PRP injections

Introduction

Platelet rich plasma (PRP) is an autologous blood product with platelet concentrations above baseline values.  The process involves the extraction of blood from the patient which is then centrifuged to obtain a concentrated suspension of platelets via plasmapheresis.  It then undergoes a two stage centrifugation process to separate the solid and liquid components of the anticoagulated blood.  PRP owes its therapeutic use to the growth factors released by the platelets which possess multiple regenerative properties.

In the knee, PRP has been utilized in patients with articular cartilage pathology, ligamentous and meniscal injuries.  There is a growing body of evidence to support its use in select indications and this review looks at the most recent evidence.

Platelet rich plasma (PRP) has been used since the 1950s to manage maxillofacial and dermatological conditions. The use of biologics including PRP and MSC (mesenchymal stem cells) in an orthopaedic setting has increased exponentially over the last few years due to its autologous nature, supposed effectiveness and lack of side effects.

Platelet rich plasma is an autologous blood product with platelet concentrations above baseline values. The process involves the extraction of blood from the patient which is then centrifuged to obtain a concentrated suspension of platelets via plasmapheresis It then undergoes a two-stage centrifugation process to separate the solid and liquid components of the anticoagulated blood. The initial phase separates the plasma and platelets from the erythrocytes and leukocytes.  The second stage uses a hard spin to concentrate the platelets further into platelet rich and poor plasma components. The final platelet rich plasma product is then injected into the knee joint space.  There is debate on the potential benefits of platelet poor plasma on healing and some formulations do not incorporate this step.

As well as platelets, PRP contains white blood cells and some proteins. The neutrophils and monocytes may instigate a localized inflammatory effect which some studies believe facilitate tissue healing.

PRP owes its therapeutic use to the growth factors released by the platelets which possess multiple regenerative properties.  Tissue repair is a complex process comprising chemotaxis, angiogenesis, cell proliferation and matrix formation.  Platelets are involved in all these functions by the release of factors

High concentrations of proteins such as platelet derived growth factor (PDGF), vascular endothelial growth factor (VEG F), endothelial cell growth factor and fibroblast growth factor have led to suggestions that PRP may be useful in conditions requiring tissue healing. Conversely, the other protein in PRP, transforming growth factor (TGF-Beta 1), has an inhibitory effect and can lead to non predictable results.

Preparation and Delivery Techniques

There are essentially three different methods for PRP production.

1. Blood filtration and plateletpheresis.  These result in high concentrations of human platelets and platelet-derived growth factors and low numbers of contaminating leucocytes
2. Single spinning centrifugation and results in platelets up to 3 times that of baseline level
3. Double spinning centrifugation and results in platelets up to 8 times the baseline level with a high leucocyte content.

These result in four categories of products.

(1) Pure PRP with a low content of leukocyte (P-PRP).  This can be injected as a liquid or a gel.
(2) Leukocyte rich PRP (L-PRP) has a greater concentration of platelets that Pure PRP.  Similarly to P-PRP, it can be used as an activated gel or in a liquid form to be injected intra-articularly.
(3) Pure platelet-rich fibrin (P-PRF). This is obtained by double spinning centrifugation.  The end product is a platelet-rich fibrin scaffold, which is stiffer than the conventional PRP and takes the form of a gel.
4) Leukocyte- and platelet-rich fibrin (L-PRF) which is a leucocyte rich gel which is non injectable and is locally applied.

The activation of PRP also varies between studies.  Some add calcium chloride whilst others prefer unactivated PRP.

However, there is a variation between final platelet concentrations between techniques and even within a given technique. A higher concentration of platelets is not necessarily more efficacious with one study suggesting the ideal concentration being 1.5 x 106 platelets per microliter.

The final platelet concentration is influenced by a number of factors  e.g. initial volume of whole blood, concentration of other cells, preparation technique, age and co morbidities of the patient.

There are a number of delivery techniques ranging from direct injection into the knee to application via a collagen membrane giving a gel like consistency.

Adverse events have been reported.  One study reported 19 adverse events including dizziness, headaches, nausea, gastritis, sweating and tachycardia. These were all self limiting. Another group reported 31 adverse events in those receiving PRP injections including post injection pain, swelling at the site of injection and limitation in activities.  These resolved by day 4 in all patients.

In terms of contraindications, one study suggests that patients undergo a minor hematological evaluation to exclude blood disorders or platelet dysfunction.  They  suggest the relative contraindications for PRP are: a platelet count less than 105/μL, a haemoglobin level less than 10 g/dL, presence of a tumor in the wound bed or metastatic disease, and other active infections.

