Damage to and repair of the acetabular labral-chondral complex are areas of clinical interest in the treatment of young adults with pain in the hip and in the prevention of degenerative arthritis of the hip. There are varying theories as to why most acetabular tears are located anterosuperiorly. We have studied the prenatal development of the human acetabular labral-chondral complex in 11 fetal hips, aged from eight weeks of gestation to term.

There were consistent differences between the anterior and posterior acetabular labral-chondral complex throughout all ages of gestation. The anterior labrum had a somewhat marginal attachment to the acetabular cartilage with an intra-articular projection. The posterior labrum was attached and continuous with the acetabular cartilage. Anteriorly, the labral-chondral transition zone was sharp and abrupt, but posteriorly it was gradual and interdigitated. The collagen fibres of the anterior labrum were arranged parallel to the labral-chondral junction, but at the posterior labrum they were aligned perpendicular to the junction.

We believe that in the anterior labrum the marginal attachment and the orientation of the collagen fibres parallel to the labral-chondral junction may render it more prone to damage than the posterior labrum in which the collagen fibres are anchored in the acetabular cartilage. The anterior intra-articular projection of the labrum should not be considered to be a pathological feature.

The purpose of this study was to clarify the effect of delay of the reattachment of the supraspinatus tendon into a bony trough to the strength of the repaired tendon-bone complex. The supraspinatus tendon of rabbits were transected and reattached into bony troughs at the greater tuberosity immediately and six weeks after transection. The tensile strength of the tendon-bone complex, harvested twelve weeks after reattachment, were measured.

The tensile strength showed no difference between immediate and delayed reattached shoulders. Six weeks delay of supraspinatus tendon repair seems not to weaken the tensile strength of repaired tendon-bone complex.

The purpose of this study was to clarify the effect of timing of surgery on the strength of the supraspinatus tendon-bone complex after the reimplantation of the tendon into a bony trough.

In eight rabbits, the supraspinatus tendon was transected and reinserted into a bony trough at the greater tuberosity (early reattachment group). In seven rabbits, the supraspinatus tendon was reinserted six weeks after transection (delayed reattachment group). In both groups, the rabbits were sacrificed twelve weeks after reattachment, and the tensile strength of the tendon-bone complex was measured. The contralateral shoulders served as controls.

None of the operated tendons failed at the site of reimplantation. The ratio of tensile strength of the operated tendon-bone complex to the controls showed no difference between two groups (Immediate reattachment group: 79.9± 1 S.E. 16.5%, delayed reattachment group: 80.4± 12.6%, P> 0.05).

This is the first experimental study to compare the tensile strength of supraspinatus tendon-bone complex repaired after different time intervals.

Stress-shielded tendon & bone tend to decrease their tensile strength. Given the six weeks duration of detachment, a weaker tensile strength of delayed reattachment group was expected than of the early reattachment group. The fact that both groups did not show a difference might be due to the recovery of tensile strength of tendon & bone in twelve weeks after reattachment.

Six weeks delay of repair of supraspinatus tendon does not weaken the tensile strength of repaired tendon-bone complex.

Fundings This study has been supported in part by a grant from the American Shoulder and Elbow Surgeons.

Aims: The purpose of this in-vitro study is to understand the mechanical behaviour of a fracture plate incorporating biodegradable inserts. Methods: A new, innovative fracture plate design incorporating biodegradable inserts was tested. These plates allow for micromotion during the union phase, which allows for increased healing. Resorption of the inserts over time works to decrease stress shielding during the remodelling phase. Two separate bone models were used to simulate a fracture during both the union phase of healing and the remodelling phase. This plate, termed an axially compressible plate (ACP) was mounted to the bone models in four different conþgurations. On the model simulating the union phase, stiffness and micromotion were measured using an LVDT for bending and an extensometer for compression. With the model simulating the remodelling phase, strain was measured on the bone model using a strain gage mounted directly below the plate midpoint.

Conclusions: The results show that during the union phase, the ACP should allow for micromotion, which increases with successive loss of inserts. Results also show that during the remodelling phase, the loss of inserts increases the amount of strain in bone and thus decreases stress shielding.

We studied 16 club feet and 27 normal feet from spontaneously aborted human fetuses in the second trimester of gestation and measured the length of the spring ligament, and the declination angle and size of the talus. We also studied the cellular characteristics of the spring ligament and the immunohistochemical features of the medial ankle ligaments using monoclonal antibodies against type-III collagen, desmin, vimentin, and smooth muscle actin. Histomorphometric results indicated that the talar deformity was not the primary lesion. Histological and immunohistochemical findings showed that the cells and collagen fibres of the medial ankle ligaments of club feet appeared to be the site of the earliest changes, in that they had lost their spatial orientation and had contracted. In severe club feet before the third trimester of gestation, myofibroblast-like cells seemed to create a disorder of the ligaments resembling fibromatosis. This led to contraction and resulted in typical club-foot deformity.

