Effects of age and platelet‐rich plasma on ACL cell viability and collagen gene expression

Platelet‐rich plasma (PRP) has shown in vivo potential to stimulate anterior cruciate ligament (ACL) healing at early time points in large animal models. However, in animal models, the healing potential of the ACL is dependent on animal age. In this study, we hypothesized that there are age‐dependent differences in ACL cell metabolism, collagen gene expression, and the ability of the cells to respond to growth factors in PRP. To test this hypothesis, ACL cells were obtained from skeletally immature, adolescent and adult pigs, and cultured in a collagen type I hydrogel with or without PRP for 14 days. When cultured in collagen‐only hydrogel, ACL cells from adult pigs had a 19% lower apoptotic rate as compared to immature pigs (p = 0.001) and a 25% higher cellular metabolic activity as compared to adolescent pigs (p = 0.006). The addition of PRP to the collagen hydrogel resulted in a significantly increased cellular metabolic activity, reduced apoptotic rate, and stimulation of collagen production in the cells from the immature and adolescent animals (p < 0.05 for all comparisons) but had less effect on adult cells. These findings suggest that skeletal maturity may influence ACL cells' metabolic activity, apoptosis, collagen production, and response to PRP. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:79–85, 2012     

Increasing platelet concentration in platelet‐rich plasma inhibits anterior cruciate ligament cell function in three‐dimensional culture

Tissue engineering is one new strategy being developed to treat ACL ruptures. One such approach is bio‐enhanced ACL repair, where a suture repair is supplemented with a bio‐active scaffold containing platelets. However, the optimal concentration of platelets to stimulate ACL healing is not known. We hypothesized that increasing platelet concentrations in the scaffold would enhance critical cell behaviors. Porcine ACL fibroblasts were obtained from explant culture and suspended in platelet poor plasma (PPP), 1× platelet‐rich plasma (PRP), 3× PRP, 5× PRP, or phosphate buffered saline (PBS). The cell suspensions were cultured in a 3D collagen scaffold. Cellular metabolism (MTT assay), apoptosis (TUNEL assay), and gene expression for type I and type III collagen were measured. 1× PRP significantly outperformed 5× PRP in all parameters studied: Type I and III collagen gene expression, apoptosis prevention, and cell metabolism stimulation. ACL fibroblasts cultured with 1× PRP had the highest type I and type III collagen gene expression. 1× PRP and PPP groups had the highest cell metabolism and lowest apoptosis rates. Concentration of platelets had significant effects on the behavior of ACL fibroblasts; thus, it is an important parameter that should be specified in clinical or basic science studies. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:291–295, 2014.     

The central ACL defect as a model for failure of intra-articular healing.

Intra-articular soft tissues, such as the anterior cruciate ligament (ACL), fail to heal in contrast to the extra-articular medial collateral ligament (MCL), which undergoes classic healing. The goal of this study was to validate a model for failure of intra-articular healing that could be used in the future to test new repair strategies. We conducted a two-part experiment, the first part ex vivo, and the second in vivo. Our initial ex vivo experiments were used to determine the optimal width of the central defect in the canine ACL that would produce reproducible structural properties at time zero. The second experimental series used this optimal scalpel blade width to create a central defect in the canine ACL followed by measurement of structural properties in the ACL after either a 3- or 6-week in vivo healing period. A 3.5-mm beaver blade resulted in a maximum tolerated load of 56.8 +/- 4.7% (mean +/- SEM) of control at time zero. After the 3- and 6-week in vivo healing periods, the maximum load was 74.6 +/- 5.3 at 3 weeks and 64.9 +/- 3.8% at 6 weeks compared to control. Thus, biomechanical parameters tested at 6 weeks after creation of a defect showed no significant gains from defects tested immediately after the creation of injury. The centrally placed ACL defect in this canine model demonstrates failure to mechanically heal, which should prove suitable for future in vivo evaluation of the biomechanical and histological response to tissue engineering repair strategies for intra-articular soft tissues.     

