What staging actually tells you — and what it doesn't

An X-ray report that says 'stage 3' or 'KL grade 3 changes' is a useful shorthand — but it is not a prediction of how much pain you will experience, how quickly things will progress, or whether surgery is inevitable.

Hip osteoarthritis is staged using two complementary frameworks. The four-stage clinical model (Minor, Mild, Moderate, Severe) describes the overall arc of the disease, from barely detectable cartilage changes through to near-complete cartilage loss and bone-on-bone contact. The Kellgren-Lawrence (KL) system grades the same progression on plain X-ray from 0 (normal) to 4 (severe), scoring features such as osteophytes (bony spurs), joint space narrowing, and subchondral sclerosis. In practice these two frameworks map reasonably closely, and your clinician may use either or both.

What neither system captures well is individual symptom experience. NHS inform data confirm that some patients have striking X-ray changes yet manage with only mild discomfort, while others report significant functional limitation with comparatively modest imaging findings. This divergence is not unusual — it reflects the complexity of how pain is perceived, and it is why staging guides a conversation between patient and clinician rather than settling it.

The hip itself is a ball-and-socket synovial joint: the femoral head articulates with the acetabulum of the pelvis, allowing the range of movement needed for walking, climbing stairs, and bearing the body's weight. Staging describes where on the continuum of cartilage loss a patient sits at a given point in time — a useful map, but not a fixed sentence.

Stages 1 and 2: before and just after symptoms appear

For many people, the first sign that something is changing in the hip is not pain — it is a subtle stiffening on getting out of bed, or an ache that settles in after a longer walk and then fades at rest. By the time most patients mention it to a GP, they are already in Stage 2.

Stage 1 (Minor / KL Grade 1) tends to go entirely unnoticed. Minor osteophytes — small bony spurs — may be forming at the joint margins, but the joint space remains intact and cartilage loss is minimal. Some people recall, in hindsight, an occasional twinge in the groin or a vague tightness through the front of the hip, usually put down to a pulled muscle or overdoing it at the weekend. There is rarely anything compelling enough to prompt an X-ray, which is why Stage 1 is most often found incidentally — picked up during imaging ordered for a different reason altogether.

Stage 2 (Mild / KL Grade 2) is the point at which symptoms become harder to dismiss. Morning stiffness — the familiar need to "loosen up" after rising from bed or from a chair — is one of the clearest early signals. Discomfort after activity is another: a walk that felt fine at the time leaves the hip aching an hour or two later. Painless crepitus, a clicking or mild grinding sensation during hip movement, may also begin at this stage without being a cause for alarm in itself. On X-ray, bone spurs are now clearly defined and mild joint space narrowing may be visible. A clinician will combine these imaging findings with a physical examination — assessing range of motion and which movements provoke discomfort, including internal hip rotation — rather than relying on the X-ray picture alone.

Stage 3: when hip pain starts to limit everyday activities

The shift from Stage 2 to Stage 3 often announces itself not as a sudden worsening but as a narrowing of what feels manageable without planning ahead. Walking any distance, climbing stairs, rising from a low chair, or squatting to pick something up — activities that were merely uncomfortable before — now produce frequent pain rather than occasional ache.

What is happening in the joint

At KL Grade 3 (Moderate), X-ray findings include multiple osteophytes, definite joint space narrowing, and the early appearance of subchondral sclerosis — a hardening of the bone beneath thinning cartilage. Cartilage erosion is significant but not yet complete; some cushioning remains, which explains why this stage can be the most prolonged and variable of the four. Crepitus — the grinding or grating sensation that may have been mild or intermittent at Stage 2 — often becomes more pronounced, particularly during weight-bearing movement.

Functional limitations also tend to become more intimate. Putting on socks, getting in and out of a car, crossing the legs, and turning in the seat while reversing can all provoke stiffness or discomfort that was not there before. Pain that once faded with rest may now linger into the evening.

Conservative care is still first-line

Stage 3 does not automatically mean that surgery is imminent. Physiotherapy — aimed at hip strength, range of motion, and movement patterns — and weight management form the backbone of conservative care at this stage, supported by appropriate analgesia and activity adjustment. Some patients also benefit from injection therapies such as corticosteroid or hyaluronic acid as adjuncts within a broader plan, though these are options in context rather than the primary focus at this decision point. A 2026 study found that conservative treatment can meaningfully improve pain levels and day-to-day function even when structural X-ray changes continue to progress — a finding that reflects how much a patient's functional quality of life and their imaging appearance can diverge, and why symptom experience rather than radiology grade should guide management decisions at this stage.

Stage 4: end-stage hip OA and the total hip replacement decision

Broken sleep is often what finally brings Stage 4 patients to a specialist. The hip that ached after a long walk in Stage 2, or hurt reliably on the stairs in Stage 3, now wakes them at three in the morning when they roll over — and the ache lingers through the day regardless of how little has been done. Walking to the end of the street can feel like a negotiation with pain; walking to the shops may no longer be realistic at all.

