Placement of Bone Screws in a Standing Horse for Treatment of a Fracture of the Greater Tubercle of the Humerus M

EQUINE VETERINARY EDUCATION / AE / AUGUST 2013 381

Case Report Placement of bone screws in a standing horse for treatment of a fracture of the greater tubercle of the humerus M. Madron,S.Caston* and K. Kersh Department of Veterinary Clinical Sciences College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA. *Corresponding author email: [email protected]

Keywords: horse; greater tubercle; fracture; internal fixation; standing

Summary report of 16 fractures of the shoulder region identified only one A mature Thoroughbred gelding that was used as a high level fractured tubercle which was the intermediate (Dyson 1985). jumper presented for evaluation of a nonweightbearing One case series specifically describing greater tubercle forelimb lameness following a fall. Radiographs revealed a fractures is available and includes 15 horses with information complete, noncomminuted, minimally displaced sagittal on clinical signs, radiographic technique, treatment and fracture of the greater tubercle. Supporting limb laminitis was a outcome (Mez et al. 2007). Prior to this study, published major concern in the short term based on the severe lameness information on greater tubercle fractures included a limited at presentation. Open reduction with internal fixation was number of individual case reports (Allen and White 1984; chosen over stall rest in an attempt to more rapidly return the Yovich and Aanes 1985; Dyson and Greet 1986; Adams and weightbearing function to the limb. The procedure was Turner 1987; Thomas and Livesey 1997; Tudor et al. 2001). performed standing and 3 bone screws were placed standing Fractures of the greater tubercle can often be diagnosed in an attempt to avoid implant or catastrophic bone failure that based on patient history, physical examination findings and can accompany recovery from general anaesthesia. The day radiography (Mez et al. 2007). Common examination findings following surgery the lameness was significantly improved as include lameness, pain on flexion and extension of the the horse was able to bear some weight on the heel. The shoulder, resentment to palpation, reduction in the cranial gelding was discharged 5 days following surgery and was fully phase of the stride and swelling over the shoulder region (Allen weightbearing at the walk. Six months following surgery the and White 1984; Yovich and Aanes 1985; Dyson and Greet horse was free of lameness and resumed training. This report 1986; Adams and Turner 1987; Mez et al. 2007). Less common describes our experience and rationale in placing bone findings include palpable crepitus, atrophy of the supra- and screws in a standing horse for treatment of a greater tubercle infraspinatus muscles and instability of the shoulder with lateral fracture. excursion when weightbearing (Adams and Turner 1987; Thomas and Livesey 1997; Tudor et al. 2001). Radiography is commonly used to identify greater Introduction tubercle fractures. Mediolateral, craniocaudal and the The greater tubercle of the humerus is a palpable bony craniomedial-caudolateral oblique projections are standard prominence commonly referred to as the point of the shoulder. radiographic views for locating fractures of the greater tubercle It is located on the craniolateral aspect of the proximal (Butler et al. 2000). In addition, the cranioproximal-craniodistal humerus and is divided into cranial and caudal parts. The oblique view has proven useful for identifying fractures not cranial part serves as the insertion for the tendon of the lateral readily seen on the standard views as well as improving branch of the supraspinatus muscle, while the caudal part evaluation of fracture configuration (Mez et al. 2007). Surgical serves as the insertion for the tendons of the infraspinatus and nonsurgical treatments have been successful in returning muscle (Dyce et al. 2002). These tendons span the shoulder horses in a number of different disciplines to work. Surgical joint providing lateral stability and serving as collateral treatment has included removal of the fracture fragment or ligaments. open reduction with internal fixation (Allen and White 1984; Two additional tubercles, the lesser and the intermediate, Dyson and Greet 1986; Adams and Turner 1987; Thomas and are present on the proximal humerus. The lesser tubercle is Livesey 1997; Mez et al. 2007). located on the medial aspect of the humerus and serves as the insertion site for the medial branch of the supraspinatus muscle as well as the tendon of the subscapularis muscle History and case details providing medial stability to the shoulder joint (Dyce et al. An 8-year-old Thoroughbred gelding (502 kg) used as a high 2002). The intermediate tubercle separates the greater and level jumper was referred for evaluation of a left forelimb lesser tubercles and forms a sulcus on either side known as the lameness. A caretaker had witnessed the horse falling onto his intertubercular groove. This groove provides a pathway for left side earlier in the day while running in a paddock. At the tendon of the biceps brachii muscle and also contains the presentation the horse was nonweightbearing on the limb. The intertubercular (bicipital) bursa (Dyce et al. 2002). point of the shoulder was mildly swollen, painful to palpation Fractures of the greater tubercle are uncommon and and painful to flexion and extension. No crepitus was generally do not extend into the weightbearing articular appreciated during palpation and no abrasions or lacerations portion of the humerus (Dyson 1985, 1986; Mez et al. 2007). A were present in the shoulder region. Pulse and respiratory rates retrospective study of 54 cases of equine humeral fractures did were mildly elevated with the remainder of the physical not include any tubercle fractures (Carter et al. 1993). Another examination being within normal limits.

