The effect of instrumentation on human spinal fusion mass.

STUDY DESIGN: This study is a prospective histomorphometric evaluation of human spinal fusion bone using video dimensional analysis. OBJECTIVES: Little information exists regarding the biology of fusion mass (FM) and the effect that instrumentation has on FM quality. Concerns regarding potential for "stress shielding" of FM with rigid implants have arisen. The goal of this study was to determine what effect spinal implants have on the quality and metabolism of FM bone. METHODS: Fifty-six patients underwent surgeries to remove spinal implants or extend a fusion after pulse-dose labeling with fluorochrome. Twelve patients had undergone fusions without instrumentation. Duplicate biopsies of FM and iliac crest (IC) were obtained and evaluated blindly for mineralized volume, trabecular thickness, mineralization rate, and bone formation rate. Iliac crest, instrumented FM, and noninstrumented FM were compared. RESULTS: Instrumental FM had superior material properties relative to noninstrumented FM or IC. No significant difference in metabolic activity was present. CONCLUSION: Instrumentation does not lead to FM "stress-shielding."

Extraspinal causes of lumbosacral radiculopathy.

Twelve of 12,125 patients who had been referred during a seven-year period to a specialist in spinal disorders were found to have an extraspinal cause of radiculopathy or neuropathy of the lower extremity. The records of these twelve patients were reviewed retrospectively. The average age of the twelve patients was sixty-five years (range, forty-two to seventy-seven years). The cause of the symptoms was an occult malignant tumor in nine patients and a hematoma, an aneurysm of the obturator artery, or a neurilemoma of the sciatic nerve in the others. The average time from the onset of symptoms to the final diagnosis was eight months (range, one month to two years). The most useful test for determination of the correct diagnosis was computed tomography or magnetic resonance imaging of the abdomen and pelvis. Computed tomography or magnetic resonance imaging of the spine and bone-scanning of the whole body were of little help in localizing the disease. In four of the twelve patients, an operation was performed on the basis of an incorrect diagnosis. In dealing with elderly patients who have radiculopathy, one should be suspicious that the cause is outside the spine.

Relationship between vertebral intraosseous pressure, pH, PO2, pCO2, and magnetic resonance imaging signal inhomogeneity in patients with back pain. An in vivo study.

The cause of back pain in many patients in unknown. The pain experienced by patients with osteoarthritis of large joints has been associated with intraosseous abnormalities of elevated pressure, venous dilatations, and abnormalities of pH, pCO2, and pO2. Magnetic resonance imaging demonstrates an abnormal signal in the vertebral bodies of some patients with degenerative disc disease. The intraosseous pressure as well as the intraosseous pH, pO2, and pCO2 in a group of patients undergoing anterior spine surgery was studied, and the results were correlated to the preoperative magnetic resonance imaging appearance. Vertebral bodies with an abnormal magnetic resonance imaging signal had pressures 55% higher than vertebral bodies with a homogeneous signal; they also had significantly decreased pH and increased pCO2. Bodies with Type I changes had pressures 73% higher than those with a normal signal. No differences in pO2 were identified. These findings suggest that abnormalities of intraosseous pressure or blood gas concentrations may be related to mechanisms of pain production in some patients with back pain. These abnormalities can be identified by magnetic resonance imaging. Further investigation is needed to determine if therapeutic manipulation of these variables can be effective in relieving axial spinal pain.

The value of bupivicaine hip injection in the differentiation of coxarthrosis from lower extremity neuropathy.

A series of 18 consecutive patients with roentgenographically proven osteoarthrosis (osteoarthritis, OA) of the hip and spine were evaluated because of concomitant lower extremity pain below the knee. To determine whether the leg symptoms were coxalgic or neuropathic, intraarticular hip bupivicaine was injected as a provocative test. This test allowed correct identification of the source of the pain with a sensitivity of 87%, a specificity of 100%, and an efficiency of 88%. This office test also provides significant savings in terms of diagnostic tests and patient discomfort.

Early histologic, metabolic, and vascular assessment of anterior cruciate ligament autografts.

A rabbit model for anterior cruciate ligament (ACL) reconstruction using autogenous patellar tendon was utilized to study the early events of autograft cellular dynamics. Biochemical, autoradiographic, histological, and vascular injection techniques demonstrated that the native autograft cell population rapidly necroses. This repopulation occurs without a vascular contribution; cells entering the autograft are reliant upon synovial fluid nutrition.

The chondrogenesis of rib perichondrial grafts for repair of full thickness articular cartilage defects in a rabbit model: a one year postoperative assessment.

