The baseline: when hip replacement becomes the right conversation

The first question is a simple but important one: does the hip joint itself qualify for replacement? Before the choice of surgical approach matters at all, two clinical criteria must both be met.

First, imaging should confirm advanced joint destruction — typically Kellgren-Lawrence grade 3 or 4, meaning significant loss of joint space and structural damage visible on X-ray. Second, that damage must be causing pain or functional loss that an adequate trial of conservative treatment has not resolved. In practice, that means at least three to six months of physiotherapy, anti-inflammatory medication, and where appropriate, joint injections, without sufficient improvement.

The most common underlying diagnosis is osteoarthritis, but avascular necrosis, rheumatoid arthritis, and joint damage following a hip fracture all follow the same two-part logic: joint destruction confirmed on imaging, conservative options exhausted.

SPAIRE is a modified approach to total hip arthroplasty — not a separate operation. It changes how a surgeon accesses and reconstructs the joint, not whether replacement is warranted in the first place. Once general eligibility is established, the more personalised question of which surgical approach best suits the individual patient can then begin.

Patient profiles that suit SPAIRE particularly well

Several distinct patient groups, all of whom already meet the replacement threshold, tend to gain specific additional benefit from SPAIRE's tendon-preserving posterior route.

Active and sporty patients are often described as ideal candidates. Preserving the piriformis and obturator internus tendons keeps the hip's natural stabilising mechanics intact from the outset, supporting earlier return to movement and physical activity. Kumar et al. (2024) confirmed that this minimally invasive tendon-sparing approach provides excellent hip stability and early return to pre-injury activities — an outcome that matters most to patients who want to remain active after surgery.

Patients with higher BMI or significant abdominal girth are well suited because SPAIRE uses a posterior route that does not require a specialised traction table or depend on a slender abdominal profile. The direct anterior approach, by contrast, can present access difficulties related to body habitus; SPAIRE sidesteps that constraint entirely.

Those with complex bony anatomy — including severe hip dysplasia, Perthes disease, or slipped capital femoral epiphysis — may also benefit. The broad posterior exposure of SPAIRE accommodates difficult surgical access more reliably than approaches optimised for straightforward anatomy.

Elderly patients with femoral neck fractures requiring hemiarthroplasty represent a fourth group. This population already carries elevated dislocation risk, and preserving the short external rotators provides a meaningful mechanical safeguard at a stage of recovery when frailty limits other protective strategies.

Patients who want to avoid strict post-operative movement precautions — no hip flexion beyond 90°, no crossing the legs — may also be a natural fit. Because the posterior stabilisers are left intact rather than divided, those restrictions can often be relaxed in suitable individuals, reducing the dependency burden in the early weeks of recovery. Paus et al. (2025) found that SPAIRE patients achieved better functional outcomes, including walking speed, compared with those who received a lateral approach.

None of these profiles guarantee that SPAIRE is appropriate; anatomical suitability is confirmed at individual consultation through imaging and clinical assessment.

Why preserving the tendons makes a difference

The intact obturator internus tendon runs directly across the back of the femoral head, and when it remains undisturbed, it behaves as a natural tether — pulling the joint closed against posterior dislocation from the first moment after surgery. Surgeons describe this as the 'strap effect': a biological stabiliser that no reattachment technique can fully replicate once the tendon has been divided.

The second mechanism is neurological. Running within those preserved tendons are mechanoreceptors — Golgi tendon organs and muscle spindles — that give the hip a continuous ability to sense its own position. This proprioceptive feedback lets the body instinctively guard the joint from extreme ranges of motion, long before conscious thought intervenes. When those structures are severed in a traditional posterior approach, that reflex is lost until the tissues reheal — which is precisely why strict movement restrictions (no bending beyond 90°, no crossing the legs) have historically been necessary in the early weeks.

Together, mechanical tethering and preserved sensory feedback underpin both the lower dislocation risk and the earlier, more confident recovery associated with SPAIRE in published outcomes data. The anatomy does the protective work; that is what allows selected patients to move with greater freedom sooner.

