Arthrodesis of the Distal Interphalangeal Joint in Two Horses Using Three Parallel 5.5-mm Cortical Screws

The distal interphalangeal joint was successfully arthrodesed in two horses using three parallel 5.5-mm cortical screws and an autogenous cancellous bone graft. The screws were directed from the palmar proximal border of the second phalanx dorso-distally across the joint space and into the third phalanx. The technique was first developed on a normal horse. The second horse, a clinical case, ruptured its deep digital flexor tendon with complete luxation of the distal interphalangeal joint. Bony fusion of the distal interphalangeal joint occurred in both horses, but both also had residual lameness at a walk. Twenty-one months after the arthrodesis procedure, the clinical patient died from complications related to a subsolar abscess in the operated limb.     

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.     

Arthrodesis of the equine proximal interphalangeal joint: a mechanical comparison of 2 parallel 5.5 mm cortical screws and 3 parallel 5.5 mm cortical screws

OBJECTIVE: To compare the biomechanical characteristics and mode of failure of 2 techniques using parallel 5.5 mm screws for pastern joint arthrodesis in horses. STUDY DESIGN: Randomized block design, for horse (1-5), method of fixation (two 5.5 mm screws versus three 5.5 mm screws), side (right, left), and end (front, hind). Constructs were tested to failure in 3-point bending. SAMPLE POPULATION: Twenty limbs (5 cadavers). METHODS: A combined aiming device was used to facilitate screw placement. Two parallel 5.5 mm screws were inserted in lag fashion in 1 limb of a pair, and three 5.5 mm screws were inserted in the contralateral limb. Constructs were then tested in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials testing machine at a loading rate of 19 mm/s. Maximal bending moment at failure and stiffness were obtained from bending moment-angular deformation curves. RESULTS: There was no significant difference between two and three 5.5 mm screw constructs for bending moment and stiffness (P<.05). All constructs ultimately failed by bone fracture or screw bending. For proximal interphalangeal (PIP) joint arthrodesis constructs loaded in 3-point bending, no significant effect of treatment, side, or end on maximal bending moment or stiffness was detected. CONCLUSIONS: Two 5.5 mm cortical screws inserted in parallel should provide a surgically simpler and equally strong PIP joint arthrodesis compared with three 5.5 mm cortical screws. CLINICAL RELEVANCE: Two 5.5 mm cortical screws inserted in parallel for PIP joint arthrodesis should perform similarly under conditions used in this study, as three 5.5 mm screws inserted in a similar manner, when loaded under bending.     

A Technique for Laser‐Facilitated Equine Pastern Arthrodesis Using Parallel Screws Inserted in Lag Fashion

Objective— To report a technique for laser‐facilitated, minimally invasive proximal interphalangeal joint (PIJ) arthrodesis in horses. Study Design— Case series. Animals— Horses (n=6); 5 thoracic and 2 pelvic limb PIJ. Methods— PIJ osteoarthritis (OA) diagnosis was confirmed by radiography. A diode laser was used to apply 2000 J of energy to the joint followed by insertion of 3 parallel 5.5 mm screws in lag fashion through stab incisions to achieve PIJ arthrodesis. After anesthetic recovery, limbs were maintained in bandages (n=2) or bandage casts (5) for 3 weeks. Horses were allowed exercise or turnout by 3 months. Results— Three horses (4 limbs) were sound throughout follow‐up (6–18 months). One horse remained lame the 1st month, another had mild lameness at pasture at 6 weeks, and another had persistent low‐grade lameness and delayed joint fusion (1 year). Within 6 months, 5 horses were sound, 4 had radiographic evidence of successful joint fusion, and 5 had returned to intended use. Conclusion— Diode laser‐facilitated, 3 parallel screw arthrodesis for PIJ OA costs less and is associated with less pain compared with standard, open PIJ arthrodesis using 3 parallel screws inserted in lag fashion. Clinical Relevance— In horses with advanced PIJ OA, this technique appears to be a viable alternative for PIJ arthrodesis. Further study including characterization of the effects of the laser, ideal case selection indications, and optimal laser dose is indicated before this technique is recommended for routine PIJ arthrodesis.     

