Osteochondritis Dissecans and Large Osteochondral Defects of the Knee

 

 

 

 

 

DEFINITION

Osteochondritis dissecans (OCD) is a focal idiopathic alteration of subchondral bone with risk for instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis.

OCD and other traumatic injuries can lead to large osteochondral defects of the knee.

 

 

ANATOMY

 

Many of these injuries will include the medial or lateral femoral condyle, in both OCD and acute cartilage injury.

 

PATHOGENESIS

 

The etiology of OCD is not known, although many theories have been suggested, including trauma, vascular anomaly/injury, overuse or repetitive stress injury, genetic predisposition, etc.

 

Acute traumatic injuries can cause displacement of preexisting OCD lesions or the development of acutely displaced cartilage fragment on otherwise normal bone and cartilage structures.

 

NATURAL HISTORY

 

The natural history of OCD runs a variable course.

 

Many patients, especially those who are skeletally immature, with significant growth remaining, have good potential for healing with appropriate activity modification, and in select cases, subchondral bone drilling.

 

 

Patients close to or beyond skeletal maturity have a worse prognosis for healing with activity modifications. The older patients may not respond to less invasive surgeries such as subchondral bone drilling.

 

Patients with acute, traumatic cartilage injury with displaced fragments may be candidates for surgery.

 

Cases in which the cartilage damage is so severe that the fragment is unsalvageable, osteochondral defects may be addressed with a variety of cartilage restoration procedures.

 

 

This chapter focuses on the use osteochondral allografts to address these large, irreparable defects.

 

PATIENT HISTORY AND PHYSICAL FINDINGS

 

Review of previous imaging studies (typically radiographs and/or magnetic resonance imaging [MRI]), operative reports, and arthroscopic imaging is critical in the evaluation of these patients. In many of these patients, previous surgery and arthroscopic imaging have been performed. Reviewing these studies can provide useful information about the location, depth, and perimeter of the lesion (FIG 1).

 

The presence of a “kissing lesion” on the opposite articular surface is important, as its presence may alter or preclude certain allograft approaches. Significant osteoarthritis, especially if more diffuse, rather than focal, may be a contraindication to osteochondral allograft use.

 

Patient factors: Individual patient factors, including patient preferences, alignment of the lower extremities, social resources, work/job demands, and medical comorbidities must be considered when evaluating these patients. Some research has also shown factors such as age older than 30 years and a history of two or more

previous surgeries on the joint are associated with poorer outcomes.14

 

In patients with more advanced osteochondral pathology, the history frequently includes episodes of pain, mechanical symptoms, giving way, and swelling. Both traumatic injuries and patients with OCD may present after months or years of milder symptoms.

 

 

These patients may describe the feeling of a loose body within the joint that can occasionally be palpated on the anterior aspect of the knee.

 

Notable findings include effusion, joint line tenderness, and, in some cases, a mobile free body may be palpated.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

The most valuable tools for evaluating osteochondral lesions are high-quality imaging studies, the most basic of which is the weight bearing, plain radiograph of the knee. The authors prefer standing anteroposterior, tunnel, lateral, and Merchant views.

 

A wealth of information can be gleaned from properly performed radiographs, including the approximate dimensions and location of the lesion and the precedence of diffuse osteoarthritis. Long-standing radiographs are valuable in assessing limb length discrepancy and malalignment.

 

 

 

 

FIG 1 • Arthroscopic view of failed microfracture, subsequent allograft.

 

 

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MRI provides a more detailed look at the condition of the lesion and surrounding cartilage. The MRI may also reveal kissing lesions, in which there is chondral injury on opposing articular surfaces. Careful inspection for malalignment, kissing lesions, or signs of more diffuse cartilage injury is essential, as these factors may

change the surgical management of the patient.14 The lesions are less common in younger patients but may increase in frequency in older patients or those with a prolonged history of symptoms.

 

DIFFERENTIAL DIAGNOSIS

OCD

Acute osteochondral fracture Osteochondral defect

 

 

NONOPERATIVE MANAGEMENT

 

Nonoperative management may consist of activity modifications, maintenance of ideal body weight, and low-impact conditioning programs.

 

Significant mechanical symptoms may not be addressed with this approach.

