Early Roentgenological Grading of Femoral Shortening is Correlated to the Late Outcome after Femoral Neck Fractures

Using orthoradiography, the distance between the centre of the femoral head and the intercondylar notch was assessed at regular intervals in 144 patients who were followed for a 2-year period after osteosynthesis of a femoral neck fracture. Late complications, such as segmental collapse and non-union, occurred in 27% of the patients. The degree of femoral shortening was significantly correlated to the incidence of late complications. At 1 month, femoral shortening of more than 5 mm was observed in 85% of patients who developed late complications, and in only 5% of patients without such complications. Thus, the observation of a shortening of more than 5 mm predicted a greater than 6-fold increase of the incidence of late complications. The prognostic accuracy of this observation 1 month after treatment was 92%.

A capsular incision leads to a fast osteoarthritic response, but also elevated levels of activated osteogenic protein-1 in rabbit knee joint cartilage

We studied whether a small capsular incision alone, or combined with meniscectomy could induce early osteoarthritic changes in the rabbit knee. Thirty-one rabbits were operated on with a capsular incision in the left knee and meniscectomy in the right knee. Another 12 rabbits were used as controls. The rabbits were killed 3, 6 and 12 weeks after surgery. Osteoarthritic changes in the articular cartilage were evaluated by the modified Mankin score. The subchondral bone was evaluated by scintimetry ((99m)Tc-HDP) and semiquantitative grading of histological changes. Osteogenic protein (OP-1) in its mature and pro-form was examined by immunohistochemistry. Both a capsular incision and meniscectomy induced articular cartilage fibrillation and increased bone metabolic activity during the initial weeks after surgery. Capsular incision led to lesser changes than meniscectomy. Mature OP-1 was elevated, and its pro-form reduced, in meniscectomized knees. A similar pattern was observed in knees with capsular incision. Already 3 weeks after surgery, the articular cartilage and subchondral bone showed typical signs of early osteoarthritis (OA), and a reparative response was suggested by increased intensity of OP-1 staining. As these signs were also found in knees with capsular incision only, it appears that trauma-related factors such as increased bleeding and inflammation are critical for the development of OA.

TGF-beta1 as a prognostic factor in the process of early osteoarthrosis in the rabbit knee

OBJECTIVE

To assess changes in knee joint fluid concentrations of transforming growth factor-beta1 (TGF-beta1) and proteoglycan (PG) fragments during the early course of post-traumatic osteoarthrosis (OA) after meniscectomy in the rabbit knee, and to ascertain whether the concentrations of these substances shortly after operation could be used as prognostic markers for the OA process.

DESIGN

In 15 rabbits with medial meniscectomy in one knee and a sham operation in the other knee, synovial lavage fluid samples were taken repeatedly, before operation, every third week post-operatively until 12 weeks, thereafter every sixth week, and at death. Five rabbits each were killed at 13, 25 and 40 weeks. Synovial lavage fluid samples from five non-operated rabbits served as controls. At death, two histological scores were formed that characterized the highest (MAX) and the overall (ALL) degree of OA changes in each joint.

RESULTS

TGF-beta1 and PG fragment concentrations in synovial lavage fluid correlated highly (R=0.81, P< 0.001). Both OA scores were higher in meniscectomized than controls (P< 0.05). The synovial lavage fluid concentration of TGF-beta1 at 3 weeks, but no other time point, correlated to the histological scores (ALL, R=0.58; MAX, R=0.52;P< 0.001).

CONCLUSION

Higher concentrations of TGF-beta1 in synovial lavage fluid early after surgery seemed indicative for the later development of more severe OA changes in contrast to lower concentrations. The association between TGF-beta1 and the changes found later in the cartilage was underlined by the high correlations between this substance and PG fragment concentrations in synovial lavage fluid at all time points.

Radiographic joint space narrowing and histologic changes in a rabbit meniscectomy model of early knee osteoarthrosis

The purpose of this study was to compare weightbearing radiographs with histologic cartilage evaluation in a rabbit meniscectomy model of the early stage of osteoarthrosis. Fifteen rabbits had a medial meniscectomy performed in one knee and a sham operation in the other knee. Five rabbits each were sacrificed at 13, 25, and 40 weeks after surgery. Radiographic joint space width and histologic cartilage changes of the medial knee compartment were quantified. Five non-operated knees and five knees in which the meniscus had been removed immediately before the evaluations served as control specimens. Overall, the joint space of the peripheral part of the medial knee compartment was narrower in knees operated on for meniscus removal than in sham-operated knees (P < 0.003). In the knees with the meniscus removed, more cartilage changes were seen at the joint surface area of contact on radiographs than in the sham-operated knees (P < 0.0015). Indeed, the area of contact had cartilage changes similar to those in the whole medial compartment. However, there was no correlation between the degree of histologic cartilage change and the corresponding joint space measurements. Joint space width as measured on weightbearing radiographs is reduced after meniscectomy in the rabbit, but it does not reflect the degree of cartilage damage of the loaded joint surfaces in early stages of osteoarthrosis.

[Injury pattern and overuse stress syndrome in young sport climbers]

The rapidly growing interest in sports climbing in recent years among young climbers raises the question about the risk of injuries and overstrain syndromes in this group. This paper investigates injuries and overstrain syndromes of 99 adolescent climbers aged between 8 and 19 years. The authors interviewed climbers from Austria, Germany and Switzerland. Besides the type and pattern of injuries and overstrain syndromes, the level and duration of climbing, intensity of training and gender were recorded as potential risk factors. 47 climbers were asked about setting up fingers on small holds, which is considered a main reason for epiphyseal injuries of fingers in the literature. Injuries and overstrain syndromes, as well as their frequency and pattern are reported and classified. Descriptive data analysis and statistical models are used to assess the influence of risk factors. Among the potential risk factors only the climbing level has a significant influence on the risk of injuries and overstrain syndromes (p = 0.0427). Furthermore the risk of injuries and overstrain syndromes in the area of the fingers is significantly higher for climbers who reported setting up fingers on small holds (OR = 8.24, p = 0.0022). Finally we found a higher frequency of injuries and overstrain syndromes in lower extremities (43% of all injury and overstrain occurrences) and a lower frequency of injuries and overstrain syndromes in general (43% of all the climbers under investigation) compared to other studies. As a result special guidelines for training and competition are given. In order to increase the accuracy of the reports and to investigate long-term effects we recommend a study with clinical assessment and a longer period of observation.

