The relation between meniscal dynamics and tibiofemoral kinematics

Over the past 30 years, research on meniscal kinematics has been limited by challenges such as low-resolution imaging and capturing continuous motion from static data. This study aimed to develop a computational knee model that overcomes these limitations and enables the continuous assessment of meniscal dynamics. A high-resolution MRI dataset (n = 11) was acquired in 4 configurations of knee flexion. In each configuration, the menisci were modeled based on the underlying osseous anatomy. Principal Polynomial Shape Analysis (PPSA) was employed for continuous meniscal modeling. Maximal medial anterior horn displacement occurred in 60° of flexion, equaling 6.24 mm posteromedial, while the posterior horn remained relatively stable. At 90° of flexion, the lateral anterior and posterior horn displaced posteromedially, amounting 5.70 mm and 6.51 mm respectively. The maximal observed Average Surface Distance (ASD) equaled 0.70 mm for lateral meniscal modeling in 90° of flexion. Based on our results, a strong relation between meniscal dynamics and tibiofemoral kinematics was confirmed. Expanding on static meniscal modeling and employing PPSA, we derived and validated a standardized and systematic methodological workflow.

Quantifying walking speeds in relation to ankle biomechanics on a real-time interactive gait platform: a musculoskeletal modeling approach in healthy adults

Background: Given the inherent variability in walking speeds encountered in day-to-day activities, understanding the corresponding alterations in ankle biomechanics would provide valuable clinical insights. Therefore, the objective of this study was to examine the influence of different walking speeds on biomechanical parameters, utilizing gait analysis and musculoskeletal modelling. Methods: Twenty healthy volunteers without any lower limb medical history were included in this study. Treadmill-assisted gait-analysis with walking speeds of 0.8 m/s and 1.1 m/s was performed using the Gait Real-time Analysis Interactive Lab (GRAIL®). Collected kinematic data and ground reaction forces were processed via the AnyBody® modeling system to determine ankle kinetics and muscle forces of the lower leg. Data were statistically analyzed using statistical parametric mapping to reveal both spatiotemporal and magnitude significant differences. Results: Significant differences were found for both magnitude and spatiotemporal curves between 0.8 m/s and 1.1 m/s for the ankle flexion (p < 0.001), subtalar force (p < 0.001), ankle joint reaction force and muscles forces of the M. gastrocnemius, M. soleus and M. peroneus longus (α = 0.05). No significant spatiotemporal differences were found between 0.8 m/s and 1.1 m/s for the M. tibialis anterior and posterior. Discussion: A significant impact on ankle joint kinematics and kinetics was observed when comparing walking speeds of 0.8 m/s and 1.1 m/s. The findings of this study underscore the influence of walking speed on the biomechanics of the ankle. Such insights may provide a biomechanical rationale for several therapeutic and preventative strategies for ankle conditions.

Application of external torque enhances the detection of subtle syndesmotic ankle instability in a weight-bearing CT

PURPOSE

Acute syndesmotic ankle injuries continue to impose a diagnostic dilemma and it remains unclear whether weightbearing and/or external rotation should be added during the imaging process. Therefore, the aim of this study was to assess if combined weightbearing and external rotation increases the diagnostic sensitivity of syndesmotic ankle instability using weightbearing CT (WBCT) imaging, compared to isolated weightbearing.

METHODS

In this retrospective study, patients with an acute syndesmotic ankle injury were analysed using a WBCT (N = 21; Age = 31.6 ± 14.1 years old). Inclusion criteria were an MRI confirmed syndesmotic ligament injury imaged by a WBCT of the ankle during weightbearing and combined weightbearing-external rotation. Exclusion criteria consisted of fracture associated syndesmotic injuries. Three-dimensional (3D) models were generated from the CT slices. Tibiofibular displacement and talar rotation were quantified using automated 3D measurements (anterior tibiofibular distance (ATFD), Alpha angle, posterior Tibiofibular distance (PTFD) and Talar rotation (TR) angle in comparison to the contralateral non-injured ankle.

