Hip and knee wear simulators have been used by implant manufacturers and researchers for many years as a performance predictor and comparator for hip and knee implants. The clinical accuracy of these simulators in predicting wear depends heavily on the type of simulator as well as the methodology used. The joint lubricant used in the simulators is one crucial aspect that has been well studied in hip simulators. This study will compare the wear performance of a modern total knee replacement system using two commonly used simulator lubricants at various dilutions (Alpha Calf Serum and Bovine Calf Serum, Hyclone Labs). The Triathlon knee implant system (Stryker Orthopaedics) was used along with a six station knee wear simulator from MTS Systems to determine the effect of lubricant type and dilution.

Wear rates were found to be dependent on the type and dilution of the lubricant. At 0g/L protein concentration (100% water) wear rates were 4.8mm3/million cycles (mc). With the introduction of Bovine serum, wear rates increase to a peak of 24mm3/mc at 5g/L of concentration. Increased concentration of Bovine serum resulted in a decrease of wear rates. Wear rates for Alpha serum peaked at 28mm3/mc at 20g/L concentration with decreased wear rates at higher concentrations.

Knee implant wear performance is often characterized by wear simulation. As has been previously shown for hip simulations, this study shows the importance of choosing the correct lubricant type and dilution to correctly simulate wear performance. While this study cannot correlate any of the lubricants to the synovial fluid present in vivo, this study shows that 20g/L of Alpha serum produces the highest wear rates and should be used to determine worst case wear rates in the wear performance characterization of knee implants.

High tensile stress has been considered as a contributing factor to the rim fracture of polyethylene acetabular cup liner. We performed the 3 D Finite Element Analysis (FEA) to compare the stress patterns at the polyethylene liner rim as a function of polyethylene thicknesses and whether or not rim was supported by the titanium acetabular shell extension. Two 3.1 mm thick generic 52 mm titanium alloy acetabular shells with and without 2 mm high rim support extension were modelled. Six corresponding Ultra High Molecular Weight Polyethylene (UHMWPE) liners with inner bearing diameters ranging from 22 mm to 44 mm and same outer diameters, were fixed in the shells. A 2 450 N load was applied through the corresponding CoCr femoral heads to the rims of liners while the acetabular shells were fixed on the outer spherical surface. The FEA was performed in half body of the assembly. The maximum principal stresses at the rim regions of UHMWPE liners were recorded.

The results showed that in all rim supported conditions, the maximum principal stress were in compressive patterns, a preferred pattern to reduce the potential polyethylene liner fracture. In rim unsupported conditions, the stresses was in tensile on the internal bearing surface when polyethylene liner thickness was bellow 5 mm, or was bellow 9 mm if the average maximum principal stress cross the rim was considered.

We conclude that the metal rim support changes the stress pattern in the rim region of UHMWPE liner to compressive for all liner thicknesses. The stress pattern turns to tensile, or there will be a higher potential for rim fracture, if UHMWPE liner is unsupported and the polyethylene rim thickness is less than 9 mm.

Although components used this study did not include the locking details which add higher stress concentrations, the trend of stress patterns should follow the results found in this study.

Large and retracted rotator cuff tendon tears fail to repair, or re-tear following surgical intervention. This study attempted to develop novel tissue engineering approaches using tenocytes-seeded bioscaffolds for tendon reconstruction of massive rotator cuff tendon defect in rabbits. Porcine small intestine submucosa (Restore™) and type I/III collagen bioscaffold (ACI-MaixTM) were chosen as bioscaffold carriers for autologous tenocytes. Biological characterization of autologous tenocytes was conducted prior to the implantation. The tenocyte-seeded bioscaffolds were implanted as interposition grafts to reconstruct massive rotator cuff tendon defects in rabbits. In situ re-implantation of the autologous rotator cuff tendon, excised during defect creation served as a positive control. Histological outcomes were analysed and semi-quantitatively graded at four and eight weeks after surgery.

