[Rotational Laxity of the Knee Joint - In Vivo MRI Study]. / Rotacní laxita kolenního kloubu ­ in vivo NMR studie.

PURPOSE OF THE STUDY The purpose of the study was to evaluate tibio-femoral rotation during a simulated squat and to investigate the relationship between the rotational position of the femur in full extension and the amount of external rotation of the femur on the tibia during flexion. MATERIAL AND METHODS Part 1: MRIs of volunteers Data on healthy knees of 10 volunteers were obtained using 2D MRI measurements. The foot and the ankle were fixed to prevent rotation and adduction/abduction movements. Sagittal MRIs of the knees have been performed in 4 positions of flexion. The amount of longitudinal rotation in each position of flexion was calculated. Part 2: Mathematical model experiment a) The model of the femur has been positioned in the 3D coordinate system in full extension and at 12.8° of internal rotation and then flexed to 90° without longitudinal rotation. The distance between the centre of the femoral head and the sagittal plane passing through the centre of the knee was then measured. b) Subsequently, the femur was flexed and rotation allowed to retain femoral head within the sagittal plane. The amount of femoral rotation was then calculated. RESULTS Part 1: In full extension the femur was on average in 12.8° of IR relative to the tibia. By 90° flexion femur rotated on average 12.2° externally. Part 2: a)From full extension to 90° flexion the femoral head moved 93.1 mm laterally from the sagittal plane. b)Between full extension and 90° flexion the femur rotated 12.8° externally, a degree which corresponds to the amount of initial internal rotation of the femur in full extension. DISCUSSION The most important finding of the presented in vivo study lies in the fact that in normal knees with tibia rotationally fixed flexion is always coupled with femoral external rotation in order to keep the femoral head in the acetabulum. This rotation is obligatory. CONCLUSIONS We have demonstrated that if the tibia is rotationally fixed, the knee flexion is possible only when accompanied by femoral external rotation to keep the femoral head in the acetabulum. A mathematical description of the experiment has been proposed, the results of which confirm the stated premise. This finding can be explained by initial internal rotation of the femur in full extension of the knee and is allowed by the shape of articulating bones and tension of soft tissues Key words: knee, terminal extension, knee rotation, knee movement, MRI, hip joint.

Does lateral lift-off occur in static and dynamic activity in a medially spherical total knee arthroplasty? A pulsed-fluoroscopic investigation.

OBJECTIVES: The medially spherical GMK Sphere (Medacta International AG, Castel San Pietro, Switzerland) total knee arthroplasty (TKA) was previously shown to accommodate lateral rollback while pivoting around a stable medial compartment, aiming to replicate native knee kinematics in which some coronal laxity, especially laterally, is also present. We assess coronal plane kinematics of the GMK Sphere and explore the occurrence and pattern of articular separation during static and dynamic activities. METHODS: Using pulsed fluoroscopy and image matching, the coronal kinematics and articular surface separation of 16 well-functioning TKAs were studied during weight-bearing and non-weight-bearing, static, and dynamic activities. The closest distances between the modelled articular surfaces were examined with respect to knee position, and proportions of joint poses exhibiting separation were computed. RESULTS: Overall, 1717 joint poses were analyzed. At a 1.0 mm detection threshold, 37 instances of surface separation were observed in the lateral compartment and four medially (p < 0.001). Separation was activity-dependent, both laterally and medially (p < 0.001), occurring more commonly during static deep flexion in the lateral compartment, and during static rotation in the medial compartment. Lateral separation occurred more frequently than medial during kneeling (7/14 lateral vs 1/14 medial; p = 0.031) and stepping (20/1022 lateral vs 0/1022 medial; p < 0.001). Separation varied significantly between individuals during dynamic activities. CONCLUSION: No consistent association between closest distances of the articular surfaces and knee position was found during any activity. Lift-off was infrequent and depended on the activity performed and the individual knee. Lateral separation was consistent with the design rationale. Medial lift-off was rare and mostly in non-weight-bearing activities.Cite this article: S. Key, G. Scott, J.G. Stammers, M. A. R. Freeman†, V. Pinskerova, R. E. Field, J. Skinner, S. A. Banks. Does lateral lift-off occur in static and dynamic activity in a medially spherical total knee arthroplasty? A pulsed-fluoroscopic investigation. Bone Joint Res 2019;8:207-215. DOI: 10.1302/2046-3758.85.BJR-2018-0237.R1.

