Endoprosthetic reconstruction after resection of musculoskeletal tumors.

In the literature, long-term survival of endoprosthetic reconstruction varies widely. Few long-term reports analyze both anatomical and disease-specific implant and patient survival. We retrospectively reviewed the results of 489 patients who underwent resection of musculoskeletal tumor and reconstruction using an endoprosthetic device between December 1980 and August 2009. Implants were considered to have failed if the cemented components were revised for any reason, or the major body segment was removed for any reason. Implant survival, limb survival, and patient survival were determined using the Kaplan-Meier method. Sixty-one (12.5%) of the 489 cases were revised at a mean follow-up of 6.6 years (range, 1 month to 27.3 years). Kaplan-Meier analysis revealed overall implant survival of 23.1% at 27 years (95% CI, 5.0% to 100.0%). At 15 years, modular implants outperformed older custom designs (90.8% and 59.6% survival, respectively; P < .05). Complications that led to failure of the limb-salvage effort included local recurrence (21 cases), infection (11), positive surgical margins (3), and intractable pain (1). Thirty-six amputations (7.4%) were performed. There were no cases of amputation performed as a direct outcome of mechanical failure. Endoprosthetic implants provide a reliable, durable method of reconstruction after resection of musculoskeletal tumors.

How long do endoprosthetic reconstructions for proximal femoral tumors last?

BACKGROUND: As the life expectancy of patients with musculoskeletal tumors improves, long-term studies of endoprosthetic reconstructions are necessary to establish realistic expectations for the implants and compare them to other reconstruction approaches. QUESTIONS/PURPOSES: (1) What is the long-term survival of cemented bipolar proximal femoral replacements? (2) How does prosthesis survival compare to patient survival among patients with Stage I, II, and III disease? (3) Do modular implants outperform custom-built prostheses? (4) Do some proximal femoral replacements require conversion to THA? PATIENTS AND METHODS: We retrospectively reviewed all 86 proximal femoral replacements used for tumor reconstruction from 1982 to 2008. Primary diagnoses were 43 high-grade tumors (IIA/IIB), 20 low-grade tumors (IA/IB or benign), and 23 with metastatic disease. We reviewed prosthesis survival, patient survival, complication rates, functional outcomes, and rates of conversion to THA. RESULTS: Five of 86 patients (5.8%) required revision of the femoral component. Five-, 10-and 20-year implant survivorships were 93%, 84%, and 56%, respectively. All patients with low-grade disease survived; the 5-year survival rate for patients with metastatic disease was 16%; the 5-, 10-, and 20-year survival for IIA/IIB patients was 54%, 50%, and 44%, respectively. Five of 86 patients (5.8%) underwent conversion to THA for groin pain. CONCLUSIONS: Cemented bipolar proximal femoral replacements after tumor resection proved a durable reconstruction technique. The implants outlived patients with metastatic disease and high-grade localized disease while patients with low-grade disease outlived their implants. The survival of modular prostheses was comparable to that of older, one-piece custom designs.

Cemented endoprosthetic reconstruction of the proximal tibia: how long do they last?

BACKGROUND: The few available studies documenting the long-term survival of cemented proximal tibial endoprostheses for musculoskeletal tumors do not differentiate between stem designs or patient diagnosis. There is wide variation in survival rates reported, possibly a result of this heterogeneity in patient population and implant design. QUESTIONS/PURPOSES: We therefore asked: (1) How long do proximal tibial endoprostheses last? (2) What is the typical long-term functional result after proximal tibial replacement? And (3) what are the short- and long-term complications associated with endoprosthetic reconstruction of the proximal tibia, particularly with respect to the soft tissue reconstruction? PATIENTS AND METHODS: We retrospectively reviewed 52 patients with 52 proximal tibial endoprosthetic reconstructions for a tumor-related diagnosis. Kaplan-Meier survivorship analysis was performed using revision of the stemmed components for any reason as an endpoint for implants, and death due to disease progression for patients. Function was assessed using the MSTS scoring system. The minimum followup was 1 month (mean, 96 months: range, 1-284 months; median, 69 months). RESULTS: Using revision of the stemmed components for any reason as an end point, overall prosthesis survival at 5, 10, 15, and 20 years was 94%, 86%, 66%, and 37%, respectively. The 29 modular implants demonstrated a trend toward improved survival compared to the 23 custom-designed components, with a 15-year survivorship of 88% versus 63%. The mean postoperative Musculoskeletal Tumor Society score at most recent followup was 82% of normal function (mean raw score, 24.6; range, 4-29). CONCLUSIONS: Cemented endoprosthetic reconstruction of the proximal tibia provides a reliable method of reconstruction following tumor resection.

