Rehabilitation following Patellar Instability

Theresa A. Chiaia

Sarah M. Baker

INTRODUCTION

Patellar dislocation is a common injury found in children and adolescents, accounting for 2% to 3% of all knee injuries.¹ Four clinical categories of patellar instability for the pediatric and adolescent population have been described to conceptualize pathology: posttraumatic, syndromic, obligatory, and fixed.² Traumatic dislocations are the most common and are then further categorized as first-time or recurrent dislocators.

There are many variables that can affect the course of postoperative rehabilitation such as the nature of the injury (traumatic or atraumatic), concomitant injuries and/or procedures, the level of dysfunction (development of compensatory patterns), the chronicity of the dysfunction, the degree of pathology, the age of the patient, and the surgical procedure. Predisposing factors must be recognized: prior history of dislocation, genetic, ligamentous laxity, skeletal dysplasias, collagen disorders, muscular imbalances, and/or faulty movement strategies.

The medial patellofemoral ligament (MPFL), a discrete component of the medial retinaculum, guides the patella to properly engage the trochlea during early knee flexion. MPFL reconstruction (MPFLR) uses allograft or autograft tissue tensioned to balance the patella within the trochlear groove—it is a soft tissue procedure which requires 12 weeks of healing (Fig. 20.1A).

A tibial tubercle transfer (TTT) is a bone procedure—an osteotomy of the tibial tubercle (Fig. 20.1B). Due to the more extensive pathology and more invasive nature of a distal realignment, or TTT, the patient will have restricted weight bearing. Once the bone has healed and patients are fully weight bearing and functioning pain free, their progression is criterion-based and individualized, much like the patient with an MPFLR. These patients are about 6 weeks behind those status post isolated MPFLR in the earlier stages due to the restricted weight bearing. This will delay the introduction of postural stability, neuromuscular (NM) control, quadriceps strengthening, and, obviously, gait training.

The following guidelines and time frames are based on an isolated MPFLR. Please note the different time frames for an MPFL (Appendix 1) versus a TTT (Appendix 2). The presence of underlying or concomitant pathology will lengthen the rehabilitation process for these patients.

PREOPERATIVE PHASE

Build a Foundation

The individual can work toward building a foundation of muscular balance prior to surgery. Emphasis will be on the core, the pelvis, hips, and quadriceps and can include postural retraining, soft tissue lengthening, progressive strengthening, and NM control. With chronic dislocators, this is achieved with a home exercise program (HEP) and/or working with a performance coach. In the case of the acute traumatic dislocator, the goal of physical therapy (PT) is to prepare the knee for surgery: control effusion, regain quadriceps function, regain full ROM, and normalize gait.

Set Realistic Expectations

Prepare the patient for the road ahead. The course of rehabilitation, with emphasis on progression of function, is discussed with the patient. If a patient is not seen preoperatively, this should be done at the initial evaluation postoperatively.

Patients tend to be more compliant and less frustrated when they understand what to expect. Realistic expectations are outlined regarding ambulation/crutches, brace, pain, activity modification, exercise progression, function, PT visits, and the patient’s goals. Ballpark time frames are discussed in the context of criterion-based progression.

Gait/Ambulation

The first inquiries we hear from the patient are related to crutches and the brace: When will I be off crutches? How long will I have to wear this brace? In the athletic individual, the first question is when can I play again?

Following MPFLR, the patient will be weight bearing as tolerated (WBAT) with the brace locked in extension for the initial 4 to 6 weeks. After 2 to 3 weeks, the patient may be ambulating without crutches as long as the knee is tolerating the load. This is determined by the absence of active swelling, well-controlled pain, return of quadriceps contraction, and progression of range of motion (ROM). With progression of quadriceps strength and NM control at the knee, the brace
will be unlocked from 0 to 60 degrees at a minimum depending on the available ROM (with increased knee flexion ROM, the brace will be opened to a greater degree); however, the patient will be returned to crutches WBAT when the brace is unlocked to help foster a normal gait pattern. Always confirm weight bearing and ROM restrictions with the surgeon because they might change based on graft choice and/or surgeon preference.

Figure 20.1. A. Medial patellofemoral ligament reconstruction incision. B. Tibial tubercle transfer incision.

