Why sleep becomes so difficult after hip replacement

For many people recovering from hip replacement, the operating table is not the hardest part — the first few nights at home are. Pain that flares when you shift position, a mattress that suddenly feels all wrong, and a nagging worry that any unexpected movement might undo the surgery: together, these make sleep one of the most commonly reported difficulties in the weeks following the procedure.

Much of that anxiety has a specific source. Most patients are sent home with a clear set of instructions: sleep on your back, keep a pillow between your legs, avoid rolling onto the operated side. For six to twelve weeks, these rules govern the night as much as the day. They are not arbitrary — they exist because standard hip replacement technique involves cutting and reattaching tendons at the back of the joint, which then need time to heal.

But the rules that protect one patient may not apply to another. Whether those restrictions are necessary at all depends, in large part, on what happened inside the joint during surgery — and that is the question this article explores.

Where the traditional sleeping rules come from

The posterior approach is the most widely used route into the hip joint. To reach the socket and femoral head, the surgeon must pass through the back of the hip — and that means detaching the short external rotator tendons that sit across the posterior capsule: principally the piriformis and obturator internus. Once the joint has been replaced, these tendons are repaired and sutured back, but sutured tissue is not the same as intact tissue. Biology demands roughly 90 days for those structures to heal to meaningful strength.

During that window, one specific movement pattern poses the greatest risk. When a patient lies on their side with the operated hip uppermost, the leg can fall forward under its own weight — combining hip flexion with internal rotation. That compound movement is exactly the direction that loads the posterior capsule under tension while it is still fragile. The result, if forces exceed what the healing repair can bear, is dislocation.

The standard sleeping rules — back-flat with a pillow between the legs, or non-operated-side only with two pillows between the knees and ankles — are designed to block that specific movement from happening during sleep, when conscious muscle control is absent.

The stakes of getting it wrong are high. Once a dislocation occurs in this early period, approximately 57% of patients go on to dislocate again, and close to half ultimately require revision surgery within two years.

Crucially, every element of this reasoning traces back to a single anatomical event: tendon division. Change that event, and the logic supporting the restrictions changes with it.

What the evidence now says about routine hip precautions

The clinical case for dropping routine hip precautions rests on solid, if still-growing, evidence. A 2024 systematic review and meta-analysis pooling data from three randomised controlled trials — 1,215 patients in total — found no statistically significant difference in dislocation rates between patients who followed standard hip precautions and those who did not. More striking, the group without precautions showed better functional scores on the HOOS JR outcome measure and stopped using walking aids sooner.

The practical picture is complicated by how slowly that evidence has reached clinical practice. A 2026 implementation project at a German university hospital found that just 16.7% of patients were being managed without precautions before an educational intervention — even though the supporting evidence already existed at that point.

Neither study addresses sleeping positions specifically within muscle-sparing approaches such as SPAIRE, and no randomised trial data yet exists for that particular combination — a gap worth acknowledging honestly. The HIPSTER trial, currently in progress, is designed to generate precisely this kind of comparative evidence on tendon-sparing surgery and return to unrestricted function; its results will add considerably to what can be said with confidence.

What the existing data does establish is that routine precautions carry a real evidence burden. The question is no longer whether they are always necessary, but for which patients and which surgical approaches they remain warranted — a distinction that matters considerably when thinking about sleep.

What SPAIRE preserves and why it changes the calculation

SPAIRE — an acronym for Saves Piriformis And (Obturator) Internus with Repair of (Obturator) Externus — was formalised in 2016 as a modified posterolateral approach that leaves those key posterior tendons undisturbed rather than detaching and re-attaching them. The anatomical event that drives the traditional precaution logic, tendon division, simply does not occur in a well-executed SPAIRE procedure.

Two distinct mechanisms follow from that preservation. The first is mechanical. The intact obturator internus tendon passes directly over the posterior aspect of the femoral head, creating what is sometimes described as a 'strap effect': under load, it acts as a biological tether that actively resists internal rotation and posterior subluxation — the very movement that standard sleeping rules are designed to block. In a traditional posterior approach this tendon has been cut, repaired, and placed on a 90-day healing clock. In SPAIRE, it continues to perform its stabilising function from the moment the patient wakes from anaesthesia.

