Two corridors, two sets of risks

Choosing between a SPAIRE hip replacement and the Hardinge (lateral) approach is not primarily a matter of surgical preference or tradition — it is a matter of which muscles the surgeon must move through to reach the joint, and what happens to those muscles as a result.

The lateral approach, developed by Hardinge and still widely used, enters the hip from the side. To create that corridor, the surgeon must split or partially detach the gluteus medius — the primary hip abductor — from the greater trochanter. The gluteus minimus is involved in the same manoeuvre. Disrupting these muscles is not incidental; it is the price of the route.

SPAIRE is a posterolateral approach: it reaches the joint from behind. Because it never enters the abductor compartment, the gluteus medius and gluteus minimus remain anatomically untouched. The muscles placed at potential risk instead sit at the back of the hip — the short external rotators, specifically the piriformis and the conjoint tendon of the obturator internus and gemelli. What distinguishes SPAIRE from the standard posterior approach is that it preserves even these: described originally by Kim et al. in 2008, SPAIRE keeps the piriformis tendon and obturator internus attached to bone throughout the procedure, sectioning only the obturator externus, which is then repaired.

The practical consequence is straightforward: the lateral approach puts abductor function at direct surgical risk; SPAIRE does not. That single anatomical fact underpins every clinically meaningful difference in muscle trauma, joint stability, and recovery between the two techniques.

What the Hardinge approach does to the abductor muscles

The gluteus medius and gluteus minimus are the muscles that keep the pelvis level the moment a person lifts one foot from the ground. Damage either, and the opposite side of the pelvis drops — a characteristic lurch known as a Trendelenburg gait, named after the test used to detect it. Patients often describe it as a limp that persists long after the pain of their original arthritis has gone.

Because the Hardinge approach must split or partially detach these abductor muscles from the greater trochanter to create its lateral corridor, Trendelenburg-positive gait and abductor weakness are recognised sequelae rather than rare complications. The superior gluteal nerve, which runs close to the operative field and supplies both the gluteus medius and minimus, is at risk of traction or direct injury during the approach; nerve damage can produce persistent weakness independent of whether the muscle itself heals cleanly. In some patients the repaired gluteus medius fails to re-integrate with the greater trochanter — a condition termed abductor dehiscence — leaving a structural gap in the lateral stabiliser that is difficult to address through further surgery.

Severity varies considerably. Many patients recover meaningful abductor strength within months, particularly in experienced hands, and the Hardinge approach remains widely used with broadly acceptable outcomes across large registries. The risk is not a technical error, however — it is an inherent consequence of the chosen corridor. When the abductor mechanism must be moved to gain access, its integrity is placed at stake regardless of how carefully it is subsequently repaired.

For patients whose main concern after hip replacement is returning to confident, unassisted walking, abductor disruption is the functional liability that most clearly sets the lateral approach apart from techniques that reach the joint without entering the abductor compartment.

How SPAIRE spares the posterior soft tissues

Running directly over the posterior surface of the femoral head, the obturator internus tendon sits like a retaining strap across the back of the joint. In SPAIRE, it is never cut. The tendon remains attached to bone throughout the procedure, so its active contraction and passive viscoelastic tension are available from the moment the patient wakes — acting as a biological tether that resists the prosthetic head from moving backwards out of the socket.

This is the mechanism clinicians working with SPAIRE refer to as the 'strap effect'. It arises from a precise decision about what to preserve and what to section. The piriformis tendon and the conjoint tendon of the obturator internus and gemelli stay intact on bone throughout. The obturator externus alone is divided, and it is repaired at closure. The gluteus medius and minimus, which occupy the lateral compartment, are never approached at any point — a distinction that separates SPAIRE from the Hardinge approach at the most fundamental anatomical level.

Because neither the piriformis nor the obturator internus is released and reattached, both tendons remain under the physiological tension they carried before surgery. That uninterrupted tension serves a second practical purpose: it gives the operating surgeon direct tactile feedback about leg length and femoral offset while the implant is being positioned — a reference that would otherwise be lost if the structures were released and later repaired.

Professor Paul Lee, whose specialist practice with SPAIRE informs the clinical perspective set out here, works within this posterior corridor to protect each of these structures in turn.

