The in vivo relationship between anterior neutral tibial position and loss of knee extension after transtibial ACL reconstruction

BackgroundRestoration of anterior tibial stability while avoiding knee extension deficit are a common goal of anterior cruciate ligament (ACL) reconstruction. However, achieving this goal can be challenging. The purpose of this study was to determine whether side-to-side differences in anterior tibial neutral position and laxity are correlated with knee extension deficit in subjects 2 years after ACL reconstruction.MethodsIn the reconstructed and contralateral knees of 29 subjects with transtibial reconstruction, anterior tibiofemoral neutral position was measured with MRI and three-dimensional modeling techniques; terminal knee extension at heel strike of walking and during a seated knee extension were measured via gait analysis; and anterior laxity was measured using the KT-1000.ResultsKnees that approached normal anterior stability and anterior tibial position had increased extension deficit relative to the contralateral knee. On average the reconstructed knee had significantly less (2.1 ± 4.4°) extension during active extension and during heel strike of walking (3.0 ± 4.3º), with increased anterior neutral tibial position (2.5 ± 1.7 mm) and anterior laxity (1.8 ± 1.0 mm). There was a significant correlation between side-to-side difference in anterior neutral tibial position with both measures of knee extension (walking, r = − 0.711, p < 0.001); active knee extension, r = − 0.544, p = 0.002).ConclusionThe results indicate a relationship between the loss of active knee extension and a change in anterior neutral tibial position following non-anatomic transtibial ACL reconstruction. Given the increasing evidence of a link between altered kinematics and premature osteoarthritis, these findings provide important information to improve our understanding of in vivo knee function after ACL reconstruction.     

Radiographic evaluation of factors affecting bearing dislocation in the domed lateral Oxford unicompartmental knee replacement

BackgroundThe rate of bearing dislocation with the domed lateral Oxford Unicompartmental Knee Replacement (OUKR) in different series varies from 1% to 6% suggesting that dislocation is influenced by surgical technique. The aim of this study was to identify surgical factors associated with dislocation.MethodsAligned post-operative antero-posterior knee radiographs of seven knees that had dislocated and 87 control knees were compared. Component alignment and position and the alignment of the knee were assessed. All bearing dislocations occurred medially over the tibial wall.ResultsKnees that dislocated tended to be overcorrected: Compared with those that did not dislocate, they were in 2° less valgus (p = 0.019) and the tibial components were positioned 2 mm more proximal (p < 0.01). Although the relative position of the centre of the femoral component and the tibial component was the same (p = 0.8), in the dislocating group the gap between the edge of the femoral component and the top of the wall in flexion was 3 mm greater (p = 0.019) suggesting that the components were internally rotated.ConclusionsTo minimise the risk of dislocation it is recommended that the knee should not be overstuffed. This is best achieved by selecting the bearing thickness that just tightens the ligaments in full extension, and re-cutting the tibia if necessary. In addition to minimise the gap between the femoral and tibial components through which the bearing dislocates, the femoral component should be implanted in neutral rotation and should not be internally rotated.Level of evidenceLevel IV     

In vivo kinematic analysis of posterior-stabilized total knee arthroplasty for the valgus knee operated by the gap-balancing technique

BackgroundMost in vivo kinematic studies of total knee arthroplasty (TKA) report on the varus knee. The objective of the present study was to evaluate in vivo kinematics of a posterior-stabilized fixed-bearing TKA operated on a valgus knee during knee bending in weight-bearing (WB) and non-weight-bearing (NWB).MethodsA total of sixteen valgus knees in 12 cases that underwent TKA with Scorpio NRG PS knee prosthesis and that were operated on using the gap balancing technique were evaluated. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibial tray using a 2-dimensional to 3-dimensional registration technique.ResultsThe average flexion angle was 111.3° ± 7.5° in WB and 114.9° ± 8.4° in NWB. The femoral component demonstrated a mean external rotation of 5.9° ± 5.8° in WB and 7.4° ± 5.2° in NWB. In WB and NWB, the femoral component showed a medial pivot pattern from 0° to midflexion and a bicondylar rollback pattern from midflexion to full flexion. The medial condyle moved similarly in the WB condition and in the NWB condition. The lateral condyle moved posteriorly at a slightly earlier angle during the WB condition than during the NWB condition.ConclusionsWe conclude that similar kinematics after TKA can be obtained with the gap balancing technique for the preoperative valgus deformity when compared to the kinematics of a normal knee, even though the magnitude of external rotation was small. Level of evidence: IV.     

