Is your knee pain actually cartilage damage?

Anterior knee pain is one of the most common reasons people visit a sports medicine or orthopaedic clinic — and one of the most misunderstood. The ache under or around the kneecap when climbing stairs, the grinding sensation on a long car journey, the discomfort that builds with squatting: these point towards the patellofemoral joint, but they do not, on their own, confirm how much cartilage has actually been lost.

Chondromalacia patellae (CMP) describes a spectrum of cartilage change on the underside of the kneecap, ranging from early softening through to full structural breakdown. The universally accepted staging framework is the Outerbridge classification, which runs from Grade 0 (normal cartilage) through Grade 1 (softening and swelling with an intact surface), Grade 2 (partial-thickness defect involving less than half the cartilage depth), and Grade 3 (deep fissuring or ulceration extending more than halfway through), to Grade 4, where cartilage has been lost entirely and the underlying subchondral bone is exposed. The grade matters because it shapes what treatment options are realistic — and because symptoms map to it only loosely. A person with Grade 2 changes can report more daily pain than someone with Grade 3, making clinical examination and imaging essential rather than optional.

The condition primarily affects young and middle-aged adults, is roughly twice as common in women as in men, and accounts for approximately three-quarters of knee pain presentations in active populations. The sections that follow explain why the anatomy predisposes certain knees to cartilage wear, how clinicians confirm the diagnosis, and what the treatment pathway looks like at each stage.

Why the kneecap wears unevenly

Two overlapping factors predispose certain knees to cartilage damage at the patellofemoral joint, even before overuse or trauma plays any role.

The first is bony anatomy. The trochlear groove — the channel in which the kneecap runs — varies considerably between individuals. A 2025 MRI study found that patients with confirmed chondromalacia had a measurably shallower groove (mean depth 3.14 mm versus 5.3 mm in healthy controls), a wider sulcus angle (145° versus 130°), and a lower lateral patellar tilt angle — all differences reaching statistical significance at p<0.001. A shallower groove gives the kneecap less track to run in; even ordinary loading can push it off-centre and concentrate stress on a single cartilage facet rather than distributing it across the joint surface. In knees with frank trochlear dysplasia the risk compounds further: a 2025 cohort of 363 knees found that one in four (25.1%) already had full-thickness cartilage loss at the time of patellar instability surgery, with supratrochlear spur height correlating independently with defect severity (r=0.196, p<0.001).

The second category is dynamic. Quadriceps weakness, hip abductor deficit, and a high Q-angle each alter the pull on the patella with every step, accelerating wear in a groove that anatomy has already made shallow. This is also where the outlook shifts: well-coordinated proximal musculature — the quadriceps, glutes, and hip stabilisers — can reduce abnormal patellar tracking without changing the underlying bony shape. Anatomy predisposes; biomechanics either compounds or counteracts. Neither operates alone, and that distinction matters at every stage of management.

What a proper assessment involves

A specialist assessment begins with clinical examination, not a scan. Clarke's test — in which the examiner presses on the superior pole of the kneecap while the patient contracts their quadriceps — remains the standard screening manoeuvre, but a positive result is a starting point rather than a confirmed diagnosis. The test lacks the specificity to distinguish cartilage grades reliably, and symptom reproduction alone does not map directly onto structural damage.

Imaging adds precision. Conventional MRI is the standard next step and captures structural defects at Grades 2 and above, but it can miss early compositional change in the collagen network and proteoglycan content. T2 mapping MRI addresses this gap: a 2024 study demonstrated sensitivity of 59.1% for detecting chondromalacia with 100% specificity — meaningfully higher than conventional sequences alone. This matters when a patient reports clear symptoms but standard imaging appears unremarkable, as it opens a window for earlier intervention before structural loss advances. It is equally important to note that the inverse holds: cartilage signal changes seen incidentally on MRI are common and do not always correspond to a meaningful clinical problem. Imaging is one input to the assessment, not a verdict.

Isokinetic dynamometry offers a third dimension: objective measurement of quadriceps and hamstring strength. Patients with chondromalacia show reduced extensor and flexor parameters at 60°/s, and altered extensor curve morphology alongside prolonged time-to-peak torque carry independent predictive weight beyond pain scores. A significant deficit on this testing typically directs the pathway back to structured physiotherapy before imaging-led escalation is considered — it is a functional staging tool with direct treatment implications.

The value of bringing these elements together is precisely this: combining clinical examination, advanced imaging, and functional data allows accurate staging, and staging is what determines which treatment options are genuinely appropriate.

What conservative care involves — and what to expect

For most patients with Grade 1 or Grade 2 disease — and many with Grade 3 — structured physiotherapy is the appropriate first response, and genuinely effective rather than a holding measure.

