Augmentation with a reinforced acellular fascia lata strip graft limits cyclic gapping of supraspinatus repairs in a human cadaveric model.

BACKGROUND: A reinforced biologic strip graft was designed to mechanically augment the repair of rotator cuff tears that are fully reparable by arthroscopic techniques yet have a likelihood of failure. This study assessed the extent to which augmentation of human supraspinatus repairs with a reinforced fascia strip can reduce gap formation during in vitro cyclic loading. METHODS: The supraspinatus tendon was sharply released from the proximal humerus and repaired back to its insertion with anchors in 9 matched pairs of human cadaveric shoulders. One repair from each pair was also augmented with a reinforced fascia strip. All repairs were subjected to cyclic mechanical loading of 5 to 180 N for 1000 cycles. RESULTS: All augmented and nonaugmented repair constructs completed 1000 cycles of loading. Augmentation with a reinforced fascia strip graft significantly decreased the amount of gap formation compared with nonaugmented repairs. The average gap formation of augmented repairs was 1.5 ± 0.7 mm after the first cycle vs. 3.0 ± 1.2 mm for nonaugmented repairs (P = .003) and 5.0 ± 1.5 mm after 1000 cycles of loading, which averaged 24% ± 21% less than the gap formation of nonaugmented repairs (7.0 ± 2.8 mm, P = .014). CONCLUSION: Cadaveric human supraspinatus repairs augmented with a reinforced fascia strip have significantly less initial stroke elongation and gap formation than repairs without augmentation. Augmentation limited gap formation to the greatest extent early in the testing protocol. Human studies are necessary to confirm the appropriate indications and effectiveness of augmentation scaffolds for rotator cuff repair healing in the clinical setting.

Bone Graft Substitute Provides Metaphyseal Fixation for a Stemless Humeral Implant.

Stemless humeral fixation has become an alternative to traditional total shoulder arthroplasty, but metaphyseal fixation may be compromised by the quality of the trabecular bone that diminishes with age and disease, and augmentation of the fixation may be desirable. The authors hypothesized that a bone graft substitute (BGS) could achieve initial fixation comparable to polymethylmethacrylate (PMMA) bone cement. Fifteen fresh-frozen human male humerii were randomly implanted using a stemless humeral prosthesis, and metaphyseal fixation was augmented with either high-viscosity PMMA bone cement (PMMA group) or a magnesium-based injectable BGS (OsteoCrete; Bone Solutions Inc, Dallas, Texas) (OC group). Both groups were compared with a control group with no augmentation. Initial stiffness, failure load, failure displacement, failure cycle, and total work were compared among groups. The PMMA and OC groups showed markedly higher failure loads, failure displacements, and failure cycles than the control group (P<.01). There were no statistically significant differences in initial stiffness, failure load, failure displacement, failure cycle, or total work between the PMMA and OC groups. The biomechanical properties of magnesium-based BGS fixation compared favorably with PMMA bone cement in the fixation of stemless humeral prostheses and may provide sufficient initial fixation for this clinical application. Future work will investigate the long-term remodeling characteristics and bone quality at the prosthetic-bone interface in an in vivo model to evaluate the clinical efficacy of this approach.

Reinforced fascia patch limits cyclic gapping of rotator cuff repairs in a human cadaveric model.

BACKGROUND: Scaffolds continue to be developed and used for rotator cuff repair augmentation, but clinical or biomechanical data to inform their use are limited. We have developed a reinforced fascia lata patch with mechanical properties to meet the needs of musculoskeletal applications. The objective of this study was to assess the extent to which augmentation of a primary human rotator cuff repair with the reinforced fascia patch can reduce gap formation during in vitro cyclic loading. MATERIALS AND METHODS: Nine paired human cadaveric shoulders were used to investigate the cyclic gap formation and failure properties of augmented and non-augmented rotator cuff repairs with loading of 5 to 180 N for 1000 cycles. RESULTS: Augmentation significantly decreased the amount of gap formation at cycles 1, 10, 100, and 1000 compared with non-augmented repairs (P < .01). The mean gap formation of the augmented repairs was 1.8 mm after the first cycle of pull (vs 3.6 mm for non-augmented repairs) and remained less than 5 mm after 1000 cycles of loading (4.7 mm for augmented repairs vs 7.3 mm for non-augmented repairs). Furthermore, all augmented repairs were able to complete the 1000-cycle loading protocol, whereas 3 of 9 non-augmented repairs failed before completing 1000 loading cycles. CONCLUSIONS: This study supports further investigation of reinforced fascia patches to provide mechanical augmentation, minimize tendon retraction, and possibly reduce the incidence of rotator cuff repair failure. Future investigation in animal and human studies will be necessary to fully define the efficacy of the reinforced fascia device in a biologic healing environment.

