The effect of distal femur bony morphology on in vivo knee translational and rotational kinematics

The morphology of the femoral posterior condyle affects the external rotation of the femur

PURPOSE

The purpose of this study was to identify factors related to the external rotation of the femur during knee flexion.

METHODS

Three-dimensional (3D) digital models of the femur and tibia were reconstructed from computed tomography images of 41 healthy Japanese subjects. Thirteen parameters related to femoral and tibial morphology and alignment of the lower extremities were evaluated, including the inclination angle of the posterior lateral and medial femoral condyles, the ratio of the medial and lateral posterior condyle radii approximated as spheres, the spherical condylar angle, the posterior condylar angle, the medial and lateral posterior tibial slope, the difference of medial and lateral posterior tibial slope, the tibiofemoral rotation angle, the 3D femorotibial angle, the 3D hip-knee-ankle angle, and the passing point of the weight-bearing line (medial-lateral and anterior-posterior). The rotation angle of the femur relative to the tibia during squatting was investigated using a 3D to 2D image matching technique and the relationships with the13 parameters were determined.

RESULTS

The femur externally rotated substantially up to 20° of knee flexion (9.2° ± 3.7°) and gently rotated after 20° of knee flexion (12.8° ± 6.2°). The external rotation angle at 20°-120° of knee flexion correlated with the spherical condylar angle, the tibiofemoral rotation angle and the inclination angle of the posterior medial condyles (correlation coefficient; 0.506, 0.364, 0.337, respectively).

CONCLUSION

The parameter that was most related to the external rotation of the femur during knee flexion was the spherical condylar angle.

LEVEL OF EVIDENCE

IV.

Local torsion of distal femur is a risk factor for patellar dislocation

PURPOSE

It has been widely reported that femoral anteversion is a risk factor for patellar dislocation. This study aims to evaluate whether internal torsion of the distal femur is noticeable in patients without increased femoral anteversion and to assess whether it is a risk factor for patellar dislocation.

METHODS

A retrospective analysis was conducted on 35 patients (24 females, 11 males) with recurrent patellar dislocation but without increased femoral anteversion treated in our hospital from January 2019 to August 2020. All patients underwent knee X-rays, digital radiography of lower-limbs, and CT scans of hip, knee, and ankle joints to measure femoral anteversion angle, distal femoral torsion angle, TT-TG and Caton-Deschamps index. Thirty-five control cases were matched on age and sex to compare the difference of anatomic parameters between the two groups, and the logistic analysis was used to analyze risk factors for patellar dislocation. Perman correlation coefficient was used to evaluate the correlation among femoral anteversion, distal femoral torsion and TT-TG.

RESULTS

Greater distal femoral torsion was still observed in patients with patellar dislocation but without increased femoral anteversion. The torsion angle of distal femur, TT-TG distance and incidence of Patella Alta in patients with patellar dislocation were greater than those in control group, and the inter-group differences were statistically significant (P < 0.05). The torsion angle of distal femur (OR = 2.848, P < 0.001), TT-TG distance (OR = 1.163, P = 0.021) and Patella Alta (OR = 3.545, P = 0.034) were risk factors for patellar dislocation. However, no significant correlation was found among femoral anteversion, distal femoral torsion and TT-TG in patients with patellar dislocation.

CONCLUSION

On the condition that femoral anteversion did not increase, increased distal femoral torsion was commonly observed in patients with patellar dislocation, which represents an independent risk factor for patellar dislocation.

Study on the correlation between the severity of patellofemoral arthritis and the morphology of the distal femur

PURPOSE

Distal femoral torsion is a key factor for poor alignment of patellofemoral joint. This study aims to evaluate the correlation between distal femoral torsion and the severity of patellofemoral arthritis, and to analyze the correlation between distal femoral torsion and the morphology of femoral condyle.

METHODS

A retrospective analysis was performed on 125 patients awaiting surgical treatment for knee osteoarthritis from January 2021 to March 2022(79 females, 46 males, average age: 65.78 years, SD 6.61). All patients underwent knee joint radiography, lower-limb digital radiography, and knee joint CT scans. The ratio of length of each distal femoral condyle, TT-TG, patellar tilt, DFL-PCL, DFL-TEA, TEA-PCL and TEA-ACL were measured. The Pearson correlation coefficient was used to evaluate the correlation between distal femoral torsion and ratio of distal femoral condyle, TT-TG and patellar tilt. Logistic regression was used to evaluate the correlation between each parameter and the severity of PFOA.

RESULTS

With the increased severity of PFOA, TT-TG, patellar tilt, DFL-PCL, DFL-TEA and PCA all tended to increase. Patellar tilt was correlated with DFL-PCL (r = 0.243) and TEA-PCL(r = 0.201), but TT-TG had no evident correlation with distal femoral torsion. Compared with Grade I patients of PFOA, DFL-PCL, DFL-TEA, and TEA-PCL were risk factors for increased severity of patellofemoral arthritis in Grade III patients of PFOA, but there was no significant statistic difference in Grade II patients of PFOA.

CONCLUSIONS

Distal femoral torsion correlates with the severity of patellofemoral arthritis. Variation of the femoral transepicondylar axis caused by the change of ratio of the femoral condyle is particularly important in the distal femoral torsion. In patients with severe PFOA, abnormal variation of the femoral condyle axis should be not ignored.

Bone-patellar tendon-bone autograft and female sex are associated with the presence of cyclops lesions and syndrome after anterior cruciate ligament reconstruction

PURPOSE

Associated risk factors for the development of cyclops lesions have been little. Investigated, because most previous studies have limited their research to cases with symptomatic cyclops lesions (cyclops syndrome). The purpose of this study was to evaluate the presence of cyclops lesions using magnetic resonance image (MRI) at 6 and 12 months after anterior cruciate ligament reconstruction (ACL-R), and to investigate the associated risk factors of cyclops lesions and syndrome.

