2.1 Literature search methodology

A comprehensive search of PubMed, Embase, and Cochrane Library databases was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in December 2024. The following search strategy was utilized: “('PRP' OR 'platelet-rich plasma' OR 'platelet gel' OR 'platelet derived' OR 'platelet concentrate') AND ('meniscus' OR 'meniscal' OR 'meniscectomy' OR 'meniscus repair' OR 'menisci').” The search was conducted by author (initials blinded for peer review).

Studies were included if they evaluated males and females of any age group who underwent meniscal repair without any concomitant procedures, were comparative studies with either prospective or retrospective design, compared outcomes in patients who underwent meniscal repair with and without PRP treatment, and were published between 2000 and 2024. Reference lists of all included studies were reviewed for additional studies that met inclusion criteria. Translational studies or cadaveric studies, meniscectomy patients, revision meniscus repair patients, studies that did not directly compare patients receiving PRP to patients not receiving PRP, and studies that had non-comparative study designs such as case series, case studies, systematic reviews, narrative reviews, conference abstracts, technical notes, letters to editors, and meta-analyses were excluded. All author lists were reviewed for redundant authors and institutions and were carefully screened for potential repeat patient cohorts. Two authors (initials blinded for peer review) independently screened titles, abstracts, and full article texts using the online software program Covidence (Veritas Health Innovation Ltd; Melbourne, Australia). Any disagreements were resolved with discussion leading to consensus between the two screening authors and a third senior author (initials blinded for peer review).

2.2 Data extraction and quality assessment

Data items extracted from each study included the total number of patients who underwent meniscus repair with or without PRP treatment, patient sex, follow-up time, type of meniscus tear, meniscus repair technique, pre-operative and post-operative patient-reported outcomes (PROs) including International Knee Documentation Committee (IKDC) score, Lysholm scores, complications, and meniscus re-rupture rates. Disaggregation of study data by sex was not performed because no included studies divided patients based on gender or sex, and the effects of patient gender or sex on outcomes were not evaluated in our systematic review. Assessment of study quality for randomized controlled trials was performed using the revised Version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2).³¹ Non-randomized retrospective study quality assessment was performed with the Methodological Index for Non-Randomized Studies (MINORS) criteria.³²

2.3 Statistical analysis

Pre-operative measures, post-operative measures, and changes in mean scores were computed when applicable. Two-proportion z-tests were performed to assess if there was a statistically significant difference in the proportion of each complication within the PRP cohort versus the control cohort.³³ A heatmap was created using Python (Python Software Foundation, Beaverton, OR) to display statistical significance in complication rates.

3.1 Search results

A total of 862 studies were identified in the initial search, 234 of which were duplicates and were subsequently excluded. The remaining 628 studies underwent a title and abstract screening, 617 were found to be irrelevant to the study aims and were therefore excluded. The remaining 11 studies were assessed for eligibility with full-text review. Of these 11 studies, two were excluded for evaluating meniscectomy patients rather than meniscus repair patients, and one study was excluded for presenting data for PRP combined with other orthobiologics. Eight studies were ultimately included for data extraction (Fig. 1). Table 1 summarizes the study characteristics. Studies included were randomized controlled trials (RCTs) or retrospective case-control studies, and all evaluated patient outcomes.

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Fig. 1 PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) study selection flow diagram. The numbers of screened, excluded, and included studies are shown.

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3.2 Study quality and risk of bias assessment

Table 1 summarizes study quality based on MINORS criteria for non-randomized studies.³² The ideal MINORS score for non-comparative studies is 16, with scores ≤8 being the accepted cut-off for poor study quality.³² Each of the included studies had a score greater than 8, indicating moderate to high quality and sufficiently low risk of bias. Of note, none of the included non-randomized studies utilized prospectively collected data, and only Dai et al. and Pujol et al. scored any points for unbiased assessment of the study endpoint.^23,34 Each included study had a low risk of bias.

Fig. 2 summarizes study quality based on the Cochrane RoB 2 tool for RCTs.³¹ The RoB 2 tool divides bias into five different domains: the randomization process, deviations from intended interventions, missing outcome data, outcome measurement, and selection of reported results.³¹ Determination of bias in each domain is then used to produce an overall risk of bias determination for the RCT, ranging from “low risk of bias,” to “some concerns,” to “high risk of bias.” Each of the RCTs included in this study had a low overall risk of bias. The only domain with some concern resulted from deviation from the intended intervention in the study by Elnemr et al.³⁵ Overall, each of the three RCTs included in this systematic review and meta-analysis had a sufficiently low risk of bias for inclusion.

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Fig. 2 Summary of study quality and risk of bias assessment based on Version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2).