 

SURGICAL MANAGEMENT

 

With regard to stable OCD lesions, many procedures are designed to promote healing, including subchondral drilling, both antegrade11, 15, 24 and retrograde.26, 28 For unstable lesions, drilling in combination with internal fixation, bone grafting, and other procedures may promote healing. Excision of loose fragments may provide

reasonable short-term results, but long-term outcomes are generally poor.17, 18 Although less invasive procedures may improve mechanical symptoms, they may not address the long-term impact of the cartilage or bone defect in a weight-bearing region of the joint.

 

For patients in whom native cartilage and bone cannot be successfully repaired, or those that have failed previous attempts at repair of native tissue, osteochondral allograft is one option to be considered. Other options to be considered for cartilage loss are outlined in the following text, although some of them may have limitations especially in larger lesions and those with deep subchondral bone loss.

 

For patients that have focal, full-thickness cartilage defects, several techniques can be used to restore the joint cartilage surface. These techniques include the following:

 

 

 

Marrow stimulation (microfracture) Osteochondral autograft transfer (OAT)

 

 

Cell-based therapies, including autologous cartilage amplification and implantation Osteochondral allograft implantation

Marrow Stimulation

 

Marrow stimulation, although relatively simple to perform, has several limitations.

 

Clot formation secondary to marrow stimulation produces disorganized fibrocartilage characterized by a high concentration of type I collagen rather than type II collagen, which comprises hyaline cartilage.

 

Fibrocartilage lacks the mechanical integrity and ultrastructural organization of hyaline cartilage and often deteriorates after a few years.9

 

In addition to poor wear properties, the fibrocartilage formed after marrow stimulation may not restore congruity of the articular surface in cases of OCD, where loss of the subchondral bone and débridement of

fibrous tissue results in a deep crater with significant bone loss.

 

Restoring this subchondral bone loss can present many challenges to the surgeon, both with microfracture, and other cartilage restoration procedures.21

Osteochondral Autograft

 

OAT may have some advantages for treating OCD, as it can directly address the loss/abnormalities of subchondral bone.

 

The depth of the osteochondral autograft donor plug can be adjusted to fill the entire defect with viable bone and articular cartilage, which has the capacity to integrate with the adjacent tissue.

 

There are limitations to the OAT procedure.

 

 

Large defects cannot be filled due to donor site morbidity, and there may be problems with articular cartilage incongruence.

 

The technique precludes filling the entire defect when multiple grafts are used and fibrocartilage forms around the periphery of the grafts.

 

Wang27 and Horas et al10 reported poor results when osteochondral autografting was used to treat lesions24 larger than 6 cm.

 

This approach may be reasonable for smaller OCD lesions. In a prospective randomized trial, mosaic osteochondral autograft transplantation demonstrated superior result compared to microfracture for the

treatment of OCD in children and adolescents.9

 

 

At an average follow-up of 4.2 years, 63% of the microfracture group had good or excellent outcomes, but this group had some deterioration in outcome over 1 to 4 years.

 

For the mosaic osteochondral autograft transplantation group, 83% had good or excellent outcomes.

 

There were 41% failures in the microfracture group compared with none in the mosaic osteochondral autograft transplantation group at the final follow-up.

 

Consequently, in lesions that are small, mosaic osteochondral autograft transplantation is a reasonable procedure that produces outcomes that are superior to microfracture.

 

As mentioned, one challenge with mosaic osteochondral autograft transplantation is donor site morbidity as well as the differences in cartilage thickness in donor and recipient sites.

 

Autologous Cartilage Implantation

 

 

The use of autologous cartilage implantation (ACI) has been reported for treatment of OCD.23 The subchondral bone abnormalities may present special challenges to ACI techniques.

 

Due to the loss and/or abnormalities of the subchondral bone base, special ACI approaches have been developed.

 

 

Collagen-covered ACI (ACI-C) has been described in a case series, showing positive clinical results at 4 years, but most cases that underwent biopsy revealed fibrocartilage.12

 

Another multicenter case series using ACI for OCD demonstrated significant improvements, but more than a third of patients required secondary surgical débridement.6

 

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In cases in which the subchondral bone is minimally involved, standard ACI may be considered.

