REVIEW ARTICLE
The Use of PRP in Ligament and Meniscal Healing Hillary J. Braun, BA,*w Amy S. Wasterlain, MD,* and Jason L. Dragoo, MD*
Abstract: Platelet-rich plasma (PRP) has become a popular treatment for acute and chronic soft tissue injuries. Although the majority of research has focused on its use in tendinopathy, PRP may have potential in meniscus and ligament healing. Some level II studies support a possible benefit for anterior cruciate ligament (ACL) allograft maturation, and preliminary animal studies point to a potential role for PRP in primary ACL repair. However, randomized controlled trials have not demonstrated a benefit of PRP for ACL tendon allograft-tunnel integration. To date, 2 studies document the use of PRP for meniscal applications, but this field is largely unexplored. With respect to ligament and meniscal applications, the current literature suggests PRP may be promising for primary ACL repair in skeletally immature patients, ACL graft maturation, and repair of meniscal tears in the avascular zone. Key Words: platelet-rich plasma, ligaments, menisci, anterior cruciate ligament
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P
latelet-rich plasma (PRP) has been used to augment tissue healing and repair in the fields of dentistry, oral maxillofacial surgery, and orthopedic surgery since the 1990s.1,2 The allure of PRP is that it provides an autologous source of platelets, which contain alpha and dense granules rich in growth factors. PRP delivers growth factors in supraphysiological concentrations while still maintaining physiological ratios of these growth factors.3–5 Specific healing and regeneration pathways vary by tissue, but the need for blood supply and growth factor signaling is uniform. PRP is commonly used in many orthopedic applications, including wound hemostasis6,7 and treatment of tendinopathies.8–10 To date, the majority of PRP research in orthopedics has focused on its potential in acute and chronic tendinopathy. The use of PRP in anterior cruciate ligament (ACL) reconstruction and meniscal repair is an area of growing interest. The use of PRP in ACL applications focuses primarily on ACL reconstruction,11–14 with some preliminary basic science studies exploring the use of PRP for primary repair of the ACL.15–18 A handful of studies have evaluated the use of PRP for healing of the medial collateral ligament (MCL)19–22 and meniscal repair,23,24 but these areas remain largely unexplored. Despite anecdotal evidence to support the use of PRP in other ligaments, including the medial and lateral ligaments of the ankle and the ulnar collateral ligament of the elbow, From the *Department of Orthopaedic Surgery, Stanford University, Redwood City; and wSchool of Medicine, University of California, San Francisco, San Francisco, CA. H.J.B. and A.S.W. contributed equally. Disclosure: The authors declare no conflict of interest. Reprints: Jason L. Dragoo, MD, Department of Orthopaedic Surgery, Stanford University, 450 Broadway Street, Pavilion C, 4th Floor, Redwood City, CA 94063-6342. Copyright r 2013 by Lippincott Williams & Wilkins
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at the time of writing no trials in these or other ligaments have been published.
LIGAMENT APPLICATIONS ACL After ACL reconstruction with tendon grafts, the graft undergoes 4 phases of integration: acute inflammation, angiogenesis, matrix synthesis, and collagen remodeling. The acute inflammatory phase begins immediately upon release of the tourniquet due to bleeding from the surrounding bone. Circulating platelets aggregate and degranulate within the forming fibrin clot, releasing cytokines and growth factors such as transforming growth factor beta (TGF-b) and platelet-derived growth factor (PDGF).25 TGF-b1 stimulates chemotaxis of neutrophils and monocytes, and exogenous TGF-b1 has been shown to increase granulation tissue, collagen formation, and wound tensile strength in animal models.26 As PRP contains elevated quantities of many growth factors, including TGF-b1 and PDGF, PRP could facilitate the acute inflammatory phase of ACL graft integration and contribute to osteoconduction, thereby accelerating the healing process.27–30 The growth factors contained in PRP and their potential roles in promoting ligament and meniscus healing are summarized in Table 1. Although anatomic ACL reconstruction attempts to replicate the patient’s tibial and femoral bone insertion sites, the structure and attachment of the direct ligament insertion into bone cannot be reproduced. Rather, the tendon graft heals with a fibrovascular scar and perpendicular collagen bundles resembling Sharpey fibers of an indirect insertion site.12,33,34 These Sharpey-like fibers begin to form within 3 to 4 weeks after ACL reconstruction, and are gradually replaced as osteointegration occurs over the ensuing year.
PRIMARY ACL REPAIR Although reconstruction is currently the gold standard for most ACL tears, recent observations of high healing capacity in skeletally immature patients have generated interest in biological approaches to primary nonoperative ACL repair. One of the challenges with primary ACL repair is that the ACL does not form a fibrin-platelet clot at the tear site, whereas this clot is the main scaffolding material at the MCL. Without this clot there is no bridge between the 2 torn ligament ends, and the inflammatory and clotting cascades are halted.16 Steadman et al35 demonstrated improved outcomes in active adults after using the arthroscopic “healing response” technique, which involves perforating the femoral attachment and body of the ACL to generate bleeding and reinitiate the clotting cascade. In combination with a collagen scaffold, PRP may offer a solution to augment primary ACL repair; together,
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TABLE 1. Growth Factors Contained Within PRP That Have a Potential Role in Ligament or Meniscus Healing
Growth Factors bFGF (FGF-2) PDGF
TGF-b1
VEGF
Role in Ligament Healing
Role in Meniscus Healing
Endothelial cell Meniscal cell replication proliferation and and extracellular matrix angiogenesis13 production31 Fibroblast proliferation Macrophage and fibroblast chemotaxis Initiation of clotting cascade Fibronectin and glycosaminoglycan deposition3 Neutrophil and Collagen and proteoglycan monocyte chemotaxis production10 Collagen synthesis and deposition30 Regulation of cell proliferation, division and apoptosis5,28 Angiogenesis21,32 Angiogenesis
bFGF indicates basic fibroblast growth factor; PDGF, platelet-derived growth factor; TGF-b1, transforming growth factor beta; VEGF, vascular endothelial growth factor.
collagen and PRP could offer both structural support for a clot and a source of growth factors. Collagen also acts as a platelet activator, initiating the release of growth factors to stimulate healing, and could protect platelets from the degradative effects of synovial fluid plasmin.14 Murray et al16,18 demonstrated enhanced ACL repair using a collagen-platelet composite in a canine model. In a porcine model, 2 groups found that suture repair of the torn ACL augmented with collagen-platelet composite significantly improved repair strength at 4 weeks and 3 months compared with suture repair alone.15,16 In human ACL cell cultures in vitro, platelet-rich clot releasate triggered a significant increase in cell number and type III collagen production relative to cells treated with platelet-poor clot releasate.36 Furthermore, PRP enhanced ACL cell viability in a dose-dependent and time-dependent manner, with increasing cell number over the 4 days of the study. The authors propose that PRP promoted cell viability and collagen synthesis through providing TGF-b1 and PDGF-AB, 2 growth factors that have been shown to have similar effects in a previous study.37 Although these studies support a potential role for PRP in primary ACL repair, another group has found no difference in collagen metabolism when PRP is applied to tendon cells.38 Interestingly, age seems to be inversely related to fibroblast response to platelet concentrates. For example, both migration and proliferation were significantly higher in immature relative to mature ACL fibroblasts, which suggests that younger patients might respond more favorably to PRP treatment.39 This finding could be especially relevant to young skeletally immature patients with ACL tears.
ACL RECONSTRUCTION The success of ACL reconstruction is dependent on 2 biological processes: (1) bone-graft healing or graft integration into the tibial and femoral tunnels (Table 2) and (2) r
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ligamentization or maturation of the articular portion of the graft (Table 3). The logic behind using PRP in ACL repair is that growth factors released from platelet degranulation could facilitate one or both of these processes.
