Why both techniques exist — and what they have in common

If a surgeon has mentioned both SPAIRE and STAR as options for your hip replacement, the first useful thing to understand is what they share — because it is considerable.

In a traditional posterior (back-of-hip) approach to total hip arthroplasty, the surgeon must cut through the piriformis tendon and several other small tendons at the back of the joint — known as the short external rotators — to reach the hip socket. These tendons are repaired at the end of the operation, but healing is variable. While they mend, the back of the hip lacks its normal structural support, which historically raised the risk of early dislocation and led surgeons to impose strict movement precautions for weeks afterwards: no bending the hip beyond 90 degrees, no crossing the legs, no certain sleeping positions.

Both SPAIRE and STAR were developed specifically to avoid that detachment. Each technique keeps the piriformis tendon intact throughout the operation, so it continues to act as a natural stabilising strap around the new hip joint from the moment surgery ends. A 2025 systematic review in EFORT Open Reviews found that piriformis-preserving posterior approaches, as a principle, are associated with improved hip stability and better postoperative outcomes across multiple named techniques.

One point patients sometimes misunderstand: neither technique uses a different or superior prosthetic implant. The artificial hip components — the socket, the ball, and the bearing surfaces — are identical to those used in a standard posterior replacement. What changes is how the surgeon reaches the joint, not what is placed inside it.

How SPAIRE works and where it comes from

The acronym itself is the clearest summary of what the technique does. SPAIRE — Save Piriformis And Internus, Repair Externus — describes a posterior hip replacement in which the piriformis and obturator internus tendons are left completely undisturbed throughout the operation. Only the obturator externus is detached and then repaired at the close of surgery.

The concept was first described by Kim et al. in 2008 as a Modified Posterior Approach, then formally named in a 2017 publication from the Exeter Hip Unit (PubMed ID 28218374). Professor Paul Lee trained at Exeter under Professor Timperley and performs SPAIRE as his routine approach to total hip replacement.

Preserving those two tendons matters beyond simple mechanics. Both the piriformis and obturator internus contain muscle spindles and Golgi tendon organs — mechanoreceptors that continuously signal joint position to the brain. A traditional posterior approach severs these structures, leaving the hip temporarily without that positional feedback until tissues heal. SPAIRE keeps the signalling intact from the moment surgery ends, which may contribute to the low dislocation rates reported in published series.

For suitable patients, intact tendons also reduce or eliminate the strict post-operative movement rules typically imposed after traditional posterior replacement — no hip flexion beyond 90 degrees, no crossing the legs. The tendons provide the protective function those precautions were designed to supply.

The most rigorous prospective evidence currently comes from the NIHR-funded HemiSPAiRE randomised trial, which compares SPAIRE against the lateral approach for hemiarthroplasty. No randomised controlled trial has yet compared SPAIRE directly with STAR.

How STAR works and where it comes from

STAR — Superior Transverse Anatomic Reconstruction, sometimes expanded as Superior Transverse Atraumatic Reconstruction — is a newer named technique whose publication record begins in 2022, originating primarily from US institutional centres including HSS and Johns Hopkins.

The anatomical scope differs from SPAIRE in a specific way. Rather than preserving the obturator internus, STAR retains the quadratus femoris alongside the piriformis, and conserves approximately two-thirds of the posterior joint capsule. The surgical corridor runs beneath the piriformis tendon — the joint is accessed without detaching it — which is a different anatomical route than SPAIRE uses but rests on the same founding principle of non-detachment.

The most detailed published outcomes come from a prospective single-surgeon cohort of 522 patients undergoing primary THA via the STAR approach between 2019 and 2023 (Kenanidis et al., 2024, mean follow-up 2.13 years). Mean hospital length of stay was 1.50 days. Across the full cohort there was one deep infection and one traumatic dislocation. Mean cup inclination was 42.8°, anteversion 19.9°, and mean leg-length discrepancy 3.3 mm. These figures reflect one surgeon's prospective series and should be read as early-to-mid-term data rather than a universal benchmark.

A March 2026 publication in Bone & Joint Open examined the transition from standard posterior to STAR, describing the learning curve as accessible for surgeons already experienced in the posterior approach — lower, in those terms, than switching to the direct anterior route. In terms of availability, Johns Hopkins lists STAR as currently practised at only a few centres in the United States, and documented UK uptake remains limited.