Can tibio-femoral kinematic and kinetic parameters reveal poor functionality and underlying deficits after total knee replacement? A systematic review

BackgroundExtensive efforts have been made to understand joint kinematics and kinetics in total knee arthroplasty (TKA) in subjects with satisfactory outcomes during daily functional activities and clinical tests, but it remains unclear whether such movement characteristics hold the potential to indicate the underlying aetiology of unsatisfactory or bad TKA outcomes.PurposeTo investigate which kinematic and kinetic parameters assessed during passive clinical tests and functional activities of daily living are associated with poor functionality and underlying deficits after total knee replacement.MethodsWe focused on studies characterizing the kinematic or kinetic parameters of the knee joint that are associated with poor clinical outcome after TKA. Seventeen articles were included for the review, and kinematic and kinetic data from 719 patients with minimal follow up of 6 months were extracted and analyzed.ResultsPassive posterior translation at 90° flexion exhibited good potential for differentiating stable and unstable TKAs. Anterior-posterior (A-P) translation of the medial condyle at 0–30° and 30–60° flexion, A-P translation of the lateral condyle at 60–90° during closed chain exercises, as well as knee extension moment during stair ascent and descent, knee abduction moment during stair descent, knee internal rotation moment and plantar flexion moment during walking, 2nd peak ground reaction force during stair ascent and walking showed the greatest promise as functional biomarkers for a dissatisfied/poor outcome knee after TKA.ConclusionIn this study, we systematically reviewed the state-of-the-art knowledge of kinematics and kinetics associated with functional deficits, and found 11 biomechanical parameters that showed promise for supporting decision making in TKA.     

Aligning the tibial component with medial border of the tibial tubercle—is it always right?

IntroductionCorrect rotational alignment of the tibial component is crucial for total knee arthroplasty (TKA). Several studies have indicated that the best rotational orientation of the tibial component is close to the medial border of the tibial tubercle. However, it remains obscure whether it is always right. Thus, the objective of current study was to quantify tibial rotational alignment in 120 primary rotating platform TKAs using the medial border of tibial tubercle as a landmark between July 2008 and June 2010.MethodsThe femoral component was positioned parallel to the transepicondlylar axis, and a rotating platform trial insert was used to determine tibial insert rotational alignment relative to the most medial aspect of the tibial tubercle with the knee in full extension. Rotational alignment of the components was detected based on radiograph and CT scan. This investigation is based on the premise that all neutral points would lie within 10° of the mean.ResultsThe mean divergence external to the medial border of the tubercle was 2.3° ± 3.5°. However, six of the knees (5%) had neutral points ≥ 10° from the mean, including two valgus knees measured 10° of internal rotation and four varus knees measured 10° of external rotation.ConclusionUsing the medial border of tibial tubercle as a landmark does not always result in a good femoro-tibial rotational alignment. Surgeons using fixed bearings component should be aware of this effect to avoid suboptimal outcomes resulting from tibiofemoral rotational malalignment in full extension.Level of evidenceDiagnostic study, Level II-3.     

Satisfactory results at 8 years mean follow-up after ADVANCE® medial-pivot total knee arthroplasty

