Individualization

One of the most important principles involving rehabilitation after articular cartilage repair procedures is the need for an individualized approach for each patient. Several variables must be considered when developing a unique rehabilitation progression for each patient. These include specifics regarding the patient, lesion, and surgery (Table 37–2).

TABLE 37-2 Specific Variables that Must be Considered when Designing Postoperative Rehabilitation Protocols after Articular Cartilage Procedures

The quality of each individual’s articular cartilage is the result of several factors including age, BMI, general health, nutrition, history of previous injuries, and genetics. The composition of articular cartilage undergoes a gradual degeneration over time that results in a breakdown of tissue matrix and a reduction in the load-bearing capacity of the cartilage.⁸ The specific factors that contribute to this deterioration remain controversial, but it appears that age, obesity, poor nutrition, and a history of repetitive impact loading (through work or sport activities) may result in osteoarthritic changes.⁸ Thus, younger patients with isolated defects and relatively healthy surrounding articular cartilage will progress more rapidly than older individuals with more degenerative changes and less dense cartilage structure. Furthermore, the patient’s motivation and previous activity levels must be considered when determining the rehabilitation approach to ensure that the goals of each patient are addressed. The rehabilitation program should be individualized to the specific demands of each patient’s activities of daily living, work, and/or sport activities.

Several variables must be considered in regard to the lesion that may have a dramatic effect on the rehabilitation process. Most important are the exact location and size of the lesion. Lesions on a weight-bearing surface of a femoral condyle must avoid deleterious compressive forces and will require a different rehabilitation approach than those located within the trochlea or undersurface of the patella, where shear forces should be avoided. Furthermore, the size, depth, and containment of each lesion must be considered. Lesions that are large or deep or that have poor containment with healthy surrounding articular cartilage may require a slightly slower rehabilitation progression to ensure that the repair tissue or graft has an adequate amount of time to heal. In addition, the patient’s lower extremity alignment must be carefully considered. A patient’s knee in a genu varum alignment with a medial compartment lesion may also require a high tibial osteotomy or an osteoarthritis unloader brace.

BMI is another factor to consider. Mithoefer and coworkers³⁰ reported a correlation between BMI and outcomes after microfracture, because the greater the BMI, the more likely the clinical outcome would be less favorable.

Lastly, the specifics of each surgical procedure will vary the rehabilitation process. Arthroscopic procedures such as chondroplasty or microfracture may progress at a different pace than those with larger incisions and greater tissue involvement, such as OATS or ACI, which require a slower rehabilitation process to protect the healing structures. Each specific surgical procedure has different biologic healing responses postoperatively, which are discussed in detail later in this chapter. Furthermore, any concomitant procedures to address alignment, stability, or meniscal function may also alter the rehabilitation program because of the need to protect other healing tissues. The importance of communication between the surgical team and the rehabilitation team cannot be overemphasized. Appropriate information regarding the specifics of each surgical procedure must be shared to ensure the highest quality of care for each individual.

Create a Healing Environment

The next principle of articular cartilage rehabilitation involves creating an environment that facilitates the healing process while avoiding potentially deleterious forces to the repair site. This involves a thorough knowledge of the physiologic repair process after surgery. Through animal studies, as well as closely monitoring the maturation of repair tissue in human patients via arthroscopic examination, the biologic phases of maturation have been identified after several articular cartilage repair procedures.^4,5,16,36,38 Knowledge of the healing and maturation process after these procedures will ensure that the repair tissue is gradually loaded and that excessive forces are not introduced too early in the healing process. These are discussed in detail in regard to each specific surgical procedure.

Two of the most important modes of rehabilitation of articular cartilage procedures are weight-bearing restrictions and range of motion (ROM) limitations. Unloading and immobilization have been shown to be deleterious to healing articular cartilage, resulting in proteoglycan loss and gradual weakening.^2,17,50 Therefore, controlled weight-bearing and ROM are essential to facilitate healing and prevent degeneration. This gradual progression has been shown to stimulate matrix production and improve the tissue’s mechanical properties.^6,7,51

Controlled compression and decompression forces observed during weight-bearing may nourish the articular cartilage and provide the necessary signals to the repair tissue to produce a matrix that will match the environmental forces.^2,17,50 A progression of partial weight-bearing with crutches is used to gradually increase the amount of load applied to the weight-bearing surfaces of the joint. The use of a pool or aquatic therapy may also be beneficial to initiate gait training and lower extremity weight-bearing exercises. The buoyancy of the water has been shown to decrease the amount of weight-bearing forces to approximately 25% of the individual’s body weight when submerged to the level of the axilla and 50% of the individual’s body weight when submerged to the level of the waist.²⁰ Commercially available devices to unload the patient’s body weight during treadmill ambulation may also be useful.

