The Use of the Prone Knee-Chest Position: Examiner Habit or Medical Necessity?
By Gretchen Overstolz, RN, MSN, FNP and Elizabeth Baker-Gibbs, MD

The use of the prone knee-chest position has become standard practice in the evaluation of child sexual abuse; however, there are no data available in the literature confirming the necessity of its use. No differences in the reliability of examinations of children performed in this position compared to full labial traction have been determined, and the need for confirmation of findings determined by supine labial traction using the knee-chest approach has not been quantified or qualified. Still, many examiners believe that they must put children in this position in order to validate their findings. It is possible that children who are placed in the knee-chest position may feel an increased violation of their personal boundaries, since they are less able to participate in their examinations due to the logistics of the position. There are examination techniques that can be used in order to confirm findings that are less likely to jeopardize a child's sense of personal empowerment and increase a child's comfort, while assuring a high quality forensic evaluation.

Although many child sexual abuse examiners have come to utilize the "prone knee-chest" position in the forensic assessments of their patients, the use of this technique may be traumatizing to children, or at the very least disempowering, and provides little, if any, objective data by which to form a medical diagnosis of inflicted genital trauma that can not be gained from other, less distressing methods of evaluation. How the use of this technique became so widely accepted and even portrayed by some experts as required, with no scientific proof of its validity, is a mystery. The American Academy of Pediatrics states in the guidelines for the evaluation of sexual abuse of children that "Various methods for visualizing the hymenal opening in prepubertal children have been described ... the technique used is less important than maximizing the view and recording the method and results." In contrast, a recent article published by the American Family Physician reads, "It is necessary to perform an examination in the prone knee-chest position to confirm or exclude abnormalities of the posterior aspect of the hymen."¹ There is, however, no empirical evidence to justify the requirement of the use of this method as a component of any child sexual abuse evaluation.

History of the Prone Knee-Chest Method

The use of the prone knee-chest method was introduced in and associated with changes in the hymenal anatomy during examination of abused girls.² This method was soon after examined in comparison to two other techniques: labial separation and labial traction, and found to be superior to labial separation in 12 percent of cases in opening the vaginal introitus for colposcopic inspection  and in order to measure hymenal orifice diameters.³ Only a 2 percent difference was found between the use of the knee-chest position and labial traction in measuring hymenal orifice diameters, although the extent of this labial traction (mild or moderate) was not noted. These same researchers later found no statistically significant differences between any of the three methods when studying genital findings of girls selected for non-abuse with regard to the symmetry of hymenal orifices, percentage of the vaginal introitus covered by the hymen, nor in the width of the hymen rim at its posterior attachment when hymenal separation was achieved.⁴

Although other "soft tissue changes" are alluded to in this paper, they are not specifically mentioned nor quantified. There is no mention of any findings whatsoever that currently are considered concerning for inflicted genital trauma, nor is there any data to qualify or confirm any differences between the use of the prone knee-chest and labial traction methods in observing hymenal findings that are diagnostic of blunt force penetrative trauma, including acute hymenal lacerations, hymenal ecchymosis, healed full thickness hymenal transactions or absence of hymenal tissue. The authors state that "further research is needed to delineate the soft tissue changes that occur with each of these techniques" and that "once that data is available, it may be then possible to determine if one method is superior to another in the identification of the abused child." This particular paper was published 11 years ago, and no studies have been conducted since to verify any necessity for the use of this technique. In fact, the original use of the knee-chest position for measuring hymenal orifice diameters has been proven null, since there is no data to confirm any differences in these measurements when studying both abused and non-abused girls.⁵

The Lack of Empirical Evidence

A more recent study⁶ looked at 1,383 child and adolescent females suspected of having been sexually abused. Both supine labial traction and prone knee-chest methods were used in determining the occurrence and possible significance of concave hymenal variations. Although the authors briefly mention Bays' and McCann's hypothesis of the importance of the prone knee-chest position for defining anatomic detail of the posterior rim of the hymen, they make no mention of any differences noted within their very large sample population between the two methods of examination.