BackgroundAlthough good overall results have been reported with TKA, certain problems and limitations remain, primarily due to postoperative differences in joint kinematics, when compared with the normal knee. ADVANCE® Medial-Pivot TKA involves replicating the medial pivoting behavior observed in normal knees. Here, we aimed to investigate the clinical and radiological results and complications of TKA using this implant, at mid-term follow-up.MethodsFrom January 2001 to March 2012, we retrospectively selected 76 patients (85 knees; mean age at operation, 70.2 ± 8.1 years; range, 51–88 years) with a mean follow-up period of 93.1 ± 14.3 months (range, 72–132 months). Indications for TKA included primary degenerative osteoarthritis (60 knees), rheumatoid arthritis (22 knees), osteonecrosis (two knees), and osteoarthritis following high tibial osteotomy (one knee). The clinical and radiographic results were evaluated.ResultsKaplan–Meier survivorship analysis indicated a success rate of 98.3% (95% confidence interval, 96.6–99.9%). Comparison of pre- and postoperative knee extension angles and ranges of motion showed significant improvement postoperatively, in both the Knee Society Scores (KSS) and Knee Society Functional Scores (KSFS) (p < 0.05). In one case, radiographic assessment indicated implant loosening due to infection; however, despite this complication, significant improvement of postoperative varus or valgus deformity angles were noted in all cases (p < 0.05).ConclusionPatients undergoing ADVANCE® Medial-Pivot TKA achieved excellent clinical and radiographic results without any implant-related failures at mid-term follow-up.Level of evidence: Level IV     

Comparison of kinematics of ACL-deficient and healthy knees during passive flexion and isometric leg press

BackgroundStudying the kinematics of the ACL deficient (ACLD) knees, during different physiological activities and muscle contraction patterns, can improve our understanding of the joint's altered biomechanics due to ACL deficiency as well as the efficacy and safety of the rehabilitations exercises.MethodsTwenty-five male volunteers, including 11 normal and 14 unilateral ACLD subjects, participated in this study. The kinematics of the injured knees of the ACLD subjects was compared with their intact knees and the healthy group during passive flexion and isometric leg press with the knees flexed from full extension to 45° flexion, with 15° intervals. An accurate registration algorithm was used to obtain the three dimensional kinematical parameters, from magnetic resonance images.ResultsThe ACL deficiency mainly altered the tibial anterior translation, and to some extent its internal rotation, with the change in other parameters not significant. During leg press, the anterior translation of the ACLD knees was significantly larger than that of the normal knees at 30° flexion, but not at 45°. Comparison of the anterior translations of the ACLD knees during leg press with that of the passive flexion revealed improved consistency (CVs changed from 1.2 and 4.0 to 0.6 and 0.6, at 30° and 45° flexion, respectively), but considerable larger translations (means increased by 6.2 and 4.9 mm, at 30° and 45° flexion, respectively).ConclusionThe simultaneous contraction of the quadriceps and hamstrings during leg press, although reduces the knee laxity, cannot compensate for the loss of the ACL to restore the normal kinematics of the joint, at least during early flexion.     

The location of the popliteal artery in extension and 90 degree knee flexion measured on MRI

We measured the location of the popliteal artery (PA) in extension and 90 degree of knee flexion by magnetic resonance images (MRI) to provide practical information to avoid PA injury. The MRIs of 30 knees of Korean male subject whose mean age was 20.7 were acquired in knee extension and 90 degree flexion. The distance from the posterior aspect of knee joint to the PA was measured at three levels on the axial images and one sagittal image. At the joint line level, the PA was located lateral to the PCL 2.4 mm in extension and 3.2 mm in flexion (p = 0.247), and 3.9 mm in extension and 7.6 mm in flexion from the posterior capsule (p < 0.001). At 1 cm distal to the joint line, it is 2.7 mm in extension and 7.2 mm in flexion (p < 0.001), and at 2 cm distal to the joint line, 4.9 mm in extension and 9.7 mm in flexion from the posterior tibial cortex (p < 0.001). In sagittal plane, the nearest distance between PA and posterior tibial cortex was 1.8 mm in extension, and 6.2 mm in flexion (p < 0.001). The PA was located around 3 mm lateral to the PCL, and within 5 mm in extension and 10 mm in 90 degree flexion of the knee behind knee joint. It moves farther posteriorly in 90 degree flexion than in extension of the knee. The conventional wisdom of flexing the knee to prevent the PA injury was supported by this study.     