METHODS

A retrospective analysis of patients who underwent ACL-R using bone-patellar tendon-bone (BTPB) or hamstring tendon autograft from 2008 to 2017 was conducted. Predictor variables (age, sex, body mass index [BMI], time from injury to ACL-R, preinjury Tegner activity score, graft, meniscal and cartilage injury, and notch width index on MRI for the presence of cyclops lesions and syndrome were analyzed with multivariate logistic regression.

RESULTS

Four hundred and fifty-five patients (225 males and 230 females) were enrolled. One hundred and four patients (22.9%) had cyclops lesions, and all cyclops lesions were detected on MRI at 6 months post-operatively. In addition, 20 patients (4.4%) had cyclops syndrome which means that these were symptomatic cases. The risk factors for presence of cyclops lesions were BPTB autograft (OR = 2.85; 95% CI 1.75-4.63; P < 0.001) and female sex (OR = 2.03; 95% CI 1.27-3.25; P = 0.003). The presence of cyclops syndrome increased with graft (BPTB) (OR = 18.0; 95% CI 3.67-88.3; Powered by Editorial Manager^® and ProduXion Manager^® from Aries Systems Corporation P < 0.001), female sex (OR = 3.27; 95% CI 1.07-10.0; P = 0.038), and increased BMI (OR = 1.21; 95% CI 1.05-1.39; P = 0.008).

CONCLUSIONS

All cyclops lesions were detected 6 months after ACL-R, and the majority of them were asymptomatic. BPTB autograft and female sex were the significant risk factors for the presence of cyclops lesions and syndrome. In addition, increased BMI was associated with a higher risk of developing cyclops syndrome. When BPTB autograft is used for a female patient, full active knee extension should be encouraged in the early period after ACL-R to prevent cyclops lesion formation.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Correlation between knee anatomy and joint laxity using principal component analysis

Knee articular geometry and surface morphology greatly affect knee joint mechanics. Intra-subject variations in bone morphology and the passive range of motion have been well documented in the literature; however, the relationship between these two characteristics is not well understood. The objective of this study was to describe the correlation between knee joint anatomical features and passive range of motion using a statistical model. A principal component model was developed using femoral and tibial articular geometry, knee joint initial stance position, and the passive laxity envelope obtained from 27 cadaveric knees. The results from the principal component analysis showed high correlation between the anatomical features and the tibiofemoral passive envelope; an increase in the average femoral condyle radii, an increase in slope of the tibial spine, and a higher tibial plateau concavity correlated with a decrease in varus-valgus and internal-external range of motion. Understanding the correlation between anatomical features and tibiofemoral laxity could aid in the development of orthopedic implant designs by quantifying the effect of perturbing specific anatomical features on knee laxity and identifying specific implant femoral and tibial articular geometry necessary to obtain a targeted passive range of motion.

Cartilage contact characteristics of the knee during gait in individuals with obesity

Obesity increases the risk of knee osteoarthritis (OA). Knee joint contact characteristics have been thought to provide insights into the pathogenesis of knee OA; however, the cartilage contact characteristics in individuals with obesity have not been fully described. We conducted cartilage-to-cartilage contact analyses through high-precision fluoroscopy imaging with subject-specific magnetic resonance cartilage models. Twenty-five individuals with obesity were recruited for this study, and previously published data consisted of eight nonobese individuals who were used as the comparator group. In both groups, knees were imaged by a dual fluoroscopic imaging system during treadmill walking, and the tibiofemoral cartilage contact locations were analyzed and described on the tibial plateau in the medial-lateral (ML) and anterior-posterior (AP) directions and on femoral condyle surfaces using contact angles in the sagittal plane and deviation angles in a plane perpendicular to the sagittal plane. On the medial tibial plateau, the ML contact locations in the individuals with obesity were located more medially than in the nonobese group throughout the stance phase. The medial plateau AP contact locations in individuals with obesity showed a different pattern compared with the nonobese group. The ML contact excursions on the medial plateau in the individuals with obesity were larger than in the nonobese group. These findings suggest that obesity affects the contact location mainly in the medial compartment, which explains, in part, the high prevalence of medial knee OA in the obese population.

Posterior Tibial Slope, Notch Width, Condylar Morphology, Trochlear Inclination, and Tibiofemoral Mismatch Predict Outcomes Following Anterior Cruciate Ligament Reconstruction

PURPOSE

To provide a comprehensive summary of the available literature on the influence of bone morphology on outcomes after anterior cruciate ligament reconstruction (ACLR).

METHODS

Our protocol was prospectively registered with PROSPERO (International Prospective Register of Systematic Reviews) and followed PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. The PubMed, Embase, and MEDLINE databases were searched for studies investigating knee morphologic features and outcomes after ACLR. Articles were screened and references lists were reviewed to identify relevant studies, after which methodologic quality was assessed for each study included in this review. Because of significant variability in terminology and methodology between studies, no meta-analyses were conducted.

RESULTS

Systematically screening a total of 19,647 studies identified from the search revealed 24 studies that met the inclusion and exclusion criteria. Among tibial shape features identified as predictors of poor outcomes after ACLR, increased posterior tibial slope was most common (16 studies). Other features such as increased tibial plateau area (1 study), decreased medial plateau width (1 study), and increased medial plateau height (1 study) were also associated with poor outcomes. For the femur, features related to notch width and condylar morphology were most common (4 studies and 7 studies, respectively). An increased condylar offset ratio, increased lateral femoral condylar ratio, and larger notch width were each found to be associated with negative ACLR outcomes, including increased cartilage degeneration, worse patient-reported outcomes, and graft failure.

CONCLUSIONS

Posterior tibial slope, notch width, condylar morphology, trochlear inclination, and tibiofemoral mismatch are associated with and predictive of outcomes after ACLR.

LEVEL OF EVIDENCE

Level IV, systematic review of Level II-IV studies.

Increased lateral and medial femoral posterior radius ratios are risk factors for anterior cruciate ligament injury

Background

Many studies have shown that distal femoral sagittal morphological characteristics have a clear relationship with knee joint kinematics. The aim of this study was to determine the relationship between distal femoral sagittal morphological characteristics and noncontact anterior cruciate ligament (ACL) injury.

