Surgical Techniques in Sports Medicine
1st Edition

The microfracture technique was initially developed by the senior author (JRS) in the mid-1980s to treat full thickness cartilage defects in the knee. These defects are common and have been shown rarely to heal spontaneously.^1,2 The microfracture technique has been modified to its current format over the past 20 years and has been used to treat cartilage lesions in the hip, talus, elbow, and shoulder.^3,4,5,7 The procedure began with puncture holes created in exposed bone with a simple awl. The most dramatic modification in technique came after animal studies revealed the importance of removal of the calcified cartilage layer.⁸ The other significant modifications also involve bed preparation, as discussed below. The rehabilitation protocol has remained essentially the same aside from minor modifications and is also described below.

Indications for microfracture chondroplasty include full thickness articular cartilage defects in the weight-bearing area between the tibia and femur or in the contact area between the patella and femoral condyles.^9,10 Unstable cartilage flaps in these regions that extend to the subchondral bone are also lesions that are suitable for the microfracture technique. Microfracture can be performed on any size lesion, but Steadman et al.¹⁰ reported trends of better results with lesions smaller than 400 mm² without statistical significance. It is preferable, but not required, to have articular cartilage surrounding the lesion that forms an appropriate border for the lesion rather than a lesion that gradually transitions to a full thickness defect. These borders provide some degree of protection and containment for the marrow elements and clot that provide the repair tissue.

Patients with acute injuries to the knee that result in full thickness cartilage loss are treated as soon as appropriate and practical. Patients with chronic lesions or degenerative lesions in the knee are treated conservatively initially for a period of at least 12 weeks. Conservative management for these types of lesions includes: activity modification, physical therapy, nonsteroidal anti-inflammatory medications, and joint injections, as appropriate. Patients who have failed conservative treatment for chronic or degenerative lesions then become candidates for microfracture.

Microfracture should only be performed in patients who are able and willing to undergo the specified postoperative rehabilitation described below. Patients who are unreliable or are unable to complete the rehabilitation required are less likely to benefit from the procedure. Another relative contraindication is malalignment, which could leave the regenerating region under inappropriately high stress during the early phase of repair when the tissue is less durable.¹¹ Advanced age can be a relative contraindication if completion of the rehabilitation protocol is not possible, and it has been demonstrated that age is significant in outcome after microfracture.^9,12 Generalized degenerative changes, inflammatory arthritis, and unstable knees are also relative contraindications. None of these are absolute contraindications because of the low morbidity associated with the procedure, but appropriate patient expectations must be created before the procedure is undertaken.^{9,10,12,13,14}

Microfracture can be performed on patients with either regional or general anesthesia. Microfracture under local
anesthesia with sedation has not been studied and should be used with care because of the potentially adverse environment created by the local analgesia.

We place our patients in a supine position on a standard operating room table for knee arthroscopy. We apply a tourniquet but generally do not inflate it for microfracture procedures.

Standard arthroscopic portals can be used for microfracture. We make three portals: a superior and medially placed inflow portal and medial and lateral parapatellar portals. Accessory portals are occasionally made as needed for lesions in difficult locations. We perform a standard and thorough diagnostic arthroscopy of the knee prior to microfracture. If other pathology is present in the knee that requires treatment, we complete such treatment prior to microfracture, with the exception of ligament reconstruction. This technique decreases the amount of time that the microfractured bone is exposed to the elevated intra-articular pressures and fluid flow that can decrease the formation of the clot, which is critical to success.

Once a lesion is identified for microfracture (Fig. 58-1), it is probed thoroughly to ensure that all bordering cartilage is stable (Fig. 58-2). It is then debrided of all loose flaps of cartilage using a shaver (Fig. 58-3). Creation of stable full-thickness borders of cartilage surrounding a central lesion is optimal for microfracture as it provides some degree of protection to the regenerating tissue that is forming in the treated lesion. All loose cartilage and cartilage flaps should be removed regardless of border conditions.