关节内注射富含血小板血浆在兔膝骨关节炎动物模型中的作用

目的评估关节内注射富含血小板血浆(PRP)对胶原酶诱导的兔膝骨关节炎(OA)动物模型的影响。方法 20只新西兰大白兔在超声引导下行右侧膝关节内胶原酶注射,建立兔OA动物模型。实验的第4周随机分为PRP组和生理盐水组,每组10只,每周给药1次,共4次。实验第9周取关节软骨观察软骨总体形态及软骨微形态的变化。结果 PRP组软骨总体形态评分为(1.7±0.3)分,明显低于生理盐水组的(3.5±0.6),分,差异有统计学意义(P0.05),提示PRP组软骨总体形态损伤较小;PRP组软骨微形态评分为(3.2±1.0)分,明显低于生理盐水组的(7.4±1.2)分,差异有统计学意义(P0.05),提示PRP组软骨微形态损伤较小。结论关节内注射PRP有保护软骨作用。     

Collagen-platelet rich plasma hydrogel enhances primary repair of the porcine anterior cruciate ligament.

The anterior cruciate ligament (ACL) fails to heal after suture repair. One hypothesis for this failure is the premature loss of the fibrin clot, or provisional scaffolding, between the two ligament ends in the joint environment. To test this hypothesis, a substitute provisional scaffold of collagen-platelet rich plasma (PRP) hydrogel was used to fill the ACL wound site at the time of suture repair and the structural properties of the healing ACLs evaluated 4 weeks after surgery. Bilateral ACL transections were performed in five 30-kg Yorkshire pigs and treated with suture repair. In each animal, one of the repairs was augmented with placement of a collagen-PRP hydrogel at the ACL transection site, while the contralateral knee had suture repair alone. In addition, six control knees with intact ACLs from three additional animals were used as a control group. No postoperative immobilization was used. After 4 weeks the animals underwent in vivo magnetic resonance imaging to assess the size of the healing ACL, followed by biomechanical testing to determine tensile properties. The supplementation of suture repair with a collagen-PRP hydrogel resulted in significant improvements in load at yield, maximum load, and linear stiffness at 4 weeks. We conclude that use of a stabilized provisional scaffold, such as a collagen-PRP hydrogel, to supplement primary repair of the ACL can result in improved biomechanical properties at an early time point. Further studies to determine the long-term effect of primary repair enhancement are needed.     

透明质酸、富血小板血浆及两者联合应用对膝骨关节炎的疗效评估

目的 本研究旨在评估透明质酸（hyaluronic aicd , HA）与富血小板血浆（platelet rich plasma , PRP）对膝骨关节炎的疗效,同时探讨两者联合应用的潜在治疗效果。方法 纳入从2016年1月至2017年12月就诊于南京市第一医院的膝骨关节炎患者101例,按治疗方法的不同分为A组（膝关节腔内注射HA）37例、B组（膝关节腔内注射PRP）33例、C组（联合应用）31例。采用膝关节损伤与骨关节炎评分（knee injury and osteoarthritis outcome score , KOOS)在治疗前和治疗后1、3、6个月对疗效进行评估。结果 ①治疗1个月后,三组KOOS评分均较治疗前明显改善（P＜0.05）,其中C组的KOOS疼痛评分显著优于A组及B组（P＜0.05）;②治疗3个月后,3组较治疗前仍维持较好的疗效（P＜0.05）,其中B组与C组KOOS部分评分优于A组（P＜0.05）,B组与C组之间无明显差异（P＞0.05）;③治疗6个月后,B组与C组KOOS评分仍优于治疗前（P＜0.05）,两组无显著差异,而A组KOOS评分较治疗前无明显优势（P＞0.05）。结论 关节腔内注射PRP治疗膝骨关节炎可获得至少6个月的疗效,且在治疗3个月后,疗效优于HA。对于HA+PRP疗法,优势主要表现在短期内更为显著的改善了患者的疼痛症状。     

Intraarticular injection autologous platelet‐rich plasma and bone marrow concentrate in a goat osteoarthritis model

