Christian N. Anderson

Serial SimCoal: A population genetics model for data from multiple populations and points in time

UNLABELLED We present Serial SimCoal, a program that models population genetic data from multiple time points, as with ancient DNA data. An extension of SIMCOAL, it also allows simultaneous modeling of complex demographic histories, and migration between multiple populations. Further, we incorporate a statistical package to calculate relevant summary statistics, which, for the first time allows users to investigate the statistical power provided by, conduct hypothesis-testing with, and explore sample size limitations of ancient DNA data. AVAILABILITY Source code and Windows/Mac executables at http://www.stanford.edu/group/hadlylab/ssc.html CONTACT senka@stanford.edu.

Bayesian estimation of the timing and severity of a population bottleneck from ancient DNA.

In this first application of the approximate Bayesian computation approach using the serial coalescent, we demonstrated the estimation of historical demographic parameters from ancient DNA. We estimated the timing and severity of a population bottleneck in an endemic subterranean rodent, Ctenomys sociabilis, over the last 10,000 y from two cave sites in northern Patagonia, Argentina. Understanding population bottlenecks is important in both conservation and evolutionary biology. Conservation implications include the maintenance of genetic variation, inbreeding, fixation of mildly deleterious alleles, and loss of adaptive potential. Evolutionary processes are impacted because of the influence of small populations in founder effects and speciation. We found a decrease from a female effective population size of 95,231 to less than 300 females at 2,890 y before present: a 99.7% decline. Our study demonstrates the persistence of a species depauperate in genetic diversity for at least 2,000 y and has implications for modes of speciation in the incredibly diverse rodent genus Ctenomys. Our approach shows promise for determining demographic parameters for other species with ancient and historic samples and demonstrates the power of such an approach using ancient DNA.

Correlation of Meniscal and Articular Cartilage Injuries in Children and Adolescents With Timing of Anterior Cruciate Ligament Reconstruction

Background: In pediatric patients, anterior cruciate ligament (ACL) reconstruction is controversial; however, delaying surgery until skeletal maturity is complete may increase the risk of secondary meniscal and articular cartilage injury. Purpose: To assess the risk of meniscal and chondral injuries with delay of ACL reconstruction. Study Design: Cohort study; Level of evidence, 3. Methods: Records were reviewed in patients younger than 17 years (median age, 14 years) who had ACL reconstruction. Patients were consecutively enrolled and assigned to 1 of 3 surgical groups based on timing of surgery: acute (<6 weeks after surgery), subacute (6-12 weeks), or chronic (>3 months). The type and grade of meniscal injuries was documented according to the International Society of Arthroscopy, Knee Surgery, and Orthopaedic Sports Medicine (ISAKOS) meniscal classification criteria. International Cartilage Repair Society (ICRS) criteria were used to document location and grade of chondral injuries. Associations between patient characteristics and meniscal injury were tested using rank sum and chi-square tests. Regression analyses were conducted to model incidence and severity of lateral and medial meniscal tears. There were 130 patients who had 135 ACL reconstructions between the years of 2000 and 2012. Results: Sixty-two ACL injuries were treated acutely, 37 were subacute, and 36 were chronic. Meniscal injuries (n = 112) included 70 lateral and 42 medial tears. Time to surgery had bivariate association with lateral and medial meniscal tears (P = .016 and .007, respectively). Independent risk factors for incidence of lateral meniscal tears were younger age (P = .028) and return to sports activities before surgery (P = .007). Patients with 1 episode of instability had 3-fold higher odds of higher grade lateral meniscal tear (95% CI, 1.30-7.60). Compared with acute reconstruction, subacute and chronic reconstruction patients had 1.45 and 2.82 times higher odds, respectively, of lateral meniscal tear severity (P = .12). Independent risk factors for incidence of medial meniscal tears were female sex (P = .03), older age (P = .01), and any episode of instability (P = .01). Adjusted odds ratio for medial meniscal tear was 4.7 for an instability episode (vs no episode; P = .01). Adjusted odds ratio for increased severity of medial meniscal tears included any instability episode, 5.6 (P < .01); playing sports before reconstruction, 15.2 (P < .01); and time to surgery greater than 3 months, 4.3 (P = .046). Seventeen patients had 23 chondral injuries. The risk factors for chondral injury included increased time to surgery (P = .005) and any instability episode (P = .001). For increased grade of chondral injury, risk factors were time to surgery (P ≤ .001) and any instability episode (P = .003). Conclusion: Delayed ACL reconstruction increased the risks of secondary meniscal and chondral injuries in this population of pediatric patients.