Methods

A retrospective case-control study of 148 patients was conducted. Two age- and sex-matched cohorts (each n = 74) were analysed: a noncontact ACL injury group and a control group. Several characteristics were compared between the two groups, including the lateral femoral posterior radius (LFPR), medial femoral posterior radius (MFPR), lateral height of the distal femur (LH), medial height of the distal femur (MH), lateral femoral anteroposterior diameter (LFAP), medial femoral anteroposterior diameter (MFAP), lateral femoral posterior radius ratio (LFPRR), and medial femoral posterior radius ratio (MFPRR). Receiver operating characteristic (ROC) analysis was used to evaluate the significance of the LFPRR and MFPRR in predicting ACL injury.

Results

Compared with patients in the control group, patients in the ACL injury group had an increased LFPR, MFPR, MFAP, LFPRR, and MFPRR. ROC analysis revealed that an increased LFPRR above 31.7% was associated with noncontact ACL injury, with a sensitivity of 78.4% and a specificity of 58.1%; additionally. an increased MFPRR above 33.4% was associated with noncontact ACL injury, with a sensitivity of 58.1% and a specificity of 70.3%.

Conclusion

This study showed that increased LFPRR and increased MFPRR are risk factors for developing noncontact ACL injury. These data could thus help identify individuals susceptible to ACL injuries.

Tibiofemoral bony morphology features associated with ACL injury and sex utilizing three-dimensional statistical shape modeling

Statistical shape modeling was employed to assess three-dimensional (3D) bony morphology between distal femurs and proximal tibiae of anterior cruciate ligament (ACL) injured knees, the contralateral uninjured knees of ACL injured subjects, and knees with no history of injury. Surface models were created by segmenting bone from bilateral computed-tomography scans of 20 subjects of their ACL injured knees and non-injured contralateral knees, and 20 knees of control subjects with no history of a knee injury. Correspondence particles were placed on each surface, and a principal component analysis determined modes of variation in the positions of the correspondence particles describing anatomical variation. ANOVAs assessed the statistical differences of 3D bony morphological features with main effects of injury state and sex. ACL injured knees were determined to have a more lateral femoral mechanical axis and a greater angle between the long axis and condylar axis of the femur. A smaller anterior-posterior dimension of the lateral tibial plateau was also associated with ACL injured knees. Results of this study demonstrate that there are more bony morphological features predisposing individuals for ACL injury than previously established. These bony morphological parameters may cause greater internal and valgus torques increasing stresses in the ACL. No differences were determined between the ACL injured knees and their uninjured contralateral knees demonstrating that knees of ACL injured individuals are at similar risk for injury. Further understanding of the effect of bony morphology on the risk for ACL injury could improve individualized ACL injury treatment and prevention.

Tibiofemoral bony morphology impacts the knee kinematics after anterolateral capsule injury and lateral extraarticular tenodesis differently than intact state

Anterolateral capsule injury, often concomitant with anterior cruciate ligament (ACL) injuries, may result in high-grade rotatory instability. Lateral extraarticular tenodesis (LET) is sometimes added to ACL reconstruction to address this instability. However, LET is a non-anatomic procedure and concerns regarding increased tibiofemoral contact pressure and reduced internal rotation exist for some individuals which may be due to their tibiofemoral bony morphology. Therefore, the objective of this study was to analyze the effect of bony morphology on knee kinematic and contact pressure before and after anterolateral capsule injury and LET. A (1) 134-N anterior tibial load with 200-N axial compression and (2) a 7-Nm internal torque with a 200-N axial compression were applied to cadaveric knees (n = 8) using a 6 degree-of-freedom robotic testing system. Tibiofemoral bony morphology was captured with computed tomography scans and analyzed using 3D statistical shape modeling. Kinematics at each state were correlated with the results from the statistical shape model. Two femoral and three tibial modes of variation correlated with kinematic and contact pressure data before and after anterolateral capsule injury and LET. A decreased lateral tibial plateau elevation correlated with greater internal rotation and anterior tibial translation after anterolateral capsule deficiency and LET. Decreased notch width correlated with decreased contact area after anterolateral capsule deficiency and LET demonstrating it as a risk factor for ACL injury. The results of this study demonstrate that bony morphology if properly understood, could help improve the efficacy of LET procedures and that bony morphology has different effects after injury and repair.

Statistical-Shape Prediction of Lower Limb Kinematics During Cycling, Squatting, Lunging, and Stepping-Are Bone Geometry Predictors Helpful?

Purpose: Statistical shape methods have proven to be useful tools in providing statistical predications of several clinical and biomechanical features as to analyze and describe the possible link with them. In the present study, we aimed to explore and quantify the relationship between biometric features derived from imaging data and model-derived kinematics. Methods: Fifty-seven healthy males were gathered under strict exclusion criteria to ensure a sample representative of normal physiological conditions. MRI-based bone geometry was established and subject-specific musculoskeletal simulations in the Anybody Modeling System enabled us to derive personalized kinematics. Kinematic and shape findings were parameterized using principal component analysis. Partial least squares regression and canonical correlation analysis were then performed with the goal of predicting motion and exploring the possible association, respectively, with the given bone geometry. The relationship of hip flexion, abduction, and rotation, knee flexion, and ankle flexion with a subset of biometric features (age, length, and weight) was also investigated. Results: In the statistical kinematic models, mean accuracy errors ranged from 1.60° (race cycling) up to 3.10° (lunge). When imposing averaged kinematic waveforms, the reconstruction errors varied between 4.59° (step up) and 6.61° (lunge). A weak, yet clinical irrelevant, correlation between the modes describing bone geometry and kinematics was observed. Partial least square regression led to a minimal error reduction up to 0.42° compared to imposing gender-specific reference curves. The relationship between motion and the subject characteristics was even less pronounced with an error reduction up to 0.21°. Conclusion: The contribution of bone shape to model-derived joint kinematics appears to be relatively small and lack in clinical relevance.

