SPAIRE is an approach, not a separate procedure

The question many patients arrive with — 'Can I have the SPAIRE technique?' — actually has two parts to it, in a specific order.

SPAIRE is a surgical approach: a route the operating surgeon uses to reach and replace the hip joint. It is not a different type of implant, a separate category of operation, or an elective upgrade that can simply be requested. The hardware placed during a SPAIRE procedure — the socket, stem, and bearing surface — is the same as in any total hip arthroplasty.

The first decision is whether hip replacement is appropriate at all. The standard criteria apply: end-stage arthritis confirmed on imaging, significant pain and functional loss that affects daily life, and conservative management that has been tried without lasting benefit. SPAIRE does not change any of that threshold.

Only once THA candidacy is established does the choice of approach become relevant. At that point, SPAIRE is one option among several — including anterior, anterolateral, and standard posterior routes — and which is most appropriate depends on individual anatomy, the integrity of the posterior soft tissues, and surgical judgement. At Lincolnshire Hip, it is pre-operative imaging and anatomical assessment that determine whether SPAIRE can proceed as planned, not the patient's preference alone.

The anatomy SPAIRE relies on

The posterior capsule of the hip joint is reinforced by a cluster of short external rotator muscles — piriformis, obturator internus, obturator externus, and the paired gemelli — that together act as a natural restraint against the femoral head slipping backwards out of its socket. In a conventional posterior hip replacement, these tendons are released from the bone to open a clear route to the joint, then reattached once the prosthesis is in place. The reattachment heals, but the tendons' mechanical continuity has been interrupted.

SPAIRE — Save Piriformis And Internus, Repair Externus — takes a different path through the same anatomy. The piriformis and obturator internus tendons remain attached to the bone throughout the operation; only the obturator externus is divided and then repaired at the end. Because the main posterior stabilisers are never detached, the restraint they provide is intact from the moment the patient leaves the operating table. In practice, this supports earlier confident weight-bearing and is intended to reduce the risk of early posterior dislocation in suitable patients.

The technique was developed and published at the Exeter Hip Unit, one of the UK's most respected centres for hip surgery. Professor Paul Lee trained there under Professor Timperley, who established SPAIRE — the clinical background that informs its use at Lincolnshire Hip.

That same anatomical logic — working around intact tendons rather than through detached ones — also shapes when the approach can proceed as planned and when it cannot, which is what the next section examines.

What BMI means for SPAIRE planning

Published figures give a clearer picture of BMI's role than many patients expect. Surgical complications after total hip arthroplasty begin rising from a BMI of 32; periprosthetic joint infection risk increases sharply above 37.4 kg/m². Those numbers apply to any approach to hip replacement — they represent the background risk that shapes how a surgeon weighs the decision, irrespective of technique.

Where BMI class matters further is in the pattern of how implants fail over time. Patients with morbid obesity are approximately 90% more likely to need revision surgery for infection compared with normal-weight patients, while underweight patients face a 131% higher risk of revision for dislocation and a 63% higher risk of periprosthetic fracture. For an approach whose central aim is posterior stability, that dislocation-risk gradient at the lower end of the BMI range is worth noting in the planning conversation.

What high BMI alone does not do is disqualify. A 2017 published series reported SPAIRE used for hemiarthroplasty irrespective of skeletal dimension and BMI. That cohort involved acute hip fractures rather than elective total hip replacement for arthritis — soft-tissue geometry and exposure planning differ between the two contexts — but the finding does indicate the technique is not inherently foreclosed by body size. No SPAIRE-specific BMI threshold has been formally published for elective THA.

Functional outcomes point in a similar direction: patient-reported scores after THA do not consistently vary by BMI class, and higher-BMI patients in some cohorts reported greater absolute improvements at 90 days. BMI enters the planning picture as one variable that changes the operative conversation — not one that predetermines the answer.

Skeletal anatomy and structural factors that affect access

Anatomy shapes access before any incision is made. SPAIRE works by working around intact tendons — which means the posterior soft-tissue corridor must be clear enough to allow that. Several structural variables can narrow or distort that corridor in ways that shift the surgeon's thinking.

