Fragmentation of the Medial Coronoid Process in Toy and Small Breed Dogs: 13 Elbows (2000–2012)
ABSTRACT
Fragmentation of the medial coronoid process (FCP) is an uncommon cause of thoracic limb lameness in toy and small breed dogs. Arthroscopic findings and treatment remains poorly described. The objective of this study was to describe the arthroscopic findings and short-term outcome following arthroscopic treatment in toy and small breed dogs with FCP. Medical records were retrospectively reviewed. Arthroscopic findings were available from 13 elbows (12 dogs). Outcome data ≥4 wk postoperatively were available for nine elbows. Owner satisfaction scores were available for 10 elbows. Common preoperative findings included lameness, elbow pain, and imaging abnormalities consistent with FCP. Displaced FCP was the most common FCP lesion identified. Cartilage lesions at the medial coronoid process were identified in 92.3% of elbows (n = 12), with a median Outerbridge score of 4 (range 1–5). Concurrent cartilage lesions of the medial humeral condyle were identified in 76.9% of elbows (n = 10). Seven of nine elbows had full or acceptable function postoperatively. Median owner outcome satisfaction was 91% (range 10–100). FCP should be considered a cause of thoracic limb lameness in toy and small breed dogs. Arthroscopy can be safely and effectively used to diagnose and treat FCP in these breeds.
Introduction
Fragmentation of the medial coronoid process (FCP) is a frequent cause of thoracic limb lameness in dogs.1 A variety of medial coronoid process lesions have been arthroscopically described including: displaced fragmentation, nondisplaced fragmentation, fissuring without complete fragmentation, and osteochondral erosion without fragmentation or fissuring.2–4 The pathogenesis of FCP has yet to be determined, although chronic repetitive overload, joint incongruity, alterations of the thoracic limb weight-bearing axis, and repetitive loading by the tendon of the biceps brachii tendon have all been implicated.5–8 Traumatic FCP has also been described.9
Imaging modalities, such as radiography, computed tomography (CT), and MRI, are often used to diagnose FCP and secondary medial compartment osteoarthritis. Although radiographs are a useful screening tool, they are insensitive for the diagnosis of FCP and correlate poorly with arthroscopic and histologic findings.4,10–12 CT can be used to examine the subchondral and trabecular bone of the medial coronoid process in multiple viewing planes. As a result, CT is both sensitive and specific for the diagnosis of FCP in medium to giant breed dogs.13,14 However, nondisplaced fragments or microfissures within the medial coronoid process may not be visible.13 MRI is extremely sensitive, specific, and accurate when used to diagnose FCP in medium to large breed dogs.15 Furthermore, MRI can be used to evaluate articular cartilage, the cartilage-bone interface, and subchondral bone. Accuracy of MRI is reduced in small or chondrodystrophic breeds due to the comparatively thin articular cartilage of these dogs.16 For this reason, MRI may not be sufficient for the diagnosis of FCP in toy or small breed dogs with pathology isolated to articular cartilage.
Arthroscopy is commonly used to diagnosis and treat FCP in medium to giant breed dogs.2,4,17 During elbow arthroscopy, the medial coronoid process and associated articular cartilage of the humeroradial, humeroulnar, and radioulnar joints are directly visualized and probed.18 Arthroscopy is more accurate in the diagnosis of FCP when compared to arthrotomy due to superior magnification and illumination.3,17 However, use of arthroscopy as the sole method of diagnosis of FCP also has limitations, as isolated subchondral bone lesions with normal overlying articular cartilage are not visible.13 For these reasons, arthroscopy and CT are considered complimentary imaging techniques and, when used in combination, provide the most accurate assessment of the canine elbow joint.13
To date, very few toy or small breed dogs have been included in reports describing the arthroscopic diagnosis and treatment of FCP.4,11 The arthroscopic appearance of the elbow joints and the response to arthroscopic treatment for these toy and small breed dogs were not specifically described. The purpose of this study was to describe the clinical presentation, imaging findings, arthroscopic appearance, and short-term outcome following arthroscopic surgery for toy and small breed dogs with FCP.
