Ferris M. Pfeiffer

Pedicle Screw Design and Cement Augmentation in Osteoporotic Vertebrae Effects of Fenestrations and Cement Viscosity on Fixation and Extraction

Study Design. Experimental, human cadaveric study. Objective. To assess the fixation effects of injecting cement augmentation before screw insertion or after insertion of fenestrated screws; the effect of modulating cement viscosity; and the effects of these techniques on screw removal. Summary of Background Data. It seems clear that cement augmentation can enhance pedicle screw fixation in osteoporotic bone. What remains to be demonstrated is the aspects of optimal technique such that fixation is enhanced with the greatest safety profile. Methods. Part I: Human osteoporotic vertebrae were instrumented with solid (nonaugmented) screws, solid screws with polymethylmethacrylate (PMMA), partially cannulated fenestrated (Pfen) screws, or fully cannulated fenestrated (Ffen) screws through which PMMA was injected. Screw fixation was tested in pullout. Part II: Ffen screws were augmented with standard low-viscosity PMMA versus high-viscosity PMMA. Part III: Sample cohorts were extracted from vertebrae to assess required torque and characterize difficulty of extraction. Results. Part I: Pfen screws demonstrated the greatest fixation with mean failure force of 690 ± 182 N. All methods of cement augmentation demonstrated significant increases in screw fixation. Part II: Ffen screws did not demonstrate a significant difference in pullout strength when high-viscosity PMMA was used as compared with low-viscosity PMMA. Part III: Mean extraction torque values for solid augmented screws, Ffen screws, and Pfen screws were 1.167, 1.764, and 1.794 Nm, respectively, but these differences did not reach significance. None of the osteoporotic vertebrae sustained catastrophic failure during augmented screw extraction. Conclusion. Polymethylmethacrylate cement augmentation clearly enhances pedicle screw fixation in osteoporotic vertebrae when tested in pure pullout. The technique used for cement injection and choice of specialty screws can have a significant impact on the magnitude of this effect. Fenestrated screws have the capacity to confine cement placement in the vertebral body and may provide enhanced safety from cement extrusion into the spinal canal. It is feasible to inject high-viscosity PMMA through this fenestration geometry, and higher-viscosity cement may enhance the fixation effect.

Animal models of cartilage repair

Cartilage repair in terms of replacement, or regeneration of damaged or diseased articular cartilage with functional tissue, is the ‘holy grail’ of joint surgery. A wide spectrum of strategies for cartilage repair currently exists and several of these techniques have been reported to be associated with successful clinical outcomes for appropriately selected indications. However, based on respective advantages, disadvantages, and limitations, no single strategy, or even combination of strategies, provides surgeons with viable options for attaining successful long-term outcomes in the majority of patients. As such, development of novel techniques and optimisation of current techniques need to be, and are, the focus of a great deal of research from the basic science level to clinical trials. Translational research that bridges scientific discoveries to clinical application involves the use of animal models in order to assess safety and efficacy for regulatory approval for human use. This review article provides an overview of animal models for cartilage repair. Cite this article: Bone Joint Res 2014;4:89–94.

Biomechanical analysis of pedicle screws in osteoporotic bone with bioactive cement augmentation using simulated in vivo multicomponent loading.

Study Design. Biomechanical analysis of bioactive cements augmenting pedicle screw resistance to loosening in osteoporotic synthetic bone. Objective. To simulate in vivo loading-loosening of pedicle screws in osteoporotic vertebrae; and to compare biomechanical efficacy of the following bioactive cements: calcium phosphate (CP), calcium sulfate (CS), and proprietary mixture (M). Summary of Background Data. Pedicle screw instrumentation in osteoporotic spines is limited by poor bone-screw interface strength, resulting in screw loosening fixation failure. Previous in vivo studies evaluated augmented pedicle screw resistance to pure pullout, not simulating in vivo loading/failure. Methods. A pedicle screw—instrumented osteoporotic thoracic vertebra subjected to combined pullout, transverse, moment loading was simulated. Unconstrained 3-dimensional screw motion relative to vertebra was optically measured during quasi-static, and dynamic loading. Results. Augmented groups (CP, CS, M) produced (P < 8.0E-07) higher quasi-static failure initiation force (61.2,45.6, 40.3 N) than those by the nonaugmented group (21.0 N), with no significant difference in small screw displacement up to these loads. Nonaugmented screw motion after failure initiation was primarily rotation (toggle-migration) with minimal pullout until the screw tip contacted the superior endplate, followed by more prominent screw pullout. Augmented screw motion (with cement remaining intact on screw) was similar, but with eventual bone fracture anterior to the pedicle region. Dynamic loading produced similar failure initiation force and screw motion. Conclusion. We believe our test protocol produced screw loosening failure similar to that observed clinically, and that it has the ability to detect differences in failure initiation force and failure modes to compare short-term efficacy of screw augmentation techniques. All cements improved screw resistance to failure. The CP > CS > M failure initiation force (P < 0.006) was because of differences in cement distribution. Animal studies may be required to characterize the remodeling activity of bioactive cements and their longer term efficacies.

