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.

Does the second-generation intercalary humeral spacer improve on the first?

UNLABELLED: Since publication of the results of a first-generation intercalary humeral spacer, a newer design has been available that addressed the weaknesses of the first. This study evaluated the hypothesis that the second-generation lap joint junction intercalary humeral spacer reduced complications compared with the original male-female taper design. We retrospectively reviewed the charts of 32 consecutive patients who had undergone placement of an intercalary humeral spacer. Twenty-one with the male-female taper (minimum followup 0 months, mean 19.2 months) were compared with 11 with the lap joint configuration (minimum followup 0 months, mean 20.3 months). Demographic, tumor, treatment, and radiographic variables were similar between groups. We observed a lower complication rate in the lap joint group (three of 11 versus 11 of 21). The most common complications in the male-female group, neuropraxia, periprosthetic fracture, and disengagement, were not seen in the lap joint group. Aseptic loosening was more frequent in the lap joint group. There were no differences in blood loss, operative time, or Musculoskeletal Tumor Society scores between groups. We noted improvement in Musculoskeletal Tumor Society scores from preoperatively to postoperatively in both groups. Use of these implants should be reserved for patients with limited life expectancy. LEVEL OF EVIDENCE: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Intraarterial chemotherapy for extremity osteosarcoma and MFH in adults.

UNLABELLED: The neoadjuvant treatment of osteosarcoma using intravenous agents has resulted in survival rates of 55% to 77% [3, 5, 6, 20, 22, 35]. We designed a neoadjuvant chemotherapy protocol using combined intraarterial and intravenous agents to treat high-grade osteosarcoma and malignant fibrous histiocytoma of bone in an attempt to improve survival. We report the results of treating 53 adults (age 18-77 years) diagnosed with nonmetastatic extremity osteosarcoma or malignant fibrous histiocytoma. Preoperative chemotherapy consisted of intravenous doxorubicin followed by intraarterial cisplatinum administered repetitively every 3 weeks for three to five cycles, depending on tumor response assessed by serial arteriography. Dose and duration of cisplatin were adjusted for tumor size. After resection, good responders (90% or greater necrosis) underwent treatment with the same agents and poor responders were treated with alternative agents for longer duration. Minimum followup was 24 months (mean, 111 months; range, 24-235 months). Estimated Kaplan-Meier survival at 10 years was 82% and event-free survival was 79%. Forty-one patients (77%) had a good histologic response and 92% (49 of 53) underwent limb-sparing procedures. Local recurrence occurred in two patients (4%). These results compared favorably with those reported in the current literature. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Transcutaneous tibial implants: a surgical procedure for restoring ambulation after amputation of the distal aspect of the tibia in a dog.

OBJECTIVE: To report surgical planning, technique, and long-term outcome of custom transcutaneous tibial implants used to restore ambulation after bilateral pelvic limb amputation in a dog. STUDY DESIGN: Case report. ANIMALS: A 4-year-old, 25.5 kg, female spayed, Siberian Husky. METHODS: Computed tomographic scans of the pelvic limbs were used to build sterolithographic models of the remaining tibia after bilateral amputation of the distal aspect of the tibiae. The sterolithographic models facilitated fabrication of implants that would replace the missing distal segments of the tibiae. Custom implants were surgically placed in both limbs. RESULTS: Assisted ambulation was restored immediately postoperatively and unassisted locomotion occurred at 7 days. At 14 months, aseptic loosening of the right implant occurred, it was removed and a 2nd transcutaneous implant was fabricated and implanted. At 26 months after initial surgery and 17 months after revision of the right implant, function is restored at a walk, trot, and run. CONCLUSION: Based on over a 2-year follow-up, transcutaneous tibial implants allowed for restoration of locomotion. CLINICAL RELEVANCE: Transcutaneous tibial implants offer a potentially viable treatment option for restoring ambulation after amputation of the distal aspect of the tibiae in the dog.

Surgical management of conventional grade I chondrosarcoma of long bones.

We retrospectively reviewed 70 patients with low-grade (Grade I) chondrosarcoma of the appendicular skeleton treated at the Mayo Clinic from 1980 to 2001. Fifty-four patients underwent wide resections and three patients underwent marginal excision for radiographically aggressive lesions. Thirteen patients were treated with intralesional curettage for more indolent lesions. The mean age of the patients was 43 years (range, 5-85 years) and the minimum followup was 0.2 year (mean, 8.5 years; range, 0.2-22.8 years). Of the patients who had wide resection, one experienced local recurrence and one had metastasis develop. One patient in the group treated with intralesional curettage had local recurrence and metastasis. We observed no difference in overall survival rate between the intralesional curettage group and the wide resection group. Although there was no difference in the treatment outcome between the two groups, patients with more radiographically aggressive lesions underwent more extensive surgery. The data suggest in selected patients less radiographically aggressive Grade I chondrosarcoma can be safely treated with intralesional curettage without compromising patient outcome.

Effects of screw eccentricity on the initial stability of the acetabular cup.

One of the major failure modes of cementless acetabular components is the loosening of the acetabular cup, which is mostly attributable to insufficient initial stability. A hemispherical cup with a porous coating which is inserted with press-fit fixation and secured with several screws is one of the most widely used approaches. Many studies have found that bone screws are very helpful aids for cup fixation, but the optimal surgical technique for inserting screws has not been clearly reported. In this study, hemispherical cups were fixed into blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity (a 1-mm offset and angular eccentricities of 15 degrees and 25 degrees ) on the initial stability of the acetabular cup were evaluated. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing (i.e., with no eccentricity). An angular eccentricity of 15 degrees did not affect the cup stability for fixation with one or two screws. However, the presence of 25 degrees of angular eccentricity significantly reduced the stability of the cup, while 1 mm of offset eccentricity produced an even greater impact.

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.

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.

Accuracy of computed tomography in assessing thoracic pedicle screw malposition.

OBJECTIVE: Transpedicular instrumentation of the thoracic spine is potentially dangerous because of the close proximity of vital structures and the morphologic variability seen. Computed tomography has become the gold standard in evaluating the position of thoracic pedicle screws in vivo. Unfortunately, despite its common use, the accuracy of computed tomography has not been adequately investigated. The objective of this work was to evaluate the accuracy of computed tomography in evaluating the position of thoracic pedicle screws. METHODS: One hundred ninety-four thoracic pedicles in nine cadaveric specimens were instrumented and evaluated postoperatively with computed tomography and open dissection. Computed tomography films were assessed by three blinded observers who noted the position of each pedicle screw on two separate occasions. These data were subsequently compared with the open dissection data. RESULTS: Computed tomography was found to be 76 +/- 16% sensitive and 75 +/- 13% specific when compared with open dissection. Overall accuracy was 76 +/- 8%. Intraobserver accuracy was 79 +/- 5% in assessing thoracic pedicle screws by computed tomography. Fair to moderate degree of agreement was demonstrated for both interobserver and intraobserver data using kappa values. CONCLUSIONS: Computed tomography was found to be relatively insensitive in assessing thoracic pedicle screw position. In the face of postoperative complications, surgical exploration and hardware removal may still be necessary despite negative computed tomography.