Simultaneous changes in bone mineral density and articular cartilage in a rabbit meniscectomy model of knee osteoarthrosis

OBJECTIVE

It was hypothesized that increased bone mineral density of the medial proximal tibia would precede or coincide with the development of more severe cartilage changes after meniscectomy.

METHODS

In a rabbit knee model, mineral density of subchondral bone and changes of articular cartilage were monitored 13 to 40 weeks after medial meniscectomy or a sham operation.

RESULTS

Both procedures resulted in a decrease of bone mineral density, especially of the medial proximal tibia, which persisted up to 40 weeks (P< 0.02-0.0007). Meniscectomy induced cartilage changes typical for osteoarthrosis (P< 0.009), which progressed over time on the posterior aspect of the medial tibial plateau (P< 0.009), which is physiologically covered by the meniscus, but the procedure also induced iatrogenic changes which were located mainly on the anterior aspect of the concerned compartment, and which did not progress or develop to osteoarthrosis.

CONCLUSIONS

The data suggest that the cartilage changes after meniscectomy in this animal model are caused by the surgical trauma, subsequent limb misuse, and altered load distribution, and initially associated by a decrease not an increase in bone mineral density of the proximal tibia. Moreover, the cartilage changes progressed without a simultaneous increase of the bone mineral density at corresponding sites.

Long-term results of meniscus repair and meniscectomy: a 13-year functional and radiographic follow-up study

This study investigated the long-term outcome of common meniscus treatment (meniscectomy, repair). A consecutive series of 30 patients with open meniscus repair were compared retrospectively to 30 patients who had an arthroscopic partial or subtotal meniscectomy. The groups were matched according to sex, age, meniscus lesion, and follow-up time. The patients were aged 13-43 years at the time of operation; all had intact cruciate ligaments, and none had had previous surgery on the knee. Patients were reexamined at a mean of 13 years after the operation. In addition, for a subgroup of 22 matched pairs, data were available from a 7-year follow-up. Four of the repaired menisci did not heal, and another three reruptured during the 13-year follow-up; these menisci were all excised (23%). Meniscal remnant surgery was needed in 6 cases (20%) after initial meniscectomy. At the 13-year follow-up there was no difference between the groups in knee function, subjective complaints, or manual findings. Almost 90% of the patients in both groups had no knee problems during daily activities. At the late follow-up radiographic signs for bone spurs, sclerosis, or flattening of the femoral condyle were found in around half of the cases in each group. Three patients (10%) with initial repair and 8 (27%) with meniscectomy had minor joint space reduction, but no patient had more severe radiographic changes. After 7 years (subgroup) joint space reduction was more common after initial meniscectomy than after repair (P < 0.05). After 13 years the incidence and severity of arthrosis did not differ significantly between the two groups, even when only the successful repairs were compared to meniscectomy (P = 0.06).

Estrogen-dependent tensile properties of the rabbit knee medial collateral ligament

The influence of oophorectomy or continuous administration of estradiol on the tensile properties of the rabbit knee medial collateral ligament was investigated. Young postpubertal female New Zealand white rabbits were either oophorectomized or underwent a sham operation. The sham-operated animals received in addition a daily dosage of 4 mg 17beta-estradiol. After 5 months the animals were killed, and the material properties of the bone-ligament-bone complex in one knee were determined using a material testing machine and video system, and compared to non-treated control animals. There was no difference in elastic modulus between the groups. However, the ligaments from low-dose estrogen-treated animals had a smaller cross-sectional area and a higher ultimate tensile strength than those from controls or oophorectomized rabbits (P<0.04-0.0003).

Extracellular lipid peroxidation of selective white-rot fungus, Ceriporiopsis subvermispora

Ceriporiopsis subvermispora is capable of decomposing lignin without penetration of enzymes into wood cell walls. To elucidate the mechanism of lignolysis at a site far from enzymes, peroxidation of low molecular mass compounds produced by this fungus was analyzed. C. subvermispora produced free 9,12-octadecadienoic, 9-octadecenoic, 11-octadecenoic, hexadecanoic and octadecanoic acids, predominantly at an early stage of cultivation on wood meal cultures. In prolonged cultivation period after 2 weeks, the amount of intact fatty acids decreased with increasing organic hydroperoxide and TBARS production. These results suggest that lignin degradation by C. subvermispora is related to extracellular lipid peroxidation.

Eighteen- to twenty-four-year follow-up after complete rupture of the anterior cruciate ligament

A unilateral, complete rupture of the anterior cruciate ligament was diagnosed in 60 consecutive patients by arthroscopy within 1 week of trauma. Most ruptured ligaments were treated by acute nonaugmented repair immediately after the arthroscopy. Fifty-five and 56 patients were reevaluated after 12 years and 20 years, respectively. Twenty-five patients (45%) had at least one reoperation during the follow-up period of 20 years, primarily for meniscal problems. Seven patients (13%) had repeat anterior cruciate ligament surgery. The overall Lysholm knee function score remained at a median of 90 points from 12 to 20 years, but patients had decreased their sporting activities from team sports at full rehabilitation to physical fitness activities at the late follow-up. Patients who had repeat surgery had a worse knee function score, were less satisfied with their knees, and also had to change activities and change work more often than patients without reoperation. The majority of patients had, at both follow-up periods, unstable knees. At 20 years, weightbearing radiographs showed slight-to-moderate changes equivalent to osteoarthrosis in 84% (47) of patients and a 32% increase in osteoarthrosis since the 12-year evaluation.

Maturation-dependent durability of spontaneous cartilage repair in rabbit knee joint

The spontaneous healing of osteochondral defects in the knee joints of immature rabbits within the first 12 weeks after surgery showed a faster filling and earlier tissue specialization than in adult animals. The purpose of the present study was to investigate whether the better short-term quality of spontaneous repairs in immature animals lasted over a period of 48 weeks. A full-thickness osteochondral defect was created on the medial femoral condyle in both knees of 10 young, 10 adolescent, and 10 adult rabbits. Equal numbers of animals were evaluated after 24 and 48 weeks. At both time intervals, bonding to adjacent cartilage and proteoglycan content of the matrix were better in the repairs of young than in adult animals. Repairs in the former had cellularity similar to the adjacent cartilage and were composed of 90% hyaline-like cartilage, which did not decrease with time. In contrast, repairs in older animals formed less hyaline-like cartilage and had a lower cellularity than the adjacent cartilage. However, the surface of the repaired tissue was similarly disrupted in all age groups, and the mechanical properties remained inferior to adjacent or normal cartilage. Repairs in older animals showed signs of degeneration with time. The initial better repair quality in a young, growing animal remained up to 48 weeks when the animal had already reached maturity, indicating that successful initial promotion of cartilage repair may even lead to better results in the long term. However, it has to be pointed out that the morphologically good repairs with hyaline-like cartilage appearance, normal cellularity, and durability of up to 48 weeks were unable to reestablish and maintain a cartilage-like mechanical function.

