Application of a robotics path planning algorithm to assess the risk of mobile bearing dislocation in lateral unicompartmental knee replacement.

Due to ligament laxity, bearing dislocation occurs in 1-6% of Oxford Domed Lateral (ODL) replacements with most dislocations occurring medially. Dislocations were studied using a previously built mechanical rig, however testing using the rig was inefficient. The aim of this study was to develop a better tool that was more reliable and efficient. An established robotics software package, the Open Motion Planning Library, was modified to accept the ODL components. Using a robotics path planning algorithm, the mobile bearing was allowed to find a way out from between the femoral and tibial components i.e. to dislocate. Testing assessed a range of clinically relevant positions of the femoral component relative to the tibial component. Dislocations were labelled as medial, lateral, anterior or posterior depending on the dislocation direction. The Distraction to Dislocation (DD) measured the minimum vertical distraction of the femoral component from the tibial component for a dislocation to occur. Results were validated against the mechanical rig. Statistical analysis of medial dislocation showed excellent agreement with an intraclass correlation value of 0.993 (95% CI 0.982-0.998). All DDs from the dislocation analysis tool were within 1 mm of the mechanical rig DDs with results sharing a remarkably similar trend. The robotics dislocation analysis tool output DDs which were marginally higher than the manual mechanical rig: 0.50 mm anteriorly, 0.25 mm posteriorly and 0.50 mm laterally. Medially, the computational DD differed on average by 0.09 mm (stand deviation: 0.2026 mm). Our study describes the development and validation of a novel robotics dislocation analysis tool, which allows mobile bearing dislocation risk quantification. The tool may also be used to improve surgical implantation parameters and to assess new implant designs that aim to reduce the medial dislocation risk to an acceptable level.

Effect of anteromedial and posterolateral anterior cruciate ligament bundles on resisting medial and lateral tibiofemoral compartment subluxations.

PURPOSE: This study analyzed the interaction of the anteromedial and posterolateral portions of the anterior cruciate ligament (ACL) in resisting medial and lateral tibiofemoral compartment subluxations under multiple loading conditions. METHODS: By use of a 6-df robotic simulator, 10 human cadaveric knees were tested in 3 states: intact ACL, partial ACL (loss of either the anteromedial bundle [AMB] or posterolateral bundle [PLB]), and deficient ACL. The testing profile involved anterior-posterior translation and internal-external rotation, as well as 3 pivot-shift loading conditions with varying internal rotation torque (1- or 5-Nm) and coupled anterior force (35- or 100-N). Digitization of anatomic landmarks provided tibiofemoral compartment translations and centers of tibial rotation. RESULTS: During pivot-shift testing (100-N anterior force, 1-Nm internal rotation torque, and 7-Nm valgus), the lateral and medial compartment anterior translation increased by a mean of 2.5 ± 0.8 mm (P = .016) and 3.4 ± 2.0 mm (P = .001), respectively, on AMB sectioning and 1.3 ± 0.9 mm (P = .329) and 0.6 ± 0.7 mm (P = .544), respectively, on PLB sectioning. Higher internal rotation torque (5 Nm v 1 Nm) on pivot-shift testing reduced central and medial anterior translation after ACL sectioning. There was no change in internal rotation on AMB or PLB sectioning. During the Lachman test (100-N), AMB and PLB sectioning increased central translation by 3.6 ± 1.6 mm (P = .001) and 0.7 ± 0.6 mm (P = .498), respectively. CONCLUSIONS: Both ACL bundles function synergistically in resisting medial and lateral compartment subluxations on the Lachman and pivot-shift tests. The AMB provided more restraint to anterior tibial translation during both tests as compared with the PLB. PLB sectioning produced no statistically significant change in anterior translation on the Lachman or pivot-shift test. Neither bundle contributed to resisting internal rotation. CLINICAL RELEVANCE: An ACL graft designed to duplicate the AMB would theoretically resist medial and lateral compartment anterior subluxations under multiple loading conditions. The PLB provides a secondary restraint at low flexion angles. Neither ACL bundle resists internal tibial rotation or allows a positive pivot-shift subluxation.

