Operative treatment options for osteoarthritis of the knee and cartilage defects

Brian J. Cole, MD, MBA; Sudeep Taksali

From A Special Report: Osteoarthritis of the Knee

Keeping Aging Adults Active


Preview: When nonoperative treatment of osteoarthritis of the knee fails to alleviate pain and knee function is compromised, operative intervention is warranted. Surgical options include arthroscopy, joint reconstruction, or both. Joint reconstruction options include osteotomy and knee replacement. Joint replacement can be unicompartmental or total. Symptomatic focal chondral defects can be managed by marrow-stimulating techniques, autologous chondrocyte implantation, and osteochondral grafting. Allograft meniscal transplantation can be a viable option following subtotal or total meniscectomy when arthritis is unicompartmental and less severe. The appropriate surgical procedure is made jointly by the physician and patient and is based on the diagnosis, disease severity, and the level of activity desired by the patient.


Patients with severe symptomatic osteoarthritis of the knee who have pain that has failed to respond to medical therapy and have progressive limitations in activities of daily living should be referred for surgical consideration. The principles of surgical management of the adult arthritic knee follow an intuitive algorithm:

  • Arthroscopy is primarily indicated as a first-line procedure in patients who report an acute or subacute onset in pain. Mechanical symptoms caused by unstable articular cartilage flap tears, meniscal tears, or loose bodies are common indications to proceed with arthroscopy and debridement.
  • Osteotomy is principally indicated for unicompartmental arthritis and corresponding malalignment or for symptomatic posttraumatic malunions about the knee associated with painful knee arthritis.
  • Unicompartmental knee replacement is primarily indicated for patients who have arthritis of a single compartment, an intact anterior cruciate ligament, and no limb malalignment.
  • Total knee replacement is indicated in patients who are not candidates for arthroscopy or osteotomy, in patients with more diffuse arthritic involvement, and to salvage a failed osteotomy or unicompartmental knee replacement.
  • Symptomatic focal chondral defects can be managed by reparative measures such as marrow-stimulation techniques (MSTs) and restorative techniques such as autologous chondrocyte implantation (ACI) and osteochondral grafting.
  • Allograft meniscal transplantation can be done after subtotal or total meniscectomy when arthritis is unicompartmental and not severe.

The choice of treatment depends on the severity and location of the osteoarthritis. With this information, the physician and patient must explore the surgical options to decide which procedure best fits the patient's activity needs.


Arthroscopy

In osteoarthritis, degenerating articular cartilage and synovium release proinflammatory cytokines that induce chondrocytes to release lytic enzymes. This leads to the degradation of type II collagen and proteoglycans. Arthroscopic lavage and debridement may "wash out" or dilute these inflammatory mediators. The effect is temporary, so arthroscopy in most cases is a palliative measure (delaying tactic).1

Patients who benefit most from arthroscopy have a history of mechanical symptoms such as knee locking of short duration (<6 months), normal alignment, and only mild to moderate radiographic evidence of osteoarthritis (table 1).2 Patients often have unrealistic expectations following arthroscopic debridement, so it is important to counsel patients about the limited indications and often palliative results. Patients who have undergone at least 3 months of supervised nonsurgical treatment and have normal alignment and only mild to moderate osteoarthritis on 45º flexion weight-bearing posteroanterior radiographs are considered candidates for arthroscopic debridement.

Table 1. Prognostic factors for arthroscopic debridement
History Physical examination Radiographic findings Arthroscopic findings

Good  

Short duration Medial tenderness Unicompartmental Outerbridge I or II changes
Associated trauma Effusion Normal alignment Meniscal flap tear
First arthroscopy Normal alignment Minimal Fairbank's changes Chondral fracture/flap
Mechanical symptoms Ligaments stable Loose bodies Loose bodies
  Osteophytes at symptom site
Poor  

Long duration Lateral tenderness Bi-/tri-compartmental Outerbridge III or IV changes
Insidious onset No effusion Malalignment Degenerative meniscus
Multiple procedures Malalignment
    Varus >10°
    Valgus >15°
Significant Fairbank's changes Diffuse chondrosis
Pain at rest Ligaments unstable Irrelevant osteophytes Osteophyte away from symptom site
Litigation  
Work-related  


