Introduction: Flexor tendon repair in zone 2 has a high re-rupture rate. Various pulleyplasties were described to reduce gliding resistance. In an experimental study on pig trotters, we performed pulleyplasty by meshing alike split skin graft and determined its effect on breaking strength and gliding resistance of repaired tendon.

Method: Phase 1: Two pairs of middle pulley of the same pig were pulled apart from bone on Universal testing machine. One of each pair were meshed (10 rows of 1mm slits 2 mms apart longitudinally).

Phase 2: The two ends of two repaired flexor tendons were attached to a tension load cell each. The proximal end load cell was connected to Universal testing machine. Gliding resistance was measured under saline before and after meshing.

Phase 3: The test was repeated on 4 specimens using a digital load scale. Ten observations of peak resistance were obtained each with normal pulley, meshed pulley, after edge tying of the pulley.

Results: Breaking strengths were 162 and 59 N in one pair and 89 and 50 N in another. The pulleys became 1.5 – 4 times stretchable.

Meshing increased the gliding resistance by approximately 20% and 30% in phase 2 and 3 respectively. Edge tying decreased the gliding resistance by 27% below that of normal pulley

Discussion and Conclusion: Meshing weakens significantly but breaking strength stayed above 50 N, which is more than average breaking strength of a tendon repair (30N, Norris et al). Meshed pulley were dragged farther and preventing it by edge tying decreased the gliding resistance.

No animal was killed for the study.

The treatment of bony defects of the tibia at the time of revision total knee replacement is controversial. The place of compacted morsellised bone graft is becoming established, particularly in contained defects. It has previously been shown that the initial stability of impaction-grafted trays in the contained defects is equivalent to that of an uncemented primary knee replacement. However, there is little biomechanical evidence on which to base a decision in the treatment of uncontained defects. We undertook a laboratory-based biomechanical study comparing three methods of graft containment in segmental medial tibial defects and compared them with the use of a modular metal augment to bypass the defect.

Using resin models of the proximal tibia with medial defects representing either 46% or 65% of the medial cortical rim, repair of the defect was accomplished using mesh, cement or a novel bag technique, after which impaction bone grafting was used to fill the contained defects and a tibial component was cemented in place. As a control, a cemented tibial component with modular metal augments was used in identical defects. All specimens were submitted to cyclical mechanical loading, during which cyclical and permanent tray displacement were determined.

The results showed satisfactory stability with all the techniques except the bone bag method. Using metal augments gave the highest initial stability, but obviously lacked any potential for bone restoration.

Wear of metal-on-metal bearings causes elevated levels of cobalt and chromium in blood and body fluids. Metal-on-metal bearings have two distinct wear phases. In the early phase, the wear rate is high. Later, it decreases and the bearing enters a steady-state phase. It is expected that as the wear rates decline, the level of cobalt detected in plasma will also decrease. We studied the baseline and exercise-related cobalt rise in 21 patients (13 men and eight women) with a mean age of 54 years (38 to 80) who had undergone successful hip resurfacing at a mean of 44 months (10 to 96) earlier. Our results showed that circulating baseline cobalt levels were not significantly correlated with the time since implantation (r = 0.08, p = 0.650). By contrast, the exercise-related cobalt rise was directly correlated with the inclination angle of the acetabular component (r = 0.47, p = 0.032) and inversely correlated with the time since implantation (r = −0.5, p = 0.020).

Inclination of the acetabular component should be kept less than 40° to decrease the production of wear debris.

Purpose: To find if there is any difference in gapping of tendon repair on cylcic loading and energy to failure of tendon repair when the circumferential suture knot is placed on the same side of the core suture knot or to the opposite side of the core suture knot.

Methods: Ten pig flexor tendons were repaired using 3 0 braided Polyester (Ethibond) as core suture (modified Kessler) and 6 0 Nylon as circumferential stitch (Hal-stead). Five tendons were repaired with the circumferential suture knot placed on the same side as the core suture (Group I) and the other five placed on the opposite side (Group II). Allocation to either of the groups was random. Using a testing machine the tendons were cyclically loaded and the energy to failure was calculated. Gapping during cylical loading was recorded using digital images.

