Open reduction and internal fixation of proximal humeral fractures with use of the locking proximal humerus plate. Surgical technique.

BACKGROUND: The treatment of unstable displaced proximal humeral fractures, especially in the elderly, remains controversial. The objective of the present prospective, multicenter, observational study was to evaluate the functional outcome and the complication rate after open reduction and internal fixation of proximal humeral fractures with use of a locking proximal humeral plate. METHODS: One hundred and eighty-seven patients (mean age, 62.9 +/- 15.7 years) with an acute proximal humeral fracture were managed with open reduction and internal fixation with a locking proximal humeral plate. At the three-month, six month,and one-year follow-up examinations, 165 (88%), 158 (84%), and 155 (83%) of the 187 patients were assessed with regard to pain, shoulder mobility, and strength. The Constant score was determined at each interval, and the Disabilities of the Arm, Shoulder and Hand (DASH) score was determined for the injured and contralateral extremities at the time of the one-year follow-up. RESULTS: Between three months and one year, the mean range of motion and the mean Constant score for the injured shoulders improved substantially. Twelve months after surgery, the mean Constant score for the injured side was 70.6 +/- 13.7 points, corresponding to 85.1% +/- 14.0% of the score for the contralateral side. The mean DASH score at the time of the one-year follow-up was 15.2 +/- 16.8 points. Sixty-two complications were encountered in fifty-two (34%) of 155 patients at the time of the one-year follow-up. Twenty-five complications (40%) were related to incorrect surgical technique and were present at the end of the operative procedure. The most common complication, noted in twenty-one (14%) of 155 patients, was intraoperative screw perforation of the humeral head. Twenty-nine patients (19%) had an unplanned second operation within twelve months after the fracture. CONCLUSIONS: Surgical treatment of displaced proximal humeral fractures with use of the locking proximal humeral plate that was evaluated in the present study can lead to a good functional outcome provided that the correct surgical technique is used. Because many of the complications were related to incorrect surgical technique, it behooves the treating surgeon to perform the operation correctly to avoid iatrogenic errors.

Open reduction and internal fixation of proximal humeral fractures with use of the locking proximal humerus plate. Results of a prospective, multicenter, observational study.

BACKGROUND: The treatment of unstable displaced proximal humeral fractures, especially in the elderly, remains controversial. The objective of the present prospective, multicenter, observational study was to evaluate the functional outcome and the complication rate after open reduction and internal fixation of proximal humeral fractures with use of a locking proximal humeral plate. METHODS: One hundred and eighty-seven patients (mean age, 62.9 +/- 15.7 years) with an acute proximal humeral fracture were managed with open reduction and internal fixation with a locking proximal humeral plate. At the three-month, six-month, and one-year follow-up examinations, 165 (88%), 158 (84%), and 155 (83%) of the 187 patients were assessed with regard to pain, shoulder mobility, and strength. The Constant score was determined at each interval, and the Disabilities of the Arm, Shoulder and Hand (DASH) score was determined for the injured and contralateral extremities at the time of the one-year follow-up. RESULTS: Between three months and one year, the mean range of motion and the mean Constant score for the injured shoulders improved substantially. Twelve months after surgery, the mean Constant score for the injured side was 70.6 +/- 13.7 points, corresponding to 85.1% +/- 14.0% of the score for the contralateral side. The mean DASH score at the time of the one-year follow-up was 15.2 +/- 16.8 points. Sixty-two complications were encountered in fifty-two (34%) of 155 patients at the time of the one-year follow-up. Twenty-five complications (40%) were related to incorrect surgical technique and were present at the end of the operative procedure. The most common complication, noted in twenty-one (14%) of 155 patients, was intraoperative screw perforation of the humeral head. Twenty-nine patients (19%) had an unplanned second operation within twelve months after the fracture. CONCLUSIONS: Surgical treatment of displaced proximal humeral fractures with use of the locking proximal humeral plate that was evaluated in the present study can lead to a good functional outcome provided that the correct surgical technique is used. Because many of the complications were related to incorrect surgical technique, it behooves the treating surgeon to perform the operation correctly to avoid iatrogenic errors.

