Purpose

To determine the effect that Titanium Nitride (TiN) coatings have on wear rates of ultra high molecular weight polyethylene (UHMWPE)

Purpose: To determine if Cobalt-Chrome (CoCr) femoral components of knee replacement components roughen significantly, and when significant roughening may start.

Methods:

Retrieval study:

14 knee replacement components were retrieved after revision procedures. The average surface roughness (Ra) of the articulating regions of each condyle was measured by surface profilometry and compared to Ra of non-articulating regions, which acted as controls on each implant.

In vitro testing:

Pin-on-plate testing of 6 paired CoCr pins and vacuum γ-irradiated UHMWPE discs was carried out under a force of 2.3kN at 1Hz to investigate how the articular Ra of CoCr pins varied with increasing number of cycles. Ra was measured at 0, 10, 100 and 1000 cycles using surface profilometry.

Results:

Retrieval analysis:

Average medial femoral condyle Ra was significantly greater than control Ra (p=0.040). Average lateral femoral condyle Ra was not significantly greater than control Ra (p=0.158). Significantly higher average Ra was seen on the medial condyles when compared with the lateral condyles (p < 0.05). 8/14 retrieved femoral components had ≥1 significantly roughened condyle (p< 0.05).

In vitro testing:

At 100 and 1000 cycles the Ra of the CoCr pins was significantly greater than Ra at 0 cycles (p< 0.05).

Conclusion: A large proportion of femoral components of knee replacement implants roughen significantly in vivo, a finding supported by our in vitro testing which indicates that roughening may begin very early on. This may have important implications for aseptic loosening of knee replacement components. However, the average Ra of those CoCr surfaces significantly (p< 0.05) roughened was within acceptable limits for orthopaedic implants (0.050μm).

There has been only one limited report dating from 1941 using dissection which has described the tibiofemoral joint between 120° and 160° of flexion despite the relevance of this arc to total knee replacement. We now provide a full description having examined one living and eight cadaver knees using MRI, dissection and previously published cryosections in one knee.

In the range of flexion from 120° to 160° the flexion facet centre of the medial femoral condyle moves back 5 mm and rises up on to the posterior horn of the medial meniscus. At 160° the posterior horn is compressed in a synovial recess between the femoral cortex and the tibia. This limits flexion. The lateral femoral condyle also rolls back with the posterior horn of the lateral meniscus moving with the condyle. Both move down over the posterior tibia at 160° of flexion.

Neither the events between 120° and 160° nor the anatomy at 160° could result from a continuation of the kinematics up to 120°. Therefore hyperflexion is a separate arc. The anatomical and functional features of this arc suggest that it would be difficult to design an implant for total knee replacement giving physiological movement from 0° to 160°.

Introduction: Long term performance of total knee replacements is governed by wear of ultra-high molecular weight polyethylene (UHMWPE) which leads to aseptic loosening of the implant. Little has been done to reduce wear due to the femoral component properties in knee joint replacement. Scratching of the femoral component has been identified in retrieved knee replacements. Using a material that has a higher scratch resistance than current metals may reduce the rate of UHMWPE wear in knee replacements. In this study we investigated the effects of using an oxidized Zirconium femoral component has on wear in knee replacements.

Methods: Total knee replacements made of CoCr and oxidised zirconium were tested in a four station, six degrees of motion knee simulator for 4 million cycles. The surface roughness values (Ra, Rz and Sm) for the metal counterfaces was measured through the test. In addition gravimetric wear of the UHMWPE inserts was recorded. Scanning electron microscopy of the two counterface surfaces was performed to provide information on possible mechanisms involved in the wear process.

Results: The starting surface roughness for both CoCr and oxidised zirconium were similar (Ra=0.03m). Oxidised zirconium was significantly more scratch resistant than CoCr; Ra (mean average roughness) of 0.7m compared to 0.43m (p< < 0.01) at end of test, with similar differences in the other surface roughness parameters. This was accompanied by a 4 fold reduction in wear of UHMWPE 49.60mg to 12.48mg (p=0.02).

SEM analysis of the surfaces of the metals revealed large deep scratches of the CoCr implants which were aligned in the A-P sliding direction. Barium sulphate particles were seen embedded in the surface of the femoral component. Voids were seen in the surface of the cobalt chrome and particles of silicate polishing powder were seen in these voids. There was also evidence of scratches originating at these voids. By contrast oxidised zirconium, showed small amounts of superficial scratching with an intact surface and no evidence of third body particles.

Summary and conclusions: Oxidised zirconium leads to a reduction in wear of UHMWPE due to its increased resistance to third body wear. It has the potential to increase the longevity of total knee replacements by reducing wear of UHMWPE. Additionally, polishing powder used in the manufacture of cobalt chrome femoral components of knee joint replacements is a potential source of third body particles.

Introduction and Aims: Retrospective analysis of all uncemented massive endoprostheses inserted at our unit in the management of primary bone tumors with a minimum follow-up of five years.

Method: The case notes and radiographs of all patients were reviewed. The group consisted of a total of 52 patients, of which four (8%) were lost to follow-up. Kaplan-Meier Cumulative Survival Graphs were created for mortality, amputation, revision and infection for the whole group and for each individual prosthesis.

