TissueDB/Simulators/Soft Tissue Lesion Simulator

The Soft Tissue Lesion Simulator is a set of three single-use models built from locally sourced materials for teaching abscess drainage, subcutaneous nodule excision and wound debridement. The abscess and nodule models layer a sponge base, an approximately 2 cm layer of pigmented gelatin, and felt covered with clear packing tape, so a scalpel passes through a firm skin-like surface into a soft layer; only the lesion between those layers differs. The wound model is a cut sponge with vinyl debris and red liquid latex. All three were evaluated with 62 third-year Rwandan medical students over three course iterations.^[1]

The three models share one core set of materials, so it is quicker to build all three together than one at a time. The two gelatin models must be made the day before, because the source's Table 1 footnote states the setting time it excludes is overnight. Keep them refrigerated until use.

The source's own figures, per model: abscess drainage US$1.19 and about 3 minutes of active work; nodule excision US$1.07 and about 2 minutes; wound debridement US$1.17 and about 5 minutes. Setting time for the gelatin is on top of those.

Step 1: Make the abscess. Fill a hospital glove fingertip with basic body lotion and tie a simple knot at the top.

Step 2: Lay the base. Place the filled fingertip on top of a thick small sponge. The sponge represents the tissue beneath the abscess.

Step 3: Add the subcutaneous layer. Pour an approximately 2 cm layer of pigmented gelatin over the fingertip and allow it to set. The abscess sits beneath this layer.

Step 4: Add the skin. Cover the gelatin with felt, then cover the felt with clear packing tape. The tape gives a firm surface to incise and holds the layers together.

Step 5 (optional): Check it with ultrasound. The lotion-filled fingertip is detectable with a handheld ultrasound, so the same model serves the guided and unguided versions of the procedure.

Step 6: Build it as above, with one substitution. Use the same sponge, gelatin, felt and tape layers, and place a kidney bean where the lotion-filled fingertip would go. The bean gives a small, solid lesion that can be palpated through the skin layer.

Step 7: Cut the wound. Cut a large sponge to represent wounded skin and tissue. This model has no gelatin, felt or tape.

Step 8: Add the debris. Place vinyl pieces into the cuts in the sponge.

Step 9: Paint it. Paint the model with red liquid latex to represent blood.

The source sets five objectives, built on Bloom's taxonomy:

1. Explain the common types and classification of soft tissue lesions, and understand their management at medical-student level, including incision and drainage, factors affecting wound healing, useful lab tests and the role of antibiotics.
2. Understand the purpose of ultrasound in managing soft tissue lesions and perform basic technique — orienting the probe, achieving appropriate depth, identifying basic subcutaneous structures — and know the diagnostic alternatives when ultrasound is not available.
3. Excise and drain an abscess, removing all purulence and the surrounding abscess sac, with and without ultrasound guidance, within 20 minutes.
4. Excise a small, solid subcutaneous nodule by palpating it and making a targeted incision, then close the wound in layers, within 20 minutes.
5. Debride a superficial wound until the exposed flesh is clean, then apply appropriate dressings, within 20 minutes.

The source runs these models as three stations of about 30 minutes each, with 4 to 8 students per group and 1 to 2 instructors per station, after a 30-minute, 16-slide talk on lesion presentation, examination, wound classification and ultrasound. The instructor demonstrates the procedure step by step; students then work in pairs on a model and coach each other, following the "see one, do one, teach one" model and Miller's pyramid.

• Knowledge rose from an average 4.2 out of 5.0 before the session to 4.7 out of 5.0 (p = 0.01). On "After draining an abscess, what should you do with the wound?", 69.8% answered correctly before and 93.5% after (p = 0.005).
• Confidence rose on all three procedures: nodule excision 2.3 to 4.0 (+1.7), abscess drainage 2.5 to 3.9 (+1.4), wound debridement 2.4 to 4.1 (+1.7), all p < 0.001.
• How representative the models felt, rated by 25 to 26 students per model: abscess drainage 3/26 "very representative" and 20/26 "somewhat representative"; nodule excision 3/26 and 19/26; wound debridement 7/25 and 16/25.
• Prior exposure was very low: 55/60 students had never seen a nodule excision, 54/60 had never seen an abscess drainage, and 43/59 had never seen a wound debridement. None had performed any of the three.

• The gelatin models need refrigeration, which is a constraint where electricity is not reliable.
• No model is reusable: the abscess is drained, the nodule is cut out and closed, and the wound is debrided, each with substantial loss of the model's structure.
• Air in the sponge base introduces reverberation and shadowing artefacts on ultrasound that do not occur in living tissue.

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