The removal of the calcified cartilage layer is important and is usually performed carefully using a hand held curette (Fig. 58-4).⁸ Care must be taken at this stage. Subchondral bone destabilization or loss of the articular morphology results from overly aggressive debridement. Debridement and bed preparation that are inadequate will leave cartilage on the underlying bone, potentially inhibiting the regeneration process.⁸

After the bed is prepared (Fig. 58-5), arthroscopic awls are used to complete the microfracture chondroplasty. These specifically designed manual devices are used rather than powered devices to minimize thermal damage to the surrounding tissue and maximize control. A 30- or 45-degree device is most commonly employed, but 90-degree awls are also used (most commonly on the patella). The awls are advanced through the subchondral bone to create multiple small holes or “microfractures” to a depth that allows the return of fat droplets or blood from the cancellous bone. The depth required is typically 2 to 4 mm. The holes in the bone are made as close together as possible without breaking one into the next. A mallet is generally used with the awls to produce these holes, but manual advancement of the awls is sometimes helpful and should be used at all times with the 90-degree awl. The peripheral microfractures are made first at the junction of the surrounding cartilage and the exposed bone (Fig. 58-6). Finally, the central holes are made to complete the grid (Fig. 58-7).

The microfracture awl produces a roughened surface in the subchondral bone to which the marrow clot can adhere more easily. The integrity of the subchondral plate is also maintained during this process when done correctly. Microfracture chondroplasty using awls virtually eliminates thermal necrosis that could occur with power drills. The various awls with different angles also allow subchondral penetration at all locations within the knee. The awls provide not only perpendicular holes but also improved control of depth penetration compared to drilling.

After all holes are made, the arthroscopic fluid pump pressure should be reduced and the entire microfracture grid should be observed (Figs. 58-8 and 58-9) for bleeding and fat
droplet leakage into the joint from each hole. If blood and marrow contents are noted to return to the joint, the holes are sufficiently deep. If there is no return to the joint, the holes can be deepened and rechecked.

Once the microfracture is complete, the arthroscopic equipment is removed from the joint. Intra-articular drains should not be used because the goal of the procedure is to keep the marrow clot in the joint at the site of the lesion. We close all portal sites with an absorbable suture and dress the wounds appropriately. We use a cooling device in nearly all patients as a component of the postoperative therapy.

Alternatives to the microfracture procedure are numerous and include autogenous chondrocyte implantation, osteochondral autograft transplantation, osteochondral allograft transplantation, simple chondroplasty without microfracture, limited or total arthroplasty, or continued conservative treatment. The appropriate procedure to perform will depend on the patient and the defect.¹⁵ Microfracture has many advantages. The results obtained with the microfracture technique have been shown to be reliable and durable.^9,10,14 The procedure is technically relatively simple when compared to autograft placement, autologous chondrocyte implantation (ACI), or allograft placement.^12,16,17,18 There is no requirement for arthrotomy or multiple procedures with the microfracture technique. Simple chondroplasty or debridement-type procedures have not been shown to be effective.¹⁹

Pitfalls and complications are rare, usually resolve within a short period of time, and are generally not severe.^{9,10,12,13,14} Patients will occasionally experience transient pain, most commonly after microfracture in the patellofemoral joint.¹³ Clicking, catching, or gritty sensations have also occasionally been noticed after microfracture. Usually these symptoms are transient and not associated with pain. Effusions in the knee after microfracture usually resolve within 2 months after surgery, but effusions and swelling may recur when the patient begins weight bearing after the initial period of limited weight bearing. The effusions are also generally self-limiting and usually do not require treatment.

Care must be taken during the operative procedure not to debride stable cartilage and not to destabilize or alter the geometry of the subchondral bone. It is equally important, however, to debride all cartilage including the calcified cartilage layer in lesions to be treated. Care should be exercised with the awls and motorized shaver as well. Awls can skive during the procedure, resulting in injury to surrounding healthy cartilage or fracture of one hole into another. The most common pitfall associated with microfracture is not an operative one, but rather it is incomplete or inappropriate rehabilitation.

The rehabilitation program after the microfracture procedure is critical to its success.^{9,10,13,14,20} The postoperative protocol is designed to provide the optimal environment for the differentiation of the marrow elements and the production of the extracellular matrix. These two processes are intimately involved in the generation of durable repair tissue.

The rehabilitation protocol is also frequently modified for specific patients. Patients that have concurrent surgical procedures will most often complete some variation of our two main programs, which are detailed below.

