BACKGROUND:Lateral epicondylitis is a common orthopaedic condition often massively restricting the quality of life of the affected patients. There are a wide variety of treatment options - with varying levels of evidence. METHOD:The following statements and recommendations are based on the current German S2k guideline Epicondylopathia radialis humeri (AWMF registry number: 033 - 2019). All major German specialist societies participated in this guideline, which is based on a systematic review of the literature and a structured consensus-building process. OUTCOMES:Lateral epicondylitis should be diagnosed clinically and can be confirmed by imaging modalities. The Guidelines Commission issues recommendations on clinical and radiological diagnostic workup. The clinical condition results from the accumulated effect of mechanical overload, neurologic irritation and metabolic changes. Differentiating between acute and chronic disorder is helpful. Prognosis of non-surgical regimens is favourable in most cases. Most cases spontaneously resolve within 12 months. In case of unsuccessful attempted non-surgical management for at least six months, surgery may be considered as an alternative, if there is a corresponding structural morphology and clinical manifestation. At present, it is not possible to recommend a specific surgical procedure. CONCLUSION:This paper provides a summary of the guideline with extracts of the recommendations and statements of its authors regarding the pathogenesis, prevention, diagnostic workup as well as non-surgical and surgical management.

Introduction Soft tissue swelling of the knee joint can be caused by many diseases. Lipomas are one of the most reasonable differential diagnoses we have to consider. Therefore, we now present the uncommon case of a Lipoma arborescens (LA) and differentiate it from a quite similar manifesting spindle cell lipoma as follows. Case Report A 49-years old patient reports about progressive knee pain for four years and observes an increasing joint swelling. This swelling is a soft tissue, shiftable tumour, not painful. The magnetic resonance imaging (MRI) with contrast agent brings the diagnosis of an advanced osteoarthritis of the knee joint and classifies the tumour as LA. Subsequently, we treat the osteoarthritis by implanting a total knee arthroplasty with simultaneous intraoperative tumour resection performed as total synovectomy. The histopathological processing confirms the clinically and radiologically made diagnosis of LA. Summary Lipoma arborescens presents an uncommon subgroup of Lipomas, which is characterized by a slowly progressive increasing soft tissue swelling, especially around bigger human joints. Due to its intraarticular location, the LA might become clinically relevant when it reaches a certain tumour size. Looking at the diagnostics, sonography, MRI and especially the histopathological processing give the crucial results. Final proof can only be made by histopathological examination. Additionally, we have some differential diagnoses to exclude. Under these we predominantly find the spindle cell lipoma, synovial haemagioma, vascular synovial malformations and tenosynovial giant-cell tumour. Furthermore, an atypical lipomatous tumour should be excluded by FISH-analysis via determining the MDM2-Genamplification.