Secondary Ligament Research Articles

MRI of patellar stabilizers: Anatomic visibility, inter-reader reliability, and intra-reader reproducibility of primary and secondary ligament anatomy.

To compare MRI features of medial and lateral patellar stabilizers in patients with and without patellar instability. Retrospective study of 196 patients (mean age, 33.1 ± 18.5years; 119 women) after diagnosis of patellar instability (cohort-1, acute patellar dislocation; cohort-2, chronic patellar maltracking) or no patellar instability (cohort-3, acute ACL rupture; cohort-4, chronic medial meniscus tear). On MRI, four medial and four lateral stabilizers were evaluated for visibility and injury by three readers independently. Inter- and intra-reader agreement was determined. Medial and lateral patellofemoral ligaments (MPFL and LPFL) were mostly or fully visualized in all cases (100%). Of the secondary patellar stabilizers, the medial patellotibial ligament was mostly or fully visualized in 166 cases (84.7%). Other secondary stabilizers were mostly or fully visualized in only a minority of cases (range, 0.5-32.1%). Injury scores for all four medial stabilizers were higher in patients with acute patellar dislocation than the other 3 cohorts (p < .05). Visibility inter- and intra-reader agreement was good for medial stabilizers (κ 0.61-0.78) and moderate-to-good for lateral stabilizers (κ 0.40-0.72). Injury inter- and intra-reader agreement was moderate-to-excellent for medial stabilizers (κ 0.43-0.90) and poor-to-moderate for lateral stabilizers (κ 0-0.50). The MPFL and LPFL were well visualized on MRI while the secondary stabilizers were less frequently visualized. The secondary stabilizers were more frequently visualized medially than laterally, and patellotibial ligaments were more frequently visualized compared to the other secondary stabilizers. Injury to the medial stabilizers was more common with acute patellar dislocation than with chronic patellar maltracking or other knee injuries.

Radially Displaced Perilunate Injuries: A Report of Two Cases.

We present two unusual cases of radially displaced perilunate dislocations, one of which involved acute ulnar nerve compression requiring Guyon's canal release. The first case underwent closed reduction and cast immobilization but developed scapholunate instability, necessitating secondary ligament reconstruction. The second case, treated with open reduction and fixation, resulted in persistent volar intercalated segment instability of the proximal row and ulnar nerve paresthesia 1 year after surgery.

Treatment of Knee Dislocation With Primary Repair and Suture Augmentation: A Viable Solution.

Different surgical techniques have been described for the treatment of knee dislocation (KD). Nonoperative approaches are frequently combined with surgical reconstruction using auto- or allograft. To evaluate the midterm results of primary surgical repair and suture augmentation to treat KD. Case series; Level of evidence, 4. A total of 22 patients (5 women, 17 men; mean age, 45 ± 15 years) with KD were evaluated at a mean of 49 ± 16 months after surgical treatment that included primary repair and suture augmentation. Magnetic resonance imaging, stress radiographs, and outcome scores were obtained at the follow-up. Clinical examination including hop tests and force measurements for flexion and extension was performed. The mean difference in pre- to postinjury Tegner scores was -2 ± 1. The outcome scores showed mean values of 84 ± 15 (Lysholm), 73 ± 15 (International Knee Documentation Committee) and 65 ± 25 (Anterior Cruciate Ligament-Return to Sport after Injury scale). Compared with the uninjured knee, the range of motion of the injured knee was reduced by 21° ± 12°. Twelve patients felt fit enough to perform hop tests and showed a mean deficit of 7% ± 17%° compared with the uninjured leg. The mean force deficit was 19% ± 18% for extension and 8% ± 16% for flexion. Stress radiographs revealed an 11 ± 7-mm higher anteroposterior translation on the injured side. Four patients had secondary ligament reconstructions due to persistent instability and 7 underwent arthroscopic arthrolysis due to stiffness. A significant increase of osteoarthritis was found for the medial, lateral, and patellofemoral compartments (P = .007, .004, and .006, respectively). Primary repair and suture augmentation of KD led to satisfactory clinical midterm results despite persistent radiological instability and a significant increase in osteoarthritis. This technique allows the return to activities of daily living without subjective instability in most nonathletic patients. Secondary ligament reconstructions should be performed if relevant instability persists to decrease the risk of secondary meniscal and cartilage damage.

