The aim of this study was to develop an in vitro GAG-depleted patella model and assess the biomechanical effects following treatment with a SAP:CS self-assembling hydrogel. Porcine patellae (4–6 month old) were harvested and subject to 0.1% (w/v) sodium dodecyl sulfate (SDS) washes to remove GAGs from the cartilage. Patellae were GAG depleted and then treated by injection with SAP (∼ 6 mM) and CS (10 mg) in Ringer's solution through a 30G needle. Native, GAG depleted and SAP:CS treated patellae were tested through static indentation testing, using 15g load, 5mm indenter over 1hr period. The degree of deformation of each group was assessed and compared (Mann-Whitney, p<0.05). Native, GAG depleted, sham (saline only) and SAP:CS treated paired patellae and femurs were additionally characterized tribologically through sequential wear testing when undergoing a walking gait profile (n=6 per group). The cartilage surfaces were assessed and compared (Mann-Whitney, p<0.05) using the ICRS scoring system, surface damage was illustrated through the application of Indian ink.Abstract
Objectives
Methods
The clinical success of osteochondral autografts is heavily reliant on their mechanical stability, as grafts which protrude above or subside below the native cartilage can have a negative effect on the tribological properties of the joint [1]. Furthermore, high insertion forces have previously been shown to reduce chondrocyte viability [2]. Commercial grafting kits may include a dilation tool to increase the diameter of the recipient site prior to insertion. The aim of this study was to evaluate the influence of dilation on the primary stability of autografts. Six human cadaveric femurs were studied. For each femur, four 8.5 × 8mm autografts were harvested from the trochlear groove and implanted into the femoral condyles using a Smith & Nephew Osteochondral grafting kit. Two grafts were implanted into dilated recipient sites (n=12) and two were implanted with no dilation (n=12). Insertion force was measured by partially inserting the graft and applying a load at a rate of 1 mm/min, until the graft was flush with the surrounding cartilage. Push-in force was measured by applying the same load, until the graft had subsided 4mm below congruency. Significance was taken as (p<0.05). Average maximum insertion force of dilated grafts was significantly lower (p<0.001) than their non-dilated equivalent [28.2N & 176.7N respectively]. There was no significant difference between average maximum push-in force between the dilated and non-dilated groups [1062.8N & 1204.2N respectively]. This study demonstrated that significantly less force is required to insert dilated autografts, potentially minimising loss of chondrocyte viability. However, once inserted, the force required to displace the grafts below congruency remained similar, indicating a similar degree of graft stability between both groups.
PEEK-OPTIMA™ has been considered as an alternative to cobalt chrome in the femoral component of total knee replacements. Whole joint wear simulation studies of both the tibiofemoral and patellofemoral joints carried out to date have shown an equivalent wear rate of UHMWPE tibial and patella components against PEEK and cobalt chrome (CoCr) femoral components. In this study, the influence of third body wear on UHMWPE-on-PEEK was investigated, tests on UHMWPE-on-CoCr were carried out in parallel to compare PEEK to a conventional femoral component material. Wear simulation was carried out in simple geometry using a 6-station multi-directional pin-on-plate simulator. 5 scratches were created on each PEEK and CoCr plate perpendicular to the direction of the wear test using a diamond stylus to produce scratches with a geometry similar to that observed in retrieved CoCr femoral components. To investigate the influence of scratch lip height on wear, scratches of approximately 1, 2 and 4µm lip height were created. Wear simulation of GUR 1020 UHMWPE pins (conventional, non-sterile) against the plates was carried out for 1 million cycles (MC) using 17g/l bovine serum as a lubricant using kinematic conditions to replicate the average contact pressure and cross-shear in a total knee replacement. Wear of UHMWPE pins was measured gravimetrically and the surface topography of the plates assessed using a contacting Form Talysurf. Wear factors of the pins against the scratched plates were compared to unscratched controls (0µm lip height). Minimum n=3 for each condition and statistical analysis carried out using ANOVA with significance taken at p<0.05.Introduction
Methods