Fig 1: Mediolateral radiograph of the fractured greater tubercle.

Radiographs of the shoulder region revealed a complete, noncomminuted, minimally displaced sagittal fracture of the greater tubercle of the humerus that extended just proximal to the deltoid tuberosity. The fracture was readily identified on the mediolateral, craniomedial-caudolateral oblique and the cranioproximal-craniodistal oblique projections (Figs 1 and 2). There was no radiographic evidence that the fracture extended into the humeral head and no other abnormalities were noted. Open reduction with internal fixation was the treatment Fig 2: Cranioproximal-craniodistal oblique radiograph of the selected in an attempt to return the weightbearing function to fracture gap (arrows), fractured greater tubercle (A) and the the limb and reduce the risk of supporting limb laminitis. The intermediate tubercle (B). temperament of the gelding was such that a standing repair was considered possible to avoid implant complications as continued to 5 cm proximal to the deltoid tuberosity. The well as catastrophic bone failure that can occur with a incision was made parallel to the cranial edge of the deltoid general anaesthetic recovery (Adams and Turner 1987; muscle and a tissue plane between the brachiocephalic Thomas and Livesey 1997; Mez et al. 2007). muscle and the deltoid muscle was identified and incised to expose the greater tubercle (Nixon and Watkins 1996). A Gelpi Preoperative care retractor was used to separate the muscle bellies to increase exposure. At this time a 1.2 mm ¥ 25.4 mm needle was used to Prior to surgery a 14 gauge 5.5 inch (14 cm) i.v. catheter was infiltrate multiple areas of the periosteum around the fracture placed in the left jugular vein and the area over the point of line as well as areas of proposed screw placement with the shoulder was clipped and cleaned with 4% chlorohexidine. mepivacaine. The fracture line was identified, debrided with a Procaine penicillin (22,000 u/kg bwt i.m. twice daily), small bone curette and flushed with 1 litre of saline. The gentamicin sulphate (6.6 mg/kg bwt i.v. once daily) and fragment was minimally displaced proximally and reduction flunixin meglumine (1.1 mg/kg bwt i.v. twice daily) were was achieved by placing traction distally on the 4.0 mm insert initiated 1 h before surgery. Sedation and analgesia were placed into the first glide hole. Additional local anaesthesia provided by an i.v. infusion of detomidine (loading dose was provided by infiltrating the initial glide hole with 30–40 ml 6 mg/kg bwt; continuous rate infusion of 0.8 mg/kg bwt/min) as mepivacaine to bathe the fracture gap as mepivacaine well as preoperative butorphanol (0.02 mg/kg bwt i.v.). could be visualised exiting multiple sites of the fracture line. Reduction was evaluated by digital palpation and minimal Surgical technique traction was necessary to reduce the fragment. The gelding was placed in treatment stocks and the surgical One cancellous (6.5 mm ¥ 95 mm) and 2 cortical (5.5 mm site aseptically prepared, quadrant drapes placed and an ¥ 90 mm) bone screws were placed in lag fashion across the incise drape (Ioban)a applied. Local anaesthesia was fracture gap. The order of screw placement included the most provided by infiltrating the skin, subcutaneous tissues and proximal followed by the most distal with the middle screw muscles in the surgical site with 60 ml of 2% mepivacaine in an being placed last. A washer was used with each screw and all inverted-V pattern. A 1.2 mm ¥ 88.9 mm spinal needle was screws were placed according to AO/ASIF technique. Digital used to infiltrate the deeper tissues with mepivacaine. A 15 cm radiography was used to assess accuracy of screw skin incision beginning just proximal to the greater tubercle was placement. Prior to closure the surgical site was lavaged with

