Posterior ankle arthroscopy for posterior ankle synovitis with an enlarged posterior talar process caused by a cat bite or scratch: A case report

Highlights • Posterior ankle synovitis with enlarged posterior talar process was caused by cat bite/scratch.• Infected and swollen ankle was treated successfully by posterior arthroscopic debridement.• There were many advantages in posterior ankle arthroscopy, compared to open ankle surgery.


Introduction
Cat bites represent 3%-15% of all animal bites [1][2][3][4] and cause local infection in 30%-50% of cases [5]. Infected cat bites commonly present as cellulitis but severe infection with tenosynovitis, abscess, arthritis, or osteomyelitis may also occur. In one report, 48% of patients who were hospitalized for an infected cat bite developed complications [6]. Moreover, although polyarthritis is a rare manifestation of cat scratch disease, there has been only one report of bilateral ankle arthritis [7].
The posterior talar process is comprised of medial and lateral tubercles that serve as the respective attachments for the posterior talotibial and talofibular ligaments. A secondary ossification center forms on the posterolateral aspect of the talus between the ages of 7 and 13 years, usually fuses within 1 year, and articulates with the talus via a synchondrosis [8][9][10]. In 7%-14% of adults, this center remains as a separate accessory bone [11]. If abnormal struc-tures are present, such as an enlarged, prominent, elongated, or hypertrophic posterior talar process (known as a trigonal or Stieda process), the surrounding soft tissue becomes impinged between the posterior distal surface of the tibia and the superior surface of the calcaneus [12]. To our knowledge, there have been no reports of synovitis with an enlarged posterior talar process in the posterior ankle caused by a cat bite or scratch wound.
Here we report a rare case of posterior ankle synovitis with an enlarged posterior talar process caused by a cat bite or scratch which was treated by resection of the enlarged posterior talar process, synovectomy, and release of the flexor hallucis longus (FHL) tendon via posterior ankle arthroscopy. This has been reported in line with the SCARE criteria [13].

Presentation of case
Informed consent was obtained from the patient for this report to be published.
The patient was a 58-year-old woman who was referred to our department with an approximately 5-month history of slight pain on loading and swelling of the left ankle without obvious trauma. Seven months before presentation, her family had started keeping   A weight-bearing lateral plain radiographic view of the posterior ankle revealed an enlarged posterior talar process (Fig. 2), which was also seen on computed tomography scans ( Fig. 3a-c). Cystic masses and bone marrow edema-like signal intensity in the enlarged posterior talar process with an adjacent soft tissue edema-like signal were seen in the posterior ankle on T1-weighted, T2-weighted, and fat-suppressed T2-weighted magnetic resonance images in the coronal (Fig. 4a, b), sagittal (Fig. 4c), and transverse ( Fig. 4d) planes. The preoperative diagnosis was infectious synovitis of the posterior ankle with an enlarged posterior talar process caused by a cat bite or scratch. A plan was made to reduce the patient's swelling surgically using a minimally invasive arthroscopic approach. The surgery was performed by I.T. who graduated from the medical university in 2004 and was a foot and ankle surgeon.
The procedure included irrigation, extensive debridement, and synovectomy with removal of the enlarged posterior talar process via standard anteromedial and anterolateral portals. The patient was positioned prone and a thigh tourniquet was placed. Two portals were created 1 cm above the insertion of the Achilles tendon, one just medial and one just lateral to the tendon, in line with the tip of the lateral malleolus using the standard two-portal technique described by van Dijk et al. [14] The lateral portal was used for visualization and the medial one was used as the working portal. A 4-mm, 30-degree arthroscope was introduced through the portals and directed towards the second toe. Intraoperatively, dense fibrous tissue and aggressive hypertrophic synovitis was seen in the posterior ankle (Fig. 5a, b). There was marked friction between the enlarged posterior talar process and the FHL tendon (Fig. 5c). After endoscopic resection of the hypertrophic posterior process of the talus in the posterior ankle, the severe synovitis and inflamed FHL in the posterior ankle were removed (Fig. 5d). A sample of synovial tissue was obtained for culture and pathological examination. The entire FHL tendon sheath could be visualized and was released down to the entrance of the fibroosseous tunnel using a shaver (Fig. 5e). We confirmed that the FHL moved smoothly with motion of the great toe. There were no intraoperative complications. The resected enlarged posterior process was 18 mm wide and 9 mm in length (Fig. 6). Histological examination indicated chronic synovitis with infiltration of neutrophils and lymphocytes, angiogenesis, and accumulation of hemosiderin, suggesting chronic inflammation with an infectious etiology (Fig. 7a). Histological findings were consistent with infectious synovitis but synovial tissue culture was negative for organisms such as Pasteurella multocida or Bartonella henselae. Histological examination of the resected enlarged posterior talar process also indicated chronic inflammation with infiltration of neutrophils and lymphocytes and accumulation of hemosiderin (Fig. 7b). A bulky dressing was placed postoperatively without immobilization. A lateral plain radiograph confirmed that the enlarged posterior talar process was resected successfully (Fig. 8). The patient was encouraged to actively move her ankle and toes. Weight bearing was allowed after surgery as tolerated, and she was allowed to return to daily activities after 3 weeks. The postoperative course was unremarkable. Her left lower leg swelling had decreased by 2 months after surgery (Fig. 9), at which time her white blood cell count and C-reactive protein level had decreased to 4800 cells/L and 0.04 mg/dL, respectively.
At the 1-year follow-up visit, the patient was very satisfied with her surgery and reported no limitation of daily activity. Her JSSF scale score had improved from 79/100 to 97/100 (pain 40/40, function 47/50, alignment 10/10).