Editorial Commentary: The Pivot Shift and Lachman Examinations: Teammates With Distinct Roles

The pivot shift and Lachman examinations are "teammates" with complementary but distinct roles in the successful diagnosis and treatment of anterior cruciate ligament rupture and injury to the surrounding soft-tissue envelope of the knee. The Lachman test measures anterior tibial translation in response to an applied anterior tibial load. This test assesses the integrity of the native or reconstructed anterior cruciate ligament and the secondary medial restraints including the medial meniscus and medial collateral ligament. In contrast, the pivot shift exam creates coupled tibiofemoral motions in response to a complex combination of multiplanar loads. This test assesses the stabilizing role of the native or reconstructed anterior cruciate ligament and the secondary lateral restraints including the lateral meniscus and anterolateral complex. The pivot shift grade depends not only on the soft the tissue stabilizers of the knee but also on the shape of the proximal tibia and the distal femur including lateral tibial slope and femoral condylar offset. Both examinations have unique strengths and weaknesses, but when combined as diagnostic tools, they achieve far more collectively than what each can achieve alone.

There are isoheight points that measure constant femoral condyle heights along the knee flexion path

PURPOSE

It is a challenge to evaluate the maintenance of medial and lateral soft tissue balance in total knee arthroplasty (TKA). This study aimed to determine the "isoheight" points and the "isoheight" axis (IHA) that can measure constant medial/lateral condyle heights during flexion of the knee, and compare the IHA with two major anatomical axes, the transepicondylar axis (TEA) and the geometric center axis (GCA).

METHODS

Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging system while performing a single-legged lunge (0°-120°). The isoheight points of the medial and lateral femoral condyles were defined as the locations with the least amount of changes in heights during the knee flexion; an IHA is the line connecting the medial and lateral isoheight points. The measured changes of the condyle heights using the IHA were compared with those measured using the TEA and GCA.

RESULTS

Overall, the IHA was posterior and distal to the TEA, and anterior to the GCA. The isoheight points measured condyle height changes within 1.2 ± 2.3 mm at the medial and 0.7 ± 3.3 mm at the lateral sides during the knee flexion. Between 0° and 45°, the condyle height changes measured using the GCA (medial: 3.0 ± 1.8 mm, lateral: 2.3 ± 2.0 mm) were significantly larger than those of the IHA and the TEA (p < 0.05). Between 90° and 120°, the changes of the condyle heights measured using the TEA (medial: 5.3 ± 1.8 mm, lateral: 3.3 ± 1.8 mm) were significantly larger than those of the IHA and GCA (p < 0.05).

CONCLUSION

There are isoheight points in the medial and lateral femoral condyles that can measure constant heights along the full range of knee flexion and could be used to formulate an "isoheight" axis (IHA) of the femur. The condyle height changes measured by the TEA and GCA were greater than the IHA measurements along the flexion path. These data could be used as a valuable reference to evaluate the condyle height changes after TKA surgeries and help achieve soft tissue balance and optimal knee kinematics along the flexion path.

LEVEL OF EVIDENCE

IV.

Shape is only a weak predictor of deep knee flexion kinematics in healthy and osteoarthritic knees

Tibiofemoral shape influences knee kinematics but little is known about the effect of shape on deep knee flexion kinematics. The aim of this study was to examine the association between tibiofemoral joint shape and kinematics during deep kneeling in patients with and without osteoarthritis (OA). Sixty-one healthy participants and 58 patients with end-stage knee OA received a computed tomography (CT) of their knee. Participants completed full flexion kneeling while being imaged using single-plane fluoroscopy. Six-degree-of-freedom kinematics were measured by registering a three-dimensional (3D)-static CT onto 2D-dynamic fluoroscopic images. Statistical shape modeling and bivariate functional principal component analysis (bfPCA) were used to describe variability in knee shape and kinematics, respectively. Random-forest-regression models were created to test the ability of shape to predict kinematics controlling for body mass index, sex, and group. The first seven modes of the shape model up to three modes of the bfPCAs captured more than 90% of the variation. The ability of the random forest models to predict kinematics from shape was low, with no more than 50% of the variation being explained in any model. Furthermore, prediction errors were high, ranging between 24.2% and 29.4% of the data. Variations in the bony morphology of the tibiofemoral joint were weakly associated with the kinematics of deep knee flexion. The models only explained a small amount of variation in the data with high error rates indicating that additional predictors need to be identified. These results contribute to the clinical understanding of knee kinematics and potentially the expectations placed on high-flexion total knee replacement design.

Knee Kinematics of Healthy Adults Measured Using Biplane Radiography

A dataset of knee kinematics in healthy, uninjured adults is needed to serve as a reference for comparison when evaluating the effects of injury, surgery, rehabilitation, and age. Most currently available datasets that characterize healthy knee kinematics were developed using conventional motion analysis, known to suffer from skin motion artifact. More accurate kinematics, obtained from bone pins or biplane radiography, have been reported for datasets ranging in size from 5 to 15 knees. The aim of this study was to characterize tibiofemoral kinematics and its variability in a larger sample of healthy adults. Thirty-nine knees were imaged using biplane radiography at 100 images/s during multiple trials of treadmill walking. Multiple gait trials were captured to measure stance and swing-phase knee kinematics. Six degrees-of-freedom kinematics were determined using a validated volumetric model-based tracking process. A bootstrapping technique was used to define average and 90% prediction bands for the kinematics. The average ROM during gait was 7.0 mm, 3.2 mm, and 2.9 mm in anterior/posterior (AP), medial/lateral (ML), and proximal/distal (PD) directions, and 67.3 deg, 11.5 deg, and 3.7 deg in flexion/extension (FE), internal/external (IE), and abduction/adduction (AbAd). Continuous kinematics demonstrated large interknee variability, with 90% prediction bands spanning approximately ±4 mm, ±10 mm, and ±5 mm for ML, AP, and PD translations and ±15 deg, ±10 deg, and ±6 deg in FE, IE, and AbAd. This dataset suggests substantial variability exists in healthy knee kinematics. This study provides a normative database for evaluating knee kinematics in patients who receive conservative or surgical treatment.

