Do cats with a cranial cruciate ligament injury and osteoarthritis demonstrate a different gait pattern and behaviour compared to sound cats?

Intra-subject sample size effects in plantar pressure analyses

Background

Recent work using large datasets (>500 records per subject) has demonstrated seemingly high levels of step-to-step variation in peak plantar pressure within human individuals during walking. One intuitive consequence of this variation is that smaller sample sizes (e.g., 10 steps per subject) may be quantitatively and qualitatively inaccurate and fail to capture the variance in plantar pressure of individuals seen in larger data sets. However, this remains quantitatively unexplored reflecting a lack of detailed investigation of intra-subject sample size effects in plantar pressure analysis.

Methods

Here we explore the sensitivity of various plantar pressure metrics to intra-subject sample size (number of steps per subject) using a random subsampling analysis. We randomly and incrementally subsample large data sets (>500 steps per subject) to compare variability in three metric types at sample sizes of 5–400 records: (1) overall whole-record mean and maximum pressure; (2) single-pixel values from five locations across the foot; and (3) the sum of pixel-level variability (measured by mean square error, MSE) from the whole plantar surface.

Results

Our results indicate that the central tendency of whole-record mean and maximum pressure within and across subjects show only minor sensitivity to sample size >200 steps. However, <200 steps, and particularly <50 steps, the range of overall mean and maximum pressure values yielded by our subsampling analysis increased considerably resulting in potential qualitative error in analyses of pressure changes with speed within-subjects and in comparisons of relative pressure magnitudes across subjects at a given speed. Our analysis revealed considerable variability in the absolute and relative response of the single pixel centroids of five regions to random subsampling. As the number of steps analysed decreased, the absolute value ranges were highest in the areas of highest pressure (medial forefoot and hallux), while the largest relative changes were seen in areas of lower pressure (the midfoot). Our pixel-level measure of variability by MSE across the whole-foot was highly sensitive to our manipulation of sample size, such that the range in MSE was exponentially larger in smaller subsamples. Random subsampling showed that the range in pixel-level MSE only came within 5% of the overall sample size in subsamples of >400 steps. The range in pixel-level MSE at low subsamples (<50) was 25–75% higher than that of the full datasets of >500 pressure records per subject. Overall, therefore, we demonstrate a high probability that the very small sample sizes (n < 20 records), which are routinely used in human and animal studies, capture a relatively low proportion of variance evident in larger plantar pressure data set, and thus may not accurately reflect the true population mean.

Measurement of ground reaction forces in cats 1 year after femoral head and neck ostectomy

OBJECTIVES

The objective of this study was to compare ground reaction forces (GRFs) of a group of cats after femoral head and neck ostectomy (FHO) with those of a historical control group.

METHODS

We searched the database of the Small Animal Clinic of the Veterinary University in Vienna for cats that had undergone unilateral FHO at least 1 year previously. Owners were telephoned and invited to the clinic with their cats for a re-examination. An in-house owner questionnaire-based evaluation, complete orthopaedic examination, hip radiography and gait analysis with a pressure-sensitive plate were performed, and results were compared within and between groups (FHO group and control group [CG]).

RESULTS

Seventeen cats that had undergone FHO (FHO group) at least 1 year previously and 15 healthy cats (CG) from a previous study were included. Measured GRFs (peak vertical force and vertical impulse [IFz] normalised to total force [%TF]) of the FHO legs were lower than those of the other legs of the FHO group and the legs of the CG. Results of the owner questionnaire were generally good and did not match the results of the GRF comparison. Furthermore, the gaits evaluated during the orthopaedic examination did not correlate with the measured GRFs where we identified a certain degree of lameness (reduced IFz, %TF) in all cats. Cats with limb shortening (dorsally displaced major trochanter major) were not revealed to have different GRF measurements.

CONCLUSIONS AND RELEVANCE

This is the first study to assess GRFs in a large group of cats that had undergone FHO, comparing findings with those in healthy cats. Even if the differences are statistically significant, but rather small, our findings point to a long-term residual gait abnormality that could be detected using a pressure-sensitive plate but not always with an orthopaedic examination, in cats 1 year after FHO.

Feline musculoskeletal ageing: How are we diagnosing and treating musculoskeletal impairment?

PRACTICAL RELEVANCE

An understanding of the process of musculoskeletal ageing - which all senior and geriatric cats will experience - is vital to maintaining the health and welfare of our ageing cat population.

CLINICAL CHALLENGES

Assessment of the feline musculoskeletal system is not always straightforward. Diagnosis of impairment relies on input from owners and veterinarians in terms of visual observation, and clinical and orthopaedic examination, in addition to diagnostic imaging.

AUDIENCE

This review is written for the primary care veterinary team.

AIMS

The goals are to raise awareness and improve clinical diagnosis of musculoskeletal impairment as a result of ageing. The article also reviews therapeutic options and considers the evidence available for the prevention/deceleration of musculoskeletal ageing and impairment.

EVIDENCE BASE

There is good evidence of a high prevalence of osteoarthritis (OA) and degenerative joint disease (DJD) in older cats. There is also good evidence to indicate that functional impairment and chronic pain are sequelae of musculoskeletal disease. However, there is a paucity of information for what is best practice for the management and treatment of musculoskeletal impairment in a clinical situation. There is also a lack of evidence on how prevention of central stimulation of the nervous system caused by musculoskeletal impairment and, in turn the development of chronic pain, can be avoided.