 

 

In cases with more significant loss of subchondral bone, staged procedures to supplement regional bone loss may be an option.14

Fresh Osteochondral Allograft

 

For larger cartilaginous or osteocartilaginous defects, marrow stimulation, osteochondral autografts, and ACI have limitations.

 

Restoring both bone and cartilage loss is especially challenging in larger lesions. Fresh osteochondral allografts address both the cartilage and bone deficits. In addition, osteochondral allografts produce enough

graft material to resurface larger lesions.4

 

 

Osteochondral allograft transplantation has a long history, dating back to 1957, when Smillie proposed its use for OCD.27 Several centers in North America developed osteochondral allograft transplantation programs in the 1970s.29

 

The rationale for fresh osteochondral allograft transplantation is to replace diseased, unsalvageable bone, and cartilage defects in the context of an otherwise healthy joint.

 

 

The living chondrocytes from the transplant become a viable part of the recipient's cartilage matrix, and the transplanted bone is incorporated by the host bone.3

 

The osseous component of the graft incorporates in the host bone through creeping substitution, in a manner similar to that seen with bone grafting for bone defects or allograft tumor reconstruction.

 

Chondrocytes and cartilage matrix in allograft transplantation generates minimal host immunologic response. The lack host tissue response to the allograft means immune suppression medications are not necessary.

 

 

Unlike solid organ transplantations, human leukocyte antigen (HLA)/immune marker matching has not been

required. In both rat and rabbit models,13 transplantation of chondrocytes in an intact matrix produced no host cellular immune response. In contrast, when either chondrocytes without matrix or cartilage shavings were transplanted, a host cell-mediated immune response was generated. Furthermore, transplantation of intact cartilage produced no immune response, even in a previously sensitized host.

 

More recently, Williams and colleagues29 demonstrated no evidence of immune rejection in 26 retrieval specimens, which had failed at a mean survival of 42 months following implantation. These grafts failed for a variety of reasons, but there was no evidence that a host immune response was a contributing factor.

 

Recent studies have used MRI to evaluate host immune response, and in some cases, evidence of humoral immune responses have been suggested. Further research in this area will be helpful to evaluate immune response in grafts.

 

Histologic studies on failed grafts have not identified significant signs of graft rejection, and chondrocytes remain viable for years after implantation.29

 

Providing viable tissue for treating large cartilage defect includes the transfer of living cartilage cells between the donor and recipient. The need for both thorough testing of donor tissue to ensure recipient safety and rapid turnaround to preserve living tissue must be considered during the harvest and implantation process.

 

There is a long history of bone, ligament, and cartilage transplantation, and disease transmission is thought to

be exceedingly rare. Unfortunately, a standard reporting system for these events does not exist.

 

 

A preoperative discussion with the patients, which outlines these risks, is an important part of the informed consent process and patient-centered care.

 

Most tissue banks are members of the American Association of Tissue Banks (AATB), which publishes standards for tissue procurement. These standards include extensive medical history review of donors, serologic testing, bacterial cultures, storage requirements, and expiration periods. The standards for live, fresh osteochondral transfer are critical to ensure that these processes do not significantly alter the viability of the cartilage/chondrocyte tissues. For any practitioner involved with these procedures, a thorough review of the tissue bank accreditation and processes is important.

 

Many steps are taken to ensure graft safety, which include the following:

 

 

 

Review of the donor medical record Review of serologies and cultures

 

These processes may require 10 to 14 days. During this interval, chondrocyte preservation is critical. Different preservation solutions include physiologic saline solutions or more complex media that may include amino acids, glucose, and inorganic salts.

 

 

The more complex solutions may increase both quality and duration of chondrocyte viability.27

 

 

Williams et al30 demonstrated chondrocyte viability to remain unchanged for up to 14 days when preserved in culture medium. These solutions may work optimally for 10 to 14 days, but after this time, chondrocyte viability starts to decrease, with changes in cellular contents, and extracellular matrix.

 

Current AATB requirements include harvest within 24 hours of donor demise and grafts stored at 4° C within culture medium. For these reasons, earlier transplantation within 14 to 28 days may be ideal, after donor testing is completed.

 

Other studies have evaluated the relationship between time of harvest and chondrocyte viability,1 and early implantation is correlated with higher cell viability, especially at the articular surface of the grafts.19

 

 

Frozen grafts have significantly lower cellular viability compared with fresh, non-frozen grafts.20 The dowel and shell techniques are commonly used in the setting of unsalvageable OCD.7

 

Both techniques begin with a medial or lateral parapatellar arthrotomy, and appropriate retractor use

precludes the need for patellar dislocation in most cases (FIG 2).

