Why no single test decides

Patients often arrive hoping for a clear answer: a scan result, a score, or a number that settles the question of whether surgery is the right move. In practice, no such threshold exists. A 2021 peer-reviewed study by Atsma and colleagues confirmed that uniform, standardised criteria for recommending hip replacement are currently lacking — which is precisely why surgery rates vary between clinicians and regions, and why two patients with similar X-rays may receive different advice.

What surgeons actually use is a three-stream framework, weighing each input together rather than in isolation:

• Symptom severity — the nature, duration, and impact of pain, including whether it disturbs sleep or persists at rest
• Failure of conservative treatment — evidence that physiotherapy, anti-inflammatory medication, weight management, and walking aids have been tried and found insufficient over several months
• Imaging findings — X-ray evidence of structural joint damage, ranging from early joint space narrowing through to bone-on-bone contact

None of these three streams overrides the others. A patient whose X-ray shows bone-on-bone contact but who is managing daily life reasonably well may not yet be at the point where surgery offers a clear advantage over continued non-operative care. Equally, severe pain and functional loss carry weight even when imaging appears less dramatic.

This is why experienced clinical judgement matters: the assessment is a structured conversation, not a checklist — and the surgeon's role is to read all three streams together and help the patient understand what the combined picture genuinely means for them.

Symptoms that carry the most weight

Of all the information a surgeon gathers in an initial assessment, symptom pattern carries the most immediate weight — and within that, the distinction between pain on movement and pain at rest is the clearest dividing line.

Pain that wakes a patient at night, or that is present while sitting or lying still, tells a surgeon the joint is struggling to tolerate even the body's resting load. This is not an automatic green-light for surgery, but it is the symptom that most reliably signals the hip is no longer compensating. Groin pain — felt deep in the front of the hip or radiating into the upper thigh — is the characteristic location for hip joint pathology, as distinct from referred pain arising elsewhere. Deep buttock pain is also common. Pain limited to activity, without rest or night pain, sits at a lower point on the urgency scale.

Alongside pain character, surgeons look at four practical functional markers:

• Walking distance — being unable to walk for more than a short distance before stopping due to pain
• Stairs and rising — struggling to climb steps or get up from a low chair
• Dressing — being unable to put on shoes or socks without sitting down or asking for help
• Driving — loss of the ability to drive comfortably, particularly when rotating the hip to check mirrors

Osteoarthritis is the underlying diagnosis in the great majority of cases. Avascular necrosis, rheumatoid arthritis, and post-fracture joint damage account for a smaller proportion but follow a broadly similar symptom pathway.

Trajectory also matters. A pattern that has worsened noticeably over six to twelve months carries more clinical weight than long-standing stable discomfort that has reached a plateau — even if the current symptom level looks similar on paper.

What counts as failed conservative treatment

The phrase 'failed conservative treatment' puzzles many patients who feel they have already tried everything. In clinical terms, it means documented evidence — not just a recollection — that a structured programme of physiotherapy, regular anti-inflammatory medication (NSAIDs), appropriate walking aids, and weight management has been pursued and has not delivered adequate relief.

No fixed number of months is mandated, but several months of structured non-surgical care is the typical minimum. What matters is that the attempt was genuine and the limitations it exposed are clear: persistent pain, continued functional decline, or inability to tolerate the medications themselves.

On the question of who qualifies for referral, NICE guideline NG157 is explicit: age, BMI, smoking status, gender, and co-existing health conditions must not be used as barriers to referring a patient for orthopaedic assessment. Eligibility is symptom- and function-led.

The listing stage — being placed on a surgical waiting list — is a separate step. Many NHS integrated care boards add pre-operative optimisation requirements before listing: achieving a lower BMI if above 30, completing smoking cessation, and committing to an aerobic exercise programme. These requirements exist because they genuinely reduce surgical risk, particularly around wound healing and infection.

Surgeons will also delay or decline to proceed where specific contraindications are present: active joint or systemic infection, uncontrolled diabetes, and current nicotine use each carry meaningful risks of wound complications that make operating unsafe until resolved.