The therapeutic schedule used by the lead author is a course of three injections which are two weeks apart with 3ml of PRP injected each time.

Articular cartilage

Articular cartilage disease represents a spectrum of conditions that can have a debilitating impact on patients’ well being.  The natural history is to progressive osteoarthritis and subsequent functional impairment and pain. Articular cartilage is avascular and alymphatic which accounts for its lack of inherent healing potential. Treatment includes microfracture, autologous chondrocyte implantation and osteochondral implantation.  However, despite good short term results, these treatments may not prevent the long term development of osteoarthritis.

In vitro studies have shown that chondrocytes stimulated with PRP increase  proteoglycan and collagen synthesis which have similar histological and biochemical qualities to normal hyaline cartilage. PRP also contains factors such as TGF-Beta1, thrombospondin-1 and insulin like growth factor which have been shown to be useful to treat symptomatic cartilage lesions or osteochondral defects.

A retrospective cohort study examining the use of PRP in the knee looked at 60 patients with unilateral Ahlback grades 1 to 4 osteoarthritis. The first 30 patients were treated with three injections of PRP and the remainder had hyaluronic acid injections.  At five weeks follow up those injected with PRP had significantly higher WOMAC (Western Ontario and McMaster Universities Arthritis Index) scores.  These results were only marred by the short follow-up

An earlier study with similar findings had a larger cohort of 150 patients with a six month follow up.  There were three treatment arms: activated PRP (infiltration every 21 days), single dose high molecular weight hyaluronic acid (HMWHA) and low molecular weight hyaluronic acid (LMWHA).  Outcome measures used were visual analogue scale of quality of life related to health status (EQ VAS) and knee function using the International Knee Documentation Committee index (IKDC).  The authors reported better response rates in PRP-treated patients than any treated with hyaluronic acid (P<0.005).  In all groups, the response was better in younger patients and in those who had recent onset osteoarthritis.

A randomized control trial (RCT) with 120 participants demonstrated significantly superior outcomes up to 24 weeks after local PRP injection compared with hyaluronic acid (P<0.001). A double blind prospective RCT in which 78 patients with bilateral osteoarthritis were randomized to receive PRP, two PRP injections three weeks apart or a single saline injection both the PRP groups had significantly better six month outcomes.

An Italian level 1 study demonstrated that PRP injections, compared to hyaluronic acid injections, showed a significant improvement up to one year.  However, for middle-aged patients with moderate signs of OA, PRP results were no better than those who had with HA injections.

A systematic review looked at a total of ten studies in the final analysis with the majority of studies looking at the use of PRP in degenerative osteoarthritis of the hip or knee.  Most patients reported improvement in pain and functional outcome scores at 6 months with no studies reporting worsening scores.  However, none reported any long term follow up.  They concluded that PRP may be beneficial in the short term but that there is a poverty of long term high quality data

Another systematic review looked at six level 1 and 2 studies overall.  They found improved function in adult patients with mild or moderate knee OA at 6 months who had PRP injections compared to hyaluronic acid or normal saline. 33 Four of the studies reported an increase in adverse non specific events in those treated with PRP ranging from pain, stiffness, syncope, dizziness, nausea, gastritis, sweating and tachycardia which were all self limited.

A Taiwanese group carried out a meta-analysis of single arm studies, quasi-experimental studies and randomized controlled studies.  This equated to 1543 participants. They concluded that PRP improves function for 12 months in patients with knee joint cartilage pathology and is more effective that hyaluronic acid administration.

Ligament tears

Ligaments connect bones and are important for joint stability and proprioception. They comprise 70% water and 30% solid material with the latter being extracellular matrix and fibroblasts. The most abundant collagen is type 1 which is arranged in a haphazard manner to cope with the different direction of pull.

Ligament healing undergoes four indistinct phases. The inflammatory phase occurs in the first week with an increase in growth factors (TGF-Beta1, IGF, PDGF, BMPS). The proliferation phase occurs at days 7 to 21 where type 3 collagen is replaced by type 1.  The final stages of remodeling and maturation begin at 2 weeks. PRP can increase growth factors and so may be of benefit in the initial inflammatory phase.

ACL reconstruction is a successful procedure with very good outcomes and patient satisfaction.  Maturation of the graft is important for biomechanical strength and return to activity.  This may be facilitated by PDGF, TGF-Beta1 and IGF -1. Studies have shown PRP has the capacity to improve ACL cell viability and function and may be given to hasten ACL graft healing.