Materials and Methods
Medical records from three referral surgical practices (2000–2012) were retrospectively examined for toy or small breed dogs arthroscopically diagnosed and treated for FCP. Dogs with the following criteria were included: (1) less than 13 kg in size; (2) FCP diagnosed via arthroscopy; (3) a complete medical record and operative report with archived images of the medial compartment; and (4) an in-hospital veterinary examination ≥4 weeks following surgery and/or a returned client questionnaire. Exclusion criteria included the presence of elbow incongruity secondary to antebrachial angular limb deformity or an incomplete operative report. Data collected from the medical records included: signalment, history, general and orthopedic exam abnormalities with lameness description, results of preoperative imaging, surgical report findings, arthroscopic still and/or video images, number and type of complication, and in-hospital follow-up exam findings. Owner follow-up data was collected using a visual analogue scale (VAS) questionnaire.19
Elbow Arthroscopy
Arthroscopy was performed in each case by a board certified veterinary surgeon or a resident under direct supervision. Standard medial portals using either a 1.9 mm or 2.3 mm 30° fore-oblique arthroscopea were used as described previously.18 For all cases, the arthroscopic observations within the medial compartment were recorded with either still images or live video. Medial coronoid process lesions were classified similarly to previous reports (Table 1).2,18 In addition to describing medial coronoid process lesion morphology, the articular surface of the remaining medial coronoid process and the medial humeral condyle were individually graded using the modified Outerbridge scoring system (Table 2).4 All cases were treated with either fragment removal and/or abrasion chondroplasty (motorized shaver or manual curettage). In select cases, subtotal coronoid ostectomy (SCO) or biceps ulnar release procedure (BURP) were performed.20,21
Postoperative Management
All dogs were administered a subcutaneous injection of an anti-inflammatory (carprofenb at 2.2–4.4 mg/kg; meloxicamc at 0.1 mg/kg) immediately following surgery. Intravenous opioids (hydromorphoned at 0.1 mg/kg q6 hrs; buprenorphinee 0.01–0.03 mg/kg q 6–8 hr) were administered a maximum of 24 hours following surgery. Activity restriction with controlled leash walks was recommended until follow-up examination. Oral anti-inflammatories (meloxicamc 0.1 mg/kg q 24 hr; carprofenb 2 mg/kg q 12 hr; firocoxibf 5 mg/kg q 24 hr) and/or tramadolg (2–5 mg/kg q 8–12 hr) were prescribed for 2–4 wk postoperatively.
Short-Term Clinical Outcome
Short-term clinical outcome was reported for cases with an in-hospital veterinary examination ≥4 wk following surgery. Information collected from in-hospital follow-up exam included gait evaluation (lameness description), orthopedic exam abnormalities (normal versus decreased range of motion, presence or absence of pain), and any postsurgical complications. Short-term outcome was categorized as “full function,” “acceptable function,” or “unacceptable function.”22 “Full function” was defined as restoration to full intended level and duration of activities and performance without the need for additional medical therapy. “Acceptable function” was defined as restoration to intended activities and performance that is limited in level or duration, and may require additional intermittent medical therapy. “Unacceptable function” was defined as failure to achieve any improvement following treatment and the dog had persistent and permanent clinical signs. If outcome was considered questionable between groups then the worse status was selected to prevent bias.
Owners were additionally contacted by mail with a questionnaire to separately assess owner outcome satisfaction and clinical signs following surgery. The questionnaire contained 10 VAS questions.19 Owners were instructed to answer each question by placing a single mark on a 100 mm line, representing the continuum of poor (0 mm) to excellent (100 mm) response. An example question was completed by hand on all questionnaires for reference. If a dog underwent single session bilateral elbow arthroscopy, owners were instructed to complete a single questionnaire for evaluation purposes. If two separate arthroscopic procedures were performed at different dates for the same dog, then owners were instructed to evaluate the functional status of each limb individually by completing two separate questionnaires. A single investigator (Eric C. Hans, DVM) reviewed all questionnaires. A numerical score was assigned to each question by measuring the distance from VAS point 0 to the mark placed by the client.
Statistical Analysis
Descriptive statistics were generated using a commercially available software programh. Data were reported as median and range.
