Charles Radcliffe, Father of Prosthetic Biomechanics

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By Sherry Metzger, MS

Professor Charles Radcliffe, MS, ME, is a world-renowned engineer lauded as the father of prosthetic biomechanics. He began his distinguished career in the orthotics and prosthetics field in 1948 while in the US Navy as an engineering officer in World War II. He learned of a research opportunity at the University of California in Berkeley while working on laminated plastic aircraft components.

Radcliffe is largely responsible for such pioneering con­tributions as the quadrilateral socket, patellar-tendon-bearing (PTB) prosthesis, solid ankle cushion heel (SACH) Foot and the four-bar prosthetic knee. In addition, he is credited with providing the fundamental principles of the biomechanics of prosthetic alignment and socket force transfer throughout the amputee gait cycle. His legendary principles still are taught to prosthetists and therapists to this day.

From 1947 to 1956, Radcliffe earned degrees in mechanical engineering at the University of California in Berkeley. He was a principal investigator in the Prosthetics Research Group of the Biomechanics Laboratory at Berkeley for 35 years, when the study of human locomotion and improved artificial limb designs were the highest-funded projects. During this time he also lectured in the Design Division of the Mechanical Engineering Department and was a professor of mechanical engineering from 1956-1988. Currently serving as professor emeritus of mechanical engineering, Radcliffe is involved in continuing to improve the understanding of the four-bar prosthetic knee design.

Quad Socket Development

His first major project as a graduate student, studying the factors underlying alignment of transfemoral prostheses, led to the development of the AK adjustable leg and the alignment duplication jig. These advancements revealed the limitations of the wooden sockets used at that time, which led to the development of the quadrilateral socket. Introduced in 1954, the quad socket was the primary socket used in transfemoral amputees for 20 years. Though this socket has since been redesigned, the fundamental principles of socket design introduced by Radcliffe still are relevant today.

Clinical Theories

As a Fulbright Scholar in the 60s, Radcliffe studied in the Bioengineering Unit of the University of Strathclyde in Glasgow, Scotland, and at the Orthopaedic Hospital in Copenhagen, Denmark. During that time he lectured in several European countries on the proper fitting of lower-extremity prostheses. As one of the major pioneers who studied in Europe, he returned to the US with a number of ideas on how to enhance American socket design for transfemoral and transtibial prostheses.

His clinical theories, particularly on alignment, still are widely accepted in the field to this day. "Ninety-five percent of the clinical theories followed on a day-to-day basis today can be traced back to Radcliffe's work in the 60s," commented John Michael, CPO, FAAOP, who began his career in 1976. Michael continued, "Radcliffe made a broad range of contributions to clinical thinking. He changed the face of lower-limb prosthetic practice."

Before Radcliffe, there was no concept of the biomechanics of walking; no one knew the "science" behind gait. Michael credits Radcliffe with "developing a cohesive, scientific basis underlying the alignment of lower-limb prosthetic components." One of Radcliffe's greatest contributions was a biomechanical description of walking. In its simplest form, the gait cycle is broken into primarily two phases: stance and swing. The stance phase is the time when the foot is in contact with the ground, while the swing phase describes the foot off the ground and swinging forward. The phases comprise various proportions of the gait cycle depending on the speed of walking or running. Radcliffe applied basic principles of the normal gait cycle to that of transtibial amputees and transfemoral amputees to develop prostheses that would enable the patient more control during the swing phase.

Technological Advances

In the 50s the Prosthetics Research Group developed the patellar-tendon-bearing (PTB) below-knee prosthesis in an effort to improve the fitting of transtibial sockets. Until then, wooden sockets had to be carved and then reinforced by shrinking rawhide over the wood. The PTB socket achieved significant weight bearing on the patellar tendon, allowing pressure to vary according to the pain threshold of different tissues in the residual limb. PTB socket biomechanics were developed with respect to each of the progressive phases of the gait cycle, accommodating softer tissues.

In addition to transfemoral and transtibial socket designs, Radcliffe also is credited with the development of the solid ankle cushion heel (SACH) foot. Made of a flexible rubber shell surrounding a wooden core, the heel compresses and the toes bend when the amputee walks. An extension of his other work, a SACH foot allowed amputees a more natural gait.

The polycentric pneumatic knee, also developed during this time, is a mechanical knee with multiple axes and fluid control. The versatility of this knee makes it suitable for a variety of amputees from those looking for greater stability to those who desire greater movement control. An individual's prosthetic needs can be determined by observing his walking cycle and providing the proper balance between stability and motion control for each individual.

The most common type of polycentric knee is the four-bar prosthetic knee. With four axes of rotation connected by four rigid "bars," these knees provide greater toe clearance during the swing phase of walking than do single-axis knees. Other advantages include stance-phase stability and less bulging of the prosthetic knee when the amputee is sitting down.

Radcliffe commented in the October 2003 issue of The O&P EDGE, "Current pneumatic and hydraulic swing control devices are more than adequate for all but very active amputees. There will be a continued effort to incorporate microprocessors into the control systems for artificial knees. Current designs are extremely simple devices compared to the possibilities of the engineering field of mechatronics. Engineers in school today are eager to design components that will benefit amputees, and I am sure they will create designs far better and less expensive than what is available today." He predicted, "In the future there will be many improvements in the inputs [from sensors measuring control] and control strategies used."

Honored for O&P Contributions

The coupling of Radcliffe's prosthetic research and his mechanical engineering educational background produced a legendary pioneer with significant, wide-ranging contributions to the O&P field that are still relevant more than 50 years later. In 1997, Radcliffe received the Honorary Membership Award from the American Academy of Orthotists and Prosthetists (the Academy) as a credit to his high level of knowledge and dedication to the field. In February of this year, he received a Lifetime Achievement Award at the Hanger Educational Fair. Though he is honored by these accolades, he humbly said, "Oh, I'm just one of many pioneers in this field." He added with a laugh, "I just happen to be one of the few survivors."


Sherry Metzger, MS is a freelance writer with degrees in anatomy and neurobiology. She is based in Westminster, Coloradok and may be reached at