The results demonstrate that at four weeks both tenocyte-seeded bioscaffolds display inflammatory reaction similar to bioscaffold-only cuff reconstruction and the histological grading were inferior to control repair. However, at eight weeks inflammatory reaction of both tenocyte-seeded bioscaffolds were dramatically reduced as compared to bioscaffold alone. In addition, bioscaf-folds seeded with tenocytes generated similar histological appearance to that of the positive control.

The implantation of autologous tenocytes on collagen-based bioscaffold offers improved rotator cuff tendon healing and remodelling compared to the implantation of bioscaffold alone.

Remelted highly cross linked UHMWPEs have no detectable free radicals but the mechanical and fatigue properties are reduced because remelting changes the microstructure. Annealed highly cross linked UHMWPEs maintain the microstructure and mechanical properties but contain free radicals. A novel sequential irradiation and annealing process preserves the microstructure while providing enhanced oxidation resistance.

6_B_Material_e_Methods: GUR 1020 polyethylene was sequentially cross linked using three separate gamma radiation doses of 3 Mrad with an annealing step at 130 degrees C after each irradiation (SXL). Density was measured according to ASTM D1505. Crystallinity and thermal properties were determined according to ASTM D3417. Crystallite size/lamellar structure was determined by small angle x-ray scattering. Accelerated aging was carried out in an oxygen bomb under 5 atmospheres of oxygen at 70 degrees C for 14 days.

SXL density was 939.2 kg/cubic meter, identical to that for unirradiated UHMWPE and UHMWPE irradiated in nitrogen to 3 Mrad (gamma-N2). SXL crystallinity was 61.7%, compared to 61.3% and 59.2% for gamma-N2 and virgin UHMWPE, respectively. The long period spacing, crystal thickness and amorphous thickness were 38.2, 23.6 and 14.6 nm respectively for SXL and 38.9, 23.0 and 15.9 for gamma-N2. There was no statistical difference. Accelerated aging resulted in a white band for gamma-N2 with an oxidation index of 1.27. The response of SXL was the same as virgin UHMWPE e.g. crystallinity and density were unchanged with no white band formation and an oxidation index of 0.09.

By avoiding remelting, sequential irradiation and annealing preserves polyethylene microstructure. The sequential process allows more efficient cross linking of free radicals resulting in an oxidation resistance equivalent to that of virgin UHMWPE.

Neutron beam irradiation is currently being explored as an alternative modality to improve local control of sarcomas. The purpose of this study was to investigate the effects of a sarcoma-dose fast neutron therapy on the wear properties of standard and highly cross-linked polyethylene total hip arthroplasty liners

Two groups of 28 mm I.D. polyethylene liners were used in this study – conventional polyethylene liners (N2vac: 3Mrads innitrogen, Howmedica Osteonic, Allendale, NJ), and highly cross-linked liners (Crossfire: 10.5MRads total radiation dose, Howmedica Osteonics, Allendale, NJ). All liners were sterilized in a oxygen free environment and stored in inert nitrogen packages. The plastic cups were sandwiched between two tissue-equivalent blocks to simulate the human hip region and brought to the fast neutron therapy unit. The neutron beam is produced in a super conducting cyclotron by bombarding an internal beryllium target with 48.5 MeV deuterons [d(48.5)+BE]. The cups were exposed to a dose of 15 Gy represented a typical neutron-dose given to a sarcoma patient. Wear testing was then performed utilizing a hip simulator (MTS, EdenPrairie, MN) with matched 28 mm diameter CoCr femoral heads. Physiologic loading was simulated with biaxial cross-path motion and peak loads of 2450 N. All tests were performed in 50 percent diluted alpha-calf serum(Hyclone Laboratories, Logan, UT) to simulate human serum exposure. Every 250,000 cycles the serum was changed and samples were removed from the machine, cleaned and weighed. The volume loss measurement shown below used the weight loss to calculate the wear rate. The wear rate was converted to volume loss by dividing by the density. The value is given as millimeter scubed per million cycles (mm3/mc). Phase one cups were tested within one month of radiation. Phase two cups served as soaked controls, and spent 7months in calf serum prior to wear testing. A total of five million wear cycles were performed for each cup to simulate five years worth of use.