RESULTS

The difference in neutral-stressed Alpha angle and ATFD showed a significant difference between patients with a syndesmotic ankle lesion and contralateral control (P = 0.046 and P = 0.039, respectively). The difference in neutral-stressed PTFD and TR angle did not show a significant difference between patients with a syndesmotic ankle lesion and healthy ankles (n.s.).

CONCLUSION

Application of combined weightbearing-external rotation reveals an increased ATFD in patients with syndesmotic ligament injuries. This study provides the first insights based on 3D measurements to support the potential relevance of applying external rotation during WBCT imaging. In clinical practice, this could enhance the current diagnostic accuracy of subtle syndesmotic instability in a non-invasive manner. However, to what extent certain displacement patterns require operative treatment strategies has yet to be determined in future studies.

LEVEL OF EVIDENCE

Level III.

A new look at osteoarthritis: Threshold potentials and an analogy to hypocalcemia

Cartilage is a tissue that consist of very few cells embedded in a highly negatively charged extracellular matrix (ECM). This tissue is dealing with several electrical potentials which have been shown to control the production of ECM. Cartilage is present at joints and is constantly prone to degradation. Failing to repair the damage will result in the occurrence of osteoarthritis (OA). This perspective aims to link biophysical insights with biomolecular research in order to provide an alternative view on the possible causes of OA. Firstly, we hypothesize the existence of a threshold potential, which should be reached in order to initiate repair but if not met, unrepaired damage will evolve to OA. Measurements of the magnitude of this threshold electrical potential would be a helpful diagnostic tool. Secondly, since electrical potential alterations can induce chondrocytes to synthesize ECM, a cellular sensor must be present. We here propose an analogy to the hypocalcemia ‘unshielding’ situation to comprehend electrical potential generation and explore possible sensing mechanisms translating the electrical message into cellular responses. A better understanding of the cellular voltage sensors and down-stream signalling mechanisms may lead to the development of novel treatments for cartilage regeneration.

Personalized statistical modeling of soft tissue structures in the knee

Background and Objective: As in vivo measurements of knee joint contact forces remain challenging, computational musculoskeletal modeling has been popularized as an encouraging solution for non-invasive estimation of joint mechanical loading. Computational musculoskeletal modeling typically relies on laborious manual segmentation as it requires reliable osseous and soft tissue geometry. To improve on feasibility and accuracy of patient-specific geometry predictions, a generic computational approach that can easily be scaled, morphed and fitted to patient-specific knee joint anatomy is presented.

Methods: A personalized prediction algorithm was established to derive soft tissue geometry of the knee, originating solely from skeletal anatomy. Based on a MRI dataset (n = 53), manual identification of soft-tissue anatomy and landmarks served as input for our model by use of geometric morphometrics. Topographic distance maps were generated for cartilage thickness predictions. Meniscal modeling relied on wrapping a triangular geometry with varying height and width from the anterior to the posterior root. Elastic mesh wrapping was applied for ligamentous and patellar tendon path modeling. Leave-one-out validation experiments were conducted for accuracy assessment.

Results: The Root Mean Square Error (RMSE) for the cartilage layers of the medial tibial plateau, the lateral tibial plateau, the femur and the patella equaled respectively 0.32 mm (range 0.14–0.48), 0.35 mm (range 0.16–0.53), 0.39 mm (range 0.15–0.80) and 0.75 mm (range 0.16–1.11). Similarly, the RMSE equaled respectively 1.16 mm (range 0.99–1.59), 0.91 mm (0.75–1.33), 2.93 mm (range 1.85–4.66) and 2.04 mm (1.88–3.29), calculated over the course of the anterior cruciate ligament, posterior cruciate ligament, the medial and the lateral meniscus.

Conclusion: A methodological workflow is presented for patient-specific, morphological knee joint modeling that avoids laborious segmentation. By allowing to accurately predict personalized geometry this method has the potential for generating large (virtual) sample sizes applicable for biomechanical research and improving personalized, computer-assisted medicine.