Results
A total of 13 elbows were identified in 12 toy or small breed dogs (Table 3). Median age at the time of surgery was 6 yr (range 1–11 yr). Median body weight was 6.5 kg (range 3.1–11.2 kg). The breeds represented were Jack Russell Terriers (n = 2), Cavalier King Charles spaniels (n = 2), mixed-breed dogs (n = 2), a Shetland sheepdog, a Japanese chin, a West Highland white terrier, a Chihuahua, a bichon frise, and a Maltese. There were seven spayed females and five neutered males.
The presenting complaint for all dogs was unilateral thoracic limb lameness. Median duration of lameness was 5 mo (range 1.5–12 mo). Thoracic limb lameness was identified on examination in 9/13 dogs (69.2%). Pain or decreased range of motion was identified in 10/13 elbows (77%). Either elbow pain or lameness was identified in all dogs. The left elbow was affected in seven cases and the right elbow was affected in six cases. One dog presented for lameness of the right and left thoracic limb at separate occasions.
Preoperative diagnostic imaging was performed in all cases. Imaging modalities utilized were radiography (9/13; 69.2%), CT (5/13; 38.5%), or both (1/13; 7.7%). Either a visible fragment or findings, such as subtrochlear sclerosis, indistinct margins of the medial coronoid process, and/or anconeal enthesiophytosis, were identified in 7/9 elbows (77.8%) radiographically. Abnormalities of the medial coronoid process were identified in 5/5 elbows (100%) imaged with CT, with fragmentation present in 4/5 elbows and decreased bone opacity of the medial coronoid process without visible fragmentation or fissuring in one elbow.
Elbow Arthroscopy
Arthroscopy was performed using a 1.9 mm arthroscope (n = 12) or 2.3 mm arthroscope (n = 1). Single session bilateral elbow arthroscopy was performed in two dogs. Recommendation for single session bilateral arthroscopic examination was due to inconclusive preoperative imaging results for the contralateral elbow or inconclusive orthopedic exam findings, or lameness reported by the owner. In both cases, the primary elbow was confirmed to have FCP while the contralateral elbow was arthroscopically normal.
The arthroscopic appearance of the medial coronoid process was as follows: single displaced fragmentation 7/13 elbows (53.8%), multiple displaced fragmentation 2/13 elbows (15.3%), nondisplaced fragmentation 1/13 elbows (7.7%), and osteochondral erosion in 3/13 elbows (23.1%). Cartilage lesions of the remaining medial coronoid process were observed in 12/13 elbows (92%), with a median Outerbridge score of 4 (range 1–5). Cartilage lesions of the medial humeral condyle were observed in 10/13 elbows (76.9%), with a median Outerbridge score of 4 (range 2–5). Cartilage lesions of the medial humeral condyle were observed concurrently with the following FCP lesions: displaced fragmentation (n = 5), osteochondral erosion (n = 3), and multiple displaced fragmentation (n = 2).
Arthroscopic removal of an osteochondral fragment was performed in 10/13 elbows. Abrasion chondroplasty was performed in 7/13 elbows (53.8%). BURP was performed in 10/13 elbows (76.9%). SCO was performed in 3/13 elbows (23.1%). All dogs that received SCO had Outerbridge grade 5 cartilage lesions of the medial coronoid process.
Short-Term Clinical Outcome
Short-term clinical outcome data was available for nine elbows. Nine of 13 elbows (69.2%) were evaluated postoperatively by in-hospital examination ≥4 wk following surgery. The median time from surgery to in-hospital examination was 57 days (range 33–119 days). Five of nine elbows (55.6%) evaluated by in-hospital examination had complete resolution of clinical signs on orthopedic exam. The remaining four elbows (44.4%) exhibited lameness, elbow pain, or abnormal range of motion; however, in two of these elbows, lameness was reduced in comparison to the preoperative exam status. Five elbows (55.6%) were categorized as returning to full function. Two elbows (22.2%) were categorized as having acceptable function. Two elbows (22%) were categorized as having unacceptable function. Cumulatively, arthroscopic surgery resulted in full or acceptable function at follow-up examination for 7/9 elbows (77.8%).
