THE DEMOGRAPHICS OF ATYPICAL AND IDIOPAHTIC SLIPPED CAPITAL FEMORAL EPIPHYSIS: IMPLICATIONS FOR FURTHER DIAGNOSITC INVESTIGATION AND THE DESCRIPTION OF THE AGE-WEIGHT TEST (AWT)
Participants: R.T. Loder, M.L.V.H. Greenfield
Keywords: slipped capital femoral epiphysis, radiation therapy, renal failure, endocrine disorder, age, weight, age-weight test
Introduction
Slipped capital femoral epiphysis (SCFE) is a well-known adolescent hip disorder that may be classified as atypical or idiopathic. Atypical SCFEs (1) are those associated with endocrine disorders (2, 3) with other metabolic disorders such as renal failure osteodystrophy (4, 5, 6), or with radiation therapy for malignancies in the pelvic areas (7, 8). While the majority of SCFEs are idiopathic (9), a differential diagnosis regarding the underlying etiology should be considered when the physician encounters a newly diagnosed case of SCFE.
If it is present, the parents or patient will generally give a pre-existing history of radiation therapy. However, SCFE may be the initial presentation a metabolic disorder. In this latter situation the clinician must decide whether further diagnostic work-up is indicated. Such a work-up is important, not only to diagnose and treat the underlying medical condition, but also to anticipate and minimize anesthetic problems during surgery (10, 11). Anesthetic problems, which stem from the underlying metabolic disorder, may be potentially fatal to the patient (11). Some clinicians recommend an aggressive approach to further work-up (3). However, in this era of health care cost containment, the luxury of such an approach is not always possible.
The purpose of this study was to investigate demographic variables of both idiopathic and atypical SCFE to determine when further evaluation is warranted.
Materials and Methods
The demographic variables of 433 children with 612 SCFEs was compile and divided into 4 subgroups: I—idiopathic (ID), II—renal failure (RFA), III—radiation therapy (RTA), and IV—endocrine disorders (ENDA). Statistical analyses consisted of univariate, bivariate, and stepwise forward multiple logistic regression.
Results
There were 285 ID, 31 RTA, and 85 ENDA children. Logistic regression analysis demonstrated that both age and weight percentile groups were predictive of an atypical SCFE: age less than 10 years or greater than 16 years (p = 0.0003, OR 4.2, 95%CI 1.9, 9.3) and weight less than the 50th percentile (p < 0.0001, OR 8.4, (95%CI 3.8, 18.4).
That is, at the time of initial presentation both age and weight were predictive of a patient having an atypical SCFE. For two patients of equal weights, those less than 10 years old or greater than 16 years old are 4.2 time more likely to have an atypical SCFE; for two patients of equal age, the one who weight falls in the 50th percentile or less is 8.4 times more likely to have an atypical SCFE.
On the basis of this information, we defined the age-weight test (AWT) to help predict the idiopathic or atypical nature of a SCFE.
| Age < 16 years | Age > 16 years | |
| Weight > 50th percentile | AWT (-) | AWT (+) |
| Weight < 50th percentile | AWT (+) | AWT (+) |
This AWT has a negative predictive value of 93%; the chance of a child with a negative AWT having an idiopathic SCFE is 93%. The positive predictive value is 52%; the chance of a child with a positive AWT having an atypical SCFE is 52%.
Conclusion
Further clinical investigation into the etiology of the SCFE should be considered for any child with a positive AWT.
References