 

Unlike posttraumatic chondral defects, which often have associated ligamentous instability and mechanical axis malalignment, OCD is generally a focal defect in an otherwise healthy knee in a younger patient.

 

If associated pathology is present, such as varus or valgus malalignment, or ACL deficiency, many authors agree that these should be addressed in conjunction with osteochondral allografting procedures.7, 24

 

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FIG 2 • Medial parapatellar arthrotomy with retractors.

 

 

As the surgeon gains experiences, more complicated osteochondral techniques may be employed. The techniques are used to address larger lesions or those with irregular contours.

 

There are several approaches to larger lesions, including “snowman” and “shell” techniques. Using multiple grafts, the snowman technique can increase the area covered by the dowel graft technique.

 

 

The dowel technique is simply repeated adjacent to the first graft. The second graft is placed in such a manner that it interdigitates with the first graft.

 

Most OCD lesions lend themselves to the single-graft dowel technique, which is relatively straightforward, and we encourage surgeons to perform this both with saw-bone skill sessions and cadaver labs, prior to clinical use. Participation with an experienced surgeon for the first several cases may also be advantageous.

 

Several companies provide instrumentation for these dowel procedures to allow a size-matched press-fit technique. Steps in the process are well outlined in these instrumentation sets.

 

Preoperative Planning

 

Patient-centered decision making is a critical part of the planning process. A thorough discussion of the risk, benefit, and alternatives are important. Risks associated with allograft tissue, including disease transmission, need to be reviewed with the patients.

 

If the patient is interested in proceeding with an allograft, the first step is to confirm an anatomic match between the donor and recipient anatomy, based on donor and recipient radiographs and/or MRI. Although these measurements may not ensure exact matching, the assessment should show minimal deviations of a few millimeters or less in the frontal and coronal planes. After confirmation of anatomic match is completed, surgery scheduling may proceed.

 

Evaluation of the lower extremity alignment is an important step, as significant deformities may require surgery to address alignment. Preoperative clinical evaluations, and if indicated, appropriate alignment images may be helpful in surgical planning. Examination under anesthesia may include the evaluation of ligamentous laxity.

Positioning

 

The patient may be placed in a traditional arthroscopic position, if knee arthroscopy is part of the planned surgery.

 

Another option is to position the patient supine, without using an arthroscopic knee holder.

 

The lower extremity portion of the operating table is left at full extension rather than using a bend at the knee, which is commonly used in some arthroscopic procedures.

 

An adjustable foot rest and thigh post can be used to hold the knee on the table at around 90 degrees of flexion and adjusted for more or less flexion, depending on the location of the lesion on the femoral condyle.

 

This position allows for the knee to be held at the appropriate degree of flexion throughout the procedure, to optimize surgical exposure, and allow the surgical assistant to have two free hands to assist with the procedure (FIG 3).

 

Approach

 

In most cases, smaller miniarthrotomies over the medial or lateral condyle are adequate, and patellar dislocation is usually not necessary for exposure.

 

The use of Z retractors can improve tissue retraction, allow for excellent exposure, and prepare the recipient bed for the allograft.

 

Caution is advised with all retractors to avoid inadvertent injury to other cartilaginous areas about the condyles, tibial plateau, and the patella.

 

The use of regular physiologic saline application to the exposed cartilaginous surfaces is also advised.

 

Tourniquet use is at the discretion of the surgeon, although in our experience, tourniquets are not routinely used for osteochondral allograft cases.

 

 

 

FIG 3 • Lateral leg holder.

 

 

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TECHNIQUES

• Dowel Technique

Recipient Site Reaming

The technique includes the use of “hole saws” to harvest the graft from the donor and reamers to prepare the recipient bed. Size matching of these instruments is critical to ensure appropriate fit and stability of the allograft.

The selection of the proper diameter is first determined with a set of sizers. These sizers are placed over the defect to ensure the hole saw will remove the entire defect, leaving a peripheral zone of mostly normal cartilage and bone (TECH FIG 1A).