Rat model of Achilles tendon disorder. A pilot study

Three-month-old male rats were subjected 3 times weekly for 1 h to eccentric exercise of one triceps surae muscle (30 stimulations/min) under general anesthesia in order to induce Achilles tendon disorder corresponding to paratenonitis and tendinosis in man. Net muscle work during the sessions ranged between 0.67 and 4.37 mJ (mean 1.72, SD 0.77). After 9 and 13 sessions, respectively, 2 rats started to show gait alterations during the functional test which was performed 2-3 times weekly. These rats were killed after additional sessions which showed a worsening of the limp. The other trained rats and controls did not limp and were killed after 7-11 weeks. Histologic evaluation of the Achilles tendons from the exercised limb showed in the majority of the cases hypervascularization, increased number of nerve filaments and increased immunoreactivity for substance P and calcitonin gene-related peptide. The tendons from the nonstimulated limb looked normal. The distribution of collagen types I and II appeared normal in the tendon and its insertion to the calcaneus. Inflammation of the epi- and paratenon could be provoked in the rat, but tendon changes corresponding to chronic tendinosis did not develop within 11 weeks with the used training regime. The clinical relevance of this model for chronic tendon disease needs to be evaluated further.

Eighteen- to twenty-five-year follow-up after acute partial anterior cruciate ligament rupture

Of 22 consecutive patients with minor knee instability after a partial rupture of the anterior cruciate ligament, all could be reexamined after a mean of 12 years and all but 1 could be reexamined after a mean of 20 years. Three patients needed surgery during the follow-up period, but nobody had an anterior cruciate ligament reconstruction. The Lysholm knee function score was excellent and did not change between 12 and 20 years. Patients had decreased their activities from contact sports before injury to physical fitness activities at the late follow-up. Four patients changed activities because of a knee problem. The quality of life score was somewhat higher than may be expected in an age-matched average population. At late follow-up, eight patients had a 1+ Lachman sign, two a 2+ Lachman sign, and one a positive pivot shift. Also at late follow-up, 7 knees showed no signs of radiographic osteoarthrosis, 10 had Fairbank's signs, and 3 had minor and 1 a major joint space reduction. Of the 12 patients with longitudinal radiographic observation, 3 knees had developed a higher degree of osteoarthrosis, and 9 had remained unchanged. The patients had a mean age of 48 years at the late follow-up. This suggests that the results may be regarded as final outcome after this specific knee injury.

Future research in meniscal replacement

To study the remodelling process after meniscus replacement and to learn how to control it will be a key topic for future research. Not enough is known about the importance of precision in meniscal fixation and how to make the insertions as strong as in the normal meniscus. Methods to measure load-distribution, mechanical properties of the graft and status of the cartilage should be developed. A number of different auto- and allografts have been shown to heal and revascularize, but whether the grafts are functioning is not known. Meniscal scaffolds, which can be used for replacement of partial meniscal loss, need to be tested. Scaffolds and tissue engineering will be the subject of intensive research in the future.

Meniscal regeneration or meniscal transplantation?

Owing to the initial necrosis to which any freely transplanted biological graft is subjected, meniscus transplantation is based on similar principles to meniscal regeneration. Both methods rely on repopulation of extrinsic cells of the graft. In the former procedure a biological matrix (meniscus, tendon, fatpad) is used as graft (scaffold), whereas in meniscal regeneration commercially available resorbable or non-resorbable scaffolds are implanted. However, the cellular (re)population and (re)vitalization process is deleterious rather than beneficial for the function of the graft as the remodelling of the tissue leads to shrinkage and narrowing of the implant. In addition, improper fixation and subsequent elongation of the anterior and posterior bony attachments leads to peripheral graft dislocation, loss of the load distribution function, and subsequently to cartilage degeneration. Hence, meniscus transplantation or regeneration faces two major problems: 1) remodelling of graft to inferior tissue properties after allograft transplantation, or lacking establishment of normal tissue properties after use of biological matrixes other than the meniscus (fatpad, tendon), or commercially available matrixes; 2) improper fixation with elongation of the anterior and posterior attachments. Furthermore, use of allografts incorporates the risk for disease transmission. Today we are unable to control these problems, and therefore the concept of meniscal replacement does not work yet. Further research is necessary to control remodelling and improve fixation to make this procedure a successful one in the future.

Articular cartilage compressive stiffness following oophorectomy or treatment with 17beta-estradiol in young postpubertal rabbits

BACKGROUND

Changes in estrogen concentrations during adolescence (contraceptives, secondary amenorrhea) may influence cartilage mechanics and therefore its capacity to respond adequately to physical demands. The purpose of this study was to investigate the influence of oophorectomy or continuous administration of estradiol on cartilage compressive properties in an immature animal model.

METHODS

Young postpubertal female New Zealand white rabbits were either oophorectomized (n=9) or underwent a sham-operation (n=8). The sham-operated animals received in addition a daily dosage of 4 mg 17beta-estradiol orally starting 3 weeks after surgery until death. After 5 months the animals were killed, and cartilage compressive properties (ramp and creep moduli) were determined at 4 defined knee joint regions by in situ indentation tests. Five age-matched rabbits were used as controls.

RESULTS

Femoral cartilage stiffness (ramp and 15-s creep moduli) and thickness in oophorectomized animals were significantly higher than those in controls or estradiol-treated animals (p<0.05 and less), but there was no difference between the latter groups. Tibial cartilage showed less obvious treatment-dependent differences. The cartilage in the medial compartment was thicker than in the lateral one, and femoral cartilage was thinner than tibial cartilage (p<0.00005), irrespective of the treatment.

CONCLUSIONS

Oophorectomy during adolescence led to increased femoral cartilage thickness and stiffness. The relevance of these findings for the development of cartilage disease has to be elucidated in the future.

