Introduction

Meniscal healing occurs following two distinct patterns related to the location of the lesion. In lesions occurring in the vascular area, the blood supplies undifferentiated mesenchymal cells with nutrients thought to induce healing [5]. In lesions occurring in the avascular zone, the healing process is mainly based on the self-repair capacity of the meniscal tissue [2, 22].

Symptomatic horizontal meniscal lesions occurring in young patients are often extensive and located both in the vascular and avascular zone [7]. A meniscectomy of such lesions would be a subtotal meniscectomy. This is unacceptable in young patients, unless the lesion is irreparable, because of the risk of deterioration and flattening of the articular cartilage surfaces and subchondral bone sclerosis with time [31]. In a population of young patients with horizontal meniscal lesions, meniscal repair should be first considered even though potential healing of such lesions is questionable [30]. In these cases, biological factors may be needed to promote the biological response.

Platelet-rich plasma (PRP) has been widely used for treating tendinous, muscle, ligament and chondral problems, but its efficacy is a matter of controversy [14, 25]. Many in vitro or animal studies have demonstrated that injection of various growth factors including platelet-derived growth factor could increase meniscal cell activity and stimulate repair [6, 18, 49].

However, little is known about the clinical outcomes of repaired meniscal tissue with PRP augmentation. Literature review puts in evidence numerous publications discussing the theoretical benefit without clinical proof [9, 29, 37, 43]. So, there is need for clinical evidence of the healing enhancement effect of PRP on a repaired meniscus.

The purpose of this study was to augment repair and promote meniscal healing by the use of PRP within horizontal cleavage meniscal tears repaired via an open approach. The hypothesis was that the clinical outcomes and healing process would be improved using this meniscal healing augmentation technique.

Materials and methods

Thirty-seven consecutive patients underwent an open repair to treat a symptomatic horizontal cleavage of the meniscus between January 2009 and June 2012 at our hospital. The inclusion criteria for this study were patients younger than 40 years with a symptomatic horizontal cleavage (Grade II or III) of the meniscus [11] and persisting pain after complete medical treatment (rest, physiotherapy, intraarticular injections of corticosteroids) for at least 6 months.

The exclusion criteria were as follows: surgery of the knee for concurrent injuries, loss of cartilage (Outerbridge >2), ACL injury, PCL injury and collateral ligament injuries. Three patients were excluded due to severe concomitant chondral injuries, leaving thirty-four patients included in the study.

The first 17 patients (Group 1) had an isolated open meniscal repair. The last 17 patients (Group 2) had an open meniscal repair and an in situ injection of PRP. Preoperative data for the two groups are presented in Table 1. There were no patients insured through workers compensation. There were no differences between groups.

Table 1 Demographic data
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Operative technique

The same surgical procedure was used for all patients.

Anteromedial and anterolateral portals were created, and a diagnostic arthroscopy was performed. The meniscal tear was identified in cases of Grade 3 lesions. In the case of Grade 2 lesions, no lesion was identified during arthroscopy. If present in Grade 3 lesions, unstable meniscal fragments and fibrous tissue were removed using a motorized shaver or basket forceps. To repair the medial meniscal tear, a posteromedial mini-arthrotomy was performed. To repair the lateral meniscal tear, a posterolateral mini-arthrotomy was performed. The capsule was open on the upper side of the meniscus, and the meniscosynovial junction was detached vertically in order to create access to the horizontal cleavage. The lesion was abraded with a rasp and a curette. Meniscal repair was performed by vertical sutures with type N°0 polydioxamone (PDS; Ethicon, Somerville, NJ, USA), in order to close the two layers (Fig. 1). The capsule was then closed. In Group 2 (PRP), 5 ml of PRP was obtained using the GPS®III system (Biomet, Warsaw, Indiana, USA) and injected directly into the repaired lesion before the closure of the wound (Fig. 2). No drainage was used.

Fig. 1
figure 1

Technique of open repair of horizontal cleavage of the meniscus

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Fig. 2
figure 2

Technique of in situ injection of PRP into the repaired lesion

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All patients followed the same rehabilitation protocol. In the first week postoperatively, a passive range of motion from 0° to 90° was initiated, allowing partial weight-bearing for 4 weeks. For the first 4 weeks, a hinged knee brace locked in full extension was used. Jogging was not permitted until 3 months postoperatively. Return to pivoting sports was allowed 6–7 months after surgery.

Clinical assessment

Clinical outcome was assessed using the 2000 IKDC Knee Examination Score. The KOOS and the subjective IKDC scores were implemented to assess patient-oriented outcomes. Clinical evaluation using the IKDC and KOOS scores was performed at a minimum of 24 months after surgery. Clinical failure was defined by a reoperation on the same knee for a meniscectomy or an iterative repair of the same meniscus.