Rehabilitation after microfracture of lesions in the weight-bearing regions of the femur or tibia is different from that after microfracture of lesions in the contact area of the patellofemoral articulation.^10,20 After microfracture of lesions on the weight-bearing surfaces of the femoral condyles or tibial plateaus, continuous passive motion (CPM) is started immediately after surgery in the recovery room. The initial range of motion (ROM) typically is 30 degrees to 70 degrees, and then it is increased as tolerated by 10 degrees to 20 degrees until full passive ROM is achieved. The rate of the machine is usually one cycle per minute, but the rate can be varied based on patient preference and comfort. We apply the CPM during the night for those who tolerate its use at night and exclusively during the day for those who do not have night tolerance. The goal is to use the CPM for 6 to 8 hours every 24 hours. If a CPM is unavailable or not appropriate for some other reason, we will instruct the patient to undergo approximately 500 cycles of passive ROM three times daily. Full passive motion is achieved in all cases as soon as possible.

Patients with weight-bearing lesions are also prescribed toe-touch weight bearing with crutches for 6 to 8 weeks. This regimen may be modified for small lesions, but caution must be taken when decreasing this period because of the fragility of the newly formed and immature repair tissue.¹¹ We generally do not use a brace for these patients during the immediate postoperative period, but we often use braces to unload the treated regions after the initial postoperative period as the patient begins to increase activity levels.

Patients begin stationary biking without resistance and a deep-water exercise program at 1 to 2 weeks after microfracture. The deep-water exercises include use of a kick board and a flotation vest for deep-water running. Patients progress to full weight bearing after 8 weeks and begin a more vigorous program of active motion of the knee and strengthening of the periarticular muscles. They also begin elastic resistance cord exercises at approximately 8 weeks after microfracture. We generally allow patients to begin weight training after they have reached an appropriate level with the above-described protocol, but not before 16 weeks postoperatively. If patients are to consider weight training, we emphasize proper form and an interval type program. Athletes will return to sports involving cutting or pivoting at 4 to 6 months after microfracture.

Rehabilitation after microfracture of lesions in the patellofemoral is significantly different from that after microfracture in a weight-bearing region. Patients who have undergone microfracture in the patellofemoral joint are treated in a locking brace with flexion limited to 20 degrees for at least 8 weeks. We limit the motion of the knee in these patients to 20 degrees in order to eliminate shear forces across the treated lesion that would occur at increased flexion angles with active quadriceps function during walking. We allow removal or unlocking of the brace only for passive range of motion and utilization of the CPM. These patients generally also achieve full range of motion rapidly despite the use of the brace because of the passive range of motion and CPM programs.

Patients are treated initially with crutches, but they rapidly progress to weight bearing as tolerated after treatment of patellofemoral lesions. All weight bearing is to be completed in a brace locked as described above for the first 8 weeks. The brace is then discontinued after full range of motion is gradually achieved over approximately 1 week.

We allow the patients to begin strengthening after the brace is discontinued. In patients with patellofemoral lesions, the contact areas are observed arthroscopically during knee motion and recorded. The ranges of motion of the knee during this contact are avoided during strengthening exercises for 4 months postoperatively.

We use cryotherapy for all microfracture patients in the postoperative period for 1 to 7 days in an effort to decrease inflammation, maximize rehabilitation, and control postoperative pain regardless of the location of the treatment. Anti-inflammatory medications and physical therapy modalities are also prescribed as appropriate.

Steadman et al.⁹ presented results of microfracture in 75 knees. This study presented long-term follow-up (7 to 17 years, average 11.3 years) on patients with traumatic chondral defects in the knee treated with microfracture. Patients were excluded from the study if other pathology existed that required surgical treatment. The patients averaged 30 years of age and had lesions averaging 277 mm². The authors report an improvement in pain, swelling, and Lysholm scores. Improvements were also reported in patients’ ability to perform activities of daily living, strenuous work, and sports.

A recent prospective randomized study compared autologous chondrocyte implantation and microfracture in 80 patients without generalized osteoarthritis and with stable knees.¹² This study compared the two methods of cartilage defect treatment histologically and using various outcome measures. The authors found no significant difference in improvements in Lysholm scores, visual analog scale pain scores, or histological evaluation. The authors reported that microfracture patients achieved significantly better results based on the short form 36 Physical Component score.

Animal and human studies have demonstrated promising results regarding histological and cellular analysis of microfracture regeneration tissue.^8,11,12 There have been no studies to date, however, that demonstrate regeneration tissue that is identical to normal hyaline cartilage. More research is needed to enhance key matrix component production after microfracture.