Restoration of the mechanical axis is thought to be a critical factor in determining the Outcome of knee replacement surgery. There is strong theoretical evidence that reproduction of this axis improves mechanical loading and hence longevity of the implant. Clinical studies are small in number. Per-operative use of intra-and-extra-medullary alignment jigs help to determine the distal femoral and proximal tibial cuts. Studies have shown large margins of error using the standard jigs provided with most total knee replacement systems. On this basis computer assisted guidance systems are being introduced such as Orthopilot and BrainLab. These systems allow more accurate placement of the bony cuts and hence improve overall lower limb alignment. No study has shown conclusively that accurately reproducing the mechanical axis of the lower limb improves survivorship of the implant. Prior to investing in these systems we felt it would be prudent to investigate how critical reproduction of the mechanical axis was in the primary total knee replacement. We assessed 100 primary kinematic total knee replacements performed in 1990. All case notes were reviewed looking for basic demographics, pathology and clinical outcome. All cases had a long leg film weight-bearing alignment film taken post-operatively. These were digitised and then analysed using Design CAD 97 software and from this the mechanical axis calculated. Using these data the patients were divided into two groups. The first were within 3 degrees varus/valgus of the mechanical axis. The second were outside this range. These two groups were then correlated to clinical outcome.
Restoration of the mechanical axis is thought to be a critical factor in determining the outcome of knee replacement surgery. There is strong theoretical evidence that reproduction of this axis improves mechanical loading and hence longevity of the implant. Per operative use alignment jigs help to determine the bony cuts. Studies have shown large margins of error using the standard jigs. On this basis computer navigation systems are being introduced. No study has shown conclusively that accurately reproducing the mechanical axis of the lower limb improves survivorship of the implant. Prior to investing in these systems we felt it would be prudent to investigate how critical reproduction of the mechanical axis was in the primary total knee replacement. We assessed 100 primary total knee replacements performed in 1990. All case notes were reviewed looking for basic demographics, pathology, and clinical outcome. All cases had a long leg þlm weight bearing alignment þlm taken post operatively. These were digitised and then analysed using CAD software. From this the mechanical axis calculated. Using this data the patients were divided into two groups. The þrst were within 3 degrees varus/valgus of the mechanical axis. The second were outside this range. These two groups were then correlated to clinical outcome. Our results suggest that accurate reproduction of the mechanical axis improves clinical outcome and survi-vorship of the implant. Our data would support the use of intra operative computer navigation systems
The use of rim mesh to augment acetabular defects at the time of revision hip surgery is a valuable technique. Where acetabular containment is compromised by segmental rim defects, it can be achieved by using a flexible wire mesh fixed to the wall of the ilium by multiple screws. Morsilised bone graft is then impacted onto the acetabular bed and wire mesh thus creating a new hemi-spherical acetabular bed for cementation of a new socket. Standard AP and lateral radiographs are acceptable methods for assessing conventional socket revisions. However if a rim mesh has been used the mesh itself will obscure the socket and both columns of the acetabulum making interpretation difficult. We have modified the Judet views classically used in acetabular fracture surgery to allow better imaging of the socket. The views taken are dependant upon rim mesh position at surgery. Technique: Positioning for posterior acetabular rim mesh From the supine position the patient is rotated 45° so that the side under examination is raised. Radiolucent pads are used to support the pelvis and leg. The hips and knees should not be flexed. Positioning for anterior acetabular rim mesh From the supine position the patient is rotated 45° so the non affected side is raised. Using radiolucent pads the pelvis is supported. The femur should not be flexed and externally rotated as they would be for an oblique hip The film is centred approximately 2cm below the ASIS of the hip being examined. These views of the hip allow complete imaging of the socket and the reconstructive construct. Radiographic evaluation of the bone graft and bone cement-graft interface can be reliably made. We would recommend these views for the radiographic follow up of socket revisions involving the rim mesh technique.