A force platform is another useful tool during the early phases of rehabilitation when weight-bearing is limited. This can be used to monitor the percentage of weight-bearing on each extremity during closed kinetic chain (CKC) exercises such as weight-shifts, mini-squats, and leg press (Fig. 37–1).

FIGURE 37-1 Exercises such as a weight-shift (A) and leg press (B) performed on a force platform (Balance Trainer, Unicam Corporation, Ramsey, NJ) that can measure the amount of weight distribution between each extremity (C).

The pool and force platforms may be used during early phases of rehabilitation to perform limited weight-bearing activities designed to facilitate a normal gait pattern and enhance strength, proprioception, and balance. The goal of these techniques is to initiate weight-bearing activities during the early protective phases of rehabilitation, rather than remain strictly non–weight-bearing and immobilized. The authors’ opinion is that beginning controlled weight-bearing activities is a critical component to the overall successful outcome of the procedure. Although the return to functional activities will differ for each patient, early initiation of controlled exercise enables the individual to return to functional activities sooner than those who are immobilized and non–weight-bearing. This may have a positive effect on patient satisfaction.

Passive range of motion (PROM) activities, such as continuous passive motion (CPM) machines or manual PROM, performed by a rehabilitation specialist are also begun immediately after surgery in a limited ROM to nourish the healing articular cartilage and prevent the formation of adhesions. Motion exercises may assist in creating a smooth low-frictional surface by sliding against the joint’s articular surface and may be an essential component in cartilage repair.^44,45 The authors’ opinion is that PROM is a safe and effective exercise to perform immediately postoperatively, with minimal disadvantageous shear or compressive forces, if done with patient relaxation. This ensures that muscular contraction does not create deleterious compressive or shearing forces. Furthermore, the use of CPM has been shown to enhance cartilage healing and long-term outcomes after articular cartilage procedures.^41,42 In a study comparing the outcomes of patients after microfracture procedures, Rodrigo and associates⁴¹ reported an 85% satisfactory outcome in patients who used a CPM machine for 6 to 8 hours per day for 8 weeks as compared with a 55% satisfactory outcome in patients who did not use a CPM machine. PROM may also be performed on an isokinetic device (Biodex Corporation, Shirley, NY) in the passive mode or with a bike with adjustable pedals that can alter the available ROM (Unicam Corporation, Ramsey, NJ) (Fig. 37–2). The authors advocate low-intensity (light-resistance) bicycling for long duration to stimulate articular cartilage regeneration.

FIGURE 37-2 Bicycle riding on a Unicam machine (A) that can adjust the pedal axis (B) to alter the range of motion performed.

Biomechanics of the Knee

The next rehabilitation principle involves the biomechanics of the tibiofemoral and patellofemoral joints during normal joint articulation. Articulation between the femoral condyle and the tibial plateau is constant throughout knee ROM. The anterior surface of each femoral condyle is in articulation with the middle aspect of the tibial plateau near full knee extension. With weight-bearing, as the knee moves into greater degrees of knee flexion, the femoral condyles progressively roll posteriorly and slide anteriorly causing the articulation to shift posteriorly on the femoral condyle and tibial plateaus.^24,28

The articulation between the inferior margin of the patella and the trochlea begins at approximately 10° to 20° of knee flexion depending on the size of the patella and the length of the patella tendon.²³ As the knee proceeds into greater degrees of flexion, the contact area of the patellofemoral joint moves proximally along the patella. At 30°, the area of patellofemoral contact (inferior facets) is approximately 2 cm².²³ The area of contact gradually increases as the knee is flexed. At 60° of knee flexion, the middle facets of the patella articulate with the trochlea. At 90° of knee flexion, the contact area increases up to 6 cm² and the superior facets articulate.²³

Using this knowledge of joint arthrokinematics, the rate of weight-bearing, PROM, and exercise progression may be based on the exact location of the lesion (Fig. 37–3).^3,12,14,15 For example, a patient with a lesion on the anterior aspect of the femoral condyle may perform exercises into deeper degrees of knee flexion without causing articulation at the repair site. Conversely, lesions on the posterior condyle may require the avoidance of exercise in deep knee flexion owing to the rolling and sliding component of the articulation during deeper knee flexion. Furthermore, the rehabilitation program for lesions on a non–weight-bearing surface, such as the trochlea, may include immediate partial weight-bearing with a brace locked in full knee extension without causing excessive compression on the repair site.