PEEK-OPTIMA™ has been considered as an alternative to cobalt chrome in the femoral component of total knee replacements. Wear simulation studies of both the tibiofemoral and patellofemoral joints carried out to date have shown an equivalent wear rate of UHMWPE tibial and patella components against PEEK and cobalt chrome (CoCr) femoral components implanted under optimal alignment conditions. In this study, fundamental pin-on-plate studies have been carried out to investigate the wear of UHMWPE-on-PEEK under a wider range of contact pressure and cross-shear conditions. The study was carried out in a 6 station multi-axial pin-on-plate reciprocating rig. UHMPWE pins (conventional, non- sterile) were articulated against PEEK-OPTIMA™ plates, initial Ra ∼0.02µm. The lubricant used was 25% bovine serum (17g/l) supplemented with 0.03% sodium azide. The contact pressure and cross-shear ratio conditions were selected to replicate those in total knee replacements and to be comparable to previously reported studies of UHMPWE-on-CoCr tested in the same pin-on-plate simulators. Contact pressures from 2.1 to 25.5MPa were created by changing the diameter of the contact face of the pin, the cross-shear ratios ranged from 0 (uniaxial motion) to 0.18. Wear of the UHMWPE pins was measured gravimetrically and the surface topography of the plates assessed using a contacting Form Talysurf. N=6 was carried out for each condition and statistical analysis carried out using ANOVA with significance taken at p<0.05.Introduction
Methods
Bone void fillers are increasingly being used for dead space management in arthroplasty revision surgery. The aim of this study was to investigate the influence of calcium sulphate bone void filler (CS-BVF) on the damage and wear of total knee arthroplasty using experimental wear simulation. A total of 18 fixed-bearing U2 total knee arthroplasty system implants (United Orthopedic Corp., Hsinchu, Taiwan) were used. Implants challenged with CS-BVF were compared with new implants (negative controls) and those intentionally scratched with a diamond stylus (positive controls) representative of severe surface damage (n = 6 for each experimental group). Three million cycles (MC) of experimental simulation were carried out to simulate a walking gait cycle. Wear of the ultra-high-molecular-weight polyethylene (UHMWPE) tibial inserts was measured gravimetrically, and damage to articulating surfaces was assessed using profilometry.Objectives
Methods
PEEK-OPTIMA™ has been considered as an alternative bearing material to cobalt chrome in the femoral component of total knee replacements. To better understand the tribology of UHMWPE-on-PEEK-OPTIMA™ and to find the most appropriate environmental conditions under which to test this novel bearing material combination, a series of tests under different protein lubricant concentrations at rig (∼24°C) and elevated temperature (∼35°C) were carried out in simple geometry wear and friction rigs. Under all conditions, the wear of UHMWPE-on-PEEK-OPTIMA™ was compared to UHMWPE-on-cobalt chrome (CoCr). The pins used were GUR1020 UHMWPE (conventional, non-sterile) and the plate material was either polished CoCr (Ra<0.01µm) or PEEK-OPTIMA (Ra∼0.03µm) provided by Invibio Ltd, UK. The wear simulation was carried out in a six station reciprocating rig. The kinematic conditions were consistent for all tests and reflected the average cross shear and contact pressure (3.2MPa) in a total knee replacement. Tests were carried out at either rig running temperature (∼24°C) or at elevated temperature (∼35°C) and in varying protein lubricant concentrations (0, 2, 5, 25 and 90%). Wear of the UHMWPE pins was determined by gravimetric analysis. The pin-on-plate friction rig study was carried out at rig temperature in 0, 2, 5, 25 and 90% serum and reflected the contact pressure used in the wear tests. Measurements were taken using a piezoelectric sensor and the steady state friction derived. At least 3 repeats were taken for each study, statistical analysis carried out using ANOVA with significance taken at p<0.05.Introduction
Methods
