Discussion: The results reported here support our hypothesis that the restored ACL/graft structural properties, both mechanical and anatomical, are valid predictors of risk of post-traumatic knee OA, regardless of treatment type (no treatment, ACL reconstruction or bio-enhanced ACL repair). With the advent of advanced imaging techniques that are able to accurately predict the mechanical properties and cross sectional area of an ACL graft or repaired ACL [5], these data in a large animal model suggest that in the future we may be able to use this imaging technique to begin to understand which patients are at risk for
Background: Bridge-enhanced anterior cruciate ligament repair (BEAR) has noninferior patient-repo... more Background: Bridge-enhanced anterior cruciate ligament repair (BEAR) has noninferior patient-reported outcomes when compared with autograft anterior cruciate ligament reconstruction (ACLR) at 2 years. However, the comparison of BEAR and autograft ACLR at earlier time points—including important outcomes such as resolution of knee pain and symptoms, recovery of strength, and return to sport—has not yet been reported. Hypothesis: It was hypothesized that the BEAR group would have higher outcomes on the International Knee Documentation Committee and Knee injury and Osteoarthritis Outcome Score, as well as improved muscle strength, in the early postoperative period. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 100 patients aged 13 to 35 years with complete midsubstance anterior cruciate ligament injuries were randomized to receive a suture repair augmented with an extracellular matrix implant (n = 65) or an autograft ACLR (n = 35). Outcomes were as...
Background: Magnetic resonance–based measurements of signal intensity have been used to track hea... more Background: Magnetic resonance–based measurements of signal intensity have been used to track healing of surgically treated anterior cruciate ligaments (ACLs). However, it is unknown how the signal intensity values in different regions of the ligament or graft change during healing. Hypotheses: (1) Normalized signal intensity of the healing graft or repaired ACL is heterogeneous; (2) temporal changes in normalized signal intensity values differ among the tibial, middle, and femoral regions; and (3) there are no differences in regional normalized signal intensity values 2 years postoperatively among grafts, repaired ACLs, and contralateral native ACLs. Study Design: Cohort study; Level of evidence, 2. Methods: Magnetic resonance imaging scans were analyzed from patients in a trial comparing ACL reconstruction (n = 35) with bridge-enhanced ACL repair (n = 65). The ACLs were segmented from images acquired at 6, 12, and 24 months postoperatively and were partitioned into 3 sections alon...
Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartm... more Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartment of the knee, even after surgical treatment. How the chondrocyte distribution within the articular cartilage changes early in this process is currently unknown. The study objective was to investigate the chondrocyte distribution within the medial femoral condyle after an anterior cruciate ligament transection in a preclinical model. Forty-two adolescent Yucatan minipigs were allocated to receive unilateral anterior cruciate ligament surgery (n = 36) or no surgery (n = 6). Central coronal sections of the medial femoral condyle were obtained at 1- and 4 weeks after surgery, and the chondrocyte distribution was measured via whole slide imaging and a cell counting batch processing tool utilized in ImageJ. Ki-67 immunohistochemistry was performed to identify proliferating cells. Empty lacunae, karyolysis, karyorrhexis, and pyknosis were used to identify areas of irreversible cell injury. T...
