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Liability Issues Continue to Evolve in Computer-Assisted Surgery

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Device manufacturers of CAS systems should keep abreast of the changing legal issues.

Computer-assisted surgery (CAS) is rapidly growing as a treatment option in orthopaedics, especially for total joint replacement surgeries. Although CAS has the potential to improve the accuracy of component alignment and implant positioning, recent peer-reviewed medical journal articles explore whether the technology is more effective than traditional surgical methods. This article addresses the legal implications of these articles for manufacturers of CAS systems, which FDA has recognized as an important new treatment option.

What Is Computer-Assisted Surgery?

            CAS refers to any type of procedure that uses advanced technologies in the planning or execution of surgical procedures. Today commentators typically categorize CAS as passive, semi-active, and active systems depending upon the involvement of the surgeon. For example, some CAS systems use software to map patient anatomy to create more-personalized surgical plans (a passive system). Others integrate software and surgical instruments to allow surgeons to perform minimally invasive surgeries by maneuvering the instruments to create and work through small incisions in the body (a semi-active system). A third type of system would independently perform tasks without any direct human control (an active system).

            CAS systems have existed in orthopeadics since 1985 and have steadily increased over time. Today, all of the major medical device manufacturers have released plans or received FDA clearance for new CAS systems to be used in orthopedic surgical procedures. 

What Are the Benefits of CAS?

            The recent rise of CAS is no surprise, given that studies show it provides important benefits to patients. Chief among them is improved accuracy in positioning prosthetic joint components as compared to conventional surgery. 2 Improved component alignment, in turn, is expected to lead to reduced implant wear, reduced revision rates, and improved patient satisfaction overall. But questions remain. While studies confirm that CAS does, in fact, deliver better-aligned implants than traditional surgical methods, the same studies do not show that this necessarily translates to higher survivorship rates.3  Rather, it seems that surgeons may achieve similar long-term clinical outcomes using either computer-assisted or traditional surgical methods.4 Commentators speculate that this may be due to improvements made in the prosthetic joint components themselves, which may now be more tolerant of variabilities in alignment and are more resistant to wear and loosening.5

Legal Implications for Manufacturers of CAS

            FDA recognizes CAS as an important new treatment option that device manufacturers should be encouraged to develop and refine. But because it remains uncertain whether CAS systems offer better long-term results over conventional surgical methods, traditional lines of legal defense typically taken by medical device manufacturers may change when applied to these systems. 

Is CAS “State of the Art”?

In a standard product liability case, a plaintiff typically must prove that a product is in a defective condition and is unreasonably dangerous. Resolving that issue involves looking the design of the product as compared to the design of similar, competing products, and the state of available technology. A common—nearly universal—defense asserted by defendant-device manufacturers is the so-called “state of the art” defense: that the product used the best technology reasonably feasible at the time the product was manufactured.6

Faced with some evidence that CAS may not be safer, more effective, or producing better outcomes than traditional surgical methods, device manufacturers may face challenges regarding whether CAS systems reflect the “state of the art.” This may be especially true in cases with surgeons who are newer users of CAS. Some articles concluded that while surgeons experienced with CAS achieve outcomes similar to traditional surgical methods, new and occasional users of CAS achieved poorer outcomes.7 This raises a legal question: if a patient treated by an inexperienced user of CAS claims to have been injured as a result of the surgery, will “state of the art” remain a viable defense for a medical device manufacturer when traditional surgery would have produced a better outcome? 

The answer may lie in product warnings rather than product design. Manufacturers of CAS systems will likely have specific guidance and training for hospital customers and surgeon users, offering them “hands-on” experience and practice before performing procedures on patients. Robust training regimes may minimize the learning curve for surgeons using CAS systems and allow even new users of the technology the opportunity to produce outcomes equivalent to traditional surgical methods. FDA confirms that CAS “is an important treatment option that is safe and effective when used with proper training,” and emphasizes that “training development and implementation is the responsibility of the manufacturer, physicians, and healthcare facilities."8 If the design is sound and the teaching current, both factors should contribute to a state of the art defense.

What Will Be Required to Be Communicated to Patients?

Traditional product liability law holds that doctors are uniquely suited to advise their patients of the risks and benefits of a surgical procedure in response to the patient’s individual medical history and future needs. Given the medical complexities involved, medical device manufacturers typically are not expected to warn patients directly about surgical risks and benefits. Instead, the surgeon stands between the medical device manufacturer and the patient as a “learned intermediary” responsible for adequate warnings, because the surgeon has unique knowledge of the patient’s treatment options and the associated risks and benefits.  

CAS does not alter this bedrock principle. CAS, like any other medical device, is one treatment option available to surgeons and patients. Thus, surgeons continue to play a key role in recommending traditional surgery versus CAS depending on the nature and complexity of the case, explaining the pros and cons of each method, and discussing alternative options. Thus, CAS manufacturers should continue to assert this valuable defense in product liability litigation.

What Will Be the Regulatory Pathway to Market?