Experimental wear simulation of an all-polymer knee implant has shown an equivalent rate of wear of UHMWPE tibial components against PEEK-OPTIMA™ and cobalt chrome femoral components of a similar initial geometry and surface topography. However, when the patella is resurfaced with an UHMWPE patella button, it is important to also ascertain the wear of the patella. Wear debris from the patella contributes to the total volume of wear debris produced by the implant which should be minimised to reduce the potential for osteolysis and subsequent implant loosening. The aim of this study was to investigate the wear of the patellofemoral joint in an all-polymer knee implant. The wear of UHMWPE patellae articulating against PEEK-OPTIMA™ femoral components was compared to UHMWPE articulating against cobalt chrome femoral components. Six mid-size (size C) PEEK-OPTIMA™ femoral components (Invibio Knee Ltd., UK) and six cobalt chrome femoral components of similar initial surface topography and geometry were coupled with 28mm all-polyethylene GUR1020 patellae (conventional, EO sterile) (Maxx Orthopaedics, USA). The implants were set up in a ProSim 6 station electromechanical knee simulator (Simulation Solutions, UK) which was modified for testing the patellofemoral joint. 3 million cycles (MC) of wear simulation was carried out under kinematics aiming to replicate a gait cycle adapted for an electromechanical simulator from previous work by Maiti et al. The simulator used has six degrees of freedom of which four were controlled; axial force up to 1200N, flexion/extension 22°, superior-inferior (SI) displacement (22mm) and Abduction-adduction (AA) (4°). The SI and AA were displacement controlled and driven through the patella. The medial-lateral displacement and tilt (internal/external rotation) of the patella were passive so the patella button was free to track the trochlear groove. The lubricant used was 25% bovine serum supplemented with 0.03% sodium azide to retard bacterial growth. The wear of patellae was determined gravimetrically with unloaded soak controls used to compensate for the uptake of moisture by the UHMWPE. The mean wear rate ± 95% confidence limits were calculated and statistical analysis was carried out using ANOVA with significance taken at p<0.05.Introduction
Materials and Methods
Calcium sulfate bone void fillers (CS-BVF) are increasingly being used for dead space management in infected arthroplasty revision surgery. The use of loose beads of CS-BVF close to the articulating surfaces of an implant means there is potential for them to migrate between the articulating surfaces acting as a third body particle. The aim of this study was to investigate the influence of CS-BVF on the third body wear of total knee replacements. The influence of CS-BVF on wear was investigated using the commercially available CS-BVF ‘Stimulan’ (Biocomposites Ltd., UK) and posterior stabilised U2 total knee replacement system implants (United Orthopaedic Corp., Taiwan). The experimental wear simulation was performed using a six station ProSim electropneumatic knee simulator (Simulation Solutions, UK) running the Leeds intermediate kinematics input profile [1]. To investigate the damage that could be caused by the third body particles, 5cc of CS-BVF beads (excess) were placed on the tibial component of the implant, the simulator was run dry for 60 cycles before adding lubricant (25% bovine serum supplemented with 0.03% sodium azide) and running for an additional 115,000 cycles representative of the 6–8 weeks the CS-BVF are present in the body prior to their resorption. The surface topography of the cobalt chrome femorals was analysed using contacting profilometry to ascertain whether the third body particles of CS-BVF had damaged the surfaces. To investigate the influence of CS-BVF on the third body wear of the UHMWPE tibials, 3 million cycles (MC) of wear simulation was subsequently carried out. The wear of the UHMWPE tibials was assessed gravimetrically and the wear of implants tested with CS-BVF was compared to the wear against negative controls (initial Ra∼0.02µm) and positive controls (initial Ra ∼0.4µm) damaged with a diamond stylus. N=6 was completed for each condition, statistical analysis was carried out using ANOVA with significance taken at p<0.05.Introduction
Methods
There is a demand for longer lasting arthroplasty implants driving the investigation of novel material combinations. PEEK has shown promise as an arthroplasty bearing material, with potentially relatively bio inert wear debris [1]. When coupled with an all-polyethylene tibial component this combination shows potential as a metal-free knee. In this study, the suitability of PEEK Optima® as an alternative to cobalt chrome for the femoral component of total knee replacements was assessed using experimental knee wear simulation under two kinematic conditions. Three cobalt chrome and three injection moulded PEEK Optima® (Invibio Biomaterial Solutions, UK) femoral components of similar geometry and surface roughness (mean surface roughness (Ra) ∼0.02µm) were coupled with all-polyethylene GUR1020 (conventional, unsterilised) tibial components in a 6 station ProSim knee simulator (Simulation Solutions, UK). 3 million cycles (MC) of wear simulation were carried out under intermediate kinematics (maximum anterior-posterior (AP) displacement 5mm) followed by 3MC under high kinematics (AP 10mm) [2] with 25% serum as the lubricant. The wear of the tibial component was assessed gravimetrically. At each measurement point, the surface roughness of the femoral components was determined using contacting profilometry and throughout testing, the bulk lubricant temperature was monitored close to the articulating surfaces. Statistical analysis was carried out using ANOVA, with significance at p<0.05.Introduction