The Averaged volumetric wear loss data demonstrated significantly less wear in CrossfireÒ compared to N2vac in both neutron irradiated and non-irradiated samples. This suggests that in sarcoma cases of the hip involving adjuvant fast neutron therapy, highly crosslinked poly-ethylene should be utilized. Averaging all data there was no statistically significant difference between the neutron radiation and non-treated components for both material conditions (N2VacÒ and CrossfireÒ). A trend towards decreasing wear in phase two samples was noted which may represent a material change in the liners exposed to serum over time. In addition, larger than normal variability in wear rates was seen within each group. Further testing of these liners is planned to elucidate these phenomenon. Table 1: – Volumetric wear loss per group. UHMWPE Material Volumetric wear Loss (mm3/mc) Standard Deviation N2VacÒ Phase 1 29.6 1.6 N2VacÒ Phase 2 14.0 N/a Neutron treated N2VacÒ Phase 1 52.2 18.1 Neutron treated N2VacÒ Phase 2 20.9 0.8 CrossfireÒ Phase 1 3.0 0.9 CrossfireÒ Phase 2 2.0 0.6 Neutron treated CrossfireÒ Phase 1 2.5 0.5 Neutron treated CrossfireÒ Phase 2 1.9 0.03 Graph 1– Averaged volumetric wear loss values

Sarcoma-dose (15Gy) fast neutron therapy adversely affects the wear of standard polyethylene acetabular cups. The wear rate of the conventional gamma-inert sterilized polyethylene increased by more than 50% following a 15Gy fast neutron treatment. The highly cross-linked polyethylene (Crossfire), on the other hand, was immune to the effect of neutron treatment at the same dose. The mechanisms responsible forth is difference are unclear and warrant further investigation. The clinical implication of this study is that for sarcoma patient receiving total hip replacement, highly crosslinked poly-ethylene rather than standard polyethylene should be used for the acetabular cup.

Highly cross linked polyethylenes fall into two classes depending on whether annealing or remelting are used in processing. Annealed polyethylenes contain free radicals. Remelted polyethylenes have reduced mechanical properties but no free radicals. Research has now produced a highly cross linked polyethylene (SXL) that combines the advantages of each class.

GUR 1020 polyethylene was sequentially cross linked using three separate gamma radiation doses of 3 Mrad with an annealing step at 130 degrees C after each irradiation (Mrad total). Free radical concentration was measured by electron spin resonance. Accelerated aging was carried out in an oxygen bomb under 5 atmospheres of oxygen at 70 degrees C for 14 days. Tensile properties were determined according to ASTM D638. Wear measurements to 5 million cycles were made on an MTS hip joint simulator at 1 Hz using the Paul load curve with maximum load of 2450 N with alpha fraction bovine calf serum.

Free radical concentration was 14 x 10(14) spins/g for SXL compared to 1550 x 10(14)spins/g for GUR 1020 irradiated to 3 Mrad in nitrogen (gamma-N2). The maximum oxidation index was 0.09 for SXL, 0.09 for unirradiated UHMWPE, and 1.27 for gamma-N2 respectively. Mechanical properties exceeded the ASTM F648 specification and were unchanged by oxidative challenge. Wear rates were 1.35 cubic mm per million cycles for SXL and 46 cubic mm per million cycles for gamma-N2 respectively. Wear particle sizes were similar for the two materials

Sequential irradiation and annealing provides more complete cross linking of free radicals with a consequent reduction in free radical level. SXL has the same resistance to oxidative challenge as unirradiated polyethylene. Mechanical properties exceed the ASTM F648 values. Wear is reduced by 97% compared to that of gamma-N2. Sequential irradiation and annealing preserves the microstructure by avoidance of melting yet minimizes free radicals.

