VIDEO
ANALYSIS OF STANDING – AN ALTERNATIVE FOOTPRINT ANALYSIS TO ASSESS FUNCTIONAL LOSS FOLLOWING INJURY TO THE RAT
SCIATIC NERVE
Department for plastic and reconstructive
surgery, Maribor general hospital, Ljubljanska ul. 5, 2000 MARIBOR, SLOVENIA
. Tel.: 00386 2 3211 000; Fax.: 00386 2 3312 393; e-mail: marijan.bervar@sb-mb.si
Key words:
Peripheral nerve; Nerve injury; Nerve regeneration; Functional recovery
The rat sciatic nerve
is a well-established animal model for the study of recovery from peripheral
nerve injuries. Footprint analysis is the most widely used non-invasive method
of measuring functional recovery after injury in this model. We describe a new,
alternative video analysis of standing (or static footprint video analysis) to
assess functional loss following injury to the rat sciatic nerve, during animal
standing or periodic rest on a flat transparent surface. We found that this
alternative video analysis is technically easier to perform than the corresponding
footprint video analysis during walking, but still preserves all advantages of
video versus conventional ink track method: i.e. there are few non-measurable
footprints, better repeatability, high accuracy and more precise quantification
of the degree of functional loss after sciatic nerve injury in the rat.
1.
INTRODUCTION
Characteristic gait changes occur
after unilateral sciatic nerve injury in rats. Gradual disappearance of these
changes in time reflects nerve regeneration and fun- ctional recovery. The
degree of functional loss (or recovery) can be quantified by the method known
as footprint analysis (De Medinaceli et al., 1982). The method is simple,
non-invasive and has been shown to measure a combination of motor and sensory
recovery. It can be used repeatedly to measure functional recovery over time in
the same animal.
Since its introduction, it has been
modified several times (Carlton and Goldberg, 1986; Bain et al., 1989).The
measurements required to make the calculations, which include print length and
toe spreads, is limited with up to 25% of the prints unreadable and is
unreliable when contractures or injured toes are present (Dellon and Mackinnon
, 1989). In addition, the print length demonstrates significant variation with
uncontrolled gait velocity, which may incurs the functional loss estimation
errors (Walker et al., 1994).
The video imaging technique to
record the footprints was a considerable advancement in this field (Lin et al.,
1992). It allowed digital analysis of the video images and better
repeatability. It significantly diminished the number of useless footprints and
minimised printing errors in comparison with previous meth- ods. But the
problems with changeable gait velocity remained and the special kind of
contrasting to increase the visibility
of footprints was necessary too.
The
self-evident question raised: can we accurately predict the functional loss by
the footprint video analysis in the technically more acceptable static conditi-
ons during animal standing?
2.
MATERIALS AND METHOD
Twenty-four adult male white Wistar
A rats weighing 250 to 350 g were used. Under intraperitoneal Ketamine
anesthesia we exposed the sciatic nerve unilaterally and two types of injuries were performed: a crush injury
(n=12) and a transection injury with a immediate epi- neurial repair (n=12).
Opposite leg and sciatic nerve were not operated upon and served as a control.
Functional recovery after the sciatic nerve injury was assessed
serially using video recording of the
plantar aspect of the animal hind feet during occasional rest periods in a
glass-bottomed box. For recording we used video camera, set at focal length of
9 mm and placed 20 cm apart from the bottom. No additional contrasting was
necessary.
Under such conditions, the positions
of the toes and the sole pale skin discoloured areas, caused by spontaneous
body weight pressure, were clearly visible in most instances in the footprints
during the video tape playback in super-still mode. The distance between the
tip of the third toe and the most posterior margin of the sole discoloured area
was defined as the print length parameter on the video images.
A single recording of each animal
lasted approximately 60 seconds. Video assessment of the hind footprints were
obtained twice preoperatively and on post-injury days 1, 7, 14, 17, 21, 24, 28,
35 and 42 for a crush injuries, and on post-injury days 1, 21, 45, 75, 105, 135
and 165 for a transection injuries.
On the same days, assessment of the hind footprints was obtained
by applying a quick-drying non-toxic water-soluble ink to both hind feet and
allowing the animal to walk freely down the walled walkway, leaving tracks on
the underlying paper.
The parameters of print length, 1-5
toe spread, and 2-4 toe spread of four injured and four uninjured hind
footprints were measured from both the video recordings and the ink tracks of
each animal on each assessment day. The measurements from these four footprints
were averaged to determine the parameter values for that day. Ratios of
(injured-uninjured)/uninjured hind feet parameters (or factors PLF, TSF and
ITF) were determined by both static video and dynamic ink track method. The
latter were used for assessment of the functional loss by sciatic functional
index SFI as described by Bain et al., (1989).