Winter sports injuries to the elbow joint

Elbow injuries occur quite often when practicing winter sports. Due to the high sports dynamics and risk of fall the elbow joint is prone to injuries. Hereby, the most common injury is the dislocation of the elbow. Isolated ligamentous instabilities can usually be treated non-operatively when the joint is centered on post-reduction imaging. In the case of persistent symptomatic instability, secondary ligament reconstruction surgery is associated with reliable and good results. Most fractures of the elbow involve the radial head in terms of postero-lateral rotation instability, whereas distal humerus and olecranon fractures are more likely to occur in high-energy or direct trauma. Indication for surgical treatment is given according to common guidelines, including involvement of the joint line, fragment dislocation and instability with risk of secondary fracture dislocation. Minimally invasive techniques for the radial head as well as anatomic preformed locking plate systems seem to have reached a wide acceptance.

Arthroscopic thermal stabilization for distal radioulnar joint instability: 3 to 19 years follow-up.

This retrospective study investigated the clinical outcomes of patients treated for chronic distal radioulnar joint instability with arthroscopic thermal annealing of the superficial radioulnar ligaments, ulnar palmar wrist ligaments, and dorsoulnar wrist capsule using a radiofrequency probe. Sixty patients (62 wrists) were treated over an 18-year period. At mean follow-up of 10 years (range 3 to 19), 30 of 33 patients were satisfied with their surgical outcomes. There were statistically significant improvements in ulnar-sided wrist pain on a visual analogue scale and in distal radioulnar joint stability on the dorsopalmar stress test after surgery compared with preoperative status. The modified Mayo Wrist Score and Quick Disabilities of the Arm, Shoulder, and Hand score of the patients were favourable. Early failure occurred in 11 of 62 wrists. Nine of these 11 wrists needed a secondary procedure. We conclude that arthroscopic thermal shrinkage is effective for the majority of the patients with mild to moderate chronic distal radioulnar joint instability in long-term follow-up. Secondary open ligament reconstruction is an option in the case of early failure.Level of evidence: IV.

Engagement of the Secondary Ligamentous and Meniscal Restraints Relative to the Anterior Cruciate Ligament Predicts Anterior Knee Laxity

Background: Patients with high-grade preoperative side-to-side differences in anterior laxity as assessed via the Lachman test after unilateral anterior cruciate ligament (ACL) rupture are at heightened risk of early ACL graft failure. Biomechanical factors that predict preoperative side-to-side differences in anterior laxity are poorly understood. Purpose: To assess, in a cadaveric model, whether the increase in anterior laxity caused by sectioning the ACL (a surrogate for preoperative side-to-side differences in anterior laxity) during a simulated Lachman test is associated with two biomechanical factors: (1) the tibial translation at which the secondary anterior stabilizers, including the remaining ligaments and the menisci, begin to carry force, or engage, relative to that of the ACL or (2) the forces carried by the ACL and secondary stabilizers at the peak applied anterior load. Study Design: Controlled laboratory study. Methods: Seventeen fresh-frozen human cadaveric knees underwent Lachman tests simulated through a robotic manipulator with the ACL intact and sectioned. The net forces carried by the ACL and secondary soft tissue stabilizers (the medial meniscus and all remaining ligaments, measured as a whole) were characterized as a function of anterior tibial translation. The engagement points of the ACL (with the ACL intact) and each secondary stabilizer (with the ACL sectioned) were defined as the anterior translation at which they began to carry force, or engaged, during a simulated Lachman test. Then, the relative engagement point of each secondary stabilizer was defined as the difference between the engagement point of each secondary stabilizer and that of the ACL. Linear regressions were performed to test each association (P < .05). Results: The increase in anterior laxity caused by ACL sectioning was associated with increased relative engagement points of both the secondary ligaments (β = 0.87; P < .001; R2 = 0.75) and the medial meniscus (β = 0.66; P < .001; R2 = 0.58). Smaller changes in anterior laxity were also associated with increased in situ medial meniscal force at the peak applied load when the ACL was intact (β = −0.06; P < .001; R2 = 0.53). Conclusion: The secondary ligaments and the medial meniscus require greater anterior tibial translation to engage (ie, begin to carry force) relative to the ACL in knees with greater changes in anterior laxity after ACL sectioning. Moreover, with the ACL intact, the medial meniscus carries more force in knees with smaller changes in anterior laxity after ACL sectioning. Clinical Relevance: Relative tissue engagement is a new biomechanical measure to characterize in situ function of the ligaments and menisci. This measure may aid in developing more personalized surgical approaches to reduce high rates of ACL graft revision in patients with high-grade laxity.

