Femoral Neck Stress Fractures

Femoral neck stress fractures are overuse injuries occurring from repetitive submaximal loading, most common in endurance athletes and military recruits. They represent a high-risk stress fracture location due to displacement potential and AVN risk.

Historical context:

• First described in military populations
• Recognition of tension vs compression distinction critical
• Female athlete triad identified as major risk factor

Epidemiology:

• Femoral neck stress fractures account for approximately 3% of all sport-related stress fractures (Robertson & Wood 2017)
• Distance/marathon runners are the commonest athletic population affected; military recruits in basic training are the other key high-risk group
• Female predominance, strongly linked to the female athlete triad / 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
• Across military 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) — the femoral neck is a small but high-consequence subset

Risk factors:

• Training errors (too much, too soon)
• Female athlete triad (low energy availability, amenorrhea, low BMD)
• Low vitamin D
• Smoking
• Previous stress fracture
• Rapid increase in activity

Femoral neck anatomy:

The femoral neck is vulnerable to stress fractures due to:

• High bending loads during weight-bearing activities
• Limited blood supply (risk of AVN)
• Thin cortical bone especially superiorly

Biomechanics of loading:

Stress fracture pathophysiology:

1. Bone remodeling imbalance: Resorption exceeds formation
2. Microdamage accumulation: Repetitive loading
3. Stress reaction: Bone edema without fracture line
4. Stress fracture: Fracture line develops
5. Complete fracture: Full-thickness propagation

Early detection at stress reaction stage allows conservative management.

History:

Typical presentation:

• Young athlete or military recruit
• Insidious onset groin pain
• Activity-related symptoms
• Pain worse with impact activities
• May have preceding prodromal ache

Key history questions:

• Training history (recent increases?)
• Menstrual history (females)
• Dietary intake and RED-S screening
• Previous stress fractures
• Medication history (steroids, bisphosphonates)

Physical examination:

Key tests:

Hop test:

• Should NOT be performed if high clinical suspicion
• Risk of displacing an incomplete fracture
• Use clinical judgment

Differential diagnosis of activity-related groin/hip pain in the young athlete:

Clinical Imaging

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Imaging approach:

Plain radiographs:

• Often negative for 2-4 weeks
• May show sclerotic line, periosteal reaction
• Full-length views recommended
• Compare to contralateral side

MRI (Gold Standard):

• Detects stress reaction before fracture line visible
• Shows bone marrow edema (T2/STIR hyperintense)
• Identifies fracture line if present
• Determines tension vs compression involvement
• Essential for early diagnosis

When to order MRI:

• Clinical suspicion with negative X-rays
• Early diagnosis critical (athletes in-season)
• Determine extent and location
• Monitor healing progress

CT scan:

• Better for visualizing cortical fracture lines
• Less sensitive for early stress reaction
• Useful if MRI contraindicated or equivocal

Bone scan:

• Highly sensitive but less specific
• Shows focal uptake at fracture site
• Less commonly used now due to MRI availability
• Cannot distinguish tension vs compression

Laboratory investigations:

• Vitamin D level
• Calcium
• TSH (if RED-S suspected)
• Consider DEXA for BMD (if triad/RED-S)

Avascular necrosis:

• Most feared complication
• Risk increases with displacement
• Time to treatment matters
• May occur despite optimal care
• Monitor long-term

Nonunion:

• More common if displaced
• Risk factors: smoking, metabolic bone disease, poor fixation
• Treatment: revision with bone graft, valgus osteotomy, or arthroplasty

Postoperative protocol:

Return to sport criteria:

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

Timeline for return:

• Compression side (conservative): 3-4 months
• Tension side (surgical): 4-6 months
• Displaced fracture: 6-12 months (depends on AVN)

Prognostic factors:

Expected outcomes by type (figures are approximate; outcome is dominated by displacement and time-to-diagnosis):

Compression-side (non-operative):

• High union rate with compliant non-weight bearing and serial imaging
• Return to sport typically 3-4 months
• Long-term prognosis excellent once healed, provided RED-S/metabolic drivers are corrected

Tension-side (operative):

• Good union with timely fixation
• Return to sport typically 4-6 months
• AVN risk increases with any displacement or delay

Displaced fractures:

• Markedly worse: high AVN and non-union risk; sporting outcomes considerably worse once displaced (Robertson & Wood 2017)
• May require arthroplasty if AVN develops

Primary prevention:

Training principles:

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

Nutritional factors:

• Adequate caloric intake
• Calcium: 1000-1500mg daily
• Vitamin D: maintain greater than 75 nmol/L
• Avoid relative energy deficiency

Female athlete screening:

• Menstrual history in all female athletes
• RED-S screening questionnaire
• Low threshold for endocrine referral
• Bone health assessment if abnormalities

Secondary prevention:

• Address all modifiable risk factors
• Gradual return to sport
• Cross-training during recovery
• Long-term bone health monitoring

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).

Registry note: FNSF is not separately tracked in arthroplasty registries (NJR, AJRR, AOANJRR, SHAR), but those registries do inform salvage outcomes when AVN or non-union leads to arthroplasty in a young patient — generally good implant survival but a high revision burden over a long expected lifespan, reinforcing the priority of joint-preserving early fixation.

Global practice variation:

• High-resource settings: ready MRI access enables early diagnosis at the stress-reaction stage; multidisciplinary RED-S pathways (sports physician, dietitian, endocrinologist).
• Limited-resource settings: reliance on radiographs and bone scan delays diagnosis, increasing displacement and AVN; a higher index of suspicion and earlier protected weight-bearing partly offset limited cross-sectional imaging.

Multidisciplinary pathway (universal): sports/orthopaedic assessment → urgent MRI → operative vs protected non-operative care by location → metabolic and RED-S work-up → staged return to load with bone-health optimisation.