Radial Shortening

Symmetric premature closure of the distal radial physis has been created in juvenile dogs experimentally through irradiation, thus serving as a model for the clinical scenario.⁴⁰ Through this study, it was determined that when the distal radial physis is symmetrically insulted, the proximal physis assumes the majority of longitudinal growth in the radius, as the amount of elongation of the distal radius slows dramatically. However, this compensatory increase in growth at the level of the proximal radius falls short of maintaining appropriate overall radial length, and the radius subsequently shortens to the point where humeroradial and humeroulnar subluxation occur. With increasing space between the radial head and the capitulum of the humeral condyle, the condyle becomes cranially displaced, putting pressure on the coronoid processes of the ulna (Figure 55-5). The rapid decline in growth that occurs at the level of the distal radius also slows growth at the distal ulnar physis. The decrease in pressure on the radial head from lacking humeroradial contact results in thickening of the articular cartilage and increased growth from the proximal radial epiphysis. Although most of the dogs in this study did not develop angulation secondary to the uniform insult to the distal radial physis, concomitant distal displacement of the ulnar styloid process resulted in a varus deformity with internal rotation of the carpus in 3 of 8 dogs.⁴⁰ Despite the fact that the proximal radial physis contributes less to longitudinal radial growth than the distal physis does in normal dogs,⁸ premature closure of the proximal radial physis can result in overall radial shortening.

Radial shortening can range from being extremely pronounced to very subtle. Diagnosing and quantifying the condition can be challenging if the degree of shortening is very slight. Most imaging modalities focus on examining the radioulnar relationship at the level of the elbow joint to document the presence and severity of radial shortening. Utilizing a cadaver model, Mason et al.³⁴ determined the sensitivity and specificity of lateral radiographic projections to be 78% and 86%, respectively. They further concluded that the amount of radial shortening required to achieve 90% diagnostic sensitivity with radiographs was between 1.5 mm and 4.0 mm. Although conflicting sentiment is seen in the literature regarding the use of radiography, with some reports suggesting high sensitivity and specificity,³ the consensus resulting from most research is that more sensitive diagnostics are required to adequately assess radioulnar congruity. Conventional computed tomography (CT) has been reported to allow accurate determination of radioulnar incongruence,^22,25 but a recent report comparing both radiology and CT to arthroscopic examination of the elbow joint found the latter to be most sensitive and specific (94% and 81.9%, respectively), with the highest amount of agreement noted between individuals interpreting the images (89.8%) when diagnosing the condition of a shortened radius.⁵⁷ Attempts to mimic gross examination of the radioulnar relationship for evidence of radial shortening in a manner less invasive than arthroscopy have been investigated with the use of three-dimensional (3D) image rendering based on CT.⁴ This study determined that 3D modeling was readily achievable, and allowed the diagnosis of radioulnar incongruence when the radius was shortened by as little as 1 mm, with a sensitivity of 82%, a specificity of 100% and interobserver agreement of 87%. Thus 3D modeling can serve as a diagnostic alternative to arthroscopy.

Treatment options for radial shortening vary, depending on the severity of the condition and the age of the patient. In the absence of concurrent angulation, the goal of any surgical intervention is to reestablish radioulnar congruency at the level of the elbow joint while maintaining appropriate bone alignment. Consideration of the age of the animal is important, as young animals may outgrow the correctional measures taken, thus necessitating additional surgery. Elbow joint congruence can be reestablished by lengthening the radius or shortening the ulna. Radial lengthening can be completed acutely or gradually, and gradual elongation can be controlled or semi-controlled.

In general, gradual, dynamic elongation following the principles of distraction osteogenesis (discussed in greater detail in Chapter 41) has advantages in the young animal, as these techniques allow some adjustability to adapt to the dog’s continued growth. Semi-controlled, gradual elongation of a shortened radius (due to symmetric closure of the distal radial physis) in young dogs was reported by Mason and Baker.³⁵ This report described a transverse osteotomy of the proximal radius and the placement of separate pins in the radial metaphysis and across the humeral condyle. Elastic material was placed between the pins, thus applying a traction force on the proximal radius. Over a period of 14 days, the radial head was able to slide proximally, eventually matching the coronoid process and reestablishing contact with the humeral capitulum. Subsequent bone regeneration occurred at the osteotomy gap.³⁵ The main advantage of this technique is that there appears to be little risk that the radial head will reposition itself too far proximally, as it should cease its migration when the articular cartilage contacts the humeral capitulum. What remains unknown is how large of a defect can be treated successfully this way.

