The case for preserving a knee rather than replacing it

Being told you are too young for a knee replacement sounds, at first, like good news. In practice it often leaves patients in a difficult position: in real pain, with a joint that is visibly wearing down, and no clear sense of what the next step actually is. Joint preservation exists to answer that question.

The phrase covers a coordinated clinical strategy — not a single treatment — designed to extend the working life of the native knee before total knee arthroplasty (TKA) becomes the only remaining option. Its value is partly biological and partly actuarial. A knee replaced in a patient's mid-forties carries roughly a 35% lifetime risk of needing further revision surgery; the same operation in someone over seventy carries a risk closer to 5%. Revision surgery is more complex, more hazardous, and less likely to restore full function than the original procedure. Delaying TKA by even a decade — ideally two — materially reduces the cumulative burden of surgery over a lifetime.

But preservation is not simply a waiting strategy. It targets the two underlying mechanisms that drive a damaged knee towards replacement: the mechanical and the biological. Abnormal load distribution concentrates compressive force on already-compromised cartilage, accelerating wear. At the same time, articular cartilage has no meaningful capacity to repair itself — its avascularity means untreated focal defects reliably progress towards diffuse joint damage. Leaving both drivers unaddressed while hoping for the best is not a clinical plan.

The three pillars — realigning load through osteotomy, restoring damaged cartilage through biological resurfacing, and protecting the joint through targeted load management — are explored in detail in the sections that follow. Used individually or in combination, they represent a structured, evidence-supported pathway for patients who have more to gain from preserving what they have than from replacing it prematurely.

Why cartilage damage doesn't heal on its own

Focal cartilage defects are far more common than most patients realise: studies of consecutive knee arthroscopies have found them in 63 to 66% of cases. What makes this clinically significant is that these lesions are not benign incidental findings. Because cartilage has no blood supply — as noted above — even a contained injury cannot mount the healing response that a muscle tear or bone fracture can. Left without treatment, a symptomatic focal defect tends to expand into the surrounding cartilage as the exposed bone beneath it changes shape and the mechanical loading pattern around the lesion shifts.

The standard grading systems — Outerbridge and ICRS — give patients and clinicians a shared language for where a lesion sits on this spectrum. Grade I and II defects involve surface softening or partial-thickness damage; the cartilage layer is intact enough that restoration is technically straightforward. Grade III and IV defects involve full-thickness loss down to the subchondral bone, where the repair challenge is substantially greater and the risk of progressive joint-wide deterioration is higher.

This grading matters because it defines a clinical window. The conditions that make cartilage restoration most likely to succeed — a contained focal defect, reasonable overall alignment, and limited spread to adjacent surfaces — are present early and erode with time. Waiting for symptoms to worsen does not improve the biological substrate; it narrows the options available.

Osteotomy: correcting the load before treating the surface

Bone alignment shapes how load travels through the knee with every step. In a varus (bow-legged) knee, the weight-bearing axis passes medially, concentrating compressive force on the very compartment that is already worn. High tibial osteotomy (HTO) corrects this by making a precise cut through the upper tibia and holding it open — or closed — at a calculated angle, shifting the load path laterally onto the healthier compartment. The effect is not subtle: musculoskeletal modelling in patients after HTO has shown a significant reduction in medial compartment compressive force during midstance and a corresponding rise in lateral compartment loading. Clinicians often use the external knee adduction moment (KAM) as a proxy for medial compartment stress, though modelling work has confirmed it does not always track the change in intra-articular load directly — a useful guide, but not a perfect measure.

The long-term evidence for HTO is meaningful. A systematic review of 18 studies covering 1,296 knees found average 10-year survivorship free from total knee replacement of 74.6%, with some series reaching 98% — even in patients with radiologically advanced medial OA (Kellgren-Lawrence grade ≥ 3). That is a clinically substantial delay for a population typically in their late forties or fifties.

Indications have expanded considerably beyond isolated varus deformity. HTO is now used alongside cartilage restoration procedures, meniscus transplant, and ligament reconstruction — in each case, realignment creates a protected mechanical environment that gives the biological repair a reasonable chance of surviving.

Technique choice involves genuine trade-offs. Distal HTO preserves patellofemoral cartilage more effectively than proximal HTO — a deterioration rate of 4% versus 29% — but carries a higher rate of posterior tibial slope increase, which carries its own implications for knee stability. For patients with both malalignment and surface cartilage damage, osteotomy alone addresses only half the problem; the section that follows examines what happens when realignment and cartilage repair are combined.

Cartilage repair: the options for restoring the joint surface

Choosing a repair technique starts with a practical question: how large and how deep is the damage? That answer — combined with the patient's age and prior treatment history — determines which options are realistic, roughly in ascending order of invasiveness and recovery commitment.

Smaller defects up to around 2 cm² suit single-stage surgical approaches. Osteochondral autograft transfer (OATS — or mosaicplasty when multiple plugs are needed) transplants a cylinder of healthy bone and cartilage from a low-load zone of the same knee into the damaged site in one operation; recovery is meaningful because the donor site within the knee needs time to settle, not just the repair site. AMIC (matrix-augmented microfracture) pairs marrow stimulation with a collagen scaffold that retains the progenitor cells migrating into the defect, bridging older microfracture technique and the more resource-intensive cell-based methods below.