Discussion
We encountered a rare case of posterior ankle synovitis with an enlarged posterior talar process in a patient with a history of cat bite and scratch wounds to the lower legs who was treated successfully by posterior ankle arthroscopic debridement P. multocida is a common causative pathogen in human infections from cat or dog bite. A small gram-negative coccobacillus, Pasteurella has been isolated in up to 80%-90% of feline gingival tissue samples (where P. multocida predominates) [15,16]. However, it was not cultured in this case. Westling et al. recommended local treatment for an infected cat bite, including drainage and debride-  ment of the wound and irrigation of the affected tendon sheath or joint [6]. Therefore, in this case, we performed debridement in the posterior ankle because we strongly suspected infectious synovitis caused by a cat bite or scratch. Posterior ankle endoscopy is a useful tool when treating various pathologies of the posterior ankle [14]. It is a minimally invasive surgical procedure that allows good visualization of the involved structures and yields good results [17]. Endoscopic removal of the posterior talar process and synovectomy has the advantages of fewer wound complications, thorough assessment of the posterior ankle, and access to the posterior recesses at this site [18]. Therefore, we selected a posterior ankle arthroscopic approach rather than open surgery to avoid the need for extensive soft tissue dissection. In this case, the outcome was excellent and the patient returned to work within 3 weeks.
A Stieda process can be seen in 14%-25% of normal ankle radiographs [19]; therefore, its presence does not in itself imply posterior ankle impingement syndrome. The posterior talar process could be enlarged in a patient who has posterior ankle impingement syndrome without an os trigonum12 and may be compressed during  extreme plantar flexion. Thus, the presence of an enlarged posterior talar process in itself is not sufficient to produce the syndrome. In our patient, the synovitis adjacent to the enlarged posterior talar process might have been worsened by the cat bite or scratch. In a report by Frigg et al., 13.3% of patients (4/30 feet) developed a painful stress reaction in the posterior subtalar joint after arthroscopic resection of an os trigonum or posterior talar process [20] such that the uncovered calcaneal joint surface was significantly longer in feet that sustained permanent damage than in feet that did not (6.4 mm vs 1.06 mm). They called this the Brisk configuration (the radius of the talus ending within the subtalar joint). Fortunately, in this case, there was no persistent inability to engage in daily activities due to a painful stress reaction in the posterior subtalar joint. However, as recommended by Frigg et al., patients should be informed about the possible risk of a Brisk configuration, although a posterior ankle arthroscopic approach is useful for avoiding this pathology.
The differential diagnosis in this case included cat scratch disease, which was first described in 1950 by Debre and Mollaret [21]. The majority of reported cases have been in persons under 20 years of age, who are usually male [22,23]. However, our patient was a 58year-old woman. The typical clinical manifestations of cat scratch disease are skin changes at the inoculation site and benign lymphadenopathy. These features were not consistent with this case because lymphadenopathy was absent. The causative agent of cat scratch disease, B. henselae [24], was not isolated in this case. Therefore, we ruled out a diagnosis of cat scratch disease. This report has some limitations. One was the short followup duration. Although there was no recurrence of left lower leg swelling due to posterior ankle synovitis at the most recent followup visit 1 year after surgery, further follow-up is necessary. Another limitation is that we could not obtain a positive culture from the sample of synovial tissue taken from the posterior ankle. However, we believe that posterior arthroscopic debridement was appropriate based on the diagnosis of infectious posterior ankle synovitis.

Conclusion
We have encountered a rare case of posterior ankle synovitis with an enlarged posterior talar process caused by a cat bite or scratch. The patient was treated by resection of the enlarged pos-