Matthew J. Allen

The effects of diamond-like carbon coatings on macrophages, fibroblasts and osteoblast-like cells in vitro.

The elaboration of metallic and polymeric particles from the wear of joint replacement components is widely implicated in the pathogensis of aseptic loosening of these implants. Diamond-like carbon (DLC) coatings show great potential as wear-retardant coatings and may offer a possible solution to this problem. We have studied the effects of DLC coatings on cells derived from the tissues that surround a total joint replacement (macrophages, fibroblasts and osteoblast-like cells). There was no evidence that DLC coatings, deposited on a variety of different substrates, caused cytotoxicity in vitro. Cells grown on the coated substrates exhibited normal cellular growth and morphology. DLC coatings are biocompatible in vitro and should now be tested in animal models to determine their behaviour in vivo.

Lactate dehydrogenase activity as a rapid and sensitive test for the quantification of cell numbers in vitro

Lactate dehydrogenase (LDH) has been used extensively as a marker for cell death both in vitro and in vivo. The release of LDH into tissue culture medium accurately reflects cell viability in vitro. We have investigated the relationship between cell concentration and total LDH activity in samples of cell lysate. Although there are differences in the amount of LDH present in different cell types, the total enzyme activity in a sample of cell lysate is directly proportional to the concentration of cells in the sample. The measurement of LDH activity in vitro provides a sensitive, accurate and cost-effective alternative to the use of either radioisotopic or dye-based assays for the determination of cell numbers.

A randomized controlled trial of the efficacy of autologous platelet therapy for the treatment of osteoarthritis in dogs

OBJECTIVE To determine efficacy of a single intra-articular injection of an autologous platelet concentrate for treatment of osteoarthritis in dogs. DESIGN Randomized, controlled, 2-center clinical trial. ANIMALS 20 client-owned dogs with osteoarthritis involving a single joint. PROCEDURES Dogs were randomly assigned to a treatment or control group. In all dogs, severity of lameness and pain was scored by owners with the Hudson visual analog scale and the University of Pennsylvania Canine Brief Pain Inventory, respectively, and peak vertical force (PVF) was determined with a force platform. Dogs in the treatment group were then sedated, and a blood sample (55 mL) was obtained. Platelets were recovered by means of a point-of-use filter and injected intra-articularly within 30 minutes. Control dogs were sedated and given an intra-articular injection of saline (0.9% NaCl) solution. Assessments were repeated 12 weeks after injection of platelets or saline solution. RESULTS Dogs weighed between 18.3 and 63.9 kg (40.3 and 140.6 lb) and ranged from 1.5 to 8 years old. For control dogs, lameness scores, pain scores, and PVF at week 12 were not significantly different from pretreatment values. In contrast, for dogs that received platelet injections, lameness scores (55% decrease in median score), pain scores (53% decrease in median score), and PVF (12% increase in mean PVF) were significantly improved after 12 weeks, compared with pretreatment values. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that a single intra-articular injection of autologous platelets resulted in significant improvements at 12 weeks in dogs with osteoarthritis involving a single joint.

Kinematic Motion Patterns of the Cranial and Caudal Canine Cervical Spine

OBJECTIVE To define the kinematic motion patterns of the canine cervical spine, with a particular emphasis on identifying differences between the cranial (C(2)-C(4)) and caudal (C(5)-C(7)) segments, and to determine the significance of coupled motions (CM) in the canine cervical spine. STUDY DESIGN Cadaveric biomechanical study. SAMPLE POPULATION Cervical spines of 8 Foxhounds. METHODS Spinal specimens were considered free of pathology based on radiographic, computed tomography, and magnetic resonance imaging examinations. All musculature was removed without damaging ligaments or joint capsules. Spines were mounted in a customized pure-moment spine testing jig, and data were collected using an optoelectronic motion capture system. Range of motion, neutral zone and CM in flexion/extension, left/right lateral bending and left/right axial rotation were established. Data were analyzed using mixed-effects maximum likelihood regression models. RESULTS Total flexion/extension did not change across the 4 levels. There was no difference between flexion and extension, and no CM was identified. Lateral bending was not different across levels, but tended to be greater in the cranial spine. Axial rotation was ∼2.6 times greater in the caudal segments. Lateral bending and axial rotation were coupled. CONCLUSIONS Kinematics of the cranial and caudal cervical spine differed markedly with greater mobility in the caudal cervical spine.