McCann observes in a study of a sample of three abused girls "the jagged, irregular margins of the hymen created by these acute injuries smoothed out and became difficult to detect without the use of a multi-examination technique." Yet later in the same article he states that the "sharp jagged edges of the damaged hymens in both the 4-month-old and the 9-year-old gradually smoothed out as healing took place." However, the use of the knee-chest position was never used on the 4-month-old.

Another study looked at the appearance of the hymen in 211 girls selected for non-abuse.⁷ The use of the knee-chest position was never used and the necessity of this technique was not mentioned as a weakness of the study. A popular article known as "Normal to be Normal,⁸ reports as a finding of clear evidence of penetrating injury, absence of hymenal tissue between 3 and 9 o'clock, which is confirmed in the knee-chest position. However, no evidence is presented documenting the observed differences in the methods used as seen in the examinations of 213 cases studied.

More recently, Berensen, et al,⁹ studied 392 children who had been screened for abuse and non-abuse. Both labial traction and knee-chest position methods were used for examination in all but four of the children, who refused to assume the prone knee-chest position. However, this study makes no reference as to the differences between the two methods in assessing anatomical changes resulting from sexual abuse.

Adams⁵ states in the most recent and comprehensive classification of ano-genital findings available, that hymenal clefts (extending to greater than 50 percent of the hymenal rim) that are concerning for abuse or trauma should be confirmed in the knee-chest position, as they may be artifacts of examination. However, considering the lack of empirical data substantiating the use of this method and the possible negative effects on children's perceptions of forensic medical examinations, it is unlikely that the use of this method need be employed. Additionally, there are probably more reliable, less traumatizing methods of reducing the artifacts of examination techniques.

Anal Findings and the Prone Knee-Chest Method of Examination

Adams⁵ also suggests that "marked anal dilation that occurs within 30 seconds" of assumption of the prone knee-chest position, exclusive of any history of encopresis, chronic constipation, neurological deficits or sedation, is concerning for abuse or trauma. However, McCann¹⁰ found in  a sample of 267 children selected for non-abuse, anal dilation in 49 percent. Thirty percent of the children in this sample had anal dilation within 30 seconds of assuming this position. Only 44 percent of these children had stool that was visible within the rectal vault. Hobbs and Wynne¹¹ state, "The anus is inspected with the child lying on the left side with hips and knees flexed, the child must be relaxed in order to achieve a satisfactory examination," and "Some children find this (knee-chest) position less dignified." There have been no more recent or reliable studies of anal findings that substantiated the necessity of the use of the prone knee-chest method when using MEDLINE as of August .

Preventing Artifacts of Examination

Use of moderate traction as opposed to mild traction can be extremely useful in not only separating the hymenal orifice, but also decreasing any artifacts of examination. By using the thumb and forefinger to grasp the labia majora and gently pulling downward and outward, the unestrogenized hymen will assume nearly the same appearance as it would by using the knee-chest position. It is important that the fossa navicularis be visualized in relation to the hymen, especially when transections or other anomalies are suspected. Small concavities, bumps and mounds, although often still observable, will become obvious in their nature as normal findings. This is a painless and quick approach, and if the examination is videotaped as well as photographed, it is possible to use manual manipulation to observe each area of the hymen and surrounding tissue and to provide documentation for inter-rater reliability, without further traumatization or distress to the child being examined.

Estrogenized hymens are especially difficult to examine. The use of the Foley catheter technique has been described in visualizing the hymenal edges in children and adolescents at this particular stage of development.¹² However, the use of the Foley catheter is less cost-effective and more invasive than other methods of visualizing hymens of estrogenized and neo-estrogenized children. Two methods that are more easily utilized and less invasive are the use of water and the use of colored cotton swabs.