Anterior cruciate ligament reconstruction and the long-term incidence of gonarthrosis

Knee ligament injuries are common in sport. A rupture of the anterior cruciate ligament (ACL) is the most serious of these injuries because it may cause long term disability. In this literature review, the frequency of post-traumatic gonarthrosis is examined. There are few long term prospective studies but a number of retrospective studies with follow-up times between 5 and 20 years have been published. These studies show that radiographic gonarthrosis is significantly increased after all knee injuries compared with the uninjured joint of the same patient. Isolated meniscus rupture and subsequent repair, or partial or total ruptures of the ACL without major concomitant injuries, seem to increase the risk 10-fold (15 to 20% incidence of gonarthrosis) compared with an age-matched, uninjured population (1 to 2%). Meniscectomy in a joint with intact ligaments further doubles the risk of gonarthrosis (30 to 40%), and 50 to 70% of patients with complete ACL rupture and associated injuries have radiographic changes after 15 to 20 years. Thus, an ACL rupture combined with meniscus rupture or other knee ligament injuries results in gonarthrosis in most patients. Ten to 20 years after ACL injury, gonarthrosis often presents as a slight joint space reduction or, occasionally, joint space obliteration (Ahlbäck grades I to II), but is usually not associated with major clinical symptoms. According to the few longitudinal studies, the progress of gonarthrosis is slow, and in some cases the condition seems to remain stable. Time is an important determinant for the degree of gonarthrosis and problems demanding treatment may be encountered only at > 30 years after the initial accident.

[Cartilage replacement operation using pre-cultured cells]

Clinical results using transplantation of precultivated autologous chondrocytes for treatment of circumscribed chondral injuries in the knee joint have been presented 1994. The quality of this method for clinical use can not be evaluated at the moment since controlled randomized trials comparing this method with bone drilling, use of periostal flaps or conservative treatment do not exist. According to recent experimental results, techniques using precultivated cells, growth factors and different scaffolds for repair of limited cartilage defects are not satisfactory yet, and it is unproven whether these methods are superior to simple bone-drilling. Use of precultivated cells and growth factors might nevertheless have a potential in the future, when we have learned to use them under optimized conditions. Unless these conditions have been developed and proven to reliably improve cartilage repair above previous methods, in a clinical case the treatment should be chosen which is the least invasive.

Maturation-related compressive properties of rabbit knee articular cartilage and volume fraction of subchondral tissue

OBJECTIVE

Knowledge about the physiologic change in cartilage biomechanics, accompanying the structural remodeling of the cartilage bone unit during maturation, may have relevance to understand the development of joint disease. The purpose of this study was to investigate maturation-dependent changes of compressive properties of articular cartilage and volume fraction of subchondral tissue in healthy rabbit knees.

METHODS

Cartilage compressive properties (instantaneous and creep moduli) were tested at seven defined knee joint regions of five young (ten weeks), five adolescent (eighteen weeks) and five adult (above thirty-one weeks) healthy rabbits with in-situ indentation tests. Morphometric analysis of volume fraction of subchondral tissue was carried out at four regions.

RESULTS

Cartilage stiffness (instantaneous modulus) decreased between infancy and adolescence (P < 0.009), and stayed then the same. A simultaneous significant change in (50-second) creep modulus was only observed at one region, but both moduli correlated to each other. Subchondral tissue consisted of cancellous bone in the young, and formed a more solid bone plate not before adolescence. Its volume fraction increased from infancy to adolescence (P < 0.001), but stayed then the same. There was a significant inverse correlation between the volume fraction of subchondral tissue and cartilage stiffness at the four measured regions (R2 = -0.59). The arrangement of collagen fiber bundles in the deeper cartilage layers changed from a mesh-like structure in the young to a more perpendicular alignment in the adolescent and adult.

CONCLUSION

The maturation-related change in compressive properties coincided with a conspicuous change in volume fraction of the subchondral tissue. The main change appeared around puberty.

[Current advances in sports-related cartilage research. Meniscus and ligament injuries are associated with increased risk of knee joint arthrosis]

The majority (up to 87%) of patients with meniscus and ligament injuries of the knee develop degenerative radiological changes in a 10-20-year perspective, patients with knee injuries involving several structures being at the greatest risk. A high level of activity has been shown to be a correlate both of repeat injury and the development of osteoarthrosis. However, it has not been determined when or in what proportion of cases such changes result in joint destruction and permanent disability. The incidence of isolated cartilage injuries is low, and it is unclear whether such injuries predispose to osteoarthrosis. No validated method is yet available for the effective treatment of circumscribed or more extensive cartilage injuries, which would be preferable to conservative treatment.

Postnatal development of the cruciate ligament insertions in the rat knee. morphological evaluation and immunohistochemical study of collagens types I and II

The postnatal structural remodelling and calcification patterns in the insertions (entheses) of both cruciate ligaments were studied in a rat model with histology and immunohistochemical analysis of collagens types I and II. In the neonate, both ligaments which labelled only for type I collagen attached to epiphyseal cartilage which solely labelled for collagen type II. The entheses calcified between days 20 and 35, and a subchondral bone plate formed under the entheses between days 30 and 55. Thus, within a period of 35 days the tissue to which the ligaments attached increased multifold in stiffness. Interestingly, the process of enthesial calcification and formation of compact bone did not happen simultaneously in both ligaments, not even synchronous at both ends of the same ligament or within a single insertion. This asynchronous calcification of the different knee ligament insertions may make the sudden change in mechanical environment at the entheses less dramatic for the ligaments and knee joint surfaces as anticipated from mechanical models. In addition, a fibrocartilaginous tissue, rich in collagen type II, formed in the ligament at a time when the epiphyseal cartilage was replaced by bone, and grew wider with time. The interposition of a fibrocartilaginous zone in the insertion may diminish the sudden change in stiffness between ligament soft tissue and hard bone.

The menisci of the knee joint. Anatomical and functional characteristics, and a rationale for clinical treatment

The menisci and their insertions into bone (entheses) represent a functional unit. Thanks to their firm entheses, the menisci are able to distribute loads and therefore reduce the stresses on the tibia, a function which is regarded essential for cartilage protection and prevention of osteoarthrosis. The tissue of the hypocellular meniscal body consists mainly of water and a dense elaborate type I collagen network with a predominantly circumferential alignment. The content of different collagens, proteoglycans and nonproteoglycan proteins shows significant regional variations probably reflecting functional adaptation. The meniscal horns are attached via meniscal insertional ligaments mainly to tibial bone. At the enthesis, the fibres of the insertional ligaments attach to bone via uncalcified and calcified fibrocartilages. This anatomical configuration of gradual transition from soft to hard tissue, which is identical to other ligament entheses, is certainly essential for normal mechanical function and probably protects this vulnerable transition between 2 biomechanically different tissues from failure. Clinical treatment of meniscal tears needs to be based on these special anatomical and functional characteristics. Partial meniscectomy will preserve some of the load distribution function of the meniscus only when the meniscal body enthesis entity is preserved. Repair of peripheral longitudinal tears will heal and probably preserve the load distribution function of the meniscus, whereas radial tears through the whole meniscal periphery or more central and complex tears may be induced to heal, but probably do not preserve the load distribution function. There is no proof that replacement of the meniscus with an allograft can reestablish some of the important meniscal functions, and thereby prevent or reduce the development of osteoarthrosis which is common after meniscectomy. After implantation, major problems are the remodelling of the graft to inferior structural, biochemical and mechanical properties and its insufficient fixation to bone which fails to duplicate a normal anatomical configuration and therefore a functional meniscal enthesis.