Introduction Contemporary highly crosslinked polyethylenes fall into two classes (annealed or remelted). Annealed polyethylenes contain free radicals. Remelted polyethylenes have reduced mechanical properties but no free radicals. SXL provides the advantages of both classes.

Materials and Methods GUR 1020 polyethylene was sequentially crosslinked using three separate gamma radiation doses of 3 Mrad with an annealing step at 130 degrees C after each irradiation (SXL).

The following were measured: free radical concentration (electron spin resonance), oxidation resistance (5 atmospheres of oxygen at 70 degrees C for 14 days), and tensile properties (ASTM D638). Hip simulator wear was determined (MTS machine, 5 million cycles, 1 Hz, Paul load curve with maximum load of 2450 N, alpha fraction bovine calf serum)

Results Free radical concentrations were 14 x 1014 and 1550 x 1014 spins/g for SXL and GUR 1020 irradiated to 3 Mrad in nitrogen (gamma-N2) respectively. Maximum oxidation index was 0.09 for SXL, 0.09 for unirradiated UHMWPE, and 1.27 for gamma-N2.

SXL tensile properties exceeded ASTM F648 and were unchanged by oxidative challenge.

Wear rates were 1.35 and 46 mm3 per million cycles for SXL and gamma-N2 respectively; wear particle sizes were similar.

Discussion and Conclusions Sequential irradiation and annealing provides more complete crosslinking with reduction in free radical level. SXL has the same resistance to oxidative challenge as unirradiated polyethylene. Mechanical properties exceed the ASTM F648 values. Wear is reduced by 97% compared to that of gamma-N2. SXL is the basis for next generation highly crosslinked UHMWPE.

Introduction: Highly crosslinked UHMWPEs have been widely used in total hip replacements but have seen limited use at the knee due to concerns over strength characteristics. A new process, sequential irradiation and annealing, overcomes these limitations.

Materials and Methods: GUR 1020 polyethylene was sequentially crosslinked using three separate gamma radiation doses of 3 Mrad with an annealing step at 130 degrees C after each irradiation (SXL).

Wear was determined by weight loss under normal walking and stair climbing conditions (MTS knee simulator, 5 to 10 million cycles, 1 Hz, maximum load of 2600 N to 3800 N, alpha fraction bovine calf serum). Scorpio CR and PS knees were evaluated using SXL and UHMWPE gamma sterilized to 3 Mrad in nitrogen (gamma-N2). Oxidative challenge was in 5 atmospheres of oxygen at 70 degrees C for 14 days.

Results: Scorpio gamma-N2 CR knees under normal walking conditions had a weight loss of 32.6 +/− 1.9 mg/million cycles compared to 6.5 +/− 1.6 mg/million cycles for SXL (p of 0.024). With Scorpio PS knees, the wear was 33.5 +/− 1.6 for gamma-N2 versus 7.7 +/− 0.7 mg/million cycles for SXL (p of 0.000009) subject to stair climbing simulation. Wear particle size was similar for SXL and gamma-N2. SXL knees showed no effect of oxidative challenge in a 10 million-cycle knee study.

Discussion and Conclusions: Wear is reduced by 80 percent and 77 percent respectively for CR and PS knees with SXL compared to gamma-N2. SXL has high resistance to oxidative challenge as shown by the lack of effect on knee wear results.

Introduction and Aims: Large or recurrent rotator cuff tendon tears are difficult to treat effectively. Collagen bio-scaffolds have become available to reinforce a tendon repair or as an interpositional graft. This study compares the suitability of two collagen bio-scaffolds for autologous tenocyte implantation, and assesses the in vivo rotator cuff healing response with these grafts in a rabbit model.