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3.3 General study, demographics, and platelet-rich plasma characteristics

Eight studies^23,34–40 with a total of 354 patients met inclusion criteria and were included in this systematic review. Three of the included studies were randomized control trials (RCT)^35,39,40 and five of the included studies were retrospective case-control studies.^{23,34,36–38} Of studies that reported platelet-rich plasma composition, preparations included sodium citrate,^34,38 calcium chloride,^35,40 calcium chlorate,³⁹ and acid citrate.³⁷

3.4 Platelet rich plasma augmented meniscal repair cohort characteristics and demographics

Of the 354 included patients, 180 patients received PRP augmentation at the time of their meniscus repair. Of these 180 patients, 118 (65.6 %) were male and 62 (34.4 %) were female.^23,34–40 The mean age among patients who received PRP augmentation ranged from 26.0 years to 70.0 years.^23,34–40 Five studies reported mean body mass index (BMI) for patients who received PRP augmentation, ranging from 23.7 kg/m² to 27.2 kg/m².^35–38,40 Six studies reported mean follow-up time, ranging from 3.0 months to 48.0 months,^34–39 and two studies reported median follow-up time, ranging from 23.0 months to 34.0 months.^23,40 Five studies reported 79 total patients with medial meniscus repair,^{23,35–37,40} six studies reported 48 total patients with lateral meniscus repair,^{23,34–37,40} one study reported 6 patients who underwent bilateral meniscus repair,³⁷ and two studies reported 47 total patients who underwent meniscus repair with unspecified laterality.^38,39 Six studies reported types of tears for patients who received PRP augmentation, including 65 horizontal cleavage, 24 bucket handle, 34 vertical longitudinal, 8 complex degenerative, 4 transverse radial, 1 peripheral horizontal, 1 root, and 1 bucket handle + horizontal tear.^{23,35–37,39,40} Of note, Dai et al. reported types of tears for all patients included in the study, with a total of 11 longitudinal, 10 complex, 7 horizontal, and 1 radial tear.³⁴ Five studies reported meniscus repair technique for patients who received PRP augmentation, including 39 all-inside, 37 inside-out, 1 outside-in, 10 all-inside + inside-out, 3 all-inside + outside-in, and 3 all-inside + inside-out + outside-in.^34–37,39

3.5 Control meniscal repair cohort characteristics and demographics

Of the 354 included patients, 174 patients were part of the control group and did not receive PRP augmentation at the time of their meniscus repair. Of these 174 patients, 114 (65.5 %) were male and 60 (34.5 %) were female.^23,34–40 The mean age among control patients ranged from 26.0 years to 69.5 years.^23,34–40 Five studies reported mean body mass index (BMI) for control patients, ranging from 24.8 kg/m² to 28.0 kg/m².^35–38,40 Six studies reported mean follow-up time, ranging from 3.0 months to 48.0 months,^34–39 and two studies reported median follow-up time, ranging from 23.0 months to 34.0 months.^23,40 Five studies reported 54 total patients with medial meniscus repair,^{23,35–37,40} five studies reported 68 total patients with lateral meniscus repair,^23,34–37 one study reported 6 patients who underwent bilateral meniscus repair,³⁷ and two studies with 46 total patients underwent meniscus repair with unspecified laterality.^38,39 Six studies reported types of tears for control patients, including 51 horizontal cleavage, 22 bucket handle, 37 vertical longitudinal, 8 complex degenerative, 8 transverse radial, 2 root, 2 undersurface, and 1 peripheral horizontal tear.^{23,35–37,39,40} Of note, Dai et al. reported types of tears for all patients included in the study, with a total of 11 longitudinal, 10 complex, 7 horizontal, and 1 radial tear.³⁴ Five studies reported meniscus repair techniques for control patients, including 60 all-inside, 31 inside-out, 3 outside-in, 3 all-inside + outside-in, and 2 all-inside + inside-out techniques.^34–37,39Table 2 summarizes demographics of patients included in each study. Table 3 summarizes characteristics of meniscus tears, operative techniques, and PRP techniques used during meniscus repairs included in this systematic review and meta-analysis.