Evaluation of the Safety of a Novel Knee Load-Bypassing Device in a Sheep Model

BACKGROUND Unloading treatments for osteoarthritis of the knee, such as valgus braces, have been shown to reduce medial joint-loading and pain. The purpose of this preclinical study was to investigate the tissue response to an extracapsular implantable device (KineSpring System; Moximed, Hayward, California) that is designed to reduce loading across the medial compartment of the knee. METHODS Eleven sheep were implanted with the KineSpring System, consisting of bases secured to the medial femoral and tibial cortices with bone screws and also consisting of a joint-spanning load-absorber composed of a piston and spring assembly inside a polymeric sheath. In nine sheep, titanium alloy washers with either an uncoated or a plasma-sprayed titanium-hydroxyapatite (TPS-HA) coated undersurface were fixed with screws to the contralateral femur and tibia to investigate the effects of surface treatment on extracortical bone apposition. The functionality of the KineSpring System was assessed by fluoroscopy, tissue response was determined by gross and microscopic histology, and implant fixation was determined by radiography, microradiography, and histomorphometry at four, twelve, twenty-six, and fifty-two weeks. RESULTS The function of the KineSpring System was confirmed in all sheep. Seventeen of eighteen TPS-HA coated bases and thirty-six of thirty-six washers had stable bone fixation; one coated base was loose with evidence of infection. At four weeks, there was an early, expected inflammatory response, but this response resolved by twelve weeks and a pseudosynovial membrane formed around the sheath. Bone apposition increased over time for the TPS-HA coated bases and for uncoated washers (p < 0.05). There was good apposition of the TPS-HA coated washers even at early time points, with no subsequent increase in apposition over time. CONCLUSIONS The KineSpring System demonstrated safety in a simulated use model for periods of up to fifty-two weeks. Screws result in stable implant fixation and TPS-HA coating allows for early and long-lasting cortical bone apposition and integration. CLINICAL RELEVANCE This implant warrants further investigation as a means of reducing medial compartment loading and pain in patients with osteoarthritis of the knee.

Biomechanical comparison between bicortical pin and monocortical screw/polymethylmethacrylate constructs in the cadaveric canine cervical vertebral column

OBJECTIVE To compare biomechanical stiffness of cadaveric canine cervical spine constructs stabilized with bicortical stainless steel pins and polymethylmethacrylate (PMMA), monocortical stainless steel screws with PMMA, or monocortical titanium screws with PMMA. STUDY DESIGN Biomechanical cadaver study. ANIMALS Eighteen canine cervical vertebral columns (C2-C7) were collected from skeletally mature dogs (weighing 22-32 kg). METHODS Specimens were radiographed and examined by dual energy X-ray absorptiometry. Stiffness of the unaltered C4-C5 intervertebral motion unit was measured in extension, flexion and lateral bending using non-destructive 4-point bend testing. Specimens were then stabilized by (1) bicortical stainless steel pins/PMMA, (2) monocortical stainless steel screws/PMMA, or (3) monocortical titanium screws/PMMA. Mechanical testing was repeated and stiffness data from unaltered specimens and the 3 treatment groups were compared. RESULTS All 3 surgical methods significantly increased stiffness of the C4-C5 motion unit compared with the unaltered specimen (P < .001 for all treatments), but stiffness was not significantly different among the 3 fixation groups (P = .578). CONCLUSIONS In this model, monocortical screw fixation (with stainless steel or titanium screws) was biomechanically equivalent to bicortical fixation.

An association between the inferior humeral head osteophyte and teres minor fatty infiltration: evidence for axillary nerve entrapment in glenohumeral osteoarthritis

BACKGROUND Glenohumeral osteoarthritis often results in inferior humeral osteophytes. Anatomic studies suggest that the axillary neurovascular bundle is in close proximity to the glenohumeral capsule. We therefore hypothesize that an inferior humeral osteophyte of sufficient magnitude could encroach on the axillary nerve and result in measurable fatty infiltration of the teres minor muscle. MATERIALS AND METHODS Preoperative magnetic resonance imaging studies of 91 consecutive arthritic shoulders were retrospectively reviewed. Two cohorts were established based on the presence of a humeral osteophyte. The distances from the axillary neurovascular bundle to various osseous structures were measured using calibrated software. Objective quantitative measurements of the degree of fatty infiltration of the teres minor muscles were obtained with image analysis software. Results were compared between cohorts. RESULTS The distance between the inferior humerus and axillary neurovascular bundle was inversely correlated to the size of the inferior humeral osteophyte (ρ = -0.631, P < .001). Fatty infiltration of the teres minor was greater when an inferior osteophyte was present (11.9%) than when an osteophyte was not present (4.4%) (P = .004). A statistically significant correlation between the size of the humeral head spur and quantity of fat in the teres minor muscle belly (ρ = 0.297, P = .005) was identified. CONCLUSION These data are consistent with our hypothesis that the axillary nerve may be entrapped by the inferior humeral osteophyte often presenting with glenohumeral osteoarthritis. Entrapment may affect axillary nerve function and lead to changes in the teres minor muscle. Axillary neuropathy from an inferior humeral osteophyte may represent a contributing and treatable cause of pain in patients with glenohumeral osteoarthritis.

