Where SPAIRE and SuperPATH sit in the hip replacement landscape

When a surgeon mentions 'muscle-sparing hip replacement', patients often assume they are choosing between fundamentally different operations. In most cases, they are not. Both SPAIRE and SuperPATH are modifications of the posterior approach to total hip arthroplasty (THA) — the same family of surgery that has been used for decades, approached from the back of the hip with the patient lying on their side.

What separates these newer techniques from standard posterior THA is what they choose not to cut. The conventional posterior route severs the short external rotator tendons — the piriformis, obturator internus, and their neighbours — to gain access to the joint. Those tendons stabilise the hip mechanically and carry the nerve endings that tell the joint where it is in space. Dividing them leaves the hip both physically and neurologically exposed during the weeks of tissue healing that follow.

SPAIRE (Saves Piriformis And Obturator Internus with Repair of Obturator Externus) resolves this by keeping every major tendon intact throughout the procedure. SuperPATH takes a different route to the same goal, working entirely above the hip capsule through a small percutaneous incision without opening it at all. Both approaches aim to eliminate the strict post-operative movement restrictions that standard posterior THA has historically required and to shorten the overall recovery arc.

The choice between them is not simply a matter of preference. It turns on individual anatomy, how much surgical exposure the procedure demands, and how dislocation risk is best managed for a given patient — all of which the sections below address.

Dislocation risk after hip replacement: why the approach matters

'Will my hip dislocate?' is often the first safety question patients ask when weighing up surgical options — and rightly so. After standard posterior total hip arthroplasty, the risk is not theoretical. Post-operative dislocation peaks during the first 90 days, which corresponds to the biological timeline for severed capsular and tendinous tissues to heal. During that window the hip lacks both its mechanical restraints and the nerve receptors that would normally signal dangerous end-range positions.

The downstream consequences are serious. Once dislocation occurs, 57% of patients experience it more than once; 11% experience five or more events. Within two years of a first dislocation, 45.6% of patients require revision surgery — a significantly more complex procedure than the original replacement.

Not every patient carries the same level of risk. Multivariate analysis identifies female sex, age under 65, a BMI below 20, a high comorbidity burden, and the use of cemented prostheses as independent factors that increase dislocation likelihood. These patient-level variables compound whatever risk the surgical approach itself contributes.

Muscle- and capsule-sparing variants such as SPAIRE and SuperPATH were developed specifically to eliminate this vulnerable window by keeping the natural restraints in place from day one rather than waiting for healing tissue to restore them. Even so, the surgical approach is one variable among several: patient risk factors and accurate implant positioning remain relevant regardless of technique, and no approach reduces dislocation risk to zero.

How SPAIRE preserves the hip joint's natural restraints

The obturator internus tendon exits the pelvis through the lesser sciatic foramen and passes directly over the back of the femoral head before attaching to the greater trochanter. In standard posterior THA, it is divided to clear the field. In SPAIRE, it is left exactly where it is — and that single anatomical decision drives most of what distinguishes the technique clinically.

With the tendon intact, it functions as a natural seatbelt across the posterior hip joint. Muscle contraction and passive viscoelastic tension in the obturator internus create what the literature describes as a 'strap effect': a dynamic tether that actively resists the femoral head sliding backward out of its socket. No tissue healing is needed for this restraint to function, because nothing has been divided.

The same principle applies to the nerve receptors embedded within these structures. The Golgi tendon organs and muscle spindles in the preserved short external rotators continue transmitting positional signals the moment the patient wakes from anaesthesia. After conventional posterior THA, this proprioceptive feedback is absent until slow tissue regeneration restores some afferent pathways — leaving the hip unable to sense or reflexively resist dangerous positions during precisely the 90-day window established in the preceding section.

Because both the mechanical and sensory restraints remain in place, post-operative hip precautions — no bending past 90°, no crossing the legs, no internal rotation — are not required from day one. This supports earlier mobilisation and structured rapid-recovery discharge pathways for suitable patients.

SPAIRE also retains the full posterior exposure that makes the approach broadly applicable: complex anatomy, heavier patients, and cases requiring intraoperative extension are all accommodated, in contrast to SuperPATH's more restricted percutaneous access. Preserved posterior soft-tissue tension gives the surgeon direct tactile feedback for judging leg length and femoral offset — a cue lost when the posterior field is fully cleared — and is compatible with Mako robotic-arm assistance for sub-millimetre implant positioning. Across the published literature, dislocation prevention is the dimension on which SPAIRE's evidence base is most consistently reported, underpinned by these dual mechanical and neurological mechanisms.