Less gap imbalance with restricted kinematic alignment than with mechanically aligned total knee arthroplasty: simulations on 3-D bone models created from CT-scans

Background and purpose — Mechanical alignment techniques for total knee arthroplasty (TKA) introduce significant anatomic alteration and secondary ligament imbalances. We propose a restricted kinematic alignment (rKA) protocol to minimize these issues and improve TKA clinical outcomes.Patients and methods — rKA tibial and femoral bone resections were simulated on 1,000 knee CT scans from a database of patients undergoing TKA. rKA was defined by the following criteria: independent tibial and femoral cuts within 5° of the bone neutral mechanical axis, with a resulting HKA within 3° of neutral. Imbalances in the extension space, flexion space at 90°, medial compartment and lateral compartment were calculated and compared with measured resection mechanical alignment (MA) results. 2 MA techniques were simulated for rotation using the surgical transepicondylar axis (TEA) and 3° to the posterior condyles (PC).Results — Extension space imbalances ≥ 3 mm occurred in 33% of TKAs with MA technique versus 8.3% with rKA (p < 0.001). Similarly, more frequent flexion space imbalance ≥ 3mm was created by MA technique (TEA 34% or 3° PC 15%) versus rKA (6.4%, p < 0.001). Using MA with TEA or PC, there were only 49% and 63% of the knees respectively with < 3 mm of imbalance throughout the extension and flexion spaces and medial and lateral compartments versus 92% using rKA (p < 0.001).Interpretation — significantly fewer imbalances are created using rKA versus MA for TKA. rKA may be the best compromise, by helping the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range.

Reconstruction of chronic scapholunate dissociation with the modified scapholunate axis method (SLAM).

Injury to the scapholunate (SL) ligament represents a common trauma of the wrist but is frequently misdiagnosed because of non-specific pain. Established methods for SL reconstruction mainly focus on reducing pain and maintaining the reposition result at the expense of mobility and strength. This study aimed at restoring stability and reducing pain while simultaneously maintaining mobility and strength using the scapholunate axis method (SLAM). 22 patients (19 male and 3 female) aged between 26 and 64years with an SL ligament lesion underwent SLAM reconstruction. Mean duration between injury and operation was 7.9 ± 5 (1-24) months. Hand functions using DASH, Mayo Wrist Score, range of motion, pain (at rest and weight-bearing) and grip strength were assessed prior and 12months postoperative. Additionally SL angle was collected pre- and postoperative. Each of the 22 patients improved significantly postoperative in DASH and Mayo Wrist Score with regard to pain at rest and under weight-bearing. Additionally, grip strength could be improved up to 31% compared to preoperatively. In contrast, range of motion and SL angle and grip strength did not change essentially. The secondary SL ligament reconstruction technique SLAM shows promising results. Pain was significantly relieved and grip strength was significantly increased. Additionally, DASH and Mayo Wrist Score could be significantly improved. However, SL angle and range of motion could not be improved in every patient and plane.

PH-Controlled Dealloying Route to Hierarchical Bulk Nanoporous Zn Derived from Metastable Alloy for Hydrogen Generation by Hydrolysis of Zn in Neutral Water

Dealloyed nanoporous metals made of very-reactive elements have rarely been reported. Instead, reactive materials are used as sacrificial components in dealloying. The high chemical reactivity of nonprecious nanostructured metals makes them suitable for a broad range of applications such as splitting water into H2 gas and metal hydroxide. On the other hand, the same high chemical reactivity hinders the synthesis of nanostructured metals. Here we use a pH-controlled dealloying strategy to fabricate bulk nanoporous Zn with bulk dimensions in the centimeter range via the selective removal of Al from metastable face-centered cubic bulk Zn20Al80 at. % parent alloys. The corresponding bulk nanoporous Zn exhibits a hierarchical ligament/pore architecture characterized by primary ligaments and pores with an average feature size in the submicrometer range. These primary structures are made of ultrafine secondary ligaments and pores with a characteristic feature size in the range of 10–20 nm. Our bulk nanoporous Zn can split water into H2 and Zn(OH)2 at ambient temperature and pressure and continuously produce H2 at a constant rate of 0.08 mL/min per gram of Zn over 8 h. We anticipate that in this hierarchical bulk architecture, the macropores facilitate the flow of water in the bulk of the material, while the mesopores and ultrafine ligaments provide a high surface area for the reaction of water with Zn. The bulk nanoporous Zn/water system can be used for on-board or on-demand H2 applications, during which H2 is produced when needed, without prior storage of this gas compressed in cylinders as it is currently the case.