Effect of pretension and suture needle type on mechanical properties of acellular human dermis patches for rotator cuff repair.

BACKGROUND: Dermal grafts are used for rotator cuff repair and augmentation. Although the in vitro biomechanical properties of dermal grafts have been reported previously, clinical questions related to their biomechanical performance as a surgical construct and the effect of surgical variables that could potentially improve repair outcomes have not been studied. METHODS: This study evaluated the failure and fatigue biomechanics of acellular dermis constructs tested in a clinically relevant size (4 × 4 cm patches) and manner (loaded via sutures) for rotator cuff repair. Also investigated were the effect of 2 surgical variables: (1) the fixation of grafts under varying magnitudes of pretension (0, 10, 20N), and (2) the use of reverse-cutting vs tapered needles for suturing grafts. RESULTS: Dermis constructs stretched ∼25% before bearing significant loads in the high stiffness region. Although 91% of the patches withstood 2500 cycles of loading to 150 N, the constructs stretched 13 to 19 mm after fatigue loading. This elongation could be reduced by 20% to 32% when reverse-cutting needles were used to prepare constructs or by applying 20 N of in situ circumferential pretension to the constructs before loading. CONCLUSIONS: Although dermis patches demonstrated robustness for use in rotator cuff repair, the patches underwent significant, substantial, and presumably nonrecoverable elongation, even at low physiologic loads. This study indicates that use of reverse-cutting needles for suture passage, preconditioning (cyclically stretching several times), and/or surgical fixation under at least 20 N of circumferential pretension could be developed as strategies to reduce compliance of dermis for its use for rotator cuff repair.

Improved time-zero biomechanical properties using poly-L-lactic acid graft augmentation in a cadaveric rotator cuff repair model.

HYPOTHESIS: Rotator cuff repair failure rates range from 20% to 90%, and failure is believed to occur most commonly by sutures cutting through the tendon due to excessive tension at the repair site. This study was designed to determine whether application of a woven poly-L-lactic acid device (X-Repair; Synthasome, San Diego, CA) would improve the mechanical properties of rotator cuff repair in vitro. MATERIALS AND METHODS: Eight pairs of human cadaveric shoulders were used to test augmented and non-augmented rotator cuff repairs. Initial stiffness, yield load, ultimate load, and failure mode were compared. RESULTS: Yield load was 56% to 92% higher and ultimate load was 56% to 76% higher in augmented repairs. No increase in initial stiffness was found. Failure by sutures cutting through the tendon was reduced, occurring in 17 of 20 non-augmented repairs but only 7 of 20 augmented repairs. CONCLUSIONS: Our data show that application of the X-Repair device significantly increased the yield load and ultimate load of rotator cuff repairs in a human cadaveric model and altered the failure mode but did not affect initial repair stiffness.

Rotator cuff repair augmentation in a canine model with use of a woven poly-L-lactide device.

BACKGROUND: Despite advances in surgical treatment options, failure rates of rotator cuff repair have continued to range from 20% to 90%. Hence, there is a need for new repair strategies that provide effective mechanical reinforcement of rotator cuff repair as well as stimulate and enhance the intrinsic healing potential of the patient. The purpose of this study was to evaluate the extent to which augmentation of acute repair of rotator cuff tendons with a newly designed poly-L-lactide repair device would improve functional and biomechanical outcomes in a canine model. METHODS: Eight adult, male mongrel dogs (25 to 30 kg) underwent bilateral shoulder surgery. One shoulder underwent tendon release and repair only, and the other was subjected to release and repair followed by augmentation with the repair device. At twelve weeks, tendon retraction, cross-sectional area, stiffness, and ultimate load of the repair site were measured. Augmented repairs underwent histologic assessment of biocompatibility. In addition, eight pairs of canine cadaver shoulders underwent infraspinatus injury and repair with and without device augmentation with use of identical surgical procedures and served as time-zero biomechanical controls. Eight unpaired, canine cadaver shoulders were included as normal biomechanical controls. RESULTS: At time zero, repair augmentation significantly increased the ultimate load (23%) (p = 0.034) but not the stiffness of the canine infraspinatus tendon repair. At twelve weeks, the poly-L-lactide scaffold was observed to be histologically biocompatible, and augmented repairs demonstrated significantly less tendon retraction (p = 0.008) and significantly greater cross-sectional area (137%), stiffness (26%), and ultimate load (35%) than did repairs that had not been augmented (p < 0.001, p = 0.002, and p = 0.009, respectively). CONCLUSIONS: While limiting but not eliminating tendon repair retraction, the augmentation device provided a tendon-bone bridge and scaffold for host tissue deposition and ingrowth, resulting in improved biomechanical function of the repair at twelve weeks.

