Two routes into the same hip joint

If you have come across both 'SPAIRE' and 'lateral hip replacement' while researching your options, the first thing worth knowing is that they are not two different operations — they are two different routes into the same joint. The prosthetic components placed inside the hip are identical whichever route a surgeon takes. What differs is the path used to reach the joint, which muscles are disturbed along the way, and what that means for your nerves, your recovery, and the precautions you may need to follow afterwards.

The lateral approach — sometimes called the Hardinge approach after the surgeon who popularised it — enters the hip from the side. To create a clear view of the joint, the surgeon splits or partially detaches the front fibres of the gluteus medius and minimus, the main abductor muscles that sit at the outer side of the hip and pelvis.

SPAIRE (Save Piriformis And Internus, Repair Externus) is a modified posterolateral approach: it enters from the back of the hip. Rather than disturbing the abductor muscles, it works around them, preserving two key tendons — the piriformis and the obturator internus — intact throughout the procedure. The obturator externus is sectioned and then repaired at the end of the operation, which is where the 'Repair Externus' part of the name comes from.

Because the implants are the same, the long-term durability of the joint replacement is not determined by which route is used. The meaningful differences lie in which soft tissues are disturbed, which nerves are near the surgical field, and how the hip stabilises itself in the weeks and months that follow.

The superior gluteal nerve and lateral approach risk

Running on the deep surface of the gluteus medius, roughly 5 centimetres above the greater trochanter, is the superior gluteal nerve — the branch of the sacral plexus that provides motor power to the gluteus medius, gluteus minimus, and tensor fasciae latae. These are the muscles that hold the pelvis level each time your weight shifts onto one leg.

The anatomy creates a structural tension within the lateral approach. Reaching the hip joint from the side requires splitting or retracting the gluteus medius, and the further that retraction extends above the greater trochanter, the closer the surgical field comes to the superior gluteal nerve. If retraction reaches or exceeds the nerve's position, traction injury or, in more severe cases, division of the nerve can occur. Experienced surgeons work within established safe-zone limits to reduce this risk, and in skilled hands the complication is not inevitable — but it is an anatomical constraint that is intrinsic to how the lateral approach gains its exposure, not an avoidable technical error.

Injury to the superior gluteal nerve weakens the abductor muscles on the operated side. In practical terms, this shows up as Trendelenburg gait: a characteristic dip of the pelvis toward the unsupported side with each step, because the operated leg's abductors can no longer hold the pelvis horizontal during single-leg stance. For some patients the weakness resolves; for others it persists.

SPAIRE and conventional posterior approaches work entirely behind the hip, leaving the abductor mechanism undisturbed. The superior gluteal nerve is not in the surgical field, so this particular risk does not arise. That distinction is the central nerve-related tradeoff between the lateral route and posterolateral alternatives such as SPAIRE.

How SPAIRE stabilises the hip without reattachment

Behind the hip joint, the short external rotators — the piriformis, obturator internus, and gemelli — function as dynamic stabilisers, drawing the femoral head firmly into the acetabulum with each movement. Because SPAIRE leaves these tendons completely intact, two compounding advantages follow.

The first is mechanical. The obturator internus tendon takes a curved path around the lesser sciatic notch and inserts on the greater trochanter, passing directly over the posterior femoral head close to the joint's centre of rotation. When the tendon is preserved, it acts as a biological tether: an always-present passive restraint that physically resists the femoral head moving backward out of the socket. This is what clinicians refer to as the 'strap effect'. Standard posterior approaches cut these same tendons to gain access and then reattach them at closure — meaning that until the repaired tissue heals and regains tensile strength, the posterior tether is functionally absent.

The second advantage relates to proprioception — the joint's ability to sense its own position and resist unsafe movements automatically. Golgi tendon organs and muscle spindles embedded in the preserved short external rotators send continuous sensory signals to the nervous system, so from the moment a patient wakes from surgery the hip is not neurologically blind to its own position. Clinicians believe this continuity helps the joint instinctively resist subluxating positions before voluntary muscle control is fully re-established. That mechanism, while anatomically plausible and clearly articulated, has not yet been confirmed by direct measurement in controlled trials — the anatomy supports the hypothesis rather than settling it. Together, preservation of both the mechanical tether and the sensory architecture of the posterior soft tissues represents a meaningfully different starting point compared with standard posterior hip replacement.

