[Popliteal cysts: sonography evaluation after arthroscopic treatment].

PURPOSE: To identify a set of sonomorphological parameters to evaluate the outcome of arthroscopic surgery for popliteal cysts by sonography. MATERIAL AND METHODS: We examined 30 patients (18 males, 12 females) before treatment and 3/6 months after arthroscopy. Patients were classified by clinical (4 groups) and sonographic criteria. The sonographic criteria were the morphological classification of the cysts (beak-shaped, X-shaped, grape-like, slit-shaped) and the volume measurement. RESULTS: Sonography identified beak-shaped popliteal cysts (the most frequent Baker cyst shape), 5 grape-like (the usual shape of complicated Baker cysts) and 1 X-shaped . The volume of cysts before treatment ranged from 5 to 38 cl. Most cysts were clinically rated as grade 2 (symptomatic and evident at physical examination, with a reduction of range of motion up to 20 degrees of flexion). No patient was rated as grade 0 (normal). After surgery the cyst was still evident at sonography. After 3 months we recorred a cyst volume decrease in all cases. Six months after surgery 29/30 cysts had a volume <5 cl with an almost virtual cavity that changed their appearance in to slit-shaped . In one case cyst volume increased. The clinical classification showed an increase of the grade 0 group unsymptomatic cysts (not detectable at physical examination). DISCUSSION AND CONCLUSIONS: Sonographic evaluation of popliteal cysts after arthroscopic surgical treatment allowed to recognize the cysts, which are not removed by this approach. The follow-up at 3 months showed a reduction in cyst volume. After six months, in the cases with a good surgical response, the cysts reached a volume <5 cl regardless of their original volume. The morphology of the cysts with a good surgical result, is slit-shaped with virtual cavity regardless of their original appearance. There is a high correlation between sonographic and clinical data. We believe that the volume reduction of the cyst three months after surgery is a good predictive element. After six months the preesence of a cyst with a volume <5 cl and a slit-shape with virtual cavity is a sign of good surgical result.