Regional differences in cell shape and gap junction expression in rat Achilles tendon: relation to fibrocartilage differentiation

Tendon cells have complex shapes, with many cell processes and an intimate association with collagen fibre bundles in their extracellular matrix. Where cells and their processes contact one another, they form gap junctions. In the present study, we have examined the distribution of gap junction components in phenotypically different regions of rat Achilles tendon. This tendon contains a prominent enthesial fibrocartilage at its calcaneal attachment and a sesamoid fibrocartilage where it is pressed against the calcaneus just proximal to the attachment. Studies using DiI staining demonstrated typical stellate cell shape in transverse sections of pure tendon, with cells withdrawing their cell processes and rounding up in the fibrocartilaginous zones. Coincident with change in shape, cells stopped expressing the gap junction proteins connexins 32 and 43, with connexin 43 disappearing earlier in the transition than connexin 32. Thus, there are major differences in the ability of cells to communicate with one another in the phenotypically distinct regions of tendon. Individual fibrocartilage cells must sense alterations in the extracellular matrix by cell/matrix interactions, but can only coordinate their behaviour via indirect cytokine and growth factor signalling. The tendon cells have additional possibilities--in addition to the above, they have the potential to communicate direct cytoplasmic signals via gap junctions. The formation of fibrocartilage in tendons occurs because of the presence of compressive as well as tensile forces. It may be that different systems are used to sense and respond to such forces in fibrous and cartilaginous tissues.

Copper-dependent depolymerization of lignin in the presence of fungal metabolite, pyridine

Thus far, it has not been recognized that copper complexes are able to depolymerize lignin under physiological conditions of white rot decay. However, we have found that both phenolic and non-phenolic synthetic lignins were intensively depolymerized by Cu(II) and lipid hydroperoxide model compounds in the presence of a metabolite of ligninolytic fungi, pyridine at room temperature in aqueous media. Treatment of 14C-labeled oxygen-prebleached kraft pulp (OKP) by the copper-dependent reaction evidenced effectiveness of this reaction for the delignification of kraft pulps. In contrast to the organic peroxide system, Cu(II)/pyr/H2O2 system was much less effective for the lignin depolymerization. However, treatment of unbleached kraft pulp (UKP) by Cu(II)/H2O2 and Cu(II)/pyr/H2O2 systems demonstrated that the damage of cellulose was suppressed by the coordination of pyridine although high brightness gain was obtained independently of the presence of the coordinator. Spin trapping experiments demonstrated that not hydroxyl radical but superoxide anion is involved in the Cu(II)/pyr/H2O2 system. This finding not only introduces a new concept of non-enzymatic lignin biodegradation by wood-degrading fungi but also presents a new strategy for decomposing lignin and lignin-related compounds by copper complexes and peroxide-producing system.

Oxidation of phenanthrene by a fungal laccase in the presence of 1-hydroxybenzotriazole and unsaturated lipids

Phenanthrene, a polycyclic aromatic hydrocarbon, was efficiently oxidized by laccase in the presence of both 1-hydroxybenzotriazole and unsaturated lipids. 73% of initially added phenanthrene was degraded within 182 hours to give phenanthrene-9,10-quinone and 2,2'-diphenic acid as the major products. The system was also able to peroxidize linoleic acid to its corresponding hydroperoxides suggesting the involvement of lipid peroxidation in laccase catalyzed phenanthrene oxidation. Lipid peroxidation by laccase required 1-hydroxybenzotriazole and did not depend on Mn2+ and H2O2 suggesting that the chemical reactions involved differ from those previously reported for manganese peroxidase.

Healing of the anterior attachment of the rabbit meniscus to bone

In a rabbit model the healing process of the anterior attachment of the medical meniscus was observed during the first 12 weeks after sharp transection and refixation in a tibial bone channel. Evaluations of the healing tissue were histologic analysis, application of immunohistochemical methods to show collagen types and nerve regeneration, and mechanical load to failure tests. Secondary changes to knee joint cartilage, as signs of eventual dysfunction of the refixed meniscus, were evaluated by analysis of proteoglycan fragment concentration in joint fluid and histologic analysis of knee joint articular cartilage and synovium. The healing tissue between the refixed attachment and bone matured from highly cellular, nonspecific granulation tissue at 1 week, to bone, fibrocartilaginous, and fibrous tissues, which at some sites developed an insertion specific tissue arrangement within a 12-week period. However, the irregular interface between the fibrocartilaginous tissue and the underlying bone, which is typical for a normal insertion, was not reestablished. Labeling for collagen Types I and II in the newly formed insertion did not return to normal. In addition a few collagen fibers connected the refixed attachment tissue to bone. New bone formation turned the initially cancellous bone tunnel walls into more solid cortical bone. However, new bone formation did not fill the distal part of the channel. The refixed meniscal attachment underwent necrosis and was revitalized by cell ingrowth from the periphery. Nerve fibers were found in the newly formed insertion by 12 weeks. The failure load at tensile testing never reached more than 20% that of a normal attachment. Degeneration of articular cartilage and increased proteoglycan fragment in the joint fluid were common after this procedure. These data suggest that, despite the focal appearance of insertion specific tissues and healing of collagen fibers to bone, the tissue architecture of a normal meniscal insertion and a normal meniscal joint protective function were not reestablished.

Barriers to implementing a quality improvement program

Critical barriers can prevent the implementation of an effective quality improvement (QI) program in the health care setting, including organizational culture, restructuring, quality assurance/quality control functions, QI teams and costs. Common pitfalls encountered that cause QI programs to falter--or worse, to fail--are discussed.

Age- and injury-dependent concentrations of transforming growth factor-beta 1 and proteoglycan fragments in rabbit knee joint fluid

OBJECTIVE

The purpose of the study was to characterize maturation-related changes of TGF-beta 1 and proteoglycan fragment (PG) concentrations in joint fluid of healthy rabbit knees, and to investigate changes associated with osteochondral injury and spontaneous repair.