Once the size is determined, a guide pin is placed through the center of the sizer with the sizer in even contact with the articular surface; this ensures that the trajectory of the reamer is perpendicular to the

 

articular surface.

 

It is critical that this step place the pin as normal as possible to the cartilage surface to ensure both donor and recipient bed have well-matched chondral surface contour.

 

The guide pin is left in place, and the edge of the area to be prepared is scored to prevent peeling of the surrounding cartilage during reaming (TECH FIG 1B).

 

The corresponding recipient site reamer is selected, and the site is reamed over the guide pin until healthy, bleeding subchondral bone is encountered, generally 7 to 15 mm from the chondral surface (TECH FIG 1C).

 

 

 

TECH FIG 1 • A. Use of sizing dowel for osteochondral implantation. B. Use of guide pin for drilling. C. Use of appropriate-sized reamer for drilling donor bed. D. View of recipient bed, confirm complete vascularization of the bone.

 

 

We prefer to drill no deeper than necessary to identify viable bone throughout the base of the lesion (TECH FIG 1D).

 

The vascularity of the recipient bed is best assessed if the tourniquet is not used during the case, and for this reason, we prefer not to use tourniquets during these procedures.

 

The visible edge of this reamer has metal-etched markers to look for the depth of penetration circumferentially around the recipient bed. In many cases, the recipient bed depth of penetration is nearly equivalent circumferentially, but in some cases, differences of 1 to 2 mm may occur.

 

These differences will be addressed during the preparation of the donor graft.

Preparation of the Donor Graft

 

Following reaming of the recipient site, the 12 o'clock position is marked on the articular surface. Depth measurements are taken and recorded at the 12, 3, 6, and 9 o'clock positions. A written record and diagram of these measurements will be helpful later in the case.

 

The donor condyle is now positioned precisely in the drilling jig. This step of the procedure is critical to ensure contour match of the recipient bed and donor graft.

 

Prior to surgery, it is advisable that the surgeon become familiar with the constraints of using this jig and each of the adjustable components for precisely and securing holding the condyle.

 

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The surgeon can compare the size, arc, and width of the harvest site by placing the donor condyle next to the recipient condyle and also using the sizing dowels to ensure the location of harvest is appropriate.

 

At least four points of fixation to the graft are ideal to ensure that the graft does not move during the drilling (TECH FIG 2A).

 

After securing the donor condyle to the jig, the orientation of the hollow saw for drilling is performed. This step is also critical to ensure graft recipient contour match (TECH FIG 2B).

 

A guide pin can be placed through the sizer to assist with maintaining a perpendicular trajectory with the reamer. Again, the cartilage of the donor is scored, the 12 o'clock position is marked, and the appropriately sized dowel reamer is used to ream the graft.

 

The graft is then reamed to a depth well beyond the depth of the recipient site so that it may be trimmed. The graft is then removed from the donor condyle with a sagittal saw, taking care to preserve the appropriate depth (TECH FIG 2C).

 

Several authors recommend that the osteochondral allograft be limited in depth to approximately 10 mm. This may be related to the clinical observations in tumor allograft surgery that creeping substitution

occurs over a limited distance. Levy et al14 recommends that for recipient depth more than 10 mm, supplemental recipient autograft be used to elevate the depth of the recipient bed to about 10 mm.

 

 

 

TECH FIG 2 • A. Initial securing of the donor condyle in jig. B. Orientation of drill guide. C. Drilling the osteochondral allograft for removal from condyle. D. Trimming the osteochondral allograft to match the donor bed depth in all four quadrants.

 

 

While releasing the graft from the donor condyle, the surgeon should be prepared for the dowel graft to be ejected from the donor condyle, possibly sending the graft to the floor, which significantly complicates this procedure.

 

When the dowel is free, the corresponding depths from the 12, 3, 6, and 9 o'clock positions are marked, and the sagittal saw and cutting guide are used to achieve the proper depth (TECH FIG 2D).

 

Pulsatile irrigation is used to remove marrow elements from the donor bone.

Graft Placement

 

The graft is placed and trimmed if proud.

 

Care must be taken to remove the graft for trimming. Forcibly prying the graft out can damage both the recipient site and graft. The blunt end of the guide pin can be placed into the guide pinhole to gently toggle the graft from the recipient site (TECH FIG 3A).