Cemented distal femoral endoprostheses for musculoskeletal tumor: improved survival of modular versus custom implants.

BACKGROUND: Advocates of newer implant designs cite high rates of aseptic loosening and failure as reasons to abandon traditional cemented endoprosthetic reconstruction of the distal femur. QUESTIONS/PURPOSES: We asked whether newer, modular distal femoral components had improved survivorship compared with older, custom-casted designs. PATIENTS AND METHODS: We retrospectively reviewed 254 patients who underwent distal femoral endoprosthetic reconstruction. We excluded two patients with cementless implants, 27 with expandable prostheses, and 39 who had a nontumor diagnosis. This left 186 patients: 101 with older custom implants and 85 with contemporary modular implants. The minimum followup was 1 month (mean, 96.0 months; range, 1-336 months). The tumor was classified as Stage IIA/IIB in 122 patients, Stage IA/IB or benign in 43, and Stage III or metastatic in 21. RESULTS: Kaplan-Meier analysis revealed overall 10-, 20-, and 25-year implant survival rates of 77%, 58%, and 50%, respectively, using revision of the stemmed components as an end point. The 85 modular components had a greater 15-year survivorship than the 101 custom-designed implants: 93.7% versus 51.7%, respectively. Thirty-five stemmed components (18.8%) were revised for aseptic loosening in 22 patients, implant fatigue fracture in 10, infection in two, and local recurrence in one. CONCLUSIONS: Cemented modular rotating-hinge distal femoral endoprostheses demonstrated improved survivorship compared with custom-casted implants during this three-decade experience. Patients with low-grade disease and long-term survivors of high-grade localized disease should expect at least one or more revision procedures in their lifetime. LEVEL OF EVIDENCE: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Proximal interphalangeal joint stiffness: measurement and analysis.

PURPOSE: The purpose of this study was to quantify the stiffness of the human finger proximal interphalangeal (PIP) joint and to study its relationship to different common clinical parameters. METHODS: Eighty-nine normal adult subjects had their PIP joints of the index, middle, and ring fingers evaluated using a computer-controlled moment-angle plotter. This device was used to measure stiffness and energy absorbed at the PIP joint during passive flexion and extension. RESULTS: The average overall stiffness was 0.05 N-cm/degree. There was a weak correlation between stiffness and energy absorbed and the size of the finger: they both increased with the size of the finger. The men's fingers were stiffer and absorbed more energy than the corresponding women's fingers. No significant associations were found between the time of day when the test took place, occupation, hobbies, or age with stiffness or absorbed energy. No significant differences were associated with hand dominance. The finger on the dominant hand had a larger circumference for both genders. Heavier individuals had more stiffness and absorbed more energy than lighter individuals. CONCLUSIONS: The PIP joint stiffness was defined quantitatively and measured over a wide cross-section of a normal population. This may allow future studies to record the outcome of different treatments for finger joint stiffness objectively. The stiffness was greater in men and in larger fingers.

The effect of uniform heating on the biomechanical properties of the intervertebral disc in a porcine model.