Biomechanical characteristics of hybrid hook-screw constructs in short-segment thoracic fixation.

STUDY DESIGN: Ex vivo biomechanical testing of human cadaveric thoracic spine segments. OBJECTIVE: To determine whether a hybrid construct, using a combination of pedicle screws (PSs) and lamina hooks, was equivalent to a PS construct, in a short-segment thoracic spine fixation model. SUMMARY OF BACKGROUND DATA: Comparisons have been made among PS, lamina hook, and hybrid screw-hook constructs, but these have generally been in long-segment scoliosis correction. In this study, we compared the hybrid and screw-only constructs in a short-segment thoracic fixation. METHODS: For pullout testing, matched specimens were used for PS (n = 8) and hybrid (n = 8) constructs. Construct stiffness, and the force required for construct failure, were measured. Dynamic testing was carried out on specimens in the PS (n = 7) and hybrid (n = 7) groups in compression, flexion, extension, and left and right lateral bending. Each group was tested intact, after instrumentation, and after corpectomy. RESULTS: When compared with the hybrid group, a significantly greater force was required for construct failure in the PS group, and these PS constructs were significantly stiffer. No differences were found between groups in dynamic testing. CONCLUSION: A construct employing PSs is significantly stiffer and more resistant to pullout failure than a hook-screw hybrid construct.

A preliminary biomechanical evaluation in a simulated spinal fusion model. Laboratory investigation.

OBJECT: A preliminary in vitro biomechanical study was conducted to determine if the pressure at a bone graft-mortise interface and the load transmitted along a ventral cervical plate could be used as parameters to assess fusion status. METHODS: An interbody bone graft and a ventral plate were placed at the C3-4 motion segment in six fresh cadaveric goat spines. Polymethylmethacrylate (PMMA) was used to simulate early bone fusion at the bone graft site. The loads along the plate and the simultaneous pressures induced at the graft-endplate interfaces were monitored during simulated stages of bone healing. Each specimen was nondestructively tested in compression loading while the pressures and loads at the graft site were recorded continuously. Each specimen was tested under five conditions (Disc, Graft, Plate, PMMA, and Removal). RESULTS: The pressure at the interface of the bone graft and vertebral endplate did not change significantly with the addition of the ventral plate. The interface pressure and segmental stiffness did increase following PMMA augmentation of the bone graft (simulating an intermediate phase of bone fusion). The load transmitted along the ventral plate in compression increased after the addition of the bone graft, but decreased after PMMA augmentation. Thus, there was an increase in pressure at the graft-endplate interface and a decrease in load transferred along the ventral plate after the simulation of bone fusion. Upon removal of the ventral plate, the simulated fusion bore most of the axial load, thus explaining a further increase in graft site pressure. CONCLUSIONS: These observations support the notions of load sharing and the redistribution of loads occurring during and after bone graft incorporation. In the clinical setting, these parameters may be useful in the assessment of fusion after spine surgery. Although feasibility has been demonstrated in this preliminary study, further research is needed.

Primary pedicle screw augmentation in osteoporotic lumbar vertebrae: biomechanical analysis of pedicle fixation strength.