Arthroscopic treatment for the five elbows with full function included: fragment removal with abrasion chondroplasty and BURP (n = 3); abrasion chondroplasty and BURP (n = 1); and fragment removal, BURP, and SCO (n = 1). Arthroscopic treatment for the two elbows with acceptable function included fragment removal only (n = 1) and fragment removal with BURP (n = 1). Arthroscopic treatment for the two elbows with unacceptable function included fragment removal only (n = 1) and abrasion chondroplasty, BURP, and SCO (n = 1).
The specific cartilage scores of the medial compartment with associated short-term outcome are provided in Figure 1. The five elbows with full function had median Outerbridge scores of 4 (range 4–5) for both the medial coronoid process and medial humeral condyle. Specific lesions for the medial coronoid were multiple displaced fragmentation (n = 2), single displaced fragmentation (n = 1), nondisplaced fragmentation (n = 1), and osteochondral erosion (n = 1). The two elbows with acceptable function had a median Outerbridge score of 2.5 (range 1–4) for the base of the medial coronoid process and a median Outerbridge score of 3 (range 2–4) for the medial humeral condyle. In both of these elbows the medial coronoid process lesion identified was a single displaced fragment. The two elbows with unacceptable function had median Outerbridge scores of 4.5 (range 4–5) for both the medial coronoid process and medial humeral condyle. Specific lesions of the medial coronoid process were osteochondral erosion (n = 1) and single displaced fragment (n = 1).
Citation: Journal of the American Animal Hospital Association 52, 4; 10.5326/JAAHA-MS-6295
VAS questionnaires were completed and returned at a median time of 14.5 mo (range 2.5–144 mo) from the date of surgery. Owners expressed a high outcome satisfaction at a median score of 91% (range 10–100). VAS scores describing at-home clinical signs varied between owners. The most consistent signs reported were lameness, morning stiffness, and evening stiffness. VAS scores for all questions are graphically summarized in Figure 2.
Citation: Journal of the American Animal Hospital Association 52, 4; 10.5326/JAAHA-MS-6295
Discussion
This is the first report to detail arthroscopic findings and present outcome information following arthroscopic surgery in a cohort of toy and small breed dogs with FCP. Previous reports describing the use of elbow arthroscopy for the diagnosis and treatment of FCP have primarily focused on medium to giant breeds.2–4,11,17,23,24 A case series containing 263 dogs did contain a select few small breed dogs; however, the body weight, intra-articular findings, and clinical outcome specific to those dogs was not reported.4 Dogs less than 13 kg were selected for our case series to ensure only those dogs considered as toy or small breed would be included. Previous reports regarding arthroscopic diagnosis and treatment for FCP have generally lacked inclusion of dogs less than 13 kg, and, as stated, failed to sufficiently describe the clinical presentation, arthroscopic findings, and associated clinical outcome.
The arthroscopic findings of large breed dogs with FCP have been extensively described. Displaced fragmentation, nondisplaced fragmentation, and osteochondral erosion are typical.2–4,23 Similar variation was appreciated in the small and toy breed dogs described in our study. The most common arthroscopic finding was single displaced fragmentation of the medial coronoid process, identified in 7/13 elbows (53.8%). Discrete FCP has been the most frequent arthroscopic finding in multiple FCP reports containing large breed dogs.2–4 The predominance of displaced fragmentation in our population may explain the severity of articular lesions observed at the remaining medial coronoid process and medial humeral condyle. Ten of 13 (76.9%) elbows were identified as having articular damage at the medial humeral condyle. For comparison, Van Ryssen and Van Bree (1997) and Fitzpatrick et al. (2009) documented cartilage lesions of the medial humeral condyle in 56.1% and 51.3% of elbows, respectively.3,4 Fitzpatrick et al. (2009) suggested that humeral condylar lesions were more likely to occur in conjunction with displaced FCP.4 These authors correlated the severity of cartilage damage at the medial coronoid process to that of the medial humeral condyle.4 The arthroscopic findings we describe suggest similar patterns in small and toy breeds, as 7/10 elbows with lesions of the humeral condyle were concurrently diagnosed with displaced FCP. Furthermore, the median Outerbridge score for the medial coronoid process and medial humeral condyle was each 4. Based on the 13 elbows described in our case series, joint surface pathology in toy and small breeds affected by FCP appears to be similar to that previously described in large breed dogs.