More controlled methods of gradually elongating the radius are possible and were first reported with the use of a Stader apparatus. The Stader apparatus is a type of external skeletal fixation device with a threaded connecting bar. This apparatus allows controlled distraction at the level of the osteotomized radius.³⁸ More recently, radial distraction osteogenesis has been completed with circular external skeletal fixators, and lengthening of up to 50% of the original radial length has been achieved.⁴⁵ Advantages of controlled distraction include the ability to adjust the latency, rate, and rhythm of the distraction according to the patient’s signalment and the radiographic appearance of bone regeneration within the osteotomy gap. The main disadvantage is that the proximal repositioning of the radial head is under the direction of the surgeon, and its final relationship to the ulna and humeral condyle must be confirmed through some type of imaging modality.

Treatment of radial shortening in skeletally mature dogs can be accomplished with any of the more gradual dynamic lengthening procedures. Gradual dynamic lengthening techniques may be particularly advantageous if the length discrepancy of the radius is very large. Acute distractions can be hampered by the strength of the large amount of soft tissue connection (described in anatomy section) between radius and ulna; thus dynamic distraction may be a more feasible option for stretching the soft tissues joining the two bones. However, acute one-stage radial elongations are an option in the adult dog, particularly in those with less severe radial shortening, because there is no risk that the animal will outgrow the correction. No guidelines currently exist to govern how much relative shortening necessitates gradual versus acute correction.

Acute elongation techniques involve an osteotomy of the radius, the use of bone spreaders for radial distraction, and subsequent stabilization with a bone plate or an external skeletal fixator. If a transverse osteotomy has been performed, a large bone gap and lack of load sharing with the implant may result, unless a cortical bone graft of identical size is inserted into the distracted osteotomy. An alternative technique, which provides acute radial elongation while preserving load sharing, is the completion of a sagittal sliding (or “stairstep”) osteotomy. The osteotomy is stabilized with screws placed, in lag fashion, transverse to the sagittal portion of the osteotomy. Sagittal sliding osteotomy can be performed with or without the application of a neutralization plate or external coaptation (Figure 55-6).⁵⁵ Irrespective of the technique used to perform an acute correction, confirmation that the final position of the radial head is appropriate requires radiography or, optimally, arthroscopy, following distraction.

An alternative to radial lengthening is shortening of the ulna by completion of an ulnar ostectomy.19,46 The advantage of this technique is that, if the ulnar ostectomy is completed in a dynamic fashion (without rigid fixation), the dog’s humerus will compress the ostectomized ulna to a level where the coronoid processes match the radial head during weight bearing. This technique obviates the need to move the radial head to a specific position, as occurs with any of the radial lengthening procedures. Ulnar shortening is predominantly recommended for skeletally mature animals. If attempted in puppies, the risk exists that the narrowed ostectomy gap may heal before cessation of longitudinal growth (even if slowed) of the radius, resulting in loss of elbow joint congruence yet again. A recent study suggests that when ulnar shortening is performed, the ulnar ostectomy should be performed proximal to the interosseous ligament, and an intramedullary pin should be applied to the ulna to optimize normalization of contact patterns in the elbow joint and avoid subsequent varus deformity.⁴⁶

Ulnar Shortening

Premature closure of the distal ulnar physis has been reported to be the most frequent growth plate injury in dogs, accounting for 63% of all physeal insults.⁴⁸ It is well accepted that the geometric configuration of the distal ulnar growth plate is the primary reason why the distal ulna is affected by premature physeal closure. Most physes, such as the proximal and distal radial physes, are relatively flat and thus are predisposed to shear fractures. Longitudinal growth may continue uninterrupted from these relatively flat physes, as long as the germinal cells are uninjured and remain attached to the epiphysis. However, the distal ulnar physis is conical in shape and thus is unable to shear, regardless of whether the offending force is axial or lateral in nature. Thus, excessive force applied from any direction can cause compression of one side of the conical physis, resulting in injury to the germinal cells and subsequent retardation or cessation of ulnar growth.¹⁸ Although trauma is a frequent cause of premature closure of this growth plate, the heritability of premature ulnar physeal closure as related to conformational development of specific breeds has also been reported.²⁸