Multiple injections of leukoreduced platelet rich plasma reduce pain and functional impairment in a canine model of ACL and meniscal deficiency

Platelet rich plasma (PRP) is used to treat many musculoskeletal disorders. We used a canine model to determine the effects of multiple intra‐articular injections of leukoreduced PRP (ACP) on anterior cruciate ligament healing, meniscal healing, and progression of osteoarthritis (OA). With Animal Care and Use Committee (ACUC) approval, 12 dogs underwent partial ACL transection and meniscal release in one knee. At weeks 1, 2, 3, 6, and 8 after insult, dogs were treated with intra‐articular injections (2 ml) of either ACP (n = 6) or saline (n = 6). Dogs were assessed over 6 months to determine comfortable range of motion (CROM), lameness, pain, effusion, kinetics, and radiographic and arthroscopic assessments. At 6‐month endpoint, dogs were assessed for ACL material properties and histopathology. Saline‐treated dogs had significantly (p < 0.04) more CROM loss, significantly (p < 0.01) more pain, significantly (p < 0.05) more severe lameness, significantly (p < 0.05) lower function, and significantly (p < 0.05) lower %Total Pressure Index in affected hindlimbs compared to ACP‐treated dogs. Radiographic OA increased significantly (p < 0.01) over time within each group. Arthroscopically, saline‐treated knees showed moderate to severe synovitis, further ACL disruption, and medial compartment cartilage loss, and ACP‐treated knees showed evidence of ACL repair and less severe synovitis. ACL material properties in ACP‐treated knees were closer to normal than in saline‐treated knees, however, the differences were not statistically significant. ACL histopathology was significantly (p< 0.05) less severe in ACP‐treated knees compared to saline‐treated knees. Five intra‐articular injections of leukoreduced PRP had beneficial effects for ACL healing, improved range of motion, decreased pain, and improved limb function for up to 6 months in this model.

Comparison of a Novel Bone-Tendon Allograft With a Human Dermis–Derived Patch for Repair of Chronic Large Rotator Cuff Tears Using a Canine Model

PURPOSE This study tested a bone-tendon allograft versus human dermis patch for reconstructing chronic rotator cuff repair by use of a canine model. METHODS Mature research dogs (N = 15) were used. Radiopaque wire was placed in the infraspinatus tendon (IST) before its transection. Three weeks later, radiographs showed IST retraction. Each dog then underwent 1 IST treatment: debridement (D), direct repair of IST to bone with a suture bridge and human dermis patch augmentation (GJ), or bone-tendon allograft (BT) reconstruction. Outcome measures included lameness grading, radiographs, and ultrasonographic assessment. Dogs were killed 6 months after surgery and both shoulders assessed biomechanically and histologically. RESULTS BT dogs were significantly (P = .01) less lame than the other groups. BT dogs had superior bone-tendon, tendon, and tendon-muscle integrity compared with D and GJ dogs. Biomechanical testing showed that the D group had significantly (P = .05) more elongation than the other groups whereas BT had stiffness and elongation characteristics that most closely matched normal controls. Radiographically, D and GJ dogs showed significantly more retraction than BT dogs (P = .003 and P = .045, respectively) Histologically, GJ dogs had lymphoplasmacytic infiltrates, tendon degeneration and hypocellularity, and poor tendon-bone integration. BT dogs showed complete incorporation of allograft bone into host bone, normal bone-tendon junctions, and well-integrated allograft tendon. CONCLUSIONS The bone-tendon allograft technique re-establishes a functional IST bone-tendon-muscle unit and maintains integrity of repair in this model. CLINICAL RELEVANCE Clinical trials using this bone-tendon allograft technique are warranted.