Results: Mean gapping in Group I was 0.01 mm and in Group II was 0.03mm. This was not statistically signifi-cant (2x3 ANOVA, p > 0.3). The mean load to failure in group I was 58.7 N (55 to 65) and in group II was 59.5 N (54 to 67). This was also not statistically significant (p > 0.3 one way ANOVA).

Conclusion: There is no difference in gapping and energy to failure of tendon repair when the circumferential suture knot is placed on the same side of the core suture knot or to the opposite side of the core suture knot.

Objective: To compare the ability of a new composite bio-absorbable screw and two conventional metal screws to maintain fixation of scaphoid waist-fractures under dynamic loading conditions.

Methods: Fifteen porcine radial carpi, whose morphology is comparable to that of human scaphoids, were osteotomized at the waist. Specimens were randomized in three groups: those in group I were fixed with a headed metal screw, in group II with a headless tapered metal screw, and in group III with a bio-absorbable composite screw. Each specimen was oriented at 45° and cyclically loaded using four blocks of 1000 cycles, with peak loads of 40, 60, 80 and 100 N, respectively. In case of gross failure the number of cycles to failure was determined. Otherwise, permanent displacement at the fracture site was measured after each loading block from a standardized high-magnification photograph using image analysis software (Roman v1.70, Institute of Orthopaedics, Oswestry). Statistical analysis was by ANOVA and tolerance limits.

Results: Nogross failure occurred. Average displacements after 4000 cycles up to 100N were 0.05mm±0.03SD (headed metal), 0.15mm±0.16SD (headless metal) and 0.29mm±0.11SD (composite) and differed significantly (p< 0.02). Using tolerance limits, the data allowed us to predict that with 95% certainty, displacement in 95% of any sample fixed with a headed metal screw will be below 0.17mm, headless metal screw below 0.84mm, and composite screw below 0.76mm.

Conclusion: Comparing two types of conventional metal screws and a new composite bio-absorbable screw to maintain scaphoid fixation under cyclic loading conditions, we found small average fracture displacements for all three screws. Moreover, even following severe cyclic loading conditions, clinically meaningful displacements of more than 1 mm are highly unlikely for any of the three screws. We therefore conclude that a new bio-absorbable composite screw can serve as an alternative to conventional screws when fixing scaphoid fractures.

The Ilizarov technique of distraction osteogenesis is becoming a more common way of treating complicated fractures. It has been shown that shear IFMs will delay bone healing whilst axial IFMs are beneficial to the bone healing. Therefore to measure IFMs in conditions of mobility will provide critical information for research and clinic diagnosis. Such data are not provided by static measurements. Traditionally the IFMs were measured by implanting transducers to the bone or using radiological methods. However, these methods are not suitable for either clinic utilization or measurement of IFMS when patients are doing movements which simulate their daily activities. We have designed a dynamic IFMs measuring device.

It includes a displacement transducer array, which is connected to the Ilizarov wires. This transducer array consists of 6 parallel linear displacement transducers, each of which is attached to the fixing wires of the fix-ator. This arrangement of transducers can fit into the configuration of Stewart Platform. The Reverse Stewart Platform algorithm was employed to calculate IFMs. Without measuring the bone fracture segments directly, the two segments were fitted into two planes virtually. By studying the relative movements of the two virtual planes, the algorithm transfers the relative movement to relative axial & shear translation, and relative bending & torsion rotation, between the two fracture segments. Wireless interface was used to transfer the displacement readings from the transducer array to the computer. This setup allows patient perform activities which represent their routine activities.

In laboratory studies, we found the error of this system to be related to the IFMs. For small movements around 100 micron, the absolute error was 50 micron, whereas for larger movements around 1 mm, the error was within 0.22mm.

This real time monitoring method will allow kinematical and kinetic studies on fracture patients treated with Ilizarov frame. Measurements obtained using this novel device will reflect the natural pattern of IFMs during the patients’ daily life. Since use of the device requires no additional pin, wire or operative procedure, it will be clinically applicable. The accurate real-time IFMs measurements will help elucidate the complex interplay between movement and bone formation.