Background: While a sex effect on outcomes following anterior cruciate ligament (ACL) reconstruct... more Background: While a sex effect on outcomes following anterior cruciate ligament (ACL) reconstruction surgery has been previously documented, less is known following bridge-enhanced ACL repair (BEAR). We hypothesized that female sex would have significantly worse early functional outcomes and higher retear rates following primary repair of the ACL enhanced with a tissue-engineered scaffold. Methods: Sixty-five patients (28 males and 37 females), age 14-35 with a complete ACL tear underwent primary repair of the ACL enhanced with a tissue-engineered scaffold (bridge-enhanced ACL repair) within 45 days of injury. International Knee Documentation Committee (IKDC) and Knee Injury and Osteoarthritis Outcome (KOOS) scores, as well as instrumented anteroposterior (AP) laxity through KT-1000 testing and functional outcome measures were obtained at time points up to 2 years postoperatively and compared between males and females using mixed model repeated measures analyses and chi square tests. Results: There was no significant sex difference on the postoperative IKDC Subjective Score at 3, 6, 12, or 24 months or any of the five KOOS scores at 12 and 24 months. Instrumented AP laxity testing demonstrated mean (standard deviation) side-to-side differences that were similar in the two sexes at 2 years; 1.7 (2.7) mm and 1.5 (3.7) mm in females and males, respectively, p = 0.72. At 6 months postoperatively, males had a larger deficit in hamstring strength on the operated leg (14.0% vs. 1.7%; p = 0.03) and a larger deficit in quadriceps strength on the operated leg (11.3% vs. 2.0%; p = 0.004); however, no sex difference was noted at 12 or 24 months. Females demonstrated superior single leg hop testing at 6 and 12 months ([91.3% vs. 78.1%, p = 0.001], [96.9% vs. 87.0%, p = 0.01] respectively). There were no significant sex differences on ipsilateral (males; 14.3% vs. females; 13.9%, p = 1.00) or contralateral (males; 3.6% vs. females; 2.8%, p = 1.00) ACL reinjury rates. Conclusions: Female subjects had better hamstring and quadriceps strength indices at 6 months than males as well as better hop test results at the 6 and 12-month time period. Despite this, there was no significant sex difference on patient-reported outcomes and objective AP laxity testing at time points up to 2 years postoperatively.
Background: A bridge-enhanced anterior cruciate ligament (ACL) repair (BEAR) procedure places an ... more Background: A bridge-enhanced anterior cruciate ligament (ACL) repair (BEAR) procedure places an extracellular matrix implant, combined with autologous whole blood, in the gap between the torn ends of the ligament at the time of suture repair to stimulate healing. Prior studies have suggested that white blood cell (WBC) and platelet concentrations significantly affect the healing of other musculoskeletal tissues. Purpose/Hypothesis: The purpose of this study was to determine whether concentrations of various blood cell types placed into a bridging extracellular matrix implant at the time of ACL repair would have a significant effect on the healing ligament cross-sectional area or tissue organization (as measured by signal intensity). We hypothesized that patients with higher physiologic platelet and lower WBC counts would have improved healing of the ACL on magnetic resonance imaging (MRI) (higher cross-sectional area and/or lower signal intensity) 6 months after surgery. Study Desi...
Anterior cruciate ligament (ACL) injuries are one of the most well-known orthopaedic injuries and... more Anterior cruciate ligament (ACL) injuries are one of the most well-known orthopaedic injuries and are treated with one of the most common orthopaedic procedures performed in the United States. This surgical procedure, ACL reconstruction, is successful at restoring the gross stability of the knee. However, the outcomes of ACL reconstruction can be limited by short and long term complications, including muscle weakness, graft rupture and premature osteoarthritis. Thus, new methods of treating this injury are being explored. This review details the pathway of how a tissue engineering strategy can be used to improve the healing of the ACL in preclinical studies and then translated to patients in an FDA-approved clinical study. This review paper will outline the clinical importance of ACL injuries, history of primary repair, the pathology behind failure of the ACL to heal, pre-clinical studies, the FDA approval process for a high risk medical device, and the preliminary results from a first-inhuman study.
The last few years have witnessed significant advancements in arthroplasty. The procedure is main... more The last few years have witnessed significant advancements in arthroplasty. The procedure is mainly used to treat osteoarthritis of the hip and knee joint. Other joints such as the shoulder or ankle are also being successfully replaced by arthroplasty. The success of the operation depends on the implantation technique as well as the choice of material and fixation technique. Excellent results have been achieved especially in hip arthroplasty, with long-term survival rates of 90 %. However, the potential complications and sequelae are also worthy of mention, although they concern just a fraction of the treated patients. Careful preoperative planning, informing the patient accurately about the chances of success, and discussing the patient&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s expectations are essential aspects of the treatment.
The relationship between cartilage and synovium is a rapidly growing area of osteoarthritis resea... more The relationship between cartilage and synovium is a rapidly growing area of osteoarthritis research. However, to the best of our knowledge, the relationships in gene expression between these two tissues have not been explored in mid-stage disease development. The current study compared the transcriptomes of these two tissues in a large animal model one year following posttraumatic osteoarthritis induction and multiple surgical treatment modalities. Thirty-six Yucatan minipigs underwent transection of the anterior cruciate ligament. Subjects were randomized to no further intervention, ligament reconstruction, or ligament repair augmented with an extracellular matrix (ECM) scaffold, followed by RNA sequencing of the articular cartilage and synovium at 52 weeks after harvest. Twelve intact contralateral knees served as controls. Across all treatment modalities, the primary difference in the transcriptomes was that the articular cartilage had greater upregulation of genes related to im...
