The infection of Mycoplasma hominis after total knee replacement: Case report and literature review.

The Mycoplasma hominis infection is a rare postoperative complication after joint replacement. Based on our knowledge, there were only two cases reported by Korea all over the world currently. A case of postoperative Mycoplasma hominis infection after total knee replacement in our hospital was reported in this article. It was confirmed through mass spectrometer and Mycoplasma cultivation and treated by the first stage debridement, polyethylene insert replacement, and then drainage and irrigation combined with sensitive antibiotics after the operation. We observed that the C reactive protein (CRP) level correlates with the development of disease, while the erythrocyte sedimentation rate (ESR) remains at a high level, indicating the relevance between the Mycoplasma hominis infection caused by knee joint replacement and CRP. This study aims to report the case and review relevant literature.

Introduction

Total knee replacement (TKR) is a common operation in orthopedic surgery to treat diseases such as osteoarthritis, arthritis deformans, rheumatoid arthritis. But infection after TKR proves to be a severe complication. Clinical research discovered that the probability of postoperative infection in patients who received TKR for the first time was 0.5%–2.0%,1, 2 and infection was the major cause of an operation failure. Bacteria, the most common pathogen, often result in infection. However, Mycoplasma hominis infection is extremely rare as few literature have reported on it. Mycoplasma hominis, as one of the mycoplasma, exists mainly in the urinary tract and genital3, 4 and can also cause inflammation. As far as we know, there were only two cases reported in Korea all over the world currently. This article reports a case of Mycoplasma hominis infection after knee joint replacement and reviews relevant literature.

Case report

A 62-year-old man diagnosed as having “left knee osteoarthritis” was sent to our department for treatment. There has been intermittent pain on the patient's knee without obvious causes since eight years ago. In addition, pain and joint function got worsened despite treatments of taking medicines, calcium supplement and intra-articular injection of sodium hyaluronate. Because of the repetitive pain on the patient's knee which cannot be relieved by local hospitals and lasted for about half a month, the patient came to our hospital for further treatment. He was admitted to our hospital after receiving physical examination and X-ray. The results of ESR- and CRP-related examinations and some other index checking were all negative. Then the patient accepted the left total knee replacement surgery with nerve block anesthesia. Pulsed irrigation was conducted regularly after the surgery with silicone drainage tube placed. Twenty-four hours after the surgery, the drainage tube was pulled out and the patient took cefazolin for treatment. Blood seeping and pale clear liquid exudation from the wound were observed on the 3rd and 4th day after the surgery respectively (Fig. 1) with increased body temperature. The results of blood test suggested that CRP concentration markedly increased to 208.3 mg/l while other indexes did not change significantly. Then cefazolin was replaced by vancomycin and bacterial culture was conducted using wound exudation. The results indicated a negative bacterial growth. As secretion continued exudating from the wound, bacterial culture and fungal culture were conducted, both with negative results. Ten days after the surgery, a positive Mycoplasma growth was observed on Mycoplasma mass spectrometer of the secretion. Considering that it was Mycoplasma infection, we performed the first phase of the debridement surgery in which seepage was cleaned up and used for culture (Fig. 1). At the same time, synovium was removed and the polyethylene insert was replaced. Complete debridement was achieved through repeated irrigation of hydrogen peroxide, iodine and 5000 ml saline solution. Meanwhile, we inserted four drainage tubes to irrigate the knee joint which were douched by minocyline. X-ray examination (Fig. 2) and pathology checking were conducted for the knee joint and the synovium respectively, demonstrating a large number of inflammatory cells infiltration (Fig. 3). The mass spectrometer results of secretion collected in the operation suggested a strongly positive Mycoplasma growth and the result of bacterial culture indicated Mycoplasma hominis. Therefore, Mycoplasma hominis infection was confirmed. We then first performed a drug sensitivity test, during which time, a combination of clindamycin, ciprofloxacin and minocyline was skillfully applied. Then we changed the combination into erythromycin, clindamycin and minocyline according to the test findings. As a result, the secretion was gradually decreased with the wound scabbed and cured in the end. Based on the changes of ESR and CRP we recorded, it was found that there was significant relevance between the level of CRP and the infection, while the level of ESR remained high during the treatment.