For focal defects up to roughly 3 cm² — extendable to 6 cm² in some cases — ChondroFiller injection provides a non-surgical route: an injectable collagen scaffold placed under ultrasound guidance in an outpatient setting, with no theatre or general anaesthetic required. The scaffold gels in situ and recruits the patient's own progenitor cells to initiate cartilage-like tissue formation.

Defects in the 2–10 cm² range — larger than a small coin — are the domain of two-stage cell-based techniques. Autologous chondrocyte implantation (ACI) harvests cartilage cells from the patient, cultures them in a laboratory over several weeks, then re-implants them; matrix-induced ACI (MACI) seeds those cells onto a collagen membrane, streamlining some of the technical demands of the first generation. Both require two separate procedures with weeks of cell culture in between. The trade-off for that commitment is evidence of sustained durability across nine-year and longer follow-up periods.

Where defects are large or post-traumatic and autograft tissue is insufficient, fresh osteochondral allograft — donor bone and cartilage — provides a single-stage option backed by established long-term data.

One-step minced autologous cartilage places fragments of the patient's own cartilage immediately at arthroscopy. Five-year published data from 34 patients show pain scores falling from 7 to 2 out of 10, 75% reaching a meaningful functional threshold on the IKDC scale, and a revision rate of only 3.5% — supporting mid-term graft durability.

Microfracture alone is now used with declining frequency: evidence shows the fibrocartilage it produces tends to degrade within two to three years, and the technique can damage the subchondral bone layer in ways that compromise any future repair attempt.

Why osteotomy, cartilage repair, and load management work in combination

Think of a road repaired by relaying the surface without addressing the subsidence beneath — the new layer fails early because the underlying cause was never resolved. Osteotomy shifts the mechanical load; cartilage repair restores the biological surface. Each targets a distinct driver of degeneration, and neither alone is sufficient when both problems are present. The osteotomy creates a protected mechanical environment within which a cartilage graft can integrate and mature; place that same graft into an uncorrected, overloaded compartment and compressive forces impede healing from the outset.

For patients with coexisting malalignment and a focal surface defect, combined correction is the evidence-backed approach. Whether osteotomy and cartilage repair are delivered in the same operative session or staged across separate dates is a clinical judgement shaped by the severity of each problem, the patient's capacity for a lengthier surgical episode, and rehabilitation logistics — evidence on optimal timing is still accumulating and practices vary between centres.

Non-surgical load management belongs inside this strategy rather than alongside it. Quadriceps strengthening, gait modification, unloader bracing, and weight reduction all reduce the compressive forces traversing the joint at each stride — the same forces that osteotomy redistributes mechanically. A structured preservation programme treats these measures as its first active layer: before surgery, they may slow the rate of cartilage breakdown; after a procedure, they protect the repair site during the months of biological maturation when the graft is most vulnerable.

What the evidence does not yet provide is a randomised trial comparing combined HTO plus cartilage repair against either technique alone. The clinical case rests on mechanistic logic, biomechanical modelling, and cohort-level outcome data — a sound foundation, but one that clinicians and patients should hold alongside an honest awareness of that evidential gap.

Who is a candidate and what assessment involves

Not every patient with a damaged knee is a candidate for preservation — clarity on that point matters as much as the evidence in favour of it.

The strongest candidates are active patients, typically under 60, with damage confined to one compartment: a focal cartilage defect or unicompartmental OA secondary to varus malalignment. Adequate bone stock, preserved space in the unaffected compartment, and the absence of inflammatory or rheumatoid arthritis are the baseline requirements that make the biology viable. Diffuse multi-compartment damage, fixed deformity beyond the correctable range, osteoporosis, or systemic inflammatory disease reduces or removes suitability — in those cases, replacement is likely the appropriate pathway, and clinicians should say so plainly rather than deferring a conversation the patient needs.

A specialist assessment typically begins with weight-bearing long-leg X-rays to map the mechanical axis of the whole limb, followed by MRI for cartilage thickness, bone integrity, and soft-tissue evaluation. Where osteotomy is under consideration, gait or functional load analysis can quantify compartmental loading and define a measurable correction target rather than an estimated one. Professor Paul Y. F. Lee at the London Cartilage Clinic on Harley Street brings this breadth of assessment expertise — imaging, alignment analysis, and cartilage restoration — to patients considering surgical joint preservation; assessments can be arranged via londoncartilage.com.

Advanced preservation surgery remains under-offered in many settings. Patients told that replacement is their only option may not have received a specialist preservation opinion, and for those under 60 with a single-compartment problem, that assessment can alter the treatment trajectory entirely. The evidence is clearest for younger, active patients with unicompartmental disease and adequate bone stock; where those conditions are met, published data support deferral of replacement as a well-grounded clinical decision — not merely an optimistic one.

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