Following TTT, the patient will be non-weight bearing or toe-touch weight bearing (TTWB)—depending on the surgeon’s preference—with the brace locked in extension for the initial 6 weeks. Radiographs at 6 weeks will guide the progression of weight bearing with crutches and the brace locked in extension over the course of the next 2 to 3 weeks (equals 8 weeks postoperatively). The progression of weight bearing will be guided by the surgeon. The knee’s tolerance to weight bearing is monitored. During weeks 9 and 10, the patient ambulates full weight bearing (FWB) with the brace locked in extension, devoid of an assistive device. Crutches are reintroduced when the brace is unlocked at week 11 and are used WBAT until the patient demonstrates the ability to achieve full knee extension at heel strike and tolerate adequate knee flexion and weight bearing during the loading response.

Cryotherapy

The patient is encouraged to continue to use cryotherapy throughout the rehabilitation process as the level of activity continues to change.

Activity Modification

The patient’s activity level will be guided by the knee’s tolerance, not the patient’s tolerance, to activity. This is determined by pain, swelling, ROM progression, and quadriceps function.

Therapy Visits

How many times a week do I have to come to therapy? PT visits must be managed. In this school-age population, use all resources available to the patient: the school athletic trainer, the school nurse, and school equipment.

Therapeutic Exercise

Exercise is discussed as it relates to functional progression and activity level. Progression will be based on the return of muscle balance and strategy of movement. Emphasis is on quality of movement: movement strategy, alignment, symmetry, and control.

PHASE I: PROTECTION PHASE (WEEKS 0 TO 6)

The stage is set for the rehabilitation process in this initial 6 weeks. Postoperative treatment includes a home-based program of a continuous passive motion (CPM) machine, quadriceps setting with neuromuscular electrical stimulation (NMES), and cryotherapy. Following TTT, a bone stimulator will be added to the home program. The goals of controlling pain and effusion, minimizing quadriceps inhibition, regaining knee ROM, and patellar mobility are interrelated. The patient is seen once during this phase at 3 to 4 weeks for an ROM check and progression of the HEP to include ROM in the seated position, quadriceps setting, straight-leg raise (SLR) series as tolerated— pain-free SLR in supine (with brace or without brace), hip abduction in side lying or prone, and hip extension in prone; heel raises (MPFLR) or plantarflexion with resistance bands (TTT); and gastrocnemius stretching. If ROM is less than 90 degrees, then formal PT is continued. If ROM is 90 degrees with a good end feel, then the patient continues with a home-based program until the 6-week mark.

Cryotherapy

Even minimal quadriceps effusion has been shown to inhibit quadriceps function. After dextrose saline was injected at 50 mm Hg into nonpathologic knees, quadriceps peak torque, muscle fiber conduction velocity, and root mean square of electromyography (EMG) signals of the vastus medialis were significantly decreased. After 20 minutes of ice application, quadriceps torque and muscle fiber conduction velocity significantly increased as compared to controls.³ Joint effusion can lead to increased pain and decreased ROM, so it is imperative that patients use cryotherapy immediately and often postoperatively.

Gait/Ambulation

The patient is in a brace locked in extension with an appropriate assistive device: WBAT following MPFLR and NWB following TTT.

Therapeutic Exercise

Balance and Proprioception

Weight shifting onto the operative side can be introduced with the brace locked in extension for the MPFLR patient.

Strength

Quadriceps: NMES is used for quadriceps reeducation to abate loss of quadriceps strength and control. Most research with NMES has been done with patients after ACL reconstruction but the same benefits are observed clinically.⁴

Patients are instructed in quad sets over a towel roll both with and without NMES. The use of the towel roll provides tactile feedback and minimizes fat pad irritation. The goal is to do a pain-free SLR with no lag by the end of this phase. When that is accomplished, they have demonstrated enough quad control to ambulate with brace unlocked.

Proximal and Distal: Evaluation-based gluteal strengthening is initiated. The patient can begin NWB hip strengthening including abduction while standing on the contralateral leg, then progress to side-lying hip abduction against gravity.⁵ Distal strengthening is initiated to address weaknesses and prepare for push-off.