Introduction: The Trent arthroplasty register reported that results of Hip arthroplasty in general setup were less than that reported from specialist centres by 5%. This independent prospective study tests the hypothesis that results of Birmingham Hip Resurfacing arthroplasty from specialist centres would not accurately represent the outcome of hip resurfacing when performed in general setup.

Material and Methods: All patients were prospectively followed for at least five years at Oswestry Hip outcome centre. The surgeons carrying out the operation prospectively provided surgical details and thereafter patients were followed using Oswestry hip questionnaire (OSHIP) at fixed intervals. Survival was assessed by Kaplan-Meier method. The results were compared to the published results of BHR from specialist centers

Results: There were 679 patients, and 58 surgeons in the study. Mean age at operation was 51 years and mean follow up was 5.63 years. The predominant preoperative diagnosis was osteoarthritis. The mean OSHIP score was 89.5. There were 29 (4.2%) failures mostly due to fracture neck of femur (62%); all of them were revised to conventional THR. The Kaplan-Meier survival at seven years is 95.354%.

Discussion: Compared to the published results, there were 2 to 19 times high failure rate which is significantly higher (p=0.001) than the published studies. Hence we prove our hypothesis, as the results of BHR from specialist centres do not accurately reflect on the outcome in general setup. The discrepancy in the results that we have identified would help to identify the weak areas in the general setup, where most of the patients get benefited from BHR arthroplasty.

Introduction: The wear particles produced from the metal-on-metal hip prosthesis causes measurable rise of metal ion levels in the patient’s body fluids. Wear of the bearing is directly related to its use. The goal of this study is to test two hypotheses. Firstly, that exercise causes increased wear particles in vivo which can cause immediate measurable rise in the serum metal ion levels. Secondly, that this rise in metal ion level is different for different types of bearings.

Material and Methods: Eighteen participants were allocated to four different groups i.e. Birmingham Hip Resurfacing prosthesis group, Cormet 2000 resurfacing prosthesis group, Thrust plate prosthesis group (28mm metasul articulation) and group four with out any metal work. Blood samples were taken immediately before, immediately after and one hour after exercise. Plasma cobalt and chromium was determined using Inductively-Coupled-Plasma-Mass-Spectrometry and Dynamic-reaction-cell respectively with detection limit of 2nmol/l each.

Results: The four patient groups were comparable. A significant increase (p< 0.005) in serum cobalt and chromium of 13% and 11% respectively, was noticed after the exercise. Rise of cobalt levels in patients with a resurfacing MOM was 8.5 times (BHR group) and 6.5 times (Cormet group) larger than in those with a Metasul (p=0.021 and p=0.047). Neither rise of metal levels nor baseline levels correlated with any other factor (p> 0.27).

Discussion: Physiologic exercise causes immediate detectable rise in the serum metal ion levels. The increase is predominantly related to the size of the bearing surface. Exercise-related-cobalt-rise could be used to assess the tribology of the different metal on metal designs in vivo for future research

Aim: Concerns have been expressed that DMARDS may interfere with bone healing. Previous studies give conflicting advise and no consensus exist in current practise especially with the newer DMARDS such as Leflunomide, Etanercept, and Infliximab. The aim of this study was to assess the in-vitro effect of DMARDS and cox-2 inhibitors on Osteoblast activity.

Method: Osteoblasts were cultured from femoral heads obtained from five young otherwise healthy patients undergoing total hip replacement The cells were cultured using techniques that have been previously described. A computer aided design of experiment was used as a model for setting up the experiment on samples obtained from the five patients. Normal therapeutic concentration of the various DMARDS was added alone and in combination to the media. The cell growth was estimated after two weeks using spectrophotometric technique using Roche Cell proliferation Kit. Multiple regression analysis was used to estimate the best predictor of the final result.

Results: The most significant factor (p< 0.001) in predicting the ultimate response was the patient themselves. Cox-2 inhibitor (Etoricoxib) was found to have the most consistent effect although always in combination with some other drug which varied amogst different patients. Etoricoxib in fact had a stimulatory effect (R=0.219) on the osteoblast growth.