3D in vivo femoro-tibial kinematics of tri-condylar total knee arthroplasty during kneeling activities

BackgroundKneeling position can serve as an important posture, providing stability and balance from a standing position to sitting on the floor or vice-versa. The purpose of the current study was to determine the kinematics during kneeling activities after subjects were implanted with a tri-condylar total knee arthroplasty.Materials and methodsKinematics was evaluated in 54 knees using fluoroscopy and a three-dimensional model fitting approach.ResultsThe average knee flexion at before contact status, at complete contact and at maximum flexion was 98.1 ± 9.0°, 107.2 ± 6.7°, and 139.6 ± 12.3°, respectively. On average, there was no gross anterior displacement from before contact status to complete contact. Only slight posterior rollback motion of both condyles from complete contact to maximum flexion was observed. Three of 39 (7.7%) knees experienced anterior movement of both condyles more than 2 mm from before contact status to complete contact. Reverse rotation pattern from before contact status to complete contact and then normal rotation pattern from complete contact to maximum flexion were observed. Condylar lift-off greater than 1.0 mm was observed in 45 knees (83.3%).ConclusionThe presence of the ball-and-socket joint articulation provides sufficient antero-posterior stability in these designs to enable the patients to kneel safely without the incidence of any dislocation.Clinical relevanceThis study suggests a safe implant design for kneeling.     

In vivo weight-bearing kinematics with medial rotation knee arthroplasty

Knee arthroplasties are designed to accommodate flexion, axial rotation and anteroposterior (AP) translation. Axial rotation during extension varies, with some rotating platform devices allowing unrestricted rotation while some conforming fixed-bearing designs almost none. The purpose of this study was to examine in vivo kinematics of a fixed-bearing medial rotation-type arthroplasty (MRK) during weight-bearing activities. Fifteen knees with a medial pivot TKA design were studied during step and pivot activities using lateral fluoroscopy and model-image registration. Average knee kinematics during the step activity showed little AP translation or rotation from 0°–100° flexion. During the pivot activity, the mean tibial internal rotation in individual knees was 7° (3°–19°). Mean condylar translations for individual knees were 3 mm medially and 5 mm laterally. The medial pivot prosthesis design provides anteroposterior stability during demanding activities, and exhibits a medial pivot motion pattern when subjected to twisting.     

Evaluating rotational kinematics of the knee in ACL reconstructed patients using 3.0 Tesla magnetic resonance imaging

IntroductionInjury to the anterior cruciate ligament (ACL) is common. While prior studies have shown that surgical reconstruction of the ACL can restore anterior–posterior kinematics, ACL-injured and reconstructed knees have been shown to have significant differences in tibial rotation when compared to uninjured knees. Our laboratory has developed an MR compatible rotational loading device to objectively quantify rotational stability of the knee following ACL injuries and reconstructions. Previous work from our group demonstrated a significant increase in total tibial rotation following ACL injuries. The current study is a prospective study on the same cohort of patients who have now undergone ACL reconstruction. We hypothesize that ACL reconstructed knees will have less tibial rotation relative to the pre-operative ACL deficient condition. We also hypothesize that ACL reconstructed knees will have greater rotational laxity when compared to healthy contralateral knees.MethodsPatients. Six of the ACL injured patients from our initial study who had subsequently undergone ACL reconstruction were evaluated 8.1 ± 2.9  months after surgery. All patients underwent single-bundle ACL reconstruction using anteromedial portal drilling of the femoral tunnel with identical post-operative regimens.Magnetic Resonance (MR) Imaging. Patients were placed in a supine position in the MR scanner on a custom-built loading device. Once secured in the scanner bore, an internal/external torque was applied to the foot. The tibiae were semi-automatically segmented with in-house software. Tibial rotation comparisons were made within subjects (i.e. side-to-side comparison between reconstructed and contralateral knees) and differences were explored using paired sample t-tests with significance set at p = 0.05.ResultsRegarding tibial rotation, in the ACL deficient state, these patients experienced an average of 5.9 ± 4.1° difference in tibial rotation between their ACL deficient and contralateral knees. However, there was a ?0.2 ± 6.1° difference in tibial rotation of the ACL reconstructed knee when compared to the contralateral uninjured knee. Regarding tibial translation, ACL deficient patients showed a difference of 0.75 ± 1.4mm of anterior tibial translation between injured and healthy knees. After ACL reconstruction, there was a 0.2 ± 1.1mm difference in coupled anterior tibial translation of the ACL reconstructed knee compared to the contralateral knee. No significant differences in contact area between the two time points could be discerned.DiscussionThe objective of our study was to assess the rotational laxity present in ACL reconstructed knees using a previously validated MRI-compatible rotational loading device. Our study demonstrated that ACL reconstruction can restore rotational laxity under load. This may speak to the benefit of an anteromedial drilling technique, which allows for a more horizontal and anatomically appropriate graft position.     

