Robotic technology in adult reconstruction – initially the placement of the stem during THR – was introduced in the early nineties of last century, starting in the US. The underlying technology dated back to the year 1986. Because of regulatory restrictions the technology could not spread in the US, but was exported to Europe in 1994. There the technology – primarily distributed in Germany – had a great success and by the year 2000 roughly 50 centers were using Robodoc – the first robot on the market – and a very similar German competitor’s product, CASPAR.

The initial robot was a crude machine, basically the unchanged beta version. Cumbersome fixation, a registration process using three fiducials, the requirement for second surgery to place the fiducials, and last but not least raw and hardly elaborated cutting files made surgery with Robodoc a demanding undertaking. Yet feedback from the surgeons, sometimes vigorously expressed during regular user meetings, let to continuous evolution of the system and resulted in an advanced and stable technology. Also training – with important input from the already experienced sites – improved significantly, which can best be demonstrated by procedure time for first surgery: in Frankfurt 1994 roughly four hours, while today first surgeries at new sites rarely exceed two hours. Further applications – revision surgery, total knee replacement – helped to justify the significant investment into the system.

While robotic technology underwent evolution, other related technologies were developed and entered the market. Main products were the navigation systems, which initially were developed for neurosurgery and spine surgery and which, due to easier handling and lower costs, found more acceptance on behalf of the surgeons. Although the navigation technology in some regards is a step back from the robotic technology, it appealed for just that reason: the surgeon stays in the loop. The surgeon uses the traditional instruments, and the navigator helps him to achieve precision in reaming or placement of implants. In orthopaedic surgery navigators became very popular in TKR, but also in THR.

Another development, completely unrelated to the mentioned technology, presented a new challenge: minimal invasive surgery. While in knee surgery the introduction of arthroscopy in the late seventies already proved the feasibility of minimal invasive techniques, adult reconstruction remained the domain of sometimes aggressive and robust surgery. Only recently minimal invasive procedures were introduced and standardized for a couple of applications. It is important to stress the fact that the term ‘minimal invasive’ did not relate to the size of skin incision only, but to the overall degree of soft tissue damage necessary to prepare for and place the implants. Some companies now offer new instruments allowing for very minimal incisions and reduced soft tissue compromise. In contrast to this development robot assisted surgery remained – in spite of numerous improvements – a rather invasive piece of surgery. These separate developments – navigators and minimal invasive surgery – made robot assisted joint surgery in the eyes of many potential users a rather outdated, superfluous and expensive type of technology. It is therefore time to revisit the original intentions that let to the development of robot assisted surgery.

The original ideas were sponsored by veterinary surgeons specializing in cementless THR for dogs. They experimented with custom implants, but they identified two fields of concerns: fractures and poor placement. Both problems are – still – common in human THR. Robot-assisted surgery was supposed to mainly address these problems. Another asset of robot-assisted surgery is seen in machine milling, which was invented as part of the robotic procedure and which turned out to be superior to conventional reaming.

The published results of robot-assisted THR (i.e. Nishihara et al, 2006) prove that these requirements were met. In our own series in Spain we had no fracture and every single implant was seated according to the preoperative plan. Animal experiments allowing for histological examination of the bone-implant interface showed the uncompromised cancellous scaffolding supporting the implant, while hand-reamed interfaces showed signs of destruction and atrophy.

On the other hands there are concerns that current minimal invasive approaches do cause problems in these regards: control of position is mainly feasible by use of intraoperative x-ray, and fractures do occur.

Therefore robot-assisted surgery seems to be the ideal complement for the minimal invasive approach. The deficits of MIS regarding orientation and visualization of the surgical object can be compensated by the robots proven ability to execute preoperative established plans. The challenge is the current invasiveness of robotic surgery, which – as primary tests and studies show – can be easily accounted for.

In conclusion there is an ever increasing role for robot-assisted surgery in adult reconstruction. It is up to the surgeons to define the requirements and ask for specifications that will meet their and the patient’s expectations regarding the degree of invasiveness involved.

Hip resurfacing is a challenging task. Not only because of the historic failure of the early resurfacings, like the Wagner cup, that mainly failed due to deficits in technology. But two other issues make resurfacing such a difficult undertaking: the femoral head and neck are not removed, which makes access to the acetabulum more difficult.