Evaluation of ethyl alcohol for use in a minimally invasive technique for equine proximal interphalangeal joint arthrodesis

Objective: To determine whether intra‐articular 70% ethyl alcohol alone (IAEA) or in combination with 2 percutaneously placed transarticular lag screws (EA‐TLS) would result in arthrodesis of the equine proximal interphalangeal (PIP) joint. Study Design: Experimental. Animals: Healthy horses (n=6), aged 1.5–3 years, free of lameness, diagonally paired front and hind PIP joints. Methods: Six milliliters 70% ethyl alcohol was injected into randomly selected diagonally paired front and hind PIP joints. Thirty days later, 2 parallel 5.5 mm cortical screws were inserted in lag fashion across the hind PIP joints and the limbs were cast. Horses were confined for 60 days after surgery before free exercise was permitted. Serial lameness examinations were performed at 1, 6, and 10 months. Radiographs of the PIP joints were obtained before injection with alcohol (front, hind PIP joints), at 6 and 10 months (front PIP joints) and 1, 3, 6, and 10 months (hind PIP joints). At 10 months, horses were euthanatized and gross and histopathologic examination of the treated joints was performed. Results: Horses had variable cartilage thinning (more severe in hind PIP joints) and dorsal bone proliferation. One front and 1 hind PIP joint were fused 10 months after alcohol injection. Conclusions: Ethyl alcohol injected alone or in combination with percutaneously placed transarticular lag screws failed to reliably produce fusion of the PIP joint.     

Scapulohumeral arthrodesis in miniature horses

OBJECTIVES: To describe surgical arthrodesis of the scapulohumeral joint and to evaluate its efficacy in reducing morbidity associated with severe shoulder dysfunction in miniature horses. STUDY DESIGN: Retrospective study. ANIMALS: Four miniature horses. METHODS: Medical records and radiographs were reviewed for history, physical examination findings, lameness evaluation, radiographic evaluation, surgical techniques, postoperative complications, and outcome. A 10- or 11-hole, 4.5-mm narrow dynamic compression plate and 4.5-mm cortical screws were applied to the cranial surface of the scapula and cranial surface of the humerus after osteotomy of the intermediate tubercle. In most horses, 1 or 2 screws were inserted in lag fashion across the joint, through holes in the plate. RESULTS: Scapulohumeral osteoarthritis was diagnosed radiographically in 4 horses, and 3 horses had concurrent shoulder luxation or subluxation. All horses had grade 3 or 4 lameness before surgery, and most improved by 1 to 2 grades after surgery. Despite complications of implant failure (2 horses), infection (2 horses), scapular fracture (1 horse), and atrophy of the shoulder muscles (1 horse), functional arthrodesis reduced morbidity in all horses. CONCLUSIONS: Scapulohumeral arthrodesis facilitates early return to weight bearing in miniature horses with severe scapulohumeral joint osteoarthrosis. Despite functional gait abnormality, the horses ambulated quite well after surgery. CLINICAL RELEVANCE: Scapulohumeral arthrodesis should be considered for debilitating conditions of the shoulder joint in miniature horses, especially when the intended outcome is breeding or pasture soundness.     

