Abstract

Aims

Bi-unicondylar arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL)-preserving alternative to total knee arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA.

Aims

Unicompartmental knee arthroplasty (UKA) and bicompartmental knee arthroplasty (BCA) have been associated with improved functional outcomes compared to total knee arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function.

In this in vitro study of the hip joint we examined which soft tissues act as primary and secondary passive rotational restraints when the hip joint is functionally loaded. A total of nine cadaveric left hips were mounted in a testing rig that allowed the application of forces, torques and rotations in all six degrees of freedom. The hip was rotated throughout a complete range of movement (ROM) and the contributions of the iliofemoral (medial and lateral arms), pubofemoral and ischiofemoral ligaments and the ligamentum teres to rotational restraint was determined by resecting a ligament and measuring the reduced torque required to achieve the same angular position as before resection. The contribution from the acetabular labrum was also measured. Each of the capsular ligaments acted as the primary hip rotation restraint somewhere within the complete ROM, and the ligamentum teres acted as a secondary restraint in high flexion, adduction and external rotation. The iliofemoral lateral arm and the ischiofemoral ligaments were primary restraints in two-thirds of the positions tested. Appreciation of the importance of these structures in preventing excessive hip rotation and subsequent impingement/instability may be relevant for surgeons undertaking both hip joint preserving surgery and hip arthroplasty.

Cite this article: Bone Joint J 2015; 97-B:484–91.

There have been differing descriptions of the anterolateral structures of the knee, and not all have been named or described clearly. The aim of this study was to provide a clear anatomical interpretation of these structures. We dissected 40 fresh-frozen cadaveric knees to view the relevant anatomy and identified a consistent structure in 33 knees (83%); we termed this the anterolateral ligament of the knee. This structure passes antero-distally from an attachment proximal and posterior to the lateral femoral epicondyle to the margin of the lateral tibial plateau, approximately midway between Gerdy’s tubercle and the head of the fibula. The ligament is superficial to the lateral (fibular) collateral ligament proximally, from which it is distinct, and separate from the capsule of the knee. In the eight knees in which it was measured, we observed that the ligament was isometric from 0° to 60° of flexion of the knee, then slackened when the knee flexed further to 90° and was lengthened by imposing tibial internal rotation.

Cite this article: Bone Joint J 2014;96-B:325–31.

Introduction

Differing descriptions of patellar motion relative to the femur have resulted from many in-vitro and in-vivo studies. The aim of this study was to examine the tracking behaviour of the patella. We hypothesized that patellar kinematics would correlate to the trochlear geometry.

This annotation considers the place of extra-articular reconstruction in the treatment of anterior cruciate ligament (ACL) deficiency. Extra-articular reconstruction has been employed over the last century to address ACL deficiency. However, the technique has not gained favour, primarily due to residual instability and the subsequent development of degenerative changes in the lateral compartment of the knee. Thus intra-articular reconstruction has become the technique of choice. However, intra-articular reconstruction does not restore normal knee kinematics. Some authors have recommended extra-articular reconstruction in conjunction with an intra-articular technique.

The anatomy and biomechanics of the anterolateral structures of the knee remain largely undetermined. Further studies to establish the structure and function of the anterolateral structures may lead to more anatomical extra-articular reconstruction techniques that supplement intra-articular reconstruction. This might reduce residual pivot shift after an intra-articular reconstruction and thus improve the post-operative kinematics of the knee.

The purpose of this study was to assess the stability of a developmental pelvic reconstruction system which extends the concept of triangular osteosynthesis with fixation anterior to the lumbosacral pivot point. An unstable Tile type-C fracture, associated with a sacral transforaminal fracture, was created in synthetic pelves. The new concept was compared with three other constructs, including bilateral iliosacral screws, a tension band plate and a combined plate with screws. The pubic symphysis was plated in all cases. The pelvic ring was loaded to simulate single-stance posture in a cyclical manner until failure, defined as a displacement of 2 mm or 2°. The screws were the weakest construct, failing with a load of 50 N after 400 cycles, with maximal translation in the craniocaudal axis of 12 mm. A tension band plate resisted greater load but failure occurred at 100 N, with maximal rotational displacement around the mediolateral axis of 2.3°.