Is locking nailing of humeral head fractures superior to locking plate fixation?

UNLABELLED: The optimal surgical treatment of displaced proximal humeral fractures is controversial. New implants providing angular stability have been introduced to maintain the intraoperative reduction. In a multi-institutional study, we prospectively enrolled and followed 152 patients with unilateral displaced and unstable proximal humeral fractures treated either with an antegrade angular and sliding stable proximal interlocking nail or an angular stable plate. Fractures were classified according to the Neer four-segment classification. Clinical, functional, and radiographic followups were performed 3, 6, and 12 months after surgery. Absolute and relative (to the contralateral shoulder) Constant-Murley scores were used to assess postoperative shoulder function. Using age, gender, and fracture type, we identified 76 pairs (152 patients) for a matched-pairs analysis. Relative Constant-Murley scores 12 months after treatment with an angular and sliding stable nail and after plate fixation were 81% and 77%, respectively. We observed no differences between the two groups. Stabilization of displaced proximal humeral fractures with either an angular stable intramedullary or an extramedullary implant seems suitable with both surgical treatment options. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Humeral head necrosis rate at mid-term follow-up after open reduction and angular stable plate fixation for proximal humeral fractures.

INTRODUCTION: Short-term follow-up of angular stable fixation for proximal humeral fractures has been well documented in the literature. Longer follow-up series are difficult to find. However, especially regarding the risk of avascular humeral head necrosis longer follow-up series are high of clinical relevance. METHODS: Forty-eight patients with a mean age of 66 years and treated with open reduction and angular stable internal fixation for proximal humeral fractures were followed up for a mean of 45 months. The clinical and radiographic follow-up (Constant Score (CS), age and gender related Constant Score (agCS), Constant Score in comparison to the contralateral side (%CS) and shoulder anterior-posterior and lateral view and axial view X-rays) was performed postoperatively. RESULTS: Clinical results after 45 months showed a mean CS of 66.2+/-15.4 points with a mean agCS of 90.0+/-23.1%. Evaluation of the %CS showed 77.7+/-17.8%. %CS results showed no significant differences after 45 months in comparison to those obtained after 12 months. However, incidence of avascular necrosis of the humeral head doubled over the follow-up period from 4 cases at 12 months follow-up to 9 cases at final follow-up. CONCLUSION: Results of open reduction and internal fixation with angular stable implants for proximal humeral fractures are reliable, however long-term complications such as avascular necrosis of the humeral head need to be evaluated further on since its incidence increases over the time.

[Management of bicondylar fractures of the tibial plateau with unilateral fixed-angle plate fixation]. / Versorgung von bikondylären Tibiakopf-Frakturen mit einem unilateral platzierten winkelstabilen Plattensystem.

BACKGROUND: This study was initiated to evaluate early results of a locked screw plate for unilateral fixation of bicondylar fractures of the tibial plateau. Emphasis was laid on malreduction, secondary loss of reduction, union rate, and infection. MATERIAL AND METHODS: A case series of patients with AO/ASIF 41-C type fractures treated with the less invasive stabilization system for the proximal lateral tibia (LISS PLT) were prospectively followed up until 11-13 months after surgery. Malreduction and malalignment were defined as an intra-articular step-off of 2 mm or more or as a malalignment in the frontal or sagittal plane of more than 5 degrees. RESULTS: Sixty-eight patients with 69 fractures were involved. Fourteen fractures were open. Primary bone grafting was performed in 13 patients. Significant malreduction was seen in 16 patients. Sixty-two (91%) patients returned for follow-up. All but one fracture healed eventually. The number of infections was low (4 superficial, 1 deep). Nine patients had a significant loss of reduction. Of 54 patients outcome scores were good to excellent in 47 patients on the Lysholm score (average 87.2) and in 44 patients on the Rasmussen score (average 26.7). CONCLUSION: We concluded that unilateral locked screw plating is a good alternative in the treatment of problematic fractures of the tibial plateau that are associated with soft tissue damage and metaphyseal comminution. The reduction technique for exact alignment is demanding.