Proximal interphalangeal arthrodesis in 22 horses

The purpose of this study was to evaluate a new method of internal fixation technique for pastern arthrodesis. Pastern arthrodeses are performed commonly in horses with chronic osteoarthritis of the pastern joint or, in cases of acute traumatic injury to the pastern, in which the weightbearing bony column must be restored. Chronic osteoarthritis of the pastern is a frequent cause of lameness in the equine athlete and is evidenced by chronic lameness localised to the pastern joint, and supported radiographically by periosteal proliferation and loss of joint space. Nonsurgical and surgical treatments have both been described in the literature. Complications following pastern arthrodesis have been reported on several occasions and appear to focus on excessive periarticular exostoses and increased time in a cast due to prolonged time to bony fusion. The hospital records of horses presenting for pastern arthrodesis to the Rood and Riddle Equine Hospital in Lexington, Kentucky, were reviewed and 22 met criteria for inclusion in the study. Horses with chronic osteoarthritis of the proximal interphalangeal joint or horses with an acute traumatic injury to the pastern undergoing pastern arthrodesis with one of the following techniques were included in the study. Horses with severe comminution of the middle phalanx were excluded. Three 5.5 mm cortical bone screws placed in lag fashion alone or in combination with a 4 or 3 hole dynamic compression plate affixed with 4.5 mm cortical bone screws were compared. A lower limb fibreglass cast was applied in all cases. Period in cast, time to return to intended use, complications encountered and outcome were evaluated. Seven of the 8 hindlimbs treated with the combination technique became sound. Three out of 6 of the front limbs treated with the combination technique became sound. Four of the 5 horses with hindlimbs, and one of the 2 with front limbs, treated with screws only returned to their intended use. The type of internal fixation did not appear to influence the overall number of horses returning to the intended level of performance. The period spent in cast and the time to return to soundness were decreased in horses operated on using the combination technique. We concluded that, in the immediate postoperative period, the combination of the parallel screw technique with a dorsally-applied dynamic compression plate provides the most stable and secure fixation, minimising motion, expediting bone remodelling and therefore favouring rapid fusion of that joint.     

Arthrodesis of the Equine Proximal Interphalangeal Joint: A Biomechanical Comparison of Two Parallel Headless, Tapered, Variable-Pitched, Titanium Compression Screws and Two Parallel 5.5 mm Stainless-Steel Cortical Screws

Objective— To compare the biomechanical characteristics, failure mode, and effects of side (left or right limb) and end (forelimb or hindlimb) of different screws in 2-screw, parallel-screw proximal interphalangeal joint arthrodesis constructs in horses.
Study Design— In vitro experimental study.
Sample Population— Twenty limbs from 6 cadavers (4 complete limb sets, 2 partial sets—total of 4 forelimb and 6 hindlimb pairs).
Methods— Two parallel 5.5 mm cortical (AO) screws were inserted in lag fashion in 1 randomly allocated limb of a pair, and 2 parallel headless, tapered, variable-pitched, titanium compression screws (Acutrak-Plus^®) were inserted in the contralateral limb. Constructs were tested in 3-point bending in a dorsopalmar (plantar) direction using a materials-testing machine at a loading rate of 5.83 mm/s. Maximal bending moment at failure and composite stiffness were calculated from data generated on load–displacement curves. Data were analyzed using a Friedman 2-way analysis of variance and Wilcoxon's signed-rank tests.
Results— No significant difference was detected for bending moment or stiffness values in proximal interphalangeal joint arthrodesis constructs using 2 parallel Acutrak-Plus^® or AO screws for fixation. Mean stiffness values were significantly different between forelimb and hindlimb constructs.
Conclusions— Performance of 2 parallel Acutrak-Plus^® screws was biomechanically comparable with 2 parallel AO 5.5 mm cortical screws in in vitro pastern arthrodesis constructs.
Clinical Relevance— Acutrak-Plus^® screws may provide an alternative means of fixation for proximal interphalangeal joint arthrodesis.     