Wear patterns in knee OA correlate with native limb geometry

Background: To date, the amount of cartilage loss is graded by means of discrete scoring systems on artificially divided regions of interest (ROI). However, optimal statistical comparison between and within populations requires anatomically standardized cartilage thickness assessment. Providing anatomical standardization relying on non-rigid registration, we aim to compare morphotypes of a healthy control cohort and virtual reconstructed twins of end-stage knee OA subjects to assess the shape-related knee OA risk and to evaluate possible correlations between phenotype and location of cartilage loss.

Methods: Out of an anonymized dataset provided by the Medacta company (Medacta International SA, Castel S. Pietro, CH), 798 end-stage knee OA cases were extracted. Cartilage wear patterns were observed by computing joint space width. The three-dimensional joint space width data was translated into a two-dimensional pixel image, which served as the input for a principal polynomial autoencoder developed for non-linear encoding of wear patterns. Virtual healthy twin reconstruction enabled the investigation of the morphology-related risk for OA requiring joint arthroplasty.

Results: The polynomial autoencoder revealed 4 dominant, orthogonal components, accounting for 94% of variance in the latent feature space. This could be interpreted as medial (54.8%), bicompartmental (25.2%) and lateral (9.1%) wear. Medial wear was subdivided into anteromedial (11.3%) and posteromedial (10.4%) wear. Pre-diseased limb geometry had a positive predictive value of 0.80 in the prediction of OA incidence (r 0.58, p &lt; 0.001).

Conclusion: An innovative methodological workflow is presented to correlate cartilage wear patterns with knee joint phenotype and to assess the distinct knee OA risk based on pre-diseased lower limb morphology. Confirming previous research, both alignment and joint geometry are of importance in knee OA disease onset and progression.

Three-dimensional displacement after a medializing calcaneal osteotomy in relation to the osteotomy angle and hindfoot alignment

BACKGROUND

A medializing calcaneal osteotomy is frequently performed to correct adult-acquired flatfoot deformities, but there is lack of data on the associated three-dimensional variables defining the final correction. The aim of this study was to assess the correlation between the pre-operative hindfoot valgus deformity and calcaneal osteotomy angles and the post-operative calcaneal displacement.

METHODS

Weight-bearing CT scans obtained pre- and post-operatively were retrospectively analyzed for sixteen patients. Corresponding three-dimensional bone models were used to measure valgus deformity pre- and post-operatively, inclination of the osteotomy and displacement of the calcaneus. Linear regression was conducted to assess the relationship between these measurements.

RESULTS

On average, the hindfoot valgus changed from 13.1° (±4.6) pre-operatively to 5.7° (±4.3) post-operatively. A mean inferior displacement of 3.2mm (±1.3) was observed along the osteotomy with a mean inclination of 54.6° (±5.6), 80.5° (±10.7), -13.7° (±15.7) in the axial, sagittal and coronal planes, respectively. A statistically significant positive relationship (p<.05, R²=0.6) was found between the pre-operative valgus, the axial osteotomy inclination, and the inferior displacement.

CONCLUSIONS

This study shows that the degree of pre-operative hindfoot valgus and the axial osteotomy angle are predictive factors for the amount of post-operative inferior displacement of the calcaneus. These findings demonstrate the added value of a computer-based pre-operative planning in clinical practice. Level of evidence II Prospective comparative study.