Graft Integration Into Tunnels Grafts with a bone plug rely on bone-to-bone healing, in contrast to soft tissue grafts, which require tendon-bone healing. ACL reconstruction with a bone-patellar tendonbone (BTB) graft can be advantageous because it preserves the original tendon attachment to bone and therefore does not require tendon integration into the tibial and femoral tunnels. In a canine model of BTB ACL reconstruction, the structure of the graft-bone interface contained Sharpey-like fibers and resembled the normal ACL.12 To our knowledge, there are no studies evaluating PRP for bone-bone healing in BTB grafts. In a recent meta-analysis including 4 randomized controlled trials and 3 prospective cohort studies, Sheth et al13 conclude that there is no evidence to support a benefit of PRP for ACL tendon allograft healing. They found methodological limitations, unexplained heterogeneity, and overall low quality of evidence to support a positive effect of PRP. In a systematic review of 5 studies, Vavken et al48 also concluded that platelet concentrates have little to no effect on tunnel healing. Interestingly, some studies suggest that PRP could even have a deleterious effect on graft integration. For example, Figueroa et al11 found a greater frequency of synovial fluid within the bone tunnels in the autologous platelet concentrate group compared with the control group. One possible explanation is that PRP contains high levels of cytokines, which may contribute to tunnel widening.42 The application of PRP for ACL bone tunnel healing has technical challenges and limitations. Many of the groups who have studied the effect of PRP on ACL graft integration point out that it is difficult to tell how much PRP stays in the tunnels after being injected.11,42 Diffusion of the PRP contents away from the tunnel site could lead to variability in the volume of PRP at the graft-bone interface. It is possible that more PRP could be placed accurately throughout the tunnel length if this were done before securing the graft. Many mechanical factors affect tunnel healing as well, including graft positioning, length, fixation, tensioning, and micromotion within the tunnels. Other factors that may affect outcomes include graft type and PRP formulation. All studies to date have used hamstring grafts. PRP may also have different effects on tendon allografts and autografts. Some of the published studies discussed here do not explicitly state whether they used allografts or autografts.11,41,44 Although the biological healing pathway for allografts is similar, it generally takes longer than in autografts. This difference in healing rate may make PRP even more advantageous for allografts relative to autografts.32 With respect to PRP formulation, all studies except one40 have used leukocyte-rich PRP formulations. Leukocyte-rich formulations increase local tissue inflammation and may delay or alter healing.49,50 Finally, an important outcome that has not yet been assessed in the literature is graft failure. Long-term follow-up will be necessary to understand whether augmentation with PRP affects the longevity of ACL reconstruction. www.sportsmedarthro.com |
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TABLE 2. Clinical Trials of PRP in ACL Reconstruction—Graft Integration (Graft-Bone Interface Healing)
References
Level of Evidence
Graft and PRP Type
Groups (n)
Outcome Measures
Time
Results (P)
Conclusion
Figueroa et al11
III
STG APC (30) Magellan APC Control (20) injected into tunnels and applied in graft
MRI presence of 6 mo synovial fluid at tunnel-graft interface
Mirzatolooei et al40
II
Quadrupled hamstring autograft Arthrex PRP
PRP (25) Control (25)
CT tunnel diameter Clinical laxity
Orrego et al41
II
Quadrupled ST graft Biomet GPS II (LR-PRP)
PRP (26) MRI 3 mo Bone plug (28) osteoligamen6 mo PRP + bone plug (27) tous interface Control (27) MRI femoral tunnel widening
Silva and Sampaio42
II
PRP (10) MRI signal PRP (10) intensity of PRP + thrombin (10) femoral tunnel PRP + postoperative fibrous PRP (10) interzone Control (10)
3 mo
Ventura et al43
II
PRP (10) Control (10)
CT MRI KOOS, IKDC, Tegner scores KT-1000
6 mo
Vogrin et al44
I
Double-bundle STG autograft Biomet Mini GPS III (LR-PRP) injected between graft strands into femoral tunnels, ± intraarticular PRP at 2 and 4 wk postoperative Hamstring autograft Biomet-Merck GPS (LR-PRP) applied on graft and in tunnels 2 STG graft Magellan PG coated onto graft and injected into tunnels
PG (25) Control (25)
MRI graft vascularization at tibial osteoligamentous interface
4-6 wk 4-6 wk: 0.33 PG enhances 10-12 wk vascularization early graft rate at revascularizaosteoligamention in tous interface in osteoligamenPG vs. 0.16 in tous interface control zone (< 0.001) 10-12 wk: no difference
Negative for synovial fluid interface in 87% of APC vs. 95% of control (0.72) 3 mo: mean 24%40% tunnel widening in control vs. 19%-34% in PRP (0.18-0.36) 3 mo: no difference 6 mo: 78% lowintensity signal in control vs. 100% in PRP (0.04) No difference
3 mo
No difference
No difference
No effect on osteoligamentous interface or tunnel widening No difference; PRP does not accelerate tendon integration
Unable to assess PRP may graft-bone accelerate graft interface by CT integration due to bony sclerosis
Levels of evidence: I, double-blind randomized controlled trial (RCT); II, lesser quality RCT; III, case-control or cohort study. ACL indicates anterior cruciate ligament; APC, autologous platelet concentrate; CT, computed tomography; LR-PRP, leukocyte-rich platelet-rich plasma; MRI, magnetic resonance imaging; PG, platelet gel; PRP, platelet-rich plasma; ST, semitendinosus; STG, semitendinosus/gracilis.
Ligamentization (Maturation) of Graft ACL graft maturation is commonly assessed by arthroscopic and histologic criteria. At 6 weeks the graft is covered with thick synovial tissue and abundant capillaries grossly, and is composed of irregularly oriented collagen fibers microscopically. At 6 months the graft is thinly covered with synovium and is markedly less vascular, and fibroblasts and collagen fibers are reoriented in a regular direction. Finally, by 1 year the graft is a thick ligamentous tissue resembling normal ACL,
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and collagen fibers are organized in a high-frequency crimp pattern with spindle-shaped fibroblasts interspersed between collagen fibers.51 Graft maturation can also be assessed by magnetic resosnance imaging (MRI); high-intensity signals similar to synovial fluid suggest poor graft maturation, whereas lowintensity signals similar to the native posterior cruciate ligament are positively associated with graft maturation. As summarized in a systematic review by Vavken and colleagues, 7 studies published from 2005 to 2010 reported r
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TABLE 3. Clinical Trials of PRP in ACL Reconstruction—Graft Maturation/Ligamentization
Level of References Evidence Figueroa et al11
III
Graft and PRP Type STG Magellan APC injected into tunnels and applied in graft BTB allograft Authors’ own PRP protocol PRP clot enveloped in graft and implanted into tibial tunnel 4 ST graft Biomet GPS II (LR-PRP)
Groups (n)
Outcome Measures
Time
Conclusion
APC (30) Control (20)
MRI signal intensity (1-3 pts)
6 mo
PRP (50) Control (50)
MRI signal intensity C-reactive protein VAS score IKDC score KT-1000
2y
PRP (26) Bone plug (28) PRP + BP (27) Control (27) PRPG (25) Control (25)
MRI signal intensity of graft
3 mo 6 mo
Time to graft 3homogenization 12 mo
369 d to maturation in PRP vs. 177 d in control
(+) PRP accelerates time to graft maturation by 48%
PRGF (22) Control (15)
Arthroscopic score Ligament Tissue Maturity Index (histology)
Excellent arthroscopic score in 57% of PRGF vs. 33% of control (0.05) New connective tissue by histology in 40% of control vs. 77% of PRGF (0.02) ACL density more homogenous in PRP vs. control group (< 0.01) No difference in KOOS, KT-1000, or Tegner scores Synovitic reaction in 1 PRP pt No intra-articular graft revascularization in either group at any time
No macroscopic difference (+) More uniform remodeling in PRGF group
Nin et al45
I
Orrego et al41
II
Radice et al46
III
Sanchez et al47
III
Ventura et al43
II
Autologous PRP (10) CT hamstring Control (10) KOOS, IKDC, Biomet-Merck Tegner scores GPS (LRKT-1000 PRP) applied on graft and in tunnels
6 mo
Vogrin et al44
I
2 ST/gracilis graft Magellan platelet gel PRP applied on graft and into tunnels
4-6 wk 10-12 wk
BTB autograft or hamstring autograft Biomet GPS (LR-PRP) applied around graft with Gelfoam Autologous ST graft undergoing second look arthroscopy BTI System II PRGF Graft soaked in PRGF
Results (P)
PRP (25) Control (25)
MRI graft vascularization
6-25 mo (mean 15 mo)
Mean signal intensity Trend toward score 2.6 in PRP improved vs. 2.3 in control maturation with (0.32) PRP, but not statistically significant 21%-23% lower No clinical or MRI signal in PRP biomechanical vs. control (0.10effect 0.45)
3 mo: no difference (+) PRP enhances 6 mo: 78% lowgraft maturation intensity signal in control vs. 100% in PRP (0.036)
(+) PRP enhances graft maturation
No difference
Levels of evidence: I, double-blind randomized controlled trial (RCT); II, lesser quality RCT; III, case-control or cohort study. ACL indicates anterior cruciate ligament; APC, autologous platelet concentrate; BP, bone plug; BTB, bone-patellar tendon-bone; CT, computed tomography; LR-PRP, leukocyte-rich platelet-rich plasma; MRI, magnetic resonance imaging; PRPG, platelet-rich plasma gel; PRP, platelet-rich plasma; PRGF, plasma rich in growth factors; pt, patient; pts, patients; ST, semitendinosus; STG, semitendinosus/gracilis; VAS, visual analog scale.