Intraoperative assessment of midflexion laxity in total knee prosthesis

BackgroundSoft-tissue balancing of the knee is fundamental to the success of a total knee arthroplasty (TKA). In posterior-stabilized TKA, there is no stabilizer of the anterior–posterior translation in the midflexion range in which the cam-post mechanism does not engage yet. Therefore, instability in the midflexion range is suspected to occur in posterior-stabilized TKA. The purpose of this study was to measure the joint gap throughout a full range of motion and to analyze the joint gap laxity in the midflexion range after implantation of a mobile-bearing posterior-stabilized total knee prosthesis.MethodsJoint gap kinematics in 259 knees with varus osteoarthritis were measured during TKAs using a tensor device with the same shape of a total knee prosthesis of the same design was used. After the implantation of a mobile-bearing posterior-stabilized prosthesis and the reduction of the patellofemoral joint, the joint gap was measured at 0°, 30°, 60°, 90°, 120°, and 145° of flexion.ResultsThe center size of the joint gap was tight in extension and deep flexion and loose at midflexion ranges, especially at 30° of flexion (p < 0.001). The symmetry of the joint gap was varus at 0° and 145° of flexion (p < 0.001).ConclusionsOur results showed the joint gap laxity in the midflexion range after the implantation of a mobile-bearing posterior-stabilized prosthesis. Our new tensor device, which can attach the polyethylene insert trial, will provide the important information about the joint gap kinematics after implantation of total knee prostheses.Level of evidenceIV.     

AM bundle controls the anterior–posterior and rotational stability to a greater extent than the PL bundle — A cadaver study

BackgroundThe purpose of this study was to evaluate the influence of both bundles of the anterior cruciate ligament (ACL) on knee stability, anterior–posterior translation (APT) and internal (IR) and external (ER) rotation in cadaveric knees using a computer navigation system.MethodsThe APT, IR, and ER of the knees were recorded in the intact condition, the anterolateral bundle (AM) or the posterolateral bundle (PL) deficit condition and in the ACL-deficient condition. The KT-1000 arthrometer was used for APT evaluation. The measurement of rotational movements was done using a rollimeter. All tests were performed at 30°, 60° and 90° of flexion.ResultsAt 30° of flexion: In the intact knee APT was 5.8 mm, IR 12.1°, ER 10.1°. After the AM was cut, the APT increased to 9.1 mm, IR to 13.9° and ER to 12.6°. After the PL was cut, the APT was 6.4 mm, IR 13.1° and ER 10.6°. After the AM and PL were cut, the APT was 10.8 mm, IR 15.7° and the ER was 12.9° on average.ConclusionsThe AM has a greater impact on the APT than the PL in all knee joint flexion angles. The PL does not resist the rotational stability more than the AM. The rotational stability is better controlled by both bundles of ACL as compared to one bundle of the ACL.Clinical RelevanceThis study acknowledges the fact that the both bundles of the ACL are importants for AP and rotational stability of the knee joint.     

Joint line position in revision total knee arthroplasty: the role of posterior femoral off-set stems

BackgroundElevation of the joint line frequently occurs in revision total knee arthroplasty (RTKA) because of a wider flexion space than extension space. One solution to balance this flexion-extension space involves the introduction of couplers between the stem and femoral components, and the use of posteriorly offset femoral stems that we hypothesized would improve gap balancing and facilitate joint line restoration.MethodsWe retrospectively reviewed a selected series of 43 RTKA. Postoperative joint line height was subtracted from intended height using postoperative lateral radiographs. The value was negative if the joint line position was lowered, and positive if raised.ResultsForty knees were followed for a mean of 3.5 years. Mean postoperative joint line position change from intended position was 1.5 mm (range ? 2.5–7.5 mm). In 28 knees (70%), the joint line position was restored to within ± 2 mm of the intended position; in eight knees (20%), from 2–4 mm; and in four knees (10%), > 4 mm. Joint line position was raised in 32 knees (80%) and lowered in eight (20%). In the offset stem knees, the intended joint line position was 0.9 mm (range ? 1.2–3.4 mm) as compared with 3.2 mm (range ? 2.5–7.5 mm) for the straight stem knees.ConclusionsA coupler system between the femoral stem and femoral component restored the joint line in 70% of cases. The posterior offset stem provided increased posterior condylar offset, addressed the wider flexion space, provided better positioning of the stem, and restored the joint line.Level of evidenceTherapeutic Study Level IV     

