Non-Thermal Vein Treatment: Flebogrif and ClariVein (MOCA) — How Mechanochemical Ablation Works, and Where the Trials Put It

Closing a vein without heat

When people think of varicose vein treatment they usually think of laser or radiofrequency. These thermal methods, established since the early 2000s, close the refluxing vein by heating it from inside, and they remain the standard first-line treatment.

There is also a way to close a vein without heat. The best-known is mechanochemical ablation (MOCA), of which Flebogrif and ClariVein are the two main devices. This article explains the principle, why it was developed, and — because a new technique should be judged by its data rather than its novelty — what the randomised trials show.

What MOCA is

MOCA combines two things, as the name says: mechanical disruption of the vein's inner lining and a chemical sclerosant that seals it.

A fine catheter is passed into the vein. Its tip abrades the vein wall from inside while a sclerosant is delivered at the same time. The mechanical injury makes the endothelium far more receptive to the sclerosant, so the vein closes with a fraction of the drug that sclerotherapy alone would need. No heat is involved.

ClariVein uses a rapidly rotating wire tip to abrade the wall, with liquid sclerosant infused through the catheter.

Flebogrif uses a set of small hooks that deploy from the catheter tip and scratch the wall as the catheter is withdrawn, with polidocanol foam delivered simultaneously. It is non-rotational.

Why non-thermal methods were developed

Two features of thermal ablation explain the motivation.

Tumescent anaesthesia. To protect the tissues around the vein from heat, and to anaesthetise them, thermal ablation requires the space around the vein to be filled with dilute local anaesthetic solution — typically 200–500 mL per leg, delivered through multiple injections along the vein's course. It is necessary and safe, but it is the part of the procedure patients find most uncomfortable, and the fluid can leave the leg feeling swollen for a day or two. Non-thermal methods do not need it.

The below-knee segment. Below the knee, the great saphenous vein runs close to the saphenous nerve, and the small saphenous vein close to the sural nerve. Heat delivered there can injure them, so thermal ablation of below-knee segments is approached cautiously. Before non-thermal options existed, below-knee reflux was often left untreated after above-knee ablation, or managed with repeated sclerotherapy. MOCA was designed in part as an option for exactly these segments.

What the trials show: the advantages

Less pain during the procedure. In the first randomised trial of ClariVein against radiofrequency (Bootun et al., Phlebology, 2016; 119 patients), maximum intra-procedural pain was 19 mm versus 35 mm on a 100 mm scale. A 2026 meta-analysis of MOCA against radiofrequency (Cheng et al.; 737 patients) confirmed lower perioperative pain and a faster return to normal activities — by about three-quarters of a day.

Less nerve injury. The 2023 systematic review and meta-analysis of randomised trials comparing thermal against non-thermal ablation (Shahzad et al., European Journal of Vascular and Endovascular Surgery; 8 trials, 1,956 patients) found non-thermal ablation was better tolerated and carried less risk of nerve injury, with moderate-quality evidence. A 2023 network meta-analysis (Bontinis et al.; 14 studies, 4,177 patients) put the risk of postoperative paraesthesia after laser at roughly ten times that after MOCA (RR 9.61).

Same quality of life. Across the trials, disease-specific quality of life improved to the same degree after MOCA as after thermal ablation — at one year in the pooled analysis (Lim et al., British Journal of Surgery, 2023), at three years and at seven years in the Helsinki trial.

What the trials show: the trade-off

The trade-off is durability of vein closure, and it should be stated plainly.

The Helsinki randomised trial (Vähäaho and colleagues) allocated 125 patients 2:1:1 to MOCA, laser or radiofrequency. At one year the treated great saphenous vein was fully closed in 100% of the laser and radiofrequency patients and 82% of the MOCA patients (British Journal of Surgery, 2019). At three years the figures were the same, 82% versus 100%. At seven years (2026), reflux in the upper 20 cm of the treated vein was found in 23% after MOCA versus 7% after thermal ablation, with two MOCA patients needing re-operation on the treated segment and none in the thermal group. Quality of life did not differ at any time point.

The pooled data agree. Lim's meta-analysis of four randomised trials (654 patients) found one-year anatomical occlusion lower after MOCA (risk ratio 0.85). Bontinis's network meta-analysis found radiofrequency, adhesive and laser all had higher odds of closure than MOCA. Cheng's 2026 meta-analysis found radiofrequency superior for anatomical success in both the short and long term.

Two nuances deserve mention. First, the Helsinki investigators identified vein diameter as the key factor: great saphenous veins wider than 7 mm before treatment were the ones most likely to recanalise after MOCA. Their conclusion was that MOCA's use in large-calibre veins should be considered carefully — not that it should not be used. Second, Lim's meta-analysis found no significant difference in procedural or post-procedural pain between MOCA and thermal ablation, contrary to the individual trials above. The pain advantage is probably real but smaller and less consistent than early reports suggested.

Flebogrif specifically

Most of the randomised evidence above comes from ClariVein. Flebogrif is newer and its evidence is at an earlier stage, but it is accumulating.

