Below-Knee Polyethylene Semi-Rigid Dressing

Vein M. Swanson, CPO

ABSTRACT

This article will discuss an early postoperative patient management technique, below-knee polyethylene semi-rigid dressings. This approach is a contemporary alternative to the directly molded removable rigid dressing. The polyethylene socket dressing is lightweight, washable and flexible to enhance patient comfort and acceptance.

Introduction

Early postoperative fitting of below-knee (BK) amputations expedites the rehabilitation process of lower-extremity patients. The goals of early postoperative fitting are to promote healing, protect the wound from trauma, prevent edema, reduce pain and allow for residual limb maturation and early ambulation (1).

Two postoperative patient management techniques are the immediate postsurgical prosthesis and removable rigid dressings (2-4).

The immediate postsurgical prosthesis is a technique wherein a nonremovable rigid plaster dressing is applied to the residual limb immediately after BK amputation. Usually a pylon is applied at the first cast change so the patient can begin partial weightbearing. One disadvantage of immediate postsurgical fitting is surgeons are unable to inspect the amputation wound (5).

The second technique is the application of a BK removable rigid dressing (RRD). The RRD is fabricated with plaster or fiberglass bandage and is suspended by a stockinette and supracondylar plastic cuff. No pylon is attached. The advantage of the RRD is it allows frequent inspection of the wound after amputation.

The purpose of this article is to describe a removable polyethylene semirigid dressing (PSRD) for postoperative patient management (see Figure 1 ). This patient management technique is a variant of the well-established directly molded RRD technique. The PSRD differs from the RRD in that the socket is flexible, and the patient also wears a shrinker.

The combination of the BK shrinker and the PSRD reduces edema and provides residual limb maturation. As shrinkage occurs, the patient adds additional residual limb socks over the shrinker to maintain the socket fit of the PSRD.

In the author's experience, this combination is more effective than using either a BK shrinker or an RRD by itself. When a PSRD is used with a shrinker, it provides additional volume reduction and shaping of the residual limb.

There is additional cost to provide the PSRD for postoperative patient management. However, in the author's opinion, the PSRD will reduce costs to patients and third-party payers over time. Patients will have fewer problems with the fit of the preparatory prosthesis due to the early shrinkage that occurred while wearing the PSRD. This result is particularly important with diabetic patients who might develop abrasions due to excessive shrinkage during early ambulation.

PSRD Advantages

Two years of clinical experience fitting the PSRD have shown several benefits to the patient.

The PSRD is a lighter-weight thermoplastic dressing, weighing six to seven ounces. No pylon or foot is attached to minimize weight.
The PSRD improves socket hygiene. Polyethylene is nonporous and may be cleaned daily whereas a plaster cast provides limited protection against bacterial infection (5). In addition. drainage from the wound may be absorbed into the cast.
The PSRD improves patient comfort in donning and doffing due to the polyethylene's flexible characteristics.
The PSRD has partial weightbearing similar to an actual BK socket. Partial weightbearing helps the residual limb become accustomed to tolerating socket pressures.
The PSRD helps patients become involved in their own rehabilitation. Patients learn about donning and doffing, adding residual limb socks for shrinkage and keeping the socket clean.

The PSRD is helpful to the prosthetist in patient management and clinical evaluation since it helps the prosthetist evaluate a patient as a candidate for a prosthesis. Improved patient management reduces work stress.

Impression Method

The PSRD is applied five to seven days postoperatively after the drain has been removed. The staples are often intact when the PSRD is applied (see Figure 2 ). In some cases the PSRD is not applied until three to four weeks postoperatively when the physician refers the patient to the prosthetist.

The only contraindication to fitting a PSRD is the presence of a deep wound infection that requires surgical intervention (4). To obtain an impression for the PSRD:

Measure the amputation (see Figure 3 ) for a BK shrinker. A Juzo shrinker is used for insensate amputations because it exerts 25 mm of Hg pressure (6). For more sensitive amputations, use a Knit-Rite shrinker with 10 to 15 mm of Hg pressure or one layer of Compressogrip sewn across the distal end with 8 to 12 mm of Hg pressure (7-10).
Apply a one-ply cotton sock and the medium compression BK shrinker chosen in the previous step (see Figure 4 ).
Apply a one-ply wool sock over the shrinker. Suspend the one-ply wool sock with 25.4-mm (one-inch) elastic and yates clamps (see Figure 5 ).
Apply another one-ply cotton sock and mark the bony prominences.
Take standard measurements over all the socks to allow room in the socket for the shrinker and socks (see Figure 6 ).
The patient's knee should be in 10 degrees of flexion. Take the impression with one roll of elastic bandage followed by one roll of regular fast-setting bandage. Lightly define the sides of the patella tendon (see Figure 7 ).