Micromorphometry and Cellular Characteristics of the Canine Cervical Intervertebral Discs

BACKGROUND Dogs have a high prevalence of disc-associated cervical spinal cord disorders. Despite this, there are no descriptions of the micromorphometry or cellular characteristics of canine cervical intervertebral discs. HYPOTHESIS/OBJECTIVES To compare micromorphometric and cellular characteristics at 4 disc regions (outer annulus [OA], inner annulus [IA], transitional zone [TZ], nucleus pulposus [NP]). We hypothesized that measurements would differ between chondrodystrophic (CH) and nonchondrodystrophic (NCH) dogs. ANIMALS Six CH dogs and 6 NCH dogs, under 3 years old. METHODS Histologic sections of all cervical discs from each dog were examined. Micromorphometric variables included relative ratio of ventral to dorsal annulus fibrosus (AF), number and mean width of AF fibers, and relative percentage of NP. Cellular variables included cell density, morphology, and grouping. RESULTS The NP from CH dogs was smaller, more rounded, and more dorsally located compared with that from NCH dogs. The NP occupied a greater proportion of the disc in NCH dogs compared with CH dogs (27.7 versus 15.8%; P<.001). The ratio of ventral to dorsal AF was approximately 3:1 in the CH group and 2:1 in the NCH group. Cellular variables were region dependent. Cell density was 2.4-fold higher in the OA compared with the NP. Approximately 50 of NP cells and 4.5% of OA cells occurred in groups. CONCLUSIONS AND CLINICAL IMPORTANCE Micromorphometric variables differed by CH status. Cellular variables differed by disc region. Our findings potentially can explain the high incidence of intervertebral disc extrusions in CH dogs compared with NCH dogs.

Force Plate Gait Analysis in Doberman Pinschers with and without Cervical Spondylomyelopathy

BACKGROUND The most accepted means of evaluating the response of a patient with cervical spondylomyelopathy (CSM) to treatment is subjective and based on the owner and clinicians perception of the gait. OBJECTIVE To establish and compare kinetic parameters based on force plate gait analysis between normal and CSM-affected Dobermans. ANIMALS Nineteen Doberman Pinschers: 10 clinically normal and 9 with CSM. METHODS Force plate analysis was prospectively performed in all dogs. At least 4 runs of ipsilateral limbs were collected from each dog. Eight force platform parameters were evaluated, including peak vertical force (PVF) and peak vertical impulse (PVI), peak mediolateral force (PMLF) and peak mediolateral impulse, peak braking force and peak braking impulse, and peak propulsive force (PPF) and peak propulsive impulse. In addition, the coefficient of variation (CV) for each limb was calculated for each parameter. Data analysis was performed by a repeated measures approach. RESULTS PMLF (P = .0062), PVI (P = .0225), and PPF (P = .0408) were found to be lower in CSM-affected dogs compared with normal dogs. Analysis by CV as the outcome indicated more variability in PVF in CSM-affected dogs (P = 0.0045). The largest difference in the CV of PVF was seen in the thoracic limbs of affected dogs when compared with the thoracic limbs of normal dogs (P = 0.0019). CONCLUSIONS AND CLINICAL IMPORTANCE The CV of PVF in all 4 limbs, especially the thoracic limbs, distinguished clinically normal Dobermans from those with CSM. Other kinetic parameters less reliably distinguished CSM-affected from clinically normal Dobermans.

Hydroxyapatite coating on PEEK implants: Biomechanical and histological study in a rabbit model

A bioactive two-layer coating consisting of hydroxyapatite (HA) and yttria-stabilized zirconia (YSZ) was investigated on cylindrical polyetheretherketone (PEEK) implants using ion beam assisted deposition (IBAD). Post-deposition heat treatments via variable frequency microwave annealing with and without subsequent autoclaving were used to crystallize the as-deposited amorphous HA layer. Microstructural analysis, performed by TEM and EDS, showed that these methods were capable of crystallizing HA coating on PEEK. The in vivo response to cylindrical PEEK samples with and without coating was studied by implanting uncoated PEEK and coated PEEK implants in the lateral femoral condyle of 18 rabbits. Animals were studied in two groups of 9 for observation at 6 or 18weeks post surgery. Micro-CT analysis, histology, and mechanical pull-out tests were performed to determine the effect of the coating on osseointegration. The heat-treated HA/YSZ coatings showed improved implant fixation as well as higher bone regeneration and bone-implant contact area compared to uncoated PEEK. The study offers a novel method to coat PEEK implants with improved osseointegration.