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 login to view 3 more bullets 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 login to view 3 more bullets ischiofemoral ligament login to view 2 more bullets pubofemoral ligament login to view 2 more bullets Muscles hip extensors induce highest tensile strain in proximal-posterior neck cortex and compressive strain in anterior neck primary hip extensors login to view 6 more bullets knee extensors lowest potential to load femoral neck due to low hip reaction force generated by rectus rectus femoris login to view 1 more bullet hip flexors highest compressive strain in proximal-posterior neck cortex and tensile strain in anterior neck primary hip flexors login to view 3 more bullets hip abductors induced highest compressive strain in distal and superolateral neck primary abductors login to view 3 more bullets Blood supply of femoral head provided by three main branches medial femoral circumflex artery login to view 1 more bullet lateral femoral circumflex artery artery of ligamentum teres login to view 1 more bullet 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 login to view 3 more bullets late findings login to view 5 more bullets 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 login to view 1 more bullet utility sensitivity 100% specificity 100% Bone scan indication negative radiographs with contraindication to MRI login to view 1 more bullet findings increased uptake in femoral neck login to view 1 more bullet 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 login to view 2 more bullets outcomes login to view 1 more bullet Operative cannulated screw fixation indications login to view 5 more bullets technique login to view 1 more bullet outcomes login to view 3 more bullets open reduction internal fixation indications login to view 1 more bullet technique login to view 2 more bullets outcome login to view 1 more bullet 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 login to view 4 more bullets 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 login to view 7 more bullets Watson-Jones login to view 4 more bullets technique anatomic reduction is paramount to mitigate risk of osteonecrosis login to view 1 more bullet reduction tools login to view 3 more bullets 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 login to view 1 more bullet 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 login to view 1 more bullet collapse login to view 1 more bullet 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 login to view 2 more bullets return to sports login to view 2 more bullets