summary A Femoral Neck Stress Fracture (FNSF) is caused by repetitive loading of the femoral neck that leads to either compression side (inferior-medial neck) or tension side (superior-lateral neck) stress fractures. Diagnosis can be be made with radiographs but findings often lag behind often resulting in negative radiographs early on. MRI is the diagnostic study of choice in the presence of normal radiographs. Nonoperative treatment is indicated for compression sided fractures with < 50% femoral neck width. Cannulated screw fixation is indicated for tension sided stress fractures or compression sided fractures with > 50% width or hip effusion. Epidemiology Incidence 0.04% of military personnel 20 per 10,000 recruits per year 3-5% of sports-related stress fractures 9% of lower extremity stress fractures Demographics age range 16-56 years of age male: female ratio female > male race most commonly caucasian Risk factors demographic female caucasian older age activity-related military personnel track and field or cross-country athlete high training volume and intensity medical lower BMI decreased bone mineral density energy deficiency (energy expenditure > caloric intake) tobacco use anatomical femoroacetabular impingement (FAI) coxa vara abnormal running gait pattern Etiology Pathophysiology mechanism repetitive loading of femoral neck exceeds elastic properties of bone causing microscopic fracture continuous microscopic fractures exceed osteoblastic activity resulting in stress fracture Genetics 3x higher risk with absent gene calcitonin receptor C allele vitamin D recepter C-A haplotype Associated conditions "female athlete triad" amenorrhea, eating disorder, and osteoporosis must be considered in any female athlete with stress fracture 2-4x increased risk hormonal dysregulation of hypothalamic-pituitary-gonadal (HPG) axis decrease in estrogen levels which is necessary for osteoblast maturation increased osteoclast activity relative to osteoblast activity oral-contraceptives use increases bone mineral density FAI associated with 50% of FNF stress fractures 42% CAM lesion 78% pincer lesion Anatomy Osteology neck-shaft angle 130 +/- 7 deg anteversion 10 +/- 7 deg calcar region strongest part of femoral neck with dense bone along posteromedial neck Ligaments hip capsule reinforced by 3 ligaments iliofemoral ligament composed of lateral (superior) and medial (inferior) fibrous branches insert onto AIIS and extends out to IT line forming Y-shaped ligament of Bigelow reinforce capsule during ER and extension ischiofemoral ligament inserts on ischium posteroinferior to acetabular rim and attaches to posterior IT line reinforce capsule during IR in neutral and flexion-adduction positions pubofemoral ligament inserts on superior pubic ramus and insert onto femur (with medial iliofemoral and inferior ischiofemoral ligaments) reinforcing inferior capsule to restrict excessive abduction and ER during hip extension Muscles hip extensors induce highest tensile strain in proximal-posterior neck cortex and compressive strain in anterior neck primary hip extensors gluteus maximus hamstring muscles semitendinosus semimembranosus bicep femoris long head biceps femoris short head knee extensors lowest potential to load femoral neck due to low hip reaction force generated by rectus rectus femoris only hip-spanning muscle of knee extensor muscle group hip flexors highest compressive strain in proximal-posterior neck cortex and tensile strain in anterior neck primary hip flexors iliopsoas sartorius rectus femoris hip abductors induced highest compressive strain in distal and superolateral neck primary abductors gluteus medius gluteus minimus tensor fascia lata Blood supply of femoral head provided by three main branches medial femoral circumflex artery predominant blood supply to femoral head lateral femoral circumflex artery artery of ligamentum teres small contribution (~10%) greater displacement of fracture leads to greater risk of disruption of vascular supply Biomechanics 3-5x body weight across femoral neck with jogging 8.4x body weight with running compression-sided fractures compressive forces occur primarily along inferior femoral neck near calcar region microfracture propagates at 45 deg of applied forces leading to more stable oblique pattern tension-sided fractures bending forces along superolateral neck are stabilized by abductor forces adbuctors fatigue and fracture propagates at 90 deg of cortex unstable transverse pattern CLASSIFICATION Femoral Neck Stress Fracture Classifications Fullerton-Snowdy Shin Rohen-Quinquilla Steele Modality Radiographs and Bone scan Radiographs and MRI MRI Radiographs and MRI Categories Compression-sided Compression-sided edema + no fracture Fracture line <50% Fracture line > 50% Low grade I : Endosteal edema ≤ 6 mm Low grade II: Endosteal edema >6 mm + no fracture Compression-sided edema no fracture Fracture <50% without hip effusion Fracture <50% with hip effusion Fracture >50% with hip effusion Tension-sided Tension-sided High grade III: fracture <50% neck width High grade IV: fracture >50% neck width Tension-sided Displaced Displaced Displaced Presentation History history of overuse running activities recent increase in training high impact activities Symptoms insidious onset of thigh or groin pain may radiate to knee pain increases with repetitive weight-bearing activities pain improves with cessation of activity completion of fracture may be associated with cracking or popping and inability to bear weight Physical exam palpation tenderness directly over groin region (62%) motion pain with extremes of hip motion (79%) antalgic gait provocative tests pain with straight leg raise, log roll, or axial load Imaging Radiographs recommended views AP pelvis AP hip cross-table lateral of hip findings early findings usually normal 90% of initial radiographs normal 50% of repeat radiographs at 4-6 weeks late findings may take 6-8 weeks to see radiographic changes "grey cortex sign" linear lucency endosteal callous formation sclerotic line traversing trabeculae MRI indications modality of choice when radiographs are negative findings