What makes SPAIRE different — and why its trade-offs matter

SPAIRE — Saves Piriformis And (Obturator) Internus with Repair of (Obturator) Externus — is a muscle-sparing variant of the posterior approach to hip arthroplasty, not a fundamentally different operation. Where a conventional posterior approach divides the deep external rotator tendons to widen the surgical field, SPAIRE leaves the piriformis and obturator internus intact and repairs the obturator externus, preserving the soft-tissue structures that stabilise the joint from behind.

That single decision — cut or preserve — is the source of both the technique's strengths and its constraints. Intact tendons maintain the Golgi tendon organs and muscle spindles that deliver continuous proprioceptive feedback, which is thought to contribute to the low dislocation rates associated with the approach. Yet those same uncut structures narrow the surgeon's direct line of sight into the operative field, creating a technical demand that simply does not arise when the tendons are divided and moved aside. Stability is gained precisely because nothing is cut — and that is also what makes the exposure tighter.

The visualisation trade-off: what surgeons see less of, and why it matters

Those preserved tendons sit directly in the surgeon's line of sight. In a standard posterior approach, the piriformis and obturator internus are divided and moved aside, opening a wider corridor into the acetabulum and femoral canal. SPAIRE leaves them in place, which means the surgeon works around intact structures rather than through a cleared field.

The practical consequence is a shift in how key intraoperative measurements are made. Leg-length and femoral-offset assessment — critical to avoiding a postoperative limb-length discrepancy — cannot depend on the same broad visual landmarks available in a more open exposure. Instead, the surgeon draws on the preserved posterior soft-tissue tension as an intrinsic anatomical reference: that intact tissue provides tactile feedback that has been described as a reliable guide for judging both length and offset during implant positioning.

This is a technique-level constraint rather than a safety compromise — one that experienced SPAIRE surgeons account for in their workflow. The principal technological mitigation is Mako robotic-arm assistance, which delivers sub-millimetre precision for bone resection and implant placement and has been described as able to offset the narrower visual window entirely. That said, robotic support is not a prerequisite. A 2024 prospective case series by Kumar et al. (n=35), performed with conventional instruments by a single trained surgeon, recorded no periprosthetic fractures or sciatic nerve injuries and a mean time to orthotic-assisted ambulation of 1.5 days — demonstrating that, in appropriately trained hands, the narrower field of view can be managed without robotic assistance.

Why SPAIRE demands specific surgeon training

Not every posterior-approach surgeon performs SPAIRE. The technique demands a deliberate recalibration of intraoperative method — and that distinction matters when patients are choosing who should operate on them.

The core challenge is a shift in spatial awareness. Where standard approaches give surgeons a broad visual corridor, SPAIRE requires confidence in tactile and landmark-based cues from the outset. Surgeons must translate what they feel through preserved tissue tension into reliable positional judgements — a skill that develops through supervised operative experience, not from reading a manual.

The Exeter Hip Unit is where the technique was formalised and published in 2018, and fellowship-level mentorship under an experienced SPAIRE practitioner has become the established learning pathway. Professor Paul Lee's training at Exeter under Professor Timperley reflects that model: surgical familiarity built case by case under direct supervision, before being carried into independent practice.

That learning curve is meaningfully different in character from the one associated with the direct anterior approach (DAA), which requires surgeons to navigate an anatomical corridor that most posterior-trained arthroplasty surgeons have never worked in. SPAIRE's challenge, by contrast, lies in perceptual retraining within a posterior corridor that is already familiar — a narrower ask, even if still a real one.

For patients, two questions are worth raising with any surgeon offering SPAIRE: where did they complete their training in the technique, and how many SPAIRE procedures do they currently perform each year?

Patients for whom SPAIRE may not be the right choice

SPAIRE suits the majority of patients requiring hip arthroplasty — but not all. Several clinical factors can make a different approach the safer choice.

Active infection is an absolute bar. Any active local or systemic infection disqualifies elective hip arthroplasty by any approach, including SPAIRE; this is a general arthroplasty contraindication rather than a technique-specific one.

