Femoral nerve block (FNB) is a well documented option for post-operative analgesia following major knee surgery. However, motor blockade may be prolonged preventing early mobilisation thereby increasing the length of stay. In addition, as a consequence of persistent quadriceps weakness, patients have an increased risk of falling. We present a series of five patients who underwent total knee replacement with spinal anaesthesia and FNB who fell, sustaining complete wound disruption - including a patient with peri-prosthetic fracture requiring further surgery and prolonged hospital stay. The literature, which is largely in anaesthetic journals, reflects the high quality of analgesia of FNB but makes little or no mention of the delays or dangers in early mobilization. We believe that the potential risks to orthopaedic patients are underestimated.