In vivo glenohumeral contact forces--measurements in the first patient 7 months postoperatively.

Knowledge of forces in the glenohumeral joint is essential for understanding normal and pathologic shoulder function. It forms the basis for performing fracture treatment or joint replacement surgery, for optimizing implant design and fixation and for improving and verifying analytical biomechanical models of the shoulder. An instrumented shoulder implant with telemetric data transmission was developed to measure six components of joint contact forces and moments. A patient with humeral head arthrosis achieved good joint function after its implantation. During the first 7 postoperative months, the contact force remained below 100% BW (percent body weight) for most activities of daily living. It ranged up to 130% BW for arm positions close to the limits of motion or when acting against external resistance. When the patient tried to turn a blocked steering wheel with maximum effort, the force rose to about 150% BW, the highest level observed thus far. Of great interest were the force directions relative to the humerus, especially those in the sagittal plane, which were not greatly influenced by the type of exercise, the arm position or the external resistance. The moments due to friction in the joint reached 5.2 Nm. The friction-induced shift of contact forces relative to the implant head centre ranged up to 6.3mm. These first worldwide in vivo measurements of glenohumeral contact forces are being continued in more patients and for longer postoperative times.

Stabilisation of periprosthetic fractures with angular stable internal fixation: a report of 13 cases.

INTRODUCTION: Periprosthetic fractures of the femur present a challenging surgical problem. The aim of this study was to retrospectively evaluate the outcome of periprosthetic fractures stabilised with an angular stable, less invasive stabilisation system (LISS). PATIENTS AND METHODS: Thirteen patients (ten total hip-, two total knee-, one total hip- and knee-arthroplasty) with periprosthetic fractures were treated with the LISS internal fixator (in ten cases minimal invasive). Six patients had previous operations due to periprosthetic fractures. The average follow-up period was 20 months, follow-up rate 85%. RESULTS: All fractures showed radiographic fracture healing without implant loosening. Except one patient, all patients had returned to their pre-operative activity level. No early post-operative complications were seen. There was one implant failure after 4 months and two cases of malunion. CONCLUSION: The cases showed the internal fixator to be effective for the stabilisation of periprosthetic fractures, even in cases of poor bone quality with good functional outcomes. The internal fixator, with the option of minimal invasive application, is the preferred method of osteosynthesis in periprosthetic fractures.

Locked internal fixator: sensitivity of screw/plate stability to the correct insertion angle of the screw.

OBJECTIVE: Internal fixators with angular stability have been developed to provide high stability without compression of the plate on to the bone. Angular and axial stability of a plate-screw construct can be achieved using a conically threaded screw head undersurface and a corresponding conically threaded plate hole. Furthermore, the insertion angle of the screw must correspond precisely to the axis of the screw hole. This is not always achieved in clinical practice and may result in screw loosening. The objective of this study was to examine the relationship between the stability of the locked screw-plate on the insertion angle of the screw. METHODS: Locking screws were inserted in an isolated (Point Contact Fixator, PC-Fix) or combined (Locking Compression Plate, LCP 4.5) locking hole with the use of an aiming device. The optimal insertion angle for these plates is perpendicular to the plate surface. The screws were inserted with an axis deviation of 0 degrees (optimal condition), 5 degrees , and 10 degrees respective to the optimal angle (variance +/- 1 degrees ). The samples were tested under shear or axial (push out) loading conditions until failure occurred. An Instron materials testing machine was used. RESULTS: Locking screws inserted in the isolated locking hole (PC-Fix) showed a significant decrease of failure load if inserted at 5 degrees and 10 degrees angle. Using an optimal insertion angle (0 degrees ), failure load was 1480 +/- 390 N, with 5 degrees axis deviation 780 +/- 160 N, P = 0.0001, and with 10 degrees axis deviation 550 +/- 110 N, P = 0.0001. Screws inserted in the combined locking hole (LCP) also showed a significant decrease of push-out force of 77% (4960 +/- 1000 N versus 1120 +/- 400 N) with 10 degrees axis deviation. Compared to optimal insertion angle (0 degrees ), bending load to failure did decrease up to 69% (1240 +/- 210 N vs. 390 +/- 100 N) with 10 degrees axis deviation. CONCLUSION: A locking head screw exhibits high stability with a moderate axis deviation in the angle of insertion of up to 5 degrees . However, there is a significant decrease in stability with increasing axis deviation (>5 degrees ). An aiming device is recommended to provide optimal fixation with angular stability.

