The mechanical advantage of the Charnley cup design – flanged or unflanged and pressurisation of the cement, before cup insertion, was tested experimentally. “The ogee-flanged socket gave a consistently high injection pressure which could be maintained throughout the process of polymerization” [1]. The results show clearly the importance of the details of the design, surgical technique and the properties of the cement. They are the important aspects of this type of surgery and must be understood and put into practice at each and every operation. The benefits will be available – long-term.

The importance of the stem design [2] attention to the details of the surgical technique [3, 4] and need for follow-up extending past 11 years have been well documented [5]. The benefits are long-term hence the importance of follow-up cannot be overstated. Study of the original publications is recommended.

Total hip arthroplasty, or in fact any total joint arthroplasty is, functionally, a foreign body bursa housing a neuropathic spacer – hence freedom from pain. Bursal fluid will follow the pathways dictated by changes in volume and pressure carrying wear particles and any other debris with it into spaces that may be accessible. If under any mechanical condition a one-way non-return valve condition prevails, local bone erosion will occur. When sufficient endosteal bone is resorbed, as compared with the overlying cortex, cavitation will be seen on radiographs. Their shape will be dictated by the hard materials i.e. cement, metal, and the softer cancellous and cortical bone. The appearance will be that of a compressed ellipsoid defect which will contain UHMWPE or any other debris. This sequence of events is more likely to be present on the femoral side where a one way none-return valve is more like the “piston – cylinder” arrangement of the medullary canal and the implant.