The purpose of this study was to investigate the results or rib perichondrial grafting after the creation of a full thickness articular cartilage defect. In a rabbit model, rib perichondrium was used to repair defects created in the femoral condyle. The formation of repair tissue (neocartilage) and its chondrogenesis into a tissue resembling articular cartilage was found over time. The gross, histological and biochemical characteristics of the neocartilage were evaluated at intervals of 6, 12, 18, 26 and 52 weeks post transplant, and compared to normal articular cartilage. The neocartilage was characterized by the early formation of relatively large amounts of glycosaminoglycans. A steady increase in the proportion of type II collagen over the time periods was also observed. Improved attachment of the neocartilage to host tissues was seen over the period of 6 to 52 weeks. Successful grafts were seen to proliferate to fill the articular defect and to undergo a chondrogenesis over a post transplant time period of one year.

Perichondrial autograft for articular cartilage. Shear modulus of neocartilage studied in rabbits.

Perichondrial autografts were used for the repair of large, full-thickness articular cartilage defects in the rabbit medial femoral condyle. The effects of duration of implantation and activity were studied by evaluating the neocartilage mechanically and morphologically. The complex shear moduli for the neocartilage were found to increase during the 26 weeks' observation time. Complete filling of the defect with neocartilaginous tissue was seen in a total of 24 successful experimental samples. It appeared that in the initial 6 weeks passive motion applied intermittently for 2 weeks enhanced the formation of quality neocartilage, i.e., the magnitude of the complex shear moduli was higher than those nontreated. However, these differences disappeared when longer time periods were considered.

Effects of knee flexion on the structural properties of the rabbit femur-anterior cruciate ligament-tibia complex (FATC).

Many studies have been conducted to determine the biomechanical properties of the anterior cruciate ligament (ACL). The method of holding the femur-ACL-tibia complex (FATC) test specimen, the strain rate applied, the angle of knee flexion and the direction of the applied loads have an important effect on the outcome. It is felt that the tensile properties and strength of the ligament should be measured by applying the tensile force along the axis of the ligament. A versatile clamp was designed to accomplish this purpose. Fifty-seven rabbit knee specimens were tested at angles of flexion of 0 degrees, 30 degrees or 90 degrees. In addition, a comparative study of 25 pairs of rabbit legs were performed, whereby loading was either along the ligament or along the tibial axis. Cyclic hysteresis, ultimate load, energy absorbed, and stiffness were determined. The ultimate load values for the FATC decreased with increased knee flexion for those loaded along the tibial axis, while no such change was detected for FATC tested along the ligament axis. Other structural properties measured followed similar trends. It is concluded that the structural properties of the rabbit FATC change minimally with knee flexion (from 0 to 90 degrees) when loaded along the ligament axis, but decrease significantly with knee flexion when loaded along the axis of the tibia. Therefore, the data obtained in this field of study can be compared only if the direction of loading with respect to the ACL is similar.

Collagen alteration in medial collateral ligament healing in a rabbit model.

The purpose of this study was to evaluate changes over time in surgically ruptured medial collateral ligament (MCL) with respect to collagen synthesis, collagen degradation and collagen type. Our method involved prelabeling collagen in growing rabbits using 3H-proline followed by surgical injury to the MCL. Animals were sacrificed at intervals up to 40 weeks post-injury. At each time point total hydroxyproline, changes in collagen mass, and collagen synthesis and degradation were determined and related to the unruptured control MCL. A separate semiquantitative determination of collagen type was also performed on the midsubstance of each healing and control ligament. Results showed an increase in total collagen mass and a decrease in collagen concentration in all healing ligaments. Concommitantly, an increase in the collagen turnover rate was observed. Relative turnover was greatest at 3 to 6 weeks after injury and returned toward the normal rate by 40 weeks. Type I collagen was partially replaced by type III, probably as a result of increased synthesis during scar formation. The mechanism for collagen remodeling (replacement of mass and concentration in an organized fashion) in untreated rabbit MCL scar appears functional by virtue of its chronicity but, due to a shift in collagen type, it may also be qualitatively inadequate.

The natural history of the anterior cruciate ligament autograft of patellar tendon origin.