2 l of sterile saline. The incision was closed in 3 layers. The fascia of the brachiocephalic muscle and the deltoid muscle was opposed with 0-poliglecaprone in a simple continuous pattern. The subcutaneous tissues were closed with 2-0 poliglecaprone in a simple continuous pattern. The skin was closed with 2-0 poliglecaprone in a continuous horizontal mattress pattern. A stent made of sterile rolled gauze was secured to the incision with 0-poliglecaprone and an occlusive bandage1 placed over the stent. Total surgical time was 2 h.

Post operative care The following day the bandage and stent were removed. The incision was cleaned with 4% chlorohexidine and a clean stent was reapplied. This was repeated every other day for 4 days. Preoperative antibiotics were continued for an additional 4 days. Flunixin meglumine (1.1 mg/kg bwt i.v. twice daily) was discontinued 2 days following surgery and replaced with phenylbutazone (4.4 mg/kg bwt per os once daily). In the 3 days following surgery the horse remained mildly uncomfortable at the walk but was significantly improved over the initial nonweightbearing presentation and would bear Fig 3: Mediolateral radiograph taken 6 weeks following surgery. some weight on the heel. The comfort level in the stall was None of the implants are bent, broken or show signs of loosening. greatly improved as the gelding would place the heel fully on the ground while resting in the stall. The gelding was discharged 5 days following surgery and was fully weightbearing at the walk. Discharge instructions included 4 weeks of strict stall rest followed by an additional 4 weeks of stall rest with 15 min of hand walking twice daily. Phenylbutazone (4.4 mg/kg bwt per os once a day) was administered for 2 weeks following surgery with the dose halved the second week.

Follow-up At a 6 week recheck the gelding had remained fully weightbearing at the walk with slight lameness noted when turning. There was significant atrophy of the supra- and infraspinatus muscles as well as mild shortening of the cranial phase of the stride at the walk. The fracture line remained visible and wider than on previous films with normal osteolysis present (Figs 2 and 4). None of the implants were bent, broken or showed signs of loosening and the incision had healed without complication (Figs 3 and 4). No evidence of osteoarthritis of the scapulohumeral joint was present (Fig 3). Instructions were given to continue stall rest for one month with 15 min of hand walking twice daily. The following month instructions were given to begin lungeing for 5–10 min a day with increasing time on the lunge line of 5 min each week for an additional month. Following this the gelding was gradually started back under saddle and 6 months after surgery began Fig 4: Cranioproximal-craniodistal oblique radiograph 6 weeks work over ground poles and small jumps; at this time he was following surgery. Osteolysis is present with a widened fracture gap sound at the walk and trot. It has been one year since surgery, as well as loss of reduction when compared to the preoperative with 6 months of training and he continues to be sound with radiographs. increasing work and has returned to his original level of use. Atrophy of the supra- and infraspinatus muscles resolved with increasing exercise. (Mez et al. 2007). In addition, several horses have returned to athletic soundness despite implants bending or breaking Discussion during recovery from general anaesthesia (Adams and Turner Fractures of the greater tubercle of the humerus are 1987; Thomas and Livesey 1997; Mez et al. 2007). The type of uncommon and, as such, large numbers of cases for treatment selected has been based on a number of evaluation are limited (Dyson 1985, 1986). Reports of successful considerations. These include degree of lameness, fragment treatments have included stall rest with controlled exercise, size, presence of comminution, presence of an articular/bursal fragment removal and open reduction with internal fixation component, level of desired athletic performance and

