Recently published data out of Tuft University’s School of Medicine could lead to reduced joint overloading and improved gait in lower limb prosthesis users.
The study, results published in Nature Scientific Reports, demonstrate that subperiosteal hydrostatic pressures can be transmitted between synovial capsules, which may represent a natural mechanism to help maintain joint connectivity over extended periods of time.
Mark Pitkin, PhD, DSc, professor of Physical Medicine and Rehabilitation at the university and lead author of the study, hypothesized on the existence of a hydrostatic net for redistributing individual pressures in synovial joints more than 20 years ago — calling it the floating skeleton theory.
“[There has been] a lot of research in this area, but there are no direct techniques for measuring untapped pressures between bones,” Pitkin told O&P News. “So, we conducted a study to measure pressure in angulated joints and simultaneously measure pressure in silent joints.”
The floating skeleton
Using 10 rabbits at the Pine Acres Rabbitry Farm in Norton, Mass., the researchers performed a series of pressure measurements in passively ranged and stationary joints.
The joints were paired in varying combinations and put through a full range of motion in order to record all potential pressure transmissions. Flexion and extension articulations were made manually by the examiner.
Baseline pressure was zeroed when each joint was in a neutral position, and vitals including temperature, blood pressure, heart rate and oxygen saturation were monitored.
The researchers noted that pressure in stationary joints changed in response to pressure variations in driving joints; however, it did not change after the periosteum above the driving joint was transected. Changes in venous pressure also occurred but were statistically insignificant and did not correlate with stationary changes.
This suggests that transmission occurred through the muscloskeletal system, specifically in the space between the periosteum and the bone surface.
This was the first experimental confirmation of the floating skeleton theory, Pitkin said. Although synovial fluid is contained in a particular joint capsule, the intra-joint pressure is a part of a hydrostatic net that includes synovial capsules and a periosteal shell covering the bones between them.
“The shell covers the entire skeleton and is practically unstretchable. There are tiny spaces between the periosteal and the bone filled with transmittable fluids, which can lower contact pressure in specific joints.”
Foundation for the future
Although this theory may be accurate, more studies are needed to understand the morphology and physiology of the hydrostatic net discovered, Pitkin said.
These findings shed light on the future of O&P care, Pitkin said. Researchers are exploring new roles for the periosteum and osteogenesis, as well as ways to initiate transmission from muscle to the bone. They are also looking into ways of more richly mapping pressure transmission from one synovial capsule to another.
Pitkin said this data could provide new insight into understanding joints and help develop more effective prevention, treatment and rehabilitation strategies in the future.
The team at Tuft University is looking to conduct further studies with larger sample sizes that place a higher emphasis on human subjects.
“[These data] may not have immediate relevance to O&P, but they will eventually,” Pitkin said. “Patients who employ compensatory strategies for locomotion could be susceptible to overloading, or other side effects like arthritis.
“Understanding mechanisms to maintain healthy joints is vital for the profession, as it will help providers not only apply their devices, but achieve the maximum functionality of those devices…and maximum ability of the patients,” he said. – by Shawn M. Carter
Pitkin M, et al. Sci Rep., 2015; doi:10.1038/srep08103.
Pitkin M. J Biomech., 1994; doi: 10.1016/0021-9290(94)91368-4.
Disclosure: Pitkin reports no relevant financial disclosures.