Abstract
Introduction
Two principal targets are dominating the spectrum of goals in total knee arthroplasty: first of all the orthopedic surgeon aims at achieving an optimal pain-free postoperative kinematic motion close to the individual physiologic range of the individual patient and secondly he aims for a concurrent high ligament stability within the entire range of movement in order to establish stability for all activities of daily living. This study presents a modified surgical procedure for total knee replacement which is ligament-controlled in order to put both component into the “ligamentous frame” of the patients individual kinematics.
Methods
The posterior femero-condylar index (PFC-I) is defined as being the posterior condylar offset divided by the distal antero-posterior diameter on a lateral radiograph. After careful preoperative planning the positions and orientations of the osteotomies is controlled intraoperatively via ligamentous guidance. Anterior and distal femoral osteotomy are planned on antero-posterior and lateral radiographs considering intramedular and mechanical axes as well as the orientation of the posterior condyles. Osteotomies are carried out in a stepwise fashion, starting with the anterior femoral osteotomy followed by the distal femoral osteotomy as planned. Then the extension gap is finalized by tensioning the ligaments and “top-down” referencing the level of the tibial osteotomy. After rotating the femur into the 90°-flexion position the flexion gap is finalized by referencing the level of the posterior condyle osteotomy in a “bottom-up” fashion to the tibial osteotomy. Hence, this technique determines the size of the femoral component with the last osteotomy. It likewise respects the new, ACL-lacking ligamentous framework and it drives the prosthetic components to fit into the new ligamentous envelope to follow the modified kinematics.
Results
More than 130 patients have been operated on using this surgical technique, 104 of them have been followed-up after a minimum of one year: age 73+/−9, m/f 37/67, 71% had a varus, 29% a valgus-deformity. In all patients a subvastus approach was applied, 12 from medial, 92 from lateral. Mean flexion reached 122°+/−7.4 and a 120°-flexion or more was achieved by 86% of the patients. All patients reveived a LCS total knee prosthesis with either a rotating or an antero-posterior gliding inlay. No fixed tibial inlays were used. Antero-posterior translation of the APG-insert was 13 to 16mm immediately postoperatively whereas after one year it decreased to 4 to 10mm. We succeeded in reconstructing the posterior femero-condylar index (PFC-I) and found a linear correlation of 0.98 +/−0.06 of pre- to postoperative PFC-I.
Conclusion
This PCL-retaining surgical technique respects the new, ACL-lacking kinematics in total knee replacement. The anterior and distal femoral osteotomies are femur-axis-controlled while the extension and flexion gaps are ligament-controlled. The size of the femoral component is regarded as a variable within the procedure and is only determined while performing the last osteotomy, i.e. the posterior condylar osteotomy. This technique is suitable for both PCL-retaining and also for PCL–sacrificing techniques.
