Femoral Neck Stress Fracture

The history is the diagnosis. The typical patient is a young athlete or military recruit with:

• •Insidious-onset groin or anterior hip pain
• •Pain worse with running, jumping, or weight-bearing
• •Initial relief with rest, but pain returns and progresses
• •Often weeks to months of "groin strain" or "hip flexor tendonitis" labels before the correct diagnosis
• •Night pain or rest pain in advanced cases (a red flag for impending completion)

Examination - safer provocation tests preferred:

• •Anterior groin tenderness
• •Pain at extremes of hip range, particularly internal rotation
• •FABER (Patrick's) test may be positive
• •Heel strike (axial load) test can reproduce pain with less risk than hopping
• •Antalgic gait or limp in advanced disease

A note on the hop test: the single-leg hop is a classic textbook sign and a positive result is highly suggestive. However, in current UK SEM practice, do NOT repeatedly perform the hop test if FNSF is highly suspected - the impact can complete and displace a tension-side fracture in clinic. Use heel strike, FABER, and ROM provocation instead, and proceed directly to MRI.

Always assess for predisposing factors: training history, menstrual history, nutrition, sleep, previous stress fractures, and red flags for inflammatory or sinister causes.

High-risk stress fracture sites to recognise: femoral neck (tension-side), navicular, anterior tibial cortex, patella, talus, medial malleolus, sesamoids, and proximal fifth metatarsal.

Differentials: hip flexor or iliopsoas tendinopathy (resisted hip flexion pain, no axial-load pain); adductor tendinopathy or groin strain (squeeze positive); sacral or pubic rami stress fracture (same RED-S demographic; sacral or pubic tenderness); femoroacetabular impingement (positive FADIR, cam or pincer); acetabular labral tear (catching, clicking); hip OA (older, joint-space narrowing); septic arthritis (fever, raised inflammatory markers); inguinal hernia or sportsman's groin (cough impulse); bone tumour or metastasis (night pain, weight loss, raised inflammatory markers).

Plain radiographs (AP pelvis and lateral hip) are first-line but negative in up to two-thirds of acute cases. When positive, look for a cortical lucent line, sclerosis, periosteal reaction, or a frank cortical break in the inferomedial (compression) or superolateral (tension) cortex.

A negative or equivocal X-ray does NOT exclude FNSF. In any athlete with persistent impact-related groin pain and high clinical suspicion, normal X-rays should be followed by urgent MRI - not delayed repeat X-rays.

MRI of the hip and pelvis is the investigation of choice. It demonstrates:

• •Marrow oedema (early stress reaction before a fracture line is visible)
• •The fracture line
• •The anatomical position (compression vs tension side) that drives management
• •Concerning features such as hip joint effusion, increasing fracture-line extent, or progression despite offloading

This pathway aligns with NICE CG124, which states that when hip fracture is suspected despite negative adequate radiographs, MRI should be offered, with CT considered if MRI is unavailable within 24 hours or contraindicated.

CT is selectively useful for cortical fracture-line detail and surgical planning but does not show marrow oedema reliably. Bone scan is sensitive but non-specific and is largely superseded by MRI.

Investigate underlying contributors as guided by history:

• •Vitamin D, calcium profile, FBC, ferritin, thyroid function
• •Coeliac screen if iron deficiency, low BMD, or recurrent stress fractures
• •RED-S assessment using the IOC REDs CAT2 (a clinician-facing assessment tool led by an SEM physician or experienced multidisciplinary team, not a standalone screening questionnaire)
• •DXA for high-risk patients. Use Z-score in premenopausal women and men under 50 (not T-score). A Z-score of -2.0 or lower is "below the expected range for age". In weight-bearing athletes (who should naturally have positive Z-scores), per IOC RED-S and ACSM guidance, a Z-score under -1.0 is considered low BMD and prompts intervention - rather than waiting for the -2.0 non-athlete threshold

The defining decisions are anatomical pattern (compression vs tension side), extent (under or over 50% of femoral neck width on the compression side), and displacement.

Stress reaction (marrow oedema, no fracture line):

• •Strict offloading; urgent specialist review
• •Tension-side oedema still needs urgent orthopaedic input - location drives risk before a visible fracture line appears
• •Address bone health and RED-S contributors

Compression-side, incomplete (under 50% of neck width), undisplaced:

• •Strict non-weight-bearing on crutches for typically 6-8 weeks
• •Early specialist follow-up with serial imaging - do not wait passively until 6-8 weeks if symptoms persist or worsen
• •Progressive return to weight-bearing only after clinical and imaging clearance, followed by graduated rehabilitation
• •VTE risk assessment per NICE NG89: assess VTE and bleeding risk; consider LMWH or fondaparinux if VTE risk outweighs bleeding risk; consider stopping if immobilisation continues beyond 42 days. (LMWH and fondaparinux were off-label in under-18s when NICE published; relevant for adolescent athletes)
• •Address bone health: vitamin D, calcium, dietary review, RED-S management with multidisciplinary input