Non-invasive methods to document healing anterior cruciate ligament (ACL) structural properties c... more Non-invasive methods to document healing anterior cruciate ligament (ACL) structural properties could potentially identify patients at risk for revision surgery. The objective was to evaluate machine learning models to predict ACL failure load from magnetic resonance images (MRI) and to determine if those predictions were related to revision surgery incidence. It was hypothesized that the optimal model would demonstrate a lower mean absolute error (MAE) than the benchmark linear regression model, and that patients with a lower estimated failure load would have higher revision incidence 2 years post-surgery. Support vector machine, random forest, AdaBoost, XGBoost, and linear regression models were trained using MRI T2* relaxometry and ACL tensile testing data from minipigs (n = 65). The lowest MAE model was used to estimate ACL failure load for surgical patients at 9 months post-surgery (n = 46) and dichotomized into low and high score groups via Youden’s J statistic to compare revi...
Background: Quantitative magnetic resonance imaging (qMRI) methods were developed to establish th... more Background: Quantitative magnetic resonance imaging (qMRI) methods were developed to establish the integrity of healing anterior cruciate ligaments (ACLs) and grafts. Whether qMRI variables predict risk of reinjury is unknown. Purpose: To determine if qMRI measures at 6 to 9 months after bridge-enhanced ACL restoration (BEAR) can predict the risk of revision surgery within 2 years of the index procedure. Study Design: Cohort study; Level of evidence, 2. Methods: Originally, 124 patients underwent ACL restoration as part of the BEAR I, BEAR II, and BEAR III prospective trials and had consented to undergo an MRI of the surgical knee 6 to 9 months after surgery. Only 1 participant was lost to follow-up, and 4 did not undergo MRI, leaving a total of 119 patients for this study. qMRI techniques were used to determine the mean cross-sectional area; normalized signal intensity; and a qMRI-based predicted failure load, which was calculated using a prespecified equation based on cross-sectio...
Background: Anterior cruciate ligament (ACL) revision surgery is challenging for both patients an... more Background: Anterior cruciate ligament (ACL) revision surgery is challenging for both patients and surgeons. Understanding the risk factors for failure after bridge-enhanced ACL restoration (BEAR) may help with patient selection for ACL restoration versus ACL reconstruction. Purpose: To identify the preoperative risk factors for ACL revision surgery within the first 2 years after BEAR. Study Design: Case-control study; Level of evidence, 3. Methods: Data from the prospective BEAR I, II, and III trials were used to determine the preoperative risk factors for ACL revision surgery. All patients with a complete ACL tear (aged 13-47 years, depending on the trial), who met all other inclusion/exclusion criteria and underwent a primary BEAR procedure within 30 to 50 days from the injury (dependent on the trial), were included. Demographic data (age, sex, body mass index), baseline patient-reported outcomes (International Knee Documentation Committee [IKDC] subjective score, Marx activity s...
Background: The cross-sectional area (CSA) of the anterior cruciate ligament (ACL) and reconstruc... more Background: The cross-sectional area (CSA) of the anterior cruciate ligament (ACL) and reconstructed graft has direct implications on its strength and knee function. Little is known regarding how the CSA changes along the ligament length and how those changes vary between treated and native ligaments over time. Hypothesis: It was hypothesized that (1) the CSA of reconstructed ACLs and restored ACLs via bridge-enhanced ACL restoration (BEAR) is heterogeneous along the length. (2) Differences in CSA between treated and native ACLs decrease over time. (3) CSA of the surgically treated ACLs is correlated significantly with body size (ie, height, weight, body mass index) and knee size (ie, bicondylar and notch width). Study Design: Cohort study; Level of evidence, 2. Methods: Magnetic resonance imaging scans of treated and contralateral knees of 98 patients (n = 33 ACL reconstruction, 65 BEAR) at 6, 12, and 24 months post-operation were used to measure the ligament CSA at 1% increments a...