The combination of a plate and screws led to an improvement in stability at the 100 N load level, but rotational failure still occurred around the mediolateral axis. The pelvic reconstruction system was the most stable construct, with a maximal displacement of 2.1° of rotation around the mediolateral axis at a load of 500 N.

Objective patellar instability has been correlated with dysplasia of the femoral trochlea. This in vitro study tested the hypothesis that trochleoplasty would increase patellar stability and normalise the kinematics of a knee with a dysplastic trochlea. Six fresh-frozen knees were loaded via the heads of the quadriceps. The patella was displaced 10 mm laterally and the displacing force was measured from 0° to 90° of flexion. Patellar tracking was measured from 0° to 130° of knee flexion using magnetic sensors. These tests were repeated after raising the central anterior trochlea to simulate dysplasia, and repeated again after performing a trochleoplasty on each specimen. The simulated dysplasia significantly reduced stability from that of the normal knee (p < 0.001). Trochleoplasty significantly increased the stability (p < 0.001), so that it did not then differ significantly from the normal knee (p = 0.244). There were small but statistically significant changes in patellar tracking (p< 0.001).

This study has provided objective biomechanical data to support the use of trochleoplasty in the treatment of patellar instability associated with femoral trochlear dysplasia.

Anatomical descriptions of the lateral retinaculum have been published, but the attachments, name or even existence of its tissue bands and layers are ill-defined. We have examined 35 specimens of the knee. The deep fascia is the most superficial layer and the joint capsule is the deepest. The intermediate layer is the most substantial and consists of derivatives of the iliotibial band and the quadriceps aponeurosis. The longitudinal fibres of the iliotibial band merge with those of the quadriceps aponeurosis adjacent to the patella. These longitudinal fibres are reinforced by superficial arciform fibres and on the deep aspect by transverse fibres of the iliotibial band. The latter are dense and provide attachment of the iliotibial band to the patella and the tendon of vastus lateralis obliquus.

Our study identifies two important new findings which are a constant connection of the deep fascia to the quadriceps tendon superior and lateral to the patella, and, a connection of the deeper transverse fibres to the tendon of vastus lateralis obliquus.

The menisci of the knee have an important role in load-bearing and shock absorption within the joint. They may also function as secondary stabilisers, have a proprioceptive role, and aid the lubrication and nutrition of the articular cartilage. Complete or partial loss of a meniscus can have damaging effects on a knee, leading to serious long-term sequelae.

This paper reviews the consequences of meniscectomy and summarises the body of evidence in the literature regarding those factors most relevant to long-term outcome.

Introduction: By characterising ACL strain behaviour in intact and posteromedial deficient knees under a variety of external loading conditions the aim of this work was to demonstrate whether posteromedial corner insufficiency could increase strain in an ACL reconstruction graft.

Materials and Methods: 15 fresh cadaveric knees were mounted on a materials testing machine. A miniature extensometer was implanted onto the anteromedial bundle (AMB) of the ACL. The knees were loaded in: Anterior draw (150N), varus/valgus rotation (5Nm) and internal/external rotation (5Nm) at 0°, 15°, 30°, 60° & 90° flexion. The posteromedial corner structures – posteromedial capsule, superficial MCL and deep MCL – were cut sequentially and the effect AMB strain measured.

Results: Strain data for analysis was available for 11 intact knees: Tibial internal rotation produced increased strain in the AMB at all angles of knee flexion (p< 0.05). Tibial external rotation reduced ACL strain at 0° to 30° (p< 0.05) and 60° to 90° knee flexion (p> 0.05).

Anterior loading of the tibia increased AMB strain. With the tibia free to rotate, strain was highest at 90 degrees knee flexion (5.3%) and lowest at 0 degrees (1.6%). Fixed internal and external tibial rotation reduced AMB strain produced by a 150 N anterior drawer force at all knee flexion angles.

Strain data for analysis was available for 6 Posteromedial Corner deficient knees:

With the tibia free to rotate or when locked in internal rotation, cutting the posteromedial structures had no effect on AMB strain with a 150 N anterior drawer force applied to the tibia. However, with the tibia locked in external rotation, cutting the posteromedial structures increased AMB strain at 60 and 90 degrees flexion. This difference however did not reach statistical significance.

