Volume 04 / Issue 04 / December 2016
Page 38
boa.ac.uk
JTO Features
How I Do… a SupraAcetabular Pin Placement for an Anterior Pelvic External Fixator Andrew Carrothers As an adjunct to pelvic binders, applying a stable anterior pelvic external fixator is a skill that should be mastered by all orthopaedic surgeons who treat acutely injured patients. Stabilising a pelvis during resuscitation allows clot formation and can help to reduce the volume of the true pelvis. Supra-acetabular (SA) Pin placement (slightly superior and lateral to the anterior inferior iliac spine (AIIS)), is less familiar to orthopaedic surgeons than iliac wing pins, but provides a more reliable pin-bone interface and allows improved reduction in
the plane of the deformity, with fewer soft-tissue complications. In addition, SA pins are better tolerated than iliac crest pins in the definitive management of pelvic ring disruption. Kit: l Image intensifier (II) and radiolucent table l Two large (6.5 mm) hydroxyapatite-coated AO Schanz pins l “MRI compatible” large AO ex-fix bar and connectors l 4.5mm drill. An oblique 2cm skin incision is made at the level of AIIS. The lateral femoral cutaneous nerve is identified and protected. An ‘obturator outlet’ view (Figure 1) is used to identify the entry point. This will show the safe corridor as a teardrop. The obturator oblique view shows the pin insertion site 2cm above the hip. The outer cortex is broached with 4.5mm drill in the identified SA zone, checking progress with an ‘iliac oblique view’ to ensure the appropriate trajectory just above the sciatic notch (Figure 2), where there is dense bone. The obturator inlet view assures that the pin is contained within the bone for its entire length.
Andrew Carrothers
The “MRI compatible” bars for the fixator are placed with the
Figure 1: Obturator outlet view identifies ‘teardrop’ entry point
apex slightly distal and asymmetric to one side to allow the patient to sit up and be nursed. Tips and Cautions: l Hydroxyapatite-coated pins are favoured as they appear to confer better longevity of the pins and potentially reduce local soft tissue infection l Meticulous pin site l Image intensification to avoid intra-pelvic or sciatic notch pin placement l Insertion of pins at least 2cm above the hip avoids hip capsule penetration l The fixator can be placed with a pelvic binder in situ. Andrew is a pelvic and acetabular surgeon working as a full time Consultant at Addenbrookes, Cambridge University Hospital NHS Foundation Trust. In addition he is a Trauma and Orthopaedic
Figure 2: Iliac oblique view to ensure the appropriate trajectory in the direction of the sacroiliac joint above the sciatic notch
Surgeon in the Royal Army Medical Corps (V), having served in both Iraq and Afghanistan. He is an Associate University Lecturer at the University of Cambridge. Recently, he has been awarded an NIHR RfPB grant, as chief investigator for a feasibility RCT in the management of elderly acetabular fractures (AceFIT).