Comparison of Femoral Rotation in Total Knee Arthroplasty with Measured Resection Technique and Balanced Flexion Gap Technique

摘要

Purpose: Avoiding femoral malrotation has always been a technical challenge for orthopaedic surgeons in total knee arthroplasty. While modern surgical techniques have made the surgeon’s task easier, nevertheless it remains unclear which of the two most common techniques- the measured resection or balanced flexion gap techniques- more accurately restores femoral component rotation. This study aimed to compare the femoral rotation produced by these two surgical techniques and the relationship between the femoral rotation and coronal tibial alignments.This retrospective cohort study compared 20 posterior stabilized Anatomic Modular Knee (AMK), aligned using a measured resection technique to 20 mobile bearing Low Contact Stress knee (LCS) aligned using a balanced flexion gap referencing system. Long leg standing x-rays and CT scans of knees were used to measure rotation of the femoral component in the axial plane and tibial alignment in the coronal plane. Results: Average femoral component rotations were 2.98 (SD 3.21) degrees and 2.26 (SD 1.20) degrees for the AMK and LCS, respectively. Tibial component alignments were 0.66 (SD 1.94) degrees valgus and 0.4 (SD 1.09) degrees valgus for the AMK and LCS, respectively. These differences were not statistically significant. Conclusion: There were no statistically significant differences in femoral rotation between the two referencing systems. However, the balanced flexion gap method had a narrower range of implant rotational position. No statistically significant relationship was found between femoral rotation and tibial alignment in either system. Introduction Total Knee Arthroplasty (TKA) is the most common type of arthroplasty performed with 40,675 TKA’s performed in Australia in 2009[1]. The overall satisfaction from TKA procedures irrespective of type and technique is about 95%[2]. Advancements in TKA technology have enhanced the design and fit of knee implants resulting in improved short and long term outcomes [3]. Nevertheless, one of the complications of a TKA is malrotation of the prosthesis [4]. In particular, appropriate axial alignment of the femoral component is challenging, as it requires adequate knowledge of anatomy as well as expertise in the surgical technique. The importance of femoral rotation can be gauged by the fact that discrepancies can lead to patello-femoral mal-tracking [5], arthrofibrosis [6], flexion instability [7], accelerated polyethylene wear [8], anterior knee pain [9] and decreased range of movement[4].The two most commonly used techniques for insertion of the femoral component of the TKA are the posterior condylar referencing measured resection (PCRMR) technique and tibia first balanced flexion gap (TFBFG) technique. The PCRMR technique starts with resection of the distal femur. It uses bony landmarks such as the femoral epicondyles[10], anteroposterior axis (Whitesides line)[11] and the posterior femoral condyles as references to resect the appropriate amount of the femoral condyles[12]. The TFBFG technique starts with the tibial cut. The femoral component is then positioned by ligamentous balancing parallel to the resected proximal tibia.There has been an ongoing debate whether the PCRMR technique or the TFBFG technique achieves more optimal femoral component axial rotation. The comparison becomes difficult when parameters such as surgical expertise, manufacturers of the TKA systems, heterogeneity of populations and institutions are taken into consideration. The question also arises whether femoral rotation is somehow related to coronal tibial component alignment, especially in the TFBFG technique. The rationale for this is as follows: the TFBFG technique starts with the tibial cut, followed by the femoral cut after balancing of the soft tissues of the knee [13]. As these steps are interdependent, error in the varus/valgus tibial component placement may have the knock-on effect of altered femoral component rotation[14]. On the contrary, it is less