Stress Fractures Presented by M.A. Kaeser, DC Summer 2009

General considerations Term is applied to a bone injury incurred as the result of repetitive stress of lower magnitude than required for an acute traumatic fracture Occurs in normal or abnormal bone Radiographs are insensitive in the early course Bone scans are modality of choice MRI will depict neoplasm versus stress fracture

Definitions Fatigue fracture –Occurs secondary to an abnormal amount of stress or torque applied to a normal bone –Examples: military recruits, runners, dancers, people who inadequately train Insufficiency Fracture –Occurs with normal stress placed on abnormal bone –Examples: Paget’s, osteoporosis, osteomalacia or rickets, osteopetrosis, fibrous dysplasia, OI

Causes Major cause is abnormal degree of repetitive trauma Related to increased physical trauma May be related to muscular imbalance or altered biomechanics (rigid supination of foot, varus deformities of foot, LLI) May follow certain surgical procedures (bunionectomies, hip replacement, knee surgery, fusion of the lumbosacral junction) Deformity from OA, esp. at knee Menstrual irregularities may predispose women to stress fractures

Common sites Metatarsals are M/C, esp. middle and distal portions of the shaft of the second and third metatarsals –Frequent in military recruits (march fracture, Deutschlander’s disease) Due to fatigue of the peroneus longus muscle leading to instability of the foot –Stress fractures of the 2 nd and 3 rd metatarsals may complicate Morton’s syndrome (congenitally shortened first metatarsal)

Common sites continued Proximal tibia –High incidence in joggers, marchers and ballet dancers Calcaneus –Found in military recruits and long-distance runners Proximal or distal metaphyses of the fibula –Runners and ballet dancers Ribs –Rowers (12%)

Common sites continued Pars interarticularis of the lower L/S –M/C site for stress fracture of the entire skeleton –May be found w/ or w/o spondylolisthesis Sacrum –M/C in elderly women with osteoporosis –Associated with neural compromise (paraesthesias and sphincter dysfunction)

Clinical Features More common in women than men Pain, related to activity and relieved by rest Soft tissue swelling with localized tenderness over the area of stress Bones of lower extremity are most frequently involved More than one site can be present

Radiologic Features Initial radiographic examination may fail to reveal the fracture line Minimum radiographic latent period is days CT may be helpful in demonstrating the fracture line Bone scan is modality of choice –Focal uptake at the site of fracture on delayed images is characteristic but not specific –Scan may be active for up to 12 months after healing

Radiologic Features continued Combination bone scan with tomography (SPECT) is useful for active stress in pars CT is useful when diagnosis is in doubt MRI –Low signal on T1 –High signal on T2 if local hemorrhage is present (if not the signal is low on T2)

Roentgen Signs Periosteal response –Most frequently seen and reliable signs are periosteal and endosteal cortical thickening –Solid pattern of periosteal response –Cortical thickening is localized to the area of stress fracture Fracture line –Exuberant periosteal new bone will obscure the radiolucent fracture line –Fracture may be too thin to see –Oblique fractures are most common, transverse and longitudinal may occur –CT will depict fracture when plain film doesn’t

Transverse opaque bands Enface –Periosteal callus forms a linear, transverse, radiopaque band –Margins are hazy and pooly defined (this differentiates it from growth lines)

Differential Diagnosis Osteomyelitis –Creates a significant periosteal response –Lytic bone destruction adjacent to periosteal callus confirms osteomyelitis Osteosarcoma –Both produce a periosteal response (stress fracture = solid, o-sarc = spiculated) –Bone destruction will be seen with o-sarc –CT depicts a linear radiolucent fracture line which diagnoses a stress fracture

Differential Diagnosis continued Osteoid Osteoma –Oval radiolucent nidus of osteoid oseoma vs radiolucent fracture line Growth Arrest Lines –Discrete radiopaque lines through the metaphysis (growth arrest lines) –Radiopaque line is broad, hazy, ill-defined margin to its edge in stress fractures –GALs are usually found in other bones as bilateral, symmetrical, well-defined radiopaque bands

Calcaneusparachuting Claviclepersistent tic First ribbackpacker 7 th -9 th ribscoughing, golfing, rowing Scapula (coracoid)trap shooting Ulnapitchfork work, wheelchair Phalanx tuftguitar playing 5 th metatarsalrunning on banked track fields Hook of hamateequipment holding (tennis, golf, baseball)