Differential diagnosis

Look for ^a

• crepitus on flexing the knee
• a history of arthritis
• a positive ultrasound scan

Arthritis, knee crepitus or a positive ultrasound scan make a Bakers' cyst more likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected Baker's cyst a (pre-test probability: 37%)	Baker's cyst (arthrogram)	crepitus on flexing knee	3.0 (1.2 to 7.5)	64%	0.54 (0.30 to 0.96)	24%
		history of arthritis	3.4 (1.2 to 9.4)	67%	0.59 (0.35 to 0.98)	26%
		ultrasound scan	infinity (0.16 to infinity)	100%	0.88 (0.73 to 1.1)	34%

Note:

• Bakers' cysts are common - a third of patients with a suspected DVT have a Baker's cyst (ruptured or not). ^a
• Remember the presence of a Baker's cyst does not exclude a DVT. ^a

Why?

A Baker's cyst (ruptured or not) does not exclude a deep vein thrombosis

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected DVT a (pre-test probability: 33%)	deep vein thrombosis (venogram)	presence of Baker's cyst	0.77 (0.33 to 1.8)	31%	1.2 (0.74 to 1.8)	41%
		presence of ruptured Baker's cyst	1.1 (0.21 to 6.0)	40%	0.98 (0.78 to 1.2)	37%