BACKGROUND CONTEXT: The use of minimally invasive lumbar intradiscal heating techniques, including intradiscal electro-thermal therapy (IDET), endoscopic radio-frequency annuloplasty, nucleoplasty and laser discectomy, for chronic lumbar discogenic pain and contained disc herniation has recently gained popularity. The purported therapeutic mechanisms of these interventions include subtotal nuclectomy, annular nociceptor ablation, and stabilization of the annular fibers. Basic science data elucidating the biomechanical and histomorphologic alterations of heat treatments on disc remain sparse. PURPOSE: The purpose of this study is to examine the effects of uniform heating on biomechanical properties and histomorphology of intervertebral disc tissues using a porcine model. STUDY DESIGN/SETTING: In a laboratory setting, porcine functional spinal units consisting of vertebra-nucleus pulposus-vertebra core and porcine hamstring tendons were harvested. Studies were performed on these tissue samples by uniformly heating the specimens in a constant temperature water bath. Ten porcine lumbar disc core and twenty-five porcine hamstring tendons were utilized as the subjects for this study. The effects of uniform heat treatments on disc core and hamstring tendon were measured for shrinkage, stiffness, and load to failure strength. Histomorphological study was also carried on the same specimen. METHODS: The porcine vertebra-nucleus pulposus-vertebra segments were cored to a uniform 1-cm diameter. The hamstring tendons were cut to uniform 1.2-inch lengths. The tendon specimens were divided into groups of five each and heated in constant temperature water baths of 60 degrees C, 65 degrees C, 70 degrees C, or 75 degrees C for 10 min. Unheated specimens served as controls. The disc core specimens were divided in two group of five each, and tested at room temperature or after immersion in a 70 degrees C bath. The shrinkage was monitored during immersion in the water bath. Biomechanical testing to failure was carried out using mechanical loading on an MTS servohydraulic testing machine operating under stroke control. Strength and stiffness of the tissue was determined. Histomorphology was studied by staining the specimen with hematoxylin and eosin (H&E), and examined under 200 times magnification. Non-heated controls were used for comparisons. RESULTS: The porcine hamstring tendons had no measurable shrinkage in specimens heated up to 65 degrees C. At temperatures above 65 degrees C, the shrinkage was concluded within 2 min of immersion and 70 degrees C appeared to be the optimal temperature, as temperatures higher than this did not demonstrate incremental effects. The disc core samples were heated to 70 degrees C (optimum temperature), and there appeared to be gross contraction of the disc core circumference to visual inspection, but no measurable lengthwise shrinkage could be appreciated. Histologically, the specimens demonstrated progressive loss of individual collagen fiber outline as the temperature increased. In the tendons, at 75 degrees C all of the fibers appear to be fused together, and the voids between individual collagen fibers were no longer present. Biomechanical testing revealed that the tendons undergo a substantial reduction in stiffness after heating. The mean tendon stiffness for the unheated specimens was 19,356 psi, while the corresponding value for the heated tendons was 1023 psi. These were significantly different using the paired t-test at p=0.0043. For the disc core samples, there was no significant difference in either stiffness (p=0.182) or failure strength (p=0.998) after heating. All failures occurred in mid-substance of the specimen. CONCLUSIONS: The application of uniform heating to nucleus pulposus disc core caused visible contraction of its circumference but not lengthwise shrinkage. The same heating shrinks the hamstring tendon and reduces its stiffness. Ultimate failure strength of the disc core specimen remains unchanged. The failure data was not obtainable for the tendon due to premature slippage from the fixation apparatus before failure. The results of this study fail to support a biomechanical justification for the application of uniform heat treatment to the whole intervertebral disc. Heating annulus fibrosus and nucleus pulposus separately to specific temperatures may have potential clinical benefits.

Metabolic measurement techniques to assess bone fracture healing: a preliminary study.

The purpose of this study was to project the effectiveness of using positron emission tomography for evaluation of fracture healing using the analogous method of liquid scintillation. A reproducible comminuted fracture model in rabbit femurs was stabilized with external fixation. Thirty-nine rabbits were divided into four groups: Group A had slight distraction, Group B had shortening, Group C had a bone defect, and Group D was the sham control group. At 2 and 4 weeks after fracture, the femurs had liquid scintillation measurements using 2-[14C]-deoxyglucose (2DG C-14). Glucose uptake was significantly elevated in the experimental limb relative to the contralateral control femurs at both times. The distraction group showed a significant decrease in uptake from 2-4 weeks. There was a high correlation between the liquid scintillation measurements and the radiographic fracture healing scores, with higher levels of 2DG C-14 uptake corresponding to lower levels of fracture healing calcification. The high correlation found between 2DG C-14 uptake and radiographic scores suggests that positron emission tomography used in conjunction with a glucose-based radiopharmaceutical such as 2-[18F]fluoro-2-deoxyglucose can monitor the fracture healing process effectively.

Mathematical modeling of human secondary osteons.

