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.     

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.     

Proximal Interphalangeal Arthrodesis in the Horse A Retrospective Study and a Modified Screw Technique

Arthrodesis of the proximal interphalangeal joint was used to treat lameness resulting from osteoarthrosis and for closed subluxation in 35 horses. Six horses had bilateral arthrodeses. Several conventional internal fixation techniques and a three converging screw method were used. Criteria for success included the horse performing its previous or intended athletic activity and the owner being satisfied with the outcome. Using these criteria, a successful outcome was obtained in 65% of the 26 animals in which adequate follow-up was available. A successful outcome was observed in four of six horses with bilateral arthrodeses. The internal fixation technique used did not influence the success rate, and the duration of postoperative casting was similar in successful and unsuccessful cases. The success rate of proximal interphalangeal arthrodeses was 46% in the fore limbs and 83% in the hind limbs. Complications included infection, cast ulcers, bone or implant failure, implant loosening, and laminitis.     

Surgical Repair of Tibial Tuberosity Avulsion Fractures in Four Horses

Four horses, 2 to 17 years old, were treated for unilateral avulsion fractures of the tibial tuberosity. Two horses were treated successfully with tension band wiring or plating in combination with lag screw fixation. One horse was euthanatized because of implant failure during recovery and one was euthanatized on day 11 because a longitudinal fracture of the tibial tuberosity occurred through the plane of the screws used for stabilization.     

Comminuted First Phalanx Fractures in 30 Horses: Surgical vs. Nonsurgical Treatments

Comminuted first phalanx fractures were diagnosed in 30 horses. One leg was involved in each horse. Five horses were presented with open fractures. Nine horses had a portion of intact cortex (strut) extending from the proximal to distal joint. Ten horses were euthanized, including one with an open fracture, without treatment. The remaining 20 horses were treated by open reduction with a neutralization plate (8 horses, including one with an open fracture), open reduction with lag screw fixation (3 horses), lag screw fixation through stab incisions (2 horses), external coaptation with a cast (3 horses), and external skeletal fixation using a weight supporting shoe (4 horses, including 3 with open fractures).
Thirteen horses were euthanized following treatment because of persistent infection (9), chronic lameness (2), and third metacarpal bone fractures (2). Seven horses survived longer than 1 year after treatment. Six were lame and used as breeding animals, and one horse went on to race successfully. All four horses with open fractures that were treated were subsequently euthanized.
Significantly more horses with an intact strut of bone survived after treatment (4 of 7 [57%]) when compared to horses without an intact strut of bone that were treated (3 of 13 [23%]) (p < 0.05).
Invasive surgical approaches used for the repair of comminuted first phalanx fractures in this study were associated with an unacceptable infection rate (55%). Techniques involving less trauma to the compromised soft tissue around the fracture should afford a better chance for a successful outcome.     

Application of a Hook Plate for Management of Equine Ulnar Fractures

Closed fractures of the proximal aspect of the ulna were repaired in 10 horses younger than or equal to 6 months of age by application of a hook plate using a tension band principle. Ulnar fractures were classified as type 1A (2 horses), type 1B (4 horses), type 2 (1 horse), type 3 (1 horse), and type 4 (2 horses); all fractures had displacement of a proximal fragment. Complications were implant deformation (4 horses), screw pullout (1 horse), osseous sequestration (1 horse), ulnar fracture through a hole used to apply a tension device (1 horse), and metacarpophalangeal deformity associated with a displaced anconeal fragment (1 horse). Hook deformation was likely associated with failure to insert screws in all of the proximal holes of the plate and also in two horses, possibly with difficult recovery from anesthesia. Seven horses were discharged from the hospital and were being used for athletic activities. Insertion of the hook through the tendon of the triceps muscle and incorporation of the fragment within the hook can be used to effectively reduce and stabilize a fragment that might otherwise not hold screws.     