STUDY DESIGN: Pedicle screw pullout testing in osteoporotic and control human cadaveric vertebrae, comparing augmented and control vertebrae. OBJECTIVE: To compare the pullout strengths of pedicle screws fixed in osteoporotic vertebrae using polymethyl methacrylate delivered by 2 augmentation techniques, a standard transpedicular approach and kyphoplasty type approach. SUMMARY OF BACKGROUND DATA: Pedicle screw instrumentation of the osteoporotic spine carries an increased risk of screw loosening, pullout, and fixation failure. Osteoporosis is often cited as a contraindication for pedicle screw fixation. Augmentation of the vertebral pedicle and body using polymethyl methacrylate may improve fixation strength and construct survival in the osteoporotic vertebrae. While the utility of polymethyl methacrylate has been demonstrated for salvage of screws that have been pulled out, the effect of the cement technique on pullout strength in osteoporotic vertebrae has not been previously studied. METHODS: Thirteen osteoporotic and 9 healthy human lumbar vertebrae were tested. All specimens were instrumented with pedicle screws using a uniform technique. Osteoporotic pedicles were augmented with polymethyl methacrylate using either a kyphoplasty type technique or a transpedicular augmentation technique. Screws were tested in a paired testing array, randomly assigning the augmentation techniques to opposite sides of each vertebra. Pullout to failure was performed either primarily or after a 5000-cycle tangential fatigue conditioning exposure. After testing, following screw removal, specimens were cut in the axial plane through the center of the vertebral body to inspect the cement distribution. RESULTS: Pedicle screws placed in osteoporotic vertebrae had higher pullout loads when augmented with the kyphoplasty technique compared to transpedicular augmentation (1414 +/- 338 versus 756 +/- 300 N, respectively; P < 0.001). An unpaired t test showed that fatigued pedicle screws in osteoporotic vertebrae augmented by kyphoplasty showed higher pullout resistance than those placed in healthy control vertebrae (P = 0.002). Both kyphoplasty type augmentation (P = 0.007) and transpedicular augmentation (P = 0.02) increased pullout loads compared to pedicle screws placed in nonaugmented osteoporotic vertebrae when tested after fatigue cycling. CONCLUSIONS: Pedicle screw augmentation with polymethyl methacrylate improves the initial fixation strength and fatigue strength of instrumentation in osteoporotic vertebrae. Pedicle screws augmented using the kyphoplasty technique had significantly greater pullout strength than those augmented with transpedicular augmentation technique and those placed in healthy control vertebrae with no augmentation.

Atlantoaxial fusion: a biomechanical analysis of two C1-C2 fusion techniques.

BACKGROUND CONTEXT: Different atlantoaxial fusion techniques are used for instability. Transarticular screws are biomechanically superior to wiring techniques and equivalent to C1 lateral mass to C2 pedicle (C1LM-C2P) fixation. Recently, C1 lateral mass to C2 laminar (C1LM-C2L) fixation has been shown to have flexibility similar to C1LM-C2P fixation in flexion, extension, lateral bending, and axial rotation. PURPOSE: Compare the stiffness of C1LM-C2P with C1LM-C2L screw rod fixation. STUDY DESIGN: In vitro biomechanical study. OUTCOME MEASURES: Stiffness in flexion/extension, lateral bending, axial rotation, and anterior-posterior (AP) translation. METHODS: Eight fresh-frozen human cadaveric cervical spines (C1-C3) were tested intact and, after a type II odontoid fracture, were instrumented and tested with two fixation constructs: C1LM-C2P screws and C1LM-C2L screws. The testing involved flexion, extension, lateral bending, AP translation, and axial rotation. Stiffness was measured and compared with a repeated-measures analysis. RESULTS: C1LM-C2P was significantly stiffer than the intact in AP translation (p<.001), lateral bending (p=.001), and axial rotation (p=.002) and equivalent in flexion/extension (p=.09). C1LM-C2L was significantly stiffer than the intact in AP translation (p<.01) and axial rotation (p<.004) and equivalent in lateral bending (p<.71) and flexion/extension (p=.22). C1LM-C2P was stiffer than C1LM-C2L in right/left lateral bending (p<.001) and axial rotation (p=.009) and equivalent in AP translation (p=.06) and flexion/extension (p=.74). CONCLUSION: C1LM-C2P fixation is equivalent to C1LM-C2L fixation in flexion/extension and AP translation and superior in lateral bending and axial rotation.

Biomechanical comparison of adjacent segmental motion after ventral cervical fixation with varying angles of lordosis.

