Introduction: The intricate biomechanical function of the alar ligaments in the craniocervical articular complex has received considerable scientific attention. While allowing the greatest range of axial rotation of the entire spine with 40° to each side, definitive restraint at the extremes of motion by the alar ligaments is of vital importance. Detailed knowledge of the function of these ligaments is essential for comprehending the factors leading to potentially devastating instability.

Methods: Bilateral alar ligaments including the bony entheses were removed from six adult cadavers aged 65–89 years within 48 hours of death. All specimens were judged to be free of abnormalities with the exception of non-specific degenerative changes. Dimensions of the alar ligaments were measured. Schematic multipla-nar reconstruction of axial atlanto-axial rotation was done in the transverse and frontal planes for the neutral position and for rotation to 30° and 40° in the neutral plane to assess schematic fibre elongation during axial rotation and to determine the change in the angle of insertion at the odontoid and condylar entheses. This was repeated with a 1mm descending translation of the occipital condyles at 30° and 3mm descending translation of the occipital condyles at 40° rotation.

Results: The average diameter of the odontoid process measured in the sagittal plane was 10.6 mm (SD 1.1). The longest fibre length was measured from the posterior border of the odontoid enthesis to the posterior border of the condylar enthesis with an average of 13.2 mm (SD 2.5) and the shortest between the lateral (anterior) border odontoid enthesis and the anterior condylar enthesis with an average of 8.2 mm (SD 2.2). Attachment areas of the enthesis revealed an average of 60 mm2 (SD 12.4) for the odontoid and 50,6 mm2 (SD12.6) for the condylar enthesis. Schematic fibre elongation reaches 27,1% for the longest fibres at 40° axial rotation. This is reducible to 7,8% elongation by 3mm caudal translation of the atlas.

Conclusions: This theoretical model confirms that the bi-convex shape of atlanto-axial joint allows for rotation when modelled with oblique alar ligaments. This provides baseline for further research with functional MRI which will be useful for rheumatoid and post traumatic spine.

Purpose: A fibrous element between the radial capitulum and the fovea is classically described; it is often called a synovial fringe. The term “meniscus” has been proposed to designate a truly rigid peripheral structure partially inter-postioned between the joint surfaces and susceptible of producing joint disease by internal disregulation of repeated pronation supination movements. This led us to study the anatomic and histological properties of this intra-articular structure.

Material and methods: Fifty adult cadaver shoulders were dissected. The en bloc resection included the capsule of the humeroradial joint and the entire annular ligament. We searched for a fibrous structure, noting its soft or rigid aspect, its position relative to the five-part segmentation of the capsuloligament resection, and its size and thickness. Vertical sections were made for the histology study to determine the organized connective tissue or synovial nature of the structure.

Results: An intra-articular element was visible in 43 cases, two structures were observed in two cases, on the deep aspect of the junction between the capsule and the annular ligament. The main positions observed were: circular (n=3), lateral and posterior (n = 11), posterior (n = 10). The anterior (n = 4), or lateral (n = 5) positions were rare. Mean length was 21.4 mm (9–51), mean width between the capsular attachment and the free edge was 2.9 mm (1–10), maxiam mean thickness was 1.7 mm (1–4 mm). The histology report showed two types of structures: a rigid structure with an oriented fibrous armature that had a triangular peripheral base continuous with the superior border of the annular ligament and covered with synovial on both sides of the free edge; a soft flexible structure formed uniquely by two layers of synovial and a more or less villous free edge. Fibrochondroid structures of the meniscal type were not observed. Small nerve fibers were demonstrated in some cases.

Discussion: Certain lateral epiconylalgias of the elbow would suggest involvement of the humeroradial joint, possibly related to injury of the humeoradial “mensiscus”. This study points out the frequency of this synovial or fiborsynovial fringe of variable dimensionts interpose between the radial capitulum and fovea. The structure has a more or less marked connective armature, basically in the lateral and posterior portion, and correctly cannot be termed a “meniscus”. This structure might be involved in inflammatory and painful syndromes observed in epicondylalgias of the humeroradial joint.

Hypertrophy of lumbar articular facets and dorsal joint capsule are well documented in degenerative instability, the molecular changes occurring in the extracellular matrix (ECM) are however unknown.

The L4/L5 posterior articular complex was removed from seven individuals undergoing fusion for degenerative instability. After methanol fixation and decalcification in EDTA, specimens were cryosectioned at 12 μm and immunolabelled with monoclonal antibodies for collagen types I, II, III, V and VI; chondroitin-4 and 6 sulphates; dermatan and keratan sulphate; versican, tenascin, aggrecan and link-protein. Antibody binding was detected using the Vectastain ABC ‘Elite’ kit. Labelling patterns were compared to corresponding healthy specimens examined previously.

In comparison, the degenerative capsule was more dense and hypertrophied and the enthesis more fibrocartilaginous, with immunolabelling extensive for collagen type II, chondroitin–6-sulfate, chondroitin-4-sulfate, aggrecan and link-protein. The articular surface showed extensive evidence of degeneration, while the thickened capsular entheses encircled the articular facets dorsally. Bony spurs capped with regions of cartilaginous metaplasia were prominent in this region, the ECM labelling strongly for type II collagen and chondroitin-6-sulfate.

The hypertrophy of lumbar facet joints subject to instability of the functional spinal unit therefore appears to be due to proliferation of the capsular enthesis rather than the actual articular facet. In view of the physiological function of the dorsal joint capsule as a wrap-around ligament in assisting the limitation of axial rotation, the molecular changes found in degenerative instability suggest rotational instability, such as results from degenerative disc disease, to be a decisive factor in the development of spondylarthropathy. It is furthermore probable, that the pronounced sagittal joint orientation in degenerative instability is the result of reactive joint changes rather than a predisposing factor of instability.

In 16 cadaver humeroulnar joints, the distribution of subchondral mineralisation was assessed by CT osteoabsorptiometry and the position and size of the contact areas by polyether casting under loads of 10 N to 1280 N. Ulnas with separate olecranon and coronoid cartilaginous surfaces showed matching bicentric patterns of mineralisation. Under small loads there were separate contact areas on the olecranon and coronoid surfaces; these areas merged centrally as the load increased. They occupied as little as 9% of the total articular surface at 10 N and up to 73% at 1280 N. Ulnas with continuous cartilaginous surfaces also had density patterns with two maxima but those were less prominent, and in these specimens the separate contact areas merged at lower loads. The findings indicate a physiological incongruity of the articular surfaces which may serve to optimise the distribution of stress.