What the evidence actually shows — and what is still unknown

As of mid-2026, no published randomised controlled trial has directly compared SPAIRE and STAR. Any comparison draws on separate cohort datasets rather than controlled head-to-head outcomes — worth stating plainly before evaluating what the current evidence does show.

SPAIRE carries the longer publication record, formalised in 2017 following its 2008 origins. The NIHR-funded HemiSPAiRE trial is the first prospective randomised study of the technique, though it compares SPAIRE against the lateral approach for hemiarthroplasty rather than against STAR — a different research question to the one patients asking about this article's comparison most want answered.

STAR's principal evidence base is a single-surgeon prospective cohort of 522 patients (Kenanidis et al., 2024, mean follow-up 2.13 years) — one traumatic dislocation, one deep infection, and a mean hospital stay of 1.50 days across the full cohort. These are encouraging early-to-mid-term figures, but they come from a single centre and a single surgeon; multi-centre or randomised evidence for STAR does not yet exist.

Neither approach changes the core risk profile of posterior hip arthroplasty. Both carry the same possibilities as any THA: infection, venous thromboembolism, dislocation, leg-length discrepancy, and nerve injury. The approach label alters neither implant choice, anaesthetic risk, nor the principles of rehabilitation. Outcomes depend on individual anatomy, general health, implant selection, and surgical experience — not on which named piriformis-preserving technique a surgeon uses.

For patients weighing these options, the most defensible reading of the current evidence is that both techniques represent the same underlying principle applied with slightly different anatomical scope, practised by different surgical communities. Neither is demonstrably superior in published data. The practically useful question for any individual is whether the surgeon offering the procedure has genuine training and experience in the specific technique.

Patient suitability — who each technique suits and why it varies

The question most patients reach by this point is direct: which one should I have? The answer is that the technique is the surgeon's decision, not the patient's — but the reasoning behind that choice is worth understanding.

Both SPAIRE and STAR require workable posterior soft-tissue planes. Factors that may limit suitability for either include significant obesity, severe hip deformity, acetabular dysplasia, or prior posterior hip surgery that has left substantial scarring. In those situations, a different approach may be safer regardless of which named technique a patient has read about.

Where the two techniques may diverge in anatomical fit is their surgical corridor. STAR's route passes beneath the piriformis tendon, which must be mobile enough to retract safely; patients with prior posterior surgery, or anatomy that restricts sub-piriformis access, may find that corridor compromised. SPAIRE works in a slightly different plane — preserving the piriformis and obturator internus by keeping them attached throughout, rather than retracting beneath them — a different anatomical transaction that some surgeons describe as more adaptable to varied hip morphology. Whether this translates into a meaningful suitability advantage for specific patient profiles remains a matter of surgical judgement rather than published comparative evidence; no head-to-head data currently settles the question.

Geography is also a practical suitability factor. SPAIRE is the more established option within the UK, practised by trained consultants including Professor Paul Lee, whose approach is rooted in the Exeter Hip Unit tradition. STAR is currently concentrated in a small number of US centres, and documented UK uptake remains limited. For most patients in the UK, SPAIRE is simply the more accessible muscle-sparing posterior choice.

The decision follows thorough preoperative assessment — imaging, anatomy review, and functional evaluation. No patient should arrive at a consultation having selected a technique label; the surgeon's training, volume, and individual anatomy assessment determine which approach, if any, is appropriate.

Questions worth asking at your hip replacement assessment

Arriving at a surgical consultation with specific questions shifts the conversation from passive to informed. These are worth asking regardless of which technique is on the table:

• 'Do you offer a muscle-sparing posterior approach — and which one do you perform routinely?' Training and case volume in a named technique matter more than the technique's reputation.
• 'Am I anatomically suitable for a piriformis-preserving approach, and what would make me unsuitable?' Not every patient is a candidate; the honest answer is the useful one.
• 'What are your personal dislocation and complication rates for the approach you recommend?' Surgeon-level data, not published cohort averages, reflects what you can expect from that specific operator.
• 'Will I need strict hip precautions after surgery — and does your chosen approach change that?' The answer reveals how confident the surgeon is in the soft-tissue reconstruction.

Patients who want this kind of structured, consultant-led assessment without an NHS waiting list or GP referral can book directly through Hip Replacement Lincolnshire, part of the MSK Doctors group, at hipreplacementlincolnshire.co.uk.