Luxación congénita de rodilla: a propósito de 2 casos / Congenital dislocation of the knee: Report of 2 cases

La luxación congénita de rodilla (LCR) es una patología muy poco frecuente cuyo diagnóstico se realiza al nacimiento por los hallazgos clínicos, confirmándose radiológicamente. Se ha relacionado con diversas etiologías, desde malas posiciones fetales intraútero hasta trastornos genéticos. El pronóstico dependerá del inicio precoz del tratamiento y de la asociación de otras anomalías congénitas. Presentamos 2 nuevos casos de LCR observados en nuestro hospital en el período de un mes, diagnosticados en los primeros momentos tras el nacimiento, ambos con buena evolución clínica

Congenital dislocation of the knee is a rare disease. The diagnosis is made at birth by clinical findings, and confirmed radiologically. It has been associated with various etiologies from intrauterine fetal malpositions to genetic disorders. The prognosis depends on early treatment and whether there are other congenital anomalies. We report two new cases of congenital dislocation of the knee, observed in our hospital during the period of a month, diagnosed immediately after birth, and both with a good clinical outcome

[Spin out - an avoidable complication in total knee replacement]. / "Spin-out" - eine vermeidbare Komplikation in der Knieendoprothetik.

Spin out of a rotating polyethylene (PE) platform after total knee replacement leads to rotation of the bearing compared to the fixed metal components of the prosthesis at the femur and tibia of approximately 90°. This complication occurs only in prosthesis designs which do not have a rotation limitation. Identification of this complication and its management are described exemplified by two cases. Strategies to avoid spin out are discussed. The most promising way is to avoid using prosthesis designs in which spin out can occur.

An analysis of dislocation of the domed Oxford Lateral Unicompartmental Knee Replacement.

BACKGROUND: The Oxford Unicompartmental Knee Replacement (OUKR) uses a mobile bearing to minimise wear. Bearing dislocation is a problem in the lateral compartment as the ligaments are loose in flexion. A domed tibial component has been introduced to minimise the risk of dislocation, yet they still occur, particularly medially. The aim of this mechanical study was to compare the domed and flat tibial components and to identify surgical factors that influence the risk of dislocation. METHOD: A jig was constructed to assess the amount of vertical distraction of the lateral OUKR for a dislocation to occur. Three methods of dislocation were assessed: laterally, medially, 'over the wall' and anteriorly. The study focused on medial dislocation. RESULTS: Significantly (p=0.02) greater vertical distraction was required to dislocate the bearing with the domed tibia rather than the flat. For medial dislocation bearing distance from the wall, femoral component external rotation and tibial rotation were associated with significantly less distraction for dislocation. With the optimal technique with the domed tibia the distraction required to dislocate the bearing medially was 6.4 mm, whereas with poor technique it was 4.6 mm. CONCLUSIONS: This study suggests that to minimise the risk of dislocation the domed tibia should be used. The component should be implanted so the bearing is close to the wall, but does not hit it, and in flexion the femoral and tibial components should be neutrally aligned.

Gracilis autograft for recurrent posttraumatic instability of the superior tibiofibular joint.

BACKGROUND: Several reconstruction procedures have been proposed to manage recurrent dislocation of the superior tibiofibular joint. HYPOTHESIS: Reconstruction of the superior tibiofibular joint using a gracilis tendon autograft is effective in recurrent dislocation of the superior tibiofibular joint. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Eight patients with recurrent dislocation of the superior tibiofibular joint without anatomical predisposing factors and who practiced sports were included in the study. Evaluation included the modified Cincinnati rating system and the Kujala score, anthropometry, plain radiography, and isokinetic dynamometry. RESULTS: The average follow-up was 44 ± 13 months. The mean modified Cincinnati score increased from 54 preoperatively to 92 (P = .01). The mean Kujala scores increased from 48 preoperatively to 85 (P = .05). The muscle volume of the thigh of the operated limb remained less well developed than the muscle volume of the nonoperated limb (P = .05). Significant isokinetic strength differences were found between the operated and the contralateral limb (P = .02) even at the latest follow-up. CONCLUSION: Gracilis autograft for posttraumatic instability of the superior tibiofibular joint is a safe, reliable management option for recurrent dislocation of the superior tibiofibular joint in patients without any predisposing factors.

