Much of the success of microfracture surgery for articular cartilage lesions in the knee depends on what happens after the surgery is over. Progressive, controlled loading of the repaired joint is the key to safe and effective rehabilitation.
By Jon Fravel, ATC, and Michael Shaffer PT, ATC, OCS
Injuries to the articular cartilage of the knee are serious, with potentially debilitating consequences if not managed appropriately. Articular cartilage injuries can occur from either an acute traumatic event or from chronic degeneration.1 Acute traumatic injuries producing cartilage lesions are most often seen in a younger athletic population, while chronic degenerative lesions most often occur in older individuals. Articular cartilage injuries are diagnosed both by clinical exam and imaging. A positive clinical exam includes mechanical symptoms of clicking, popping, catching, effusion and warmth.
Cartilage lesions occur across a spectrum of injury. Outerbridge classification defines these as normal cartilage (grade 0), softening (grade 1), fibrillations (grade 2), fissuring (grade 3), and exposed subchondral bone (stage 4).2 Articular cartilage injuries resulting in full thickness defects to the subchondral bone have been shown to have poor healing without surgical intervention.3-5 As surgical technology has evolved, new techniques to address chondral defects have appeared. Surgical techniques fall into several broad categories: marrow stimulation, grafting, and autologous chondrocyte implantation (ACI). Microfracture, drilling, and abrasion arthroplasty are considered marrow stimulation techniques, whereas grafting includes both osteoarticular transfer system (OATS) and mosaicplasty.
Among the different surgical techniques available to address the articular cartilage of the knee, microfracture is generally considered to be the least invasive.6,7 Use of this surgical technique does not affect the surrounding anatomy of the knee, so that other techniques, such as grafting, could still be attempted should microfracture fail. This technique removes loose cartilage flaps followed by debridement of the walls of the lesion with the calcified cartilage removed down to the bony base. A microfracture awl perforates the subchondral bone to a depth of approximately 2 mm to 3 mm to induce bleeding. These perforations are separated by 2 to 4 mm. Bleeding and fat droplets are observed arthroscopically if the technique has been performed correctly. This bleeding creates a clot that will develop into the new fibrocartilage base.5,8
Appropriate candidates for microfracture surgery have been defined as young individuals with isolated lesions, no degenerative changes, and normal knee alignment. Microfracture should not follow previous surgical techniques used to repair the cartilage lesion. This treatment should not be used if there is subchondral bone loss, malalignment, other degeneration, or if the patient is suspected of being non-compliant with post-operative protocol.4,8,9
In recent years, microfracture has come to the attention of the lay public as it has been successfully used on several high profile athletes. Despite the fact that these athletes have been able to fairly quickly and successfully return to competition following microfracture, it is our belief that articular cartilage is a vital tissue for joint health, and that surgical procedures and subsequent rehabilitation techniques to address articular cartilage injuries should be regarded as serious undertakings. Although microfracture is often the first surgical choice for small, full thickness articular cartilage injuries, articular cartilage lesion healing is a difficult process and these cases should be advanced cautiously through the rehabilitation process. The rehabilitation protocol utilized at our institution and outlined in the section that follows has been adapted from that described by microfracture pioneer Richard Steadman,MD, and colleagues.10
Phase I (0-6 Weeks): Immediate post-operative care
The patient typically spends the first six weeks after microfracture on crutches, either non-weight bearing or toe touch weight bearing. Because the success of this procedure relies on the formation of a blood clot at the site of the defect, protection of the clot is paramount during this early time frame. The use of a continuous passive motion device (CPM) as a tool to assist nourishing the surrounding articular cartilage is commonly advocated.4,8,9,11-13 In the only trial investigating the use of CPM after microfracture, there was no difference in the amount of improvement, as measured by Lysholm outcome scores, between those patients who used a CPM and maintained non-weight bearing (NWB) status for the first six weeks and those patients who were allowed to bear weight as tolerated and didn’t use a CPM device.14 In our practice, a CPM is not routinely ordered for patient use at home. Instead patients are encouraged to perform a regular program of non weight-bearing, active assisted range of motion (ROM) activities. Home exercises are supplemented with the use of stationary bicycle or aquatic ROM exercises when patients come to the physical therapy clinic or athletic training room.
It is also crucial during this first phase of rehabilitation to maximize lower extremity strength and quadriceps function in particular. A strong, well functioning quadriceps muscle appears to be beneficial for healing of the fibrocartilaginous clot by absorbing ground reaction forces, which would otherwise be partially borne by the joint surfaces. However, maximizing quadriceps function in this early post operative period often proves to be a more difficult task than expected, since the patient is nonweightbearing. Therefore, the rehabilitation specialist must try to maximize quadriceps function through the use of exercises such as quadriceps sets, hip flexion straight leg raises, and/or open kinetic chain knee extension exercises. It is important to remember that if microfracture is performed on the patellar undersurface or trochlea of the femur, the clinician must be more cautious about the amount of load placed on the quadriceps as that force will be transferred through the patellofemoral articulation. In contrast, if microfracture is performed on the femoral condyles, there is no particular restriction to the use of progressive loading of the quadriceps muscle or the use of electrical stimulation if quadriceps inhibition is clinically obvious.