Imageless versus image-based registration in navigated arthroscopy of the hip: a cadaver-based assessment

The aim of this study was to determine the accuracy of registration and the precision of the resection volume in navigated hip arthroscopy for cam-type femoroacetabular impingement, using imageless and image-based registration. A virtual cam lesion was defined in 12 paired cadaver hips and randomly assigned to either imageless or image-based (three-dimensional (3D) fluoroscopy) navigated arthroscopic head-neck osteochondroplasty. The accuracy of patient-image registration for both protocols was evaluated and post-operative imaging was performed to evaluate the accuracy of the surgical resection. We found that the estimated accuracy of imageless registration in the arthroscopic setting was poor, with a mean error of 5.6 mm (standard deviation (sd) 4.08; 95% confidence interval (CI) 4.14 to 7.19). Because of the significant mismatch between the actual position of the probe during surgery and the position of that probe as displayed on the navigation platform screen, navigated femoral osteochondroplasty was physically impossible. The estimated accuracy of image-based registration by means of 3D fluoroscopy had a mean error of 0.8 mm (sd 0.51; 95% CI 0.56 to 0.94). In terms of the volume of bony resection, a mean of 17% (sd 11; -6% to 28%) more bone was resected than with the virtual plan (p = 0.02). The resection was a mean of 1 mm deeper (sd 0.7; -0.3 to 1.6) larger than on the original virtual plan (p = 0.02). In conclusion, given the limited femoral surface that can be reached and digitised during arthroscopy of the hip, imageless registration is inaccurate and does not allow for reliable surgical navigation. However, image-based registration does acceptably allow for guided femoral osteochondroplasty in the arthroscopic management of femoroacetabular impingement.

Hip arthroscopy in patients with painful hip following resurfacing arthroplasty

PURPOSE

Determining the etiology of persistent groin pain after hip resurfacing arthroplasty (HRA) can be very challenging, even for the experienced surgeon. The purpose of the present study was to evaluate the use of hip arthroscopy as a diagnostic and therapeutic tool for the painful hip following resurfacing arthroplasty.

METHODS

In the present paper, the indications for arthroscopy and the arthroscopic findings in 15 patients with persistent and incapacitating groin pain following HRA are described. In all patients, nonsurgical diagnostic investigations such as ultrasound and radiography, blood sample analysis, and technetium and leukocyte-labeled scanning were inconclusive so that a definite diagnosis could not be established.

RESULTS

In seven patients, synovial biopsies were taken arthroscopically to rule out metal sensitivity, low-grade infection, or excessive metal wear. A definite diagnosis from histological evaluation could be made in 5 out of the 7 patients. Five patients were clinical suspicious of iliopsoas tendinitis. Diagnostic arthroscopy and histological analysis of the synovial samples provided an alternative diagnosis in 2 out of the 5 patients. Three patients underwent femoral osteoplasty for impingement due to reduced anterior femoral offset with subsequent symptom relief.

CONCLUSION

Hip arthroscopy after HRA is a valuable diagnostic alternative to open procedures in case of persistent groin pain, when noninvasive investigations fail to explain the symptoms. Multiple tissue samples should always be taken for histological examination and culture, as they are crucial in the final identification of the origin of the complaints.

A method for three-dimensional evaluation and computer aided treatment of femoroacetabular impingement

Several theoretical models have shown that the range of motion of the hip joint is impaired in patients with femoroacetabular impingement, and that the acetabular cartilage is at risk of being damaged as a result of abnormal shear stresses, even during normal everyday activities. Computer aided technologies might add to the early diagnosis and adequate treatment of such lesions. This paper describes the technique, theories and algorithms we have developed for patient-specific detection, analysis and computer aided surgery of femoroacetabular impingement. Currently available models applicable to femoroacetabular impingement offer modeling based on collision analysis of a constrained hip joint. Such an approach implies that neither the femur nor the acetabulum can be analyzed completely separately for the presence of structural lesions responsible for the impingement problem. Moreover, a constrained model does not allow for comprehensive prediction of the possible locations and extent of secondary cartilage lesions (so-called contre-coup lesions) of the posterior acetabulum opposite the anterior impingement site. We report a new technique for the subject-specific morphological analysis of the proximal femur, acetabulum and hip joint. The technique offers a number of advantages compared to currently used techniques for the diagnosis and evaluation of hip impingement, and has direct orthopaedic applications as it allows computer aided planning and minimally invasive surgery for patients with femoroacetabular impingement.