Compression-side, extensive (over 50% of neck width):

• •Biomechanically unstable - urgent orthopaedic review with consideration of prophylactic surgical fixation, even when undisplaced
• •The same threshold applies for any progression on serial imaging, persistent or worsening pain, inability to comply with non-weight-bearing, or failure of conservative care

Tension-side (superolateral):

• •Urgent orthopaedic referral for surgical fixation (typically cannulated screw fixation)
• •Strict non-weight-bearing pending surgery
• •Surgery is usually recommended even for undisplaced tension-side fractures because of the high risk of displacement, non-union, and AVN

Displaced (any side):

• •Emergency orthopaedic referral
• •AVN risk of the femoral head rises sharply with displacement and time to fixation
• •Surgical closed or open reduction and internal fixation; arthroplasty in selected older or salvage cases

Analgesia: simple analgesia and short-course NSAIDs per BNF (lowest effective dose, shortest period, with GI / renal / cardiovascular risk assessment). Do not rely on NSAIDs to continue training - analgesia must not mask symptoms during return to impact.

Counselling: this is a high-risk fracture and the priority is preventing progression, displacement, and AVN. Return-to-sport is imaging- and function-led, not time-led alone. Address upstream contributors aggressively (running biomechanics, training periodisation, RED-S, bone health, smoking cessation) to prevent contralateral recurrence.

Compression-side, conservative:

• •Phase 1 (weeks 0 to 6-8): strict non-weight-bearing on crutches; hip and core strengthening off the affected leg; cardiovascular work via deep-water running or upper-body ergometer (NO impact)
• •Phase 2 (transition): wean to full weight-bearing only after clinical and imaging clearance; hip ROM, glute and core work
• •Phase 3 (return to running): walk-jog progression; progressive surface and volume per stress fracture protocol
• •Phase 4 (return to sport): sport-specific reconditioning, biomechanical correction
• •Total recovery typically 4-6 months

Tension-side or post-fixation:

• •Surgeon-led protocol; protected weight-bearing typically 6-8 weeks
• •Progressive rehabilitation from around 6-12 weeks
• •Return to running often 4-6 months
• •Return to high-impact sport 6-12 months and only after imaging confirmation of healing

Address modifiable risk factors throughout: training load, footwear, RED-S, vitamin D, smoking cessation. Failure to address upstream causes risks recurrence on the contralateral side.

• •NICE CG124 (Hip fracture: management): UK framework supporting MRI when hip fracture is suspected despite negative adequate radiographs, with CT considered if MRI is unavailable within 24 hours.
• •NICE NG89 (VTE in over-16s): UK risk-assessment framework for VTE prophylaxis in lower-limb immobilisation, including LMWH or fondaparinux decision-making and the 42-day duration review.
• •2023 IOC Consensus Statement on REDs (BJSM 2023): current international consensus on Relative Energy Deficiency in Sport, including the REDs CAT2 clinician-facing tool integral to stress-fracture risk stratification.
• •ACSM and IOC athlete BMD guidance: weight-bearing athletes should have positive Z-scores; a Z-score under -1.0 is "low BMD" in this population and prompts intervention, rather than waiting for the non-athlete -2.0 threshold.
• •Devas (1965) compression vs tension classification: foundational anatomical classification that still drives modern management decisions on the femoral neck.
• •BASEM RED-S resources: UK SEM-facing guidance for athlete bone health, energy availability, and recurrent stress fracture management.

• •Compression-side (inferomedial calcar) under 50% of neck width = conservative offloading; over 50% = consider fixation. Tension-side (superolateral) = urgent surgical fixation usually recommended even when undisplaced.
• •Displaced FNSF = orthopaedic emergency. AVN of the femoral head is the catastrophic complication via disruption of MFCA-derived retinacular vessels.
• •Anterior groin pain, pain at extremes of internal rotation, heel-strike axial load, and FABER are the safer bedside provocations. Do NOT repeatedly hop-test if FNSF is highly suspected - risk of completion.
• •Plain X-rays are negative in up to two-thirds of acute cases. Negative X-ray does NOT exclude the diagnosis. MRI is the investigation of choice per NICE CG124.
• •High-risk stress fracture sites: femoral neck tension-side, navicular, anterior tibial cortex, patella, talus, medial malleolus, sesamoids, and proximal fifth metatarsal.
• •VTE: NICE NG89 risk assessment if immobilised; LMWH or fondaparinux when VTE risk outweighs bleeding risk. DXA Z-score (not T-score) in premenopausal women and men under 50; under -1.0 is "low BMD" in weight-bearing athletes per IOC / ACSM.
• •RED-S (IOC 2023, REDs CAT2 clinician-facing tool) is integral to management. Hormone replacement or OCP alone does NOT correct the underlying low energy availability. Return-to-sport is imaging- and function-led.