Journal of Musculoskeletal Research

The purpose of this communication is to present an idea, and its technical implementation, on how to estimate experimentally in vivo joint contact pressure distributions. The idea is illustrated for the cat patellofemoral joint. For this particular joint, the approach requires muscle force and hindlimb movement measurements during unrestrained locomotion, and the quantification of the joint contact pressures in situ for conditions approximating the in vivo conditions as closely as possible. Although the approach is time-consuming and has its limitations, it is, as far as we know, the first purely experimental approach to determine the in vivo joint contact pressures during normal movement. "Purely experimental" refers to the idea that the required movements, muscle forces and contact pressures are all measured rather than estimated theoretically.

We investigated whether controlled dynamization enhanced regenerate bone healing in callotasis of the tibia in 12 adult mongrel dogs. An average of 2 cm (≒ 10%) lengthening was obtained. The left hindlimb was allowed dynamization of 1 mm, 2 mm, and 3 mm in magnitude when 1 cm (≒ 5%) of lengthening was achieved, whereas the right hindlimb was not dynamized and served as a control. Bone mineral density (BMD) of the regenerate bone was measured periodically until nine weeks after the end of distraction. After sacrifice, uniaxial compression testing was performed. Relative BMD ratio and mechanical properties of the regenerate bone were significantly higher in the dynamization group than in the nondynamization group; no significant difference was found among dynamization subgroups, however. We conclude that 1 mm to 3 mm of elastic dynamization accelerates regenerate bone healing in callotasis of the canine tibia.

The objective of this study was to assess the reliability of a new computerized technique for measuring epiphyseal plate zonal height. A fully crossed two factor generalizability experiment in which the effect of observers and time on the reliability of measurements of zonal height within different regions (center and periphery) of the epiphyseal plate was examined. Photomicrographs from both the central and peripheral regions of each of the 30 canine distal ulna epiphyseal plate histological sections were considered; within each region, the proliferative and hypertrophic zones were outlined and, after calibration of the computer program, the zonal height was computed. Irrespective of whether the measures were taken from photomicrographs of the central or the peripheral region of the epiphyseal plate, results indicated higher generalizability coefficients for hypertrophic zone measurements than for those of the proliferative zone in seven of the eight intra-observer and inter-observer calculations. In addition, higher generalizability coefficients were achieved for intra-observer than for inter-observer measurement situations. It was concluded that this is a reliable technique if the sample is measured by one observer and the average of three repeated measurements is used for each specimen.

We investigated the serial changes in MR appearance of anterior cruciate ligament (ACL) grafts after reconstruction, and looked for a correlation between MRI and clinical results. Fifty-four patients underwent serial MRI examinations at 5, 11 and 24 months after arthroscopically-assisted ACL reconstruction. The MR appearance of the graft was categorized into three types depending on the signal intensity and continuity of the ligament: low signal type, intermediate type and high signal type. For the low signal type, a homogeneous low signal band with continuity was visualized over the entire course; for the intermediate type, the signal intensity increased and low signal band was visualized only in part of the graft; and for the high signal type, the graft was not identified through the joint cavity due to markedly increased signal. Forty-three of the 54 patients retained normal low signal type during the first two years of reconstruction. They were classified as Group A. Four of the remaining 11 patients showed intermediate type at five months and altered to high signal type after 12 months. The remaining seven patients showed high signal type at five months and persisted with the same MR type until 24 months. These 11 patients with increased signal intensity were classified as Group B. The mean injured-to-uninjured differences of KT-2000 arthrometer measurements were significantly greater in Group B than that in Group A. Moreover, the percentage of cases with a difference of 5 mm or more was significantly higher in Group B (54.5%) than in Group A (9.3%). It is concluded that the majority of the grafts showed no changes in signal intensity during the first two years of reconstruction. The increase in signal intensity observed in some patients may be a reflection of a deterioration in graft integrity following reconstruction.