Dislocation risk and early recovery differences

Translated into the first weeks after surgery, these structural differences matter in practical ways for both patient and surgeon.

Historically, standard posterolateral approaches have carried dislocation rates in the range of 0.5–3%, somewhat higher than the lateral approach, which benefits from the intact abductor mechanism holding the hip anteriorly. SPAIRE is designed to close that gap from the posterior side: by preserving the obturator internus tether and proprioceptive continuity described in the previous section, the hip's resistance to posterior subluxation is present from day one rather than depending on tendon-repair healing. No large prospective trial has yet compared SPAIRE directly against the lateral approach for dislocation outcomes; the comparison rests on mechanistic reasoning and observational data rather than head-to-head controlled results. Benchmark language is therefore more appropriate than specific comparative figures: SPAIRE targets the lower end of the posterior-approach dislocation range.

For patients recovering from a lateral approach, post-operative abductor function deserves attention even in the absence of frank nerve injury. Muscle splitting and retraction alone can temporarily weaken the gluteus medius, meaning that restoring a level, Trendelenburg-free gait may take longer to achieve regardless of whether the superior gluteal nerve was directly affected.

On the surgical side, SPAIRE's preserved posterior soft-tissue tension gives the operating surgeon meaningful tactile feedback during implant positioning — useful for judging leg length and femoral offset in real time, which directly affects the symmetry patients notice when they first start walking.

In suitable patients, the additional inherent stability of the SPAIRE approach means some of the strict early movement restrictions applied after traditional posterior replacement may be relaxed, supporting earlier functional confidence during rehabilitation.

Which patients suit each approach

Choosing between approaches is not a matter of one being universally superior — it is a question of which access route best matches an individual patient's anatomy, surgical history, and clinical priorities.

For most patients presenting with primary hip osteoarthritis and no significant prior surgery, SPAIRE's posterolateral route is anatomically flexible. It accommodates a wider range of body types and pelvic anatomies than the direct anterior approach and does not require a specialist traction table. Patients who might find anterior-approach positioning more demanding — those with higher body mass, particular pelvic geometry, or bilateral disease planned in stages — tend to fall comfortably within SPAIRE's accessible range.

The lateral approach occupies a different clinical niche. Where anterior stability is the dominant concern — for instance, in revision settings where the posterior soft tissues have already been disrupted — the anterior tension created by a lateral repair may take precedence. Similarly, when the abductor mechanism is already compromised by prior injury or surgery, the specific advantage SPAIRE offers over a lateral route is reduced, and surgeon judgement may favour the lateral as the more appropriate access strategy.

Both profiles carry caveats. Clinical guidelines do not yet specify which patients should have SPAIRE versus a lateral approach on the basis of comparative trial data; head-to-head published suitability criteria remain absent. Anatomy, surgical history, body habitus, surgeon training, and individual goals all factor into the decision. A specialist assessment — where a surgeon reviews imaging and functional status directly — remains the appropriate next step for any patient working through this choice.

Getting a specialist assessment in Lincolnshire

The comparison between SPAIRE and a lateral approach ultimately resolves not at the level of technique but at the level of individual anatomy, surgical history, and clinical priorities. No two hips present identically, and the considerations covered across this article — nerve risk, soft-tissue preservation, early stability, abductor recovery — carry different weights depending on a patient's specific circumstances. A thorough consultant assessment, grounded in imaging review and functional evaluation, is what translates general knowledge about each approach into a decision that fits a particular patient.

For patients in Lincolnshire or the wider non-London catchment who want to explore which approach may suit their hip, Hip Replacement Lincolnshire — part of the MSK Doctors group — offers consultant-led appointments at its Sleaford and Grantham centres without the need for a GP referral or NHS-style waiting. Prof Paul Lee, whose clinical expertise in the SPAIRE technique informs the content across this site, leads those assessments, bringing direct surgical experience to bear on approach selection, implant planning, and recovery expectations.

Appointments can be booked directly at hipreplacementlincolnshire.co.uk.

1. [1] Superior gluteal nerve. https://en.wikipedia.org/?curid=3934840 https://en.wikipedia.org/?curid=3934840