Importance Of Donor Chondrocyte Viability in Osteochondral Allografting

Objectives: Osteochondral allografting (OCA) provides a biologic treatment option for functional restoration of large articular cartilage defects in multiple joints. While successful outcomes after OCA have been linked to viable donor chondrocytes, the importance of donor cell viability has not been comprehensively validated. The purpose of this study was to use a canine model to determine the importance of donor chondrocyte viability at the time of implantation with respect to functional success of femoral condylar OCAs based on gross, cell viability, histologic, biochemical, and biomechanical outcome measures. Methods: With IACUC approval, adult female dogs (n = 16) were implanted with 8-mm cylindrical osteochondral allografts from male dogs in the lateral and medial femoral condyles of one knee. Osteochondral allografts were preserved for 28 or 60 days after procurement and chondrocyte viability was quantified prior to implantation. Two different storage media, temperatures and time points were used in order to obtain a spectrum of %chondrocyte viability at the time of implantation. A successful outcome was defined as an osteochondral allograft that was associated with graft integration, maintenance of hyaline cartilage, lack of associated cartilage disorder, and lack of fibrillation, fissuring, or fibrous tissue infiltration of the allograft based on subjective radiographic, arthroscopic, gross, and histologic assessments at 6 months after implantation. Results: Chondrocyte viability ranged from 23% to 99% at the time of implantation. All successful grafts had greater than 70% chondrocyte viability at the time of implantation and no graft with chondrocyte viability <70% was associated with a successful outcome. Live-dead stained sections and histologic findings with respect to cell morphology suggested that successful grafts were consistently comprised of viable chondrocytes in lacunae, while grafts that were not successful were comprised of non-viable chondrocytes with infiltration of fibroblasts from the surrounding recipient tissues. In situ PCR (FISH) assays were performed in an attempt to distinguish donor (male) cells from recipient (female) cells. Unfortunately, this technique was exceptionally difficult to perform on intact articular cartilage sections, and consistent, repeatable data could not be obtained from this testing. However, the data did support histologic and live-dead data, which strongly suggested that successful grafts retained viable donor (male) chondrocytes and unsuccessful grafts degraded and were replaced by fibrous tissue populated with recipient (female) fibroblasts. Conclusion: Viable chondrocytes in osteochondral allografts at the time of transplantation are primarily responsible for maintenance of donor articular cartilage health long term. Optimizing chondrocyte viability in all aspects of osteochondral allografting - including procurement, processing, storage, transportation, and surgical implantation - needs to be a primary focus for clinical use of OCA.

The histologic and biomechanical response of two commercially available small glenoid anchors for use in labral repairs

BACKGROUND This study examined histologic characteristics and biomechanical performance of 2 commercially available, small glenoid anchors. METHODS Adult research dogs (n = 6) were used for histologic analysis. Anchors were inserted into the lateral rim of the glenoid using the manufacturers protocol. The dogs were humanely euthanatized 8 weeks after anchor implantation, and the glenoids were collected for histologic analysis. Bone socket width data were compared for statistically significant (P < .05) differences. In addition, 4 matched pairs (n = 8) of human cadaveric glenoids were instrumented with 1 BioComposite SutureTak (Arthrex, Naples, FL, USA) and 1 JuggerKnot (Biomet, Warsaw, IN, USA) suture anchor in the anterior-inferior quadrant. Anchor constructs were preloaded to 5 N, cycled from 5 to 25 N for 100 cycles, and then pulled to failure. RESULTS All JuggerKnot anchor sites were cyst-like cavities with a rim of dense lamellar bone. All BioComposite SutureTak anchor sites contained intact anchors with close approximation of anastomosing trabeculae of lamellar bone. At 8 weeks after implantation, mean socket width of the JuggerKnot anchor sites was 6.3 ± 2.5 mm, which was significantly (P = .013) larger than the mean socket width of 2.7 ± 0.7 mm measured for the BioComposite SutureTak anchor sites. The JuggerKnot anchor demonstrated larger displacements during subfailure cyclic loading (2.9 ± 1.0 mm compared with 1.3 ± 0.4 mm) and load to failure tests (13.7 ± 6.6 mm compared with 3.2 ± 0.5 mm). Statistical differences (P < .01) existed in every category except ultimate load. CONCLUSIONS Based on the biomechanical in human bone and histologic findings in canine subjects, the all-suture anchor may be at risk for clinical failure.

