What hip OA is and why the hip joint is vulnerable

Osteoarthritis of the hip is not simply 'wear and tear' — it is a progressive breakdown of articular cartilage that the joint cannot repair at the same rate it loses it. As cartilage thins, the joint space narrows, the underlying bone reacts, and movement that was once smooth becomes painful and restricted. Understanding why the hip is particularly susceptible starts with its structure: it is a ball-and-socket joint in which the rounded femoral head sits within the cup-shaped acetabulum, with a thin layer of cartilage lining both surfaces. That cartilage absorbs compressive load with every step, stair, and change of direction — hundreds of times a day.

When the geometry of the joint is slightly off, that load concentrates in ways cartilage was not designed to handle. Two structural precursors are well recognised. Femoroacetabular impingement (FAI) — an abnormal shape of the femoral head, the acetabular rim, or both — causes repeated contact between surfaces during movement, gradually damaging cartilage over years. Hip dysplasia, in which the acetabulum does not cover the femoral head adequately, concentrates load on a smaller surface area, accelerating the same process. Neither condition inevitably leads to OA, but both are established risk factors in younger and middle-aged adults.

Hip OA is estimated to affect hundreds of millions of people globally — osteoarthritis as a whole is believed to affect around 240 million — and is the single leading reason for total hip replacement. One important caveat: radiological changes and pain levels do not always correspond. Mild joint space narrowing or early osteophyte formation on an X-ray may produce little or no discomfort in some people, whilst others experience significant pain at a similar imaging stage. This means a scan result is one piece of clinical information, not a verdict on how a patient is actually living with their hip.

The four stages of hip OA — what changes in the joint and how it feels

Four recognisable stages mark the progression of hip OA, each with a distinct structural picture and a corresponding shift in how the joint feels day to day. Progression pace varies considerably between individuals — some move through stages over years, others remain at one stage for a long time — so these descriptions are a guide to location on the spectrum, not a timeline.

Stage 1 — Minor wear

Early cartilage changes are accompanied by the first osteophytes (bone spurs) at the joint margins. At this point, pain is typically felt in the groin, occasionally into the thigh or buttock, and is activity-related: a long walk or session in the garden brings it on, but rest settles it within minutes to hours. Many people at Stage 1 attribute the discomfort to muscle soreness and do not seek advice.

Stage 2 — Definite cartilage breakdown

The cartilage surface shows clear deterioration and bone spurs become more established. Pain is now more consistent — present most days rather than occasionally — and morning stiffness lasting 20–30 minutes after waking is a common new complaint. Reduced range of movement may begin, most noticeable when rotating the leg or putting on socks and shoes.

Stage 3 — Marked joint space narrowing

As the joint space narrows significantly, the anatomy of the hip starts to alter. Pain frequently disrupts sleep, a limp may develop to offload the hip, and tasks such as climbing stairs or rising from a low chair become effortful. Daily function is measurably reduced.

Stage 4 — Bone-on-bone contact

Cartilage is near-completely eroded. Pain at rest and at night is common, and even minimal activity can provoke significant discomfort. Mobility is severely compromised.

The shift in pain character — from activity-triggered and rest-relieved in Stages 1 and 2, to constant, nocturnal, and only partially eased by rest in Stages 3 and 4 — is a reliable clinical marker of how far disease has advanced.

How hip OA is graded on imaging — the Kellgren-Lawrence scale explained

Most patients with hip OA will encounter a Kellgren-Lawrence (KL) grade at some point — typically noted on an X-ray report or mentioned at a GP or outpatient appointment. The KL system runs from Grade 0 (a normal joint) to Grade 4, and it remains the radiographic framework most widely cited in UK surgical guidance, including NICE and NHS England criteria for hip replacement.

Grades 1 and 2 correspond broadly to early and mild OA. At Grade 1, there may be a faint suggestion of joint space narrowing and possible minor osteophytes, though changes can be subtle. Grade 2 shows definite osteophytes with possible slight narrowing — findings that align with the clinical picture of consistent but manageable pain. Grades 3 and 4 shift the picture considerably: Grade 3 indicates moderate-to-marked joint space narrowing, multiple osteophytes, and possible small cysts or early bone deformity; Grade 4 represents severe narrowing, dense sclerosis, and large osteophytes — the radiological correlate of bone-on-bone contact. It is at Grades 3 and 4 that total hip replacement enters the conversation as a clinical option.

The OARSI grading system adds a layer of precision by recording both the depth of cartilage damage (grade) and how much of the joint surface is involved (stage), but patients are unlikely to encounter it in routine NHS or private consultations — KL is the common currency.

One point worth emphasising: a KL grade is not a treatment decision in itself. Clinical guidelines, including the 2021 Günther systematic review and NHS England's shared-decision framework, require radiological grading to be weighed alongside subjective symptom burden and functional impact before surgical referral is appropriate. A KL 3 finding in someone managing well with conservative treatment does not automatically mean surgery is next; equally, a KL 4 with severe daily pain and failed conservative management makes a compelling case for surgical assessment.