Conclusion: Different patients respond differently to the drugs. None of the DMARDS tested inhibit osteoblast proliferation and differentiation in-vitro. If osteoblastic activity is considered to be the primary factor responsible for bone healing, then an inhibition should not result in patients who are on these drugs.

The Trent arthroplasty register reported that results of Hip arthroplasty in general setup were less than that reported from specialist centres by 5%. This independent prospective study tests the hypothesis that results of Birmingham Hip Resurfacing (BHR) arthroplasty from pioneering centres would not accurately represent the outcome of hip resurfacing when performed in general setup.

All patients were prospectively followed for at least five years at Oswestry Hip outcome centre. The surgeons carrying out the operation prospectively provided surgical details and thereafter patients were followed using Oswestry hip questionnaire (OSHIP) at fixed intervals. Survival was assessed by Kaplan-Meier method. Results were compared to the published results of BHR from specialist centres.

There were 679 patients, and 58 surgeons in the study. Mean age at operation was 51 years and mean follow up was 5.63 years. The predominant preopera-tive diagnosis was Osteoarthritis. Mean OSHIP score was 89.5. There were 29 (4.2%) failures mostly due to fracture neck of femur (34%). Out of 14 failures in the first year, 9 (64%) were due to fracture neck of femur. The Kaplan-Meier survival up to eight years is 95.354% in the current study.

Compared to the published results, there were 2 to 19 times high failure rate which is significantly higher (p=0.001) than the published studies. Most of the early failures were due to fracture neck of femur in the first year. Hence we prove our hypothesis, as the results of BHR from specialist centres do not accurately reflect on the outcome in general setup. The discrepancy in the results is mostly due to fracture neck of femur in the early postoperative time. The results of this study will enhance awareness of the early trend in failures. Appropriate patient selection and meticulous surgical technique will help avoid this complication in the general setup, where most of the patients get benefited from BHR arthroplasty.

Objective: To compare the ability of a new composite bio-absorbable screw and two conventional metal screws to maintain fixation of scaphoid waist-fractures under dynamic loading conditions. Methods: Fifteen porcine radial carpi, whose morphology is comparable to that of human scaphoids, were osteotomized at the waist. Specimens were randomized in three groups: those in group I were fixed with a headed metal screw, in group II with a headless tapered metal screw, and in group III with a bio-absorbable composite screw. Each specimen was oriented at forty-five degrees and cyclically loaded using four blocks of 1000 cycles, with peak loads of 40, 60, 80 and 100 N, respectively. In case of gross failure the number of cycles to failure was determined. Otherwise, permanent displacement at the fracture site was measured after each loading block from a standardized high-magnification photograph using image analysis software (Roman v1.70, Institute of Orthopaedics, Oswestry). Statistical analysis was by ANOVA and tolerance limits.

Results: Nogrossfailureoccurred. Averagedisplacements after 4000 cycles up to 100N were 0.05mm±0.03SD (headed metal), 0.15mm±0.16SD (headless metal) and 0.29mm±0.11SD (composite) and differed significantly (p< 0.02). Using tolerance limits, the data allowed us to predict that with 95% certainty, displacement in 95% of any sample fixed with a headed metal screw will be below 0.17mm, headless metal screw below 0.84mm, and composite screw below 0.76mm.

Conclusion: Comparing two types of conventional metal screws and a new composite bio-absorbable screw to maintain scaphoid fixation under cyclic loading conditions, we found small average fracture displacements for all three screws. Moreover, even following severe cyclic loading conditions, clinically meaningful displacements of more than 1 mm are highly unlikely for any of the three screws. We therefore conclude that a new bio-absorbable composite screw can serve as an alternative to conventional screws when fixing scaphoid fractures.

Purpose: To investigate whether cement mantle thickness influence early migration of the stem after impaction grafting

Methods: Twelve artificial femora were prepared to mimic cavitary defects. After compacting morselized bone into the cavities, Exeter stems were cemented in place. By using all combinations of three sizes tamps and stems (0, 1 and 2), we created cement mantles of 0, 1, 2, 3 and 4 mm thickness. Bones with stems were placed in a testing machine and loaded cyclically to 2,500 N while measuring stem migration. Statistical analysis was by regression analysis. Outcomes were stem subsidence and retroversion, predictors were mantle thickness, tamp size and stem size.

