The whole is greater than the sum of its parts…

This week in Neuromechanics Weekly, we will explore proprioception and total hip replacements.

You would think proprioception (ie body position awareness) would be impaired in a total hip replacement (THR). Not according to this study (see below) BUT Balance, the dynamic interaction of proprioception and the ability to maintain ourselves upright in the gravitational plane AND GAIT were…

We remember there are 3 systems that keep us upright: vision, the vestibular system and the proprioceptive system (ie joint and muscle mechanoreceptors). A THR would effect mostly the latter, especially in this case, whee they REMOVED the hip capsule (capsulectomy). This, of course, would remove any of the joint mechanoreceptors, but probably not the muscle mechanoreceptors (ie spindles and golgi tendon organs).

Look at the conclusion “Compared with the healthy age- and sex-matched controls, patients with total hip replacement did not have any proprioceptive deficit. Patients required extrasensory input, and there was a delayed motor response. Gait and dynamic balance results also indicated the motor deficit and required a compensatory strategy. Restoration of the postural control in these patients is thus essential.”

So, they required a GREATER amount of sensory input and the response was DELAYED. This leads us to believe that is must be the integration of the systems that is the key.

The whole is greater than the sum of the parts… 

All this information is integrated in the cerebellum. Think about the 4 types of joint mechanoreceptors: Type 1 on the outside of the joint (tonic or respond to small movements); Type 2 on the inside of the joint phasic, or respond to large amplitude movements); Type 3, basically a golgi tendon organ type receptor, and Type 4, pain receptors. All this is taken away and they can still tell you where the limb is in space.

What does that mean? ..It means there are MORE receptors, somewhere, providing this info to the brain. They also required “extra input”. Hmmm…something needed to tell the brain that the action (in this case balance and gait) were happening. What was providing it? Muscle spindles and golgi tendon organs (see last weeks high heels post for more info); the former responds to length change and the latter to tension change.

The whole is greater than the sum of the parts.

Rehab it. Work on motor control strategies. Skill, endurance, strength; in that order. Ivo and Shawn. The Gait Guys. Exploring the literature to bring you the best of the best and help you to help others….better.

Balance and gait in total hip replacement: a pilot study. Nallegowda M, Singh U, Bhan S, Wadhwa S, Handa G, Dwivedi SN.

2003 Sep;82(9):669-77. AM J Phys Med Rehabil

Abstract OBJECTIVE:

Evaluation of balance, gait changes, sexual functions, and activities of daily living in patients with total hip replacement in comparison with healthy subjects.

DESIGN:

A total of 30 patients were included in the study after total hip replacement. Balance was examined using dynamic posturography, and gait evaluation was done clinically. Sexual functions and activities of daily living were also assessed. A total of 30 healthy subjects of comparable age and sex served as a control group.

RESULTS:

Dynamic balance and gait differed significantly in both the groups. Despite capsulectomy, no significant difference was observed on testing proprioception. In the sensory organization tests with difficult tasks, patients needed more sensory input from vision and vestibular sense, despite normal proprioceptive sense. Significant difference was observed for limits of stability, rhythmic weight shifts, and for gait variables other than walking base. Some of the patients had major difficulties with sexual functions and activities of daily living.

CONCLUSIONS:

Compared with the healthy age- and sex-matched controls, patients with total hip replacement did not have any proprioceptive deficit. Patients required extrasensory input, and there was a delayed motor response. Gait and dynamic balance results also indicated the motor deficit and required a compensatory strategy. Restoration of the postural control in these patients is thus essential. Necessary training is required for balance, gait, and activities of daily living, and proper sexual counseling is necessary in postoperative care.

http://www.ncbi.nlm.nih.gov/pubmed/12960908

hip replacement image from: http://www.wpclipart.com

champagne lady from: icr.org