Method: Tenocytes were isolated from rabbit tendon, cultured and seeded onto the Restore patch (DePuy), or the Matricel (Verigen) collagen membrane. Serial scanning electron microscopy examined tenocyte integration with the bio-scaffold, and extra-cellular matrix synthesis over time. A rotator cuff tendon defect was created in 50 rabbits and repaired by either: a) direct suture to tuberosity; b) Matricel interposition graft; c) Matricel interposition with autologous tenocytes; d) Restore patch interposition graft; e) Restore patch interposition with autologous tenocytes. Gross and histological evaluation were performed at four weeks and eight weeks post-surgery.

Results: Scanning electron microscopy of the Matricel membrane showed a rough surface characterised by a loose arrangement of collagen fibres capable of cell adhesion. SEM at one, three and five days after cell seeding, showed progressive integration of tenocytes into the three-dimensional membrane structure with extra-cellular matrix neosynthesis in the spaces between the native collagen fibres. SEM of the Restore patch showed a relatively smooth surface of highly compacted collagen fibres. Serial SEM after cell seeding showed relatively less tenocyte integration onto the membrane surface though tenocyte replication and matrix neo-synthesis was observed. All 50 rabbits regained normal gait at two weeks post-surgery. At sacrifice, no tendon ruptures had occurred at either time point in any of the five groups. At four weeks, the Matricel and Restore bio-scaffold membranes were partially absorbed, and a florid lymphocytic inflammatory response was evident surrounding the remaining membrane. By eight weeks, graft tissue had been resorbed further, the inflammatory response had decreased, and the regenerating tendon showed progressive remodelling. Autologous tenocyte implantation on both membranes improved the reparative tendon histological grade at eight weeks compared to membranes without cell implantation, and was equivalent to the direct repair group.

Conclusion: Autologous tenocytes can be implanted onto both Matricel and Restore collagen bio-scaffolds. Though both Xeno grafts induce an anti-inflammatory response in vivo, membrane resorption subsequently occurs. The healing response of large rotator cuff defects treated with interpositional collagen grafts is improved with autologous tenocyte implantation in a rabbit model.

Introduction A procedure of selective musculo-tendinous lengthenings is presented as treatment for chronic lateral elbow pain. The rationale for surgery is to decrease tensile force at the lateral epicondyle and simultaneously reduce posterior interosseous nerve compression in the radial tunnel. This study presents biomechanical and clinical data on this surgical technique.

Methods In a human cadaver study, force transducer measurements were made in the common extensor tendon, and after sequential tensioning of the muscles arising from the lateral epicondyle. In a separate cadaver study, a balloon catheter measured pressure in the radial tunnel after sequential musculo-tendinous lengthening of the forearm extensor muscles. A preliminary clinical study was performed on 12 subjects (13 elbows). All had failed extensive conservative treatment and subsequently underwent combined musculo-tendinous lengthening of ECRB, EDC, and superficial head of supinator (SHS). In the clinical series, 75% of subjects were involved in Work Cover claims. Clinical outcomes in this small series were reviewed.

Results ECRB and EDC tensioning produced the largest force transducer measurements in the common extensor tendon at the lateral epicondyle. SHS increased force transducer measurements moderately, suggesting this muscle may also contribute to the clinical syndrome of lateral epicondylitis. ECRL and ECU tensioning lead to non significant increases in force transducer measurements. Radial tunnel pressure dropped substantially (77%) after musculo-tendinous lengthening of SHS. Lengthening of other forearm extensors had little effect on measured radial tunnel pressure. All subjects recorded improvement in visual analogue pain scores, with post-operative scores between zero and two. Grip strength was preserved or improved. By the criteria of Roles and Maudsley, nine elbows were excellent, two good, one fair and one poor. Overall 11 of the 12 subjects reported they would have the procedure again.

Conclusions This study demonstrates a biomechanical basis for SHS in the aetiology of lateral epicondylitis and radial tunnel syndrome, and supports a combined musculo-tendinous lengthening of ECRB, EDC, and SHS in the treatment of chronic lateral elbow pain. Satisfactory clinical results are reported in this group of patients including those involved in Work Cover claims.

