Total Hip replacement: Stryker Mako robotic assisted Trident Accolade femur first and Trident acetabulum (Stryker)
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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 a 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 this will benefit 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.
The Mako robotic system is an image guided, active, haptic feedback system. It is based on high resolution CT scans to map the anatomy of the knee and lower resolution images of the limb to measure alignment. This has potential advantages of accuracy but does require more planning and forethought. It is active in the sense that there is a robotic arm that moves into the plane of cuts to be performed. More passive systems like the Smith and Nephew Navio are simply active when in the right field and off when they are not. The Mako provides boundaries which allow for protection of soft tissues such as the patella tendon and (in cruciate retaining cases) the posterior cruciate ligament. Their haptic feedback system stops the blade from cutting if any part of the cutting teeth stray outside of the boundaries. The final part of the system is interactive planning and analytics to allow for assessments of implant size and position as well as soft tissue tension.
The MAKO Hip system has two main options in terms of which aspects of the operation are assisted, known as the enhanced or alternatively the express workflows.
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.
Stryker govern the use of the system and it is only compatible with their approved implants. It is only available to surgeons who have been trained on an approved Stryker course and is always done with a Makoplasty Technician present in theatre. You should spend time with your technician so they understand how you work and the philosophies you use in knee reconstruction. It doesn’t take long to get used to each other and learn each other’s ways. I strongly recommend spending time going through cases preoperatively and postoperatively with each other to start with. You will find different subtle changes which can help to streamline the process and save quite a lot of time. As you develop, most surgeons find the cases will take less than 20 percent longer than conventional techniques, within around 20 cases.
Using a robotic system like this is more expensive, time consuming and there is as always learning curve. In order to be worthwhile, the surgeon must believe that the increased accuracy of ligament tension and bone cuts provide an improvement in function, longevity or both.
The Mako system provides the most information and input of any robotic knee system and is the only robot advanced enough to remove the need for cutting blocks. However, it is the bulkiest and requires the most pre-operative imaging as well as a dedicated technician. If you enjoy control and freedom, the Navio system may be more to your liking. If you want masses of information and are willing to be part of a team with robot, technician and surgeon working together, the Mako system will be rewarding.
In terms of the implants themselves 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. The published advantages of this femoral implant include a low intra-operative fracture rate, improved component stability and excellent survivorship, though over relatively short time frames.
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.
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Author: Jonathan Miles FRCS (Tr & Orth)
Institution: The Royal National Orthopaedic Hospital, Stanmore, London, UK.
Clinicians should seek clarification on whether any implant demonstrated is licensed for use in their own country.