The third trochanter is a prominent tuberosity that is slightly curved in the cranial direction and is located on the lateral aspect of the proximal third of the femur. Its base provides insertion for the quadriceps femoris muscle, a strong extensor of the stifle joint, whereas the apex of the third trochanter provides insertion for the tendon of the gluteus superficialis muscle, which is mainly a flexor of the coxofemoral joint and internal rotator of the thigh.1 The superficial position (under the gluteofemoralis muscle) makes the third trochanter prone to traumatic injury such as falls, but it has been suggested that fractures may also be caused by avulsion of the tendon of the gluteus superficialis muscle.2 In the absence of physical findings and when the horse has no history of trauma, diagnosis can be difficult to achieve without nuclear scintigraphy. Lesions or injuries to the distal portion of the limb should be excluded before consideration of the pelvic or thigh regions as the source of pain.3
Reports of fractures of the third trochanter are uncommon,2–4 and to our knowledge, there is no report involving a group of horses that describes the clinical signs, imaging features, management, and outcome of horses with third trochanter fractures. The purpose of the study reported here was to determine the history; clinical, radiographic, ultrasonographic, and scintigraphic findings; management; and outcome of horses with third trochanter fractures. The hypothesis was that long-term outcome would be positive.
Materials and Methods
Case selection—Medical records of horses admitted to the Center of Imaging and Research on Locomotor Affections in Equines, Goustranville, France, between 2000 and 2012 were reviewed. Horses were included in the study if a diagnosis of fracture of the third trochanter had been made on the basis of history, physical examination findings, and radiographic, ultrasonographic, or nuclear scintigraphic findings.
Medical records review—Data collected from the records included age, breed, sex, use, history, severity and duration of lameness, results of physical and lameness examinations, diagnostic imaging findings, management, and outcome. Long-term follow-up information was obtained through reassessment of the horses at the Center of Imaging and Research on Locomotor Affections in Equines or by telephone communication with owners, trainers, and referring veterinarians. The shortest follow-up was 5 months, and the longest was 9 years. A return to a similar level of previous athletic activity or, if untrained at the time of injury, the ability to be used for the specific activity intended by the owner was used as a criterion for a positive outcome.
Examination protocol—A lameness examination was performed for each horse. The degree of lameness and response to flexion tests were graded on a scale of 0 to 5 in accordance with the lameness scale of the American Association of Equine Practitioners.5
Two horses were referred for whole-body nuclear scintigraphic examination. These horses received 10 MBq/kg (4.5 MBq/lb) of technetium 99m diphosphonate injected IV. Furosemide (200 mg, IV) was injected 1.5 hours later to allow them to urinate and to decrease background radiation. Bone phase images were obtained 3 hours after injection, with horses sedated with detomidine (0.1 mg/kg [0.045 mg/lb], IV) and chlorhydrate morphine (0.1 mg/kg, IV). Images of 60 seconds' duration were acquired with motion correction by a gamma camera. In the standard protocol, each third trochanter was imaged in 2 views: a lateral view of the stifle joint region and a craniolateral oblique view of the femur and coxofemoral regions (Figure 1). For the lateral view of the stifle joint region, the upper part of the camera was placed approximately 5 cm proximally to the third trochanter. In 1 case, additional views were obtained: a caudal view of both femoral and ischiatic regions and a caudolateral oblique view of the femoral region of the affected limb. Bone scan images were evaluated subjectively and with uptake ratios. Subjective evaluation was performed by one of the authors (JMD), and areas of IRU were identified as a lack of left-to-right symmetry and by comparison with reference images. Increased radiopharmaceutical uptake severity was graded subjectively as mild, moderate, or intense. Objective evaluation of uptake ratios was performed with a method adapted from that described by Geissbühler et al.2 Regions of interest were defined on the craniolateral oblique view, in the cranial part of the greater trochanter, and on the third trochanter. The uptake ratio was defined as the maximum pixel activity of the third trochanter divided by the maximum pixel activity of the cranial part of the ipsilateral greater trochanter.
Craniolateral oblique scintigraphic views of the left (LH) and right (RH) femur and coxofemoral regions (A), caudal scintigraphic view of both femoral and ischiatic regions (B), and caudolateral oblique scintigraphic view of the left femoral region (C) of a horse. In B, notice the intense IRU of the left third trochanter, which appears enlarged (arrow), compared with the contralateral third trochanter; in C, notice bifocal uptake (double arrow).
