Presentation
The Instruments Neurosurgeons Despise: Posture, Muscle Activation, and Discomfort Associated with the use of Kerrison Rongeurs and Rod Benders
DescriptionMusculoskeletal disorders (MSDs) constitute a significant occupational hazard for surgeons, with neurosurgeons and especially spine surgeons demonstrating some of the highest reported rates. Modern surgical work demands prolonged static postures, repetitive and forceful movements, and interaction with often non-ergonomic tools. These demands lead to muscle fatigue, discomfort, and cumulative risk of injury. The literature has consistently shown a high prevalence of work-related MSDs among surgeons (with rates up to 70–80%), driving absenteeism, career shortening, and diminished quality of life for affected practitioners.
Within spine surgery, instrument design and the mismatch between surgical tools and the anthropometric characteristics of the user, most notably hand size and grip structure, emerge as critical contributors to discomfort, impaired performance, and heightened MSD risk. Reports illustrate that commonly used metrics, such as glove size, are an imprecise proxy for true hand dimensions, with glove sizing overlooking essential factors like finger length, palm breadth, and grip diameter. Small-handed individuals report significantly lower comfort and more frequent difficulty when handling standard neurosurgical tools. These challenges persist even after controlling for glove size and operative workload, highlighting the importance of both accurate anthropometric assessment and tailored ergonomic design.
Despite the abundance of cross-sectional survey data and the recognition of the issue, there is a lack of objective, experimental research directly relating specific hand anthropometry measures to the biomechanics and muscle activation required for using neurosurgical tools, such as Kerrison rongeurs and rod benders. Most ergonomic literature in neurosurgery focuses on posture, technique modification, or the adoption of certain assistive devices, while the biomechanical interaction between surgeon and instrument has remained under-investigated. This gap persists even as the surgical workforce diversifies.
This research directly addresses this gap through a prospective, objective study, approved by the University of Michigan IRB HUM00208343: it measures 14 neurosurgeons’ hand dimensions (including grip diameter, fist circumference, finger width and length, and palm width), and correlates these anthropometric variables to both force production via dynamometry and muscle activity via surface electromyography (EMG) from 16 muscles, during simulated surgical tasks. The muscles are brachioradialis, flexor carpi ulnaris, flexor carpi radialis, and abductor pollicis brevis, from the hand and forearm, as well as bicep, triceps, upper trapezius, and pectoralis major across both right and left upper extremities. The surgical tasks are using a Kerrison rongeur to take 20 bites of simulated bone, using a rod bender to bend a rod with maximum force, and using a rod bender to bend a rod to match a template. These EMG from these tasks were compared to individual’s maximum voluntary contraction (MVC). A secondary focus of this study compares the position of the surgeon, using inertial measurement units (IMUs), during each of these simulated tasks. A tertiary focus of this study compares BORG CR10 and NASA/SURG TLX survey results before and after the tasks that capture elements such as discomfort and difficulty performing the tasks. These tasks reflect the range of tasks that are known to cause MSDs in surgeons over time, including repetitive tasks with the Kerrison rongeur, as well as exerting great amounts of force with the rod bender. Hypotheses explicitly examine whether smaller hands are associated with lower force readings, higher relative muscle activation, greater required joint angles, and longer task times, all indicative of increased ergonomic burden.
The intended application extends beyond documentation of risk: understanding these relationships supports recommendations for instrument redesign. By identifying the specific biomechanical disadvantages faced by users with smaller hands, the project can inform manufacturers about the need for a range of grip sizes, improved handle ergonomics, and perhaps even individualized tool recommendations. If ergonomic mismatches are rectified through redesign, there is the strong potential to decrease the incidence and impact of MSDs among spine surgeons, extend career longevity, and foster a more inclusive environment for all practitioners regardless of hand size.
The presentation will provide:
- An overview of the prevalence and impact of MSDs among neurosurgeons.
- A summary of survey findings on anthropometry-based disparities in instrument comfort and use.
- A description of the experimental protocol, including the rationale for focusing on precise anthropometric measurements.
- Results data on force, muscle activation, and position in surgical simulations.
- Implications for instrument design, clinical practice, and occupational health policies in neurosurgery.
