What the posterior approach actually does to your hip

Nine in ten surgeons performing total hip arthroplasty (THA) use some form of the posterior, or posterolateral, approach — and for good reason. It offers reliable access to the joint, a clear sightline for implant positioning, and decades of outcome data. What it also requires, by design, is a degree of structural disruption that most pre-operative conversations do not explore in full.

To reach the hip's ball-and-socket joint, the surgeon first splits the gluteus maximus along its fibres to open the field. Then comes the step that carries longer consequences: the short external rotator tendons — the piriformis, the gemelli, and the obturator internus — must be detached from their insertions on the femur before the joint can be dislocated and replaced. These are not minor support structures. They are the primary posterior stabilisers of the hip, active in every movement from rising off a chair to climbing stairs.

The tendons are not simply moved aside; they are severed and then sutured back at the end of the operation. What heals is not reconstituted tendon but scar tissue, and that biological process takes weeks — during which the hip lacks its native posterior anchoring. The prosthesis itself contributes stability through geometry and fixation, but soft-tissue tension is a critical component of a hip joint's security, particularly in the early post-operative period.

This is not a surgical flaw — it is an inherent feature of the technique, accepted because the overall outcomes are well established. The structural trade-off nonetheless has real downstream consequences for stability, nerve proximity, and recovery pace, which the sections below examine directly.

Dislocation risk: the range patients are rarely given

Published dislocation rates after posterior total hip arthroplasty span 0.2% to 10% — a range wide enough to represent meaningfully different clinical realities, yet patients are rarely shown the full interval during pre-operative discussion. The variation is not random: surgical technique, implant design, patient anatomy, and surgeon volume all determine where an individual procedure sits within that span.

At the lower end, the difference between a 0.2% and a 10% rate is not simply luck. A 2023 prospective series of 580 hips using a mini-posterior approach with a monoblock dual-mobility implant — and no post-operative hip precautions — recorded just one dislocation (0.2%). Implant selection, that series suggests, is as consequential as approach choice in determining stability outcomes.

The downstream consequences of a dislocation are more serious than the initial event implies. The data show that 57% of patients who dislocate go on to dislocate more than once; 11% experience more than five episodes; and 45.6% require revision surgery within two years — an operation substantially more complex than the primary procedure.

Standard practice addresses this instability risk through strict post-operative hip precautions: no hip flexion beyond 90°, no leg crossing, no internal rotation, typically for six weeks. The evidence base for these restrictions is, however, thinner than their routine use implies. A multicentre randomised controlled trial of 313 patients found no statistically significant difference in dislocation rate between those given standard precautions (1.3%) and those given none (0.7%; p=0.62).

Implant selection and surgical technique, then, appear to be the more modifiable variables in determining where a patient's individual risk sits within that published range.

Sciatic nerve proximity and proprioceptive loss

Two further consequences of the posterior approach are worth understanding before surgery, though they receive far less attention than dislocation rates.

The nerve that runs behind the hip

The sciatic nerve — the long nerve that travels down the back of the leg and into the foot — passes directly behind the hip joint, making it an immediate neighbour to the surgical field in any posterior approach. Retractors, blood pooling, and forces created by lengthening the leg during implantation can each affect it. Studies report sciatic nerve injury in approximately 0.2%–3% of posterior-approach procedures, with symptoms ranging from temporary numbness or tingling to, in rarer cases, foot drop. This risk is approach-specific: anterior techniques route the surgical exposure away from the nerve's path entirely, removing it as a variable.

A less-discussed variant of the same risk arises after the operation. When the piriformis tendon is detached and then reattached to the femur at closure, the reconstructed tendon can exert pressure on the adjacent sciatic nerve — a post-operative mechanism distinct from intra-operative stretching, and one rarely mentioned during pre-operative consent.

Proprioceptive feedback after tendon detachment

The short external rotator tendons contain mechanoreceptors — specifically Golgi tendon organs and muscle spindles — that send continuous positional signals to the brain. When those tendons are cut, as they are in the traditional posterior approach, those receptors are severed with them. Specialist clinical experience and anatomical reasoning both suggest this leaves the hip with reduced awareness of its own position and load until healing progresses — a period during which the joint cannot reflexively protect itself. Published RCT evidence directly quantifying this proprioceptive deficit is still emerging, and patients should be aware the mechanism, while well-supported by anatomy, has not yet been confirmed in large prospective trials. It is worth raising at any pre-operative assessment.

Six weeks of hip precautions: what life actually looks like

For most patients, the list of posterior hip precautions looks manageable on paper: no hip flexion past 90°, no crossing the legs, no turning the foot inward — typically maintained for six weeks while the detached tendons heal. The reality is more demanding.