Citation: Journal of the American Veterinary Medical Association 243, 2; 10.2460/javma.243.2.261
The lateral aspect of the femoral region of all horses was examined ultrasonographically on transverse and longitudinal scans with a 3.5- to 6-MHz multifrequency convex transducer and compared with the contralateral limb (Figure 2). In 1 case, additional images of each third trochanter were obtained by the use of a 7.5-MHz linear transducer. A craniolateral-caudomedial 25° oblique radiographic view of the affected femoral region was then obtained in 3 cases (Figure 3) with a ceiling-mounted x-ray tube and a flat panel detector placed in a bucky column, with the horses standing while sedated with detomidine (0.1 mg/kg, IV). Mean peak voltage was 50 kV, and mean amperage was 120 mA.
Transverse ultrasonographic images of the third trochanter in 3 horses (cranial is to the left). A—Image of a normal third trochanter. B—Image of a horse with a fracture of 1 month's duration. C—Image of a horse with a fracture of 4 months' duration. In panels B and C, there is a bone fragment displaced cranially (arrow) with echogenic tissue in the fracture space (star) suggestive of a fibrous union. In panel B, the fracture is surrounded by a diffuse hypoechogenic area (arrowheads), and there is bone remodeling of the surface of the third trochanter with thickening and heterogeneous echogenicity of the tendon of the gluteus superficialis muscle, indicating enthesopathy. 1 = Femur. 1a = Third trochanter. 2 = Quadriceps femoris muscle. 3 = Gluteus superficialis muscle. 3a = Tendon of the gluteus superficialis muscle. 4 = Gluteofemoralis muscle. 5 = Skin.
Citation: Journal of the American Veterinary Medical Association 243, 2; 10.2460/javma.243.2.261
Craniolateral-caudomedial 25° oblique radiographic view of the third trochanter in a horse obtained 5 months after the onset of lameness, during a follow-up examination. Notice that there is a simple complete longitudinal fracture (arrow) between the midlevel and the base of the third trochanter with minimal displacement and bone remodeling.
Citation: Journal of the American Veterinary Medical Association 243, 2; 10.2460/javma.243.2.261
Management and outcome—Nonsurgical management (1 month of stall rest followed by 1 month of hand walking, then trotting exercise for 2 to 4 months, depending on the severity of the lameness) was advised in all cases, with additional recommendation of administration of NSAIDs for horses with severe lameness (> 3/5 grade).
Results
During the study period, 13,495 horses were admitted to the Center of Imaging and Research on Locomotor Affections in Equines for lameness examination, and a fracture of the third trochanter responsible for the lameness was diagnosed for 8 (0.05%), including 2 females, 4 geldings, and 2 males. The mean ± SD age was 3.6 ± 2.4 years (median, 4 years; range, 8 months to 6 years). Three horses were < 2 years old and were untrained. Mature horses were used for steeplechase racing (n = 1), trot racing (1), or show jumping (3). Affected breeds included Thoroughbred (n = 2), French Trotter (2), and Warmblood (4). All fractures were unilateral; the left third trochanter was affected in 6 horses and the right third trochanter in 2 horses.
All horses were examined because of hind limb lameness with a history of acute onset of severe lameness (mean reported grade, 4.5; range, 3 to 5). According to owners or trainers, horses developed lameness after falling on the affected side (n = 3) or after training (2) or were found lame in the stall (1), at pasture (1), or after transport (1). At the time of examination, duration of the lameness ranged from a few minutes to 1 week (n = 3), to 2 weeks (2), and to 1 to 4 months (3).
Physical examination results—Four horses had indicative physical signs, including mild to moderate soft tissue swelling over the hip or thigh regions with signs of sensitivity to local palpation and pressure for one of them. These 4 horses were admitted within 2 weeks after the onset of clinical signs. Nonspecific findings (ipsilateral gluteal or thigh muscle atrophy) were present in 3 horses, and no physical abnormality was identified in 2 horses.
Lameness examination results—All horses had unilateral lameness of the affected limb at the time of examination. Three horses had severe lameness (grade 3 to 4/5) of < 6 days' duration. The caudal phase of the stride was reduced at the walk for 1 horse. Flexion tests were not performed on these 3 horses to avoid any worsening of the lameness. Five horses had mild lameness of the affected limb (grade 1/5) and had been admitted ≥ 2 weeks after the onset of lameness. Lameness was exacerbated on soft ground for 2 horses and at the walk with a decrease in the cranial phase of the stride for 1 horse. Flexion tests were performed on these 5 horses, with mild to moderate exacerbation of the lameness in 3 of them.
Diagnostic imaging results—Nuclear scintigraphy was performed on 2 of the 8 horses because of persistent hind limb lameness without a relevant cause identified by the referring veterinarian, 1 month (n = 1) and 4 months (1) after the onset of clinical signs, despite rest followed by controlled exercise. Both had IRU over the affected third trochanter, compared with the contralateral third trochanter, which could be seen on all views obtained. The caudolateral oblique view in 1 case revealed a bifocal uptake over the affected third trochanter (Figure 1). One horse had moderate IRU over the affected third trochanter (uptake ratio, 0.84), and the other had intense IRU (uptake ratio, 0.95). The radiopharmaceutical uptake was normal for the contralateral third trochanter of both horses (with respective uptake ratios of 0.44 and 0.37).
