Femoral Neck Stress Fractures

Femoral neck stress fractures are overuse injuries caused by repetitive submaximal loading, most common in endurance athletes and military recruits. The femoral neck is a high-risk stress fracture site because a fracture here can displace, and displacement brings AVN and nonunion. It is managed more aggressively than low-risk stress fractures such as those of the tibial shaft or metatarsals.

Management turns on which cortex is involved, tension or compression. That is the exam question, and it is set out under Pathophysiology and Classification below.

History. The injury was first described in military populations. Since then the distinction between the tension and compression sides has become critical, and the female athlete triad has been identified as a major risk factor.

Who. Femoral neck stress fractures account for approximately 3% of all sport-related stress fractures (Robertson & Wood 2017).

• Distance and marathon runners are the commonest athletic population affected
• Military recruits in basic training are the other key high-risk group. Across basic training the baseline incidence of stress fracture of any site is several percent over an 8-week cycle (5.9% per 8 weeks in the female Navy recruit RCT; Lappe 2008), and the femoral neck is a small but high-consequence subset
• Women predominate, strongly linked to the female athlete triad and RED-S; in mixed surgical military cohorts roughly half of operatively treated cases are women (Shaw 2022)
• Ballet dancers and other high-volume, leanness-emphasis athletes are also over-represented

Risk factors. The recognised risk factors are these:

• Training errors: too much, too soon, or a rapid increase in activity
• The female athlete triad: low energy availability, amenorrhoea and low BMD
• Low vitamin D
• Smoking
• A previous stress fracture

Why the femoral neck. It takes high bending loads during weight-bearing activity, its cortical bone is thin, especially superiorly, and its limited blood supply carries the risk of AVN.

How a stress fracture develops. The injury progresses through stages:

1. Remodelling imbalance: resorption exceeds formation
2. Microdamage accumulation with repetitive loading
3. Stress reaction: bone oedema without a fracture line
4. Stress fracture: a fracture line develops
5. Complete fracture: full-thickness propagation

Detected at the stress-reaction stage, the injury can be managed conservatively.

Bending in single-leg stance. During single-leg stance the femoral neck is subjected to a bending moment. The superior cortex is under tension, pulled apart, and the inferior cortex under compression, pushed together.

The tension side. Tension makes a crack in the superior cortex propagate rather than close. The risk of a complete fracture is higher and the fracture can displace suddenly, which is why a tension-side stress fracture is a surgical emergency.

The compression side. Compression tends to close a crack in the inferior cortex rather than propagate it, so the risk of complete fracture is lower. These fractures are more stable, less likely to displace, and can often be managed conservatively, but some progress, and close monitoring is essential.

The abductors. The tension on the superior neck is not fixed; it is modulated by the hip abductors. Body weight in single-leg stance creates a bending moment that tenses the superior cortex, but a contracting gluteus medius and minimus pull on the proximal femur and add a compressive, offsetting load across the neck, lowering the net superior tensile strain.

Why late in the race. Late in a marathon or a long march the tiring abductors stop neutralising the bending moment, superior tensile strain rises and the fatigue fracture propagates. That explains the classic onset late in an endurance event, and the same idea has practical consequences:

• Hip-abductor and core conditioning are part of prevention and of graded return to sport
• Gait retraining that reduces excessive hip adduction (and contralateral pelvic drop) unloads the superior neck
• It reinforces the tension-side rule: once the protective muscle force is overwhelmed, the superior crack only ever sees distraction, so it cannot be trusted to heal without fixation

Blood supply. The femoral head is supplied mainly by the medial femoral circumflex artery, with the lateral femoral circumflex artery and a minor contribution from the artery of the ligamentum teres. A displaced fracture can disrupt the retinacular vessels and lead to AVN, which is why preventing displacement is critical.

Location is the key factor in management decisions: always determine whether the fracture involves the superior (tension) or the inferior (compression) cortex. Fullerton and Snowdy's classification is built on that split, dividing femoral neck stress fractures into tension-side, compression-side and displaced types. The imaging gradings stage the injury from stress reaction to complete fracture.

View larger

View larger

History. The typical patient is a young athlete or military recruit with groin pain of insidious onset, related to activity and worse with impact; there may be a preceding prodromal ache. The questions that matter:

• Training history, and any recent increase
• Menstrual history in women
• Dietary intake, screening for RED-S
• Previous stress fractures
• Medications, particularly steroids and bisphosphonates

RED-S. Relative Energy Deficiency in Sport is the updated term for the female athlete triad. Screen every athlete with a stress fracture for it, female athletes without exception, and refer to endocrinology if the triad is suspected.

Examination. The key tests, each with its finding:

Differential diagnosis. The differential of activity-related groin or hip pain in the young athlete:

Radiographs. Plain films are often negative for 2-4 weeks, so a normal radiograph does not exclude the diagnosis. When positive they may show a sclerotic line or periosteal reaction. Full-length views are recommended, with comparison against the contralateral side.

View larger

MRI. The gold standard. It detects the stress reaction before a fracture line is visible and identifies a fracture line if one is present. Order it:

• Always, when clinical suspicion is high and radiographs are negative
• When early diagnosis is critical, as in the athlete in season
• To determine the extent and location of the injury
• To monitor healing

View larger

View larger

View larger

CT. Better for visualising cortical fracture lines, but less sensitive for the early stress reaction. It is useful if MRI is contraindicated or equivocal.