Evaluation of a pressure plate for detection of hind limb lameness in cats

Detection of lameness in cats can be very time-consuming and frustrating. Feline studies have shown that the success of treatment can be evaluated by measurement of the ground reaction force (GRF). However, the possibility of multiple limb involvement or the presence of a compensatory mechanism has not been investigated. Furthermore, there has been no research in cats on possible differences in GRFs between those with stifle problems and those with hip problems, as reported in dogs. In this study, we compared temporospatial parameters and GRFs in 20 lame cats after femoral head and neck ostectomy (FHO) or stifle disease to those in 15 healthy cats. An orthopedic examination was performed in all cats and radiographs were obtained to confirm the disease. GRFs, including peak vertical force (PFz), vertical impulse (IFz), time to PFz, and temporospatial parameters, including step length, paw contact area, and stance phase duration, were calculated. We also calculated the symmetry index (SI) in the forelimbs and hind limbs. The GRFs were normalized to total force (% TF). We found that the IFz (% TF) and PFz (% TF) were lower in the affected limb than in the other limbs in the lame cats. When the lame cats were compared with the sound cats, this difference was only significant for IFz (% TF). The SI values for the PFz and IFz were significantly higher in the hind limbs than in the forelimbs in the lame cats group but there was no difference in the SI according to whether the problem was in the hip or stifle. There were also differences in stance phase duration and paw contact area in both the forelimbs and hind limbs between the sound group and the lame group. There was no difference in PF_Z (% TF) or IF_Z (% TF) in the affected limb between the lame cats with stifle and those after FHO; however, there were changes in time to PFz and step length. In conclusion, mild to moderate lameness can be detected and measured in cats using pressure plates. The compensatory mechanisms in cats at a walk appear to involve shifting the weight to the other three legs without favoring either the contralateral or the diagonal limb.

Inter-rater and inter-device reliability of mechanical thresholds measurement with the Electronic von Frey Anaesthesiometer and the SMALGO in healthy cats

OBJECTIVES

The aim of this study was to compare the Electronic von Frey Anaesthesiometer (EVF) and the Small Animal ALGOmeter (SMALGO), used to measure sensory thresholds in 13 healthy cats at both the stifle and the lumbosacral joint, in terms of inter-rater and inter-device reliability.

METHODS

Two independent observers carried out the sets of measurements in a randomised order, with a 45 min interval between them, in each cat. The inter-rater and inter-device reliability were evaluated by calculating the inter-rater correlation coefficient (ICC) for each pair of measurements. The Bland-Altman method was used as an additional tool to assess the level of agreement between the two algometers.

RESULTS

The mean ± SD sensory thresholds measured with the EVF were 311 ± 116 g and 378 ± 178 g for the stifle and for the lumbosacral junction, respectively, whereas those measured with the SMALGO were 391 ±172 g and 476 ± 172 g. The inter-rater reliability was fair (ICC >0.4) for each pair of measurements except those taken at the level of the stifle with the SMALGO, for which the level of agreement between observers A and B was poor (ICC = 0.01). The inter-device reliability was good (ICC = 0.73; P = 0.001). The repetition of the measurements affected reliability, as the thresholds obtained after the 45 min break were consistently lower than those measured during the first part of the trial (P = 0.02).

CONCLUSIONS AND RELEVANCE

The EVF and the SMALGO may be used interchangeably in cats, especially when the area to be tested is the lumbosacral joint. However, when the thresholds are measured at the stifle, the inter-observer reliability is better with the EVF than with the SMALGO. The reliability decreases when the measurements are repeated within a short time interval, suggesting a limited clinical applicability of quantitative sensory testing with both algometers in cats.

Comparison of ground reaction force measurements in a population of Domestic Shorthair and Maine Coon cats

Current research on gait analysis mostly involves horses and dogs. Feline kinetics and kinematics are being investigated and receiving more clinical interest at present. Ground reaction forces measured on pressure-sensitive mattresses have been established in healthy Domestic Shorthair cats (DSH). Currently, no further information exists on either breed-specific measured gait reaction forces or comparisons among breeds. Because Maine Coon (MC) cats appear to be over-represented with orthopaedic diseases of the hind limb (hip dysplasia, patellar luxation), we evaluated ground reaction force GRF measurements in MC cats and compared them with those of DSH cats. Pre-evaluation radiological and clinical exams determined that the cats were not lame. The parameters evaluated were peak vertical force (PFz), vertical impulse (IFz), time to PFz (TPFz), step length (SL), paw contact area (PCA), stance phase duration (SPD) and symmetry index (SI) for the fore- and hind limbs. In both breeds, PFz and IFz were greater in forelimbs than in hind limbs. The PFz and IFz in Newtons were higher in the MC cats compared to the DSH cats, but not after normalisation for total force (%TF) and body mass (%BM). Furthermore, due to their body conformation, MC cats have a longer SL, larger PCA, and higher body weight than DSH cats. No other parameters differed significantly, except that the TPFz displayed an earlier value in the MC hind limbs. Measured symmetry indices were similar to those reported in dogs and did not differ between breeds. This is the first study to report GRF values and temporospatial parameters in a healthy MC cat population. However, our results could not confirm differences between normalized PFz and IFz and temporospatial parameters between the breeds. The authors therefore conclude that genetic or other causes may be involved in orthopaedic hind limb pathogenesis seen in MC cats more often than in other breeds.