METHODS

In 26 young (age range: 12-15 weeks), 26 adolescent (18-25 weeks), and 26 adult (33-44 weeks) New Zealand white rabbits, TGF-beta 1 and PG concentrations were analyzed in joint fluid samples which were taken before, and at several time intervals (max. 1 year) after creation of a osteochondral defect in the knee medial femoral condyle. At death, the characteristics of the regenerated tissue in the defect and any signs of degeneration of adjacent cartilage were recorded and graded.

RESULTS

In preoperative samples, TGF-beta 1 and PG concentrations decreased with maturation (P < 0.01), and were moderately correlated (r = 0.51, P < 0.001). Shortly after trauma, the concentrations of both substances were found increased, which was followed by a decrease up to 3 months, and then again an increase up to 1 year. However, meanwhile PG concentrations had similar magnitude irrespective of age, TGF-beta 1 concentrations never reached similarly high levels in adulthood as in infancy or adolescence. The cartilage adjacent to the defect had more signs for degeneration in younger rabbits, and also osteophytes were more common in young than adult animals.

CONCLUSION

The similar pattern for TGF-beta 1 and PG concentrations during postnatal maturation may reflect the stimulatory effect of TGF-beta 1 on proteoglycan synthesis. The higher TGF-beta 1 concentrations in younger animals may be a reason for their better healing capacity, but also for their higher susceptibility to osteoarthritic change compared to adult animals.

Ten-year prognosis of isolated and combined medial collateral ligament ruptures. A matched comparison in 40 patients using clinical and radiographic evaluations

In a matched-pair study of 40 patients, the prognoses of patients with acute isolated partial medial collateral ligament injuries and acute combined medial collateral and anterior cruciate ligament injuries were compared 10 years after initial treatment. All patients in the first group were treated nonoperatively. In the latter group, most medial collateral ligament injuries were total ruptures, which were thoroughly repaired; the torn anterior cruciate ligament was repaired with augmentation in half of the cases. At the follow-up evaluation, both patient groups had similarly high knee functions according to the Lysholm score and similar activity levels (recreational team sports). Knees with combined injuries had increased sagittal laxity at manual and instrumented assessment. Radiographic signs of knee osteoarthritis were present in half of the knees with combined injuries, but they were absent in knees with isolated injuries. The long-term functional prognosis was similarly good after isolated or combined medial collateral ligament injuries, but patients with combined ruptures had more reinjuries and repeat surgeries, increased sagittal laxity, and a higher incidence of radiographic osteoarthritis.

Maturation-dependent repair of untreated osteochondral defects in the rabbit knee joint

Repair of untreated full-thickness cartilage defects in the medial femoral knee condyle was studied in 17 young, 21 adolescent, and 19 adult rabbits. At 6 weeks, the defect was completely filled by tissue regeneration in all young and adolescent animals, but in only few of the adults (p < 0.05). The morphology of all repairs improved from fibrous tissue to hyaline-like cartilage over time (p < 0.05), but at 3 and 6 weeks, the repair tissue in young and adolescent rabbits was more cartilage-like than in the adults (p < 0.05). In addition, bonding of the repair tissue to the adjacent cartilage was better in the young and adolescent than in the adult animals (p < 0.05). At 12 weeks, subchondral bone had formed in some young and adolescent repairs, but in no case in the adults. None of the repairs showed normal cartilage appearance, but formation of hyaline-like cartilage was common at 12 weeks. Irrespective of age or observation time, the repair site showed decreased stiffness and larger strain values compared to adjacent or control cartilage (p < 0.001) with no tendency for improvement over time. Younger animals showed a faster filling of the defect and an earlier specialization of the repair tissue than adult animals, but the mechanical quality of the regenerated tissue remained inferior to normal.

Sequential scintigraphy and orthoradiographic measurement of femoral shortening after femoral neck fracture

The objective of the study was to assess scintigraphic patterns and femoral shortening after femoral neck fracture in order to select predictive parameters for late complications. Eighty-eight patients with osteosynthesized femoral neck fractures were followed for 2 years with regular scintigraphic evaluations and orthoradiographic measurements of femoral length shortening. Four different patient categories were identified with regard to the late outcome two different groups with uneventful healing and two different groups with late complications. Accordingly, a high scintigraphic uptake at 1 month may either point to an uneventful healing if combined with minor femoral shortening or indicate failure if combined with a high degree of femoral shortening. In contrast, low scintigraphic uptake may either reflect primary fracture healing if accompanied by minor femoral shortening or predict failure if a high degree of femoral shortening is present. Compared with using scintigraphy alone, combined scintigraphic evaluation and assessment of femoral shortening increased the accuracy for prediction of late failures from 80% to 93%. Early scintigraphic patterns after osteosynthesis of femoral neck fractures have to be validated with care. Radiographic assessment of femoral shortening, which is less invasive, gives better prognostic accuracy and should therefore be preferred for this purpose.

Evaluation of knee-joint cartilage and menisci ten years after isolated and combined ruptures of the medial collateral ligament. Investigation by weight-bearing radiography, MR imaging and analysis of proteoglycan fragments in the joint fluid

PURPOSE

To compare radiography, MR imaging, and chemical analysis in posttraumatic knees.

MATERIAL AND METHODS

Ten matched pairs with either isolated partial rupture of the medial collateral ligament or combined medial collateral ligament/anterior cruciate ligament rupture were compared with matched controls 10 years after trauma. Weight-bearing radiographs and MR examinations were compared with proteoglycan fragment concentrations in the joint fluid.

RESULTS

The chemical analyses were similar in both trauma groups. The radiographs showed mild signs of arthrosis in half the patients with combined injury. MR images showed almost all injured knees to have degenerative changes of various degrees in the cartilage and menisci. More frequent and more advanced changes were found after combined injury than after isolated injury (p < 0.01). There were no changes in the controls.

CONCLUSION

MR imaging is the best method for detecting and differentiating early posttraumatic knee arthrosis.