Range of Motion

The MPFL tightens in early to midflexion and then slackens during deeper flexion after 60 degrees.⁶,⁷ A CPM is used 2 to 3 hours per day or 6 to 8 hours with a concomitant cartilage procedure. If a joint is immobilized too long, there will be a loss of ground substance and dehydration in the extracellular matrix, leading to approximation of the fibers.⁸,⁹ This approximation causes friction and the formation of adhesions. Active and passive ROM at the knee joint will reverse damaging effects of immobilization by stimulating collagen synthesis and optimizing the alignment of healing tissues.

Patients begin seated at the edge of the plinth for active-assistive range of motion (AAROM) into knee flexion. They then use the contralateral leg for passive knee extension to avoid open chain knee extension early on with quadriceps weakness and especially with cartilage injury. Communication with the surgeon is imperative in this phase if knee flexion is not progressing.

A loss of passive extension is not often seen, but full extension must be maintained via gastrocnemius and hamstring stretching and intermittent heel prop so an antalgic gait on a flexed knee does not occur.

Passive patellar mobility is assessed postoperatively to make sure there is appropriate mobility and end point. The quadrant system¹⁰ can be used for assessment, as the contralateral leg may not be a good reference if bilateral hypermobility is present. Patients will sometimes demonstrate apprehension with this due to a history of instability.

Precautions

Patellar mobilization in the lateral direction is avoided in this early phase to allow for healing; however, it is evaluated by the physical therapist to get a sense of its end point. Be cautious not to load the knee with slight knee flexion, as this is the ROM that the MPFL is most vulnerable because there is no bony stability offered by the trochlea. Following TTT, the patient must obey the restricted weight bearing because this is a bony procedure and complications are related to fixation and possible fracture through the osteotomy or screw holes.

PHASE II: GAIT PHASE (MEDIAL PATELLOFEMORAL LIGAMENT RECONSTRUCTION: WEEKS 7 TO 10; TIBIAL TUBERCLE TRANSFER: WEEKS 7 TO 12)

The goal is to foster a normalized gait pattern. The hallmark of this phase is NM control, alignment, and postural stability in single limb stance.

Control Symptoms

Monitoring the knee for active swelling and pain with resultant loss of motion and quadriceps function is necessary, as the patient’s activity level usually increases during this phase. Staying within his or her envelope of function is continually reinforced.

Standing Posture

Postural retraining with a neutral pelvis with sternal lift and soft knees with symmetrical weight bearing is reinforced throughout the day. (A simple reminder of postural checks when “texting” with friends.) Weight bearing through one hip only is discouraged as is hanging on ligaments with recurvatum in double-limb weight bearing.

Gait/Ambulation

Gait training is performed with an assistive device, or on a hydro-treadmill (with adequate wound healing) or antigravity treadmill, if available. During this time, a normal gait pattern is emphasized:

Full knee extension at heel strike. Without active knee extension ROM to 0 degree, the individual will not achieve full knee extension during heel strike and will walk with a bent knee gait. This will continually load the extensor mechanism and result in anterior knee pain.
Adequate knee flexion during loading response. Inadequate NM/eccentric control at the knee and/or pain will not allow the knee to go from knee extension to slight knee flexion during the loading response, resulting in knee extension with sinking into the hip during the loading response. This will, in essence, make the stance leg longer and lead to hip adduction and lengthening of the abductors with resultant weakness (Fig. 20.2). This gait pattern is one of quad avoidance and is often present preoperatively. It will continue postoperatively if not addressed and is often present on the contralateral limb. Decreased shock absorption is a consequence which then leads to increased loading at the tibiofemoral joint and progressive deterioration.¹³

The individual will be weaned from the assistive device as eccentric quadriceps strength and NM control improve, thereby increasing the tolerance to load and normalizing gait. The assistive device also slows the patient down and encour-ages quality of gait while discouraging quick, unpredictable movements inherent in this population. In an urban setting or school environment, the assistive device also provides a sign to others to go around. The individual may be allowed to ambulate without an assistive device in a controlled setting such as at home.

Figure 20.2. Poor NM/eccentric control during the loading response results in hip adduction.

Figure 20.3. Release of the knee at heel off to initiate swing phase. Length of two joint hip flexors is required.

Therapeutic exercise can be used to break down the gait cycle. Release of the knee at heel off (to initiate swing phase) (Fig. 20.3) and weight shift (retrostepping or forward stepping) onto involved limb with a soft knee (stance) are practiced.