Treatment of radial fractures in adult horses: an analysis of 15 clinical cases

Fifteen cases of radial fractures in adult horses weighing more than 300 kg are discussed. Four of the horses were destroyed on humane grounds immediately because of a poor prognosis and expense of internal fixation; and two horses at five days and five weeks, respectively after treatment by cast application was initiated. Internal fixation was used in nine horses but of these only two horses recovered completely and resumed their former activities. In eight cases, two plates were applied, one lateral or medial and the other cranial. The internal fixation techniques of all nine horses were scrutinised and suggestions made for the future treatment of radial fractures. These suggestions are (1) the use of ASIF 5.5 mm cortical bone screws using the total width or thickness of the bone in each case. (2) Application of the dynamic condylar screw with its plate in distal or proximal fractures to allow more support. (3) Incorporation of a cancellous bone graft to the fracture. (4) Possible table recovery to prevent breakdown of the fixation during recovery. It is important that bone plates are applied over the total length of the bone. The fact that only two out of 15 horses survived and recovered completely underlines the problems associated with treatment of radial fractures in the adult horse.     

Arthrodesis of the Equine Proximal Interphalangeal Joint: A Biomechanical Comparison of Two 7-Hole 3.5-mm Broad and Two 5-hole 4.5-mm Narrow Dynamic Compression Plates

OBJECTIVE: To compare the biomechanical characteristics and mode of failure of two different dynamic compression plate (DCP) techniques for proximal interphalangeal joint (PIPJ) arthrodesis in horses. STUDY DESIGN: Randomized block-design blocking on horse (1-5), method of fixation (two 7-hole, 3.5-mm broad DCP vs two 5-hole, 4.5-mm narrow DCP), side (left, right), and end (front, hind). Constructs were loaded to failure in 3-point bending in a dorsal-to-palmar (plantar) direction. SAMPLE POPULATION: Ten paired limbs from 5 equine cadavers. METHODS: Two 7-hole, 3.5-mm broad dynamic compression plates (bDCP) were used in 1 limb of a pair, and two 5-hole 4.5-mm narrow dynamic compression plates (nDCP) were used on the contralateral limb. Plates were positioned abaxially across the dorsomedial and dorsolateral aspect of the PIPJ. Arthrodesis constructs were loaded (19 mm/s) in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials-testing machine. Composite stiffness, yield point, and maximal bending moment at failure were obtained from bending moment-angular deformation curves. Data were analyzed using ANOVA, X(2) analysis, and Fisher's exact tests; the power of the test was calculated when differences were not significant. RESULTS: There were no significant differences in composite stiffness (P >.05; power = 0.8 @ delta = 21.9%), yield point (P >.05; power = 0.8 @ delta = 34.4%), or maximal bending moment (P >.05; power = 0.8 @ delta = 17.8%) between the two fixation techniques. For bDCP constructs, 11% (15 of 140) of the 3.5-mm screws were damaged; 7 of the screw heads pulled through plates where the plates bent, 1 screw head broke off, and 7 screws were bent or pulled out of the phalanx. For nDCP constructs, 8% (8 of 100) of the 4.5-mm screws were damaged; 1 screw head pulled through a plate, 1 screw head broke off, and 6 screws were bent or pulled out of the phalanx. CONCLUSIONS: There were no biomechanical or failure differences between bDCP and nDCP fixation of the PIPJ in horses when evaluated in single-cycle 3-point bending to failure. CLINICAL RELEVANCE: There is no biomechanical advantage to the use of two 7-hole, 3.5-mm bDCP in equine proximal interphalangeal arthrodesis compared with two 5-hole, 4.5-mm nDCP. Two 5-hole, 4.5-mm nDCP may be easier to place, whereas two 7-hole, 3.5-mm bDCP may provide more versatility in fracture repair.     

Plate Luting* A Preliminary Report of Its Use in Horses

Plate luting, a new method of interfacing a compression plate to bone for the repair of fractures, was proposed as a method to help facilitate immediate full weight bearing following internal fixation with plates and screws in horses. Theoretical mechanisms relating bone-plate contact and screw support were discussed. Preliminary mechanical testing showed increased endurance of luted bone-plate composites to cyclic loading when compared with the same devices without plate luting. Screw loosening, which often precedes plate failure, did not occur. In vivo studies showed results similar to in vitro experiments.     

