The Enhancement of Prosthetics Through Xeroradiography®
David Varnau, C.P.O. *
Keith E. Vinnecour, C.P.O. *
Monalee Luth *
David F. Cooney, R.P.T., C.P.O. *
Today's prosthetist finds himself searching for new tools to enhance his fitting skills. With transparent test sockets, he is now able to visualize the residual limb inside the prosthetic socket. With Xeroradiography®, the contemporary prosthetist is able to identify his patient's unique bony anatomy before even commencing work on the prosthesis.
The concept of using x-ray images to improve prosthetic fit is by no means new. As early as 1963, King wrote of using x-rays as an adjunct to patellar tendon bearing (PTB) fittings.6 Much more recently, Haslam, C.P. and Wilson briefly cited some merits of x-rays and Xeroradiographs® for prosthetics.2 Credit for introducing Xeroradiography® into the field of prosthetics, however, must be given to Jan Stokosa, C.P.t
Xeroradiography® is a dry, photoelectric process t for recording x-ray images on paper. Although its usefulness today is usually considered to be confined to the examination of the breast, Xeroradiography® is well-suited for any peripheral part of the body.
Advantages of Xeroradiography®
The primary advantage that Xeroradiography® imaging offers the prosthetist over that of conventional film radiography (x-ray) is the clarity of the bone's boundary lines (Fig. 1 ). This fact is due to the character of the Xeroradiographic® imaging process itself.
Previously, when consulting x-rays of a residual limb, prosthetists either had to accept the blurred contours of the patient's bony anatomy, or were deprived of a lucid image of the soft tissue edges. Instead, each Xeroradiograph® can replace two x-ray film pictures (a bone picture and a soft tissue picture) and thus provide the prosthetist with more accurate and easily observable information at a glance.
The Xeroradiograph® is developed on opaque paper, usually on a blue format. Unlike x-rays, the Xeroradiograph® can be easily stored as a part of the patient's chart since there is no need for a viewing box. The rich blue color of the properly exposed negative mode Xeroradiograph® serves to enhance the clarity of the image. Further, usefulness of Xeroradiography® for prosthetics becomes even more obvious when it is pointed out that less magnification takes place in the procedure. More magnification typically occurs on conventional film x-ray because the x-ray cassette is positioned further from the residual limb (Fig. 2 ).
Disadvantages of Xeroradiography®
The Xeroradiographic plate is 9 1/2" x 13 5/8". As a result, it is not possible to photograph a long residual limb in its entirety. Symes level as well as long above knee residual limbs require two pictures merely to complete the image for one projection. To rectify this problem, the radiology technician must tape a radiographically opaque reference marker onto the midsection of the residual limb prior to imaging. The marker aids the prosthetist in piecing the two pictures together correctly. An alternative to this mosaic approach, of course, is to obtain conventional radiographs of the longer residual limbs.
A second disadvantage of Xeroradiography® is that the image is backwards. As a result, when consulting the Xeroradiograph,® the prosthetist must recognize that the Xeroradiograph® is a mirror image of the object.
Finally, with Xeroradiography,® the patient is usually exposed to a greater radiation dose. The exact difference in radiation exposure between Xeroradiography® and x-ray varies, depending on the type of x-ray screen, film, filters, and resulting technique that is used for a comparison. Generally, using the Xeroradiography® technique that we suggest (see technical information in Fig. 20 ), the local bone radiation dose appears to be as much as nine times that of conventional x-ray film technique"+ (Fig. 3 ). Although this is undesirable, the amount of radiation both in terms of skin dose, as well as estimated bone marrow dose, is neither alarming nor considered dangerous to the patient, mainly because usually only one Xeroradiograph® series is necessary for the adult (see Method Section). Even so, for the juvenile patient, the benefits of Xeroradiography® must be weighed against the greater radiation dose.
USES OF THE XERORADIOGRAPH®
Because contours are intensified on Xeroradiographs,® the boundary lines between bone and soft tissue are pronounced. Thus, the Xeroradiograph® is well-suited for the prosthetist's interest in bony contours. Further, the Xeroradiograph(R) provides valuable and sometimes surprising information that is not readily apparent through clinical examination. Since the Xeroradiograph® is only slightly magnified, numerous measurements can be obtained directly from it.