The efficacy of lavage with or without debridement is controversial; well-designed randomized prospective controlled trials have not been performed. When appropriately indicated, arthroscopic lavage and debridement will relieve pain in 50% to 70% of patients for several months to several years (ie, 2 to 4 years).2 Drilling and abrasion arthroplasty do not seem to offer additional benefit to arthroscopic debridement, although intermediate-term results in uncontrolled trials suggest that microfracture may offer some benefit.3 Patients who have flexion deformities associated with pain or discomfort and osteophyte formation around the tibial spines may benefit from osteophyte removal and notchplasty.4

Arthroscopy is also a sensitive way to evaluate the extent and location of articular disease when considering osteotomy or unicompartmental knee replacement, because plain radiographs and magnetic resonance imaging often underestimate the extent of osteoarthritis.5

Postoperative rehabilitation involves weight-bearing as tolerated and early strengthening exercises. Complications are rare and include persistent pain, stiffness, and infection.


Joint reconstruction

Patients with malalignment who are obese, relatively young, active, or heavy laborers should be considered for osteotomy and not for joint replacement. According to Nagel et al,6 activities that are inappropriate after total knee replacement (ie, climbing, jumping, impact sports, and jogging) are possible after osteotomy (in patients who were symptomatic but able to perform these activities before osteotomy).

Arthroplasty and osteotomy most reliably relieve pain that is produced by weight-bearing activities. The best results for both procedures are achieved when preoperative pain at rest is minimal. Appreciable pain at rest usually indicates an inflammatory process. Patients with unicompartmental disease secondary to inflammatory arthritis, such as rheumatoid arthritis and possibly, chondrocalcinosis, are best treated with a total knee replacement because the other compartments may subsequently become involved.

Although any joint replacement is at risk for mechanical failure and loosening owing to heavy or prolonged cyclic loads, unicompartmental and total knee replacement have advantages. Compared with proximal tibial osteotomy, arthroplasty has fewer postoperative complications and a higher rate of early and long-term successful results. In a comparative study by Broughton et al,7 46% of knees that had proximal tibial osteotomy and 76% of knees that had a unicompartmental knee replacement maintained a good result at follow-up after 5 to 10 years. These authors reported that patients who underwent knee replacement surgery walked with a range of motion approaching normal more quickly than did those who underwent an osteotomy. Furthermore, no cast or immobilization is required. Arthroplasty has the additional advantage of removing osteophytes and releasing intra-articular adhesions, which improves postoperative range of motion. In patients with bilateral disease, arthroplasties can be performed simultaneously or staged over a short period of time, but bilateral osteotomies must be done 3 to 6 months apart, leading to a prolonged total recovery period.

OSTEOTOMY—General indications for osteotomy include varus alignment with medial-compartment arthrosis and valgus alignment with lateral-compartment arthrosis in relatively young or obese patients. For patients in whom there is uncertainty regarding the status of the contralateral tibiofemoral compartment or coexisting patellofemoral arthrosis, a trial of a short-leg walking cast to "off-load" the affected compartment is especially useful, using contact points that are placed laterally for varus deformity or medially for valgus deformity. Patients are asked to walk with the corrective cast in place for 3 days and are then asked about pain reduction during ambulation.

One advantage of osteotomy is that activity restrictions are minimal because no prosthetic material is used. However, the results of proximal tibial osteotomy are successful only when mechanical alignment is adequately corrected. Compared with unicompartmental knee replacement, relief of pain and restoration of motion are not as predictable. Finally, if the osteotomy faºils, conversion to a total knee replacement can be more difficult than primary knee replacement because of secondary deformity and soft-tissue scarring.

Indications for osteotomy and unicompartmental knee replacement are similar in some respects. The procedures are similar in that mild preoperative deformity is acceptable, ligamentous stability is required, and no significant joint subluxation can be present. Compared with unicompartmental knee replacement, osteotomy is better suited for younger patients with higher physical demands. Thin patients have better results after osteotomy, but any body weight is acceptable. In addition, unlike unicompartmental knee replacement, in which preoperative motion is improved postoperatively, osteotomy candidates require at least 90° of motion without flexion contracture because motion is less likely to be improved following osteotomy. Today, most osteotomy patients are young persons who are motivated to maintain high levels of physical activity. They generally have early arthritis involving a single tibiofemoral compartment, minimal patellofemoral involvement, more than 100º of flexion, no fixed flexion deformity, and no instability or subluxation.