Arthroscopically assisted arthrodesis of the distal interphalangeal joint with transarticular screws inserted through a dorsal hoof wall approach in a horse

CASE DESCRIPTION: A 16-year-old Thoroughbred gelding was examined because of chronic right forelimb lameness. CLINICAL FINDINGS: On radiographs of the right front foot, the distal interphalangeal (DIP) joint space was narrow, and osteophytes and periarticular bony proliferation indicative of severe osteoarthritis were seen. Arthrodesis of the right DIP joint was recommended to improve the horse's comfort on the limb. TREATMENT AND OUTCOME: The horse was anesthetized, and palmar and dorsal arthroscopic approaches were used to remove as much of the articular cartilage as was accessible. Holes were then drilled through the dorsal aspect of the hoof wall, and 3 transarticular, 5.5-mm cortical screws were placed in lag fashion through these holes across the distal phalanx and into the middle phalanx. Defects in the hoof wall were filled with gentamicin-impregnated polymethyl methacrylate plugs and sealed with cyanoacrylate. Eight months after surgery, fusion of the DIP joint was evident radiographically and the horse was sound at a walk. CLINICAL RELEVANCE: Transarticular placement of cortical screws through a dorsal hoof wall approach combined with arthroscopically guided cartilage removal can result in fusion of the DIP joint in horses.     

Proximal interphalangeal joint arthrodesis using a combination plate-screw technique in 53 horses (1994-2003)

REASONS FOR PERFORMING STUDY: A method for proximal interphalangeal joint (PIP joint) arthrodesis that provides a stable fixation and minimal duration of cast support is evaluated retrospectively. OBJECTIVES: Evaluate the clinical use of a combined plate-screw method for PIP joint arthrodesis in a large number of horses. METHODS: The records of 53 horses undergoing PIP joint arthrodesis were reviewed. Arthrodesis was performed with a dorsally placed 3-, 4- or 5-hole narrow dynamic compression plate (DCP) with 2 transarticular cortex screws placed in lag fashion either side of the plate. Subject details, clinical presentation, radiographic findings, surgical technique, post operative treatment and complications were recorded. Long-term follow up (mean 3 years) was obtained for 46 horses. RESULTS: Arthrodesis procedures (n = 58) were performed on 53 horses with a DCP in combination with transarticular cortex screws placed in lag fashion. Conditions treated were osteoarthritis (OA) of the PIP joint, fracture of middle phalanx, PIP joint subluxation, subchondral cystic lesions and degenerative joint disease secondary to sepsis. Time of post operative cast application was 14 days. Overall 40/46 (87%) horses could be used as intended including 20/25 (81%) forelimb and 20/21 (95%) hindlimb arthrodeses. Twenty-three of 27 (85%) horses used for performance had successful outcomes. Complications included implant infection, cast sores and partial implant failure. CONCLUSIONS: PIP joint arthrodesis using a DCP and transarticular cortex screws placed in lag fashion provides a stable construct and short casting period with minimal complications. The prognosis for return to performance was excellent for horses treated with hindlimb PIP joint arthrodesis and good for forelimb arthrodesis. POTENTIAL RELEVANCE: Use of a combination technique for PIP joint arthrodesis allows a high proportion of horses with pastern joint disease to be returned to their athletic potential.     

Comparison of a 3-hole 4.5-mm Dynamic Compression Plate and a 7-hole 5.5-mm Y Locking Compression Plate for Arthrodesis of the Proximal Interphalangeal Joint in Horses—an Ex Vivo Biomechanical Study

The objective of this study was to compare the biomechanical properties in a single cycle axial loading test and the types of failures in two constructs (a 3-hole 4.5-mm dynamic compression plate (DCP) and 7-hole 5.5-mm Y locking compression plate (Y-LCP)) in equine proximal interphalangeal joint (PIJ) arthrodesis. One limb in each pair was randomly assigned to PIJ arthrodesis using a 3-hole 4.5-mm DCP combined with two transarticular 5.5-mm cortical screws, whereas the contralateral limb was submitted to PIJ arthrodesis using a 7-hole Y-shaped 5.0-mm LCP in conjunction with one transarticular 4.5-mm cortical screw inserted through the central plate hole. Cortical screws were inserted in lag fashion. Constructs were submitted to a single axial load cycle to failure. Construct stiffness, load, and deformation were analyzed. Dynamic compression plate and Y-LCP arthrodesis constructs did not differ significantly and were equally resistant to axial loading under the conditions studied (DCP and Y-LCP group stiffness, 5685.22 N/mm and 6591.10 N/mm, respectively). Arthrodesis of the PIJ using a DCP and two transarticular 5.5-mm cortical screws or a Y-LCP yielded biomechanically equivalent outcomes under the test conditions considered. However, Y-LCP provides less impact in the palmar/plantar bone. Application of Y-LCP with unicortical screws has equivalent biomechanical characteristics of DCP and may be a safe option for PIJ arthrodesis, where potential trauma secondary to applying bicortical screws in the palmar/plantar aspect of the pastern can be avoided.     