The second mechanism is neurological. Muscle spindles and Golgi tendon organs embedded within those preserved short external rotators maintain continuous proprioceptive feedback to the hip. The joint retains an instinctive awareness of its own position and loading — something that is lost when the mechanoreceptors are severed and must regenerate over months. That neurological continuity means the hip is not left, as the literature describes it, 'neurologically blind' during the period when conscious muscle control is absent.

Together, these two properties — mechanical tethering and intact proprioception — underpin the argument that selected SPAIRE patients do not carry the same positional vulnerability during sleep that justifies traditional restrictions.

Professor Paul Lee has used SPAIRE in over 1,000 primary total hip replacements and has built a recovery pathway around this mechanical logic — which is why the practical guidance that follows reflects a different set of starting assumptions from those that govern a conventional posterior approach.

What sleeping positions may look like within a SPAIRE recovery pathway

For patients on a no-restriction SPAIRE pathway, the practical answer is simpler than the preceding weeks of traditional advice might suggest: sleeping position is led by comfort, not by a mandatory regime.

Back sleeping with a pillow beneath the knees or calves remains an easy starting point — not because it is required, but because many people find it restful in the first week. Side sleeping on either the operated or non-operated side is generally possible as soon as wound tenderness allows, without the strict two-pillow enforcement and non-operated-side-only rule that governs a standard posterior recovery. A pillow between the knees or ankles when side-lying can help with alignment and reduce rotational pull on healing soft tissues — but within this pathway it functions as a comfort aid, not a clinical enforcement.

What changes for selected SPAIRE patients is the absence of the 90-day tendon-healing clock that generates those positional rules in the first place. Because the posterior stabilisers were never divided, that specific rationale does not apply in the same way.

Sleep disruption in the early weeks remains common regardless of approach. Swelling, wound sensitivity, and the general effort of healing mean that comfortable positions may need adjusting night by night — that is a normal part of recovery, not a sign that something has gone wrong.

Specific guidance is always confirmed individually by the surgical team before discharge, since the no-restriction pathway is not automatic and depends on the procedure performed and each patient's recovery progress.

Patient selection, realistic expectations, and next steps

None of the preceding discussion changes the guidance for anyone already managing with traditional precautions after a standard posterior approach — those restrictions exist for a clear biological reason and should be followed as advised by the treating team until they are formally reviewed at follow-up.

The no-restriction pathway described throughout this article applies to selected patients: those whose surgeon has confirmed a SPAIRE procedure, whose anatomy and implant positioning support unrestricted early movement, and whose progress has been assessed before discharge. Individual factors — bone quality, baseline muscle strength, body weight, home support, and the precise surgical findings — all shape what a team recommends. That selection happens in clinic and in theatre, not through an article.

The evidence base on this specific question is still growing. Published trial data directly examining how SPAIRE patients fare across different sleeping positions does not yet exist, and acknowledging that gap honestly is part of understanding what a muscle-sparing pathway currently offers — and what remains to be confirmed.

For anyone considering hip replacement and wanting to understand whether this kind of approach is appropriate for them, a specialist consultation that includes imaging and functional assessment is the right place to start. The most useful questions to bring to that conversation are not primarily about sleep positions — they are about which tendons will be involved, what that means for the healing process, and how the surgical plan is matched to individual anatomy.

Professor Paul Lee's assessment process centres on exactly that kind of surgical planning: confirming whether the clinical picture supports a tendon-sparing approach, and what a realistic recovery looks like for that specific patient.

1. [1] Hip precautions after total hip replacement and their discontinuation from practice: patient perceptions and experiences. (2020). https://doi.org/10.1080/09638288.2020.1722262 https://doi.org/10.1080/09638288.2020.1722262
2. [2] No need for hip precautions after total hip arthroplasty with posterior approach: A systematic review and meta-analysis. (2024). https://doi.org/10.1097/MD.0000000000040348 https://doi.org/10.1097/MD.0000000000040348
3. [3] De-implementation of movement precautions after total hip replacement in a German university hospital. (2026). https://doi.org/10.1097/xeb.0000000000000573 https://doi.org/10.1097/xeb.0000000000000573
4. [4] A Standard of Care in Hip Arthroplasty: Routine Use of the Tendon-Sparing SPAIRE Technique with MAKO Robotic Assistance. (2024). https://doi.org/10.1302/1358-992x.2024.16.030 https://doi.org/10.1302/1358-992x.2024.16.030