Anatomic double-bundle reconstruction with free tendon graft for chronic ulnar instability of the thumb metacarpophalangeal joint.

Failed primary treatment of thumb metacarpophalangeal ligament injuries may lead to chronic instability. Different treatments have been described such as secondary ligament suture, fusion, dynamic or static procedures. Techniques to restrain the joint stability with various grafts of different configurations have been published, but most of these address only the proper collateral ligament. Experimental data revealed the importance of the accessory collateral ligament in stabilizing the metacarpophalangeal joint. In a former, true anatomic ligament reconstruction a bone-tendon graft was used; the tendon was split longitudinally to reconstruct both parts of the collateral ligament. This technique was modified by the author: a resorbable interference screw was used to fix a free tendon graft double in the metacarpal head, creating 2 identical bundles for reconstruction of both the proper and the accessory collateral ligament. The results of the first 10 patients with chronic ulnar instability in their otherwise intact thumb are reported. The mean follow-up was 15 months. Eight patients had excellent result and 2 patients had good result according to the Glickel grading system. The mean loss of motion in the metacarpophalengeal joint was 9% and the mean loss of pinch strength was 9% compared with the contralateral thumb. The technical details, pitfalls, complications, and rehabilitation are described in this paper.

Clinical and radiological outcomes after management of traumatic knee dislocation by open single stage complete reconstruction/repair

BackgroundThe purpose of our study was to analyze the clinical and radiological long-term outcomes of surgically treated traumatic knee dislocations and determine prognostic factors for outcome.MethodsRetrospective consecutive series of patients treated surgically for traumatic knee dislocation with reconstruction/refixation of the anterior (ACL) and posterior cruciate ligaments (PCL) and primary complete repair of collaterals and posteromedial and posteromedial corner structures. 68 patients were evaluated clinically (IKDC score, SF36 health survey, Lysholm score, Knee Society score, Tegner score, visual analogue scale - VAS pain and satisfaction, Cooper test) and radiologically (weight bearing and stress radiographs) with a mean follow up of 12 ± 8 years. Instrumented anterior-posterior translation was measured (Rolimeter, KT-1000). Pearson correlation and stepwise regression analysis was used.Results82% of patients (n = 56) returned to their previous work. At final follow-up 6 patients (9%) suffered from pain VAS > 3. The mean side-to-side difference of anterior/posterior translation (KT-1000, 134N) was 1.6 ± 1.6 mm and 2.6 ± 1.4 mm. Valgus and varus stress testing in 30° flexion was <3 mm (normal) in 57 patients (86%). The IKDC score was normal/nearly normal in 38 (58%) patients and the mean Lysholm score 83 ± 17 (intact 98 ± 7). The median Tegner score decreased from 7 preinjury (range 3-10) to 5 at follow-up (range 0-10). The mean Knee Society score was 187 ± 15 (out of maximum 200). In 7 patients (10%) a secondary ligament reconstruction was performed. Three patients (4%) underwent a high tibial osteotomy and four (6%) received a primary unconstrained total knee replacement. According to the Kellgren Lawrence osteoarthritis score only mild degenerative changes were present. The stress radiographs showed stable results for anteroposterior translation. Injury of the lateral collateral ligament, refixation of the ACL/PCL and delayed surgery >40 days were significantly associated with worse outcome (p < 0.05).ConclusionsEarly complete reconstruction can achieve good functional results and patient satisfaction with overall restoration of sports and working capacity. Negative predictive factors for outcome were injury pattern, type of surgical procedure and timing of surgery.