Follow-up MRI

MRI was performed 1 year after surgery. These conventional MRI scans were obtained on a 1.5-Tesla MRI scanner (Symphony, Siemens Medical Solutions, Erlangen, Germany). The signal intensity within the repaired meniscal area was evaluated (T2 fatsat). For MRI assessment, we described a new classification of the horizontal features of the repaired meniscus included the following: no hypersignal (Type I), low- or intermediate-intensity hypersignal in the white-white zone without hypersignal in the red-red zone (Type II), high-intensity hypersignal (red-red and white-white zones, Type III). The MRI was interpreted by an orthopaedic surgeon who did not participate in the surgery and who was blinded to the treatment received by the patient (PRP or no PRP). In type III, the hypersignal in the repaired meniscus was as high as the hypersignal in the preoperative lesion. In type II, there was a less intense remaining signal when compared to the preoperative lesion.

This study was approved by the institutional review board of the hospital and by the scientific committee of the A. Mignot Hospital in Versailles. This study was performed in accordance with the ethical standards outlined in the 1964 Declaration of Helsinki. All patients signed a written informed consent explaining the potential benefit of PRP, surgical procedure and follow-up. No patients declined to participate in this study.

Statistical analysis

The SSPS 13.0 Software was used for data processing. Pre- and postoperative quantitative variables were compared by the coefficient of correlation. Independent samples (t test and Mann–WhitneyU test) were used for group comparison. In all analyses, p values less than 0.05 were considered statistically significant. Post hoc power analysis was performed using G*Power version 3.1.9.2.

Results

The median follow-up period was 34 months (range 24–40 months) in Group 1 and 30 months (range 24–36 months) in Group 2.

In Group 1, the median active flexion was 130° (range 120–145). There were no extension lag signs. The objective IKDC score was grade A in nine patients, B in five, and C in two.

In Group 2, the median active flexion was 135° (range 120–145). There were no extension lag signs. The objective IKDC score was grade A in 10 patients, B in six, and C in one.

The median IKDC score was 87.9 (range 44–99) in Group 1 and 90.7 (range 48–100) in Group 2 (ns).

The mean KOOS distribution is shown in Fig. 3. The difference between groups was significant for pain and sports activities parameters (p = 0.046 and 0.03, respectively). There were no differences between the other subscales of the KOOS.

Fig. 3
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KOOS profile at follow-up

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Topography, presence or absence of a cyst, and preoperative MRI grade were all shown to have no significant influence on the clinical outcome at final follow-up in either group.

In Group 1, two symptomatic patients with an unhealed medial meniscus underwent partial meniscectomy 12 and 18 months after surgery. In Group 2, one patient underwent a subtotal medial meniscectomy 12 months after initial surgery. The failure rate was 11.8 and 5.8 % in Group 1 and Group 2, respectively.

One patient in Group 1 had a local haematoma requiring surgical drainage.

One patient in Group 2 had a septic arthritis 1 month after the procedure, requiring arthroscopic lavage of the joint and oral antibiotics for 45 days. When initially present, there was no recurrence of a cyst in either group (Fig. 4).

Fig. 4
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a Preoperative MRI, Grade 2, cyst, lateral meniscus. b Same patient at 1 year, Type 1

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MRI interpretations of meniscal healing after surgery are shown in Table 2. The three types of MRI features of the repaired menisci are presented in Figs. 5a, b, 6a, b and 7a, b. There was a statistically significant difference in the healing appearance of repaired menisci by MRI evaluation between the two groups (p < 0.01). Nevertheless, there was no correlation between the postoperative signal in the repaired meniscus and the clinical outcomes (KOOS, IKDC).

Table 2 Distribution of the postoperative MRI of the open repaired menisci (reoperations for meniscectomy excluded)
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Fig. 5
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a Preoperative MRI, Grade 3, medial meniscus. b Same patient at 1 year, Type 1

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Fig. 6
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a Preoperative MRI, Grade 3, medial meniscus. b Same patient at 1 year, Type 2

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Fig. 7
figure 7

a Preoperative MRI, Grade 3, lateral meniscus. b Same patient at 1 year, Type 3

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Post hoc power analysis for pain, sports parameters of the KOOS and for MRI signal (effect size 0.88, 0.69, 0.91, respectively; α = 0.05) resulted in 0.81, 0.63, 0.83 (1−β err prob), respectively.

Discussion

The most important finding of this study is that PRP slightly improved clinical outcomes after open repair for horizontal cleavage.

The global failure rate (subsequent meniscectomy) was low in both groups, despite the extension of the lesion into the avascular zone. This is consistent with the results of meniscal repair for traumatic vertical lesions [26, 30, 36]. In systematic literature reviews, the mean rate of failure after meniscal repair of vertical lesions with all-inside repair devices was 15–19 % [15, 26]. There are few reports about the surgical treatment of horizontal meniscal cleavages [8, 20, 33]. Their incidence is relatively low, when compared to vertical lesions. Kurzweil et al. published recently a literature review about meniscal repair of horizontal meniscus tears. Among nine eligible articles (a total of 98 repairs), the overall success rate without subsequent surgery was 77.8 % [24].

