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The diagnosis may be obvious if the patient is noted to favour the position of greatest comfort. This is the supine position with the knee moderately flexed and the hip mildly externally rotated

About

• Early management reduces morbidity and mortality.
• Psoas and Iliacus muscle
• Commoner in young than elderly
• Commoner in males than females

Anatomy

• The psoas muscle originates from the lateral borders of T12 to L5 vertebrae in the retroperitoneal space and inserts at the lesser trochanter of the femur.
• In 70% of people it is a single structure known as the psoas muscle, but 30% have the psoas minor that lies anterior to the major.
• The fibres of the psoas muscle blend with those of the iliacus to form the iliopsoas, which functions as the chief flexor of the hip.
• Innervation arises from the lumbar plexus via branches of the L2–L4 nerves.
• The psoas is surrounded by a rich venous plexus, which could explain its predisposition to infection from hematogenous spread.

Aetiology

• Infection of the lumbar spine (Spinal TB)
• IV Drug abusers
• Diabetes mellitus.
• AIDS, Renal failure
• Immunosuppression
• Crohn’s disease is commonest cause of secondary iliopsoas abscess

Types

• Primary iliopsoas abscess: blood spread of an infectious process from an occult source in the body e.g. TB
• Secondary iliopsoas abscess: Patients with Crohn's disease or who have had instrumentations or procedures performed in the groin, lumbar, or hip areas are at a particular risk of developing an iliopsoas abscess

Microbiology

• Staphylococcus aureus: 88% with primary iliopsoas abscess.
• Streptococcus species 4.9%
• E coli 2.8%
• Mycobacterium tuberculosis: common in developing countries.
• Rest: proteus,Pasteurella multocida, bacteroides, clostridium,Yersinia enterocolitica,klebsiella, methicillin resistant Staphylococcus aureus,salmonella, Mycobacteriumkansasii, and Mycobacterium xenopi.

Clinical

• Pyrexia, fever, weight loss, loin to groin pain, Fever
• Flank/back/abdominal pain, Limp, Malaise, Lump in the groin
• Lies with the knee moderately flexed and the hip mildly externally rotated
• Tests to elicit iliopsoas inflammation
  • The examiner places his hand just proximal to the patient's ipsilateral knee and the patient is asked to lift his thigh against the examiner's hand. This will cause contraction of the psoas and results in pain.
  • With the patient lying on the normal side, hyperextension of the affected hip results in pain as the psoas muscle is stretched.
  • These tests may be positive in appendicitis in which there is inflammation of the iliopsoas without the formation of iliopsoas abscess.

Investigations

• FBC: Elevated WCC and ESR and CRP
• U&E: may be an AKI. Lactate may be high.
• CT of the abdomen and pelvis
• Get abscess fluid culture and sensitivity

Complications

• Deep vein thrombosis A large iliopsoas abscess may lead to extrinsic compression of the iliac vein from the iliopsoas abscess and DVT
• Ureteric involvement
• Haemorrhage
• Generalised sepsis

Management

• ABC, Oxygen, Analgesia and acute management of any sepsis
• Broad spectrum Antibiotics based on cultures. Initially cover Staphylococcus and Streptococcus.
• Early management and drainage of the abscess reduces morbidity and mortality. Computed tomography guided percutaneous drainage (PCD) tends to be favoured over an open surgical drainage
• Manage medical comorbidities e.g. diabetes

References

• Iliopsoas abscesses review