Osteochondral autograft transplantation in the porcine knee

BACKGROUND: Knee articular cartilage defects are not an uncommon problem. Because articular cartilage is limited in its ability to heal, these defects are difficult to manage. HYPOTHESIS: Osteochondral autografts will provide less of a cavitary defect and more viable hyaline articular cartilage than will control knees. STUDY DESIGN: Controlled laboratory study. METHODS: Osteochondral autografts were grossly and microscopically evaluated in the porcine knee and compared with a control at 6 weeks, 3 months, and 6 months. In 18 porcine specimens, a 1-stage surgical procedure was performed to harvest an osteochondral graft from a nonweightbearing articular cartilage surface, and the graft was transplanted into a defect created in the weight-bearing region of the medial femoral condyle. In the opposite control knee, a similar defect was created in the medial femoral condyle; an osteochondral transplant was not performed. Six pigs each were sacrificed at 6 weeks, 3 months, and 6 months. RESULTS: Gross inspection of the control knees showed a cavitary defect. The defect grossly decreased in size with fibrous ingrowth seen on microscopic analysis. An increasing amount of fibrous tissue and fibrocartilage was present at the 3 time periods. Gross inspection of the graft knee showed a healed osteochondral plug with no obvious displacement, cavitary defects, or surrounding necrotic tissue at each time interval. Microscopic analysis revealed the graft knee contained viable hyaline cartilage and healed viable subchondral bone. At all time intervals, 75% to 100% of the hyaline cartilage was viable in all specimens. In 6-month specimens, bridging cartilage at the autograft-host junction was incomplete in 50%, partial in 33%, and complete in 17%. CONCLUSION: Osteochondral autografts in the porcine knee resulted in viable hyaline cartilage for up to 6 months; there was inconsistent bridging hyaline cartilage at the periphery. Grafts appeared to heal into existing subchondral bone without displacement or evidence of necrosis. CLINICAL RELEVANCE: This type of osteochondral transplant can be used as a reliable reconstructive alternative for osteochondral defects.     

Treatment algorithm for osteochondral injuries of the knee

The treatment of osteochondral fractures and OCD lesions in the knee is controversial. Many new procedures and techniques have been developed recently to address osteochondral lesions, indicating that no single procedure is accepted universally. Our treatment algorithm is based on the age of the patient, skeletal maturity, and the presence of adequate subchondral bone attached to the chondral lesion. Most nondisplaced lesions in the patient with open physes will heal with conservative treatment. The onset of skeletal maturity indicates a need for a more aggressive treatment approach. If adequate cortical bone is attached to the fragment, drilling of stable lesions, or drilling with fixation of unstable or loose fragments is appropriate. Autologous bone graft can be necessary to stimulate healing and properly reconstruct the subchondral bony contour. For failed fixation attempts or lesions not amenable to fixation, each treating surgeon must be proficient and comfortable with an articular surface reconstruction technique. The goal for the reconstructive procedure, to produce a smooth gliding articular surface of hyaline or hyaline-like cartilage, is possible using current techniques including mosaicplasty, osteochondral allograft transplantation, and autologous chondrocyte transplantation. Débridement, drilling, microfracture, and abrasion chondroplasty have been shown to result in fibrocartilage with inferior mechanical properties when compared with hyaline cartilage. No long-term studies have been published, however, to confirm the benefits of replacing osteochondral defects with hyaline cartilage rather than fibrocartilage. Although the results of many reconstructive procedures are quite encouraging with early follow up, the ultimate goal is to prevent long-term degenerative arthritis. Only well-designed prospective studies with long-term follow up will determine the adequacy of these procedures in reaching the ultimate goal. This treatment algorithm is based on the senior author's (WGC) experience with the complex dilemma of osteochondral lesions of the knee.     