Global optimization method for combined spherical-cylindrical wrapping in musculoskeletal upper limb modelling

In musculoskeletal modelling, many muscles cannot be represented as straight lines from origin to insertion because the bony and musculotendinous morphology of neighboring structures causes them to wrap. The majority of these passive structures can be adequately described as simple geometric shapes such as spheres and cylinders. Techniques for describing smooth muscle paths around multiple obstacles have been developed for modelling use. Until now obstacle-set methods have combined the path of single structures. This does not analytically define the shortest smooth path around multiple objects. When a sphere is included in a multiple-object wrapping algorithm, muscle paths around that sphere are restricted to a bundle of planes containing the sphere center. This assumed restriction can compromise the iterative process for finding the true shortest muscle path that satisfies all restrictions of a smooth path. This can cause model instability. The new method involves the determination of the shortest smooth muscle path in a spherical and cylindrical wrapping algorithm. A typical example is musculoskeletal modelling of the upper limb, where the muscle fibers have to wrap over this combination of obstacles.

Conservative treatment of a cervical thoracic duct cyst: a case report

Cysts of the thoracic duct are uncommon entities that can occur in the abdominal segment, the cisterna chyli, the thoracic segment and the cervical segment of the thoracic duct. The rarest presentation is in the cervical segment, with only seventeen cases reported in English literature. The diagnosis can be made by puncture and with the use of computed tomography or ultrasonography. The cystic fluid always contains an excess of T-lymphocytes and triglycerides. Except for two cases, all reported cervical thoracic duct cysts were surgically treated by excision and ligation of the lymphatics connected to the cyst. We present a case of a successful non-operative treatment of a cervical thoracic duct cyst that was resolved by repeated aspiration and dietary changes only.

Reconstruction of massive rotator cuff lesions with a synthetic interposition graft: a prospective study of 41 patients

In the present prospective study, we report about our experience with massive rotator cuff tears treated by means of a non-resorbable transosseously fixated patch combined with subacromial decompression. Forty-one patients were followed clinically and radiographically for a mean duration of 43 months. Their mean preoperative Constant and Murley score improved (P<0.001) from 25.7 preoperatively to 72.1 postoperatively. Substantial pain relief and improvement in the performance of activities of daily living were obtained. Anatomically, the repair resulted in a mean acromiohumeral interval of 8.6 mm. At the latest follow-up, three patients presented with a new tear between the inserted mesh and the supraspinatus musculotendinous unit. Reoperations were not performed. For short-term periods, restoring a massive rotator cuff tendon defect with synthetic grafts combined with subacromial decompression can give significant pain relief and improvement of range of motion and strength with few complications.

Detecting Holocene divergence in the anadromous-freshwater three-spined stickleback (Gasterosteus aculeatus) system

The anadromous-freshwater three-spined stickleback (Gasterosteus aculeatus) system allows for inferring the role of adaptation in speciation with a high level of accuracy because the freshwater ecotype has evolved multiple times from a uniform anadromous ancestor. A cause for concern is that independent evolution among drainages is not guaranteed in areas with a poorly resolved glacial history. This is the case for the west European great rivers, whose downstream valleys flanked the southern limit of the late Pleistocene ice sheet. We tested for independent and postglacial colonization of these valleys hypothesizing that the relationships among anadromous and freshwater sticklebacks correspond to a raceme structure. We compared the reduction in plate number accompanying this colonization to the genetic differentiation using 13 allozyme and five microsatellite loci in 350 individuals. Overall microsatellite differentiation (F(ST) = 0.147) was twice as large as allozyme differentiation (F(ST) = 0.066). Although habitat-specific gene flow may mask the ancestral relationships among both ecotypes, levels of microsatellite differentiation supported the hypothesis of raceme-like divergence, reflecting independent colonizations rather than the presence of two distinct evolutionary clades. Under an infinite alleles model and in the absence of gene flow, the observed freshwater divergence might be reached after 440 (microsatellites) to 4500 (allozymes) generations. Hence, the anadromous-freshwater stickleback system most likely diverged postglacially. We conclude that the reduction in plate number in two freshwater basins probably occurred independently, and that its considerable variation among populations is not in agreement with the time since divergence.

