Abstract
Introduction: The red, hot swollen knee is commonly seen in the A& E department and can present a diagnostic dilemma for the casualty officer. While superficial cellulites and bursitis are the most common diagnoses, anxiety is induced by the spectre of septic arthritis. The potential sequalae from aspirating a knee through infected superficial tissues further emphasise the importance of making an accurate clinical diagnosis.
The lymph drainage of the superficial tissues of the lower limb is via lymphatics that accompany the long saphenous vein and drain to the lower group of the superficial inguinal nodes. Drainage from the knee joint is to a popliteal node situated between the knee joint capsule and the popliteal artery. Efferents from this node ascend in close relation to the femoral vessels and drains to the deep inguinal nodes. We hypothesise that the differences in lymphatic drainage mean that palpable inguinal nodes are more likely with superficial infections than with septic arthritis. We reviewed the clinical findings in a group of patients with superficial or deep infections to test this theory.
Patients and Methods: From January 1995 until June 2000, twenty-seven patients were admitted with septic arthritis of the knee and fifty-one with superficial cellulites or bursitis about the knee. The former were diagnosed on the basis of clinical findings and a knee aspirate, the latter on clinical findings and response to treatment. The presence or absence of palpable inguinal lymph nodes was determined and compared for each diagnostic group.
Results: Joint aspirates from the group with septic arthritis grew organisms in twenty patients (staph aureus in 19, strep pneumoniae in one). The remaining seven patients had no growth but purulent fluid on aspirate with leukocyte counts in excess of 50,000/mm3. Six patients had rheumatoid arthritis and two were HIV positive IVDA’s but the rest had no pre-disposing factors. The average age was 52 (range 16–83). All were treated with arthroscopic washout (average 2.2/patient) and antibiotic chemotherapy.
In the superficial infection group 28 (56%) had pre-patellar bursitis and 23 (54%) cellulites. All were treated with antibiotics while eight of the bursitis group required incision and drainage. In the patients with superficial infection 32 (63%) had palpable inguinal lymphadenopathy while no patient with septic arthritis of the knee had palpably enlarged inguinal lymph nodes. This result is highly statistically significant (p< 0.01).
Discussion: It is well recognised that neoplastic or inflammatory conditions of the superficial tissues of the lower limb may be associated with inguinal lymphadenopathy. A similar association for septic arthritis of the knee has not to our knowledge been described. Our study would suggest that palpably enlarged lymph nodes are unusual in this condition. While it is worth emphasizing that the presence of lymph nodes does not rule out absolutely the possibility of septic arthritis, their presence or absence may be useful in differentiating superficial from deep infections about the knee.
The abstracts were prepared by Mr Ray Moran. Correspondence should be addressed to him at Irish Orthopaedic Associaton, Secretariat, c/o Cappagh National Orthopaedic Hospital, Finglas, Dublin 11.