Disease-specific clinical problems associated with the subchondral bone

The subchondral bone is involved in a variety of diseases affecting both the articular cartilage and bone. Osteochondral defects in distinct locations and of variable sizes are the final results of different etiologies. These include traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis. Traumatic osteochondral defects are caused by osteochondral fractures, separating an osteochondral fragment that includes articular cartilage and both subchondral and trabecular bone from the joint surface. In osteochondritis dissecans, the disease originates in the subchondral bone and secondarily affects the articular cartilage. Location, stage, size, and depth of osteochondral lesions play a role in the treatment of traumatic osteochondral defects and osteochondritis dissecans. Surgical options include fragment refixation, transplantation of osteochondral autografts, or bone restoration by impacted cancellous bone grafts combined with autologous chondrocyte transplantation. An insufficiency fracture of the subchondral bone may be the initiating factor of what was formerly believed to be a spontaneous osteonecrosis of the knee (SPONK). Recent histopathological studies suggest that each stage of SPONK reflects different types of bone repair reactions following a fracture of the subchondral bone plate. Osteoarthritis is a disease that does affect not only the articular cartilage, but also the subchondral bone. Reconstructive surgical techniques aim at preserving joint function, inducing fibrocartilaginous repair, and at correcting malalignment. This review summarizes the current status of the clinical treatment of traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis as they affect the subchondral bone region and its adjacent structures.     

Autologous chondrocyte implantation: Prospective MRI evaluation with clinical correlation

PURPOSE: This study was done to assess the progression of cartilage repair after autologous chondrocyte implantation (ACI) with magnetic resonance imaging (MRI) and to correlate the findings with the clinical outcome. MATERIALS AND METHODS: Forty-one patients (mean age 30 years) affected by chondral defects of the knee (27 patients) and ankle joint (14 patients) who underwent arthroscopic autologous osteochondral grafting were studied 6 months and 1 year postoperatively with MRI. Cartilage repair after chondrocyte implantation was studied by assessing the degree of defect filling, graft integration, graft signal intensity, integrity of the subchondral lamina and trabecular oedema underneath the graft. MR findings were correlated with clinical data. RESULTS: Postoperative MRI evaluation at 6 months demonstrated complete filling of the osteochondral defect in 12/41 cases, complete integration in 18/41, mild hyperintensity in 28/41, intact subchondral lamina in 38/41 and trabecular oedema in 11/41. Postoperative MRI evaluation at 1 year demonstrated complete filling of the osteochondral defect in 9/41 patients, complete integration in 22/41, mild hyperintensity in 23/41, intact subchondral lamina in 36/41 and trabecular oedema in 8/41. Filling of the osteochondral defect and incomplete integration, nonintact subchondral lamina, high signal intensity and absence of oedema were found to correlate with worse clinical-functional outcomes. CONCLUSIONS: MRI shows direct prognostic signs of the clinical outcome of ACI.     

MR imaging of osteochondral grafts and autologous chondrocyte implantation

Surgical articular cartilage repair therapies for cartilage defects such as osteochondral autograft transfer, autologous chondrocyte implantation (ACI) or matrix associated autologous chondrocyte transplantation (MACT) are becoming more common. MRI has become the method of choice for non-invasive follow-up of patients after cartilage repair surgery. It should be performed with cartilage sensitive sequences, including fat-suppressed proton density-weighted T2 fast spin-echo (PD/T2-FSE) and three-dimensional gradient-echo (3D GRE) sequences, which provide good signal-to-noise and contrast-to-noise ratios. A thorough magnetic resonance (MR)-based assessment of cartilage repair tissue includes evaluations of defect filling, the surface and structure of repair tissue, the signal intensity of repair tissue and the subchondral bone status. Furthermore, in osteochondral autografts surface congruity, osseous incorporation and the donor site should be assessed. High spatial resolution is mandatory and can be achieved either by using a surface coil with a 1.5-T scanner or with a knee coil at 3 T; it is particularly important for assessing graft morphology and integration. Moreover, MR imaging facilitates assessment of complications including periosteal hypertrophy, delamination, adhesions, surface incongruence and reactive changes such as effusions and synovitis. Ongoing developments include isotropic 3D sequences, for improved morphological analysis, and in vivo biochemical imaging such as dGEMRIC, T2 mapping and diffusion-weighted imaging, which make functional analysis of cartilage possible.     