All data were computerised and
statistically analysed with the SPSS program. An alpha value of 0.01 was used
as an index of statistical significance.
3. RESULTS
We found good correlation between
video recording during standing and dynamic ink track footprint parameter
measurements for both 1-5 and injured 2-4 toe spreads only. Reproducibility for
these three parameters was also better using the video method. Uninjured 2-4
toe spread by video showed a poor correlation and similar reproducibility as
compared with ink. However, both print length parameters measured by video had
poorer correlation and reproducibility, particularly the print length factor
(PLF) was weakly correlated with that determined by ink.
Contribution of the footprint
factors on the estimated functional loss has also changed in conditions during
standing. It was most prominent for the 1-5 toe spread factor (TSF), near
marginal for the 2-4 or intermediary toe spread factor (ITF) and weak,
statistically insignificant for the print length factor (PLF).
Thus, the introduction of a new
functional loss index, or so called static sciatic index (SSI), and its
estimating formula:
SSI = 108.44 TSF + 31.85 ITF – 5.49
was mandatory.
Moreover, using a simple ratio of
injured/uninjured 1-5 video toe spread (Walker et al., 1994) as a substitute
for the static sciatic index (SSI), we could achieve considerable
simplification of the method without any significant loss of accuracy.
Recovery patterns over time
determined by the three methods for two types of sciatic nerve injuries in the
rat were generally very similar as far as the beginning and the plateau of functional recovery is concerned.
For more details see the reference
(Bervar, 2000).
4.
DISCUSSION
The toes and the heel position on
the video recordings were evaluated during standing and this probably involves
different neurophysiological mechanism from those effective during walking. The
position during standing is mainly dependent upon postural muscle tone while
the toe and the heel position during walking depends upon dynamic changes in
muscle activity. This might very well be the cause for the considerable changes
of the proposed formula for the functional loss estimation in the static
conditions.
On the other hand, our observations
confirmed the fact that the 1-5 toe spread is the most useful parameter for
measuring functional recovery after a sciatic nerve injury. It is dependent on
anatomic contri- butions from both the peroneal and tibial divisions of the
sciatic nerve (Bain et al., 1989) and, therefore, closely follows the sciatic
functional recovery as a whole. This parameter also demonstrates the greatest
deviation from the normal of all studied parameters allowing measurement of
smal- ler changes after injury and during reco- very. As such, this parameter
has the greatest “weight” in all proposed formulas and can be used alone in the
form of simple ratio of injured/uninjured hind foot video 1-5 toe spread
expressed in % to assess functional loss by the video recor- ding method during
standing.
5. CONCLUSION
Although our static video footprint
analysis requires more expensive technical
equipment we think it has significant advantages in comparison to
conventional ink track method: i.e. there are few non-measurable footprints, it
displays better repeatability, and therefore higher accuracy and more precise
quantification of the degree of functional loss and recovery after sciatic
nerve injury in the rat.
REFERENCES
Bain
JR, Mackinnon SE and Hunter DA. Functional evaluation
of complete sciatic, peroneal, and posterior tibial nerve lesions in the rat,
Plast Reconstr Surg 1989; 83: 129-138.
Bervar
M. Video analysis of standing - an alternative footprint
analysis to assess functional loss
following injury to the rat sciatic nerve.. J Neurosci Meth 2000; 102: 109-116.
Carlton
JM and Goldberg NH. Quantitating integrated
muscle function following reinnervation. Surg Forum 1986; 37: 611-612.
Dellon
AL and Mackinnon SE. Sciatic nerve regeneration
in the rat. Validity of walking track assessment in the presence of chronic
contractures. Microsurgery 1989; 10: 220-225.
De
Medinaceli, L, Freed WJ and Wyatt RJ. An index of the functional condition of rat
sciatic nerve based on measurements made from walking tracks, Exp Neurol 1982;
77: 634 – 643.
Lin
FM, Pan YC, Sabbahi M, Shenaq S and Spira M.
Video imaging technique for assessment of motor function recovery after rat
sciatic nerve repair, Proc Plast Surg
Res Council, 1992: 139-140.
Walker
JL, Resig P, Guarnieri S, Sisken BF and Evans JM. Improved
fotprint analysis using video recording
to assess functional recovery following injury to the rat sciatic nerve, Restor
Neurol Neuro Sci 1994; 6: 189-193.