How to Take a Muscle Biopsy

Summary

Muscle biopsy is indicated for further investigation of myopathy and unexplained muscle atrophy. The procedure is straightforward to perform in a clinic setting and can be performed ‘on the road’ with some planning to ensure adequate aseptic technique, diligent wound closure and appropriate handling of the biopsy sample. Safety of the sampler should also be considered due to the risk of kick injury when sampling from the hindquarters. Prior communication with the laboratory and efficient delivery is essential to prevent spoiling of the sample [1].

Before the biopsy

Contact the laboratory and arrange a courier at least 2 days prior to sampling to coordinate sampling, transport and analysis. Ensure no delay in delivery due to weekends/bank holidays.

Equipment required

Preparation of biopsy site

• Tail bandage/clippers/surgical preparation materials • Sedation (detomidine and butorphanol)
• Local anaesthesia (mepivacaine)
• Sterile drape (e.g. buster drape) and trolley/table

Biopsy

• Sterile gloves
• Scalpel/No 10 blade
• (Metzenbaum scissors)
• Rat tooth forceps and needle holders
• Small Gelpi retractors (one or two)
• Suture material (e.g 3 metric monocryl and 3.5 metric nylon/skin staples)

Preparation and transport

• Chilled 0.9% sterile saline
• Sterile gauze swabs
• Screw top containers (two)
• 10% formalin (10–20 mL)
• Ice packs and polystyrene box

Muscle biopsy procedure

The biopsy site is selected depending upon the muscle affected [2]. The semimembranosus muscle is routinely sampled for investigation of exertional myopathy. The sacrocaudalis dorsalis muscle is sampled for investigation of suspected motor neuron disease (Fig 1). Otherwise, the muscle most affected is sampled.

Collecting the biopsy

• Position the horse safely for the procedure with a reliable handler, ideally in stocks or over a stable door if you are standing behind the horse. Apply a tail bandage.
• Sedate the horse, clip and surgically prepare the biopsy site.
• Perform subcutaneous local infiltration of the biopsy site with 5–10 mL local anaesthetic (e.g. mepivacaine). Take care not to infiltrate the muscle to be sampled.
• Complete final skin preparation and prepare a sterile table or tray with the materials required to perform the biopsy. Wet sterile gauze swabs with chilled sterile saline and squeeze out well so they are not too damp.
• Make a 4 cm linear incision through skin and subcutaneous tissue overlying the site parallel to tail head/in the same orientation as muscle fibres.
• Place Gelpi retractors to expose the underlying muscle belly.
• Make two parallel incisions in the muscle, parallel to the muscle fibres. Incisions should be 3 cm long, 1 cm apart and approximately 8 mm deep.
• Hold the strip of muscle with forceps at the proximal end of these incisions and transect the strip of muscle proximally. Elevate an approximately 8 mm strip of muscle and transect the distal end to complete the biopsy.
• Place the muscle sample between two layers of damp gauze while closing the biopsy site.
• Close the site in two or three layers using absorbable suture to close dead space/subcutaneous layer and nylon simple interrupted skin sutures or skin staples.
• Cover the site, if possible, for 48 hours. A Primapore dressing covered with Polsterplast can be effective.

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