MR imaging of cartilage repair surgery of the knee

Articular cartilage is a complex tissue with unique properties that are essential for normal joint function. Many processes can result in cartilage injury, ranging from acute trauma to degenerative processes. Articular cartilage lacks vascularity, and therefore most chondral defects do not heal spontaneously and may require surgical repair. A variety of cartilage repair techniques have been developed and include bone marrow stimulation (microfracture), osteochondral autograft transfer system (OATS) or osteochondral allograft transplantation, autologous chondrocyte implantation (ACI), matrix-assisted chondrocyte implantation (MACI), and other newer processed allograft cartilage techniques. Although arthroscopy has long been considered as the gold standard for evaluation of cartilage after cartilage repair, magnetic resonance (MR) imaging is a non-invasive method to assess the repair site and can be scored using Magnetic resonance Observation of Cartilage Repair Tissue (MOCART). MR also provides additional evaluation of the subchondral bone and for other potential causes of knee pain or internal derangement. Conventional MR can be used to evaluate the status of cartilage repair and potential complications. Compositional MR sequences can provide supplementary information about the biochemical contents of the reparative tissue. This article reviews the various types of cartilage repair surgeries and their postoperative MR imaging appearances.     

MR imaging of cartilage repair surgery of the knee

Articular cartilage is a complex tissue with unique properties that are essential for normal joint function. Many processes can result in cartilage injury, ranging from acute trauma to degenerative processes. Articular cartilage lacks vascularity, and therefore most chondral defects do not heal spontaneously and may require surgical repair. A variety of cartilage repair techniques have been developed and include bone marrow stimulation (microfracture), osteochondral autograft transfer system (OATS) or osteochondral allograft transplantation, autologous chondrocyte implantation (ACI), matrix-assisted chondrocyte implantation (MACI), and other newer processed allograft cartilage techniques. Although arthroscopy has long been considered as the gold standard for evaluation of cartilage after cartilage repair, magnetic resonance (MR) imaging is a non-invasive method to assess the repair site and can be scored using Magnetic resonance Observation of Cartilage Repair Tissue (MOCART). MR also provides additional evaluation of the subchondral bone and for other potential causes of knee pain or internal derangement. Conventional MR can be used to evaluate the status of cartilage repair and potential complications. Compositional MR sequences can provide supplementary information about the biochemical contents of the reparative tissue. This article reviews the various types of cartilage repair surgeries and their postoperative MR imaging appearances.     

Experimental autologous osteochondral plug transfer in the treatment of focal chondral defects: magnetic resonance imaging signs of technical success in sheep

PURPOSE: To describe the magnetic resonance imaging (MRI) signs of technically successful osteochondral plug transfer and to correlate the findings with histology using the Mankin score. MATERIAL AND METHODS: The study was done in a prospective animal experiment: 11 adult black-head sheep underwent surgical treatment with osteochondral plug transfer of a knee joint. The animals were killed 6 months later and MRI of the joints was done immediately. MRI was applied with a 1.5T MR scanner using a spin-echo (SE) T1-weighted, turbo spin-echo (TSE) T2-weighted with spectral fat suppression and a fat-suppressed 3D-spoiled gradient echo (GRE) sequence (manufacturer's acronym: FLASH) (TR 50.0 ms, TE 11.0 ms, flip 35 degrees). After MRI, all knee joints were dissected and a biopsy of the plug and the adjacent cartilage was taken. Classification of the cartilage biopsies was carried out in accordance with a modified Mankin score. RESULTS: Cartilage repairs with a hypointense cartilage signal in the FLASH 3D sequence were correlated with poor histological results (lower Mankin score). Histologically, the regions of cartilage with a hypointense signal showed a fibrocartilage-like repair tissue. Hyaline cartilage with well-defined layers had the same signal intensity in the FLASH sequence relative to adjacent hyaline cartilage. There were two plugs with a surface defect, graded as Outerbridge grade 1 in MRI and histology. Both had a poor outcome in the histologic Mankin score. Grade 2-4 lesions were not observed in the MRI study nor in the histologic study. CONCLUSION: MRI is a useful non-invasive tool for evaluating the morphologic status of osteochondral plug transfers. A good postoperative result of the cartilage repair was found histologically if an isointense cartilage signal of the graft was documented in the FLASH 3D sequence, and the graft had good congruity with the articular surface without defects.     

