Why femoral neck fractures usually lead to hip replacement

If you or a relative has fractured the neck of the femur, surgery is almost always the recommended next step — and for most older adults, that surgery means replacing the femoral head (the ball at the top of the thigh bone) rather than attempting to repair the broken bone.

The reason lies in anatomy. The femoral head receives its blood supply through a small number of vessels that run along the femoral neck. A displaced fracture — one where the bone ends have moved apart — typically tears or compresses those vessels at the moment of injury. Without a reliable blood supply, the femoral head cannot heal; even with perfect fixation, the bone may gradually collapse over the following months in a process called avascular necrosis. In older adults, where the bone is already osteoporotic and healing reserves are reduced, surgeons generally judge that the risk of fixation failure outweighs any benefit of trying to save the original bone. Hip hemiarthroplasty — replacing only the femoral head with a prosthesis while leaving the natural socket (acetabulum) untouched — restores a stable joint quickly and reliably.

The population affected by femoral neck fractures is characteristically frail. Most fractures occur after low-energy falls in people over 70, many of whom are managing multiple health conditions and may be on anticoagulants or have reduced cardiorespiratory reserve. The operative window is narrow: delay increases the risk of complications, but the surgery itself carries meaningful perioperative risk in this group. Speed, surgical precision, and minimising tissue disruption all matter.

Critically, the choice of surgical approach — which muscles and tendons are cut or preserved to reach the joint — has a direct bearing on two outcomes that matter most to patients and families: the risk of the new joint dislocating after surgery, and how quickly the patient can stand, walk, and regain independence. These are the questions that the rest of this article addresses.

The dislocation problem with standard posterior hemiarthroplasty

Standard posterolateral hemiarthroplasty requires the surgeon to cut through the short external rotator tendons — principally the piriformis and obturator muscles — to gain clear access to the hip joint. Severing these structures removes the posterior soft-tissue curtain that normally holds the prosthetic head in its socket, and simultaneously destroys the mechanoreceptors woven into the tendon fibres that help the brain track joint position, leaving the hip neurologically unguarded during the healing period.

The consequences are measurable. Registry data show that among patients who suffer a dislocation after posterior hemiarthroplasty, 57% go on to dislocate again, and 45.6% require revision surgery within two years — a high-risk chain of events for patients who are already frail at the time of their original fracture.

To reduce this risk, traditional protocols mandate strict postoperative hip precautions: no bending the hip beyond 90°, no crossing the legs, no internal rotation. For a fit adult these restrictions are inconvenient; for an older patient managing cognitive impairment, mobility aids, or reduced proprioception from other causes, they can be genuinely hazardous — increasing the risk of a compensatory fall and lengthening the time spent in hospital beyond the typical three-to-five-day stay. Rehabilitation slows, confidence erodes, and the window for restoring independence narrows at exactly the point where speed matters most.

It is this cluster of problems — dislocation vulnerability, neurological exposure, and precaution burden — that prompted development of muscle-sparing alternatives such as the SPAIRE approach.

What SPAIRE actually does differently at the hip joint

The name is more than a label. SPAIRE — Saving Piriformis And Internus, Repair of Externus — maps directly onto four anatomical decisions the surgeon makes during the procedure, and understanding those decisions explains why the approach behaves so differently from the standard technique described above.

At the back of the hip sit a group of small but functionally critical tendons known collectively as the short external rotators. SPAIRE identifies two distinct subsets. The first — the piriformis tendon and the conjoint tendon formed by the superior gemellus, obturator internus, and inferior gemellus — is left completely untouched throughout the operation. Together these structures are sometimes called the 'quadriceps coxa', a term reflecting their shared role as a functional stabilising unit analogous to the quadriceps at the knee. The second tendon, the obturator externus, sits at a slightly different angle and is the only structure that needs to be released to allow the surgeon sufficient access to the joint. It is then meticulously repaired at closure, restoring its mechanical contribution before the wound is closed.

Preserving the obturator internus matters for a specific anatomical reason. This tendon exits the pelvis through the lesser sciatic foramen and passes directly over the posterior aspect of the femoral head at or just below the hip's true centre of rotation. When kept intact, it behaves as a dynamic biological tether — a 'strap effect' — that physically resists posterior displacement of the prosthetic head. This is a passive mechanical safeguard, not a guarantee of zero dislocation, but it meaningfully changes the forces acting on the joint from the moment the patient wakes from anaesthesia.

The second benefit is neurological. The preserved tendons contain intact Golgi tendon organs and muscle spindles — sensory receptors that relay continuous positional information to the nervous system. These allow the body to reflexively adjust before the patient is consciously aware the hip is at risk. Standard posterior approaches sever these mechanoreceptors, leaving the joint, in effect, proprioceptively blind during the weeks of tissue healing. SPAIRE was formally named and published in 2017, building on a modified posterior approach first described by Kim et al. in 2008, and this neurological rationale has remained central to its clinical case ever since.

What the clinical evidence shows

Dislocation rates in published SPAIRE series are routinely reported below 1% — against the several-percent figures recorded for standard posterior hemiarthroplasty and the downstream cascade of re-dislocation and revision that follows.