Contraindications to osteotomy include panarthrosis, severe patellofemoral disease, severely restricted range of motion (ie, extension loss of >15º to 20º or flexion <90º), instability, and inflammatory arthritis.

Varus malalignment. In younger, active patients with varus malalignment and medial compartment arthrosis, a valgus-producing high tibial osteotomy is recommended. This procedure decreases medial-compartment loads, diminishes symptoms, and improves function. It is better to perform an osteotomy sooner rather than later (ie, when <5º of varus is present) and to overcorrect by 2º to 3º. Mild to moderate patellofemoral osteoarthritis is still compatible with a successful result following high tibial osteotomy.

Valgus malalignment. Lateral-compartment osteoarthritis is much less common than isolated medial-compartment osteoarthritis. Mild deformities (<10º valgus) can be treated with a medial high tibial closing-wedge osteotomy. In patients who have significant valgus deformity (ie, >10º) or a lateral sloping joint line, a distal femoral osteotomy is indicated. Indications, complications, and features for osteotomies to correct valgus deformities are similar to those for varus deformity with unicompartmental arthritis.

Results. In a prospective study of 41 patients who underwent high tibial osteotomy, Noyes et al8 found that after a mean of 58 months postoperatively, 36 patients (88%) were satisfied and would undergo the operation again, and 32 patients (78%) felt that their knee condition was improved by the operation.

In a report of 1,364 cases of proximal tibial osteotomy at up to 10 years' follow-up, 76% had good to excellent results, 19% had fair results, and 14% had poor results.9 Overall, 60% of the patients were satisfied with their proximal tibial osteotomy after 10 years.

More than 80% of outcomes rated good to excellent have been reported following the treatment of valgus deformities.10 Recently, Finkelstein et al11 determined that the probability of symptom relief following a distal femoral varus-producing osteotomy at 19 years was 64%. Following this procedure, activity levels are maintained but not improved.

Complications. The most common problem with proximal tibial and distal femoral osteotomy is undercorrection. This leads to inadequate stress transfer to the opposite compartment, resulting in insufficient pain relief. Other common problems include nonunion, malunion, intra-articular fracture, thromboembolic events, and infection. In addition, patella infra or contracture with associated motion loss can occur.

UNICOMPARTMENTAL KNEE REPLACEMENT—Unicompartmental knee replacement has a well-established role in the treatment of symptomatic osteoarthritis that is limited to a single compartment in selected patients.12 Contemporary studies of unicompartmental knee replacement report excellent clinical results even after 10 years and have stimulated new interest in this treatment option. Furthermore, when compared with total knee replacement, unicompartmental knee replacement offers reduced implantation costs, shorter hospital stays, and less use of blood products. These advantages account for a renewed interest in the procedure.

Although osteotomy is preferred for young, active, and overweight patients, unicompartmental knee replacement has the potential advantage of preserving bone stock and cartilage. If necessary, a technically well-performed unicompartmental knee replacement can be easily revised to a total knee replacement.

Patient selection for unicompartmental knee replacement, as with most procedures, is critical to a successful outcome. Unicompartmental knee replacement is limited to patients with osteoarthritis in either the medial or the lateral compartment.

The angular deformity of the knee should be between 10º of varus and 15º of valgus. Patients should have a preoperative range of motion of at least 90º of flexion with a minimal flexion contracture (ie, <5º). The best candidates for a unicompartmental knee replacement are older than 55 years of age with noninflammatory arthritis who are not obese and who have low activity level demands. The decision to perform a unicompartmental knee replacement is made at the time of the surgical inspection of the articular surfaces.

At the time of surgery, both cruciate ligaments should be examined and intact to ensure the best results for a unicompartmental knee replacement. Patellofemoral joint pain is a relative contraindication to unicompartmental knee replacement but asymptomatic chondromalacia of the patella is not. The opposite tibiofemoral compartment and the patellofemoral joint should have Outerbridge changes no more than grade II. If more extensive disease exists, a unicompartmental knee replacement should be abandoned and a total knee replacement performed.