Although Xeroradiography® is valuable when fitting prostheses for all amputation levels, this paper will deal only with its use in the treatment of below knee amputations.
By inspecting the Xeroradiograph® of a given patient, the prosthetist can better appreciate the actual length of the tibia,* the contour of the anterior distal tibial margin (Fig. 4 ), as well as the thickness of the distal soft tissue. Much of the guesswork is eliminated from this important aspect of the casting and cast modification procedures. Frequently, in cases of hard-packed distal edema, the prosthetist imagines that the length of the patient's tibia extends further distally than it actually does (Fig. 5 ). The Xeroradiograph® thenenables the prosthetist to correctly locate the anterior distal tibial relief during cast modification.
The relative position of the inferior border of the patella to the tibial plateau also varies significantly from one individual to the next. Customarily, the so-called "patellar bar" is placed just below the inferior border of the patellar. Yet many patients have a condition termed patellar altaor a high-riding patella, while still others have patella infera4 or a low-riding patella (Fig. 6, Fig. 6b ).
The existence of one condition versus the other has important ramifications for the prosthetist when he is identifying the proper position for the patellar bar. It is evident, then, that the placement of the patellar bar "midway between the lower edge of the patella and the tubercle of the tibia" as advocated by Radcliff and Foort10 is in fact incorrect for certain patients (Fig. 7 ). The Xeroradiograph,® thus, aids the prosthetist in correctly positioning the patellar bar at the femorotibial joint space.
Prosthetists who routinely use transparent test sockets have noted the presence of an airspace just proximal to the tibial tubercle. This appears to be caused by the patellar bar forcing the patient's tissues posteriorly. Another contributing factor may be that the positive model does not reflect the patient's anatomical contours just proximal to the tibial tubercle. Contrary to popular notion, plaster may be removed and flared from the level of the tubercle into the patellar bar. The angle of the flare is dictated by the contour of the patient's proximal tibia as seen on the lateral Xeroradiograph.® The contour of the proximal tibias in Fig. 4 are examples where the flare above the tubercle would be less dramatic than that shown in Fig. 5 .
The length of the fibula, like that of the tibia, is readily apparent on a Xeroradiograph.® Briefly consulting the anteroposterior (AP) projection will provide a quick reference for the terminus of the fibular shaft. Guessing as to the shape, position, and size of the fibular head is unnecessary with the Xeroradiograph® (Fig. 8 ). Also, cases of absence of the fibula are obvious on a Xeroradiograph.® Problems of pressure on the cut end of the fibula and fibular head are diminished while medio-lateral (ML) stabilization on the fibular shaft can be maximized. The lateral projection, on the other hand, is useful for identifying whether the patient's fibula is positioned posterior to, or on, the midline.
The shape of the medial tibial metaphysis varies from one patient to the next (Fig. 9 ). With an AP projection of a given patient's Xeroradiograph,® the prosthetist can anticipate the amount of flare possible in the tibial metaphyseal region. This information aids the prosthetist in creating an anatomically-shaped, weight-bearing area.
After reviewing the Xeroradiographs® of nearly 100 adult below knee residual limbs, we found in our practice that fully 13 percent of our below knee amputees have tibias shorter than three inches and are PTS candidates. As pointed out by Marshall and Nitzchke, the patient with a four-inch length residual limb is a good candidate for the PTS socket. However, as they also point out, the PTS prosthesis requires "more skill and knowhow" of the prosthetist for successful fitting.
One important anatomical consideration for the FTS socket, particularly the suprapatellar PTS, is the relative position of the proximal patella to the adductor tubercle. Here again, the existence of patella alta or patella infera is crucial (Fig. 10 ). This information aids the prosthetist both during casting and cast modification to ensure optimum suspension and correct proximal PTS socket contours.