Biomechanical Comparison of Five Posterior Cruciate Ligament Reconstruction Techniques

Abstract No surgical technique recreates native posterior cruciate ligament (PCL) biomechanics. We compared the biomechanics of five different PCL reconstruction techniques versus the native PCL. Cadaveric knees (n = 20) were randomly assigned to one of five reconstruction techniques: Single bundle all‐inside arthroscopic inlay, single bundle all‐inside suspensory fixation, single bundle arthroscopic‐assisted open onlay (SB‐ONL), double bundle arthroscopic‐assisted open inlay (DB‐INL), and double bundle all‐inside suspensory fixation (DB‐SUSP). Each specimen was potted and connected to a servo‐hydraulic load frame for testing in three conditions: PCL intact, PCL deficient, and PCL reconstructed. Testing consisted of a posterior force up to 100 N at a rate of 1 N/s at four knee flexion angles: 10, 30, 60, and 90 degrees. Three material properties were measured under each condition: load to 5 mm displacement, maximal displacement, and stiffness. Data were normalized to the native PCL, compared across techniques, compared with all PCL‐intact knees and to all PCL‐deficient knees using one‐way analysis of variance. For load to 5 mm displacement, intact knees required significantly (p < 0.03) more load at 30 degrees of flexion than all reconstructions except the DB‐SUSP. At 60 degrees of flexion, intact required significantly (p < 0.01) more load than all others except the SB‐ONL. At 90 degrees, intact, SB‐ONL, DB‐INL, and DB‐SUSP required significantly more load (p < 0.05). Maximal displacement testing showed the intact to have significantly (p < 0.02) less laxity than all others except the DB‐INL and DB‐SUSP at 60 degrees. At 90 degrees the intact showed significantly (p < 0.01) less laxity than all others except the DB‐SUSP. The intact was significantly stiffer than all others at 30 degrees (p < 0.03) and 60 degrees (p < 0.01). Finally, the intact was significantly (p < 0.05) stiffer than all others except the DB‐SUSP at 90 degrees. No technique matched the exact properties of the native PCL, but the double bundle reconstructions more closely recreated the native biomechanics immediately after implantation, with the DB‐SUSP coming closest to the native ligament. This study contributes new data for consideration in PCL reconstruction technique choice.

Evaluation of synthetic osteochondral implants.

This translational animal model study was designed to assess function, bone ingrowth and integration, and joint pathology associated with two different synthetic, bilayered osteochondral implants over a 3-month period after implantation into the femoral condyles of dogs. SynACart-Titanium (n = 6) and SynACart-PEEK (n = 6) (Arthrex, Naples, FL, and Sites Medical, Columbia City, IN) implants were press-fit into the lateral or medial femoral condyle (alternating location) of purpose-bred adult research dogs. Dogs were humanely euthanized 3 months after surgery and the operated knees were assessed radiographically, arthroscopically, grossly, and histologically. Based on all assessments, both types of implants were well tolerated and safe with no evidence for infection, migration, or rejection. Half of the SynACart-PEEK implants showed radiographic and histologic evidence of poor incorporation with all of these being in the lateral femoral condyle. SynACart-Titanium implants were considered effective in terms of integration into bone, lack of damage to surrounding and apposing articular cartilage, and maintenance of implant integrity and architecture for the duration of the study.

Myostatin deficiency partially rescues the bone phenotype of osteogenesis imperfecta model mice

SummaryMice with osteogenesis imperfecta (+/oim), a disorder of bone fragility, were bred to mice with muscle over growth to test whether increasing muscle mass genetically would improve bone quality and strength. The results demonstrate that femora from mice carrying both mutations have greater mechanical integrity than their +/oim littermates.IntroductionOsteogenesis imperfecta is a heritable connective tissue disorder due primarily to mutations in the type I collagen genes resulting in skeletal deformity and fragility. Currently, there is no cure, and therapeutic strategies encompass the use of antiresorptive pharmaceuticals and surgical bracing, with limited success and significant potential for adverse effects. Bone, a mechanosensing organ, can respond to high mechanical loads by increasing new bone formation and altering bone geometry to withstand increased forces. Skeletal muscle is a major source of physiological loading on bone, and bone strength is proportional to muscle mass.MethodsTo test the hypothesis that congenic increases in muscle mass in the osteogenesis imperfecta murine model mouse (oim) will improve their compromised bone quality and strength, heterozygous (+/oim) mice were bred to mice deficient in myostatin (+/mstn), a negative regulator of muscle growth. The resulting adult offspring were evaluated for hindlimb muscle mass, and bone microarchitecture, physiochemistry, and biomechanical integrity.Results+/oim mice deficient in myostatin (+/mstn +/oim) were generated and demonstrated that myostatin deficiency increased body weight, muscle mass, and biomechanical strength in +/mstn +/oim mice as compared to +/oim mice. Additionally, myostatin deficiency altered the physiochemical properties of the +/oim bone but did not alter bone remodeling.ConclusionsMyostatin deficiency partially improved the reduced femoral bone biomechanical strength of adult +/oim mice by increasing muscle mass with concomitant improvements in bone microarchitecture and physiochemical properties.