What is happening in the joint

KL Grade 4 (Severe) on plain X-ray shows large osteophytes, marked joint space narrowing, severe subchondral sclerosis, and definite deformity of the bone ends. The phrase most patients will have encountered — 'bone-on-bone' — is a fair shorthand: the cartilage that once cushioned the femoral head against the acetabulum is almost entirely absent, and the two surfaces are moving in direct contact. Chronic low-grade inflammation in the joint lining compounds the mechanical problem, contributing to the persistent ache at rest and at night.

The total hip replacement conversation

Total hip replacement (THR) becomes the standard-of-care discussion at Stage 4 because conservative measures — physiotherapy, analgesia, activity modification — routinely fail to provide adequate relief once structural damage reaches this level. The 2024 PROHIP randomised trial found that hip replacement produced a mean Oxford Hip Score improvement of 15.9 points at six months, compared with 4.5 points for resistance training alone, in patients with severe hip OA and a surgical indication.

That said, the decision to proceed is individual. A patient whose Stage 4 changes are confirmed radiographically but whose symptoms remain manageable is not obliged to have surgery; the threshold is functional impact and quality of life, not X-ray grade alone. A specialist assessment can clarify which options remain open and what the likely trajectory is without surgery.

What makes hip OA progress faster

Several factors influence how quickly hip OA moves from one stage to the next — and understanding them matters because some are within a person's control.

Weight and joint load. Excess body weight places additional mechanical stress on the hip joint at every stage, accelerating cartilage loss and complicating conservative management as disease advances. High body mass is one of the most consistently identified contributors to hip OA progression across the evidence base.

Cardiovascular health. A five-year cohort study of non-obese hip OA patients (KL grade ≥ 2) found that cardiovascular disease was independently associated with radiological progression, with an odds ratio of 3.45 (95% CI 1.06–11.17). This suggests that vascular and metabolic health influences the hip joint beyond mechanical load alone — a reminder that managing cardiovascular risk is not separate from managing the joint.

Hip joint shape. Femoroacetabular impingement (FAI) — an abnormality in how the femoral head and socket fit together — can drive focal cartilage damage that may progress toward more widespread joint degeneration if left unaddressed.

Non-modifiable factors. Age, sex, and genetic background all play a part. Symptomatic hip OA is more common in women, while radiographic changes are more frequently detected in men; the reasons for this difference are not fully understood and may reflect hormonal and biomechanical factors.

Importantly, no one factor determines an individual's trajectory. The molecular mechanisms driving early cartilage degeneration remain incompletely understood, and the rate of progression varies considerably between patients — it cannot be reliably predicted from staging alone.

What to do at each stage: the management pathway

Managing hip OA effectively depends on matching treatment to stage — and on recognising that conservative care is a meaningful intervention in its own right, not a holding pattern until surgery becomes unavoidable.

Stages 1–3: conservative care first

For most patients at Stages 1 through 3, the evidence-based starting point is a supervised programme combining strengthening exercises, range-of-motion work, activity adjustment, and appropriate analgesia. This is not passive management: regular, guided exercise is among the most consistently supported interventions for hip OA across its earlier stages, and improvements in pain and function are achievable even when structural changes in the joint continue.

Addressing weight is worthwhile at any stage: reducing mechanical load on the hip supports symptom relief and may slow progression, particularly for patients with higher body mass.

When conservative care provides insufficient relief — typically at Stages 2 or 3 — injection therapies (corticosteroid, hyaluronic acid, or platelet-rich plasma) may be considered as an adjunct. These are covered in detail separately on Lincolnshire Hip.

Stage 4: the surgical conversation

If conservative measures have been genuinely optimised and symptoms are still severely restricting daily life, total hip replacement becomes the appropriate discussion. The threshold is quality of life and functional limitation — not X-ray grade alone. A patient with confirmed Stage 4 changes who is coping adequately is not required to proceed; the decision remains individual.

When to seek a specialist opinion

Consider requesting a specialist assessment if:

• pain has not settled after three to six months of GP-led management
• symptoms are limiting work, sleep, or routine daily activities
• clarity on your current stage and realistic options would help you make a decision

Lincolnshire Hip accepts patients without referral for hip assessment and is accessible from Sleaford and Grantham.

1. [1] Effectiveness of Conservative Treatment for Hip OA: Radiographic Structural Changes vs Clinical Symptom Improvement. (2026). https://doi.org/10.1016/j.joca.2026.01.567 https://doi.org/10.1016/j.joca.2026.01.567
2. [2] Whole-Genome RNA Sequencing of Femoral Head Impingement Cartilage Identifies FGF18 as Biomarker in Hip OA Progression. (2022). https://doi.org/10.1101/2022.05.23.492951 https://doi.org/10.1101/2022.05.23.492951
3. [3] Association of Baseline Cardiovascular Diseases with 5-Year Hip Osteoarthritis Progression (KHOALA Cohort). (2021). https://doi.org/10.3390/jcm10153353 https://doi.org/10.3390/jcm10153353
4. [4] High Body Mass as a Weight Factor for Hip Osteoarthritis Progression. (2024). https://doi.org/10.61186/aassjournal.1400 https://doi.org/10.61186/aassjournal.1400