Comparison of locking and conventional screws for maintenance of tibial plateau positioning and biomechanical stability after locking tibial plateau leveling osteotomy plate fixation

Objective— To compare locking screws with conventional screws inserted in the tibial plateau fragment for reduction and stability of the construct after tibial plateau leveling osteotomy (TPLO), using a locking TPLO plate.
Study Design— Experimental biomechanical study.
Animals— Cadaveric canine pelvic limbs (n=8 pairs).
Methods— TPLO was stabilized with either conventional cortical screws or locking screws in a compressed osteotomy model. Titanium pins inserted into the tibial plateau and proximal metaphysis were used to track bone fragment location by computed tomography (CT) imaging. CT imaging was performed after osteotomy reduction, after plate stabilization, and after 30,000 cycles of axial compression testing. After 30,000 cycles, cyclic loading was continued with monotonically increasing peak-load until failure.
Results— The magnitude of rotation about the sawing axis was significantly greater for the conventional screw group because of plate application ( P =.009). Translational movement of the tibial plateau fragment toward the plate was significantly greater for the conventional screw group ( P =.006). There were no significant differences between groups in stiffness or number of cycles to failure.
Conclusion— Maintenance of tibial plateau position was significantly superior for the locking screw group during plate application; however, screw type had no effect on fixation stability under cyclic loading.
Clinical Relevance— These results suggest that conventional screws and careful contouring of the TPLO plate can provide comparable mechanical stability to fixation with locking screws in the tibial plateau under load-sharing conditions, but potentially at the expense of osteotomy reduction.     

Evaluation of Surgical Removal of Fractured Distal Splint Bones in the Horse

Between January 1977 and June 1980, 38 Standardbred and 23 Thoroughbred horses had fractured distal splint bones removed surgically. Standardbred horses were treated significantly more frequently compared with the hospital population. The incidence of distal splint bone fractures in the front legs was significantly greater (p 0.05) than in the rear legs in both breeds. Associated suspensory desmitis was present in 81% of Standardbred and 67% of Thoroughbred horses at the time of surgery.
The most common radiographic sign was fracture with associated callus. It was not possible to correlate preoperative radiographic signs with presence of associated suspensory desmitis. One Thoroughbred horse developed a large mass of amorphous bone at the surgical site which required a second surgical procedure.
Follow-up information was available on 21 of 38 Standardbred and 17 of 23 Thoroughbred horses. There was no correlation found between preoperative radiographic signs or the location and number of distal splint bone fractures with postoperative results. Twenty-five percent of Standardbreds that had preoperative suspensory desmitis eventually reached at least their previous level of performance. None of the Thoroughbred racehorses with preoperative suspensory desmitis returned to their previous level of performance. Five of 17 Thoroughbred horses were pleasure horses, and all were reported "sound for intended use" following surgery; however, only four of five were used at their previous level of performance.
The significant feature in the prognosis of distal splint bone fractures in this series was the presence of associated suspensory desmitis. Postsurgical performance was limited by the recurrence of suspensory desmitis.     

Treatment of long bone fractures in South American camelids: 5 cases

An adult llama and four alpacas were referred with long bone fractures. The llama presented with a closed, comminuted fracture of the right metatarsal bones. Two of the alpacas presented with comminuted fractures of the proximal radius. One fracture was closed and one was open. One alpaca had a closed, comminuted fracture of the distal radius, and the final alpaca had a closed, oblique fracture of the metatarsus. A diagnosis was made in each animal on the basis of clinical examination and radiographs. All fractures were managed by open reduction and internal fixation using selective placement of lag screws and dynamic compression plates. Four animals made uneventful recoveries and no long-term complications were encountered. One alpaca was re-admitted for plate failure and non-union of the fracture 5 weeks after surgery. The plate and screws were removed and a transfixation cast was applied. The fracture healed, however the alpaca showed signs of radial nerve paralysis after the cast was removed. With confinement in a small yard, full function gradually returned to the leg over the ensuing 4 months. Using techniques recommended in other species, South American camelids are suitable candidates for long bone fracture repair using open reduction and internal fixation.     

Proximal interphalangeal joint arthrodesis in 34 horses using two parallel 5.5-mm cortical bone screws