MRI data on ACL graft maturation with and without the addition of PRP.11,41,43–47,51 Four of these studies reported positive effects of platelets on intra-articular graft maturation, as measured by increased level or rate of tissue homogeneity by histology or MRI.41,43,46,47 The authors note that 2 of the studies found a 20% relative r
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improvement in the PRP group, but may have fallen short of statistical significance due to being underpowered.11,45 Another possibility is that PRP provides the growth factors necessary to accelerate the early maturation process, but that this benefit is attenuated over time such that no difference is observed at later time points. In contrast, all 4 www.sportsmedarthro.com |
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studies reporting a positive effect of PRP on graft maturation were level II studies, whereas the 2 higher quality level I studies by Nin and colleagues and Vogrin and colleagues reported no difference in clinical, biomechanical, or revascularization outcomes.
OTHER LIGAMENTS The use of PRP for treatment and regeneration of other ligamentous injuries is less well explored than ACL applications. Several groups have investigated the effect of specific growth factors on MCL healing and repair. Letson and Dahners52 reported that application of PDGF to an injured rat MCL resulted in stronger, stiffer ligaments compared with controls. Hildebrand and colleagues delivered recombinant human PDGF-BB and TGF-b1 in fibrin clot to ruptured MCLs and conducted histologic and mechanical evaluation of the ligaments at 6 weeks postoperatively. Application of PDGF-BB to the site of MCL injury significantly improved the ultimate load, energy absorbed to failure, and elongation of the femur-MCL-tibia complex.20 Similarly, Spindler and colleagues examined the effect of TGF-b2 on MCL healing in a rabbit model. Recombinant human TGF-b2 was delivered locally to the injury site through fibrin clot and ligament healing and mechanical strength was assessed at 6 weeks postoperatively. The addition of TGF-b2 to the healing MCL resulted in higher stiffness of the ligament but did not affect scar load to failure or energy to failure.21 Although these studies did not utilize PRP, they helped establish the rationale for growth factor delivery to ligamentous sites of injury. Yoshioka et al22 recently evaluated the effect of leukocyte-poor plasma rich in growth factors (PRGF) on MCL healing in a rabbit model. MCL ruptures were induced and either treated immediately with PRGF or left untreated. Animals were euthanized at 3 and 6 weeks postoperatively and biomechanical and histologic analyses were performed. In the PRGF group at 3 weeks, cellularity and blood vessel density were the highest; both of these findings decreased at 6 weeks. The biomechanical evaluation revealed that all ligaments failed in the proximal edge of the MCL repair; load to failure testing demonstrated that ultimate load and stiffness were significantly greater in MCLs treated with PRGF compared with the controls at 6 weeks. The early increases in cellularity and vascularity combined with the greater mechanical strength led the authors to conclude that early administration of PRGF post-MCL injury may afford healing advantages and accelerate return to play activities. Harris et al19 injected leukocyte-rich autologous platelet gel into healthy tissues of skeletally mature New Zealand white rabbits, including the MCL. At 2 weeks postinjection, the MCL showed a monocytic and lymphocytic inflammatory infiltrate and thickening of tissue. At 12 weeks postinjection, inflammation persisted but was less marked. By contrast, all saline-injected sites were histologically normal. The authors concluded that application of autologous platelet gel to normal rabbit tissues caused a reaction that histologically approximated the acute “healing response.”
PRP IN MENISCUS HEALING Meniscal repair is considered for traumatic tears near the peripheral, vascular zone of the meniscus in younger patients. Vascular supply is provided by capillaries from the
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perimeniscal capillary plexus and infiltrate up to 30% of the width of the meniscus in the “red-red” zone.53 The inner two thirds of the menisci, the “red-white” and the “whitewhite” zones, contain little or no nerves or blood vessels.31,37,54 The meniscus has some ability to heal tears occurring in the outer one-third region due to a fibrin clot rich in inflammatory cells that forms at the site of injury. Fibrous repair tissue grows over the injured area as a result of local undifferentiated mesenchymal cells.55 Because of this mechanism, biological augmentation strategies aimed at increasing meniscal vascularity have been proposed to enhance tissue healing and repair techniques. Common methods of biological augmentation include trephination, synovial abrasion, and application of a fibrin clot. Several anabolic growth factors have been identified in meniscal tissue repair and regeneration: basic fibroblast growth factor, TGF-b1, bone morphogenic proteins, insulin-like growth factor-I, vascular endothelial growth factor, PDGF-AB. Interleukin-1 and epidermal growth factor have been shown to stimulate meniscal cell migration; bone morphogenic protein-2 and insulin-like growth factor-I stimulate fibrochondrocyte migration from the middle to avascular zone.56 PRP is a promising autologous source of these, and other, growth factors. However, to date, there is a relative paucity of literature on the use of PRP for the treatment of meniscal injury or the augmentation of meniscal repair. Currently only 2 studies have evaluated the use of PRP for meniscal applications. Ishida et al23 investigated the use of PRP prepared with a double-spin technique for meniscal tissue regeneration both in vitro and in vivo. In vitro, cells were isolated from rabbit tissue harvested from the inner two thirds of the meniscus and treated with PRP or platelet poor plasma (PPP) at concentrations of 3%, 10%, and 30% for 48 hours. Treatment with PRP resulted in significant and dosedependent upregulation of meniscal cell viability and synthesis of sulphated glycosaminoglycans compared with PPP and controls. Gene expression analyses revealed no difference in type I collagen, significant downregulation of aggrecan expression, and significant upregulation of biglycan and decorin compared with cultures treated with PPP. In the in vivo arm of the study, 30 mL PRP, PPP, or phosphate buffered saline was added to freeze-dried gelatin hydrogels and implanted into a 1.5 mm defect in the avascular zone of the meniscus in adult female rabbits. The animals were euthanized at 4, 8, and 12 weeks postoperatively and tissue sections were stained with hematoxylin and eosin and safranin-O to evaluate tissue repair using a semiquantitative scoring system. At 12 weeks, tissue defects treated with PRP showed significantly greater scores for number of fibro-chondrocytes and production of extracellular matrix. The sum of these in vitro and in vivo results led the authors to conclude that PRP enhances the healing properties of inner, avascular meniscus. The second study, conducted by Zellner et al,24 evaluated the use of mesenchymal stem cells (MSCs) for meniscal tissue engineering. MSCs were seeded onto hyaluronan-collagen composite matrices loaded with leukocyte-rich PRP and implanted into 2 mm defects in the avascular zone of the meniscus in adult male rabbits. The animals were euthanized at 6 and 12 weeks and macroscopic, histologic, and immunohistochemical evaluation of the tissue was performed. Defects treated with MSCs and PRP showed no improvement at 6 or 12 weeks compared r
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with to an implantation of a cell-free scaffold. The authors postulated that the discrepancy in this result versus those reported by Ishida and colleagues may have been related to the larger defect size. The conflicting results in these 2 studies highlight the need for further investigation into the use of PRP in meniscal healing and repair. Studies using human meniscal tissue or assessing clinical applications of PRP for meniscal injury may be warranted.
