Two muscle-sparing claims — but not the same muscles

Both the SPAIRE technique and the direct anterior approach (DAA) are regularly described as 'muscle-sparing' hip replacements — and that shared label is where a great deal of patient confusion begins. The two operations do not spare the same muscles, and they do not even approach the hip from the same direction.

SPAIRE is a posterior technique. The surgeon accesses the hip from behind, through the buttock region, and the defining feature of the approach is that the piriformis and obturator internus tendons — small but mechanically important structures that wrap around the back of the joint — are kept attached to the bone throughout the procedure.

The DAA comes from the opposite direction entirely. The incision is made at the front of the groin, and the surgeon works between natural muscle planes — separating rather than cutting the muscles in that region — to reach the joint from the front.

Asking which approach 'spares more muscle' does not have a straightforward answer, because the question compares the wrong things. The two techniques protect different anatomy in different anatomical territories. What matters is which structures are most relevant to an individual patient's hip, their surgical anatomy, and their recovery priorities. That is the distinction worth understanding before comparing anything else.

What SPAIRE preserves and the stability argument behind it

Keeping a tendon attached is quite different from detaching it and sewing it back. That distinction sits at the heart of SPAIRE's anatomical argument.

In a traditional posterior hip replacement, the piriformis and obturator internus tendons are released from the bone to allow the surgeon access to the joint, then repaired at the end of the procedure. In SPAIRE — Save Piriformis And Internus, Repair Externus — those tendons are never detached in the first place. The obturator internus passes directly over the back of the femoral head as it exits the pelvis, and when left intact it may act as a biological tether, sometimes described as a 'strap effect', designed to resist unwanted rearward movement of the femoral head. Think of it as a seatbelt that has stayed connected, rather than one that has been cut and re-stitched: structurally present from the moment surgery ends.

The second mechanism is neurological. Intact tendons contain Golgi tendon organs and muscle spindles — sensory structures that relay continuous positional information to the central nervous system. Preserving them may help the hip maintain some proprioceptive awareness in early recovery, a degree of reflexive guarding that severed and reattached tissues cannot reliably provide until healing is complete.

Both mechanisms are design intentions and mechanistic arguments for the approach. They are not guarantees of individual outcome.

Professor Paul Lee trained in the SPAIRE technique under Professor Timperley at the Exeter Hip Unit — one of the internationally recognised centres for hip surgery — and has since adopted it as his routine posterior approach, reflecting a clinical philosophy built around preserving what is healthy rather than repairing what has been divided.

Where the DAA has genuine early recovery advantages

Surgeons and patients who choose the direct anterior approach do so for reasons grounded in real data, and those reasons deserve a straightforward account.

In available comparison data, patients undergoing the DAA show faster recovery on Harris Hip Score measurements at six and twelve weeks after surgery — a validated functional scale that captures pain, mobility, and daily activity. They also tend to spend less time using walking aids in the immediate postoperative period. For patients whose priority is getting back to baseline as quickly as possible in those first three months, this early trajectory is a meaningful advantage, not a marginal one.

There is also a structural logic to the DAA's early recovery profile. Because the surgeon approaches from the front and works between existing muscle planes rather than releasing posterior structures, the operation bypasses the posterior soft tissues that historically required patients to observe strict movement precautions after surgery. The front approach simply does not disturb that anatomy — so the precaution question does not arise in the same way.

These are genuine clinical strengths of the DAA. The comparison in the sections that follow is not an argument that SPAIRE outperforms the DAA across all measures — it is a more specific question about what each approach trades and where the risks sit.

The risk profile is different, not just the recovery speed

Every surgical approach carries a distinct risk profile, and understanding which risks belong to which route matters when weighing options.

The DAA's most specific risk is lateral femoral cutaneous nerve (LFCN) neurapraxia — temporary numbness or altered sensation along the outer thigh, caused by traction on a small sensory nerve that runs close to the anterior incision. This is not associated with the posterior SPAIRE route, which has its own distinct anatomical considerations. Beyond the nerve risk, the DAA typically involves longer operative times and, in available data, higher intraoperative blood loss than the posterior approach. The learning curve is steeper, and in less experienced hands the technique carries a higher risk of intraoperative femoral fracture during canal preparation — a complication not linked to SPAIRE's posterior exposure.

On the posterior side, the traditional approach has historically carried a higher dislocation risk and imposed strict postoperative movement precautions — restrictions on bending, crossing the legs, and rotating the foot inward. SPAIRE's preservation of the piriformis and obturator internus is specifically designed to address both of these concerns. Keeping those posterior restraints intact may reduce the mechanical circumstances in which dislocation occurs and, for suitable patients, may allow the removal of precautions that traditional posterior patients were routinely given.

This principle is not exclusive to SPAIRE. The HSS institution describes a modified posterior technique called STAR that similarly preserves the posterior muscles and piriformis tendon, removing the need for postoperative precautions in appropriate cases. The underlying surgical logic is the same — which confirms that anatomy-respecting posterior surgery is recognised practice across major centres, not a single-institution claim.

Neither approach is free of risk. The relevant question is which risk profile fits a patient's anatomy, their surgeon's training, and their own priorities.

Long-term implant outcomes and what remains uncertain

The strongest finding in any comparison of hip replacement approaches is also the most reassuring: long-term implant survival appears equivalent across the posterior and anterior routes. No significant difference in all-cause revision rates has been demonstrated between the two. Whatever a surgeon and patient are weighing between approaches — early recovery speed, nerve risk, soft-tissue preservation — they are weighing perioperative and early functional factors, not which prosthesis is likely to last longer. That is a genuinely important distinction.

Where the evidence is less settled is in the specific claims around stability and proprioception. SPAIRE's rationale for preserving the piriformis and obturator internus — the strap effect, the retention of intact mechanoreceptors — is grounded in biomechanical reasoning and supported by the clinical logic of keeping healthy tissue undisturbed. Whether those mechanisms translate into measurable dislocation-rate differences for any individual patient is something the treating surgeon can contextualise against published data and each person's anatomy; the answer varies considerably between people and is not something that generalises cleanly.

The same careful framing applies to recovery pathway outcomes. Professor Lee's biological rapid recovery programme is designed to support same-day or next-day discharge for selected suitable patients — a meaningful possibility for those who meet the criteria, and not a baseline expectation for all posterior hip replacement patients.

How approach choice actually gets made

Deciding between SPAIRE and the DAA is not a matter of selecting the more modern or fashionable option from a list. It is a clinical conversation shaped by the individual.

Several factors bear on the choice. Patient anatomy and BMI both matter: the DAA has specific positioning and anatomical candidacy requirements, and not every patient is well-suited to its theatre setup. Femoral anatomy, bone quality, and the achievability of preserving posterior soft tissues all influence whether SPAIRE can deliver its intended benefits in a given case. Equally important is the surgeon's own training, technique experience, and audit record — an approach performed well within the surgeon's expert hands is safer than an approach performed outside of it.

Patient priorities play a part too. Someone who places significant weight on the earliest possible return to low-level activity may weigh the DAA's six-week recovery data differently from someone whose primary concern is longer-term joint security.

Professor Paul Lee's pre-operative assessment draws on his experience with SPAIRE-style anatomy-respecting surgery to match technique to the individual — reviewing imaging, considering recovery goals, and forming a plan where the approach follows the anatomy rather than the anatomy being made to fit the approach.

For patients at an earlier stage, a specialist consultation is the practical route to that kind of individual clarity.

1. [1] Hip replacement. https://en.wikipedia.org/?curid=1125423 https://en.wikipedia.org/?curid=1125423