Knee pain/thigh pain in an obese boy

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This is a large 10-year old male who presents to the acute care clinic with a two week history of right thigh and knee pain. He states that the pain is mainly in his thigh (points to his upper thigh) but radiates down to his knee.

He was playing basketball when he collided with another player and fell. He noted severe pain in his thigh and had to limp home, mostly on his left leg. Since then, he has been complaining of pain in his right thigh when bearing weight.

However, the pain would subside when lying in bed. He did not appear to improve much and he was finally brought to an acute care clinic. He had no history of fever, rash, chest discomfort, or pains in other joints.

 

 

Exam findings

T37.0 (oral), P66, R20, BP 112/65, weight 69.3 kg (>>95th percentile), height 152 cm (>95th percentile). Alert, cooperative, in no distress while lying down. Obese and large for age.

HEENT unremarkable. Neck normal range of motion. Heart regular without murmurs. Lungs clear. Abdomen round contour, soft, non-tender, bowel sounds active.

Right lower extremity: moderate tenderness in the upper anterior thigh. Severely tender in the hip. Pubic symphysis non tender. Mid thigh and knee non-tender. Tibia/fibula and foot non-tender. No joint swelling noted. Range of motion about the hip is not done. Range of motion of the right knee is good.

Left lower extremity: mild tenderness of the hip on palpation. Mild tenderness on range of motion testing. Good range of motion. Otherwise unremarkable. Although his chief complaint is thigh pain, his exam indicates that his injury is in his hip. He probably perceives this hip pain as pain in his upper thigh and this is how he expressed his pain to others. Radiographs of the hips are ordered.

 hips

A common pitfall is to focus on the patient’s chief complaint. In this case, focusing on the thigh may lead one to focus on the mid thigh and ignore the hip. His exam clearly points to his hip as the source of his pain. Whenever a patient complains of thigh pain, always examine the hip since this is frequently the source of the thigh pain. Hip injuries may also present with knee pain. Whenever a patient complains of knee pain, always examine the hip since this is occasionally the source of the knee pain.

The history of his collision and fall suggests an acute injury such as a non-displaced fracture. An obese child with hip pain in this age group should always raise the possibility of slipped capital femoral epiphysis. His hip radiographs show a slipped capital femoral epiphysis on the right. His left hip appears to be normal. However, it is difficult to rule out an early slip on the left as well.

He is very heavy and he has been putting most of his weight on his left hip for two weeks because of the pain in his right hip. He now has mild tenderness in his left hip. He is hospitalized and put at bedrest. After a few hours of bedrest, his left hip is no longer tender. His left hip exam is completely normal.

He is taken to the operating room for internal fixation of his right femoral capital epiphysis. The radiographic diagnosis of slipped capital femoral epiphysis (SCFE) can be subtle. In this case, the physis appears to be wider and more lucent in the patient’s right hip compared to his left. This is probably due to SCFE, however, this sign cannot be relied upon alone. The position of the femoral head epiphysis should resemble a cap over the physis. Subtle cases may just show a slight malpositioning of the epiphysis. Examine the diagram of our patient’s hips.

hip diagram

The lines drawn along the superior border of the proximal femur metaphysis (the Klein line) should intersect part of the proximal femoral epiphysis. The patient’s right hip (left on the screen) shows the line just touching the lateral margin of the epiphysis. This is abnormal, indicating that the femoral capital epiphysis has slipped inferiorly and medially. The patient’s normal left hip (right on the screen) shows the line intersecting the lateral part of the femoral epiphysis. This is normal. Some cases of SCFE are very obvious.

scfe

You don’t need to draw the lines here to appreciate that the patient’s left hip (right on the screen) is abnormal. This is a severe left slipped capital femoral epiphysis. However, the slipped capital femoral epiphysis on the right may not be as obvious, especially if the left hip distracted your attention. This patient has bilateral SCFE, severe on the left, and moderately severe on the right.

Slipped capital femoral epiphysis is a diagnosis that will occasionally present to an emergency department with acute, subacute, or chronic pain in the hip, thigh, or knee. The diagnosis of SCFE is not difficult if it is considered. However, patients may have vague symptoms that don’t precisely point to the hip. Their degree of pain may range from severe to non-existent. Their ambulatory ability may range from non-weight bearing to a normal gait.

The pitfall of misdiagnosing SCFE as a pulled muscle, a hip bruise, a hip sprain, a Charlie horse, or a knee sprain should be avoided by carefully examining the hip in any patient presenting with hip, thigh, or knee pain. Most SCFE patients prefer to keep their hip externally rotated. A major clinical finding in SCFE is their inability to fully internally rotate their hip. SCFE can be detected radiographically in most instances. In obvious cases, the epiphysis is obviously displaced. In subtle cases, the epiphyseal plate (physis) may be widened or irregular compared to the normal side. A line drawn along the superior border of the metaphysis (the Klein line) may intersect less of the epiphysis compared to the normal side (as noted in the diagram).

In other subtle cases, the physis may appear to be thinner than the normal side. This can occur if the slip occurs posteriorly. Early slips can be difficult to demonstrate radiographically. AP views of the hips can only detect inferior and medial slips. Early slips tend to slip only in the posterior direction. Posterior slips are best seen on lateral views of the hips, but these are difficult to obtain.

CT scanning can be helpful for orthopedic surgeons, but this is not usually needed in the emergency department. MRI scanning is not useful in SCFE.

Treatment is largely the responsibility of the orthopedic surgeon. However, one of the major goals of treatment is to prevent further slipping. Further slipping cannot be prevented unless the diagnosis of SCFE is made on the initial presentation.

Avoid the pitfall of missing this diagnosis since sending the patient home with the wrong diagnosis will likely worsen the slip. These patients should be put at bedrest. Simple traction is reasonable, however, it is best to discuss this with an orthopedic surgeon.

 

References

Morrissy RT. Slipped Capital Femoral Epiphysis (Chapter 24). In: Morrissy RT (ed). Lovell and Winter’s Pediatric Orthopedics, third edition. Philadelphia, JB Lippincott Co., 1990, pp. 885-902.

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Prof Loren Yamamoto MD MPH MBA. Professor of pediatrics at the University of Hawaii and a practising pediatric emergency doctor in Honolulu. | Contact | View Loren's DFTB posts