Therapeutic Exercise

Neuromuscular Control and Proprioception

Reestablishing NM control at the knee joint is an important piece of the rehabilitation process and is required for full functional recovery. The objective of NM training is to improve the nervous system’s ability to generate fast and optimal muscle firing patterns and thus increase dynamic joint stability and decrease joint forces.²² This training can enhance the patient’s awareness of peripheral sensations and thus process these signals into more coordinated motor strategies. It is required during daily life and sports-specific activities. Balance training with double-limb support is introduced in the sagittal plane on a balance board, rocker board, or commercial balance system. With good alignment and NM control, single limb stance is performed on a level surface. The rehabilitation specialist must
watch for quality and ensure that the patient is not working in genu recurvatum but has a “soft knee” with the quadriceps engaged (Fig. 20.4).

Water is a good medium to practice this until full weight is tolerated on land. With enhanced NM control, the patient can hopefully protect the joint from further injury.²³

The MPFL seems to resist lateral patellar subluxation most near knee extension, and it has been shown that proprioception is of great importance to protect the joint against extreme flexion and extension movements. Enhanced proprioception will help decrease stress on a newly reconstructed MPFL near full knee extension when it is relied on the most.²⁴ It is important to consider the patient population you are working with and their preoperative status. Jerosch and Prymka²⁴ showed that patients with posttraumatic recurrent patellar dislocation had highly significant deterioration in the proprioception of the injured knee joint. Compared to controls, these patients also had a worse position sense in their uninjured contralateral leg. Because they often already have a deficit, it is even more important to train this system postoperatively.

Strength

Quality of movement is emphasized with functional strength training.

Quadriceps: Quadriceps strengthening is essential and must be performed in a pain-free arc of motion. Understanding the biomechanics of the patellofemoral joint, patellofemoral joint stress, joint reaction forces, contact areas, and, if present, the location of cartilage lesion will aid exercise prescription.¹⁶,¹⁷,¹⁸ Closed-chain quadriceps strengthening, such as leg press, is introduced at latter phase 1/early phase 2 (MPFLR) with adequate ROM and quadriceps function. The weight lifted is a delicate balance between stimulating the quadriceps muscle and not overloading the patellofemoral joint. In an effort to compensate for weakness and/or pain, a number of compensations may be observed: hip hike to open up the knee angle to decrease patellofemoral stress and high or deep foot placement on the leg press or the step, respectively, to increase use of posterior musculature (the knee is extended through the action of the hip extensors instead of the quadriceps).

Proximal: Proximal strengthening continues to progress with emphasis on the gluteus maximus, gluteus medius, and abdominals to control limb alignment.¹⁹ Non-weight-bearing hip extension with knee flexion can be performed in prone, quadruped, or bent over the side of the table until bridging and other weight-bearing exercises are tolerated. To preferentially train the gluteals while minimizing contribution from tensor fascia lata, the clamshell, side steps, unilateral bridge, and quadruped hip extension are used.²⁰ The Sahrmann²¹ deep abdominal progression can be introduced along with planks. All exercises when performed correctly should engage the core. The authors believe that Sahrmann level 3 is important for athletes to achieve.

Range of Motion/Flexibility

Progression of ROM is without limits. At 60-degree knee flexion, the patella is fully engaged in the groove and the MPFL is at its maximum length. As quadriceps control is gained, and knee flexion ROM increases to approximately 125 degrees, the patient can begin supine wall slides and a stair stretch. Short crank cycle ergometry can be initiated with 80 to 90 degrees of knee flexion. As knee flexion increases to 115 degrees, a standard upright stationary bike is tolerated.¹⁴ With increased ability on the standard stationary bike, the individual is instructed to consistently pedal at 80 revolutions per minute (RPMs) to control the compressive forces.

Figure 20.4. Single limb stance requires alignment + neuromuscular control + stability. This demonstrates NM control which is important for normal loading response.

Two joint hip flexor length must be addressed because 60 degrees of knee flexion with hip extension is required for limb advancement in gait.¹⁵ Initially, the patient can perform active knee flexion with the hip in neutral extension in prone and then in standing to begin to achieve this.

Mobility of the patella is monitored for postoperative complications such as medial subluxation, lateral subluxation, knee flexion ROM as a result of scarring, overtightening of the medial restraints, and/or an overzealous lateral release.

Precautions

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