Methods
UHMWPE articulating against PEEK-OPTIMA® has the potential for use as a novel bearing couple in joint arthroplasty due to its potentially low wear rates and the bioinertness of its wear debris. The aim of this study was to investigate the role of protein in the lubricant on the wear of UHMWPE articulating against PEEK at both room and physiological temperature. The wear of GUR1020 UHMWPE pins articulating against PEEK plates (Ra ∼0.06µm) was compared to highly polished cobalt chrome plates (Ra <0.01µm) in a 6-station multi-axial pin-on-plate rig using kinematics to replicate those in total knee arthroplasty. Tests were carried out at either ∼20°C or ∼36°C and wear was investigated under varying concentrations of bovine serum (0, 25 or 90%). Studies were carried out for 1 Million cycles with wear of the UHMWPE pins assessed gravimetrically using unloaded soak controls to compensate for moisture uptake. Statistical analysis was carried out using ANOVA with significance taken at p<0.05.Introduction
Methods
When third body particles originating from bone cement or bone void fillers become trapped between articulating surfaces of joint replacements, contact surfaces may be damaged leading to accelerated wear and premature failure of the implant. In this study, the damage to cobalt chrome counterfaces by third body particles from PMMA bone cement (GMV, DePuy) and various bone void fillers was investigated; then wear tests of UHMWPE were carried out against these surfaces. Third body particles of polymerised GMV bone cement and the bone void fillers; OsteoSet (with tobramycin), Stimulan and Stimulan+ (with vancomycin and tobramycin) (provided by Biocomposites Ltd.) were trapped between an UHMWPE pin and a highly polished cobalt chrome plate. A load of 120N was applied to the pin and using an Instron materials testing machine, the plate was pulled beneath the pin to recreate third body damage [1]. The resulting surface topography of the plate was analysed using white light interferometry (Bruker NPFLEX). Pin on plate wear tests of GUR 1020 UHMWPE pins were carried out against the plates perpendicular to the direction of damage for 500,000 cycles in 25% bovine serum using a 6-station multi-axial reciprocating rig under conditions to replicate the kinematics in total knee replacement. Wear of the pins was determined by gravimetric analysis and results were compared to negative (highly polished) control plates and positive controls scratched with a diamond stylus (lip height 2µm). Statistical analysis was carried out using one-way ANOVA with significance taken at p<0.05.Introduction
Methods
Extracorporeal irradiation and re-implantation of a bone segment is a technique employed in bone sarcoma surgery for limb salvage in the setting of reasonable bone stock. There is neither consensus nor rationale given for the dosage of irradiation used in previous studies, with values of up to 300Gy applied. We investigated the influence of extracorporeal irradiation on the elastic and viscoelastic properties of bone. Bone specimens were extracted from mature cattle and subdivided into thirteen groups; twelve groups exposed to increasing levels of irradiation and a control group. The specimens, once irradiated, underwent mechanical testing in saline at 37°C. Mechanical properties were calculated by experimental means which included Young's Modulus, Poisson's Ratio, Dissipation Factor, Storage Modulus, Loss Modulus and Dynamic Modulus. These were all obtained for comparison of the irradiated specimens to the control group. We found there to be a statistically significant increase in Poisson's ratio after increasing irradiation doses up to 300Gy were applied. However, there was negligible change in all other mechanical properties of bone that were assessed. Therefore, we conclude that the overall mechanical effect of high levels of extracorporeal irradiation (300Gy) is minute, and can be administered to reduce the risk of malignancy recurrence.
