Computer-assisted patellar resection for total knee arthroplasty

Abstract

Incorrect patellar resection during total knee arthroplasty can lead to anterior knee pain, patellar maltracking, patellofemoral impingement, patellar fracture, component loosening and reduced range of motion. A computer-assisted surgery (CAS) system was developed to improve the accuracy of the patellar cut. Twelve cadaveric knee specimens (6 pairs) were surgically prepared and the patella resected by two senior orthopaedic residents using either a conventional sawguide technique (right knee) or a computer-assisted sawguide technique (left knee). Multiple cuts and measurements were permitted for the conventional technique, to reflect the clinical situation, whereas only a single cut was permitted for the CAS technique. Prior training had been provided on artificial bones for both techniques. Custom marker arrays were mounted on the sawguide and patella. The user positioned the sawguide based on a real-time display that compared the current sawguide plane to the ideal resection. The resulting mediolateral and superoinferior resection angles and central thickness were measured from CT scans of the specimens, relative to the anterior surface of the patella. Both techniques resulted in symmetric cuts (<7 ). Repeatability in the mediolateral direction was better for the CAS technique than for the conventional technique ( p < 0.01). This study demonstrated that computer-assisted patellar resection is a feasible approach that can produce results equal to or better than those obtained with conventional techniques, even when the experimental conditions favor the conventional technique. Improvements in the CAS hardware could further improve the accuracy and usability of the system, resulting in reductions in postoperative complications. Patellar CAS could also serve as a valuable tool for feedback and training.

Shape Analysis of the Patellar Bone Surface and Cutting Plane for Knee Replacement Surgery

“…A variety of contact configurations were tested and compared to the resection planes by modelling the geometry of the contact plane in comparison to the anterior surface and resection planes. Possible contact configurations included different distances and layouts of pegs, a flat plate corresponding to the previously-developed CAS system [ 11 , 12 ] and a ring corresponding to the existing reamer. Applying flat-jawed callipers, i.e., the standard clinical measurement instrument, to the patella has been shown previously to cause it to rotate [ 8 ], showing that this is not a suitable contact mechanism.…”

“…Unfortunately, using these devices can still lead to asymmetry and incorrect thickness, resulting in the clinical complications listed above. Computer-assisted surgery (CAS) can be used to improve accuracy [ 11 ] but remains invasive due to attaching a marker array onto the bone and is still only as accurate as the placement of the attachment plate. Many surgeons prefer to resect the patella freehand, since they consider the current devices to be inaccurate.…”

“…Although various landmark guidelines, such as the medial-lateral (side-to-side) extents, have been suggested for performing the patellar cut, the ultimate goal is to be parallel to the anterior surface, producing a visually rectangular cut, with equal thicknesses in all quadrants [ 13 ]. Since asymmetry with respect to the anterior surface, considered to be within ±7° [ 11 ], has been correlated with anterior knee pain [ 2 , 3 ], it is essential to reference a device off of the anterior surface.…”

Computer-assisted surgery simulations and directed practice of total knee arthroplasty: Educational benefits to the trainee

“…Both of these systems allow the user to plan the desired femoral and tibial component positions on a patient-specific virtual model of the knee, and then guide the user to achieve the desired cuts accurately. The patellar CAS system ( Figure 5) was developed at our institution [25,26]. With this system, the user navigates the position and orientation of the patellar sawguide compared to the desired resection line; both lines are displayed on the monitor.…”

Guiding Device for the Patellar Cut in Total Knee Arthroplasty: Design and Validation

“…A symmetric cut is considered to be parallel to the front (anterior) surface of the patella [ 3 , 4 , 8 ]; however, existing devices either have no connection with the anterior surface or the contact points can cause the device to tilt because of high or low points on the surface [ 8 , 9 , 10 ]. A patellar computer-assisted surgery system addressed many of these factors, but the screw attachment of the bone reference frame was considered invasive; a better system to define the anterior surface was desired; and the greater simplicity of a mechanical interface was attractive [ 10 , 11 ].…”