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Purpose This paper is a review of the biomechanical principles that support limb realignment surgery via osteotomy around the knee, principally high (proximal) tibial osteotomy. Methods The basic biomechanical principles have been described, and the related literature examined for evidence to support the recommendations made. Results The forces on the knee when walking are shown to lead to most of the load acting through the medial compartment, the most frequent site of degeneration of the knee, due to the adduction moment that acts during the weight-acceptance phase. Realignment of the limb to move the mechanical axis to a desired point within the knee is described, and the resulting joint contact pressures in the medial and lateral compartments are shown to be higher in the less-congruent lateral articulation when the load passes through the centre of the knee. At the same time, there can be changes of the posterior slope of the tibial plateau, and a slope of ten degrees can induce a shearing force, which stretches the ACL, of 0.5 body weight when the knee force is 3 times body weight. The options regarding tibial or femoral or even double osteotomies are discussed in relation to medial–lateral slope of the joint line. Secondary effects such as alteration of collateral ligament tension or of the height of the patella are described. Conclusion Critical review of the publications supporting osteotomy surgery suggests that many of the accepted ‘rules’ have little scientific evidence to show that they represent the best practise for long-term preservation of the joint.

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.

Purpose To define the bony attachments of the medial ligaments relative to anatomical and radiographic bony landmarks, providing information for medial collateral ligament (MCL) surgery. Method The femoral and tibial attachments of the superficial MCL (sMCL), deep MCL (dMCL) and posterior oblique ligament (POL), plus the medial epicondyle (ME) were defined by radiopaque staples in 22 knees. These were measured radiographically and optically; the precision was calculated and data normalised to the sizes of the condyles. Femoral locations were referenced to the ME and to Blumensaat’s line and the posterior cortex. Results The femoral sMCL attachment enveloped the ME, centred 1 mm proximal to it, at 37 ± 2 mm (normalised at 53 ± 2%) posterior to the most-anterior condyle border. The femoral dMCL attachment was 6 mm (8%) distal and 5 mm (7%) posterior to the ME. The femoral POL attachment was 4 mm (5%) proximal and 11 mm (15%) posterior to the ME. The tibial sMCL attachment spread from 42 to 71 mm (81–137% of A-P plateau width) below the tibial plateau. The dMCL fanned out anterodistally to a wide tibial attachment 8 mm below the plateau and between 17 and 39 mm (33–76%) A-P. The POL attached 5 mm below the plateau, posterior to the dMCL. The 95% CI intra-observer was ± 0.6 mm, inter-observer ± 1.3 mm for digitisation. The inter-observer ICC for radiographs was 0.922. Conclusion The bone attachments of the medial knee ligaments are located in relation to knee dimensions and osseous landmarks. These data facilitate repairs and reconstructions that can restore physiological laxity and stability patterns across the arc of knee flexion.

Purpose The infrapatellar fat pad (IFP) is a common cause of knee pain and loss of knee flexion and extension. However, its anatomy and behavior are not consistently defined. Methods Thirty-six unpaired fresh frozen knees (median age 34 years, range 21–68) were dissected, and IFP attachments and volume measured. The rectus femoris was elevated, suprapatellar pouch opened and videos recorded looking inferiorly along the femoral shaft at the IFP as the knee was flexed. The patellar retinacula were incised and the patella reflected distally. The attachment of the ligamentum mucosum (LMuc) to the intercondylar notch was released from the anterior cruciate ligament (ACL), both menisci and to the tibia via meniscotibial ligaments. IFP strands projecting along both sides of the patella were elevated and the IFP dissected from the inferior patellar pole. Magnetic resonance imaging (MRI) of one knee at ten flexion angles was performed and the IFP, patella, tibia and femur segmented. Results In all specimens the IFP attached to the inferior patellar pole, femoral intercondylar notch (via the LMuc), proximal patellar tendon, intermeniscal ligament, both menisci and the anterior tibia via the meniscotibial ligaments. In 30 specimens the IFP attached to the anterior ACL fibers via the LMuc, and in 29 specimens it attached directly to the central anterior tibia. Proximal IFP extensions were identified alongside the patella in all specimens and visible on MRI [medially (100% of specimens), mean length 56.2 ± 8.9 mm, laterally (83%), mean length 23.9 ± 6.2 mm]. Mean IFP volume was 29.2 ± 6.1 ml. The LMuc, attached near the base of the middle IFP lobe, acting as a ‘tether’ drawing it superiorly during knee extension. The medial lobe consistently had a pedicle superomedially, positioned between the patella and medial trochlea. MRI scans demonstrated how the space between the anterior tibia and patellar tendon (‘the anterior interval’) narrowed during knee flexion, displacing the IFP superiorly and posteriorly as it conformed to the trochlear and intercondylar notch surfaces. Conclusion Proximal IFP extensions are a novel description. The IFP is a dynamic structure, displacing significantly during knee motion, which is, therefore, vulnerable to interference from trauma or repetitive overload. Given that this trauma is often surgical, it may be appropriate that surgeons learn to minimize injury to the fat pad at surgery.