About the variability of the shape of the glenoid cavity

The morphology of the glenoid cavity is highly variable, and no consensus exists regarding how to classify the different forms. We examined 98 dry scapulae to identify a common morphological entity and to define reproducible bony references of the glenoid cavity. The glenoid cavities were photographed perpendicularly in a standardized fashion. The bony peripheral rim was studied on these two-dimensional images, defined by randomly chosen points in order to define one or more circles. This study showed that only the peripheral rim of the inferior quadrants of the articular surface was found to be located on a circle ( P=0.926) with a radius of 12.8 mm (SD 1.3 mm). Defining the center of this circle appeared to be more reliable (ICC 0.98) than determining the middle point of the longitudinal axis (0,0) between the most cranial and most caudal points, defined as Saller's line (ICC 0.89). The distance of the center of this projected circle to the middle point of Saller's line had a unimodal distribution, suggesting the existence of only one glenoid cavity morphotype. We then investigated the relationship between the center of the circle and the area of subchondral bone thickening under the bare spot, the so-called tubercle of Assaki. Ten phenolized cadaveric glenoid cavities were examined with computed tomography. A circle was projected on the first image showing the bony peripheral rim, and this circle was copied on the consecutive slices until the tubercle of Assaki came across. The center of the circle was located within the area of the tubercle of Assaki, in all but one specimen. To investigate the clinical implications of this finding, the cadaver specimens were used to compare the position of the center of the circle with the postulated center of implantation according to the literature, and to the reference guide for a commonly used total shoulder prosthesis. The center of the circle was consistently situated more distal than the postulated center of the guide (mean 5.5 mm, range 4-8 mm) and the middle point of the glenoid cavity (mean 2 mm, range 1-3 mm). These findings could offer a reproducible point of reference for the glenoid cavity in osseous anthropometry and a valuable reference in shoulder replacement surgery, and might help in the definition of osseous glenohumeral instability.

Consequences of deltoid muscle elongation on deltoid muscle performance: a computerised study

BACKGROUND

The deltoid muscle plays an important role in normal shoulder function. Knowledge of the position of the glenohumeral rotational centre and of the deltoid muscle length is essential to understand optimal placement of a total shoulder prosthesis.

OBJECTIVE

This study is designed to analyse the effect of deltoid muscle elongation on shoulder joint function.

DESIGN

A three-dimensional model of the glenohumeral joint with deltoid muscle analysis in the scapular plane.

METHODS

A geometrical three-dimensional ball-and-socket model of the shoulder joint was developed. From dry bones, the position of the origins and insertions of the three parts of the deltoid muscle relative to the calculated centre of rotation of the humeral head was defined. The position and the direction of the muscle force working lines relative to this humeral centre were calculated using former measurements and CT-data of the deltoid. Muscle length-tension data were applied to obtain angle-force relationships. The model was used to calculate the angle-force relationships, the moment arm and the moment of the deltoid muscle components for successive arm elevation angles in the scapular plane. These data were compared to those of a theoretical situation assuming a 10% elongation of the muscle.

RESULTS

Muscle angle-force curves show a more favourable slope after moderate (10%) deltoid muscle elongation. Elongating the muscle by changing the distance between the humeral rotation point and the deltoid insertion along the humeral axis does not affect moment arms. The moments of the deltoid muscle forces themselves, however, seem more adapted to elevation in the scapular plane. The deltoid maximal moment exceeds the arm-weight moment by about 40% instead of being approximately equal, and that the maximum is situated around 100 degrees of elevation.

CONCLUSIONS

From a biomechanical point of view, stretching the deltoid muscle by 10% seems to result in a significantly more favourable position in case of shoulder elevation at 90 degrees of abduction in the scapular plane in a centred glenohumeral joint.