The most substantive direct evidence comes from a 2025 prospective study by Paus et al. in International Orthopaedics (PubMed 40279802), the first study specifically designed to assess complication rates and functional outcomes of SPAIRE hemiarthroplasty for femoral neck fractures. Its findings are consistent with low complications and faster return to baseline mobility versus traditional lateral approaches; granular outcome data will become clearer as the study accumulates wider follow-up and independent replication.

Sifi et al. (Journal of Trauma and Injury, 2025; PMC12489149) contribute a case-level illustration: a 79-year-old woman with a transcervical femoral neck fracture who underwent cemented bipolar SPAIRE hemiarthroplasty achieved an excellent functional outcome at three months. The authors note this result is particularly significant given the frailty and co-morbidity burden typical in this patient group. A single case report cannot establish generalisability, but it confirms the procedure's feasibility and early recovery profile in a high-risk geriatric patient — and it is important to read it as supporting context for the Paus study, not as equivalent evidence.

Two larger evidence streams are under way. The HemiSPAiRE clinical trial and the Norwegian Hip Fracture Register are both generating registry-level comparative data on SPAIRE hemiarthroplasty versus conventional approaches; their fuller reporting will provide the statistical weight needed for guideline-level conclusions.

The evidence base is early-stage. Randomised comparisons of SPAIRE hemiarthroplasty against the lateral or direct anterior approach in hip fracture populations are still completing. What currently exists — a prospective outcomes study and a case report, with registry data in progress — is not yet sufficient to displace established techniques by guideline, but the trajectory is consistent with the biomechanical rationale: sub-1% dislocation risk, no mandatory precautions, and earlier mobilisation in a patient group for whom speed of recovery is not optional.

How SPAIRE compares with other hemiarthroplasty approaches

Four surgical routes are commonly used for hip hemiarthroplasty after a femoral neck fracture, and each opens a different set of trade-offs for the patient.

Standard posterior approach remains the most widely performed. It is familiar to nearly all hip surgeons, operatively efficient, and readily extensible if unexpected anatomy is found. Its documented disadvantage — the posterior dislocation burden and the precaution framework that accompanies it — has been covered in the sections above; the practical problem for elderly fracture patients is that strict positioning restrictions are among the hardest post-operative demands to observe reliably.

Direct anterior approach (DAA) avoids violation of the posterior soft-tissue structures and can reduce posterior dislocation risk, which is why patients frequently encounter it online as a forward-looking option. In fracture cases, however, it tends to carry longer operative times and higher intraoperative blood loss than the posterior route, and it carries a recognised risk to the lateral femoral cutaneous nerve — a sensory branch whose injury can produce persistent numbness or burning sensation across the front of the thigh. The DAA also has a steeper surgical learning curve, which limits its availability outside specialist units.

Lateral (Hardinge) approach reaches the joint from the side, preserving the posterior structures. Its trade-off falls on the gluteus medius — the primary hip abductor — which must be split or partially detached to gain access. Compromise of this muscle can produce a Trendelenburg gait pattern, the characteristic sideways lurch seen when abductor function is reduced, and may meaningfully prolong walking recovery after a fracture.

SPAIRE uses the same posterior corridor as the standard technique, keeping operative time and surgeon orientation broadly comparable. By preserving the piriformis–conjoint tendon unit, it addresses the posterior dislocation vulnerability without introducing hip precautions. If complex bony anatomy is encountered intraoperatively, the approach converts to a full standard posterior technique without a second incision — a practical safety net in fracture surgery, where pre-operative imaging cannot always anticipate every finding.

Approach selection depends on individual anatomy, fracture pattern, and the operating surgeon's specific training and experience; no single route is the correct choice for every patient.

Who is suitable and how assessment works

Most femoral neck fractures managed with hemiarthroplasty occur in adults over 65, typically presenting within 24 to 48 hours of a low-energy fall on osteoporotic bone. SPAIRE hemiarthroplasty is not predetermined — it is confirmed at the point of surgical access once fracture pattern and anatomy have been assessed directly.

Several factors inform suitability: fracture classification, residual bone quality, the patient's functional level before the fall, and anatomical variables encountered intraoperatively. Because the approach converts to a standard posterior technique without a second incision if needed, it functions as the opening position for suitable candidates rather than a narrowly indicated option. Medical comorbidities affect overall operative risk but do not inherently preclude the approach — the 2025 Sifi case report documented an excellent three-month outcome in a 79-year-old patient whose comorbidity profile was broadly representative of the geriatric fracture population.

What the technique offers is most relevant to patients with limited recovery reserves: maintained proprioception and mechanical continuity of the posterior soft-tissue envelope from the outset, rather than an extended wait for severed tendons to heal.

Prof Paul Lee, whose clinical practice integrates the SPAIRE muscle-sparing approach for hemiarthroplasty and total hip replacement, applies structured assessment — imaging review, fracture classification, and evaluation of pre-fracture mobility — to determine the most appropriate approach for each individual. No technique is correct for every patient; the decision is a consultant-led clinical judgement.

As the HemiSPAiRE trial and Norwegian Hip Fracture Register data mature, the evidence base will sharpen. What currently exists consistently supports a technique whose biomechanical logic — preserved muscle, preserved proprioception, restored posterior stability — aligns directly with what hip fracture patients need most: the fastest defensible path back to independent movement.