FIGURE 37-3 A, The lesion location diagram from the International Knee Documentation Committee evaluation form used to document the location of articular cartilage lesions on the patella, trochlea, and femoral condyles. This form may be used to correlate with the exact location of lesion articulation with the patella (B), trochlea (C), and femoral condyles (D). The diagrams represent the point of articulation of the patellofemoral and tibiofemoral joints at various degrees of knee range of motion. Surface displacements (mm) and surface stresses (MPa) at 45° and 90° of knee flexion are depicted on D.

(A, Reprinted with permission from the International Knee Documentation Committee; B and C, Reprinted with permission from McConnell, J.; Fulkerson, J.: The knee: patellofemoral and soft tissue injuries. In Zachazewski, J. E.; Magee, D. J.; Quillen, W. S. [eds.]: Athletic Injuries and Rehabilitation. Philadelphia: W. B. Saunders, 1996; pp. 693-729; D, Reprinted with permission from Blankevoort, L.; Kuiper, J. H.; Huiskes, R.; Grootenboer, H. J.: Articular contact in a three-dimensional model of the knee. J Biomech 24:1019–1031, 1991.)

Rehabilitation exercises are altered based on the biomechanics of the knee to avoid excessive compressive or shearing forces. Whereas the exact ROM in which articulation of the lesion occurs is the most important factor to consider when designing the rehabilitation program, the amount of compressive and shear forces observed at the joint also vary throughout the ROM. Open kinetic chain (OKC) exercises, such as knee extension, are commonly performed from 90° to 40° of knee flexion. This ROM provides the lowest amount of patellofemoral joint reaction forces while exhibiting the greatest amount of patellofemoral contact area,^22,23,49 thus distributing the force along a greater surface area. CKC exercises such as the leg press, vertical squats, lateral step-ups, and wall-squats are performed initially from 0° to 30° and then progressed to 0° to 60° where tibiofemoral and patellofemoral joint reaction forces are lowered.^22,23,49 Clinically, these exercises are begun using a leg press machine rather than the vertical mini-squat owing to the ability to control the amount of weight applied to the lower extremities in the horizontal position in comparison with the vertical squat. As the repair site heals and symptoms subside, the ROM in which exercises are performed is progressed to allow greater muscle strengthening in a larger arc of motion. Exercises are progressed based on the patient’s symptoms and the clinical assessment of swelling and crepitation.

Reduce Pain and Effusion

Numerous authors have studied the effect of pain and joint effusion on muscle inhibition. A progressive decrease in volitional quadriceps activity has been noted as the knee exhibits increased pain and distention.^48,52 Therefore, the reduction in knee joint pain and swelling is crucial to minimize this reflexive inhibition and restore normal quadriceps activity. Furthermore, any increase in intra-articular joint temperature has been shown to stimulate proteoglytic enzyme activity, which has a detrimental effect on articular cartilage.^21,34

Treatment options for swelling reduction include cryotherapy, elevation, high-voltage stimulation, and joint compression through the use of a knee sleeve or compression wrap (Fig. 37–4). Patients presenting with chronic joint effusion may also benefit from a knee sleeve or compression wrap to apply constant pressure while performing everyday activities in an attempt to minimize the development of further effusion (Fig. 37–5).

FIGURE 37-4 Cryotherapy and intermittent compression applied through a commercial cold device (Gameready, Coolsystems Corporation, Berkeley, CA) with elevation and high-voltage electrical stimulation (300PV, Empi Corporation, St. Paul, MN) for swelling control.

FIGURE 37-5 A, Knee compression sleeve (Bauerfeind Corp, Atlanta, GA). B, Compression sleeve (DJ Orthopaedics, Carlsbad, CA).

Pain can be reduced passively through the use of cryotherapy, transcutaneous electrical nerve stimulation, and analgesic medication. Immediately after injury or surgery, the use of a commercial cold wrap can be extremely beneficial. PROM may also provide neuromodulation of pain during acute or exacerbated conditions.⁴³

Restore Soft Tissue Balance

One of the most important aspects of articular cartilage rehabilitation involves the avoidance of arthrofibrosis, particularly with the OATS and ACI procedures, owing to the large open incision and extensive soft tissue trauma. This is achieved through the restoration of full passive knee extension, patellar mobility, and soft tissue flexibility of the knee and entire lower extremity. The inability to fully extend the knee results in abnormal joint arthrokinematics and subsequent increases in patellofemoral and tibiofemoral joint contact pressure, increased strain on the quadriceps muscle, and muscular fatigue.³⁵ Therefore, a drop-lock postoperative knee brace locked into 0° of extension is used during ambulation, and PROM out of the brace is performed immediately after surgery.

