Surgical Technique of Cemented Acetabulum Component Insertion Using Robot Arm-assisted Surgery

Robotic arm-assisted surgery is becoming more widely used in total hip arthroplasty (THA) to aid surgeons in accurate component positioning. Surgical techniques describe cementless and hybrid THA implantation using robot arm-assisted systems, there is no description of cemented acetabular cup positioning and its use is considered off-label. Cemented THA has undergone technical and component improvement since the 1980s when studies first indicated high rates of loosening.1 Since this time, improved cementing techniques and cross-linked polyethylene cup introduction have demonstrated excellent results and improved survivorship.2,3 The Australian Joint Registry (AOANJRR)4 demonstrated that cemented THA has no difference from hybrid THA and a lower revision rate compared with cementless implants in the short term but with no difference long term. These results are not echoed in all registries as the later introduction of cross-linked polyethylene for cemented acetabular components compared with cementless creates a “polyethylene bias” when trying to interpret results. Since 2017, the AOANJRR has published data excluding non–cross-linked polyethylene articulations. Cemented acetabular cups are indicated for most patients who undergo THA but are particularly relevant for patients with poor quality acetabular bone stock (ie, osteoporosis and inflammatory arthritis or deficiencies that would lead to inadequate cementless fixation and revision of cup arthroplasty). These outcomes are maintained when surgeons maintain technique proficiency. The use of cemented acetabular implants also carries health and economic benefits with cemented implants costing significantly less than cementless acetabular components. The benefits extend into the postoperative period with decreased costs associated with reduced revision rates.5 We describe the surgical technique of cemented acetabular cup placement using the robot arm-assisted MAKO system (Stryker Kalamazoo). This technique is not currently described on the label, but it may be useful for surgeons who would like the benefit of haptic-controlled reaming and navigation of cemented cup implantation, as well as the potential benefits of the virtual range of motion impingement tool. TECHNIQUE Informed consent was obtained from the patient and the institution's ethical approval was obtained. Preoperative planning using the robot arm-assisted system is performed as though an uncemented acetabular component is being used. When the patient is placed in a lateral decubitus position, side support is placed at the sacral promontory and pubic bone, as a support on the anterior superior iliac spine leaves little sterile space between the post and iliac crest pins. (Fig. 1)FIGURE 1: Pelvic post against ASIS and pubic body. Note increased surgical field with post placed at the pubic body (Iliac crest marked with a dotted line and lower border of rib cage with solid line). ASIS indicate Anterior Superior Iliac Spine.Acetabular bone registration and reaming are carried out as per standard acetabular cup preparation for the robot arm-assisted system. Once the acetabulum is reamed a trial acetabular component 2 mm smaller than the final reamer is attached to the cup insertion handle and temporarily inserted into the acetabulum (leaving the handle attached). Once in the reduced position a recording is taken which is necessary for the MAKO software to progress with surgery and the window trial is removed. Further acetabular bone preparation is carried out as per the surgeons' usual technique. The author often eccentrically reams the superolateral manually with a small reamer to remove the sclerotic bone. As part of the surgical technique, lug holes are drilled into the 3 bones of the pelvis to increase the cross-sectional area of cement fixation. These are identified by changing the guidance module screen to computed tomography ream view. The planar probe can be used to identify each pelvic bone and guide lug hole placement. The author drills lug holes with the 9 mm acetabular step drill into the trabecular bone, taking care not to perforate the inner table of the acetabulum. (Fig. 2)FIGURE 2: Planar pointer positioning to determine pelvic bone.Once bone preparation is completed the final acetabular cup is cemented in place using a standard surgical technique (washing with pulse lavage, bone grafting the true floor, raytec temporarily in the lug holes to prevent hematoma, and the use of an ilial wing sucker). With the final acetabular component in place, before the cement sets, run the planar probe around the rim of the acetabular component to register 5 points using the surgical results feature under the final results tab. This will be recorded on the guidance system and give feedback regarding the acetabulum inclination and version. (Fig. 3)FIGURE 3: Rim of cup used for recording 5 points for acetabular position and registration of acetabular component positioning.Use a Howarth or Bristow to adjust the cup position, rechecking the position of the cup with the planar probe before the cement sets to obtain measurements as planned. This stage needs to be performed quickly to ensure the component is in the desired position before the cement sets. It is useful to practice with a trial component before cementing the definitive one in place. Once the cement has been set, the THA continues as a standard surgical procedure. EXPECTED OUTCOMES This method allows for the continuation of cemented acetabular components in modern arthroplasty, ensuring that this skill set is not, a concern with <3% of acetabular components cemented in Australian THA.4 Not only does this method continue to benefit the patient but also the health care system with decreased costs, a pertinent issue in a busy health care system with limited resources. The precise implantation of cemented acetabular components ensures preoperative planning and improved patient outcomes are maintained with the use of robot arm-assisted systems. One author has implanted 23 cemented cups using this technique, with a follow-up range of 1 to 4 years. All cups have been implanted within 3 degrees of planned inclination and anteversion. There have been no observed dislocations, revisions, or major complications. COMPLICATIONS Common complications, such as poor access and difficulty registering measurements, poor cement interdigitation, and cup positioning can be avoided by the techniques described. Access to the acetabulum and compromise of implant positioning can be avoided by positioning the patient as described. An increase in the surgical field allows for easy registration of measurements. Poor cement interdigitation of the acetabulum can affect acetabular cup stability, this can be reduced by drilling lug holes as described. Lug holes allow for greater cement interdigitation in the pelvis and increased cup stability. Improper positioning of the cemented implant can be prevented by using a Howarth or Bristow to adjust the cup position while the cement is being set. The position of the cup can be measured while the cement is set to ensure placement as planned. Cemented implants can be removed as per the surgeons' preferred technique.