These lesions should be differentiated from so-called degenerative horizontal lesions occurring typically after the age of 50 in patients with cartilage damage, meniscal extrusion or even advanced osteoarthritis [19, 21, 42]. In our cases, there was neither subchondral bone oedema, significant cartilage loss, nor meniscal extrusion on preoperative MRI, and all patients were under 40 with a failed medical treatment of at least 6 months.

Biedert was the first to describe four different treatments for such lesions (no operative treatment, partial meniscectomy, trephination, meniscal repair) [8]. We have previously reported a retrospective series of 30 cases operated on using the same surgical technique (open meniscal repair) and a mean follow-up of 4 years [33]. The clinical outcomes were good (median subjective IKDC score at 89 ± 14, 15 % reoperation rate). The functional results decreased significantly with age after 30. No postoperative imaging (MRI) was available.

The magnetic resonance imaging of the postoperative repaired meniscus is difficult to interpret [46]. A persisting hypersignal is frequent (>60 % of cases), even 10 years after open [28] or arthroscopic meniscal repair [34], even in the vascularised zones.

In our series, MRI at 2 years showed a persisting hypersignal in 84 % cases in the avascular zone. The intensity of the signal was lower than in preoperative imaging in all cases. Such a signal may reflect either immature fibrovascular granulation tissue or mature fibrocartilaginous scar tissue at the repair site. In the vascularised zone (outer third of the meniscus), the hypersignal was still present on MRI in 60 % of cases in Group 1 and in 25 % in Group 2. This difference was significant. These MRI features were not surprising, because the presented surgical technique allows the suture of the outer third of the meniscus, by an open approach. In the avascular zone, the cleavage was left in situ. Even when the signal was still present on postoperative MRI, it did not appear to have any clinical consequences. For example, Zanetti et al. [48] did bilateral MRI of the knees of 100 patients with clinical symptoms of unilateral meniscal lesion. He found a meniscal lesion in 36 % of the contralateral asymptomatic knees. Healing of the meniscocapsular junction with strong vertical sutures may be the most important factor in order to achieve durable pain relief in such horizontal meniscal lesions.

Tears extending into the avascular zone of the meniscus are generally complex and broad and are often associated with a poor prognosis following repair.

Once torn, the meniscus, because of its low cellularity and spontaneous healing response, is unable to fully repair itself in the avascular zone [35].

Several different therapeutic approaches have been proposed, with a variety of reported results. The most notable of these approaches are the following: the use of parameniscal synovial tissue or collagen matrix [27, 32], trephination of the peripheral meniscus rim with suture of the meniscus tear [50], creation of vascular access channels, use of fibrin clot [3, 4, 16, 20, 39] and fibrin glue [38].

The use of PRP remains controversial in orthopaedics [40]. A number of randomised clinical trials have reported limited or no clinical efficacy for pathologies including patellar tendon healing [12], lateral epicondylitis [23], Achilles tendinopathy [13] and rotator cuff tears [10]. To our knowledge, there are no randomised or even comparative studies evaluating the use of PRP to augment meniscus repair [1].

Nevertheless, many in vitro studies have demonstrated that injection of various growth factors could stimulate repair of the meniscus tissue [37]. Platelet-derived growth factor (PDGF) has mostly been evaluated in sheep menisci. Following the use of PDGF, cell proliferation and migration and extracellular collagen matrix formation were increased in torn meniscus zones when compared to the control [17, 41, 44, 45], even in white-white zones [47]. The main difficulty when assessing the efficacy of PRP on meniscal healing after arthroscopic repair is accessed to the lesions located in the posterior segments of the meniscus and the risk of dilution of the PRP in the joint under arthroscopy. In this case–control series, the open approach allowed us to place the PRP precisely into the repaired lesion of the meniscus.

There are some limitations in this study. The number of cases is low; therefore, it involves a consecutive series of patients without randomisation. The observed differences between groups might have been statistically different with higher power. Patients were not blinded.

The strengths are the case–control design with two consecutive series of comparable patients. Finally, we did not lose any patients during follow-up. The clinical relevance of this could be that PRP might improve outcomes and enhance healing process when injected directly into the lesion (open approach) without any risk of dilution (arthroscopy).

Conclusion

Open meniscus repair of horizontal tears extending into the avascular zone was effective at midterm follow-up in young patients. Clinical outcomes were slightly improved by the addition of PRP in this case–control study. Although encouraging, no recommendation can be made. This technique should be further evaluated in larger studies with a longer follow-up.