[Anterior Cruciate Ligament Tears - Influence on Terminal Extension]. / Ruptury predního zkrízeného vazu ­ vliv na terminální extenzi.

PURPOSE OF THE STUDY The aim of this paper was to compare terminal extension in normal and anterior cruciate ligament (ACL) deficient knees, and therefore to determine the role of the ACL during this motion. MATERIAL AND METHODS Ten knees with ACL tears (7 knees with recent ACL tears, 3 knees with long-standing tears) and 10 normal contralateral knees have been examined using MRI in passive hyperextension, 20° flexion and 20° flexion with a 9 kg posteriorly directed load on the femur. Movements of the femoral condyles on the tibia were calculated using previously described methods. RESULTS 1. Under the load at 20° flexion, knees with ACL tear showed posterior femoral subluxation (equivalent to a Lachman test), chronic tears being more unstable. Contralateral normal knees were antero-posteriorly stable. In hyperextension, both femoral condyles subluxed posteriorly in ACL tears but not in normal knees. 2. In all knees with ACL tear, the lateral femoral condyle moved posteriorly from hyperextension to 20°, equating to femoral external rotation. 3. The longitudinal rotation axis during terminal extension in normal knees was medial but in ACL tears it was central causing the medial femoral condyle to move forward from hyperextension to 20°. In normal knees, the medial femoral condyle did not move antero-posteriorly from hyperextension to 20° flexion. DISCUSSION Internal rotation of the femur during terminal extension has been recognized for 150 years. The question remains: what causes the usual combination of longitudinal rotation and extension? In the current literature ACL is considered to be responsible for internal rotation of the femur during terminal extension of the knee. So far, as we are aware, the kinematics of terminal extension, including hyperextension, have not been reported after ACL tear in the living knee. CONCLUSIONS Results of this study imply that: 1. The ACL prevents anterior tibial subluxation in hyperextension. 2. The ACL does not cause rotation in terminal extension. 3. The ACL locates the axis of longitudinal rotation in terminal extension. We hope that by studying living knees with and without ACL tear we may not only clarify the nature and mechanism of rotation in terminal extension, and hence the role of the ACL, but do so in a context of direct clinical relevance. Key words: knee, terminal extension, ACL tear, axis of longitudinal rotation, antero-posterior instability, MRI.

Can a total knee arthroplasty be both rotationally unconstrained and anteroposteriorly stabilised? A pulsed fluoroscopic investigation.

OBJECTIVES: Throughout the 20th Century, it has been postulated that the knee moves on the basis of a four-bar link mechanism composed of the cruciate ligaments, the femur and the tibia. As a consequence, the femur has been thought to roll back with flexion, and total knee arthroplasty (TKA) prostheses have been designed on this basis. Recent work, however, has proposed that at a position of between 0° and 120° the medial femoral condyle does not move anteroposteriorly whereas the lateral femoral condyle tends, but is not obliged, to roll back - a combination of movements which equates to tibial internal/ femoral external rotation with flexion. The aim of this paper was to assess if the articular geometry of the GMK Sphere TKA could recreate the natural knee movements in situ/in vivo. METHODS: The pattern of knee movement was studied in 15 patients (six male: nine female; one male with bilateral TKAs) with 16 GMK Sphere implants, at a mean age of 66 years (53 to 76) with a mean BMI of 30 kg/m(2) (20 to 35). The motions of all 16 knees were observed using pulsed fluoroscopy during a number of weight-bearing and non-weight-bearing static and dynamic activities. RESULTS: During maximally flexed kneeling and lunging activities, the mean tibial internal rotation was 8° (standard deviation (sd) 6). At a mean 112° flexion (sd 16) during lunging, the medial and lateral condyles were a mean of 2 mm (sd 3) and 8 mm (sd 4) posterior to a transverse line passing through the centre of the medial tibial concavity. With a mean flexion of 117° (sd 14) during kneeling, the medial and lateral condyles were a mean of 1 mm (sd 4) anterior and 6 mm (sd 4) posterior to the same line. During dynamic stair and pivoting activities, there was a mean anteroposterior translation of 0 mm to 2 mm of the medial femoral condyle. Backward lateral condylar translation occurred and was linearly related to tibial rotation. CONCLUSION: The GMK Sphere TKA in our study group shows movements similar in pattern, although reduced in magnitude, to those in recent reports relating to normal knees during several activities. Specifically, little or no translation of the medial femoral condyle was observed during flexion, but there was posterior roll-back of the lateral femoral condyle, equating to tibiofemoral rotation. We conclude that the GMK Sphere is anteroposteriorly stable medially and permits rotation about the medial compartment.Cite this article: Professor G. Scott. Can a total knee arthroplasty be both rotationally unconstrained and anteroposteriorly stabilised?: A pulsed fluoroscopic investigation. Bone Joint Res 2016;5:80-86. DOI: 10.1302/2046-3758.53.2000621.

