Standardisation of the description of patellofemoral motion and comparison between different techniques.

Accepted versio

Incidence and mechanism of the pivot shift. An in vitro study.

Accepted versio

Posterior capsular release is a biomechanically safe procedure to perform in total knee arthroplasty

Purpose Surgeons may attempt to strip the posterior capsule from its femoral attachment to overcome flexion contracture in total knee arthroplasty (TKA); however, it is unclear if this impacts anterior–posterior (AP) laxity of the implanted knee. The aim of the study was to investigate the effect of posterior capsular release on AP laxity in TKA, and compare this to the restraint from the posterior cruciate ligament (PCL). Methods Eight cadaveric knees were mounted in a six degree of freedom testing rig and tested at 0°, 30°, 60° and 90° flexion with ± 150 N AP force, with and without a 710 N axial compressive load. After the native knee was tested, a deep dished cruciate-retaining TKA was implanted and the tests were repeated. The PCL was then cut, followed by releasing the posterior capsule using a curved osteotome. Results With 0 N axial load applied, cutting the PCL as well as releasing the posterior capsule significantly increased posterior laxity compared to the native knee at all flexion angles, and CR TKA states at 30°, 60° and 90° (p < 0.05). However, no significant increase in laxity was found between cutting the PCL and subsequent PostCap release (n.s.). In anterior drawer, there was a significant increase of 1.4 mm between cutting the PCL and PostCap release at 0°, but not at any other flexion angles (p = 0.021). When a 710 N axial load was applied, there was no significant difference in anterior or posterior translation across the different knee states (n.s.). Conclusions Posterior capsular release only caused a small change in AP laxity compared to cutting the PCL and, therefore, may not be considered detrimental to overall AP stability if performed during TKA surgery. Level of evidence Controlled laboratory study

A cadaveric model to evaluate the effect of unloading the medial quadriceps on patellar tracking and patellofemoral joint pressure and stability

Background Vastus Medialis Muscles (VMM) damage has been widely identified following patellar dislocation. Rehabilitation programmes have been suggested to strengthen the VMM and reduce clinical symptoms of pain and instability. This controlled laboratory study investigated the hypothesis that reduced Vastus Medialis Obliquus (VMO) and Vastus Medialis Longus (VML) muscle tension would alter patellar tracking, stability and PFJ contact pressures. Methods Nine fresh-frozen dissected cadaveric knees were mounted in a rig with the quadriceps and iliotibial band loaded to 205 N. An optical tracking system measured joint kinematics and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Measurements were repeated for three conditions: 1. With all quadriceps heads and iliotibial band (ITB) loaded; 2. as 1, but with the VMO muscle unloaded and 3. as 1, but with the VMO and VML unloaded. Measurements were also repeated for the three conditions with a 10 N lateral displacement force applied to the patella. Results Reduction of VMM tension resulted in significant increases in lateral patellar tilt (2.8°) and translation (4 mm), with elevated lateral and reduced medial joint contact pressures from 0.48 to 0.14 MPa, and reduced patellar stability (all p < 0.05). Conclusions These findings provide basic scientific rationale to support the role of quadriceps strengthening to resist patellar lateral maltracking and rebalance the articular contact pressure away from the lateral facet in patients with normal patellofemoral joint anatomy

Neural Structures within Human Meniscofemoral Ligaments: A Cadaveric Study.

Aim. To investigate the existence of neural structures within the meniscofemoral ligaments (MFLs) of the human knee. Methods. The MFLs from 8 human cadaveric knees were harvested. 5 μm sections were H&E-stained and examined under light microscopy. The harvested ligaments were then stained using an S100 monoclonal antibody utilising the ABC technique to detect neural components. Further examination was performed on 60–80 nm sections under electron microscopy. Results. Of the 8 knees, 6 were suitable for examination. From these both MFLs existed in 3, only anterior MFLs were present in 2, and an isolated posterior MFL existed in 1. Out of the 9 MFLs, 4 demonstrated neural structures on light and electron microscopy and this was confirmed with S100 staining. The ultrastructure of these neural components was morphologically similar to mechanoreceptors. Conclusion. Neural structures are present in MFLs near to their meniscal attachments. It is likely that the meniscofemoral ligaments contribute not only as passive secondary restraints to posterior draw but more importantly to proprioception and may therefore play an active role in providing a neurosensory feedback loop. This may be particularly important when the primary restraint has reduced function as in the posterior cruciate ligament—deficient human knee

Medial collateral ligament reconstruction for anteromedial instability of the knee: a biomechanical study in vitro.