The 3-in-1 procedure for recurrent dislocation of the patella in skeletally immature children and adolescents.

BACKGROUND: Recurrent patellar dislocations are common injuries in children and adolescents. The subjective and functional results of soft tissue surgical management in a population that was skeletally immature at the time of surgery have not been reported. HYPOTHESIS: The 3-in-1 procedure is an effective treatment for recurrent patellar dislocation in skeletally immature patients. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Twenty-five skeletally immature patients (age at operation, 13.5 +/- 3.8 years) who were practicing sports and suffering from recurrent unilateral patellar dislocation were included in the study and followed until skeletal maturation. Clinical evaluation included the modified Cincinnati rating system and the Kujala score, anthropometry, plain radiography, and isokinetic dynamometry. RESULTS: The average follow-up was 3.8 years (range, 2.5-6 years). The mean modified Cincinnati score increased from 51.7 +/- 12.6 preoperatively to 94.3 +/- 10.8 (P < .02), while the mean Kujala scores increased from 52.4 +/- 12.7 preoperatively to 93.8 +/- 14.2 (P < .02). The Insall-Salvati index remained essentially unchanged, being 1.04 +/- 0.2 preoperatively and 1.02 +/- 0.3 at latest follow-up. Significant differences were found between the operated and the contralateral limb in the various isokinetic strength variables at all angular velocities measured at the latest follow-up (.05 < P < .0042). CONCLUSION: The 3-in-1 procedure is a safe, reliable management option for recurrent patellar dislocation in skeletally immature patients. Side-to-side differences in isokinetic strength and in anthropometric indices persist despite subjective success of the procedure.

Bone landmarks are more reliable than tensioned gaps in TKA component alignment.

Two distinct techniques have been used to achieve alignment and ligament balance in TKA. We hypothesized a bone landmark technique would result in normal alignment, stability, and load-bearing characteristics and that the tensioned gap technique results in malalignment. We studied 12 normal cadaveric knees (six with each technique) for stability, alignment, load-bearing stress transfer characteristics, and patellar groove position after TKA. The tensioned gap technique used tensioners to establish equal loads in the medial and lateral ligaments at 90 degrees flexion and to resect the posterior femoral surfaces parallel to the cut tibial surfaces. The bone landmarks technique aligns the anterior and posterior femoral cuts perpendicular to the median sagittal plane as defined by the anteroposterior axis and then resects bone to match implant thickness. The tensioned gap technique maintained nearly equal laxity medially and laterally but the knee shifted into varus malalignment in flexion. Compressive stress in the knee shifted medially in flexion, and the patellar groove shifted laterally. The bone landmarks technique produced near normal varus and valgus and rotational stability; alignment, patellar groove position, and load transfer characteristics remained near normal throughout flexion.

[Lengthening of proximal femoral focal deficiency using a hybrid fixation with inclusion of the knee joint]. / Verlängerung des kongenital kurzen Femurs (PFFD) mittels Hybridfixateur unter Einbeziehung des Kniegelenks.