A standard UK toilet seat sits at roughly 40–45 cm, below the safe threshold for most patients post-operatively. Raised toilet seat aids, long-handled shoehorns, perching stools, and elevated chair cushions become household essentials overnight. Getting into a car means reclining the passenger seat fully and sliding in sideways; a low hatchback or sports car may effectively be off-limits for the duration. Bending to pick up something dropped — a phone, a grandchild's toy, a set of keys — requires a reaching aid or a willing bystander. Sleeping on one's side is restricted, and many patients are limited to a single position for several weeks.

Patients who were not fully briefed pre-operatively often describe this six-week period as harder to live with than the surgery itself — particularly those with caring responsibilities, limited household support, or bathrooms that cannot easily be adapted.

The restrictions exist for a genuine anatomical reason: reattached tendons are healing on scar tissue rather than native bone, and dislocation during this window carries serious downstream consequences. Whether the evidence base fully justifies their routine imposition remains a live clinical question. More practically, for anyone planning recovery around work, independent living, or family commitments, the prospect of reducing or removing this burden is one of the most consequential arguments for considering a muscle-sparing surgical approach.

How SPAIRE and muscle-sparing approaches change the picture

SPAIRE — Saves Piriformis And Internus, Repairs Externus — uses the same posterior route as the conventional approach but achieves joint access without detaching the piriformis or obturator internus tendons. The obturator externus, which does need to be managed for adequate exposure, is repaired at closure. Everything else that stabilises the hip during rising, walking, and stair-climbing remains anchored to bone throughout the procedure.

The strap effect

Keeping the obturator internus intact has a direct mechanical consequence. The tendon passes over the posterior aspect of the prosthetic femoral head, creating what is described clinically as a 'strap effect' — a biological tether against posterior dislocation that is present from the moment the patient leaves the operating theatre. In conventional posterior THA, equivalent resistance depends on reattached scar tissue that is still maturing during the six-week precautions window.

Proprioception and the precautions burden

Because the tendons are not severed, the Golgi tendon organs and muscle spindles they contain remain functional — the same mechanoreceptors whose loss was described in the previous section. Positional feedback is maintained from day one rather than interrupted during the healing period. The anatomical case for this is well-supported; large prospective trial evidence directly quantifying the functional benefit is still accumulating, and patients should be aware the claim rests on mechanistic reasoning as well as early clinical series.

Patients assessed as suitable for SPAIRE may avoid or substantially reduce the six-week precautions burden imposed after conventional posterior THA. In appropriate cases, day-case surgery is achievable rather than the traditional three-to-five-day inpatient stay, though individual suitability always requires full clinical assessment.

The technique was first described by Kim et al. in 2008 and has been developed further at the Exeter Hip Unit. Professor Paul Lee, a consultant hip surgeon specialising in muscle-sparing posterior arthroplasty, is the clinical lead whose approach to SPAIRE shapes assessment and surgical decision-making at Hip Replacement Lincolnshire.

Assessing your options: what a specialist consultation covers

The five preceding sections document a specific set of trade-offs: a dislocation range spanning 0.2% to 10% depending on technique and implant; a six-week precautions burden whose evidence base is contested by at least one multicentre RCT; sciatic nerve proximity that is approach-specific; and a proprioceptive mechanism that muscle-sparing surgery preserves and conventional posterior THA interrupts. What none of those findings can determine is how those trade-offs weigh for a given patient — because that depends on individual anatomy, bone stock, BMI, prior surgical history, and personal priorities.

At any hip replacement consultation, four questions are worth raising directly:

• What surgical approach is planned, and why for my anatomy specifically?
• What implant type is proposed, and what dislocation rate does the published evidence associate with that combination?
• What precautions will apply post-operatively, and for how long?
• Am I a candidate for a muscle-sparing technique such as SPAIRE?

Not every patient is suitable for SPAIRE. The decision depends on bone geometry, soft-tissue quality, and overall operative risk — factors that require direct clinical assessment, not self-selection from written materials.

Hip Replacement Lincolnshire, part of the MSK Doctors group, offers consultant-led hip replacement assessment at Sleaford (NG34) and Grantham (NG31) without an NHS referral or waiting list. The purpose of that assessment is to map your specific anatomy to the approach and implant combination the evidence suggests is most appropriate — which is the same clinical reasoning this article has been working through from the other direction.

1. [1] Analysis of posterior hip joint impingement about developmental dysplasia of the hip after total hip arthroplasty. (2024). https://doi.org/10.1016/j.clinbiomech.2024.106422 https://doi.org/10.1016/j.clinbiomech.2024.106422
2. [2] Posterior Approach THA Utilizing a Monoblock Dual-Mobility Construct Without Posterior Hip Precautions: A Series of 580 Hips with One Dislocation. (2023). https://doi.org/10.1016/j.arth.2023.03.027 https://doi.org/10.1016/j.arth.2023.03.027
3. [3] Posterior Hip Precautions Do Not Impact Early Recovery in Primary THA: A Multicenter, Randomized, Controlled Study. (2019). https://doi.org/10.1016/J.ARTH.2019.02.057 https://doi.org/10.1016/J.ARTH.2019.02.057