SuperPATH's capsular approach: what it offers and where it is limited

SuperPATH (Supercapsular Percutaneously-Assisted Total Hip) takes a different structural philosophy to stability. Rather than opening the joint capsule at all, the surgeon works entirely above it — inserting instruments through a percutaneous incision of approximately 3 cm and manipulating the hip joint without ever breaching the capsular envelope. Where SPAIRE conserves the tendons while opening the capsule to access the joint, SuperPATH leaves the capsule itself completely undisturbed.

This distinction matters clinically. An intact capsule provides its own form of static restraint, enclosing the hip in its natural fibrous container. In selected patients with straightforward anatomy and a normal body habitus, this capsular preservation may be sufficient mechanical protection, achieving the same absence of post-operative restrictions that SPAIRE achieves through tendinous preservation — the feature patients notice most clearly.

The tradeoff is exposure. Working through a narrow percutaneous portal, the surgeon's view of the acetabulum and femoral canal is considerably restricted. Achieving accurate cup anteversion and femoral stem positioning under these conditions is technically demanding, and errors in component alignment carry meaningful dislocation and bearing-wear consequences. Outcomes depend closely on surgeon experience and case selection: the technique is better suited to patients with a normal BMI, uncomplicated bony geometry, and no previous hip surgery. In heavier patients or those with significant deformity, the restricted field becomes a practical constraint rather than a manageable inconvenience.

SuperPATH also requires dedicated specialist instrumentation that is not widely available outside high-volume units. No large randomised trials or registry studies directly comparing SuperPATH with SPAIRE have been published, and long-term survivorship data for the technique remain more limited than for established posterior approaches. It is best understood as a method with a genuine but narrowly defined indication profile — one that suits a specific patient group well, rather than a universal alternative to conventional hip replacement.

Patient suitability: which approach fits which clinical picture

Approach selection is rarely a patient choice — it is a clinical judgement shaped by anatomy, risk profile, and available technology. A concrete example illustrates the reasoning: a 58-year-old woman with a BMI of 31 who has undergone previous ipsilateral hip surgery sits at the intersection of several factors that favour SPAIRE. The prior hardware means adhesions and anatomical distortion are likely; SPAIRE's full posterior exposure allows the surgeon to address these without working blind. Her age and sex place her in the higher-risk group identified in the dislocation data discussed in section two, making preservation of the mechanical and proprioceptive restraints — rather than reliance on capsular healing — the more defensible strategy.

Contrast that with a 68-year-old man with a BMI of 24, straightforward acetabular geometry, no previous hip surgery, and no significant comorbidities. For this patient, SuperPATH's capsular-preserving approach may be technically appropriate, provided the operating team has sufficient case volume and dedicated instrumentation.

Patients at elevated dislocation risk — those whose profile matches the multivariate factors reviewed earlier — benefit most from an approach that leaves the natural restraints in situ from the outset, rather than one that depends on soft-tissue regeneration to recover that protection. SPAIRE's evidence base addresses this group most directly.

Where Mako robotic-arm assistance is available, it integrates with SPAIRE without compromising tissue preservation, adding sub-millimetre implant positioning to the technique's other advantages. That said, cup anteversion and stem alignment remain key predictors of dislocation risk regardless of which muscle-sparing approach is used — no technique removes the importance of accurate component positioning.

Determining which approach is appropriate requires a specialist assessment: a consultant can weigh anatomy, risk profile, and surgical history together in a way no checklist can replicate.

Getting a specialist assessment for muscle-sparing hip replacement

About this resource and clinical assessment

The clinical guidance throughout this article reflects the specialist practice of Professor Paul Lee, a consultant orthopaedic surgeon whose work centres on muscle-sparing hip arthroplasty and SPAIRE technique.

Determining which approach — SPAIRE, SuperPATH, or an alternative — is appropriate for a given patient requires a consultant-led review of imaging, anatomy, and individual risk profile. That assessment cannot be replicated by a self-referral checklist or a phone consultation; it draws on the full clinical picture.

Hip Replacement Lincolnshire, part of the MSK Doctors group, sees patients at centres in Sleaford and Grantham. No GP referral is required, and there are no NHS-style waiting lists. Where relevant, assessment may include MRI review and objective biomechanical evaluation. Patients from across Lincolnshire and the wider non-London catchment are welcome.

Book an assessment at hipreplacementlincolnshire.co.uk.