There are two critical steps during hip resurfacing that call for utmost precision: the placement of the central guiding rod in the femoral head and neck and the orientation of the cup. The central head/neck rod is crucial for the success of the surgery: it decides upon the alignment of the femoral component and whether any impingement with the femoral neck occurs or not. Initially this rod was introduced in a retrograde fashion from the lateral side, using a jig similar to those used during arthroscopic k-wire placement. This worked well and safely, yet required a large extension of the incision, which seems unacceptable in these minimal invasive days. The new jig allows for smaller incisions and seems to be working well, but still requires a lot of talent and/or training on behalf of the surgeon, and certainly is not fail safe. It is rather based on trial and error. Simple computer navigated placement of the central rod is feasible, cheap and fast, and it will guarantee precision in every case.

The same goes for cup placement. As the method requires a rather big cup, there is not much room for correction once the acetabulum is reamed. The very enlightening publications from Tony DiGioia and Branko Jaramaz have shown the susceptibility for error during cup reaming and placement. Adaptation of the existing navigation systems for the purposes of hip resurfacing is simple and fast. One should not hesitate to incorporate this extra quantum of security for the sake of the patients, for the sake of the method and, last but not least, for the sake of the surgeons.

Modern hip-replacement requires fixation of the femoral component, the stem, in the proximal femur. After resection of head and neck, the surgeons prepare the shaft in order to make room for the stem. Cemented fixation of the stem requires over-reaming, because the surgeon needs to provide space for the cement mantle, usually between 2 and 4 mms wide. Reaming for cemented fixation means removal of (cancellous) bone stock. Precision of reaming is not of utmost importance, as cement will fill gaps and will provide close contact between implant and bone. Cementless fixation on the other hand requires rather precise reaming, as for the biological fixation to occur, a close contact between implant and bone is crucial. There are two ways to achieve such contact: ream the bone to the precise negative form of the implant, or compress the cancellous bone into this shape. Compressing is technically easier and is regarded by some as the better option: the supposedly weak cancellous bone is compressed and provides a firm contact surface for the implant. The other option is precise reaming of the surface, sparing the scaffolding of the cancellous bone to provide biological support for the implant. It is difficult though to achieve this precise cutting with traditional tools: an animal experiment conducted by the author showed fractured and destroyed bone in the hand broached group, resulting in defects and lasting atrophy in the periphery, due to inadequate load transfer. These results coincide with a cadaver study performed by v.Hasselbach et al in 1996. The alternative to traditional hand broaching in both studies was using a high speed cutter with 70,000 rpm. As such a cutter can not be applied by hand due to the high torque; surgery was performed in both studies using a robot guiding the cutter. Cuts were performed according to a preoperatively established plan.

In the animal experiment, histological examination after one year showed no signs of atrophy in the high speed cutter group, whilst atrophy was still present in the hand broached group. These results coincide with significantly better performance in the postoperative force plating.

Conclusion: Application of navigation systems has helped to solve the problems in orientation of both cup and stem. Yet the preparation of the interface of the stem remains an unaddressed issue both in navigated and minimal invasive surgery. The use of high speed cutters (which prove to be helpful also in total knee replacement – Acrobot and Robodoc) seems an option that should not be neglected. The interface between bone and implant is the location where the fate of the implant is decided.

The traditional stem in cement-less total hip replacement was designed as a straight stem. This design was chosen to compensate for lack of initial stability provided by cement. Specifically the box shape of the implant achieved rotational stability and the wedge shape promised proximal press fit. Therefore also the first robot-assisted surgeries were performed using straight stems.

Primarily those surgeons using the antero-lateral approach soon felt limitations of the use of straight stems during robot-assisted surgery. The reamer, in order to guarantee a straight positioning of the implant, used a straight approach to the proximal femur, thereby damaging the insertion site of the gluteus muscle in some cases. This then led to persisting muscular deficit with a consecutive positive Trendelenburg sign.

Surgeons began to monitor during computer–assisted planning not only the final position, but also the cutting path, which was – as requested by the surgeons – displayed on the screen. At the same time anatomic stems became available for computer-assisted planning and surgery. With the introduction of anatomic stems also oblique cutting became available, thus avoiding compromising the greater Trochanter.

Clinical results of anatomic stems in robot-assisted surgery seem to be satisfactory. Although most users allow immediate weight bearing, no loosening or visible subsidence was reported. Cadaver studies and animal experiments suggest that exactness of robot-assisted preparation with the resulting close fit of the implant – no press fit though – provide sufficient stability to allow for anatomic designed stems in cement-less procedures.