Proprioception and muscle signalling after surgery

The piriformis and obturator internus do more than provide mechanical support — they contain sensory structures that continuously tell the brain where the hip is positioned. Embedded within the tendon and muscle tissue are Golgi tendon organs and muscle spindles: mechanoreceptors that transmit afferent signals about load, stretch, and joint angle to the central nervous system. Clinicians call this proprioception — the body's sense of where a joint sits in space at any given moment.

When an approach severs these tendons, whether lateral or standard posterior, that signalling pathway is cut. Until the tissues heal and nerve continuity is restored, the hip is neurologically blind to its own position — a period that coincides with the weeks of highest dislocation risk. SPAIRE leaves both tendons attached to bone throughout, so afferent feedback continues without interruption from the moment of surgical closure.

This is a distinct mechanism from the mechanical strap effect described in the previous section: it is a neurological contribution to early stability that operates alongside it. Evidence linking preserved proprioception to lower dislocation rates is mechanistic and observational rather than from randomised controlled trials, so the relationship is best described as likely rather than established — but it is consistent with what is known about how intact tendons behave compared with repaired ones.

Recovery differences: mobilisation, precautions, and gait

The recovery distinction between these two approaches is felt most concretely in the weeks of rehabilitation that follow surgery, not in the operating theatre itself.

After a Hardinge (lateral) procedure, the gluteus medius must heal where it was split or partially detached from the greater trochanter. Until sufficient strength returns, patients may walk with what clinicians describe as a Trendelenburg pattern — a hip-drop limp in which the pelvis dips toward the non-operated side with each step. This can persist for several weeks or, in some cases, months, with gait aids typically needed throughout that period. Physiotherapy must balance protecting the healing abductor repair whilst simultaneously working to rebuild muscle power.

SPAIRE's early recovery starts from a different biological baseline. Because the piriformis and obturator internus remain attached to bone throughout the procedure, there is no reattachment site waiting to consolidate. The tendons are already under physiological tension at surgical closure, which supports more confident early weight-bearing. This reduced structural disruption is also associated with lower dislocation anxiety during rehabilitation — and in suitable patients, the strict 90-day movement restrictions standard after traditional posterior THA (no flexion beyond 90°, no internal rotation) may be relaxed, since the intact posterior soft-tissue envelope provides the stability those precautions are designed to compensate for.

It is worth noting that these differences concern function and early recovery; neither approach has been shown to alter long-term prosthesis performance, so the choice ultimately turns on anatomy, existing muscle condition, and individual activity goals — factors a consultant assessment is best placed to weigh.

Patient suitability and how to approach the decision

Patient factors that genuinely influence which approach a surgeon selects include body habitus, existing abductor muscle condition, prior hip surgery, and whether the exposure may need to be extended intraoperatively. In patients whose abductors are already compromised — following earlier Hardinge surgery, for example — a further lateral approach may carry unacceptable additional risk to already-weakened tissue; SPAIRE's posterior corridor avoids this entirely. Conversely, certain anatomical configurations or the need for broader intraoperative access may make a lateral approach the technically sounder choice in experienced hands.

The strongest SPAIRE candidates are generally those with an intact posterior soft-tissue envelope, no prior posterior hip surgery, and a clinical priority around early, unencumbered mobility. Published case evidence also suggests the technique may be especially advantageous in patients with neurological conditions or significant frailty, for whom prolonged dislocation precautions carry their own functional risks.

No randomised controlled trial has directly compared SPAIRE against the Hardinge approach; the mechanistic case for SPAIRE's abductor-preservation advantage is robust, but the comparison rests on anatomical reasoning and observational data rather than head-to-head trial evidence. Implant survival and all-cause revision rates are broadly equivalent across all principal approaches, so this decision turns on functional and early-recovery priorities rather than prosthesis longevity.

Professor Paul Lee, who assesses patients at the Lincolnshire centres, is trained in multiple surgical approaches and tailors the choice to each individual's anatomy, muscle condition, and functional goals. Hip Replacement Lincolnshire accepts patients without a GP referral; a consultant assessment is the appropriate starting point for establishing which approach — if either — fits a particular clinical presentation.