What the X-ray actually shows — and what changes the decision

Plain X-ray remains the first-line imaging tool in hip assessment — not MRI. A standing anteroposterior (AP) view of the pelvis, usually paired with a lateral view of the affected hip, gives a surgeon the structural picture needed to interpret symptoms and plan the conversation about next steps.

Surgeons apply the Kellgren-Lawrence scale to grade what they see across four hallmarks: narrowing of the joint space, hardening of the bone beneath the cartilage surface (subchondral sclerosis), bony spurs at the joint margins (osteophytes), and small fluid-filled pockets within the bone (subchondral cysts). A deformed or collapsed femoral head — the ball of the hip — adds weight to the finding where present. None of these features alone triggers surgery, but together they map the extent of structural damage.

The most clinically significant threshold is joint space width. A healthy hip produces a visible gap of roughly 3 to 5 mm on X-ray, representing intact cartilage. Narrowing to 2 mm or less indicates severe cartilage loss; when the gap disappears entirely and bone presses against bone, the nature of the clinical discussion changes. At that point, hip replacement shifts from being one option among several to the likely best option for meaningful, lasting pain relief. It is not automatic surgical consent — the patient's symptoms and functional status must still support it — but bone-on-bone contact on X-ray is a clear inflection point that surgeons treat differently from earlier-stage disease.

Where X-ray findings and symptoms do not fully align, or where additional detail on cartilage quality or tendon integrity is needed, MRI can provide a more complete picture. It is not, however, a routine requirement before confirming a THR indication — the plain X-ray, read alongside how the patient is actually functioning day to day, carries the central weight.

How the Oxford Hip Score structures the conversation

The Oxford Hip Score (OHS) gives patients a structured way to describe their hip's impact on daily life before they set foot in a consultation room. Freely available online, it consists of 12 questions covering pain severity, walking ability, sleep disturbance, and capacity for everyday tasks such as dressing or using public transport. Each question is scored, producing a total between 0 and 48 — where higher numbers reflect better function.

The four clinical bands offer a rough map of where a patient currently sits:

• 0–19 — severe arthritis with a high likelihood of benefit from surgery
• 20–29 — symptoms significant enough to warrant an orthopaedic consultation
• 30–39 — non-surgical management should remain the primary focus
• 40–48 — function is adequate; surgery is not indicated at this stage

Completing the OHS before a first appointment helps the conversation move quickly toward the questions that matter most. It is not a verdict, however — a score in the 20s does not confirm someone needs an operation any more than a score in the 30s rules one out. The OHS is one structured layer in the assessment, sitting alongside symptom history, imaging, and the functional picture described in the preceding sections.

The specialist assessment — bringing it all together

Arriving at a specialist consultation means the symptom history, functional loss, Oxford Hip Score, and X-ray findings reviewed in preceding stages are read together for the first time as a composite — and a senior surgeon's role is to translate that composite into a specific recommendation for this patient, not a population average.

Three questions tend to shape the shared decision-making conversation. Is this the right moment for surgery, or does the picture suggest a bridging measure and a re-review in six to twelve months? If surgery is appropriate, how long can a modern replacement realistically be expected to last — evidence suggests roughly 58% of implants survive 25 years, and with appropriate patient selection and technique, over 30 years may be achievable in selected cases? And what does continuing without surgery mean practically: further functional decline, worsening dependence on walking aids, or persistent sleep disruption?

Surgical approach planning also begins at this stage. Posterior techniques vary considerably in how much surrounding soft tissue they preserve, and that choice has real consequences for recovery trajectory. Professor Paul Lee, Consultant Orthopaedic Surgeon at the Royal London Hospital and a member of the British Hip Society, routinely uses the SPAIRE approach — which preserves the piriformis and obturator internus tendons rather than detaching them. For selected patients, maintaining these posterior structures may support hip stability and allow more confident early mobilisation than approaches that do not.

Patients who have not yet reached bone-on-bone contact may leave the consultation without a surgical date, but with something equally useful: a structured plan, clear criteria for re-referral, and an honest account of what their imaging trajectory is likely to mean over time. Arriving prepared — with an Oxford Hip Score already completed and a clear account of what conservative treatment has and has not achieved — puts that conversation on solid ground from the outset.