Posterior cruciate and posterolateral ligament reconstruction in an adolescent with open physes. A case report.

Intrasubstance tears of the posterior cruciate ligament and posterolateral structures of the knee, a relatively common injury in adults, are very rare in children and adolescents. Most injuries of the posterior cruciate ligament in this age-group are osteochondral avulsions of either the femoral or tibial attachment1-12. When nonoperative treatment or primary repair of a torn or avulsed posterior cruciate ligament fails and a child or adolescent experiences instability, meniscal damage, and early degenerative changes, the physician is confronted with a dilemma: continued nonoperative treatment will probably result in progressive deterioration of the knee, but surgical intervention may cause an iatrogenic physeal injury. We report the case of an adolescent patient with posterior instability and posterolateral instability of the knee for whom nonoperative treatment had failed and who was successfully treated with use of a physeal sparing intra-articular reconstruction of the posterior cruciate ligament and an extra-articular reconstruction of the posterolateral structures. The patients family was informed that data concerning the case would be submitted for publication. The patient sustained a hyperextension injury of the right knee while jumping on a trampoline when he was eight years old. He was initially seen by a local physician who made a diagnosis of a sprained knee. The pain and swelling of the knee gradually subsided without treatment. He sustained a second injury of the right knee while playing football when he was eleven years and eight months old. Magnetic resonance imaging revealed partial tears of the anterior and posterior cruciate ligaments and a medial meniscal tear. Arthroscopy, which was performed at another institution, revealed a small radial tear in the white zone of the medial meniscus with an unstable component, and approximately 10% of the meniscus was excised. The articular surfaces of the medial femoral condyle and the medial …

Biomechanical evaluation of physeal-sparing fixation methods in tibial eminence fractures.

