Aims

This aim of this study was to assess the feasibility of designing and introducing generic 3D-printed instrumentation for routine use in total knee arthroplasty.

Introduction. Conventional total knee instrumentation is used for most total knee replacements. Computer-assisted total knee arthroplasty (CA-TKA) including custom guides has gained popularity due to its reported accuracy in restoring optimal alignment. CA-TKA has demonstrated increased surgical time and cost, with know risks of pin-site infection and fracture. We assessed the radiographic alignment of conventional TKA by one surgeon and determined whether preoperative alignment has an effect on postoperative alignment. Methods. A prospective series of 100 primary total knee arthroplasties (in 95 patients) from 1/2012-3/2013 were performed by the senior author, using a single conventional instrument system and a consistent methodology of 5° valgus distal femoral cut, intramedullary femoral entry-point, and minor cement balancing. Mechanical axis and component alignment were measured digitally on preoperative and postoperative lower extremity scanograms. Target alignment was set at neutral ± 3°. Knees with preoperative deformity within 0 ± 5° (non-deformed group) and those with >5° varus/valgus (deformed group) were compared using chi-square test. Results. Target mechanical axis alignment (0 ± 3°) was achieved in 79% cases, while 21% remained in varus alignment (Fig 1). The non-deformed group achieved target alignment in 93.2% cases versus 62.2% in the deformed group (p = 0.0006). The femoral component fell within target alignment (90 ± 3°) 80% of the time and most often was in 1° of varus. The tibial component achieved target alignment (90 ± 3°) 96% cases and was most often in neutral (Fig 2). Conclusion. Our results were consistent with those reported in the literature for conventional TKA, with a trend towards under-correction of varus deformity. The majority of the variability stemmed from the femoral component position and careful adjustments should be made to accommodate the individual differences of each patient. Given the significant difference in achieving target alignment between the deformed and non-deformed groups, perhaps CA-TKA could be useful in patients with preoperative deformity > ± 5°

Aims

This study aimed to evaluate if total knee arthroplasty (TKA) femoral components aligned in either mechanical alignment (MA) or kinematic alignment (KA) are more biomimetic concerning trochlear sulcus orientation and restoration of trochlear height.

Introduction: Correct prosthesis alignment and joint line reproduction in total knee replacement (TKR) is vital for a successful clinical outcome. It is acknowledged that the ideal coronal alignment of the knee following TKR should be between 4–10 degrees of valgus. A neutral or varus knee is associated with a higher failure rate. Previous studies have shown that ideal alignment is achieved in only around two-thirds of cases. Joint line elevation > 8mm has been associated with inferior clinical outcome, and depression associated with retropatellar pain and increased risk of patella subluxation. Recently, modifications have been made to the Kine-max-Plus Total Knee System instrumentation, theoretically providing better internal fixation to prevent a varus cut and a 12 mm measured resection from the “normal” tibial plateau. This study aims to examine whether these changes result in an improvement in alignment, and a more reliable restoration of joint line. Materials and Methods: Two consecutive series, each of 75 patients who had undergone TKR using either the old (Group A) or the new (Group B) instrumentation were included in the study. Antero-posterior and lateral preoperative and postoperative knee radiographs were assessed using the American knee society radiographic analysis for prosthesis postionoing by 2 independent observers. The Tibial and Femoral Component Angles in the coronal plane (cTCA and cFCA) and in the sagittal plane (sTCA and sFCA) were measured, as was the change in joint line height. Conclusion: Our results suggest that use of the new instrumentation is associated with better restoration of joint line, and is more effective in preventing implantation of the tibial component in varus. These figures relating to a modern instrumentation system provide a yardstick against which computer assisted and robotic surgery can be judged. Long-term follow-up will be required to assess the clinical significance of these results

Purpose: This cadaveric study examines how changes in femoral entry point for intramedullary instrumentation of total knee replacements affects femoral component positioning. Methods: Twelve cadaveric lower limb specimens with intact hip, knee and ankle joints were obtained. Total knee navigation instrumentation was secured. Anatomical landmarks required for axes generation were obtained. An initial entry point was made at the center of the distal femur. An intramedullary rod was the introduced into the femur. Five and seven degree cutting blocks were placed onto the rod and positioned against the distal femur with the rotation parallel to the epicondylar axis. The navigation system was then used to generate a varus/valgus angle and flexion/extension angle with respect to the previously generated femoral mechanical axes. This allowed determination of an angle at which the distal femoral cutting block would need to be set to make a neutral distal femoral cut. The guide rod was removed and reinserted five times and measurements recalculated. Data was then collected with entry points 5mm medial, 5mm anterior and 5mm medial and anterior to the initial entry point. Results: There was no significant difference in varus/ valgus angle with a central compared with 5mm anterior entry point and no difference with a 5mm medial versus 5 mm medial and anterior entry point. The valgus angle required to give a neutral distal femoral cut with a central entry point was 4.98o (SD 0.91o; range 3.5o–6.0o). The valgus angle for a 5mm medial entry point was 6.92o (SD 0.97o, range 5.5o–8.0o). With regards to the sagittal plane a 5mm anterior translation of the entry point changed the flexion/extension angle by 1.58o (SD 0.52o, range 0.5o–2.5o). Conclusions: Small changes in the entry point can significantly affect component alignment. When moving more medial with the entry point a more valgus angle is required for the cutting block. An entry point at the deepest point of the trochlea may be more reproducible than an anteromedial one but requires a valgus cutting block closer to 5 degrees. Funding: Commerical funding. Funding Parties: Stryker

Aims

The results of kinematic total knee arthroplasty (KTKA) have been reported in terms of limb and component alignment parameters but not in terms of gap laxities and differentials. In kinematic alignment (KA), balance should reflect the asymmetrical balance of the normal knee, not the classic rectangular flexion and extension gaps sought with gap-balanced mechanical axis total knee arthroplasty (MATKA). This paper aims to address the following questions: 1) what factors determine coronal joint congruence as measured on standing radiographs?; 2) is flexion gap asymmetry produced with KA?; 3) does lateral flexion gap laxity affect outcomes?; 4) is lateral flexion gap laxity associated with lateral extension gap laxity?; and 5) can consistent ligament balance be produced without releases?