Effect of lower limb malalignment in the frontal plane on transverse plane mechanics during gait in young individuals with varus knee alignment

BackgroundVarus knee alignment has been identified as a risk factor for the progression of medial knee osteoarthritis (OA). This study tested the hypothesis that not only frontal plane kinematics and kinetics but also transverse plane lower extremity mechanics during gait are affected by varus malalignment of the knee.MethodsEighteen, otherwise healthy children and adolescents with varus malalignment of the knee were studied to examine the association between static varus malalignment and functional gait parameters. Kinematic data were collected using a Vicon motion capture system (Vicon Motion Systems, Oxford, UK). Two AMTI force plates (Advanced Mechanical Technology, Inc., Watertown, MA, USA) were used to collect kinetic data.ResultsThe results indicated that changes in transverse plane mechanics occur concomitantly with changes in knee malalignment in the frontal plane. A mechanical consequence of varus knee malalignment is obviously an increased endorotation of the foot (internal foot placement) and an increased internal knee rotation (tibia rotation) during stance phase. The linear correlation between the maximum external knee adduction moment in terminal stance and the internal knee rotation in terminal stance (r = 0.823, p < 0.001) shows that this transverse plane gait mechanics is directly in conjunction with intrinsic compressive load on the medial compartment during gait.ConclusionsUnderstanding factors that influence dynamic knee joint loading in healthy, varus malaligned knees may help us to identify risk factors that lead to OA. Thus, three-dimensional gait analysis could be used for clinical prognoses regarding the onset or progression of medial knee OA.     

Measuring patellar height using the lateral active flexion radiograph: Effect of total knee implant design

Patellar position during knee flexion was studied in 41 patients with bicruciate substituting (BCS), 41 patients with posterior cruciate retaining (CR) and 41 patients with posterior stabilized (PS) TKA's. The perpendicular height of the patella above the tibial tubercle was compared to the length of the patellar tendon on maximum flexion lateral radiographs. BCS knees had greater active flexion compared to PS and CR knees (BCS = 124 ± 9.8, PS = 112 ± 9.5, CR = 110 ± 10.9). In flexion, apparent patella infera (API) or the height of the patella above the tibial tubercle was 3.5% lower than the patellar tendon length for BCS knees, 1.7% lower in PS knees and 0.5% lower in CR knees. API in PS and BCS knees correlated with active knee flexion, but not in CR knees. Our findings indicate that an apparent inferior position of the patella occurs in BCS knees during deep flexion which is not caused by significant patellar ligament shortening or joint line elevation, but associated with normal posterior rollback of the femur.     

Biomechanics of single-tunnel double-bundle anterior cruciate ligament reconstruction using fixation with a unique expandable interference screw

BackgroundSingle-tunnel double-bundle (STDB) anterior cruciate ligament (ACL) reconstruction can restore biomechanical function and anatomic structure, but existing methods of graft fixation are not adequate. The aims of this study are to examine knee biomechanics after STDB reconstruction using a unique expandable interference screw for fixation.MethodsThe biomechanical parameters of six pairs of human cadaveric knee specimens were measured with the ACL intact, after ACL removal, and after STDB reconstruction using the interference screw or single-tunnel single-bundle (STSB) reconstruction. Anterior tibial translation under 134 N anterior tibial load in a neutral position as well as in 15° and 30° internal and external knee rotation and the internal tibial rotation angle under the rotatory load (5 N · m internal tibial rotation) were measured.ResultsAnterior tibial translations at each degree of knee flexion in the STDB group were significantly less than in the STSB group (all, P < 0.05). The internal rotation angles in the STSB group at five flexion angles were significantly higher than in the ACL intact group, whereas there were significantly less than those of the ACL absent group (P < 0.05). Under rotatory loads in the neutral position, the tibial internal rotation angles of the STDB group were significantly lower than in the STSB group at all flexion angles (all, P < 0.05).ConclusionsSTDB ACL reconstruction with the expandable interference screw provides better anteroposterior and rotational stability than STSB reconstruction.Clinical relevanceThe technique provides the advantages of double-bundle reconstruction using a single-tunnel technique.     