To evaluate the effects of intraarticular injections of autologous platelet‐rich plasma (PRP) or bone marrow concentrate (BMC) on osteoarthritis (OA), 24 adult goats were equally divided into control (Ctrl), saline (NS), PRP, and BMC groups, and OA was induced by surgery in NS, PRP, and BMC groups. Autologous PRP and BMC were obtained from whole blood and bone marrow aspirates, respectively. The data revealed, platelets were increased in BMC by 1.8‐fold, monocytes by 5.6‐fold, TGF‐β1 by 7.7‐fold, and IGF‐1 by 3.6‐fold (p < 0.05), and platelets were increased in PRP by 2.9‐fold, and TGF‐β1 by 3.3‐fold (p < 0.05). From the sixth week post‐operation, saline, PRP, and BMC were administered by intraarticular injection once every 4 weeks, three consecutive times. After the animals were sacrificed, inflammatory cytokines in the synovial fluid was measured, and bone and cartilage degeneration progression was observed by macroscopy, histology, and immunohistochemistry. Compared with the NS group, the level of inflammatory cytokines was reduced in the PRP and BMC groups (p < 0.05). Histologically, delayed cartilage degeneration and higher levels of extracellular matrix (ECM) were observed in both PRP and BMC treated groups (p < 0.05). Furthermore, the BMC group showed greater cartilage protection and less ECM loss than the PRP group (p < 0.05). In summary, this study showed that intraarticular injection of autologous PRP and BMC has therapeutic efficacy in a goat osteoarthritis model, with the greater benefit in terms of cartilage protection being observed in the BMC‐treated group than PRP. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2140–2146, 2018.

     

Relationship between altered knee kinematics and subchondral bone remodeling in a clinically translational model of ACL injury

Abnormal joint kinematics are commonly reported in the acute and chronic stages of recovery after anterior cruciate ligament (ACL) injury and have long been mechanistically implicated as a primary driver in the development of posttraumatic osteoarthritis (PTOA). Though strongly theorized, it is unclear to what extent biomechanical adaptations after ACL injury culminate in the development of PTOA, as data that directly connects these factors does not exist. Using a preclinical, noninvasive ACL injury rodent model, our objective was to explore the direct effect of an isolated ACL injury on joint kinematics and the pathogenetic mechanisms involved in the development of PTOA. A total of 32, 16-week-old Long-Evans rats were exposed to a noninvasive ACL injury. Marker-less deep learning software (DeepLabCut) was used to track animal movement for sagittal-plane kinematic analyses and micro computed tomography was used to evaluate subchondral bone architecture at days 7, 14, 28, and 56 following injury. There was a significant decrease in peak knee flexion during walking (p < .05), which had a moderate-to-strong negative correlation (r = ?.59 to ?.71; p < .001) with subchondral bone plate porosity in all load bearing regions of the femur and tibia. Additional comprehensive analyses of knee flexion profiles revealed dramatic alterations throughout the step cycle. This occurred alongside considerable loss of epiphyseal trabecular bone and substantial changes in anatomical orientation. Knee flexion angle and subchondral bone microarchitecture are severely impacted after ACL injury. Reductions in peak knee flexion angle after ACL injury are directly associated with subchondral bone plate remodeling.     

Variations in the three-dimensional location and orientation of the ACL in healthy subjects relative to patients after transtibial ACL reconstruction

Recent reports have indicated that anatomical placement of the anterior cruciate ligament (ACL) graft is an important factor for restoration of joint function following ACL reconstruction. The objective of this study was to address a need for a better understanding of anatomical variations in ACL position and orientation within the joint. Specifically, variations in the ACL anatomy were assessed by testing for side-to-side ACL footprint location symmetry in a healthy population relative to the operative and contralateral knee in a patient population after traditional transtibial single-bundle ACL reconstruction. MRI and three-dimensional modeling techniques were used to determine the in vivo tibiofemoral ACL footprint centers and the resulting ACL orientations in both knees of 30 healthy subjects and 30 subjects after transtibial ACL reconstruction. While there were substantial inter-subject variations in ACL anatomy, the side-to-side RMS differences in the ACL footprint center were 1.20 and 1.34 mm for the femur and tibia, respectively, for the healthy subjects and no clinically meaningful intra-subject differences were measured. However, there were large intra-subject side-to-side differences after transtibial ACL reconstruction, with ACL grafts placed 5.63 and 7.64 mm from the center of the contralateral femoral and tibial ACL footprint centers, respectively. Grafts were placed more medial, anterior, and superior on the femur and more posterior on the tibia; producing grafts that were more vertical in the sagittal and coronal planes. Given the large variation among subjects, these findings advocate the use of the contralateral ACL morphology for retrospectively evaluating patient-specific anatomic graft placement.     

