Primary total hip arthroplasty in patients with osteoarthrosis secondary to developmental hip dysplasia is often more complex due to anterolateral acetabular bone deficiency. Femoral head (shelf) autograft provides a non-immunogenic, osteoconductive lateral support with the potential for enhanced bone stock should revision surgery be required. The technique has been shown in other series to give reliable early results but may be complicated by graft revascularisation and collapse. As yet, no study has assessed shelf grafts long term or quantified the need for further bone graft at revision surgery.

This study aims to assess initial graft union rate; quantify long term graft resorption and; quantify the need for further bone graft in the patients requiring revision surgery.

A retrospective analysis of a single surgeon's series of 31 THR in 25 patients was conducted. Post-operative, biplanar radiographic analysis was performed at 3 and 6 months and annually thereafter for a mean of 14 years (range 8-18). Grafts were assessed for union, resorption and displacement. Intra-operative necessity for bone graft at revision surgery was recorded.

Union, osseous 93%, fibrous 7%. No grafts displaced. In 71% less than one-third of the graft resorbed, in 29% one-third to one-half resorbed and in no grafts did greater than a half resorb. Of 10 patients revised, 2 required bone graft for inadequate bone stock.

Femoral head autograft allows effective acetabular coverage with excellent rates of union, minimal graft resorption in the long term and improves bone stock in revision surgery.

Introduction: The failure rate of cemented hip replacements is about 1% per year, mainly due to aseptic loosening. PMMA acts as a grout, therefore high pressure is needed to ensure fixation. Various plug designs are used to increase pressure. No data is available on their ability to occlude the canal. Factors including canal size, canal shape and cement viscosity may affect performance. The two aims of this study are (I) to determine the effect of cement viscosity, canal shape and canal size on the ability of cement restrictors to withstand cementation pressures, and (II) to determine which of the currently commercially available designs of cement restrictor is able to withstand cementation pressures, regardless of values of other potentially influential factors.

Methods: Artificial femoral canals were drilled in oak blocks. Circular canals had diameters of 12 or 17.5 mm. Oval canals had short axes equal to the diameter of the circular canals and long axes 1.3 times longer. This ellipticity of 1.3 is average for human femoral canals. One of four types of cement plugs (Hardinge, DePuy, UK; Exeter, Stryker, UK; Amber Flex, Summit Medical, UK; and OptiPlug, Scandimed, Sweden) was inserted. A pressure transducer was fitted in the canal just proximal to the plug. Bone cement (Palacos LV-40 low viscosity or Palacos R-20 high viscosity, both Schering Plough, UK) was prepared in a mixing device for 1 min at 21°C, and inserted in the artificial canal after 4 minutes. A materials testing machine was used to generate pressure in the cement. Cement pressure and plug position were measured. All combinations of canal size and shape, plug design and cement viscosity were pre-selected according to a D-optimal experimental design which was optimised to perform a four-way ANOVA to analyse the four main factors plus the interactions between plugs and the other three factors. A total of 23 experiments was performed.

Results: Average cement pressures achieved differed between implants (OptiPlug 448±66 kPa, Hardinge 142±66, Exeter 705±66, Amber Flex 475±72; p=0.002, all mean±SEM). They also differed between canal sizes (12 mm 529±49, 18 mm 356±47; p=0.03), canal shapes (Round 631±45, Oval 254±51; p=0.004) and cement viscosity (High 535±54, Low 350±43; p=0.03). No significant interaction between factors was found.

Discussion and Conclusion: All plugs resisted lower pressures in large canals, oval canals or with low viscosity cement. When comparing plugs, these different circumstances should therefore be taken into account. Of the four tested, the Exeter plug performed best in all adverse circumstances. The OptiPlug and AmberFlex, which are both resorbable, had an intermediate performance. The Hardinge plug performed worse.

Modern cementation techniques in hip arthroplasty are enhanced by the use of a cement restrictor. Failure of cemented hip replacements is commonly caused by aseptic loosening. Cement plugs which occlude the medullary canal are widely used to increase cementation pressures. Many plug types with variable performance exist. Ideally, plug performance should be sufficient regardless of other factors. All plug designs are circular in cross section, yet the vast majority of human femora are of oval section, the average ellipticity for human femora being 1.3. This study aims to determine (I) the effect of cement viscosity, canal shape and canal size on plug performance and (II) which designs of cement restrictor are able to withstand cementation pressures, regardless of values of other potentially influential factors.

Methods: Artificial femoral canals were drilled in oak blocks. Canals had diameters of 12 or 17.5 mm and oval or circular cross section. Four synthetic plug types (Hardinge, Exeter, Summit and OptiPlug.) and a bone plug (human allograft, Sulzer instrumentation) were tested. The effect of canal diameter, canal shape and low or regular cement viscosity was assessed.

Results: Maximal pressures achieved varied significantly between plugs. (OptiPlug 448±66 kPa, Hardinge 142±66, Exeter 705±66, Amber Flex 475±72, Bone plug 502±97 kPa; p=0.002, all mean±SEM). Al plugs performed worse in canals of increased size and of elliptical canal cross section (12 mm 529±49, 18 mm 356±47; p=0.03), canal shapes (Round 631±45, Oval 254±51; p=0.004). Cement viscosity had no statistical effect.

Discussion: Elliptical canal cross section and increased canal diameter adversely affects performance of all plug designs. Of the five tested, the Exeter and bone plugs performed best in all adverse circumstances. The Opti-Plug and AmberFlex, which are both resorbable, had an intermediate performance. The Hardinge plug performed worse. These factors should be considered when selecting plug design.

Aim: To determine the histological changes in discs retrieved at the time of fusion following failed Intra-Discal Electrothermal Therapy (IDET).

Method: Three patients who had failed IDET treatment underwent lumbar interbody fusion. At the time of the operation the disc material and the endplate were sent for histopathology. The histological changes were compared to a degenerate disc and endplate. The staining techniques used were Haematoxylin Eosin stain, Elastic Van Geison and Alcian stains.

Results: In the post IDET specimens there was stromal disorganisation, paucity of chondrocytes and chondrocyte degeneration. These changes were seen in the nucleus pulposus, annulus fibrosis and the endplate as well. Comparatively cadaveric studies using intra-discal radiofrequency thermocoagulation showed histological change only in the nucleus pulposus.

Conclusion: The endplate changes at the cellular level can be widespread following IDET therapy, which can potentially cause alteration of its mechanical properties.