As the techniques to diagnose injuries to the posterior cruciate ligament (PCL) and multiligament injuries have advanced, as well as the knowledge of the sequelae and pathomechanics that occur at the knee if left untreated, surgical procedures to address these injuries continue to evolve. Like its anterior cruciate ligament (ACL) counterpart, the PCL and associated ligament disruption may result in knee pain, instability, and functional impairment if not addressed surgically [1]. Although more technically demanding, PCL reconstruction can result in improved functional stability and greater patient satisfaction when compared to preoperative measures [2]. A significant factor in the outcome is the design and implementation of a rehabilitation program that will allow the patient to return to a satisfactory level of function without jeopardizing the surgical repair. As we continue to treat and follow these patients, many things are clear. First and foremost is that there is great individual patient variance in regard to pain perception, healing response, and outcome expectations. In this regard, although protocols are necessary for providing guidelines, their implementation must have sufficient flexibility to account for patient difference. Second, rehabilitation following these complex procedures cannot be as simple as ACL rehabilitation done backwards. Especially when one considers that is common for multiple ligaments to be involved and that all structures must be protected during the early phase of the rehabilitation process. Finally, the learning curve for designing an extensive and thorough rehabilitation program is very large, and we are far from writing the final chapter.

There are several chapters in this book that have examined the function and biomechanics of the PCL as well as the other major ligamentous stabilizers of the knee, so it is not necessary to duplicate them for the purpose of this chapter. However, in order to design a rehabilitation program that promotes the restoration of function, while minimizing potentially detrimental forces on the healing graft tissue, it is crucial to understand how various exercises and activities impact these structures following reconstruction. More specifically, what is occurring at the tibiofemoral joint and what effect will this have on the healing tissues. To be fair, it is difficult to determine with any certainty the pure biomechanics in vitro since most studies have utilized physiological models or imaging studies to calculate joint forces [3–7]. Obviously, the implantation of force transducers in vivo to accurately assess ligamentous dynamics as well as joint translation is not practical or feasible at this time. Subsequently, we must take the research that is available and combine this with critical observation when progressing exercises and activities.

In reviewing the literature, most studies have examined the tibiofemoral joint in the isolated PCL or posterolateral corner-deficient knee [3–10]. There are no available studies that examine these forces in the knee that has undergone reconstruction of these structures. Is it realistic that surgical intervention has restored “normal” joint mechanics? Although techniques continue to evolve, it is impractical that the exact biomechanical properties of the native PCL can be duplicated. Conversely, it is reasonable to assume that reconstruction has improved ligamentous integrity of the knee and restored a near physiological and biomechanical equivalent. It would appear that the best course of action would be to apply a combination of the results found in the normal knee and those reported in the ligament-deficient knee when determining the appropriate implementation and timing of various exercises and activities.

In a study by Goyal and colleagues [4], an in vivo analysis of the PCL -deficient knee during functional activities was conducted. Only subjects with isolated grade II PCL injuries were included, and the activities studied were level running and stair ascent. As expected, increased posterior translation on the effected knee with both activities was observed, and this decreased at the point where the greatest degree of quadriceps activity occurred. This happened prior to heel strike in running, but not until late heel strike with ascending stairs. In addition, the velocity associated with the tibia moving from a posterior subluxed position to its normal anterior position was greater during stair ascension, thus creating higher axial joint loading and shear forces. Therefore, in regard to early postoperative rehabilitation, it may be safer to have the patient ascend stairs with the uninvolved leg only, and to take one step at a time. Fortunately, this is the method taught to the majority of patients who ascend stairs during partial weight-bearing (PWB) gait (up with the good and down with the bad) regardless of the injury. In regard to joint forces at various degrees of knee flexion , Eisenhart-Rothe and associates noted minimal posterior translation of the tibia from 0 to 60°, but there was significant anterior tibial translation at 90° as well as a prominent lateral shift of the patella on the femur. Ironically, when subjects performed isometric contraction of the hamstrings at 90°, the anterior translation was greater than in a state of muscle relaxation. These findings, as they relate to tibiofemoral forces, agree with previous studies that have found greater anterior translation at knee angles of 90° or greater. Accordingly, this range of motion (ROM) needs to be avoided during functional activities and rehabilitation exercises during the early phase of graft maturation.

Although these studies give us greater insight into the tibiofemoral kinematics of the PCL -deficient knee, they are limited to single-plane analysis and do not consider the effects of combined ligamentous instability. In addition, there is a dearth of studies that have examined joint forces in the reconstructed knee. Therefore, until these studies are designed and implemented, the best assessment of the effectiveness of any rehabilitation program should be based on patient satisfaction outcomes and objective measurements of ligamentous integrity, both through instrumented and radiological assessment.