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Bacterial septic arthritis in 19 dogs
Division of Veterinary and Biomedical Sciences, Murdoch University, South Street, Murdoch, Western Australia 6150

    Objective        To provide information on the clinical features, diagnosis and treatment of bacterial septic arthritis in dogs.
    Design A retrospective study examining case records of all dogs diagnosed with bacterial septic arthritis at Murdoch
    University Veterinary Hospital between 1988 and 1997.
    Results Nineteen dogs were diagnosed with bacterial septic arthritis, which most commonly occurred after surgery
    involving the stifle joint. Haematogenous infection occurred in only five dogs. Diagnosis was based on clinical signs,
    joint fluid analysis, radiography, microbiology and/or response to treatment. Chronic lameness was the most common
    problem at presentation. Analysis of joint fluid invariably revealed large number of nucleated cells, which consisted
    primarily of neutrophils. In all but one case the neutrophils were nondegenerate. Culture of joint fluid was frequently
    successful. Staphylococcus spp were the most common bacteria isolated. Treatment involved antimicrobial drugs only
    in five dogs. Other dogs received antimicrobial drugs in combination with surgical procedures such as joint lavage and
    removal of nonabsorbable suture material (eight), arthrodesis (two) or amputation (one). Two dogs were euthanased.
    Most dogs responded well to treatment and were free of signs of septic arthritis at follow-up.
    Conclusion Bacterial septic arthritis may often be mild and manifest as chronic lameness. Analysis of joint fluid will
    detect an inflammatory arthropathy but the presence of toxic neutrophils should not be relied on as an indicator of sep-
    sis. Culture of infected joint fluid is likely to be successful if antimicrobials are not given prior to collection and if the sam-
    ple is inoculated into enrichment broth. Treatment should involve antimicrobial drugs, open-joint lavage and removal of
    joint prostheses if the infection is associated with previous surgery.
    Aust Vet J 1999;77:233-237
    Key words: Dog, septic arthritis, haematogenous, joint fluid, toxic neutrophils, cruciate surgery, arthrotomy, joint lavage.

    CCL              Cranial cruciate ligament
    MUVH             Murdoch University Veterinary Hospital

                                                          by Gram stain and/or culture.3,5 Culture                    Materials and methods

       acterial septic arthritis is an
       inflammatory arthropathy that                      of joint fluid is not always successful in                     Case records of all dogs that had been
       may result from haematogenous                      septic arthritis,2,6 but incubating joint                   computer coded with a diagnosis of
spread, an accidental or surgical wound                   fluid in enrichment broth increases                         septic arthritis between 1988 and 1997
or, rarely, by extension from                             success.7 Culture of capsule is a more                      at MUVH were examined. The records
surrounding tissues.1 Unlike in cattle,                   sensitive method of detecting bacteria                      of all 612 animals that had undergone
horses and other farm animals, joint                      but more invasive and expensive than                        arthrotomy during this same period
infection in dogs is usually monoartic-                   arthrocentesis.2,8                                          were also examined. Diagnostic evalua-
ular and is typically associated with                        Treatment of septic arthritis involves                   tion for each case included one or more
acute onset of lameness.1,2 However,                      an extended course of antimicrobial                         of the following: physical examination,
joint infection may manifest as chronic                   drugs based on sensitivity testing.3,5 In                   palpation of the affected joint, rectal
lameness, which may be misdiagnosed as                    addition, sepsis associated with a pene-                    temperature measurement, blood cell
osteoarthritis if arthrocentesis is not                   trating wound, whether surgical or acci-                    counts and serum biochemical tests,
performed.2 Early recognition of joint                    dental, should be treated by joint lavage                   arthrocentesis and joint fluid analysis,
infection is important to limit the                       using 0.9% saline. This may be accom-                       radiography, arthrotomy and joint
damage to articular cartilage caused by                   plished by arthrotomy and open lavage                       capsule biopsy. Bacterial culture of joint
proteolytic enzymes released from                         or by insertion of ingress/egress                           fluid, joint capsule or any prosthesis that
damaged synoviocytes and the forma-                       drains.2,5 The former is more likely to                     may have been used at a previous
tion of pannus which invades through                      result in complete debridement and                          surgery was performed as applicable.
the articular cartilage into subchondral                  removal of purulent material and avoids                        Arthrocentesis was performed asepti-
bone.3                                                    difficulties associated with managing                       cally and joint fluid placed into plain or
  Analysis of joint fluid from septic                     drains in small animals.4                                   EDTA-coated tubes. Total and differen-
joints reveals markedly increased counts                     This study examines the case records                     tial nucleated cell counts were
of nucleated cells, usually in excess of 50               of 19 dogs that were diagnosed with                         performed on all joint fluid samples that
x 109/L, consisting primarily of                          septic arthritis at MUVH between 1988                       were not clotted. The proportion of
neutrophils. In chronic cases the                         and 1997. It provides information on                        neutrophils and whether they were
increase in cell numbers may be less                      clinical features, diagnosis and treatment                  degenerate were also recorded. Gram
dramatic.3,4 A diagnosis of septic                        and highlights some difficulties associ-                    stains were performed on all samples.
arthritis is confirmed by demonstration                   ated with differentiating septic arthritis                  Culture was performed by direct inocu-
of bacteria in the joint fluid or capsule                 from other arthropathies.                                   lation onto blood agar plates (Oxoid