Osteochondral erosion of the medial coronoid process without discrete fragmentation or fissuring was observed in 3/13 (23.1%) elbows. CT was performed in one of these elbows and confirmed the absence of localized subchondral fragmentation or fissuring. To our knowledge, these are the first toy or small breed dogs reportedly diagnosed with this type of medial coronoid process lesion. Osteochondral erosion was first described by Vermote et al. (2010) as a finding in older (>6 yr old) large breed dogs.2 Complete loss of the articular cartilage (Outerbridge score ≥4) at the medial coronoid process and medial humeral condyle was reported with this particular lesion type, and each of the three elbows with osteochondral erosion described in this case series exhibited complete articular cartilage loss in these regions. The pathogenesis of this particular lesion type is poorly understood, especially considering the magnitude of cartilage loss observed with the absence of a discrete intra-articular fragment; however, it appears this phenomenon is not limited to large breed dogs.
The arthroscopic treatments performed were at surgeon discretion based on the intra-articular pathology observed. Fragment removal and abrasion chondroplasty were routinely performed. Procedures designed to unload the medial compartment, such as BURP and SCO, were selectively performed to address potential FCP etiologies. Several etiologies have been hypothesized in the formation of FCP including joint incongruity and rotational instability from musculotendinous mismatch.7,8,21 In our study, elbows were specifically excluded when overt incongruity was identified with preoperative imaging, although the presence of micro incongruity cannot be ruled out. BURP was performed in 10/13 elbows (76.9%) to prevent rotation of the medial coronoid process into the radial head by contraction of the biceps/brachialis complex, and hypothetically reduce medial compartment joint load.8,21 SCO, which has shown to improve lameness by reducing joint pain associated with continued microfissuring at the remaining coronoid process, was performed in three elbows each exhibiting Outerbridge grade 5 lesions of the medial coronoid process.20
Short-term outcome based on physical examination findings following arthroscopic surgery was available for nine elbows. Seven dogs (77.8%) were characterized as having full or acceptable function following surgery, while two dogs (22.2%) were characterized as having unacceptable function following surgery. Owner outcome satisfaction was high, suggesting that the majority of owners perceived arthroscopic treatment to provide improvement in their pet's function. Four dogs did not have in-hospital outcome data available and three dogs did not have questionnaire results available. The lack of in-hospital outcome was due to follow-up examination being performed prior to 4 wk. Four wk was selected as the minimum follow-up for reporting clinical outcome based on the results of Meyer-Lindberg et al. (2003).17 In that study, 271 elbow joints from medium and large breed dogs were arthroscopically treated for FCP and demonstrated resolution of lameness at an average of 4 wk following surgery. Based on the results of this study, elbow arthroscopy can be effectively utilized for the diagnosis and treatment of FCP in toy and small breed dogs.
Comparison of clinical outcome following arthroscopic treatment in toy and small breed dogs diagnosed with FCP and larger breed dogs diagnosed with FCP in previous studies is difficult, as differences exist regarding descriptions of intra-articular pathology, outcome definitions, and specific arthroscopic treatments performed. Similar to our results, multiple studies in larger breed dogs have reported positive clinical outcomes following arthroscopic surgery for FCP.17,24,25 A meta-analysis of the veterinary literature also concluded arthroscopy was a superior treatment option for FCP when compared to arthrotomy or medical management alone.26 However, a recent report by Burton et al. (2011) utilizing long-term objective gait analysis was unable to detect a significant difference between large breed dogs treated arthroscopically and those managed medically.27 That study was not without limitation; however, as dogs were specifically excluded based on the presence of cartilage lesions of the medial humeral condyle. Furthermore, elbows within the medical management group were not arthroscopically examined making it difficult to assume equal stratification of coronoid pathology between the two treatment groups. The goal of the present study was to describe the arthroscopic appearance and report the short-term outcome following arthroscopic surgery for toy and small breed dogs diagnosed with FCP. Presently, it remains unknown if medical management alone would have produced similar clinical results to those described following arthroscopic treatment. Further comparison of arthroscopic surgery to other treatment options for FCP in toy and small breed dogs is warranted.