CLINICAL VERSUS XERORADIOGRAPH® MEASUREMENTS: SURVEY RESULTS
The Xeroradiographs® of 92 adult below knee amputees were reviewed and the following observation was made. It is virtually impossible to conclusively correlate the AP and ML diameter measurements on the Xeroradiograph® to the clinical measurement taken on the patient. That is, no formula could be devised that would reliably allow the prosthetist to predict the patient's clinical AP and ML measurements solely from the corresponding diameters measured on the Xeroradiograph.® This lack of correlation is attributable to three variables:
- The methods that practitioners use to obtain their clinical diameter measurements vary, resulting in a variance of as much as 3/8" in the clinically measured AP and ML dimensions of a given patient.
- The amount of soft tissue thickness at the knee is quite different from one patient to the next.
- The extent of magnification that occurs on the Xeroradiograph® varies among patients and is due to the vertical distance of the patient's knee from the Xeroradiography® cassette. That distance is determined by:
- The size of the patient's residual limb.
- Presence of a knee flexion contracture (Fig. 11 ).
- The amount of soft tissue compression of the residual limb where it contacts the cassette.
Thus, using identical radiographic technique, magnification of the image on the Xeroradiograph® may vary between six and 14.5 percent (Fig. 12 ). The amount of magnification and, hence, image dimensional distortion of the AP and ML diameters, also depends on the focal tube distance to the cassette+ (Fig. 13 ). Although most radiology offices can only accommodate 40-54 inches, a 72-inch focal tube distance will reduce magnification to a minimum.
In summary then, magnification is minimized with a small-boned patient who has no knee flexion contracture and some soft tissue compression (i.e., a = 5cm). In addition, magnification is diminished when the focal tube distance is large (i.e., b = 72 in.). Even so, in such an instance, the Xeroradiograph® will be magnified three percent. Exact correlation of clinical and Xeroradiograph® measurements, therefore, is possible only with time-consuming computations.
INCIDENCE OF OSTEOPHYTE FORMATION
A review of the Xeroradiographs® for ninety-two adult below knee amputees bore out surprising information. Namely, on 41 percent of the patients, osteophytes were present on either the distal tibia and/or fibula (Fig. 14 and Fig. 15 ). For many of these patients, the osteophytes seemed to pose no fitting problems. For others, the prosthetist used the Xeroradiograph® information together with test socket fittings, and, later, a gel liner, to avoid fitting problems. In two cases, patients required residual limb revisions to have the osteophyte resected. Without the use of Xeroradiographs,® prosthetists have no means of ascertaining the presence, location, and size of osteophyte formation on the patient's bony anatomy.
CAUSE OF OSTEOPHYTE FORMATION
A comprehensive statistical review of the charts for the surveyed below knee amputee population was performed to identify the cause(s) of osteophyte formation. Neither the patient's age (Fig. 16 ), sex (Fig. 17 ), cause of amputation (Fig. 18 ), nor tibia length (Fig.19 ) seemed to be a reliable predictor of osteophyte formation. In fact, three bilateral below knee amputees exhibited osteophytes on one residual limb and none on the other.++
In the absence of any specific reference in the orthopedic literature to this phenomenon as a sequela to amputation surgery in adults, our impression is that osteophyte formation in adult amputees is decidely not bony overgrowth as found in juveniles. Radiographically, osteophyte formation appears grossly similar to the heterotopic ossification seen as a complication following other types of surgical resection. It is not clear whether osteophytes in residual limbs are an outgrowth from the periosteum or from the cortical bone. The authors feel that the unwanted ossification may result from the manner in which the bone is handled during amputation surgery.
Some orthopedists have expressed interest in conducting a retrospective study to assess the effect that myoplasty has in discouraging osteophyte formation. Further investigation that conclusively identifies the cause of the osteophyte formation phenomenon is warranted in the interest of the amputee's comfort and of optimal amputation technique.
To obtain useful Xeroradiographs,® specific instructions must be provided to the radiology technician. We have found that the request form which is pictured (Fig. 20 ) is useful and assures that the necessary projections will be provided to the prosthetist. Although only AP and lateral views are necessary, internal and external oblique views are useful for visualizing bony anomalies in additional planes.
It has proven to be difficult for some radiology technicians to obtain true lateral projections of the below knee residual limb. This can be attributed to the technician's failure to note inadvertent axial rotation of the knee when taking the picture. This oversight is obviously due to the absence of the foot on the extremity for axial rotational reference. A true lateral projection is also sometimes elusive since side-lying on the hard surface of an x-ray table can prove to be difficult for the unilateral patient and certainly is so for the bilateral below knee amputee.