Purpose This study aims to identify and summarize the evidence on the biomechanical parameters and the corresponding technologies which have been used to quantify the pivot shift test during the clinical and functional assessment of anterior cruciate ligament (ACL) injury and surgical reconstruction. Methods Search strategy Internet search of indexed scientific articles on the PubMed database, Web of Science and references on published manuscripts. No year restriction was used. Selection criteria Articles included were written only in English and related to search terms: “pivot shift” AND (OR “ACL”). The reviewers independently selected only those studies that included at least one quantitative parameter for the analysis of the pivot shift test, including both in vitro and in vivo analyses performed on human joint. Those studies that analysed only clinical grading were excluded from the analysis. Analysis After evaluating the methodological quality of the articles, the parameters found were summarized. Results Six hundred and eight studies met the inclusion criteria, and finally, 68 unique studies were available for the systematic review. Quantitative results were heterogeneous. The pivot shift test has been quantified by means of 25 parameters, but most of the studies focused on anterior-posterior translations, internal–external rotation and acceleration in anterior-posterior direction. Conclusion Several methodologies have been identified and developed to quantify pivot shift test. However, clinical professionals are still lacking a ‘gold standard’ method for the quantification of knee joint dynamic laxity. A widespread adoption of a standardized pivot shift manoeuvre and measurement method to allow objective comparison of the results of ACL reconstructions is therefore desirable. Further development of measurement methods is indeed required to achieve this goal in a routine clinical scenario. Level of Evidence Systematic review of—at least—level II studies, Level II.

The iliotibial band (ITB) has an important role in knee mechanics and tightness can cause patellofemoral maltracking. This study investigated the effects of increasing ITB tension on knee kinematics. Nine fresh-frozen cadaveric knees had the components of the quadriceps loaded with 175N. A Polaris optical tracking system was used to acquire joint kinematics during extension from 100° to 0° flexion. This was repeated after the following ITB loads: 30, 60 and 90N. There was no change with 30N load for patellar translation. On average, at 60 and 90N, the patella translated laterally by 0.8 and 1.4mm in the mid flexion range compared to the ITB unloaded condition. The patella became more laterally tilted with increasing ITB loads by 0.7°, 1.2° and 1.5° for 30, 60 and 90N, respectively. There were comparable increases in patellar lateral rotation (distal patella moves laterally) towards the end of the flexion cycle. Increased external rotation of the tibia occurred from early flexion onwards and was maximal between 60° and 75° flexion. The increase was 5.2°, 9.5° and 13° in this range for 30, 60 and 90N, respectively. Increased tibial abduction with ITB loads was not observed. The combination of increased patellar lateral translation and tilt suggests increased lateral cartilage pressure. Additionally, the increased tibial external rotation would increase the Q angle. The clinical consequences and their relationship to lateral retinacular releases may be examined, now that the effects of a tight ITB are known.