Distal Femoral Shortening Osteotomy for Severe Knee Flexion Contracture and Crouch Gait in Cerebral Palsy

Although there have been advancements of surgical techniques to correct gait abnormalities seen in patients with cerebral palsy, the crouch gait remains one of the most difficult problems to treat. The purpose of this retrospective study was to examine our results of distal femoral shortening osteotomy (DFSO) and patellar tendon advancement (PTA), performed in patients with crouch gait associated with severe knee flexion contracture. A total of 33 patients with a mean fixed knee contracture of 38° were included in the study. The mean age at the time of surgery was 12.2 years and the mean follow-up was 26.9 months. The measurements of clinical, radiological, and gait parameters were performed before and after surgery. The mean degrees of knee flexion contracture, Koshino index of patella height, and Gait Deviation Index were found to be significantly improved at the time of final follow-up. The maximum knee extension during the stance phase improved by an average of 25°, and the range of knee motion during gait increased postoperatively. On the other hand, the mean anterior pelvic tilt increased by 9.9°. Also, the maximum knee flexion during the swing phase decreased and the timing of peak knee flexion was observed to be delayed. We conclude that combined procedure of DFSO and PTA is an effective and safe surgical method for treating severe knee flexion contracture and crouch gait. However, the surgeons should be aware of the development of increased anterior pelvic tilt and stiff knee gait after the index operation.

Distal femur morphology affects rotatory knee instability in patients with anterior cruciate ligament ruptures

PURPOSE

Distal femur morphology has been shown to influence knee joint kinematics and may affect rotatory knee laxity. The purpose of this study was to determine the relationship between rotatory knee laxity and distal femoral morphology in patients with complete anterior cruciate ligament (ACL) rupture. It was hypothesized that increased posterior femoral condylar depth on standard lateral radiographs, quantified as the "lateral femoral condyle ratio" would correlate with increased rotatory knee laxity, measured by a quantitative pivot shift test.

METHODS

Consecutive patients who underwent ACL reconstruction from 2014 to 2016 were retrospectively reviewed. A standardized pivot shift test was performed preoperatively on both knees and quantified using tablet technology. Using standard lateral radiographs of the knee, the ratio of posterior condylar distance over total condylar distance was defined as the lateral femoral condyle ratio.

RESULTS

Data sets were obtained for 57 patients. The mean anterior translation of the lateral knee compartment during a quantitative pivot shift test was found to be 4.0 ± 2.4 mm and 1.3 ± 0.9 mm for the injured and uninjured knees, respectively. The mean lateral femoral condyle ratio on X-ray was 63.2 ± 4.5%. There were significant correlations between the lateral femoral condyle ratio and the absolute quantitative (ρ = 0.370, p < 0.05) and side-to-side differences in anterior translation of the lateral knee compartment (ρ = 0.419, p < 0.05).

CONCLUSION

The most important finding from this study is that increased posterior femoral condylar depth, quantified as a lateral femoral condyle ratio, is associated with increased rotatory knee laxity in ACL-deficient patients. This suggests that distal femur morphology may influence rotatory knee laxity. This study may assist clinicians in evaluating ACL injuries and identifying patients at greater risk for persistent increased rotatory knee laxity after ACL reconstruction.

LEVEL OF EVIDENCE

III.

Influence of knee position and examiner-induced motion on the kinematics of the pivot shift

Background

Grading of the pivot shift test varies significantly depending on the examiner’s technique. Thus, the purpose of this study was to determine the influence of knee starting position and the magnitude of motion during the reduction event on the magnitude of the pivot shift test.

Methods

Twenty-five clinical providers each performed a total of twenty pivot shift tests on one of two fresh-frozen cadaveric full lower extremity specimens with different grades of rotatory knee laxity. By means of ACL transection and lateral meniscectomy, one specimen was prepared to have a high-grade pivot shift and one to have a low-grade pivot shift. Six-degree-of-freedom kinematics were recorded during each pivot shift test using an electromagnetic-tracking-system. Successful pivot shift tests were defined and selected using an automated, mathematical algorithm based on the exceeding of a threshold value of anterior translation of the lateral knee compartment. The kinematics were correlated with the magnitude of anterior translation of the lateral knee compartment based on varying degrees of rotatory knee laxity using the Pearson correlation coefficient.

Results

Only mild correlations between anterior translation of the lateral knee compartment and internal tibial rotation at the start of the reduction event were observed in both specimens. The ability to generate a successful reduction event was significantly dependent on the rotatory knee laxity, with a 54% success rate on the high-laxity specimen compared to a 30% success rate on the low-laxity specimen (p < 0.001). Nearly 80% of the variability of the anterior translation of the lateral knee compartment in both specimens was accounted for by external rotation during the reduction event (r = 0.847; p < 0.001). Varus rotation during the reduction event also showed a strong correlation with the anterior translation of the lateral knee compartment in the low-laxity specimen (r = 0.835; p < 0.001).

Conclusion

Magnitude of motion during the reduction event affected the magnitude of anterior translation of the lateral knee compartment more than the starting position. External rotation during the reduction event accounted for most of the variability in the pivot shift test. More uniform maneuvers and improved teaching are essential to generate repeatable quantitative results of the pivot shift test.

The effect of articular geometry features identified using statistical shape modelling on knee biomechanics

Articular geometry in the knee varies widely among people which has implications for risk of injury and pathology. The goals of this work were to develop a framework to systematically vary geometry in a multibody knee model and to use this framework to investigate the effect of morphological features on dynamic knee kinematics and contact mechanics. A statistical shape model of the tibiofemoral and patellofemoral joints was created from magnetic resonance images of 14 asymptomatic knees. The shape model was then used to generate 37 unique multibody knee models based on -3 to +3 standard deviations of the scores for the first six principal components identified. Each multibody model was then incorporated into a lower extremity musculoskeletal model and the Concurrent Optimization of Muscle Activations and Kinematics (COMAK) routine was used to simulate knee mechanics for overground walking. Changes in articular geometry affected knee function, resulting in differences up to 17° in orientation, 8 mm in translation, 0.7 BW in contact force, and 2.0 MPa in mean cartilage contact pressure. Understanding the relationship between shape and function in a joint could provide insight into the mechanisms behind injury and pathology and the variability in response to treatment.