Results: Average stem subsidence after 2500 cycles when using size 1 tamp and stem (2 mm mantle) was 0.94 mm. Cement mantle thickness significantly influ-enced stem subsidence (r=0.68, p=0.015). For a 0 mm mantle, subsidence was 0.59 mm and for a 4 mm mantle it was 2.54 mm. Cement mantle thickness also signifi-cantly influenced stem retroversion (r=0.62, p=0.031). Cement mantle thickness was a better predictor than tamp or stem size.

Discussion: Concern exists that inadequate cement mantles may affect stability of impaction-grafted stems. In our study, larger difference between tamps and stems gave substantially more subsidence and rotation, whereas a smaller difference reduced them. Concerns over thin mantles may have been premature.

In-vitro studies have shown that wear rates of the metal on metal (MOM) bearing hip prostheses decline once the bearing runs-in and the bearing subsequently enters a steady state wear phase. Baseline cobalt levels are thus expected to decline with time in patients. Several clinical studies have not found such a decline. Baseline cobalt levels are hence limited in their capacity to provide information on the wear performance of the bearing couple. We have demonstrated in a previous study that exercise causes a rise in plasma metal ion levels in patients with MOM bearing hip replacement. Would the exercise related cobalt rise be more sensitive to detect change in wear behaviour of the bearing couple? We tested the alternate hypothesis that exercise related rise in the plasma cobalt levels will correlate inversely with the duration of MOM implantation.

Sixteen patients with three different well functioning MOM bearing hip replacement [two types of resurfacing (BHR, Cormet) and Metasul] were included into the study. Patients were divided in to two groups based on time since implantation, an early group of mean 18 months and a late group of mean 57 months. Plasma levels of cobalt were measured before (baseline) and after 1 hour of maximal exercise (peak). The difference between baseline and peak for each patient provided the exercise related cobalt rise. A significant increase in plasma cobalt levels of 13% was noticed after the exercise (p < 0.005). Baseline Cobalt levels in the late group (53nmol/l) were higher than early group (44nmol/l) but the difference was not significant (p=0.45). However, the mean exercise related Cobalt rise levels was lower in late group (3.5nmol/l) than the early group (6.5nmol/l). This lower rise in cobalt level in the late group precisely reflects on the steady state wear as seen in in-vitro tests.

Baseline cobalt levels are limited in determining the in-vivo performance of the bearing couple. Exercise related rise in cobalt levels can differentiate the running in and steady state wear phases of metal on metal bearings and is thus a more accurate tool of assessing in-vivo wear performance of the bearing couple.

Introduction: Tension band wiring is a common technique for olecranon fracture fixation. The most commonly used material for the tension band is stainless steel wire. There are however problems associated with stainless steel wire. Ethibond (Ethicon Ltd, Edinburgh) has previously been cited as a suitable alternative material but not FiberWire. The biomechanical properties of FiberWire (Arthrex Ltd, Sheffield) as a tension band material have not been evaluated. This study aimed to investigate the properties of FiberWire and compare them with stainless steel wire and Ethibond.

Methods: Saw-bone olecranons were osteotomised identically to create an olecranon fracture. Identical tension band constructs were produced using stainless steel wire, Ethibond and FiberWire. The construct was tested by cyclical loading with an ESH dynamic testing machine (Brierley Hill, West Mids). A preload of 5N was applied before cyclical loading at levels up to 200N. The fracture gap was measured with a displacement transducer (Tokyo Sokki Kenkyujo Co, Japan).

Results: At loading up to 100N, the stainless steel wire allowed an average fracture gap of 200 micrometers. 5 gauge Ethibond allowed a larger fracture gap of 350 micrometers (p< 0.05). 2 gauge Fiberwire did not allow a significantly different fracture gap to Ethibond.

Discussion: The fracture gap with suture material was greater than with stainless steel wire, but still less then 0.5mm with loading of 100N. Free body diagram calculations determine that in a 70 kg man, this would correspond to the forces expected in extending the elbow against gravity. This means that these alternative materials are mechanically suitable for use in clinical practice for tension bands. This can avoid some of the complications of stainless steel wire.

