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Purpose The purpose of this study was to determine the contribution of each of the ACL and medial ligament structures in resisting anteromedial rotatory instability (AMRI) loads applied in vitro. Methods Twelve knees were tested using a robotic system. It imposed loads simulating clinical laxity tests at 0° to 90° flexion: ±90 N anterior–posterior force, ±8 Nm varus–valgus moment, and ±5 Nm internal–external rotation, and the tibial displacements were measured in the intact knee. The ACL and individual medial structures—retinaculum, superficial and deep medial collateral ligament (sMCL and dMCL), and posteromedial capsule with oblique ligament (POL + PMC)—were sectioned sequentially. The tibial displacements were reapplied after each cut and the reduced loads required allowed the contribution of each structure to be calculated. Results For anterior translation, the ACL was the primary restraint, resisting 63–77% of the drawer force across 0° to 90°, the sMCL contributing 4–7%. For posterior translation, the POL + PMC contributed 10% of the restraint in extension; other structures were not significant. For valgus load, the sMCL was the primary restraint (40–54%) across 0° to 90°, the dMCL 12%, and POL + PMC 16% in extension. For external rotation, the dMCL resisted 23–13% across 0° to 90°, the sMCL 13–22%, and the ACL 6–9%. Conclusion The dMCL is the largest medial restraint to tibial external rotation in extension. Therefore, following a combined ACL + MCL injury, AMRI may persist if there is inadequate healing of both the sMCL and dMCL, and MCL deficiency increases the risk of ACL graft failure.

Patellofemoral pain (PFP) is a highly prevalent condition, affecting up to 23% of the general and 28% of the adolescent population [1]. Recent evidence suggests that patellofemoral joint (PFJ) osteoarthritis is a sequelae of PFP [2, 3] challenging the traditional notion that adolescent anterior knee pain is a benign pathology. Furthermore, high levels of depression and anxiety are reported amongst patients suffering PFP [4]. It is therefore concerning that despite the implementation of evidence-based interventions including exercise therapy, the prognosis of this condition remains poor, with 40–56% of patients reporting ongoing symptoms 1–2 years following conservative treatment [5, 6]. It is estimated that over 50% of people with the condition will report symptoms continuing beyond 5 years following diagnosis [7]. In addition, those patients who complain of high base levels of pain and longer duration of symptoms are typically found to have the most unfavourable recovery [5]. These poor long-term outcomes highlight that despite PFP populations being widely investigated, at present the answers on how best to manage these patients are lacking. With this in mind, how then does the treating clinician go about designing a successful rehabilitation programme for these patients? This chapter reviews current evidence in this field and discusses biomechanical principles to help guide how this might be achieved. We note that growing evidence highlights the importance of also considering psychological factors affecting this population [4], and these are discussed in a separate chapter.

The medial patellofemoral complex, consisting of the medial patellofemoral ligament (MPFL) and the medial patellotibial ligament, is the main passive stabiliser of the patellofemoral joint. Since it has been shown that rupture of the MPFL is the main pathological consequence of patellar dislocation and biomechanical studies have demonstrated that the MPFL is the main restraint against lateral patellar displacement, reconstruction of the MPFL has become a widespread technique for restoration of patellofemoral stability.