Lateral femoral notch depth is not associated with increased rotatory instability in ACL-injured knees: a quantitative pivot shift analysis

PURPOSE

A deep lateral femoral notch (LFN) on lateral radiographs is indicative of ACL injury. Prior studies have suggested that a deep LFN may also be a sign of persistent rotatory instability and a concomitant lateral meniscus tear. Therefore, the purpose of this study was to evaluate the relationship between LFN depth and both quantitative measures of rotatory knee instability and the incidence of lateral meniscus tears. It was hypothesized that greater LFN depth would be correlated with increased rotatory instability, quantified by lateral compartment translation and tibial acceleration during a quantitative pivot shift test, and incidence of lateral meniscus tears.

METHODS

ACL-injured patients enrolled in a prospective ACL registry from 2014 to 2016 were analyzed. To limit confounders, patients were only included if they had primary ACL tears, no concurrent ligamentous or bony injuries requiring operative treatment, and no previous knee injuries or surgeries to either knee. Eighty-four patients were included in the final analysis. A standardized quantitative pivot shift test was performed pre-operatively under anesthesia in both knees, and rotatory instability, specifically lateral compartment translation and tibial acceleration, was quantified using tablet image analysis software and accelerometer sensors. Standard lateral radiographs and sagittal magnetic resonance images (MRI) of the injured knee were evaluated for LFN depth.

RESULTS

There were no significant correlations between LFN depth on either imaging modality and ipsilateral lateral compartment translation or tibial acceleration during a quantitative pivot shift test or side-to-side differences in these measurements. Patients with lateral meniscus tears were found to have significantly greater LFN depths than those without on conventional radiograph and MRI (1.0 vs. 0.6 mm, p < 0.05; 1.2 vs. 0.8 mm, p < 0.05, respectively).

CONCLUSION

There was no correlation between lateral femoral notch depth on conventional radiographs or MRI and quantitative measures of rotatory instability. Concomitant lateral meniscus injury was associated with significantly greater LFN depth. Based on these findings, LFN depth should not be used as an indicator of excessive rotatory instability, but may be an indicator of lateral meniscus injury in ACL-injured patients.

LEVEL OF EVIDENCE

Prognostic level IV.

Lower Limb Anatomy and Alignment Affect Natural Tibiofemoral Knee Kinematics: A Cadaveric Investigation

BACKGROUND

During flexion, normal knee kinematics consists of a complex combination of rolling, gliding, and rotation between femur and tibia. Although in vivo studies have shown wide interindividual variability, we hypothesized that knee kinematics is either correlated to the anatomy of the individual knee joint or to the anatomic alignment of the entire lower extremity.

METHODS

The passive kinematics of 10 healthy knees was assessed in whole cadavers using a commercial computed tomography-free navigation device with intracortical pins. Rotational limb alignment or local anatomic parameters obtained by computed tomography scan or within a navigational procedure were correlated to tibial internal rotation and tibiofemoral abduction during flexion.

RESULTS

Mean tibial adduction in full extension was 3.3° (range -2.2° to 7.8°). Tibial abduction and internal rotation showed significant interindividual variability, measuring 3.9° (range -0.8° to 9.7°) and 4.9° (range -3.5° to 14.8°) during flexion. An increase in both the mechanical tibiofemoral axis and the mechanical lateral distal femoral angle correlated with increased tibial internal rotation, whereas a decrease in the mechanical medial proximal tibial angle and an increase in the mechanical tibiofemoral axis were associated with increased tibial adduction.

CONCLUSION

The main finding of the present study is that knee kinematics is influenced by both intra-articular and extra-articular parameters. These results may be of interest in component alignment in total knee arthroplasty, correction of deformities, and malalignment after fracture healing of the lower extremity. Possible relationships should be investigated in future studies.

Functional knee assessment with advanced imaging

The purpose of anterior cruciate ligament (ACL) reconstruction is to restore the native stability of the knee joint and to prevent further injury to meniscus and cartilage, yet studies have suggested that joint laxity remains prevalent in varying degrees after ACL reconstruction. Imaging can provide measurements of translational and rotational motions of the tibiofemoral joint that may be too small to detect in routine physical examinations. Various imaging modalities, including fluoroscopy, computed tomography (CT), and magnetic resonance imaging (MRI), have emerged as powerful methods in measuring the minute details involved in joint biomechanics. While each technique has its own strengths and limitations, they have all enhanced our understanding of the knee joint under various stresses and movements. Acquiring the knowledge of the complex and dynamic motions of the knee after surgery would help lead to improved surgical techniques and better patient outcomes.

Statistical modeling to characterize relationships between knee anatomy and kinematics

The mechanics of the knee are complex and dependent on the shape of the articular surfaces and their relative alignment. Insight into how anatomy relates to kinematics can establish biomechanical norms, support the diagnosis and treatment of various pathologies (e.g., patellar maltracking) and inform implant design. Prior studies have used correlations to identify anatomical measures related to specific motions. The objective of this study was to describe relationships between knee anatomy and tibiofemoral (TF) and patellofemoral (PF) kinematics using a statistical shape and function modeling approach. A principal component (PC) analysis was performed on a 20-specimen dataset consisting of shape of the bone and cartilage for the femur, tibia and patella derived from imaging and six-degree-of-freedom TF and PF kinematics from cadaveric testing during a simulated squat. The PC modes characterized links between anatomy and kinematics; the first mode captured scaling and shape changes in the condylar radii and their influence on TF anterior-posterior translation, internal-external rotation, and the location of the femoral lowest point. Subsequent modes described relations in patella shape and alta/baja alignment impacting PF kinematics. The complex interactions described with the data-driven statistical approach provide insight into knee mechanics that is useful clinically and in implant design.