Unicompartmental knee replacement (UKR) is associated with higher revision rates than total knee replacement and it has been suggested that surgeons should receive specific training for this prosthesis. We investigated the outcome of all UKR in a district general hospital over ten years. All patients who had received UKR from 2003 to 2013 were identified from theatre records, as were all revision knee arthroplasties. We contacted all patients (or their GP) with no known revision to ascertain UKR status. A life table analysis was used for three categories: all surgeons and types of UKR, Oxford UKR only and Oxford UKR by surgeons with specific training. There were 319 UKR (one loss to follow up), four types of prosthesis, 21 failures and a 5-year cumulative survival rate of 91.54%. There were 310 Oxford UKR with 17 failures and 5-year survival 93.56%. Surgeons with training in use of Oxford UKR completed 242 replacements with 10 failures and 5-year survival of 95.68%. In comparison with results for Oxford UKR in 11th annual NJR report, our results are satisfactory and support continued use of this prosthesis in a non-specialist centre. Our established programme of surveillance will monitor the survival of UKR in our hospital.
Extracorporeal irradiation and re-implantation of a bone segment is a technique employed in bone sarcoma surgery for limb salvage in the setting of reasonable bone stock. There is neither consensus nor rationale given for the dosage of irradiation used in previous studies, with values of up to 300Gy applied. We investigated the influence of extracorporeal irradiation on the elastic and viscoelastic properties of bone. Bone specimens were extracted from mature cattle and subdivided into thirteen groups; twelve groups exposed to increasing levels of irradiation and a control group. The specimens, once irradiated, underwent mechanical testing in saline at 37°C. Mechanical properties were calculated by experimental means which included Young's Modulus, Storage Modulus and Loss Modulus. These were all obtained for comparison of the irradiated specimens to the control group. There were non-significant negligible changes in all of the mechanical properties of bone that were assessed with increasing dosage of irradiation. Therefore, we conclude that the overall mechanical effect of high levels of extracorporeal irradiation (300Gy) is minute, and can be administered to reduce the risk of malignancy recurrence.
First-time anterior dislocation of the shoulder is associated with the development of recurrent instability. It is recognised that patients with recurrent instability often have osseous defects. Using 3D computerised tomography (3DCT) it is possible to quantify these defects. Whether these defects are present after the primary dislocation or occur progressively from multiple dislocations is unclear. We correlated the presence of Hill-Sachs lesions and anterior glenoid bone loss with evidence of recurrent dislocation and clinical outcomes. 78 patients were followed up for two years. All underwent a 3DCT within a week of injury. Standardised images of the humeral head and glenoid were produced. Using standardised digital techniques bone loss was measured. 39% of the patients developed further instability. Average Hill-Sachs circumferential length = 15.23%. Average Hill-Sachs surface area = 5.53%. The length and surface area of the Hill-Sachs lesions were significantly associated with further instability. (p=0.019 and p=0.003). Average en face glenoid surface area loss=1.30% with no association to instability (p=0.685). There was poor correlation between the size of the glenoid lesion and the size of the Hill-Sachs lesion. Results showed that age and increasing size of the Hill-Sachs lesions result in a higher rate of instability. Interestingly glenoid bone loss was relatively low and did not predict recurrent instability. The size of the Hill-Sachs lesion does not have a linear relationship with glenoid bone loss. Further work defining the morphology of the Hill-Sachs lesion and its engagement with a glenoid defect is required.