Gender differences in the morphology of the trochlea and the distal femur.

PURPOSE: The objective of this study was to provide a morphologic description of the distal femur and to determine whether there are any gender differences in the shape that might have an important consequence for the design of a femoral component of a total knee prosthesis. METHODS: Anthropometric data on the distal femur of 200 normal knees were obtained using two-dimensional MRI measurements. In all 18 parameters of the distal femur were measured including the anteroposterior (AP) dimension of femoral condyles, the mediolateral (ML) width of the distal femur at four levels, and the AP dimension and ML width of the trochlea. The aspect ratios between the AP and ML dimensions were calculated to determine whether there is a shape difference between genders. RESULTS: The female distal femur is significantly smaller in all measured parameters. The mean AP/ML aspect ratio of the female distal femur is significantly larger (p<0.05) at all measured ML levels except that of the anterior edge of the anterior chamfer. The AP dimensions of both the medial and lateral trochlea were significantly greater in men (p<0.001), but AP/ML aspect ratio did not differ between genders. CONCLUSIONS: We have found that although the female distal femur is relatively narrower (larger AP/ML aspect ratio) than the male in three of the four measured levels, there is no significant difference between genders at the level of the anterior edge of the anterior chamfer. It is at this level that it has been suggested that impingement between soft tissues and an overhanging prosthesis is most likely to be painful. Equally, there were no gender-related differences in the shape of the trochlea. These data therefore do not support the provision of narrow femoral components for TKA for women.

The knee in full flexion: an anatomical study.

There has been only one limited report dating from 1941 using dissection which has described the tibiofemoral joint between 120 degrees and 160 degrees of flexion despite the relevance of this arc to total knee replacement. We now provide a full description having examined one living and eight cadaver knees using MRI, dissection and previously published cryosections in one knee. In the range of flexion from 120 degrees to 160 degrees the flexion facet centre of the medial femoral condyle moves back 5 mm and rises up on to the posterior horn of the medial meniscus. At 160 degrees the posterior horn is compressed in a synovial recess between the femoral cortex and the tibia. This limits flexion. The lateral femoral condyle also rolls back with the posterior horn of the lateral meniscus moving with the condyle. Both move down over the posterior tibia at 160 degrees of flexion. Neither the events between 120 degrees and 160 degrees nor the anatomy at 160 degrees could result from a continuation of the kinematics up to 120 degrees . Therefore hyperflexion is a separate arc. The anatomical and functional features of this arc suggest that it would be difficult to design an implant for total knee replacement giving physiological movement from 0 degrees to 160 degrees .

Variation in the anatomy of the tibial plateau: a possible factor in the development of anteromedial osteoarthritis of the knee.

From a search of MRI reports on knees, 20 patients were identified with evidence of early anteromedial osteoarthritis without any erosion of bone and a control group of patients had an acute rupture of the anterior cruciate ligament. The angle formed between the extension and flexion facets of the tibia, which is known as the extension facet angle, was measured on a sagittal image at the middle of the medial femoral condyle. The mean extension facet angle in the control group was 14 degrees (3 degrees to 25 degrees ) and was unrelated to age (Spearman's rank coefficient, p = 0.30, r = 0.13). The mean extension facet angle in individuals with MRI evidence of early anteromedial osteoarthritis was 19 degrees (13 degrees to 26 degrees , SD 4 degrees ). This difference was significant (Mann-Whitney U test, p < 0.001). A wide variation in the extension facet angle was found in the normal control knees and an association between an increased extension facet angle and MRI evidence of early anteromedial osteoarthritis. Although a causal link has not been demonstrated, we postulate that a steeper extension facet angle might increase the duration of loading on the extension facet during the stance phase of gait, and that this might initiate failure of the articular cartilage.