Conclusion: 5 gauge Ethibond and 2 gauge FiberWire are biomechanically suitable as alternatives to stainless steel wire in tension band wire fixation of olecranon fractures.

Background: Articular cartilage injuries are very common. Small defects don’t heal on their own and large defects can’t regenerate new cartilage. This would largely be due to the fact that chondrocytes are embedded in a firm and tough matrix and hence can’t migrate to the defect site to regenerate a new cartilage tissue. So ultimate fate is patient getting early osteoarthritis. Cartilage defects in the knee may be symptomatic and cause pain, swelling and catching. There are several different surgical procedures available to treat cartilage injuries, but no method has been judged superior. The ultimate aim of the treatment is restoration of normal knee function by regeneration of hyaline cartilage in the defect, and to achieve a complete integration to the surrounding cartilage and underlying bone. Arthroscopic debridement and lavage may give symptomatic relief for a limited time. Autologous Chondrocytes Implantation (ACI) was first described in 1994. Encouraging primary results were reported, and further research was promoted. Long-term results are encouraging. ACI is being done in Robert Jones & Agnes Hunt orthopaedic Hospital, Oswestry since last 8 years.

Methods: We studied a cohort of first 118 patients who underwent ACI for knee joint in this institute, focussing on their mid-term results. Patients having chondral defects were offered ACI. They all were explained the procedure and informed written consent was obtained. Patients filled in a self-assessed Lysholm forms before the operation. They also underwent pre-operative MRI scan of knee joint. ACI procedure consisted of three stages— Stage I —Arthroscopic harvest biopsy of cartilage and chondrocytes culture in lab. Stage II—Arthrotomy of the knee. The defect edges were freshened, covered by periosteum or chondroguide, which was sutured to the cartilage with 6-0 vicryl. Chondrocytes were injected underneath this patch. Post-op CPM and Physiotherapy. Stage III—1-year arthroscopic surgery. Assessment was done with Lysholm score, MRI scan, histological and arthroscopic analysis. Patients were followed up clinically thereafter with yearly Lysholm scores.

Results: 118 patients with an average age of 35 years (15–59) underwent ACI for knee in last 8 years. 93 patients had single defect, 24 had multiple (> 1) chondral defects, with mean area 4.81 cm2. MRI showed a good integration of defect with surrounding cartilage with varied signal intensities. About 55–56% patients underwent some or other form of trimming, which improved immediate results. However only 50 % of these were symptomatic. Defects on MFC did well as compared to other sites, followed by on trochlea. Defects on patella showed poor results, though the number is less for comparison. Total 79 specimens of 1-year histology showed good healing with formation of fibrocartilage (40), mixed (20) and hyaline (8), fibrous tissue (6), bone in 1 case and inconclusive in 2 cases. Mean pre-op Lysholm score was 50.16. Average score at one year was found to be 69.52.

Conclusion: Results of ACI are encouraging. Patients continued to improve slowly over a period of time, achieving maximum function between one and 2 years post-surgery. Our study showed that there after their scores remained static.

Introduction: Diaphyseal fracture at a cortical perforation is the commonest postoperative complication of hips revised with impacted morsellised bone. To reduce fracture risk, surgeons can apply mesh, augment the bone with plate or strut graft, or bypass the perforation with a longer stem. No biomechanical data exists to choose between these alternatives. The objective of this study was to compare the above methods of cortical repair in terms of (i) bone fracture risk and (ii) stem migration.

Methods: Fourteen large composite femora (Sawbones, Malmö, Sweden) were prepared to simulate cavitary defects. An 18×40 mm lateral cortical perforation was made in 12 diaphyses. These diaphyses were repaired with mesh only, mesh and plate, or mesh and strut graft (n=4 each). Strut graft and plate were fixed with cables. Porcine cancellous bone was morsellised and impacted into each cavitary defect. Simplex P bone cement was injected. In the 12 femora with repaired perforation, a standard or a long Exeter prosthesis, bypassing the perforation 2 cortical diameters, was implanted. Thus, 6 methods of defect repair were created (mesh, plate and strut, combined with either long or short stem, each n=2). Standard stems impaction-grafted in the two femora without perforation served as control (n=2). Femora were placed in a testing machine and loaded at 1 Hz with 100 cycles of joint and abductor force. Peak joint force was 2,500 N. Strain amplitudes at the perforation and stem migration were determined. Statistical analysis was by 2-way and 1-way ANOVA, and the Student-Newman-Keuls (SNK) post-hoc test.