BACKGROUND CONTEXT: Complications, such as graft subsidence and adjacent segment degeneration, are not uncommon after ventral cervical fusion. It has been theorized, but not proven, that sagittal alignment may affect this process. It is therefore hypothesized that increasing lordosis during anterior cervical fusion decreases adjacent segment motion (ASM) and thus decreases the rate of adjacent disc degeneration. A study was designed to test the first portion of this hypothesis; ie, that increasing lordosis during anterior cervical fusion decreases ASM. PURPOSE: To determine the effect on the adjacent segment motion (ASM) after ventral cervical spine fusion obtained by varying the angle of lordosis using interbody spacers with different heights (small: 6-mm interbody spacer; large: 9-mm interbody spacer). STUDY DESIGN: A biomechanical study comparing the segmental motion at adjacent disc levels after cervical fusion with varying angles of lordosis. Sample and outcome measures: six human cadaveric spines C2-C7, range of motion (ROM). METHODS: Six fresh human cadaveric cervical spines (C2-C7) were embedded at C2 and C7 and biomechanically tested to 0.7 Nm flexion and 0.5 Nm extension. Lordosis was measured at C4-C5 from radiographs; range of motion (ROM) at C3-C4, C4-C5, and C5-C6 was measured using markers during flexion and extension in the intact state, after ventral cervical fixation at C4-C5 with a small (6-mm) and with a large (9-mm) interbody spacer. A repeated measures analysis of variance was used to compare lordosis and the ROM for the different states. RESULTS: Six cervical spines with a mean age of 55.3+/-1.6 years were studied. The mean sagittal angles of the specimens measured at C4-C5 using the Cobb angle method were -6.4+/-1.3 degrees intact, -8.8+/-1.4 degrees with small interbody spacer (intact vs. small spacer p=.02), and -12.4+/-0.9 degrees with large interbody spacer fixation (intact vs. large spacer p=.005). The lordotic angle of the specimens was lowest in the intact state, higher with the small spacer, and highest with the large spacer. The greatest ROM in the intact state testing was at C4-C5 (10.6+/-1.3 degrees), followed by at C5-C6 (7.2+/-1.5 degrees), and then at C3-C4 (7.1+/-0.9 degrees). After C4-C5 fusion, the ROM at C3-C4 and C5-C6 was significantly increased with the small spacer only. No significant change in ROM was observed with the large spacer. The greatest overall ROM (all three motion segments) was observed in the intact state (24.9+/-1.8 degrees), followed by the small spacer (21.4+/-2.0 degrees) and the large spacer (15.1+/-1.7 degrees). CONCLUSIONS: Under the conditions of this study, there is a significant increase in ASM with the achievement of a modest increase in lordosis (small spacer) that is not observed with a greater increase in lordosis (large spacer).

Adjacent level load transfer following vertebral augmentation in the cadaveric spine.

STUDY DESIGN: In vitro biomechanics. OBJECTIVE: To determine if osteoporotic vertebral compression fracture (VCF) augmentation increases adjacent level load transfer. SUMMARY OF BACKGROUND DATA: Osteoporotic VCF subsequent to augmentation may result from disease progression or increased adjacent level load transfer, or both. METHODS: There were 11 T3-T7 and 10 T8-T12 divided by lumbar bone mineral density into a normal group (No. 1; n = 11) and an osteoporotic group (No. 2; n = 10). Strain and centrum stress were measured on T4 and T6 (T3-T7), and T9 and T11 (T8-T12) during tests in the intact state, following a centrum defect, during and after an augmented VCF at T5 or T10, and during a subsequent VCF. Stiffness and strength were compared: between groups 1 and 2; among intact, defect, and augmented VCF states; and between the initial and subsequent VCF. RESULTS: Group 1 was stiffer than 2 in compression (P = 0.01) and flexion (P = 0.07), with no difference in adjacent level load transfer (strain P = 0.72, centrum stress P = 0.36) or strength (P = 0.07). The centrum defect reduced compressive stiffness from the intact (P = 0.001), which was partially restored following VCF augmentation (P = 0.006). There were no differences in flexion stiffness (P > or = 0.14). Adjacent level load transfer in flexion exceeded that in compression (strain P = 0.001, centrum stress P = 0.19). Initial and subsequent VCF occurred at similar forces (P = 0.26) with higher adjacent level load at subsequent (strain and centrum stress P = 0.04). CONCLUSIONS: Augmentation of multilevel spinal segments with VCF produced by combined compression, flexion, and a centrum defect normalizes adjacent level load transfer at physiologic loads. In both normal and osteoporotic spinal segments, as loads approach those of the initial VCF, protection from augmentation is lost, and subsequent adjacent level VCFs occur from extreme loading, and not the augmentation process.

The mechanics of polymethylmethacrylate augmentation.

Osteoporosis frequently leads to vertebral compression fractures. Percutaneous cement augmentation, one recent technique, may alter the biomechanics of the vertebral body and spinal segment. These alterations reportedly predispose the spinal segment to additional vertebral compression fractures. We investigated the changes in segment stiffness and strength after polymethylmethacrylate augmentation. Twelve thoracic segments consisting of five vertebral bodies were divided into two groups, a pure moment group (Group 1) and an eccentric compression group (Group 2). Baseline measurements of stiffness were taken on each segment followed by the creation of an initial vertebral compression fracture during which stiffness and strength were measured. After augmentation, stiffness was again measured. Finally, a second vertebral compression fracture was created measuring stiffness and strength again. Augmentation did not alter stiffness before and after augmentation in either group. Augmentation also did not result in any difference in strength measured at subsequent fracture when compared with strength measured at initial fracture in either group. The augmentation of vertebral compression fractures by kyphoplasty does not alter the stiffness or the strength of the multilevel segments and eccentric compression in contrast to pure moments leads to a lower strength during mechanical testing.