Deformation of chondrocytes in articular cartilage under compressive load: a morphological study.

The main function of articular cartilage is to transmit load. The objective of this study was to describe the deformation of chondrocytes under static loading and its relation to collagen matrix deformation. Whole intact rabbit knee joints were loaded statically with either high or low magnitude and long or short duration. Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. With this method an immediate preservation of the chondrocyte in its loaded state was possible. Static compression of articular cartilage produced a zone-specific deformation of chondrocyte shape, depending on the magnitude and duration of load. Under high-force and long-duration loading, the chondrocytes showed considerable deformation concomitant with the highly deformed collagen fibres. Chondrocyte deformation occurred mostly in the transitional and upper radial zones and less in the lower layers. There was no significant change of the chondrocyte shape in the tangential zone under high- or low-force short-duration loading. These results show that the chondrocytes undergo significant changes in shape ex vivo and that they are sensitive to differences in the magnitude and duration of loads being applied. Chondrocyte deformation is strongly linked to the deformation of the surrounding cartilage collagen matrix.

Stabilization of proximal tibial fractures with the LIS-System: early clinical experience in Berlin.

The Proximal Tibia Less Invasive Stabilization System (LISS PLT) is an internal fixator for the treatment of proximal tibial fractures according to the principles of "Minimally invasive surgery". From July 1998 to August 2000 22 fractures were treated in our clinic with the new Proximal Tibia LISS and the prospective course of healing was documented. The period of follow-up was 12 months. The inclusion criteria were defined as proximal tibial shaft fractures and intraarticular proximal tibial fractures of all degrees of severity. A total of 15 proximal medial and lateral tibial plateau fractures (AO 41) and 7 metaphyseal fractures were treated (AO 42), seven of these fractures presented with open soft tissue damage. The average age of the patients treated was 42 years. With a follow-up rate of 91% (2 patients lost to follow-up), definite consolidation of the fracture was seen in 19/20 cases. In one patient, the fracture had only been partially bridged and secondary bone grafting was performed. Radiologically, there was one case of a varus malalignment of 6 degrees, in two further cases there were valgus malalignments of 5 degrees and 7 degrees at the time of surgery. The other cases all healed in correct alignment. In one case, the implant became loose on the distal shaft and was stabilized again using bicortical screws. In a case with type IIIB soft tissue damage, a soft tissue infection became manifest, but healed uneventfully after a revision operation with the implant in situ.

[Accuracy of routine MRI in lesions of the supraspinatus tendon--comparison with surgical findings]. / Treffsicherheit der nativen und kontrastverstärkten MRT im Routineeinsatz bei Supraspinatussehnenrupturen--Vergleich mit operativen Ergebnissen.