Model Modification

Extend the impression 50.8-mm (2-inches) proximally before filling with plaster to help the polyethylene maintain a more uniform thickness on the proximal walls.
Check the measurements of the positive model. These measurements also represent the thickness of the shrinker and the residual limb socks. Often the circumference of the bulbous distal end will be larger than the proximal circumference (see Figure 8 ). This is the advantage of using polyethylene. Its flexible characteristics will allow the proximal socket to expand for donning and doffing.
Modify the positive model for partial weightbearing. Remove only two mm of plaster in the pretibial areas. Remove only four mm of plaster on the patella tendon bar. Remove plaster proximally to blend in the 50.8-mm (two-inch) extension (see Figure 9 ).
Do not reduce the ML dimension. The goal for the ML dimension is to equal the measured ML over the shrinker and the socks plus 6 mm (1/4 inch). The goal for the AP dimension is to equal the measured AP over the shrinker and the socks plus 6 mm.
The posterior trimline should be 6 mm (1/4-inch) below MTP level.
Apply buildups over the bony prominences. Apply a one-mm buildup on the crest of the tibia, two mm on the fibula head, three mm on the distal fibula and four mm on the distal tibia (see Figure 10 ).

Fabrication of the PSRD

Apply two layers of nylon, twisted and reflected back over the model. Powder the nylons with cornstarch.
Heat 10 mm (3/8-inch) modified polyethylene in the oven at 204°C (400°F) for about 15 minutes supported by a frame (11,12). Let the plastic
droop or bubble about half the length of the model (see Figure 11 ).
Invert the plastic on the model and let it fall slowly. Use cups to keep the frame from falling too low, which would thin out the plastic. Pull from the corners of the polyethylene to create a seal around the vacuum table.
The vacuum should be applied slowly to ensure no webbing occurs, then apply full vacuum (see Figure 12 ).
Let PSRD sit overnight to help prevent shrinkage (see Figure 13 ). The next day cure the PSRD in the oven for 20 minutes at 93°C (200°F) to relieve stress in the plastic and help prevent shrinkage.
After curing, let the PSRD cool for about three minutes. Cut the trimlines 50.8 mm above MTP, and pull the PSRD off while it's still warm. Sand and buff the proximal trimlines.

Patient Instructions

Usually the patient receives the PSRD two to three days after the impression is taken. Instruct the patient to apply the medium compression shrinker. Initially, if the amputation is too sensitive, substitute a one-ply wool for the shrinker until the amputation desensitizes.

Have the patient apply the appropriate number of socks over the shrinker (generally a one- or two-ply wool sock will do) then show the patient how to apply the PSRD (see Figure 14 ). Show the patient how to don and doff the Juzo suspension sleeve (see Figure 15 ) (13).

Tell the patient to wear the PSRD during the day. The patient can remove the PSRD at bedtime but should keep the shrinker on. The patient should then redon the PSRD in the morning.

The patient should apply clean socks daily and add additional socks if the socket fit becomes loose. The patient should also clean the PSRD daily with rubbing alcohol and a washcloth.

The patient should stop wearing the PSRD if it causes irritation.

Instruct the patient to apply 4.55 kg minutes under the supervision of a to 9.1 kg (10 to 20 pounds) of weight on physical therapist (see Figure 16 ). Give the PSRD twice a day for one to two the patient a copy of these instructions.

Patient Follow-Up

Check the patient's progress with the PSRD in one week (see Figure 17 ). Is the patient following instructions? Wearing the socket regularly? Tolerating socket pressure? Reinstruct the patient if necessary.

Evaluate the patient's progress again in another week. Take the impression for the BK preparatory prosthesis at this appointment if the patient has followed directions, tolerated wearing the socket and the residual limb is ready.

The BK preparatory prosthesis is fitted in one week. In the meantime, the patient continues to wear the PSRD.

The BK preparatory is delivered two to three days after the fitting (see Figure 18 ). The patient is instructed to start wearing the preparatory three hours per day and to don the PSRD when he or she doffs the preparatory.

If the patient is not following the instructions or has poor tolerance to wearing the PSRD, the preparatory prosthesis should not be started until there is improvement. Instead, encourage the patient to follow the instructions and get involved in his or her own rehabilitation. If this approach doesn't work, consult with the patient's physician. In this way, the PSRD assists the prosthetist in evaluating a patient as a prosthesis candidate.

Conclusion

During the past two years the PSRD assisted in the rehabilitation and evaluation of 43 BK patients (see Figure 19 , and Figure 20 ).

Forty patients successfully tolerated the PSRD and were subsequently fit with BK preparatory prostheses. Two patients were not fit with preparatory prostheses due to poor tolerance of the PSRD and were evaluated to be nonprosthetic candidates. One patient died due to congestive heart failure be fore being fit with the preparator prosthesis.

The PSRD offers improvements in weight, hygiene and socket design. It also encourages patient participation and assists the prosthetist in patient evaluation and management.

Future improvements to the PSRI could include the use of CAD/CAM to expedite the procedure and collect data about residual limb shrinkage. The data could be used to study the effects of different postoperative management techniques and to justify medical necessity.

Vern M. Swanson, CP, is manager of Swanson Orthotic and Prosthetic Center Inc., 3102 Sylvania Ave., Toledo, OH 43613. He is past president of the Ohio Chapter of the American Academy of Orthotists and Prosthetists Inc.

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