Because 100% of ulnar growth distal to the elbow joint arises from the distal ulnar physis, injury to this physis frequently results in greater alteration in antebrachial morphology than injury to either of the radial physes. Retardation of growth of the distal ulnar physis can result not only in a shortened ulna but, because of intimate attachments between radius and ulna, in conformational changes in the radius. Although this is not always the case, typical changes seen in the radius subsequent to premature closure of the distal ulnar physis include shortening, procurvatum, distal valgus, and torsion. These changes occur as the radius continues to grow “around” the distal ulna, which is located caudolateral to the distal radius. The severity of these changes is dependent on the degree of ulnar growth retardation and growth potential remaining at the time of the insult. In addition to its effect on the radius, shortening of the ulna can cause humeroulnar incongruity, resulting in alteration of the trochlear notch and placement of excessive biomechanical loads on both the radial head and the anconeal process (Figure 55-7). These changes may ultimately lead to elbow joint osteoarthritis.

Pure shortening of the ulna at the level of the elbow joint can occur in the absence of closure of the distal ulnar physis. Any condition that results in radioulnar synostosis before closure of the proximal radial physis may produce a shortened ulna.³⁹ In the absence of antebrachial angulation, the main surgical treatment for a shortened ulna is a lengthening procedure. Similar to radial lengthening, surgical options include both acute and gradual techniques.

In skeletally immature patients, dynamic ulnar ostectomy has been advocated as the treatment of choice. This procedure frees the proximal aspect of the ulna, so it is no longer constrained by retarded growth of the distal physis, thereby allowing the ulna to move proximally and optimize congruency with the humerus. The act of releasing the retarding (bowstring) effect of a slower growing ulna may also prevent the worsening of coincident radial angulation if growth potential still resides in the radius. In the immature patient, ostectomy is preferable to an osteotomy if the degree of ulnar lengthening required is relatively small, in that the resulting bone gap will be larger. This larger gap will help prevent the ulna from completing osseous union before cessation of radial growth. If the ulna heals before completion of longitudinal growth of the radius, additional surgery may be required.

Following ostectomy, the proximal ulna can be guided in a semi-controlled or controlled fashion. Executing a dynamic ulnar ostectomy just distal to the coronoid processes alone utilizes a semi-controlled method, as contraction of the triceps brachii muscle group, which inserts on the olecranon, exerts a traction force on the proximal ulna and thus pulls the articular surface of the ulna into congruency with the humerus. However, numerous complications can arise with this procedure and must be considered. It is important to recognize that the pulling force of the triceps brachii muscle is not perfectly axial, but rather the triceps brachii muscle pulls on the olecranon at an angle, thereby exerting a bending moment at the level of the ostectomy. This causes bending and caudal displacement of the proximal ulna, in addition to its proximal distraction, and can result in the formation of an iatrogenic recurvatum deformity of the ulna. Two methods to counteract this bending at the proximal ulnar ostectomy site can be used, while still allowing dynamic movement of the proximal ulna. For the immature patient, the most important technique utilizes the placement of an intramedullary pin in the ulna, thus combating bending at the ostectomy site. Although used more frequently in skeletally mature patients with a simple osteotomy (discussed later), an oblique ostectomy can also be completed in a proximocaudal-distocranial fashion, such that the geometry of the ostectomy will prevent excessive displacement (Figure 55-8). Important to note with this technique, however, is that with more aggressive ostectomies (in younger patients), or with cases of more severe ulnar shortening (where the resulting gap will be larger), the resulting gap may be so great as to prohibit the ends of an oblique osteotomy from contacting one another, thus rendering the technique to combat bending nonuseful.