Ultrasonographic examination was performed on all 8 horses and revealed unilateral abnormalities in all. The same findings were detected by use of the 3.5- to 6-MHz convex transducer and the 7.5-MHz linear transducer in the case in which both transducers were used. There was a single fragment of bone displaced cranially in 7 horses (Figure 2) and multiple bony fragments in 1 horse. Bone remodeling of the surface of the affected third trochanter was identified in 1 horse. The fracture site was surrounded by a diffuse hypoechogenic region suggestive of a hematoma in 2 horses. Seven horses had concurrent thickening and heterogeneous echogenicity of the tendon of the gluteus superficialis muscle, with bone remodeling at its insertion site, indicating enthesopathy. Follow-up ultrasonographic examinations were obtained in 4 horses to assess healing. There was a progressive increase in bone remodeling at the fracture site, indicating callus formation with persistence of an interruption of the bone continuity that was filled with echogenic tissue suggestive of a fibrous union. In 1 case, irregularity developed at the insertion of the gluteus superficialis muscle, indicating an enthesopathy.
Radiographic examination of the third trochanter was performed on 3 horses, with 2 examined within 6 days after injury and 1 examined 1 month after injury. It revealed in all cases a simple complete longitudinal fracture between the midlevel and the base of the third trochanter, with a minimal displacement of the fragment in 2 horses. All 3 horses underwent a follow-up examination with reassessment of the affected third trochanter. Radiographs were taken 2 and 4 months after injury for 1 horse and at 5 or 6 months after injury for the 2 others. Follow-up radiography revealed increased bone remodeling without further displacement of the fragment and persistence of a radiolucent line suggestive of a fibrous union (Figure 3).
Management and outcome—The 8 horses were managed nonsurgically in the acute stage. The rehabilitation program included 1 month of stall rest, controlled hand walking for another month, and 2 to 4 months of trotting exercise or exercise in a small paddock before returning gradually to full athletic activity or, for immature horses, returning to a larger pasture. In addition to rehabilitation, 4 of these horses received NSAIDs for 7 to 15 days after the injury. For all horses, the lameness grade was reported to have improved substantially in the first 15 days after injury.
Follow-up information was available for all horses. Seven horses had a positive outcome, either returning to their previous athletic activity within 1 to 6 months after the onset of clinical signs or, if not ridden at the time of diagnosis, being able to be used for the intended activity. For the 1 remaining horse, lameness did not recur after the rehabilitation program, but the horse was retired from athletic use for reasons unrelated to the lesion.
Discussion
Fracture of the third trochanter has been reported.2–4 The present study provided further information and data on this specific condition. Eight cases of fracture of the third trochanter were identified over a 12-year period in a population of horses referred for orthopedic problems (0.05%), suggesting that this condition is an uncommon cause of lameness. Interestingly, the left hind limb was more commonly affected than the right hind limb, a result similar to that described in a previous report.2 Median age of horses was 4 years, suggesting that fracture of the third trochanter is more frequent in young horses, but more clinical cases are needed to make a statement about influence of age and activity on occurrence of this injury. Fracture of the third trochanter was responsible for an acute onset of severe lameness in all cases in the present study, with a rapid improvement of the degree of lameness, as reported elsewhere.3
There are several possible causes of fractures of the third trochanter, and the cause cannot always be precisely determined.2,6 Similarly to previous reports,2,3 a fall or an external trauma was reported or suspected in 6 horses and was followed by acute onset of severe lameness. The cause was unknown in the remaining 2 horses, possibly because trauma had been unnoticed. Another possible cause of fracture of the third trochanter is traction by the tendon of the gluteus superficialis muscle, either traumatic in origin (marked extension and lateral rotation of the hip joint occurring during a fall or if the hind foot slips on the ground) or the result of repetitive cyclic strains on the third trochanter, resulting in avulsion of the cranial part of the third trochanter.2 This is consistent with the history of the 2 horses in the present study that developed lameness after having sustained strenuous training, with ultrasonographic evidence of an enthesopathy of the tendon of the superficial gluteal muscle.
As reported elsewhere,2,3 physical assessment of anatomic structures of the thigh and eliciting signs of pain via palpation over the third trochanter area are not easily accomplished in a well-muscled horse. In the present study, short duration of lameness, young age, and light conformation were correlated with the presence of localized clinical findings such as swelling or increased sensitivity to palpation over the trochanteric region. Half the horses had no specific physical abnormality and no particular gait characteristics, making diagnosis difficult.