Use of a collagen-platelet rich plasma scaffold to stimulate healing of a central defect in the canine ACL.

The anterior cruciate ligament (ACL) of the knee fails to heal after primary repair. Here we hypothesize that a beneficial biologic repair response can be induced by placing a collagen-platelet rich plasma (collagen-PRP) material into a central ACL defect. A collagen-PRP scaffold was used to treat a central ACL defect in vivo. In the first experiment, the histologic response in treated and untreated defects was evaluated at 3 (n = 5) and 6 weeks (n = 5). In the second experiment, biomechanical testing of the treated ligaments (n = 8) was performed at 6 weeks and compared with the results of biomechanical testing of untreated defects at the same time-point (n = 6). The percentage filling of the defects in the treated ACLs was significantly higher at both the 3- and 6-week time-points when compared with the untreated contralateral control defects (50 +/- 21% vs. 2 +/- 2% at 3 weeks, and 43 +/- 11% vs. 23 +/- 11 at 6 weeks; all values mean +/- SEM. Biomechanically, the treated ACL defects had a 40% increase in strength at 6 weeks, which was significantly higher than the 14% increase in strength previously reported for untreated defects (p < 0.02). Placement of a collagen-PRP bridging scaffold in a central ACL defect can stimulate healing of the ACL histologically and biomechanically.     

Peripheral blood mononuclear cells enhance the anabolic effects of platelet‐rich plasma on anterior cruciate ligament fibroblasts

Use of platelet‐rich plasma (PRP) has shown promise in various orthopaedic applications, including treatment of anterior cruciate ligament (ACL) injuries. However, various components of blood, including peripheral blood mononuclear cells (PBMCs), are removed in the process of making PRP. It is yet unknown whether these PBMCs have a positive or negative effect on fibroblast behavior. To begin to define the effect of PBMCs on ACL fibroblasts, ACL fibroblasts were cultured on three‐dimensional collagen scaffolds for 14 days with and without PBMCs. ACL fibroblasts exposed to PBMCs showed increased type I and type III procollagen gene expression, collagen protein expression, and cell proliferation when the cells were cultured in the presence of platelets and plasma. However, addition of PBMCs to cells cultured without platelets had no effect. The increase in collagen gene and protein expression was accompanied by an increase in IL‐6 expression by the PBMCs with exposure to the platelets. Our results suggest that the interaction between platelets and PBMCs leads to an IL‐6 mediated increase in collagen expression by ACL fibroblasts. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:29–34, 2012     

Partial anterior cruciate ligament tears treated with intraligamentary plasma rich in growth factors

AIM: To evaluate the effect of the application of plasma rich in growth factors (PRGF)-Endoret to the remaining intact bundle in partial anterior cruciate ligament (ACL) tears.METHODS: A retrospective review of the rate of return to play in football players treated with the application of PRGF-Endoret in the remaining intact bundle in partial ACL injuries that underwent surgery for knee instability. Patients with knee instability requiring revision surgery for remnant ACL were selected. PRGF was applied in the wider part of posterolateral bundle and the time it took patients to return to their full sporting activities at the same level before the injury was evaluated.RESULTS: A total of 19 patients were reviewed. Three had a Tegner activity level of 10 and the remaining 16 level 9. The time between the injury and the time of surgery was 5.78 wk (SD 1.57). In total, 81.75% (16/19) returned to the same pre-injury level of sport activity (Tegner 9-10). 17 males and 2 females were treated. The rate of associated injury was 68.42% meniscal lesions and 26.31% cartilage lesions. The KT-1000 values were normalized in all operated cases. One patient was not able to return to sport due to the extent of their cartilage lesions. The 15 patients with Tegner activity level 9 returned to play at an average of 16.20 wk (SD 1.44) while the 3 patients with Tegner activity level 10 did so in 12.33 wk (SD 1.11).CONCLUSION: With one remaining intact bundle the application of PRGF-Endoret in instability cases due to partial ACL tear showed high return to sport rates at pre- injury level in professional football players.     