Results. The clinical results of unicompartmental knee replacement are similar to those of total knee replacement and superior to osteotomy. In a prospective study, Mackinnon et al13 reported that 86% of 115 knees had an excellent or good result after a mean follow-up of 4.8 years. Marmor14 reported that 42 (70%) of 60 consecutive unicompartmental knee replacements had a satisfactory result, and 52 (87%) had continued relief of pain 10 to 13 years postoperatively. Sullivan et al15 reported that of 107 patients who had only 4 revisions, 96% had no limitation of activities 5 to 11 years postoperatively. In a comparison of unicompartmental with total knee replacement, many patients reported that the knee with the unicompartmental knee replacement felt better and more normal than the knee with a total knee replacement.15

TOTAL KNEE REPLACEMENT—Total knee replacement is one of the most successful procedures performed in orthopedic surgery today. Introduced as a simple concept in the late 1960s by Gunston,16 it has evolved into a fairly sophisticated procedure. The indications for total knee replacement are well defined and universally applied. Consequently, the results have been uniformly excellent. Approximately 200,000 total knee replacements are performed annually in the United States. The procedure is best suited for patients older than 50 years of age who are willing to forgo high-impact activities that involve running, cutting, and pivoting. However, there are no restrictions on bicycling, swimming, golf, or walking.

Long-term reports of excellent pain relief and recovery of function following total knee replacement has made it the treatment of choice for most end-stage arthritic conditions of the knee depending on the patient's age, extent of disease, and lack of indications for alternative procedures. The indications are expanding to include younger patients who are otherwise candidates for osteotomy and older patients who are otherwise candidates for unicompartmental knee replacement. Although earlier reports suggested that total knee replacement in younger patients predisposed them to premature implant wear, loosening, and osteolysis, recent reports have indicated similar results for both younger and older patients.17

Total knee replacement is readily performed following a failed unicompartmental knee replacement provided that standard bone-sparing cuts are made during the original implantation and the holes for fixation with cement do not deeply invade the condylar bone stock. As the population ages, however, an increasing number of patients may live long enough to see the failure of these knee prostheses.

Results. Total knee replacement provides reliable pain relief and improved function for patients with degenerative and inflammatory arthritis of the knee. Implant survival is reported to be more than 94% at 10 years.18 Various series report that, at least in the short term, the results of cemented total knee replacement in young patients are comparable to those in patients older than 55 years of age.19 Both cemented and cementless fixation for total knee replacement provide excellent functional and durable results.20


Management of focal chondral defects

An estimated 900,000 Americans suffer cartilage injuries each year.21 In a recent attempt to delineate the prevalence of chondral lesions, Curl et al22 reviewed 31,516 arthroscopies over a 4-year period. The authors noted 53,569 articular cartilage lesions in 19,827 patients.

Lesions amenable to some form of cartilage restoration technique are ideally full-thickness and located on the weight-bearing surface of the femoral condyle. For patients younger than 40 years, full-thickness lesions of the femur were present in only 5% of all arthroscopies.22

Isolated superficial cartilage injuries that do not penetrate the vascular subchondral bone do not heal and may enlarge for several years following the initial injury, potentially leading to overt degenerative arthritis. Full-thickness cartilage injuries that penetrate the more vascular subchondral bone permit local access to an undifferentiated cell pool (primitive mesenchymal stem cells) capable of forming fibrocartilage or "scar cartilage." Fibrocartilage is composed predominantly of type I collagen and is biochemically and mechanically inferior to normal hyaline articular cartilage, which is composed predominantly of type II collagen. Fibrocartilage formation is the biological basis for the MSTs commonly used to treat symptomatic full-thickness cartilage defects.

Abnormal shear and blunt forces are manifested at the junction of the uncalcified and calcified cartilage layers, potentially creating isolated cartilage injury extending to the subchondral bone. This is otherwise known as a focal or full-thickness cartilage defect. Typically, femoral lesions result from shear stress due to a twisting injury; patellofemoral joint lesions result from direct trauma to the front of the knee. The natural history of an asymptomatic full-thickness cartilage defect and its relationship to the development of secondary degenerative changes typically seen in osteoarthritis is poorly understood. However, lesions that become symptomatic inexorably progress, leading to reciprocal degenerative changes at the opposing articular surface.23

The goals of any surgical option used to treat articular cartilage defects are to restore the joint surface, leading to full, painless range of motion; and halting cartilage degeneration. Surgical options can be palliative (ie, arthroscopic debridement and lavage), reparative (ie, MSTs), or restorative (ie, ACI and osteochonral grafts). Osteochondral grafts can be obtained from the patient (ie, autografts) or from cadaveric donors (ie, allografts). Arthroscopic debridement and lavage was discussed previously. Most studies reflect outcomes following the treatment of established osteoarthritis, not of isolated focal chondral defects.