Weightbearing ovine osteochondral defects heal with inadequate subchondral bone plate restoration: implications regarding osteochondral autograft harvesting

Purpose

It is unknown what causes donor site morbidity following the osteochondral autograft transfer procedure or how donor sites heal. Contact pressure and edge loading at donor sites may play a role in the healing process. It was hypothesized that an artificially created osteochondral defect in a weightbearing area of an ovine femoral condyle will cause osseous bridging of the defect from the upper edges, resulting in incomplete and irregular repair of the subchondral bone plate.

Methods

To simulate edge loading, large osteochondral defects were created in the most unfavourable weightbearing area of 24 ovine femoral condyles. After killing at 3 and 6?months, osteochondral defects were histologically and histomorphometrically evaluated with specific attention to subchondral bone healing and subchondral bone plate restoration.

Results

Osteochondral defect healing showed progressive osseous defect bridging by sclerotic circumferential bone apposition. Unfilled area decreased significantly from 3 to 6 months (P?=?0.004), whereas bone content increased (n.s.). Complete but irregular subchondral bone plate restoration occurred in ten animals. In fourteen animals, an incomplete subchondral bone plate was found. Further common findings included cavitary lesion formation, degenerative cartilage changes and cartilage and subchondral bone collapse.

Conclusions

Osteochondral defect healing starts with subchondral bone plate restoration. However, after 6 months, incomplete or irregular subchondral bone plate restoration and subsequent failure of osteochondral defect closure is common. Graft harvesting in the osteochondral autograft transfer procedure must be viewed critically, as similar changes are also present in humans.

Level of evidence

Prognostic study, Level III.     

Treatable chondral injuries in the knee: frequency of associated focal subchondral edema

OBJECTIVE: In the knee, chondral flaps and fractures are radiographically occult articular cartilage injuries that can mimic meniscal tears clinically; once correctly diagnosed, these injuries can be treated surgically. We investigated an associated MR imaging finding--focal subchondral bone edema--in a series of surgically proven lesions. MATERIALS AND METHODS: Two musculoskeletal radiologists retrospectively reviewed the MR studies of 18 knees with arthroscopically proven treatable cartilage infractions, noting articular surface defects and associated subchondral bone edema; subchondral edema was defined as focal regions of high signal intensity in the bone immediately underlying an articular surface defect on a T2-weighted or short inversion time inversion recovery (STIR) image. RESULTS: The first observer saw focal subchondral edema deep relative to a cartilage surface defect in 15 (83%) of the 18 cases; in two additional cases a surface defect was seen without underlying edema. The second observer identified 13 knees (72%) with surface defects and associated subchondral edema and three with chondral surface defects and no associated edema. Subchondral edema was seen more frequently on fat-suppressed images and on STIR images than non-fat-suppressed images. CONCLUSION: Focal subchondral edema is commonly visible on MR images of treatable, traumatic cartilage defects in the knee; this MR finding may prove to be an important clue to assist in the detection of these traumatic chondral lesions.     