The primary source of synovial fluid inflammatory mediators is currently unknown and may include ... more The primary source of synovial fluid inflammatory mediators is currently unknown and may include different tissues comprising the joint, including the synovium and articular cartilage. Prior work in a porcine model has demonstrated that anterior cruciate ligament (ACL) surgery leads to significant changes in early gene expression in the synovium and articular cartilage, which are the same whether concomitant ligament restoration is performed or not. In this study, 36 Yucatan minipigs underwent ACL surgery, and a custom multiplex assay was used to measure synovial fluid protein levels of MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-12, MMP-13, IL-1α, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18, GM-CSF, and TNFα in 18 animals at 1 and 4 weeks after surgery. Linear regressions were used to evaluate the relationships between synovial fluid protein levels and the previously reported gene expression levels in the articular cartilage and synovium from the same animal cohort. Synovial fluid levels of MMP-13 and IL-6 were significantly correlated with synovial gene expression (P=.003 and P<.001 respectively), while IL-1α levels were significantly correlated with articular cartilage gene expression (P=.037). The synovium may be an important source of MMP-13 and IL-6, and the articular cartilage may be an important source of IL-1α in post-surgical inflammation. In developing treatments for post-surgical inflammation, the synovium may therefore be a promising target for modulating inflammatory mediators such as MMP-13 and IL-6 in the synovial fluid.
The inflammatory response to joint injury has been thought to play a key role in the development ... more The inflammatory response to joint injury has been thought to play a key role in the development of osteoarthritis. In this preclinical study, we hypothesized that synovial fluid presence of inflammatory cytokines, as well as altered loading on the injured leg, would be associated with greater development of macroscopic cartilage damage after an ACL injury. Thirty-six Yucatan minipigs underwent ACL transection and were randomized to: 1) no further treatment, 2) ACL reconstruction, or 3) scaffold-enhanced ACL restoration. Synovial fluid samples and gait data were obtained pre-operatively and at multiple time points post-operatively. Cytokine levels were measured using a multiplex assay. Macroscopic cartilage assessments were performed following euthanasia at 52 weeks. General estimating equation modeling found the presence of IL-1α, IL-1RA, IL-2, IL-4, IL-6, and IL-10 and MMP-2, MMP-3, MMP-12, and MMP-13 in the synovial fluid was associated with better cartilage outcomes. Higher peak...
Background: Previous clinical studies have shown that psychological factors have significant effe... more Background: Previous clinical studies have shown that psychological factors have significant effects on an athlete’s readiness to return to sport after anterior cruciate ligament (ACL) reconstruction (ACLR). Hypothesis: We hypothesized that patients who underwent bridge-enhanced ACL restoration (BEAR) would have higher levels of psychological readiness to return to sport compared with patients who underwent ACLR. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 100 patients (median age, 17 years; median preoperative Marx activity score, 16) with complete midsubstance ACL injuries were randomized to either the BEAR procedure (n = 65) or autograft ACLR (n = 35 [33 hamstring and 2 bone--patellar tendon—bone]) and underwent surgery within 45 days of injury. Objective, functional, and patient-reported outcomes, including the ACL--Return to Sport after Injury (ACL-RSI) scale, were assessed at 6, 12, and 24 months postoperatively. Results: Patients who u...
Research article Hypertrophy is induced during the in vitro chondrogenic differentiation of human... more Research article Hypertrophy is induced during the in vitro chondrogenic differentiation of human mesenchymal stem cells by bone morphogenetic protein-2 and bone morphogenetic protein-4 gene transfer
Background: Little is known about sex-based differences in anterior cruciate ligament (ACL) tissu... more Background: Little is known about sex-based differences in anterior cruciate ligament (ACL) tissue quality in vivo or the association of ACL size (ie, volume) and tissue quality (ie, normalized signal intensity on magnetic resonance imaging [MRI]) with knee anatomy. Hypothesis: We hypothesized that (1) women have smaller ACLs and greater ACL normalized signal intensity compared with men, and (2) ACL size and normalized signal intensity are associated with age, activity levels, body mass index (BMI), bicondylar width, intercondylar notch width, and posterior slope of the lateral tibial plateau. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Knee MRI scans of 108 unique ACL-intact knees (19.7 ± 5.5 years, 62 women) were used to quantify the ACL signal intensity (normalized to cortical bone), ligament volume, mean cross-sectional area, and length. Independent t tests were used to compare the MRI-based ACL parameters between sexes. Univariate and multivariate linear...