If completing the ostectomy with a pneumatic or battery-powered sagittal saw, it is easy to be overzealous and accidentally score the caudal cortex of the radius, which could result in the formation of a synostosing callus between the two bones. Placement of Hohmann retractors around the ulna will isolate the ulna and protect the radius while the ostectomy is completed. Further, sawing may be ceased before cutting entirely through the cranial ulnar cortex, thus allowing the ostectomy to be completed with an osteotome, again protecting the disruption of the periosteum or cortex on the caudal aspect of the adjacent radius. Despite creating an oblique ulnar ostectomy and placing an intramedullary pin, inherent instability can persist. Instability may result in the formation of an exuberant callus, which has the potential to form a bridging synostosis with the radius and to be a source of irritation because of the sparse soft tissue coverage overlying the caudal aspect of the ulna (Figure 55-9). Other complications involving the intramedullary pin include pin migration, irritation of the tendon of insertion of the triceps brachii muscle, and pin failure (Figure 55-10).

Another method used to avoid instability and recurvatum of the ostectomized ulna is completion of an ostectomy of the distal ulnar diaphysis or removal of the physis itself. This technique allows the interosseous ligament to help stabilize the ulna from the bending force created by the triceps brachii muscle, while still allowing the ulna to slide proximally. What remains unknown is the comparative efficacy of low versus high dynamic ulnar ostectomies in the skeletally immature dog in reestablishing humeroulnar congruence. When applied in vitro to compensate for the opposite condition of radial shortening, ostectomy of the ulna distal to the interosseous ligament did not allow adequate movement of the ulna in one study. Important to distinguish in this study was that the ulna was being encouraged to move distally under the weight of the dog, rather than proximally under the pull of the triceps brachii muscle, as is the desired outcome with ulnar shortening. However, another study has reported clinical success with low ulnar osteotomies for treatment of premature closure of the distal ulnar physis.²¹

When treating the skeletally immature patient with a semi-controlled dynamic ulnar ostectomy, the goal is to allow unrestricted longitudinal bone growth of the radius. Therefore, bone regeneration at the ulnar ostectomy site, before the patient reaches skeletal maturity, may limit the corrective benefit of the ostectomy procedure, and in some instances may necessitate additional surgery. Using a method to prevent premature bone regeneration at the ostectomy site may be valuable. Methods used to try to prevent the ostectomy site from healing too quickly include creation of an ostectomy gap greater than 1.5 times the diameter of the bone,*^,54 removal of all periosteum in the vicinity of the ostectomy,¹⁰ and insertion of a fat graft.⁹

Semi-controlled and controlled systems of guiding the movement of the proximal ulna are similar to what was previously discussed for the radius, including older methods of distracting fixators and using pins in both the humerus and the proximal ulna connected by an elastic band.³⁵ These methods have largely been replaced by the use of circular external skeletal fixators. Other older techniques to deal with a prematurely closed distal ulnar physis in the skeletally immature dog include distal radial physeal stapling⁴⁸ and ulnar styloid transposition with aggressive distal ulnar ostectomy.¹³

The basic principles employed with any of the dynamic ulnar ostectomy (semi-controlled and controlled) procedures can also be used for the skeletally mature animal diagnosed with humeroulnar incongruity due to a shortened ulna. However, osteotomies, rather than ostectomies, are commonly performed when the patient is mature, as early osseous union is encouraged in this situation. In addition, acute, one-stage static lengthening techniques may be used. All one-stage lengthening techniques utilize a distracted osteotomy, where the gap is maintained with a bone plate placed in bridging or buttress function, or where the gap is filled by the insertion of an autologous or autogenous cortical bone graft before plate placement. This author has also utilized a sagittal sliding osteotomy with subsequent placement of transverse cortical screws in lag fashion (Figure 55-11). As with radial lengthening, performing static ulnar elongation requires confirmation of appropriate elbow joint congruity, as the movement of the proximal ulna is under the direction of the surgeon.

Asymmetric Physeal Disturbance and Angulation During Development

Developmental abnormality resulting in pure shortening of the radius or the ulna is rare, as asymmetric physeal damage seems to occur more frequently than symmetric closure. Developmental antebrachial angulation can arise from (1) asymmetric premature closure of the physis of the proximal or distal radius or both, (2) premature closure of the distal ulnar physis with continued radial development, or (3) a combination of the two.

When an antebrachial angular limb deformity is first detected, the surgeon is faced with a number of decisions regarding timing and the type of correction to be completed. For a skeletally immature dog, the risk of performing any kind of correction before development ceases is that the angulation can return and additional surgery will be required. The alternative is to delay surgery until the animal is mature, at which time a definitive correction can be completed with no risk of subsequent reangulation. The risk of waiting is that the angulation will negatively affect the distribution of biomechanical loads placed on the joints, thereby creating stress on the joint and resulting in uneven wear of the articular surfaces. These changes can result in early-onset osteoarthritis and potential remodeling of the subchondral bone.