Conclusions: The findings that division of the posteromedial structures may cause increased AMB strain and that there is significant load sharing by the peripheral ligamentous structures, suggests that valgus and rotational stresses to the knee in a patient with posteromedial corner insufficiency could lead to increased strain in the ACL graft, that would otherwise have been restrained by the posteromedial corner complex. It would also therefore seem to be appropriate to recommend the use of a collateral ligament brace in the post-operative period when combining a repair of the posteromedial structures and the ACL, to again prevent excessive graft strains.

Normal function of the patellofemoral joint is maintained by a complex interaction between soft tissues and articular surfaces. No quantitative data have been found on the relative contributions of these structures to patellar stability. Eight knees were studied using a materials testing machine to displace the patella 10 mm laterally and medially and measure the force required. Patellar stability was tested from 0° to 90° knee flexion with the quadriceps tensed to 175 N. Four conditions were examined: intact, vastus medialis obliquus relaxed, flat lateral condyle, and ruptured medial retinaculae. Abnormal trochlear geometry reduced the lateral stability by 70% at 30° flexion, while relaxation of vastus medialis obliquus caused a 30% reduction. Ruptured medial retinaculae had the largest effect at 0° flexion with 49% reduction. There was no effect on medial stability. There is a complex interaction between these structures, with their contributions to loss of lateral patellar stability varying with knee flexion.

The tensile strength of the medial patellofemoral ligament (MPFL), and of surgical procedures which reconstitute it, are unknown. Ten fresh cadaver knees were prepared by isolating the patella, leaving only the MPFL as its attachment to the medial femoral condyle. The MPFL was either repaired by using a Kessler suture or reconstructed using either bone anchors or one of two tendon grafting techniques. The tensile strength and the displacement to peak force of the MPFL were then measured using an Instron materials-testing machine.

The MPFL was found to have a mean tensile strength of 208 N (SD 90) at 26 mm (SD 7) of displacement. The strengths of the other techniques were: sutures alone, 37 N (SD 27); bone anchors plus sutures, 142 N (SD 39); blind-tunnel tendon graft, 126 N (SD 21); and through-tunnel tendon graft, 195 N (SD 66). The last was not significantly weaker than the MPFL itself.

We have reviewed the literature on the anatomy of the posteromedial peripheral ligamentous structures of the knee and found differing descriptions. Our aim was to clarify the differing descriptions with a simplified interpretation of the anatomy and its contribution to the stability of the knee.

We dissected 20 fresh-frozen cadaver knees and the anatomy was recorded using video and still digital photography. The anatomy was described by dividing the medial collateral ligament (MCL) complex into thirds, from anterior to posterior and into superficial and deep layers. The main passive restraining structures of the posteromedial aspect of the knee were found to be superficial MCL (parallel, longitudinal fibres), the deep MCL and the posteromedial capsule (PMC). In the posterior third, the superficial and deep layers blend. Although there are oblique fibres (capsular condensations) running posterodistally from femur to tibia, no discrete ligament was seen. In extension, the PMC appears to be an important functional unit in restraining tibial internal rotation and valgus.

Our aim was to clarify and possibly simplify the anatomy of the posteromedial structures. The information would serve as the basis for future biomechanical studies to investigate the contribution of the posteromedial structures to joint stability.

We have tested the hypothesis that the meniscofemoral ligaments make a significant contribution to resisting anteroposterior and rotatory laxity of the posterior-cruciate-ligament-deficient knee. Eight cadaver human knees were tested for anteroposterior and rotatory laxity in a materials-testing machine. The posterior cruciate ligament (PCL) was then divided, followed by division of the meniscofemoral ligaments (MFLs). Laxity results were obtained for intact, PCL-deficient, and PCL-MFL-deficient knees.

Division of the MFLs in the PCL-deficient knee increased posterior laxity between 15° and 90° of flexion. Force-displacement measurements showed that the MFLs contributed 28% to the total force resisting posterior drawer at 90° of flexion in the intact knee, and 70.1% in the PCL-deficient knee. There was no effect on rotatory laxity.