Conservative management — what to try before considering surgery

Before any conversation about surgery becomes meaningful, UK guidelines — including NICE NG226 and NHS England's shared-decision framework — require that conservative management has been tried in earnest: at minimum, three months of structured non-surgical treatment. That three-month figure is a floor, not a finish line; many patients with Stage 1–3 hip OA manage their symptoms well for considerably longer.

Conservative management is not a single intervention but a set of complementary approaches:

• Physiotherapy and targeted exercise. The primary goal is strengthening the muscles surrounding the hip — particularly the gluteals and hip flexors — so that load through the joint itself is reduced. Improved muscular support can meaningfully reduce pain and slow functional decline.
• Weight management. For patients who are overweight, even modest reduction takes a disproportionate amount of force out of every step. Clinical guidance, including the Günther 2021 systematic review, recommends a BMI below 30 kg/m² as a target before THR is considered, which underscores how important this is even beyond conservative management.
• Anti-inflammatory medication. Over-the-counter NSAIDs can reduce pain and stiffness sufficiently to allow greater engagement with exercise — the treatment most likely to deliver lasting benefit.
• Intra-articular injections. Supervised corticosteroid or hyaluronic acid injections can provide a window of reduced pain that enables more effective physiotherapy. They are a useful adjunct, not a long-term solution.

At Stage 3, and particularly at Stage 4, these measures offer diminishing returns — the structural damage is too advanced for exercise and injection alone to compensate. That is not a failure of conservative management; it is the natural limit of what it can achieve.

When hip replacement becomes a realistic option

Three converging criteria, rather than a single threshold, inform the decision to proceed with total hip replacement. Radiological evidence of KL Grade 3 or 4 OA is the first requirement; a high subjective burden — pain and functional limitation that significantly affects daily life — is the second; and failure of at least three months of conservative management is the third. The 2021 Günther systematic review and NHS England's shared-decision framework align on this structure. NHS England describes surgery as appropriate when 'severe pain has lasted a long time and other things have not helped.'

'Failure of conservative management' deserves clarification. It does not mean the measures covered in the previous section provided no benefit whatsoever — it means that what is available conservatively no longer provides adequate relief for daily functioning. Physiotherapy, weight management, anti-inflammatories, and injections may have helped at an earlier stage; the question is whether they continue to help enough.

The Oxford Hip Score gives clinicians and NHS commissioners a standardised, objective picture of how hip symptoms are affecting day-to-day tasks. It is one of the functional measures used alongside clinical examination and imaging when assessing suitability for surgery.

Age and timing genuinely matter because implant longevity is finite. Evidence suggests approximately 90% of hip replacements remain functional at 15 years; around 60% do so at 20 years. This is not a reason to deter younger patients — THR is most commonly performed in adults aged 60–80 but can be appropriate earlier where symptoms and circumstances warrant it — yet it does mean revision surgery is a realistic prospect over a long lifetime, making timing part of the shared decision rather than an afterthought.

Total hip replacement itself replaces both the acetabulum and the femoral head with prosthetic components, restoring the entire joint surface. The threshold for doing so is not a fixed line; symptom pattern, level of disability, overall health, and personal priorities all shape the decision, which is why a formal consultant assessment is the appropriate place to have it.

Why timing matters and what assessment at Lincolnshire Hip involves

The decision on timing sits between two real pressures. Implant longevity is finite — approximately 60% of hip replacements remain functional at 20 years — so operating before the threshold is genuinely met is a concern, particularly for younger patients who may face revision surgery within their lifetime. Waiting too long carries its own consequences: a hip that has deteriorated into severe anatomical distortion, with accumulated scar tissue and progressive bony remodelling, presents substantially greater operative complexity, and evidence suggests the outcomes are more limited than those achieved with surgery performed at an appropriately judged earlier stage.

The clinical evidence on this point is direct. A worse preoperative condition is associated with a poorer post-operative outcome after total hip replacement. Once KL Grade 3 or 4 is confirmed and conservative management genuinely exhausted, deferring further does not simply preserve the status quo — it may reduce what surgery can ultimately achieve.

For suitable patients, minimally invasive techniques such as SPAIRE offer a meaningfully different approach to standard hip replacement: the key muscles and tendons surrounding the hip are preserved rather than divided and reattached. Keeping that soft-tissue envelope intact from the outset supports a more stable mechanical environment around the new joint, which is what underpins a faster rehabilitation course. Suitability depends on anatomy and other clinical factors established during assessment.

Assessment itself — whether the conclusion is further conservative management, an injection, or a surgical plan — begins with clinical history, physical examination, and imaging review. Open MRI is available on-site at MSK House in Sleaford, and consultations are also held at The Keep Clinic in Grantham, making specialist review accessible locally without travelling to a major centre.

Lincolnshire Hip is part of the MSK Doctors group and accepts patients without referral for hip assessment.