An immunohistochemical study of enthesis development in the medial collateral ligament of the rat knee joint

The changing distributions of collagens and glycosaminoglycans have been studied at the attachments of the medial collateral ligament during postnatal development. The ligament is of particular interest because it has a fibrocartilaginous attachment to the femoral epiphysis, but a fibrous one to the tibial metaphysis. Ligaments were examined in rats killed at birth and at 2, 4, 6, 8, 10, 20, 30, 45, 60, 90 and 120 days after birth. Cryosections were immunolabelled with monoclonal and polyclonal antibodies against types I and II collagen, chondroitin 4 and 6 sulfate, dermatan and keratan sulfate. Although the ligament is attached at both ends to bones that develop from cartilage, there was a striking difference in collagen labelling. Type II collagen was only found in spicules of calcified cartilage in bone beneath the tibial enthesis after ossification had commenced, but there was a continuous band of labelling at all stages of development at the femoral enthesis. Initially, the cartilage at the femoral attachment lacked type I collagen, but by 45 days labelling was continuous from ligament to bone. Continuity of labelling was seen much earlier at the tibial enthesis, as soon as bone had formed. There were also marked changes in glycosaminoglycan distribution. Keratan sulfate was present at both entheses up to 45 days, but only at the femoral enthesis thereafter. Both attachments labelled throughout life for dermatan sulfate, but chondroitin 4 and 6 sulfate were only found at the femoral end. The results suggest that enthesial cartilage at the femoral attachment was initially derived from the cartilaginous bone rudiment but was quickly eroded on its deep surface by endochondral ossification as bone formed at the attachment site. It was replaced by fibrocartilage developing in the ligament. This mechanism allows enthesis cartilage/fibrocartilage to contribute to the growth of a bone at a secondary centre of ossification in addition to dissipating stress at the ligament-bone junction.

The morphology of ligament insertions after failure at low strain velocity: an evaluation of ligament entheses in the rabbit knee

The morphology of failed rabbit knee entheses is described after in vitro load to failure testing at low strain velocity. Avulsion fracture was the dominant failure mode both for the cruciate ligaments and the medial collateral ligament. The patellar ligament became avulsed in most cases from the patellar insertion. The ligamentous anterior attachment of the medial meniscus failed by a midsubstance rupture and the posterior fibrocartilaginous attachment by a rupture near to the meniscal horn. On histological inspection the failure characteristics usually appeared more elaborate, involving to different degrees all portions of the bone-ligament-bone complexes. Avulsion fracture through subchondral bone was often combined with a partial ligament midsubstance rupture. In few cases avulsion from the cement line was combined with a rupture between the uncalcified fibrocartilage and the ligament. The medial collateral ligament failed in one case entirely at the cement line of its femoral insertion. Horizontal rupture through the calcified fibrocartilage and a vertical cleavage crossing the tidemark were also observed. The superficial portion of the patellar ligament failed with a midsubstance rupture, and the deeper part with an avulsion through the calcified fibrocartilage or an avulsion fracture. The complex failure characteristics may be attributed to uneven loading, nonuniformity of the structure, and specific anatomical location. Subchondral bone beneath femoral and tibial insertions seems to be weaker than the transitional zone between soft tissue and hard bone at the enthesis. The overall inferior structural quality of a ruptured ligament has to be taken into account when parts of the original structure are used for suturing or reconstruction.

In vitro femoral stiffness after femoral neck osteotomy and osteosynthesis with defined surgical errors

In our search for an osteosynthesis device that would tolerate the surgical errors of the inexperienced surgeon, we tested in vitro femoral stiffness in 75 human osteoporotic femora after internal fixation of a cervical neck osteotomy using three commonly used devices: two von Bahr screws (A. Ericsson AB, Sweden), two cannulated screws (Uppsala type, Olmed AB, Sweden), and two hookpins (LiH, PSAB, Sweden). The first device has its main grip in the cancellous bone by threads; the second has grip in cancellous and subchondral bone by threads; and the third, which has no threads, has its grip in cancellous bone by a hook pin. The intact specimen was in all instances stiffer (22-63%) than the osteosynthesized specimen (p < 0.001). An osteosynthesized femur with perfectly reduced bone ends was 14-23% stiffer than when reduction of the bone ends was insufficient, irrespective of device malposition (p < 0.001). Insufficient reduction of the osteotomy leaving a 20 degrees dorsal angulation of the femoral head combined with too far ventrally placed screws resulted in the lowest femoral stiffness. If reduction of osteotomy was sufficient, screws placed too far ventrally or converging screws did not result in decreased stiffness compared with optimal screw placement. Irrespective of the quality of reduction, osteosynthesis with the Uppsala screw resulted in all instances in a higher stiffness than using the other devices (p < 0.01). With the Uppsala screw design, femoral stiffness after optimal osteosynthesis was reduced by 22% compared with the intact femur, and in the most unfavorable position with combined malreduction and malpositioning it was reduced by 42%. Corresponding values for the von Bahr screws were 29% and 46%, respectively, and for the LiH screws 47% and 63%, respectively. Use of a device with threads and grip in the subchondral bone is recommended for fixation of femoral neck fractures in osteoporotic bone. Furthermore, the importance of anatomical reduction for fracture fixation is emphasized.

Regional variations of indentation stiffness and thickness of normal rabbit knee articular cartilage

The rabbit knee is frequently used as an experimental model for cartilage repair, but the choice of different joint regions for such studies makes comparisons between methods difficult. Furthermore, there is only limited information available about the regional variations of the biomechanical properties in normal rabbit knee articular cartilage. In the present study in situ indentation tests were used to map the short-term stiffness and thickness of articular cartilage at seven locations (anterior and posterior areas of the medial and lateral femoral condyles, the patellar groove, and the central areas of the medial and lateral tibial plateaus) in nine normal rabbit knee joints. Short-term cartilage stiffness was described by elastic moduli under ramp loading and 15-s creep conditions. The moduli were calculated according to Hayes' single-phase elastic model. A moderate positive correlation (r = 0.54) between cartilage stiffness and thickness was found for rabbit femoral cartilage, but was not confirmed for tibial cartilage, which had the thickest, but also the softest cartilage of all areas. The cartilage in the patellar groove and the medial compartments of both femoral condyles and tibial plateaus was stiffer and thicker than that in the lateral components, similar to previous findings in dogs. However, the dog femoral cartilage was found to be stiffer at the anterior than at the posterior regions, but we found the opposite in the rabbit. These dissimilarities between animal models may be caused by different joint loading characteristics. Accordingly, in rabbits repair processes in the more anterior femoral areas with less stiff cartilage may not be comparable to repairs in more posterior areas where cartilage is stiffer.

