Objectives-(a) To determine the topographical variations in cartilage thickness over the entire surfaces of cadaveric lower limb joints, and (b) to examine the correlations between: cartilage thickness and its site specific modulus; cartilage thickness and donor age, weight, height, and body mass index. Methods-The cartilage thickness of 11 sets of cadaveric human joints each comprising an ankle, knee, and hip was measured using a needle probe technique. Statistical analysis was used to compare the cartilage thickness of the diVerent lower limb joints and the diVerences in cartilage thickness over the surface of individual joints. It was further examined whether cartilage had a correlation with its stiVness, and any of the details of the specimen donors such as age, weight, height, and body mass index. Results-The mean cartilage thickness of the knee was significantly greater than that of the ankle and hip (p<0.001) in all 11 sets of joints, while the cartilage thickness of the hip was significantly greater than that of the ankle in 10 sets of joints (p<0.001). The mass of specimen donors was found to correlate with the mean cartilage thickness of all three lower limb joints. A correlation was also found between the height of donors and the mean cartilage thickness of the knee and hip joints, while only in the ankle joint was a correlation found between the mean cartilage thickness and the body mass index of the specimen donors. A further correlation was found between cartilage thickness and its modulus; the thinner the cartilage, the higher the modulus. Conclusions-The thickness of articular cartilage seems to be related to the congruance of a joint; thin cartilage is found in congruent joints such as the ankle, whereas thick cartilage is found in incongruent joints such as the knee. The correlations in this study imply that the larger and heavier was a donor the thicker was the cartilage in the lower limb joints. The data further suggest the presence of an inverse relation between the mean cartilage thickness and mean compressive modulus in each of the joints examined.

The topographical variations in the cartilage instantaneous compressive modulus over the surfaces of the lower limb joints were matched by differences in the stresses occurring in different areas of each joint. The results of the present study corroborate previous findings and show that the site-specific stresses and corresponding values of the instantaneous cartilage compressive modulus over the surfaces of lower limb joints were correlated (r = 0.82 at P < 0.01), thus adding credence to the conditioning hypothesis of cartilage by prevalent stress.

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The menisci of the knee joint transmit a considerable fraction of the total load acting on the joint. This paper describes an investigation into the load carrying capacity of the individual meniscus. Interest is also directed to an examination of the function of the degenerate meniscus and that of thc meniscus with different kinds of tears. Quantifying the meniscal loads is based on afour-spring model representing the load bearing areas in the knee with intact menisci. The assumptions underlying the model are discussed and the problems of loading associated with the four-spring model are described. These problems called for careful consideration of the methods of loading and aligning the joint. A loading machine with a special aligning device was built for the experimental work.The experimental procedure is described in Part II. The intact individual meniscus wasshown to transmit 70 -99 per cent of the load acting on the respective side. The load carrying capacity of the meniscus was shown to decrease following the removal of a simulated 'bucket-handle' tear but in some cases it remained virtually unaltered. The stresses in the knee with redundant menisci were shown to increase by three to five fold their magnitude in the knee with intact menisci. Following removal of a simulated 'bucket-handle' tear, the stresses increased, but much less dramatically. The clinical implications of total and partial meniscectomy are discussed.

The joint and muscle forces arising from and generated in the knee during the activity of squatting, and rising from a deep squat have been calculated. The analysis involved the consideration of a two-dimensional model. Data was then collected from each of the subjects performing the activity using: a force platform; a ciné film used in conjunction with the X-rays to describe accurately the configuration of the lower limb; EMG data; anthropometric data. A computer program was developed to analyse the data and compute the forces in the leg. Six subjects were tested and graphs of joint and muscle forces versus knee angle were obtained for each of them. A discussion follows. The results for ascent and descent, and slow and fast activities are compared.

Current techniques used for total knee arthroplasty rely on conventional instrumentation that violates the intramedullary canals. Accuracy of the instrumentation is questionable, and assembly and disposal of the numerous pieces is time consuming. Navigation techniques are more accurate, but their broad application is limited by cost and complexity. We aimed to prove a new concept of computer-assisted preoperative planning to provide patient-specific templates that can replace conventional instruments. Computed tomography-based planning was used to design two virtual templates. Using rapid prototyping technology, virtual templates were transferred into physical templates (cutting blocks) with surfaces that matched the distal femur and proximal tibia. We performed 45 total knee arthroplasties on 16 cadaveric and 29 plastic knees, including a comparative trial against conventional instrumentations. All operations were performed using patient-specific templates with no conventional instrumentations, intramedullary perforation, tracking, or registration. The mean time for bone cutting was 9 minutes with a surgical assistant and 11 minutes without an assistant. Computer-assisted analyses of six random computed tomography scans showed mean errors for alignment and bone resection within 1.7 degrees and 0.8 mm (maximum, 2.3 degrees and 1.2 mm, respectively). Patient-specific templates are a practical alternative to conventional instrumentations, but additional clinical validation is required before clinical use.

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