This is the first study which shows a function for the MFLs as secondary restraints to posterior tibial translation. The integrity of these structures should be assessed during both imaging and arthroscopic studies of PCL-injured knees since this may affect the diagnosis and management of such injuries.

Differential strain has been proposed to be a causative factor in failure of the supraspinatus tendon. We quantified the strains on the joint and bursal sides of the supraspinatus tendon with increasing load (20 to 200 N) and during 120° of glenohumeral abduction with a constant tensile load (20 to 100 N).

We tested ten fresh frozen cadaver shoulders on a purpose-built rig. Differential variable reluctance extensometers allowed calculation of the strain.

Static loading to 100 N or more increased strains on the joint side significantly more than on the bursal side. During glenohumeral abduction an increasing and significant difference in strain was measured between the joint and bursal sides of the supraspinatus tendon, which reached a maximum of 10.6% at abduction of 120°. The joint side strain of 7.5% reached values which were previously reported to cause failure.

Differential strain causes shearing between the layers of the supraspinatus tendon, which may contribute to the propagation of intratendinous defects that are initiated by high joint side strains.

Aim: To accurately assess cross-sectional areas of the MFLs and distinguish between the mechanical properties of the anterior and posterior meniscofemoral ligaments.

Methods: Twenty-eight fresh frozen cadaveric knees were dissected to isolate the lateral meniscus and MFLs, which remained attached to the femur. The cross-sectional areas of MFLs were determined using the Race-Amis¹ casting method for measurement. The ligaments were then tensile tested in an Instron materials testing machine. The stress and strain in each sample was calculated from measurements of cross sectional area, load applied, and increase in length,.

Results: The mean cross sectional area for the anterior MFL (aMFL) was 14.7 mm² (±14.8mm²) whilst that of the posterior MFL (pMFL) was 20.9mm² (±11.6mm²). The mean loads to failure were 300.5N (±155.0N) for the aMFL and 302.5N (±157.9N) for the pMFL, with elastic moduli of 281MPa (±239MPa) and 227MPa (±128MPa) respectively. There were no significant differences in structural or material properties between the two MFLs. When compared with the posterior cruciate ligament (PCL), the mean ultimate loads of the MFLs were similar to those of the posterior bundle of the PCL (pPC), and their elastic moduli were analogous to the anterior bundle (aPC).

Discussion: This is the first study to distinguish between the properties of the aMFL and pMFL, and indicates that both ligaments must be given equal consideration when formulating hypotheses on function. The aMFL and pMFL may also serve mutually distinct functions in the human knee. Previous authors² have commented that the reciprocal tightening and slackening of the aPC (taut in flexion) and pPC (taut in extension) indicates a difference in function of these two components of the PCL. Others³ have similarly commented on the reciprocal tightening and slackening of the two MFLs. This may also indicate differing functions for these ligaments. It is proposed that the aMFL supplements the function of the aPC, whilst the pMFL supplements the function of the pPC. This hypothesis stimulates debate on preservation of these structures during PCL reconstruction.

Race A., Amis A.A., 1996. Cross-sectional area measurement of soft tissue. A new casting method. Journal of Biomechanics 29(9), 1207–1212.

Aim: To accurately identify the meniscofemoral ligaments in cadaveric human specimens, and to determine anatomical variations in the posterior cruciate ligament that may lead to mis-identification of these structures.

Methods: A total of 79 fresh frozen knees were examined from 45 cadavers Combined anterior and posterior approaches were used to inspect the vicinity of the posterior cruciate ligament (PCL) for the presence of the anterior and posterior meniscofemoral ligaments. The anterior approach utilised a medial parapatellar incision followed by division of the anterior cruciate ligament, whilst a midline posterior arthrotomy was used for the posterior approach. Further dissection facilitated inspection of the meniscal and femoral attachments of the MFLs, and measurement of their lengths. Videos of MFL and PCL motion during passive flexion of the cadaveric were also performed.

