A stress fracture in the hip is a serious overuse injury where repetitive loading forces cause microscopic damage to the bone. Unlike an acute fracture from a single traumatic event, this injury occurs when the bone cannot repair itself quickly enough to keep up with continuous mechanical stress. The most common location is the femoral neck, the short segment connecting the ball of the hip joint to the thigh bone. This specific location makes the injury particularly concerning and warrants prompt medical attention. Due to the unique biomechanics and blood supply, a femoral neck stress fracture is classified as a high-risk injury because of the potential for devastating complications if diagnosis is delayed.
Anatomy and Mechanism of Injury
The hip joint is a ball-and-socket structure where the head of the femur fits into the pelvis. The femoral neck, the segment beneath the femoral head, absorbs significant forces, often three to five times the body weight during activities like running. This constant, high-magnitude loading can initiate tiny cracks, known as a stress reaction, which can progress into a full stress fracture.
The location of the fracture line determines its stability and treatment. Weight-bearing loads place compressive forces on the inferomedial (lower, inner) side of the neck and tensile forces on the superolateral (upper, outer) side.
Fractures on the inferomedial side are compression-sided and considered stable because the bone’s internal structure resists collapse. Conversely, fractures on the superolateral side are tension-sided and categorized as unstable. The tension-sided fracture is more likely to displace, meaning the bone fragments shift out of alignment. This displacement severely threatens the blood supply of the femoral head, potentially leading to avascular necrosis, or bone death.
Causes and Risk Factors
The primary cause of a hip stress fracture is a sudden or excessive increase in physical activity that overwhelms the bone’s natural remodeling capacity. Athletes, particularly high-mileage runners and military recruits, frequently experience this overuse injury due to rapid changes in training volume or load.
Extrinsic Factors
Extrinsic factors include using worn-out or improper footwear that fails to adequately absorb impact forces during repetitive activities.
Intrinsic Factors
Intrinsic factors involve underlying physiological conditions that compromise bone strength. Low bone mineral density, reduced body mass index, and poor nutritional status can predispose an individual to an insufficiency fracture, where normal stress breaks abnormal bone. In female athletes, the “female athlete triad”—combining energy deficiency, menstrual dysfunction, and low bone density—significantly increases the risk.
Biomechanical Factors
Muscle fatigue contributes to the injury mechanism by altering force distribution across the hip. Muscles like the gluteus medius normally stabilize the joint and counteract tensile forces on the femoral neck. When these muscles fatigue, their protective function diminishes, placing excessive strain directly on the bone. Underlying biomechanics, such as an abnormal gait pattern or muscle imbalance, further contribute to uneven stress distribution.
Recognizing Symptoms and Urgency
The onset of a hip stress fracture is typically gradual, beginning as a dull ache in the groin area related to activity. Initially, the pain may subside quickly with rest, but as the fracture progresses, it becomes more persistent and occurs earlier in a training session. In advanced cases, the pain may be present even while resting and can wake the patient at night, signaling a more severe injury.
Localized tenderness over the front of the hip or groin is a common finding. Any pain with weight-bearing activities, such as a noticeable limp, should raise immediate concern. Seeking immediate medical evaluation is important due to the high potential for the fracture to displace and disrupt blood flow to the femoral head.
Diagnostic Procedures
Diagnosis begins with a detailed medical history and a physical examination to assess pain location and severity. Standard X-rays are usually the first imaging tool, but they are often insufficient for an early diagnosis. In the first few weeks, the microscopic fracture line may not be visible on X-rays, potentially leading to a false-negative result.
Magnetic Resonance Imaging (MRI) is considered the gold standard for confirming a hip stress fracture, especially in the early stages. An MRI detects subtle bone marrow edema that signifies a stress reaction or early fracture. This advanced imaging is crucial for differentiating between stable compression-sided and unstable tension-sided fractures. Bone scans can also confirm a stress injury by showing increased metabolic activity in the affected area, though they provide less anatomical detail than an MRI. A CT scan may be used if surgical planning is required, providing a high-resolution, three-dimensional view of the fracture pattern.
Treatment and Recovery Expectations
Treatment for a femoral neck stress fracture is determined by its location and severity, primarily whether it is a low-risk compression-sided or a high-risk tension-sided injury.
Non-Operative Management
Incomplete compression-sided fractures are managed non-operatively with immediate and strict non-weight bearing on the affected leg. The patient must use crutches or a mobility aid to prevent load from passing through the fracture site. This period is followed by a gradual return to weight-bearing activities, guided by a physical therapist.
Recovery for these fractures typically takes three to six months before a full return to sport or high-impact activity is possible. Nutritional deficiencies, such as low Vitamin D or calcium levels, must be corrected during healing to optimize bone repair.
Surgical Intervention
Tension-sided fractures, or any displaced fracture, require urgent surgical intervention. The standard procedure involves internal fixation, where metal screws are inserted across the fracture site to stabilize the bone and prevent further displacement. Surgery protects the blood supply to the femoral head and minimizes the risk of avascular necrosis. Following fixation, patients begin a period of protected weight-bearing, with full recovery often taking at least six months, depending on the severity of the injury and the healing response.