Arthrodesis of the Proximal Interphalangeal Joint in the Horse: A Cyclic Biomechanical Comparison of Two and Three Parallel Cortical Screws Inserted in Lag Fashion

Objective— To compare the biomechanical cyclic fatigue properties of 2 and 3 parallel transarticular 5.5 mm cortical screws used in arthrodesis of the proximal interphalangeal (PIP) joint.
Study Design— Randomized block design, for horse, fixation method (2 versus three 5.5 mm cortical screws), side (right, left) and end (front, hind) in cadaveric equine limbs.
Sample Population— Cadaveric adult equine fore- and hindlimbs (n=5 pairs each).
Methods— Two parallel 5.5 mm cortical screws were inserted in lag fashion, transarticularly through the PIP joint in 1 limb of a pair, and in the contralateral limb, three 5.5 mm cortical screws were inserted in similar fashion. Constructs were then tested in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials testing machine using a cyclic load of −500 to −3500 N at a rate of 6 Hz.
Results— There was no significant difference in displacement at failure, force at failure or number of cycles between limbs. Forelimb constructs tended to fail at a greater mean displacement than hindlimb constructs but this difference was not significant ( P =.06). There was no statistical difference in any tested biomechanical variable between left- and right-sided limbs.
Conclusions— There was no significant difference in the number of cycles to failure for the 2 methods tested.
Clinical Relevance— Two 5.5 mm cortical screws inserted in parallel for PIP joint arthrodesis is surgically simpler, results in comparable biomechanical performance in the current model and should perform as well as three 5.5 mm screws under cyclic fatigue conditions.     

Use of a bone plate for treatment of middle phalangeal fractures in horses: seven cases (1979-1984)

Four adult horses and 3 foals with middle phalangeal fractures were treated by arthrodesis of the proximal interphalangeal joint, using a bone plate. Six of the 7 horses survived greater than 2 years; 2 of the 6 horses had intermittent lameness after hard work, and 4 horses didn't have evidence of lameness. The use of a bone plate for arthrodesis of the proximal interphalangeal joint was a successful treatment alternative for middle phalangeal fractures in horses.     

Arthrodesis of the proximal interphalangeal joint affected with septic arthritis in 8 horses

Arthrodesis was performed to treat septic arthritis of the proximal interphalangeal joint of 8 horses. Records of the horses were reviewed to determine outcome and possible factors that influenced success or failure. All horses were female. Seven horses had 1 joint treated and 1 horse was treated for bilateral pelvic limb involvement. The duration of sepsis before surgery ranged from 1 to 66 days. Bone lysis and production was radiographically apparent in 7 horses before surgery. Six horses had multiple bacterial organisms cultured from bone or synovial tissues; 2 horses had single isolates identified. After aggressive curettage, arthrodesis was accomplished with 3 parallel screws in 1 horse, 2 divergent narrow dynamic compression plates in 3 horses, and a single broad dynamic compression plate in 4 horses. Casts were applied to all horses for 1 to 6 weeks. Four horses survived to successful brood mare status. Four horses were euthanized during hospitalization because of continued discomfort or complications of sepsis. Arthrodesis of the proximal interphalangeal joint affected with septic arthritis appears to be an acceptable alternative to euthanasia for some horses.     