The goal is to achieve at least 0° of knee extension within the first few days after surgery. Specific exercises include manual PROM exercises performed by the rehabilitation specialist, supine hamstring stretches with a wedge under the heel, and gastrocnemius stretching with a towel. Overpressure of 6 to 12 pounds may be used for a low-load long-duration stretch as needed to achieve full extension (Fig. 37–6). Patients are instructed to perform low, long-duration stretches for 10 to 12 minutes several times each day (usually five to six times per day). Modalities such as moist heat and ultrasound may also be applied to facilitate greater ROM improvements before and/or during these stretching techniques.^25,40

FIGURE 37-6 Low-load long-duration stretching into knee extension using 8 to 10 pounds of overpressure. A wedge is applied under the heel to facilitate full extension (ERMI device, Get Motion Corporation, Atlanta, GA).

The loss of patellar mobility after surgery may be due to various reasons including excessive scar tissue adhesions from the incision anteriorly as well as along the medial and lateral gutters. The loss of patellar mobility may result in ROM complications and difficulty in recruiting a quadriceps contraction. Patellar mobilizations in the medial-lateral and superior-inferior directions are performed by the rehabilitation specialist and independently by the patient during his or her home exercise program.

Soft tissue flexibility and pliability are also important for the entire lower extremity. Soft tissue mobilization and scar management are performed to prevent the development of adhesions around the anterior, medial, and lateral aspects of the knee. In addition, flexibility exercises are performed for the entire lower extremity including the hamstrings, hip, and calf musculature. As ROM improves and the lesion begins to heal, quadriceps stretching may be performed as tolerated by the patient.

Restore Muscle Function

The next principle involves restoring muscle function of the lower extremity. As previously stated, inhibition of the quadriceps muscle is a common clinical enigma in the presence of pain and effusion during the acute phases of rehabilitation. Electrical muscle stimulation (EMS) and biofeedback are often incorporated with therapeutic exercises to facilitate the active contraction of the quadriceps musculature (Fig. 37–7A).

FIGURE 37-7 Neuromuscular electrical stimulation (300PV, Empi Corporation, St. Paul, MN) applied to the quadriceps muscle (A) during exercises such as knee extension (B).

EMS and biofeedback on the quadriceps musculature appear to facilitate the return of muscle activation and may be valuable additions to therapeutic exercises.^9,46 Clinically, EMS is begun immediately after surgery while the patient performs isometric and isotonic exercises such as quadriceps sets, straight leg raises, hip adduction and abduction, and knee extensions (see Fig. 37–7B). EMS is used before biofeedback when the patient presents acutely with the inability to activate the quadriceps musculature. EMS is useful to attempt to recruit a maximum amount of muscle fibers during active contraction and may be used throughout the rehabilitation process. Once independent muscle activation is present, biofeedback may also be incorporated to facilitate further neuromuscular activation of the quadriceps. The patient must concentrate on neuromuscular control to independently activate the quadriceps during rehabilitation. The quadriceps and the hip/core muscles are emphasized to assist in dissipating ground reaction forces.

Exercises that strengthen the entire lower extremity, such as machine weights and CKC exercises, may be included as the patient progresses to more advanced phases of rehabilitation. It is important that total leg strength be emphasized rather than concentrating solely on the quadriceps. Furthermore, the importance of incorporating core stability exercises cannot be overlooked. Training of the core, hip, and ankle located proximally and distally along the kinetic chain is emphasized to assist in controlling the production and dissipation of forces in the knee. In addition, the hip and ankle assist in controlling abduction and adduction moments at the knee joint.

Enhance Proprioception and Neuromuscular Control

Proprioceptive and neuromuscular control drills of the lower extremities should be included to restore dynamic stabilization of the knee joint postoperatively. Proprioceptive deficits have been noted in the injured and postoperative knee.^10,39 Specific drills initially include weight-shifting side-to-side, weight-shifting diagonally, mini-squats, and mini-squats on an unstable surface such as a tilt board (Fig. 37–8). Perturbations can be added to challenge the neuromuscular system as well as additional exercises including lunges, step-ups, and balance onto unstable surfaces (Figs. 37–9 and 37–10).

FIGURE 37-8 A and B, Mini-squats on an unstable surface such as a tiltboard. The patient is instructed to squat while preventing movement of the board.

FIGURE 37-9 Single-leg balance on an unstable surface such as foam. The patient may use a weighted ball while performing reciprocal movement patterns with the uninvolved upper and lower extremities to alter the center of gravity throughout the exercise.