Thoracic transfacet pedicle screw fixation: a new instrumentation technique.

OBJECT: Pedicle screw instrumentation of the thoracic spine remains technically challenging. Transverse process and costotransverse screw fixation techniques have been described as alternatives to pedicle screw fixation (PSF). In this study, the authors introduce thoracic transfacet PSF and compare its experimental biomechanical results with those of standard PSF in short-term cyclic loading in cadaveric thoracic specimens. METHODS: Specimens were tested intact for six cycles at compressive loads of 250 N offset by 1 cm along appropriate axes to induce flexion, extension, and left and right lateral bending. The specimens were then fixed with either a pedicle screw/rod construct or transfacet pedicle screws and retested in the same fashion. After this sequence, specimens were loaded until failure in flexion mode at a rate of 5 mm/minute was observed. Both fixation constructs provided significantly greater stiffnesses than that demonstrated when the specimen was intact (p < 0.05, two-way analysis of variance). Additionally, the two constructs were statistically equivalent in terms of stiffness and load-to-failure values (p < 0.05, two-tailed nonpaired t-test). The only difference observed was that the low midthoracic region (T7-9) was biomechanically weaker than the upper midthoracic and lower thoracic areas in flexion after the destabilization and instrumentation-augmented stabilization procedures. CONCLUSIONS: In selected thoracic surgical procedures, transfacet PSF may, after analysis of long-term biomechanical data, potentially become a reasonable alternative to conventional PSF.

The effects of the antiresorptive agents calcitonin and pamidronate on spine fusion in a rabbit model.

BACKGROUND CONTEXT: As the population ages, the number of individuals undergoing pharmacotherapy to prevent or treat osteoporosis is increasing. Drugs of the bisphosphonate family prevent bone resorption, as does calcitonin, though by different mechanisms. Bisphosphonates are deposited in bone, preventing resorption by osteoclasts. Calcitonin is a direct inhibitor of osteoclasts, but is not itself incorporated in bone. The same late middle-aged and elderly patients who are being treated for osteoporosis frequently come to spine fusion. Bone remodelling is a vital part of graft incorporation. Interventions that interfere with remodelling may have a detrimental effect on the rate, time course, and strength of the fusion mass. PURPOSE: To delineate the effects of these anti-osteoporosis medications on the fusion process. STUDY DESIGN: Randomized, prospective, double-blind, animal model. METHODS: Posterolateral arthrodesis was performed at L5/6 in 60 skeletally mature 4.0-4.5 kg New Zealand white rabbits, using 3 cc of autologous iliac crest graft per side. Rabbits were randomized to one of three groups: PAM--pamidronate 1.2 mg subcutaneously 3 times/week for 4 weeks preoperatively, then 0.6 mg/day via miniosmotic pump for 4 weeks postoperatively; CAL--calcitonin 14 IU/day via pump for 4 weeks postoperatively only; CON--no drug intervention. All animals were killed 5 weeks after surgery. Fusion, defined by absolute lack of intersegmental motion, was assessed by manual palpation by two spine surgeons. Where there was disagreement, a third surgeon made the final determination. Stiffness and peak load to failure were determined by mechanical testing of each operated motion segment, and normalized to the adjacent, unoperated level. RESULTS: Four rabbits excluded (1 each: death; euthanasia for hind-limb palsy; infection; incorrect level). Number fused at 5 weeks: CON 10/18 (56%), PAM 7/19 (37%), CAL 13/19 (68%). Fisher exact test showed no significant differences between groups. Analysis of variance (ANOVA) showed no significant differences in mechanical testing between CAL and CON, but PAM specimens had significantly less peak load than CON or CAL animals (p<.01) and were less stiff than CON (p<.01) or CAL (p<.05) animals. CONCLUSIONS: Though one must be careful in extrapolating animal data to humans, this study suggests that calcitonin is not detrimental to spine fusion. Pamidronate, however, does lead to a mechanically less robust fusion. Based on this study, there is no evidence to support a recommendation to stop antiresorptive therapy for osteoporosis in the spine fusion patient.