Generally, it is considered to be safe in preventing iatrogenic instability if half of the facet joint is left intact during decompression surgeries.

By removing half of the facets can we get adequate decompression of the nerve roots? Is there a difference at different levels in the lower lumbar spine? What is the inclination of the facet joint at each level and how does it affect the stability?

Retrospective study

We analysed 200 consecutive magnetic reasonance imaging (MRI) scans of the lumbosacral spine at L3/4, L4/5, and L5/S1 levels. We measured the difference in the distance from midline to the lateral border of the foramen and from midline to the middle of the facet joint at each level on either sides. The angle of the facet joint was also noted.

The distance to the foramen from the level of the middle of the facet joints seem to be between 5-6mm lateral at every level. The angle of the facet joints at L3/4 is 35.9°+/−7.4°, while at L4/5 it is 43.2°+/−8.0°, and at L5/S1 it is 49.4°+/−10.1°.

In lumbar spine decompression surgeries, after the midline decompression extending up to half of the facet joints, a further undercutting of the facet joints to 5-6mm is therefore required to completely decompress the nerve root in the foramen. The more coronal orientation of the facet joint at L5/S1 conforms better stability than that at L3/4level. Therefore, stabilisation of the spine should be considered if more than 2cm of the posterior elements are removed from midline at L3/4 level.

Introduction: Prophylactic systemic antibiotics are commonly used peri-operatively in primary hip and knee arthroplasty in the UK. ‘Fast-Track’ (FT) peri-operative care – a multimodal concept aiming to accelerate postoperative rehabilitation and reduce general morbidity – is also becoming more common in arthroplasty surgery. There are no published reports of acute kidney injury (AKI) as a result of a single-dose prophylactic Gentamicin. The renal impact of hypotensive anaesthesia and reduced routine post-operative intravenous fluid therapy, both features of FT protocol, has not yet been reported. Aim: To evaluate the renal impact of prophylactic Gentamicin and FT perioperative care in hip and knee arthroplasty surgery.

Methods: Four hundred and eighty-four total hip/knee arthroplasty patients had their pre-operative, first and third post-operative day serum creatinine concentration measured and recorded. The first 180 patients (group A) received 1.5g Cefuroxime at induction and two further doses of 750mg at 8 hours and 16 hours post-operatively as antibiotic prophylaxis. The next 160 patients (Group B) received 5mg/kg single-dose Gentamicin at induction instead of Cefuroxime. These patients (Group A and B) were not treated as per FT protocol. The final 144 patients (Group C) received the same Gentamicin as Group B and were treated as per FT protocol. Outcome measures were overall change and an increase of > 30 μmol/L, the latter signifying an AKI.

Results: Mean creatinine change at day 1 was −4.63 in Group A, −3.95 in Group B and 4.19 in Group C. Mean creatinine change by day 3 was −5.28 in Group A, −2.53 in Group B and 8.89 in Group C. No patients in Group A, 4 patients (2.56%) in Group B and 9 patients (6.66%) in Group C had a rise of > 30 μmol/L in day 1 creatinine concentrations.

Conclusions: Comparing the groups, there was no statistically significance change in the day 1 creatinine when Gentamicin replaced Cefuroxime (p=0.625,) however this became significant once FT was also introduced (p=0.001.) In terms of an important creatinine rise (AKI,) the change to Gentamicin produced a statistically significant rise in the number of patients with a day 1 creatinine rise > 30 μmol/L (p=0.048.) By day 3 there is no significant difference in the number of patients with a creatinine rise > 30 μmol/L.

Discussion: FT protocol aims to encourage haemostatic surgery and early ambulant patients (free from drip stands) at the expense of mild hypovolaemia. When these patients are also receiving Gentamicin, the kidneys are concentrating urine and Gentamicin in the tubules thus causing and AKI in some cases. It appears that Gentamicin and FT are cumulative in their effect on renal function.

Background: Iatrogenic instability can be produced by lumbar spine decompression surgery not only if decompression extends beyond the lateral border of pars but also if there is insufficient pars left at the end of the procedure resulting in its fracture and hence instability on weight bearing. Generally, it is considered to be safe in preventing iatrogenic instability if half of the facet joint is left intact during decompression surgeries.

Purpose: We aimed to answer the following questions. By removing half of the facets can we get adequate decompression of the nerve roots? Is there a difference at different levels in the lower lumbar spine? What is the inclination of the facet joint at each level and how does it affect the stability?

Material and Methods: We analysed 200 consecutive magnetic reasonance imaging (MRI) scans of the lumbosacral spine at L3/4, L4/5, and L5/S1 levels. We measured the difference in the distance from midline to the lateral border of the foramen and from midline to the middle of the facet joint at each level on either sides. The angle of the facet joint was also noted. The vertebral body diameters in both the sagittal and coronal plane were noted.

Results: At L3/4, the mean distance from the midline to the middle of facet joint was 15.5 +/−1.9 mm (11–23mm), while the mean distance from the midline to the foramen was 21.2 +/− 2.6 mm (13–28mm). At L4/5, the mean distance from the midline to the middle of facet joint was 18.1 +/−2.3 mm (13–25mm), while the mean distance from the midline to the foramen was 23.6 +/− 2.9 mm (16–34mm). At L5/S1, the mean distance from the mid-line to the middle of facet joint was 15.5 +/−1.9 mm (11–23mm), while the mean distance from the midline to the foramen was 26.8 +/− 2.9 mm (20–34mm). The angle of the facet joints at L3/4 is 35.90 +/− 7.40, while at L4/5 it is 43.20 +/− 8.00, and at L5/S1 it is 49.40 +/− 10.10.

Conclusion: The distance to the foramen from the level of the middle of the facet joints seem to be between 5–6mm at every level with the lateral border of the foramen being lateral to the middle of the facet joint. Hence, in lumbar spine decompression surgeries, after the mid-line decompression extending up to half of the facet joints, a further undercutting of the facet joints to 5–6mm is therefore required to completely decompress the nerve root in the foramen. The more coronal orientation of the facet joint at L5/S1 conforms better stability than that at L3/4level. Therefore, stabilisation of the spine should be considered if more than 2cm of the posterior elements are removed from midline at L3/4 level.