PURPOSE: To determine the correlation of the extent of lesions of the supraspinatus tendon in MRI's of the shoulder with surgical or arthroscopic findings using the classification of Snyders and Batemann, respectively. MATERIALS AND METHODS: The preoperative MRI's of 80 patients (age: 16 - 76/47.4 +/- 14.0 years) which were performed due to various complaints of the shoulder were analyzed retrospectively by two experienced and blinded radiologists. We evaluated the incidence and the extent of partial or complete ruptures of the supraspinatus tendon. After MRI, an arthroscopic or open surgical intervention was performed (= gold standard). Various MR-scanners were used with a field strength of 1.0 T (17 cases), or 1.5 T (63 cases) and flexible or inflexible arthro coils. Additionally to plain MRI, 38 of 80 patients underwent contrast enhanced MRI. The MR and the surgical or arthroscopic findings were compared and statistically analyzed. RESULTS: Neglecting the localization and the extent of discontinuity of the supraspinatus tendon, the sensitivity of the 80 MRI's was 0.93, the specificity 0.69, and the accuracy 0.85. The sensitivity increased to 0.96 with constant specificity and an accuracy of 0.83 excluding the lesions with an extent below 1 cm. Compared with non-enhanced examinations, the contrast enhanced MRI revealed higher sensitivity (+ 7 %, 0.89 vs. 0.96), higher specificity (+ 11 %, 0.64 vs. 0.75), and higher accuracy (+ 8 %, 0.81 vs. 0.89) in depicting lesions of the supraspinatus tendon at all. On T 1 -weighted images, the detection of lesions at all and the differentiation between partial and complete ruptures were improved significantly by contrast enhancement, especially in lesions with an extent below 1 cm. Diagnostic failures were seen in examinations without intravenous contrast application, artifacts, extent of the lesion below 1 cm, differentiating between degeneration and partial rupture of the tendon, differentiating between severely degenerated tendons with partial rupture and complete rupture, and covered ruptures. CONCLUSIONS: The performance and consecutively the analysis of the widely used MRI of the shoulder is often not sufficiently reliable in its present routine form. To be able to compete with other imaging modalities such as sonography, standardized MR protocol, contrast enhancement as needed, avoiding the described source of failure, and an exact analysis should be applied.

Less invasive stabilization system (LISS) in the treatment of distal femoral fractures.

The treatment of distal femoral fractures has been associated with a high rate of complications for a long time. Although implants and surgical techniques have improved, plate osteosynthesis and intramedullary nailing have been accompanied by a high occurrence of infection, non-union and malalignment. The treatment of soft tissue envelopes using "biological" osteosynthesis and minimally invasive approaches has resulted in a decrease in complication rates and ultimately led to the concept of the less invasive stabilization system (LISS). This is an extramedullary-applied, internal fixator shaped according to the implantation site anatomy, with minimal invasiveness. The purpose of this study was to present this new surgical technique and draw attention to its advantages and importance. Although this is not a scientific paper, we hope to provide enough evidence of the LISS usefulness. The main LISS components include multiple-fixed angle screws and an insertion handle for submuscular sliding of a fixator and placement of percutaneous, self-drilling, unicortical screws for fixation of the diaphyseal fracture fragments. The LISS has been designed to preserve periosteal perfusion and to facilitate a minimally invasive application. Since the first implantation of the LISS, only a few studies have been published on its use in treatment of distal femoral fractures. The rate of infection has been low, ranging from 0 to 4%. The rate of delayed union has been between 2.4 and 6.1%, but delayed unions do not necessarily lead to secondary bone grafting or repeat osteosynthesis as the LISS has a high and lasting stability. When the LISS is used, bone grafting is rarely necessary (0 to 1.6% in primary and 0 to 5% in secondary grafting). Also implant failure differs from the failure of plate osteosynthesis because, with the use of LISS, no screw loosening or secondary malalignment occurs. Implant failures (up to 7.4%) were recorded particularly at the time of LISS introduction in surgical practice and were attributed to the technique of implantation rather than to the implant itself. Good treatment outcomes have been reported. The average knee flexion has been 103 degrees and 107 degrees. In 72.5% of the patients, flexion has been more than 90 degrees and an extension lag of > or = 10 degrees has been found in only 7.5% of all cases. The average Neer score has ranged from 73.9 to 77.2 points. In conclusion, the LISS is a useful implant for treatment of distal femoral fractures, especially when bone quality is poor. Infection, delayed union and non-union rates are low, as shown by yet unpublished data from our clinic. Primary bone grafting, which is rarely necessary with this system, is carried out only when there is a great bone loss. Implant failure, such as screw loosening or secondary malalignment, is not seen.