Determining the appropriate surgical option is a complex process.24 Decision-making is affected by the following variables: the size of the defect (ie, smaller or larger than 2 cm2), the number and type of previous surgeries (ie, primary or secondary), location of the defect (ie, femoral condyle, trochlea, or patella), patient demands and expectations, and coexisting pathologic lesions (ie, ligament tears, malalignment) (table 2).

Table 2. Surgical treatment options for symptomatic focal cartilage defects of the femur*
Lesion Treatment Rehabilitation Comments

  Primary  
<2 cm2 Debridement and lavage Straightforward Provides short-term symptomatic relief
  Marrow-stimulation techniques Significant Ideal for smaller lesions located on femoral condyle; provides intermediate short-term relief; low-cost
  Osteochondral autograft Moderate Relatively new procedure; probably as good as, if not better than, marrow-stimulation techniques; provides potentially long-term relief
 
>2 cm2 Debridement and lavage Straightforward Provides short-term symptomatic relief
  Marrow stimulation techniques Significant Has lower success rate for larger lesions; good choice for symptomatic relief in low-demand individuals; intermediate-term relief is possible; low-cost
  Cartilage biopsy for future autologous chondrocyte implantation Straightforward Staged procedure
  Osteochondral autograft Significant With larger lesions, potential for donor site morbidity exists; results are variable
  Osteochondral allograft Significant Useful for larger lesions with significant bone stock loss; small concern for disease transmission and allograft availability; provides potentially long-term relief
 
  Secondary  
<2 cm2 Osteochondral autograft Moderate Relatively new procedure; probably as good as, if not better than, marrow-stimulation techniques; provides potentially long-term relief
  Autologous chondrocyte implantation Significant High success rate for return to activities; potentially long-term relief; relatively high cost
 
>2 cm2 Osteochondral autograft Significant With larger lesions, potential for donor site morbidity exists; results are variable
  Osteochondral allograft Significant Useful for larger lesions with significant bone stock loss; small concern for disease transmission and allograft availability; provides potentially long-term relief
  Autologous chondrocyte implantation Significant High success rate for return to activities; potentially long-term relief; relatively high cost
* Procedure selection depends on patient's age, expectations, demand, and activity level, coexisting pathology, and extent and location of disease.
Straightforward, early weight-bearing and return to activities within 4 weeks; moderate, short-term protected weight-bearing and return to activities within 12 weeks; significant, prolonged protected weight-bearing and significant delay until return to activities (6 to 8 months).
Follows failed primary treatment

Adapted with permission.29



REPARATIVE TREATMENT—Unlike partial-thickness cartilage injuries that do not extend to the underlying bone, full-thickness cartilage injuries can undergo repair from marrow-derived primitive mesenchymal stem-cell migration and vascular ingrowth.25 This limited capacity to form repair cartilage provides the rationale for MSTs. Despite techniques such as abrasion arthroplasty, subchondral drilling, and microfracture, the goal is to penetrate the subchondral zone of vascularization within the cartilage defect, allowing a conduit and site for clot formation containing mesenchymal stem cells capable of forming fibrocartilage repair tissue.3

Postoperatively, partial weight-bearing for 6 to 8 weeks and the use of continuous passive motion will enhance the extent and quality of the repair tissue within the defect.26 About two thirds of patients with lesions smaller than 2 cm2 experience symptom relief at 2 to 3 years' follow-up.3 As a result, MSTs are ideal for lesions less than 2 cm2 located on the femoral condyle. MSTs appear to have a lower success rate when lesions are located on the trochlea or tibial condyle and are larger than 2 cm2. Furthermore, results may deteriorate with time because fibrocartilage is biochemically (ie, predominantly type I collagen) and biomechanically inferior to normal articular cartilage. However, MSTs are low-cost procedures with low morbidity, and they are a mainstay for the initial treatment of small chondral lesions.