Introduction Displaced fractures of the midshaft clavicle often results in malunion with angulation and foreshortening. The purpose of this study is to determine the secondary effects of clavicular shortening on the sternoclavicular joint and scapulo-thoracic relationship, and to evaluate the symptomatic and biomechanical outcome in these patients.

Methods A series of 10 patients each with a malunited fractured clavicle defined by relative shortening of more than 15 mm were examined. A self-administered questionnaire for assessment of symptoms and function of the ipsilateral shoulder was completed for each patient. Computer tomography and three dimensional reconstructions of both shoulders were undertaken for static anatomical measurements. Biomechanical testing comparing both shoulders in each patient measured strength and velocity of movement. All subjects were symptomatic in the injured shoulder.

Results There were statistically significant differences between injured and uninjured shoulders for both mean shoulder scores and visual analog global assessments of shoulder function. Clavicular shortening produced statistically significant increased upward angulation of the clavicle at the sternoclavicular joint (p< 0.005), increased lateral displacement of the scapula on the posterior wall, and anterior scapular version (p< 0.05). Biomechanical differences were also recorded including a reduction in muscular strength for adduction, extension, and internal rotation of the humerus and also a reduced peak abduction velocity in the injured shoulder (p< 0.05).

Conclusions Changes in static sternoclavicular and scapulothoracic relationships occur following short malunion of the clavicle and are possible mechanisms limiting shoulder function after this injury. This study provides evidence that consideration should be given to prevention of clavicle malunion by open reduction and internal fixation, especially in the young and active age group.

Introduction: Rotator cuff tears are a common injury which affects both the young athlete and the sedentary elderly alike. This condition is commonly treated with glucocorticoid injections as part of initial management. The effects, however, of these injections on the histology of collagen and the metabolism of tendon fibroblasts are still controversial.

Materials and methods: In this study, samples from 19 patients with rotator cuff tears were taken during definitive surgery to manage these tears. There was a history of glucocorticoid injections in all of the patients. The samples were examined in terms of histopathology using light microscopy, in situ hybridization to detect the presence of glucocorticoid receptor mRNA and TUNEL assay to determine the incidence of apoptosis.

Results: Light microscopy of hematoxylin-eosin stained samples from the study group showed marked cellularity although there were no signs of inflammation. The nuclei were noted to be rounded and a significant number showed pyknosis. Angiogenesis was also noted in the sections, consistent with previous finding of angio-fibroblastic hyperplasia as a characteristic of tendinosis. Collagen structure was noted to be abnormal, with longitudinal clefts and focal areas of marked disorganization of fibers. In situ hybridization showed a strong signal for glucocorticoid receptor mRNA in all of the samples. TUNEL assay also showed a strong signal for apoptosis of the tendon fibroblasts in the study group as compared to the control group which showed almost no signal.

Conclusion: Our results suggest that although an overall picture of hypercellularity is seen in cases of tendinosis and tendon tears, a high percentage of these cells are undergoing apoptosis. This may reflect a natural high rate of turnover of cells during the process of repair or may be due to exogenous factors. Glucocorticoids almost certainly affect metabolism of tendon fibroblasts and subsequently collagen structure as seen by the abundant expression of the receptor mRNA. However, a causal relationship between glucocorticoids and apoptosis of tenocytes is yet to be established.

Of 232 patients with evidence of lumbar spinal stenosis, 13 had symptoms of meralgia paraesthetica. Myelography demonstrated that in all but one of these 13 cases the L3-4 level was involved by stenosis; in 12 matched control patients with spinal stenosis, none had involvement at this level. We found that both the ligamentum flavum and the laminae at L3-4 level were thicker than in a control group. Decompressive laminectomy at the L3-4 level significantly reduced the area of hypo-aesthesia in the thigh, effecting complete cure in seven of the 11 cases. Meralgia paraesthetica is not uncommon in patients with spinal stenosis and is referable to changes at the L3-4 level. It seems that many cases of meralgia may have a spinal origin.