As a result of the increased popularity of metal-on-metal bearings for total hip arthroplasty, concerns have been expressed about patient exposure to increased serum metal ion levels.

We therefore performed a retrospective review of patients with metal-on-metal, uncemented Ring total hip replacements with a minimum follow up of thirty years.

After allowing for prosthesis revision and patient mortality, 6 hips in 5 patients were reviewed and serum ion levels measured. Similar cohorts of patients with other combinations of bearings were compared with an age-matched osteoarthritic control group.

Serum cobalt and chromium levels in the metal-on-metal hip arthroplasty group were significantly higher than in all other groups and approximately five and three times greater respectively than in the group with no implants. Unlike the stainless steel-on-plastic group, the cobalt/chrome-on-plastic group showed significantly raised serum cobalt levels compared with the control group. It is of interest that patients who have had their metal-on-metal hip replacements revised to metal-on-plastic, have metal ion levels that are not statistically different to those of the osteoarthritic control group.

Though we acknowledge the small numbers of patients studied, no identifiable harmful effects were found.

We conclude that serum metal ions remain elevated throughout the life of the metal-on-metal articulation. Metal bearing hip arthroplasty is being used in ever younger patients and together with increased life expectancy we are exposing our patients to potentially harmful levels of metal ions throughout the life of the implant.

We have evaluated the function of a trabecular metal augmentation patella to restore knee kinetics and kinematics after revision total knee arthroplasty. An “Oxford type” rig was used with fresh frozen cadaveric knees, for an active model that maximally retained the soft tissue envelope.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

The purpose of this study is to evaluate the kinetic and kinematic function of a new trabecular metal augmentation patella.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

This study demonstrates that the augmentation patella restorers the abnormal tracking and higher extensor mechanism forces seen after patelloplasty in revision TKA to those normal after a TKA.

The mean, maximum extensor mechanism force in extension for the TKA group as compared to the patelloplasty group (p=0.0000032), reduced to near normal with the augmentation patella (p=0.198).

The mean, maximum patella maltracking in extension for the TKA group as compared to the patelloplasty group (p=0.025), reduced to near normal with the augmentation patella (p=0.301).

Eight frozen human cadaveric knees (mean age sixty-eight years) were prepared for an “Oxford type” knee rig. Alignment ands offset were addressed and the soft tissue envelope kept as intact as possible. A load cell was introduced into the extensor mechanism. Femoral, patella and tibial motion were assessed using the Optotrak system.

Patella bone loss at revision TKA remains an unsolved problem, with the patella often too thin to accept a new prosthesis. Leaving the patella shell to articulate against the femoral component can lead to disappointing results.

Funding - Zimmer

We have evaluated the function of a trabecular metal augmentation patella to restore knee kinetics and kinematics after revision total knee arthroplasty. An “Oxford type” rig was used with fresh frozen cadaveric knees, for an active model that maximally retained the soft tissue envelope.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

The purpose of this study is to evaluate the kinetic and kinematic function of a new trabecular metal augmentation patella.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

This study demonstrates that the augmentation patella restorers the abnormal tracking and higher extensor mechanism forces seen after patelloplasty in revision TKA to those normal after a TKA.

The mean, maximum extensor mechanism force in extension for the TKA group as compared to the patelloplasty group (p=0.0000032), reduced to near normal with the augmentation patella (p=0.198).

The mean, maximum patella maltracking in extension for the TKA group as compared to the patelloplasty group (p=0.025), reduced to near normal with the augmentation patella (p=0.301).

Eight frozen human cadaveric knees (mean age sixty-eight years) were prepared for an “Oxford type” knee rig. Alignment ands offset were addressed and the soft tissue envelope kept as intact as possible. A load cell was introduced into the extensor mechanism. Femoral, patella and tibial motion were assessed using the Optotrak system.

Patella bone loss at revision TKA remains an unsolved problem, with the patella often too thin to accept a new prosthesis. Leaving the patella shell to articulate against the femoral component can lead to disappointing results.

Funding - Zimmer

Metal-on-metal bearings for total hip replacement (THR) are becoming increasingly popular. Improved wear characteristics mean that these articulations are being inserted into younger patients in the form of THR and resurfacing procedures. This has led to concerns regarding potential carcinogenicity because of the increased exposure to metal ions that the procedure brings.

