Why thumb base pain is so often written off

Persistent pain at the base of the thumb — sharp during pinching, aching at rest, accompanied by a grip that feels weaker than it should — is one of the more commonly dismissed complaints in hand clinics. Patients are frequently told they have tendinopathy, or early carpal tunnel involvement, or simply wear and tear, and sent away with a splint and perhaps a corticosteroid injection. What is rarely explained is that the joint itself may be losing cartilage.

That joint — the trapeziometacarpal (TMC), sometimes called the CMC-1 — is the second most frequently affected site in degenerative hand disease, after the distal interphalangeal joint. Around 30% of postmenopausal women develop trapeziometacarpal osteoarthritis (TMO), yet awareness of what is actually happening structurally, and what options exist beyond symptom control, lags far behind knowledge of knee or hip cartilage problems.

The standard non-surgical pathway — activity modification, anti-inflammatories, splinting, steroid or hyaluronic acid injection — addresses pain but leaves the cartilage itself untouched. At the other end of the spectrum sits trapeziectomy, which involves removing the trapezium bone entirely: effective in advanced disease, but irreversible and requiring substantial rehabilitation.

The question this article addresses is whether a single-stage, joint-preserving injectable treatment can occupy the gap between those two endpoints — and for which patients it is most likely to help.

How cartilage damage is graded at the thumb base

The Eaton-Littler classification divides trapeziometacarpal osteoarthritis into four grades, each describing a further stage of joint deterioration — from mild narrowing through to near-complete destruction of the joint surface and involvement of the adjacent scaphotrapezial joint.

Grades 1 and 2 represent early-to-moderate disease. The joint space is reduced and small osteophytes may be forming at the margins, but the structural architecture remains largely intact. This is where cartilage restoration is most feasible. In the 2025 Corain study of 64 patients, those in this group achieved statistically significant improvements in Jamar grip strength and pinch strength at more than two years after injection, alongside substantial reductions in pain scores (P < 0.001).

Grades 3 and 4 involve more extensive damage: marked joint space loss, larger osteophyte formation, and in grade 4, involvement of the scaphotrapezial joint. Regenerative injection can still reduce pain and improve daily function at these stages. The same study found significant gains in DASH questionnaire scores — a measure of ability to perform everyday tasks — in this group. Strength gains tend to be more limited at this stage, though pain relief and improved hand use remain realistic goals.

Grading is established at clinical assessment, typically using weight-bearing X-ray; ultrasound or MRI may be added to characterise the cartilage surface in greater detail. Symptom severity alone does not reliably indicate grade — a patient with moderate pain may be at grade 3, while someone with pronounced functional difficulty may still be at grade 2. Assessment by a specialist is the only way to determine where a patient sits on this spectrum.

What the injectable collagen scaffold does inside the joint

Liquid Cartilage / ChondroFiller is described as acellular — meaning it contains no donor cells of any kind. What it does contain is a purified Type I collagen matrix derived from murine tissue, CE-marked as a Class III medical device. Injected as a liquid into the joint, it self-gels within minutes to form a stable scaffold that conforms to the contours of the cartilage defect.

Think of the scaffold as a structural framework rather than a ready-made cartilage replacement. Once in place, it acts as a chemotactic signal: the patient's own stem cells and progenitor cells migrate into the matrix, where they differentiate into chondrocytes and begin synthesising new, hyaline-like cartilage. Over the following months, the scaffold is progressively replaced by host tissue. This process — matrix-induced chondrogenesis — does not guarantee cartilage regrowth, but published studies suggest it can produce structurally superior repair tissue compared with older marrow-stimulation approaches.

The relevant comparison is microfracture, which drills small channels into the subchondral bone to release marrow cells. Although historically the standard first-line approach for smaller cartilage defects, marrow stimulation tends to generate fibrocartilage rather than hyaline tissue — a mechanically inferior material that commonly breaks down within two to three years. It also disrupts the subchondral bone plate, which can compromise the success of any subsequent repair procedure.

Cell-based techniques such as ACI and MACI can produce durable tissue in certain settings, but both require a first-stage biopsy, a period of laboratory cell culture, and a theatre-based implantation procedure. ChondroFiller, by contrast, is delivered in a single outpatient appointment under ultrasound guidance — no biopsy, no culture delay, no operating theatre involved.