 

Generally, the graft is very secure with a press-fit. If further fixation is desired, small, absorbable pins may be used.

 

Recent studies have suggested that high-impact forces on osteochondral allografts may have an impact on chondrocyte viability.2 For these reasons, we recommend firm, intermittent pressure, and impact forces as low as possible, rather than significant impacts, to help seat the graft22 ( TECH FIG 3B).

 

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TECH FIG 3 • A. Graft position prior to implantation. Note the 12 o'clock position on the graft to maintain orientation. B. Final position of osteochondral implant.

 

 

 

MRI sequences may

underestimate size of cartilage defect.

• Preoperative evaluation of images is essential for planning.

Contours of the graft and

recipient do not match.

• Cut the allograft dowel from the same area of the condyle as

the recipient site.

Graft edges are proud on one

side but recessed on another.

• Make sure that both the reaming of the recipient site and

allograft dowel are performed at an angle perpendicular to the surrounding articular surface. This can be aided by placing a guide pin in the graft to guide the dowel saw.

Graft is uncontained and feels

loose after implantation.

• Supplement “press-fit” fixation with small absorbable pins.

Mechanical axis malalignment

causes overload of the compartment receiving the graft, leading to a higher failure rate.

• Perform a realignment osteotomy as a staged procedure or in

conjunction with the osteochondral allograft.

PEARLS AND PITFALLS

 

POSTOPERATIVE CARE

 

Postoperative care consists of immediate range of motion to allow for optimal environment for cartilage healing.

 

Deep venous thrombosis (DVT) pharmacologic prophylaxis is not given routinely in younger patients, unless risk factors for DVT exist. The use of DVT prophylaxis continues to evolve, and in some cases, prophylaxis may be advantageous, even in younger patients.

 

We encourage early motion in the first 24 hours, and start formal PT-supervised physical therapy sessions at 48 to 72 hours when possible.

 

 

Weight bearing is generally protected for 6 to 12 weeks with resumption of full activity at 4 to 6 months.7 We encourage our patients to develop an exercise fitness lifestyle that emphasizes lower impact exercises,

including swimming, cycling, and elliptical training. Although running is not prohibited, we do encourage them to incorporate other lower impact fitness activities.

 

We also emphasize optimal body mass index, as this may also have an impact on long-term outcome.

 

 

OUTCOMES

Good results have been reported using fresh osteochondral allografts for the reconstruction of posttraumatic cartilage defects about the knee.16, 25

Emmerson et al7 reported on the long-term results of fresh osteochondral allografting in a group of patients with the specific diagnosis of OCD.

The study group included 66 knees in 64 patients, with a mean age of 28.8 years. The mean follow-up was 7.7 years (range 2 to 22 years).

The authors reported 72% good or excellent results with a 15% reoperation rate. Factors associated with reoperation were older age and larger lesions.

The 5-year survivorship was 91%.

 

Garret8 reported his experience with osteochondral allografts for OCD of the lateral femoral condyle.

Defects up to 3 cm showed good results at 2 to 9 years follow-up for 16/17 patients. One large lesion (3 × 4.5 cm) failed early in this series.

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Levy et al14 reported a relatively long-term follow-up (91% of 129 grafts) of osteochondral allografts at 10 years.

Thirty-one knees (24%) failed at a mean of 7.2 years. Survivorship was 82% at 10 years, 74% at 15

years, and 66% at 20 years.

Age older than 30 years at time of surgery and having two or more previous surgeries for the operated knee were associated with allograft failure.

 

COMPLICATIONS

In a systematic review, Chahal et al5 reported on the complications associated with osteochondral

 

allograft transplantation.

Overall, the short-term complication rate was low at 2.3% (14 of 595 knees reported across 19 eligible studies).

These postoperative complications included removal of hardware (n = 3), repeat arthroscopy (n = 3), superficial infection (n = 2), deep infection (n = 2), DVT (n = 1), hyperemic reaction (n = 1), and early loosening of the graft (n = 1).

The most frequent long-term complication rate was failure, which was reported variably as graft fragmentation or conversion to total knee arthroplasty.

The overall failure rate was approximately 18%, based on the individual authors' definitions. The failure rate of bipolar grafts (opposing femoral and tibial grafts) was 65%.

 

 

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