When SPAIRE may not be the right fit

Not every hip that qualifies for replacement qualifies for SPAIRE. The technique is anatomy-dependent: whether the piriformis and obturator internus can be preserved is determined by the condition and configuration of each patient's posterior rotator complex — assessed through imaging and direct clinical examination at consultation — and some anatomies do not permit full tendon-sparing.

Standard hip arthroplasty contraindications apply regardless of which surgical route is taken. Active joint infection, uncontrolled systemic illness, and insufficient bone stock to anchor a stable implant are barriers to replacement itself; SPAIRE modifies how the joint is accessed, not what the joint must be capable of tolerating.

Some patients are also better served by a different approach altogether. Where a direct anterior route, a lateral approach, or SuperPATH offers demonstrably cleaner access for a particular anatomy — or where posterior visualisation is less reliable for a given hip geometry — those alternatives carry their own merits. No single approach is right for every hip, and surgeon judgement about which route best serves an individual's anatomy is the meaningful variable.

On the imaging review, the assessment looks beyond the degree of joint destruction to tendon condition and posterior muscle quality. A structurally compromised rotator complex may not deliver the 'strap effect' even if the tendons remain nominally intact, and identifying that before surgery — rather than discovering it intraoperatively — is precisely what the pre-operative workup is designed to establish.

How suitability is assessed in practice

The assessment at consultation moves through three overlapping stages. A detailed history comes first: the pattern and duration of hip pain, how far daily activities are curtailed, and which conservative measures — physiotherapy, anti-inflammatories, injections — have already been attempted. That history confirms whether the replacement threshold has genuinely been reached.

Imaging review follows. X-rays are graded against the Kellgren-Lawrence scale; the structural damage expected before arthroplasty is considered — significant joint-space narrowing and bony change at grades 3 or 4 — is assessed against the individual clinical picture, not as a standalone number. For SPAIRE specifically, the posterior rotator tendon anatomy is evaluated alongside joint destruction, because whether the piriformis and obturator internus can be preserved is an anatomical question that cannot be answered from symptoms alone. A tendon complex that appears preserved on imaging may still be structurally compromised in a way that limits the technique's applicability — which is why that judgement belongs to the operative consultation rather than to a checklist.

Clinical examination — range of motion, gait, and joint mechanics observed in person — rounds out the standard workup. Where it adds value, objective gait assessment using MAI Motion® can capture a functional baseline before surgery, giving a reference point for measuring recovery progress afterwards.

Professor Paul Lee's clinical approach, informed by his training at the Exeter Hip Unit under Professor Timperley and by published SPAIRE outcomes, shapes the assessment framework used at Hip Replacement Lincolnshire. Consultations are available at clinics in Sleaford (NG34) and Grantham (NG31), and patients do not need a GP referral to be seen.

What the current evidence shows — and its limits

The evidence supporting SPAIRE is real but proportionate. Kim et al. first described the technique in 2008, and it has since accumulated observational and short-term outcomes data at the Exeter Hip Unit and elsewhere. Kumar et al. (2024) confirmed in a published analysis that the tendon-sparing posterior approach provides excellent hip stability and early return to pre-injury activity. Paus et al. (2025) found that SPAIRE patients achieved better functional scores — measured by walking speed and standardised physical performance batteries — than those receiving a lateral approach. These are meaningful findings.

The gaps are equally real. Available studies are largely short-term and observational; no large randomised controlled trial has yet compared SPAIRE against the standard posterior approach over ten or more years of follow-up, so long-term implant survivorship specific to this route remains unconfirmed. Stratified data by precise sub-group — how outcomes vary across BMI bands or dysplasia severity grades, for example — are also sparse, which means counselling at those margins draws on surgical experience rather than published criteria.

For patients weighing these uncertainties, a few specific questions are worth raising at consultation: whether a surgeon's own case-series results align with published figures, how tendon quality will be evaluated before the operative approach is confirmed, and — for those particularly concerned about longevity — how implant choice, not just the surgical route, is expected to perform over decades.