BACKGROUND: Although a medial collateral ligament (MCL) injury is associated with anteromedial rotatory instability (AMRI) and often with an anterior cruciate ligament (ACL) injury, there has been little work to develop anteromedial (AM) reconstruction to address this laxity. PURPOSE: To measure the ability of a novel "anatomic" AM reconstruction technique to restore native knee laxity for isolated AM insufficiency and combined AM plus posteromedial insufficiency. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 12 cadaveric knees were mounted in a kinematic testing rig that allowed the tibia to be loaded while the knee flexed-extended 0° to 100° with 88-N anteroposterior translation, 5-N·m internal rotation-external rotation (ER), 8-N·m valgus, and combined anterior translation plus ER to simulate AMRI. Joint motion was measured using optical trackers with the knee intact, after superficial MCL (sMCL) and deep MCL (dMCL) transection, and after AM reconstruction of the sMCL and dMCL with semitendinosus autografts. The posteromedial capsule (PMC)/posterior oblique ligament (POL) was then transected to induce a grade 3 medial injury, and kinematic measurements were repeated afterward and again after removing the grafts. Laxity changes were examined using repeated-measures analysis of variance and post-testing. RESULTS: sMCL and dMCL deficiency increased valgus, ER, and AMRI laxities. These laxities did not differ from native values after AM reconstruction. Additional PMC/POL deficiency did not increase these laxities significantly but did increase internal rotation laxity near knee extension; this was not controlled by AM reconstruction. CONCLUSION: AM reconstruction eliminated AMRI after transection of the dMCL and sMCL, and also eliminated AMRI after additional PMC/POL transection. CLINICAL RELEVANCE: Many MCL injuries occur in combination with ACL injuries, causing AMRI. These injuries may rupture the AM capsule and dMCL. Unaddressed MCL deficiency leads to an increased ACL reconstruction failure rate. A dMCL construct oriented anterodistally across the medial joint line, along with an sMCL graft, can restore native knee ER laxity. PMC/POL lesions did not contribute to AMRI

The attachments of the anteromedial and posterolateral fibre bundles of the anterior cruciate ligament: Part 1: tibial attachment.

Accepted versio

Reduced tibial strain-shielding with extraosseous total knee arthroplasty revision system

Background Revision total knee arthroplasty (RTKA) has poorer results than primary total knee arthroplasty (TKA), and the prostheses are invasive and cause strain-shielding of the bones near the knee. This paper describes an RTKA system with extracortical fixation. It was hypothesised that this would reduce strain-shielding compared with intramedullary fixation. Methods Twelve replica tibiae were prepared for full-field optical surface strain analysis. They were either left intact, implanted with RTKA components with cemented intramedullary fixation stems, or implanted with a novel design with a tibial tray subframe supported by two extracortical fixation plates and screw fixation. They were loaded to simulate peak walking and stair climbing loads and the surface strains were measured using digital image correlation. The measurements were validated with strain gauge rosettes. Results Compared to the intact bone model, extracortical fixation reduced surface strain-shielding by half versus intramedullary fixation. For all load cases and bone regions examined, the extracortical implant shielded 8–27% of bone strain, whereas the intramedullary component shielded 37–56%. Conclusions The new fixation design, which offers less bone destruction than conventional RTKA, also reduced strain-shielding. Clinically, this design may allow greater rebuilding of bone loss, and should increase long-term fixation