Femoral intramedullary canal referencing is utilized by most of the total knee arthroplasty (TKA) systems. Violation of the canal is performed in order to engage rod instruments in the femoral diaphysis and to refer of the anatomical axis of the femur. Fat embolism, activation of the coagulation cascade, and bleeding may occur from the reamed femoral canal. The purpose of our study was to validate a new set of _minimally-invasive friendly_ instruments which allow to prepare the femur without violating the intramedullary canal. Twenty-five consecutive patients undergoing primary TKA through a mini-subvastus approach were enrolled in the study after informed consent had been obtained. Results of this cohort (group 1) were compared to another contemporary group (group 2) of 25 TKAs operated by the same surgeon using intramedullary instruments. The two groups were matched for gender, deformity, degree of arthritis, and surgical approach. Reliability of the new extramedullary set of instruments was first tested in ten cadaveric limbs. Preoperative long weight-bearing AP and lateral view of the knee were obtained taking care of neutral limb positioning. Template of the mechanical and anatomical axis were performed. Distal femoral resection was planned according to the template, and considering a bone cut perpendicular to the mechanical axis of the femur. Measurement from the template were reproduced on the distal femoral cutting jig. Flexion-extension control of the distal femoral resection was obtained using the anterior meta-diaphyseal cortex reference. Depth of resection, and varus-valgus angulation were selected according to the previous measurements and referring over the most prominent distal femoral condyle. A double check was performed using an extra-medullary rod referring two and a half finger-breaths medially to the antero-superior iliac spine. Postoperative blood loss, pain, swelling, functional recovery, and complications were recorded. Radiographic alignment was measured with long film. Mechanical axis was within 0±2° in 88% of group 1 and 84% of group 2 (p> 0.05). There were no difference between the two groups regarding the operative time. In group 1, postoperative blood loss (740 vs 820 mL) was reduced but this difference did not reach the statistical significance (p=0.07). No difference was found in terms of postoperative pain, knee swelling, and functional recovery. Extramedullary reference with careful preoperative templating can be safely utilized during total knee arthroplasty. Avoiding the violation of the femoral canal may enhance the benefits of a less invasive approach.

Introduction: Patello-femoral complications are a major problem after total knee arthroplasty (TKA). Purpose of the present study was to analyze patello-femoral complications and function after two different posterior-stabilized TKA designs (Optetrak 913 vs IB-II).

Materials and Methods: This study was performed in two consecutive phases. In the first phase 1410 TKA’s performed by the senior author between 1994 and 1998 were considered for chart review. Within this period, the last 300 IB-II and the first 300 913 performed were analyzed for patello-femoral complication rate. In the second phase, of the 600 charts analyzed, two matched groups (50 patients each of IB-II and 913), were selected for a clinical (Knee Society score), functional (HSS Patellar score) and radiological assessment (AP, Lateral, Merchant, modified-wb Merchant views).

Results: A lateral retinacular release was performed in 30% for the IB-II and 16% for the 913 (p=0.02). The following patello-femoral complications were encountered (phase-1):

IB-II 913

Patellar clunk 3.5% 0.3%

Dislocation 0% 0.3%

Fracture 0% 0.3%

Loosening 0% 0%

Clinical results at follow-up (phase-2) did not show any significant difference between the two matched groups in terms of Knee and Function scores (p=0.7). Patellar score showed a higher rate of excellent and good results in the 913 group (88% vs 81%: p=.043). Anterior knee pain was only mild and activity related in 26% of the IB-II and 14% of the 913 (p=.025). In a multivariate regression analysis, radiographic patellar tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed a trend towards a higher incidence of pain, particularly when associated with asymmetric patellar resection.

Discussion: At an intermediate follow-up, the Optetrak 913 prostheses showed fewer complications and an improved patello-femoral function compared to the IB-II prosthesis.