View larger

Bone scan. Highly sensitive but less specific, showing focal uptake at the fracture site. It cannot distinguish tension from compression and is less commonly used now that MRI is available, so it is a fallback when MRI is unavailable or contraindicated, not the preferred test for classifying cortical-side risk.

Laboratory tests. Look for the metabolic contributors:

• Vitamin D level
• Calcium
• TSH, if RED-S is suspected
• DEXA for BMD, to be considered in the triad or RED-S

Abnormal results should trigger correction of the metabolic deficit and, where appropriate, sports-medicine, dietetic or endocrinology review before return to impact loading.

The decision. The side of the fracture, and whether it has displaced, decide the treatment.

Algorithm

View larger

The technique below is for cannulated screw fixation; the fixed-angle alternatives are covered under Management.

View larger

Set-up. The patient lies supine on a fracture table or radiolucent table, with image-intensifier access for AP and lateral views, the leg in slight internal rotation and the unaffected leg in the lithotomy position. Confirm the fracture location on imaging, mark the skin incision, make sure the fluoroscopy images are adequate and be prepared for a closed or open approach. Most cases can be done percutaneously under fluoroscopic guidance.

Screw placement.

1. Guide wires: start on the lateral femur below the greater trochanter and aim for the inferior femoral neck first. Place the wires for the inverted triangle, one inferior and two superior, and verify each on AP and lateral views
2. Drilling: measure screw length and drill over the guide wires
3. Screws: insert the screws, typically 6.5-7.3mm, and tighten them sequentially

Configuration. The inverted triangle puts one inferior screw along the calcar and two superior screws parallel to each other, with all the threads across the fracture site. Posterior cortex engagement is important. No screw should enter the weight-bearing dome or penetrate the weight-bearing articular surface.

Starting point. Below the greater trochanter, which allows the optimal trajectory. A starting point that is too distal creates a subtrochanteric stress riser; too proximal is also wrong.

Imaging confirmation. AP and lateral views are mandatory, to check for joint penetration and to confirm that the screws cover the fracture site.

Pitfalls. The intraoperative errors to avoid:

• Joint penetration: check on fluoroscopy
• Over-compression, which can cause shortening
• Inadequate fixation: add screws if needed

If reduction is needed. A limited open approach may be required. Use gentle reduction manoeuvres and avoid devascularising the fragments.

View larger

View larger

Avascular necrosis. The most feared complication. Its risk is directly related to the degree of displacement and the time to treatment, so tension-side fractures, being the more likely to displace, carry the higher AVN risk, and urgent surgical fixation minimises it. AVN may occur despite optimal care, and needs long-term monitoring.

Nonunion. More common in displaced fractures. Smoking, metabolic bone disease and poor fixation are risk factors, and treatment is revision with bone graft, valgus osteotomy or arthroplasty.

View larger

View larger

Weight bearing is protected at first and progressed as healing is confirmed.

Return to sport. Return when united and pain-free, judged against these criteria:

• Union confirmed on imaging
• Full, pain-free ROM
• Strength symmetry
• Functional testing passed
• Underlying risk factors addressed

How long. The timeline is approximate and depends on the fracture:

• Compression side, treated conservatively: 3-4 months
• Tension side, treated surgically: 4-6 months
• Displaced fracture: 6-12 months, depending on AVN

Prognostic factors. Five factors separate the better outcomes from the worse:

Outcome is dominated by displacement and time to diagnosis.

Compression side, non-operative. A high union rate with compliant non-weight bearing and serial imaging. The long-term prognosis is excellent once healed, provided the RED-S or metabolic drivers are corrected.

Tension side, operative. Union is good with timely fixation.

Displaced fractures. Markedly worse, with a high AVN and nonunion risk and sporting outcomes considerably worse once displaced (Robertson & Wood 2017). Outcomes are worse than for prophylactically fixed fractures, and arthroplasty may be required if AVN develops.

View larger

Training. The principles of primary prevention:

• Gradual load progression (the 10% rule)
• Adequate rest days
• Cross-training to reduce impact
• Proper footwear
• Appropriate running surfaces

Nutrition. Adequate caloric intake avoids relative energy deficiency. Calcium intake should be 1000-1500mg daily, and vitamin D maintained above the target given under Management.

Screening female athletes. Take a menstrual history from every female athlete; absent periods are a red flag. Use a RED-S screening questionnaire, keep a low threshold for endocrine referral, and assess bone health if anything is abnormal.

View larger

Secondary prevention. After a fracture, address every modifiable risk factor as set out under Management, and monitor bone health over the long term.

Femoral neck stress fracture (FNSF) is a globally consistent diagnosis with a single overriding management principle — location (tension vs compression) and displacement drive treatment — that holds across every major board and health system.

Global epidemiology:

Major guidance, side by side:

There is no genuine international disagreement on the core algorithm: the tension/compression split and the imperative to fix tension-sided and displaced injuries are universal. Practice variation lies mainly in implant choice (cannulated screws vs sliding hip screw / cephalomedullary nail) and in the surgical threshold for compression-sided injuries — a commonly cited operative trigger is involvement of more than ~50% of the neck width or any fracture-line progression (Shaw 2022).