Beyond infection, three further categories warrant careful evaluation:

• Complex deformity or significant anatomical distortion. Severe dysplasia, post-traumatic remodelling, or marked bone loss around the acetabulum can demand the wider operative corridor that a standard posterior, lateral, or extensile approach provides. SPAIRE's narrower field — a feature that protects soft tissue in typical anatomy — becomes a constraint when greater intraoperative exposure is needed to navigate safely.
• Severely compromised bone quality. Advanced osteoporosis or substantial bone loss may require greater intraoperative flexibility and direct visualisation during implant fixation than the muscle-sparing exposure reliably allows.
• Prior disruption of the relevant posterior tendons. The technique's passive stability relies partly on the obturator internus functioning as a posterior tether — referred to as the 'strap effect'. Patients who have previously undergone posterior hip surgery in which the piriformis or obturator internus was divided no longer have the intact tissue geometry this mechanism depends on; working around structures that have already been divided does not reproduce the intended effect.

The evidence behind these limits deserves an honest note. Published guidance on SPAIRE-specific contraindications is largely expert consensus and observational rather than derived from randomised controlled trials. The technique was formally named and described at the Exeter Hip Unit as recently as 2018, and long-term comparative outcome data remains limited. These categories represent sound clinical reasoning — not contraindications confirmed by controlled head-to-head evidence.

How SPAIRE compares with other approaches at the point of decision

Every approach to hip arthroplasty involves a trade-off. Understanding those trade-offs side by side puts SPAIRE's visualisation limitation in its proper context — one constraint among several, each belonging to a different technique.

Standard posterior approach divides the piriformis and obturator internus tendons to create a wider operative field, giving surgeons broad visual access to the acetabulum and femoral canal. That exposure simplifies certain intraoperative judgements, but the severed tendons must be repaired at closure, and dislocation risk is higher if that repair fails or if the posterior capsule heals poorly.

Direct anterior approach (DAA) avoids the posterior structures entirely by working through a muscle interval at the front of the hip. It does not require tendon division, and some series report faster early recovery for selected patients. The counter-balancing constraints are significant: the DAA carries a steeper surgeon learning curve than posterior techniques, a documented risk of periprosthetic femoral fracture during canal preparation, and limited suitability for patients with larger body habitus or short femoral necks.

Lateral (Hardinge) approach offers good visualisation and is widely used, but requires splitting the gluteus medius — part of the abductor mechanism. Abductor weakness or a Trendelenburg gait pattern in the months after surgery is a recognised recovery challenge with this route.

SPAIRE stays within the posterior corridor — territory that most hip arthroplasty surgeons know — but preserves the tendons that a standard posterior approach divides. The narrower field of view that results is a real trade-off, addressed by tactile expertise and, where available, robotic assistance. The technique does not introduce an unfamiliar anatomical corridor, but it does require perceptual retraining.

No single approach is the right choice for every patient. Anatomy, bone quality, deformity, surgeon training, and available technology all bear on the decision — and different combinations of those factors point in different directions.

Asking the right questions before choosing SPAIRE

Three questions can cut through much of the uncertainty before any final commitment to surgical approach.

Has your surgeon completed dedicated SPAIRE training, and how many procedures do they perform per year? Fellowship-level grounding matters here more than in standard posterior surgery — the technique's learning curve involves a genuine shift in spatial awareness, not simply a modified set of steps applied in a familiar field.

Is robotic assistance available, and will it be used in your case? The Mako system addresses the technique's narrower operative window with sub-millimetre precision; knowing in advance whether it is part of the planned procedure shapes the intraoperative risk picture.

Does your specific anatomy and bone stock make SPAIRE a safe fit? Complex deformity, compromised bone quality, or a history of previous posterior hip surgery can change the calculus entirely. Pre-operative imaging and clinical assessment are the only reliable way to answer this.

Patients who would like a consultant-led evaluation — without a GP referral or NHS waiting list — can access that assessment through Hip Replacement Lincolnshire, part of the MSK Doctors group, at clinics in Sleaford and Grantham. The aim of such an assessment is not simply to confirm or rule out SPAIRE, but to establish whether the full balance of factors — preserved tendons, narrower field, individual anatomy, and surgeon experience — points toward it or toward a different approach altogether.