The influence of tibial morphology on the design of an anatomical tibial baseplate for TKA

BackgroundFinding the right balance between tibial coverage and minimal implant overhang is an important factor in TKA. Another significant cause of failure is component malrotation.MethodsAn average master shape of the proximal tibia at TKA resection level was calculated using fine slice computed tomographies of 117 cadaveric knees. To find out whether alternate implant contours would be necessary depending on the patient's body size, we established five subgroups to compare. CAD-Analysis was performed to simulate the overhang produced after ± 4°/± 7°/± 10° rotation.ResultsA master shape for the tibial resection cut (with a 5° posterior slope, 7 mm under lateral joint line) could be determined. Neither left vs. right knee joint, nor male vs. female nor the size subdivision appears to alter the calculated master shape significantly. The optimized shape allowing for ± 4° of rotational freedom was found to be the best variant.ConclusionsValid methods have been obtained to design a two-dimensional average shape of the tibial plateau. The modifications described in this study might come in useful, when designing future implant designs.Clinical relevanceAn optimized fit at the tibial plateau and lower rates of component malrotation may result in better outcomes after TKA.     

Anatomic proximity of the peroneal nerve to the posterolateral corner of the knee determined by MR imaging

BackgroundThe pie crusting technique has been extensively used to release the lateral soft tissue in total knee arthroplasty. However, it may place the peroneal nerve at direct injury risk when performed in a valgus knee. The aim of this study was to determine the anatomic proximity of the peroneal nerve to the posterolateral corner of the knee.MethodsOne hundred knees were measured on axial MR images for the proximity of peroneal nerve to the closest edge of the inner surface of joint capsule or the posterolateral corner of proximal tibia at the level of the joint line and the level of the tibial cut respectively.ResultsThe distance between the peroneal nerve and the closest edge of the inner surface of joint capsule at the level of the joint line was 15.0 ± 2.6 mm (range, 8.5-22.3 mm), and the distance between the peroneal nerve and the posterolateral corner of proximal tibia was 14.0 ± 2.7 mm (range, 8.0-23.2 mm). These distances were correlated with the anteroposterior diameter of the soft tissue of the knee, but not correlated with the size of the tibia.ConclusionsThese results suggest that it is safe enough providing that the scalpel blade does not pierce more than 8 mm deep. However, patients with smaller legs are at greater risk of direct peroneal nerve injury.     

Design and validation of a cadaveric knee joint loading device compatible with magnetic resonance imaging and computed tomography

PurposeDesign and validation of a magnetic resonance and computed tomography compatible device capable of applying physiologically relevant muscle forces to cadaveric knee joints with high levels of repeatability and reproducibility.MethodsRepeatability and reproducibility were assessed with two porcine stifle joints. Load was applied to joints at full extension, five and 15 degrees of flexion through two cables simulating the lines of action of the quadriceps and hamstrings muscles. Five repeatability and five reproducibility trials were performed at each flexion angle. Standard deviations (SDs) of joint angle and load were recorded.ResultsFor repeatability, the maximum SDs for joint angle were 1.26° (flexion), 1.54° (ab/adduction) and 0.90° (in/external rotation). The maximum SDs for joint load were 4.60 N (anterior/posterior), 7.36 N (medial/lateral), and 42.6 N (axial). For reproducibility, the maximum SDs for joint angle were 0.84° (flexion), 0.66° (ab/adduction) and 0.92° (in/external rotation). The maximum SDs for joint load were 6.40 N (anterior/posterior), 11.7 N (medial/lateral), and 39.7 N (axial).ConclusionsThis level of repeatability and reproducibility is within intra-subject variability of measured gait kinematics. Therefore, this device is considered to be an effective tool for in vitro testing of knee soft tissue repair.