Natural healing of anterior and posterior attachments of the rabbit meniscus

The natural healing capacity of the anterior or posterior medial meniscal attachment after radial transection and the effect of such procedures on knee joint cartilage were investigated in 28 skeletally mature New Zealand white rabbits. Either the anterior (n = 14) or the posterior attachment (n = 14) was radially transected in the right knee joint. Fifty percent of the rabbits with each procedure were euthanized at 6 weeks and 50% at 12 weeks. The histologic characteristics of the healing tissue were evaluated, including immunohistochemical demonstration of nerve fibers. Histologic changes in the synovium and articular cartilage were graded for severity and extent. The concentration of proteoglycan fragments in joint fluid was analyzed before operation and at euthanasia. After both procedures, the transected attachment healed in a prolongated position resulting in peripheral displacement of the meniscus. The healing tissue at 6 weeks was composed mainly of granular tissue. By 12 weeks, the healing tissue at the anterior attachment had a ligament like structure, but at the posterior attachment, fibrocartilage like tissue had formed. Nerve fibers were found in the healing tissue, but connections to nerves in normal attachment or meniscal tissues were not found. Increased concentrations of proteoglycan fragments, articular cartilage degeneration, and synovitis were found in the operated knees. These data indicate that although the meniscal attachment can heal in a prolongated position, such a meniscus has lost its mechanical functions. Further, a joint protective function of the neoneurons is doubtful because of the lack of continuity with the adjacent meniscus. Rigid fixation of the attachment seems essential for a functional meniscal substitute.

The effect of partial meniscectomy on the long-term prognosis of knees with localized, severe chondral damage. A twelve- to fifteen-year followup

We retrospectively matched 42 patients with unilateral chondral damage in the weightbearing zone of one knee compartment according to sex, age, location of chondral damage, and follow-up time. Two groups of 21 patients were formed. One group had chondral damage only. The other group had chondral damage and a meniscal tear treated with partial meniscectomy. After 12 to 15 years, all patients were reexamined. Twenty-nine percent (N = 6) of the patients who had a partial meniscectomy needed repeat meniscal surgery during followup. No patients with isolated chondral damage developed meniscal symptoms, and only three patients underwent minor surgeries (P < 0.02). At the follow-up evaluation, both groups had similar knee function with a mean Lysholm score of 87 points. However, most patients had reduced their sports activities from competitive individual sports before injury to noncompetitive physical fitness exercise at followup. At the roentgenologic examination, patients who had partial meniscectomies had more severe roentgenologic signs of osteoarthritis than patients who had chondral damage only (P < 0.03). Meniscectomy, varus knee alignment at the follow-up evaluation (P < 0.04), and age older than 30 years (P < 0.04) at the time of the operation were associated with a higher incidence of osteoarthritis.

The diagnostic validity of magnetic resonance imaging in acute knee injuries with hemarthrosis. A single-blinded evaluation in 69 patients using high-field MRI before arthroscopy

Sixty-nine patients with traumatic knee hemarthrosis were evaluated an average of 3 days after trauma by high field (1.5T) magnetic resonance imaging (MRI) using sagittal T1, T2-weighted and coronal 3D-gradient echo images. All knees were arthroscopically examined shortly afterwards. The diagnostic validity of MRI for intraarticular pathology was determined using arthroscopy as golden standard. All patients had pathological findings on arthroscopy. The injuries were sports-related in 77% of the cases. MRI was highly sensitive (86%) and specific (92%) for diagnosis of anterior cruciate ligament tears. Diagnosis of medial meniscal tears showed a 74% sensitivity and 66% specificity. MRI detected lateral meniscal tears in 50% with an 84% specificity. As such, MRI missed 10 significant meniscus ruptures requiring surgical treatment. The sensitivity for partial or total medial collateral ligament tears was 56%, the specificity 93%. Rupture of the medial retinaculum in cases with patellar dislocation or significant damage of articular cartilage were only detected by MRI in a few cases (27% and 20% sensitivity, respectively). MRIs low diagnostic validity for intraarticular pathology with hemarthrosis may be attributed to the shifting paramagnetic properties of the blood remains and catabolic processes in meniscal and chondral tissues during the hemoglobin degradation process. Accordingly, MRI, with the technique used, could neither replace arthroscopy in the diagnosis and screening of acute knee injuries, nor select patients with need for immediate arthroscopic meniscal surgery.

The long-term prognosis for severe damage to weight-bearing cartilage in the knee: a 14-year clinical and radiographic follow-up in 28 young athletes

We examined 28 young athletes with isolated severe chondral damage in the weight-bearing area of the knee joint clinically and radiographically 14 years after arthroscopic diagnosis. Except for Pridie drilling in 3 cases and occasional cartilage shaving or removal of free bodies, no special treatment was given initially. 21 patients were able to return to preinjury team sport activity levels. During the follow-up period, only 3 patients needed repeat surgery with removal of free bodies, and another 2 underwent diagnostic arthroscopy because of persistent pain. At the latest follow-up evaluation, 22 patients had excellent or good knee function. At this time, the patients were mainly involved in individual sports on a physical fitness level. 12 cases had radiographic joint space reduction (< 50%) which was limited to the compartment concerned.

Quantitative comparison of soft tissue-bone interface at chondral ligament insertions in the rabbit knee joint

At chondral ligament insertions the calcified fibrocartilage interdigitates deeply with the lamellar bone. The shape of this interface is formed under physiological loading conditions. For the purpose of morphological comparison between different ligament entheses in the rabbit knee, the number and frequency of interdigitations and thickness of calcified fibrocartilage were quantitated at the femoral insertion of the medial collateral ligament, both insertions of the cruciate ligaments, and the tibial insertion of the patellar ligament. Among the insertions, the femoral insertion of the medial collateral ligament showed the lowest frequency and depth of interdigitations at the soft tissue-bone interface, but had the thickest zone of calcified fibrocartilage. An inverse relationship was found at the insertion interface of the cruciate and patellar ligaments. The frequency and depth of interdigations at the bone-soft tissue interface at different chondral entheses seem to be related to the mechanical strength of the respective ligament; meanwhile it may be hypothesised that the thickness of the calcified fibrocartilage might be more related to the amount of motion which takes place at an insertion.

Concentrations of proteoglycan fragments in relation to maturation, sex and time of day: physiologic variations in knee joint fluid of rabbits

We analyzed the concentrations of proteoglycan fragments in knee joint fluid in 142 rabbits to investigate the effect of physiologic variations--i.e., maturation, sex and time of day. The concentrations of proteoglycan fragments differed significantly between young, adolescent and adult animals and showed an inverse correlation to the stage of maturation of the rabbit. Adolescent male rabbits had higher concentrations than age-matched females. Morning and evening samples had similar concentrations. No relation was found between the proteoglycan fragment concentrations in joint fluid and the cartilage mass. The proteoglycan fragment concentrations in knee joint fluid apparently reflect the metabolic status of growing articular cartilage. There are considerable physiologic variations associated with maturation and sex, and these need to be taken into account when using the proteoglycan fragment concentration as a marker for joint diseases.