A new technique for reconstruction of the proximal humerus after three- and four-part fractures.

The results of proximal humeral replacement following trauma are substantially worse than for osteoarthritis or rheumatoid arthritis. The stable reattachment of the lesser and greater tuberosity fragments to the rotator cuff and the restoration of shoulder biomechanics are difficult. In 1992 we developed a prosthesis designed to improve fixation of the tuberosity fragments in comminuted fractures of the proximal humerus. The implant enables fixation of the fragments to the shaft of the prosthesis and the diaphyseal fragment using screws, washers and a special toothed plate. Between 1992 and 2003 we used this technique in 50 of 76 patients referred to our institution for shoulder reconstruction after trauma. In the remaining 26, reconstruction with a prosthesis and nonabsorbable sutures was performed, as the tuberosity fragments were too small and too severely damaged to allow the use of screws and the toothed plate. The Constant score two years post-operatively was a mean of 12 points better in the acute trauma group and 11 points better in the late post-traumatic group than in the classical suture group. We recommend this technique in patients where the tuberosity fragments are large enough to allow fixation with screws, washers and a toothed plate.

[Observations of normal and ACL-deficient knee joints after stress MRI]. / Beobachtungen an gesunden und VKB-insuffizienten Kniegelenken nach Belastungs-MRT.

BACKGROUND: The Lachman test is the most reliable clinical test for diagnosing rupture of the anterior cruciate ligament (ACL). Previous X-ray studies have presented a "radiologic Lachman test". Recently anterior tibial translation was demonstrated using open access MRI. Two methods were developed to transfer a similar technique to a more widely available closed MRI. METHODS: Using closed MRI we investigated 22 knees in 21 patients with pure rupture of the ACL. Anteriorly and posteriorly directed shear forces were applied to the tibiofemoral joint at 20 degrees flexion either by positioning a 9-kg load on the distal femur (method 1) or performing a semi-manual Lachman test with a custom-made orthosis (method 2). RESULTS: Both methods produced relative anterior tibial translation in both compartments of the normal and ACL-deficient knee which could be measured on sagittal images. They were greater laterally than medially and in injured than in uninjured knees. However, instability of the medial compartment predicted clinical and symptomatic instability as translation was posterior to positions achieved in normal knees during the active and passive flexion arc. CONCLUSION: A Lachman sign can be produced in a closed magnet with different methods and findings can be used for more precise information regarding kinematics and degree of instability and could be helpful if surgical treatment is necessary.

The movement of the normal tibio-femoral joint.

This review describes the anatomy of the articular surfaces and their movement in the normal tibio-femoral joint, together with methods of measurement in volunteers. Forces and soft tissues are excluded. To measure movement, the articular surfaces and natural or inserted movement markers must be imaged by some combination of MRI, CT, RSA or fluoroscopy. With the aid of computer-imaging, the movements can then be related to an anatomy-based co-ordinate system to avoid kinematic cross-talk. Methods of depicting these movements which are understandable to engineers and clinicians are discussed. The shapes of the articular surfaces are reported. They are relevant to landmarks and co-ordinate systems and form a basis for inferring the nature of the movements which take place in the knee. The movements of the condyles are described from hyperextension to full passive flexion. Medially the condyle hardly moves antero-posteriorly from 0 degrees to 120 degrees but the contact area transfers from an anterior pair of tibio-femoral surfaces at 10 degrees to a posterior pair at about 30 degrees . Thus because of the shapes of the bones, the medial contact area moves backwards with flexion to 30 degrees but the condyle does not. Laterally the femoral condyle and the contact area move posteriorly but to a variable extent in the mid-range causing tibial internal rotation to occur with flexion around a medial axis. From 120 degrees to full flexion both condyles roll back onto the posterior horn so that the tibio-femoral joint subluxes.

Imaging knee position using MRI, RSA/CT and 3D digitisation.