The use of carbon fiber pads inchondral injury and early osteoarthritis

Articular cartilage damage in young active individuals is a cause of pain and disability and may lead to earlyosteoarthritis. Methods proposed for treatment include intact cartilage grafting, osteochondral grafting, and isolated chondrocyte autografts. However, in some joints it is possible to repair the surface by stimulating the patient's repair mechanisms with techniques such as drilling and abrasion arthroplasty The repair tissue produced by such procedures, however, is usually of inferior quality with regard to the collagen (type I and III) and the proteoglycans. The use of carbon fiber pads as a support for such repair material has proved successful, particularly for the medial femoral condyle of the knee over a period of 5.8 years. The concept of supporting the matrix of the repair material which is formed from the subchondral bone by the use of a carbon fiber matrix is valuable and may be developed by the use of other biodegradable matrices in the future.     

The subchondral bone in articular cartilage repair: current problems in the surgical management

As the understanding of interactions between articular cartilage and subchondral bone continues to evolve, increased attention is being directed at treatment options for the entire osteochondral unit, rather than focusing on the articular surface only. It is becoming apparent that without support from an intact subchondral bed, any treatment of the surface chondral lesion is likely to fail. This article reviews issues affecting the entire osteochondral unit, such as subchondral changes after marrow-stimulation techniques and meniscectomy or large osteochondral defects created by prosthetic resurfacing techniques. Also discussed are surgical techniques designed to address these issues, including the use of osteochondral allografts, autologous bone grafting, next generation cell-based implants, as well as strategies after failed subchondral repair and problems specific to the ankle joint. Lastly, since this area remains in constant evolution, the requirements for prospective studies needed to evaluate these emerging technologies will be reviewed.     

Trends in the surgical treatment of articular cartilage defects of the knee in the United States

Purpose

The purpose of this study was to evaluate trends in surgical treatment of articular cartilage defects of the knee in the United States.

Methods

The current procedural terminology (CPT) billing codes of patients undergoing articular cartilage procedures of the knee were searched using the PearlDiver Patient Record Database, a national database of insurance billing records. The CPT codes for chondroplasty, microfracture, osteochondral autograft, osteochondral allograft, and autologous chondrocyte implantation (ACI) were searched.

Results

A total of 163,448 articular cartilage procedures of the knee were identified over a 6-year period. Microfracture and chondroplasty accounted for over 98 % of cases. There was no significant change in the incidence of cartilage procedures noted from 2004 (1.27 cases per 10,000 patients) to 2009 (1.53 cases per 10,000 patients) (p = 0.06). All procedures were performed more commonly in males (p < 0.001). This gender difference was smallest in patients undergoing chondroplasty (51 % males and 49 % females) and greatest for open osteochondral allograft (61 % males and 39 % females). Chondroplasty and microfracture were most commonly performed in patients aged 40–59, while all other procedures were performed most frequently in patients <40 years old (p < 0.001).

Conclusions

Articular cartilage lesions of the knee are most commonly treated with microfracture or chondroplasty in the United States. Chondroplasty and microfracture were most often performed in middle-aged patients, whereas osteochondral autograft, allograft, and ACI were performed in younger patients, and more frequently in males.

Level of evidence

Cross-sectional study, Level IV.     

Subchondral bone marrow edema in patients with degeneration of the articular cartilage of the knee joint

PURPOSE: To retrospectively determine at magnetic resonance (MR) imaging the prevalence of subchondral bone marrow edema beneath arthroscopically proved articular cartilage defects. MATERIALS AND METHODS: The study was performed in compliance with HIPAA regulations, and a waiver of informed consent was obtained from the institutional review board before the study was performed. The study consisted of 132 patients (70 men, 62 women; average age, 53 years) with articular cartilage defects of the knee joint who underwent MR imaging of the knee and subsequent arthroscopic knee surgery. At the time of arthroscopy, each articular cartilage lesion was graded by using the Noyes classification system. MR examinations were retrospectively reviewed to determine the size, depth, and location of subchondral bone marrow edema without knowledge of the arthroscopic findings. Pairwise Fisher exact tests and two-sample t tests were used to correlate MR imaging findings of subchondral bone marrow edema with the arthroscopic grade of articular cartilage degeneration. RESULTS: Subchondral bone marrow edema was seen beneath 105 (19%) of 554 articular cartilage defects identified at arthroscopy. It was not observed beneath any of the six grade 1 cartilage defects but was observed beneath eight (4.9%) of 163 grade 2A defects, 40 (14.4%) of 278 grade 2B defects, 54 (55.1%) of 98 grade 3A defects, and three (33.3%) of nine grade 3B defects. Subchondral bone marrow edema was also seen beneath four (1.4%) of 238 articular surfaces that appeared normal at arthroscopy. The mean depth and cross-sectional area of subchondral bone marrow edema increased with increasing grade of the articular cartilage lesion. CONCLUSION: Higher grades of articular cartilage defects are associated with higher prevalence and greater depth and cross-sectional area of subchondral bone marrow edema.     

