What hip precautions are and why surgeons prescribe them

After a standard hip replacement, most patients leave hospital with a list of things they must not do — and 'no bending past 90 degrees' tends to be the one that surprises them most. These movement restrictions are known collectively as hip precautions, and they exist for a specific biological reason rather than out of caution alone.

The three core restrictions are straightforward:

• No hip flexion beyond 90° — the joint should not fold further than a right angle, so low chairs, car seats, and bending to put on shoes all require care.
• No crossing the legs or ankles — in any position, sitting or lying.
• No internal rotation or pivoting on the operated leg.

NHS guidance formalises these for at least six weeks following a posterior-approach total hip replacement, with dislocation risk persisting for up to three months.

The reason comes down to how a posterior approach reaches the joint. To access the hip from the back, the surgeon must divide the short external rotator tendons — including the piriformis and obturator internus — that run across the back of the joint. Once divided, those tendons need roughly 90 days to heal and re-attach. During that window, they can no longer act as a natural tether to hold the femoral head in place. Hip precautions step in as a temporary mechanical substitute, keeping the joint within a safe range of motion until the body's own tissues have recovered the job.

What happens when a dislocation occurs — and why the stakes are high

The statistics that follow a first post-operative dislocation are sobering. Of patients who experience one dislocation after a posterior-approach total hip replacement, 57% go on to dislocate again — and 11% dislocate more than five times. Nearly half (45.6%) require revision surgery within two years of that first event. Revision hip replacement is substantially more complex than the primary operation, carrying greater surgical risk and a longer, harder recovery. A single dislocation is therefore a clinically significant turning point rather than a recoverable setback.

Not every patient faces the same level of risk. Surgeons weigh several individual variables at assessment: younger age (under 65), female sex, low BMI (below 20), a higher burden of co-existing conditions, and the use of cemented prostheses are each associated with elevated susceptibility. These factors contribute to an individual risk profile — not a fixed list of exclusions from surgical care — and recognising them is part of how surgeons plan the approach and post-operative pathway.

The cascade from one dislocation to multiple further events is precisely why conservative movement guidance has been the default standard of care after posterior-approach surgery. The precautions described above are not arbitrary caution; they are a proportionate clinical response to a well-documented trajectory, and any pathway that modifies or removes them requires a sound mechanical rationale.

Why precautions vary by surgical approach, not just by time

Movement restrictions after hip replacement are not a standard feature of the operation itself — they are a consequence of which tissues were divided to reach the joint.

Patients who receive a direct anterior approach (DAA), for instance, typically face no formal movement prohibitions afterwards. Because the DAA accesses the hip from the front, the posterior capsule and the short external rotator tendons remain untouched. Without a healing wound at the back of the joint, there is no equivalent biological vulnerability to protect against, and the formal restriction list does not apply in the same way.

The same logic extends further: even within the posterior approach family, surgical modifications that preserve more of the posterior soft tissues can materially shift the risk profile. How much tissue is spared — and which specific structures — directly shapes whether precautions are warranted, and for how long.

Individual patient factors still carry weight regardless of approach. Baseline muscle strength, BMI, age, comorbidities, and home environment all inform recovery, and a surgeon's assessment of those variables does not disappear because the technique was muscle-sparing.

The operating surgeon makes this determination case by case, based on what was done intraoperatively and what was preserved. What SPAIRE specifically preserves — and why that matters mechanically — is the focus of the next section.

How SPAIRE preserves the structures that precautions were compensating for

SPAIRE — Saves Piriformis And (Obturator) Internus with Repair of (Obturator) Externus — is a modified posterior approach that reaches the hip joint while keeping the key short external rotator tendons intact rather than dividing them.