Treatment of diaphyseal fractures of the forearm using the Point Contact Fixator (PC-Fix): results of 387 fractures of a prospective multicentric study (PC-Fix II).

Fractures of the forearm are considered to be a very good indication for plating. Conventional plating is still technically demanding. Extensive animal studies show that there is potential for improvement. The method consists of using an internal fixator that minimizes implant contact to the bone to reduce biological damage. Furthermore, foregoing the need for precise reduction and interfragmental compression makes it easier to use and, therefore, it should be safer. The goal of the study was to observe handling qualities, healing, and complications. For this purpose the study was designed to yield a very high follow-up in clinics with adequate experience and with a number of different surgeons performing the internal fixation. The study was designed as a prospective multicentre investigation in 16 trauma centres worldwide. To test the new approach to internal fixation, diaphyseal fractures of the forearm were stabilized surgically with the PC-Fix (Point-Contact Fixator) system, namely, 387 fractured bones involving 277 forearms in 272 patients. Internal fixation was performed using 387 PC-Fixators. 21% of the fractures were open and 25% occurred in polytraumatized patients. The rate of follow-up was 97%. 355 fractured bones healed uneventfully within four months. Overall, there were 32 complications before bone union occurred; 27 of these bones required re-operation (27 of 387, 7%). All of them subsequently healed without further complications. There were 15 delayed or non-unions and seven implant loosenings, two of which were associated with infection. Two superficial (0.6%) and two deep infections (0.6%) occurred in 306 closed fractures. Deep infection developed in one of 81 osteosyntheses of open fractures (1.2%). Other complications included one synostosis, fractures with the implant in situ with adequate trauma involving three bones, and two secondary correction procedures for postoperative malalignment. There were seven refractures occurring at a mean of three weeks after the removal of 150 PC-Fixators (4.7%). This study demonstrated that the technique of using an internal fixator is a simple one for the fixation of forearm fractures, resulting in shorter duration of surgery with a low rate of complications compared with the data reported in the literature on conventional techniques for forearm fracture stabilization.

Chondrocyte death precedes structural damage in blunt impact trauma.

Joint impact trauma has been shown to cause fissures, fibrillation, and other structural damage of the cartilage or subchondral bone. Previous studies used impact energies sufficient to fracture the underlying bone. Under these circumstances, the initial influence of impact trauma on cellular components and cartilage structure is unknown. The goal of this study was to determine whether an impact trauma first causes cellular or structural damage to a cartilage layer. Such damage might be the starting point of degenerative changes found in osteoarthrosis. Porcine patellas (n = 12) were subjected to standardized low-impact loading of three magnitudes with a spherical impactor attached to a drop tower device (0.06, 0.1, and 0.2 J). India ink staining and scanning electron microscopic analysis were used for analysis and showed no evidence of gross structural disruption. Chondrocyte viability assessed with thiazole blue staining and propidium iodide counterstaining was reduced significantly in the tangential and middle zones with increasing impact energy. These results indicate that chondrocyte death may precede excessive structural damage reported in earlier studies and might be a crucial factor in posttraumatic osteoarthrosis.

The acute structural changes of loaded articular cartilage following meniscectomy or ACL-transection.