Serial sections, in the frontal plane, of 12 human fetuses showed that the iliolumbar ligament was always present at the gestational age of 11 to 15 weeks; in younger specimens, it could not be identified. The ligament develops during the prenatal period and is not formed by metaplasia of the quadratus lumborum muscle during the second decade of life.

We examined biopsy specimens obtained during surgery on 115 patients with complete rotator cuff rupture. The vascularised connective tissue covering the area of rupture and the proliferating cells in the fragmented tendons reflected more of the features of repair than of degeneration and necrosis. The main source of this fibrovascular tissue was the wall of the subacromial bursa. These features clearly indicated a vigorous reparative response which might play an important role in tendon reconstitution and remodelling. We therefore suggest that extensive debridement along with subtotal bursectomy, commonly practised during surgical repair of rotator cuff rupture, should be avoided. Although strong suture margins are essential for good operative results, debridement should be judicious and preserve as much as possible of the bursa and the associated fibrovascular tissue.

We describe a new method for the accurate measurement of the angle of anteversion of an acetabular cup from standard anteroposterior radiographs, and provide the conversion tables required. The effect of the centering of the radiograph is discussed and a method of distinguishing between anteversion and retroversion by using a caudally directed x-ray beam is described.

A study of the attachment of the joint capsule to the scapula, and of the shape of the humeral head, has been carried out in 52 fetal and embryonic shoulders. In 77% of cases the anterior capsule was attached to the labrum or close to it; in the remaining 23% it was inserted into the neck of the scapula, so creating a pouch. In all 52 specimens the humeral head was spherical. It was concluded that the pouched and redundant anterior capsule sometimes seen during surgery for recurrent dislocation of the shoulder, may not be traumatic in origin, but could be a developmental variant.

The long-term effect of stainless steel and titanium alloy plates on structural remodelling and bone mass of osteotomised canine femora was studied and the effects of early and late removal of plates were compared in 27 adult Beagles. Radiological, histological, histomorphometric and tetracycline fluorescence studies led to three conclusions. First, the continuous (60 weeks) presence of plates, irrespective of their composition, delays remodelling and leads to a reduction of bone mass. This loss is significantly greater under stainless steel plates. Secondly, the removal of plates at eight weeks leads during the 52 ensuing weeks to a marked and widespread structural remodelling and to a return to normal bone mass, irrespective of the type of plate used. However, remodelling is more intense after titanium alloy plates have been used; it is not complete 60 weeks after osteotomy. Thirdly, removal of plates at 40 weeks activates remodelling during the ensuing 20 weeks to a lesser degree and to a more limited extent than early plate removal. The clinical significance of this study is that less rigid but stable internal fixation permits the radiological assessment of healing and thus the determination of the optimal moment for removal of the plates. It also reduces the degree of bone loss should the plate be left in situ for any reason.

An experimental study is reported of fracture healing in the femora of 36 Beagle dogs, comparing the results of using stainless steel plates with those of using less rigid titanium alloy plates. The alloy plates led to the appearance of a small amount of periosteal callus without any histological evidence of fracture instability, thus allowing the radiological assessment of fracture union. This also produced less bone loss during the remodelling phase. Radiological measurements 24 weeks after osteotomy showed cortical thickness to be reduced by six per cent under titanium alloy and by 19 per cent under stainless steel, while histological measurements showed a total bone loss of 3.7 per cent under titanium alloy and of 11 per cent under stainless steel plates. Removal of the titanium alloy plates after eight weeks followed by a recovery period of 16 weeks produced an increase of cortical thickness of 69 per cent and a gain in total bone mass of 30 per cent. Titanium alloy plates also produced less soft-tissue reaction than stainless steel plates. It is concluded that this alloy is a promising material for internal fixation devices.

The histodynamic response to long-term "non-traumatic" immobilisation was studied in young adult Beagle dogs by means of radiomorphometry and histomorphometry, the right forelimb being encased in plaster and the left forelimb serving as a control. The dogs were killed at two, four, six, eight, twelve, sixteen, twenty, twenty-four, thirty-two and forty weeks and the third metacarpal, radius, ulna and humerus removed for analysis of the contributions of the periosteal, haversian and endosteal envelopes to the bone loss at the mid-diaphysis. The bone mass responded to long-term immobilisation in three stages. First there was a rapid initial loss of bone, reaching its maximum (some 16 per cent of original mass) at six weeks, to which all three bone envelopes, to some extent, contributed. A rapid reversal followed, the bone mass approaching the control values between eight and twelve weeks after immobilisation. A second stage of slower but longer lasting bone loss ended twenty-four to thirty-two weeks after immobilisation; the periosteal envelope was the main contributor (80 to 90 per cent of the total loss). The third stage was characterised by maintenance of the bone mass which had been reduced by some 30 to 50 per cent of original values. This pattern was qualitatively similar in all four bones but the distal bones lost more bone than the proximal bones. The extent of resorption surface and the total histologically "active" periosteal envelope increased parallel to the phases of bone loss. The linear mineralisation rate did not differ significantly between the experimental and control sides.