Background: Tibial eminence fractures occur most commonly in skeletally immature children. Several techniques using physeal-sparing fracture fixation have been described, but their structural properties have not been evaluated. Purpose: To determine the strength and resistance to displacement of physeal-sparing techniques used to fix tibial eminence fractures. Study Design: Controlled laboratory study. Methods: Skeletally immature porcine knees were randomized into 4 treatment groups: (1) ultra–high molecular weight polyethylene suture–suture button (UHMWPE/SB), (2) suture anchor, (3) polydioxanone suture–suture button (PDS/SB), and (4) screw fixation. A prospective analysis of bone mineral density using dual-energy x-ray absorptiometry was performed on all specimens. Fracture fragments were created in a standardized manner and measured for size comparison. After fracture fixation, biomechanical testing was performed with cyclical and load-to-failure protocols by loading the tibia with an anterior shear force. Results: In load-to-failure testing, screw fixation had a significantly lower median peak failure load (186.4 N; lower quartile [LQ], 158.4 N; upper quartile [UQ], 232.6 N) than did UHMWPE/SB (465.8 N; LQ, 397.8 N; UQ, 527.8 N), suture anchors (440.5 N; LQ, 323.0 N; UQ, 562.3 N), and PDS/SB (404.3 N; LQ, 385.9 N; UQ, 415.6 N). UHMWPE/SB demonstrated a significantly higher median yield load (465.8 N; LQ, 397.8 N; UQ, 527.8 N) than did PDS/SB (306.7 N; LQ, 271.4, N; UQ, 405.7 N) and screw fixation (179.0 N; LQ, 120.2 N; UQ, 232.5 N). During cyclical testing, screw fixation demonstrated significantly lower percentage survival of specimens (0%) compared with the other groups (UHMWPE/SB, 100%; suture anchor, 78%; PDS/SB, 78%). After 1000 cycles of loading, PDS/SB fixation had significantly more median creep (6.76 mm; LQ, 6.34 mm; UQ, 8.28 mm) than did UHMWPE/SB (4.43 mm; LQ, 3.80 mm; UQ, 4.73 mm) and suture anchor fixation (3.06 mm; LQ, 2.59 mm; UQ, 4.28 mm). The lowest median stiffness was observed in the PDS/SB group (48.6 N/mm; LQ, 45.3 N/mm; UQ, 54.2 N/mm). UHMWPE/SB fixation demonstrated a significantly higher median peak failure load after cyclic testing (469.0 N; LQ, 380.6 N; UQ, 507.2 N) than did PDS/SB (237.7 N; LQ, 197.3 N; UQ, 298.3 N) and screw fixation (132.4 N; LQ, 123.7 N; UQ, 180.9 N). Suture anchor fixation had significantly more variance, as demonstrated by width of interquartile range, in peak failure load, yield load, and creep than did other techniques. Conclusion: Physeal-sparing fixation of tibial eminence fractures with UHMWPE suture–suture button is biomechanically superior to both PDS suture–suture button and a single screw at the time of surgery and provides more consistent fixation than do suture anchors. Clinical Relevance: Suture anchors provide inconsistent fixation for tibial eminence fractures.

Transepiphyseal Anterior Cruciate Ligament Reconstruction in Pediatric Patients: Surgical Technique

The prevalence of anterior cruciate ligament (ACL) tears in children and adolescents is relatively low due to anatomic and biomechanical factors that predispose skeletally immature knees to bone injury rather than ligament tears.17 Nevertheless, ACL tears in this age group appear to be increasing.1,7,8,12,14-16,18 Management of these injuries presents a unique challenge; evidence in the literature indicates that the outcome of nonoperative treatment of ACL tears in skeletally immature patients is poor.1,9,11,14,15 Conversely, surgical intervention may cause iatrogenic physeal injury, which can result in leg-length discrepancy or angular deformity.6,11,13,14 Management decisions are complicated by deficiency in the basic science on physeal response to injury and by the limitations of the clinical studies that document surgical treatment for ACL insufficiency in children and adolescents. Despite these uncertainties, a rational approach based on current understanding of normal growth and development can be implemented.2-5 This article describes a technique for transepiphyseal reconstruction of the ACL using autogenous hamstring tendon grafts. The procedure adheres to the generally accepted principles of ACL replacement in adults, but theoretically minimizes the risk of physeal injury by not transgressing either the tibial or femoral physis. The decision as to whether to use this procedure to treat an ACL tear in a child or adolescent can be based on estimates of the relative risk of physeal injury (high, intermediate, or low), which can be determined by assessing the patient’s skeletal and physiological age. The consequences of iatrogenic physeal injury may be severe in children who have a great deal of growth remaining and insignificant in teenagers who have minimal growth remaining in the distal femur and proximal tibial physes. The central issue in treatment of ACL tears in the pediatric age group is the patient’s skeletal age, which determines the potential risk of injurious consequences. The most common method of estimating skeletal age is by comparing an anteroposterior radiograph of the patient’s left hand and wrist with the age-specific radiographs in the Greulich and Pyle Atlas.10 Physiological age can be classified according to Tanner’s staging of sexual maturation.19 Prepubescent patients are categorized in Tanner stages I and II of development, pubescent patients are in Tanner stage III, late pubescent in Tanner stage IV, and postpubescent patients are in Tanner stage V.3-5 The success of transepiphyseal ACL reconstruction, with meniscal repair, without evidence of growth disturbance, supports a recommendation for aggressive treatment of these injuries.2-5 Transepiphyseal replacement is recommended for prepubescent patients in Tanner stage I or II of development, including boys younger than 12 years and girls younger than 11 years; these patients are at high risk of growth disturbance if physeal injury occurs. Pubescent Tanner stage III patients, including boys 13 to 16 years of age and girls 12 to 14 years of age, are at intermediate risk. Transepiphyseal replacement is also recommended in early Tanner stage III patients because the threshold of safety for transphyseal drilling is currently unknown.

