Fixed-angle screws vs standard screws in acetabular prosthesis fixation: a cadaveric biomechanical study.

Secure fixation of acetabular components in total hip arthroplasty can be challenging. The purpose of this study was to perform biomechanical analysis of cup fixation strength using fixed-angle vs standard screw fixation. Multihole, porous-backed acetabular prostheses were implanted in both acetabuli of 8 cadaveric pelves using standard press-fit techniques. Fixed-angle screws were used on the left side, and standard cancellous screws were used in the right. The use of fixed-angle screws enhanced acetabular fixation substantially under subfailure cyclic loading conditions and load-to-failure. The triradiate screw configuration increases the bending moment required to fail the specimens as well. Fixed-angle screws may be useful for achieving rigid fixation of acetabular prostheses in challenging clinical scenarios.

Direct tendon attachment and healing to porous tantalum: an experimental animal study.

BACKGROUND: The ability to directly attach soft-tissue to metal would have broad clinical application. Previous attempts to obtain normal tendon-to-bone attachment strength have been unsuccessful. In the present study, we hypothesized that when the initial interface mechanical environment is carefully controlled, a highly porous form of tantalum metal would allow the ingrowth of tendon tissue with clinically relevant tendon-to-implant fixation strength approaching that of an intact tendon-to-bone insertion. METHODS: Supraspinatus tendons from forty skeletally mature dogs were reattached to the greater tuberosity between two custom-designed porous tantalum washers. Clinical function as judged on the basis of gait analysis, reattachment fixation strength and stiffness, and tendon function as seen through muscle volume were evaluated preoperatively, immediately postoperatively, and at three, six, and twelve weeks after surgery. Qualitative and quantitative histomorphologic evaluation was performed at three, six, and twelve weeks after surgery. RESULTS: Gait analysis with use of force-plate measurements demonstrated return to a normal gait pattern by three weeks after surgery. Tendon-implant strength as a percentage of normal, contralateral controls increased significantly, from 39% at the time of surgery to 67% at three weeks, 99% at six weeks, and 140% at twelve weeks (p < 0.0014). The stiffness of the construct also increased and approached that of normal tendon, measuring 47% at the time of surgery, 62% at three weeks, 94% at six weeks, and 130% at twelve weeks (p < 0.0299). Supraspinatus muscle volume initially decreased by 33% but recovered to 92% of normal by twelve weeks (p < 0.01). Histomorphologic evaluation showed Sharpey-like fibers inserting onto the surface of the porous tantalum. Quantitative histomorphometric analysis revealed a time-dependent increase in the density of the collagen tissue filling the metal voids below the implant surface of first the bottom washer and then the top washer. CONCLUSIONS: Robust biologic ingrowth of tendon into a porous tantalum implant surface can be achieved under conditions of secure initial mechanical fixation. The strength and stiffness of the tendon-implant construct reached normal levels by six to twelve weeks in this animal model.

Internet-based reference case managers for clinical practice and research collaboration.

Historically in medicine, the internet has been used for unidirectional information extraction via search engines that provide database and literature output. Current Web-based case managers allow submission and reception of digital media and have been used to link specialists and provide forums for rapid, bidirectional information sharing.

Mechanical effects of partial sacrectomy: when is reconstruction necessary?

We examined the mechanical consequences of high partial transverse sacrectomy. Ten human cadaveric pelves were randomly assigned to three groups. In the Control Group, the sacrum was left entirely intact. In Group I, transverse partial sacrectomy was performed just caudal to the S1 neural foramina. In Group II, transverse partial sacrectomy was performed just cephalad to the S1 neural foramina. Each pelvis was mounted on a testing apparatus and loaded vertically at the L4/L5 disk space until failure occurred. The average resection of the sacroiliac joints was 16% in Group I, and 25% in Group II. The average load to failure was 3014 N in the Control Group, 2166 N in Group I, and 1045 N in Group II. The average stiffness was 353 N/mm in the Control Group, 222 N/mm in Group I, and 100 N/mm in Group II. All specimens failed because of fractures through the sacrum (mostly Denis Zone II) in the sagittal plane. Using the literature to predict normal forces at the lumbosacral junction, we suggest Group I pelves could withstand postoperative mobilization without fracture, whereas Group II would probably not. Reconstruction should therefore be considered when performing transverse partial sacrectomy above the S1 nerve root.

