An in-depth examination of the recovery process
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The cranial cruciate ligament (CCL) has several mechanical roles. It counters hyperextension, internal rotation, and cranial translation of the tibia relative to the femur and provides important proprioceptive feedback for neuromuscular control of the limb.1-5 Deficiency in the ligament is nearly always degenerative in dogs, progressing toward ligament laxity, joint instability, inflammation, pain, and osteoarthritis.2 Consequently, canine CCL disease alters both kinetic (weight-bearing forces) and kinematic (motion) properties of the normal hindlimb, resulting in lameness. A deeper understanding of the normal canine physiology and anatomy allow for the development of more targeted physiotherapy protocols.
The knee consists of both passive and active stabilizers.2 Examples of passive stabilizers include ligaments, joint capsule, menisci, adhesion/cohesion properties of joint fluid, and finite joint volume. Active stabilization is provided by the surrounding muscle and tendon units. The role of proprioception is vital for active stability and relies in part on information from mechanoreceptors within the soft tissues of joints including the capsule, ligaments, menisci, surrounding muscle/tendon units, and associated skin.2 These proprioceptors provide afferent feedback to the central nervous system regarding joint and limb position and velocity, contributing to spinal reflexes and supraspinal motor control on both the conscious and unconscious level. Active stabilization may be further enhanced by feed-forward mechanisms such as sight and conscious anticipation of a certain movements during specific activities, work, or sport.6 Mechanoreceptors have been identified in the canine CCL and tend to be concentrated in the proximal third of the ligament.7 CCL stretch elicits reflexive hamstring contraction in people, and a similar reflex may be present in dogs. The hamstring group has been identified as agonists of the CCL in both people and dogs during mechanical testing.8,9 Dogs with CCL deficiency have been shown to have a decreased hamstring contraction and those dogs with deafferent hindlimbs have more rapid progression of osteoarthritis when already CCL deficient.1,10 In other words, dogs lacking proprioceptive feedback from their CCL have poor neuromuscular joint control and osteoarthritis progresses more rapidly.
The ideal solution for dogs suffering from CCL disease remains surgical stabilization whenever possible. Standard surgical solutions for dog CCL disease differ from those for the human ACL. As direct ligament replacement in dogs fails to provide ideal outcomes, other interventions such as tibial plateau leveling osteotomy (TPLO) or a type of extracapsular repair are used to minimize instability.2,3 Even in those surgeries providing consistently good clinical outcomes, some degree of residual instability remains.2,11 Furthermore, not all surgical interventions address the CCL’s role countering medial rotation or hyperextension.2,11 To accomplish good clinical outcomes, the current surgeries must alter kinetic and kinematic parameters of the normal knee.3,12-15 For all these reasons, rehabilitation aimed at improving active stabilization by re-education of proprioception and neuromuscular control should nicely augment surgery to further optimize outcomes.
To best suit the patient, physical therapy targeting the hamstring groups, especially the biceps femoris, may help reduce unwanted or remaining translational, internal rotational, and hyperextensive movements.4,16 Furthermore, some patients are not surgical candidates for medical or financial reasons and may benefit more with the addition of physical therapy. In fact, weight loss and targeted therapeutic exercise increased function including objective peak vertical force measurements in a group of overweight dogs with CCL disease that did not undergo surgery.17 Human physiotherapy for ACL deficiency or postsurgical rehabilitation often targets the hamstring group and begins with open-chain (non–weight-bearing) concentric contractions and moves toward lower load eccentric contractions in midrange of motion.18 Unfortunately, studies describing CCL rehabilitation in dogs lack well-defined and repeatable protocols, have often not been prospective or controlled, and have variability in the type of surgery, study timeline, outcome measures, patient cohort, and exercise routine.17,19-23 On the other hand, none of the published canine studies report increased complications associated with rehabilitation and most of them demonstrate some benefit when assessing outcome measures such as range of motion, weight bearing, and strength.
Without further prospective research into canine rehabilitation for cruciate deficiency, we cannot confidently define nonsurgical or postoperative protocols; however, our understanding of the biomechanics of the stifle joint, its neuromuscular control, and insight into human physiotherapy provide a foundation to make reasonable recommendations.
Beyond a diagnosis, this clinician identifies impairments such as atrophy or loss of extension, as well as functional limitations such as inability to sit with a normal posture (abducts affected leg during sit test). Physiotherapy goals and exercises are then created to address these impairments and limitations. For example, in a TPLO repair we may have atrophy, disuse, incomplete extension of the stifle, pain, and postoperative inflammation. Physiotherapy may target this with oral analgesia, cryotherapy, passive or active range of motion exercise, strengthening exercises, and activities that encourage limb use.13 Given the known role of the hamstring group in stifle stability, many of the strengthening exercises will preferentially target these muscles and begin with isometric and concentric loading before moving toward eccentric loading. Examples of isometric and concentric hamstring contractions in dogs include weight shifting while standing, Cavaletti rails, and underwater treadmill. Examples of eccentric hamstring contractions include sitting down and walking backward; progressing toward performing these exercises while facing up an incline increases their load and intensity. Lastly, we must adjust our exercise therapy as the patient improves, which requires periodic reassessment. More advanced strengthening and proprioceptive activity is typically initiated once the patient attains the desired postoperative healing and has achieved certain goals set by the rehabilitation specialist such as jogging pain-free, climbing stairs normally without pain, bearing equal weight at a trot, etc. Working and sporting dogs require further consideration and longer duration of staged rehabilitation.
The number of exercises given for home therapy must be safe and catered to both the client and patient. I typically find that leash-walking combined with 2 or 3 other activities is the maximum weekly home regimen in which we may expect 60% to 80% compliance. Additionally, scheduling the rehabilitation rechecks with the surgical rechecks or imaging furthers this compliance and allows the client or patient to progress into or continue an active hospital/clinical program in addition to home PT. Below I have included a fairly generic example of a home TPLO postoperative rehabilitation program with the exercises described. It remains important to remember that some dogs may have different problems and comorbidities such as weight, endocrine, cardiac, or other orthopedic/neurological disease that would warrant a more individually catered protocol.
These are general recommendations of therapeutic exercises to assist the typical patient during recovery from TPLO surgery on a single leg. These instructions assume normal progress in an otherwise healthy patient without any compensatory orthopedic abnormalities. These recommendations are not patient or client specific and therefore cannot necessarily be expected to provide an optimal recovery situation, but they are a good starting point if your dog is recovering in a typical fashion. If during recovery your dog is having difficulties using the surgical limb, it’s best to recheck with your surgeon and/or seek advice from a canine rehabilitation expert after discussing progress with your surgeon.
From now until instructed otherwise, it is essential to restrict any exercise that is not specifically addressed as part of the patient’s physical therapy protocol. Often, patients will begin feeling better before healing is complete. All postoperative patients should adhere to the activity restriction guidelines provided by their surgical team. We understand that these may be difficult, but it is imperative for complete healing without complications.
At 8 weeks, the patient should recheck with their surgical team to ensure appropriate healing of the surgical site including postoperative imaging. If the x-rays show proper healing of the bone, more aggressive strengthening exercises may be added to his protocol.