CONCLUSIONS Although PRP has many applications in clinical orthopedics, evidence to support its use in the applications of ACL reconstruction and repair and meniscal injuries is incomplete. It seems that PRP may be clinically useful for ACL graft maturation and meniscal repair, but further investigations are warranted. Existing human studies do not support the use of PRP for ACL graft integration. Animal studies suggest PRP may promote healing in avascular meniscal tears, however, these effects have yet to be observed in humans. REFERENCES 1. Slater M, Patava J, Kingham K, et al. Involvement of platelets in stimulating osteogenic activity. J Orthop Res. 1995;13:655–663. 2. Whitman DH, Berry RL, Green DM. Platelet gel: an autologous alternative to fibrin glue with applications in oral and maxillofacial surgery. J Oral Maxillofac Surg. 1997; 55:1294–1299. 3. Anitua E, Andia I, Sanchez M, et al. Autologous preparations rich in growth factors promote proliferation and induce VEGF and HGF production by human tendon cells in culture. J Orthop Res. 2005;23:281–286. 4. Creaney L, Hamilton B. Growth factor delivery methods in the management of sports injuries: the state of play. Br J Sports Med. 2008;42:314–320. 5. Mishra A, Woodall J Jr, Vieira A. Treatment of tendon and muscle using platelet-rich plasma. Clin Sports Med. 2009; 28:113–125. 6. Berghoff WJ, Pietrzak WS, Rhodes RD. Platelet-rich plasma application during closure following total knee arthroplasty. Orthopedics. 2006;29:590–598. 7. Gardner MJ, Demetrakopoulos D, Klepchick PR, et al. The efficacy of autologous platelet gel in pain control and blood loss in total knee arthroplasty. An analysis of the haemoglobin, narcotic requirement and range of motion. Int Orthop. 2007;31:309–313. 8. Barrett SE, Erredge ES. Growth factors for chronic plantar fasciitis. Podiatry Today. 2004;17:37–42. 9. Mishra A, Pavelko T. Treatment of chronic elbow tendinosis with buffered platelet-rich plasma. Am J Sports Med. 2006;34:1774–1778. 10. Scioli M. Treatment of recalcitrant enthesopathy of the hip with platelet rich plasma- a report of three cases. Clin Orthop Soc News. 2006;6–7. 11. Figueroa D, Melean P, Calvo R, et al. Magnetic resonance imaging evaluation of the integration and maturation of semitendinosus-gracilis graft in anterior cruciate ligament reconstruction using autologous platelet concentrate. Arthroscopy. 2010;26:1318–1325. 12. Rodeo SA, Arnoczky SP, Torzilli PA, et al. Tendon-healing in a bone tunnel. A biomechanical and histological study in the dog. J Bone Joint Surg Am. 1993;75:1795–1803. 13. Sheth U, Simunovic N, Klein G, et al. Efficacy of autologous platelet-rich plasma use for orthopaedic indications: a metaanalysis. J Bone Joint Surg Am. 2012;94:298–307. 14. Vavken P, Murray MM. The potential for primary repair of the ACL. Sports Med Arthrosc. 2011;19:44–49. r
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15. Joshi SM, Mastrangelo AN, Magarian EM, et al. Collagenplatelet composite enhances biomechanical and histologic healing of the porcine anterior cruciate ligament. Am J Sports Med. 2009;37:2401–2410. 16. Murray MM, Spindler KP, Abreu E, et al. Collagen-platelet rich plasma hydrogel enhances primary repair of the porcine anterior cruciate ligament. J Orthop Res. 2007;25:81–91. 17. Murray MM, Spindler KP, Ballard P, et al. Enhanced histologic repair in a central wound in the anterior cruciate ligament with a collagen-platelet-rich plasma scaffold. J Orthop Res. 2007;25:1007–1017. 18. Murray MM, Spindler KP, Devin C, et al. Use of a collagenplatelet rich plasma scaffold to stimulate healing of a central defect in the canine ACL. J Orthop Res. 2006;24:820–830. 19. Harris NL, Huffer WE, von Stade E, et al. The effect of platelet-rich plasma on normal soft tissues in the rabbit. J Bone Joint Surg Am. 2012;94:786–793. 20. Hildebrand KA, Woo SL, Smith DW, et al. The effects of platelet-derived growth factor-BB on healing of the rabbit medial collateral ligament. An in vivo study. Am J Sports Med. 1998;26:549–554. 21. Spindler KP, Murray MM, Detwiler KB, et al. The biomechanical response to doses of TGF-beta 2 in the healing rabbit medial collateral ligament. J Orthop Res. 2003;21:245–249. 22. Yoshioka T, Kanamori A, Washio T, et al. The effects of plasma rich in growth factors (PRGF-Endoret) on healing of medial collateral ligament of the knee. Knee Surg Sports Traumatol Arthrosc. 2013;21:1763–1769. 23. Ishida K, Kuroda R, Miwa M, et al. The regenerative effects of platelet-rich plasma on meniscal cells in vitro and its in vivo application with biodegradable gelatin hydrogel. Tissue Eng. 2007;13:1103–1112. 24. Zellner J, Mueller M, Berner A, et al. Role of mesenchymal stem cells in tissue engineering of meniscus. J Biomed Mater Res A. 2010;94:1150–1161. 25. Singer AJ, Clark RA. Cutaneous wound healing. N Engl J Med. 1999;341:738–746. 26. Shah M, Foreman DM, Ferguson MW. Control of scarring in adult wounds by neutralising antibody to transforming growth factor beta. Lancet. 1992;339:213–214. 27. Castillo TN, Pouliot MA, Kim HJ, et al. Comparison of growth factor and platelet concentration from commercial platelet-rich plasma separation systems. Am J Sports Med. 2011;39:266–271. 28. Eppley BL, Woodell JE, Higgins J. Platelet quantification and growth factor analysis from platelet-rich plasma: implications for wound healing. Plast Reconstr Surg. 2004;114:1502–1508. 29. van den Dolder J, Mooren R, Vloon AP, et al. Platelet-rich plasma: quantification of growth factor levels and the effect on growth and differentiation of rat bone marrow cells. Tissue Eng. 2006;12:3067–3073. 30. Wasterlain AS, Braun HJ, Harris AH, et al. The systemic effects of platelet-rich plasma injection. Am J Sports Med. 2013;41:186–193. 31. Day B, Mackenzie WG, Shim SS, et al. The vascular and nerve supply of the human meniscus. Arthroscopy. 1985;1:58–62. 32. Li H, Tao H, Cho S, et al. Difference in graft maturity of the reconstructed anterior cruciate ligament 2 years postoperatively: a comparison between autografts and allografts in young men using clinical and 3.0-T magnetic resonance imaging evaluation. Am J Sports Med. 2012;40:1519–1526. 33. Goradia VK, Rochat MC, Grana WA, et al. Tendon-to-bone healing of a semitendinosus tendon autograft used for ACL reconstruction in a sheep model. Am J Knee Surg. 2000;13: 143–151. 34. Grana WA, Egle DM, Mahnken R, et al. An analysis of autograft fixation after anterior cruciate ligament reconstruction in a rabbit model. Am J Sports Med. 1994;22:344–351. 35. Steadman JR, Matheny LM, Briggs KK, et al. Outcomes following healing response in older, active patients: a primary anterior cruciate ligament repair technique. J Knee Surg. 2012;25:255–260.
