Percutaneous cartilage biopsy.

A needle is described for obtaining specimens of non weight-bearing hyaline cartilage from the lateral femoral condyle. The hyaline cartilage of the femur continues onto the lateral surface of the condyle as a 'lip' which lies deep to the capsule of the knee joint and is readily accessible for biopsy. The cylindrical needle is hollow with a sharpened cutting edge and is 5 mm. in diameter. Within the cylinder is a removable blade, which resembles an Archimedes screw. On rotating the needle, a flat spiral of cartilage is raised into the body of the cylinder and can be withdrawn. In contrast, a bone biopsy trephine will fail to remove a plug of tissue unless a deep biopsy is made and the plug levered 'to and fro'. The Archimedes blade is detachable and may be resharpened or renewed (Fig. 1, overleaf). Considerable practice is necessary on cadaveric knees before specimens are taken from patients. In a preliminary series, these knees were opened to confirm that the biopsy had been taken from the correct area and that it included subchondral bone (Fig. 2). The site of the biopsy is determined by palpation of the lateral femoral condyle and is best found with the knee flexed at about 45°. With full asepsis and under local anaesthesia, the operator makes a 2 cm. incision through the skin, soft tissues, and joint capsule over the biopsy site (Fig. 3, overleaf). A finger tip may be introduced into the wound to confirm the biopsy site by direct palpation. The needle is then pressed against the cartilage and rotated through at least 3600 in a clockwise direction. Some discomfort may be experienced but is no more than for most biopsy procedures. Closure with three silk sutures is usual and the patient may walk after 24 hours.