Iliopsoas: Pathology, Diagnosis, and Treatment.

Disorders of the iliopsoas can be a significant source of groin pain in the athletic population. Commonly described pathologic conditions include iliopsoas bursitis, tendonitis, impingement, and snapping. The first-line treatment for iliopsoas disorders is typically conservative, including activity modification, physical therapy, nonsteroidal anti-inflammatory drugs, and corticosteroid injections. Surgical treatment can be considered if the patient fails conservative measures and typically involves arthroscopic lengthening of the musculotendinous unit and treatment of concomitant intra-articular abnormality. Tendon release has been described: in the central compartment, in the peripheral compartment, and at the lesser trochanter, with similar outcomes observed between the techniques.

The anterior meniscofemoral ligament of the medial meniscus: case series.

have been performed to facilitate meniscal preservation or transplantation. These studies have demonstrated several common patterns of attachment for the anterior horn of the medial meniscus. Anomalous insertions, however, are thought to be rare; only 4 cases of insertion of the medial meniscus into the intercondylar notch have been previously reported. The purpose of this study was to describe a case series of 12 patients who were found to have an anterior meniscofemoral ligament of the medial meniscus that attached to the intercondylar notch and to review the literature pertinent to the development, anatomy, function, and treatment of this structure.

Femoral Neck Stress Fractures and Imaging Features of Femoroacetabular Impingement

Prior literature has suggested an association between the radiographic signs of femoroacetabular impingement (FAI) and femoral neck stress fractures (FNSF) or femoral neck stress reactions (FNSR). At the time of the writing of this article, no study has described the association of FAI and FNSF/FNSR along with the need for surgical intervention and outcomes.

Management of Osteochondritis Dissecans of the Knee

The primary goals of treatment of osteochondritis dissecans (OCD) of the knee are healing of the subchondral bone, preservation of the articular cartilage, and, ultimately, prevention of arthritis. The methods used to accomplish these goals depend on the pathologic changes of the lesion and the healing capacity of the patient. The skeletally immature knee has a greater capacity for healing; consequently, nondisplaced lesions with intact articular cartilage in children and adolescents may be treated conservatively. This method of treatment should be abandoned in patients who show no signs of healing after 6 months or in those approaching skeletal maturity. The generally accepted principles of surgical treatment of OCD are to improve blood flow to the fragment, provide bony support if necessary to reestablish congruency, and stabilize loose or separated fragments. The type of surgical treatment depends on many factors, including the age of the patient, stage of the lesion, and preference of the surgeon. Arthroscopic drilling is a relatively reliable procedure in adolescents with a stable lesion who are skeletally immature (juvenile osteochondritis dissecans, JOCD). Adult osteochondritis dissecans (AOCD) is less likely to heal with drilling, and, therefore, a more aggressive surgical procedure is indicated. Retrograde bone grafting and drilling may be performed for AOCD with a stable fragment with good subchondral support. Revascularization and stabilization of the fragment is the procedure of choice for JOCD or AOCD patients with loose or separated fragments. Replacement and stabilization of the lesion may not be possible if the articular cartilage has completely deteriorated. Although excision of the fragment is easier, and the short-term results are good, long-term results of excision are extremely poor. Consequently, resurfacing should be performed in preference to excision.