Total Hip replacement: Stryker MAKO robotic assisted with Accolade II and Tritanium implants
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The MAKO robot was first used in 2010 for a total hip replacement(THA). In 2015 FDA approval was granted and its use since then has increased dramatically. Whilst THA is a very successful operation, there continues to be an potentially reducible incidence of early failure from dislocation and malpositioning of components. The MAKO system has been designed by Stryker to increase the accuracy of component positioning, as well as sizing and it is hoped the longevity of lower limb joint replacement. Other systems are in their infancy at present and the Stryker MAKO is arguably the most common system currently used.
Stryker describe both an enhanced and express “workflow” for the MAKO total hip replacement. The express technique uses the MAKO technology to prepare the acetabular component and the enhanced technique assists with the femoral neck cut, broach version and combined component ante-version as well as acetabular preparation. The express workflow is a quicker surgical technique and focuses on accurate acetabular placement.
The MAKO technique requires a pre-operative CT scan of the patients pelvis and axial slices through the patients knee (to identify the epicondylar axis) and ankle. Using the information from this scan, exact sizing and positioning of the implants can be achieved. Intra-operatively a haptic arm from the MAKO robot is utilised to perform parts of the procedure such as acetabular reaming and cup placement. Intra-operatively the surgeon has real time feedback on the component position, leg length and hip offset.
If the surgeon is unhappy intra-operatively with any element of the MAKO plan (such as cup size, inclination, version), it can be immediately adjusted and the implantation executed to the new parameters. For instance if the planned cup anteversion doesn’t look correct in relation to the patient’s native transverse acetabular ligament, the version can be increased or decreased and the cup repositioned to suit the intra-operative findings.
It is vitally important that the position of the markers and arrays, which are applied to the operated limb and used for the robotic guidance, are not disturbed or adjusted during surgery as this will lead to inaccuracies unless re-calibration is performed.
The Accolade II stem is a tapered wedge designed stem. Increased stability has been designed into the stem by increasing its canal fit and fill. The stem was designed from information gained from the SOMA (Stryker Orthopaedic Modeling and Analytics) database. This database has CT scans of over 16,500 bones. Particular attention has been paid to the medial curvature of the stem to fit the femoral canal and the stem has unique size-specific curvatures as the stems increase in size. It has a metaphyseal Purefix HA coating Titanium plasma spray.
The Accolade II stem comes in two neck angle sizes 127° (increased offset) and 132°, both in sizes ranging from 0 to 11. The stem lengths gradually increase from 93mm (size 0) to 126mm (size 11). The offsets increase with each size, for a 127° stem the offset range from 28mm (size 0) to 53mm (size 11), for a 132° stem the offset range from 32mm (size 0) to 58mm (size 11).
Femoral head sizes range from 22mm to 44mm. with varying head offsets and materials.
Its current ODEP rating is 5A (2018).
The Tritanium cup is available as a hemispherical solid back shell, or with cluster holes. It can be used with polyethylene or a ceramic insert. It comes in 2mm incremental sizes ranging from 44mm to 66mm.
Author: Mr Richard Baker MD, MSc, MB.ChB, FRCS (Tr & Orth).
Institution: The Avon Orthopaedic Centre, Bristol, UK.
Clinicians should seek clarification on whether any implant demonstrated is licensed for use in their own country.