Vascular lesions associated with bicruciate and knee dislocation ligamentous injury

The incidence of associated vascular lesions in biligamentous cruciate injuries of the knee ranges from 16 to 64%, with a mean rate of 30%. Treatment of ischemic vascular lesions associated with ligaments injury is well established, comprising emergency arterial vascular repair, most of the times combined to external fixation. In the absence of clinical symptoms of vascular lesion, some authors recommend systematically performing arteriography, while others advocate selectively prescribing this examination in doubtful clinical situations. The present study analyzed data extracted from the prospective series of the 2008 SOFCOT Symposium (dedicated to management of bicruciate knee lesions) and from an analysis of the literature, with emphasis on developing a diagnostic strategy for vascular lesions associated with bicruciate lesions. This multicenter prospective study included all patients treated in the reference centers for dislocation or bicruciate lesion of the knee between January 2007 and January 2008. All patients underwent early objective vascular imaging. Sixty-seven patients were included. Mean dislocation reduction time was 2 hrs 45 min (max, 21 hrs). There were nine vascular lesions (12%). Absence of vascular lesion could be confirmed in 58 of the 59 patients exhibiting presence of peripheral pulses at initial examination. In one case, a vascular lesion was found on early imaging, but with no clinical consequence. In all eight cases with associated clinical pulse abnormality, complementary vascular check-up confirmed the presence of a vascular lesion. Angioscan induced no error of vascular assessment in this series, with no false positives or false negatives. One patient underwent amputation for critical ischemia. Three patients had vascular surgical treatment, two not undergoing secondary ligament surgery. Four of the five patients whose vascular lesion was conservatively managed by simple observation were able to undergo the scheduled treatment for their ligament lesions. At initial examination, it is essential to look for the peripheral pulse. In case of ischemic syndrome, the priority is a revascularization procedure associated to intraoperative arteriography. In case of abnormal pulse without obvious ischemia, emergency imaging (usually arteriogram or angioscan) is essential. Where there is no initial clinical vascular abnormality, good practice is less clearly cut. Initially, present pulses are found in a mean 30% (17-55%) of cases of popliteal artery lesion, according to the series. Different authors draw diverging conclusions from this fact. For some, the absence of frank abnormality on clinical examination is sufficient to exclude not any possible anatomic vascular lesion but any vascular lesion requiring surgery. However, even without pulse abnormality, we consider systematic imaging to be justified, partly by the difficulty of ensuring strict monitoring, and partly by the decompensation risk of clinically asymptomatic intimal lesions during the ligament surgery under consideration in most cases. Although many authors cling to the dogma of late emergency arteriography, recent reports argue against this attitude. Angio-MRI has good diagnostic value, but in practice is difficult to obtain in emergency. We would rather advocate angioscanning, which is easily available in emergency and does not incur the risk of local complication associated with arteriography.

Knee Dislocation With Ipsilateral Femoral Shaft Fracture

We report the management and outcome of 4 patients with 5 knee dislocations associated with ipsilateral femoral shaft fractures. All patients were managed by immediate reduction of the knee dislocation, intramedullary nailing of the femur, and angiography, followed by postoperative immobilization of the knee (brace or external fixation) for a minimum of 6 weeks. Four of the 5 dislocations underwent a secondary ligament reconstruction. At the 2-year follow up, the mean Knee Society Score was 133 (range 99-170).

Revision anterior cruciate surgery with use of bone-patellar tendon-bone autogenous grafts.

A prospective study was done to determine the functional results, patient satisfaction, and graft failure rate after fifty-seven consecutive revision replacements of the anterior cruciate ligament with use of a bone-patellar tendon-bone autogenous graft. Fifty-four patients (fifty-five operations) were followed in this study. Concurrent operative procedures were performed during the revision procedure in thirty-seven knees (67%). These procedures included repair of a meniscal tear in twenty knees (36%) and reconstruction of deficient posterolateral or medial ligament structures in seventeen knees (31%). Nine knees (16%) had a high tibial osteotomy to correct varus malalignment before the revision operation. The results were evaluated with the Cincinnati Knee Rating System. There were significant improvements in the scores for pain (p < 0.0001), activities of daily living (p < 0.01), sports participation (p < 0.001), patient satisfaction (p < 0.0001), and overall rating of the knee (p < 0.0001). Thirty-three (60%) of the replaced ligaments were functional, nine (16%) were partially functional, and thirteen (24%) had failed. Many knees (93%) had compounding problems, including articular cartilage damage, prior meniscectomy, loss of secondary ligament restraints, varus malalignment, and concomitant ligament replacement or meniscal repair. Therefore, the results were generally less favorable than those following primary operations. The rate of graft failure was three times higher than our previously reported failure rate after primary replacements of the anterior cruciate ligament with a bone-patellar tendon-bone autogenous graft. Even so, symptoms and functional limitations with regard to daily and sports activities were found to have decreased and patient satisfaction improved. We advocate correction of varus malalignment prior to anterior cruciate procedures. Associated posterolateral ligament deficiencies should be surgically corrected during anterior cruciate procedures to prevent excessive loading on the graft from abnormal lateral tibiofemoral joint opening. Meniscal tears, including complex tears that extend into the avascular zone, can be concurrently repaired successfully during the revision.