The results suggest that there is a trend between grip size and percent of muscle activation used during the tasks. For example, in the Kerrison Rongeur task, all four of the hand and forearm muscles of the dominant hand exhibited a negative coefficient, such that the larger the grip size, the smaller percent of muscle activation was used compared to the maximum voluntary contraction. Of these four muscles, the flexor carpi radialis (FCR) had the largest coefficient, across all three tasks, at -0.065, -0.038, and -0.020 for using the Kerrison Rongeur, performing a maximum rod bend, and matching a rod to a template, respectively. Also, while the coefficient is still negative, the value decreases across the three tasks, as the forearm muscles are not recruited as much for those latter tasks. On average, participants used 56% of their MVC for the FCR for the Kerrison Rongeur tasks. Across all 16 muscles, participants used 31% muscle activation for the Kerrison Rongeur tasks, 47% muscle activation for the maximum rod bending task, and 40% muscle activation for the template matching task. In addition to using great amounts of force these tasks, the surgeons are in awkward positions to perform them. The Kerrison Rongeur tasks caused the participants to be in the most extreme positions, particularly for the neck and shoulder, with the neck at 60° flexion (chin to chest) and shoulder at 70° elevation, away from the side of their body. The discomfort survey captured these changes qualitatively. The results show the greatest amount of discomfort from the Kerrison Rongeur task, which primarily requires the use of the participant’s dominant hand, being in the dominant wrist (increasing from their baseline approximately 2.4 points on a scale of 0 to 10), followed by the dominant elbow and shoulder (increasing from their baseline 1 point). The rod bender tasks, which require the use of both hands, also increased a participant’s discomfort, in both wrists (increasing from their baseline approximately 1.4 points), as well as both shoulders and elbows (increasing about 1 point from their baseline). Interestingly, the results of each question on the TLX surveys were within one point of each other for the Kerrison Rongeur and Rod bender except mental demand, which was twice as high for the template matching task.
The central message stresses that the safety, health, and career sustainability of neurosurgeons, particularly those in spine surgery, depend on the optimization of both the working environment and the tools they use. The evidence shows that a “one-size-fits-all” approach to instrument design is outdated, potentially exclusionary, and may put some surgeons at unnecessary risk. By quantifying the ergonomic burden associated with hand-instrument mismatch, this work highlights the urgent need for collaboration between clinicians, researchers, and device manufacturers.
Key takeaways for the audience include:
- MSDs in neurosurgery are common, costly, and impact career trajectories.
- Existing ergonomic interventions have largely neglected individual anthropometry and instrument matching.
- There is a demonstrable relationship between hand size, required force/muscle activity, and task efficiency.
- Highlighting the need for re-engineering tools or customizing surgical tools.
- Improving the ergonomic fit of neurosurgical tools could reduce injuries, foster greater equity for surgeons of all body types, and ultimately improve patient care by enabling safe, long, and effective surgical careers.
Within spine surgery, instrument design and the mismatch between surgical tools and the anthropometric characteristics of the user, most notably hand size and grip structure, emerge as critical contributors to discomfort, impaired performance, and heightened MSD risk. Reports illustrate that commonly used metrics, such as glove size, are an imprecise proxy for true hand dimensions, with glove sizing overlooking essential factors like finger length, palm breadth, and grip diameter. Small-handed individuals report significantly lower comfort and more frequent difficulty when handling standard neurosurgical tools. These challenges persist even after controlling for glove size and operative workload, highlighting the importance of both accurate anthropometric assessment and tailored ergonomic design.
Despite the abundance of cross-sectional survey data and the recognition of the issue, there is a lack of objective, experimental research directly relating specific hand anthropometry measures to the biomechanics and muscle activation required for using neurosurgical tools, such as Kerrison rongeurs and rod benders. Most ergonomic literature in neurosurgery focuses on posture, technique modification, or the adoption of certain assistive devices, while the biomechanical interaction between surgeon and instrument has remained under-investigated. This gap persists even as the surgical workforce diversifies.
This research directly addresses this gap through a prospective, objective study, approved by the University of Michigan IRB HUM00208343: it measures 14 neurosurgeons’ hand dimensions (including grip diameter, fist circumference, finger width and length, and palm width), and correlates these anthropometric variables to both force production via dynamometry and muscle activity via surface electromyography (EMG) from 16 muscles, during simulated surgical tasks. The muscles are brachioradialis, flexor carpi ulnaris, flexor carpi radialis, and abductor pollicis brevis, from the hand and forearm, as well as bicep, triceps, upper trapezius, and pectoralis major across both right and left upper extremities. The surgical tasks are using a Kerrison rongeur to take 20 bites of simulated bone, using a rod bender to bend a rod with maximum force, and using a rod bender to bend a rod to match a template. These EMG from these tasks were compared to individual’s maximum voluntary contraction (MVC). A secondary focus of this study compares the position of the surgeon, using inertial measurement units (IMUs), during each of these simulated tasks. A tertiary focus of this study compares BORG CR10 and NASA/SURG TLX survey results before and after the tasks that capture elements such as discomfort and difficulty performing the tasks. These tasks reflect the range of tasks that are known to cause MSDs in surgeons over time, including repetitive tasks with the Kerrison rongeur, as well as exerting great amounts of force with the rod bender. Hypotheses explicitly examine whether smaller hands are associated with lower force readings, higher relative muscle activation, greater required joint angles, and longer task times, all indicative of increased ergonomic burden.