Results: Stem length did not affect average defect strain if used with plate or strut graft (2x2 ANOVA, p=0.62). Four combinations remained for further analysis: standard stem with mesh, long stem with mesh, plate, and strut graft, with defect strains of 5250, 3620, 2940, and 2480 μstrain. In controls, strains were 1750 μstrain. Defect strains differed significantly (ANOVA, p=0.0004), with strains for standard stems with mesh significantly higher than all other groups, those for long stems with mesh significantly higher than controls, and those for plate or strut graft no different from controls (SNK). Maximum permanent subsidence was 0.71 mm and retroversion 1.6°. For repaired perforations, stem length did not affect subsidence (p=0.96), but repair method did (p=0.03, both 2-way ANOVA). For further analysis, subsidence of the three repair methods (mesh, plate and strut graft with subsidence of 0.24, 0.47 and 0.19 mm, resp.) was compared with that of controls (0.52 mm). Subsidence differed significantly (ANOVA, p=0.02), and stems with strut graft subsided significantly less than those with plate or controls (SNK). Permanent retroversion was similar for each group.

Dicussion: Non-reinforced defects with a standard stem generated high defect strain amplitudes. A long stem bypassing the defect reduced these strains by 30%, and might suffice in case of otherwise strong cortex. In other cases, augmentation of the perforated diaphysis with either strut graft or plate needed to minimise fracture risk. Stem migration in reconstructed perforated diaphyses was always less than control cases, suggesting stem migration is no specific problem in reconstruction.

Introduction: Many designs exist for the femoral component of cemented total hip arthoplasty, but cemented acetabular cups are largely similar. All are essentially hemispheres, made of polyethylene. An important factor determining survival time of cemented implants is cement penetration into the surrounding bone. To ensure sufficient penetration, many surgeons remove the smooth subchondral bone in the acetabulum and drill anchoring holes. This may however weaken the bone. Larger cement pressure during setting will improve penetration. For an acetabular cup, fixation at the rim is most important to prevent loosening, and therefore cement pressure should be high at the rim. A spherical geometry is not ideal to ensure high rim cement pressures. Based on a computer model of cement pressure generation during cup insertion, we designed an improved geometry to ensure higher rim pressures. The aim of this study is to compare the fixation strength of this new design to a conventional design. The effect of the design change will be compared with that of drilling anchoring holes and removing subchondral bone.

Methods: From a larger stock of young bovine acetabula, 14 similarly sized specimens were chosen. Twelve were prepared for a factorial experiment with three factors, based on three cup designs (Ogee either with or without flange, DePuy, Leeds, and the alternative design), preservation or removal of subchondral bone, and presence or absence of anchoring holes. Depth, diameter and position of the anchoring holes were chosen to optimise fixation strength. Two were prepared for replicates of two experiments with the new design, both with sub-chondral bone removed. The order of the experiments was randomised. CMW-3 cement (CMW-DePuy, UK) was hand-mixed for one minute. After four minutes, it was packed in the acetabulum and pressurised for one minute. Then a cup was inserted and manual force applied until setting of the cement. Next, acetabulum and cup were mounted in a materials testing machine and torque applied to the cup until gross failure. Applied force and displacement were sampled into a computer, and used to determine maximum torque.

Results and Discussion: Analysis was done in two steps. First, two-way ANOVA of main effects plus first order interactions was performed. Anchoring holes significantly increased strength (41±8 vs. 114±9 Nm; p=0.004, mean±SEM). No significant effect of reaming or cup design was found. For all experiments, the conventional cups with or without flange behaved almost identical. In step two, these two variations were combined into one “conventional” group, and three-way ANOVA with interactions was performed. Significant interaction between all three factors was found (p=0.02). This indicates that one unique combination (new cup design in acetabula with subchondral bone removed and without anchoring holes) achieved a high average strength. Under these circumstances, the fixation strength of the new design (114±9 Nm) was equal to the overall average achieved with anchoring holes. On average, the new design also had significantly larger fixation strength than a conventional spherical design (95±5 vs. 69±4 Nm; p=0.009). These results justify further studies.