A rabbit model for ACL reconstruction using autogenous patellar tendon (PT) was used to study graft viability, its response to new physical forces, and the intrasynovial milieu. The autograft was assessed grossly, histologically, and biochemically with respect to time. Histologic observations demonstrated that autografts were centrally acellular with a peripheral rim of cells at 2 weeks, and had a central focal proliferation of cells at 3 weeks and cellular homogeneity by 4 weeks postoperation. Necrosis followed by cellular proliferation suggested that a population of cells other than the native PT fibroblasts may be inhabiting the graft. Graft sequestration experiments demonstrated that autografts are repopulated by cells of extrinsic origin after transplantation. Autografts showed a gradual assumption of the microscopic properties of normal ACL; by 30 weeks posttransplant the tissue characteristics were ligamentous in appearance. Histologic changes paralleled the biochemical metamorphosis: Type III collagen was not observed in PT; however, a gradual increase in its concentration was seen in the grafts; by 30 weeks its concentration (10%) was the same as in normal ACL. Similarly, glycosaminoglycan content increased from its normally low level in PT to that found in native ACL. Collagen-reducible cross-link analysis revealed that grafted tissue changed from the normal PT pattern of low dihydroxylysinonorleucine and high histidinohydroxymerodesmosine to the opposite pattern seen in normal ACL by 30 weeks. These data suggest that PT autografts undergo a process of "ligamentization" when placed in the ACL environment, and that cells responsible for this metamorphosis are of extragraft origin.

Origin of replacement cells for the anterior cruciate ligament autograft.

A rabbit model for anterior cruciate ligament (ACL) reconstruction using autogenous avascular patellar tendon (PT) was utilized to study the early events of graft incorporation. Histological observations demonstrated that autografts were centrally acellular with a peripheral rim of cells at 2 weeks, a central focal proliferation of cells at 3 weeks, and a cellular homogeneous distribution by 4-weeks postoperation. Graft necrosis followed by cellular proliferation suggested that a different population of cells other than the native PT fibroblasts may be inhabiting the graft. The extrinsic contribution of cells was studied by selective destruction of native PT cells with liquid nitrogen immersion prior to reconstruction of the ACL. The intrinsic contribution of cells was evaluated by sequestration of the PT graft in a semipermeable membrane before it was used to reconstruct the ACL. Histological analysis of tissue that was liquid N2 treated, used as an autograft, and then harvested 3-weeks postoperation revealed fibroblastic incorporation of the graft. In contrast, no cells were observed in semipermeable membrane sequestered autografts. These data suggest that autogenous ACL autografts of PT origin are repopulated by cells of external origin. In vitro control studies that were carried out in parallel demonstrated that PT fibroblasts could survive in tissue culture, but not in the synovial environment of the ACL. This suggests that fibroblasts from different sources have different, tissue-specific nutritional requirements.

The phenomenon of "ligamentization": anterior cruciate ligament reconstruction with autogenous patellar tendon.

Reconstruction of the anterior cruciate ligament (ACL) with patellar tendon (PT) is a common procedure for the symptomatic ACL-deficient knee. Questions regarding graft incorporation, viability, and nutrition of the transplanted tissue are of concern. This relates to the graft's response to its new intrasynovial milieu and new physical forces. These factors were studied in a rabbit model of ACL reconstruction using PT and were evaluated with histological and biochemical parameters with respect to time. A histological and biochemical metamorphosis of the grafted PT occurred in this study. Autografts demonstrated a gradual assumption of the microscopic properties of normal ACL; by 30 weeks postoperatively, cell morphology was ligamentous in appearance. Normally, type III collagen is not observed in PT, however, a gradual increase in its concentration was seen in the grafts; by 30 weeks its concentration (10%) was the same as in normal ACL. Similarly, glycosaminoglycans content increased from its normally low level in PT to that found in native ACL. Collagen-reducible crosslink analysis demonstrated that grafted tissue changed from the normal PT pattern of low dihydroxylysinonorleucine (DHLNL) and high histidinohydroxymerodesmosine (HHMD) to the pattern seen in normal ACL (high DHLNL and low HHMD) by 30 weeks. These data suggest that when PT is placed in the anatomic and environmental milieu of the ACL, a "ligamentization" of the grafted tissue results; also the autograft initially depends on synovial fluid nutrition, as revascularization occurs after 6 weeks.

Synovial fluid nutrient delivery in the diathrial joint: an analysis of rabbit knee ligaments.

The role of synovial fluid in providing nutrition to rabbit knee ligaments and menisci was evaluated by intraarticular injection of a labeled collagen precursor, tritiated proline. Incorporation of this substrate as tritiated hydroxyproline was measured in collateral and cruciate ligaments and menisci. The injectate volume (0.35 ml) did not appreciably change the overall joint pressure as measured by a wick catheter; therefore, no alteration of synovial membrane diffusion characteristics resulted. The concentration of the injected proline (0.52 mg%) was well below that normally present in serum (2.65 mg%). Therefore, incorporation of this substrate was not driven by a concentration gradient and represented normal uptake of synovial fluid and physiological incorporation of label as measured by the presence of tritiated hydroxyproline. Autoradiography was performed on all ligaments and menisci, and demonstrated concentration of the isotope and its metabolite (tritiated proline and tritiated hydroxyproline, respectively) in and around fibroblasts. This study indicates that rabbit knee ligaments and menisci can derive nutrition from a synovial fluid source.