Making these treatment decisions can be challenging, and each case must be evaluated independently with consideration of the patient’s age and growth potential, and the nature of the angulation. For example, if a young patient is presented with premature closure of the distal ulnar physis with subsequent radial angulation, an ulnar osteotomy can be attempted to try to improve elbow joint incongruity and to release the bowstring effect of the affected ulna on radial development. However, the success rate of ulnar ostectomy as the sole treatment for premature distal ulnar physeal closure of juvenile dogs is relatively unknown. The influence of the procedure with respect to reestablishing normal antebrachial bone and joint alignment, or on the resolution of associated lameness, has never been prospectively studied in a large number of juvenile dogs. Recommendations of one small retrospective study suggest that despite diagnosing and treating affected animals at a young age (5 months), the technique was still frequently unsuccessful. Preoperative distal radial valgus greater than 25 degrees was detected in most cases unsuccessfully treated with distal ulnar ostectomy alone in this study and necessitated additional surgery, whereas those treated successfully possessed distal radial valgus less than 25 degrees.²¹ Thus, whereas ulnar ostectomy is a relatively less invasive procedure than osteotomies/ostectomies of the radius and ulna, its utility as the sole corrective procedure appears to be limited to those cases where radial valgus, procurvatum, and torsion are attributable to premature closure of the distal ulnar physis, and the radial angulation is not severe. For cases of more severe radial valgus, or when the angulation is not as previously described, but rather appears as varus, recurvatum, or internal rotation of the distal radius, then radial corrective measures are necessary. In these latter situations, it is highly likely that the distal radial physis has been damaged, thus resulting in more complex angular configurations.

Antebrachial Angular Limb Deformity Surgical Planning.: Regardless of the age of the affected dog or the method of surgical correction and fixation used, accurate localization and quantification of angular limb deformities is critical in optimizing clinical outcomes. This author has performed such localization and quantification utilizing a method of presurgical planning called the center of rotation of angulation method. The center of rotation of angulation method is discussed in Chapter 47, and that information should be used to supplement the following discussion regarding antebrachial angular limb deformity planning and correction. The primary goal of this technique is to determine the apex of the deformity or deformities (also referred to as CORAs) using the radial anatomic or mechanical axis in conjunction with the joint orientation angles as determined by orthogonal radiographs in a step-by-step process.

Step 1: If the dog has a normal contralateral antebrachium, the joint orientation lines, anatomic axis, and intersecting joint orientation angles are measured as outlined in the first section of this chapter (Figure 55-12, A) for the frontal plane. If the contralateral limb is abnormal, mean joint orientation angles (see Table 55-1) are used.

Figure 55-12 Illustrations depicting localization of the center of rotation of angulation (CORA) of an antebrachium with a uniapical angular limb deformity in the frontal plane. A, The contralateral antebrachium is used to determine the normal joint orientation angles by determining the joint orientation lines (green) and the radial anatomic axis (red). The anatomic medial proximal radial angle is denoted by *, and the anatomic lateral distal radial angle is denoted by **. B, The affected antebrachium is examined first by determining the joint orientation lines for the elbow and radiocarpal joints. Using the values of joint orientation angles as measured from the contralateral normal side, the radial anatomic axes are determined. C, The radial anatomic axes for the proximal and distal segments are completed and intersect within the cortical confines of the distal radial metaphysis. The location of this intersection demarcates the CORA. The angular magnitude of this CORA is determined (α). D, Sagittal plane (see text). The affected antebrachium is examined first by determining the joint orientation lines for the elbow and radiocarpal joints. Using the values of joint orientation angles as measured from the contralateral normal side, the radial anatomic axes are determined. These axes intersect within the cortical confines of the distal radial metaphysis. The location of this intersection demarcates the CORA in the sagittal plane. The angular magnitude of this CORA is determined (β). Note: Recall that normal procurvatum should exist, so in this case, the pathologic procurvatum should be corrected back only to whatever normal value was measured from the other side.

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