Aust Vet J Vol 77, No 4, April 1999                                                                                                                          233

trypticase soy agar) before and after          Haematogenous joint infection was             two cases were hips with severe acetab-
inoculation into enrichment broth            diagnosed in five dogs. Two had been            ular osteophyte formation that may have
(Oxoid signal blood culture medium).         chronically lame and previously treated         increased the difficulty of entering the
Joint capsule samples were crushed and       for     radiographically      confirmed         joint space. Total nucleated cell counts
mixed with enrichment broth as well as       osteoarthritis, whereas three were              performed on nine samples averaged
being inoculated onto blood agar plates.     presented as acutely lame. The femoral          100 x 109/L with a range of 15.2 to 152
Samples were cultured aerobically and        head had been excised from one of these         x 109/L (normal less than 5.0 x 109 / L).
anaerobically in all cases.                  18 months earlier but the dog had been          Differential cell counts were performed
  All dogs were treated using antimicro-     sound until presentation for the current        on 12 samples. Neutrophils made up
bial drugs with or without ancillary         problem. This case was considered a             90% or more of the cells in 10 samples
therapy such as arthrotomy, joint lavage     haematogenous infection because of the          with a range of 77 to 95%. Degenerate
and removal of prostheses where appro-       delay between surgery and onset of signs        (toxic) neutrophils were detected in only
priate. Follow-up for outcome of treat-      and because Escherichia coli was cultured       one sample. Joint fluid was collected
ment was either by revisit examination       from the blood.                                 during necropsy in one case and was
or telephone consultation with the                                                           only cultured.
owner.                                       Physical examination
                                                Rectal temperature was recorded in 15        Microbiology
Results                                      dogs and was increased (> 39.2°C) in               Gram stains were performed on 13
History and patient details                  12. The affected joint was painful and          joint fluid samples. Gram-positive cocci
   Nineteen dogs (10 male and 9 female)      swollen in 19 dogs and recorded as              were detected in six and a combination
were diagnosed with septic arthritis.        being palpably hot in 11 cases. The             of Gram-positive rods and cocci and
Eleven different breeds were represented     owners reported lethargy and depression         Gram-negative rods in one. The most
and ages were from 6 months to 8 years       in 10 of 19 cases. A discharging sinus          commonly cultured bacterium was
(median 5 years). Fourteen cases were        was present on the lateral aspect of the        Staphylococcus intermedius. Other
associated with one or more previous         stifle in only two dogs. Both had under-        bacteria isolated included S aureus, beta-
surgical procedures involving the stifle,    gone extracapsular CCL repair using             haemolytic Streptococcus and Pseudomonas
11 of which were extracapsular CCL           teflon-coated braided polyester suture          aeruginosa (Table 2). Joint fluid alone
stabilisation procedures. Suture material    (Table 1). The 20 affected joints               was submitted for culture from 12 dogs
used to stabilise the joint was prolene in   comprised 15 stifles, 2 hips, 2 hocks and       (including two samples that had insuffi-
one, braided polyester tape in one,          1 elbow. On one occasion the stifle and         cient volume to allow cytological exami-
teflon-coated braided polyester suture in    hock were both involved as a complica-          nation) and bacteria were cultured from
two, nylon leader line in four and not       tion of a tibial fracture repair. In this       all samples. In addition, joint fluid and
recorded in three animals. Eight postop-     case the pin had penetrated both joints         joint capsule submitted from four dogs
erative stifle infections occurred           and infection had spread from                   resulted in positive culture from the
following surgery at MUVH. The               osteomyelitis at the fracture site.             capsule only in one, from the fluid only
overall prevalence of joint sepsis                                                           in another and negative cultures from
following stifle arthrotomy at MUVH          Arthrocentesis                                  both in the other two dogs. In two cases
was 2.5% (8/320). Five cases which              Arthrocentesis was attempted in 17           of sepsis following CCL surgery, only
developed signs of heat, pain and            cases. On four occasions little or no           the prosthesis was submitted for culture
swelling in the immediate period after       joint fluid was collected. One of these         and bacteria were cultured in each case.
stifle arthrotomy at MUVH were               was a stifle that on exploratory arthro-        Sepsis of the joint rather than just suture
discarded from the study because joint       tomy was found to have severe destruc-          prosthesis contamination was confirmed
fluid analysis was not performed. These      tion of articular cartilage and little joint    in these cases by radiographic and
cases all responded to antimicrobial         fluid, one case was a hock and the other        surgical findings of subchondral bone
therapy. Of all MUVH arthrotomies                                                            loss, articular erosion and pannus forma-
performed the only joints affected with                                                      tion. E coli was successfully cultured
                                             Table 1. Summary of clinical findings in 19
postoperative sepsis were stifles.           dogs with septic arthritis                      from the blood of one dog where arthro-
   Of the 14 dogs with postoperative
infections, 3 developed signs of infection   Clinical findings             Number of cases
                                                                                             Table 2. Bacteria isolated from septic arthritis
within 7 to 14 days of surgery at            Lameness                             19         in 19 dogs.
MUVH. The 11 others had a gradual              Chronic                            13         Bacteria                       Number of joints
onset of lameness or, alternatively, did       Acute onset                         6
not progress well postoperatively for 6      Painful, swollen joint               19
                                                                                             S intermedius                          6
weeks to 16 months before diagnosis                                                          S aureus                               2
                                             Previous surgery                     15
was made. Six had undergone arthro-                                                          P aeruginosa                           2
tomy at other clinics and five at              CCL stabilisation                  11
                                                                                             Streptococcus spp                      2
MUVH. These cases were classified as         Pyrexia (> 39.2°C)                   12a
                                                                                             Mixed                                  3
chronic or low-grade septic arthritis        Lethargy, depression                 10
similar to the category described by                                                         E coli                                 1
                                             Discharging sinus                     2
Bennett and Taylor.2                                                                         E coli was isolated from blood culture; all others
                                             aRectal temperature recorded in 15 dogs only.
                                                                                             from joint fluid, joint capsule and/or suture.

234                                                                                                     Aust Vet J Vol 77, No 4, April 1999

