The short answer: two firm exclusions

Not everyone is a SPAIRE candidate, but the exclusions are more specific than many patients expect. Two contraindications are stated clearly in clinical practice.

The first is revision hip surgery — patients having a repeat replacement on a side that has already been operated on are not offered the SPAIRE approach. The second is anatomy or prior surgery that makes the muscle-sparing posterior route less safe: if the tissue planes that SPAIRE depends on cannot be navigated without compromising implant positioning or patient safety, the technique is not used. As the platform states, SPAIRE preserves the piriformis and obturator internus 'where it can be done safely' — that qualifying phrase matters.

Beyond these two, there is no published blanket exclusion list. No universal BMI cut-off, no fixed deformity score, no rule that applies without reference to an individual patient's imaging and physical findings. Suitability is a clinical decision reached at consultation — not a checklist a patient can complete in advance.

Patients who fall outside SPAIRE candidacy are not left without options. The approach affects only the surgical access route — the prosthesis itself is unchanged — so a conventional total hip replacement via an alternative approach remains available and clinically appropriate.

Why revision hip surgery rules out the SPAIRE approach

The reason is structural. SPAIRE works by navigating precise soft-tissue planes around the back of the hip — specifically the piriformis and obturator internus tendons — which must be identifiable, mobile, and intact for the technique to proceed as planned. A hip that has already been operated on carries scar tissue in exactly these zones. That scar tissue binds natural tissue planes together, making them unreliable as surgical landmarks and increasing the risk of inadvertent damage when attempting to separate them.

Revision cases are also more demanding in scope than primary replacements. Removing a previously implanted prosthesis may require extended femoral access, bone grafting where the original implant has caused bone loss, or longer revision-specific components. These demands call for wider surgical exposure than a muscle-sparing posterior portal can provide. The tissue-preservation logic that defines SPAIRE cannot simultaneously deliver the access that revision work requires.

For patients in this position, the absence of SPAIRE reflects an accurate match between technique and task — not a lesser standard of care. Revision hip surgery is managed through conventional approaches that are built for precisely this level of complexity.

Anatomy that makes the approach less safe

Several anatomical presentations can shift the risk calculus enough to make SPAIRE unsuitable. The most significant is severe hip dysplasia — a condition in which the acetabular socket is shallow, underdeveloped, or oriented abnormally, often combined with excess femoral neck anteversion. In cases where this distortion is marked, placing the acetabular cup at a safe and functional angle may require access or bony reconstruction steps that a muscle-sparing posterior portal cannot accommodate without compromising either implant positioning or the tendon preservation that defines the technique.

Structural deformity from other sources carries similar implications. Femoroacetabular impingement (FAI) with substantial bone irregularity, post-traumatic change — where a previous fracture has altered the proximal femur or acetabulum — and high hip dislocation can each distort the landmarks that SPAIRE depends on. When these changes are present, safely keeping the piriformis and obturator internus intact may conflict directly with achieving the implant position the hip actually needs.

Pre-operative imaging — typically plain X-ray, and MRI where soft-tissue or bony detail warrants it — is how these factors are identified. No published scoring cut-off defines the point at which dysplasia or deformity tips the balance; the phrase in clinical use is 'where it can be done safely', and that judgement rests on what the images show for that particular hip.

For most patients presenting with primary osteoarthritis, none of these anatomical complications are present. Routine X-ray appearances are more often sufficient to confirm SPAIRE eligibility than to exclude it.

Body habitus: what the evidence actually shows

Among patients considering a minimally invasive hip replacement, one of the most common concerns is whether their body size rules them out. The evidence points in the opposite direction to what many expect: SPAIRE is described in clinical practice as working across a wider range of body types and pelvic anatomies than the anterior (DAA) approach — the other minimally invasive option patients most often encounter. The anterior technique can be more technically demanding in larger patients and, in many settings, requires a specialised orthopaedic traction table that introduces its own anatomical constraints. SPAIRE avoids both.

No published BMI threshold defines the point at which SPAIRE becomes unsuitable. Body habitus is one of the factors reviewed at pre-operative assessment, not a fixed number applied as a gate. What is true across all hip replacement approaches — not SPAIRE specifically — is that marked obesity increases soft-tissue depth around the hip joint and adds broader surgical and anaesthetic risk that the full clinical team weighs during pre-operative planning.

This has a concrete implication for patients who have previously been told they are not suitable for a minimally invasive technique: that judgement may have been made in the context of an anterior approach. Patients offered a conventional replacement on those grounds can ask whether SPAIRE, reviewed at a separate consultation on the basis of their own imaging and anatomy, might be a viable alternative.

SPAIRE suitability does not replace standard hip replacement criteria

Suitability for SPAIRE sits within a broader question that comes first: is hip replacement indicated at all?

The standard threshold for any total hip replacement — including SPAIRE — requires persistent pain that has not responded adequately to conservative management, confirmed joint deterioration on imaging, fitness for anaesthesia, and realistic expectations about recovery. SPAIRE does not alter any of these criteria. It changes only the surgical route used to reach the joint; the same prostheses, the same implant-selection principles, and the same pre-operative planning apply regardless of which approach is used.

This creates a practical distinction worth separating clearly. A patient whose hip arthritis has not yet reached the point where replacement is clinically justified is not a SPAIRE candidate — but the reason is that hip replacement itself is not yet indicated, not that SPAIRE is technically unsuitable for them. Conversely, a patient who meets the standard threshold but whose anatomy rules out SPAIRE may still proceed to hip replacement via a conventional approach.

Thinking of it as two sequential questions makes the distinction concrete: first, does this hip need replacing? Second, if yes, which access route is safest for this particular anatomy? SPAIRE belongs entirely to the second question.

How suitability is assessed in practice

The decision about whether SPAIRE is appropriate is made at consultation, not in advance. Professor Paul Lee's assessment process at Lincolnshire Hip combines clinical examination with pre-operative imaging to determine whether the piriformis and obturator internus can be preserved safely, and whether the posterior muscle-sparing route offers any structural advantage for that particular hip.

For patients whose anatomy does not support SPAIRE, the consultation does not end there. Alternative approaches — a standard posterior, lateral, or anterior technique — are reviewed on the same evidence base, and there is no dead-end outcome. Lincolnshire Hip is part of the MSK Doctors group and accepts patients without referral for hip assessment, which is a practical option for anyone uncertain whether their situation might qualify before asking a GP for a pathway.

What the assessment process ultimately reflects is the principle this article has traced from the outset: SPAIRE is one technique among several, applied where anatomy supports it and withheld where it does not. The two firm exclusions — revision surgery, and anatomy or prior scarring that makes the muscle-sparing approach unsafe — define the boundaries of a surgical tool, not the boundaries of what is achievable for any given patient.