The roles that cytokines and matrix metalloproteinases play in the onset and progression of postt... more The roles that cytokines and matrix metalloproteinases play in the onset and progression of posttraumatic osteoarthritis (PTOA) remain a topic of debate. The study objective was to evaluate the concentrations of these inflammatory mediators during the development of mild to moderate PTOA in the porcine anterior cruciate ligament (ACL) surgical model. We hypothesized that there would be more animals with detectable mediators in the pigs that develop moderate PTOA (those receiving ACL reconstruction or untreated ACL transection) compared to those that develop mild PTOA (those receiving scaffold-enhanced ACL repair). 36 Yucatan minipigs underwent ACL transection and were randomized to: 1) no further treatment, 2) ACL reconstruction, or 3) scaffold-enhanced ACL repair. Synovial fluid samples were obtained pre-operatively, and at 1, 4, 12, 26 and 52 weeks post-operatively. The concentrations of inflammatory mediator in the synovial fluid samples were evaluated via multiplex assay. Macros...
Anterior cruciate ligament (ACL) reconstruction has been long considered as the gold standard in ... more Anterior cruciate ligament (ACL) reconstruction has been long considered as the gold standard in treatment of ACL injuries. The primary goal of ACL reconstruction is to re-approximate normal joint biomechanics as much as possible. However, patients who have suffered ACL injury are at high risk of developing knee osteoarthritis (OA) within 10-15 years post-injury, even with ACL reconstruction [1]. No study has yet demonstrated that a better graft or surgical technique can result in decreased risk of post-traumatic OA in the human population. Recent validation of a porcine large animal model [2,3] allows for novel testing of hypotheses around the causative relationship between outcomes of ACL repair/reconstruction and potential risk of OA. Previous investigators have hypothesized that the development of OA in a large animal model would be dependent on how well a surgical procedure (repair OR reconstruction) restored normal joint biomechanics. In this study, we hypothesized specifically that the graft (or repaired ACL) yield load and cross sectional area, as well as joint laxity, would be strong predictors of post-traumatic OA risk after an ACL injury. Methods: Following IACUC approval, 18 adolescent Yucatan mini-pigs (4 months of age) underwent ACL transection. The pigs were randomized into one of three groups: 1) no further treatment (ACL-T), 2) conventional ACL reconstruction (ACL-R) using bone-patellar tendon-bone allograft, or 3) bio-enhanced ACL repair (REPAIR) [3]. Animals were euthanized after 12 months, and both the surgical and contralateral limbs were tested for knee A-P laxity and ACL/graft mechanical properties. Biomechanical testing was performed using a universal testing machine (MTS, Eden Prairie, MN). The A-P knee laxity was measured at 30º of knee flexion through 12 cycles of ±40 N A-P shear force. The capsule and other ligaments were then dissected and ACL/graft size was measured using calipers [3]. Tissue mechanical properties were determined at 30º of knee flexion under a ramping tensile load to failure. Finally, macroscopic cartilage damage was assessed by measuring the area of all visible lesions across the tibiofemoral cartilage using India Ink and calipers [3]. Measurements were conducted by two independent examiners, blind to the treatment, and averaged values were used. Tissue structural properties and joint laxity were normalized to the contralateral intact leg (Surgical-Intact). A general linear model, an ANOVA with post-hoc Bonferroni, and multiple linear regression models were used for statistical analyses. Correlations were classified as poor (<0.4), good (0.4 to 0.74) and strong (≥0.75) based on determined Pearson's correlation coefficient (r) [4]. Results: The linear regression model (Figure 1) demonstrated strong correlations between total cartilage lesion area and normalized ACL/graft yield strength in all groups (ACL-R [r=-0.99, p<0.0005], REPAIR [r=-0.94, p=0.004], and ACL-T [r=-0.84, p=0.037]). Strong linear correlations were observed between total cartilage lesion area and normalized A-P knee laxity for the reconstructed and repaired groups but not the transected group (ACL-R [r=0.78, p=0.045], REPAIR [r=0.71, p=0.115], and ACL-T [r=0.24, p=0.647]). Finally, good to strong