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36. Fallouh L, Nakagawa K, Sasho T, et al. Effects of autologous platelet-rich plasma on cell viability and collagen synthesis in injured human anterior cruciate ligament. J Bone Joint Surg Am. 2010;92:2909–2916. 37. Meaney Murray M, Rice K, Wright RJ, et al. The effect of selected growth factors on human anterior cruciate ligament cell interactions with a three-dimensional collagen-GAG scaffold. J Orthop Res. 2003;21:238–244. 38. de Mos M, van der Windt AE, Jahr H, et al. Can platelet-rich plasma enhance tendon repair? A cell culture study. Am J Sports Med. 2008;36:1171–1178. 39. Magarian EM, Vavken P, Murray MM. Human anterior cruciate ligament fibroblasts from immature patients have a stronger in vitro response to platelet concentrates than those from mature individuals. Knee. 2011;18:247–251. 40. Mirzatolooei F, Alamdari MT, Khalkhali HR. The impact of platelet-rich plasma on the prevention of tunnel widening in anterior cruciate ligament reconstruction using quadrupled autologous hamstring tendon: a randomised clinical trial. Bone Joint J. 2013;95-B:65–69. 41. Orrego M, Larrain C, Rosales J, et al. Effects of platelet concentrate and a bone plug on the healing of hamstring tendons in a bone tunnel. Arthroscopy. 2008;24:1373–1380. 42. Silva A, Sampaio R. Anatomic ACL reconstruction: does the platelet-rich plasma accelerate tendon healing? Knee Surg Sports Traumatol Arthrosc. 2009;17:676–682. 43. Ventura A, Terzaghi C, Bordo E, et al. Use of growth factors in ACL surgery: preliminary study. J Orthopaed Traumatol. 2006;6:76–79. 44. Vogrin M, Rupreht M, Dinevski D, et al. Effects of a platelet gel on early graft revascularization after anterior cruciate ligament reconstruction: a prospective, randomized, doubleblind, clinical trial. Eur Surg Res. 2010;45:77–85. 45. Nin JR, Gasque GM, Azcarate AV, et al. Has platelet-rich plasma any role in anterior cruciate ligament allograft healing? Arthroscopy. 2009;25:1206–1213.
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46. Radice F, Yanez R, Gutierrez V, et al. Comparison of magnetic resonance imaging findings in anterior cruciate ligament grafts with and without autologous platelet-derived growth factors. Arthroscopy. 2010;26:50–57. 47. Sanchez M, Anitua E, Azofra J, et al. Ligamentization of tendon grafts treated with an endogenous preparation rich in growth factors: gross morphology and histology. Arthroscopy. 2010;26:470–480. 48. Vavken P, Sadoghi P, Murray MM. The effect of platelet concentrates on graft maturation and graft-bone interface healing in anterior cruciate ligament reconstruction in human patients: a systematic review of controlled trials. Arthroscopy. 2011;27:1573–1583. 49. Dragoo JL, Braun HJ, Durham JL, et al. Comparison of the acute inflammatory response of two commercial platelet-rich plasma systems in healthy rabbit tendons. Am J Sports Med. 2012;40:1274–1281. 50. Wasterlain AS, Braun HJ, Dragoo JL. Contents and formulations of platelet-rich plasma. Oper Tech Orthop. 2012;22:33–42. 51. Abe S, Kurosaka M, Iguchi T, et al. Light and electron microscopic study of remodeling and maturation process in autogenous graft for anterior cruciate ligament reconstruction. Arthroscopy. 1993;9:394–405. 52. Letson AK, Dahners LE. The effect of combinations of growth factors on ligament healing. Clin Orthop Relat Res. 1994; 308:207–212. 53. Arnoczky SP, Warren RF. Microvasculature of the human meniscus. Am J Sports Med. 1982;10:90–95. 54. Wilson AS, Legg PG, McNeur JC. Studies on the innervation of the medial meniscus in the human knee joint. Anat Rec. 1969;165:485–491. 55. Scordino LE, Deberardino TM. Biologic enhancement of meniscus repair. Clin Sports Med. 2012;31:91–100. 56. Bhargava MM, Attia ET, Murrell GA, et al. The effect of cytokines on the proliferation and migration of bovine meniscal cells. Am J Sports Med. 1999;27:636–643.
r
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The Use of PRP in Ligament and Meniscal Healing Hillary J. Braun, BA,*w Amy S. Wasterlain, MD,* and Jason L. Dragoo, MD*
Abstract: Platelet-rich plasma (PRP) has become a popular treatment for acute and chronic soft tissue injuries. Although the majority of research has focused on its use in tendinopathy, PRP may have potential in meniscus and ligament healing. Some level II studies support a possible benefit for anterior cruciate ligament (ACL) allograft maturation, and preliminary animal studies point to a potential role for PRP in primary ACL repair. However, randomized controlled trials have not demonstrated a benefit of PRP for ACL tendon allograft-tunnel integration. To date, 2 studies document the use of PRP for meniscal applications, but this field is largely unexplored. With respect to ligament and meniscal applications, the current literature suggests PRP may be promising for primary ACL repair in skeletally immature patients, ACL graft maturation, and repair of meniscal tears in the avascular zone. Key Words: platelet-rich plasma, ligaments, menisci, anterior cruciate ligament
(Sports Med Arthrosc Rev 2013;21:206–212)
P
latelet-rich plasma (PRP) has been used to augment tissue healing and repair in the fields of dentistry, oral maxillofacial surgery, and orthopedic surgery since the 1990s.1,2 The allure of PRP is that it provides an autologous source of platelets, which contain alpha and dense granules rich in growth factors. PRP delivers growth factors in supraphysiological concentrations while still maintaining physiological ratios of these growth factors.3–5 Specific healing and regeneration pathways vary by tissue, but the need for blood supply and growth factor signaling is uniform. PRP is commonly used in many orthopedic applications, including wound hemostasis6,7 and treatment of tendinopathies.8–10 To date, the majority of PRP research in orthopedics has focused on its potential in acute and chronic tendinopathy. The use of PRP in anterior cruciate ligament (ACL) reconstruction and meniscal repair is an area of growing interest. The use of PRP in ACL applications focuses primarily on ACL reconstruction,11–14 with some preliminary basic science studies exploring the use of PRP for primary repair of the ACL.15–18 A handful of studies have evaluated the use of PRP for healing of the medial collateral ligament (MCL)19–22 and meniscal repair,23,24 but these areas remain largely unexplored. Despite anecdotal evidence to support the use of PRP in other ligaments, including the medial and lateral ligaments of the ankle and the ulnar collateral ligament of the elbow, From the *Department of Orthopaedic Surgery, Stanford University, Redwood City; and wSchool of Medicine, University of California, San Francisco, San Francisco, CA. H.J.B. and A.S.W. contributed equally. Disclosure: The authors declare no conflict of interest. Reprints: Jason L. Dragoo, MD, Department of Orthopaedic Surgery, Stanford University, 450 Broadway Street, Pavilion C, 4th Floor, Redwood City, CA 94063-6342. Copyright r 2013 by Lippincott Williams & Wilkins
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at the time of writing no trials in these or other ligaments have been published.
LIGAMENT APPLICATIONS ACL After ACL reconstruction with tendon grafts, the graft undergoes 4 phases of integration: acute inflammation, angiogenesis, matrix synthesis, and collagen remodeling. The acute inflammatory phase begins immediately upon release of the tourniquet due to bleeding from the surrounding bone. Circulating platelets aggregate and degranulate within the forming fibrin clot, releasing cytokines and growth factors such as transforming growth factor beta (TGF-b) and platelet-derived growth factor (PDGF).25 TGF-b1 stimulates chemotaxis of neutrophils and monocytes, and exogenous TGF-b1 has been shown to increase granulation tissue, collagen formation, and wound tensile strength in animal models.26 As PRP contains elevated quantities of many growth factors, including TGF-b1 and PDGF, PRP could facilitate the acute inflammatory phase of ACL graft integration and contribute to osteoconduction, thereby accelerating the healing process.27–30 The growth factors contained in PRP and their potential roles in promoting ligament and meniscus healing are summarized in Table 1. Although anatomic ACL reconstruction attempts to replicate the patient’s tibial and femoral bone insertion sites, the structure and attachment of the direct ligament insertion into bone cannot be reproduced. Rather, the tendon graft heals with a fibrovascular scar and perpendicular collagen bundles resembling Sharpey fibers of an indirect insertion site.12,33,34 These Sharpey-like fibers begin to form within 3 to 4 weeks after ACL reconstruction, and are gradually replaced as osteointegration occurs over the ensuing year.