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.

Methotrexate and Cox-2 inhibitors are thought to interfere with bone healing. There have been controversial results published in the literature. The effect of newer antirheumatoids (Leflunomide, Etanercept, Infliximab) has not been studied. The aim of this study was to find the in-vitro effect of methotrexate, newer anti-rheumatoids, steroids and cox-2 inhibitors on Osteoblasts. Osteoblasts were cultured from femoral heads obtained from young otherwise healthy patients undergoing total hip replacement. The cells were cultured using techniques that have been previously described. A computer aided design of experiment was used as a model for setting up the experiment on samples obtained from five patients. Normal therapeutic concentration of the various antirheumatoids was added alone and in combination to the media. The cell growth was estimated after two weeks using spectrophotometric technique using Roche Cell proliferation Kit. Multiple regression analysis was done to estimate the best predictor of the final result. Patient was found to be the most significant factor (p< 0.001) in predicting the ultimate response. Cox-2 inhibitor (Etoricoxib) was found to be the next best predictor (p=0.043). Etoricoxib in fact had a stimulatory effect (R=0.219) on the osteoblast growth, which was accentuated in the presence of other agents that varied amongst different patients. Different patients respond differently to the drugs. None of the antirheumatoids inhibit osteoblast proliferation and differentiation in-vitro. If osteoblastic activity is considered to be the primary factor responsible for bone healing, then an inhibition should not result in patients who are on these drugs.

Introduction Impaction bone grafting is an established technique in revision surgery to compensate bone loss. The technique involves “dynamic compaction” (compaction using repeated impacts from a moving weight) of cancellous bone particles into a defect until the material is strong enough to carry the patient’s load. The technique has two widely documented complications, per-operative bone fracture and subsidence of the prosthesis, both related to mechanical factors. Lack of bone compaction is the main cause for subsidence of the prosthesis and the large levels of impaction energy needed to ensure sufficient bone compaction are the main cause of fractures. No work exists that relates the number and energy of impacts to the degree of compaction obtained, or the degree of compaction obtained to the amount of subsidence during cyclic loading. The aim of the current study was to determine these relations.

Methods For each sample, six grams of freshly frozen morsellised porcine bone was placed in a 15 mm diameter by 40 mm high cylinder. Samples were compacted dynamically with a range of energies by releasing a weight of 0.702 kg 20 times from a height of either 10, 20, 25 or 50 mm on an impactor. Resulting force on and deformation of the bone column during each impact were sampled at a rate of 3000 Hz. The data was summarized by collecting peak load and concurrent displacement from each consecutive impact. Compacted and non-compacted samples were placed in a testing machine (ESH Testing Ltd.) and cyclically loaded with a peak load of 50, 90 or 180 N (corresponding to 0.28, 0.51 and 1.0 MPa) while collecting applied force and displacement.

Results Peak stresses during dynamic compaction proved an exponential function of concurrent strain. Curves for all four levels of applied energy coincided on a single path in the stress-strain plane although, for an equal number of impacts, higher energy levels generated higher stresses. Permanent strain proved a logarithmic function and peak stress a power function of (impact number × energy1.5). The higher the impaction energy used for compacting the graft the lesser was the displacement and hence the subsidence under cyclical loading at a given force. With virgin bone graft under cyclical loading, the displacement was maximum in the first cycle. With subsequent cycles the subsidence was minimal and was independent of the force of cyclical loading.

Conclusions Stress was a function of (blow number × energy1.5), suggesting that halving the energy level per impact would require three times as many blows to give a comparable stability. This can potentially reduce the incidence of intra-operative fractures. Higher impaction energies might reduce the subsidence of femoral component during the first steps that the patient takes and though subsidence is dependent on the force of cyclical during initial cycles, further subsidence is independent of the same.