OBJECTIVE: To report clinical experience with arthrodesis of the proximal interphalangeal joint in horses using two parallel 5.5-mm cortical bone screws placed in lag fashion. STUDY DESIGN: Retrospective, clinical study. ANIMALS: Thirty-four horses, aged 1 to 19 years. METHODS: Medical records for all horses admitted (1991-1997) for pastern arthrodesis using two 5.5-mm ASIF cortical bone screws, in parallel orientation, and placed in lag fashion by use of a combined aiming device to facilitate accuracy were reviewed. Signalment, lameness diagnosis, duration of lameness, limb(s) involved, and outcome were recorded. Criteria for successful outcome were determined as return to previous level of function or future intended athletic use. RESULTS: Thirty-nine proximal interphalangeal joint arthrodeses were performed on 34 horses. One horse was euthanatized in the recovery room and was excluded from data analysis. Successful outcome occurred in 85% of frontlimbs and 89% of hindlimbs. Failure occurred in 5 joints; 1 horse had lameness directly associated with surgery, whereas 4 horses had unrelated lameness. CONCLUSION AND CLINICAL RELEVANCE: Age, breed, and initial disease did not affect outcome. Arthrodesis of the proximal interphalangeal joint by use of two 5.5-mm ASIF cortical bone screws, in parallel orientation, placed in lag fashion by use of a combined aiming device, resulted in sound use of the limb in >85% of the joints with shortened postoperative coaptation.     

Evaluation of transfixation casting for treatment of third metacarpal, third metatarsal, and phalangeal fractures in horses: 37 cases (1994-2004)

OBJECTIVE: To evaluate clinical findings, complications, and outcome of horses and foals with third metacarpal, third metatarsal, or phalangeal fractures that were treated with transfixation casting. DESIGN: Retrospective case series. Animals-29 adult horses and 8 foals with fractures of the third metacarpal or metatarsal bone or the proximal or middle phalanx. PROCEDURES: Medical records were reviewed, and follow-up information was obtained. Data were analyzed by use of logistic regression models for survival, fracture healing, return to intended use, pin loosening, pin hole lysis, and complications associated with pins. RESULTS: In 27 of 35 (77%) horses, the fracture healed and the horse survived, including 10 of 15 third metacarpal or metatarsal bone fractures, 11 of 12 proximal phalanx fractures, and 6 of 8 middle phalanx fractures. Four adult horses sustained a fracture through a pin hole. One horse sustained a pathologic unicortical fracture secondary to a pin hole infec-tion. Increasing body weight, fracture involving 2 joints, nondiaphyseal fracture location, and increasing duration until radiographic union were associated with horses not returning to their intended use. After adjusting for body weight, pin loosening was associated with di-aphyseal pin location, pin hole lysis was associated with number of days with a transfixation cast, and pin complications were associated with hand insertion of pins. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that transfixation casting can be successful in managing fractures distal to the carpus or tarsus in horses. This technique is most suitable for comminuted fractures of the proximal phalanx but can be used for third metacarpal, third metatarsal, or middle phalanx fractures, with or without internal fixation.     

Holding Power of Orthopedic Screws in Equine Third Metacarpal and Metatarsal Bones: Part II. Adult Horse Bone

Comparison was made of the holding power of 5.5 and 4.5 mm cortical orthopedic screws inserted into third metacarpal and metatarsal cadaver bones from 3- and 8-year-old horses. The tensile strength of these screws was tested mechanically. In nine comparative trials of these screws, 5.5 mm screws pulled out of bone in five trials at an average of 116.0 kg tensile force and broke in four trials at an average of 1383.2 kg. A 4.5 mm screw pulled out of bone at 834.5 kg in one trial, and screws broke at an average of 849.2 kg in eight trials. The larger 5.5 mm screw required a significantly greater (p = 0.022) pullout force than the mean force at 4.5 mm screw breakage. Fixation failure was due to screw breakage or bone shear, with 5.5 mm screws occasionally creating bone fragmentation during pullout. The average tensile breaking strengths of the 5.5 mm screws (1391.4 kg) and 4.5 mm screws (832.7 kg) determined mechanically were similar to forces at screw breakage during pullout testing in bone. Since the 5.5 mm screws have greater holding power and tensile strength than 4.5 mm screws, the use of the 5.5 mm screw in fracture repair in adult horses is recommended.     