A prospective single blind study with 50 participants who were treated with and without PRP after their ACL autograft found that those who had PRP gel at the time of surgery resulted in quicker biologic maturation on MRI at one year (P<0.001).

Another level 1 study where platelet concentrate was added to the semitendinosus graft and to the femoral tunnel led to a higher rate of graft maturation at 6 months as demonstrated on MRI scans.

Another group administered PRP to the femoral tunnels in 30 patients and at 3 months found no difference in MRI findings pertaining to graft maturation.42 This may be due to the shorter follow up and fewer subjects than the previous studies.  A systematic review looking at eight trials concluded that ACL maturation after reconstruction can show 20 to 30% improvement with the addition of PRP.

Other studies assessed structural changes of the ACL graft after PRP administration.  One looked at 37 patients who had ACL reconstruction using hamstring grafts with and without PRP.  Second look arthroscopies showed those who had PRP had improved graft remodeling with connective tissue enveloping the graft and the grafts were thicker.  They postulated that the PRP may enhance the ligamentisation process in tendon grafts.

On the contrary, a level 1 study with 100 patients were randomized to either receive or not receive platelet enriched gel during ACL reconstruction.  At two year follow up they found no difference in any of the functional and radiological outcome scores. They attributed these findings to several factors; PRP preparation/centrifugation, graft choice, rehabilitation protocols and application technique.

The outcome of this study was mirrored by another group who showed the use of PRP in ACL allograft reconstruction showed no discernible difference at two year follow up.

PRP has also been used at the patellar and tibial bone plug harvest site.  In a level 1 study involving 40 participants PRP gel was added to these sites. At one year follow up, knee function was significantly higher in those who had PRP (P=0.041).

In another study 12 patients received PRP in the patellar tendon defect compared with 15 who did not.   A six month MRI scan demonstrated that those who received PRP had a smaller patellar tendon gap.

Tendon and muscle

In the early stages of tendon healing there is an upregulation of PDGF and TGF-Beta resulting in new vessel formation and collagen synthesis.  These factors are present in high concentrations in PRP and may be beneficial in the early stages of tendon repair.

PRP has been utilized for chronic tendinopathy in the elbow and Achilles tendon.

A prospective level III study looked at the efficacy of PRP injections in chronic refractory patellar tendinopathy.  Fifteen patients were treated with multiple PRP injections and physiotherapy whilst sixteen were treated exclusively with physiotherapy.  Those who received PRP had a statistically significant better activity level at six months.  All other outcomes such as pain showed no difference in the two groups.

Another study evaluated the outcome of patients with patellar tendinopathy treated with platelet- rich plasma injections (PRP). Additionally, they examined whether certain characteristics, such as activity level or previous treatment influenced the results. After PRP treatment, patients with patellar tendinopathy showed a statistically significant improvement in pain during activities of daily life, work and sport. However, patients who were not treated before with ethoxysclerol, cortisone, and/or surgical treatment showed the improvement.

These limited studies are encouraging and indicate that PRP injections have the potential to promote the achievement of a satisfactory clinical outcome, even in difficult cases with chronic refractory tendinopathy after previous classical treatments have failed.

Meniscal tears

The meniscus is an intra-articular structure composed primarily of type 1 collagen.  Its main functions are shock absorption, proprioception, lubrication and increasing stability. It is vulnerable to repetitive injury which can predispose to osteoarthritis. Repair depends on the site and extent of damage.  The periphery is vascular and has greater scope for healing compared the avascular inner portion.

Laboratory experiments have shown that PRP has a positive effect on meniscal cells.  PRP may provide growth factors that enhance the meniscus healing through cell proliferation and vascularisation.  For the meniscus to heal there needs to be a blood supply.  The white-white zone is devoid of this and so the vascularisation from the PRP is important.

A level III study found that PRP augmentation at the time of meniscal repair showed no difference in reoperation rate, function and return to sports.  However, they only had 15 patients who had PRP augmentation versus 20 who did not. These small numbers may not have adequately highlighted noticeable differences.59 On the contrary a French group did a case control study looking at the addition of PRP post meniscal repair.  They found that open meniscal repair of horizontal tears extending into the avascular zone was effective at mid term follow up in young patients. Clinical outcomes were slightly improved with the addition of PRP.