Furthermore, exposure values are critical and must be specified to any radiology service if quality Xeroradiographs® are to be obtained. The exact selection of exposure may be modified for specific machines as well as for patients of varying sizes. The radiology technician must select a setting of 120 kilovolts (kV) but may vary the setting for milliamperes/seconds (mAs). Generally, however, the specifications in the technical information of the request form (Fig. 20 ) usually assure maximum prosthetic usefulness of the Xeroradiographs®.
In this prosthetic practice, standard protocol calls for all below knee patients with mature residual limbs to obtain their Xeroradiographs® prior to casting. The prosthetist, then, has the best available anatomical information with which to commence his work.
If, following the fitting of at least two dynamic transparent test sockets, fitting problems persist, a weight-bearing Xeroradiograph® may be requested to identify the source of the problem. This order is indicated in the special instructions box on the request form (Fig. 20 ). The inner surface of the socket or socket liner may be highlighted easily with self-adhesive copper foil tape+++/which is used for its radio-opacity. For maximum information regarding socket fit, the patient's residual limb may be imaged in the prosthesis full weight-bearing and partial weight-bearing. Of course, the weight-bearing Xeroradiograph® is also useful when evaluating an ill-fitting, definitive prosthesis of a patient new to the office.
The extent of the osteophyte formation appears to be well-defined six months past amputation, like that of heterotopic ossification following total hip replacement. Hence, subsequent Xeroradiographs® are unnecessary for purposes of identifying osteophyte formation if previous ones are on file.
The most important advantage of Xeroradiography® is patient management. Since the unique anatomy of a given patient is more observable, the prosthetist approaches his patient with more information and, therefore, greater confidence. That confidence is communicated to his patient.
With the addition of Xeroradiography® to the prosthetic armamentarium, the prosthetist can enhance as well as advance his skills. He becomes a better anatomist, noting the unique bony anatomy of each patient. Even the experienced prosthetist is often surprised by the Xeroradiograph® of a familiar patient and finds the new information beneficial. And while evaluating the patient who is new to him, the prosthetist will find himself groping less for information. With Xeroradiography,® he becomes a better informed professional. Still, Xeroradiographs® are no replacement for skill and experience. Like transparent test sockets, Xeroradiographs® should become an integral part of prosthetic practice.
The authors are indebted to Jan Stokosa, C.P. for introducing Xeroradiography® to Keith E. Vinnecour. Also, they would like to express their gratitude to Marion Vertun of Xerox Medical System for her technical assistance.
Anthony Alter, M.D. and Yoshio Setaguchi, M.D. assisted the authors in their literature search. Myra Feffer, M.D., Rosa Green, Caren Antler and the entire staff of Beverly Radiology have demonstrated the importance of a competent and cooperative radiology service for the prosthetist using Xeroradiography.®
Finally, Monalee Luth's talents in both graphic arts and photography were indispensable.
t Jan Stokosa, C.P. is director of the Institute for the Advancement of Prosthetics, Lansing, Michigan.
tt Whereas a photo chemical process is used in conventional film radiography.
* In order to determine actual dimensions from the Xeroradiograph,® the prosthetist must first account for the exact magnification of the image.
+The authors obtained the data for (Figure 13) as follows: A radiographic ruler was imaged on Xeroradiography® at Ocm, 2.5cm, 5cm, 7.5cm, 10cm and 12.5cm from the cassettes for each of three common focal tube distances—40 inches, 54 inches, and 72 inches. The linear magnification was then determined by measuring the ruler's image on each of eighteen Xeroradiographs® and computing the percentage enlargement.
++The three bilateral below knee patients were male. Two of the patients' amputations were due to dysvascular causes and were performed at different times. Both amputations of one patient were performed by the same surgeon. The amputations for the other patient were performed by different surgeons. The third patient's amputations were due to trauma and were performed concurrently.
+++Copper foil tape 3/16" x 1 mil Venture, Tape, 123 Moore Road, Weymouth, Massachusetts 02189, The copper foil is available in stores selling stained glass supplies.
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