Outcome of conservative and surgical treatment for luxations of the equine superficial digital flexor tendon from the calcaneal tuber

The objective of this study was to report the outcome of horses treated either conservatively or surgically for luxation of the superficial digital flexor tendon (SDFT) from the calcaneal tuber. Medical records of horses with diagnosed SDFT luxations from the calcaneal tuber were reviewed (1993–2015) and long-term follow-up examinations and owner questionnaires performed. Survival to hospital discharge, complications, final SDFT position, soundness and return to intended use were compared between conservatively or surgically treated horses. Following conservative treatment all horses (n = 8) survived to hospital discharge. At long-term follow-up 71.4% (5/7) had returned to intended use. The SDFT was unstable in all of them resulting in a mild mechanical lameness. Nine horses underwent surgical treatment. The SDFT was reduced and maintained in position with a synthetic mesh and sutures (n = 2), with a synthetic mesh, sutures and suture screws (n = 6) or with sutures and suture screws (n = 1). Only 66.7% (6/9) of the horses survived to hospital discharge. Fatal complications including support limb laminitis (1/9), implant infection (1/9), and support limb laminitis plus infection (1/9) occurred. All horses available for long-term follow-up (n = 5) were clinically sound and 80% (4/5) had returned to intended use. Following conservative treatment, a mild mechanical lameness will persist but will not prevent the horses from returning to their intended use. Surgical repair can result in a stable fixation of the SDFT with long-term soundness and return to intended use; however, fatal complications (support limb laminitis, infection) can occur leading to the euthanasia of the horse in the immediate post-operative period.     

An in vitro biomechanical comparison between prototype tapered shaft cortical bone screws and AO cortical bone screws for an equine metacarpal dynamic compression plate fixation of osteotomized equine third metacarpal bones

OBJECTIVES: To compare biomechanical properties of a prototype 5.5 mm tapered shaft cortical screw (TSS) and 5.5 mm AO cortical screw for an equine third metacarpal dynamic compression plate (EM-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones. STUDY DESIGN: Paired in vitro biomechanical testing of cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation. ANIMAL POPULATION: Adult equine cadaveric MC3 bones (n=12 pairs). METHODS: Twelve pairs of equine MC3 were divided into 3 groups (4 pairs each) for (1) 4-point bending single cycle to failure testing, (2) 4-point bending cyclic fatigue testing, and (3) torsional single cycle to failure testing. An EM-DCP (10-hole, 4.5 mm) was applied to the dorsal surface of each, mid-diaphyseal osteotomized, MC3 pair. For each MC3 bone pair, 1 was randomly chosen to have the EM-DCP secured with four 5.5 mm TSS (2 screws proximal and distal to the osteotomy; TSS construct), two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws in the remaining holes. The control construct (AO construct) had four 5.5 mm AO cortical screws to secure the EM-DCP in the 2 holes proximal and distal to the osteotomy in the contralateral bone from each pair. The remaining holes of the EM-DCP were filled with two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws. All plates and screws were applied using standard AO/ASIF techniques. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P<.05. RESULTS: Mean 4-point bending yield load, yield bending moment, bending composite rigidity, failure load and failure bending moment of the TSS construct were significantly greater (P<.00004 for yield and P<.00001 for failure loads) than those of the AO construct. Mean cycles to failure in 4-point bending of the TSS construct was significantly greater (P<.0002) than that of the AO construct. The mean yield load and composite rigidity in torsion of the TSS construct were significantly greater (P<.0039 and P<.00003, respectively) than that of the AO construct. CONCLUSION: The TSS construct provides increased stability in both static overload testing and cyclic fatigue testing. CLINICAL RELEVANCE: The results of this in vitro study support the conclusion that the EM-DCP fixation using the prototype 5.5 mm TSS is biomechanically superior to the EM-DCP fixation using 5.5 mm AO cortical screws for the stabilization of osteotomized equine MC3.     

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.     

Outcome and racing performance after internal fixation of third and central tarsal bone slab fractures in horses. A review of 20 cases

Twenty horses with central and third tarsal bone slab fractures, were treated internal fixation. Eighteen of the 20 cases were Standardbred trotters, one was a Thoroughbred racehorse and one a Swedish Warmblood. The central tarsal bone (CT) was involved in 12 cases and the third tarsal bone (T3) in 8 cases. The fractures were treated by lag screw fixation with one (18 cases) or two (2 cases) 3.5 or 4.5 mm cortical screws. Horses were confined to stall rest for one month and then put on a gradually increasing exercise programme. Convalescence time was 3-8 months until the fracture had healed and training could be resumed. Fifteen of the horses regained athletic soundness. Thirteen of the horses (72%) raced after surgery (12 Standardbreds and 1 Thoroughbred). Nine (69%) of these 13 horses won races after surgery.     

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.