Outcome of palmar/plantar digital neurectomy in horses with foot pain evaluated with magnetic resonance imaging: 50 cases (2005-2011).

REASONS FOR PERFORMING STUDY: There is limited knowledge of the foot lesions that influence the outcome of palmar/plantar digital neurectomy (PDN). OBJECTIVES: 1) To report the short- and long-term outcomes of horses that underwent PDN to alleviate chronic foot pain due to lesions diagnosed by magnetic resonance imaging (MRI) and 2) factors that may influence the outcome of PDN. STUDY DESIGN: Multicentre retrospective study. METHODS: Medical records of 50 horses subjected to PDN due to chronic foot pain were reviewed. Age, breed, sex, athletic activity, duration of lameness, affected limb(s), response to anaesthesia of the palmar/plantar digital nerves, MRI findings and surgical technique were analysed together with follow-up data to identify factors that influenced the long-term outcomes. RESULTS: Forty-six of 50 horses (92%) responded positively to surgery; 40 (80%) were able to return to their previous athletic use for a median time of 20 months (range: 12-72 months). Eighteen (36%) horses developed post operative complications including residual lameness, painful neuromas, or early recurrence of lameness. Horses with pre-existing core or linear lesions of the deep digital flexor tendon (DDFT) had significantly shorter periods of lameness resolution after surgery than horses with dorsal border lesions of the DDFT or other foot lesions. CONCLUSIONS: Palmar/plantar digital neurectomy can improve or resolve lameness in horses with foot pain unresponsive to medical therapy without serious post operative complications. However, horses with core or linear lesions of the DDFT should not be subjected to PDN as these horses experience residual lameness or early recurrent lameness after surgery. Magnetic resonance imaging can be used to identify these horses.

Comparison of radiofrequency treatment and mechanical debridement of fibrillated cartilage in an equine model.

OBJECTIVE: To compare a radiofrequency energy (RFE) prototype probe to mechanical debridement (MD) and a commercially available RFE system used for chondroplasty in the treatment of an experimentally created partial thickness cartilage lesion in horses. The study design was experimental, randomized complete block, n=8, using fifteen mature ponies. METHODS: Grade 2 to 3 cartilage lesions were prepared in both patellae. After 10 months duration, the injuries were used to study the effects of MD, a commercially available bipolar RFE device (CoVac 50; ArthroCare Corporation) and a prototype monopolar RFE device (Smith & Nephew Endoscopy). Six months after treatment the patellae were examined for chondrocyte viability and cartilage structure. RESULTS: Mean depth of cell death was significantly different among groups (controls, MD

Comparison of mechanical debridement and radiofrequency energy for chondroplasty in an in vivo equine model of partial thickness cartilage injury.

OBJECTIVE: The purpose of this study was to develop a long-term model of cartilage injury that could be used to compare the effects of radiofrequency energy (RFE) and mechanical debridement as a treatment. METHODS: Partial thickness fibrillation of patellar cartilage was created in 16 mature ponies. Three months after the initial surgery all injured patellae were randomly selected to receive one of the four treatments (n = 8/treatment): (1) control, (2) mechanical debridement with a motorized shaver, (3) TAC-CII RFE probe, and (4) CoVac 50 RFE probe. The ponies were euthanized 22 months after treatment. Macroscopic appearance of the cartilage surface was scored, vital cell staining was used to determine chondrocyte viability and light microscopy was used to grade the morphometric changes within the cartilage. Mechanical properties (aggregate modulus, Poisson's ratio and permeability) also were determined and compared to normal uninjured cartilage. RESULTS: There were no differences in the cartilage surface scores among the treatment groups and control samples (P > 0.05). The maximum depth of cell death and the percentage of dead area in control and mechanical debridement groups were significantly less than those in both RFE groups. There were no significant differences in maximum depth and the percentage of dead area between the two RFE treatment groups. Histologic scores demonstrated better cartilage morphology for the control and mechanical debridement groups than those of RFE groups. However, even with full thickness chondrocyte death, the matrix in the RFE treated sections was still retained and the mechanical properties of the treated cartilage did not differ from the mechanical debridement group. CONCLUSION: RFE caused greater chondrocyte death and more severe morphological changes compared to untreated degenerative cartilage and mechanical debridement in this model.

Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of three 4.5-mm and two 5.5-mm cortical screws.

OBJECTIVE: To compare the biomechanical characteristics and mode of failure of 2 parallel-screw techniques for proximal interphalangeal joint arthrodesis in horses. STUDY DESIGN: Randomized block design, blocking for horse (1-5), method of screw fixation (three 4.5-mm vs two 5.5-mm), side (left limb vs right limb), and end (front limb vs hind limb). Constructs were loaded to failure in 3-point bending in a dorsal-to-palmar (plantar) direction. SAMPLE POPULATION: Twenty limbs (10 limb pairs) from 5 equine cadavers. METHODS: A combined aiming device was used to facilitate consistent screw placement. Three parallel 4.5-mm cortical screws were placed in lag fashion in 1 limb of a pair, and 2 parallel 5.5-mm cortical screws were placed in lag fashion in the contralateral limb. Arthrodesis constructs were tested in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials-testing machine. Loading rate was 19 mm/s. Maximal bending moment at failure and composite stiffness were obtained from bending moment-angular deformation curves. Data were analyzed using ANOVA and chi(2) analysis. RESULTS: There were no significant differences in bending moment (P >.05, power = 0.8 @ delta = 19%) or composite stiffness (P >.05, power = 0.8 @ delta = 19%) between the 2 fixation techniques. Higher maximal bending moment was found in front limbs than hind limbs, and front limbs with two 5.5-mm screws than hind limbs with two 5.5-mm screws. In all cases, constructs completely failed. A greater number of 4.5-mm cortical screws failed than 5.5-mm cortical screws. CONCLUSIONS-In pastern arthrodesis constructs loaded in 3-point bending, end (front limb vs hind limb) affected maximal bending moment at failure of constructs. There was no significant effect of horse, treatment, or side on maximal bending moment or stiffness. Two 5.5-mm cortical screws should provide a surgically simpler pastern arthrodesis than three 4.5-mm cortical screws while maintaining similar biomechanical characteristics. CLINICAL RELEVANCE: Three 4.5-mm screws or two 5.5-mm screws will provide similar biomechanical characteristics in bending when performing equine pastern arthrodesis.

