Minimally invasive hip replacement
An anterior approach with the additional support of CT assisted 3-D planning software
By Dr Sebastian Radmer, of the orthopaedics and rheumatic surgery department at Immanuel Hospital, Berlin
However, high standards of safety and the longevity of the implant must not be compromised by reduced intra-operative visualisation. This means precise pre-operative planning to facilitate positioning of the implant with accuracy. Planning is in general performed using templates on conventional X-ray photographs, with factors such as different enlargement, angles of projection that are not always accurate and representation of the total volume clearly reducing precision. The aim of our study was to investigate both the clinical results after implantation of a THP via an anterior minimally invasive approach, and the clinical application of 3-D planning software.
117 consecutive patients attending our clinic (mean age 74.8 (41-83) years) received a total hip prosthesis (Hilock Line cup, Arcad stem, SPS and SPS modular stem, made by Symbios, Yverdon, Switzerland) in a prospective study. All patients underwent spiral CT pre-operatively for 3D planning. The data were processed on an external workstation for 3D planning using special software (SYMBIOS® 3D Hip Plan), and produced an exact view of the acetabulum and femur in all three planes. After establishing the pelvic axis and determining the original centre of rotation, first the acetabular cup was positioned, followed by the stem.
The surgical technique was able to be performed on all the patients, and the incision length was on average 7.9 cm. Mean operating time was 69 minutes, and mean blood loss in 24 hours was 365 ml. The mean value for pain on the VAS was 7.9 pre-operatively, 2.5, three days post-operatively and 1.4, seven days post-operatively. The mean pre-operative Merle d’Aubigné score was 10.2. Post-operatively it was 15.4 after 3 weeks, 16.9 after six weeks and 17.2 after 12 weeks. The CT plan relating to the cup could be implemented precisely in 108 of the 117 patients (92.3%). In three of the 117 patients, (2.6%), an individual stem was implanted as no modular stem could provide adequately in this respect. The plan was able to be implemented in 101 (88.6%) of the other 114 patients. All the prostheses were implanted without cement, and no stem burst occurred. A total of six complications arose: one prosthesis infection, two wound healing disorders, and three instances of irritation of the lateral femoral cutaneous nerve. No signs of loosening were detected on X-ray.
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