Hip dysplasia is the most consequential of these. Where the acetabulum is shallow or abnormally oriented, the working angles needed to seat the cup accurately can conflict with keeping the piriformis and obturator internus in place throughout the procedure. Significant dysplasia may therefore steer the approach toward an anterior or anterolateral route, where visualisation of the acetabulum is less constrained by posterior anatomy — not because SPAIRE is impossible in principle, but because the geometry changes what 'safely' means in practice.

Prior surgery through the posterior approach presents a different problem: the short external rotators and posterior capsule may already be scarred or mechanically altered. Where those structures have been substantially compromised, preserving them confers less of the stability benefit that distinguishes the technique — and an approach offering wider intraoperative visualisation may serve the revision context better.

SPAIRE is described as preserving the posterior structures 'where it can be done safely'. Pre-operative imaging — CT or MRI — is what tells the surgical team whether that condition is met: it shows the acetabular shape, the orientation of the posterior rim, the state of the soft tissues, and any bony deformity that changes the working corridor. No published guideline has formalised which dysplasia grades or deformity patterns foreclose the approach; what the imaging surfaces is the specific structural picture that makes approach selection, in each case, an informed rather than assumed decision.

Cases where a different approach may suit better

Choosing a different route to the hip is not a fallback — in certain clinical circumstances, it is the more deliberate plan. A published 2023 case report illustrates this with useful specificity: a patient at heightened risk of anterior dislocation, owing to a habitual pattern of sitting cross-legged, was treated using a modified rather than an abandoned SPAIRE approach. The surgical team adapted the technique to suit that individual's anatomy and lifestyle risk profile, demonstrating that SPAIRE occupies a spectrum of application rather than a binary in-or-out decision.

Where the posterior route is set aside entirely, the clinical trigger usually involves either tissue access or tissue quality. An anterior or anterolateral approach may offer a more favourable soft-tissue interval in cases of extreme obesity, where the anterior plane into the hip can provide a cleaner working corridor than the posterior aspect through a larger soft-tissue mass. Anterior-based muscle-sparing approaches also have a documented evidence base in conversion surgery — removing a failed resurfacing or revising a prior arthroplasty — where wider intraoperative visualisation of the acetabulum tends to outweigh the benefit of posterior tendon preservation.

The practical upshot is that a patient who is not a SPAIRE candidate remains, in most cases, an excellent candidate for hip replacement: the decision shifts to which access route best serves their particular hip geometry, implant requirements, and soft-tissue situation. What the pre-operative workup is identifying, in these cases, is not a reason to avoid surgery — it is the specific combination of approach and implant most likely to produce a stable, well-functioning joint.

How suitability is confirmed in practice

For most patients arriving with a diagnosis of hip osteoarthritis, the question of which surgical approach will be used is not resolved until a face-to-face assessment — and that sequencing is intentional. The consultation reviews the whole clinical picture: arthritis severity and pattern, symptom burden, general health, BMI, and any prior surgery to that hip.

Pre-operative imaging is where the structural assessment becomes specific. X-rays establish bony geometry; MRI or CT can detail the soft-tissue corridor, acetabular orientation, and the condition of the posterior structures that SPAIRE relies on. What the imaging shows — not a general expectation about the technique — is what tells the surgeon whether the posterior approach is well-suited or whether a different route will serve the hip better.

Approach selection is part of that consultation, not a decision presented without explanation. Patients can reasonably expect to understand what is proposed and why — including which anatomical or health factors have shaped that recommendation.

Lincolnshire Hip is part of the MSK Doctors group and accepts patients without GP referral for hip assessment, with local access in Sleaford and Grantham. The goal throughout — in assessment as in surgery — is to treat the specific hip in front of the surgeon: reading what the anatomy and clinical picture actually call for, rather than applying a fixed method regardless of what they show.

1. [1] Details of a Tendon–Sparing Posterior Approach in Hemiarthroplasty in the Treatment of Displaced Intracapsular Neck of Femur Fracture. (2017). https://doi.org/10.4172/2167-7921.1000243 https://doi.org/10.4172/2167-7921.1000243
2. [2] The Modified Spare Piriformis and Internus, Repair Externus Approach for Hip Arthroplasty. (2023). https://doi.org/10.7759/cureus.34999 https://doi.org/10.7759/cureus.34999