Osteoarthritis

Osteoarthritis is a non inflammatory degenerative disease of synovial joints resulting in the progressive loss of articular cartilage. Females are more predisposed than males and the incidence increases with age.  Osteoarthritis can be primary (an intrinsic defect) or secondary (due to trauma or infection).  It starts with a loss of the weight bearing surface followed by osteophyte development.  Late disease is represented by cartilage disintegration and subchondral microfractures exposing the bony surface.

Biochemically, there is an increased water content (decreased in aging), alterations in proteoglycans (decreased content and increased chondroitin/keratin sulfate ratio). There is also an increase in metalloproteinases and IL-1 which may have a catabolic effect leading to cartilage degeneration.

Histologically, there is a loss of superficial chondrocytes, breakdown of the tidemark, fissuring and cartilage destruction with eburnation of subchondral bone. Normal cartilage is avascular and abnormal cartilage is not totally avascular which accounts for its lack of inherent healing potential.

Radiographic findings include subchondral cysts/sclerosis, osteophyte formation and joint space narrowing.

Non-operative treatment comprises analgesia increasing as per the WHO analgesic ladder.  Weight management and physical therapy is also beneficial. Varus/valgus unloading bracing can be used in unicompartmental disease in patients who wish to delay arthroplasty.

Intra-articular corticosteroid injections reduce synovitis and it is assumed that their analgesic action in osteoarthritis is in some way related to this.

Surgical treatment includes microfracture, autologous chondrocyte implantation and osteochondral implantation. However, despite good short term results, these treatments may not prevent the long term development of osteoarthritis.

Intra-articular corticosteroid injections have marked anti-inflammatory effects, and it is assumed that their analgesic action in osteoarthritis is in some way related to this.  The can also reduce the synovitis. The UK National Institute of Health & Clinical Excellence (NICE) recommends that intra-articular corticosteroid injections should be considered as an adjunct to core treatments for the relief of moderate to severe pain in people with osteoarthritis.

Endogenous hyaluronan (previously known as hyaluronic acid) is a large, linear glycosaminoglycan and is a major non-structural component of both the synovial and cartilage extracellular matrix. It is also found in synovial fluid and is produced by the lining layer cells of the joint.  Its key functions in the joint are to confer viscoelasticity, lubrication and help maintain tissue hydration and protein homeostasis by preventing large fluid movements and by acting as an osmotic buffer.

In vitro studies have shown that chondrocytes stimulated with PRP increase proteoglycan and collagen synthesis which have similar histological and biochemical qualities to normal hyaline cartilage. PRP also contains factors such as TGF-Beta1, thrombospondin-1 and insulin like growth factor which have been shown to be useful to treat symptomatic cartilage lesions or osteochondral defects.

A retrospective cohort study examining the use of PRP in the knee looked at 60 patients with unilateral Ahlback grades 1 to 4 osteoarthritis. The first 30 patients were treated with three injections of PRP and the remainder had hyaluronic acid injections.  At five weeks follow up those injected with PRP had significantly higher WOMAC (Western Ontario and McMaster Universities Arthritis Index) scores.  These results were only marred by the short follow-up.

An earlier study with similar findings had a larger cohort of 150 patients with six monthly follow up.  There were three treatment arms: activated PRP (infiltration every 21 days), single dose high molecular weight hyaluronic acid (HMWHA) and low molecular weight hyaluronic acid (LMWHA).  Outcome measures used were visual analogue scale of quality of life related to health status (EQ VAS) and knee function using the International Knee Documentation Committee index (IKDC).  The authors reported better response rates in PRP-treated patients than any treated with hyaluronic acid (P<0.005).  In all groups, the response was better in younger patients and in those who had recent onset osteoarthritis.

A randomized control trial (RCT) with 120 participants demonstrated significantly superior outcomes up to 24 weeks after local PRP injection compared with hyaluronic acid (P<0.001). A double blind prospective RCT in which 78 patients with bilateral osteoarthritis were randomized to receive PRP, two PRP injections three weeks apart or a single saline injection both the PRP groups had significantly better six month outcomes.

An Italian level 1 study demonstrated that PRP injections, compared to hyaluronic acid injections, showed a significant improvement up to one year.  However, for middle-aged patients with moderate signs of OA, PRP results were no better than those who had with HA injections.

A systematic review looked at a total of ten studies in the final analysis with the majority of studies looking at the use of PRP in degenerative osteoarthritis of the hip or knee.  Most patients reported improvement in pain and functional outcome scores at 6 months with no studies reporting worsening scores.  However, none reported any long term follow up.  They concluded that PRP may be beneficial in the short term but that there is a poverty of long term high quality data.