RESTORATIVE TREATMENT—It is important to assess and correct tibiofemoral and patellofemoral malalignment and ligamentous insufficiency when considering articular cartilage restoration. Left uncorrected, these additional comorbidities can result in treatment failure. Three main techniques are used to transfer or implant cartilage: ACI, local transfer of osteochondral plugs, and allograft osteochondral implantations.

ACI is indicated for patients with persistent pain and a focal area of cartilage loss due to trauma or osteochondritis dissecans in which the joint is otherwise preserved without degenerative arthritis or significant subchondral bone loss.

ACI biologically resurfaces the knee in the presence of focal cartilage damage. With ACI, the cartilage defect in the knee joint is repaired with the patient's own healthy cartilage cells originally harvested through an arthroscopic procedure from a separate, minor load-bearing area in the knee. The arthroscopic procedure also serves as a means to assess the severity of chondromalacia at the symptomatic lesion and surrounding articular cartilage to determine appropriateness for ACI. The harvested cells are expanded and transformed into biologically active cells through cell-culturing techniques and implanted during a second procedure. At the time of implantation, an arthrotomy is performed and the cells are injected beneath a periosteal (ie, the soft tissue covering bone) patch obtained from the upper tibia. The patch is sewn over the defect and sealed with fibrin glue. The periosteum is chondrogenic and provides a paracrine effect to chondrocyte growth and a water-tight seal to contain the cells as they populate the defect and attach to the subchondral bone. Other procedures can be performed in conjunction with ACI (eg, anterior cruciate ligament reconstruction, meniscal transplantation, and patellofemoral realignment).

Research indicates that the repair tissue looks and acts more like the normal hyaline articular cartilage than does the fibrocartilage formed with the MSTs.27 Studies performed in Sweden and the United States demonstrate durable and successful results in more than 80% of patients treated with this technique at a minimum follow-up of 2 years.27 In the largest series, Peterson28 reported on 219 consecutive patients with an average 4-year follow-up (range, 2 to 10 years) and demonstrated good to excellent results in more than 90% of lesions of the femoral condyle. Prospective studies comparing ACI with MSTs and with the results of a periosteal patch without concomitant cell placement are under way.

ACI is a costly technique followed by a lengthy recovery period and a 9- to 12-month restriction on high-impact activities. It is most often used as a secondary procedure to treat smaller symptomatic focal chondral defects (<2 cm2) and a primary or secondary treatment for larger lesions. The procedure reportedly has allowed 90% of patients to return to sports and successfully complete activities of daily living.29 Postoperative rehabilitation includes protective weight-bearing and continuous passive motion. Complications are rare but include arthrofibrosis, graft detachment, incomplete graft incorporation, and infection.

Osteochondral grafting or "mosaicplasty" is a technique in which small dowels of bone and cartilage are taken from a non?weight-bearing portion of the femoral trochlea or condyle and press-fit into a recipient hole made by removing the cartilage defect with its underlying bone. This is analogous to a hair-plug transplant and is a new and successful means to manage small areas of cartilage damage on the weight-bearing portion of the medial or lateral femoral condyle. The procedure is indicated for primary treatment of symptomatic focal chondral defects on the femur less than 2 cm2 and as secondary treatment when MSTs or ACIs have failed for similarly-sized lesions. Protected weight-bearing and immediate range of motion are allowed postoperatively. Complications are generally due to technical difficulties of graft placement. Questions remain regarding the morbidity of donor sites during autograft transplantation and the biomechanical consequences of the irregularities present between the plugs themselves.29 Results obtained 5 years postoperatively suggest that this treatment is as least as good as, if not better, than MSTs.30

Similarly, larger areas of bone and cartilage loss (>2 cm2) can be managed with fresh or fresh-frozen size-matched allografts. The articular cartilage with a segment of subchondral bone, or a whole segment of an articular surface and its underlying bone, are transplanted into the knee joint.31,32 Good to excellent results are reported in at least 75% of patients treated for femoral condyle lesions at 2 to 10 years' follow-up.33,34 This procedure is an excellent secondary treatment option for failed ACI in lesions larger than 2 cm2. The risk of disease transmission and immune response is a concern, and the difficulty in procuring appropriate allografts limits the application of this technique. The logistics of procuring fresh osteochondral grafts and the requirement for surgical implantation within 2 to 3 days make this option less appealing. Newer techniques aimed at prolonged preservation of fresh osteochondral allografts are being investigated.