A canine hybrid double‐bundle model for study of arthroscopic ACL reconstruction

Development and validation of a large animal model for pre‐clinical studies of intra‐articular anterior cruciate ligament (ACL) reconstruction that addresses current limitations is highly desirable. The objective of the present study was to investigate a translational canine model for ACL reconstruction. With institutional approval, adult research hounds underwent arthroscopic debridement of the anteromedial bundle (AMB) of the ACL, and then either received a tendon autograft for “hybrid double‐bundle” ACL reconstruction (n = 12) or no graft to remain ACL/AMB‐deficient (n = 6). Contralateral knees were used as non‐operated controls (n = 18) and matched canine cadaveric knees were used as biomechanical controls (n = 6). Dogs were assessed using functional, diagnostic imaging, gross, biomechanical, and histologic outcome measures required for pre‐clinical animal models. The data suggest that this canine model was able to overcome the major limitations of large animal models used for translational research in ACL reconstruction and closely follow clinical aspects of human ACL reconstruction. The “hybrid double‐bundle” ACL reconstruction allowed for sustained knee function without the development of osteoarthritis and for significantly improved functional, diagnostic imaging, gross, biomechanical, and histologic outcomes in grafted knees compared to ACL/AMB‐deficient knees. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1171–1179, 2015.     

The pattern of cartilage damage in antero‐medial osteoarthritis of the knee and its relationship to the anterior cruciate ligament

Within antero‐medial gonarthrosis (AMG) of the knee, there is a spectrum of damage seen in the functionally intact anterior cruciate ligament (ACL). Our aim was to correlate the degree of ACL damage to the geographical extent and degree of cartilage loss on the tibial plateau. Ninety tibial plateaus resected during unicompartmental arthroplasty were photographed and digitally mapped. The ACL damage was graded (0: normal, 1: synovium loss, 2: longitudinal splits), and dimensions of full thickness cartilage loss and damage recorded. The percentage of full thickness loss in patients with a normal ACL was compared to those with a damaged, but functionally intact ligament. All specimens showed similar elliptical loss of cartilage in the antero‐medial part of the tibial plateau. A total of 45(50%) patients had a macroscopically normal ACL, 21(23%) had synovial loss, and 24(27%) had longitudinal splits. An increase in the area of cartilage damage was seen with progressive ACL damage (p < 0.001). The area of macroscopically normal cartilage found posteriorly did not change. This study demonstrates that phenotypic distribution of cartilage damage in AMG is highly reproducible with a pattern of increasing cartilage erosion associated with increasing ACL damage. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 908–913, 2013     

Platelet‐rich plasma alone is not sufficient to enhance suture repair of the ACL in skeletally immature animals: An in vivo study

In this study, we hypothesize that supplementation of suture repair of the anterior cruciate ligament (ACL) with platelet‐rich plasma (PRP) will improve the biomechanics of the repair. Six 30‐kg pigs underwent bilateral suture repair of the ACL. One side was treated with suture repair alone, while the contralateral side was treated with suture repair augmented with PRP. After 14 weeks in vivo, anterior–posterior (AP) knee laxity and the tensile properties of the repaired ligament were measured. The addition of PRP to the suture repairs did not improve AP knee laxity at 30° (p = 0.73) or 60° (p = 0.65). It also did not improve the maximum tensile load (p = 0.64) or linear stiffness (p = 0.42) of the ACL repairs after 14 weeks in vivo. The model had 80% power to detect a 30% improvement of biomechanical properties with PRP; thus, we are confident that a clinically meaningful effect as a result of adding PRP is unlikely. Use of PRP alone to supplement suture repair of the ACL is ineffective in this animal model. Published by Wiley Periodicals, Inc. J Orthop Res 27: 639–645, 2009     

Autologous platelet gel and platelet-poor plasma reduce pain with total shoulder arthroplasty