PRIMARY ACL REPAIR Although reconstruction is currently the gold standard for most ACL tears, recent observations of high healing capacity in skeletally immature patients have generated interest in biological approaches to primary nonoperative ACL repair. One of the challenges with primary ACL repair is that the ACL does not form a fibrin-platelet clot at the tear site, whereas this clot is the main scaffolding material at the MCL. Without this clot there is no bridge between the 2 torn ligament ends, and the inflammatory and clotting cascades are halted.16 Steadman et al35 demonstrated improved outcomes in active adults after using the arthroscopic “healing response” technique, which involves perforating the femoral attachment and body of the ACL to generate bleeding and reinitiate the clotting cascade. In combination with a collagen scaffold, PRP may offer a solution to augment primary ACL repair; together,
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TABLE 1. Growth Factors Contained Within PRP That Have a Potential Role in Ligament or Meniscus Healing
Growth Factors bFGF (FGF-2) PDGF
TGF-b1
VEGF
Role in Ligament Healing
Role in Meniscus Healing
Endothelial cell Meniscal cell replication proliferation and and extracellular matrix angiogenesis13 production31 Fibroblast proliferation Macrophage and fibroblast chemotaxis Initiation of clotting cascade Fibronectin and glycosaminoglycan deposition3 Neutrophil and Collagen and proteoglycan monocyte chemotaxis production10 Collagen synthesis and deposition30 Regulation of cell proliferation, division and apoptosis5,28 Angiogenesis21,32 Angiogenesis
bFGF indicates basic fibroblast growth factor; PDGF, platelet-derived growth factor; TGF-b1, transforming growth factor beta; VEGF, vascular endothelial growth factor.
collagen and PRP could offer both structural support for a clot and a source of growth factors. Collagen also acts as a platelet activator, initiating the release of growth factors to stimulate healing, and could protect platelets from the degradative effects of synovial fluid plasmin.14 Murray et al16,18 demonstrated enhanced ACL repair using a collagen-platelet composite in a canine model. In a porcine model, 2 groups found that suture repair of the torn ACL augmented with collagen-platelet composite significantly improved repair strength at 4 weeks and 3 months compared with suture repair alone.15,16 In human ACL cell cultures in vitro, platelet-rich clot releasate triggered a significant increase in cell number and type III collagen production relative to cells treated with platelet-poor clot releasate.36 Furthermore, PRP enhanced ACL cell viability in a dose-dependent and time-dependent manner, with increasing cell number over the 4 days of the study. The authors propose that PRP promoted cell viability and collagen synthesis through providing TGF-b1 and PDGF-AB, 2 growth factors that have been shown to have similar effects in a previous study.37 Although these studies support a potential role for PRP in primary ACL repair, another group has found no difference in collagen metabolism when PRP is applied to tendon cells.38 Interestingly, age seems to be inversely related to fibroblast response to platelet concentrates. For example, both migration and proliferation were significantly higher in immature relative to mature ACL fibroblasts, which suggests that younger patients might respond more favorably to PRP treatment.39 This finding could be especially relevant to young skeletally immature patients with ACL tears.
ACL RECONSTRUCTION The success of ACL reconstruction is dependent on 2 biological processes: (1) bone-graft healing or graft integration into the tibial and femoral tunnels (Table 2) and (2) r
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ligamentization or maturation of the articular portion of the graft (Table 3). The logic behind using PRP in ACL repair is that growth factors released from platelet degranulation could facilitate one or both of these processes.
Graft Integration Into Tunnels Grafts with a bone plug rely on bone-to-bone healing, in contrast to soft tissue grafts, which require tendon-bone healing. ACL reconstruction with a bone-patellar tendonbone (BTB) graft can be advantageous because it preserves the original tendon attachment to bone and therefore does not require tendon integration into the tibial and femoral tunnels. In a canine model of BTB ACL reconstruction, the structure of the graft-bone interface contained Sharpey-like fibers and resembled the normal ACL.12 To our knowledge, there are no studies evaluating PRP for bone-bone healing in BTB grafts. In a recent meta-analysis including 4 randomized controlled trials and 3 prospective cohort studies, Sheth et al13 conclude that there is no evidence to support a benefit of PRP for ACL tendon allograft healing. They found methodological limitations, unexplained heterogeneity, and overall low quality of evidence to support a positive effect of PRP. In a systematic review of 5 studies, Vavken et al48 also concluded that platelet concentrates have little to no effect on tunnel healing. Interestingly, some studies suggest that PRP could even have a deleterious effect on graft integration. For example, Figueroa et al11 found a greater frequency of synovial fluid within the bone tunnels in the autologous platelet concentrate group compared with the control group. One possible explanation is that PRP contains high levels of cytokines, which may contribute to tunnel widening.42 The application of PRP for ACL bone tunnel healing has technical challenges and limitations. Many of the groups who have studied the effect of PRP on ACL graft integration point out that it is difficult to tell how much PRP stays in the tunnels after being injected.11,42 Diffusion of the PRP contents away from the tunnel site could lead to variability in the volume of PRP at the graft-bone interface. It is possible that more PRP could be placed accurately throughout the tunnel length if this were done before securing the graft. Many mechanical factors affect tunnel healing as well, including graft positioning, length, fixation, tensioning, and micromotion within the tunnels. Other factors that may affect outcomes include graft type and PRP formulation. All studies to date have used hamstring grafts. PRP may also have different effects on tendon allografts and autografts. Some of the published studies discussed here do not explicitly state whether they used allografts or autografts.11,41,44 Although the biological healing pathway for allografts is similar, it generally takes longer than in autografts. This difference in healing rate may make PRP even more advantageous for allografts relative to autografts.32 With respect to PRP formulation, all studies except one40 have used leukocyte-rich PRP formulations. Leukocyte-rich formulations increase local tissue inflammation and may delay or alter healing.49,50 Finally, an important outcome that has not yet been assessed in the literature is graft failure. Long-term follow-up will be necessary to understand whether augmentation with PRP affects the longevity of ACL reconstruction. www.sportsmedarthro.com |
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TABLE 2. Clinical Trials of PRP in ACL Reconstruction—Graft Integration (Graft-Bone Interface Healing)
References
Level of Evidence
Graft and PRP Type
Groups (n)
Outcome Measures
Time
Results (P)
Conclusion
Figueroa et al11
III
STG APC (30) Magellan APC Control (20) injected into tunnels and applied in graft
MRI presence of 6 mo synovial fluid at tunnel-graft interface
Mirzatolooei et al40
II
Quadrupled hamstring autograft Arthrex PRP
PRP (25) Control (25)
CT tunnel diameter Clinical laxity
Orrego et al41
II
Quadrupled ST graft Biomet GPS II (LR-PRP)
PRP (26) MRI 3 mo Bone plug (28) osteoligamen6 mo PRP + bone plug (27) tous interface Control (27) MRI femoral tunnel widening
Silva and Sampaio42
II
PRP (10) MRI signal PRP (10) intensity of PRP + thrombin (10) femoral tunnel PRP + postoperative fibrous PRP (10) interzone Control (10)
3 mo
Ventura et al43
II
PRP (10) Control (10)
CT MRI KOOS, IKDC, Tegner scores KT-1000
6 mo
Vogrin et al44
I
Double-bundle STG autograft Biomet Mini GPS III (LR-PRP) injected between graft strands into femoral tunnels, ± intraarticular PRP at 2 and 4 wk postoperative Hamstring autograft Biomet-Merck GPS (LR-PRP) applied on graft and in tunnels 2 STG graft Magellan PG coated onto graft and injected into tunnels
PG (25) Control (25)
MRI graft vascularization at tibial osteoligamentous interface
4-6 wk 4-6 wk: 0.33 PG enhances 10-12 wk vascularization early graft rate at revascularizaosteoligamention in tous interface in osteoligamenPG vs. 0.16 in tous interface control zone (< 0.001) 10-12 wk: no difference
Negative for synovial fluid interface in 87% of APC vs. 95% of control (0.72) 3 mo: mean 24%40% tunnel widening in control vs. 19%-34% in PRP (0.18-0.36) 3 mo: no difference 6 mo: 78% lowintensity signal in control vs. 100% in PRP (0.04) No difference
3 mo
No difference
No difference
No effect on osteoligamentous interface or tunnel widening No difference; PRP does not accelerate tendon integration
Unable to assess PRP may graft-bone accelerate graft interface by CT integration due to bony sclerosis
Levels of evidence: I, double-blind randomized controlled trial (RCT); II, lesser quality RCT; III, case-control or cohort study. ACL indicates anterior cruciate ligament; APC, autologous platelet concentrate; CT, computed tomography; LR-PRP, leukocyte-rich platelet-rich plasma; MRI, magnetic resonance imaging; PG, platelet gel; PRP, platelet-rich plasma; ST, semitendinosus; STG, semitendinosus/gracilis.
