Analyzing Forces Across Hip Joints

The study examines the forces that can be anticipated across hips, with a focus on posterior-anterior forces during the gait cycle. The literature suggests that peak forces across an implanted hip are approximately 3.5 BW, eliminating events like stumbling. However, there is a range of data published, including different patients and varied instrumentation design. The study also explores the use of electromyography (EMG) to investigate muscle forces and activity, with EMG allowing for the recording of electrical signals from muscles. This technique has been used in various studies to validate computational models of human movement.

Bergmann et al., (1993) also treated a patient who was suffering from a bilateral hip
replacement. During gait cycle it was compared that the force magnitude and direction were
contrary for two hips. The differences between two hips may be because of differences caused by
surgery in muscle strength, or different placement position of implant or may be due to
physiological differences between right and left sides of patient. It clearly indicates that
investigations into the mechanisms behind this phenomenon are vital. Some differences between the
right and left faces of normal subjects, which can be assumed to have both hips in normal centre of
rotation, have been foreseen applying gait analysis and musculoskeletal models and therefore some
of inequality has found in bilateral hip replacement of the patient could be due to natural variation.
Some studies have also measured the forces gained during other activities. (Rydell 1966;
Davy et al. 1988; Bergmann et al. 1993; Bergmann et al. 2001) Walking at normal and fast speeds,
2-1-2 stance, stair descending and stair climbing are the activities that generate largest forces. When
patients were stumbled, the most intense forces were recorded. Two patients (Patient EB left hip and
Patient JB, Bergmann et al. 1993) were recorded while stumbling and generating 7.2 BW and 8.7
BW across their hips, but they were unable and were not interested to subsequently produce these
forces voluntarily. Commonly the literature depicts that during gait, the peak force at heel strike is
higher than at toe off (Davy et al. 1988; Lu et al. 1998; Bergmann et al. 2001).
However, it has been shown by Brand et al. (1994) that the toe off to heel strikes ratio is not
always continual within the same patient. There are studies that support the fact that some patients
possess a greater peak at toe off as compared with heel strike (Davy et al. 1988; Bergmann et al.
2001). Davy et al. (1988) examined three partial load bearing patients who were using crutches . He
identified that only one of the patient out of three has a toe off force more than heel strike. The
patient KWR in Bergmann et al‟s study had eight normal speed. Catherine Manders revise of the
hip joint gait cycles published of which two of them showed a higher or same magnitude toe off
than to the heel strike force. Definitive conclusion cannot be drawn because of limited number of
studies and various conditions under which studies were conducted. However, the range of
outcomes illustrated in literature do shows range of variability within one patient and inter-patient
variability.
Measured forces recorded through instrumented hip replacements have found an average
extreme point hip contact force at normal walking speed without aids to be 2.69 BW using the
studies by Rydell et al, (1966) Brand et al. (1994), Taylor et al. (1997; 2001) and Bergmann et al.
(1993; 2001) (Table 2). Even so there is a great spread of data with minimum value of peak force
during a gait cycle found in study by Taylor et al. Of 0.9BW (patient JB) in two varying gait cycles.
It is tough from the restricted data to acquire realistic average values or obtain variability likely in
1

general population, specially when all these patients have undergone with hip replacements. Then
also the measured data provides an indication of the forces that can be anticipated across hips. There
lies a difference between studies on forces in posterior- anterior direction throughout the gait cycle
as shown by Brand et al. (1994) and Bergmann et al (2001) who obtained very different forces in
posterior direction. Brands et al. measured forces of approximately HS and force stayed in an
anterior direction throughout gait cycle. Whereas patients in study conducted by Bergmann et al.
had measured a peak posterior force between 0.2 BW and 0.6 BW at HS.
The reported literature recommends that peak forces across an implanted hip are
approximately 3.5 BW eliminating events like stumbling. The range of data published includes
different patients and a varied range of instrumentation design. These extreme forces increase
postoperatively meeting a relatively constant level in force magnitude after 16 days approximately
(Davy et al. 1988). However, range of peak Catherine Manders review of hip joint forces in the
literature for normal gait is 2.11-3.5 BW and the majority of outcomes are in a smaller range of 2.5-
3 BW. It must be taken into account that such small number of patients do not let stiff conclusions
to be drawn for general population. It is essential to understand and quantify the forces experienced
at hip because this permits any replacement joints to be modelled and examined under reasonable
conditions.
At present there are not techniques available for measuring the muscle forces directly and
therefore indirect methods of investigating muscle force and activity has been formulated.
Musculoskeletal models can anticipate muscle forces and are elaborated in chapter 3.1.
Electromyography (EMG) allows recording of electrical signal form muscles. This technique uses
pairs of electrodes, which are indistinguishable to remove galvanic potential, to record voltage
potential across muscle. This potential is directly linked to electrical impulses causing movement in
muscle. Majorly there are two types of electrode: surface and indwelling. Surface electrodes can be
taken in use to investigate only surface muscles. For studying underlying muscles, indwelling
electrodes like wire electrodes can be inserted through skin by using a needle into muscle below.
(Vaughan et al. 1992).
EMG can be utilised to investigate which muscles are progressive during the gait cycle and
then those findings can be compared with activity levels form musculoskeletal models
(Crowninshield and Brand 1981) (Chapter 3.1). Vaughan et al. (1992) measured EMG of 28 major
muscles in lower extremity of a normal human being during gait cycle (Figure 13). Several studies
have been published which justifies use of EMG data as a validation method (Crowninshield and
Brand 1981; Glitsch and Baumann 1997; Hoek van Dijke et al. 1999). To determine if a
computational model is modelling a realistic body response to movement, onset and offset points of
2

activity form EMG readings can be used. Some studies have graduated the readings form EMG to
predict forces producted by muscles (Milner-Brown and Stein 1975; Cholewicki and Mcgill 1994;
Lloyd and Besier 2003) but this is tough as presently the methods for calibrating force are not
always reasoned reliable (Erdemir et al. 2007).
.
3

4

5

6

7