The recovery of patients undergoing total shoulder arthroplasty (TSA) can be adversely affected by a number of complications. Autologous platelet gel (APG), produced by activating platelet-rich plasma (PRP), has been shown to improve hemostasis and wound healing and reduce infections in some surgical procedures. Activated platelet-poor plasma (PPP) has also been used as a hemostatic agent. This study examines the effects of APG and PPP treatment on TSA patients postoperatively. After Institutional Review Board (IRB) approval, 40 patients undergoing TSA at our institution were prospectively enrolled in our study. They were randomized into either a control (n = 20) or study (n = 20) group, with the study group receiving APG and PPP treatment. Preoperative demographic data, pre- and postoperative laboratory data, pain scores, pain medication, complications, pre- and postoperative range of motion measurements, and postoperative lengths of stay were recorded for each group. The preoperative internal rotation index was significantly higher in the control group compared with treatment patients (4.64 +/- 4.46 vs. 1.88 +/- 2.44, p < .05). The percent hemoglobin retained postoperatively was higher in the treatment group at 24 (84.54 +/- 5.32 vs. 79.87 +/- 8.73) and 72 hours (87.46 +/- 16.03 vs. 76.70 vs. 5.96), but neither difference reached statistical significance. The treatment group had significantly lower pain scores (p = .007) and total fentanyl requirements (p < .05) compared with control patients. The internal rotation index improvement factor (postoperative internal rotation index/preoperative internal rotation index) was significantly higher in the treatment group vs. the control group (p < .05). Although it did not reach statistical significance, the treatment group was discharged almost 9 hours earlier than the control group (64.44 +/- 15.23 vs. 73.39 +/- 15.37). APG and PPP treatment decreased pain and provided a greater increase in internal rotation measurements postoperatively.     

Complete ACL/MCL deficiency induces variable degrees of instability in sheep with specific kinematic abnormalities correlating with degrees of early osteoarthritis

People are not equally disabled by combined anterior cruciate ligament (ACL)/medial collateral ligament (MCL) injuries, nor do they all develop osteoarthritis (OA). Although biological/biomechanical causes are not clear, some association presumably exists between joint instability and OA development. We hypothesized that degree of OA development following standardized complete ACL/MCL injuries will vary directly with the degree of biomechanical abnormality between individuals. Three groups of sheep were used to test the hypothesis: 17 normal, 9 ACL/MCL transected, and 7 sham animals. Normal joints were assessed morphologically while sham and experimental animals had gait assessment pre‐ and at 4 and 20 weeks post‐surgery, with cartilage and bone changes being mapped and graded at sacrifice at 20 weeks. Sham joints were morphologically normal and had only one minor kinematic change at 20 weeks. Although variable, ACL/MCL deficient animals showed significant kinematic abnormalities in 4/6 degrees of freedom (DOFs), as well as cartilage/bone damage by 20 weeks (p < 0.05). Linear regression analysis revealed that changes in medial–lateral (ML) translation were related to the current level of joint degradation as represented by total gross OA score (p = 0.0044, R² = 0.71) in the ACL/MCL transected group. Even identical ACL/MCL injuries result in inter‐animal variations in instability and OA, however significant kinematic abnormalities in ML translation do relate to early OA in sheep. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:384–392, 2012     

Release of growth factors from a reinforced collagen GAG matrix supplemented with platelet rich plasma: Influence on cultured human meniscal cells

Damage to meniscal cartilage has been strongly linked to accelerated articular wear and consequently to osteoarthritis. Damage might be ameliorated by delivery of growth factors from platelet rich plasma (PRP) via a fiber reinforced collagen matrix designed for meniscal repair. PRP composition, release of growth factors, and influence on meniscal cell growth and gene expression were investigated. PRP was prepared using Harvest Smartprep (HS‐PRP), Cascade Fibrinet (CF‐PRP), and a simple centrifuge protocol (DC‐PRP) from four donors each. CF‐PRP had the highest ratio of platelets, with very few other blood cell types. HS‐PRP had the highest total number of platelets but also contained high levels of red and white blood cells. Absorbed to collagen matrices HS‐PRP released the highest levels of TGF‐β1 and PDGF‐AB with DC‐PRP the most IGF‐1. Cumulative release from collagen matrix was 48 ng/cm³ IGF‐1, 96 ng/cm³ TGF‐β1, and 9.6 ng/cm³ PDGF‐AB. Collagen matrix with PRP was able to increase meniscal cell number above peripheral whole blood and up‐regulated gene expression of Aggrecan, Collagen type I (α1), and Elastin (3.3 ± 0.8‐fold, 2.9 ± 0.6‐fold, 4.0 ± 1.4‐fold, respectively). Demonstrating that PRP combined with fiber reinforced collagen matrix could influence meniscal cells and might be of use for treating meniscal defects. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:273–278, 2014.