The purpose of this study was to compare 3 methods of imaging knee position. Three fresh cadaver knees were imaged at 6 flexion angles between 0 degrees and 120 degrees by MRI, a combination of RSA and CT and 3D digitisation (in two knees). Virtual models of all 42 positions were created using suitable computer software. Each virtual model was aligned to a newly defined anatomically based Cartesian coordinate system. The angular rotations around the 3 coordinate system axes were calculated directly from the aligned virtual models using rigid body kinematics and found to be equally accurate for the 3 methods. The 3 rotations in each knee could be depicted using anatomy-based diagrams for all 3 methods. We conclude that the 3 methods of data acquisition are equally and adequately accurate in vitro. MRI may be the most useful in vivo.

Does the femur roll-back with flexion?

MRI studies of the knee were performed at intervals between full extension and 120 degrees of flexion in six cadavers and also non-weight-bearing and weight-bearing in five volunteers. At each interval sagittal images were obtained through both compartments on which the position of the femoral condyle, identified by the centre of its posterior circular surface which is termed the flexion facet centre (FFC), and the point of closest approximation between the femoral and tibial subchondral plates, the contact point (CP), were identified relative to the posterior tibial cortex. The movements of the CP and FFC were essentially the same in the three groups but in all three the medial differed from the lateral compartment and the movement of the FFC differed from that of the CR Medially from 30 degrees to 120 degrees the FFC and CP coincided and did not move anteroposteriorly. From 30 degrees to 0 degrees the anteroposterior position of the FFC remained unchanged but the CP moved forwards by about 15 mm. Laterally, the FFC and the CP moved backwards together by about 15 mm from 20 degrees to 120 degrees. From 20 degrees to full extension both the FFC and CP moved forwards, but the latter moved more than the former. The differences between the movements of the FFC and the CP could be explained by the sagittal shapes of the bones, especially anteriorly. The term 'roll-back' can be applied to solid bodies, e.g. the condyles, but not to areas. The lateral femoral condyle does roll-back with flexion but the medial does not, i.e. the femur rotates externally around a medial centre. By contrast, both the medial and lateral contact points move back, roughly in parallel, from 0 degrees to 120 degrees but they cannot 'roll'. Femoral roll-back with flexion, usually imagined as backward rolling of both condyles, does not occur.

The posterior cruciate ligament during flexion of the normal knee.

The posterior cruciate ligament (PCL) was imaged by MRI throughout flexion in neutral tibial rotation in six cadaver knees, which were also dissected, and in 20 unloaded and 13 loaded living (squatting) knees. The appearance of the ligament was the same in all three groups. In extension the ligament is curved concave-forwards. It is straight, fully out-to-length and approaching vertical from 60 degrees to 120 degrees, and curves convex-forwards over the roof of the intercondylar notch in full flexion. Throughout flexion the length of the ligament does not change, but the separations of its attachments do. We conclude that the PCL is not loaded in the unloaded cadaver knee and therefore, since its appearance in all three groups is the same, that it is also unloaded in the living knee during flexion. The posterior fibres may be an exception in hyperextension, probably being loaded either because of posterior femoral lift-off or because of the forward curvature of the PCL. These conclusions relate only to everyday life: none may be drawn with regard to more strenuous activities such as sport or in trauma.

The movement of the knee studied by magnetic resonance imaging.

The author's work using magnetic resonance imaging to study the relative movements (the kinematics) of the tibia and femur is reviewed. The description is understood best by reference to comparative anatomy and by dividing the flexion arc into three components. Knee activities take place mainly between 10 degrees and 120 degrees. Over this arc, the articulating surfaces of the femoral condyles are circular in sagittal section and rotate around their center. The medial condyle does not move anteroposteriorly (roll-back does not occur medially). The lateral condyle tends to roll back producing tibial internal rotation with flexion. From full extension to 10 degrees to 30 degrees tibial internal rotation is coupled with flexion. The articulating surfaces medially are a larger radiused anterior femoral facet, which articulates with an upward-sloping tibial facet. Laterally, the femoral condyle rolls forward onto the anterior horn. Flexion beyond 120 degrees only can be achieved passively. Medially, the femur rolls up onto the posterior horn. Laterally, the femur and the posterior horn drop over the posterior tibia.