Elbow arthroscopy can be challenging in toy and small breed dogs due to reduced working space within the joint, limited availability of arthroscopic instrumentation for toy and small breed elbow arthroscopy at some institutions, and surgeon experience. A 1.9 mm arthroscope was used for elbow arthroscopy in 12/13 elbows examined in this study. In addition, arthroscopy was performed by surgeons with substantial arthroscopic experience or by residents in training at institutions with large arthroscopic caseloads. Importantly, even though case numbers were limited, no complications were reported, indicating elbow arthroscopy can be safely performed in toy and small breed dogs.
Interestingly, the majority of toy and small breed dogs contained in this report were middle aged or older and were diagnosed with unilateral FCP. Medium and large breed dogs are classically diagnosed at a young age, and often have bilateral disease.1,3 These differences may be due to our small sample size, or potentially represent differences in FCP development and progression between toy and small breed dogs and larger breeds. Differences between small and large breed dogs that could potentially alter FCP pathogenesis include: the rate of skeletal growth, differences in lifestyle and activity, and possible differences in repetitive loading of the medial coronoid process. Increased awareness of FCP in toy and small breed dogs may result in earlier diagnosis and increased recognition of bilateral disease.
The preoperative imaging used to aid diagnosis of the toy and small breed dogs described in this study appeared to more accurately identify FCP and associated osteoarthritis when compared to prior reports in larger breed dogs. Radiography has been shown to be insensitive for the diagnosis of FCP, documented to be as low as 23.5% in one study.14 The sensitivity of CT for the diagnosis of FCP in large breeds has been reported between 71–88.2%.13,14 Radiography was performed on nine elbows in our study and findings consistent with FCP were identified in 7/9 (77.7%) elbows, while CT detected an abnormality in 5/5 (100%) elbows. As previously mentioned, the majority of small and toy breed dogs described in this report had severe cartilage lesions throughout the medial compartment, which may explain the higher incidence of abnormal radiographic and CT findings.
Limitations of this study include: retrospective study design, relatively small sample size, lack of long-term outcome data, and the use of subjective outcome measures. Objective outcome data, such as force platform gait analysis, would represent the ideal method of determining clinical outcome, but was unavailable given this study's retrospective, multi-institutional nature.28 Furthermore, force platform gait analysis is often not possible in toy and small breed dogs due to their small body size and limited stride length.29,30 As a result, outcome characterization in our study was subjective and adhered to previously published definitions for reporting subjective orthopedic outcome.22 Additionally, owner outcome satisfaction was obtained and reported using a VAS questionnaire. VAS questionnaires are reliable for owner assessment of clinical outcome.19 While reporting owner outcome satisfaction was the primary objective, questions regarding clinical signs at home were also completed and reported. Because these questionnaires were variably completed from the date of surgery their results were not taken into consideration when assigning clinical outcome. Elbow arthritis is progressive in cases of FCP despite arthroscopic surgery, and clinical signs may recur or worsen with time.17 The majority of owners in this report were pleased with the outcome following arthroscopic elbow surgery, even when indicating the current presence of clinical signs at home. The authors do acknowledge the potential for bias whenever subjective outcome measures are used and were cautious to not over interpret the outcome data presented here. Future studies assessing the long-term outcome for toy and small breeds with FCP using objective outcome measures should be considered.
Conclusion
FCP should be considered a differential diagnosis for thoracic limb lameness in toy and small breed dogs. Elbow arthroscopy can be safely and effectively performed for the diagnosis and treatment of FCP. As with large breed dogs, a variety of primary medial coronoid process lesions and associated cartilage injury can occur. The short-term clinical outcome of toy and small breed dogs following arthroscopic surgery for FCP is often positive, with owners expressing high satisfaction with outcome results.
Modified Outerbridge scores for the medial coronoid process (MCP) and medial humeral condyle (MHC) by outcome classification. Stacked bar graph illustrating the frequency and severity of cartilage lesions of the MCP and MHC by outcome classification. MCP, medial coronoid process; MHC, medial humeral condyle.
Visual Analog Scale (VAS) client questionnaire results. Box and whisker plot (median, 25th percentile, 75th percentile, minimum, maximum) for individual questions from the VAS client questionnaire. High VAS scores suggest an improved return to function when compared to low VAS scores. VAS, Visual Analog Scale.
Contributor Notes