Periosteal osteosarcoma: long-term outcome and risk of late recurrence.

The long-term outcome of periosteal osteosarcoma is not well defined. We sought to examine the disease-specific survival and risk of late recurrence or dedifferentiation in a cohort of 29 patients with average of 15.8 years followup. Disease-free survival was 83%, with five patients dying of disease at an average of 26 months after presentation. Survival was similar with respect to anatomic location, pathologic grade, and limb-salvage resection. All instances of local recurrence, metastatic disease, and death occurred within 3 years after presentation. There were no instances of dedifferentiation. Long-term disease-free survival is possible after resection of the local recurrence. Limb-salvage therapy seems to offer survival equivalent to amputation, and there does not seem to be a substantial risk of late recurrence, dedifferentiation, or disease progression.

Operative management of sacral chordoma.

BACKGROUND: Sacrococcygeal chordoma presents a difficult diagnostic and therapeutic problem, with a high rate of local recurrence. The purpose of this report is to define the importance of adequate surgical treatment for optimum outcome and survival. METHODS: Fifty-two patients underwent surgical treatment for sacrococcygeal chordoma between 1980 and 2001. The series included eighteen female patients and thirty-four male patients, with an average age of fifty-six years (range, thirteen to seventy-six years) at the time of the diagnosis. The surgical approach depended on the level and extent of the lesion, with a posterior approach performed in twenty-two patients and a combined anteroposterior approach used in thirty. A wide surgical margin was achieved in twenty-one patients. RESULTS: At an average of 7.8 years (range, 2.1 to twenty-three years) postoperatively, twenty-three patients were alive with no evidence of disease. Twenty-three patients (44%) had local recurrence. The rate of recurrence-free survival was 59% at five years and 46% at ten years. The overall survival rates were 74%, 52%, and 47% at five years, ten years, and fifteen years, respectively. The most important predictor of survival was a wide margin. All patients with a wide margin survived, and this survival rate was significantly different from that for patients who had had either marginal or intralesional excision (p = 0.0001). Of the twenty-one patients with a wide margin, seventeen (81%) had undergone a combined anteroposterior approach and only four had been treated with a posterior approach. CONCLUSIONS: A wide surgical margin is the most important predictor of survival and of local recurrence in patients with sacrococcygeal chordoma. Use of a combined anteroposterior approach increases the likelihood of obtaining a wide margin. LEVEL OF EVIDENCE: Therapeutic Level IV.

Reconstruction after total sacrectomy: early experience with a new surgical technique.

UNLABELLED: Nine patients had sacrectomy with ilio-lumbar arthrodesis for treatment of sacral malignancies at our institution between 2000 and 2004. Five patients had total sacrectomy, three had a sagittal hemisacrectomy, and one had an extended internal hemipelvectomy Type I-S. The average patient age was 39 years. Tumors were Stage IIB in seven patients and Stage IB in two patients. A combined anteroposterior approach was used and a wide surgical margin was attained in all seven patients. A new form of reconstruction using structural fibular grafts and pedicle screw-rod instrumentation was used to create a triangular construct along the anatomic force transmission vectors from the femoral heads to the lumbar spine. The average followup was 18 months. At latest followup, seven patients were alive with no evidence of disease, and two had died from disease. One patient suffered postoperative infection. Independent ambulation was noted in seven patients at last followup. Eight patients had stable reconstructions at latest followup (one patient, who died in December 2004, had a stable reconstruction and was walking with braces and a walker before her death). One patient had instrumentation failure twice and had additional revision instrumentation and bone grafting procedures. She eventually obtained a solid lumbopelvic fusion and walks with Canadian crutches and ankle-foot orthoses. The technique of reconstruction reported here offers promise in dealing with the challenges of reestablishing spinopelvic stability in this difficult anatomic location. LEVEL OF EVIDENCE: Therapeutic study, Level IV-1 (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Dedifferentiated chondrosarcoma: the role of chemotherapy with updated outcomes.