Several human conditions have a tendency to affect one side of the body over the other. Do lumbar disc prolapses have such a tendency? We sought to answer this question by an analysis of operated cases. Primary lumbar microdiscectomy cases were identified using the coding system. 1286 cases were identified and in 764 the laterality was not recorded. Electronic records were then examined to establish, where possible, the side of the procedure from the clinic letter or discharge summary. 22 cases were eliminated due to miscoding (laminectomy, instrumentation, revision) and in 24 the side of the operation could not be established. In the remaining 1240 cases (96.4%) the laterality was determined. Patients who underwent primary lumbar microdiscectomy in a single neurosurgical unit over a 5-year period (2002-2007). Procedures were bilateral, left or right. 126 cases were bilateral. There were 1114 defined lateral cases. 618 (55.5%) were on the left compared to 496 (44.5%) on the right. The ratio of left to right is close to 5:4. The null hypothesis was that the number of left and right sided operations would be equal. The findings of this study were statistically highly significant (p value < 0.001, binomial test) and the null hypothesis could be rejected. There is a small but definite preponderance of left sided over right sided cases at a ratio of 5:4. This finding may have implications regarding our understanding of both the epidemiology and biomechanics of lumbar disc prolapse.
A Morton's neuroma is a painful forefoot disorder characterised by plantar pain and toe paraesthesia. Many treatments have been tried including modification of shoe wear, injections and surgery. The results from different treatment modalities are extremely variable in the scientific literature. We reviewed 79 patients who presented with an ultrasound proven Morton's Neuromata at an average of 60 months following treatment in a patient blind randomised trial. 35 had surgery with resection of the Morton's Neuromata. We compared the results of the patients who had had a steroid injection and surgery, a steroid injection alone, a placebo injection and then surgery and a placebo injection alone. We looked at the requirement for further consultations, pain scores, activity restrictions, footwear restriction, overall satisfaction with their treatment and overall quality of life scores. We found no significant difference between the groups. Overall 80% of the surgical patients had a good or excellent result and 67% of the non- operatively managed patients had a good or excellent result. There was no difference in their quality of life scores. Previous studies have shown little benefit in steroid injections in the treatment of Morton's Neuromata. We conclude at the five year mark there is no significant differences between operating on Morton's Neuromata and treating them conservatively. Further research should focus on comparing operative vs conservative treatment in the short to medium term. In order to justify the risks and costs of surgery.
At one year follow up functional testing was performed including range of movement. This tested for grip strength, multiple postional strengths and a functional score looking at activities of daily living.
We also showed that fractures that are most likely to malunite show a significantly poorer functional outcome and weaker grip strength.
In an age where patients and practitioners strive to ever increasing levels of knowledge this study allows us to counsel patients in their likely functional outcomes more accurately.
Despite increasing scientific investigation, the best method for preventing post-operative deep vein thrombosis remains unclear in patients undergoing a total hip replacement. In the wake of the recent controversial National Institute for Health and Clinical Excellence Clinical Guidelines on the prevention of thrombo-embolism, we felt it was timely to survey current Scottish Surgeons thrombo-prophylactic practice when performing total hip replacements. E-mail questionnaires were sent to all Scottish Orthopaedic consultants. They were asked about routine pharmacological and mechanical prophylaxis in patients undergoing total hip replacement. Comparison was made with a previous survey done in 2003. The response rate was 75%. The survey showed an increased use of pharmacological prophylaxis from 93% to 100%. This was due to the increased use of aspirin, from 51% to 64%. The use of Low molecular weight heparin had remained the same at 51%. No surgeons routinely use Warfarin, low dose heparin or Fondaparinux. Use of graded compression stockings has increased from 59% to 70%. There is increasing evidence that patients undergoing total hip replacement should receive extended prophylaxis for up to 35 days. This could explain why aspirin is commonly used. Most guidelines, however, do not recommend this drug. With the recent launch of two new oral agents we may see a huge change in prophylaxis in Scotland, as 94% of surgeons said they would use extended prophylaxis if a safe oral agent was found.