Radiography is the imaging modality of choice to characterize fractures in most locations. However, radiographic assessment of the femoral region of a mature horse is not easy in routine practice with a portable machine because of the massive size of the thigh. High-output x-ray equipment, a focused grid, and fast rare earth screens4 or computed or digital radiographic equipment are required. In addition, it has been reported that good-quality radiographs of the third trochanter can be obtained only by use of general anesthesia.2–4 To our knowledge, the present report is the first to include radiographic projections of the proximal portion of the femur in standing horses with a craniolateral-caudomedial 25° oblique view. This technique has the advantages of being safe and noninvasive, and the view is oriented to highlight the fracture line, given that all fractures reported here were longitudinal with minimal displacement and occurred between the midpart and the base of the third trochanter. A similar view has been proposed to visualize the third trochanter by use of general anesthesia.4 In the present study, given that the diagnosis had already been established by use of ultrasonography, fractures of the third trochanter were detected radiographically in only 3 horses because of economic concerns and radiation safety concerns.
In accordance with results of a previous study7 in which ultrasonography was found preferable to radiography as an initial diagnostic approach to detect pelvic and femoral disorders, we think that ultrasonography should be considered as the primary procedure in the diagnosis of third trochanter fractures. It is a safe and noninvasive procedure that can easily and repeatedly be performed in the field by an equine practitioner for diagnosis or follow-up. In addition, it provides a cheaper and readily available alternative to imaging procedures previously recommended for diagnosis. Evaluation of the third trochanter can be achieved with a 7.5-MHz linear transducer, and better-quality images are obtained with a 5- or 6-MHz convex transducer. Ultrasonography combines excellent evaluation of bone surfaces (and assessment of the presence or absence of a fibrous union), soft tissues, and entheses.8 Muscle damage, including hematoma, was diagnosed in 2 of 8 cases, and concurrent gluteus superficialis muscle enthesopathy was identified in 7 of 8 cases at the initial examination. Follow-up ultrasonographic assessment revealed that superficial gluteal muscle enthesopathy developed during the healing process in some cases.
Nuclear scintigraphy has been considered a valuable tool for diagnosing fracture of the third trochanter.2,3 Nuclear scintigraphy revealed moderate to intense IRU over the third trochanter in horses in the present study, which directed the clinician toward this area and led to the diagnosis of fracture of the third trochanter. When there is IRU over the third trochanter, a caudolateral oblique view could be helpful to confirm fragmentation and displacement of the bony fragment characterized by a bifocal uptake. False-positive results have been suggested for nuclear scintigraphy by previous studies,2,6 where there was IRU in the third trochanter region in 9 horses, with only 2 of the 6 radiographed limbs having evidence of a third trochanter fracture2 and IRU in the third trochanter region in 10 horses, with none of them having evidence of third trochanter fracture.6 However, no systematic ultrasonographic examination of the third trochanter was performed in those studies. In addition, in our experience, mild to intense IRU over the third trochanter can be found in cases with radiographic or ultrasonographic evidence of a fracture of the third trochanter but without lameness of the affected limb. This suggests that nuclear scintigraphy provides no reliable information on the likelihood of the lesion to cause signs of pain, as has been reported.6 Rather, this technique is accepted to be sensitive for detecting active bone remodeling.8
According to previous reports,2,3 third trochanter fractures heal by either fibrous or osseous union, but results of the present study suggested that fractures are more likely to heal through a fibrous union, with persistence of cranial displacement of the fragment (Figures 2 and 3). Assessment of the evolutive stage of the lesion can be difficult in chronic cases, and the activity level should be adapted to the degree of lameness rather than to the ultrasonographic or radiographic appearance of the lesion. As reported by others,3,4 follow-up of the cases reported here suggested that prognosis for a return to athletic soundness is favorable after nonsurgical management (ie, rest followed by controlled exercise). In addition, 13 other horses with evidence of a third trochanter fracture were identified at the Center of Imaging and Research on Locomotor Affections in Equines during the study period but were excluded from the study because they had no lameness of the affected limb at the time of examination. These cases were incidental findings detected via nuclear scintigraphy or during ultrasonographic checkup (performed to explore the reason for poor performance), and this also suggests that clinical manifestations of third trochanter fractures generally resolve and that the prognosis of this condition is good.
Although it is a rare injury in horses, fracture of the third trochanter should be included in the differential diagnoses of hind limb lameness localized to the proximal portion of the limb in horses. An accurate diagnosis can easily be made under field conditions with ultrasonography. Nuclear scintigraphy is useful to orient clinicians toward the trochanteric area in cases of occult lameness with neither history of trauma nor localizing clinical signs. Prognosis for a horse with a third trochanter fracture to return to its previous athletic activity is good.
ABBREVIATION
| IRU | Increased radiopharmaceutical uptake |
References
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