Water can be very helpful in determining variants in hymenal anatomy by applying a small amount with a pipette directly to the hymen during examination. The water decreases the surface tension of the hymen thereby allowing hymenal edges and tags that are adhered, to "float" away from the inner labia minora, becoming much more easy to visualize. This method is also helpful during examinations where there is a discharge, and a swab can be taken from the water that runs down the fossa navicularis and posterior forchette to determine the presence of hyphae and clue cells when vaginitis is present. The removal of discharge can allow for a more easily visualized hymen as well. The child can be told "you are going to feel something cold and wet, but it won't hurt" just before application of the fluid.

The use of a cotton swab in viewing the hymenal anatomy, as well as separating the hymenal orifice with a fingertip, has been described in past literature.⁷ An enhanced method for visualizing the hymenal anatomy which has not been described in the literature is the use of colored-tipped cotton swabs. The colored tipped swabs are comparable to the use of a colored balloon or foley balloon in visualizing the hymenal rim in estroginzed children and adolescents, by providing contrast. Contrast is best provided by green or blue-based colors. The hymenal rim can be traced with the swab, and, especially when videotaped, takes the place of all other methods with less invasiveness and possibly less child distress during examination. It is possible to explain to a child or adolescent before the examination, "I will not do anything to hurt you, and I will not put anything inside you during this exam. I may touch you on your vagina with a cotton swab, but it will not hurt."

Increasing Children's Comfort During Forensic Medical Examinations

A focus on increasing a child's comfort and healing during a forensic medical examination may present added challenges, especially for less experienced examiners. It is just as likely, however, that such an approach will increase a child's level of cooperation, thereby allowing for a more easily performed examination. Although there is no research to confirm or disprove the likelihood that children feel less empowered when using the knee-chest approach, it has been theorized that this is a less dignifying position than optimal, especially during examinations to determine the extent of injuries to a child resulting from what has often been a chronic violation of personal boundaries. De San Lazaro¹³ suggests that "While a carefully structured approach to the examination is needed ... the assessment should at all times be a healing experience for both the child and the family" and that "the process of physical examination should build on themes of wholeness, empowerment and self-worth." Gully, et al,¹⁴ found during the development of a scale for measuring the distress of 300 children during their ano-genital examinations for sexual abuse that the children portrayed a dislike for the physician looking at their bodies, which was correlated with increased scores on the distress scale during the ano-genital examination. Unfortunately, this study did not specifically look at methods of examination with regards to children's perceptions of distress. Finally, Dubowitz¹⁵ proposes that where "optimal practices remain uncertain, such as examination of girls in the prone knee-chest position ... the practice may be recommended only in certain circumstances" and he suggests that further research be conducted as to the perceptions of children during the use of this examination method.

Conclusion

It appears from the available literature that there is really no confirmed need for the use of this method. Children are less likely during this examination position to feel empowered, and logistically, there is less ability for the examiner to communicate and maintain rapport with the child. Suspected hymenal injuries, such as full and partial thickness transactions, as well as normal anatomical variations can be confirmed using full labial traction. It is helpful to include videotape documentation or successive photography of the entire hymenal anatomy including the fossa navicularis and inner labia minora, as well as the use of water and colored cotton swabs to view suspected areas more fully. If examiners are to continue using the prone knee-chest position, especially for prolonged periods of up to four minutes as has been described in past literature,¹⁰ the relevancy of such findings should be weighed with respect to the degree of distress and loss of empowerment that children feel during such an experience. Although the need for research regarding children's perceptions is evident, the research itself poses certain ethical dilemmas if there is no true need for the use of the technique in the first place.

The guidelines for evaluation of child sexual abuse established by the American Academy of Pediatrics states that "the physical examination of sexually abused children should not result in additional emotional trauma.¹⁶ Without knowing for sure whether or not the use of the prone knee-chest position causes additional trauma, and with no empirical data to justify its use in the first place, it should probably not be used.

	Gretchen Overstolz, RN, MSN, FNP, is children's forensic coordinator at the Children's Medical Assessment Center in Charleston, S.C.
	Elizabeth Baker-Gibbs, MC, is medical director and founder of the Children's Medical Assessment Center in Charleston, S.C.By Nancy B. Cabelus, MSN, RN, DABFN

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