We have studied the serum cobalt and chromium concentrations in patients who had primary, well-fixed Ring metal-on-metal THRs for more than 30 years. The levels of cobalt and chromium were elevated by five and three times, respectively compared with those in our reference groups. Metal-on-metal articulations appear to be the source of metal ions throughout the life of the prosthesis. In three patients who had undergone revision of a previous metal-on-metal THR to a metal-on-polyethylene replacement the levels of metal ions were within the normal range. The elevations of cobalt and chromium ions seen in our study were comparable with those in patients with modern metal-on-metal THRs.

Purpose To evaluate the kinetic and kinematic function of a new trabecular metal augmentation patella.

Method Eight frozen human cadaveric knees (mean age 68 years) were prepared for an “Oxford type” knee rig. Alignment ands offset were addressed and the soft tissue envelope kept as intact as possible. A load cell was introduced into the extensor mechanism. Femoral, patella and tibial motion were assessed using the Optotrak system.

Summary of Results The mean, maximum extensor mechanism force in extension for the TKA group as compared to the patelloplasty group (p=0.0000032), reduced to near normal with the augmentation patella (p=0.198).

The mean, maximum patella maltracking in extension for the TKA group as compared to the patelloplasty group (p=0.025), reduced to near normal with the augmentation patella (p=0.301).

Conclusion Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

Purpose The tensile strength of the isolated Medial Patellofemoral Ligament (MPFL) is unknown. The strength required of reparative or reconstructive procedures to re-constitute this major patella stabilising structure are therefore unknown.

Method 10 fresh cadaveric right (6 female 4 male) knees, mean age 71.6 (SD 16.6) years, were prepared to isolate the MPFL between the patella and the Medial Femoral Condyle (MFC). The tensile strength and mode of failure were then determined.

The ligament was then repaired using a suture and the tensile strength of this determined. The ligament was then reconstructed in three ways including: Biodegradable corkscrew anchors and two tendon techniques with interference screws. One method used a blind tunnel into the MFC, while the other passed through a tunnel in the femoral condyles. Both methods passed through tunnels in the patella.

Results The mean ultimate tensile strength of the isolated MPFL was 207.9 (SD 90.1) Newtons. Seven specimens failed through a mid-substance tear while three pulled off the MFC.

The mean strength of the suture repair was 36.7 (SD 26.5) Newton. The biodegradable bone anchor gave a mean strength of 142.3 (SD 38.5) Newton. The blind tunnel hamstring reconstruction’s had a mean strength of 126 (SD 20.8) Newton. The double tunnel hamstring reconstruction’s failed at a mean of 195.0 (SD 65.6) Newton.

Conclusion The force required to rupture an isolated MPFL appears to be approximately 210 Newton. Suture repair is insufficient to reconstitute this. Reconstruction with bone anchors or hamstring tendon techniques come close to this.

The tensile strength of the medial patellofemoral ligament (MPFL), and of surgical procedures which reconstitute it, are unknown. Ten fresh cadaver knees were prepared by isolating the patella, leaving only the MPFL as its attachment to the medial femoral condyle. The MPFL was either repaired by using a Kessler suture or reconstructed using either bone anchors or one of two tendon grafting techniques. The tensile strength and the displacement to peak force of the MPFL were then measured using an Instron materials-testing machine.

The MPFL was found to have a mean tensile strength of 208 N (SD 90) at 26 mm (SD 7) of displacement. The strengths of the other techniques were: sutures alone, 37 N (SD 27); bone anchors plus sutures, 142 N (SD 39); blind-tunnel tendon graft, 126 N (SD 21); and through-tunnel tendon graft, 195 N (SD 66). The last was not significantly weaker than the MPFL itself.

Aim: To determine optimal tibial tunnel orientation that projected onto isometric positions of the LFC.

Methods: Tibial tunnels were described by transverse rotations about tibial long axes, angles of elevation and tilt. In each of 8 cadaver knees, 18 tibial positions were drilled with 2mm wires to exit at the centre and posterior end of the tibial footprint. The linear projections of these wires onto the LFC were marked by 1.6mm wires and were described as x-y co-ordinates with reference to the geometric centre of the LFC.

Results: The isometric femoral tunnel positions were approximated (within a 2mm radius) by tibial tunnels rotated 39.3°, elevated 55.7°, exiting at the posterior end of the footprint with knees flexed 90°. Tunnels rotated between 20–45° and elevated 60° had highest probability of isometric projection and those that exited at the centre of the footprint could not be linearly projected anywhere near the isometric point. Applying 50N posterior force on the tibia brought the projections proximally by 4.1mm (p=0.001).

Conclusion: Transtibial tunnel directions are known to affect siting of femoral tunnels, and hence outcome of ACL surgery. This study demonstrated the orientation of tibial tunnels that could linearly project to isometric femoral tunnel positions.