3.6 Patient reported outcomes

Three studies with PRP patients reported both mean pre-operative and post-operative Lysholm scores, ranging from 50.3 to 53.3 and 79.8 to 82.3, respectively.^34,37,38 Griffin et al. only reported a mean post-operative Lysholm score of 66.0.³⁶ Five studies with PRP patients reported both mean pre-operative and post-operative visual analogue score (VAS) scores, ranging from 4.1 to 9.0 and 0.8 to 2.0, respectively.^{34,35,38–40} Three studies with PRP patients reported both mean pre-operative and post-operative IKDC scores, ranging from 40.9 to 52.0 and 75.1 to 97.6, respectively.^37,39,40 Griffin et al. reported a mean post-operative IKDC score of 69.0.³⁶ Pujol et al. only reported a median post-operative IKDC score of 87.9.²³ Three studies with PRP patients reported on both mean pre-operative and post-operative Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores, ranging from 32.3 to 77.2 and 1.0 to 52.5, respectively.^38–40

Three studies with control patients reported both mean pre-operative and post-operative Lysholm scores, ranging from 50.2 to 55.0 and 74.6 to 79.1, respectively.^34,37,38 Griffin et al. only reported a mean post-operative Lysholm score of 89.0.³⁶ Five studies with control patients reported both mean pre-operative and post-operative VAS scores, ranging from 3.4 to 8.0 and 0.9 to 5.0, respectively.^{34,35,38–40} Three studies with control patients reported both mean pre-operative and post-operative IKDC scores, ranging from 41.7 to 54.9 and 72.6 to 88.1, respectively.^37,39,40 Griffin et al. reported a mean post-operative IKDC score of 76.0.³⁶ Pujol et al. only reported a median post-operative IKDC score of 90.7.²³ Three studies with control patients reported both mean pre-operative and post-operative WOMAC scores, ranging from 28.9 to 76.8 and 4.0 to 62.9, respectively.^38–40Table 4 summarizes patient-reported outcomes from meniscus repairs included in this systematic review.

3.7 Complications

Complications included in this systematic review consisted of re-tear or failure, re-operation, hematoma or wound complication, and deep infection or septic arthritis. Among the seven studies that reported on complications for 152 PRP patients, there were a total of 32 complications for an overall complication rate of 21.1 %.^{23,34–37,39,40} The most common complication was re-tear or failure in 25/137 (18.2 %) patients.^{23,34,36,37,39,40} A total of 6 (9.7 %) patients had reoperations, four received revision meniscus repairs and two underwent partial meniscectomies.^23,36,37 Only one (1.1 %) patient experienced a hematoma or wound complication, requiring surgical drainage.^23,35,39,40 Of note, no PRP patients experienced a deep infection or septic arthritis.^23,35,39,40 Among the seven studies that reported complications for 146 control patients, there were a total of 48 complications for an overall complication rate of 32.9 %.^{23,34–37,39,40} The most common complication was re-tear or failure in 40/131 (30.5 %) patients.^{23,34,36,37,39,40} A total of 7 (10.3 %) patients had reoperations, six received revision meniscus repairs and one underwent subtotal medial meniscectomy.^23,36,37 Only one (1.3 %) patient experienced a deep infection or septic arthritis, requiring joint lavage and antibiotics.^23,35,39,40 Of note, no control patients experienced a hematoma or wound complication.^23,35,39,40Table 5 summarizes complications from meniscus repairs included in this systematic review.

Two-proportion z-tests indicated that a statistically significant difference in re-tear/failure rate existed between patients who received PRP augmentation versus patients who did not receive PRP augmentation; however, there were no statistically significant differences with regards to re-operation, hematoma/wound complication rate, or deep infection/septic arthritis rates. Fig. 3 displays a heatmap that summarizes z-scores for two-tailed hypotheses using 0.05 as the significance level.

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Fig. 3 Heat map displaying z-scores and p-values for complication rates between the meniscal repair with platelet-rich plasma (PRP) and control (meniscal repair without PRP) cohorts. Darker blue corresponds to greater statistical significance.

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4.1 Limitations

This study is not without limitations. One major limitation is the heterogeneity of the included studies, which varied in patient demographics, type and location of meniscus tears, and operative techniques. However, all included studies were either RCTs or retrospective case-control studies, and the variations may improve the external validity of our findings across different populations, meniscal repairs, and clinical contexts. Another significant limitation is the variability in PRP preparation techniques within the included studies. Factors such as platelet concentration, leukocyte concentration, and activation methods make it difficult to standardize results across studies, however given PRP formulations vary drastically across institutions and manufacturers, we believe this again applies external validity to different practices. Furthermore, the retrospective design of many included studies introduces potential biases, such as selection bias and recall bias, which can impact the reliability of the reported outcomes, especially given studies that reported PROs were inconsistent in which PROs were reported as well as with the reporting of preoperative PROs.

4.2 Conclusions

While significant heterogeneity in study methodology exists within the comparative literature, limited evidence exists suggesting a significantly decreased rate of re-tear or failure in patients undergoing meniscus repair with PRP augmentation versus without PRP augmentation.