RELEVANCE

This model suggests that a 10% elongation of the deltoid muscle, the most important shoulder abductor, improves its ability to elevate the arm. If properly implemented, this observation can be very important in the treatment and early rehabilitation of rotator-cuff-insufficient shoulders treated by a specific total shoulder replacement design.

Low among-population genetic differentiation in Chinese bisexual Artemia populations

We studied the population genetic structure of nine bisexual Artemia sinica populations from the provinces of Inner Mongolia, Shanxi and Qinghai in China, using variation at nine allozyme loci (cellulose acetate electrophoresis). There is a clear-cut tendency for an increase in genetic variation, as measured by heterozygosity, with increasing habitat size. Although we observe a positive relationship between genetic differentiation and geographical distance, overall FST values are low: populations separated by approximately 1000 km show average FST values of 0.05-0.1, whereas populations separated by 100 km show no genetic differentiation at all.

Evidence for a post-Columbian introduction of human T-cell lymphotropic virus [type I] [corrected] in Latin America

To investigate the origin and dissemination of human T-cell lymphotropic virus type I in Latin America, we performed phylogenetic analysis on the LTR and env sequences of 13 HTLV-I isolates from Peruvians of four different ethnic groups: blacks and some mulattos of African origin; Quechuas of Inca origin; Nikkei of Japanese descendance; and Mestizos, a mixed population of white and Indian origin. All Peruvian samples could be situated within the cosmopolitan subtype HTLV-Ia, yet one sample showed an indeterminate Western blot pattern, lacking reactivity towards the HTLV-I type specific MTA1 peptide. Within the LTR, we could confirm the previously reported subdivision into four subgroups--one big transcontinental clade A, a Japanese clade B, a West African/Caribbean clade C and a North African clade D--and we identified a new separate subgroup E of black Peruvian strains. The clustering of the Peruvian samples seemed to depend on the ethnic origin of the host. The largest heterogeneity was observed in the black Peruvian samples. The mitochondrial DNA type of one of these black Peruvian strains of subgroup E was identical to that of West African source populations of the slave trade. Both findings support the idea of multiple post-Columbian introductions of African HTLV-Ia strains into the black Latin American population. Additionally, a tight cluster of Nikkei and Japanese samples implied a separate and rather recent transmission of a Japanese lineage of HTLV-I into Peru. A well-supported cluster of Latin American strains (including Peruvian Quechuas and Colombian Amerindians) could be situated within the transcontinental group. Molecular clock analysis of the Latin American and Japanese clade resulted in an equal evolutionary rate for those strains. Along with the anthropologically documented peopling of the Americas, the analysis was more in favour of a recent (400 to 100 years ago) introduction of HTLV-Ia into the American continent rather than a Palaeolithic introduction.

Two new human T-lymphotropic virus type I phylogenetic subtypes in seroindeterminates, a Mbuti pygmy and a Gabonese, have closest relatives among African STLV-I strains

Six new HTLV-I strains from seroindeterminate individuals were analyzed: four from Gabon, one from a Mbuti Efe pygmy in Congo (formerly Zaire), and one from a Congolese patient residing in Belgium. The LTR and env regions were sequenced and phylogenetic analyses were performed to characterize the new strains. Nucleotide divergence and phylogeny results showed that four of the new strains belong to the HTLV-Ib Central African subtype. The other two strains, one from the Efe pygmy and one from Gabon, lie on distinct branches of the LTR and env trees with respect to the four major HTLV-I subtypes. Despite the low bootstrap values, likelihood mapping analyses proved that these strains can be considered two new HTLV-I molecular subtypes, putatively named HTLV-Ie and HTLV-If. A relation exists in the phylogenetic trees and in the likelihood maps between the new subtypes and African STLV-I strains from Papio spp. and Cercopithecus spp., suggesting one or more interspecies transmission events in the past. This study demonstrates that the phylogenetic subtyping of HTLV-I in the African continent is far from being completed and that samples presenting an indeterminate serology can potentially belong to new subtypes in humans. In addition, present day serological tests do not reliably type strains within the HTLV-Ib Central African subtype.