Introduction The effect of hip rotation on the measurement of femoral offset is determined firstly using artificial bones in an anatomical study and then in a patient population. Its effect on the choice of femoral component in total hip arthroplasty is discussed

Methods X-rays were taken of a series of saw bone models rotated through a range of angles. The resultant offset was then measured

Standardised and Control (unstandardised) x-rays of the pelvis were taken of patients presenting to orthopaedic outpatients. Femoral offset was measured from each x-ray

Results In the anatomical study angles of rotation differed significantly with respect to measurement of offset (p< 0.0001 Friedman 2-way analysis of variance by ranks). The greatest measurement of offset was at 15 degrees internal rotation. Offset decreased with external rotation.

The clinical study had power of 80%. Femoral offset was increased in all the standardised x-rays compared with their controls (n=64, mean=8.68, SD=5.56, 95% CI (7.34,10.01) A one-sample t-test was performed to see if the standardised and control films were greater than 5mm different (t=12.94 (63df), p< 0.01).

Conclusions The clinical study confirmed the findings of the anatomical study. A standardised AP x-ray of the pelvis improves the measurement of femoral offset.

For surgeons using the Exeter hip system failure to account for offset could lead to the selection of a stem two sizes too small with regards to offset. Lesser degrees of rotation, not readily identified by looking at the x-ray, could still lead to the selection of an incorrectly sized stem.

Offset has been shown to increase the range of movement, abductor strength and stability of the hip joint whilst decreasing the rate of wear. It therefore benefits patients to account for offset, ensuring a correctly sized hip replacement.

Introduction The introduction of an air ambulance is known to have an impact on the workload at the receiving hospital. This study analysed all patients transported by an air ambulance to a new level 1 trauma centre, in particular examining their geographical location of injury, diagnoses and subsequent management.

Method Data was collected prospectively for a three month period from the commencement of the air ambulance service. Data was retrieved from the Casualty and inpatient notes. It included demographic data, trauma scores and theatre and admission details.

Results Of the 36 patients transferred by air 2 died in casualty shortly after arrival (1 drowning, 1 fatal brain injury). 24 patients were admitted under orthopaedic care. 4 of these had immediate emergency orthopaedic surgery. A further 10 had subsequent delayed surgery. 6 patients were admitted under other specialties (only one required operative intervention). 4 patients were discharged home directly from Casualty.

21 patients were transported from outside the hospital catchment area. 3 had suffered significant multisystem trauma as a result of road traffic accidents. 2 were in geographically isolated areas. In the remainder there was no specific requirement for air transportation.

Conclusions There were a significant number of minor orthopaedic cases whose clinical condition could have been met by road transport. Many patients were also from outside the catchment area of the hospital. This study highlights the potential for mistasking of an air ambulance service and the requirement for increased resources at the receiving hospital. Joint protocols need to be agreed on.

Introduction Femoral offset is the perpendicular distance from the centre line of the femur to the centre of rotation of the femoral head. In total hip replacement this is important for maintaining the correct leg length and creating a stable hip with well balanced soft tissues.

We studied the effect of hip rotation on the measurement of femoral offset and its subsequent effect on choice of femoral stem.

Method A series of saw-bone models labelled with radio-opaque markers was prepared. Serial x-rays were taken as each model was rotated though +15° internal rotation, 0°, −15° and −30° external rotation. At 0° the model was in the anatomical position. The resultant offset was measured from each x-ray.

Results Offset was significantly different when measured at different angles of rotation (p< 0.0001 Fried-man 2-way analysis of variances). Offset was greatest when measured at +15°. The greatest difference was encountered at −30° (up to 14mm). For the Exeter hip system this could lead to the selection of a stem 2 sizes too small. Even between 0° and −15°, where rotation is not readily identified on x-ray, differences of up to 7mm were found, which could still lead to the selection of an incorrect stem.