ReviewA review of the anatomical, biomechanical and kinematic findings of posterior cruciate ligament injury with respect to non-operative management
Introduction
The posterior cruciate ligament (PCL) is twice as strong the anterior cruciate ligament [1] and is the primary restraint to posterior tibial translation [2] but management of PCL injuries has been less extensively studied than its anterior counterpart [3]. Cadaveric studies have detailed the anatomy of the PCL. It consists of two components, the anterolateral and posteromedial bundle which demonstrate different strain rates at different degrees of knee flexion [4]. Cadaveric studies have also analysed the tensile strength [5], chondral deformation forces [6] and primary and secondary restraining functions of the PCL [7]. However, it is difficult to correlate the findings of cadaveric studies to clinical evaluation of the patient with a PCL injury because cadaveric studies cannot replicate the contribution to joint stability of surrounding neuromuscular structures. This issue is most accurately addressed with in vivo studies analysing the kinematic profile of the knee in patients with PCL injuries. These studies rely on imaging such as fluoroscopy, computer tomography and magnetic resonance to evaluate static and dynamic articulation profiles.
The incidence of PCL injuries varies from 3% to 44% of all knee injuries [8], [9], [10]. Motor vehicle injuries and athletic injuries are the most common causes of PCL injuries [9]. Athletic injuries are most likely to result in an isolated PCL injury whereas motor vehicle accidents produce multiple-ligament damage [11]. The majority of athletes with an isolated PCL injury return to competitive sport with non-operative rehabilitation of the knee [12]. Physical therapy encompasses adequate knee stabilisation through compensatory muscle function to resist excessive posterior tibial translation [12], [13], [14], [15], [16]. Common programmes involve a 2 to 4 week period of immobilisation with the knee braced in full extension. Extension reduces the tibiofemoral joint by preventing posterior sag and diminishes the effects of gravity and hamstring muscle contraction on tibial translation. Following this, quadriceps muscle strengthening exercises are encouraged and the use of hamstring muscles is prohibited to minimise posterior tibial load. Many athletes then return to sport one to three months after injury. Athletes are advised to return to sport once they have regained their full range of motion and 90% of the strength of the contralateral knee [8]. Many studies suggest that with physiotherapy many athletes suffer little functional loss but some studies do report functional deterioration associated with time since injury [17], [18], [19], [20].
The purpose of this review paper is to provide an overview of the anatomy, biomechanics and kinematics of the PCL injured knee and discuss the basic science findings with respect to the results of non-operative treatment and the functional outcome of isolated PCL injuries.
Section snippets
Anatomy
The PCL arises from the posterior tibia 10 mm from the joint line and extends in an anteromedial direction to insert on the lateral surface of the medial femoral condyle [21], [22]. The PCL is between 32 and 38 mm long [1]. It has a cross sectional area of 48 mm [2] at its midsubstance level [23]. The tibia and femoral insertion sites of the PCL are approximately three times larger than its midsubstance cross sectional area. The PCL arises from the tibia within a depression between the posterior
Cadaveric studies
The biomechanical properties of the PCL have largely been derived through the use of in vitro cadaveric models. In these models, cadaveric knees are tested before and after sectioning of the PCL using either simulated muscle loads or anterior, posterior and rotational loading [7]. Sectioning of the PLC, meniscofemoral ligaments or medial compartment structures further helps to determine the primary and secondary restraining functions of the PCL [33]. The main drawback of in vitro cadaveric
In vivo studies
The advantage of clinical studies over cadaveric studies is that clinical studies take into consideration the contribution of neuromuscular structures when analysing isolated ligament deficiency. Clinical studies rely on using various imaging modalities to analyse knee kinematics. Sagittal plane articulation of the tibiofemoral joint can be described by tibiofemoral contact mapping and the position of the flexion facet centre in normal [50], injured [51] or osteoarthritic knees [52], [53].
Conclusions
Understanding the kinematics of PCL deficiency and its related structures is important for diagnosis and management. The PCL in addition to the posterolateral structures, posterolateral capsule and meniscofemoral ligaments provide important primary and secondary restraints to posterior translation of the medial tibia. Injury to the PCL alters the articulation pattern of the medial compartment and increases the contact pressures within it.
Cadaveric studies have shown a strong influence of the
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