Histomorphometric description of allograft bone remodeling and union in a canine segmental femoral defect model: a comparison of rhBMP-2, cancellous bone graft, and absorbable collagen sponge.

The purpose of this study was to determine the effect of recombinant human bone morphogenetic protein type 2 (rhBMP-2) on the histomorphometry of femoral allograft-host bone union and allograft remodeling. A 6 cm mid-diaphyseal femoral defect was created and filled with an allograft stabilized with an interlocking nail in 21 dogs. Dogs were randomly divided into three equal groups and the allograft-host bone junctions and the mid-diaphyses of the allografts were treated with either an absorbable collagen sponge (ACS) loaded with rhBMP-2 (BMP group), an autogenous cancellous bone graft (CBG group), or ACS loaded with buffer solution (ACS group). All dogs received daily tetracycline until sacrifice at 24 weeks to label new bone formation. Histomorphometric analyses on sections of proximal and distal allograft-host bone junctions and the mid-diaphyseal portion of allografts were performed using fluorescent and regular light microscopy. Analyses of the host bone and junctions between allograft and host bone revealed significantly greater new bone formation and larger osteon radii in the BMP group compared to CBG and ACS groups and contralateral intact bone. Porosity in CBG and ACS groups was significantly higher than in the BMP group, which had similar values to intact bone. In transverse sections of allografts, the largest pore diameters were present in the CBG group. Based on all parameters measured, significantly higher bone turnover occurred in the outer cortical area of the allograft in all groups as compared to the inner cortical and mid-cortical areas. New bone formation and osteon radius/osteon width in allografts were similar for all three groups. Higher porosity and larger pore diameters in the CBG and ACS groups suggested higher bone resorption versus formation in these groups compared to the BMP group. The results of this study reveal more balanced allograft bone resorption and bone formation in the BMP group, with greater resorptive activity in the CBG and ACS groups. However, neither rhBMP-2 nor autogenous bone graft increased allograft incorporation when compared to the negative control (ACS group).

Thermal chondroplasty with radiofrequency energy. An in vitro comparison of bipolar and monopolar radiofrequency devices.

The purpose of this study was to examine the in vitro effects of three radiofrequency energy devices (two bipolar devices and one monopolar device) for the performance of thermal chondroplasty. Thirty-two fresh bovine femoral osteochondral sections (approximately 3 x 4 x 5 cm) from eight cows were divided into four groups (three treatment patterns and one sham-operated group with eight specimens per group). The three treatment patterns consisted of 1) radiofrequency energy delivered by a mechanical jig at 1 mm/sec in a contact mode (50 g of pressure), 2) radiofrequency energy delivered by a mechanical jig at 1 mm/sec in a noncontact mode (1 mm between probe tip and articular cartilage surface), and 3) radiofrequency energy smoothing of abraded cartilage during arthroscopic visualization. Thermal smoothing of the abraded cartilage surface was accomplished with all three devices. Significant chondrocyte death, as determined by confocal laser microscopy and cell viability staining, was observed with each device. The bipolar radiofrequency systems penetrated 78% to 92% deeper than the monopolar system. The bipolar systems penetrated to the level of the subchondral bone in all osteochondral sections during arthroscopically guided paintbrush pattern treatment. Radiofrequency energy should not be used for thermal chondroplasty until further work can establish consistent methods for limiting the depth of chondrocyte death while still achieving a smooth articular for thermal chondroplasty until further work can establish consistent methods for limiting the depth of chondrocyte death while still achieving a smooth articular surface.

Effect of bipolar radiofrequency energy on human articular cartilage. Comparison of confocal laser microscopy and light microscopy.

PURPOSE: To evaluate chondrocyte viability using confocal laser microscopy (CLM) following exposure to bipolar radiofrequency energy (bRFE) and to contrast CLM with standard light microscopy (LM) techniques. TYPE OF STUDY: In vitro analysis using chondromalacic human cartilage. METHODS: Twelve fresh chondral specimens were treated with the ArthroCare 2000 bRFE system (ArthroCare, Sunnyvale, CA) coupled with 1 of 2 types of probes and at 3 energy delivery settings (S2, S4, S6). A sham-operated group was treated with no energy delivered. Specimens were analyzed for chondrocyte viability and chondral morphology with CLM using fluorescent vital cell staining and with LM using H&E and safranin-O staining. RESULTS: LM with H&E staining showed smoothing of fine fronds of fibrillated cartilage; thickened fronds were minimally modified. Chondrocyte nuclei were present and not morphologically different than nuclei within sham-operated and adjacent untreated regions. LM with safranin-O staining showed a clear demarcation between treated and untreated regions. CLM, however, showed chondrocyte death: the depth and width of chondrocyte death increased with increasing bRFE settings. CONCLUSIONS: CLM showed that bRFE delivered through the probes investigated created significant chondrocyte death. These changes were not apparent using LM techniques.