Robotic milling may provide better long-term THA results over manual femoral preparation

Hand rasping for femoral canal preparation significantly increased blood loss, although no patients required allogenic transfusion.

Performing total hip arthroplasty using a robotic milling system to prepare the femoral canal rather than hand rasping yielded significantly better clinical results at 2 years follow-up, a study found.

Shunsaku Nishihara, MD, and colleagues at Osaka University Medical School and at Kyowakai Hospital in Osaka, Japan, compared outcomes between the two femoral preparation methods in 156 primary total hip arthroplasties (THAs) performed in 140 patients. In all cases, surgeons used the ORTHODOC system (Integrated Surgical Systems) for preoperative planning, which uses computed tomography images and 3-D modeling to aid surgeons in determining optimal femoral stem size and position, according to the study.

The researchers randomly assigned patients to undergo either hand rasping or robotic milling, which was performed using the ROBODOC system (Integrated Surgical Systems). The hand rasping group included 78 hips in 67 patients; the robotic milling group included 78 hips in 73 patients.

Surgeons performed all THAs using a posterolateral approach and implanted a fiber metal femoral stem coated with hydroxyapatite (VerSys, Zimmer). Also, surgeons manually inserted and impacted the femoral stem in all cases, the study authors noted.

The researchers found that both groups had similar Merle D'Aubigne hip scores at 3 months follow-up. However, patients treated with robotic milling had significantly better hip scores at 2 years (P<.05), according to the study.

Robotic milling resulted in significantly longer mean operating and femoral canal preparation times. However, patients treated with robotic milling had significantly lower rates of operative blood loss, the authors said.

No patients in either group required allogenic blood transfusion, they noted.

Five intraoperative femoral fractures occurred, all of which were in the hand rasping group during final femoral stem insertion. However, both groups regained the ability to walk 6 blocks unaided after a similar amount of time, although significantly more robotic milling patients regained this ability within 13 days after surgery.

According to the study, hips in the robotic milling group also had significantly better radiographic results compared to hips treated with hand rasping in all of the following:

medial gap at levels 1 to 3;
mediolateral canal filling ratio at levels 1 to 5;
canal filling ratio at level 1;
anteroposterior alignment;
femoral anteversion; and
vertical seating.

"[The] robotic milling group had no intraoperative femoral fractures and had better fit, fill and alignment in the radiographic findings. These advantages can help delay or eliminate costly repeat surgery in the longer term," the authors said.

"Moreover, the volume of intraoperative pulmonary embolisms can be reduced by robotic milling in the near term. Therefore, a complete cost-benefit evaluation of robotic surgery requires consideration of longer-term outcomes," they added.

For more information:
Nishihara S, Sugano N, Nishii T, et al. Comparison between hand rasping and robotic milling for stem implantation in cementless total hip arthroplasty. J Arthroplasty. 2006;21:957-966.