This investigation explores the structural dimensions and patterns within single secondary osteons, with consideration of their biological variation. New data from images obtained previously of osteons observed through linearly polarized light, electron microscopy, and micro-x-ray, combined with recent findings on lamellae by circularly polarized light, confocal microscopy, synchrotron x-ray diffraction, and micro-x-ray, provide the basis for novel computerized models of single osteons and single lamellae. The novelty of such models is the concurrent representation of (1) collagen-hydroxyapatite orientation, (2) relative hydroxyapatite percentage, (3) distributions of osteocytes' lacunae and canaliculae, and (4) biological variations in dimensions of the relevant structures. The mathematical software Maple realizes the computerized models. While the parts of the models are constructed on a personal computer, the voluminous data associated with the representation of lacunar and canalicular distributions require a supercomputer for assembly of the models and final analysis. The programming used to define the models affords the option to randomize the dimensional specifications of osteons, lamellae, lacunae, and canaliculae within the experimentally observed numeric ranges and distributions. Through this option, the program can operate so that each run of the file produces a unique random model within the observed biological variations. The program can also be run to implement specific dimensional requirements. The modeling has applications in the microstructural study of fracture propagation and remodeling, as well as in the simulation of mechanical testing. The approach taken here is of wide application and could be of value in other areas of microscopy such as scanning electron microscopy, microcomputerized tomography scan, and magnetic resonance imaging on cancellous bone structures.

Custom cross-pin fixation of 32 tumor endoprostheses stems.

The main cause of mechanical failure of primary and revision cemented tumor endoprosthetic stems is aseptic loosening. The placement of custom designed pins through the bone, the cement, and the stem can create a bone-cement-prosthesis composite that resists the rotatory stresses that lead to aseptic loosening. At risk situations include large primary reconstructions where the residual short metaphyseal articular segments lack sufficient length and cortical contact to provide lasting fixation, and revision prostheses that are to be recemented into straight diaphyseal segments that already have experienced aseptic loosening. Current modular tumor endoprosthetic systems have improved availability and allow for some intraoperative flexibility, but they do not provide solutions for these at risk scenarios. Additional customization is necessary. We report on the 16-year experience with 32 custom cross-pin stems at the University of California, Los Angeles (UCLA). Twenty of these patients have been followed up for more than 2 years. There were three mechanical failures, three patients were lost to followup, and five patients died of disease. There have been no cases of aseptic loosening in this series. Cross-pin fixation has been effective when used in carefully selected cases.

Endoprosthetic reconstructions for bone metastases.

The purpose of the current study was to help define the role that endoprosthetic reconstructions have in the treatment of metastatic bone disease. Of the 522 endoprostheses implanted at the University of California at Los Angeles (UCLA) between December 1980 and January 2002, 37 (6.9%) were used in 37 patients with metastatic disease. Upper extremity locations outnumbered lower extremity locations 2:1. The 20 males and 17 females ranged in age from 10 to 82 years, with a median age of 54 years. Metastatic renal and breast carcinoma predominated and accounted for 60% of the lesions. The lesion was a primary metastasis in 27 patients (73%) and a revision of failed previous surgery in 10 patients (27%). Only five patients experienced local complications none of whom required reoperation or amputation. Thirty-three of the 37 patients died of disease progression at a median of 12 months (range, 4-49 months). Function after endoprosthetic reconstruction for metastatic disease is similar to that of function for endoprosthetic reconstructions used for primary malignant tumors, but clearly is dependent on the patient's general condition. Although infrequently used to treat bone metastases, endoprosthetic reconstruction can be a useful alternative reconstruction in selected situations.

Effects of polyaxial pedicle screws on lumbar construct rigidity.

Pedicle screw constructs have been shown to increase fusion rates in the lumbar spine. Manufacturers have created pedicle screws with one or two degrees of freedom built into the screw head to allow for easier incorporation of the interlocking rod, but the effects of these screws on construct stiffness has not been tested. The purpose of this study is to compare and contrast the stiffness of lumbar pedicle screw constructs with and without the use of polyaxial pedicle screws. Nontapered, self-taping pedicle screws (6.0-mm diameter x 30-mm length, titanium) were used in the fixation of porcine spines from L3-L5. Group 1 (n = 5) contained six standard pedicle screws from one manufacturer. Group 2 (n = 5) contained six standard pedicle screws from a second manufacturer. Group 3 (n = 5) contained four standard pedicle screws placed at L3 and L5, as well as two polyaxial screws placed at L4. Group 4 (n = 5) contained six polyaxial pedicle screws. A rotational variable differential transformer was used to record angular displacement between vertebrae in the construct as it is loaded in flexion, extension, right bend, left bend, clockwise torque, and counterclockwise torque. Stiffness curves were linear throughout the range of applied force. The average r2 value for the generated stiffness graphs was 0.94 (SD = 0.06). No construct failure occurred during any of the testing. There were no significant differences (p < 0.05, two-way analysis of variance) in moment versus angle noted in any of the four groups tested. For torque tests, the all-polyaxial screw constructs showed significantly increased stiffness compared with the other groups. The current study has shown that the incorporation of polyaxial screws in pedicle screw constructs did not significantly decrease the construct stiffness. There is a suggestion that the use of all polyaxial screws may increase the resistance to torque by allowing better purchase of intervertebral rods.