In vivo length change patterns of the medial and lateral collateral ligaments along the flexion path of the knee

PURPOSE

The knowledge of the function of the collateral ligaments-i.e., superficial medial collateral ligament (sMCL), deep medial collateral ligament (dMCL) and lateral collateral ligament (LCL)-in the entire range of knee flexion is important for soft tissue balance during total knee arthroplasty (TKA). The objective of this study was to investigate the length changes of different portions (anterior, middle and posterior) of the sMCL, dMCL and LCL during in vivo weightbearing flexion from full extension to maximal knee flexion.

METHODS

Using a dual fluoroscopic imaging system, eight healthy knees were imaged while performing a lunge from full extension to maximal flexion. The length changes of each portion of the collateral ligaments were measured along the flexion path of the knee.

RESULTS

All anterior portions of the collateral ligaments were shown to have increasing length with flexion except that of the sMCL, which showed a reduction in length at high flexion. The middle portions showed minimal change in lengths except that of the sMCL, which showed a consistent reduction in length with flexion. All posterior portions showed reduction in lengths with flexion.

CONCLUSIONS

These data indicated that every portion of the ligaments may play important roles in knee stability at different knee flexion range. The soft tissue releasing during TKA may need to consider the function of the ligament portions along the entire flexion path including maximum flexion.

LEVEL OF EVIDENCE

III.

Motion analysis of Chinese normal knees during gait based on a novel portable system

Normative tibiofemoral data of Chinese or Asian subjects during gait is rarely reported. This study is aimed at investigating the six-degree-of-freedom (6DOF) knee kinematics of adult Chinese during gait, based on a novel portable system. Twenty-eight healthy Chinese subjects (56 knees) were studied during their treadmill gaits. A set of optical marker clusters were attached to the thighs and shanks of each subject, who was tracked by an optical joint kinematics measurement system. Knee landmarks were initially digitized with respect to the marker cluster sets to determine the local coordinate systems for calculation of 6DOF knee joint kinematics. The range of motion (ROM) in 6DOF and 5 kinematic parameters were calculated and compared between bilateral knees and genders. We discovered that knee rotations, as well as motion in proximodistal and mediolateral translations, showed similar patterns in flexion and extension. However, the anteroposterior translations did not show a clear pattern. The results of ROM in 6DOF obtained in this study are comparable with those reported in existing literature. No statistical difference was found between left and right knees either in the ROMs or in the 5 kinematic parameters. However, the ROM in the mediolateral direction during gait was found to be higher in men than women (P=0.014). In addition, the femurs of female subjects rotated more internally than the femurs of male during the stance phase (P=0.011). We concluded that normal Chinese knees exhibited distinct gait patterns, except for anteroposterior motion. Women and men exhibit different axial rotations and mediolateral translation patterns during their treadmill gait.

Reproducibility of condylar twist angle measurement using computed tomography and axial radiography of the distal femur

INTRODUCTION

It is essential to understand rotational alignment of the distal femur when performing total knee arthroplasty (TKA). Several rotational landmarks including condylar twist angle (CTA) are used for preoperative planning and during TKA. Axial radiography of the distal femur is used for measuring the CTA, and assessing rotational alignment in TKA. The aim of this study was to investigate the reliability and the reproducibility of the CTA using two different methods and evaluate if CTA differed between varus and valgus knees and between normal and osteoarthritic knees.

MATERIALS AND METHODS

CTA were obtained from 144 knees (77 patients) having total knee or hip arthroplasty using computed tomography (CT) and axial radiography. Subjects were divided into five groups based on femorotibial angle (FTA) and into four groups based on the severity of knee osteoarthritis. The intra-observer and inter-observer reliabilities of these methods and inter-method differences were evaluated.

RESULTS

The mean CTA was 7.02° with axial radiography, and 6.87° with CT images. There were no significant differences among the five FTA groups and among the four osteoarthritis groups. In total, intra-/inter-observer, and inter-method intraclass correlation coefficients were substantial or almost perfect in the scoring system of Landis et al. However, discrepancies ≥ 2° between the two methods were observed in more than 20% of knees.

CONCLUSION

The CTA should be reassessed by more than two observers or two methods for precise preoperative TKA planning in cases where it is difficult to identify the bony landmarks for CTA measurements.

LEVEL OF EVIDENCE

Level III.

Strong correlation between the morphology of the proximal femur and the geometry of the distal femoral trochlea

PURPOSE

Previous investigations suggested that the geometry of the proximal femur may be related to osteoarthritis of the tibiofemoral joint and various patellofemoral joint conditions. This study aims to investigate the correlation between proximal and distal femoral geometry. Such a correlation could aid our understanding of patient complications after total knee arthroplasty (TKA) and be of benefit for further development of kinematic approaches in TKA.

METHODS

CT scans of 60 subjects (30 males, 30 females) were used to identify anatomical landmarks to calculate anatomical parameters of the femur, including the femoral neck anteversion angle, neck-shaft angle (NSA), mediolateral offset (ML-offset), condylar twist angle (CTA), trochlear sulcus angle (TSA) and medial/lateral trochlear inclination angles (MTIA/LTIA). Correlation analyses were carried out to assess the relationship between these parameters, and the effect of gender was investigated.

RESULTS

The CTA, TSA and LTIA showed no correlation with any proximal parameter. The MTIA was correlated with all three proximal parameters, mostly with the NSA and ML-offset. Per 5° increase in NSA, the MTIA was 2.1° lower (p < 0.01), and for every 5 mm increase in ML-offset, there was a 2.6° increase in MTIA (p < 0.01). These results were strongest and statistically significant in females and not in males and were independent of length and weight.

CONCLUSIONS

Proximal femoral geometry is distinctively linked with trochlear morphology. In order to improve knowledge on the physiological kinematics of the knee joint and to improve the concept of kinematic knee replacement, the proximal femur seems to be a factor of clinical importance.

