Introduction: The position of the L4/5 disc inter-space is commonly believed to be represented by a line drawn between the two highest points of the iliac crests. This line is used frequently as a pre-operative guide for incision placement, in patients undergoing spinal surgery.

Aim: To investigate whether a line drawn between the two highest points on the iliac crests corresponds to the L4/5 disc inter-space, in varying patient age groups.

Patients and Methods: We reviewed 450 AP and lateral lumbar spine radiographs in patients ranging in age from 20 – 90 years. Patients with an obvious deformity or previous spinal surgery were excluded from the study. In the AP films, a line was drawn between the two highest points on the iliac crests. From this line, the distance to the midpoint of the L4/5 disc was measured.

Results: In all age groups measured, the true L4/5 disc inter-space lay below the line between the iliac crests, at an average of 4.33mm below the supracristal plane. The plane intersected the spine at the L4/5 interspace in only 31.9% of cases and was found to lie at the lower half of the L4 body or above in 49.3% of cases.

Conclusions: These results show that, using a line drawn between the two highest points on the iliac crests as a guide to the position of the L4/5 disc interspace may lead to unintentionally cranial positioning of an incision or cannulation in this area. Therefore, it is advisable to perform a pre-operative AP and lateral radiograph of the lumbar spine, to enable accurate incision placement when performing spinal surgery in this area.

Introduction: The position of the L4/5 disc inter-space is commonly believed to be represented by a line drawn between the two highest points of the iliac crests. This line is used frequently as a pre-operative guide for incision placement, in patients undergoing spinal surgery.

Aim: To investigate whether a line drawn between the two highest points on the iliac crests corresponds to the L4/5 disc inter-space, in varying patient age groups.

Patients and Methods: We reviewed 450 AP and lateral lumbar spine radiographs in patients ranging in age from 20 – 90 years. Patients with an obvious deformity or previous spinal surgery were excluded from the study. In the AP films, a line was drawn between the two highest points on the iliac crests. From this line, the distance to the midpoint of the L4/5 disc was measured. This was achieved in the lateral films, by finding the midpoint between the two iliac crests and again measuring the distance from this point to the midpoint of the L4-5 disc.

Results: In all age groups measured, the true L4-5 disc inter-space lay below the line between the iliac crests. In the patient group a 20–30 yrs, the inter-iliac crest line lay on average 1.86 mm above the true l4–5 disc space. In the patients aged 30–40 yrs the line was on average 2.49 mm above the disc space. Patients aged 40–50 yrs the line was 6.05 mm above the disc space. In patients aged 50–60 yrs and 60–70 yrs, the line was 3.17 mm above the disc space. In the 70–80 yrs age group, the line was 4.5 mm above the true disc space. In the oldest group of patients studied (80–90 yrs), the line was positioned 9.06 mm above the true disc space. The results were analysed using the ANOVA system to assess their statistical significance. Comparison of the patients aged 20–30 yrs versus patients aged 80–90 yrs yielded a p value of p=0.0045. Patients aged 60–70 yrs versus patients aged 80–90 yrs, p=0.0049. Patients aged 50–60 yrs versus patients aged 80–90 yrs, p=0.0023. Patients aged 30–40 yrs versus patients aged 80–90 yrs, p=0.0004. Patients aged 70–80 yrs versus patients aged 80–90 yrs, p=0.03. Comparison of other patient groups, were of low statistical significance

Conclusions These results show that, while the L4/5 disc inter-space does broadly correspond to a line drawn between the iliac crests, there is a significant variation between different age groups and within individual age groupings. Therefore, it is advisable to perform a pre-operative AP and lateral radiograph of the lumbar spine, to enable accurate incision placement when performing spinal surgery in this area.

Polymethylmethacrylate (PMMA) Acrylic Bone Cement is a polymer used to anchor the prosthesis during Joint Replacement Surgery. Arthroplasty with Bone Cement is associated with late loosening, compromising prosthetic stability leading to Revision arthroplasty. Different irrigating solutions such as Hydrogen Peroxide or Saline are used during arthroplasty. The aim of the study was to analyse the effects of Hydrogen Peroxide on the mechanical properties of Bone Cement.

Materials and Methods: Cement was mixed as per standard methods used in theatre, in a vacuum and at a temp of 18 degrees centigrade. Once the cement was mixed it was then placed in conical moulds and the exposed surface was either exposed to saline or Hydrogen Peroxide solution (6% from a standard theatre preparation). We studied the effect of Hydrogen Peroxide on Dough time, Curing time, Surface Analysis and Hardness of PMMA. Dough time was performed with latex examination gloves. Curing time was measured at 15 seconds intervals using a Vickers hardness transistor. Cement hardness was assessed using the same machine. Surface analysis was performed by preparing the samples using a grit rotaforce machine. Palacos Bone Cement was used and tests were conducted according to ASTM F-451 and ISO 5833 standards.

Results: The samples exposed to hydrogen peroxide showed an increase in the dough time in comparison to the controls from 3.5 minutes to 5 minutes. Curing time showed a difference of 13.5 minutes for the controls as opposed to 17 minutes for the HP contaminated samples. Surface hardness reduced from a mean of 17.5hv to 14.3hv after exposure to hydrogen peroxide (p< 0.05). There was increased staining of the Hydrogen Peroxide sample, with surface irregularities, and an associated increase in surface porosity. Surface porosity increased from 120um (SD 11.2) to 180um (SD 8.7) (p< 0.05).

Conclusion: We have shown that the use of hydrogen peroxide contamination of bone cement interferes with the biomechanical properties of the cement, leading to an overall reduction in strength and hardness of the cement. This may lead to an associated reduction in the strength of the bone cement interface and precipitate early micro-motion and loosening of the prosthesis.