centesis had been unsuccessful. All          Table 3. Treatment of 14 cases of postoperative     occurrence of CCL rupture in the
                                             infection involving the stifle joint.
Gram-positive species cultured (13                                                               general population.10 This may in part
cases) were sensitive to amoxycillin-        Treatment                                Number     explain the relatively more common
                                                                                      of cases
clavulanate, and all except one, which                                                           occurrence of septic arthritis in females
had been treated with cephalexin previ-      Antimicrobial drugs and joint lavage        8       in this study.
ously, were sensitive to cephalexin.         Arthrodesis                                 2          It has been suggested that synovial
                                             Amputation                                  1
                                                                                                 fluid of infected joints often contains
Radiography                                                                                      toxic neutrophils which may help to
                                             Euthanasia, antimicrobial drugs failed      1
  Radiographs were taken of 16 of the                                                            differentiate sepsis from other inflam-
                                             Euthanasia without treatment                1
20 affected joints. Soft-tissue swelling                                                         matory arthropathies3 and that large
associated with periarticular thickening     Lost to follow-up                           1
                                                                                                 numbers of toxic neutrophils is an indi-
and joint effusion were commonly seen                                                            cation to culture joint fluid.11 Toxic
as was periarticular growth of new bone.                                                         neutrophils were only identified in 1 of
Patchy lysis of subchondral bone was         were subsequently treated more aggres-              12 septic joints (8%), and were thus of
seen in four cases. A radiographic diag-     sively.                                             minimal diagnostic value in detecting
nosis of septic arthritis was made in only      In six dogs treatment included suture            septic arthritis in this series. To the
three cases. In these, the septic process    removal, open-joint lavage with 0.9%                authors’ knowledge, no other veterinary
continued for several months and there       saline for 5 to 7 days and delayed                  reports indicate how often toxic
was gross destruction of subchondral         primary closure. Two others were simi-              neutrophils are identified in septic
bone and severe periarticular formation      larly treated by suture removal and intra-          joints. Glucose concentrations in
of new bone.                                 operative joint lavage with 0.9% saline             synovial fluid, not determined in this
                                             but primary closure was performed. The              series, can be markedly reduced in septic
Treatment                                    condition of all eight dogs was improved            arthritis in humans and animals, but
   Haematogenous infection – The five        at time of follow-up (1 to 36 months).              there is substantial overlap between
dogs in this category were treated with      Two had no discernible lameness, one                septic and other inflammatory
antimicrobial drugs only for between 10      was lame after heavy exercise only, four            arthropathies.4,12,13 Given the limita-
days and 8 weeks. The condition of all       had a mild lameness responsive to nons-             tions regarding toxic neutrophils and
dogs had improved at time of follow-up       teroidal anti-inflammatory drugs and                glucose, it is advisable to culture the
(8 weeks to 6 years). The owners of two      one was chronically lame due to grade               joint fluid of any dog with an inflamma-
dogs reported the dogs had not been          four patellar luxation.                             tory arthropathy involving a single joint.
lame since the end of treatment 4 and 6                                                             There is disagreement as to whether
years previously. The three others were                                                          culture of joint capsule is more sensitive
examined 2, 10 and 12 months after           Discussion