There are two main regulatory pathways for medical devices to come to market following U.S. FDA review: so-called “510(k) clearance” for devices “substantially equivalent” to those already on the market, and “pre-market approval” for more innovative devices. Under traditional product liability law, medical devices that undergo pre-market approval obtain protection from many state law legal claims under a legal doctrine called “federal preemption.”  In essence, preemption holds that a lay jury may not second-guess the safety assessments of FDA professionals.  

The CAS systems that are currently on the market received FDA clearance through the 510(k) process and, therefore, do not benefit from an express preemption defense. It is important to consider, however, that CAS systems are continuing to evolve in new ways and are likely to involve more complex hardware and software—some focusing on surgical planning and some focusing on surgical performance. Thus, there is a case to be made that new CAS systems coming to market could be deemed subject to FDA’s pre-market approval process. If that is the case, state law claims against manufacturers of FDA-approved CAS systems for defective design or inadequate warnings should remain ripe for early dismissal as preempted by federal law.

Because the law and technology continue to develop, companies would be wise to consult with legal counsel at the time of decision-making to ensure the most up-to-date analysis.

What is the “Product”?

Because only “products” are subject to strict liability causes of action, defining the “product” is a key part of determining exposure to liability. CAS systems are unique in that many require both software (computer programs) and hardware (surgical instruments) to operate. While hardware is certainly a “product,” most courts do not consider software to be a “product.” In 2019, however, FDA issued draft guidance stating that software is a “medical device” subject to FDA regulation if “its functionality poses a risk to a patient's safety if the software were to not function as intended.”9 Although this guidance is not legally binding, some courts have determined that software is a “product.”

The debate about what components of CAS systems constitute “products” is not academic. Rather, it highlights an inevitable issue that manufacturers will face in defending against lawsuits: Was the patient’s injury caused by a defect in the hardware or in the software that powers it? If different manufacturers collaborated to create the final CAS system, this issue could lead to finger pointing if the co-defendant manufacturers do not collaborate to present a unified front at the outset of a litigation. 


Although joint replacement implants have evolved to produce consistently good outcomes, CAS still has value and development of CAS technologies should be encouraged. The ability to plan surgical procedures in a more individualized way and to guide surgical instruments into smaller, confined spaces within the body provides a greater chance of success in complex cases. 

In designing and developing CAS systems, device manufacturers can take comfort that traditional legal rubrics such as state of the art, the learned intermediary, preemption, and co-defendant cooperation are likely not completely eviscerated in litigation involving CAS. But manufacturers of CAS devices would be wise to stay abreast of the changing legal issues along with the changing technology.

David L. Ferrera is a partner in Nutter’s Litigation Department and chairs Nutter’s Product Liability Defense practice group. Melanie V. Woodward is an associate in Nutter’s Litigation Department and is a member of Nutter’s Product Liability Defense practice group.


  1. Food and Drug Administration, Computer-Assisted Surgical Systems (March 13, 2019), available at; Chen, et al,, Robotic Technology in Orthopaedic Surgery, The Journal of Bone and Joint Surgery, 1984 (2018).
  2.  Roberts, et al., "Outcomes of Computer-Assisted Surgery Compared with Conventional Instrumentation in 19,221 Total Knee Arthroplasties," The Journal of Bone and Joint Surgery, at 550 (2020).
  3.  Bini, "Rethinking the Value of Computer-Assisted Surgery," The Journal of Bone & Joint Surgery, e32(1) (2020); Roberts, et al., "Outcomes of Computer-Assisted Surgery Compared with Conventional Instrumentation in 19,221 Total Knee Arthroplasties," The Journal of Bone and Joint Surgery, at 555 (2020);  Vermue, et al, "How Should We Evaluate Robotics in the Operating Theatre," The Bone & Joint Journal, at 411 (2020).
  4. Roberts, et al., "Outcomes of Computer-Assisted Surgery Compared with Conventional Instrumentation in 19,221 Total Knee Arthroplasties," The Journal of Bone and Joint Surgery, at 555 (2020).
  5. Roberts, et al., "Outcomes of Computer-Assisted Surgery Compared with Conventional Instrumentation in 19,221 Total Knee Arthroplasties," The Journal of Bone and Joint Surgery, at 555 (2020).
  6. See Restatement (Third) of Torts: Products Liability §2 (3rd 1998).
  7. Roberts, et al., "Outcomes of Computer-Assisted Surgery Compared with Conventional Instrumentation in 19,221 Total Knee Arthroplasties," The Journal of Bone and Joint Surgery, at 555 (2020); Vermue, et al., How Should We Evaluate Robotics in the Operating Theatre, The Bone & Joint Journal, at 407 (2020).
  8. Food and Drug Administration, "Computer-Assisted Surgical Systems" (March 13, 2019), available at
  9. Food & Drug Administration, "Examples of Device Software Functions the FDA Regulates" (Sept. 26, 2019), available at
TAGS: Surgical
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