correlations were observed between normalized ACL/graft cross-sectional area and total cartilage area for all groups (ACL-R [r=-0.75, p=0.141], REPAIR [r=-0.7, p=0.122], and ACL-T [r=-0.61, p=0.211]). In all cases, the closer that treated knees were to the intact knee in terms of ACL/graft yield load, A-P knee laxity and ACL/graft crosssectional area, the less cartilage damage was observed. The general linear model showed that treatment type is a significant factor in overall cartilage lesion area (p=0.022). Both ACL-R (74.5±77.6 mm 2) and REPAIR (20.9±13.0 mm 2) specimens demonstrated less cartilage lesion area compared to the specimens with no treatment (125.9±61.6 mm 2). REPAIR resulted in minimum cartilage damage which was statistically significant compared to no treatment (p=0.020). As previously reported [3], both ACL-R (-546.8±269.3 N) and REPAIR (-743.5±411.7 N) resulted in significantly smaller normalized (less variation from intact) ACL yield strength compared to no treatment option (-1310±182.9 N, p<0.035). REPAIR and ACL-R resulted in similar normalized ACL yield loads (p=0.982). Similarly, both ACL-R (0.5±1.3 mm) and REPAIR (1.9±1.9 mm) resulted in smaller normalized A-P knee laxity compared to the specimens with no treatment (3.7±1.8 mm). These changes were only statistically significant between ACL-R and ACL-T groups (p=0.017). While both ACL-R (21.8±27.2 mm 2) and REPAIR (1.4±53.4 mm 2) resulted in greater ACL/graft cross-sectional area compared to the contralateral intact ACL, the specimens with no treatment (-12.0±32.0 mm 2) demonstrated smaller ACL cross-sectional compared to intact. None of these differences were statistically significant. Discussion: The results reported here support our hypothesis that the restored ACL/graft structural properties, both mechanical and anatomical, are valid predictors of risk of post-traumatic knee OA, regardless of treatment type (no treatment, ACL reconstruction or bio-enhanced ACL repair). With the advent of advanced imaging techniques that are able to accurately predict the mechanical properties and cross sectional area of an ACL graft or repaired ACL [5], these data in a large animal model suggest that in the future we may be able to use this imaging technique to begin to understand which patients are at risk for
Background: Bridge-enhanced anterior cruciate ligament repair (BEAR) has noninferior patient-repo... more Background: Bridge-enhanced anterior cruciate ligament repair (BEAR) has noninferior patient-reported outcomes when compared with autograft anterior cruciate ligament reconstruction (ACLR) at 2 years. However, the comparison of BEAR and autograft ACLR at earlier time points—including important outcomes such as resolution of knee pain and symptoms, recovery of strength, and return to sport—has not yet been reported. Hypothesis: It was hypothesized that the BEAR group would have higher outcomes on the International Knee Documentation Committee and Knee injury and Osteoarthritis Outcome Score, as well as improved muscle strength, in the early postoperative period. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 100 patients aged 13 to 35 years with complete midsubstance anterior cruciate ligament injuries were randomized to receive a suture repair augmented with an extracellular matrix implant (n = 65) or an autograft ACLR (n = 35). Outcomes were as...
Background: Magnetic resonance–based measurements of signal intensity have been used to track hea... more Background: Magnetic resonance–based measurements of signal intensity have been used to track healing of surgically treated anterior cruciate ligaments (ACLs). However, it is unknown how the signal intensity values in different regions of the ligament or graft change during healing. Hypotheses: (1) Normalized signal intensity of the healing graft or repaired ACL is heterogeneous; (2) temporal changes in normalized signal intensity values differ among the tibial, middle, and femoral regions; and (3) there are no differences in regional normalized signal intensity values 2 years postoperatively among grafts, repaired ACLs, and contralateral native ACLs. Study Design: Cohort study; Level of evidence, 2. Methods: Magnetic resonance imaging scans were analyzed from patients in a trial comparing ACL reconstruction (n = 35) with bridge-enhanced ACL repair (n = 65). The ACLs were segmented from images acquired at 6, 12, and 24 months postoperatively and were partitioned into 3 sections alon...
Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartm... more Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartment of the knee, even after surgical treatment. How the chondrocyte distribution within the articular cartilage changes early in this process is currently unknown. The study objective was to investigate the chondrocyte distribution within the medial femoral condyle after an anterior cruciate ligament transection in a preclinical model. Forty-two adolescent Yucatan minipigs were allocated to receive unilateral anterior cruciate ligament surgery (n = 36) or no surgery (n = 6). Central coronal sections of the medial femoral condyle were obtained at 1- and 4 weeks after surgery, and the chondrocyte distribution was measured via whole slide imaging and a cell counting batch processing tool utilized in ImageJ. Ki-67 immunohistochemistry was performed to identify proliferating cells. Empty lacunae, karyolysis, karyorrhexis, and pyknosis were used to identify areas of irreversible cell injury. T...
Background: While a sex effect on outcomes following anterior cruciate ligament (ACL) reconstruct... more Background: While a sex effect on outcomes following anterior cruciate ligament (ACL) reconstruction surgery has been previously documented, less is known following bridge-enhanced ACL repair (BEAR). We hypothesized that female sex would have significantly worse early functional outcomes and higher retear rates following primary repair of the ACL enhanced with a tissue-engineered scaffold. Methods: Sixty-five patients (28 males and 37 females), age 14-35 with a complete ACL tear underwent primary repair of the ACL enhanced with a tissue-engineered scaffold (bridge-enhanced ACL repair) within 45 days of injury. International Knee Documentation Committee (IKDC) and Knee Injury and Osteoarthritis Outcome (KOOS) scores, as well as instrumented anteroposterior (AP) laxity through KT-1000 testing and functional outcome measures were obtained at time points up to 2 years postoperatively and compared between males and females using mixed model repeated measures analyses and chi square tests. Results: There was no significant sex difference on the postoperative IKDC Subjective Score at 3, 6, 12, or 24 months or any of the five KOOS scores at 12 and 24 months. Instrumented AP laxity testing demonstrated mean (standard deviation) side-to-side differences that were similar in the two sexes at 2 years; 1.7 (2.7) mm and 1.5 (3.7) mm in females and males, respectively, p = 0.72. At 6 months postoperatively, males had a larger deficit in hamstring strength on the operated leg (14.0% vs. 1.7%; p = 0.03) and a larger deficit in quadriceps strength on the operated leg (11.3% vs. 2.0%; p = 0.004); however, no sex difference was noted at 12 or 24 months. Females demonstrated superior single leg hop testing at 6 and 12 months ([91.3% vs. 78.1%, p = 0.001], [96.9% vs. 87.0%, p = 0.01] respectively). There were no significant sex differences on ipsilateral (males; 14.3% vs. females; 13.9%, p = 1.00) or contralateral (males; 3.6% vs. females; 2.8%, p = 1.00) ACL reinjury rates. Conclusions: Female subjects had better hamstring and quadriceps strength indices at 6 months than males as well as better hop test results at the 6 and 12-month time period. Despite this, there was no significant sex difference on patient-reported outcomes and objective AP laxity testing at time points up to 2 years postoperatively.
Background: A bridge-enhanced anterior cruciate ligament (ACL) repair (BEAR) procedure places an ... more Background: A bridge-enhanced anterior cruciate ligament (ACL) repair (BEAR) procedure places an extracellular matrix implant, combined with autologous whole blood, in the gap between the torn ends of the ligament at the time of suture repair to stimulate healing. Prior studies have suggested that white blood cell (WBC) and platelet concentrations significantly affect the healing of other musculoskeletal tissues. Purpose/Hypothesis: The purpose of this study was to determine whether concentrations of various blood cell types placed into a bridging extracellular matrix implant at the time of ACL repair would have a significant effect on the healing ligament cross-sectional area or tissue organization (as measured by signal intensity). We hypothesized that patients with higher physiologic platelet and lower WBC counts would have improved healing of the ACL on magnetic resonance imaging (MRI) (higher cross-sectional area and/or lower signal intensity) 6 months after surgery. Study Desi...
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Papers by Benedikt Proffen