MRI Measurement of Neuroforaminal Dimension at the Index and Supradjacent Levels after Anterior Lumbar Interbody Fusion: A Prospective Study

BACKGROUND: Anterior interbody fusion has previously been demonstrated to increase neuroforaminal height in a cadaveric model using cages. No prior study has prospectively assessed the relative change in magnetic resonance imaging (MRI) demonstrated neuroforaminal dimensions at the index and supradjacent levels, after anterior interbody fusion with a corticocancellous allograft in a series of patients without posterior decompression. The objective of this study was to determine how much foraminal dimension can be increased with indirect foraminal decompression alone via anterior interbody fusion, and to determine the effect of anterior lumbar interbody fusion on the dimensions of the supradjacent neuroforamina. METHODS: A prospective study comparing pre- and postoperative neuroforaminal dimensions on MRI scan among 26 consecutive patients undergoing anterior lumbar interbody fusion without posterior decompression was performed. We studies 26 consecutive patients (50 index levels) that had undergone anterior interbody fusion followed by posterior pedicle screw fixation without distraction or foraminotomy. We used preoperative and postoperative MRI imaging to assess the foraminal dimensions at each operated level on which the lumbar spine had been operated. The relative indirect foraminal decompression achieved was calculated. The foraminal dimension of the 26 supradjacent untreated levels was measured pre- and postoperatively to serve as a control and to determine any effects after anterior interbody fusion. RESULTS: In this study, 8 patients underwent 1 level fusion (L5-S1), 12 patients had 2 levels (L4-S1) and 6 patients had 3 levels (L3-S1). The average increase in foraminal dimension was 43.3% (p 0.05). CONCLUSIONS: Anterior interbody fusion with a coriticocancellous allograft can significantly increase neuroforaminal dimension even in the absence of formal posterior distraction or foraminotomy; anterior interbody fusion with a coriticocancellous allograft has little effect on supradjacent neuroforaminal dimensions.

Therapeutic drug monitoring in the treatment of active tuberculosis.

BACKGROUND: Therapeutic drug monitoring (TDM) is used to optimize dosing that maximizes therapeutic benefit while minimizing toxicity. In the treatment of active tuberculosis (TB), TDM is not routine, yet low levels of anti-TB drugs can be associated with poorer treatment outcomes. METHODS: In a retrospective case control study, patients with active TB in whom TDM was performed were considered cases and compared with controls who did not undergo TDM, and matched according to year of diagnosis and the results of direct smear microscopy. Medical records were reviewed to abstract demographic, clinical, radiographic and microbiological data including time until smear and culture conversion. RESULTS: In total, 20 patients were identified in whom TDM was performed, of whom 17 (87%) had at least one low drug concentration. Overall, 27 of 45 (60%) initial drug concentrations were low and resulted in an increased drug dosage. Low drug levels were found in 13 of 15 (87%) isoniazid, four of five (80%) rifabutin and eight of 12 (67%) rifampin measurements, but in only two of 13 (15%) pyrazinamide measurements. Within cases only, the 17 patients with low serum drug levels were significantly more likely to have comorbid illnesses, be smear positive, have lower serum albumin levels and had nonsignificantly longer time to culture conversion, compared with the three cases in whom all drug levels were within therapeutic ranges. CONCLUSIONS: TB drug levels were frequently below clinically acceptable levels in patients with active TB, particularly in those with HIV infection or other comorbidities. TDM is potentially useful for the treatment of active TB, but is currently underused.