The programme needs to be targeted. Strengthening the quadriceps in isolation is insufficient; the proximal chain matters as much. Hip abductor and external rotator weakness shifts load distribution at the patellofemoral joint, so a sound conservative programme addresses the glutes and hip stabilisers alongside the VMO. Patellar taping or bracing may be used in parallel to modify tracking during the early loading phase.

Load management runs alongside the exercise programme. High-impact activity, prolonged stair use, and sustained squatting positions should be paced rather than eliminated entirely; the aim is to keep cumulative cartilage stress within a tolerable range while the supporting musculature strengthens. Footwear and orthotic support can help where flat-foot mechanics are contributing.

Most patients notice meaningful improvement within six to eight weeks of consistent, well-supervised work. Escalation to specialist review is appropriate when symptoms have not improved after eight to twelve weeks of structured physiotherapy, when mechanical features such as locking or giving way develop, or when imaging shows progressive full-thickness change.

When conservative care is not enough — the escalation pathway

Escalation becomes relevant when structured physiotherapy has been given adequate time — typically eight to twelve weeks — without sufficient symptom resolution, or when structural staging indicates disease that conservative care cannot adequately address on its own.

Injection therapies

Two injection-based approaches occupy the middle ground between physiotherapy and surgery, though they act through different mechanisms and should not be treated as interchangeable. A 2024 cohort study examined platelet-rich plasma (PRP) combined with hyaluronic acid for anterior knee pain due to chondromalacia in young and middle-aged adults; high-level randomised trial data comparing these agents against placebo in chondromalacia specifically remains limited. Separately, intra-articular polyacrylamide hydrogel (Arthrosamid/iPAAG) has platform evidence for reducing patellofemoral bone marrow lesions — a structural hydrogel pathway rather than a biologically active one.

Injectable collagen scaffold

For eligible focal defects, an injectable collagen scaffold (ChondroFiller injection) provides an image-guided, outpatient route based on matrix-induced chondrogenesis: the scaffold gels within the defect and recruits the patient's own progenitor cells to build new cartilage tissue. As with the injection therapies above, evidence in this area continues to mature, and individual suitability depends on defect size, grade, and anatomy — factors best assessed by a specialist rather than inferred from symptoms alone.

Surgical cartilage restoration

For more complex or extensive full-thickness defects, autologous chondrocyte implantation (ACI) carries the strongest published evidence base, with a systematic review of 35 studies reporting good clinical outcomes. Combining ACI with patellofemoral realignment procedures — including MPFL reconstruction, tibial tubercle osteotomy, and lateral retinaculum release — achieves equivalent final patient-reported scores even where pre-existing malalignment is present, addressing a concern that often complicated candidacy decisions. Patellar shape is not a disqualifying factor: a 2024 study of 59 patients found that Wiberg type had no significant effect on graft survival or outcomes at median 3.5-year follow-up.

End-stage disease

Where disease has progressed to the level warranting total knee arthroplasty, the pathway is distinct from cartilage preservation. A 2026 five-year dataset across 180 knees found that circumpatellar denervation combined with patelloplasty in a non-resurfacing protocol achieved MCID on all four patient-reported outcome measures, regardless of ICRS cartilage grade at baseline.

Getting an assessment at the London Cartilage Clinic

Chondromalacia sits on a spectrum, and where any individual sits on that spectrum — and which intervention is proportionate — can only be established through proper assessment, not by symptoms alone or an MRI report read in isolation. The evidence reviewed across this article points consistently in the same direction: early identification, targeted conservative care, and timely escalation where structural change warrants it produce better long-term outcomes than watchful waiting at each stage.

For patients based in London or the commuter belt, Liquid Cartilage™ / ChondroFiller injection is delivered at the London Cartilage Clinic on Harley Street — the UK certified centre for the product. Professor Paul Y. F. Lee leads the service; image guidance and technique precision are integral to outcomes with an injectable collagen scaffold of this kind. An assessment at LCC covers clinical examination, imaging review, and a staged treatment discussion — patients do not need to arrive with a decision already made.

Book an assessment at londoncartilage.com.

1. [1] Comparative Analysis of Isokinetic Parameters in CMP (2025). (2025). https://doi.org/10.1016/j.jisako.2024.100383 https://doi.org/10.1016/j.jisako.2024.100383
2. [2] Clarke's test — Wikipedia. https://en.wikipedia.org/?curid=42482231 https://en.wikipedia.org/?curid=42482231
3. [3] Circumpatellar Denervation With Patelloplasty in TKA by ICRS Grade — 5-Year Outcomes (2026). (2026). https://doi.org/10.1016/j.artd.2026.101963 https://doi.org/10.1016/j.artd.2026.101963
4. [4] A Study on the Causative Factors Inducing Chondromalacia Patellae (2025). (2025). https://doi.org/10.36713/epra23320 https://doi.org/10.36713/epra23320