Modifizierte Seitenbandplastik mit der Sehne des M. abductor pollicis brevis zur Behandlung der chronischen radialen Instabilität des Daumengrundgelenkes

Injuries to the radial collateral ligament of the MP joint of the thumb occur much less frequently than injuries to the ulnar collateral ligament. Ligament injury is usually a result of direct trauma. The resultant instability to the thumb usually impairs hand function. In acute lesions to the radial collateral ligament, direct repair is often possible. In cases of chronic radial joint instability, secondary ligament reconstruction with a free tendon graft, most commonly the palmaris longus tendon, is usually recommended. We describe another technique using the tendon insertion of the abductor pollicis brevis muscle. The tendon inserting distally can be used as a stable ligament after dividing it at the border to the muscle and attaching it to the head of the metacarpal bone with a wire. The follow-up for six patients treated by this method showed good and painless stability and function of the thumb in a time span of one year.

Taxonomy and phylogeny of cementing Triassic bivalves (families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae)

Based on new material from the Upper Triassic Nayband Formation of east‐central Iran and on type material from the Alpine Triassic, the taxonomy of the cementing bivalve families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae is examined and their phylogenetic relations are discussed. The Prospondylidae are characterized by the presence of an early pectiniform stage in their Palaeozoic genera which disappeared in most later forms due to ontogenetic pre‐displacement of cementation. The Plicatulidae probably evolved from an ancestor within the Prospondylidae by the formation of strong crura, which allowed the reduction of the lateral part of the ligament. Their hinge was later modified by shifting resilifer and crura in a ventral direction and by forming a secondary ligament dorsally. The emended genera EoplicatulaPseudoplacunopsis represent different early stages of this development. The species Eoplicatula parvadehensis sp. nov. and Pseudoplacunopsis asymmetrica sp. nov. from the Nayband Formation are described. The shell of some early Ostreidae is characterized by the lack of structural chambers and by the presence of an originally aragonitic inner shell layer. For such forms, the new genus Umbrostrea is proposed, and the new species Umbrostrea emamiiUmbrostrea iranica are described. The available data on shell microstructure as well as most conchological characters do not support a close relationship between Ostreidae, Plicatulidae and Dimyidae.

Scapholunate instability

Injuries to the scapholunate joint are the most frequent cause of carpal instability and account for a considerable degree of wrist dysfunction and lost time from work and activities. The complex arrangement and kinematics of the 2 rows of carpal bones allows for an enormous degree of physiologic motion, and a hierarchy of primary and secondary ligaments serve to balance an inherently unstable structure. Although insufficient to cause abnormal carpal posture or collapse on static radiographs, an isolated injury to the scapholunate interosseous ligament may be the harbinger of a relentless progression to abnormal joint mechanics, cartilage wear, and degenerative change. Once disrupted, ligament repair methods and reconstructive options seldom serve to restore this delicately balanced design. Treatment options are predicated on the stage of injury, degree of secondary ligamentous damage, and arthritic change. Copyright © 2001 by the American Society for Surgery of the Hand

BROODING AND NON-BROODING DACRYDIUM (BIVALVIA: MYTILIDAE): A REVIEW OF THE ATLANTIC SPECIES

The Atlantic species of the marine bivalve genus Dacrydium are reviewed, with particular emphasis on their hinge and protoconch characters. The basic groundplan of a Dacrydium comprises a functional primary ligament, a paired series of primary teeth, and a posterior row of secondary teeth separated from the latter by a secondary ligament; this can be transformed into a single series either by loss of the secondary ligament and merging primary and secondary teeth, or by loss of secondary teeth and ligament through paedomorphosis.Twelve species are recognized, of which eleven are illustrated. One abyssal species is not separable morphologically from the Indian Ocean D. speculum Poutiers, 1989 and is new to the Atlantic; four new species (D. wareni, D. dauvini, D. filiferum and D. balgimi) are described; a Caribbean form which is hardly distinct from the Eastern Pacific D. elegantu-lum Soot-Ryen, 1955, is described as a new subspecies D. e. hendersoni.The larvae are brooded in D. hyalinum (Mon-terosato, 1875), D. viviparum Ockelmann, 1983 and D. balgimi. The brooding species have larger larvae (protoconch 210 to 315 μm long) than the non-brooding (protoconch 120 to 150 μm long), and reach a smaller adult size (1.4 to 3 mm instead of 4.5–5 mm). A phylogenetic reconstruction is attempted using parsimony analysis of hinge and shell characters as well as the brooding/non brooding character.