Another systematic review looked at six level 1 and 2 studies overall.  They found improved function in adult patients with mild or moderate knee OA at 6 months who had PRP injections compared to hyaluronic acid or normal saline. Four of the studies reported an increase in adverse non specific events in those treated with PRP ranging from pain, stiffness, syncope, dizziness, nausea, gastritis, sweating and tachycardia which were all self limited.

A Taiwanese group carried out a meta-analysis of single arm studies, quasi-experimental studies and randomized controlled studies.  This equated to 1543 participants. They concluded that PRP improves function for 12 months in patients with knee joint cartilage pathology and is more effective than hyaluronic acid administration.

There have been a number of case series which demonstrate the use of PRP in those with knee OA.  One study described the results in 261 patients injected three times at fortnightly intervals.  At six month follow up there were significant improvements in the WOMAC, SF-36 and functional scores compared to baseline.  There were no adverse effects. Another series with 65 patients who received a single PRP injection showed pain scores were reduced at six months.  However, at nine and twelve months the scores had started to increase.  A study in 2011 had the longest follow up with 91 patients  with a minimum follow up of a year.  They demonstrated a decrease in pain and improvement in function compared to baseline.

These studies may provide evidence with respect to the safety of PRP but they lacked a control group.  Nevertheless they did provide pre PRP pain, function and quality of life scores in the same patients.

Radiological changes have also been demonstrated with PRP in osteoarthritis of the knee.  A prospective cohort study with 1-year follow up of patients after PRP for early knee osteoarthritis had 22 subjects.  All received a 6ml PRP injection.  Fifteen subjects underwent clinical assessments at baseline, week one, and 1, 3, 6, and 12 months, and MRI at one year. Pain scores decreased, whereas functional and clinical scores increased at 6 months and 1 year from baseline significantly. Qualitative MRIs demonstrated no change per compartment in at least 73% of cases at one year.

Currently,  NICE do not recommend the use of intra-articular hyaluronanan injections for the treatment of knee osteoarthritis.

NICE has recently published guidelines in May 2014 (Platelet-rich plasma injections for osteoarthritis of the knee).  These state that current evidence on platelet-rich plasma injections for osteoarthritis of the knee raises no major safety concerns.  Nevertheless, the evidence on efficacy is inadequate in quality.  NICE recommends that this procedure should only be used with special arrangements for clinical governance, consent and audit or research. They also suggest that any further research into platelet-rich plasma injections for treating osteoarthritis of the knee should categorically describe patient selection and take the form of well-designed studies that compare the procedure against other methods of management. Outcomes should include knee function scores, patient-reported outcome measures and the timing of subsequent interventions.

There have been a number of case series that demonstrate the use of PRP in those with knee OA.  One study described the results in 261 patients injected three times at fortnightly intervals.  At six month follow up there were significant improvements in the WOMAC, SF-36 and functional scores compared to baseline.  There were no adverse effects. Another series with 65 patients who received a single PRP injection showed pain scores were reduced at six months.  However, at nine and twelve months the scores had started to increase.  A study in 2011 had the longest follow up with 91 patients  with a minimum follow up of a year.  They demonstrated a decrease in pain and improvement in function compared to baseline

These studies may provide evidence with respect to the safety of PRP but they lacked a control group.  Nevertheless they did provide pre PRP pain, function and quality of life scores in the same patients

Radiological changes have also been demonstrated with PRP in osteoarthritis of the knee.  A prospective cohort study with 1 year follow up of patients after PRP for early knee osteoarthritis had 22 subjects.  All received a 6ml PRP injection.  Fifteen subjects underwent clinical assessments at baseline, week one, and 1, 3, 6, and 12 months, and MRI at one year. Pain scores decreased, whereas functional and clinical scores increased at 6 months and 1 year from baseline significantly. Qualitative MRIs demonstrated no change per compartment in at least 73% of cases at one year.

Conclusions

Platelet rich plasma (PRP) has been used since the 1950s to manage maxillofacial and dermatological conditions and applications have now been extended to the knee. There is a growing body of evidence to support its use for select indications in osteoarthritis, ligament, tendon and meniscal injuries of the knee.  The evidence is of variable quality and concerns include the heterogeneous nature of the patients, variations in treatment techniques and inconsistencies in the findings of these studies.  It is promising to note that organisations such as NICE are beginning to accept the use of PRP. However, there is no hard evidence for its effects and before widespread use can be recommended, high quality prospective randomised studies in the field are required.

 

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