The most important finding of the present study was that the attachment site of the PC differed at each femoral condyle. The PC was attached most distally at the intercondylar fossa compared with other parts of the femoral condyle in all patients of our study. This result suggested that the effectiveness of posterior capsular release differed based on the part of the PC that was released. In TKA, achieving optimal posterior clearance has a significant effect on the postoperative range of motion. Posterior condylar offset increased following implantation even with optimal bone resection and achieved a rectangular gap intraoperatively, thus demonstrating a negative effect on postoperative knee flexion . Moreover, increasing the posterior condylar offset reportedly influenced the component gap in knee extension . Considering these findings together with those of the present study, in addition to optimal bone resection, achieving an ideal posterior clearance by PC release is conclusive. Moreover, surgeons often select larger femoral components in PS-TKA on account of the influence of posterior cruciate ligament resection to ensure optimal flexion gap. This strategy may increase posterior condyle offset after implantation. Furthermore, in PS-TKA with a unique post-cam design, adjustment using posterior capsular release at the intercondylar fossa that is attached most distally to the femoral condyle is considered a refined surgical technique that helps control the soft tissue balance intraoperatively.
In addition to the posterior capsular release, previous studies have reported on surgical methods for improving intraoperative flexion contracture [1, 2, 11, 18, 24, 29]. Osteophyte removal from the posterior femoral condyle improves the knee extension angle in TKA . Moreover, additional distal femoral resection has been shown to be an efficient surgical method for improving flexion contracture [24, 29]. In contrast, joint line elevation by additional distal femoral bone resection has been a clinical concern for decades. Previous cadaveric studies have reported the relationship between additional distal femoral resection and mid-flexion instability by joint line elevation and indicated that excessive joint line elevation following TKA affected functional outcomes . However, in patients with varus knee osteoarthritis, joint elevations of < 2 mm were not correlated with mid-flexion laxity . The efficacy of 2-mm additional distal femoral resection for the knee extension angle was reported to be 3.6°–9° [12, 15, 24, 26, 29]. This study demonstrated an improvement of 11.4° ± 2.8° at the intercondylar fossa following posterior capsular release, showing an equivalent or better effect than that reported for the 2-mm additional bone resection. Moreover, as its advantage, posterior capsular release achieves an optimal knee extension angle, regardless of joint line elevation. Accordingly, dealing with intraoperative flexion contracture by posterior capsular release is a skill that surgeons performing TKA should learn to achieve better clinical results.
In this study, we performed posterior capsular release and confirmed complete PC detachment from the femoral cortex. At the level of the PC attachment site, the popliteal artery and vein run close to the capsule of the knee joint. The tibial nerves are located at the side and above the artery and vein. The popliteal artery courses through the fossa from the distal portion of the adductor magnus muscle and runs close to the PC of the knee joint. Thereafter, the artery enters diagonally and branches into the genicular arteries . Hence, excessive posterior capsular release could damage these structures owing to their anatomical location. Sanz et al. reported that the popliteal artery and the common peroneal nerve are located 1.01 and 1.74 cm (average) posterior to the posterior horn of the lateral meniscus, respectively. In addition, they mentioned that the distance from the posterior horn to the popliteal artery and common peroneal nerve did not correlate with the patient’s height, body mass index, and tibial plateau diameter . Moreover, previous studies have reported on the variations of the branches of the popliteal artery [19, 20]. They demonstrated that the posterior artery has several patterns and divides into the anterior tibial artery, posterior tibial artery, and fibular artery. The popliteal artery branches distal to the tibial plateau. To our knowledge, no study has reported anomalous branches proximal to the tibial plateau at the same level as the PC attachment. Further, Pinter et al. demonstrated the safety of posterior capsular release during TKA in their cadaveric study . They mentioned that the neurovascular band has no direct contact with the femoral cortex. Based on the results of previous studies and the anatomical form of the attachment of PC, surgeons could perform capsular release safely if they maintain the direction of the osteotome to the cortex of the femur and avoid directing it to the posterior neurovascular bundle. We have already performed this procedure in numerous cases but have never encountered neurovascular injuries. Furthermore, the flexion knee position has been proven to prevent the risk of injury to the popliteal artery . Despite the safety of this procedure, one must be cautious to avoid damage to the neurovascular band. Training with a senior surgeon to familiarize this procedure is necessary to ensure patient safety.
The strength of our study is the use of a navigation system, which enabled precise evaluation of the change in the knee extension angle. Accurate evaluation by recent technological advances, such as a navigation system, has been already demonstrated [8, 9, 11]. We were able to evaluate a slight change in the extension angle that was difficult to detect without a navigation system. Moreover, the same coordinates were used for the measurement of the knee extension angle using a navigation system before and after posterior capsular release. This procedure enabled us to compare the changes in the knee extension angle following posterior capsular release more accurately. In addition, we assessed the change in the knee extension angles following capsular release at each condyle. To our knowledge, no study has focused on the differences in improvements of knee extension angle among parts of the released capsule. Furthermore, our study has made it clear that the efficacy of capsular release is different among the parts of the femoral condyle. The novelty of our study is on the anatomical aspects of the PC and its clinical consequences.
This study has certain limitations. First, the evaluation method of the form of attachment of the PC was insufficient. We performed macroscopic assessment and did not evaluate the attachment using a pathological method. Second, we did not perform preoperative imaging assessment of the limb alignment and degree of decline of the cartilage of cadaveric knees that underwent TKA. Third, we were unable to evaluate the temporal change in the extension angle following capsular release, since it was a cadaveric study. Hence, further research is required to investigate the effect of posterior capsular release on the postoperative knee extension angle. Moreover, we released the attachment of the PC from the femoral cortex completely by the width of the osteotomy of the posterior condyle. Considering the form of attachment of the PC, the attachment site of the gastrocnemius tendon could be detached from the femoral cortex at the medial and lateral condyles. Although this procedure is effective for increasing the knee extension angle, further studies are required to examine the influence of posterior capsular release at the medial and lateral condyles on postoperative knee pain and muscle strength. Meanwhile, from the results of this study, capsular release at the intercondylar fossa is an appropriate and effective surgical technique for intraoperative flexion contracture.
Our results revealed that the attachment site of the PC differed based on the part of the femoral condyle involved. Considering the difference in the attachment sites, we should consider using selective posterior capsular release. To prevent the conflict between the cam mechanism and the PC of the knee, posterior capsular release at the intercondylar fossa is valid in PS-TKA. In this study, posterior capsular release at the intercondylar fossa resulted in 11.4° ± 2.8° improvements in the knee extension angle after PS-TKA. Moreover, in PS-TKA, additional posterior release at each condyle is necessary when dealing with flexion contracture due to the increasing incidence of posterior condylar offset caused by the increasing size of the femoral component. Our study also demonstrated the efficacy of additional posterior capsular release, which resulted in improvements of 5.5° ± 1.3° in knee extension. Thus, selective posterior capsular release is an effective surgical method for addressing flexion contracture in TKA. Our data comprise important implications for the surgeon’s selection of surgical method when they encounter flexion contracture intraoperatively.