MURINE SURGERY

2.4.1 Regulation of surgical procedure

Before surgery was performed approval was required from the Home Office to allow the procedure to be carried out. Both the project license and personal license were amended to include the surgical procedure(s) once it had been approved by the Home Office under the Animals (Scientific Procedures) Act 1986.

2.4.2 Surgical preparation

2.4.2.1 Suiting up and scrubbing of surgeons

All surgical procedures were carried in collaboration with Dr. Hazel Sutherland who has extensive experience of performing animal surgery. Upon entering the BSU surgical scrubs, gloves, a mop cap and a facemask were required to be put on before carrying out any preparation work. Scrubbing with a disinfectant and dressing in sterile gowns and gloves were required before surgery was performed.

35 2.4.2.2 Instrument preparation

All instruments were washed, wrapped and sterilised in a large oven prior to being used in surgery. A range of different sizes of surgical scissors and fine forceps were sterilised to ensure enough instruments were available to complete the surgery.

2.4.2.3 Anaesthesia

Prior to surgery the mice were anaesthetised. Inhalation anaesthetics were used as it allowed for a constant plane of anaesthesia to be maintained during surgery compared with injectable anaesthetics. The mice were anaesthetised using a combination of Isoflurane, NO2, and O2. The level of anaesthesia required by the mice varied which was usually due to weight differences between them. Mice weighing more than 30g tended to take longer to become fully anaesthetised and typically required a higher amount of Isoflurane (1.5-2.0%). Levels of NO2 and O2 were always maintained at 1.5% regardless of the weight of the mice. The amount of Isoflurane administered never went above 2.0% as this can cause terminal anaesthesia. During surgery, the mice were kept anaesthetised with the same level of Isoflurane required to initially anaesthetise them. The body temperature of the mice was also closely monitored; if a drop in temperature was recorded a heat mat was introduced to help maintain body temperature at 37oC.

2.4.2.4 Site of surgery preparation

Once anaesthetised, the mice were prepped for surgery. Baytril (Enrofloxacin), an antibiotic, was administered subcutaneously at a dose of 5mg/kg (diluted in distilled water). Temgesic (Buprenorphine), an analgesic, was administered intramuscularly into the rectus femoris muscle at a dose of 0.1mg/kg (diluted in distilled water). The area of interest was then shaved and sterilised with iodine.

36 2.4.3 Destabilization of the medial meniscus

2.4.3.1 General information

DMM is a procedure introduced by by Dr S Glasson et al [118] to induce a mild to moderate form of OA in mice. The procedure requires the transection of the medial meniscotibial ligament (MMTL) to free the MM from the tibial plateau (TP). This prevents the meniscus from distributing the body’s weight load causing increased mechanical stress and a higher risk of injury. The procedure was followed from the original publication and adapted where necessary.

2.4.3.2 DMM procedure

Using surgical scissors the skin of the left hind limb was incised over the patella and patella ligament to expose the knee joint. Micro surgical scissors were then used to make a small incision medial to the patella ligament, and small amounts of fat removed with blunt dissection. This was frequently followed by bleeding which was stemmed with a cotton bud, while saline was used to keep the joint moist. Identification of the MMTL proved to be difficult in BALB/c Hgd-/- mice as the ligament seemed to be almost translucent. As the MM was easier to identify it was used as a guide to determine where the MMTL attached on both the MM and the TP. Once definitively identified the MMTL was transected using micro surgical scissors. The ability to push the MM in and out of the joint cavity was used as confirmation the MMTL had been transected and the surgery had been successful. The incision in the patella ligament was sutured with a running stitch using 7.0 proline and the skin sutured with a subcutaneous stitch using 6.0 proline. The mice were then immediately transferred to the post-operative recovery room.

37 2.4.4 Post-operative recovery

Immediately following surgery the mice were placed in a heated room where a temperature of 25oC was maintained to aid their recovery. A second dose of temgesic was administered to help with pain relief. Once the mice had been returned to the BSU they were examined on a daily basis to ensure the surgical wound was healing properly. The general health of the mice was also checked as surgery can often cause a delayed adverse reaction. Restricted movement, weight loss and lack of grooming are known signs of abnormality and were therefore checked. If none of these were apparent upon examination of the mice they were classed as healthy.

2.4.5 Humane killing of animals using schedule 1 procedures 2.4.5.1 General information

All mice were humanely killed using Schedule 1 procedures in accordance with Home Office UK guidelines under the Animals (Scientific Procedures) Act 1986.

2.4.5.2 Overdose of an anaesthetic

Mice were euthanized by a lethal dose of pentoject (sodium pentobarbitone 20% w/v) prompting a rapid loss of consciousness. Pentoject was administered intraperitoneally to minimise any distress.

2.4.5.3 Concussion of the brain and dislocation of the neck

Concussion was caused by striking the cranium of the mice against the edge of the worktop with sufficient force to cause immediate loss of consciousness and/or death. After loss of consciousness was induced, death was confirmed by neck dislocation.

38 2.4.6 Dissection and harvesting of tissue

2.4.6.1 General information

Once death had been confirmed the mice were dissected either immediately in the BSU or later in the same day in the histology laboratory. It was imperative to collect the tissue on the day of death to prevent autolysis and necrosis. Tissues collected were fixed in either 10% phosphate buffered formalin solution (PBFS) for histological analysis, or 2.5% glutaraldehyde for ultrastructural analysis.

2.4.6.2 Harvesting of tissue 2.4.6.2.1 Hind limb

The skin was removed from the hind limbs exposing the full anatomy of the joint. The majority of the muscle was dissected away and the joint was dissected out by severing close to the femoral head which allowed for removal of the whole hind limb. The tibia was then severed just above the ankle to leave an intact knee joint. After washing in phosphate buffered saline (PBS) the limbs were fixed for analysis.

2.4.6.2.2 Heart

An incision was made into the skin of the mice to allow visualisation of the thoracic cavity which was subsequently opened by cutting through the sternum with surgical scissors. The heart was pried away from its surrounding connective tissue and was removed with its major vessels intact. The heart was washed with PBS to remove excess blood before fixation.

2.4.6.2.3 Liver and Kidneys

The liver was dissected out of the abdominal cavity ensuring none of the lobes were damaged. Once removed, the liver was washed in PBS and small sections of each

39 lobe were taken to allow for easy fixation and analysis. The kidneys were exposed after removal of the liver. They were dissected out of the abdominal cavity, washed in PBS and sectioned in half to allow for easy fixation and analysis.

2.4.7 Fixation of carcass

After the tissue(s) had been harvested the viscera (guts) were removed and discarded. The carcass was fixed in 150ml of PBFS to ensure adequate fixation. The fixing solution was changed after 24hrs and again if it altered colour as this indicated the solution had become acidic.

2.5 HISTOLOGY