                                                Septic arthritis can result from pene-           than joint fluid culture. Bennett and
treatment and had mild lameness                                                                  Taylor2 successfully cultured joint fluid
attributable to osteoarthritis that had      trating or surgical wounds, by extension
                                             from surrounding tissues or via                     and capsule in 81% and 100% of cases
been diagnosed previously in the                                                                 of septic arthritis, respectively, but the
affected joint.                              haematogenous spread.1 The literature is
                                             divided as to the most common route.                joint fluid was inoculated directly onto
   Postoperative joint infection – Of the                                                        blood agar plates. In an experimental
14 dogs that developed postoperative         Bennett and Taylor2 found that most
                                             septic arthritides are haematogenously              study where joint fluid and capsule were
septic arthritis, the diagnosis was                                                              cultured 24 h after intra-articular inocu-
confirmed at necropsy without treat-         spread whereas others4,5,9 suggest that
                                             most occur secondary to a penetrating               lation with S intermedius, Montgomery
ment in one, and another was lost to                                                             and others7 found culture of joint fluid
follow-up before commencement of             wound. In this study, the latter view is
                                             strongly supported, as only five dogs had           to be more sensitive than that of capsule
treatment (Table 3). Amputation was                                                              when the fluid was inoculated into
performed on one dog that had                no history of a surgical or other pene-
                                             trating wound. Three of these cases had             blood culture medium. In this study
osteomyelitis of the tibia and septic                                                            joint fluid was successfully cultured in
arthritis of the stifle and hock.            severe and long-standing osteoarthritis
                                             that is thought to predispose to                    12 of 15 samples (80%) but in only 1 of
Successful arthrodesis was performed on                                                          4 joint capsule samples. In two
two others. Another case was treated         haematogenous joint infection, perhaps
                                             because the increase in synovial vascula-           instances, in which neither joint fluid
with cephalexin for 4 weeks but 2 weeks                                                          nor capsule were successfully cultured,
later was diagnosed with a ruptured          ture in osteoarthritic joints may favour
                                             the penetration of bacteria into the                antibiotics had been given prior to
CCL. At this time Gram-positive cocci                                                            sampling.14,15
were seen in joint fluid. The lameness       joint.1
                                                A male-to-female ratio of 2:1 in                    There is a need to establish the effi-
did not resolve despite a further 6 weeks                                                        cacy of culturing joint capsule in
of cephalexin and extra-articular CCL        canine septic arthritis has been demon-
                                             strated previously,2 though an even                 comparison to inoculation of joint fluid
repair. The dog was euthanased because                                                           into blood culture medium in the veteri-
of persistent lameness and multiple joint    distribution was seen in this study. Over
                                             half of the present cases developed sepsis          nary clinical setting. Culture of joint
abnormalities associated with osteo-                                                             capsule is justified when arthrotomy is
chondrosis. Four other low-grade cases       after CCL stabilisation procedures. Of
                                             these, females outnumbered males by                 performed for other reasons such as
were treated initially with antimicrobial                                                        removal of a joint prosthesis and/or
drugs alone. These failed to improve and     1.5:1, which is in accordance with the