Fresh osteochondral allografting

The treatment of articular cartilage defects in the knee is a difficult challenge. Fresh, small-fragment osteochondralallografting is a technique involving the transplantation of articular (hyaline) cartilage into the defective joint surface. The graft, a composite of living cartilage and a thin layer of underlying subchondral bone, provides a mature matrix with viable chondrocytes along with an osseous component that provides a surface for fixation and integration with the host. Fresh allografting is particularly useful in larger lesions (greater than 2 cms) or when associated osseous defects are present. Clinical experience with fresh osteochondral allografts now extends over 2 decades. Up to 90% of individuals treated for femoral condyle lesions are improved. The allograft tissue appears well tolerated by the host, with documented long-termsurvival of chondrocytes and intact matrix. Successful clinical outcomes have established fresh osteochondrall allografting as an appropriate alternative in the treatment of chondral and osteochondral lesions of the knee.     

Autogenous osteochondral ”plug” transfer for the treatment of focal chondral defects: postoperative MR appearance with clinical correlation

Objective: To describe the MR appearance following autogenous osteochondral ”plug” transfer for the treatment of focal chondral defects of the knee. Design and patients: Twenty-nine 1.5-T MR knee studies including dynamic gadolinium enhancement were performed on 21 patients following autogenous osteochondral ”plug” transfer. Three musculoskeletal radiologists retrospectively reviewed images to evaluate graft and donor site appearance and MR findings were correlated with clinical outcomes. Results: MR images demonstrated graft protuberance (n=12/21; range 1–2 mm), depression (n=2/21; range 1 mm), and surface incongruity: mild (n=17/21), moderate (n=2/21), marked (n=1/21). The T2 signal of graft cartilage was similar to that of adjacent cartilage in 25 of 29 examinations, and increased in four. Graft cartilage thickness relative to adjacent cartilage was <50% in six patients, 50–100% in 15. Graft enhancement in bone was absent at 2 weeks, but present at between 4 and 6 weeks following surgery. All patients had clinical follow-up examinations and knee outcome survey scores were obtained in 15 patients with follow-up greater than 3 months after surgery. All patients demonstrated the expected short-term progressive clinical improvement. Conclusion: MR images reveal a wide range of appearances following osteochondral ”plug” transfer. Minor variations in graft orientation and surface congruity do not result in adverse clinical outcome in the short term. Received: 8 January 2001 Revision requested: 21 February 2001 Revision received: 6 March 2001 Accepted: 6 March 2001     