OBJECTIVE: Meniscectomy and anterior cruciate ligament (ACL) rupture have been identified as precursors of osteoarthrosis (OA) in clinical reviews and animal experiments. In this study, the acute effects of these injuries on articular cartilage matrix deformation, preserved in a loaded state using a cryopreservation technique, were studied by scanning electron microscopy (SEM). METHOD: Whole knee joints from adult White New Zealand rabbits (N=87) were loaded ex vivo, using a simulated quadriceps pull under static and cyclic loading conditions, following medial meniscectomy or transection of the ACL. Specimens were plunge-frozen while under load, or following a recovery period, and prepared for SEM by cryofixation. Using SEM and photographic images, the medial tibial plateau cartilage was assessed both qualitatively and quantitatively. RESULTS: After meniscectomy, significantly increased bending and crimping of radial collagen fibers occurred with static loading. Compared to intact knees, the area of tibial cartilage showing an indentation was increased by 80% (P< 0.05), the articular cartilage thickness was significantly more reduced when under load (for high force long duration static loading, intact joints had 53%+/-3 reduction in cartilage thickness compared to 39%+/-4 after meniscectomy, P< 0.05), and it took nearly twice as long for the cartilage thickness to recover following loading. These post-meniscectomy differences were either not present or were minimal when the joint was allowed to extend when loaded. ACL-transection slightly increased collagen deformation in the deeper zones, but only with cyclic loading. CONCLUSION: The findings indicate that, with static loading, significantly increased deformation of articular cartilage collagen structure can occur following meniscectomy, but is minimized by joint motion. This increased deformation may be relevant to the etiology and progression of joint degeneration.

Effect of mechanical load on articular cartilage collagen structure: a scanning electron-microscopic study.

Little is known about the morphological effect of a mechanical load upon articular cartilage. The objective of this study was to describe and quantify the deformation of the articular cartilage collagen structure of the tibial plateau under static loading. Whole intact rabbit knee joints were loaded in vitro by simulating a quadriceps force of 3x, 1x or 0.5x body weight (high, medium, low) over durations of 30 or 5 min (long, short). Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. Under high force and long duration loading the collagen fibers exhibited high deformation with an increased thickness of the layer of collagen fibers oriented almost parallel to the surface and a cartilage thickness reduced to 54%. Collagen fiber deformation occurred mostly in the transitional and upper radial zone. The area of tibial indentation and the cartilage thickness reduction increased with magnitude and duration of load. The collagen matrix did show a bulging edge at the border of the meniscus and exhibited remarkable deformation under the meniscus.

Freeze-substitution of rabbit tibial articular cartilage reveals that radial zone collagen fibres are tubules.

Investigations of the micromorphology of rabbit tibial articular cartilage using scanning and transmission electron microscopy revealed that the collagenous elements in the tissue form fluid-containing tubular structures. The commonly described radial or deep zone longitudinal fibres were found to be tubular structures with internal diameters of 1-2 microm. The walls of the tubules were composed of tightly packed fibrils of collagen. The tangential zone, close to the tibial plateau, was composed mainly of a spongy arrangement of collagen fibrils, containing bunches of tangentially lying small (< 1 microm) diameter tubules. The application of conventional chemical fixation techniques resulted in the fine detail of this tissue being obscured. When the tissue was frozen, followed by cryo-scanning electron microscopy or freeze-drying, prior to observation in the scanning electron microscope the tubule structures were not obviously present. It was only by applying freeze-substitution techniques, followed by critical point drying or resin embedding, that the structure was revealed clearly. Segregation of water into ice crystals did occur during the freezing process, but the formation of those crystals played no part in creating the tubular morphology observed. A similar structure was still revealed following pre-treatment with glycerol, methanol or Triton X-100, provided that concentration of these additives was not too high. The walls of the tubules in the radial region were composed of straight, longitudinally arranged as well as helically arranged, 30 nm diameter fibrils. The lumen of the tubules appears to be lined by a circumferentially arranged array of approximately 10 nm diameter fibres, spaced at regular intervals of 50-70 nm.