Results: In total, 74 (94%) of the 79 specimens contained at least one meniscofemoral ligament. The posterior meniscofemoral ligament (pMFL) was present in 56 (71%) specimens, whilst the anterior meniscofemoral ligament (aMFL) was present in 58 specimens (73%). Both ligaments coexisted in 40 (51%) of knees. In 15 specimens the PCL was seen to have oblique fibres, which attached proximal to the tibial attachment of the main part of the PCL. We termed this “the false pMFL”, as it could be easily mis-identified as the posterior meniscofemoral ligament. Several other anatomical variations were also identified. The mean length of the aMFL was 20.7±3.9mm, whilst that of the pMFL was 23±4.2mm. Although the lengths of the MFLs were relatively constant, there was a wide variation in thickness.

Discussion: This study confirms the high incidence of at least one MFL in humans, which suggests a functional role for these structures. The oblique fibres of the PCL can be readily mis-identfied as the pMFL. These caveats should be borne in mind, during both arthroscopic examination and in the interpretation of magnetic resonance imaging (MRI) scans of the knee. Although some variations of the MFLs have been reported on MRI imaging2, there has been no note of the oblique fibres of the PCL reported in the present study. As this variation was present in almost one in five of our specimens, its appearance on MRI scanning requires investigation.

The function of the meniscofemoral ligaments is undetermined, although many hypotheses comment on a role in guiding the motion of the lateral meniscus during knee flexion. Other possibilities include a function as a secondary restraint supplementing the posterior cruciate ligament.

Aims: To determine load to failure for four different meniscal repair techniques, and to assess gapping across repairs under cyclical loading.

Background: Studies comparing the biomechanical properties of different meniscal repair systems are limited, and most have simply investigated load to failure. Meniscal tissue is highly anisotropic, and far weaker under tension in the radial direction. Load to failure using high loads may, therefore, not be the most physiologically relevant in-vitro test for repair of circumferential tears, and measuring increases in gapping across repair sites under cyclical loading at lower loads may be of greater importance.

Methods: Bovine menisci were divided vertically, 5mm from the peripheral edge to simulate a circumferential tear, and then repaired using one to four techniques: vertical loop sutures using 1 -PDS, bioabsorbable Meniscal Arrows (Atlantech), Meniscal Fasteners (Mitek) or T-Fix Suture Bars (Acufex). Nine specimens were tested in each group using an Instron 5500 materials testing machine to determine load to failure. A further nine specimens in each group were tested by cyclic loading between 5N and 10N at 20mm/min for 25 cycles, using a digital micrometer to measure initial gapping, and a Differential Variable Reluctance Transducer to measure the progressive increase in gapping across the repair site during the cyclical loading. Data was analysed by ANOVA and Tukey’s multiple comparison post test using Prism (GraphPad) software.

Results: The mean loads to failure (with s.d.) in Newtons were: Sutures 72.7 (22.0), Arrows 34.2 (15.4), Fasteners 40.8 (13.4), and T-Fix 49.1 (13.8). The load to failure was significantly greater with the Sutures compared to the Arrows (p< 0.001), the Fasteners (p< 0.001) or the T-Fix (p< 0.05).

The mean gapping across the repairs after 25 load cycles (with s.d.) in millimetres was: Sutures 3.3 (1.0), Arrows 2.2 (0.9), Fasteners 4.0 (0.6) and TFix 3.5 (0.7). The mean gapping was significantly less for the Arrows compared to the Sutures (p< 0.05), the Fasteners (p< 0.01), or the T-Fix (p< 0.05).

Conclusions: These results confirm that meniscal repair by suturing gives the highest load to failure, but show that Arrows give superior hold with the least increase in gapping across a repair under cyclical loading by this test protocol.

Objective: To provide a functional, anatomical description of the posteromedial structures, allowing future biomechanical studies to evaluate how they act to restrain tibio-femoral joint motion and contribute to joint stability.

Methods: Twenty fresh cadaveric knee joints were dissected. The appearance of the medial ligament complex was recorded using still and video digital photography as the specimens were flexed, extended, internally and externally rotated.