Should the cement mantle around the femoral component be thick or thin?

We have compared the survival and radiological outcome at ten years after total hip replacement using two techniques for preparing the femoral canal. The same prosthesis was used throughout and all operations were performed by the same surgical team. In technique 1 the canal was over-reamed by 2 mm and in technique 2 it was reamed to the same size as the prosthesis. Technique 1 was performed on 92 patients and technique 2 on 97 patients. The survival at ten years was 97.2% (90.6 to 99.2) for technique 1 and 98.8% (92.9 to 99.8) for technique 2. Vertical migration was greater in technique 1 (1.8 mm versus 1.0 mm at five years; p = 0.36). There were significantly more lytic lesions and radiolucent lines at five years (p = 0.0061) with technique 1. We conclude that technique 2 is not worse and may produce better long-term results than current teaching suggests.

The shapes of the tibial and femoral articular surfaces in relation to tibiofemoral movement.

We report a study of the shapes of the tibial and femoral articular surfaces in sagittal, frontal and coronal planes which was performed on cadaver knees using two techniques, MRI and computer interpolation of sections of the articular surfaces acquired by a three-dimensional digitiser. The findings using MRI, confirmed in a previous study by dissection, were the same as those using the digitiser. Thus both methods appear to be valid anatomical tools. The tibial and femoral articular surfaces can be divided into anterior segments, contacting from 0 degrees to 20 +/- 10 degrees of flexion, and posterior segments, contacting from 20 +/- 10 degrees to 120 degrees of flexion. The medial and lateral compartments are asymmetrical, particularly anteriorly. Posteromedially, the femur is spherical and is located in a conforming, but partly deficient, tibial socket. Posterolaterally, it is circular only in the sagittal section and the tibia is flat centrally, sloping downwards both anteriorly and posteriorly to receive the meniscal horns. Anteromedially, the femur is convex with a sagittal radius larger than that posteriorly, while the tibia is flat sloping upwards and forwards. Anterolaterally, both the femoral and tibial surfaces are largely deficient. These shapes suggest that medially the femur can rotate on the tibia through three axes intersecting in the middle of the femoral sphere, but that the sphere can only translate anteroposteriorly and even then to a limited extent. Laterally, the femur can freely translate anteroposteriorly, but can only rotate around a transverse axis for that part of the arc, i.e., near extension, during which it comes into contact with the tibia through its flattened distal/medial surface as against its spherical posterior surface.

Tibiofemoral movement 1: the shapes and relative movements of the femur and tibia in the unloaded cadaver knee.

In six unloaded cadaver knees we used MRI to determine the shapes of the articular surfaces and their relative movements. These were confirmed by dissection. Medially, the femoral condyle in sagittal section is composed of the arcs of two circles and that of the tibia of two angled flats. The anterior facets articulate in extension. At about 20 degrees the femur 'rocks' to articulate through the posterior facets. The medial femoral condyle does not move anteroposteriorly with flexion to 110 degrees. Laterally, the femoral condyle is composed entirely, or almost entirely, of a single circular facet similar in radius and arc to the posterior medial facet. The tibia is roughly flat. The femur tends to roll backwards with flexion. The combination during flexion of no anteroposterior movement medially (i.e., sliding) and backward rolling (combined with sliding) laterally equates to internal rotation of the tibia around a medial axis with flexion. About 5 degrees of this rotation may be obligatory from 0 degrees to 10 degrees flexion; thereafter little rotation occurs to at least 45 degrees. Total rotation at 110 degrees is about 20 degrees, most if not all of which can be suppressed by applying external rotation to the tibia at 90 degrees.

Tibiofemoral movement 2: the loaded and unloaded living knee studied by MRI.

In 13 unloaded living knees we confirmed the findings previously obtained in the unloaded cadaver knee during flexion and external rotation/internal rotation using MRI. In seven loaded living knees with the subjects squatting, the relative tibiofemoral movements were similar to those in the unloaded knee except that the medial femoral condyle tended to move about 4 mm forwards with flexion. Four of the seven loaded knees were studied during flexion in external and internal rotation. As predicted, flexion (squatting) with the tibia in external rotation suppressed the internal rotation of the tibia which had been observed during unloaded flexion.