Aust Vet J Vol 77, No 4, April 1999                                                                                                    235

open-joint lavage. However, biopsy of             Two cases of haematogenous septic           study there was no obvious association
joint capsule is more difficult to justify     arthritis were manifested as chronic           of type of suture material with joint
in cases of haematogenous joint infec-         problems. These cases had been treated         infection.
tions. If culture of joint fluid is negative   for osteoarthritis with success for at least      Four cases of septic arthritis associated
and there is a strong suspicion of sepsis,     1 year prior to diagnosis. Another case,       with extracapsular CCL repair were
the clinician may have to choose               not included in this study, manifested         unsuccessfully treated with antimicro-
between capsule biopsy and empirical           similarly and had also been treated for        bial drugs alone emphasising the impor-
therapy using cephalexin or amoxycillin-       osteoarthritis for more than 12 months.        tance of removing nonabsorbable suture.
clavulanate. Given that 70 to 90% (86%         This was initially diagnosed as infectious     The antimicrobials may have killed the
in this study) of septic arthritides are       arthritis, despite a negative culture, on      bacteria within the joint but not those
caused by Gram-positive bacteria,2,6           the basis of joint fluid analysis, the         within the suture biofilm. The infection
many cases may be successfully treated if      history of single joint involvement and        in these cases resolved after more
the latter course is taken. If Gram-nega-      evidence of severe gingivitis acting as a      aggressive therapy including removal of
tive bacteria are seen but not cultured        possible source of bacteraemia.                nonabsorbable suture and joint lavage
then there may be more indication to           However, the dog failed to respond to          was performed.
perform capsule culture as the sensitivi-      amoxycillin-clavulanate and was subse-            Overall, 12 cases of joint sepsis that
ties of Gram-negative species such as P        quently placed on immunosuppressive            were associated with surgery presented
aeruginosa, Klebsiella spp and Proteus spp     doses of prednisolone, which resolved          as low-grade infections. Animals are
are less predictable.16                        the lameness and produced a pain-free          expected to be lame for 4 to 6 weeks
   In two dogs no bacteria were cultured       joint. Whilst analysis of joint fluid was      following major joint surgery such as
from joint capsule, fluid or prosthesis        not performed to confirm resolution of         CCL stabilisation. It may be difficult to
which puts the diagnosis of septic             the inflammatory arthritis, it is likely       determine whether failure to improve
arthritis in doubt.3 However, both dogs        that this was an idiopathic inflammatory       postoperatively is due to mild infection.
received antibiotics prior to collection of    arthritis associated with a remote infec-      A recent study found little correlation
the samples. The diagnosis in one case         tion.20 These cases highlight the diffi-       between infection and the success of
was made on the basis of clinical signs        culty in differentiating infectious            CCL repair procedures.26 Only 2 of 320
(heat, pain and swelling of the joint 7        arthritis from other arthropathies. They       CCL repair surgeries performed at
days postoperatively, pyrexia), a high         also demonstrate that a diagnosis of           MUVH developed low-grade septic
polymorphonuclear cell count in the            osteoarthritis should be reviewed if stan-     arthritis. The remaining cases of low-
joint fluid and complete response to           dard therapy such as nonsteroidal anti-        grade joint sepsis following CCL repair
antimicrobial drugs, open-joint lavage         inflammatory drugs with or without             were referred from other practices and
and delayed primary closure. In the            sodium pentosan polysulphate are only          the prevalence of postoperative sepsis in
other case, diagnosis was based on Gram        partially successful in relieving signs of     these practices is unknown. Despite this