stability of the shoulder joint. Clinical experience as well as client budget can also influence the type of treatment selected. The decision to repair the fracture in this case with open reduction and internal fixation was based on several considerations. The primary reason was based on the severe lameness with the potential for supporting limb laminitis. Fragment stabilisation with internal fixation was thought to be the best option for returning the weightbearing function to the limb as rapidly as possible. In addition, the fragment was large and should accommodate several bone screws for a stable fixation. Internal fixation would also allow for continued anatomic reduction of the lateral aspect of the intertubercular groove in an attempt to prevent a step defect that could result in lameness associated with inflammation of the bicipital bursa (Dyson and Dik 1995; Booth 1999). Stall rest alone was considered as the literature contains several cases of greater tubercle fractures of various sizes with and without comminution that healed with the horses returning to work following stall rest (Yovich and Aanes 1985; Tudor et al. 2001; Mez et al. 2007). However, the risk of supporting limb laminitis in this case was considered to be higher with stall rest than with surgical repair. Fragment removal was not considered in this case based upon the size of Fig 5: Mediolateral radiograph taken 13 months following surgery. the fragment, lack of comminution, minimal displacement The horse was back in full work at this time. The implants remain and involvement of the lateral sulcus of the intertubercular intact. groove. The decision to place bone screws standing was based on several considerations. The fracture configuration was not stocks worked well for restraint and did not limit surgical complex and the gelding’s demeanour was extremely quiet access. However, intra-operative radiography was difficult as and tolerable during the physical examination as well as positioning the image plate and tube around the stocks was during radiography. He was considered an excellent challenging but possible. Debridement and lavage of the candidate for a standing procedure. In addition, the potential fracture gap was possible with the horse standing. However, for implants placed under general anaesthesia to become aggressive debridement was not performed because of compromised or fail or for catastrophic failure of the humerus minimal displacement of the fragment and good anatomic from undetected fissures or stress concentration to occur reduction prior to surgery. during recovery was eliminated (Adams and Turner 1987; No immediate post operative radiographs were obtained. Markel 1996; Thomas and Livesey 1997; Nunamaker 1999; Mez However, radiographs taken at a 6 week recheck revealed et al. 2007). normal osteolysis along the fracture line as well as adequate A combination of cortical and cancellous screws placed in reduction and no implants were broken, bent or showed signs lag fashion was utilised in this case. The strength of available of loosening. Intra-operative radiographs included the implants is a limiting factor in most equine fracture repairs. One cranioproximal-craniodistal oblique projection that was used cancellous screw was used in this case as a cortical screw long for placement of the initial glide hole for the first screw. No enough to engage both the near and far cortices was additional radiographs were taken beyond placement of the not available. A washer was added to each screw to first glide hole as the fragment could be visualised and prevent the head from pulling through the fragment placement of the following 2 screws was guided by the initial during screw tightening (Shepard et al. 2002). It was felt that screw. No immediate post operative radiographs were taken this repair would counteract the distractive forces of the either as the incision allowed direct visualisation of the fracture musculotendinous insertions on the fragment providing stability line. Each screw had good purchase during tightening and the and compression. fracture gap was palpated to be reduced following screw No complications associated with performing the placement. Recheck films were also taken at 13 months and procedure standing were encountered. The sedation and showed that the screws and washers were in place and the local anaesthesia were effective as the gelding offered no fracture line no longer visible. The intertubercular groove resentment to any part of the procedure and stood quietly for appeared to be within normal limits. (Figs 5 and 6) the entire surgery. By using a constant rate infusion we were A more minimally invasive approach to repair this fracture able to maintain a level plane of sedation for a fairly long was discussed prior to surgery. This included placing screws period. Bolus injections work well but are often complicated by through stab incisions. However, it was felt that the soft tissues the horse being too sedate and unsteady or too awake and in this area would be difficult to work through and that open not standing still. The combination of the CRI and local reduction offered the ability to visualise the fragment for screw anaesthetics provided adequate sedation and analgesia to placement as it was uncertain the quality of radiographs that allow standing repair of the fracture in this horse. The horse was could be obtained during surgery. placed backwards in the treatment stocks to allow for To the authors’ knowledge, the literature contains only 5 improved access as the side could be opened as needed. The cases of greater tubercle fractures repaired with internal