Results: The mean follow-up was seven years (63–107 months). The average age at time of insertion was 19 years; 26 patients were skeletally immature. The majority of implants were distal femoral (31) and proximal tibial (14). Osteosarcoma was the most common diagnosis.

The rate of infection was 12.5%, aseptic loosening 6%, amputation due to local recurrence 10% and the mortality 21%.

All the deaths occurred within three years of the implant being inserted and were all due to systemic progression of the disease. The amputations for local recurrence occurred throughout the follow-up period, the latest being at 71 months. Revisions for infections and aseptic loosening all occurred early (within three years). All cases of aseptic loosening occurred in distal femoral replacements (10%) and were related to divergent canals. Proximal tibial replacements had the highest rate of infection (23%). Rates of infection were not higher in the minimally invasive grower (12.5 %) when compared to the group as a whole.

Conclusion: We have shown a reduced rate of aseptic loosening (6%), particularly in the skeletally immature, when compared to our unit’s results for cemented fixed hinged prostheses. The uncemented prosthesis is a successful implant that needs careful consideration, especially in the skeletally immature. Careful pre-operative planning and surgical technique are of the utmost importance.

Retrospective analysis of all uncemented massive endoprostheses inserted at our unit in the management of primary bone tumours with a minimum follow up of 5 years.

Methods. The case notes and radiographs of all patients were reviewed. The group consisted of a total of 52 patients of which 4 (8%) were lost to follow up. Kaplan-Meier Cumulative Survival Graphs were created for mortality, amputation, revision and infection for the whole group and for each individual prosthesis.

Results. The mean follow up was seven years (63–107 months). The average age at time of insertion was 19 years; twenty-six patients were skeletally immature. The majority of implants were distal femoral (31) and proximal tibial (14). Osteosarcoma was the commonest diagnosis.

The rate of infection was 12.5%, aseptic loosening 6%, amputation due to local recurrence 10% and the mortality 21%.

All the deaths occurred within 3 years of the implant being inserted and were all due to systemic progression of the disease. The amputations for local recurrence occurred throughout the follow up period, the latest being at 71 months. Revisions for infections and aseptic loosening all occurred early (within 3 years). All cases of aseptic loosening occurred in distal femoral replacements (10%) and were related to divergent canals. Proximal tibial replacements had the highest rate of infection (23%). Rates of infection were not higher in the minimally invasive grower (12.5 %) when compared to the group as a whole.

Conclusion. We have shown a reduced rate of aseptic loosening (6%), particularly in the skeletally immature, when compared to our units results for cemented fixed hinged prostheses. The uncemented prosthesis is a successful implant that needs careful consideration, especially in the skeletally immature. Careful preoperative planning and surgical technique are of the utmost importance.

A case report of an 11 year old boy who underwent tibial osteotomy to prevent angulation of his right tibia.

As a 7 year old, LH sufered a minor injury to his right tibia. A lump appeared at the same site. Soon the lump grew to be similar to “a second knee cap”. However, it only caused him pain when he traumatised it. He and his parents were disturbed by the lump, and the fact that it was creating an anterior-posterior bowing of his tibia. They sought medical advice. His original hospital carried out X rays that demonstrated the deformity and a cloud like lump at the tibial tuberosity.

A bone scan confirmed a solitary osseous lesion. In July 2002 he was referred to the RNOH, where the decision was taken to resect the tibial tuberosity and undertake a corrective osteotomy. Post surgery in August 2002, LH was mobilised in a full cast for 9 weeks and graduated slowly from non to full weight bearing. Histology revealed a probable endchondroma, or unusual growth plate reaction.

A year after the procedure LH is a symptom free, happy and active boy. Radiographs confirm normal angulation of his Tibia.

In conclusion an osteotomy can be a very successful treatment for a childhood lesion that leads to progressive deformity.

We performed a retrospective analysis of massive endoprostheses inserted at our unit in the management of Giant Cell Tumours of the distal femur with a minimum follow up of 5 years.

Methods. Twenty-five massive articulating endoprostheses were inserted between 1986 and 1998 at our unit. The case notes and radiographs of all patients were reviewed. A functional and radiological analysis was performed using the MTOS and ISOLS scoring systems. Kaplan-Meier Cumulative Survival Graphs were created for amputation and revision for septic and aseptic loosening. Two patients had died (8%) from unrelated causes. No cases were lost to Follow Up.

Results. Massive replacements were performed for stage 3 (aggressive), pathological fracture (30%) or recurrent disease. The mean follow up was twelve years (range 5–18 years). The average age at time of insertion was 37 years; no patients were skeletally immature. Fifteen implants were fixed hinge devices and ten were rotating hinge devices with HA collars (since 1993). No cases were revised for sepsis. There had been no cases of recurrent disease or amputation. There have been six (26%) revisions for aseptic loosening. Only one of these occurred in the rotating hinge and HA collar group. In the fixed hinge group (38% aseptic loosening rate) revision occurred after an average of six years. There have also been five re-bushings all of which have occurred in the fixed hinge group. The average MTOS score was 74 (range 47–97).

Conclusion. Young patients with fixed hinged devices developed a high incidence of aseptic loosening. They also had a significant rate of re-bushing. Results of the rotating hinge prosthesis with HA collar were much more promising. Functional scores were good after a period of twelve years despite the young age group.