Descriptions of mytilid species and definition of the Dacrydiinae n. subfam. (Mytilacea-Bivalvia)

Abstract Ten mytilid species are described as new, viz. Modiolus (Modiolus?) nicklesi (tropical W. Africa), M. (M.) pseudobarbatus (tropical W. Africa), M. (M.) thorsoni (tropical W. Africa), Musculus (Musculus) koreanus (Sea of Japan), Rhomboidella obesa (tropical W. Africa), R. malaccana (W. coast of Thailand), Xenostrobus mangle (W. coast of Malaysia), X. balani (W. coast of Thailand), Dacrydium angulare (S. Atlantic), and D. viviparum (Reykjanes Ridge). The latter species has suprabranchial protection of embryos as does the Mediterranean D. hyalinum (Monterosato). Modiolus lulat (Dautzenberg, 1891) is regarded synonymous with M. martorelli (Hidalgo, 1877), and Vignadula Kuroda & Habe, 1971, with Xenostrobus Wilson, 1967. — The descriptions include anatomical and biological notes for several of the species. — The so-called ‘periostracal’ hairs of mytilids are concluded to be secretions of byssus glands, shaped and applied to the shell exterior by the foot of these bivalves. — It is pointed out that the opisthodetic, parivincular ligament of mytilids is separate and secondary in ontogeny. — Species of the Dacrydiinae n. subfam. are characterized by a non-nacreous shell which is homologous with the nepioconch of other mytilids, by functional persistence of the primary ligament and absence or ontogenetically late formation of a weak secondary ligament, by simplification and, in part, reduction of the soft parts. They are thus neoteneous in several respects. The group is briefly discussed and a survey of taxobases is given.

The biology and functional morphology of Periploma (Offadesma) angasai (Bivalvia: Anomaiodesmata: Periplomatidae

The extremely rare Periploma (Offadesma) angasai Crosse &amp; Fisher 1864 is a member of the widely distributed Periplomatidae (Anomalodesmata) occurring on surf‐protected beaches in New Zealand and Australia. The species is low intertidal‐sublittoral in distribution, living 7–8 cm below the sand surface on its left valve with separate siphons projecting to the sand‐water interface above. The shell is sharply inequivalve (the right deeply, the left shallowly convex) and inequilateral, the posterior rostrate and truncate and covered by thick periostracum densely studded with sand grains. These are attached to the periostracum by a sticky secretion produced from radial mantle glands in the middle mantle fold. Similar glands have been reported for members of the Lyonsiidae and Verticordiidae. Offadesma angasai is adapted for a life in which large amounts of fine sediment may enter the mantle cavity. Thus the ciliary rejection currents are powerful, the labial palps are extremely long and the sediments are bound up in mucus produced by an extensive gland, particularly in the right mantle lobe, in the posterior region of the mantle cavity. A gland with a similar structure but different staining reactions also lines the visceral mass and the mantle of the supra‐branchial chamber and probably consolidates particles penetrating the ctenidial filter. Such glands are similar in structure and function to the primitive molluscan hypo‐branchial gland.In many respects, especially with regard to the secondary ligament of fused periostracum, a ctenidial structure with type E ciliation, the presence of a 4th pallial aperture, extensive mantle fusions and simultaneous hermaphroditism, Offadesma is clearly similar to the majority of the Anomalodesmata. As in many other anomalodesmatans also, large, yolky, encapsulated eggs are produced; these are thought to be an adaptation facilitating survival by a sparsely distributed species occupying a narrow niche.Many other features of Offadesma, notably the structure of the ligament and shell clearlyally it and the Periplomatidae with the Laternulidae and the Thraciidae in a separate line of evolution from the other families of the Pandoracea, and probably deserving of super‐family status—the Thraciacea Stoliczka 1870.