Phase II (6-12 weeks): Progressive strengthening and loading
The second phase of rehabilitation is marked by the gradual addition of weight bearing forces. At the two-week post-operative physician visit, many patients are measured for an unloader brace. If the patient lives at a distance or for some other reason has not already picked up this brace, the brace is typically dispensed at the six-week post-operative visit with the surgeon. At that visit, the patient is also counseled on the process to gradually wean themselves off the crutches.
Because articular cartilage is relatively aneural, pain level cannot be used to guide rehab progression, so it is important to remind the patient to use joint effusions and general knee discomfort as a guide for the progression of their weight bearing. The balancing act between appropriate progression and overloading the joint is a theme that will be repeated over the remainder of the rehabilitation period.
In order to progress from non-weight bearing to full weight bearing, the athlete must have well controlled joint effusion, maintenance of range of motion gains, and the absence of a limp. Sequentially, the patient progresses from bilateral axillary crutches to a contralateral axillary crutch and finally to full weight bearing without the use of an assistive device. If the patient is struggling with the progression to weight bearing, aquatic therapy and water walking can be very beneficial. The clinician is reminded that because of the buoyancy effect of the water, the amount of weight bearing progressively decreases as the percentage of the body is submerged.15
In the rehabilitation clinic, devices such as a leg press machine can serve as a transition between Phase I non-weightbearing isotonic machinery (knee extension and knee flexion hamstring curls) and closed chain, weight bearing exercises such as squats, step ups, lunges, etc. which are the hallmark of Phase II. The clinician has at his or her disposal the progression from bilateral to unilateral, progressive range of motion (progressive depth), and the addition of external weight as a means to progressively challenge the patient and load the joint surfaces. Conversely, the rehabilitation specialist can alter any of these factors as a means to unload the joint surfaces if the patient does demonstrate a joint effusion or other negative responses. In our practice, non-weightbearing exercises such as the straight leg series and open chain isotonic machines in Phase I are typically performed without the unloader brace, while weight bearing exercises in Phase II are typically performed with the use of the brace to help unload the repaired area.
Phase III (12-24 weeks): Neuromuscular retraining
The primary goal of the third phase of rehabilitation is to normalize neuromuscular function. This requires progressive strengthening with continuation of Phase II activities. But Phase III is also characterized by the addition of unstable surfaces and simulated sport activities to provide progressive neuromuscular challenges for the athlete (Figures 1a, 1b, 2, and 3). For instance, the basketball player must be prepared for return to competition through progressive jumping and cutting activities.
Given the importance of progressive but controlled joint loading, it is important to examine jumping more closely. Jumping imparts joint loading forces equal to 12 times body weight.16 Forces less than 12 times body weight can be imparted by jumping “up” onto a box, jumping in water, or jumping on a commercial device that simulates a leg press but utilizes elastic resistance. If the athlete is able to tolerate these forces without the development of joint effusions, progressive loads can be applied by changing the resistance of the commercial device, changing the level of the jumps (from initially jumping up, to level jumping [broad jumps], and finally jumping down from a height). The clinician can also control joint forces by progressing from bilateral to unilateral jumps on the affected limb. Table 1 outlines this jumping progression. Continuing with the example of the basketball player, each of these stages can be made more challenging from a neuromuscular standpoint by adding ball tossing activities or simulated rebounding drills.
Phase IV(> 24 weeks): Return to activity
The final phase of rehabilitation is return to activity. This is accomplished by gradually introducing the athlete into partial practices or team conditioning drills. If not already taking place, participation in team strength training sessions is a safe reintroduction to team activity. As the athlete starts to return to practice, drills involving straight ahead jogging are added first, taking care to avoid contact with a teammate or any changes of direction. If a brace is being worn at this point, which is optional, the brace may help protect the joint in addition to its intended function of unloading. Gradually the athlete is permitted to change direction, and sequentially take part in drills involving jumping, and finally contact with an opponent. Table 2 outlines the postoperative rehabilitation protocol detailed above.
As always, the presence of a knee effusion indicates that the joint is being negatively stressed with the addition of these progressive loads. “Rest days” or returning to the previous level of loading for a period of time should be utilized as needed. In the absence of effusion, athletes should be training at least twice a week at this stage, depending on their skill level. If the athlete is unable to resume impact activities for a prolonged period, the joint surfaces can be re-evaluated for gross macroscopic changes with a repeat MRI.
In summary, microfracture and the rehabilitation following this surgical procedure remain relatively new. Rehabilitation of athletes following microfracture requires knowledge of the goals of the procedure and patience on the part of the athlete and the rehabilitation specialist. The rehabilitation clinician must understand the process of progressive, controlled joint loading. The athlete must develop adequate strength and neuromuscular control to contend with joint stresses. Finally, the rehabilitation specialist needs to be vigilant about examining for joint effusions as progressive joint loading forces are applied, since effusions are an important marker of excessive joint stress.
Jon Fravel ATC is a certified athletic trainer at the University of Iowa in Iowa City. Michael Shaffer PT, ATC, OCS, is the Coordinator for Sports Rehabilitation at the Institute for Orthopaedics, Sports Medicine and Rehabilitation at the University of Iowa.
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