Ligamentization (Maturation) of Graft ACL graft maturation is commonly assessed by arthroscopic and histologic criteria. At 6 weeks the graft is covered with thick synovial tissue and abundant capillaries grossly, and is composed of irregularly oriented collagen fibers microscopically. At 6 months the graft is thinly covered with synovium and is markedly less vascular, and fibroblasts and collagen fibers are reoriented in a regular direction. Finally, by 1 year the graft is a thick ligamentous tissue resembling normal ACL,
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and collagen fibers are organized in a high-frequency crimp pattern with spindle-shaped fibroblasts interspersed between collagen fibers.51 Graft maturation can also be assessed by magnetic resosnance imaging (MRI); high-intensity signals similar to synovial fluid suggest poor graft maturation, whereas lowintensity signals similar to the native posterior cruciate ligament are positively associated with graft maturation. As summarized in a systematic review by Vavken and colleagues, 7 studies published from 2005 to 2010 reported r
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TABLE 3. Clinical Trials of PRP in ACL Reconstruction—Graft Maturation/Ligamentization
Level of References Evidence Figueroa et al11
III
Graft and PRP Type STG Magellan APC injected into tunnels and applied in graft BTB allograft Authors’ own PRP protocol PRP clot enveloped in graft and implanted into tibial tunnel 4 ST graft Biomet GPS II (LR-PRP)
Groups (n)
Outcome Measures
Time
Conclusion
APC (30) Control (20)
MRI signal intensity (1-3 pts)
6 mo
PRP (50) Control (50)
MRI signal intensity C-reactive protein VAS score IKDC score KT-1000
2y
PRP (26) Bone plug (28) PRP + BP (27) Control (27) PRPG (25) Control (25)
MRI signal intensity of graft
3 mo 6 mo
Time to graft 3homogenization 12 mo
369 d to maturation in PRP vs. 177 d in control
(+) PRP accelerates time to graft maturation by 48%
PRGF (22) Control (15)
Arthroscopic score Ligament Tissue Maturity Index (histology)
Excellent arthroscopic score in 57% of PRGF vs. 33% of control (0.05) New connective tissue by histology in 40% of control vs. 77% of PRGF (0.02) ACL density more homogenous in PRP vs. control group (< 0.01) No difference in KOOS, KT-1000, or Tegner scores Synovitic reaction in 1 PRP pt No intra-articular graft revascularization in either group at any time
No macroscopic difference (+) More uniform remodeling in PRGF group
Nin et al45
I
Orrego et al41
II
Radice et al46
III
Sanchez et al47
III
Ventura et al43
II
Autologous PRP (10) CT hamstring Control (10) KOOS, IKDC, Biomet-Merck Tegner scores GPS (LRKT-1000 PRP) applied on graft and in tunnels
6 mo
Vogrin et al44
I
2 ST/gracilis graft Magellan platelet gel PRP applied on graft and into tunnels
4-6 wk 10-12 wk
BTB autograft or hamstring autograft Biomet GPS (LR-PRP) applied around graft with Gelfoam Autologous ST graft undergoing second look arthroscopy BTI System II PRGF Graft soaked in PRGF
Results (P)
PRP (25) Control (25)
MRI graft vascularization
6-25 mo (mean 15 mo)
Mean signal intensity Trend toward score 2.6 in PRP improved vs. 2.3 in control maturation with (0.32) PRP, but not statistically significant 21%-23% lower No clinical or MRI signal in PRP biomechanical vs. control (0.10effect 0.45)
3 mo: no difference (+) PRP enhances 6 mo: 78% lowgraft maturation intensity signal in control vs. 100% in PRP (0.036)
(+) PRP enhances graft maturation
No difference
Levels of evidence: I, double-blind randomized controlled trial (RCT); II, lesser quality RCT; III, case-control or cohort study. ACL indicates anterior cruciate ligament; APC, autologous platelet concentrate; BP, bone plug; BTB, bone-patellar tendon-bone; CT, computed tomography; LR-PRP, leukocyte-rich platelet-rich plasma; MRI, magnetic resonance imaging; PRPG, platelet-rich plasma gel; PRP, platelet-rich plasma; PRGF, plasma rich in growth factors; pt, patient; pts, patients; ST, semitendinosus; STG, semitendinosus/gracilis; VAS, visual analog scale.
MRI data on ACL graft maturation with and without the addition of PRP.11,41,43–47,51 Four of these studies reported positive effects of platelets on intra-articular graft maturation, as measured by increased level or rate of tissue homogeneity by histology or MRI.41,43,46,47 The authors note that 2 of the studies found a 20% relative r
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improvement in the PRP group, but may have fallen short of statistical significance due to being underpowered.11,45 Another possibility is that PRP provides the growth factors necessary to accelerate the early maturation process, but that this benefit is attenuated over time such that no difference is observed at later time points. In contrast, all 4 www.sportsmedarthro.com |
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studies reporting a positive effect of PRP on graft maturation were level II studies, whereas the 2 higher quality level I studies by Nin and colleagues and Vogrin and colleagues reported no difference in clinical, biomechanical, or revascularization outcomes.
OTHER LIGAMENTS The use of PRP for treatment and regeneration of other ligamentous injuries is less well explored than ACL applications. Several groups have investigated the effect of specific growth factors on MCL healing and repair. Letson and Dahners52 reported that application of PDGF to an injured rat MCL resulted in stronger, stiffer ligaments compared with controls. Hildebrand and colleagues delivered recombinant human PDGF-BB and TGF-b1 in fibrin clot to ruptured MCLs and conducted histologic and mechanical evaluation of the ligaments at 6 weeks postoperatively. Application of PDGF-BB to the site of MCL injury significantly improved the ultimate load, energy absorbed to failure, and elongation of the femur-MCL-tibia complex.20 Similarly, Spindler and colleagues examined the effect of TGF-b2 on MCL healing in a rabbit model. Recombinant human TGF-b2 was delivered locally to the injury site through fibrin clot and ligament healing and mechanical strength was assessed at 6 weeks postoperatively. The addition of TGF-b2 to the healing MCL resulted in higher stiffness of the ligament but did not affect scar load to failure or energy to failure.21 Although these studies did not utilize PRP, they helped establish the rationale for growth factor delivery to ligamentous sites of injury. Yoshioka et al22 recently evaluated the effect of leukocyte-poor plasma rich in growth factors (PRGF) on MCL healing in a rabbit model. MCL ruptures were induced and either treated immediately with PRGF or left untreated. Animals were euthanized at 3 and 6 weeks postoperatively and biomechanical and histologic analyses were performed. In the PRGF group at 3 weeks, cellularity and blood vessel density were the highest; both of these findings decreased at 6 weeks. The biomechanical evaluation revealed that all ligaments failed in the proximal edge of the MCL repair; load to failure testing demonstrated that ultimate load and stiffness were significantly greater in MCLs treated with PRGF compared with the controls at 6 weeks. The early increases in cellularity and vascularity combined with the greater mechanical strength led the authors to conclude that early administration of PRGF post-MCL injury may afford healing advantages and accelerate return to play activities. Harris et al19 injected leukocyte-rich autologous platelet gel into healthy tissues of skeletally mature New Zealand white rabbits, including the MCL. At 2 weeks postinjection, the MCL showed a monocytic and lymphocytic inflammatory infiltrate and thickening of tissue. At 12 weeks postinjection, inflammation persisted but was less marked. By contrast, all saline-injected sites were histologically normal. The authors concluded that application of autologous platelet gel to normal rabbit tissues caused a reaction that histologically approximated the acute “healing response.”