This article reviews the evidence for the roles of the anterolateral soft-tissue structures in rotatory stability of the knee, including their structural properties, isometry, and contributions to resisting tibial internal rotation. These data then lead to a biomechanical demonstration that the ilio-tibial band is the most important structure for the restraint of anterolateral rotatory instability. Level of evidence V.

Laboratory data indicate the hip capsular ligaments prevent excessive range of motion, may protect the joint against adverse edge loading and contribute to synovial fluid replenishment at the cartilage surfaces of the joint. However, their repair after joint preserving or arthroplasty surgery is not routine. In order to restore their biomechanical function after hip surgery, the positions of the hip at which the ligaments engage together with their tensions when they engage is required. Nine cadaveric left hips without pathology were skeletonised except for the hip joint capsule and mounted in a six-degrees-of-freedom testing rig. A 5Nm torque was applied to all rotational degrees-of-freedom separately to quantify the passive restraint envelope throughout the available range of motion with the hip functionally loaded. The capsular ligaments allowed the hip to internally/externally rotate with a large range of un-resisted rotation (up to 50±10°) in mid-flexion and mid-ab/adduction but this was reduced towards the limits of flexion/extension and ab/adduction such that there was a near-zero slack region in some positions (p<0.014). The slack region was not symmetrical; the mid-slack point was found with internal rotation in extension and external rotation in flexion (p<0.001). The torsional stiffness of the capsular ligamentous restraint averaged 0.8±0.3Nm/° and was greater in positions where there were large slack regions. These data provide a target for restoration of normal capsular ligament tensions after joint preserving hip surgery. Ligament repair is technically demanding, particularly for arthroscopic procedures, but failing to restore their function may increase the risk of osteoarthritic degeneration.

Achilles’ tendon (AT) injuries such as ruptures and tendinopathies have experienced a dramatic rise in the mid- to older-aged population. Given that the AT plays a key role at all stages of locomotion, unsuccessful rehabilitation after injury often leads to long-term, deleterious health consequences. Understanding healthy in vivo strains as well as the complex muscle–tendon unit interactions will improve access to the underlying aetiology of injuries and how their functionality can be effectively restored post-injury. The goals of this survey of the literature with a systematic search were to provide a benchmark of healthy AT strains measured in vivo during functional activities and identify the sources of variability observed in the results. Two databases were searched, and all articles that provided measured in vivo peak strains or the change in strain with respect to time were included. In total, 107 articles that reported subjects over the age of 18 years with no prior AT injury and measured while performing functional activities such as voluntary contractions, walking, running, jumping, or jump landing were included in this review. In general, unclear anatomical definitions of the sub-tendon and aponeurosis structures have led to considerable confusion in the literature. MRI, ultrasound, and motion capture were the predominant approaches, sometimes coupled with modelling. The measured peak strains increased from 4% to over 10% from contractions, to walking, running, and jumping, in that order. Importantly, measured AT strains were heavily dependent on measurement location, measurement method, measurement protocol, individual AT geometry, and mechanical properties, as well as instantaneous kinematics and kinetics of the studied activity. Through a comprehensive review of approaches and results, this survey of the literature therefore converges to a united terminology of the structures and their common underlying characteristics and presents the state-of-knowledge on their functional strain patterns.

Purpose The aim of the study was to investigate varus and normal knee morphologies to identify differences that may affect knee replacement alignment or design for varus knees. Methods Computed tomography scans of varus and normal knees were analyzed, and geometric shapes, points and axes were fit to the femur and tibia independently. These points were then projected in the three anatomical planes to measure the variations between the two groups. Results In the femur, varus knees had less femoral anteversion ( p  < 0.0001) and a larger medial extension facet ( p  < 0.05) compared with normal knees. In the tibia, the tubercle was found to be externally rotated in varus knees (12°), with a significant increase in the coronal slope ( p  = 0.001) and the extension facet angle ( p  = 0.002). Conclusions The study highlighted the differences and similarities found between the two groups, which raises awareness on changes required during surgical intervention and component placement or design for a varus knee. This is particularly relevant for the design of patient-specific instrumentation and implants. Levels of evidence Diagnostic study, Level III.