In total knee replacement, a good match of the prosthesis to bone is very important. Most knees that require total knee replacement are deformed. However, most of the design parameters of knee prosthesis were based on the normal knee. In this series, the dimensions of the resected surfaces in 77 osteoarthritic knees were measured intraoperatively and compared with the corresponding surfaces of the porous-coated anatomic (PCA) (Howmedica, Rutherford, NJ, USA) knee prosthesis. The results showed that the medial femoral condyle was wider than the lateral femoral condyle (p < 0.05) in the resected surfaces. The intercondylar notch of the resected femur was wider than that of the prosthesis (p < 0.05). In the resected tibial plateau, the ratio of the anteroposterior length to the mediolateral width was larger than that of the prosthesis (p < 0.05). The length and width of the resected patella were greater than those of the implant (p < 0.05). According to the difference in morphometrical parameters between the resected surfaces and the knee prosthesis, we suggest that the dimensions of the resected surfaces of the osteoarthritic knee should be important design parameters in total knee prosthesis.

In double-door laminoplasty, several types of artificial spinous process spacers have been used instead of grafted bone from the iliac crest. However, inadequate contact between the spacer and the spinous process has recently been reported. From the observation during operation, we suspect that the main cause of the inadequate contact is the difference in shape between the spacer and the widened space created by the split spinous processes.

The purpose of this study was to investigate the shape of the widened space by means of a finite element analysis in order to confirm our observation objectively and to provide a shape design of a spacer adapting to the space.

Half-sectioned finite element models of the second cervical (C2) vertebra and the C6 vertebra were made from both the computed tomography (CT) of a clinical case and a plastic model of a cervical spine. The finite element model was designed to have almost the same size and shape as those of the genuine vertebra in the clinical case. Since cancellous bone and soft tissues were thought not to meaningfully influence the rigidity of the model, the model was made of only cortical bone with a thickness of 1.5 mm.

The x-axis was defined as the lateral direction of the vertebral body, the y-axis as the anteroposterior direction of the vertebral body and the z-axis as the craniocaudal direction along the posterior margin of the vertebral body. The boundary conditions were fixed at the inner surface of the half-sectioned vertebral body. A force of 100 N was applied to the inner surface of the half-sectioned spinous process (to the cranial side and the caudal side, 50 N each) in the direction of the x-axis. The lateral deviation of each split spinous process was defined as the degree of deviation in the x-axis direction. The degree of lateral deviation of each split spinous process was analyzed in two types of models with and without making a lateral gutter 4 mm wide along the z-axis direction.

The lateral deviation at the cranial side was larger than that at the caudal side in both the C2 and C6 vertebrae. The difference between the lateral deviation at the cranial side and the caudal side of each vertebra was larger in the type of model with the lateral gutter than in the type of model without it.

It was confirmed that the shape of the widened space is trapezoidal in not only the axial but also frontal sections. In conclusion, the optimal shape of a spacer adapting to the widened space in double-door laminoplasty is trapezoidal in not only the axial but also frontal sections.

We developed a model where a 2-cm full-thickness canine ulnar defect bridged with a tubular diaphyseal bone transplant was stabilized with an intramedullary Kirschner wire. This model was used to compare tubular autografts and allografts in the reconstruction of segmental ulnar defects in 12 adult beagle dogs. The dogs were followed for nine months and X-ray radiographs were taken every three weeks. The overall healing was good and all the dogs were able to walk normally during the follow-up. After nine months, the ulnas were harvested and mechanical testing and histological analyses were made. Of the ulnar defects, 4/6 in the autograft group and 3/6 in the allograft group had a complete union. Of the Kirschner wires, 6/12 had broken during the follow-up. This did not have any effect on the bone union, however. The autograft group had better results in mechanical testing although the difference was statistically significant only for maximal absorbed energy. We conclude that the segmental ulnar defect model fixed with an intramedullary wire seems to be a feasible alternative in bone transplant studies, although the semirigid fixation resulted in breakage of the wire in many cases. The overall healing was good after both autograft and allograft transplantations, but autografts seemed to be slightly better.

We describe here the finding of a huge perineurial cyst which eroded the sacral body. On MRI examination, a huge cyst occupied the space within the sacral spinal canal. On myelography, however, the cyst was not filled with contrast medium immediately after dye injection. Since the patient was disabled by pain, we resected the cyst microscopically. Histological examination revealed neurofibrils in the wall of the cyst. Based on these and myelographic findings, perineurial cyst was diagnosed. Surgical indications for this lesion are still controversial since most are asymptomatic. It is our opinion that if sacral cystic lesions are large enough to erode sacral bone nearly to the retroperitoneal space or sacro-iliac joint, they should be surgically resected using operative microscope.