LEVEL OF EVIDENCE

III.

Gender differences following computer-navigated single- and double-bundle anterior cruciate ligament reconstruction

PURPOSE

Female patients not only demonstrate an increased risk for injury, but also a poorer response following anterior cruciate ligament (ACL) rupture. However, no study has investigated gender-related differences between computer-navigated single-bundle (SB) and double-bundle (DB) ACL reconstruction. The aim of this study was to evaluate the effects of gender on the outcome of computer-navigated SB and DB ACL reconstruction and to present reference values.

METHODS

A retrospective review of 55 consecutive patients who underwent SB (15 males, 12 females) and DB (18 males, 10 females) ACL reconstruction with autogenous hamstring tendon grafts and showed a minimum follow-up of 24 months was conducted. Intraoperatively, the anteroposterior and rotational laxity were measured and the follow-up examination included pivot-shift testing, KT-1000 arthrometer testing, International Knee Documentation Committee (IKDC) form, the Lysholm score and Tegner score.

RESULTS

Pre-operatively, female patients showed a significant higher internal rotation in (p < 0.001) both the SB and DB group. Regarding the post-operative reduction in internal rotation, females in the SB group revealed a greater reduction compared to males (p < 0.001), whereas females in the DB group revealed a significantly greater post-operative reduction in anterior-posterior translation (p = 0.04). Female patients following DB ACL reconstruction presented a significant worse IKDC score, Lysholm score and Tegner score compared to male patients. All score values of the female DB group were worse than in the female SB group. In contrast, male patients showed better results of all examined clinical scores following DB procedure compared to SB technique.

CONCLUSION

Female patients who underwent computer-navigated DB ACL reconstruction exhibited significantly worse outcome scores than males who underwent DB ACL reconstruction. The gender-based relationship between joint function and outcome after ACL reconstruction remains unclear and requires further investigation.

LEVEL OF EVIDENCE

Retrospective case-control series, Level III.

Characteristics of femorotibial joint geometry in the trochlear dysplastic femur

The medial and lateral tibia plateau geometry has been linked with the severity of trochlear dysplasia. The aim of the present study was to evaluate the tibial slope and the femoral posterior condylar offset in a cohort of consecutive subjects with a trochlear dysplastic femur to investigate whether the condylar offset correlates with, and thus potentially compensates for, tibial slope asymmetry. Magnetic resonance imaging was used to assess the severity of trochlear dysplasia as well as the tibial slope and posterior offset of the femoral condyles separately for the medial and lateral compartment of the knee joint in 98 subjects with a trochlear dysplastic femur and 88 control subjects. A significant positive correlation was found for the medial tibial slope and the medial posterior condylar offset in the study group (r(2) = 0.1566; P < 0.001). This relationship was significant for all subtypes of trochlear dysplasia and was most pronounced in the severe trochlear dysplastic femur (Dejour type D) (r(2) = 0.3734; P = 0.04). No correlation was found for the lateral condylar offset and the lateral tibial slope in the study group or for the condylar offset and the tibial slope on both sides in the control group. The positive correlation between the medial femoral condylar offset and the medial tibial slope, that is, a greater degree of the medial tibial slope indicated a larger offset of the medial femoral condyle, appears to represent a general anthropomorphic characteristic of distal femur geometry in patients with a trochlear dysplastic femur.

Gender difference of the femoral kinematics axis location and its relation to anterior cruciate ligament injury: a 3D-CT study

PURPOSE

The variation of distal femur morphology has been often reported, especially in relation to ACL injury. However, it remains unknown how morphological differences affect knee kinematics and ACL function. The location of the transcondylar axis, a common anatomical reference line, may be a significant aspect of morphological variation. It was hypothesized that the location of this axis would be different between genders, and between ACL-injured and non-injured subjects.

METHODS

3D CT scans of contralateral healthy femurs in 38 unilateral soft tissue injured patients (20 men/18 women, 26 ACL injury/12 non-ACL injury (7 with PCL injuries and 5 with medial meniscus root tears)) were analyzed three-dimensionally. Condyle offset was calculated as the distance between the transcondylar axis and the anatomical axis of the femur. Condyle offset ratio (COR) was then calculated by dividing the condyle offset by the condyle radius. Gender and ACL-injured and non-injured group differences were assessed.

RESULTS

Larger COR was found in women, 1.10 ± 0.14, than men, 0.96 ± 0.08. In women, the ACL-injured group had significantly larger COR than the non-ACL injury group, but no difference was found in men.

CONCLUSION

COR is a unique morphological feature which is measureable from 3D CT. COR is larger in women, and could be a possible risk indicator for ACL injury in the female population.

LEVEL OF EVIDENCE

III.

Dynamic knee laxity measurement devices

PURPOSE

Studies have reported that knee kinematics and rotational laxity are not restored to native levels following traditional anterior cruciate ligament (ACL) reconstruction. This has led to the development of anatomic ACL reconstruction, which aims to restore native knee kinematics and long-term knee health by replicating normal anatomy as much as possible. The purpose of this review is to give an overview of current dynamic knee laxity measurement devices with the purpose of investigating the significance of dynamic laxity measurement of the knee. Gait analysis is not included.

METHODS

The subject was discussed with experts in the field in order to perform a level V review. MEDLINE was searched according to the discussions for relevant articles using multiple different search terms. All found abstracts were read and scanned for relevance to the subject. The reference lists of the relevant articles were searched for additional articles related to the subject.

RESULTS

There are a variety of techniques reported to measure dynamic laxity of the knee. Technical development of methods is one important part toward better understanding of knee kinematics. Validation of devices has shown to be difficult due to the lack of gold standard. Different studies use various methods to examine different components of dynamic laxity, which makes comparisons between studies challenging.

CONCLUSION

Several devices can be used to evaluate dynamic laxity of the knee. At the present time, the devices are continuously under development. Future implementation should include primary basic research, including validation and reliability testing, as well as part of individualized surgery and clinical follow-up.

LEVEL OF EVIDENCE

Diagnostic study, Level V.