Allograft meniscal transplantation

The symptomatic meniscally deficient patient with only mild postmeniscectomy arthritis is an ideal candidate for meniscus implantation in order to halt the progression of arthritis. Meniscus transplantation is indicated for patients with prior meniscectomy, persistent pain, intact cartilage or low-grade arthrosis (ie, less than Outerbridge grade III changes), normal alignment, and a stable joint.24 The ideal patient is relatively young (<55 years old). Stringent patient selection is essential for optimal outcomes. Ligament reconstruction or realignment procedures are performed simultaneously or in a staged fashion as indicated.

A cryopreserved meniscus is size-matched to the patient's plain radiographs. The procedure is typically performed using an arthroscopically assisted approach with a small arthrotomy to place the meniscus in the joint. The meniscus is anchored by either a bone block (laterally) or bone plugs (medially), and repair is performed using standard meniscal repair techniques.

With the implantation of allograft tissue the risk of immune response must be considered. However, little evidence of clinical or histological rejection has been reported.35 The meniscus, with chondrocytes deeply embedded in the collagenous structure, is thought to be immunologically privileged.36 Another concern with allograft tissue is the risk of disease transmission, because secondary sterilization techniques alter the biomechanical properties of the allograft.

Several reports of good and excellent results for allograft meniscal transplantation exist in the literature. Cameron and Saha37 reported that of 63 patients, 53 (85%) had good and excellent results at a mean follow-up of 31 months. Other authors have reported similar results over similar time periods. Current data indicate that meniscal allografts have healed to the peripheral capsule in more than 80% of patients, and the grafts have revascularized and repopulated with functional host cells. There is a low incidence of immunologic graft injury and the procedure has evolved to be time-efficient with an acceptably low complication rate. Although long-term data are not available, current results are encouraging and indicate that allograft meniscus transplantation has a role in this difficult patient population.35

Rehabilitation regimens vary widely but usually permit early full weight-bearing with immediate range of motion. Full activities are commonly allowed 4 to 6 months following surgery.


Postsurgical treatment

Recent scientific data show potential protective effects of hyaluronic acid in animal models after partial meniscectomy and effective up-regulation of meniscal collagen synthesis in meniscal repairs. These reports, currently unpublished, offer further potential uses for hyaluronic acid in postoperative patients. Further investigations are required and clinical trials are ongoing.

The future treatment of osteoarthritis is likely to involve some form of genetic engineering. Gene therapy may be used to increase growth factors that enhance matrix production, inhibit extracellular cartilage matrix degradation, or maintain chondrocyte number and function. As with all gene therapy, finding the appropriate vector, mechanism of delivery, and target tissues will be a challenge. Potential targets include the synovium and the articular cartilage chondrocytes. Current gene therapy research in osteoarthritis is limited, but the potential application for treatment is a real possibility.


Conclusion

If nonoperative treatment of osteoarthritis and cartilage defects of the knee is unsuccessful, patients can benefit from several surgical procedures: arthroscopy, osteotomy, knee replacement, ACI, osteochondral grafting, and allograft meniscal transplantation. The choice of procedure is made jointly by the physician and the patient, taking into consideration the patient's age, the extent of disease, and the level of physical activity desired by the patient. Genetic engineering shows promise for future treatment, but in the meantime, long-term studies show good results for the procedures described.


Brian J. Cole, MD, MBA is assistant professor, sports medicine and orthopedics, and medical director, Rush Cartilage Restoration Center, Rush-Presbyterian-St. Luke's Medical Center, Chicago. Dr Cole declares that he has no relationships with companies that manufacture products used to treat the patients under discussion.

Address correspondence to Brian J. Cole, MD, MBA, 1725 W Harrison St, Suite 1063, Chicago, IL 60612. E-mail address: [email protected]

Sudeep Taksali is a medical student at Rush Medical School, Chicago. Mr Taksali declares that he has no relationships with companies that manufacture products used to treat the patients under discussion.


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