Why ultrasound guidance matters for this particular joint

The trapeziometacarpal joint presents an unusually constrained injection target. The joint space is narrow — formed between the saddle surface of the trapezium and the base of the first metacarpal — and it sits immediately adjacent to two structures that must not be contacted: the superficial radial nerve, which crosses the dorsoradial aspect of the joint, and the radial artery, which curves close by. A blind or landmark-only injection carries a genuine risk of missing the joint space entirely, or of contacting these neurovascular structures.

Ultrasound guidance addresses this directly. A high-frequency 'hockey-stick' linear array transducer allows the clinician to map the joint space in real time, identify the superficial radial nerve and radial artery, and advance the needle into the precise pocket between the two articular surfaces before the collagen scaffold is released. Accurate intra-articular placement is a clinical requirement: material deposited outside the joint has no therapeutic effect, and the anatomical margin for error here is narrower than in larger joints such as the knee or hip.

The procedure is carried out as an outpatient appointment — no general anaesthetic, no theatre time, typically completed within an hour. What that brevity does not reduce is the importance of clinician experience. The 2025 Corain study enrolled patients under ultrasound-guided delivery by a team with established small-joint expertise, and the outcomes reflect that protocol. Precision of delivery and familiarity with image-guided hand anatomy are factors that directly bear on what the treatment achieves in practice.

What the clinical studies show — and what they cannot yet confirm

Two prospective studies by Corain and colleagues form the current evidence base for ChondroFiller in the trapeziometacarpal joint. The first, published in 2023, enrolled 43 patients; the follow-up, published in 2025 (PMC12213533), extended the cohort to 64 patients across Eaton-Littler grades 1 to 4. Both used ultrasound-guided intra-articular delivery and divided participants into an early-disease group (grades 1–2) and an advanced-disease group (grades 3–4).

The 2025 study is the stronger benchmark. At follow-up exceeding two years, all four outcome measures — NRS pain score, Jamar grip strength, pinch strength, and the DASH questionnaire — showed statistically significant improvement (P<0.001) in both grade groups, with no adverse events recorded in either cohort. The period of most active improvement lay between 2 and 6 months post-injection, corresponding to the window of scaffold integration and chondrogenic activity described earlier. Earlier-stage patients gained more in grip and pinch strength; those with advanced disease showed greater improvement in daily-function scores on the DASH — a pattern that helps calibrate expectations by grade in clinical practice.

The limitations deserve equal candour. Every piece of TMC-specific evidence comes from a single research group, without independent replication. No randomised controlled trial has been conducted for this joint application, and the 2025 study lacks a comparator arm — so the improvement recorded cannot be formally attributed to ChondroFiller alone versus the natural course of the condition or the non-specific effect of injection itself.

The London Cartilage Clinic's position captures this accurately: the evidence is 'encouraging but still developing', and benefits cannot be guaranteed. The two-year outcomes represent a positive signal from a well-designed prospective study — not yet a confirmed result from independent, controlled research.

Suitable candidates and how to access assessment in London

Not every patient with trapeziometacarpal pain is a candidate for this injection, and the assessment exists to answer that question honestly rather than to assume fit.

The clearest indication is Eaton-Littler grade 1 or 2 disease: focal cartilage damage on imaging, ongoing pain or weakness despite a trial of conservative measures — splinting, anti-inflammatories, or corticosteroid injection — and a wish to preserve the joint and delay surgery. Patients with grade 3 or 4 disease may still benefit, particularly for pain and daily activity, but as the 2025 Corain data show, the functional strength gains tend to be smaller than in earlier-stage disease; honest expectation-setting is part of the clinical discussion at that point.

Some patients fall outside the scope of this treatment. Those who have already undergone trapeziectomy, or who have advanced pan-trapezial involvement beyond the CMC-1 joint, are better directed towards surgical or other routes — and the assessment will say so directly.

At the London Cartilage Clinic, assessment for Liquid Cartilage covers clinical examination, imaging review, and a frank discussion of whether injection, continued conservative care, or surgical referral is the better-matched pathway. For patients caught between inadequate conservative relief and a surgery they are not yet ready for, that conversation is often long overdue — and the earlier it happens, the more options remain open.

Liquid Cartilage™ is delivered in the UK at the London Cartilage Clinic on Harley Street. Assessment can be booked at londoncartilage.com.