An In Vitro Biomechanical Comparison of Equine Proximal Interphalangeal Joint Arthrodesis Techniques: An Axial Positioned Dynamic Compression Plate and Two Abaxial Transarticular Cortical Screws Inserted in Lag Fashion Versus Three Parallel Transarticular Cortical Screws Inserted in Lag Fashion

Objectives— To compare in vitro monotonic biomechanical properties of an axial 3‐hole, 4.5 mm narrow dynamic compression plate (DCP) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion (DCP‐TLS) with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion (3‐TLS) for the equine proximal interphalangeal (PIP) joint arthrodesis. Study Design— Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Sample Population— Cadaveric adult equine forelimbs (n=15 pairs). Methods— For each forelimb pair, 1 PIP joint was stabilized with an axial 3‐hole narrow DCP (4.5 mm) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion and 1 with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion. Five matching pairs of constructs were tested in single cycle to failure under axial compression, 5 construct pairs were tested for cyclic fatigue under axial compression, and 5 construct pairs were tested in single cycle to failure under torsional loading. Mean values for each fixation method were compared using a paired t‐test within each group with statistical significance set at P<.05. Results— Mean yield load, yield stiffness, and failure load under axial compression and torsion, single cycle to failure, of the DCP‐TLS fixation were significantly greater than those of the 3‐TLS fixation. Mean cycles to failure in axial compression of the DCP‐TLS fixation was significantly greater than that of the 3‐TLS fixation. Conclusion— The DCP‐TLS was superior to the 3‐TLS in resisting the static overload forces and in resisting cyclic fatigue. Clinical Relevance— The results of this in vitro study may provide information to aid in the selection of a treatment modality for arthrodesis of the equine PIP joint.     

What is your diagnosis? Esophageal hiatal hernia.

A 14-month-old Arabian colt was admitted for treatment of an articular fracture of the supraglenoid tubercle of the right forelimb. Successful repair was achieved by use of three 5.5-mm cortical screws placed in lag fashion across the fracture line. In other reports of supraglenoid tubercle fractures in horses, investigators have preferred conservative management or surgical removal of the fragment, because of limited success with internal fixation. Use of three 5.5-mm screws placed in lag fashion may offer an alternative method of treatment in selected cases of supraglenoid tubercle fractures.     

Incomplete Longitudinal Fracture of the Proximal Palmar Cortex of the Third Metacarpal Bone in Horses

Seven horses, 2 to 4 years of age, were examined because of moderate-to-severe forelimb lameness, mild effusion of the middle carpal joint (3 horses), and pain on palpation of the origin of the suspensory ligament (4 horses). The lameness was abolished by anesthetic infiltration of the middle carpal joint in six horses. In four of them, a high palmar nerve block also abolished the lameness. A linear radiolucency in the proximal end of the third metacarpal bone (McIII) was interpreted as an incomplete longitudinal fracture. In one horse, distinct intramedullary sclerosis limited to the palmar cortex was indicative of an incomplete fracture confined to the palmar cortex. No osteoproliferative lesions were identified on the dorsal cortex of any of the horses. Surgical treatment with cortical screws in lag fashion accompanied by a rest period was successful in one horse. In four horses, rest for at least 3 months resulted in clinical soundness. In two horses, a shorter rest period resulted in recurrence of the lameness even though the horses were sound when put back into training. Careful clinical and radiographic examinations helped differentiate incomplete longitudinal fractures from lesions involving the carpus and proximal aspect of the suspensory ligament.     

Pathological fracture through a subchondral bone cyst in the proximal phalanx of a horse

A 12‐year‐old Morgan broodmare presented for a nonweightbearing right forelimb lameness. Radiography and computed tomography confirmed the presence of a pathological fracture of the proximal first phalanx through a large subchondral bone cyst (SBC) in the right forelimb and a large SBC in the proximal first phalanx of the left forelimb. Surgical repair of the large palmar medial eminence fracture of the proximal first phalanx fracture was performed using bone screws placed in lag fashion placed through stab incisions after debridement and bone grafting of the SBCs. Approximately 6 months after surgery the mare was ambulating comfortably at pasture. This case report describes a fracture through a large subchondral bone cyst in a horse despite chronicity and ongoing bone remodelling. Careful consideration regarding exercise or use should be considered in horses with large SBCs.     