periosteal or bone marrow edema on STIR or fat-suppressed T2 line of decrease of intensity on T1 coronal corresponding with signal on T2 and STIR hip effusion 8x higher risk of propagation utility sensitivity 100% specificity 100% Bone scan indication negative radiographs with contraindication to MRI largely replaced by MRI findings increased uptake in femoral neck uptake due to increased metabolic activity secondary to bone remodeling utility sensitivity 93-100% specificity 76-95% false-positive rate 32% DIFFERENTIAL DIAGNOSIS Early osteoarthritis generally older patients with limited motion, particularly IR radiographs with joint space narrowing and subchondral sclerosis Hip labral tears hip pain and snapping in young active patient commonly with FAI MRI arthrogram study of choice Chondral defects of hip significant clinical overlap with labral tears, FAI, and hip dysplasia MRI can detect chondral defect and loose bodies Rectus strain athlete with more sudden onset of hip pain and tenderness over rectus near AIIS pain with resisted hip flexion or extension Hip Osteonecrosis history of irradiation, trauma, sickle-cell, steroids, alcoholism, lupus, and other risk factors radiographic findings showing sclerotic changes, crescent sign, or flattening of femoral head Osteoid osteoma insidious onset with night time pain worse with EtOH and improves with NSAIDs radiographs with reactive bone around central nidus other neoplasms should be considered Lumbar disc herniation pain is more positional than activity-related may be associated with back pain, paresthesias and positive SLR Treatment Nonoperative non-weight bearing and activity restriction indications compression side stress fractures + fracture line <50% width tension side stress changes with no fracture line (MRI) outcomes 75-100% heal and can return to activity if correct indications met Operative cannulated screw fixation indications tension side stress fractures compression side stress fractures with fatigue line >50% femoral neck width compression side stress fracture with hip effusion 8x increase risk of progression with presence of hip effusion progression of compression side stress fractures technique inverted triangle using three cannulated screws (7.0 or 7.3 mm) outcomes similar outcomes versus lower-risk FNSF treated nonoperative effectively prevent progression to displaced fracture more likely to result in military seperation open reduction internal fixation indications displaced femoral neck stress fracture technique cannulated screws sliding hip screw outcome lower return to activity following ORIF for displaced FNSF than nondisplaced TECHNIQUES Non-weight bearing and activity restriction for 6 weeks technique increase 25% body weight per week until full painless full weight-bearing gradual return to full weight-bearing unrestricted activity at 3-4 months pros avoid hardware-related complication cons risk of refracture (case reports) progression of fracture Cannulated screw fixation pros reduce risk of progression of fracture potential for earlier weight-bearing cons hardware-related complications approach percutaneous mini-open direct lateral technique three cannulated screws in inverted triangle generally preferred over two inferior calcar inferior calcar provides higher load to failure posterosuperior anterosuperior starting point should be at or above lesser trochanter to avoid stress riser screws should be parallel with maximal spread threads should be in head fragment and not crossing fracture line washer may be used to stop the screw head from penetrating greater trochanter complications screw cutout varus collapse implant failure shortening of femoral neck nonunion Open reduction internal fixation approach anterior Smith-Peterson internervous plane is femoral and superior gluteal nerve (SGN) superficial tensor fascia lata (SGN) and sartorius (femoral) deep gluteus medius (SGN) and rectus femoris (femoral) reduction via anterior approach followed by separate lateral incision for implant insertion anterior approach allow for better direct visualization of entire femoral neck Watson-Jones intermuscular plane tensor fascia lata (SGN) and gluteus medius (SGN) reduction and insertion of implant performed through same approach limited visualization of subcapital neck region technique anatomic reduction is paramount to mitigate risk of osteonecrosis early surgical intervention also reduces risk of AVN reduction tools joysticks with k-wires or Shantz pin pointed reduction clamps medial buttress plate cannulated screws or dynamic hip screw consider autologous bone graft to mitigate nonunion risk complications surgical site infection avascular necrosis nonunion screw cutout malreduction implant failure Complications Fracture progression or completion incidence 14% associated with disabling complications avascular necrosis nonunion malunion risk factors hip effusion associated with 8x risk of progression size of fracture not associated with progression delayed diagnosis treatment cannulated screw fixation Avascular necrosis incidence unlikely with incomplete stress fracture more common with displaced FNSFs (5-42%) factors associated with AVN in displaced FNSFs delay in surgical treatment initial displacement varus malreduction treatment precollapse core decompression or vascularize free-fibula graft collapse hip arthroplasty Delayed union or nonunion incidence unlikely with incomplete stress fracture more common with displaced FNSFs (9-44%) risk factors delay in treatment noncompliance treatment valgus intertrochanteric osteotomy Varus malunion incidence 5-33% treatment revision ORIF with bone grafting hip arthroplasty Refracture case reports following nonoperative treatment Prognosis Lacking high-quality studies natural history likely for fracture to progress and displace negative predictors of return fracture displacement high athletic ability or demand (versus recreational athletes) delayed treatment survival with treatment return to military ~75% with nonoperative treatment ~40-45% with operative treatment return to sports 30-100% with nonoperative treatment 48-56% with operative treatment