PRP IN MENISCUS HEALING Meniscal repair is considered for traumatic tears near the peripheral, vascular zone of the meniscus in younger patients. Vascular supply is provided by capillaries from the
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perimeniscal capillary plexus and infiltrate up to 30% of the width of the meniscus in the “red-red” zone.53 The inner two thirds of the menisci, the “red-white” and the “whitewhite” zones, contain little or no nerves or blood vessels.31,37,54 The meniscus has some ability to heal tears occurring in the outer one-third region due to a fibrin clot rich in inflammatory cells that forms at the site of injury. Fibrous repair tissue grows over the injured area as a result of local undifferentiated mesenchymal cells.55 Because of this mechanism, biological augmentation strategies aimed at increasing meniscal vascularity have been proposed to enhance tissue healing and repair techniques. Common methods of biological augmentation include trephination, synovial abrasion, and application of a fibrin clot. Several anabolic growth factors have been identified in meniscal tissue repair and regeneration: basic fibroblast growth factor, TGF-b1, bone morphogenic proteins, insulin-like growth factor-I, vascular endothelial growth factor, PDGF-AB. Interleukin-1 and epidermal growth factor have been shown to stimulate meniscal cell migration; bone morphogenic protein-2 and insulin-like growth factor-I stimulate fibrochondrocyte migration from the middle to avascular zone.56 PRP is a promising autologous source of these, and other, growth factors. However, to date, there is a relative paucity of literature on the use of PRP for the treatment of meniscal injury or the augmentation of meniscal repair. Currently only 2 studies have evaluated the use of PRP for meniscal applications. Ishida et al23 investigated the use of PRP prepared with a double-spin technique for meniscal tissue regeneration both in vitro and in vivo. In vitro, cells were isolated from rabbit tissue harvested from the inner two thirds of the meniscus and treated with PRP or platelet poor plasma (PPP) at concentrations of 3%, 10%, and 30% for 48 hours. Treatment with PRP resulted in significant and dosedependent upregulation of meniscal cell viability and synthesis of sulphated glycosaminoglycans compared with PPP and controls. Gene expression analyses revealed no difference in type I collagen, significant downregulation of aggrecan expression, and significant upregulation of biglycan and decorin compared with cultures treated with PPP. In the in vivo arm of the study, 30 mL PRP, PPP, or phosphate buffered saline was added to freeze-dried gelatin hydrogels and implanted into a 1.5 mm defect in the avascular zone of the meniscus in adult female rabbits. The animals were euthanized at 4, 8, and 12 weeks postoperatively and tissue sections were stained with hematoxylin and eosin and safranin-O to evaluate tissue repair using a semiquantitative scoring system. At 12 weeks, tissue defects treated with PRP showed significantly greater scores for number of fibro-chondrocytes and production of extracellular matrix. The sum of these in vitro and in vivo results led the authors to conclude that PRP enhances the healing properties of inner, avascular meniscus. The second study, conducted by Zellner et al,24 evaluated the use of mesenchymal stem cells (MSCs) for meniscal tissue engineering. MSCs were seeded onto hyaluronan-collagen composite matrices loaded with leukocyte-rich PRP and implanted into 2 mm defects in the avascular zone of the meniscus in adult male rabbits. The animals were euthanized at 6 and 12 weeks and macroscopic, histologic, and immunohistochemical evaluation of the tissue was performed. Defects treated with MSCs and PRP showed no improvement at 6 or 12 weeks compared r
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with to an implantation of a cell-free scaffold. The authors postulated that the discrepancy in this result versus those reported by Ishida and colleagues may have been related to the larger defect size. The conflicting results in these 2 studies highlight the need for further investigation into the use of PRP in meniscal healing and repair. Studies using human meniscal tissue or assessing clinical applications of PRP for meniscal injury may be warranted.
CONCLUSIONS Although PRP has many applications in clinical orthopedics, evidence to support its use in the applications of ACL reconstruction and repair and meniscal injuries is incomplete. It seems that PRP may be clinically useful for ACL graft maturation and meniscal repair, but further investigations are warranted. Existing human studies do not support the use of PRP for ACL graft integration. Animal studies suggest PRP may promote healing in avascular meniscal tears, however, these effects have yet to be observed in humans. REFERENCES 1. Slater M, Patava J, Kingham K, et al. Involvement of platelets in stimulating osteogenic activity. J Orthop Res. 1995;13:655–663. 2. Whitman DH, Berry RL, Green DM. Platelet gel: an autologous alternative to fibrin glue with applications in oral and maxillofacial surgery. J Oral Maxillofac Surg. 1997; 55:1294–1299. 3. Anitua E, Andia I, Sanchez M, et al. Autologous preparations rich in growth factors promote proliferation and induce VEGF and HGF production by human tendon cells in culture. J Orthop Res. 2005;23:281–286. 4. Creaney L, Hamilton B. Growth factor delivery methods in the management of sports injuries: the state of play. Br J Sports Med. 2008;42:314–320. 5. Mishra A, Woodall J Jr, Vieira A. Treatment of tendon and muscle using platelet-rich plasma. Clin Sports Med. 2009; 28:113–125. 6. Berghoff WJ, Pietrzak WS, Rhodes RD. Platelet-rich plasma application during closure following total knee arthroplasty. Orthopedics. 2006;29:590–598. 7. Gardner MJ, Demetrakopoulos D, Klepchick PR, et al. The efficacy of autologous platelet gel in pain control and blood loss in total knee arthroplasty. An analysis of the haemoglobin, narcotic requirement and range of motion. Int Orthop. 2007;31:309–313. 8. Barrett SE, Erredge ES. Growth factors for chronic plantar fasciitis. Podiatry Today. 2004;17:37–42. 9. Mishra A, Pavelko T. Treatment of chronic elbow tendinosis with buffered platelet-rich plasma. Am J Sports Med. 2006;34:1774–1778. 10. Scioli M. Treatment of recalcitrant enthesopathy of the hip with platelet rich plasma- a report of three cases. Clin Orthop Soc News. 2006;6–7. 11. Figueroa D, Melean P, Calvo R, et al. Magnetic resonance imaging evaluation of the integration and maturation of semitendinosus-gracilis graft in anterior cruciate ligament reconstruction using autologous platelet concentrate. Arthroscopy. 2010;26:1318–1325. 12. Rodeo SA, Arnoczky SP, Torzilli PA, et al. Tendon-healing in a bone tunnel. A biomechanical and histological study in the dog. J Bone Joint Surg Am. 1993;75:1795–1803. 13. Sheth U, Simunovic N, Klein G, et al. Efficacy of autologous platelet-rich plasma use for orthopaedic indications: a metaanalysis. J Bone Joint Surg Am. 2012;94:298–307. 14. Vavken P, Murray MM. The potential for primary repair of the ACL. Sports Med Arthrosc. 2011;19:44–49. r
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