Results: We divided the medial structures into thirds, from anterior to posterior, and into three layers from superficial to deep: Layer 1: Fascia. Layer 2: Superficial MCL. Layer 3: Deep MCL and capsule. In the Posteromedial Corner (posterior third) it is not possible to separate Layers 2 and 3. The posteromedial corner (PMC) envelops the posterior medial femoral condyle. A discrete posterior oblique ligament (POL) is not identifiable. The PMC appears to be a functional unit with a role in passively restraining tibio-femoral valgus and internal rotation with the knee extended. The semimembranosus, through its tendon sheath attachments, may act as a dynamic stabiliser.

Conclusion: The MCL appears to have three functional units:Superficial MCL, Deep MCL and PMC. We believe that this description allows a logical approach to understanding the biomechanics and surgical reconstruction of the posteromedial structures. We plan to use this anatomical study as the basis for further work to evaluate the how these functional units act.

Our objectives were to establish the envelope of passive movement and to demonstrate the kinematic behaviour of the knee during standard clinical tests before and after reconstruction of the anterior cruciate ligament (ACL). An electromagnetic device was used to measure movement of the joint during surgery.

Reconstruction of the ACL significantly reduced the overall envelope of tibial rotation (10° to 90° flexion), moved this envelope into external rotation from 0° to 20° flexion, and reduced the anterior position of the tibial plateau (5° to 30° flexion) (p < 0.05 for all). During the pivot-shift test in early flexion there was progressive anterior tibial subluxation with internal rotation. These subluxations reversed suddenly around a mean position of 36 ± 9° of flexion of the knee and consisted of an external tibial rotation of 13 ± 8° combined with a posterior tibial translation of 12 ± 8 mm. This abnormal movement was abolished after reconstruction of the ACL.

The meniscofemoral ligaments were studied in 84 fresh-frozen knees from 49 cadavers. Combined anterior and posterior approaches were used to identify the ligaments. In total, 78 specimens (93%) contained at least one meniscofemoral ligament. The anterior meniscofemoral ligament (aMFL) was present in 62 specimens (74%), and the posterior meniscofemoral ligament (pMFL) in 58 (69%). The 42 specimens (50%) in which both ligaments were present were from a significantly younger population than that with one MFL or none (p < 0.05). Several anatomical variations were identified, including oblique fibres of the posterior cruciate ligament (PCL), which were seen in 16 specimens (19%). These were termed the ‘false pMFL’.

The high incidence of MFLs and their anatomical variations should be borne in mind during arthroscopic and radiological examination of the PCL. It is important to recognise the oblique fibres of the PCL on MRI in order to avoid wrongly identifying them as either a pMFL or a tear of the lateral meniscus. The increased incidence of MFLs in younger donors suggests that they degenerate with age.

We compared the ability of three different posterior cruciate ligament (PCL) reconstructions to restore normal anteroposterior laxity to the knee from 0 to 130° of knee flexion.

Cadaver knees were tested intact, after PCL rupture or after bone-patellar tendon-bone grafting. Grafts were performed isometrically or with a single bundle representing the anatomical anterior PCL fibre bulk (aPC) or with a double bundle that added the posterior PCL fibre bulk (pPC). The grafts were tensioned to restore normal knee laxity at 60° of flexion, except for the pPC which was tensioned at 130°.

The isometric graft led to overconstraint as the knee extended resulting in high graft tension in extension and excess laxity in flexion. The aPC graft matched normal laxity from 0 to 60° of flexion but was lax from 90 to 130° of flexion. Only the double-bundled graft could restore normal knee laxity across the full range of flexion.

Repair of the rotator cuff requires secure reattachment, but large chronic defects cause osteoporosis of the greater tuberosity which may then have insufficient strength to allow proper fixation of the tendon. Recently, suture anchors have been introduced, but have not been fully evaluated.

We have investigated the strength of suture-to-anchor attachment, and the use of suture anchors in repairs of the rotator cuff either to the greater tuberosity or the lateral cortex of the humerus. The second method gave a significant increase in the strength of the repair (p = 0.014).

The repairs were loaded cyclically and failed at low loads by cutting into bone and tendon, casting doubt on the integrity of the repair in early mobilisation after surgery. Repairs with suture anchors did not perform better than those with conventional transosseous attachment.