stain of the joint fluid, which had a          arthritis.                                     low rate, the effects of postoperative
mixed population of bacteria. The pres-           The only joints affected with postop-       joint sepsis are potentially devastating.
ence of a mixed bacterial population           erative sepsis in this study were stifles.     We therefore believe that joint fluid
after collection of the sample at arthro-      There are a number of possible reasons         analysis should be performed in all cases
tomy makes it unlikely that the bacteria       for this. Stifle arthrotomy involves a         of CCL stabilisation that do not
were contaminants. This case provided          large joint incision which is more exten-      improve, or that deteriorate gradually
dilemmas in other areas. Despite sepa-         sive than the standard arthrotomies of         after a period of postoperative improve-
rate courses of amoxycillin-clavulanate,       the hip, elbow, hock and shoulder              ment. This would identify those cases
norfloxacin and enrofloxacin, the joint        joints.21 As a result operative times are      that warrant microbiological investiga-
fluid maintained a high polymorpho-            likely to be longer, increasing the poten-     tion.
nuclear cell count (> 100 x 109/L),            tial for bacterial contamination.22 Addi-         In conclusion, only 19 cases of septic
although bacteria were not seen in two         tionally, with extracapsular CCL repair,       arthritis were diagnosed over a 10 year
subsequent joint fluid analyses. A             a nonabsorbable suture is placed in            period at MUVH. The most common
possible explanation for this is the           close proximity to the joint and may           cause of septic arthritis in this study was
syndrome described in man,17 dogs,2            even be in direct contact with the             acute and chronic postoperative joint
pigs18 and rabbits19 where there is persis-    fabellar extension of the lateral              infection involving the stifle joint. Anal-
tent joint inflammation in the absence         femorotibial joint pouch.23 This may           ysis of joint fluid was helpful in estab-
of bacteria. This inflammation is              facilitate entry of bacteria into the joint    lishing the presence of an inflammatory
thought to be perpetuated by antigenic         from the suture material which, like           arthropathy, but toxic neutrophils were
bacterial fragments which stimulate the        other orthopaedic implants, may be             detected in only 8% of samples and
immune response and cause immune               associated with the production of a            were not considered a reliable indicator
complex hypersensitivity.2 These cases         biofilm or glycocalyx that enhances            of sepsis. Diagnosis was confirmed by
are responsive to corticosteroids. Stifle      bacterial adhesion and protects bacteria       culture of blood, joint fluid, joint
arthrodesis was ultimately performed in        from phagocytosis.24 Multifilament             capsule or periarticular prosthesis. In
this case and resulted in pain-free use of     suture material is associated with a           some cases bacteria were not success-
the limb with no evidence of postopera-        higher infection rate and formation of         fully cultured because antimicrobials
tive osteomyelitis.                            discharging sinuses,25 though in this          had been administered before collec-

236                                                                                                  Aust Vet J Vol 77, No 4, April 1999

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                                                         MN, Hunt J. Comparison of aerobic culturette,          18. Collins DN, Goldie W. Observations on
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lish the diagnosis. Haema-togenous                       medium in detection of canine bacterial arthritis.     infection of swine. J Pathol Bacteriol 1940;50:323-
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Aust Vet J Vol 77, No 4, April 1999                                                                                                                              237