Enhancement of pedicle screw fixation through washers.

This study examined the effect of washer usage on initial pedicle screw fixation and on the salvage of replaced pedicle screws, and the effect of minor adjustments of pedicle screws on insertional torque. Titanium, nontapered pedicle screws (6.5-mm in diameter and 35-mm in length) from one manufacturer and custom-made 5-mm washers were used in the fixation of porcine lumbar spines. Insertional torque was measured with an electronic torque screwdriver and failure strength was determined by straight pullout of the screws using an MTS machine. Initial insertional torque values were significantly greater in pedicle screws placed with washers compared with screws placed without washers. When the screw placed without a washer was salvaged with the addition of a washer, a significant increase in insertional torque resulted. Pullout testing failed to show a significant difference between the screws that were placed with washers and the screws that were placed without washers. In the second part of the experiment, there was a significant decrease in insertional torque after backing out the screw as little as 90 degrees. This current study showed that (1) washers significantly increase the insertional torque of pedicle screws; (2) screws placed without a washer can be salvaged and replaced with a washer, which results in significantly increased insertional torque; and (3) backing out a pedicle screw 90 degrees significantly decreases its insertional torque. Washers can be used with pedicle screws to enhance the initial stability of the screw constructs, and to maximize insertional torque when screws need to be replaced, revised, or adjusted (backed out).

Histologic evaluation of the efficacy of rhBMP-2 compared with autograft bone in sheep spinal anterior interbody fusion.

STUDY DESIGN: The sheep anterior lumbar spinal fusion model was used to study the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2)-collagen composite in comparison with autograft to enhance spinal interbody fusion. Comparisons were drawn from temporal radiographic and end-point biomechanical and histologic data. OBJECTIVE: To analyze histologically the ability of rhBMP-2 to achieve complete arthrodesis between vertebral bodies. SUMMARY OF BACKGROUND DATA: Studies using rhBMP for enhancement of anterior interbody fusion have used numerous endpoints. However, systematic histologic evaluation of the fusion has not been conducted. METHODS: Twelve sheep underwent single-level anterior lumbar interbody fusion performed with a cylindrical fenestrated titanium interbody fusion device (INTER FIX, Medtronic Sofamor Danek, Inc., Memphis, TN). The device was filled either with rhBMP-2-collagen (n = 6) or autogenous iliac crest bone graft (n = 6). Radiologic evaluation was carried out at 2-month intervals, and all sheep were killed 6 months after surgery. Nondestructive biomechanical testing for stiffness to flexion, extension, and lateral bending moments, un-decalcified histology, and qualitative and quantitative histologic evaluation were performed. RESULTS: Radiographs revealed a bony bridge anterior to the cage in five of six rhBMP-2-treated animals, whereas it was present only in one of five in the autogenous bone graft group. Segments treated with rhBMP-2 were 20% stiffer in flexion than autograft-treated segments at 6 months. Six of six in the rhBMP-2 group and two of six in the autograft group showed complete fusion. There was a significantly higher rate of bony continuity observed at the fenestrations of the rhBMP-2 group. Three times more number of cage fenestrations in the rhBMP-2 group demonstrated "all-bone" when compared with the autograft group (P < 0.001). Further, the scar tissue in and around the autograft-treated cages was 16-fold more (P < 0.01) than that seen for rhBMP-2-treated cages. CONCLUSIONS: The study demonstrates that rhBMP-2 can lead to earlier radiologic fusion and a more consistent increased stiffness of the segments when compared with autograft in sheep anterior lumbar interbody fusion. Furthermore, a three times higher histologic fusion rate is attainable with significantly reduced fibrous tissue around the implant when rhBMP-2 is used.