BACKGROUND: There are very few published data on the survival of patients with dedifferentiated chondrosarcoma, or, more specifically, on the efficacy and role of chemotherapy, especially in the era of modern diagnostic and treatment modalities. The current study examines the influence of advancements in imaging and chemotherapy on outcome and serves as an extension to a previous study published in 1986. METHODS: Forty-two patients with dedifferentiated chondrosarcoma who had presented to our institution between 1986 and 2000 were identified, and a retrospective chart review was performed. The study group included twenty-four men and eighteen women with an average age of sixty-six years. The diagnosis of dedifferentiated chondrosarcoma was verified histologically, and data on treatment, adjuvant therapy, and survival were obtained from the medical records of all patients. All patients had been followed for a minimum of twenty-four months. RESULTS: The tumors were classified, according to the system of the Musculoskeletal Tumor Society, as grade IIA (five), grade IIB (twenty-six), and grade III (eleven). Three patients underwent biopsy only, eighteen had a limb-sacrificing procedure, and twenty-one had a limb-sparing procedure. In the group of patients who underwent resection, the surgical margins were classified as intralesional in three, marginal in two, wide in nineteen, and radical in fifteen. Twenty-seven patients received neoadjuvant therapy; of these, twenty-three received chemotherapy only, two received radiotherapy only, and two received combined therapy. The median survival time was 7.5 months, and the five-year rate of disease-free survival was 7.1%. With the numbers available, there was no significant difference in the rate of disease-free survival with respect to the use of chemotherapy (p = 0.54), the location of surgical margins (p = 0.14), the histological subtype (p = 0.87), the tumor stage at the time of diagnosis (p = 0.43), the tumor size (p = 0.79), or the performance of limb-sparing as opposed to limb-sacrificing procedures (p = 0.42). CONCLUSIONS: Despite advances in diagnostic modalities and adjuvant therapies, dedifferentiated chondrosarcoma continues to carry a poor prognosis. While local control is achieved in the majority of cases, distant disease remains the greatest clinical challenge, developing in 90% of patients. Efforts are needed to continue to encourage earlier diagnosis and to develop effective adjuvant therapies for the control of distant disease. The routine use of current adjuvant chemotherapy and its inherent risks in this population should be reconsidered.

Identification of a single nucleotide polymorphism in the MMP-1 promoter in chondrosarcoma.

Matrix metalloproteinases (MMPs) are a group of at least 26 enzymes that facilitate cellular invasion via the degradation of the extracellular matrix. Specifically, the ability to degrade collagen types III and I is important in tumor invasion and metastasis. Over expression of the MMP-1 gene has been shown to correlate with poorer outcome in GI tract and gynecological tumors. This level of expression of this gene has been shown to be significantly increased by the presence of a single nucleotide polymorphism in the MMP-1 promoter sequence as a result of the creation of an ETS binding site. This SNP results from the addition of a single guanine base at -1,607 bp 24. Two chondrosarcoma cell lines and a series of 10 resected chondrosarcoma specimens underwent DNA extraction, purification, polymerase chain reaction, and sequencing. The presence of the single nucleotide polymorphism at -1,607 bp was confirmed within the promoter region for MMP-1 in human chondrosarcoma. Because all three genotypes were found in the clinical samples, the SNP may indeed provide a mechanistic explanation for a more aggressive biologic behavior locally and distally for a subset of chondrosarcomas.