The POLFLEB prospective multicentre study (Zubilewicz et al., 2026) treated 200 patients with great saphenous veins of 4–10 mm using Flebogrif with 3% polidocanol foam. Closure was achieved in every patient at the time of treatment; at three months 95.8% of treated veins remained free of reflux; at twelve months 90.6% remained reflux-free, with complete reopening in 4.4%. No serious adverse events occurred within 30 days. A Korean single-centre series (Park & Park, 2026) of 105 great saphenous veins reported anatomical success of 100% at one month, 98.4% at six months and 95.4% at twelve months, with no nerve injury or deep vein thrombosis.

A properly powered randomised trial against laser — the Dutch REBORN trial, 310 patients, non-inferiority design, primary outcome anatomical success at twelve months — is under way. Until it reports, Flebogrif's position relative to thermal ablation rests on single-arm data.

Where this leaves the choice

Non-thermal ablation is not better in every case, and it is not worse in every case. Reading the evidence together:

• MOCA is a reasonable choice where avoiding tumescent anaesthesia matters, where the segment lies close to a nerve — particularly below the knee — and in smaller-calibre veins.
• Thermal ablation remains the more durable option for large-diameter great saphenous trunks, where MOCA recanalisation rates are highest.
• Quality of life is equivalent in every comparison, which means that for many patients the recanalisation difference on ultrasound does not translate into a difference they feel — though it does translate into more re-interventions over time.
• Cochrane's 2021 review found no clear difference between radiofrequency and MOCA in technical success or recurrence, but rated the evidence low-certainty and noted that long-term data were not available. The Helsinki seven-year data have since partly filled that gap, in thermal ablation's favour for durability.

Which method suits a particular leg depends on the vein's location, diameter and condition, and on what matters most to the patient. It is decided from the duplex ultrasound, not from a preference for the newest device — a principle we have written about elsewhere. At da Re-Fit we use both thermal and non-thermal methods, including Flebogrif, and choose between them on that basis.

---

References

• Bootun R, Lane TR, Dharmarajah B, et al. Intra-procedural pain score in a randomised controlled trial comparing mechanochemical ablation to radiofrequency ablation: The Multicentre Venefit versus ClariVein for varicose veins trial. Phlebology. 2016;31(1):61-5. (PMID: 25193822)
• Vähäaho S, Mahmoud O, Halmesmäki K, et al. Randomized clinical trial of mechanochemical and endovenous thermal ablation of great saphenous varicose veins. Br J Surg. 2019;106(5):548-554. (PMID: 30908611)
• Vähäaho S, Halmesmäki K, Mahmoud O, et al. Three-year results of a randomized controlled trial comparing mechanochemical and thermal ablation in the treatment of insufficient great saphenous veins. J Vasc Surg Venous Lymphat Disord. 2021;9(3):652-659. (PMID: 32795619)
• Hurmerinta-Kurkijärvi OL, Weselius EJ, Vähäaho SM, et al. Randomised Trial of Mechanochemical or Thermal Ablation for Great Saphenous Vein Insufficiency: 7 Year Follow Up. Eur J Vasc Endovasc Surg. 2026. (PMID: 42401285)
• Lim AJM, Mohamed AH, Hitchman LH, et al. Clinical outcomes following mechanochemical ablation of superficial venous incompetence compared with endothermal ablation: meta-analysis. Br J Surg. 2023;110(5):562-567. (PMID: 36894167)
• Shahzad N, Elsherif M, Obaidat I, et al. A Systematic Review and Meta-Analysis of Randomised Controlled Trials Comparing Thermal Versus Non-Thermal Endovenous Ablation in Superficial Venous Incompetence. Eur J Vasc Endovasc Surg. 2023;66(5):687-695. (PMID: 37295602)
• Bontinis V, Bontinis A, Koutsoumpelis A, et al. A network meta-analysis on the efficacy and safety of thermal and nonthermal endovenous ablation treatments. J Vasc Surg Venous Lymphat Disord. 2023;11(4):854-865.e5. (PMID: 37030442)
• Cheng Q, Zhao Q, Cao J, et al. Comparing the Efficacy of Mechanochemical Ablation Versus Radiofrequency Ablation for Treating Great Saphenous Vein Incompetence: A Meta-Analysis. Ann Vasc Surg. 2026;132:622-635. (PMID: 42468801)
• Zubilewicz T, Urbanek T, Janczak D, et al. The prospective multicenter study assessing safety and efficacy of mechanochemical ablation with the use of the Flebogrif catheter in patients with great saphenous vein incompetence: One year results. J Vasc Surg Venous Lymphat Disord. 2026:102584. (PMID: 42532411)
• Park I, Park S. One-year outcomes of mechanochemical ablation of incompetent saphenous veins using the Flebogrif device. J Vasc Surg Venous Lymphat Disord. 2026;14(1):102345. (PMID: 41135794)
• Oud S, Alozai T, Schreve MA, et al. Comparing mechanochemical endovenous ablation using Flebogrif with endovenous laser ablation in the treatment of primary great saphenous vein incompetence: protocol for a multicentre, open-label, non-inferiority, observer-blinded, randomised controlled trial (REBORN trial). BMJ Open. 2024;14(8):e087490. (PMID: 39117408)
• Whing J, Nandhra S, Nesbitt C, Stansby G. Interventions for great saphenous vein incompetence. Cochrane Database Syst Rev. 2021;8(8):CD005624. (PMID: 34378180)