Tubercular osteomyelitis of the patella: A report on a rare case

Level of Evidence: V Introduction Skeletal tuberculosis is the most common form of extrapulmonary tuberculosis, with the knee joint being the third most common involved joint following the spine and hip.[1] Furthermore, isolated patellar involvement is very uncommon with an incidence of 0.09 - 0.1% of skeletal tuberculosis, which is one of the rare cases of extrapulmonary skeletal tuberculosis in immunocompetent individuals.[2,3] The most common presentation of tubercular osteomyelitis of the patella is a discharging sinus over the knee with a cystic lesion within the patella.[4,5] Only 11 cases of patellar osteomyelitis are reported in the available literature, as a case report.[1] This paper aimed to present a very rare case of tubercular osteomyelitis of the patella and to discuss clinical and radiological features and its management. Case Presentation A 52-year-old man, without any comorbidities, presented with complaints of pain in the right knee and intermittent fever since 3 months, and progressive swelling of knee joint for the past 2 months, with subsequent development of limp and restriction of movements. The patient did not give a history of trauma or instability of the knee, features suggestive of inflammatory arthritis or prior contact history with tuberculosis patient. Examination of the right knee revealed a diffuse swelling with local rise of temperature, tenderness over the knee, with doughy consistency on palpation which was suggestive of synovial thickening and gross restriction of movements of the flexion (10° to 60°). Distal pulses were palpable. Further clinical assessment did not yield any significant clinical findings. Laboratory investigations revealed Hb of 10.6 gm%, total leucocyte count of 11,200 cells/mm3 (polymorph 76%). Kidney function test (KFT), liver function test (LFT), and chest X-ray were normal. X-ray of the right knee joint lateral and AP view revealed multiple osteolytic lesions with sclerosis of the anterior border of the patella [Figure 1].Figure 1: Plain radiograph of patella showing osteomyelitis changesMagnetic resonance imaging (MRI) knee joint showed marked bony erosions of the right patella with diffuse marrow edema and heterogenous marrow enhancement. Besides we noticed intraosseous peripheral enhancing collection within the patellar bone suggestive of an intraosseous abscess. Features were suggestive of chronic osteomyelitis of the patella with chronic synovitis in the right knee joint with possibility of tuberculosis [Figure 2].Figure 2: MRI of patella showing bony erosions with diffuse marrow edema and heterogenous marrow enhancement. The intraosseous peripheral enhancing collection is visualized within the patellar bone suggestive of an intraosseous abscessAfter the diagnosis of tubercular osteomyelitis of Patella, the emergency Arthrotomy with debridement and synovectomy was planned. After taking the patient’s consent for the planned procedure, the patient was taken under Spinal anesthesia in the supine position. The procedure was performed by a team of consultant orthopedic surgeons. Arthrotomy with debridement and synovectomy was performed. We did not find any involvement of the tibia or femur. The histopathological examination of specimen of debrided tissue from patella revealed multiple greyish white–brown unhealthy granulation tissue, bony and cartilaginous tissue with large areas of fibrosis, covered by caseous necrotic material. Many epitheloid granulomas with Langerhans type of giant cells were observed (features suggestive of tubercular osteomyelitis) which is displayed in Figure 3. However, synovium examination did not yield any significant findings.Figure 3: Microscopic section showed bony and cartilaginous tissue with large areas of fibrosis, covered by caseous necrotic material. Many epitheloid granulomas with Langhans type of giant cellsThe patient was then started on anti-tubercular therapy (Rifampicin 10 mg/kg, Ethambutol 15 mg/kg, Isoniazid 5 mg/kg, and pyrazinamide 25 mg/kg)as per RNTCP, the patient improved symptomatically within two months of starting treatment and was able to walk with full weight bearing but had restriction of movement flexion beyond 110°. Discussion Extrapulmonary tuberculosis accounts for less than 3% of the cases. Knee is the third most common affected site after the spine and hip (8.3%) and isolated patellar involvement is very uncommon. Earliest reported cases of patellar osteomyelitis are by D. McCrae Aitken in May 1933 followed by George Hartofilakidis - Garofalidis in 1969.[6,7] Tuli SM reviewed 1074 cases of osteoarticular tuberculous lesions. Ninty cases involved the knee of which only one (0.09%) presented with isolated patellar involvement.[2] Galois et al reported 10 cases of tuberculosis of patella. Diagnosis of isolated patellar tuberculosis is often missed owing to the rarity of the disease and nonspecific clinical features in the early stage of the disease.[7] The disease most commonly affects adolescents and young adults with male predominance.[3,8] Often patient presents with non-specific symptoms initially, constitutional symptoms may be absent making early diagnosis more challenging. Symptoms suggestive of chronic knee synovitis present later in the disease course.[7] Radiologically, osteolysis containing central bony sequestrum, bordered by peripheral sclerosis is observed which is most suggestive of tuberculosis of patella.[3,9,10] At times sclerotic margins at the articular surface may break out, leading to synovitis. This leads to difficulty in localizing the site of primary involvement to patella or knee. MRI aids in diagnosis by delineating the lesion of the patella, with associated synovitis, and assessing the extent of involvement. However, confirmation mandates a biopsy of the affected tissue.[11] It is important to treat osteoarticular tuberculosis with multiple antibiotics as an Antitubercular therapy.[5] It usually takes 12–18 months for the treatment to be completed, depending on clinical and radiological improvement and co-relation with blood parameters.[1] Recent publications have emphasized biopsy as the only surgical procedure; however, surgical curettage and debridement may be required if there is an abscess or persistent resistant bone lesion.[4] Conclusion Tubercular osteomyelitis of the patella is a rare occurrence, with a paucity of cases reported in the literature. Early diagnosis and appropriate management aid in achieving a favorable outcome in terms of the range of movements of the knee. Clinical Messages Tubercular osteomyelitis of the patella is a rare occurrence, with a paucity of cases reported in the literature. Diagnosis of isolated patellar tuberculosis is often missed. Early diagnosis and appropriate management aid in achieving a favorable outcome in terms of the range of movements of the knee. Authors contribution R. K. – Planning of study, data management, writing and revising the manuscript. N. P. - Data management, manuscript preparation. A. R. - Planning of study, data management, writing, and revising the manuscript. B. B. N. - Data management, manuscript preparation. Patient’s perspective Satisfactory with the outcome. Informed consent for publication Informed consent was obtained from the patient for publication of this case report. On request, a copy of the written consent is available for review by the Editor-in-Chief of this journal. Acknowledgment None. Financial support and sponsorship This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Conflict of interest There is no conflict of interest of any kind with the research or its outcome among the investigators. Institutional review or ethical clearance Not applicable.