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References Adams, R. and Turner, T.A. (1987) Internal fixation of a greater tubercle fracture in an adolescent horse: a case report. Equine Vet. Sci. 3, 174-176. Allen, D. and White, N.A. (1984) Chip fracture of the greater tubercle of a horse. Comp. Cont. Educ. Pract. Vet. 6, S39-S41. Booth, T.M. (1999) Lameness associated with the bicipital bursa in an Arab stallion. Vet. Rec. 145, 194-198. Butler, J.A., Colles, C.M., Dyson, S.J., Kold, S.E. and Poulos, P.W. (2000) The shoulder, humerus and elbow. In: Clinical Radiology of the Horse, Ed: J.A. Butler, Blackwell Publishing, Ames. pp 205-228. Carter, B.G., Schneider, R.K., Hardy, J., Bramlage, L.R. and Bertone, A.L. (1993) Assessment and treatment of equine humeral fractures: retrospective study of 54 cases (1972-1990). Equine Vet. J. 25, 203-207. Dyce, K.M., Sack, W.O. and Wensing, C.J.G. (2002) The forelimb of the horse. In: Textbook of Veterinary Anatomy, Ed: K.M. Dyce, W.B. Fig 6: Cranioproximal-craniodistal oblique radiograph taken Saunders, Philadelphia. pp 568-605. 13 months following surgery. The fracture gap is no longer visible. Dyson, S. (1985) Sixteen fractures of the shoulder region in the horse. Equine Vet. J. 17, 104-110. Dyson, S. (1986) Shoulder lameness in horses: an analysis of 58 suspected cases. Equine Vet. J. 18, 29-36. fixation under general anaesthesia (Dyson and Greet 1986; Dyson, S.J. and Dik, K.J. (1995) Miscellaneous conditions of tendons, Adams and Turner 1987; Thomas and Livesey 1997; Mez et al. tendon sheaths, and ligaments. Vet. Clin. North Am. Equine Pract. 2007). Implant complications occurred during recovery in 3 of 11, 315-337. the cases (Adams and Turner 1987; Thomas and Livesey 1997; Dyson, S.J. and Greet, T.R.C. (1986) Repair of a fracture of the Mez et al. 2007). All 5 horses returned to their previous level of deltoid tuberosity of the humerus in a pony. Equine Vet. J. 18, 230-232. use despite early implant complications in 3 of the horses. Markel, M.D. (1996) Bone structure and the response of bone to stress in The purpose of this case report is to share the authors’ initial equine fracture repair. In: Equine Fracture Repair, Ed: A.J. Nixon, experiences and rationale for repairing a greater tubercle W.B. Saunders, Philadelphia. pp 10-18. fracture in an adult horse standing. The goal of surgical Mez, J.C., Dabareiner, R.M., Cole, R.C. and Watkins, J.P. (2007) Fractures intervention in this case was to provide more rapid stability and of the greater tubercle of the humerus in horses: 15 cases comfort. The decision to place the screws standing was simply (1986-2004). J. Am. Vet. Med. Ass. 230, 1350-1355. to avoid implant or bone failure that can occur with a general Nixon, A.J. and Watkins, J.P. (1996) Fractures of the humerus. In: anaesthetic recovery. An examination of the literature would Equine Fracture Repair, Ed: A.J. Nixon, W.B. Saunders, Philadelphia. pp 242-253. indicate that implant failure may not be a limiting factor in returning these horses to work. Screw placement also offers no Nunamaker, D.M. (1999) General techniques and biomechanics. In: AO Principles of Equine Osteosynthesis, Eds: G.E. Fackelman, J.A. advantage over stall rest alone in reducing convalescence Auer and D.M. Nunamaker, Thieme, New York. pp 11-24. when compared to other reports in which times to resume Shepard, M.F., Wang, J.C., Oshtory, R., Yoo, J. and Kabo, J.M. (2002) training are similar to this case (Tudor et al. 2001; Mez et al. Enhancement of pedicle screw fixation through washers. Clin. 2007). The decision to use implants in this case was based Orthop. Relat. Res. 395, 249-254. primarily on providing comfort in the short term as soundness in Thomas, H.L. and Livesey, M.A. (1997) Internal fixation of a greater the long term has been successfully achieved by a variety of tubercle fracture in an adult horse. Aust. Vet. J. 75, 643-644. surgical and nonsurgical management techniques. Tudor, R., Crosier, M., Love, N.E. and Bowman, K.F. (2001) Radiographic diagnosis: fracture of the caudal aspect of the greater tubercle of the humerus in a horse. Vet. Radiol. Ultrasound 42, 244-245. Authors’ declaration of interests Yovich, J.V. and Aanes, W.A. (1985) Fracture of the greater tubercle of No conflicts of interest have been declared. the humerus in a filly. J. Am. Vet. Med. Ass. 187, 74-75.

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