Fig. 1

The wound had persistent exudate (A); in the debridement operation, a large number of exudate can be found at the medical site of the wound (B); the wound was healed after one-stage debridement, irrigation and antibiotic treatment (C).

Fig. 2

The results of pre-operative (A) and postoperative X-ray examination (B) showed that the prosthesis was in good position.

Fig. 3

Mycoplasma hominis culture was positive (A); through synovium pathology test, many inflammatory cell were observed and had infiltrated in the synovium tissue (B).

Discussion

Epidemiology indicates bacteria are the most common pathogen result of infection after TKR. Staphylococcus proves to be the most universal bacteria, accounting for approximately 70.0%–80.0% of all types, and so are gram negative bacilli, anaerobic bacterium and non-group A streptococcus.1, 2, 5, 6 The diagnosis criteria of postoperative infection after TKR proposed by American academy of orthopaedic surgeons is based on a combination of inspection results of CRP/ESR with bacterial count and bacterial culture findings, but the specificity of ESR and CRP for infection was only 56% with a low diagnosis rate which renders diagnosis in the clinic relatively difficult. Since the patient in our case demonstrated a high ESR level, frequently fluctuating CRP level and negative germiculture in the process of infection, this case couldn't be judged based on the aforementioned standard. However, results of the patient's secretion cultured in our hospital were positive in terms of Mycoplasma hominis, which suggested that if postoperative wound drainage and negative germiculture occur in the TKR patients at the same time, he/she should be suspected of Mycoplasma hominis infection. Mycoplasma hominis, as one of the Mycoplasma family members, mainly exists in the urinary tract and genital, easily causing urinary tract and genital infection. As it is rather rare in TKR, only 2 cases were reported in South Korea in literature. Based on our knowledge, this is the first report of prosthetic joint infections with Mycoplasma hominis in China.

TKR postoperative infection treatment methods include antibiotic therapy with retained prosthesis, open debridement rinse with replaced polyethylene insert and removing the prosthesis. The patient was defined as type 2 of early acute infection according to the TKR postoperative infection type formulated by Tsukayama et al. It is commonly treated by antibiotic treatment combined with open wound debridement as illustrated in many literature.7, 8, 9, 10 However, the success rate is in general less than 60%, a relatively low percentage. Peersman et al. hold that age, rheumatoid arthritis, diabetes, hypokalemia were main risk factors for failure of TKR. In our report, after the patient underwent one-stage debridement, insert replacement, postoperative irrigation and sensitive antibiotics therapy, the infected wound obtained good healing. The present study revealed that lower age, absence of diabetes and hypokalemia may improve the success rate of one-stage surgery.

Lee et al. reported that they performed arthroscopic debridement operations on the surgical site when faced with Mycoplasma hominis infection. In their report, Lee et al. found that it was in vain to treat Mycoplasma hominis infection using vancomycin, and during the treatment process, CRP levels and White Blood Count would first increase but finally return to normal levels as the disease is recovering. Han Z et al. reported a Mycoplasma pneumonia periprosthetic joint infection which was identified by 16S ribosomal RNA gene amplification and sequencing and relieved significantly through taking vancomycin and ciprofloxacin. In our study, the patient underwent one-stage debridement, synovectomy, polyethylene insert replacement and repeated washing by large amounts of salt water during the treatment. Observing the ESR and CRP levels after TKP, we concluded that the CRP level had a close relevance to the disease development, while the ESR was at a high level persistently. The infected wound was healed after Mycoplasma hominis infection was treated by erythromycin and minocycline. The pre- and post-operative X-ray examination results (Fig. 2) showed that the prosthesis was in good position.

In conclusion, we suggested that Mycoplasma hominis infection should be suspected when continuous wound seapage and negative germiculture occur at the same time after TKR. Mycoplasma culture should be regarded as the diagnosis criteria for this infection and CRP level a reminder during the whole therapy process due to its significant relevance to disease development. To relieve the Mycoplasma hominis infection, one-stage debridement combined with effective antibiotic treatment could be applied.