Compartment syndrome (CS) is a unique form of skeletal muscle ischaemia. N-acetyl cysteine (NAC) is an anti-oxidant in clinical use, with beneficial microcirculatory effects.

Sprague-Dawley rats (n=6/group) were randomised into Control, CS and CS pre-treated with NAC (0.5g/kg i.p. 1 hr prior to induction) groups. In a post-treatment group NAC was administered upon muscle decompression. Cremasteric muscle was placed in a pressure chamber in which pressure was maintained at diastolic minus 10 mm Hg for 3 hours inducing CS, muscle was then returned to the abdominal cavity. At 24 hours and 7 days post-CS contractile function was assessed by electrical stimulation. Myeloperoxidase (MPO) activity was assessed at 24-hours.

CS injury reduced twitch (50.4±7.7 vs 108.5±11.5, p<0.001; 28.1±5.5 vs. 154.7±14.1, p<0.01) and tetanic contraction (225.7±21.6 vs 455.3±23.3, p<0.001; 59.7±12.1 vs 362.9±37.2, p<0.01) compared with control at 24 hrs and 7 days respectively. NAC pre-treatment reduced CS injury at 24 hours, preserving twitch (134.3±10.4, p<0.01 vs CS) and tetanic (408.3±34.3, p<0.01 vs CS) contraction. NAC administration reduced neutrophil infiltration (MPO) at 24 hours (24.6±5.4 vs 24.6±5.4, p<0.01). NAC protection was maintained at 7 days, preserving twitch (118.2±22.9 vs 28.1±5.5, p<0.01) and tetanic contraction (256.3±37 vs 59.7±12.1, p<0.01). Administration of NAC at decompression also preserved muscle twitch (402.4±52; p<0.01 versus CS) and tetanic (402.4±52; p<0.01 versus CS) contraction, reducing neutrophil infiltration (24.6±5.4 units/g; p<0.01).

These data demonstrate NAC provided effective protection to skeletal muscle from CS induced injury when given as a pre- or post-decompression treatment.

Various reports confirm that elevations in serum markers associated with skeletal muscle injury exist and can occur after orthopaedic surgery in the absence of overt clinical manifestations of myocardial injury. The purpose of this study is to measure the influence surgical approach on these serum markers following primary Minimally Invasive THA. Consecutive enrollment of 30 patients into three different groups of 10 was performed. The MIS Modified Watson Jones THA is an approach using an inter-muscular plane, the Mini Posterior is a trans-muscular approach with some muscle detachment and repair, while the MIS II Incision THA is an inter-muscular approach anteriorly and a trans-muscular approach posteriorly. Blood samples for total creatine kinase (CK), creatine phospho-kinase (CPK), and serum myoglobin were obtained at screening and the morning before surgery as a baseline, immediately post-operatively in the recovery room and 8, 16, 24, 36, 48, and 72 hours post-operatively. Hemoglobin and hematocrit was obtained pre-operatively, 16, 36, and 72 hours (±6 hours) post-operatively. Cardiac troponin-I was measured the morning before surgery (pre-operatively) and 16 hours following surgery to monitor any contributory effect of myocardial injury. We report measurable and reproducible trends in serum enzyme levels consistent with skeletal muscle damage due to THA. Troponin-I remained normal in all but one case throughout the entire study indicating no myocardial contribution to measured serum enzyme levels. While these trends may have slight correlation with surgical approach, they were not statistically significant. We conclude that all three procedures do affect serum enzyme markers and are safe from this standpoint, but no surgical approach appears to affect the degree of muscle trauma more or less than another