Why SPAIRE is not a universal solution

SPAIRE's two defining benefits — the 'strap effect' created by the preserved obturator internus tendon, and the proprioceptive feedback from intact mechanoreceptors — depend entirely on a biological substrate: healthy, functional short external rotator tendons in the right anatomical setting. When that substrate is absent or inaccessible, the core rationale for choosing SPAIRE disappears. Three broad categories can bring a patient outside SPAIRE's operating envelope: revision hip arthroplasty, where prior surgery has typically already scarred or divided the relevant tendons; severe anatomical complexity, where structural deformity demands wider surgical access than the technique's tissue-preservation window permits; and individual patient factors, including pathologically compromised rotators that offer nothing to preserve even if technically intact. Each is examined in the sections below. Acknowledging these limits is not a qualification of SPAIRE's merits — it is the basis of responsible approach selection, in which anatomy and surgical history determine the technique, not the other way around.

Revision hip arthroplasty — the clearest case against SPAIRE

When a first hip replacement has failed and needs to be replaced or revised, SPAIRE is not the right approach — and the reasons are structural.

Revision hip arthroplasty is a categorically different operation from primary surgery. Extracting failed implant components, addressing bone-stock defects, and navigating layers of scar tissue from the original procedure all demand a wider surgical opening than SPAIRE's tissue-preservation window allows. Revision-specific tools — modular tapered stems, bone augments, acetabular cages — require the surgeon to have substantial freedom of movement around the joint, which is precisely what SPAIRE deliberately limits.

The second problem goes to the heart of what makes SPAIRE work. The 'strap effect' depends on intact piriformis and obturator internus tendons generating a dynamic biological tether. In a revision patient, those tendons are almost certain to be scarred, previously divided, or functionally attenuated from the primary operation. The biological substrate the technique relies on no longer exists in a form that can be preserved — or meaningfully benefits from preservation.

In revision cases, a conventional extensile posterior approach or another approach with wider access is used instead. These are well-established in revision practice and appropriate to the task. Suitability for any approach in revision surgery is assessed individually, taking into account what the previous operation involved, the degree of bone loss, and the patient's overall condition — a process that Prof. Paul Lee works through at consultation before any revision plan is confirmed.

Severe hip deformity and structural anatomy limits

Structural anatomy sets the outer boundary of what SPAIRE can safely achieve. The technique works within a defined soft-tissue window, and when the hip's geometry falls outside that window — through deformity, prior surgery, or degraded tissue — the surgeon requires more space and more visual freedom than the approach allows.

High-grade acetabular dysplasia is one clear example. In Crowe III or IV dysplasia, the socket sits in an abnormal position and femoral geometry is frequently altered; correcting this may require a subtrochanteric osteotomy to manage leg-length and femoral alignment. Operations of that complexity demand a surgical field that extends well beyond SPAIRE's tissue-preservation corridor. Severe protrusio acetabuli — where the femoral head migrates medially into the pelvis — creates a three-dimensional reconstruction challenge that similarly requires broader access to achieve stable implant seating.

Prior peri-articular osteotomy, such as a periacetabular or femoral osteotomy performed earlier in life, can substantially distort proximal femoral and acetabular geometry. A comparative study in patients undergoing total hip arthroplasty after failed hip-preservation surgery found that the posterior approach was associated with longer operative time and greater intraoperative blood loss in distorted anatomy — a reminder that previous surgery around the hip raises the operative stakes for any subsequent posterior-window approach.

The calcified or ossified short external rotator illustrates a different category of limit. Heterotopic bone within the posterior soft tissues can physically obstruct the surgical corridor, and a tendon that is calcified, ossified, or severely wasted cannot generate a strap effect regardless of whether it remains anatomically in place. Preserving non-functional tissue confers no protective benefit.

No fixed published threshold defines precisely when anatomy becomes too complex for SPAIRE. These judgements are made case by case, using imaging review and clinical examination, before any approach is confirmed.

Body habitus and individual patient risk factors

Patient factors sit alongside anatomy and procedural complexity in the pre-operative picture — they shape risk rather than simply disqualify. Several recognised compounding factors for dislocation risk in hip arthroplasty — low BMI (under approximately 20), younger age, female sex, and a higher comorbidity burden — warrant careful approach planning without automatically ruling out any particular technique.

BMI is the most discussed patient variable in the context of posterior-window approaches. SPAIRE is more accommodating of body-type variation than the anterior (DAA) approach, which can become technically demanding in larger patients and requires a specialised traction table that introduces its own anatomical constraints. Even so, very high BMI adds tissue depth to the posterolateral field and can limit the working space available through any posterior window — SPAIRE included. The extent to which this matters varies between individuals and is assessed through imaging before a surgical plan is confirmed.

None of these variables is, in isolation, a hard exclusion. They are risk-stratification signals that a surgeon weighs collectively: a patient with a high comorbidity score but otherwise straightforward hip anatomy presents a different calculation from one whose comorbidity coincides with structural complexity. Pre-operative assessment — imaging, clinical examination, and a detailed history — is where those signals are read together and a suitability decision is reached.

Surgeon training as a non-negotiable requirement

Technical difficulty is the thread connecting all the limitations covered so far. Even when anatomy and patient factors suggest SPAIRE is appropriate, the approach demands a level of surgical familiarity that goes beyond competence in posterior hip arthroplasty generally.

SPAIRE is a fellowship-level technique. Prof. Paul Lee's training under Prof. Timperley at the Exeter Hip Unit reflects the kind of structured specialist pathway the approach requires — one where the surgeon has learned not just the steps, but also the anatomical judgements that make those steps safe. Attempting a muscle-sparing posterior approach in anatomy that strains the technique's limits, without that grounding, compounds both problems: implant positioning may be compromised, and the deliberate tissue preservation can become inadvertent tissue damage.

Robotic assistance — such as Mako — can offset some of the visualisation constraints that come with a smaller soft-tissue window in suitable primary cases. What it cannot do is substitute for the pre-operative decision about whether SPAIRE is the right approach in the first place. That judgement belongs to the surgeon, and it rests on experience with the technique specifically.

Patients comparing surgeons or clinics are well placed to ask directly about SPAIRE case volume and training background — not merely whether a surgeon uses a posterior approach.

How suitability is assessed — and what happens next

For any patient uncertain whether SPAIRE applies to their situation, the answer comes through assessment rather than self-screening. Pre-operative workup typically involves plain X-ray at minimum, with CT or MRI where the anatomy warrants closer scrutiny, alongside a structured clinical examination and history. The variables that actually determine suitability — soft-tissue integrity, degree of structural deformity, prior surgical history — only become legible when imaging and direct clinical assessment are read together.

Where the conclusion is that SPAIRE is unsuitable, a well-conducted consultation should produce a clear alternative recommendation rather than leave a patient without direction. The standard posterior, lateral, and anterior (DAA) approaches each carry defined indications; a surgeon who understands SPAIRE's limits is well placed to explain why a different approach better serves a particular patient's anatomy and history.

Hip Replacement Lincolnshire, part of the MSK Doctors group, provides consultant-led hip arthroplasty assessments at its Sleaford and Grantham centres without requiring a GP referral. Questions about surgical approach — including when SPAIRE is and is not the appropriate choice — are addressed as part of the clinical consultation rather than deferred to a separate appointment.