Epidemiology and imaging of the subchondral bone in articular cartilage repair

Articular cartilage and the subchondral bone act as a functional unit. Following trauma, osteochondritis dissecans, osteonecrosis or osteoarthritis, this intimate connection may become disrupted. Osteochondral defects—the type of defects that extend into the subchondral bone—account for about 5% of all articular cartilage lesions. They are very often caused by trauma, in about one-third of the cases by osteoarthritis and rarely by osteochondritis dissecans. Osteochondral defects are predominantly located on the medial femoral condyle and also on the patella. Frequently, they are associated with lesions of the menisci or the anterior cruciate ligament. Because of the close relationship between the articular cartilage and the subchondral bone, imaging of cartilage defects or cartilage repair should also focus on the subchondral bone. Magnetic resonance imaging is currently considered to be the key modality for the evaluation of cartilage and underlying subchondral bone. However, the choice of imaging technique also depends on the nature of the disease that caused the subchondral bone lesion. For example, radiography is still the golden standard for imaging features of osteoarthritis. Bone scintigraphy is one of the most valuable techniques for early diagnosis of spontaneous osteonecrosis about the knee. A CT scan is a useful technique to rule out a possible depression of the subchondral bone plate, whereas a CT arthrography is highly accurate to evaluate the stability of the osteochondral fragment in osteochondritis dissecans. Particularly for the problem of subchondral bone lesions, image evaluation methods need to be refined for adequate and reproducible analysis. This article highlights recent studies on the epidemiology and imaging of the subchondral bone, with an emphasis on magnetic resonance imaging.     

MR imaging of the knee. Part II. Chronic disorders

Sixty patients with symptoms of chronic disease of the knee joint were evaluated with high-resolution, thin-section magnetic resonance (MR) imaging. MR imaging depicted a wide variety of knee joint abnormalities including osteochondritis dissecans, medullary infarcts, epiphyseal osteonecrosis, intraarticular osteochondral fragments, synovial cysts, joint effusions, intraarticular soft-tissue tumors, synovial disease, leukemic infiltration of bone marrow, Osgood-Schlatter disease, and nonossifying fibroma. In two cases MR imaging depicted bone infarcts not seen on both radionuclide bone scans and standard radiographs. The highly detailed depiction of the articular cartilage was of particular importance in predicting arthroscopic findings in cases of osteochondritis dissecans. In two cases, a soft-tissue mass (pigmented villonodular synovitis) and a large osteochondral fragment undetected at arthroscopy were accurately localized with MR imaging. The results indicate that MR imaging is capable of providing information that might otherwise require multiple, sometimes invasive diagnostic procedures.     

Long-term osseous sequelae after acute trauma of the knee joint evaluated by MRI

OBJECTIVE: To evaluate the frequency and location and to determine the long-term MR changes in patients with edema-like bone marrow abnormalities after acute knee trauma. DESIGN AND PATIENTS: A cohort of 176 consecutive patients in a 29 month period with acute injury of the knee joint was examined with MRI. Forty-nine patients with bone marrow edema-like signal alteration on the initial MR examination were re-evaluated with MRI after a minimum of 2 years (mean 44 months). Signal alterations and contour abnormalities on the initial and follow-up MR examinations were classified. The volume of the edema was also measured. RESULTS: There was a prevalence of post-traumatic edema-like signal changes of 72% in 176 patients. In the follow-up group (n=49) the initial MR examination showed 80 areas of signal change with a mean volume of 15.5 cm3 (range 0.25-175 cm3). Thirty-five (44%) were signal changes without other bony or cartilaginous injuries, 19 (24%) were subchondral impaction fractures and 26 (33%) were osteochondral or chondral fractures. Sixty-nine percent of the lesions were located in the lateral, and 29% in the medial joint compartment. Three percent were patellar lesions. In seven of the 49 patients (14%) eight signal changes were seen on the follow-up MR examination. Six lesions were located in the same anatomic area as on the initial MR examination, and two new lesions had developed. The volume of the bone marrow edema was smaller in all persisting lesions (mean volume 2.26 cm3, range 0.3-4.8 cm3). Deterioration of the subchondral impaction, chondral/osteochondral fracture or lesions resembling osteonecrosis were not found in any patient. CONCLUSIONS: The majority of acute post-traumatic marrow signal changes are found in the lateral compartment and do not show additional osseous or chondral alterations. After a minimum of 2 years acute post-traumatic bone marrow edema-like signal alterations vanish in the majority of patients. Even more severe articular surface injuries such as subchondral bone impaction or chondral/osteochondral fractures will heal without obvious osseous long-term sequelae. Post-traumatic osteonecrosis, as reported in the literature, must be a rare event after acute knee trauma.