The Dimensional Accuracy For Preparation Of Femoral Cavity In Total Hip Arthroplasty

INTRODUCTIONCementless total hip arthroplasty (THA) has become an accepted part of the orthopaedic surgeon's choices and is being used with increasing frequency as an attractive alternative to conventional cemented prostheses especially in young and active patients. However, some problems still remain after cementless THA, such as clinically or roentgenographically visible failure, intraoperative fracture and persistent thigh pain.Clinical researches found that failures of cementless THA arose mainly from the micromotion of the implant and inadequate femoral canal filling and apposition between bone and prostheses. The mechanical strength between the bone and prosthesis interface is positively related to bony ingrowth into the implants. The bony ingrowth into the implant is dependent upon the initial stability of the prosthesis and the close apposition to the bone after implantation. Stability is one of the most important factors for fixation of an implant. Initially, postoperative stability for an implant without cement is dependent upon the 'press-fit', while the permanent stability for an implant is determined by the bone ingrowth into the component. The interface between the implant and bone may play an important role in affecting early implant stabilisation, possibly by influencing tissue healing dynamics. Minimising the micromotion of the cementlessprosthetic components is a key requirement for obtaining bone ingrowth. Great efforts were made to enhance prosthetic stability, including better designs of the component, using newer materials and treating the surface of components, and modification of the operative technique. These improvements can reduce the motion of implant and osteolysis, improve proximal femoral fixation to prevent stress shielding, and promote bone ingrowth. The second important factor for fixation of an implant is the match of the bone and the prosthesis梩he femoral component should fit the femur or the femoral cavity should be precisely prepared for the component to be inserted in order to make bone ingrowth easily and load transfer properly. Both of them had been already emphasised in theoretical, experimental, and anatomic studies. The quality and quantity of bone ingrowth into the precisely fitting prostheses is different from that of the bad ones. The ingrowth process is facilitated if a satisfactory fit for the prosthesis is achieved during operation, while the spaces between the implant surface and the surrounding bone reduce implant stability and adversely affect the amount of bony ingrowth and the rate of which it occurs.The conventional way to prepare the femoral cavity for the femoral stem is to apply impact loads to a broach with a hammer. The cementless prosthesis is 'press fit* into a slightly undersized canal within the femur. Theoretically, the classical technique of preparing the femoral canal is for cemented prosthesis, it is not ideal for cementless implantation. A common complaint from patients with cementless THA is thigh pain. Engh et al have described 2 types of thigh pain. The first, which occurs in patients with undersized stems, is attributed to micromotion from fibrous stabilisation of the stem. The second comes from patients with good canal fill and osseous hypertrophy around the tip, who often complain mild delay in onset due to stress transfer. ?Some others also found out that the thigh pain is related to the fit and load transfer of the component within the proximal femur. Implants that do not fit precisely are more likely to be associated with residual pain than prostheses that fit more exactly. The fit includes two problems: the implant should fit the femur well (the problem of the femoral prosthesis), and the bone should also be shaped accurately to fit the implant (operative techniques and instruments).Many problems related to cemnetless THA could be alleviated by more precise preparation of the femoral canal and selection of an appropriately sized prosthesis as suggested by many authors. If an ideal contact is established directly between...