In Vitro Pullout Strength of Screws Inserted in Adult Equine Third Metacarpal Bone After Overdrilling a 4.5-mm Threaded Insertion Hole

Objective—To determine and compare the in vitro pullout strength of 5.5-mm cortical versus 6.5-mm cancellous bone screws inserted in the diaphysis and metaphysis of adult equine third metacarpal (MCIII) bones, in threaded 4.5-mm cortical bone screw insertion holes that were then overdrilled with a 4.5-mm drill bit to provide information relevant to the selection of a replacement screw if a 4.5-mm cortical screw is stripped. Study Design—In vitro pullout tests of 5.5-mm cortical and 6.5-mm cancellous screws in equine MCIII bones. Sample Population—Two independent cadaver studies each consisting of 14 adult equine MCIII bones. Methods—Two 4.5-mm cortical screws were placed either in the middiaphysis (study 1) or distal metaphysis (study 2) of MCIII bones. The holes were then overdrilled with a 4.5-mm drill bit and had either a 5.5-mm cortical or a 6.5-mm cancellous screw inserted; screw pullout tests were performed at a rate of 0.04 mm/second until screw or bone failure occurred. Results—In diaphyseal bone, the screws failed in all tests. Tensile breaking strength for 5.5-mm cortical screws (997.5 ± 49.3 kg) and 6.5-mm cancellous screws (931.6 ± 19.5 kg) was not significantly different. In metaphyseal bone, the bone failed in all tests. The holding power for 6.5-mm cancellous screws (39.1 ± 4.9 kg/mm) was significantly greater than 5.5-mm cortical screws (23.5 ± 3.5 kg/mm) in the metaphysis. There was no difference in the tensile breaking strength of screws in the diaphysis between proximal and distal screw holes; however, the holding power was significantly greater in the distal, compared with the proximal, metaphyseal holes. Conclusions—Although tensile breaking strength was not different between 5.5-mm cortical and 6.5-mm cancellous screws in middiaphyseal cortical bone, holding power of 6.5-mm cancellous screws was greater than 5.5-mm cortical screws in metaphyseal bone of adult horses. Clinical Relevance—If a 4.5-mm cortical bone screw strips in MCIII diaphyseal bone of adult horses, either a 5.5-mm cortical or 6.5-mm cancellous screw, however, would have equivalent pullout strengths. A 6.5-mm cancellous screw, however, would provide greater holding power than a 5.5-mm cortical screw in metaphyseal bone.     

An in vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: two parallel transarticular headless tapered variable pitch screws versus two parallel transarticular AO cortical bone screws inserted in lag fashion

Objectives: To compare the mean number of cycles to failure under axial compression of equine proximal interphalangeal (PIP) joint arthrodesis constructs created by 2 parallel transarticular Acutrak Plus screws (AP‐TS) or 2 parallel transarticular 5.5 mm cortical screws inserted in lag fashion (AO‐TLS). Study Design: Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Sample Population: Cadaveric adult equine forelimbs (n=5 pairs). Methods: For each forelimb pair, 1 PIP joint was stabilized with AP‐TS and 1 with AP‐TLS. The 5 construct pairs were tested for cyclic fatigue under axial compression. Mean number of cycles to failure for each fixation method were compared by a paired t‐test within each group with statistical significance set at P<.05. Results: The mean number of cycles to failure under axial compression for AO‐TLS fixation and AP‐TS fixation were 57,723±8488 and 35,322±4698, respectively. Conclusion: The AO‐TLS was superior to the AP‐TS in resisting cyclic fatigue under axial compression.