Hip pain after trivial trauma

A 48 year old woman attended the emergency department with a two day history of pain in the left hip. No bruising, tenderness, restriction of movement, or deformity was found on examination. She was able to bear weight on her left leg. A diagnosis of musculoskeletal pain was made, and she was discharged home with analgesia and advice.

She came back the next day with increasing pain in the left hip. Clinical examination revealed no new findings, and she was discharged with the same diagnosis and management plan.

The patient presented again four days later, unable to walk or stand because of pain. X ray examination of her left hip and pelvis was arranged (fig 1).

Fig 1 Radiograph of the pelvis

Questions

1. What are the radiological findings?
2. What is a stress fracture and what are the common sites affected?
3. What is a pseudoarthrosis?
4. What is the management in this patient?

Answers

1. The radiograph shows an old fracture of the left neck of femur with pseudoarthrosis. A stress fracture is identified in the right hip.
2. A stress fracture is a break in the bone caused by repetitive stress such as walking or running.
3. Pseudoarthrosis is the formation of a false joint caused by failure of the bones to fuse properly, either congenital or after a fracture. This condition is often associated with stress fractures. Pseudoarthrosis of the femoral neck after stress fracture has been described but is rare.
4. A hemiarthroplasty of the left hip was done. (Hip hemiarthroplasty, or arthroplasty, is a surgical procedure in which the diseased parts of the hip joint are removed and replaced with new, artificial parts. These artificial parts are called a prosthesis (fig 2).) Subsequent histological examination of the femoral head and neck did not show any evidence of osteoarthritis, osteoporosis, or malignancy. The patient was discharged and given oral analgesics and a calcium and vitamin D3 supplement.

Discussion

Radiograph of the pelvis confirmed a stress fracture in the neck of right femur, which did not extend its entire breadth.

Stress fractures are classified into two types: fatigue fractures and insufficiency fractures. Fatigue fractures occur in normal bone in healthy young or middle aged individuals, secondary to repetitive mechanical stress (for example, in runners, athletes, and military recruits).¹ Insufficiency fractures occur in elderly patients whose bone fatigue strength is reduced due to osteoporosis, osteomalacia, or other diseases. In these patients, fractures can occur even after routine non-exertional activity.^1-2

Fullerton and Snowdy described three categories of femoral neck stress fractures: tension stress fractures, compression stress fractures, and displaced femoral neck stress fractures.³ Tension stress fractures occur on the superolateral aspect of the femoral neck and are at increased risk for fracture displacement. These usually require operative stabilisation. Compression stress fractures occur on the inferomedial aspect of the femoral neck and have a lower risk of displacement and are therefore usually managed conservatively, with frequent follow-up radiographs. Displaced femoral neck stress fractures are completely displaced fractures and usually require operative treatment.

Radiographic changes consistent with femoral neck stress fractures usually appear on plain radiograph as an area of sclerosis or cortical defect on the superolateral or inferiomedial aspect of the femoral neck (fig 1).^3-5 Common sites affected are the metatarsals, calcaneum, distal shaft of fibula (the runner’s fracture), tibia shaft (proximal third in children, middle third in athletes, distal third in elderly patients), femoral shaft (chiefly lower third), and femoral neck (at any age).

A more detailed history on admission revealed that the patient had sustained stress fractures in her foot some years previously after running with her dogs every day. Full blood count, urea and electrolytes, serum calcium, and liver function tests were within normal limits.

This case reminds us of the importance of taking a detailed history in patients presenting with apparently minor symptoms after trivial injuries. Re-attendance with the same complaints should prompt more detailed consideration.

Fig 2 Diagrammatic representation of a hemiarthroplasty

1. Daffner RH, Pavlov H. Stress fractures: current concepts. Am J Roentgenol 1992;159:245-52.
2. Tountas AA. Insufficiency stress fractures of the femoral neck in elderly women. Clin Orthop 1993;292:202-9.
3. Fullerton LR, Snowdy HA. Femoral neck stress fractures. Am J Sports Med 1988;16:365-77.
4. Blickenstaff LD, Morris JM. Fatigue fracture of the femoral neck.. J Bone Joint Surg 1966;48A:103-4.
5. Devas MB. Stress fracture of the femoral neck. J Bone Joint Surg 1965;47B:728-37.