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.

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.

Comparison of static and dynamic knee kinematics during squatting.

BACKGROUND: there long has been debate whether static knee kinematics measured using magnetic resonance imaging are the same as knee kinematics in dynamic weight-bearing motion. Magnetic resonance imaging provides excellent volumetric detail but is static. Fluoroscopic imaging provides for dynamic observation of knee kinematics but provides no direct observation of the soft-tissue structures. We attempted to answer the question 'Are knee kinematics the same during static and dynamic squatting?' METHODS: knee kinematics data from two previously reported studies of healthy knee kinematics during squatting from 0° to 120° were obtained. The results of the dynamic fluoroscopic study were reformatted to perform a direct comparison of femoral anteroposterior translation and internal-external rotation with the static magnetic resonance imaging study. FINDINGS: comparison of internal-external rotations and lateral femoral condyle anteroposterior translations did not reveal significant differences between static and dynamic data. The medial femoral condyle demonstrated 0 (SD=3) mm posterior translation during dynamic squatting from 0° to 120° flexion compared to 5 (SD=3) mm posterior translation during static squatting (P=0.01, Cohen's d=1.7). INTERPRETATION: for squatting types of motions, static and dynamic study protocols appear to produce equivalent knee kinematics with no functionally important differences. Differences in medial condyle translations can be attributed to differences in foot position during the study. Investigators can choose the modality that best fits their goals and resources with the knowledge that the results for squatting activities are comparable.

The Freeman femoral component with hydroxyapatite coating and retention of the neck: an update with a minimum follow-up of 17 years.

The outcome at ten years of 100 Freeman hip stems (Finsbury Orthopaedics, Leatherhead, United Kingdom) retaining the neck with a proximal hydroxyapatite coating in a series of 52 men (six bilateral) and 40 women (two bilateral), has been described previously. None required revision for aseptic loosening. We have extended the follow-up to 20 years with a minimum of 17 years. The mean age of the patients at total hip replacement was 58.9 years (19 to 84). Six patients were lost to follow-up, but were included up to their last clinical review. A total of 22 patients (22 hips) had died, all from causes unrelated to their surgery. There have been 43 re-operations for failure of the acetabular component. However, in 38 of these the stem was not revised since it remained stable and there was no associated osteolysis. Two of the revisions were for damage to the trunnion after fracture of a modular ceramic head, and in another two, removal of the femoral component was because of the preference of the surgeon. In all cases the femoral component was well fixed, but could be extracted at the time of acetabular revision. In one case both components were revised for deep infection. There has been one case of aseptic loosening of the stem which occurred at 14 years. This stem had migrated distally by 7.6 mm in ten years and 8.4 mm at the time of revision at which stage it was found to be rotationally loose. With hindsight this component had been undersized at implantation. The survivorship for the stem at 17 years with aseptic loosening as the endpoint was 98.6% (95% confidence interval 95.9 to 100) when 62 hips were at risk. All remaining stems had a satisfactory clinical and radiological outcome. The Freeman proximally hydroxyapatite-coated femoral component is therefore a dependable implant and its continued use can be recommended.

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.

[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.

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.

Hydroxyapatite-coated femoral components in total knee arthroplasty: medium term results.

Thirty-six consecutive total knee arthroplasties with hydroxyapatite (HA)-coated femoral components were prospectively followed up according to a standardised protocol for a mean period of 10 years (range, 7-11 years). Clinical and radiologic examination was performed at each follow-up evaluation. One patient (1 knee) was lost to follow up at 7 years, and 4 other patients (6 knees) died. Radiographs were studied for signs of loosening and presence of lucencies. Survival analysis was performed using a life table with revision as the criterion for failure. Two knees (1 patient) were revised because of aseptic loosening. The tibial component of one other knee was revised because of osteolysis in the medial tibial condyle. In the remaining knees, no radiologic evidence of loosening was seen. The survival of the femoral component at a mean follow-up time of 7 years, when 31.5 knees were at risk, was 94% with revision for femoral aseptic loosening as the end point. At 10 years, when 24 knees were at risk, the survival remained 94%.

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.

The histology of "reactive lines" in well-fixed components.

The histologic findings from 2 total knee arthroplasties (TKAs) in 1 patient who died 5 years after surgery are reported. Cement was placed under the tibial and femoral metal backs but not around the stems. All components were securely fixed. "Reactive lines," present around the tips of the stems on radiography, were seen to contain thin, soft connective tissue without debris or macrophages. The histologic features of a reactive line are described.

The natural history and significance of radiolucent lines at a cemented femoral interface.

We studied 185 total hip replacements and related the identification of radiolucent lines (RLLs) at two years to the later development of lytic lesions and loosening. Linear polyethylene wear was also measured. RLLs appeared in 34 hips at a mean of 2.0 years after operation, and lytic lesions in ten hips at 5.7 years. Of 151 THRs without RLLs there was neither rapid migration nor loosening and only one developed a possible lytic lesion. Of 23 hips with non-progressive RLLs there was neither rapid migration nor loosening, but six developed a lytic lesion. By contrast, 11 THRs with progressive RLLs migrated rapidly and seven developed a lytic lesion. Six THRs with progressive RLLs failed. The wear rates were the same in all groups, although limited numbers were available for study. If the surgeon achieves secure initial fixation as shown by slow or no migration and no RLLs during the first two years, it is likely that no lytic lesions will develop by five years or aseptic loosening by ten years. If an imperfect, but adequate, interface is achieved, as shown by slow migration and non-progressive RLLs lytic lesions adjacent to the RLLs may develop by five years, but aseptic loosening will be unlikely at ten. Insecure initial fixation, as shown by more rapid migration and progressive RLLs at two years, is likely to lead to the formation of lytic lesions at five years and loosening at ten. The outcome after THR is therefore determined at the initial operation and may be predicted at two years. The presence of lytic lesions reflects soft tissue at the interface as shown by the RLLs which accompany and promote loosening but, in our study, did not cause it.