5.1 Introduction

Cranial cruciate ligament (CCL) injuries can occur at any age. In immature dogs, avulsion of the femoral origin from the lateral condyle or more commonly the tibial insertion may be seen. In cases of acute avulsion, internal fixation may be used to reattach the avulsed fragment, but in more chronic cases, contracture of the ligament fibers makes anatomical reduction and stabilization impossible.

The positive effects of tibial plateau leveling osteotomy (TPLO) in the CCL‐deficient stifle have been demonstrated [1–7], but this procedure is not appropriate in skeletally immature dogs due to the presence of an open proximal tibial physis. Tibial wedge osteotomy (TWO) or CORA‐based leveling osteotomy (CBLO) may be performed distal to the open physis in these dogs in an effort to reduce the tibial plateau angle (TPA), but both procedures require osteotomies [8].

Proximal tibial epiphysiodesis (PTE) was devised by Barclay Slocum in 1997 and described in a posthumously published case report in 2003 [9], in which a screw was inserted in the center of the cranial aspect of the tibial plateau of a 5‐month‐old Akita Inu with CCL failure in an attempt to restrict progressive increase in TPA as growth proceeds, thereby achieving the same effect of the TPLO without the need for an osteotomy (Figure 5.1). The cranial location of the screw (at the insertion site of the CCL) results in arrested growth in the cranial portion of the proximal tibia while the caudal portion proceeds normally, resulting in a significant decrease in TPA as growth progresses.

The author (AV) has performed PTE in 22 stifles, the results of which were reported in 2008 [10]. Since that time, an additional 24 stifles in 21 dogs have been treated (Table 5.1). The amount of leveling achieved at skeletal maturity was related to the age at which the procedure was performed, with greater correction achieved in dogs 4–5 months of age and less correction noted at 6 months of age. When the procedure was performed in dogs aged 7 months or greater, the degree of correction achieved was usually not enough to counteract the cranial tibial thrust. In a study published in 2010 to determine growth of the proximal tibial physis in the Labrador Retriever, a breed at risk for CCL rupture, PTE performed at 18 weeks of age should achieve the desired TPA target of 5° [11]. Although growth and the effect of PTE on a month‐to‐month basis are somewhat unpredictable because growth of individual dogs follows a model of saltation and stasis, the end effect was relatively consistent.

In clinical cases, 65% of the total correction achieved at skeletal maturity was obtained during the first month after surgery (Figures 5.2 and 5.3). Therefore, it appears that the rapid growth phase that occurs between 4 and 6 months of age is the timeframe during which PTE has the greatest chance of success. PTE has also been used as treatment for a proximal physeal tibial fracture in a dog [12].

5.2 Identification of Potential Complications

Complications specific to PTE may be mitigated by ensuring appropriate case selection and thorough understanding of proper surgical technique. As previously discussed, the outcome of the procedure is closely related to patient age at the time of surgery. Patients undergoing PTE at >6.5 months of age may be at risk for insufficient TPA leveling, resulting in failure to neutralize cranial tibial thrust and potentially requiring an osteotomy procedure for further correction when maturity is reached. Conversely, performing the procedure in dogs <5 months of age may result in overcorrection of the TPA.

The surgeon must also be aware of the potential for complications secondary to inappropriate screw placement. These include the development of a varus or valgus deformity resulting from eccentric screw placement and/or an insufficient leveling effect resulting from an excessively cranial screw placement or failure of the screw head to engage the tibial plateau (e.g., screw placement is either too superficial or too deep).

5.3 Preoperative Planning Strategies

Appropriately positioned stifle radiographs are required prior to performing surgery. These should include a mediolateral projection of the stifle in a neutral position for preoperative TPA measurement and determination of required screw length (Figure 5.4), an additional mediolateral projection with the stifle moderately flexed while undergoing the tibial compression test (TCT) for confirmation of cranial tibial subluxation when loaded (Figure 5.5), and a craniocaudal projection with the x‐ray beam centered on the tibial plateau for measurement of the mechanical medial proximal tibial angle (mMPTA) (Figure 5.6).

In addition to their use in preoperative planning, the radiographs may also be used to diagnose CCL avulsion, as evidenced by the presence of an intraarticular bone fragment and a radiolucency at either the origin or insertion of the CCL (Figures 5.7 and 5.8). Even if this is not present, it is imperative to ensure that a complete orthopedic examination has been performed to fully assess the integrity of the CCL. Diagnosis of a partial tear is based upon the presence of a slightly positive cranial drawer sign and TCT with the knee held in moderate flexion, even if these tests are negative when the knee is in extension (Figure 5.5). The presence of a complete CCL tear is confirmed by a positive cranial drawer sign and TCT with the knee in extension (Figure 5.9). These diagnoses may be further confirmed by evaluating the radiographs for cranial displacement of the infrapatellar fat pad (on the mediolateral view), increased intraarticular density of the caudal aspect of the joint, and the presence of cranial tibial subluxation.

When the stifle is examined both orthopedically and radiographically, it is important to keep other, less common differential diagnoses in mind. These include tearing of the caudal cruciate ligament, in which femoral avulsion of the ligament results in some degree of caudal tibial subluxation together with a caudal drawer sign (Figure 5.10); osteochondrosis/osteochondritis dissecans (OC/OCD) lesions of the medial or lateral femoral condyle (Figure 5.11); and avulsion of the long digital extensor (LDE) tendon (Figure 5.12).

5.4 Surgical Technique

Due to the importance of accurate screw placement, access to fluoroscopy should be considered a mandatory prerequisite for PTE. The detailed use and safety precautions specific to this imaging modality are beyond the scope of the present chapter, but surgeons should familiarize themselves with this information prior to proceeding.

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