BACKGROUND: A major problem in lengthening a short femur in proximal focal deficiency of the femur (PFFD) is the development of contractures and dislocation of the hip and knee joint. The knee joint is particularly prone to dislocation because of the cruciate ligament insufficiency associated with PFFD. Axis deviations also need specific attention. PATIENTS AND METHODS: In four patients (age 2.5-11 years) with PFFD (PAPPAS class III in one patient and VII in three patients), five femoral lengthenings with mechanical axis corrections were performed by the callotasis technique using a hybrid fixation system (Monotube/Triax) connecting the femur and the tibia with a fixed hinged knee joint to protect the knee against contracture and dislocation. RESULTS: All patients retained their hip and knee function. Hip flexion contracture during lengthening may make inclusion of the hip joint into the fixation system necessary, but was not carried out in the four patients presented. CONCLUSION: Four consecutive lengthenings of the femur with focal deficiency were carried out under protection by a hinged knee bridging external fixator. A dislocation could be prevented in all patients. We consider that such a system could be used during these lengthening procedures.

[Rotating platform spinout in LCS knee arthroplasty]. / Spinout der rotierenden Plattform bei der LCS-Knieendoprothese.

In knee arthroplasty, a lax flexion gap may cause flexion instability. Subsequently, the operated knee may subluxate or dislocate. We report on a case of recurrent subluxations with malrotation of the rotating platform (spinout) after primary LCS total knee arthroplasty. Potential causes for spinout, therapy procedures, and consequences for the primary surgical technique are discussed. In the LCS rotating platform knee arthroplasty, the flexion gap must not be laxer than the extension gap. In such an instance, we recommend a higher rotating platform and a more proximal distal transverse femoral osteotomy.

Importance of a balanced-gap technique in rotating-platform knees.

Rotating-platform knees are constructed of highly conforming polyethylene to reduce contact pressures that potentially cause wear. The mobile nature of the rotating platform can lead to bearing spin-out. The purpose of this study was to determine the prevalence of spin-out in a single series. A total of 426 knees in 393 patients were included in the study. All knees were implanted using a balanced-gap technique. The average follow up was 3.2 years. There were no cases of bearing spin-out. The author concludes that the balanced-gap technique reliably prevents spin-out in mobile-bearing total knee implantation. This implantation technique provides the potential wear benefits of the rotating platform design with a nominal bearing spin-out rate.

Surgical technique tips and pearls in rotating-platform knee arthroplasty.

Rotating-platform mobile-bearing knee arthroplasties have potential advantages over fixed-bearing knee prostheses that may lead to better long-term wear of the polyethylene articulation. Their potential disadvantages include bearing spin-out that is usually the result of a tight posterior cruciate ligament in need of release. The "slide-back test" can help determine this need during placement of the trial components. Clearing polymerized cement from the back of the knee can be difficult during rotating-platform knee arthroplasty unless cementing is completed using a trial tibial insert without a stem. Exchanging a rotating-platform insert at a future arthrotomy can be facilitated by the use of a shim that provides exposure to the polyethylene tibial post that articulates within the stem of the tibial tray. Severing the post allows extraction of the polyethylene plateau and access to the post within the tray.

Achieving ligament stability and correct rotational alignment of the femur in knee arthroplasty: a study using the Medial Pivot knee.

In a series of 90 Medial Pivot arthroplasties rotational alignment of the femur was achieved by provisionally reconstructing the lateral side of the joint and tensioning the medial side with feeler gauges. Axial CT scans were employed to measure the rotational alignment relative to surgical epicondylar axis. In valgus knees the cutting block was externally rotated to adjust for posterolateral bone loss. The mean rotational alignment of the femur was 0.6 degrees of external rotation (S.D. 1.3, range 3 degrees of ER to 4 degrees of IR). The mean laxity of the medial ligament was 1 mm in flexion (SD 1, range 0-5 mm) and 0.5 mm in flexion (S.D. 0.5, range 0-2 mm) In those knees in which the medial ligament had been released the CT alignment was perfect, but when internally rotated against the hip 3-4 mm of gapping was noted. In valgus knees the mean rotation of the femoral component was 0.8 degrees of internal rotation (S.D. 1.5, range 1 degrees of IR to 4 degrees of ER). In spite of externally rotating the cutting block there was still a tendency to internally rotate the femur in some knees. This simple technique achieves the two goals of ligament stability and correct rotational alignment in a high proportion of cases. It may be applicable to any instrument system which employs posterior referencing.