The intended application extends beyond documentation of risk: understanding these relationships supports recommendations for instrument redesign. By identifying the specific biomechanical disadvantages faced by users with smaller hands, the project can inform manufacturers about the need for a range of grip sizes, improved handle ergonomics, and perhaps even individualized tool recommendations. If ergonomic mismatches are rectified through redesign, there is the strong potential to decrease the incidence and impact of MSDs among spine surgeons, extend career longevity, and foster a more inclusive environment for all practitioners regardless of hand size.
The presentation will provide:
- An overview of the prevalence and impact of MSDs among neurosurgeons.
- A summary of survey findings on anthropometry-based disparities in instrument comfort and use.
- A description of the experimental protocol, including the rationale for focusing on precise anthropometric measurements.
- Results data on force, muscle activation, and position in surgical simulations.
- Implications for instrument design, clinical practice, and occupational health policies in neurosurgery.
The results suggest that there is a trend between grip size and percent of muscle activation used during the tasks. For example, in the Kerrison Rongeur task, all four of the hand and forearm muscles of the dominant hand exhibited a negative coefficient, such that the larger the grip size, the smaller percent of muscle activation was used compared to the maximum voluntary contraction. Of these four muscles, the flexor carpi radialis (FCR) had the largest coefficient, across all three tasks, at -0.065, -0.038, and -0.020 for using the Kerrison Rongeur, performing a maximum rod bend, and matching a rod to a template, respectively. Also, while the coefficient is still negative, the value decreases across the three tasks, as the forearm muscles are not recruited as much for those latter tasks. On average, participants used 56% of their MVC for the FCR for the Kerrison Rongeur tasks. Across all 16 muscles, participants used 31% muscle activation for the Kerrison Rongeur tasks, 47% muscle activation for the maximum rod bending task, and 40% muscle activation for the template matching task. In addition to using great amounts of force these tasks, the surgeons are in awkward positions to perform them. The Kerrison Rongeur tasks caused the participants to be in the most extreme positions, particularly for the neck and shoulder, with the neck at 60° flexion (chin to chest) and shoulder at 70° elevation, away from the side of their body. The discomfort survey captured these changes qualitatively. The results show the greatest amount of discomfort from the Kerrison Rongeur task, which primarily requires the use of the participant’s dominant hand, being in the dominant wrist (increasing from their baseline approximately 2.4 points on a scale of 0 to 10), followed by the dominant elbow and shoulder (increasing from their baseline 1 point). The rod bender tasks, which require the use of both hands, also increased a participant’s discomfort, in both wrists (increasing from their baseline approximately 1.4 points), as well as both shoulders and elbows (increasing about 1 point from their baseline). Interestingly, the results of each question on the TLX surveys were within one point of each other for the Kerrison Rongeur and Rod bender except mental demand, which was twice as high for the template matching task.
The central message stresses that the safety, health, and career sustainability of neurosurgeons, particularly those in spine surgery, depend on the optimization of both the working environment and the tools they use. The evidence shows that a “one-size-fits-all” approach to instrument design is outdated, potentially exclusionary, and may put some surgeons at unnecessary risk. By quantifying the ergonomic burden associated with hand-instrument mismatch, this work highlights the urgent need for collaboration between clinicians, researchers, and device manufacturers.
Key takeaways for the audience include:
- MSDs in neurosurgery are common, costly, and impact career trajectories.
- Existing ergonomic interventions have largely neglected individual anthropometry and instrument matching.
- There is a demonstrable relationship between hand size, required force/muscle activity, and task efficiency.
- Highlighting the need for re-engineering tools or customizing surgical tools.
- Improving the ergonomic fit of neurosurgical tools could reduce injuries, foster greater equity for surgeons of all body types, and ultimately improve patient care by enabling safe, long, and effective surgical careers.
Authors
Event Type
Oral Presentations
TimeMonday, March 232:00pm - 2:30pm EDT
LocationMurray Hill West
Hospital Environments