The most consequential of these is the obturator internus. Because this tendon passes directly over the posterior aspect of the femoral head at or close to the joint's true centre of rotation, leaving it intact creates what surgeons call the 'strap effect': the tendon acts as a continuous sling, generating passive viscoelastic tension and active contractile resistance against rearward displacement of the femoral head. This stabilising force is present from the moment the patient wakes from surgery. It does not depend on scar tissue forming over weeks — it is structurally there on day one. An analogy that sometimes helps: it is a seatbelt already buckled, rather than one that takes six weeks to install.

The structural argument is reinforced by a neurological one. Embedded within healthy tendons are Golgi tendon organs and muscle spindles — sensory receptors that relay continuous positional information to the central nervous system. When these tissues are divided, as in a standard posterior approach, those receptors go silent. The hip loses real-time positional awareness until slow neural regeneration occurs. SPAIRE leaves them intact, maintaining uninterrupted afferent feedback from the moment of recovery, so the nervous system can reflexively guard the hip before the patient is consciously aware of approaching a risky range of motion.

It is worth being transparent about what this argument is and is not. The case for reduced precautions after SPAIRE rests on anatomical and biomechanical logic, supported by observed clinical dislocation rates, rather than large randomised controlled trials — and that evidence base is still developing. Professor Paul Lee trained in the SPAIRE technique at the Exeter Hip Unit under Professor Timperley and uses it as his routine practice because the preservation rationale is, in his clinical judgement, mechanically sound. Individual patient suitability remains part of every pre-operative assessment.

What SPAIRE may mean in practice for your recovery pathway

For selected patients on a SPAIRE-based pathway, the practical consequence of tissue preservation may be a recovery paced by strength, confidence, and healing rather than by a fixed list of prohibited movements. Sitting in a low chair, crossing a room, or sleeping without vigilance about leg position — moments that can feel fraught in a traditional posterior-approach recovery — are not automatically governed by the same calendar-based restrictions when the posterior structures remain intact.

That said, the absence of formal precautions does not translate to unrestricted activity from the first day home. Early recovery still involves graduated loading, building trust in the operated leg, and working through physiotherapy milestones. The difference is the frame: progress is guided by what the hip can do, not by what an arbitrary rule prohibits.

Patients with higher baseline comorbidity, reduced muscle strength, or more complex anatomy may still benefit from some precautionary guidance even within a muscle-sparing pathway. Professor Lee's recovery-by-design approach integrates surgical technique, implant selection, early mobilisation planning, and discharge timing as a coherent whole — precaution reduction is one element of that programme, not the entirety of it. Where robotic-assisted implant positioning is used within the pathway, the sub-millimetre accuracy it provides in bone resection and component placement adds a further layer of stability that complements, rather than substitutes for, tissue preservation.

Recovery varies. Age, home support, pre-operative fitness, and the specifics of what was done intraoperatively all shape the timeline. The preoperative consultation is where those variables are assessed honestly and where realistic expectations — not generic promises — are properly set.

Questions worth raising with your surgeon before hip replacement

Going into a hip replacement consultation better prepared tends to produce better-informed consent and more realistic expectations on both sides. A few questions are worth raising directly:

• Which surgical approach is planned, and will the short external rotator tendons — particularly the piriformis and obturator internus — be preserved or divided?
• What postoperative movement restrictions, if any, apply to your specific pathway — and what is the mechanical reasoning behind them?
• What does the discharge plan involve, and what realistic milestones should you expect in the first two to six weeks at home?
• If you have been told precautions will apply for an extended or indefinite period, it is reasonable to ask whether a muscle-sparing approach was considered or used.

Patients most anxious about returning to everyday activities — sitting, driving, climbing stairs, travelling — benefit particularly from a pathway where the precaution rationale is clearly explained and tailored to their anatomy rather than applied as a default.

The specific answer this article has built toward is this: when the posterior tendons are preserved rather than severed, the biological reason strict precautions exist — a healing window for divided tissue — largely does not apply. That is the insight worth taking into the consultation room. Whether a muscle-sparing approach is appropriate for your anatomy and health baseline is a question a surgeon with specific expertise in that pathway is best placed to answer.